Today’s textile and nonwoven market is so complex that fields of application, production techniques and technologies for further processing as well as the variety of new products are difficult to grasp, even for specialists.The variety of new composite materials of fleece, paper, films and fabric as well as the numerous possibilities in terms of combinations have one requirement in common: a safe and reliable process.
Ultrasonics is also the method of choice for these materials, for example for parting fabrics so that there is no thickening of the material along the cut edges.
No consumables such as glue, staples or sewing thread are needed. The fabric remains intact, because no external thermal energy is directed into the fleece. Position, shape and displacement of the welding points can even support the desired properties of the composite.
Textiles is thus a field where ultrasonic technology can prove its uniqueness.
Low frequency mains voltage is transformed into high frequency electrical energy. A converter connected in line converts these electrical oscillations into mechanical vibrations. This is done using a piezoelectric transducer having an efficiency above 95 %.
The mechanical vibrations are transferred to a transformer element coupied to the converter, the so-called booster. This booster optimises the amplitude for the horn.
The horn is individually manufactured for each application and transfers the ultrasonic energy to the material to be processed. To build up a mechanical clamping force, a so-called anvil is required enabling the energy to effect melting on account of physical processes (internal and external absorption).
The Optimum Process for any Application
The actuator applies a defined pressure onto the anvil and hence onto the part to be welded between the two components. Usually, the ultrasonic irnpulse applied simultaneously is time-controlled. Using the weld depth or the amount of energy applied as criteria for deactivation is also possible.
Main fields of application for cyclecontrolled welding:
Overlapping welding of belts and tapes
Linear welding of fabric and nonwoven
Welding textile materials with thermoplastic contents
Joining the end of a material strip to the start of a roll to prevent costintensive drawing in of material into the production equipment.
Seal and cut edges can also be manufactured to excellent quality. This only requires a special design of horn and anvil which is important for the following particular applications:
Cut belt strips to length and/or punching
Parting of edge binding for blankets
Manufacturing buttonholes and eyes applying a certain structure to the rim in order to leave the impression of a sewn edge
This is the most commonly applied combination. Material strips (e. 9. fleece for use in agriculture) are joined at very high speeds using special profile wheels. Using profile wheels, sandwich structures can be generated. Combinations of different materials such as paper, films and textiles are particularly interesting applications. This combination can also be used for cutting processes. This usually involves cutting without sealing or with only slight edge sealling. The extension of the service life as well as the reduction of the cutting force and hence an increased cutting speed are strong arguments for the application of ultrasonic technology. Non-thermoplastic materials can also be cut. In this case ultrasonic energy supports breaking of the materials. Maximum precision is of course a prerequisite in such applications.
Rotating Horn/Rotating Anvil
In this combination horn and anvil serve both to weld and to transport the welded product. In most cases both horn and anvil are driven synchronously. As in this system only a limited amplitude can be generated. This method is usually used for thin materials having a low mass per unit area.
Fixed HornlFixed Anvil
This combination is usually used for cutting/ parting applications with simultancous sealing. However, it can also be used for continuous welding of paper, films, or textiles.
In any manufacturing enterprise production is the driving force to which most other functions react. This is particularly true with inventories; they exist because of the needs of production. In this chapter the relationship of production planning and control to work-in-process inventories is stressed.
The ultimate objective of production planning and control, like that of all other manufacturing controls, is to contribute to the profits of the enterprise. As with inventory management and control, this is accomplished by keeping the customers satisfied through the meeting of delivery schedules. Specific objectives of production planning and control are to establish routes and schedules for work that will ensure the optimum utilization of materials, workers, and machines and to provide the means for ensuring the operation of the plant in accordance with these plans.
All of the four basic phases of control of manufacture are easily identified in production planning and control. The plan for the processing of materials through the plant is established by the functions of process planning, loading, and scheduling. The function of dispatching puts the plan into effect; that is, operations are started in accordance with the plant. Actual performance is then compared to the planned performance, and, when required, corrective action is taken. In some instances re-planning is necessary to ensure the effective utilization of the manufacturing facilities and personnel. Let us examine more closely each of these functions.
The determination of where each operation on a component part, subassembly, or assembly is to be performed results in a route for the movement of a manufacturing lot through the factory. Prior determination of these routes is the job of the manufacturing engineering function.
Once the route has been established, the work required can be loaded against the selected machine or workstation. The total time required to perform the operation is computed by multiplying the unit operation times given on the standard process sheet by the number of parts to be processed. This total time is then added to the work already planned for the workstation. This is the function of loading, and it results in a tabulated list or chart showing the planned utilization of the machines or workstations in the plant.
Scheduling is the last of the planning functions. It determines when an operation is to be performed, or when work is to be completed; the difference lies in the detail of the scheduling procedure. In a centralized control situation – where all process planning, loading, and scheduling for the plant are done in a central office- the details of the schedule may specify the starting and finishing time for an operation. On the other hand, the central schedule may simply give a completion time for the work in a given department.
While it is easy to define “where” as process planning, “how much work” as loading, and “when as scheduling, in actual operations these three functions are often combined and performed concurrently. How far in advance routes, loads, and schedules should be established always presents an interesting problem. Obviously, it is desirable that a minimum of changes be made after schedules are established. This objective can be approached if the amount of work scheduled for the factory or department is equal to or slightly greater than the manufacturing cycle. For optimum control, it should never be less than the manufacturing cycle.
Authorizing the start of an operation on the shop floor is the function of dispatching. This function may be centralized or decentralized. Again using our machine-shop example, the departmental dispatcher would authorize the start of each of the three machine operations – three dispatch actions based on the foreman’s routing and scheduling of the work through his department. This is decentralized dispatching.
Reporting or Follow – up
The manufacturing activity of a plant is said to be “in control” when the actual performance is within the objectives of the planned performance. When jobs are started and completed on schedule, there should be very little, if any, concern about the meeting of commitments. Optimum operation of the plant, however, is attained only if the original plan has been carefully prepared to utilize the manufacturing facilities fully and effectively.
This is the keystone of any production planning and control activity. A plant in which all manufacturing activity runs on schedule in all probability is not being scheduled to its optimum productive capacity. With an optimum schedule, manufacturing delays are the rule, not the exception.
Re-planning is not corrective action. Re-planning revise routes, loads, and schedules; a new plan is developed. In manufacturing this is often required. Changes in market conditions, manufacturing methods, or many other factors affecting the plant will often indicate that a new manufacturing plan is needed.
Factors Affecting Production Planning and Control
The factors that affect the application of production planning and control to manufacturing are the same as the factors we have already discussed that affect inventory management and control. Let us briefly review these in relation to production planning and control.
Type of Product
Again, it is the complexity of the product that is important, not what the product is, except as this may in turn relate to the market being served. Production control procedures are much more complex and involve many more records in the manufacture of large steam turbine generator sets or locomotives to customer orders then in the production of large quantities of a standard product involving only a few component parts, such as electric blankets, steam irons, or similar small appliances.
Type of Manufacturing
This is probably the most influential factor in the control situation. For a large continuous manufacturing plant producing a standard product, we have already indicated that the routing was included in the planning of the plant layout.
Production Planning and Control Procedures
A detailed discussion of all the techniques and procedures of production planning and control is beyond the scope of this book; many complete text books exist on the subject. We have already indicated that planning and control practices will vary widely from plant to plant. Further the many ways in which of the functions might be carried out in practice were indicated earlier in this chapter.
Though no production control function can be entirely eliminated, the least control that results in effective operation of the factory is the best control. It must be remembered that production planning and control systems should be tools of management. The objective is not an elaborate and detailed system of controls and records, but rather, the optimum operation of the plant for maximum profits.
Because production planning and control places an emphasis on the control of work-in-process, the system will in effect tie together all previous records and forms developed in all planning for the manufacture of the product.
The market forecast is discussed in Chapter 26. Its value to production planning and control is that it will indicate future trends in demand for manufactured product. Work shift policies, plans for an increase or decrease in manufacturing activity, or possible plant expansions may often be based upon the market forecasts and in turn affect the planning of the production planning and control group.
This is the second of the five classes of orders. It is a rewrite of the customer’ order specifying what has been purchased – product and quantity and authorizing shipment of the goods to the customer. Multiple copies are prepared and all interested functions are furnished a copy. Sales orders may be written by marketing, inventory control, or production control.
This third class of order is not always used. In the preceding paragraph we indicated how it may be used after sales order accumulate to an economical manufacturing lot. It is, of course, the principal order when manufacturing to stock. It will authorize production in anticipation of future sales.
This fourth class of order deals with the manufacture of component parts. Customer orders, sales orders, and stock orders are for the finished product. In the preceding chapters we discussed how, by product explosion, the requirements are established for component parts to build assembled products.
Standard Process sheet
This form is prepared by process engineering and it is the source of basic data as to the type of machine to be used, the time required for processing and the sequence of operations in the manufacture of the product. Routing and scheduling of shop orders, as well as loading of workstations in advance of scheduling, depend on up-to-date standard process sheets being available to the production planning and control group.
Blueprints and bills of materials are used by production planning and control when they become a component part of the packaged instructions issued to the shop through the control office. One good planning procedure is to accumulate all necessary data for a shop order in a single package the standard process sheet, the blueprint, the bill of material (if an assembly operation is involved), the route sheet, and possibly the schedule for the production of the order.
This is the form on which the route of a shop order is indicated. In practice, this form is generally combined with one of the other forms in the system. For example, the shop order, the standard process sheet, and the route sheet are often one piece of paper- usually called the shop order or the manufacturing order.
These charts are prepared to show the productive capacity that has been “sold” – and at the same time the available productive capacity. These charts may be prepared for each workstation or machine in the plant, or they may be for groups of machines or departments.
This is the fifth and last type of order in a manufacturing situation. Job tickets authorize the performance of individual operations in the manufacturing process.
Project Planning Methods
The production planning and control methods discussed thus far in this chapter deal primarily with the production of consumer or industrial products which could be considered to fall within the area of “repetitive manufacturing”. The products to be produced are often manufactured in quantities of more than one, and their total processing time can be measured in hours, or at most, days. The best –known methods that have been developed are CPM (for Critical Path Method) and PERT (for Program Evaluation and Review Technique). The original PERT technique is now considered, more accurately, PERT TIME, whereas a later development is known as PERT COST.
From the optimistic, most likely, and pessimistic times, the expected elapsed time (te) can be obtained by statistical techniques. The relationship of the three estimates to the expected elapsed time is given by the formula
Where a = optimistic time
b = pessimistic time
m = most likely time
It can be seen from the formula that the most likely time estimate is given four times as much weight as the optimistic and pessimistic estimates when computing the expected time.
As with other manufacturing control systems and procedures, production planning, and control lends itself to modern mechanization techniques such as machine accounting and use of computers. Careful study of the control system through procedure analysis will indicate the savings that may be effected by the utilization of modern equipment. These savings may be in the clerical help required in the administration of the system or in the advantages of quick compilation of data, which in turn results in up-to-date control data.
Production Planning and Control Organization
It should be obvious that there is no single pattern for the organization of the production planning and control activity. In many small plants the routing, loading, and scheduling functions may well be included in the duties of the operating line; the shop manager, superintended, and foremen. But it is difficult to combine day-to-day work with adequate planning, and as a result it is often more feasible to break away the production planning and control functions and assign them to qualified specialists. These groups should be organized as staff sections normally reporting to the top manufacturing executive.
Centralized Production Planning and Control
Centralization or decentralization of duties of the production control staff depends upon the design of the production planning and control system. In a completely centralized setup, determination of shipping promises; analysis of sales, stock, and shop orders; preparation of routes, load charts, and schedule charts; and dispatching of work to the shop complete with job tickets and all other necessary paper would be accomplished by a central production planning and control unit. In addition, as work is completed, a careful analysis of the actual performance would be made, and if corrective action were required, it would be initiated by this group.
Decentralized Production Planning and Control
We have discussed at great length that no matter how general the planning may be in a central office, the plan must eventually be developed into a detailed plan on the shop floor. Some companies are now endeavouring to make each foreman a manager of his own departmental operation. In these cases the foreman is furnished with a complete staff for the production planning and control of the activities in the department.
We have already indicated in some details the duties involved in the production planning phase. Working from the basic data mentioned earlier, the personnel in this part of the activity routes and load and schedule charts.
The completed job ticket, or its equivalent, is the key to this phase of the production planning and control system. It is the means of reporting back from the shop floor that indicates that a job is completed; or if daily job tickets are turned in, the daily progress of a job can be determined.
Relation to Other Functions
Good relationships with all the other functions in the enterprise are essential to effective production planning and control. Full cooperation with the marketing group is necessary, particularly in view of the importance of market conditions and the goodwill of customers. Both product engineering and process engineering must keep production planning and control informed as to their plans to avoid the manufacture of goods either to incorrect specifications or by an improper method.
Measurement of Effectiveness
In determining the effectiveness of a production planning and control system, there are quite a few problems. The key criterion might well be whether or not shipping promises are being kept – the percentage of the order shipped on time. This, however, would not be a true criterion if excessive overtime of expediting costs were involved in getting any of these orders shipped. The cost of the control system in relation to the value of goods shipped is another possibility. Again, however, this may not be sound: if markets slump, a bad ratio will develop. Many good production planning and control systems have been discontinued because of “high costs” under these conditions- and have never revived after business picket up. In a study of benefits and costs of computerized production planning and control systems, Schroeder et al. list the following performance criteria by which production planning and control systems might be judged:
1. Inventory turnover
2. Delivery lead time
3. Percent of time meeting delivery promises
4. Percent of orders requiring “splits” because of unavailable material.
5. Number of expeditors
6. Average unit cost.
As far as enterprise resource planning systems (ERP) are concerned, the textile industry may still be a manageable affair. But the moment you talk about developing a production planning and scheduling software for this industry, you are asking for a difficult task to be performed. Many a veteran has failed in attempting to achieve this feat.
Some of the unique challenges posed by the textile industry to any production planning and scheduling software vendor are discussed here. These challenges can be grouped as raw material concerns, manufacturing lead time, manufacturing constraints, orders, and inventory.
Raw material concerns involve high raw material costs and seasonal raw material procurement cycles. Cotton, for example, is a seasonal commodity; therefore, the availability and price will change throughout the year. High raw material cost is another issue. Raw material costs may constitute as high as 60 to 70 percent of the total costs.
Manufacturing lead time can also pose challenges. Manufacturing lead times can be excessive, sometimes more than two months. This is because the raw cotton production process, for example, has to go through many processes and most of them have huge lead time requirements. Looms in particular take the most lead time. A loom machine can make only 500 meters of fabric in a day whereas typical order lengths are in the range of 25,000 to 50,000 meters range.
Most of the manufacturing processes also have high setup times. Quality analysis time also runs high as the finished cloth needs to be manually inspected for defects. Extra lead times also result due to unavoidable generation of inventory in the form of extra meters than the ordered lengths.
Another challenge involving manufacturing is that different processing speeds occur at different work centers, which must also be included in the equation. Dyeing machines, warping machines, spinning machines run at speeds of 30,000 to 50,000 meters of yarn per day but looms run at 500 meters of fabric per day. Because of this, there may be only 2 to 5 dyeing machines, but there may be as many as 500 looming machines in the same plant.
Likewise there are different processing requirements on the same production line. For example, up until the dyeing process, the manufacturing process fits orders that are big and similar. But at looming, the manufacturing process fits many smaller and varied orders. This poses a real challenge as fitting these two diametrically opposite requirements is next to impossible to do.
Another issue is the unpredictable generation of second quality textile and the fact that variations in color and shade is only known after the fabric has been woven and finished (though they are caused back at the dyeing stage). This can result in a lot of rejected material being processed unnecessarily, thus adding to manufacturing costs and processing time.
These manufacturing constraints ultimately impact customer orders. Because the production rates are very low on looms, customer orders are broken into smaller sub-orders, and the sub-orders are distributed to many looms to reduce the lead time for individual orders. However, variations in the color or shade from the order can also emerge, which, as explained earlier, are detected at the end of the entire process.
Not surprisingly, inventory is another challenge faced by the textile industry because there is a high generation of extra finished products. In addition to extra material resulting from second quality and color shade variations, extra yarn moves through the entire production cycle. Up to dyeing stage, the work-in-process (WIP) is in yarn form and the length of this yarn is fixed at the yarn making stage. It cannot be cut as per order lengths. These extra meters travel through the production cycle and end up as excess inventory, which is later adjusted in the next planning cycle. Consequently, plant capacity is inefficiently utilized due to unavoidable generation of extra meters—more than the lengths ordered.
After going through these constraints, it is obvious that it is difficult to develop production planning and scheduling software for the textile industry. Only a veteran who has in-depth industry knowledge as well as knowledge of how to tackle these constraints in the implementation can develop a software for planning and scheduling for the textile industry.
It is very important to understand the different requirements at the dyeing and looming processes so a suitable planning and scheduling software can be suggested. The dyeing and looming processes are the true bottlenecks in the entire production cycle of all textile plants. Both dyeing and looming have high setup time, high production time, and high change overtime, but looms are far slower than dyeing machines. Looming is more like a warehouse with a lot of WIP inventory called grey stock and this grey stock is on many looming machines, in small quantities. Dyeing machines, however produce long sets of warp (dyed yarn). One set of warp can be produced by one dyeing machine in one day but the warp can only be consumed by at least 50 looming machines in one day. To keep the ability to produce many kinds of fabric, the manufacturers generally install many kinds of looming machines. All of these looms are fed by only 2 to 5 dyeing machines. Due to these factors the dyeing area is always hard-pressed to feed the looms with small lengths and different types of dyed yarn for the next work orders in line.
So dyeing machines are better suited to produce big quantities of dyed yarn of the same type, (e.g. same color and same number of ends). For example, if the ordered length of fabric is 25,000 meters and the order has been broken into 10 work orders at 10 looms, then it will take 5 days to finish the WIP at looming. This is if all the work orders are done simultaneously and speed of looms are 500 meters of fabric woven per day. A single dyeing machine will produce 25,000 meters of warp in half a day.
These challenges in the textile industry can be met by conducting a profitable to promise analysis; grouping, breaking, and sequencing orders; and by routing WIPs. In the textile industry, orders are considered more like combinatorial meters rather than individual order meters, so the same type of orders can be grouped and sequenced to achieve production efficiency as well as reduce inventory creation. All WIPs can also considered the same way for the same purpose.
Profitable to Promise Analysis
Businesses in the textile industry mostly gets varied orders in terms of rate per meter, quantity, fabric type etc. Because of this, each order has to be evaluated on profitability, customer service levels and long and short term goals of the company. Profitable to promise analysis allows the business to find out if the particular order will be profitable to make by considering the costs of raw material, process, inventory, and other factors against the price the customer is willing to pay. Thus it can be seen that some orders will be a lot more profitable than other orders. This analysis is perfectly possible if you have the right software tool, which can provide you with this kind of information.
If raw material availability, machine capacity, and production lead time are known at the time of order taking, then it is possible to give a definite delivery date to the customer. This is known ascapable to promise. If we can also provide information about customer, production, inventory, stock out, material, and other overhead costs down to the item level, and then compare all incurred costs to the selling price, it will be possible to decide whether the incoming order should be taken and what priority it can be assigned, at the time the order is being taken. This functionality is very important for the textile industry.
In conjunction with above mentioned factors, a planning system that is also capable of grouping, breaking, and sequencing orders while it is doing total lead time calculations to determine a delivery date will solve many production planning problems. It will eliminate waste, reduce the generation of extra inventory, increase machine capacity utilization, increase customer service levels, eliminate stock out costs, and reduce production costs.
Grouping, Breaking, and Sequencing Orders
Grouping, breaking, and sequencing orders will also help to overcome textile production challenges. Group smaller orders at dyeing process. The same dyeing WIPs can be grouped so the generation of extra meters can be minimized. Break bigger orders into many smaller orders at dyeing, and sequence them with other orders. Loom areas typically have many kinds of loom machines which can produce different kinds of fabric but at very slow rates. If big orders of same material are continuously coming from dyeing, they will only go to a particular loom machine which can process it; other loom machines which cannot use these warps will go idle for want of material. Another way to minimize set up time is to sequence WIP orders with the same color at the dyeing process. This will minimize the set up time to change of color. Also, breaking individual orders into many parts will create many work orders for the same order at looming process. This will minimize lead times significantly at looming.
Also, look for already existing inventory in the form of extra meters at looms and finished stock in the inventory to allocate these meters against the matched fresh orders and plan for the remaining meters.
Synergies among makers of machinery, as well as systems and plants and the clothing industry aim both to the optimisation of the garment and to its suitability to be used according the customer’s demand.
As a consequence organisation of the production on one side, methods applied, machines, and component materials (from the fabric to the accessories) play a synergetic role which determines the product quality.
Organisation and information management, logistics, as well as specific hardware and software packages for CAD and CAM systems are representative of the high technological level offered by the Italian manufacturers
Receipt of goods
At their reception, all pieces must be immediately provided with a bar code with the following information: fabric variant, colour variant, real fabric width, total length, net length after detection of flaw lengths, entry date into the warehouse.
Today also the clothingmanufacturing companies need to have a range of equipment for printing labels and bar codes. These printers through a serial or parallel port can be connected to any system.
Fabric quality control involves the control of a series of characteristics, such as dimensional stability, shade uniformity, colour stability at fusing and ironing temperatures, light and stain removal fastness, weft squareness, consistent tensile strength, wear resistance, resistance to seam sliding pressure. Finishing products must not hinder fusing, and must not cause fabric stripiness and creases; selvedge must be regular, not too loose, not too tight or too large.
To make these controls easier Italian inspection machine makers offer a series of options, suitable both for woven and knitted/elasticised fabrics. Programmable automatic winding machines are also offered for cutting optimisation.
An interesting development is a final control for measuring and controlling colour directly on any type of inspection table for any type of textile product. Thanks to an advanced system of colorimetric quality control an exact interpretation and evaluation of the readings is provided. Advantages include automatic calculation of tolerances, instrumental control of colour differences (center/selvedges, header/end), no need of tests for sample sets, and speeding up of the control process.
Piece transport from storehouse to spreading department
A keen problem is “what to do” with the flaw lengths appearing during spreading. A solution is the CAD marking system, which is able to study and calculate the various possibilities for fault cutting-out, and the number of superimposed fabric layers needed after flaw removing. This information, together those concerning length of marking, number of layers for each single step, size, fabric/colour variant, is to be stored in the central computer for subsequent use not only by the spreader but also the robotised truck (which has to draw pieces from the warehouse), and the carousel for feeding individual piece to the spreader.
Many options of spreading equipment provide flexibility in fabric handling, and are available from Italian manufacturers, either with cradle or programmed loading of the rolls without the help of the chuck.
Special solutions are offered for tubular fabrics, big rolls up to 400 kg, home linen. A high tech solution is a two-roll spreader, which may be used to obtain the multilayer stack for laser cutting the car safety air bags. This technology can be also applied for simultaneous spreading of the three layers composing the tie material or to couple already during preading filling and fabric of windcheaters.
New fabric spreading technologies are becoming popular: these technologies are the natural answer to a more and more pressing market request, that is tailor made clothing. Customers who are no more satisfied of already made-up suits are increasing more and more; they require tailor made clothing with fabrics and sizes chosen by them. To satisfy these requirements, new completely automated lines are being planned for the motion of fabric rolls, spreading and cutting of predetermined length fabrics which will feed the systems for shape cutting. These lines, inserted in CIM systems, allow the making up of “tailor made” suits at low costs and in short time.
For these two operations, in the sector of CAD for the clothing industry, a wide range of the most recent and known software packages has been developed enabling high operating speed thanks to personal computers of the latest generation. The system is composed of a workstation with digitizer table, where the identification of the pattern design is performed. The subsequent step is carried out on a workstation for the construction of the basic model and the marking. After completing these operations, the system is arranged for interfacing with automatic cutting.
Cutting systems and cutting machines
For the cutting room various systems are offered so to meet the most diverse requirements not only of the medium and big clothing manufacturers, but also for small sized companies. The wide range of machines offered can handle the cutting of single-layer fabrics up to 15.5 cm stocked piles.
The sector of sewing machines shows continuous updating and improvement. The trend is towards the use of more and more flexible and automatic sewing units able to perform some sequential sewing operations. On the other hand there is still the need to manufacture low cost sewing machines for the developing countries. Since present day fashion needs lead more and more to continuous model changes, clothing manufacturers very often have to increase the number of machines, with consequent high investment. This problem finds a solution in adopting a flexible modular system putting together three basic units: a cylinder bed sewing machine, a cuttingsewing machine and a flat a flat bed unit that can be completed by a series of universal kit for loop stitch goods (used for underwear, corsetry and knitwear). Advantages claimed for this system consist in: a complete production system that carries out sewing operations with very high performance, possibility of modifying the initial configuration, adapting it to new production needs, possibility of technological updating without having to replace the machine, justifiable investment also in case of fashion changes. A machine with shortened cylinder bed on the left of the needles and differential feed is offered for top stitching of pre-existent seams. A new subclass unit for top stitching the seams on medium-heavy knitwear has been prepared for smoothly sew crossed seams with high thickness. It equipped with thread cutting device. Also launched a brand new unit for flat topstitched assembly seams with bartacking on light and medium outerwear in a single operation.
The automatic units adopting a multistitch method allow to reduce operation times by about 50/60%, reduce the operation steps and hence the dwelling time of the semifinished garment in the cutting room. A series of units carries out the flat and topstitched assembly seams in one single phase without interruption. They are equipped with two heads, the first one with horizontal needle bar for the assembly seams, the second one with vertical needle bar for topstitching. The sewing system adopts a new method for the introduction of the fabric into the automatic unit. In fact the two fabric edges to be assembled are presenting themselves in open state, with the right side turned towards the operator, making easier the coupling of striped and chequered fabrics. For attaching pockets on shirts, working clothes and pyjamas etc., machinery with flexible systems controlled by microchips that can fold pockets, sewing them, and pile the garments in an automatic cycle. These machines offer high productivity, constant quality and the possibility to programme various sewing patterns that can be adapted to the different pocket models. The wide range of models offered include high frequency “sewing” systems for synthetic fabrics, which fuse by means of an 800 W ultrasound generator and a vibrating ultrasound group. The fusion speed can programmed up to 50 m/min and is driven by means of a treadle.
Quilts are a popular home decoration element. Electronics broadens potential of quilting machines making them more versatile. An Italian company is engaged in the production of a series of models which mount a serious challenge to machine embroidery. The newest models of quilters, can operate at around 1,000 stitches/minute and are built with a quilting width up to 114 ins (290 cm). With three needle bars the patterning potential is immense. Giant rotating hooks with 700-mm bobbins are used in this machine which has
tack and jump mode. This is a means of still further creating more interesting surface effects.
Developments on these machines is aimed to a system of automatically cutting embroidery threads, and this will serve to conserve thread when a needles produces a discrete pattern and then needs to travel to a different position to perform its next task.
The Schiffli embroidery machines are now offered with computer control. The design preparation for multihead embroidery machines is today a normal practice. Besides punching of patterns on graphic screens and advanced systems for data processing of machine programs, one can use laser discs containing 20,000 patterns each, and affording to immediately write the embroidery design on the machine disc, so that production can start at once.
The knitwear linking is carried out exclusively to sew full-fashioned knitted goods which are loaded onto pins so that the ribs of both webs perfectly match thus avoiding the risk of sliding.
Linking machines can be quipped with one or two needles and hook- or straight-shaped needles (different stitch formation obtained). Linking machines can have internal needle (the stitch is loaded from the plain side) or external needle (the stitch is loaded on the reverse side). The working speed can reach 1,500 stitches per minute; the quantity of needles per inch ranges from seven to sixteen; in special machines it can range from 2 to max 24 needles per inch. It’s also worth mentioning that some knitwear linking machines are equipped with microcomputer to synchronise all the speed values: adjusting sewing speed, prefeeding of rib borders, and positive drive pullers, which are controlled individually by conventional motors, in order to allow accurate alignment of the ribs.
Ironing and pressing
This sector includes a great number of units that are used for different purposes, and sees the leadership of Italian makers.
There are automatic, pneumatic and rotary ironing presses for all pieces of clothing; ironing systems for intermediate and final ironing include pneumatic toppers for trousers ironing, steaming dummies, finishing cabinets, heated vacuum boards, and the blowironing units.
All ironing machines and systems are now equipped with electronic systems so that crucial parameters such as speed, temperature and pressure may be set. The safety systems installed have been further improved for a better safeguard of the staff operating on the machines.
The importance of finishing is becoming more and more crucial in the textile/clothing sector thanks also to the new “informal comfort” standard suggested by the fashion dictations in the last few years which started in the past with a new kind of treatment for jeans. Now the finished garment needs to be a “high-profile” piece of clothing not only from a purely technical point of view but also in terms of esthetical content, which must be in line with the visual, hand, and colour trends.
A wide and continuously evolving range of washers and tumblers especially studied for garment washing, dyeing and drying have been developed to allow many kinds of treatments such as bleaching and stone washing, and to obtain delavé and used look. Also worth remembering is the continuous evolution of drum type washing machines and the driers, available in a vast range of models specifically designed for washing, dyeing and drying operations on garments.
Folding and packaging
At the end of the production line, garments are arranged with reference tags, put into a bag and packed according to the forwarding specifications. These operations are carried out by means of folding and packing machines (for shirts, home linen, and underwear the complete process of folding and packing is carried out automatically in only one operation). A series of other systems are used to pile-up, pack, wrap-up and tie-up the garments.
For every industry or business, to get increased sales and better name amongst consumers and fellow companies it is important to maintain a level of quality. Especially for the businesses engaged in export business has to sustain a high level of quality to ensure better business globally. Generally quality control standards for export are set strictly, as this business is also holds the prestige of the country, whose company is doing the export. Export houses earn foreign exchange for the country, so it becomes mandatory to have good quality control of their products. In the garment industry quality control is practiced right from the initial stage of sourcing raw materials to the stage of final finished garment. For textile and apparel industry product quality is calculated in terms of quality and standard of fibres, yarns, fabric construction, colour fastness, surface designs and the final finished garment products. However quality expectations for export are related to the type of customer segments and the retail outlets. There are a number of factors on which quality fitness of garment industry is based such as – performance, reliability, durability, visual and perceived quality of the garment. Quality needs to be defined in terms of a particular framework of cost. The national regulatory quality certification and international quality programmes like ISO 9000 series lay down the broad quality parameters based on which companies maintain the export quality in the garment and apparel industry. Here some of main fabric properties that are taken into consideration for garment manufacturing for export basis:
• Overall look of the garment.
• Right formation of the garment.
• Feel and fall of the garment.
• Physical properties.
• Colour fastness of the garment.
• Finishing properties
• Presentation of the final produced garment.
There are certain problems that could be faced by garment manufacturers when sourcing for certain fabrics, so precautions should be taken for it beforehand to minimize the problems. The garment exporters source cotton fabrics mainly from handloom sectors, powerlooms and mills. Each of these sectors presents their own unique set of problems to the garment exporters. Sourcing cotton from handloom sectors might present some set of problems like colour variation, missing ends and picks, irregular weaves and unreliable supplies. However, the handloom sector is significant source of heavier cotton. Common problems faced in powerloom cotton sourcing are broken ends and reed marks, thick and thin places, difference in width and massive variation in costing. The major problem in mill-made fabric sourcing is to meet huge demands from the mills. Fabrics have to be ordered well in advance in mills and the long time taken for producing the fabric is a matter of concern for garment exporters. Mills generally hesitate to take small orders which pose a problem for small scale exporters.
It is not that sourcing problems which only confined to cotton fabrics, but also to other fabrics as well. In silk garment industry there are some sorts of problems faced by silk garment exporters. Some of the problems that could be faced by silk garment exporters are as follows:
• Shortage of imported silk yarns in the quantities required, as a result delivery is delayed.
• Silk material is very vulnerable to stains during manufacturing process as well as stocking, staining results in rejection so a lot of care has to taken during these procedures.
• Roll length of the silk yarn is often insufficient.
• Colour fastness of dyed silk material is sometimes not satisfactory.
• There are also chances of warp breakage.
For a garment exporter there are many strategies and rules that are required to be followed to achieve good business. The fabric quality, product quality, delivery, price, packaging and presentation are some of the many aspects that need to be taken care of in garment export business. Some rules that are advisable for garment exporters are listed below:
• Quality has to be taken care by the exporter, excuses are not entertained in international market for negligence for low quality garments, new or existing exporters for both it is mandatory to use design, technology and quality as major upgradation tools.
• Apart from superior quality of the garment, its pricing, packaging, delivery, etc has to be also taken care of.
• The garment shown in the catalogue should match with the final garment delivered.
• It is important to perform according to the promises given to the buyer, or else it creates very bad impression and results in loss of business and reputation.
• In international market, quality reassurance is required at every point.
• Proper documentation and high standard labels on the garment are also important aspects as these things also create good impression.
• Timely delivery of garments is as important as its quality.
• If your competitor has the better quality of garment in same pricing, it is better to also enhance your garment quality.
• Before entering into international market, garment exporters have to carefully frame out the quality standards, or else if anything goes wrong it could harm the organization. And after that strictly follow it.
• The garment quality should match the samples shown during taking the orders.
• The garment exporters should know to negotiate a premium price after quality assurance is done.
Quality is a multi-dimensional aspect. There are many aspects of quality based on which the garment exporters are supposed to work.
• Quality of the production.
• Quality of the design of the garment.
• Purchasing functions’ quality should also be maintained.
• Quality of final inspection should be superior.
• Quality of the sales has to be also maintained.
• Quality of marketing of the final product is also important as the quality of the garment itself.
See to it that………..
There are certain quality related problems in garment manufacturing that should not be overlooked: Sewing defects – Like open seams, wrong stitching techniques used, same colour garment, but usage of different colour threads on the garment, miss out of stitches in between, creasing of the garment, erroneous thread tension and raw edges are some sewing defects that could occur so should be taken care of. Colour effects – Colour defects that could occur are – difference of the colour of final produced garment to the sample shown, accessories used are of wrong colour combination and mismatching of dye amongst the pieces.
Sizing defects – Wrong gradation of sizes, difference in measurement of a garment part from other, for example- sleeves of ‘XL’ size but body of ‘L’ size. Such defects do not occur has to be seen too. Garment defects – During manufacturing process defects could occur like – faulty zippers, irregular hemming, loose buttons, raw edges, improper button holes, uneven parts, inappropriate trimming, and difference in fabric colours.
Quality is ultimately a question of customer satisfaction. Good Quality increases the value of a product or service, establishes brand name, and builds up good reputation for the garment exporter, which in turn results into consumer satisfaction, high sales and foreign exchange for the country. The perceived quality of a garment is the result of a number of aspects, which together help achieve the desired level of satisfaction for the customer. Therefore quality control in terms of garme
Today’s consumer is more sophisticated than ever. They are conscious not only of style and comfort, but also of care and durability. They demand a quality product. Market studies show that consumers make many purchase choices based on color. Therefore, a fabric’s ability to retain its original color is one of the most important properties of a textile product.
The colorfastness or color retention of cotton textiles is influenced by a number of variables that occur both pre-consumer and post-consumer. This report summarizes how variations in raw materials, chemicals, manufacturing processes and consumer practices all have an effect on the performance characteristics of a fabric. Manufacturers must understand how the many variables affect colorfastness to achieve the ultimate goal of consumer satisfaction.
Colorfastness is defined by the American Association of Textile Chemists and Colorists as “the resistance of a material to change in any of its color characteristics, to transfer its colorant(s) to adjacent materials, or both, as a result of the exposure of the material to any environment that might be encountered during the processing, testing, storage, or use of the material.” In other words, it is a fabric’s ability to retain its color throughout its intended life cycle. There are many types of colorfastness properties that must be considered to provide the consumer with an acceptable product. The American Association of Textile Chemists and Colorists has over thirty test methods that evaluate different colorfastness properties. These include, but are not limited to wash, light, crock, dry cleaning, perspiration, abrasion and heat. The type of product being manufactured determines which types of colorfastness are important and therefore which test methods are relevant. For example, upholstery fabrics must have excellent lightfastness and crockfastness properties, whereas washfastness is important for clothing fabrics. Manufacturers must know a fabric’s intended end use in order to make processing decisions that will produce a product of acceptable performance.
Many aspects in the textile manufacturing process of taking a loom state fabric to a finished product have an effect on the colorfastness properties. Preparation is the first stage of textile wet processing. Cotton fibers are approximately 95% cellulose. The non-cellulosic portion consists of natural products such as waxes, sugars, metals, and man-made products such as processing aids, grease, plastic, and rubber. To achieve optimum dyeing and finishing conditions, it is important that these impurities are thoroughly removed with minimal damage to the cotton fiber.
Dyeing is the crucial step in determining the colorfastness performance of a fabric. The American Association of Textile Chemists and Colorists define a dye as “a colorant applied to or formed in a substrate, via the molecularly dispersed state, which exhibits some degree of permanence.” Dyeing is accomplished by immersing the textile in a dye bath, applying heat and chemicals to drive the dye onto the textile, and then rinsing the substrate to remove the surface dye. These principles are illustrated below.
Different dye classes are used for each fiber type. The table below shows which dyes can be used for which fibers.
Dye selection must be based on desired performance criteria, manufacturing restrictions and the costs a market can bear for each end product. Every dye has unique colorfastness properties. Some dyes are known for their excellent washfastness characteristics and others are known for their lightfastness properties. The structure of the dye, the amount of dye, its method of bonding to the fabric and dyeing procedures all contribute to a dye’s performance characteristics. Dye combinations in a specific formulation must also be evaluated for their effect on colorfastness. Heavy shades often have reduced fastness properties. When high concentrations of dye are required, proper rinsing and washing off procedures are essential. However, due to entrapped dye particles within the cellulose structure, some unbound dye molecules can still remain and contribute to color loss and dye transfer
Dyes can be categorized based on the mechanism by which they become fixed to a fiber. Dyes used for cotton fibers can be categorized into the surface bonding, adhesion, or covalent bonding mechanisms.
Pigments are sometimes used to color cotton fabrics, however they are not considered dyes. They are completely insoluble in water and have no affinity for cotton fibers. Some type of resin, adhesive, or bonding agent must be used to fix them to the cotton fiber. Typically, they exhibit good colorfastness to light and poor colorfastness to washing.
Direct dyes are water soluble and categorized into the surface bonding type dye because they are absorbed by the cellulose. There is no chemical reaction, but rather a chemical attraction. The affinity is a result of hydrogen bonding of the dye molecule to the hydroxyl groups in the cellulose. After the dyestuff is dissolved in the water, a salt is added to control the absorption rate of the dye into the fiber. Direct dyes are fairly inexpensive and available in a wide range of shades. Typically, they exhibit good lightfastness and poor washfastness. However, by applying a fixing agent after dyeing the washfastness can be improved dramatically.
Vat, sulfur, and naphthol dyes are fine suspensions of water insoluble pigments, which adhere to the cotton fiber by undergoing an intermediate chemical state in which they become water-soluble and have an affinity for the fiber. Typically, vat dyes exhibit very good colorfastness properties. Sulfur dyes are used to achieve a low cost deep black. They exhibit fair colorfastness properties, although the lighter shades tend to have poor lightfastness. Naphthol dyes are available in brilliant colors at low cost, but application requirements limit their use. They exhibit good lightfastness and washfastness, but poor crockfastness.
Reactive dyes attach to the cellulose fiber by forming a strong covalent (molecular) chemical bond. These dyes were developed in the 1950’s as an economical process for achieving acceptable colorfastness in cellulosic fibers. Bright shades and excellent washfastness properties are the trademark of reactive dyes. One concern regarding reactive dyes is their susceptibility to damage from chlorine. Another is that lighter shades tend to have reduced lightfastness properties.
The following table summarizes the fastness properties of the dye categories or classes available for dyeing cotton fabrics. Keep in mind that these are generalizations. Every dye is unique and some dyes within a particular class may behave differently.
Finishing is the final stage of textile wet processing. Different types of finishes can be utilized depending on the desired performance characteristics of the end product. Resin and enzyme treatments are common finishing techniques that can influence the colorfastness of textile fabrics. Crosslinking resins are used to improve the durable press or wrinkle resistance of a fabric. Generally, resin treated fabrics demonstrate improved color retention to laundering. However, this increase in color retention comes at the expense of reduced physical properties of the fabric. Silicone softeners incorporated into the resin finish bath may further improve color retention for some fabrics. Softeners and resins play a key role in reducing surface abrasion and therefore improved overall wash performance. Cellulase enzymes are used to remove surface fibers that can create a fuzzy appearance on the surface of a fabric. Generally, enzyme treated fabrics show improved ability to maintain their original color and appearance after multiple home launderings. The degree of improvement from any of these finishing techniques is highly dependent on the individual dyes used in a particular formulation to achieve a given shade
Manufacturers can follow every recommendation and precaution to produce a fabric with optimum performance characteristics. However, colorfastness properties are also influenced by consumer practices. These include laundry detergent selection and wash procedures. Therefore, when evaluating colorfastness properties of a product it is important to use the appropriate test method that accurately reflects the consumer laundry practices. Due to higher energy costs consumers are laundering clothes at lower temperatures. For this reason detergent with “color safe” or activated peroxy bleaching agents, which improve cleaning efficacy at lower wash temperatures, are one of the fastest growing segments of the home laundry market. Some fabrics may fade a little when home laundered with standard detergent, but fabrics laundered with detergents containing activated bleach can show significant losses in color strength as determined by the sensitivity of the dye to those detergents. Another type of detergent available to consumers is those containing enzymes, which remove surface cellulosic fibers from the fabric. Many times the loss or apparent loss of color can be attributed to surface changes in the fabric caused by abrasion during laundering. Detergents containing enzymes generally reduce the color change associated with home laundering by decreasing the fuzziness of a fabric’s surface. Wash procedures also influence a fabric’s ability to retain its color. Consumer practices such as washing clothes inverted, reducing the wash load size, adding softener to the final rinse and reducing the tumble dry time minimize color loss.
The colorfastness of cotton textiles can be a complicated subject. Fiber quality, yarn formation, fabric construction, textile wet processes and consumer practices can all have an influence on the performance characteristics of a fabric. Of these variables, the choices made during textile wet processing have the most significant effect on the colorfastness properties. Dye selection is of the utmost importance. Consumer practices such as detergent selection and laundering techniques also play a major role in the color retention of a fabric. Customer satisfaction should improve as manufacturers gain experience and knowledge in understanding and controlling the many aspects that influence colorfastness.
One reason for the existence of the great number of commercial dyes that any textile material may be have to withstand one or more of a wide variety of processes of manufacture and later be subjected to a variety of different types of wear and tear in use. The correct of choice of dye for any given circumstance, in fact, requires considerable knowledge and experience, and nothing more than a bare outline of the underlying principles can be given here. A few typical examples, selected at random, of some of the matters to he considered in making the choice are given below under four main headings:
Many textiles must withstand severe exposure to sunlight or to repeated washing. Thus curtains and fabrics for outer garments must have good fastness to light. And fabrics for awnings and deck chair must withstand sunlight and also rain: knitted wool material should be fast to washing; shirting and handkerchiefs must withstand boiling in soap solution; and so on.
Cotton fabric having colored threads on a white ground may have to be subjected to boiling, with alkali under pressure (kier boiling) and bleaching after weaving. The first kind of dye chose for bland fabrics should be withstood the dyeing conditions of the second kind of dye.
Apart from the above treatments to which the already dyed materials are subjected, the nature of the dyeing process is important in determining the choice of dye, Thus in the dyeing of fabric only the most level-dyeing dyes can be used, because the slightest inequality in colour in different areas of the cloth would spoil the appearance. If loose fiber is being dyed, however, levelness is of less importance, because any portions of uneven appearance in the mass will be evenly distributed when the fiber is subsequently manufactured into yarn. Again, in using package dyeing machine, which the dye-liquor is pumped through a container packed tight with loose fiber, or through a cake or thick reel
of yarn. it is important for the dye to be either in true solution or present as extremely fine particles.
4 Dyeing Costs
The prices of different dyes are quite different. It is better to choose the economic dyes in Practice if all above mentioned requirements are conformed.
The testing of fibres was always of importance to the spinner. It has been known for a long time that the fibre characteristics have a decisive impact on the running behaviour of the production machines, as well as on the yarn quality and manufacturing costs. In spite of the fact that fibre characteristics are very important for yarn production, the sample size for testing fibre characteristics is not big enough. This is due to the following
The labour and time involvement for the testing of a representative sample was too expensive. The results were often available much too late to take corrective action.
The results often depended on the operator and / or the instrument, and could therefore not be considered objective
One failed in trying to rationally administer the flood of the raw material data, to evaluate such data and to introduce the necessary corrective measures.
Only recently technical achievements have made possible the development of automatic computer-controlled testing equipment. With their use, it is possible to quickly determine the more important fibre characteristics.
Recent developments in HVI technology are the result of requests made by textile manufacturers for additional and more precise fibre property information. Worldwide competitive pressure on product price and product quality dictates close control of all resources used in the manufacturing process.
Conventionally measurement of the fibre properties was mainly carried out using manual method and it included the maximum chance of getting errors involved in it due to manual errors and was also a time consuming job. Thus there was a need for development of an instrument capable of measuring all properties in minimum time for better cotton classification.
PCCA (plans cotton cooperative association) played a key role in the development of High Volume Instrument (HVI) testing to determine the fibre properties of cotton which revolutionized the cotton and textile industries. As its name implies, HVI determines the fibre properties of a bale of cotton more quickly and more accurately than the previous method of evaluating some of those properties by hand classing. The HVI system provides more information about a bale of cotton than the subjective hand classing method.
In 1960, PCCA and Motion Control, Inc., an instrument manufacturer in Dallas, Texas, began pioneering the development of a system to eliminate the potential for human error that existed with hand classing and expand the number of fibre properties that could rapidly be determined for each bale of cotton. The goal was to be able to provide seven fibre quality characteristics for every bale produced by PCCA’s farmer-owners. Laboratory instruments were available for determining most of the fibre properties, but they required up to 15 minutes or longer to determine each of the properties. The PCCA theory was based on economics: the faster cotton could be classed, the faster it could be marketed; and, the more accurate measurements of quality could result in a more adequate supply of cotton with fibre properties to meet the specific needs of textile mills.
By the mid-1960s, the United States Department of Agricultural (USDA) and the Cotton Producers Institute (now called Cotton, Incorporated) also became involved in the research required to bring this concept to the marketplace.
In 1968 three of the first five HVI lines were in operation in Lubbock, Texas. One line was at Texas Tech University’s International Textile Center and two at PCCA. These lines were the very earliest versions to have all seven-fibre properties combined into a single testing line and measure them in less than 20 seconds per test.
In 1980, USDA built a new classing office in Lamesa, Texas, (about 60 miles south of Lubbock) specifically designed only for instrument testing all of the cotton samples received at that office using the latest version of the HVI equipment. This was a daring step but was based on data collected and analysed and improvements made in the HVI system during the previous 20 years. Although met with scepticism in the initial years by many in the cotton and textile industries, the HVI system prevailed, and USDA continued to install the instrument testing lines in all government cotton classing offices. In 1991, USDA used the HVI system on all the cotton provided to the department for classing. Today, HVI class data is accepted throughout the world and is the foundation on which cotton is traded.
In total, there are five companies manufacturing rapid instrument testing machines in the world,
i. Uster technologies, Inc.,
ii. Premier Evolvics Pvt. Ltd.,
iii. Lintronics (China, Mainland)
iv. Changing Technologies (China, Mainland)
v. Statex Engineering (India).
High volume instrument (HVI) is the most common rapid instrument testing machine made by Uster Technologies, Inc. The only other company that has over 100 machines installed in the world, mostly in Asia, is Premier Evolvics Pvt. Ltd. based in India. It is estimated that close to 2,000 rapid instruments testing machines have already been stalled in the world, mostly from Uster Technologies, Inc. Not only do the machines from each company differ, but various models from each company also differ among themselves. The full fledge models of both the manufacturers are capable of measuring measure micronaire, length, length uniformity, strength, colour, trash, maturity, sugar content etc.
High volume instrument systems are based on the fibre bundle testing, i.e., many fibres are checked at the same time and their average values determined. Traditional testing using micronaire, pressley, stelometre, and fibro graph are designed to determine average value for a large number of fibres, the so called fibre bundle tests. In HVI, the bundle testing method is automated.
CONCEPTS IN BALE MANAGEMENT
This is based on the categorising of cotton bales according to their fibre quality characteristics. It includes the measurement of the fibre characteristics with reference to each individual bale, separation of bales into classes and lying down of balanced bale mixes based on these classes. The reason for undertaking this work lies in the fact that there is sometimes a considerable variation in the fibre characteristics from one bale to another, even within the same delivery. This variation will result in the yarn quality variation if the bales are mixed in an uncontrolled manner.
The bale management software, normally embedded with an HVI, helps in selection of bales for a particular mix from the available stock. Once the data are received from HVI in the software, classification of bales in groups are done with user defined criteria.
· Manual calculation errors and the tedious task of day to day manual planning of mix are avoided.
· The storage of large number of data enables for tracking long period records or results thereby helping in clear analysis.
· More cost effective mix can be made since cost factor is also included. It also helps in planning for further requirements or purchase.
· Additional details such as party name, weighment details, and rejection details can be printed along with the test results which will be useful for the mill personnel for better analysis.
· Separate range criteria shall be selected for basic samples , lot samples and mixing
· Flexible intervals in grouping of bales with reference to the selected category.
· Basic sample results and results checked after lot arrival shall be compared graphically or numerically for easy decision making of approval or rejection.
The instruments are calibrated to read in staple length. Length measurements obtained from the instrument are considerably more repeatable than the staple length determination by the classer. In one experiment the instrument repeated the same staple length determination 44% of the time while the classer repeated this determination only 29% of the time. Similarly, the instrument repeated to 1/32″ on 76% of the samples, while the classer agreed on 71% of the samples to within 1/31″.
The precision of the HVI length measurement has been improved over the last few years. If we take the same bale of cotton used in the earlier example and repeatedly measure length with an HVI system, over two-thirds of measurements will be in a range of only about 1/32 nd of an inch: 95% of the individual readings will be within 1/32nd of an inch of the bale average. In the 77000 bales tested, the length readings were repeated within 0.02″ on 71% of the bales between laboratories.
Ø Length uniformity
The HVI system gives an indication of the fibre length distribution in the bale by use of a length uniformity index. This uniformity index is obtained by dividing the mean fibre length by the upper-half-mean length and expressing the ratio as a percent. A reading of 80% is considered average length uniformity. Higher numbers mean better length uniformity and lower numbers poorer length uniformity. Cotton with a length uniformity index of 83 and above is considered to have good length uniformity, a length uniformity index below 78 is considered to show poor length uniformity.
Ø Short fibre index
The measure of short-fibre content (SFC) in Motion Control’s HVI systems is based on the fibre length distribution throughout the test specimen. It is not the staple length that is so important but the short fibre content which is important. It is better to prefer a lower commercial staple, but with much lower short-fibre content.
The following data were taken on yarns produced under identical conditions and whose cotton fibres were identical in all properties except for short-fibre content. The effects on ends down and several aspects of yarn quality are shown below.
LOT -A, (8.6% SFC)
LOT-B (11.6% SFC)
Ends down / 1000 hrs
Skein strength (lb)
Single end strength g/tex
These results show that an increase of short-fibre content in cotton is detrimental to process efficiency and product quality. HVI systems measure length parameters of cotton samples by the fibrogram technique. The following assumptions describe the fibro gram sampling process:
· The fibrogram sample is taken from some population of fibres.
· The probability of sampling a particular fibre is proportional to its length
· A sampled fibre will be held at a random point along its length
· A sampled fibre will project two ends away from the holding point, such that all of the ends will be parallel and aligned at the holding point.
· All fibres have the same uniform density
The High Volume Instruments also provide empirical equations of short fibre content based on the results of cotton produced in the United States in a particular year.
Short Fibre Index = 122.56 – (12.87 x UHM) – (1.22 x UI)
where UHM – Upper Half Mean Length (inches)
UI – Uniformity Index
Short Fibre Index = 90.34 – (37.47 x SL2) – (0.90 x UR)
Where SL2 – 2.5% Span length (inches)
UR – Uniformity Ratio
In typical fibrogram curve, the horizontal axis represents the lengths of the ends of sampled fibres. The vertical axis represents the percent of fibre ends in the fibrogram having that length or greater.
1. Strength and elongation:-
Ø Principle of measurement
HVI uses the “Constant rate of elongation” principle while testing the fibre sample. The available conventional methods of strength measurement are slow and are not compatible to be used with the HVI. The main hindering factor is the measurement of weight of the test specimen, which is necessary to estimate the tenacity of the sample. Expression of the breaking strength in terms of tenacity is important to make easy comparison between specimens of varying fineness.
The strength measurement made by the HVI systems is unlike the traditional laboratory measurements of Pressley and Stelometer in several important ways. First of all the test specimens are prepared in a very different manner. In the laboratory method the fibres are selected, combed and carefully prepared to align them in the jaw clamps. Each and every fibre spans the entire distance across the jaw surfaces and the space between the jaws.
Strength is measured physically by clamping a fibre bundle between 2 pairs of clamps at known distance. The second pair of clamps pulls away from the first pair at a constant speed until the fibre bundle breaks. The distance it travels, extending the fibre bundle before breakage, is reported as elongation.
In the HVI instruments the fibres are randomly selected and automatically prepared for testing. They are combed to remove loose fibres and to straighten the clamped fibres, also brushed to remove crimp before testing. The mechanization of the specimen preparation techniques has resulted in a “tapered” specimen where fibre ends are found in the jaw clamp surfaces as well as in the space between the jaws.
A second important difference between traditional laboratory strength measurements and HVI strength measurements is that in the laboratory measurements the mass of the broken fibres is determined by weighing the test specimen. In the HVI systems the mass is determined by the less direct methods of light absorption and resistance to air flow. The HVI strength mass measurement is further complicated by having to measure the mass at the exact point of breaks on the tapered specimen.
A third significant difference between laboratory and HVI strength measurements is the rate or speed at which the fibres are broken. The HVI systems break the fibres about 10 times faster than the laboratory methods.
Generally HVI grams per Tex readings are 1 to 2 units (3 to 5%) higher in numerical value. In some individual cases that seem to be related to variety, the differences can be as much as 6 to 8% higher. This has not caused a great deal of problems in the US, perhaps because a precedent was set many years ago when we began adjusting our Stelometer strength values about 27% to put them on Presley level.
Relative to the other HVI measurements, the strength measurement is less precise. Going back to our single bale of cotton and doing repeated measurements on the bale we shall find that 68% of the readings will be within 1 g/Tex of the bale average. So if the bale has an average strength of 25 g.tex, 68% of the individual readings will be between 24 and 26 g/Tex, and 95% between 23 and 27 g/Tex
Because of this range in the readings within a single bale, almost all HVI users make either 2 or 4 tests per bale and average the readings. When the average readings are repeated within a laboratory, the averages are repeated to within one strength unit about 80% of the time. However, when comparisons are made between laboratories the agreement on individual bales to within plus or minus 1 g/tex decreases to 55%.
This decrease in strength agreement between laboratories is probably related to the difficulty of holding a constant relative humidity in the test labs. Test data indicate that 1% shift in relative humidity will shift the strength level about 1%. For example, if the relative humidity in the laboratory changes 3% (from 63 to 66%), the strength would change about 1 g/tex (from 24 to 25 g/Tex)
2. Fibre fineness:-
Ø Principle of measurement
Fibre fineness is normally expressed as a micronaire value (microgram per inch). It is measured by relating airflow resistance to the specific surface of fibres and maturity ration is calculated using a sophisticated algorithm based on several HVI™ measurements.
The micronaire reading given by the HVI systems is the same as has been used in the commercial marketing of cotton for almost 25 years. The repeatability of the data and the operator ease of performing the test have been improved slightly in the HVI micronaire measurement over the original instruments by elimination of the requirement of exactly weighing the test specimen. The micronaire instruments available today use microcomputers to adjust the reading for a range of test specimen sizes.
The micronaire reading is considered both precise and referable. For example, if we have a bale of cotton that has an average micronaire of 4.2 and repeatedly test samples from that bale, over two-thirds of that micronaire readings will be between 4.1 and 4.3 and 95 %of the readings between and 4.0 and 4.4. Thus, with only one or two tests per bale we can get a very precise measure of the average micronaire of the bale.
This reading is also very repeatable from laboratory to laboratory. In USDA approx. 77000 bales were tested per day in each laboratory, micronaire measurements made in different laboratories agreed with each other within 0.1 micronaire units on 77% of the bales.
The reading is influenced by both fibre maturity and fibre fineness. For a given growing area, the cotton variety generally sets the fibre fineness, and the environmental factors control or influence the fibre maturity. Thus, within a growing area the micronaire value is usually highly related to the maturity value. However, on an international scale, it cannot be known from the micronaire readings alone if cottons with different micronaire are of different fineness or if they have different maturity levels.
Ø Principle of measurement
Moisture content of the cotton sample at the time of testing, using conductive moisture probe and the main principle involved in the measurement is based on the measurement of the dielectric constant of a material.
Ø Principle of measurement
Rd (Whiteness), +b (Yellowness), Colour Grade
Measured optically by different colour filters, converted to USDA Upland or Pima Colour Grades or regional customized colour chart.
Ø Other information
The measurement of cotton colour predates the measurement of micronaire, but because colour has always been an important component of classer’s grade it has not received attention as an independent fibre property. However the measurement of colour was incorporated into the very early HVI systems as one of the primary fibre properties.
Determination of cotton colour requires the measurement of two properties, the grayness and yellowness of the fibres. The grayness is a measure of the amount of light reflected from the mass of the fibre. We call this the reflectance or Rd value. The yellowness is measured on what we call Hunter’s +b scale after the man who developed it. The other scales that describe colour space (blue, red, green) are not measured becasue they are considered relatively constant for cotton.
Returning once again to the measurements on our single bale, we see that repeated measurements of colour are in good agreement. For greyness or reflectance readings, 68% of the readings will be within 0.5 Rd units of the bale average, and 95% within one Rd unit for the average.
As for yellowness, over two-thirds of these readings will be within one-fourth of one +b unit of the average, and 95% within one-half of one +b unit. The greyness (Rd) and yellowness (+b) measurements are related to grade through a colour chart which was developed by a USDA researcher. The USDA test of 77000 bales showed the colour readings to be the most repeatable of all data between laboratories; 87% of the bales repeated within one greyness(Rd) unit, and 85% repeated within one-half of one yellowness(+b) unit.
5. Trash content
Ø Principle of measurement
Particle Count, % Surface Area Covered by Trash, Trash Code
Measured optically by utilizing a digital camera, and converted to USDA trash grades or customized regional trash standards.
Ø Other information
The HVI systems measure trash or non-lint content by use of video camera to determine the amount of surface area of the sample that is covered with dark spots. As the camera scans the surface of the sample, the video output drops when a dark spot (presumed to be trash) is encountered. The video signal is processed by a microcomputer to determine the number of dark spots encountered (COUNT) and the per cent of the surface area covered by the dark spots (AREA). The area and count data are used in an equation to predict the amount of visible non-lint content as measured on the Shirley Analyser. The HVI trash data output is a two-digit number which gives the predicted non-lint content for that bale. For example, a trash reading of 28 would mean that the predicted Shirley Analyser visible non-lint content of that bale would be 2.8%.
While the video trash instruments have been around for several years, but the data suggest that the prediction of non-lint content is accurate to about 0.75% non-lint, and that the measurements are repeatable 95% of the time to within 1% non-lint content.
6. Maturity and stickiness
Ø Principle of measurement
Calculated using a sophisticated algorithm based on several HVI™ measurements.
Ø Other information
Near infrared analysis provides a fast, safe and easy means to measure cotton maturity, fineness and sugar content at HVI speed without the need for time consuming sample preparation or fiber blending.
This technology is based on the near infrared reflectance spectroscopy principle in the wavelength range of 750 to 2500 nanometres. Differences of maturity in cotton fibres are recognized through distinctly different NIR absorbance spectra. NIR technology also allows for the measurement of sugar content by separating the absorbance characteristics of various sugars from the absorbance of cotton material.
Cotton maturity is the best indicator of potential dyeing problems in cotton products. Immature fibres do not absorb dye as well as mature fibres. This results in a variety of dye-related appearance problems such as barre, reduced colour yield, and white specks. Barre is an unwanted striped appearance in fabric, and is often a result of using yarns containing fibres of different maturity levels. For dyed yarn, colour yield is diminished when immature fibres are used. White specks are small spots in the yarn or fabric which do not dye at all. These specks are usually attributed to neps (tangled clusters of very immature fibres)
NIR maturity and dye uptake in cotton yarns have been shown to correlate highly with maturity as measured by NIR. A correlation of R=0.96 was obtained for a set of 15 cottons.
In a joint study by ITT and a European research organization, 45 cottons from four continents were tested for maturity using the NIR method and the SHIRLEY Development Fineness/ Maturity tester (FMT). For these samples, NIR and FMT maturity correlated very highly (R=0.94).
On 15 cottons from different growth areas of the USA, NIR maturity was found to correlate with r2 = 0.9 through a method developed by the United States Department of Agriculture (USDA). In this method, fibres are cross-sectioned and microscopically evaluated.
Sugar Content is a valid indicator of potential processing problems. Near infrared analysis, because of its adaptability to HVI, allows for screening of bales prior to use. The information serves to selected bales to avoid preparation of cotton mixes of bales with excessive sugar content. Cotton stickiness consists of two major causes- honeydew form white flies and aphids and high level of natural plant sugars. Both are periodic problems which cause efficiency losses in yarn manufacturing.
The problems with the randomly distributed honeydew contamination often results in costly production interruptions and requires immediate action often as severe as discontinuing the use of contaminated cottons.
Natural plant sugars are more evenly distributed and cause problems of residue build-up, lint accumulation and roll laps. Quality problems created by plant sugar stickiness are often more critical in the spinning process than the honeydew stickiness. Lint residues which accumulate on machine parts in various processes will break loose and become part of the fibre mass resulting in yarn imperfections. An effective way to control cotton stickiness in processing is to blend sticky and non-stick cottons. Knowing the sugar content of each bale of cotton used in each mix minimizes day-to-day variations in processing efficiency and products more consistent yarn quality. Screening the bale inventory for sugar content prior to processing will allow the selection of mixes with good processing characteristics while also utilizing the entire bale inventory.
The relationship between percent sugar content by NIR analysis and the Perkins method shows an excellent correlation of r2=0.95. The amount of reducing material on cotton fibre in the Perkins method is determined by comparing the reducing ability of the water extract of the fibre to that of a standard reducing substance. Using the NIR method, the amount of reducing sugar in cotton is measured.
Merits of HVI testing:-
· The results are practically independent of the operator.
· The results are based on large volume samples, and are therefore more significant.
· The time for testing per sample is 0.3 minutes. The respective fibre data are immediately available.
· About 180 samples per hour can be tested and that too with only 2 operators.
· The data are clearly arranged in summarised reports.
· They make possible the best utilisation of raw material data.
· It is best applied to instituting optimum condition for raw material.
· Problems as a result of fibre material can be predicted, and corrective measures instituted before such problems can occur.
· The classing of cotton and the laying down of a mix in the spinning mill. This HVI testing is suitable for the extensive quality control of all the bales processed in a spinning mill.
· The mill is in a position to determine its own quality level within a certain operating range.
Standardized process for hvi testing:-
· Pre-season precision and accuracy tests for all HVIs:-
All offices are required to select known-value cotton samples and perform stringent and consistent performance evaluations, before machines can be placed into production.
· Instrument calibration
Strict calibration procedures used by all offices and Quality Assurance Branch Known-value cottons and tiles used for calibration, Periodic calibration checks, Data is collected, analysed and corrective actions taken when necessary
· Quality Assurance Branch,Check lot Program
Approximately 1% of entire crop is selected from each field office for retest in “QA” as Check lots. Check lot data is returned to classing offices quickly for review. Check lot system assists in monitoring office performance and ensuring proper testing levels.
· Laboratory Atmospheric Conditions:-
Testing laboratories are required to maintain conditions of 70°±1° F and 65%±2% RH. All cotton must stabilize at moisture content level of 6.75%-8.25% prior to HVI testing.
Various HVI models available in market in present date are:-
Raw material represents about 50 to 70% of the production cost of a short-staple yarn. This fact is sufficient to indicate the significance of the raw material for the yarn producer. It is not possible to use a problem-free raw material always, because cotton is a natural fibre and there are many properties which will affect the performance. If all the properties have to be good for the cotton, the raw material would be too expensive. To produce a good yarn with these difficulties, an intimate knowledge of the raw material and its behaviour in processing is a must.
Fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. Moreover, such quantified characteristics must also be assessed with reference to the following
what is the ideal value?
what amount of variation is acceptable in the bale material?
what amount of variation is acceptable in the final blend
Such valuable experience, which allows one to determine the most suitable use for the raw material, can only be obtained by means of a long, intensified and direct association with the raw material, the spinning process and the end product.
Low cost yarn manufacture, fulfilling of all quality requirements and a controlled fibre feed with known fibre properties are necessary in order to compete on the world’s textile markets. Yarn production begins with the rawmaterial in bales, whereby success or failure is determined by the fibre quality, its price and availability. Successful yarn producers optimise profits by a process oriented selection and mixing of the rawmaterial, followed by optimization of the machine settings, production rates, operating elements, etc. Simultaneously, quality is ensured
by means of a closed loop control system, which requires the application of supervisory system at spinning and spinning preparation, as well as a means of selecting the most suitable bale mix.
BASIC FIBRE CHARACTERISTICS:
A textile fibre is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibres or production factors of manmade fibres are responsible for this situation. An individual fibre, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrient-supply, seasonal, weather, or other factors influencing the rate of cell development in natural fibres. Surface characteristics also play some part in increasing the variability of fibre shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals along the cellulosic natural fibres etc.
Following are the basic characteristics of cotton fibre
STANDARD ATMOSPHERE FOR TESTING:
The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C
may be used.
The “length” of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries
It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight.
Upper quartile length:
It is that value of length for which 75% of all the observed values are lower, and 25% higher.
It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a
numerical length distribution
eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length.
It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the following way.
(Mode-Mean) = 3(Median-Mean)
Median is the particular value of length above and below which exactly 50% of the fibres lie.
2.5% Span length:
It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”.
50% Span length:
It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”.
The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths.
Effective length = 1.013 x 2.5% Span length + 4.39
Mean length = 1.242 x 50% Span length + 9.78
FIBRE LENGTH VARIATION:
Even though, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by any one of the following attributes
Co-efficient of variation of length (by weight or number)
Dispersion percentage and percentage of short fibres
Uniformity ratio is defined as the ratio of 50% span length to 2.5% span length expressed as a percentage. Several instruments and methods are available for determination of length. Following are some
Shirley comb sorter
A.N. Stapling apparatus
uniformity ration = (50% span length / 2.5% span length) x 100
uniformity index = (mean length / upper half mean length) x 100
The negative effects of the presence of a high proportion of short fibres is well known. A high percentage of short fibres is usually associated with,
– Increased yarn irregularity and ends down which reduce quality and increase processing costs
– Increased number of neps and slubs which is detrimental to the yarn appearance
– Higher fly liberation and machine contamination in spinning, weaving and knitting operations.
– Higher wastage in combing and other operations.
While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a ‘short fibre’. In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. Initially, an estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method
Short fibre content = (UB/OB) x 100
While such a simple definition of short fibres is perhaps adequate for characterising raw cotton samples, it is too simple a definition to use with regard to the spinning process. The setting of all spinning machines is based on either the staple length of fibres or its equivalent which does not take into account the effect of short fibres. In this regard, the concept of ‘Floating Fibre Index’ defined by Hertel (1962) can be considered to be a better parameter to consider the effect of short fibres on spinning performance. Floating fibres are defined as those fibres which are not clamped by either pair of rollers in a drafting zone.
Floating Fibre Index (FFI) was defined as
FFI = ((2.5% span length/mean length)-1)x(100)
The proportion of short fibres has an extremely great impact on yarn quality and production. The proportion of short fibres has increased substantially in recent years due to mechanical picking and hard ginning. In most of the cases the absolute short fibre proportion is specified today as the percentage of fibres shorter than 12mm. Fibrograph is the most widely used instrument in the textile industry , some information regarding fibrograph is given below.
Fibrograph measurements provide a relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner.
Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors.
Fibrograph tests are more objective than commercial staple length classifications and also provide additional information on fibre length uniformity of cotton fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes.
Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to toal length of all fibres in the sample and that the point of catch for a fibre is at random along its length.
Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres.
Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is micrograms per inch and the various air-flow instruments developed for measuring fibre fineness are calibrated in this unit.
Following are some methods of determining fibre fineness.
gravimetric or dimensional measurements
vibrating string method
Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value.
It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres.
AIR-FLOW METHOD (MICRONAIRE INSTRUMENT):
The resistance offered to the flow of air through a plug of fibres is dependent upon the specific surface area of the fibres. Fineness tester have been evolved on this principle for determining fineness of cotton. The specific surface area which determines the flow of air through a cotton plug, is dependent not only upon the linear density of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with caution particularly when testing samples varying widely in maturity.
In the micronaire instrument, a weighed quantity of 3.24 gms of well opened cotton sample is compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample, at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flowmeter. The sample for Micronaire test should be well opened cleaned and thoroughly mixed( by hand fluffing and opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy to operate and presents little difficulty as regards its maintenance.
Fibre maturity is another important characteristic of cotton and is an index of the extent of
development of the fibres. As is the case with other fibre properties, the maturity of cotton fibres varies not only between fibres of different samples but also between fibres of the same seed. The causes for the differences observed in maturity, is due to variations in the degree of the secondary thickening or deposition of cellulose in a fibre.
A cotton fibre consists of a cuticle, a primary layer and secondary layers of cellulose surrounding the lumen or central canal. In the case of mature fibres, the secondary thickening is very high, and in some cases, the lumen is not visible. In the case of immature fibres, due to some physiological causes, the secondary deposition of cellulose has not taken sufficiently and in extreme cases the secondary thickening is practically absent, leaving a wide lumen throughout the fibre. Hence to a cotton breeder, the presence of excessive immature
fibres in a sample would indicate some defect in the plant growth. To a technologist, the presence of excessive percentage of immature fibres in a sample is undesirable as this causes excessive waste losses in processing lowering of the yarn appearance grade due to formation of neps, uneven dyeing, etc.
An immature fibre will show a lower weight per unit length than a mature fibre of the same cotton, as the former will have less deposition of cellulose inside the fibre. This analogy can be extended in some cases to fibres belonging to different samples of cotton also. Hence it is essential to measure the maturity of a cotton sample in addition to determining its fineness, to check whether the observed fineness is an inherent characteristic or is a result of the maturity.
DIFFERENT METHODS OF TESTING MATURITY:
MATURITY RATIO: The fibres after being swollen with 18% caustic soda are examined under the microscope with suitable magnification. The fibres are classified into different maturity groups depending upon the relative dimensions of wall-thickness and lumen. However the procedures followed in different countries for sampling and classification differ in certain respects. The swollen fibres are classed into three groups as follows
Normal : rod like fibres with no convolution and no continuous lumen are classed as “normal”
Dead : convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as “Dead”
Thin-walled: The intermediate ones are classed as “thin-walled”
A combined index known as maturity ratio is used to express the results.
Maturity ratio = ((Normal – Dead)/200) + 0.70
N – % of Normal fibres
D – % of Dead fibres
MATURITY CO-EFFICIENT: Around 100 fibres from Baer sorter combs are spread across the glass slide(maturity slide) and the overlapping fibres are again separated with the help of a teasing needle. The free ends of the fibres are then held in the clamp on the second strip of the maturity slide which is adjustable to keep the fibres stretched to the desired extent. The fibres are then irrigated with 18% caustic soda solution and covered with a suitable slip. The slide is then placed on the microscope and examined. Fibres are classed into the following three categories
Mature : (Lumen width “L”)/(wall thickness”W”) is less than 1
Half mature : (Lumen width “L”)/(wall thickness “W”) is less than 2 and more than 1
Immature : (Lumen width “L”)/(wall thickness “W”) is more than 2
About four to eight slides are prepared from each sample and examined. The results are presented as percentage of mature, half-mature and immature fibres in a sample. The results are also expressed in terms of “Maturity Coefficient”
M is percentage of Mature fibres
H is percentage of Half mature fibres
I is percentage of Immature fibres
If maturity coefficient is
less than 0.7, it is called as immature cotton
between 0.7 to 0.9, it is called as medium mature cotton
above 0.9, it is called as mature cotton
AIR FLOW METHOD FOR MEASURING MATURITY:
There are other techniques for measuring maturity using Micronaire instrument. As the fineness value determined by the Micronaire is dependent both on the intrinsic fineness(perimeter of the fibre) and the maturity, it may be assumed that if the intrinsic fineness is constant then the Micronaire value is a measure of the maturity
DYEING METHODS: Mature and immature fibers differ in their behaviour towards various dyes. Certain dyes are preferentially taken up by the mature fibres while some dyes are preferentially absorbed by the immature fibres. Based on this observation, a differential dyeing technique was developed in the United States of America for estimating the maturity of cotton. In this technique, the sample is dyed in a bath containing a mixture of two dyes, namely Diphenyl Fast Red 5 BL and Chlorantine Fast Green BLL. The mature fibres take up the red dye preferentially, while the thin walled immature fibres take up the green dye. An estimate of the average of the sample can be visually assessed by the amount of red and green fibres.
The different measures available for reporting fibre strength are
tensile strength and
tenacity or intrinsic strength
Coarse cottons generally give higher values for fibre strength than finer ones. In order, to compare strength of two cottons differing in fineness, it is necessary to eliminate the effect of the difference in cross-sectional area by dividing the observed fibre strength by the fibre weight per unit length. The value so obtained is known as “INTRINSIC STRENGTH or TENACITY”. Tenacity is found to be better related to spinning than the breaking strength.
The strength characteristics can be determined either on individual fibres or on bundle of fibres.
SINGLE FIBRE STRENGTH:
The tenacity of fibre is dependent upon the following factors
chain length of molecules in the fibre orientation of molecules size of the crystallites distribution of the crystallites gauge length used the rate of loading type of instrument used and atmospheric conditions
The mean single fibre strength determined is expressed in units of “grams/tex”. As it is seen the the unit for tenacity has the dimension of length only, and hence this property is also expressed as the “BREAKING LENGTH”, which can be considered as the length of the specimen equivalent in weight to the breaking load. Since tex is the mass in grams of one kilometer of the specimen, the tenacity values expressed in grams/tex will correspond to the breaking length in kilometers.
BUNDLE FIBRE STRENGTH:
In practice, fibres are not used individually but in groups, such as in yarns or fabrics. Thus, bundles or groups of fibres come into play during the tensile break of yarns or fabrics. Further,the correlation between spinning performance and bundle strength is atleast as high as that between spinning performance and intrinsic strength determined by testing individual fibres. The testing of bundles of fibres takes less time and involves less strain than testing individual fibres. In view of these considerations, determination of breaking strength of fibre bundles has assumed greater importance than single fibre strength tests.
There are three types of elongation
Permanent elongation: the length which extended during loading did not recover during relaxation
Elastic elongation:The extensions through which the fibres does return
Breaking elongation:the maximum extension at which the yarn breaks i.e.permanent and elastic elongation together Elongation is specified as a percentage of the starting length. The elastic elongation is of deceisive importance, since textile products without elasticity would hardly be usable. They must be able to deforme, In order to withstand high loading, but they must also return to shatpe. The greater resistance to crease
for wool compared to cotton arises, from the difference in their elongation. For cotton it is 6 -10% and for wool it is aroun 25 – 45%. For normal textile goods, higher elongation are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations.
The Torsional rigidity of a fibre may be defined as the torque or twisting force required to twist 1 cm length of the fibre through 360 degrees and is proportional to the product of the modulus of rigidity and square of the area of cross-section, the constant of proportionality being dependent upon the shape of the cross-section of the fibre. The torsional rigidity of cotton has therefore been found to be very much dependent upon the gravimetric fineness of the fibres. As the rigidity of fibres is sensitive to the relative humidity of the surrounding atmosphere, it is essential that the tests are carried out in a conditional room where the relative
humidity is kept constant.
THE SLENDERNESS RATIO:
Fibre stiffness plays a significant role mainly when rolling, revolving, twisting movements are involved. A fibre which is too stiff has difficulty adapting to the movements. It is difficult to get bound into the yarn, which results in higher hairiness. Fibres which are not stiff enough have too little springiness. They do not return to shape after deformation. They have no longitudinal resistance. In most cases this leads to formation of neps. Fibre stiffness is dependent upon fibre substance and also upon the relationship between fibre length and fibre fineness. Fibres having the same structure will be stiffer, the shorter they are. The slenderness ratio can serve as a measure of stiffness,
slender ratio = fibre length /fibre diameter
Since the fibres must wind as they are bound-in during yarn formation in the ring spinning machine, the slenderness ratio also determines to some extent where the fibres will finish up.fine and/or long fibres in the middle coarse and/or short fibres at the yarn periphery.
In addition to useable fibres, cotton stock contains foreign matter of various kinds. This foreign material can lead to extreme disturbances during processing. Trash affects yarn and fabric quality. Cottons with two different trash contents should not be mixed together, as it will lead to processing difficulties. Optimising process parameters will be of great difficulty under this situation, therefore it is a must to know the amount of trash and the type of trash before deciding the mixing.
SHIRLEY TRASH ANLAYSER:
A popular trash measuring device is the Shirley Analyser, which separates trash and foreign matter from lint by mechanical methods. The result is an expression of trash as a percentage of the combined weight of trash and lint of a sample. This instrument is used
to give the exact value of waste figures and also the proportion of clean cotton and trash in the material
to select the proper processing sequence based upon the trash content
to assess the cleaning efficiency of each machine
to determine the loss of good fibre in the sequence of opening and cleaning.
Stricter sliver quality requirements led to the gradual evolution of opening and cleaning machinery leading to a situation where blow room and carding machinery were designed to remove exclusively certain specific types of trash particles. This necessitated the segregation of the trash in the cotton sample to different grades determined by their size. This was achieved in the instruments like the Trash Separator and the Micro Dust Trash Analyser which could be considered as modified versions of the Shirley Analyser.
The high volume instruments introduced the concept of optical methods of trash measurement which utilised video scanning trash-meters to identify areas darker than normal on a cotton sample surface. Here, the trash content was expressed as the percentage area covered by the trash particles. However in such methods, comparability with the conventional method could not be established in view of the non-uniform distribution of trash in a given cotton sample and the relatively smaller sample size to determine such a parameter. Consequently, it is yet to establish any significant name in the industry.
RAW MATERIAL AS A FACTOR AFFECTING SPINNING:
Fineness determines how many fibres are present in the cross-section of a yarn of particular linear density. 30 to 50 fibres are needed minimum to produce a yarn fibre fineness influences
drape of the fabric
productivity is influenced by the end breakage rate and twist per inch required in the yarn
Immature fibres(unripe fibres) have neither adequate strength nor adequate longitudinal siffness. They therefore lead to the following,
loss of yarn strength
high proportion of short fibres
processing difficulties at the card and blowroom
Fibre length is one among the most important characteristics. It influnces
handle of the product
lustre of the product
It can be assumed that fibres of under 4 – 5 mm will be lost in processing(as waste and fly). fibres upto about 12 – 15 mm do not contribute to strength but only to fullness of the yarn. But fibres above these lengths produce the other positive characteristics in the yarn.
The proportion of short fibres has extremely great influence on the following parameters
handle of the product
lustre of the product
A large proportion of short fibre leads to strong fly contamination, strain on personnel, on the machines, on the work room and on the air-conditioning, and also to extreme drafting difficulties.
A uniform yarn would have the same no of fibres in the cross-section, at all points along it. If the fibres themeselves have variations within themselves, then the yarn will be more irregular.
If 2.5% span length of the fibre increases, the yarn strength also icreases due to the fact that
there is a greater contribution by the fibre strength for the yarn strength in the case of longer fibres.
Neps are small entanglements or knots of fibres. There are two types of neps. They are 1.fibre neps and 2.seed-coat neps.In general fibre neps predominate, the core of the nep consists of unripe and dead fibres. Thus it is clear that there is a relationship between neppiness and maturity index. Neppiness is also dependent on the fibre fineness, because fine fibres have less longitudinal stiffness than coarser fibres.
Nature produces countless fibres, most of which are not usable for textiles because of inadequate strength.
The minimum strength for a textile fibre is approximately 6gms/tex ( about 6 kn breaking length).
Since blending of the fibres into the yarn is achieved mainly by twisting, and can exploit 30 to 70% of the strength of the material, a lower limit of about 3 gms/tex is finally obtained for the yarn strength, which varies linearly with the fibre strength.
Low micronaire value of cotton results in higher yarn tenacity.In coarser counts the influence of micronaire to increase yarn tenacity is not as significant as fine count.
Fibre strength is moisture dependent. i.e. It depends strongly upon the climatic conditions and upon the time of exposure. Strength of cotton,linen etc. increases with increasing moisture content.
The most important property inflencing yarn elongation is fibre elongation.Fibre strength ranks seconds in importance as a contributor to yarn elongation. Fibre fineness influences yarn elongation only after fibre elongation and strength. Other characters such as span length, uniformity ratio, maturity etc, do not contribute significantly to the yarn elongation.Yarn elongation increases with increasing twist. Coarser yarn has higher elongation than finer yarn. Yarn elongation decreases with increasing spinning tension. Yarn elongation is also influenced
by traveller weight and high variation in twist insertion.
For ring yarns the number of thin places increases, as the trash content and uniformity ratio increased For rotor yarns 50%span length and bundle strength has an influence on thin places.
Thick places in ringyarn is mainly affected by 50%span length, trash content and shor fibre content.
The following expression helps to obtain the yarn CSP achievable at optimum twist multiplier with the available fibre properties.
Lea CSP for Karded count = 280 x SQRT(FQI) + 700 – 13C
Lea CSP for combed count = (280 x SQRT(FQI) + 700 – 13C)x(1+W)/100
FQI = LSM/F
L = 50% span length(mm)
S = bundle strength (g/tex)
M = Maturity ratio measured by shirly FMT
F = Fibre fineness (micrograms/inch)
C = yarn count
W = comber waste%
Higher FQI values are associated with higher yarn strength in the case of carded counts but in combed count such a relationship is not noticed due to the effect of combing
Higher 2.5 % span length, uniformity ratio, maturity ratio and lower trash content results in lower imperfection. FQI does not show any significant influence on the imperfection.
The unevenness of carded hosiery yarn does not show any significant relationships with any of the fibre properties except the micronaire value. As the micronaire value increases, U% also increases. Increase in FQI however shows a reduction in U%.
Honey-dew is the best known sticky substance on cotton fibres. This is a secretion of the cotton louse. There are other types of sticky substances also. They are given below.
honey dew – secretions
fungus and bacteria – decomposition products
vegetable substances – sugars from plant juices, leaf nectar, over production of wax,
fats, oils – seed oil from ginning
synthetic substances – defoliants, insecticides, fertilizers, oil from harvesting machines
In the great majority of cases, the substance is one of a group of sugars of the most variable composition, primarily but not exclusively, fructose, glucose, saccharose, melezitose, as found, for example on sudan cotton. These saccharides are mostly, but not always, prodced by insects or the plants themselves, depending upon the influence on the plants prior to plucking. Whether or not a fibre will stick depends, not only on the quantity of the sticky coating and it composition, but also on the degree of saturation as a solution. Sugars are broken down by fermentation and by microorganisms during storage of the cotton. This occurs more quickly the higher the moisture content. During spinning of sticky cotton, the R.H.% of the air in the production are should be held as low as possible.