Yarn Numbering System


Textiles are often sold on a weight basis and consequently it is natural to express the size of “thickness” of a yarn in terms of weight (or mass). There are two basic ways in which this may be done. These are: (a) by saying how much a given length of yarn weighs, or (b) by saying what length of yarn one would have in a given weight. Generally these are known as the direct and indirect systems of yarn numbering, respectively. In other words:

Direct yarn number =  Weight / unit Length
Indirect yarn number = Length / unit weight

It will be noted that one is the inverse of the other. In the first case, the number gets larger as the yarn or strand gets coarser. In the second case, the number gets smaller as the yarn or strand gets coarser.

Each system has its advantages and disadvantages and each has found areas in which, by custom, it is used. It so happens that because long, thin strands are usually involved, the length figures are usually large and the weight figures are small. Consequently, the yarn numbers would get impossibly large or impossibly small unless special units are used. The following paragraphs will explain a selection of the most important sets of units used. A summary is listed in Table 1

image

The technical name used to describe the yarn size in the direct system is linear density,* and this is always expressed in terms of weight/unit length. In commerce, the technical name is used less frequently than in the fiber industry or the scientific community. Often the name of the particular unit, such as denier or tex is used instead. Sometimes the term “yarn number” is used, but this is confusing unless the system is quoted.

With the usual range of linear densities found in yarns, one pound of yarn if stretched out straight could extend up to 20 miles in length. Clearly if one were to express the linear density in lb/yd, the numbers would be impossibly small and cumbersome to use. Since scientists tend to use the metric system [grams (g) and meters (m) for weight and length, respectively] one could consider g/m as a unit, but in this case, it turns out that the number is too large to be handled conveniently.

In practice there are two major subsections, which refer to yarn. In one case, the logically minded scientists have chosen a length unit of 1000 meters, whereas the technologists have chosen 9000 meters. The reason for this latter choice is obscure.

The scientific subsystem uses the unit “tex,” where 1 tex is the weight in g of 1000 meters (1 km) of yarn and the number gets bigger as the yarn gets fatter. Thus, a 50 tex yarn weighs 50 g for every kilometer of yarn. The normal metric prefixes of kilo, deci, etc., can also be applied to the unit tex. Hence 1 decitex is 1/10 tex and 1 kilotex = 1000 tex.
The fiber industry tends to use the unit “denier” where 1 denier is the weight in g of 9000 meters of yarn. Thus a 450 denier yarn weighs 450 g for every 9000 meters. A moment’s reflection will show that the two examples given refer to the same yarn size. Denier is very often used to describe the size of the fiber; hence, a 1½ denier filament weighs 1½ g per 9000 m of that filament. In passing it might be noted that if the 450 denier yarn is made up of 1½ denier filaments, there will be 450/1½ = 300 filaments making up that yarn.
As will be shown later, there are intermediate products, such as sliver, to which the direct system of measurement can be applied. A sliver is a rope-like material and a typical linear density (or “sliver weight”) is 50 grains/yard. (A grain is 1/7000 lb. and care should be taken when handwriting the units to distinguish clearly between grain and gram.)
In this bulletin, the symbol “n” will be used to denote linear density, and in every case, the appropriate units should be quoted.

  • INDIRECT SYSTEMS

It will be remembered that the indirect system is in terms of length per unit weight. Once again, there has to be special units, but there is a large variety of systems which are a legacy of the ancient crafts, and there is no discernible logic in the choice of units. Generally, all the subsystems in this category are referred to as yarn count or yarn number, and it is necessary to specify the subsystem if confusion is to be avoided. It is normal to specify the yarn count in hanks/lb where a hank contains a specified length of yarn.

Unfortunately, each of the subsystems specifies a different length.

In cotton processing technology (and those technologies which have evolved from that technology), the units developed in England during the industrial revolution are still used in the USA. In this case, a hank is specified as containing 840 yds* of yarn. Thus, if the count of a singles yarn is 20 hanks/lb. (usually written as 20s or 20/1), there will be 20 x 840 yards in a pound of yarn. The symbol used in this bulletin will be Ne where the subscript refers to “English” and distinguishes it from Nm, which refers to the metric count (meters/gram). In the case of long staple yarns, whose technology is derived from one of the processes for making yarn out of wool, a hank is often defined as 560 yds. of yarn, and in this case, the symbol NW will be used to describe count. There are many others, and a list of some specified hank lengths is given in Table 1.

With the indirect system, the number gets larger as the yarn gets finer. In the English cotton system, a 4s yarn is very coarse whereas 40s yarn is fine.

  • CONVERSION

In normal practice, it is unnecessary to go through such a calculation each time a conversion is  required, and generally a conversion factor can be used (see Table 2). In the case of converting from one direct subsystem to another, one merely multiplies the known linear density by the conversion factor to get it into different counts, similarly, when converting from one indirect subsystem to another. When converting from indirect to direct, or vice versa, then the factor must be divided by the known quantity.

image

Digg This
Advertisements

Magnetic Ring-Spinning-Revolutionizing the Tradition


BY:- Faissal Abdel-Hady, leader; Yehia El Mogahzy
(Auburn Textile Engineering)

“By replacing the traveler in ring spinning with a disc that rotates in a magnetic field, we hope to maintain the high quality of ring spun yarn, but at much higher speeds.”

In today’s spinning technology, at least 4 types of spinning systems are commercially available. These are the tradi-tional ring spinning, rotor spinning, air-jet spinning and friction spinning. Among them, ring spinning stands alone in providing high quality yarn suitable for any type of tex-tile end product. Other more recent systems enjoy much higher production speed than traditional ring spinning, but yarn quality restricts their use to only narrow ranges of tex-tile products. The primary technological limitation of ring spinning lies in the speed of the ring-traveler system. The traveler is a C-shaped thin piece of metal that is used for a limited period of time, disposed and replaced on a frequent basis. Three specific issues must be addressed to overcome this limitation:image
Close View of Magnetically Suspended Spinning Ring
• the dependence of the yarn linear speed (or delivery speed) on the rotational speed of the traveler
• the continuous need to stabilize yarn tension during spinning and the dependence of this stability on the traveler speed
• the impact of traveler speed on fiber behavior in the spinning triangle
Research to date has only provided about a 15% improve-ment in traveler speed without affecting the traveler/ring contact thermal load capacity. Ring spinning is still at a production rate disadvantage of 15 to 20 times in compari-son with other spinning systems. Therefore, the challenge is how to break the traditional paradigm of ring spinning and revolutionize its principle in such a way that very high speeds can be achieved without sacrificing the traditional quality of ring spun yarns.
Our design approach is to totally eliminate the traveler from the ring spinning system and replace it with a mag-netically suspended lightweight annular disc that rotates in a carefully pre-defined magnetic field (See Figure below). By creating a non-touching environment of the rotating element for ring spinning, this system provides super high spinning rotation without the limitations of the current trav-eler system.

image

In the magnetic ring spinning system a bias flux is gen-erated from both permanent magnets across the air gap (shown in blue paths in Figure above), supporting the weight of the rotating disk in the axial direction. In case the floating ring is displaced from its central position, the permanent magnets will create a destabilizing force that at-tracts the ring even further away from the center. The con-trol system allows the current in the system to be controlled by feeding back information on the position of the rotor (obtained using four displacement sensors mounted radially to the floating ring) and adjusting the control currents based on this information. In simple terms, the control system re-duces the upper system current when the rotor is above the center position and increases the current when the rotor is below the center position. The total magnetic force will tend to bring the floating ring to its central position. We have now constructed the first prototype (See Photo below) and are optimizing its performance. The system was mod-eled using Simulink, to test how it performs. And the yarn balloon was analyzed using this model.

Full Artical Download

Digg This

Short Staple Processing


Yarns are continuous strands of fibers that can be woven or knitted into fabrics. The term, “spinning” refers both to the final yarn-making operation that puts a twist in the yarn and also to the entire sequence of operations that convert raw fibers into usable yarns. Yarn making from staple fibers involves picking (opening, sorting, cleaning, blending), carding and combing (separating and aligning), drawing (re-blending), drafting (drawing into a long strand) and spinning (further drawing and twisting)3. Silk and synthetic filaments are produced by a less extensive procedure. Current high-production yarn-making operations are performed on integrated machines that perform this entire sequence as one combined operation.

Picking (Including Opening and Blending)

Includes the separation of the raw fibers from unwanted material: leaves, twigs, dirt, any remaining seeds, and other foreign items. The fibers are first blended with fibers from different lots or other sources to provide uniformity. (They also may be blended with different fibers to provide improved properties in the final fabric.) When cotton fibers are processed, the raw cotton is run through a cotton ginning operation and then undergoes a cleaning sequence before it is pressed into rectangular bales for shipment to the textile mill. There, the picking starts with a blending machine operation. Bales are opened and cotton from several lots is fed to the machine. The cotton then proceeds to an opening machine that opens tufts of cotton with spiked teeth that pull the fibers apart. Up to three stages of picking follow, after which the cotton is often in the form of a lay, a roll of cotton fiber about 40 in (1 m) wide, 1 n (25 mm) thick and weighing about 40 lb. (18 kg)1. Figs. 1a, 1b and 1c show the lending, opening and picking operations.

Figure 1a: Blending and feeding cotton fibers. Cotton from bales (1), is dropped onto an apron conveyor (2), and moves to another apron conveyor (3), whose surface is covered with spikes. The spikes carry the cotton upward where some of it is knocked off by a ribbed roller(4). The cotton knocked back mixes with cotton carried by the spiked apron. Cotton that passes the knock-back roller is stripped off by another roll (5) and falls (6) to a conveyor that carries it to the next operation. (Illustration used with permission, Dan River Inc.).

image

Figure 1b: Opening cotton fibers—Cotton from the blending operation falls on an apron conveyor (1) and passes between feeder rolls (2) to a beater cylinder (3). The beater cylinder has rapidly rotating blades that take small tufts of cotton from the feeder rolls, loosen the bunches, remove trash, and move the cotton to the pair of screen rolls (4). The surfaces of these rolls are covered with a screen material. Air is drawn through the screens by a fan (5),pulling the cotton against the screens and forming a web. Small rolls (6), pull the cotton from the screen rolls and deposit it on another conveyor (7), that carries it to another beater (8), that removes more trash. The cotton then moves to the picker operation. (Illustration used with permission, Dan River Inc.)

image

Figure 1c: Picking cotton fibers—Cotton from the opening operation falls on an apron conveyor (1) which moves it to the first of a series of beaters (2), and screen rolls (3). The beaters and screen rolls in the series are all similar but are progressively more refined as the bottom moves through the equipment. Each beater removes more trash from the cotton. When it reaches the output section (4), the cotton is in the form of a web or lap that is wound into lap roll (5) by winding rolls (6). The lap roll in then ready to be transported to the carding equipment. (Illustration used with permission, Dan River Inc.)

Carding

Is a process similar to combing and brushing. It disentangles bunches and locks of fibers and arranges them in a parallel direction. It also further eliminates burrs and other foreign materials and fibers that are too short. The operation is performed on cotton, wool, waste silk,and synthetic staple fibers by a carding machine that consists of a moving conveyor belt with fine wire brushes and a revolving cylinder, also with fine wire hooks or brushes. The fibers from the picking operation are called “picker lap”, and are fed between the belt and the cylinder whose motions pull the fibers in the same direction to form a thin web. The web is
fed into a funnel-like tube that forms it into a round rope-like body about 3/4 in (2 cm) in diameter. This is called a sliver or card sliver. The carding operation is illustrated in Fig.

image

Figure:Carding cotton fibers—The lap (1) from the picking operation is unrolled and fed by the feed roll (2), to the lickerin roll (3), which has wire shaped like saw teeth. The lickerin roll moves the lap against cleaner bars (4), that remove trash, and passes it to the large cylinder (5). The surface of the large cylinder holds the cotton with thousands of fine wires.The flats (6), with more fine wires, move in the direction opposite to that of the large cylinder.The cotton remains on the large cylinder until it reaches the doffer cylinder (7), which removes it from the large cylinder. A doffer comb (8), vibrates against the doffer cylinder and removes the cotton from it. The cotton, in a filmy web, passes through condenser rolls (9),and into a can through a coiler head (10). The subsequent operation is either combing or drawing. (Illustration used with permission, Dan River Inc.)

Combing

Is an additional fiber alignment operation performed on very fine yarns intended for finer fabrics. (Inexpensive and coarser fabrics are made from slivers processed without this further refining.) Fine-tooth combs are applied to the sliver from carding, separating out the shorter fibers, called noils, and aligning the longer fibers to a higher level of parallelism. The resulting strand is called a comb sliver. With its long fibers, the comb sliver provides a smoother, more even yarn.

Drawing (Drafting), (Re-Blending)

After carding and, if performed, combing, several slivers are combined into one strand that is drawn to be longer and thinner. Drawing frames have several pairs of rollers through which he slivers pass. Each successive pair of rollers runs at a higher speed than the preceding pairso that the sliver is pulled longer and thinner as it moves through the drawing frame. The operation is repeated through several stages. The drawing operations produce a product called roving which has less irregularities than the original sliver. Afterward, the finer sliver is given a slight twist and is wound on bobbins. Fig. 10B4 illustrates the drawing operation.Figure

image

Figure : Drawing—Cans (1), filled with slivers from the carding operation, feed the slivers to the drawing frame. The slivers pass through spoons (2), that guide the slivers and stop the equipment if any should break. The rollers (3), turn successively faster as the slivers move through them, reducing the size of the slivers and increasing their length approximately six fold. At this point, the slivers are combined into one which is deposited into a can (4), by coiler head. The sliver fibers are much more parallel, and the combined sliver is much more uniform after the operation, which is usually repeated for further improvement of the cotton slivers. (Based on an illustration from Dan River, Inc. Used with permission.)

Spinning (Twisting)

Further draws out and twists fibers to join them together in a continuous yarn or thread. The work is performed on a spinning frame after drawing. The twist is important in providing sufficient strength to the yarn because twisting causes the filaments to interlock further with one another. The roving passes first through another set of drafting rolls, resulting in lengthened yarn of the desired thickness.

There are three kinds of spinning frames: ring spinning, open-end (rotor) spinning, and air-jet spinning. With the common ring spinner, the lengthened yarn is fed onto a bobbin or spool on rotating spindle. The winding is controlled by a traveller feed that moves on a ring around the spindle but at a slower speed than that of the spindle. The result is a twisting of the yarn.The yarn guide oscillates axially during winding to distribute the yarn neatly on the bobbin.The yarn can then be used to weave or knit textile fabrics or to make thread, cord or rope.Staple yarns, made from shorter fibers require more twist to provide a sufficiently strong yarn;filaments have less need to be tightly twisted. For any fiber, yarns with a smaller amount of twist produce fabrics with a softer surface; yarns with considerable twist, hard-twisted yarns,provide a fabric with a more wear resistant surface and better resistance to wrinkles and dirt,but with a greater tendency to shrinkage. Hosiery and crepe fabrics are made from hard twisted
yarns. Fig.  illustrates ring spinning.

image

Figure : Ring spinning. Spun sliver from the drawing operations, which is then called roving, and is wound on bobbins (1), and is fed through another series of drawing rollers (2),that further draw the strand to its final desired thickness. A larger bobbin (4) on a rotating spindle (3), turns at a constant speed. The speed of the final pair of drawing rollers is set a the speed that delivers the yarn so that it is twisted by the desired amount as it is wound on the bobbin. The yarn is guided by the traveller (5), which slides around the bobbin on the ring (6).Because of some drag on the traveller, the yarn winds on the bobbin at the same rate of speed as it is delivered by the final pair of rollers. (Illustration used with permission, Dan RiverInc.)

Spinning Synthetic Fibers

The term “spinning” is also used to refer to the extrusion process of making synthetic fibbers forcing a liquid or semi-liquid polymer (or modified polymer, e.g., rayon) through small holes in an extrusion die, called a spinneret, and then cooling, drying or coagulating the resulting filaments. The fibers are then drawn to a greater length to align the molecules. This increases their strength. The monofilament fibres may be used directly as-is, or may be cut into shorter lengths, crimped into irregular shapes and spun with methods similar to thoseused with natural fibers. These steps are taken to give the synthetic yarns the same feel and
appearance as natural yarns when they are made into thread, garments and other textile products. (Section A2, above, describes wet and dry spinning methods of making rayon and acetate fibers.)

Digg This

PROCESS PARAMETERS IN DRAW FRAME


it is better to use two drawframe passages after combing. This will reduce long thick places in the yarn.
· In case of two drawframe passage, first drawframe passage will reduce the periodic variation due to piecing. Therefore the life of servomotor and servo amplifier will be more , if two drawframe passage is used. Quality of sliver will also be good, because of less and stable feed variation.
· For synthetic fibres (44 mm to 51 mm), 8 of a total draft can be employed both in breaker and finisher passage. The number of doublings depends upon the feeding hank and the total draft employed. Most of the modern drawframes are capable of drafting the material without any problem, even if the sliver fed is around 36 to 40 grams per meter.
· Especially for synthetic fibres with very high drafting resistance, it is better to feed less than 38 grams per meter to the drawframe.
· Break draft setting for 3/3, or 4/3, drafting system is as follows
1. For cotton, longest fibre +(8 to 12 mm)
2. For synthetic fibre, fibre length + (20 to 30% of fibre length)
· Break draft for cotton processing is normally 1.16 to 1.26. For synthetics it is around 1.42 to 1.6
· To meet the present quality requirements , finisher drawframe should be an autoleveller drawframe.
· Since the drawframe delivery speed is very high the top roller shore hardness should be around 80 degrees. It should not be less than that.
· It is advisable to buff the rubber cots once in 30 days(minimum) to maintain consistent yarn quality.
· Coiler size should be selected depending upon the material processed. For synthetic fibres, bigger coiler tubes are used. This will help to avoid coiler choking and kinks in the slivers due to coiling in the can.
· Speed of the coiler will also affect the coiling. Speed of the coiler should be selected properly. In drawframes like RSB D-30(RIETER) , any coiler speed can be selected through the variator type pully. Since, the option is open, there is also more probability for making mistakes. One should take enough care to set the coiler speed properly.
· Whenever coiler speed is adjusted, the diameter of the coil is also changed. Hence it is necessary to check the gap between the sliver and can. If it is more than 5 mm, then turn table position (can driving unit) should be altered so that the gap between coil outer and can inner is around 5 mm.
· Pressure bar depth plays a major role in case of carded mixing and OE mixings. If it is open, U% will be affected very badly.It should always be combined with front roller setting. If the pressure bar depth is
high,Creel height should be fixed as low as possible (esepcially for combed material).
· Top roller condition should be checked properly. While processing 100% polyester fibres, fibre scum should be removed by a wet cloth from the top roller atleast once in a shift. 3
· Sliver funnel size should be selected properly. Very wide funnel will affect the U%. But very small funnel will end up in more sliver breaks at the front.
· If the department humidity variation is very big, then corresponding correction to be made for checking the wrapping of sliver ( sliver weight). Otherwise, there will be unwanted changes in the drawframe which will affect the count C.V.% of yarn.
· Most of the Autoleveller drawframes are working on the principle of OPEN LOOP control system. Sliver monitor should be set properly. Whenever there is a problem in sliver weight, this will stop the machine.
Sometimes sliver monitor may malfunction. If it is found malfunctioning , it should be calibrated immediately.
AUTOLEVELLING:
· Most of the modern autolevllers are open loop autolevellers. This system is effective on short, medium and to some extent long tem variations.
· Mechanical draft should be selected properly in autoleveller drawframes. To decide about the mechanical draft, drawframe should be run with autoleveller switched off.If the sliver weight is correct, then the mechanical draft selected is correct. Otherwise, the gears should be changed so that the sliver is weight is as per the requirement without autolevller.
· Intensity of levelling and timing of correction are two important parameters in autolevellers.
· Intensity of levelling indicates the amount of correction. i.e If 12% variation is fed to the drawframe the draft should vary 12% , so that the sliver weight is constant.
· Timing of correction indicates that if a thick place is sensed at scanning roller, the correction should take place exactly when this thick place reaches the correction point(levelling point)
· Higher the feed variation, higher the correction length. e.g. if feed variation is 1 %, and if the correction length is 8 mm, if feed variation is 5% the correction length will be between 10 to 40 mm depending upon the speed and type of the autoleveller.
· Higher the speed, higher the correction length
· Whenever the back roller setting, guide rails setting, delivery speed,break draft etc are changed, the timing of correction should also be changed. · U% of sliver will be high, if timing of correction is set wrongly
· If intensity of levelling selected is wrong , then 1 meter C.V % of sliver will be high.
· Most of the modern autolevellers can correct 25% feed variation. It is a general practice to feed 12% varition both in plus and minus side to check A%. This is called as Sliver test. The A% should not be more than 0.75%.
A% is calculated as follows
If no of sliver fed to drawframe is N, Check the output sliver weight with “N”, “N+1”, “N-1” slivers. then
A% = ((gms/mt(N-1) – gms/mt(N))/ gms/mt(N) ) x 100
A% = ((gms/mt(N+1) – gms/mt(N))/ gms/mt(N)) x 100
· Life of servo motor and servo amplifier will be good, if
1. it is used for carded material
2. feed variation is less
3. motor is checked for carbon brush damages, bearing damages etc periodicall
4. if the delivery speed is less

Digg This

Automatic bale openers or pluckers


Modern mills now a day’s uses automatic bale openers or feeders in place of conventional hopper bale openers for more accurate mixing/ blending and also helps to eliminate mane power.

Modern bale pluckers can be mainly classified into two categories viz.

1. Moving bale type

The first generation bale opening machines were mostly stationary. Only the bales were moved either backward or forward or in a circle. The examples of these types of machines are Trutzschler multi-bale plucker, karousel-beater type opener by Rieter, etc.

2. Moving beater type

The second generation machines are of the travelling type i.e. they move past the bales of the layout and extract material from top to bottom. Travelling machines have the advantages that more bales can be processed as an overall unit, and thus better long-term blend is achieved. It should be noted however that these machines extract material only in batches, i.e. they can process only one, two or maximum three bales simultaneously. If long term blend is needed to be achieved, then mixing machines must be included downstream from the bale opener. These machines are completely electrically controlled and extract material evenly from all bales evenly, independently of varying bale density.

In concept, these machines are most commonly utilized now a day. Machines similar to uni-floc by Rieter are developed by various other manufactures viz. Optimix by Hargeth Hollingsworth, B12 by marzoli and blendomat by Trutzschler. The latest uni-floc provided in modern Rieter blow room line in place of the hopper bale opener is UNI-FLOC A-11.

UNIFLOC A-11

· OPERATIONAL PRINCIPLE

The A 11 UNI-floc processes cotton from all sources and manmade fibres in staple lengths of up to 65 mm. The bales being opened are placed lengthwise or crosswise on both sides of the bale opener, and the take-off unit can process up to four different assortments.

Reduction of the raw material into micro-tufts is assured by the patented double teeth on the take-off roller and the grid with closely set clamping rails. The unique geometry of the double teeth ensures the uniform treatment of the entire bale surface. Retaining rollers travelling with the take-off unit prevent bale layers from sloughing and ensure precise, controlled operation over the entire height of the bale. The A 11 UNI-floc still produces small tufts, even at maximum output of 1400 kg/h.

The take-off unit is lowered by a preselected or computed distance at each pass. Running-in and running-out programs compensate for the differing hardness of the bales over their cross section and ensure a uniform level of production. The fan incorporated in the swivelling tower extracts the opened tufts and feeds them into the tuft channel running between the guide rails. Transport to the following machine is pneumatic.

image

Figure 1 OPERATIONAL PRINCIPLE OF UNI-FLOC A-11

· DISTINGUISHING FEATURES OF UNI-FLOC A-11

The UNI-floc is basically one type of opening which is most commonly utilized in place of “hopper bale openers”. The distinguishing features of UNI-floc are:

1. Bale opening into micro-tufts for effective cleaning and dust extraction.

image

Figure narrow grid gauge for micro-tufts

Micro tufts are the basic requirement for the production of yarn quality. Trash and dust can only be removed from natural fibres gently and efficiently on the surface of the tufts.

The take-off unit of the UNI-floc is considered to be the “heart” of the system as it is responsible for micro tuft formation. The patented take-off roller and the grid design with small gaps between the clamping rails enables small fibre tufts ( micro tufts ) to be extracted. The twin-tooth profile ensures uniform, gentle and efficient extraction of the tufts, also irrespective of the take-off roller’s direction of rotation.

image

Figure comparison of output and tuft size in modern machine(UNI-floc A-11) to conventional bale opener

2. Uniform take-off of bale lay-down by means of “BALE PROFILEING”

Bale Profiling guarantees totally uniform bale take-off. The height profile of the bale lay-down is precisely detected by light barriers and memorized. Scanning is performed at a constant speed of 9 m/min. Tufts are already taken off in the profiling phase. Continuous feeding of the subsequent machines is thus ensured from the outset.

image

 

 

Figure uniform take-off of bale lay-down by means of bale profiling

During the subsequent passes the bales are opened at the preselected speed of travel and take-off depth. In the process the system automatically compensates for differences in height in the bale profile. Labour-intensive manual levelling is eliminated. After the required height range, take-off depth and speed of travel have been entered for each group of bales, take-off proceeds fully automatically.

3. Simultaneous processing of up to 4 assortment

image

We can lay down as many as 130 bales in four groups on each side of the machine. This means that four assortments can be processed automatically at the preselected take-off speed and with the required production volume.

4. Patented, individually interchangeable double teeth on the opening roller

image

Figure Patented, individually interchangeable double teeth

The double teeth enable maintenance intervals to be halved. The teeth are mounted individually. They can easily and quickly be replaced if required, without removing the take-off roller. This explains the exceptionally high operational readiness of the A 11Uni-floc

5. Processing of cotton from all sources and man-made fibres in staple lengths of up to 65 mm

 

6. Output of up to 1 400 kg/h (carded sliver)

7. Bale lay-down over a length of 7.2 to 47.2 meters

A bale lay-down of overall lengths of 7.2 to 47.2 meters and two take-off of unit lengths of 1 700 mm and 2 300 mm. The maximum version is capable of accommodating raw material up to 40 000 kg. This ensures flexible, economical and largely autonomous processing on UNI-floc A-11.

8. Take-off width selectable between 1 700 mm and 2 300 mm

 

9. Graphic interface for easy, intuitive operation at the control panel

The control panel is placed facing the extraction duct, providing a clear view and safety for operating the machine. Setting and control of the A 11 UNI-floc can easily be performed at the screen.

10. Interface to higher-level control and information systems available

In the interests of optimum monitoring of the installation as a whole, this modern machine control unit can be connected to the UNI-control or UNI-command control system. UNI-control and NI command also provide the interface to Reiter’s higher-level SPIDER web mill monitoring system.

 

11. Maximum yield due to optimized processes

Digg This

Yarn Conditioning


Why conditioning is required?

Moisture in atmosphere has a great impact on the physical properties of textile fibres and yarns.Relative humidity and temperature will decide the amount of moisture in the atmosphere. High relative humidity in different departments  of spinning is not desirable. It will result in major problems.  But on the other hand, a high degree of moisture improves the physical properties of yarn. Moreover it helps the yarn to attain the standard moisture regain value of the fibre. Yarns sold with lower moisture content than the standard value will result in monetary loss. Therefore the aim of  CONDITIONING  is to provide an economical device for supplying the necessary moisture in a short time, in order to achieve a lasting improvement in quality.

In these days there is a dramatic change in the production level of weaving and knitting machines, because of the sophisticated  manufacturing techniques. Yarn quality required to run on these machines is extremely high. In order to satisfy these demands without altering the raw material, it was decided to make use of the physical properties inherent in the cotton fibres. Cotton fibre is hygroscopic material and has the ability to absorb water in the form of steam. It is quite evident that the hygroscopic property of cotton fibres depends on the relative humidity. The higher the humidity, more the moisture absorption. The increase in the relative atmospheric humidity causes a rise in the moisture content of the cotton fibre, following an S-shaped curve.

The relative humidity in turn affects the properties of the fibre via the moisture content of the cotton fibre. The fibre strength and elasticity increase proportionately with the increase in humidity. If the water content of the cotton fibre is increased the fibre is able to swell, resulting in  increased fibre to fibre friction in the twisted yarn structure. This positive alteration in the properties of the fibre will again have a positive effect on the strength and elasticity of the yarn.

CONTEXXOR CONDITIONING PROCESS BY XORELLA:

The standard conventional steaming treatment for  yarn is chiefly used for twist setting  to avoid snarling in further processing. It does not result in lasting improvement in yarn quality.  The steaming process may fail to ensure even distribution of the moisture, especially on cross-wound bobbins(cheeses) with medium to high compactness.  The thermal conditioning process of the yarn according to the CONTEXXOR process developed by XORELLA  is a new type of system for supplying  the yarn package.

The absence of Vacuum in conventional conditioning chambers, prevents homogeneous penetration. The outer layers of the package are also too moist and the transition from moist to dry yarn gives rise to substantial variations in downstream processing of the package, both with regard to friction data  and strength.

Since the moisture is applied  superficially in the wet steam zone or by misting with water jets, it has a tendency to become re-adjusted immediately  to the ambient humidity level owing to the large surface area. Equipment of this king also prevents the optimum flow of goods and takes up too much space.

PRINCIPLE OF WORKING:

Thermal conditioning uses low-temperature saturated steam in vacuum. With the vacuum principle and indirect steam, the yarn is treated very gently in an absolutely saturated steam atmosphere. The vacuum first removes the air pockets from the yarn package to ensure accelerated steam penetration and also removes the atmospheric oxygen in order to prevent oxidation. The conditioning process makes use of the physical properties of saturated steam or wet steam (100% moisture in gas-state). The yarn is uniformly moistened by the gas. The great advantage of this process is that the moisture in the form of gas is very finely distributed throughout the yarn package and does not cling to the yarn in the form of drops. This is achieved in any cross-wound bobbins, whether the yarn packages are packed on open pallets or in cardboard boxes.

clip_image002

pic: XORELLA CONDITIONING SYSTEM

  • ADVANTAGES OF CONTEXXOR PROCESS:
  • saturated steam throughout the process
  • even penetration of steam and distribution of moister
  • lowest energy consumption with XORELLA ECO-SYSTEM
  • short process time
  • absolute saturated steam atmosphere of 50 degree C to 150 degreees C.
  • no additional boiler required, the steam is generated in the system
  • minimum energy consumption(approx. 25 KWh for 1000 kgs of yarn)No tube buckling in case of mad-made yarns
  • treatment of all natural yarns, blends, synthetics and microfibre yarns.
  • low installation and maintenance cost
  • preheating for trollys and plastic tubes to avoid drops (Wool)
  • standardize sizes
  • length up to 20 meters (66 feet) and max. temperature deviation of 1°C
  • various loading and unloading facilities
  • no contamination of the treated packages
  • energy recovery option offered by indirect heating system using steam or hot water
  • no special location required, the systems can be operated next to the production machines.

BENEFITS ACHIEVED OUT OF CONDITIONING:

FOR KNITTING:

The treatment temperature for knitting yarn is held below the melting point of the wax. Temperatures for unwaxed

yarn are coordinated to the compatibility fo each individual type of yarn

  • Upto 20% greater efficiency due to a reduction in the unwinding tension
  • fewer needle breaks
  • uniform moisture content and friction values
  • regular stitch formation
  • no change in size of finished articles
  • no extra dampening required
  • free from electrostatic
  • less fly hence less problems. It helps if the yarn is  running on a closer gauge machines

NOTE: Please note that the wax applied should  be able to withstand min 60 degree centigrade.  If low quality wax is used, it will result in major problem. Conditioning should be done at 55 to 60 degree centigrade.

FOR WEAVING:

  • upto 15% fewer yarn breaks due to greater elongation
  • less fly, resulting in a better weaving quality
  • increased strength
  • increased take-up of size, enhanced  level of efficiency in the  weaving plant
  • softer fabrics

clip_image004 clip_image006

Pic: improved strength                                              Pic: improved elongation

FOR TWISTING:

Conditioning and fixing of the twist at the same time in a single process.

FOR DYEING:

  • no streaks
  • better dye affinity

clip_image008

Pic: dye pick up of conditioned and unconditioned yarn

clip_image009clip_image010

Digg This

Costing for Spinning Mill


INTTRODUCTION:

It is better to review the basics concepts, costing  methods and techniques and elements of costing before we work out a costing for a spinning mill.

Cost accounting is a system of determining the costs of products or services. It has primarily developed to meet the needs of management.  It provides detailed cost information to various levels of management for efficient performance of their functions.

Financial accounting provides information about profit , loss, cost etc., of the collective activities of the business as a whole. It does not give the data regarding costs by departments, products, processes and sales territories etc. Financial accounting does not fully analyse the losses due to idle time, idle plant capacity, inefficient labour, sub-standard materials, etc. Cost accounting is not restricted to past. It is concerned with the ascertainment of past, present and expected future costs of products manufactured or services supplied. Cost accounting provides detailed cost information to various levels of management for efficient performance of their functions.

“A cost  is the value of economic resources used as a result of producing or doing the things costed”

Cost is ascertained by cost centres or  cost units or by both.

For the purpose of ascertaining cost, the whole organisation is divided into small parts of sections. Each small section is treated as a cost centre of which cost is ascertained.   A cost centre is defined as ” a location, person, or item of equipment(or group of these) for which costs may be ascertained and used for the purpose of control.  A cost accountant sets up cost centres to enable him to ascertain the costs he needs to know. A cost centre is charged with all the costs that relate to it. The purpose of ascertaining the cost of  cost centre is cost control.  The person in charge of a cost centre is held responsible for the control of cost of that centre.

Cost unit  breaks up the cost into smaller sub-divisions and helps in ascertaining the cost of saleable products or services. A cost unit is defined as a ” unit of product , service or time in relation to which cost may be ascertained or expressed.”   For example in a spinning mill the cost per kg of yarn may be ascertained. Kg of yarn is cost unit.  In short  Cost unit is unit of measurement of cost.

METHODS  OF COSTING:

Method of  costing refers to the techniques and processes employed in the ascertainment of costs. The method of costing to be applied in a particular concern depends upon the type and nature of manufacturing activity.   Basically there are two methods of costing

1.Job costing:   Cost unit in job order costing is taken to be a job or work order for which costs are separately collected and computed.

2.Process costing:  This is used in mass production industries manufacturing standardised products in continuous processes of manufacturing. Cost are accumulated for each process or department. For spinning mills , process costing  is employed.

TECHNIQUES OF COSTING:

These techniques  may be used for special purpose of control and policy in any business irrespective of the method of costing being used there.

Standard costing:  This is the valuable technique to control the cost. In this technique, standard cost is predetermined as target of performance and actual performance is measured against the standard.  The difference between standard and actual costs are analysed to know the reasons for the difference so that corrective actions may be taken.

Marginal costing: In this technique, cost is divided into fixed and variable and the variable is of special interest and importance. This is because, marginal costing regards only variable costs as the costs of products.  Fixed cost is treated as period cost and no attempt is made to allocate or apportion this cost to individual cost centres   or cost units.

Cost Ascertainment is concerned with computation of actual costs. Ascertainment of actual costs reveals unprofitable activities  losses and inefficiencies  .

Cost Estimation  is the process of predetermining costs of goods or services. The costs are determined in advance of production and precede the operations. Estimated costs are definitely the future costs and are based on teh average of the past  actual costs adjusted for future anticipated changes in future. Cost estimates are used in the preparation of the budgets. It helps in evaluating performance. It is used in preparing projected financial statements. Cost estimates may serve as targets in controlling   the costs.

CLASSIFICATION OF COSTS:

Costs are classified into direct costs and  indirect costs on the basis of their identifiability with cost units or processes or cost centres.

DIRECT COST: These are the costs which are incurred for and conveniently identified with a particular cost unit, process or equipment. For a spinning mill, costs of raw material used, packing material, freight etc are direct costs

INDIRECT COST: These are general costs and are incurred for the benefit of  a number of cost units, processes or departments. These costs cannot be conveniently identified with a particular cost unit or cost centre. In a spinning mill, power cost, administrative wages, managerial salaries, materials used in repairs etc. are indirect costs.

The terms direct and indirect should be used in relation to the object of costing. An item of cost may be direct cost in one case and the same may be indirect in the other case.It is the nature of business and the cost unit chosen  that  will determine whether a particular cost is direct or indirect.

FIXED AND VARIABLE COSTS; Costs behave differently when level of production rises or falls. Certain costs change in sympathy with production level while other costs remain unchanged. As such on the basis of behaviour or variability, costs are classified into fixed, variable and sem-variable.

FIXEDCOSTS; These costs remain constant in “total” amount over a wide range of activity for a specified period of time. They do  not increase or decrease when the volume of production changes.

VARIABLE COSTS: These costs tend to vary in direct proportion to the volume of  output. In other words, when volume of output increases, total variable cost also increases and vice-versa.

ELEMENTS OF COST: A cost is composed of three elements i.e. material , labour and expense. Each of these elements  may be direct or indirect.

DIRECT COST INDIRECT COST
Direct material Indirect material
Direct labour Indirect labour
Direct expenses Indirect expenses

MATERIAL COST:

DIRECT MATERIAL  is that which can be conveniently identified with and allocated to cost units. Direct materials generally become a part of the finished product. For example, cotton used  in a spinning mill is a direct material.

INDIRECT MATERIAL is that   which can not  be conveniently identified with individual cost units.  In a spinning mill, engineering department spares, maintenance spares, lubricating oils, greases, ring travellers etc

LABOUR COST:

DIRECT LABOUR cost consists of wages paid to workers directly engaged in converting  raw materials into finished products. These wages can be conveniently identified with a particular product, job or process.

INDIRECT LABOUR is of general character and cannot be conveniently identified with a  particular cost unit. In other words, indirect labour is not directly engaged in the production operations but only to assist or help in production operations.  For example in a spinning mill, the number of maintenance workers, no of  workers in utility department etc

EXPENSES; All costs other than material and labour are termed as expenses.

DIRECT EXPENSES are those expenses which are specifically incurred in connection with a particular job or cost unit. Direct expenses are also known as chargeable expenses.

INDIRECT EXPENSES can not be directly identified with a  particular job, process and are common to cost units and cost centres.

PRIME COST = Direct material +Direct labour + Direct  expenses

OVERHEAD = Indirect material + Indirect labour + Indirect expenses

TOTAL COST = PRIME COST + OVERHEAD

ADVANTAGES OF COST ACCOUNTING:

  • It reveals profitabale and unprofitable activities.
  • It helps in controlling costs with special techniques like standard costing and budgetary control
  • It supplies suitable cost data and other related information for managerial decision making such as introduction of a new product, replacement of machinery with an automatic plant etc
  • It helps in deciding the selling prices, particularly during depression period when prices may have to be fixed below cost
  • It helps in inventory control
  • It helps in the introduction of   a cost reduction programme and finding out new and improved ways to reduce costs
  • Cost audit system which is a part of cost accountancy helps in preventing manipulation and frauds and thus reliable cost can be furnished to management

ESSENTIALS OF A GOOD COST ACCOUNTING SYSTEM:

  • The method of costing adopted. It should be suitable to the industry
  • It should be tailor made according to the requirements of a business. A ready made system can not be suitable
  • It must be fully supported by executives of various departments and every one should participate in it
  • In order to derive maximum benefits from a costing system, well defined cost centres and responsibility centres should be built within the organisation
  • controllable and uncontrollable costs of each responsiblity  centre should be separately shown
  • cost and financial accounts may be integrated in order to avoid  duplication of accounts
  • well trained and educated staff should be employed to operte the system
  • It should prepare an accurate reports and promptly submit teh same to appropriate level of management so that action may be taken without delay
  • resources should not be  wasted on collecting and compiling cost data not required. Only useful cost information should be compiled and used whenever required.

CASE 1.  Project costing for a    POLY/COTTON  PLANT with autodoffing and link to autoconer:(IN INDONESIA)

Following information is required to work out a costing for a new plant:

  • The average count of the plant
  • Capacity of the plant –  No of spindles to be installed and the number of back process and winding machines required
  • Investment on machineries
  • Investment on land
  • Investment on building
  • working capital required
  • product lay out, the count pattern
  • Selling price of individual counts
  • rawmaterial cost(including freight, duty etc)
  • packing cost per kg of yarn
  • freight per kg of yarn
  • direct labour cost
  • indirect labour cost
  • fixed power cost
  • variable power cost
  • spares consumption
  • administration costs
  • selling  overheads

Let us  work out a project cost:

For this , i have used the details of   the modern mill which is running in Indonesia from  year 2000

STEP NO.1: Contribution to be calculated.  In general for a spinning mill ,contribution per kg  of particular count is calculated    to work out the economics for a new project as well as for a running   mill.

Cotribution = selling price – direct cost

Direct cost for a spinning mill includes  rawmaterial price, packing cost, freight.  All other costs are either fixed costs or semi variable costs. The other costs can not be conveniently allocated to per kg of a particular count.

The basic idea of a new project or a running plant  is to maximise this contribution. Because once the plant is designed, spares cost, power cost, administration cost,labour cost etc almost remain constant. There will not be significant changes in these costs  for different count patterns if  the plant is utilisation is same.

The following table gives the details of count pattern, selling price, rawmaterial price, packing cost and contribution per kg of different counts for a particular period ( year 2000). This is just an example , one should understand that the selling price, rawmaterial price and all other costs keep changing.  This is the reason why costing is important for a running mill.  All the costs are changing. Some costs change every month, some  once in a year.   Therefore costing plays a major role to run the plant efficiently.

count no. of spls no of mcs prdn/mc prdn kgs/day raw material cost/kg packing cost /kg freight per kg common 2% on selling price selling price / kg contribn per kg
20s CVC 4480 4 1109 4436 1.456 0.046 0.051 0.04 2.2 2674
24s CVC 4480 4 881 3525 1.456 0.046 0.051 0.05 2.3 2470
30s CVC 5600 5 679 3394 1.456 0.046 0.051 0.05 2.4 2712
30s TC 4480 4 679 2716 1.240 0.046 0.051 0.04 2.15 2091
36s TC 6720 6 552 3315 1.240 0.046 0.051 0.05 2.4 3365
23 17385 contrbn/ day 13312

In the above table, all the costs are in US$. The ringframes are with 1120 spindles per machine with automatic doffing and link to autoconer. Packing cost is based on indonesian packing material prices for carton packing.

The ultimate aim of the project is to maximise the contribution.  Looking into the cotribution per kg of yarn, the project should produce only 36s TC. But in this project they have considered 5 different counts. Because

  • yarn market is not stable. It needs a lot flexibility
  • customers are not same, the price depends on the customers
  • the end uses are not same, the price depends on the end use.
  • this unit exports 80% of the yarn, it can not depend on one country, eg. 36sTc is only for Philippines market, it can not be sold in Malaysia, even though the quality is good
  • the count pattern depends upon the market requirement and the major counts in the market, not only on the contribution
  • A linear programming technique can be used to maximise the contribution, considering all market constraints,  and production constraints.
  • flexibility  needs more investment and more day to day expenses, if a project has to be more flexible, it has to invest more money on infrastructure
  • the major factor which will make the project feasible with less flexibility is YARN QUALITY in a spinning mill
  • Since this is a critical step for a new project, management should be clear about their  Yarn quality ,  Flexibility required for marketing and should make use of Linear Programming Techniques  to find out the best  product mix  to maximise the  contribution.

STEP NO. 2: To work out the Total Investment cost ( machineries, accessories, land and building, humidification and electrical instruments)

The following table gives the requirement of production  machines. To calculate the number of back process and winding drums  required, a detailed spin plan should be worked out with  speeds and efficiencies to be achieved in each machine.

While calculating the no of   machines required, m/c utilisation, m/c efficiency , waste percentage, twist multipliers, delivery speeds etc  should be considered properly.  These factors should be decided based on yarn quality required, end breakage rates and the capacity of machine.

INVESTMENT ON MACHINERY

MACHINERY NO. OF MCS RATE / MC TOTAL COST
Trutzschler Blowrrom line for cotton 1  line 416,640 416,640
Trutschler Blowrrom line for Polyester 1 Line 321,365 321,365
Trutshcler DK-903 cards 22 92,500 2,035,000
Rieter RSB-D30 draw frames (with autoleveller) 6 1,648,000
Rieter double delivery drawframe 10
Rieter unilap 2
Rieter E62 combers 10
Howa speed frames with overhead blower 7 144530 1,011,710
Ring frames with autodoffer 23 148,960 3,426,080
winding machines ( 26 drums per mc) 23 93,200 2,143,600
Roving transport ( manual) 1 150,000 150,000
Argus fire system 1 50,000 50,000
TOTAL 11,202,395

Some of the following points can be considered while deciding the machines.

From the above table it is clear that, 23 ringframes with 1120 spindles are working with auto doffing and with link to autoconer. The major advantage of this automation is to reduce labour and to reduce the problems related to material handling. One has to really work out the benefits achieved because of this and the pay back for the extra investment.

Drawframe contributes a lot to the yarn quality and the ringframe and winding machine working. It is always better to go in for the best drawframes like RSB-D30 drawframes with autoleveller. It is not wise to buy  a cheaper drawframe and save money.

It is always better to keep excess carding and autoleveller drawframes, so that flexibility of the project is also maintained. If the coarser counts contributes more and the market is good, overall production can be increased. If the market is for finer count, both the machines (carding and drawframes)can be run at slower speeds, which will surely contribute to yarn quality.

Speeds of speedframe , combers and ringframes do not affect the yarn quality as it is affected by card and drawframe speeds.

Blow room capacity should be utilised to the maximum, as it consumes a lot of power ,space and money.

Ringframe specification should be perfect, because the working performance and power consumption of the ringframe depends on the specifications like, lift, ring dia, no of spindles etc. Ring frame specification should be decided   to get the maximum production per spindle and to reduce the power consumed   per kg of yarn produced by that spindle. Because the investment cost and the power consumption for the  ringframe is the highest in a spinning mill.

INVESTMENT ON ACCESSORIES:

The following table gives the details of  the accessories like cans for carding, drawframe, bobbins, trollies etc

ACCESSORIES NO. OF MCS RATE / MC TOTAL COST
Carding cans  36″ x 48″ 120 160 19,200
comber cans 24″ x 48″ 350 85 29750
Drawframe cans 20″ x 48″ 1100 53 58,300
Identification bands 20″ 400 1.2 480
Identification bands 24″ 50 1.8 90
Roving and spinning bobbins 36,000
Plastic crates 400 6 2,400
trolleys 10,000
Cone trolly 80 200 16,000
Fork lift 1 27,000 27,000
hand truck 3 1000 3,000
TOTAL 202,220

SERVICE AND MAINTENANCE EQUIPMENTS:

The following table gives the details about  the investments required on service and maintenance  equipment’s

SERVICE AND MAINTENANCE EQUIPEMENTS NO OF MCS RATE/MC TOTAL PRICE
Cots buffing machine and accessories 1 20000 20000
Card room accessories 1 set 60,000 60,000
Spindle oil lubricator 1 4000 4000
Clearer roller cleaning machine 1 3000 3000
Vacuum cleaner 5 3000 15000
pneumatic cleaners 6 500 3000
Weighing balance 3 2000 6000
Strapping machine 2 2000 4000
Premier autosorter 1 2500 2500
Premier uster tester 1 45000 45000
Premier strength tester 1 45000 45000
premier fiber testing 1 45000 45000
Premier Classidata 1 25000 25000
Erection charges 150000
TOTAL 427500

Card service machines like   Flat tops clipping machine and flats grinding machine are very important for yarn quality. One should not look for cheaper machine. It is always better to go for reputed manufacturers like  GRAF, HOLLINGSWORTH etc.

Rubber cots contributes a lot to yarn quality. Bad buffing in ring frame can increase the imperfections by 15%.  Poor quality of buffing in drawframe and speedframes can affect both production and quality. It is better to go for the best cots mounting machine and cots buffing machine.

HUMIDIFICATION AND ELECTRICAL EQUIPMENTS:

The following table gives the details about the investments required on  humidification and electrical instrument’s

Electrical installation including transformer, incoming and outgoing panels, bus duct, capacitor, etc for 3800 KVA 350,000
Cables 125,000
Compressor, Dryer and pipe lines 180,000
humidifaction system 767,000
chillers 176,000
Ducting and installation for humidification system 125,000
workshops, hydrant and other equipments 100,000
TOTAL 1,823,000

In Indonesia, most of the units use PLN power and some of the spinning mills use Gensets. A detailed costing has to be done to compare the cost per unit  to decide, Whether to use the PLN power or to go in for Gensets. while working out the costing  finance cost on investment , overhauling cost, running cost, efficiency of the machine  should be considered for cost calculation in the case of Genset. In case of PLN power, the losses due to power interruption( based on the area data), finance cost on initial investment,   md charges, unit charges to be considered. It is  better to use 50% PLN and 50 % own generation.

The following table gives the details about land and building investments

Land cost 200,000
Land development 40,000
Factory building Including Service ally 192 x 62 meters11,712 Square meter @ 120 usd/sq meter 1,405,440
Road and others 40,000
TOTAL 1,445,440

STEP NO.3: To calculate the expenses ( labour, power, stores,working capital, insurance etc)

Working capital = 3,000,000

LABOUR:The following table gives the details about   labour requirement

DEPARTMENT No of people required
Production 140
packing 15
maintenance 30
utility 17
administration and personal dept 20
Total no of people required per day 222
wages at 50 usd/month including bonus and insurance 111,00
other facilities at 35 % 3,885
salaries for managerial staff 10000
Other facilities at 35 % 3500
Total labour cost / month 28485

POWER: The following table gives the details about the power

Total units(KWH) produced (consumed)per day 69559
Unit cost (cost / KWH) 0.03
Total production in Kgs 17,390
KWH/ Kg of yarn 4.0
TOTAL POWER COST /DAY 2087

SPARES:The following table shows the spares cost, repair , and insurance

spares cost at usd 8/1000 spindle shift 222,566
repairs and other overheads 200,000
Insurance at 0.175% on investment and working capital 31320
TOTAL cost per year 453886

STEP NO.4: PAY BACK CALCULATION

DETAILS IN USD
INVESTMENT:
Land and building 1,444,440
Machinery, accessories & service equipments 11,832,115
Electrical and Humidification ducts 1,823,000
TOTAL INVESTMENT 15,099,555
WORKING CAPITAL 3,000,000
GRAND TOTAL 18,099,555
RECURRING EXPENDITURES PER DAY
Salaries and Wages 949.5
Power cost 2087
Stores , repairs and insurance 1260.8
TOTAL 4297.3
INTEREST CALCULATION (per day)
On capital 8% 3355.5
on working capital 9% 750
TOTAL EXPENSES INCLUDING INTEREST 8402.8
TOTAL CONTRIBUTION PER DAY 13312
NET PROFIT( before depreciation & taxation) 4909.2
PAY BACK PERIOD 8.54 years

clip_image001clip_image002

Digg This

Roving Frame


Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. This machine is forced to use by the spinner for the following two reasons.

  1. Sliver is thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this is around 300 to 500. Drafting arrangements of ring frames are not capable of processing
    this strand in a single drafting operation to create a yarn that meets all the normal demands on such yarns.
  2. Drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame.

· TASKS OF ROVING FRAME:

  1. Attenuation- drafting the sliver into roving
  2. twisting the drafted strand
  3. winding the twisted roving on a bobbin

· Fibre to fibre cohesion is less for combed slivers. Rollers in the creel can easily create false drafts.Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance.
Therefore, a perfect drive to the creel rollers is very important.

· The drafting arrangement drafts the material with a draft between 5 and 15.The delivered strand is too thin to hold itself together at the exit of the front bottom roller.

· Bobbin and flyer are driven separately, so that winding of the twisted strand is carried out by running the bobbin at a higher peripheral speed than the flyer.

· The bobbin rail is moving up and down continuously, so that the coils must be wound closely and parallel to one another to ensure that as much as material is wound on the bobbin.

· Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after
each completed layer

· Length delivered by the front roller is always constant. Owing to the increase in the diameter of the package for every up and down movement, the peripheral speed of package should keep on changing , to maintain the same difference in peripheral speeds between package and flyer.

· There are two types of drafting systems.

  1. 3/3 drafting system
  2. 4/4 drafting system

In general 3/3 drafting system is used, but for higher draft applications 4/4 drafting system is used.

· The draft often has limits not only at the upper limit (15 to 20), but also at lower limit. It is around 5 for cotton and 6 for synthetic fibers. If drafts below these lower limits are attempted, then the fibre masses to be moved are too large, the drafting resistance becomes too high and the drafting operation is difficult to control.

It is advisable to keep the break draft (predarft) as low as possible, because lower break draft always improves roving evenness.

· In general two condensers are used in the drafting arrangement. The purpose of these condensers is to bring the fibre strands together. It is difficult to control, Spread fibre masses in the drafting zone and they cause unevenness. In addion, a widely spread strand leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving. The size of condensers should be selected according to the volume of the fibre sliver.

· Flyer inserts twist. Each flyer rotation creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate.
Turns per metre = (flyer rpm)/(delivery speed (m/min))
Higher levels of roving twist, therefore, always represent production losses in Roving frame and possible draft problems in the ring spinning machine. But very low twist levels will cause false drafts and roving breaks in the roving frame.

· Centrifugal tension is created at the bobbin surface as the layers are being wound and is created by the rotation of the package. Each coil of roving can be considered as a high-speed rotating hool of roving on which centrifugal tension increases with increasing diameter of the package. centrifugal tension in the roving is proportional to the square of the winding surface velocity.In this context, centrifugal force acts in such a manner as to lift the top roving strand from the surface of the package so that the radial forces within the strand that hold the fibres together are reduced and the roving can be stressed to the point of rupture. Breaks of this type may occur at the winding-on Point of the presser or in strands that have just been wound on the top surface of the package. This phenomenon is known as “bobbin-bursting”. This phenomenon will be prominent if the twist per inch is less or the spindle speed is extremely high when the bobbin is big.

· Apart from inserting twist, the flyer has to lead the very sensitive strand from the flyer top to the package without introducing false drafts. Latest flyers have a very smooth guide tube set into one flyer leg
and the other flyer leg serves to balance the flyer. The strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in
the previous designs. Frictional resistance is considerably reduced, so that the strand can be pulled through with much less force.

· False twisters are used on the flyers to add false twist when the roving is being twisted between the front roller and the flyer.Because of this additional twist, the roving is strongly twisted and this reduces the breakage rate. Spinning triangle is also reduced which will reduce the fibre fly and lap formation on
the front bottom roller.

· Because of the false twister, the roving becomes compact which helps to increase the length wound on the bobbin. This compactness helps to increase the flyer speed also.

· Roving strength is a major factor in determining winding limitations. It must be high enough for the fibres to hold together in a cohesive strand and low enough for satisfactory drafting at the spinning machine. The factors affecting roving strength are as follows:

  • the length, fineness, and parallelisation of fibres
  • the amount of twist and compactness of the roving
  • the uniformity of twist and linear density.

· BUILDER MOTION: This device has to perform the following tasks

  1. to shift the belt according to the bobbin diameter increase
  2. to reverse the bobbin rail direction at top and bottom
  3. to shorten the lift after each layer to form tapered ends

· Shifting of the belt is under the control of the ratchet wheel. The ratchet wheel is permitted to rotate by a half tooth. The bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. The amount of shifting, which depends upon the thickness of the roving, is modified by replacement of the ratchet wheel or by other gears.If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it moves more rapidly, and vice versa.

· To form a package, the layer must be laid next to its neighbours. For that the lay-on point must continually be moved. The shift of the winding point is effected by moving the bobbin rail. This raising and lowering is done by rails.Since the package diameter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer.

· During winding of a package, the ratchet is rotated at every change-over.Reversal of the bobbin layer occurs little earlier for every reversal.This gives a continuous reduction in the lift of the rail . Thus bobbins are built with taper.

Digg This

RING FRAME


Ring spinning machine (year of constr. 1988) i...
Image via Wikipedia

The ring spinning will continue to be the most widely used form of spinning machine in the near future,because it exhibits significant advantages in comparison with the new spinning processes.

· Following are the advantages of ring spinning frame

  • It is universally applicable, i.e.any material can be spun to any required count
  • It delivers a material with optimum characteristics, especially with regard to structure and strength.
  • it is simple and easy to master
  • the know-how is well established and accessible for everyone

· Functions of  ring frame

  • to draft the roving until the required fineness is achieved
  • to impart strength to the fibre, by inserting twist
  • to wind up the twisted strand (yarn) in a form suitable for storage, transportation and further processing.

DRAFTING

· Drafting arrangement is the most important part of the machine. It influences mainly evenness and strength The following points are therefore very important

  • drafting type
  • design of drafting system
  • drafting settings
  • selection of drafting elements like cots, apron, traveller etc
  • choice of appropriate draft
  • service and maintenance

· Drafting arrangement influence the economics of the machine – directly by affecting the end break rate and indirectly by the maximum draft possible.

· If higher drafts can be used with a drafting arrangement, then coarser roving can be used as a feeding material. This results in higher production rate at the roving frame and thus reducing the number roving machines required, space, personnel and so on.

· In fact increase in draft affects the yarn quality beyond certain limit. Within the limit some studies show that increase in draft improves yarn quality. The following draft limits have been established for
practical operation:

  • carded cotton- upto 35
  • carded blends – upto 40
  • combed cotton and blends(medium counts) – upto 40
  • combed cotton and blends(fine counts) – upto 45
  • synthetic fibres – upto 50

· The break draft must be adapted to the total draft in each case since the main draft should not exceed 25 to 30. It should be noted that higher the break draft, more critical is the break draft setting

· The front top roller is set slightly forward by a distance of 2 to 4mm relative to the front bottom roller, while the middle top roller is arranged a short distance of 2mm behind the middle bottom roller.

· Overhang of the front top roller gives smooth running of the top rollers and shortens the spinning triangle. This has a correspondingly favourable influence on the end break rate.

· Rubber cots with hardness less than 60 degrees shore are normally unsuitable because they can not recover from the deformation caused by the pressure on the top roller while running.

· Soft rubbercots for top rollers have a greater area of contact, enclose the fibre strand more completely and therefore provide better guidance for the fibres.However softer cots wear out significantly faster
and tend to form more laps.

· Normally harder rubbercots are used for back top rollers, because the roving which enters the back roller is compact , little twisted and it does not require any additional guidance for better fibre control.

· In the front top roller, only few fibres remain in the strand and these exhibit a tendency to slide apart. Additional fibre guidance is therefore necessary.Therefore rubbercots with hardness levels of the order 80 degrees to 85 degrees shore are mostly used at the back roller and 63 degrees and 65 degrees at the front roller.

· If coarse yarns and synthetic yarns are being spun, harder rubbercots are used at the front roller because of increased wear and in the case of synthetic yarns to reduce lapups.

· Three kinds of top roller weighting(loading) are presently in use

  • spring loading
  • pneumatic loading
  • magnetic weighting

· With pneumatic loading system, the total pressure applied to all top rollers is obtained by simple adjustment
of the pressure in the hose using pressure reducing valve. Moreover the rubbercots will not get deformed if
the machine is stopped for a longer duration, because the pressure on top rollers can be released to the
minimum level.

· The fibre strand in the main drafting field consists of only a few remaining fibres. There is hardly any friction field and fibre guidance provided by the rollers alone is inadequate. Special fibre guiding devices are therefore needed to carry out a satisfactory drafting operation. Double apron drafting arrangements with longer bottom aprons is the most widely used guiding system in all the modern ringframes.

· In doube apron drafting system two revolving aprons driven by the middle rollers form a fibre guiding  assembly. In order to be able to guide the fibres, the upper apron must be pressed with controlled force against the lower apron. For this purpose, a controlled spacing (exit opening), precisely adapted to the fibre volume is needed between the two aprons at the delivery. This spacing is set by “spacer” or “distance clips”. Long bottom aprons have the advantage in comparison wiht short ones, that they can be easily replaced in the event of damage and there is less danger of choking with fluff.

· Spindles and their drive have a great influence on power consumption and noise level in the machine The running characteristics of a spindle, especially imbalance and eccentricity relative to the ring flange, also affect yarn quality and of course the number of end breakage. Almost all yarn parameters are affected by poorly running spindles. Hence it should be ensured that the centering of the spindles relative to the rings is as accurate as possible. Since the ring and spindle form independent units and are able to shift relative to each other in operation, these two parts must be re-centered from time to time. Previously, this was done
by shifting the spindle relative to the ring, but now it is usually carried out by adjusting the ring.

· In comparison with Tangential belt drive, the 4-spindle drive has the advantages of lower noise level and energy consumption, and tapes are easier to replace.

· Lappet guide performs the same sequence of movements as the ringrail, but with a shorter stroke, this movement of the guide ensures that differences in the balloon height caused by changes in the ring rail
positions do not become too large. This helps to control the yarn tension variation with in control, so that ends down rate and yarn charactersitics are under control.

· Spindles used today are relatively long. The spacing between the ring and the thread guide is correspondigly long, thus giving a high balloon. This has two negative influence

  • A high balloon results in large bobbin diameter leading to space problems
  • Larger the balloon diameter , higher the air drag on the yarn.This inturn causes increased deformation of the balloon curve out of hte plane intersecting the spindle axis.This deformation can lead to balloon stability, there is increase danger of collapse.

Both these disadvantages result in higher yarn tension, thereby higher endbreaks.In order to avoid this, balloon control rings are used. It divides the balloon into two smaller sub-balloons. Inspite of its large overall
height, the double-balloon created in this way is thoroughly stable even at relatively low yarn tension.

· Balloon control rings therefore help to run the mahcine with long spindles(longer lift) and at high spindle speed, but with lower yarn tension. Since the yarn rubs against the control ring, it may cause roughening
of the yarn.

· Most ends down arise from breaks in the spinning triangle, because very high forces are exerted on a strand consisting of fibres which have not yet been fully bound together in the spinning triangle.

RING and TRAVELLER COMBINATION:

· The following factors should be considered

  • materials of the ring traveller
  • surface charecteristics
  • the forms of both elements
  • wear resistance
  • smoothness of running
  • running-in conditions
  • fibre lubrication

· For the rings two dimensions are of primariy importance. 1.internal diameter 2. flange width.

· Antiwedge rings exhibit an enlarged flange inner side and is markedly flattened on it upper surface. This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination.

· Low crown profle has the following advantage. Low crown ring has a flattened surface top and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced  and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely
used ring form now.

· The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs
mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth.

· A good ring in operation should have the following features:

  • best quality raw material
  • good, but not too high, surface smoothness
  • an even surface
  • exact roundness
  • good, even surface hardness, higher than that of the traveller
  • should have been run in as per ring manufacturers requirement
  • long operating life
  • correct relationship between ring and bobbin tube diameters
  • perfectly horizontal position
  • it should be exactly centered relative to the spindle

· In reality, the traveller moves on a lubricating film which builds up itself and which consists primarily of cellulose and wax. This material arises from material abraded from the fibres.If fibre particles are caught
between the ring and traveller, then at high traveller speeds and with correspondingly high centrifugal forces, the particles are partially ground to a paste of small, colourless, transparent and extremely thin platelets. The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on

  • yarn fineness
  • yarn structure
  • fibre raw material
  • traveller mass
  • traveller speed
  • height  of traveller bow

Modern ring and traveller combination with good fibre lubrication enable traveller speeds upto 40m/sec.

· Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behing by the spindle.

· High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of  the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited.

· When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength.

· If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict  massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring and traveller system the wear is at least an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celsius and the danger of the traveller annealing and failing is very great.

· The spinning tension is proportional

  • to the friction coefficient between ring and traveller
  • to the traveller mass
  • to the square of the traveler speed

and inversely proportional

  • to the ring diameter
  • and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop.

· The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of the fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values.

· If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness.

SHAPE OF THE TRAVELLER:

· The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running. However the flat bow must still leave adequate space for passage of the yarn. If the yarn clearance opening is too small, rubbing of the yarn on the ring leads to roughening of the yarn, a high level of fibre loss as fly, deterioration of yarn quality and formation of melt spots in spinning
of synthetic fibre yarns.

WIRE PROFILE OF THE TRAVELLER:

· Wire profile influences both the behaviour of the traveller and certain yarn characteristics, they are

  • contact surface of the ring
  • smooth running
  • thermal transfer
  • yarn clearance opening
  • roughening effect
  • hairiness

MATERIAL OF THE TRAVELLER

· The traveller should

  • generate as little heat as possible
  • quickly distribute the generated heat from the area where it develops over the whole volume of the traveller
  • transfer this heat rapidly to the ring and the air
  • be elastic, so that the traveller will not break as it is pushed on to the ring
  • exhibit high wear resistance
  • be less hard than the ring, because the traveller must wear out in use in preference to the ring

· In view of the above said requirements, traveller manufacturers have made efforts to improve the running properties by surface treatment. “Braecker” has developed a new process in which certain finishing components diffuse into the traveller surface and are fixed in place there. The resulting layer reduces temperature rise and increases wear resistance.

· Traveller mass determines the magnitude of frictional forces between the traveller and the ring, and these in turn determine the winding and balloon tension. Mass of the traveller depends upon

  • yarn count
  • yarn strength
  • spindle speed
  • material being spun

If traveller weight is too low, the bobbin becomes too soft and the cop content will be low. If it is unduly high, yarn tension will go up and will result in end breaks. If a choice is available between two traveller weights, then the heavier is normally selected, since it will give greater cop weight, smoother running of the traveller and better transfer of heat out of traveller.

· When the yarn runs through the traveller, some fibres are liberated. Most of these fibres float away as dust in to the atmosphere, but some remain caught on the traveller and they can accumulate and form a tuft. This will increase the mass of traveller and will result in end break because of higher yarn tension. To avoid this accumulation , traveller clearers are fixed close to the ring, so that the
accumulation is prevented. They should be set as close as possible to the traveller, but without affecting its movement. Exact setting is very important.

· Specific shape of the cop is achieved by placing the layers of yarn in a conical arrangement. In the ending of a layer, the ring rail is moved slowly but with increasing speed in the upward direction and quickly but with decreasing speed downwards. This gives a ratio between the length of yarn in the main up) and cross(down) windings about 2:1.

· The total length of a complete layer (main and cross windings together) should not be greater han 5m (preferably 4 m) to facilitate unwinding. The traverse stroke of the ring rail is ideal when it
is about 15 to 18% greater than the ring diameter.

· End break suction system has a variety of functions.

  • It removes fibres delivered by the drafting arrangement after an end break and thus prevents multiple  end breaks on neighbouring spindles.
  • It enables better environmental control, since a large part of the return air-flow of the air-conditioned system is led past the drafting system, especially the region of the spinning triangle.
  • In modern installations, approx. 40 to 50 % of the return air-flow passes back into the duct system of the air-conditioning plant via the suction tubes of pneumafil suction system.
  • A relatively high vacuum must be generated to ensure suction of waste fibres
    • for cotton – around 800 pascals
    • for synthetic – around 1200 pascals
  • A significant pressure difference arises between the fan and the last spindle. This pressure difference ill be greater , the longer the machine and greater the volume of air to be transported. The air flow rate is normally between 5 and 10 cubic meter/ hour.
  • Remember that the power needed to generate an air-flow of 10 cubic meter/ hour , is about 4.5 times he power needed for an air-flow of 6 cubic meter/ hour, because of the significantly higher vacuum
    level developed at the fan.

SPINNING GEOMETRY:

· From Roving bobbin to cop, the fibre strand passes through drafting arrangement, thread guide, balloon control rings and traveller. These parts are arranged at various angles and distances relative to each other.
The distances and angles together are referred to as the spinning geometry,has a significant influence n the spinning operation and the resulting yarn. They are

  • yarn tension
  • number of end breaks
  • yarn irregularity
  • binding-in of the fibres
  • yarn hairiness
  • generation of fly etc.

· Spinning Triangle:
Twist in a yarn is generated at the traveller and travel against the direction of yarn movement to the ront roller. Twist must run back as close as possible to the nip of the rollers, but it never penetrates completely to the nip because, after leaving the rollers, the fibres first have to be diverted inwards and wrapped around each other. There is always a triangular bundle of fibres without twist at the exit of the rollers, this is called as SPINNING TRIANGLE. Most of the end breaks originate at this point. The length of the spinning triangle depends upon the spinning geometry and upon the twist level in the yarn.

· The top roller is always shifted 3 to 6 mm forward compared to bottom roller. This is called top rolleroverhang.This gives smoother running and smaller spinning triangle. The overhang must not be made too large,
as the distance from the opening of the aprons to the roller nip line becomes too long resulting in poorer fibre control and increased yarn irregularity.

· Continuous variation of the operating conditions arises during winding of a cop.The result is that the tensile force exerted on yarn must be much higher during winding on the bare tube than during winding on
the full cop, because of the difference in the angle of attack of the yarn on the traveller. When the ring rail is at the upper end of its stroke, in spinning onto the tube, the yarn tension is substantially higher
than when the ring rail is at its lowermost position. This can be observed easily in the balloon on any ring spinning machine.

· The tube and ring diameters must have a minimum ratio, between approx. 1:2 and 1:2.2, in order to ensure that the yarn tension oscillations do not become too great.

· Yarn tension in the balloon is the tension which finally penetrates almost to the spinning triangle and which is responsible for the greater part of the thread breaks. It is reduced to a very small degree by
the deviation of the yarn at the thread guide. An equilibrium of forces must be obtained between the yarn tension and balloon tension.

clip_image002clip_image003

Digg This