Principle of Winding Machine


There are two widely used types of winding machine:

1.) drum winders (used to wind staple-spun yarns into random-wound packages)

2.)precision winders (for winding filament yarns into precision-wound packages).

1.) drum winders

They are also called as “Random Winders”. Drum-winding machines rotate the forming package through surface contact with a cylindrical drum, and the yarn is traversed either by an independent traverse, typically a wing cam, or by grooves in the drum. Figure  1   illustrates the two types of traverse systems

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Fig 1: Winding traverse motion

  • Wing Cam

There are several different independent traverse systems, but the simplicity of the wing cam makes it a useful example to describe. As shown, the end, A, of a yarn guide bar moves the yarn while the other, B, is made to move around the periphery of the cam, traveling one circuit of the periphery per revolution of the camshaft. As B makes one circuit of the cam, A reciprocates, moving the yarn through a return traverse (i.e., double traverse) along the length of the bobbin. The reciprocating yarn guide limits the winding speed because of the inertia on reversals. A very high rate of traverse is impeded by the mechanics of the guide system, since forces of 16 to 64 times the weight of the yarn guide can be present during the reciprocating action. The reciprocating guide can be replaced by a spirally grooved traverse roller, which moves the yarn along the traverse length. In this case, only the yarn undergoes reversal as it is held in the traversing groove of the rotating roller, and speeds in excess of 1500 m/min can be achieved. A further advantage of the grooved traverse roller is that, as a result of tension, the yarn being wound enters the groove without the need for threading up as is required with the independent traverse system.

  • Grooved Drum

With the grooved drum system, the surface speed of the drum, and the traverse speed are kept constant. A continuous helical groove (i.e., interconnected clockwise and counter clockwise helical grooves) around the drum circumference guides the yarn along the traverse length as the yarn is wound onto the bobbin. A continuous helix has points of crossover of the clockwise and counter clockwise helices. To retain the yarn in the correct groove during its traverse, particularly at the intersections, one groove is made deeper than the other, and the shallower groove is slightly angled.

2.)precision winders

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They are also known as Spindle driven Winders. the Principle of precision winder is as shown in figure.

With precision winders, the package is mounted onto a drive spindle, and a reciprocating yarn guide, driven by a cylindrical cam coupled to the spindle drive, is used to move the yarn along the traverse length. The reciprocating yarn guide limits the winding speed because of the inertia on reversals.

The term precision refers to the control of positioning each layer of yarn as it is wound onto the bobbin. There is a precise ratio of spindle to traverse speed. Therefore, as the package diameter increases, the wind and TR are kept constant.

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Knotting


Among the various types of knot, the weaver’s knot and the fisherman’s knot, illustrated in Figure 1, are the two types that may be used. The latter is suitable for most yarns. The weaver’s knot is more appropriate for short-staple yarns, as it is a smaller knot, but it slips more easily when under tension.

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FIGURE  1:-Fisherman’s and weaver’s knots.

The advantage of a knot is that its strength will be several times that of the yarn strength so, if properly tied, it gives reliability to the piecing. However, the knot has many disadvantages for the end user of the yarn and may be seen as “one fault replacing a worst fault.” Its main drawback is size, i.e., its thickness and tails. The weaver’s knot is two to three times the yarn thickness; the fisherman’s knot is three to four times as large. Often, therefore, it may be preferable to accept a thick place in the yarn as a compromise on the final fabric quality, even if it is of comparable thickness, since no tail ends will be present and, as it is less firm than the knot, it could be less visible in the fabric. In processes subsequent to winding, knots can be problematic. When passing at high speed through a tension device (e.g., a disc tensioner), a knot can give rise to a sudden high peak tension, causing a yarn break. Although smaller and hence preferable for finer yarns, the weaver’s knot is susceptible to untying when tensioned. In weaving, then, the alternating stresses on the warp yarn can cause slipped knots, especially with plied yarns. With densely woven fabrics, knots and tails can rub neighboring warp ends, hampering shedding and causing yarn breaks. The size of the knot can disturb weft insertion on air-jet looms, leading to fabric faults, and, in knitting, difficulty in passing a knot through needles can cause holes in the fabric because of dropped stitches or needle breaks.

The development of the splice has made a major reduction in the size of pieced ends and has therefore eliminated many of the processing difficulties mentioned above and greatly improved fabric quality. Consequently, splicing is seen as the industry standard and, although not all spun yarns can be spliced, the great majority of winding machines are fitted with automatic splicers.

Yarn Preparatory process


The yarn is received from spinning department in the form of ring frame bobbins or hanks to make it usable on loom it must be converted into suitable form i.e. wrap & weft as discussed earlier.

These intermediate process between spinning & weaving on loom, which converts the yarn in suitable form that can be used for weaving, are called Weaving Preparetory Process.

The process used in the manufacture of WRAP & WEFT are called ‘ Wrap Preparatory Process’ & ‘ Weft Preparatory Process’ respectively.

Wrap Preparatory Process

The process to be used depend upon the type & quality of yarns, the type of fabric to be produced, & also on the equipment & other facilities available in the mill. The process flow chart is given below which shows the various stages of wrap preparation. The solid lines indicate the basic process most commonly used & the dotted lines indicate some additional processes required for different types of fabrics.

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Windings : In the process, the yarn from a number of ring frame bobbins or hanks is put in a long continuous length on to a bigger packages such as Wraper’s bobbin, cone or cheese. During this process, the objectionable faults are removed from yarn. For the use of dyed yarn, ring frame bobbins may be taken to reeling process to obtain hanks. These hanks are dyed 2 & then sent to winding. The yarn is dyed in cone/cheese form also. Thus, winding packages ( wrapers’ bobbin, corn or cheese ) are taken to next process of wraping i.e. Direct Wraping or Sectional Wraping.

Wraping :

( DIRECT WRAPING OR BEAM WRAPING )

The object of wraping is to collect a predetermined number of single end packages (winding package from which a single thread comes out on unwinding) & convert it into sheet form with ends uniformly spaced & wind a specified length on to wraper’s beam. Thus at the end of process, we get a multiend package (package which on unwinding give no. of ends) i.e. wraper’s beam wound with a sheet of uniformly spaced (hundreds of) ends of specified length. To have a sheet, the wraper’s beam is subjective to dyeing to get dyed wrap.

( SECTIONAL WRAPING AND BEAMING )

Sectional wraping consists of winding of wraping of number of sections, each wound with a (narrow) sheet of uniformly spaced, predetermined number of ends of equal length side by side. on collecting ends from all sections, we get required number of ends required for weaving. Beaming consists of winding sheet, obtained by collecting ends from al sections, on weaver’s beam. Thus, at the end of the process, we get weaver’s beam which may be sent to loom or for drawing-in.

Sizing: Wrap thrads are subjeced to considerable stresses, strains & rubbing action duration weaving. So wrap threads are impregnated with size whose main constituent is on adhesive substance. The size binds the fibres in the yarn surface to resist stresses, strains & rubbling action without breaking. At the back of sizing machine, wrap sheets form number of wraper’s beam are combined to obtain a single sheet containing required number of ends for weaving. This sheet is impregnated with size, dried & wound on weaver’s beam. Thus, at the end of sizing, we get weaver’s beam which may be sent for drawing in or to loom.

Drawing-in & denting :- This process consists of passing ends of wrapsheet from weaver’s beam through heald eyes of healdshaft & throught dents of reed. On loom, if exactly the same fabric is to be prodused after a weaver’s beam is exhausted, then the new sheet of wrap threads is connected end by end to the old sheet. This operation is called tying-in or twisting depending upon the method of joining. Thus, this process need only weaver’s beam wound with wrap. But if other type of fabric is to be prodused after a weaver’s beam is exhausted, then we need weaver’s beam with wrap drawn & dented. Old beams with its heald shafts & reed is removed & new beam is & heald shafts & reed reset on the loom.

Wrap Preparatory Process

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The processes of Reeling,Hank dyeing,Winding & cone/cheese dyeing are same as discussed earlier.The end package of weft ring spinning frames are directly used in the shuttle.This type of weft is known as direct weft.The yarn from ring frame bobbins is subjected to Winding/Cone or Cheese dyeing.The yarn from bigger packages(Cone/Cheese or Warper’s bobbin) (from which objectionable faults are removed/may be dyed too) is wound on to pirns by means of pirn winding.These pirns are supplied to shuttle looms.

The winding packages(Cone/Cheese) are supplied to Automatic Shuttle Looms fitted with Unifil loom winder or to shuttle looms(such as gripper,air jet,water jet or rapier).

Quality requirements of Warp and Weft in weaving


TO CARRY OUT WEAVING MOST PROFITABLE, THE AIM SHOULD BE:-

– For maximum production (per loom and per operative).

– For best quality.

– To achieve this quality of warp and weft should be good. Poor quality of warp and weft causes frequent breakages. So loom has to be stopped frequently which badly affects productivity. Poor quality of warp and weft can lead to production of fabric with inferior quality. SO FOR THE BEST RESULT IN WEAVING , THE BEST QUALITY OF WARP AND WEFT IS THE MUST.

 WARP:-

1. To produce fabric of uniform quality, the tension of warp threads across the width should be same i.e if there are 500 ends, tension of all of them should be same. Similarly the tension of warp sheet as it is unwound from weaver’s beam should also be same.

2. The end should be free from any place that can cause breakage during weaving or can give bad appearance to the cloth. E.g.

(a)A weak place can cause breakage during weaving.

(b)A thick place can cause breakage and give bad appearance.

(c)A thin place can cause bad appearance. Particularly thinner place continuing over a long distance, say 1 or 2m will give bad appearance, as in that portion a fine crack like appearance may be seen.

3. During weaving warp threads are kept under considerable tension and are subjected to the abrasive action of the healds, other moving parts and also of the neighbouring threads of warp. The warp threads should be strong enough to resist these actions without breaking.

WEFT

The weft is supplied to weaving by using any of the following,

(a) For shuttle looms weft is wound on pirns. The pirn fits in to a shuttle. The shuttle is projected into the shed. So supply of weft is in the form of pirn wound with weft.

(b) For shuttle looms fitted with “UNFIL” loom winder, pirn winding is done by a special mechanism on loom itself. So supply of weft is in form of cones or cheese.

(c) For looms in which insertion of weft is not by shuttle carrying pirn are called shuttle-less looms. In these looms (generally) weft insertion takes place from one side of the loom. The weft is withdrawn from the packages such as cones or cheeses and it is inserted into the shed by some carrier (gripper, rapier or air jet or water jet).

As Stated above pirn or cone or cheese can be the package of weft supply. Here also the unwinding tension should be as uniform as possible to produce the fabric of uniform quality and also any factor, such as slough off, entanglement etc., that can cause breakage of weft, should be taken care off. The weft thread should be free from weak places, thick places, thin places, etc., that can cause breakage or give bad appearance to the fabric

Double-layer fabrics produced on the face-to-face principle


Face-to-face weaving represents an alternative method of manufacture of the cut warp fabrics in which two fabrics are woven simultaneously and the pile is produced without the aid of wires. Two separate ground fabrics with a space between them, each with its own warp and weft, are woven on the unstitched double fabric principle, while the pile warp threads interlace alternately with the picks of both fabrics and thus are common to both. The distance between the ground fabrics is regulated according to the required length of pile and as the textures pass forward the pile threads extending between them are cut by means of a transversely reciprocating knife during the weaving process. Upper fabric is thus formed the lower fabric with the pile facing up, and the upper fabric with a similar pile facing down. The fabrics pass in contact with separate take-up rollers and are wound on two fabrics. Fig.1 illustrates double-layer fabrics produced on the face-to-face principle

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Fig. 1: Double-layer fabrics produced on the face-to-face principle

Terry Fabrics


The terry pile is a class of warp pile structure in which certain warp ends are made to form loops on the surface of the fabric. The loops may be formed on one side only or on both
sides of the fabric thus producing single-sided and double-sided structures as shown in Fig. 1 & 2 respectively. A high tension is applied to a ground warp and a very low tension to
a pile warp. In traditional terry weaving, by means of a special device on the weaving machine, two picks are inserted at a variable distance ‘‘the loose pick distance’’ from the fabric fell. the two picks are beaten up short of the true fabric fell and produce a temporary false fell as indicated schematically in Fig.1 A and B. The loose pick distance is varied according to the desired loop height. On the third pick of the group full beat-up takes place the three picks being pushed forward together to the true fell position. During this action the three picks are capable of sliding between the ground ends, which are kept very taut, as depicted in Fig. 1 C, D and E.image

A. 1st. temporary false fell
B. 2nd temporary false fell
C. 3rd pick of the group
D. Whole group is pushed into
the fell point
E. Full beat-up

Fig. 1: Phases of the pile formation on terry weaving machine

It can be therefore determined some principles:
1. The smallest wefts group is three wefts.
2. The pile yarns must be always intersected with the second weft of the wefts group.
3. The warp shedding must be closed during beating-up of the third pick

The exact relation of the weft to the two warps and the principle of loop formation is depicted by means of the weft section in Fig. 2. The broken vertical lines CC, DD, and EE divide the first, second and third picks into repeating groups of three, line EE indicating the position of the fell of the fabric. On the right of the diagram, a group of three picks, which compose a repeat, is represented previous to being beaten up to the fell of the fabric. The ground threads G1, G2 , and the face and back pile threads P1 and P2 are shown connected by lines with the respective spaces in the corresponding weave given in Fig. 2. In weaving the fabric the group warp beam carrying the threads G1 and G2, is heavily tensioned. As stated earlier so that these threads are held tight all the time. The picks 16 and 17 are first woven into the proper sheds, but are not beaten fully up to the fell of the fabric at the time of insertion in their sheds; but when the pick No. 18 is inserted the mechanisms are so operated that the three picks are driven together into the fabric at the fell EE. During the beating up of the third pick the pile warp threads P1 and P2 are either given in slack, or are placed under very slight tension.

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Fig. 2: Structure of three-pick terry, pile on both sides

The picks 16 and 17 are in the same shed made by the tight ground threads G1 and G2, which, therefore, offer no obstruction to the two picks being driven toward at the same time with the third pick. The pile threads P1 and P2, on the other hand, change from one side of the fabric to the other between the picks 16 and 17, and they are, therefore, gripped at the point of contact with the two picks. As the three picks are beaten up this point of contact is moved forward to the fell of the fabric with the result that the slack pile warp threads are drawn forward and two horizontal rows of loops are formed one projecting from the upper and the other from the lower surface of the fabric in the manner  represented in Fig. 3. Setting of shedding level of the pile and ground shafts is shown in Fig. 2.15.

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Fig.3: Diagram of three-pick terry design, pile on both sides.

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Fig. 4: Setting of shedding level of the pile and ground shafts

Main methods for the production of terry fabrics

The production of terry fabrics is a complex process and is only possible on specially equipped weaving machines. Terry weaving machines are constructed so as to impart a loop
to warp yarns via weft yarns which are beaten up at a beating-up station to form a fabric. Two warps are processed simultaneously, the ground warp, with tightly tensioned ends and the pile warp, with lightly tensioned ends. In general, the reed has two beat-up positions which do not impose alternative movements to the warp, fabric and various components of the weaving machine. Special weaving methods enable loops to be performed with the lightly tensioned warp ends on the fabric surface. Those methods are divided into two mains methods as follows:
Reed control mechanism
Fabric control mechanism.

  • Weaving machine equipped with the reed control mechanism

Reed control mechanism must be used to vary the stroke of the reed to effect partial beat-up of certain picks of weft and full beat up of other picks of weft. Reciprocating motion is applied to a lay beam on which the reed is mounted by a crank arm whose motion is driven by a rotatable driving element. The rotatable driving element is coupled to the crank arm through a mechanical linkage which includes a pneumatic or hydraulic cylinder. The pneumatic or hydraulic cylinder serves to shift the arc of the reed so as to effect partial beat up of certain picks of weft and full beat up of other picks of weft.

Figures 5A and b illustrate a reed control mechanism generally indicated by numeral 1. The reed control mechanism 1 serves to control the reciprocating motion of the reed 2 which is mounted on a lay beam 3. Although not indicated in the figures, the reed 2 and the lay beam 3 extend substantially across the width of the loom. Reciprocating motion is imparted to the reed 2 and the lay beam 3 by a reciprocating motion imparting means here shown as a crank arm 4 which reciprocates about a lay shaft 5. Generally, crank arm 4 is located near the center of the lay beam 3 and the reed 2. The reciprocating movement of the crank arm 4 is driven by a driving element or crank 6 which as shown preferably rotates in the clockwise sense about a shaft crank 7 that is mounted on the loom and extends parallel to lay beam 3 and lay shaft 5. The crank 6 is connected to crank arm 4 through a mechanical linkage 8 which includes a pair of spaced apart longitudinal links 9 and 10 and an interposed adjustable member here shown to be a pneumatic piston-cylinder 11 for controlling the spacing between the longitudinal links 9, 10 and thus the length of the mechanical linkage 8. Of course, the adjustable member may be a hydraulic piston-cylinder instead of pneumatic piston-cylinder 11 or any other such member, such as, for example, an electromagnetically controlled piston-cylinder.

Longitudinal element 9 which is fastened to the piston-rod 12 of the cylinder 11 is pivotally connected to the crank 6 by axle 14. Similarly, longitudinal element 10, which is fastened to the base end 13 of the cylinder 11, is pivotally connected to the crank arm 4 by axle 15. A pressure medium, here shown as compressed air is connected to the cylinder 11 near the base 13. In the Figures, this connection is shown in a schematic manner only, the actual structure being well within the skill of the ordinary worker. The flow of the compressed air from diagrammatically illustrated standard pressure vessel 16 is controlled by diagrammatically illustrated standard timing circuit 18. When the pressure medium stored in vessel 16 enters the cylinder 11, near the base 13 through diagrammatically illustrated inlet 19, the piston-rod 12 is forced outward from the cylinder thereby extending the effective length of mechanical linkage 8.

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Fig. 5: Reed control mechanism

A pressure medium, here shown as compressed air is also connected to the cylinder 11 near end 17. The flow of compressed air from diagrammatically illustrated standard pressure
vessel 16′ into the cylinder 11 through diagrammatically illustrated inlet 19′ is regulated by diagrammatically illustrated standard timing circuit 18′. When compressed air enters the
cylinder 11 near end 17, the piston rod 12 is forced inward, thereby shortening the effective length of the mechanical linkage 8.

As previously indicated, the reed control mechanism 1 is intended to enable the reed to perform a three pick terry cycle which involves partial beat up of the first two picks of weft
followed by full beat up of the third pick of weft. The workings of the inventive reed control mechanism 1 can be understood by considering its operation during a single three pick cycle which corresponds to three rotations of the crank 6, one for each pick. Operation of the reed control mechanism 1 during the first two picks is shown in Fig. 5A, and operation of the reed control mechanism 1 during the third pick is shown in Fig. 5B.

Starting from an arbitrary initial position of the reed 2 and associated reed control mechanism 1 which is shown in phantom in Fig. 5A, as the driver element 6 rotates in the clockwise direction about the shaft crank 7, the reed 2 is driven leftward in an arc. The leftward most position of the reed 2 is indicated by position A in Fig. 5A. At this time, the orientation of the associated reed control mechanism 1 is shown in Fig. 5A. As the reed moves leftward through the arc, it carries with it a pick of weft (not shown). As the crank 6 continues in its clockwise rotation returning reed 2 and associated reed control mechanism 1 to the initial position shown in Fig. 5B, the reed 2 moves rightward through its arc leaving the pick of weft behind at position A. Note that position A is separated from the fell of the fabric whose location is schematically illustrated by position B. Thus, there has occurred partial beat up of the first pick of weft. Upon a second rotation of the crank 6, another pick of weft is positioned near position A.

Illustratively, as shown in Fig. 5B, at the start of the third rotation of the crank 6, the piston rod 12 of the cylinder 11 starts to extend outward, thus lengthening the mechanical linkage 8 and causing the arc of the reed 2 to shift leftward in an arc. The leftwardmost position of the reed 2 is indicated by Fig. 5A. As the reed 2 moves leftward through its arc the third pick of weft as well as the first two picks of weft which were previously positioned at A are positioned at position B. Position B is the leftward most position of the reed 2 as it moves through its arc and generally corresponds to the fell of the fabric. When the reed 2 reaches position B, the corresponding orientation of the reed control mechanism 1 is shown by the drawing of Fig. 5C. When this position is reached, the piston rod 12 of the cylinder 11 is maximally extended. Hence, as will be recognized by those of ordinary skill, the height of the terry pile is determined by the difference in position of points A and B. Note that, during the second half of the third rotation of the crank 6, the piston rod of the pneumatic cylinder 11 is forced inward so that the mechanical linkage is shortened and partial beat up of the first pick of the next cycle is effected.

Mechanical linkage 8 also includes continuously adjustable nut 20 for adjusting the relative positions of points A and B to thereby adjust the pile height of the resulting terry fabric. The nut 20 is incorporated as part of the piston-rod 12 and serves as a means for regulating the length of the mechanical linkage 8 during partial beat up steps. Adjustment of the nut 20 results in a leftward or rightward shift of the arc of the reed but does not appreciably change the length of the arc of the reed. When it is desired that there be a relatively short pile height, the nut 20 should be positioned adjacent end 17 of the cylinder 11 during the partial beat up steps. When the nut 20 is so positioned, the movement of the piston rod 12 into the cylinder 11 is limited by the nut. Thus mechanical linkage 8 is relatively long and the corresponding arc of the reed 2 is shifted to the left, thereby giving rise to a relatively small distance between the partially beat up first two picks of the three pick terry cycle (point A) and the fell of the fabric (point B). On the other hand where a relatively large pile height is desired, the nut may be spaced apart from the end 17 of the cylinder 11 during the partial beat up steps in which case movement of the piston-rod 12 into the cylinder is limited only by the geometry of the cylinder. This serves to shift the arc of the reed 2 to the right and results in a relatively long distance between the partially beat up first two picks of the three pick terry cycle (point A) and the fell of the fabric (point B).

  • Weaving machine equipped with the fabric control mechanism

Fabric control mechanism was developed by Sulzer and Dornier companies. Loop formation proceeds according to the principle of fabric control. That is, the reed moves in a conventional manner but the fabric or fabric is periodically moved away from beating-up station by a common movement of the breast beam and temple. Usually, two or three partial beating-ups are carried out after each complete beating-up for a subsequent looping of the pile warp

Fabric control mechanism on Sulzer weaving machine

Referring to Fig. 6, the terry weaving machine is of generally conventional structure. For example, the weaving machine has a ground warp beam 1 from which a plurality of ground
warps 2 extend via a deflecting beam 3 to a whip roll 4 as well as a pile warp beam 5 from which a plurality of pile warps 6 extend via a temple 7 and a resiliently mounted whip roll 10 which is secured to a lever pair 11.

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Fig. 6: Loop formation by using fabric control mechanism on Sulzer weaving machine

As indicated, the lever pair 11 is pivotally mounted about a pivot 12 and is biased by a spring 13 against the pile warps 6. In addition, the ground warps 2 and pile warps 6 are guided via warp yarn detectors 14 into a means for forming a shed. This means includes a plurality of heddles 15 which are able to shift the warps into a top shed position and/or a bottom shed position. In addition, a means is provided in the form of a reed 16 for beating up a weft yarn within the shed to a beating-up station to form a fabric or fabric. The machine has also a slide 17 comprised of a temple 8 having a needle roller 18 and a breast beam 19 over which the fabric is guided away from the beating up station. In addition, a needled stepping beam 20, a pressing beam 21, and a temple 9 are provided to guide the fabric onto a fabric beam 22.

As indicated, a means is provided for periodically reciprocating the temple 8 and breast beam 19 to effect a terry weave in the fabric. This means includes a pull link 23 which is connected to the breast beam 19, a pull hook or lever 24 and a cam follower lever 25 which connect the breast beam 19 to a terry cam 26. This cam 26 meshes with a worm drive 28 forming part of a warp beam drive 27. The worm drive 28 also meshes with a toothed annulus 29 of the warp beam 5. In addition, a drive motor 30 is provided for driving the warp beam drive 27. Referring to Fig. 6, a means in the form of a stationary deflecting mechanism 31 is disposed between the reed 16 and temple 8 for narrowing the shed on opposite sides, i.e., from the top and from the bottom, as viewed at least on one edge in order to maintain a tucked-in end of a weft yarn in the shed. During operation of the weaving machine, the terry cam 26 (Fig. 6) acts via the lever 25, hook 24 and link 23 to reciprocate the slide 17 in the direction indicated by the double arrow 33. The fabric 32 thus makes an operative movement (lift) H relative to the beating- up position of the reed

Fabric control mechanism on Dornier weaving machine

Pile formation by using this mechanism is based on the principle of a stable and precise shifting of the beat-up point. Using this principle the fabric is shifted towards the reed by
means of a positively controlled movement of the whip roll 6 and a terry bar together with the temples on the beat-up of the fast pick. The sturdy reed drive is free of play. It provides the necessary precision for the beat-up of the group of picks.

A compact, simplified whip roll system 6 with the warp stop motions arranged on two separate levels improves handling and has a decisive influence on reducing broken ends. Due to a drastic reduction in the number of mechanical components the amount of maintenance required is reduced. With the help of electronics the precision of measuring the Iength of pile yarn is improved. This leads to a better fabric quality due to constant pile height and fabric weight. The weaving process is so exact that precise mirrored patterns are possible and velour weavers experience minimal shearing waste. The tensions of the ground and pile warps 1 and 2 are detected by force sensors 3 and 9 and electronically regulated. In this way warp tension is kept uniform from full to the empty warp beam. To prevent starting marks or pulling back of the pile loops the pile warp tension can be reduced during machine standstill. Fig. 7 illustrates Dornier air-jet terry weaving machine

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Fig. 7: Fabric control mechanism on Dornier air-jet weaving machine

 

Drive and control of weaving machines


The latest weaving machines are equipped with microprocessor or PLC units which ensure continuously the control, the drive and the monitoring of the various machine members and of the various functions.

A variety of electronic devices and sensors permits the collection and the processing in real time of the main production and quality parameters. These parameters can also be recorded and transferred through memory cards to other machines or stored for future use (fig. 1). The control unit can be connected with outer units (terminals, servers, company managing system) to transmit/receive data concerning both the technical and productive management and the economic-commercial management (fig. 2). All this facilitated considerably the weaver’s work in respect to machines of previous generation, and enabled to improve the production yield and the product quality.

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Fig. 1 − Board computer equipped with memory card

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Fig. 2 − Example of a modern monitoring and control network

The main operations which can be carried out by simply keying in the value of the desired parameter on the keyboard of the electronic control unit are:

• selection and modification of the weft density with running machine, as both the motor driving the take-up roller (sand roll) and the motor driving the warp beam are  electronically controlled and synchronized one another. This permits also to combine a programmed automatic pick finding, obtained through correction programs based on the characteristics of the fabric in production, in order to prevent formation of starting marks (after machine stops); • electronic selection and control of warp tension through a load cell situated on the back rest roller, which last detects continuously the tension value. This permits the processor to control the movements of the warp beam and of the take-up roller, ensuring a constant tension throughout the weaving operation (fig. 3);

• programming of the electronic dobby and of the electronic weft colors selector;

• programming and managing of nozzle pressure and blowing time in air jet weaving machines;

• selection and variation of the working speed, as the machines are provided with a frequency converter (inverter) which permits to modify at will the speed of the driving  synchronous motor;

• statistics;

• monitoring;

• managing/programming of all machine functions.

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Fig. 3 − Electronic detecting and control system on thread tension. Setting and modification of tension and weft density directly via board computer

Preparation of weaving machines


To obtain satisfactory weaving performance, it is essential to have not only a correct yarn preparation, but also an efficient organization which permits to have warps available at the right moment, thus avoiding any dead time with style or beam change. All these prerequisites aim at ensuring to the weaving mills a sufficient flexibility and at permitting them to cope promptly with a variable market demand.

Currently several weaving mills have installed weaving machines which enable to perform the quick style change (QSC), leading to a considerable reduction of the waiting time of the machine.

The following chart presents the possible alternatives for the preparation of the weaving machine:

Changing style means producing a new fabric style, weaver’s beam changing means going on weaving the same fabric style just replacing the empty beam with a full beam of same type. Drawing-in consists of threading the warp yarns through the drop wires, the healds and the reed (fig.1). Depending on the styles of the produced fabrics and on the company’s size, this operation can be carried out manually, by drawing-in female workers operating in pairs (a time consuming activity which requires also skill and care), or by using automatic drawing-in machines.

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Fig. 1− Drawing-in

Fig. 2 shows one of the most established heald drawing-in machines. The drawing-in begins by placing the weaver’s beam, the harness and the row of healds on the proper anchor brackets, then the drawing-in program is typed in on the computer and the machine is started. A sort of long needle picks up in sequence the threads and inserts them with only one movement into the drop wires, the healds and the reed dents, which are selected each time and lined up to that purpose. The computer controls the different functions and supervises them electronically, ensuring the exact execution of the operation and interrupting it in case of defects. The machine can be used with the usual types of healds, drop wires and reeds and can process a wide range of yarn types and counts, from silk yarns to coarse glass fibre yarns. The drawing-in speed can in optimum conditions exceed 6,000 threads/hour.

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Fig 2.: Heddle drawing-in machine

Fig. 30 presents another automatic drawing-in machine which carries out same functions as previous machine, however without needing the weaver’s beam. In fact it is fed by a common cotton twine which it inserts among the various elements of the warp stop motion, of the harness and of the reed according to the program set up on the computer and under its control and supervision. At the end of the drawing-in, the drawn-in devices are moved on the frame of a knotting station in which an automatic warp tying-in machine joins the drawing-in threads together with the threads of the beam. This operation can be made also on board the loom.

Fig 3:- Automatic drawing-in machine (Staubli KK / Korea Branch)

This machine offers the advantage of working always under optimum operating conditions (use of same yarn), independently of the quality of the warp to be prepared and in advance in respect to warping, therefore with higher flexibility. The drawing-in rate can reach 3600 threads/hour. Fig.4  shows a harness and a reed with already drawn-in threads, ready to be brought to the knotting station.

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Fig. 4:-  A harness and a reed with drawn-in threads ready to be moved to the knotting station.

The piecing-up of the warp yarns (Fig. 5) permits to the weaving mills which are in a position to use it (not many mills at the moment) to simplify and speed up considerably the loom starting operations in case of warps which were drawn-in or tied-up outside the weaving machine. The warp threads are laid into a uniform layer by the brush roller of the piecing-up machine and successively pieced-up between two plastic sheets respectively about 5 cm and 140 cm wide, both covering the whole warp width.

The plastic sheet can be inserted into the weaving machine simply and quickly, avoiding to group the threads together into bundles; the threads are then pieced-up on the tying cloth of the take-up roller.

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Fig. 5 − Piecing-up

If a new drawing-in operation is not necessary (this expensive operation is avoided whenever possible) because no style change is needed, the warp is taken from the beam store and brought directly to the weaving room, where it is knotted on board the loom to the warp prepared with the knotting machine.

As an alternative to the usual knotting on board the loom, the knotting outside the loom or stationary knotting of a new warp with an already drawn-in warp can be carried out in the preparation department. The devices bearing the threads of the old warps are taken from the weaving machine and the knotting can be started in the preparation room under better conditions, leaving the weaving machine free for rapid cleaning and maintenance operations.

The stationary knotting, in particular, takes place in following stages:

• Taking out of the loom the prepared beam with the harness
• Transport of the beam into the weaving preparation department
• Fastening of the heald frames and of the reed on the proper frame
Knotting
• Passing of the knots by proper drawing
Warp piecing-up
• Temporary maintenance of the new warp with the harness
• Transport of the new warp inclusive of harness with proper carriage
• Loading of the weaving machine and start of the weaving process using plastic sheet (fig.7)
• Weaving

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Fig. 6 − A knotting machine in operation on a warp with colour sequence, tensioned on the proper frame.

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Fig. 7 − Harness loading in the weaving machine

The automatic knotting machines can process a wide range of yarn types and counts at highly reliable and rapid operating conditions (up to 600 knots/minute), with mechanical or electronic control on double knots and on the sequence of warp patterns in case of multi-coloured warps. Fig. 6 shows a knotting machine in operation on a warp with colour  equence, tensioned on the proper frame.

Pleated fabrics (Plissé)


Pleated or wrinkles effect in a fabric in the longitudinal or cross-direction or in diagonal direction as well as figure like folds, one describes these fabrics as pleated fabric or Plissé. The fabric formation includes 3 phases:-
• Middle fabric ‘inter-fabric’ weaving,
• Pleated length weaving,
• Formation of wrinkles.

Smooth pleated fabrics can be achieved by suitable folds structures as shown in Figs. 1, 2 which are more permanent than the wrinkles created afterward by pressing and fixing methods. Wrinkles can be achieved on one side or both sides of pleated fabrics. A ground warp needs to be much longer than tight warp as illustrated in Fig. 2, which must be more ensioned. For this reason, it is used two warp beams in the weaving machine and the weaving machine must be supplied with a special device.

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Fig. 1: The appearance of a smooth pleated fabric

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Fig. 2: The appearance of a tough pleated fabric

Wash proof pleated fabrics usually need to have more than 50% synthetic fibers such that the pleats do not fall out during wearing or washing. Pure cotton and wool fabrics also can be made pleated by applying synthetic resin finishes. It is now also possible to make permanent pleats during weaving without synthetic fibers or finishing.

It is expected that the relative cover of fold fabric less than inter-fabric, as the result of the interlacing between all warp yarns ‘‘ground and tight’’ and wefts in inter-fabric, on the other side the interlacing in fold fabric is just between the ground warp and wefts. The length of the inter-fabric must not be shorter than the half length of fold fabric, because the folds must not be overlapped with each other. Fig.  illustrates cross-section in weft direction for the formation phases of a pleated fabric as follows:

A. Pleated fabric structure, the warp threads are arranged 1 ground yarn: 1 tight yarn,
B. Before the formation of wrinkles,
C. After the formation of wrinkles.

Points a and b represent the positions of the back rest and breast-beam

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Fig. 3: Cross-section in weft direction for the formation of pleated fabric

Main methods for the production of pleated fabrics (Plissé)

The weaving machine of pleated fabrics must be equipped with two warp beams in addition to a device for displacement of the woven pleated fabric, or with variable beating up.

Weaving machine equipped with a special pleated device

At the beginning of this method both returning elements ‘back rest and breast-beam’ take the most far on the right lying position as illustrated at point A in Fig. 4 When the intended folds length is reached, they are farther on the left (B). The distance between the two limit points A and B is determined by the fold length.

After the last weft insertion within the fold length and with beginning of the next inter-fabric part, the pleated length is formed by returning back of the back rest and breast-beam into the starting position (A), at that moment the back rest pull the tight warp to the back position (A).

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Fig. 4: Device for pleated fabrics weaving

The coordination of pleated fabric and take-up mechanism are shown in Fig.5. The height of the formed fold is equal to about half of the fold length before the backward-movement of the tight warp yarns.

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Fig. 5: Movement coordination of pleated fabric and take-up device

Weaving machine equipped with a fabric displacement device

This method represents a wrinkles formation for the pleated fabrics on the weaving machine; it is somewhat old method as shown in Fig. 6. During the insertion of wrinkle wefts, the take-up device is stopped, at the same time, the fabric is held under tension by the bar 4 parallel to the breast-beam. This bar 4 is moved over the linkage 5 in direction of arrow. This movement is produced on the weaving machine supplied with a dobby device as follows: By means of the chain 6 the shift lever 7 is raised, whereby over the pawl 8 the ratchet gear 9 is turned around a certain amount. The change gear 9 is connected firmly with crank 10, at which sits the linkage 5. The ratchet gear 9 is secured by the pawl 11.

During this procedure the ground warp is let off. When the fold weaving is finished, the string 12 and the lever 13 therefore are raised by the dobby, and the slay 14 with the base 15 takes with its movement the hook-base of the lever 13 and the lever 16, whereby both pawls 8 and 11 are moved at the left side over the pin 17 and 18 at them. Now the rectangular lever 19 standing under feather-tension withdraws the ground fabric as well as tight warp so that the pleat is formed, and hereby the ground fabric can be woven without interruption.

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Fig.6 : Weaving of pleated fabrics with variable beat-up of the slay

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Fig. 7: Weaving of pleated fabrics by a shortening and lengthening of crank rod

In Fig. 7 the possibility of the formation of wrinkles on the weaving machine is represented by a shortening and lengthening of crank rod. During the fold weaving the string 1 and 2, which is controlled by dobby device, is lowered during this device. The activated-pawl 3 and the ratchet retaining-pawl 4 are in the engagement. The pawl 3 activates the ratchet gear 5 in the clockwise direction. Thus the bearing point 6 of the linkage 7 connected firmly with the ratchet gear is pushed upward, and the out-breakable crank shears 8 are expenditure-broken around a small bit, which means a shortening of the slay. The supporting rocker 9 is movable free on the shaft 10. When the ground fabric is to be woven, then the pawls 3 and 4 are out of contact with ratchet gear 5, and the linkage 7 is pulled by the spring 11 up to the attack on the support bearing 12, by what the maximum beating-movement is achieved again

Classification of Knitting Machines


The machines used for the manufacturing of knit fabrics can be divided into machines with individually driven needles and needle bar machines.

The former type of machine incorporates needles which are moved individually by cams acting on the needle butt; they are used for producing weft knits and are subdivided into circular knitting machines and flat-bed knitting machines. The needles used can be latch needles or compound needles.

The needle bar machines incorporate needles which move simultaneously, since they are all fixed to the same bar; we distinguish full-fashioned knitting machines and circular loop-wheel machines for the production of weft knit fabrics, which only use spring-beard needles, and warp knitting machines which use spring-beard needles, latch needles and compound needles.

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