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

 

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

Power Loom


  • Classification of Weaving Machines

Looms are classified mainly into handlooms and power looms. The power looms are classified further into the following categories.

a. power looms

These looms have only the basic mechanisms, viz. primary, secondary and some auxillary mechanisms. The following are examples of non-automatic power looms.

1. Tappet looms

2. Dobby looms

3. Jacquard looms

4. Drop box looms

5. Terry looms

b. Automatic looms or conventional automatic looms

To get high productivity and good quality of fabric, additional mechanisms are added to ordinary non-automatic power looms. These looms are becoming popular because of their advantages of versatility and relative cheapness. Examples : 1. Pirn changing automatic loom 2. shuttle changing automatic loom.

c. Shuttle-less looms or unconventional looms

In the non-automatic and automatic looms, shuttles are used for inserting the weft yarns. In these shuttle-looms, preparation of weft yarn and the weft insertion mechanism itself limit the loom production and fabric quality; they are also prone to mechanical problems in propelling the shuttle. Hence loom manufacturers have developed looms with various innovative and alternative means of weft insertion. These modern looms are known as “shuttleless looms” and some examples of the looms are :

1. Air-jet loom

2. Water-jet loom

3. Projectile loom

4. Rapier loom

5. Needle loom

6. Various other methods include rectilinear multiphase looms.

d. Circular looms

These looms achieve higher weft insertion rates because more than one shuttle is delivered at a time. In these looms, the shuttles move simultaneously in a circular path and tubular fabrics are produced.

A warp sheet A from a weaver’s beam B passes around a back rest C and is led around lease rods D to heald shafts E & F which are responsible for separating the warp sheet into two layers to form a shed. The purpose of the back rest and the lease rods is to separate the warp yarns uniformly and precisely, and reduce entanglement and tension in the yarns during the opening of the warp shed. The warp yarns then pass through a reed G, which holds the yarns at uniform spacing and is also responsible for beating-up the weft yarn I into the fell of the cloth. After the weft is beaten up, the warp yarns interchange positions in the shed and thereby cause interlacing to be achieved. At this point, cloth is formed and is held firmly by temples J to assist in the formation of a uniform cloth. The cloth H then passes over a front rest K, around an emery roller or take-up roller L and a guide roller M and is finally wound on to a cloth roller N.

  • Details of various parts of the loom

1. Heald shaft

This part is related to the shedding mechanism. The heald shaft is made of wood or metal such as aluminium. It carries a number of heald wires through which the ends of the warp sheet pass. The heald shafts are also known as ‘heald frames’ or ‘heald staves’. The number of heald shafts depends on the warp repeat of the weave. It is decided by the drafting plan of a weave. The main function of the heald shaft is as follows:
(i) It helps in shed formation
(ii) It is useful in identifying broken warp threads
(iii) It maintains the order or sequence of the warp threads
(iv) It determines the order of lifting or lowering the required number of healds for a pick. In other words it helps in forming the design or pattern in a fabric.
(v) It determines the warp thread density in a fabric, i.e. the numbers of heald wires per inch determine the warp thread density per inch.

2. Sley

It is made of wood and consists of the sley race or race board, reed cap and metal swords carried at either ends. The sley mechanism swings to and fro. It is responsible for pushing the last pick of weft to the fell of the cloth by means of the beat up motion. The sley moves faster when moving towards the fell of the cloth and moves slower when moving backwards. This unequal movement is known as ‘eccentricity of the sley’. It is needed in order to perform the beat up and also to give sufficient time for passage of shuttle to pass through the warp shed. The beat up of the lastly laid pick of weft is accomplished through a metal reed attached to the sley.

3. Shuttle

It is basically a weft carrier and helps in interlacement of the weft with the warp threads to form cloth. The shuttle which is made of wood passes from one end of the loom to the other. It travels along the wooden sley race and passes between the top and bottom layers of the warp sheet. The shuttle enters a shuttle box fitted at either ends of the loom, after passing through the warp shed. A shuttle normally weighs about 0.45 kgs.

4. Shuttle box

It is the housing for the shuttle and is made of wood. It has a spindle and a picker. It may also accommodate the picker without spindle. The top and side of the box towards the sley race are open. The shuttle dwells inside the box for the intermediate period between two successive picks.

5. picker

The picker is a piece made either of leather or synthetic material. It may be placed on a spindle or grooves in the shuttle box. It is used to drive the shuttle from one box to another. It also sustains the force  of the shuttle while entering the box.

6. Reed

It is a metallic comb that is fixed to the sley with a reed cap. The reed is made of a number of wires and the gap between wires is known as dents. Each dent can accommodate one, two or more warp ends. The count of the reed is decided by the number of dents in two inches. The reed performs a number of
functions which are enumerated as follows:
(i) It pushes the lastly laid pick of weft to the cloth fell
(ii) It helps to maintain the position of the warp threads
(iii) It acts as a guide to the shuttle which passes from one end of the loom to the other.
(iv) It determines the fineness of the cloth in conjunction with the healds.
(v) It determines the openness or closeness of the fabric. There are various types of reed such as ordinary reed, gauze reed, expanding reed, V reed etc.

7. Warp beam

This is also known as the weaver’s beam. It is fixed at the back of the loom. The warp sheet is wound on to this beam. The length of warp in the beam may be more than a thousand metres.

8. Back beam

This is also known as the back rest. It is placed above the weaver’s beam. It may be of the fixed or floating type. In the first case the back rest merely acts as a guide to the warp sheet coming from the weaver’s beam. In the second case it acts both as a guide and as a sensor for sensing the warp tension.

9. Breast beam

It is also known as the front rest. It is placed above the cloth roller at the front of the loom and acts as a guide for the cloth being wound on to the cloth roller. The front rest together with the back rest helps to keep the warp yarn and cloth in horizontal position and also maintain proper tension to facilitate
weaving.

10. Cloth beam

It is also known as the cloth roller. The woven cloth is wound on to this roller. This roller is placed below the front rest.


  • A Method for Indicating Loom Timing

In a loom, all the mechanisms must be set at correct timings in relation to each other. We therefore need a simple and unambiguous method for identifying and stating these timings. The loom overlooker or jobber often adjusts the loom settings. This is generally done by keeping the reed or sley at a particular distance, as measured by a steel rule or a gauge, from a fixed mark on the loom frame. This is convenient for practical purposes but not for studying the principles of weaving. To study and set the mechanisms, it is better to state their timings in terms of the angular positions of the crank shaft which activates both the sley and the reed. This can be done conveniently by means of a circle, the radius of which is equal to the length of crank and in which the centre represents the centre of the crank shaft. The circle is known as crank circle or timing circle. Figure 1.4 shows a timing circle. The circle is graduated in the direction of rotation of the crank and is divided into four quarters; the terms top, front, bottom and back centres are used to correspond to the 00, 900, 1800 and 2700 positions of the circle. Also, in these timings the crank positions correspond to the top, front, bottom and back respectively.

Figure 1.4:-Method of indicating Loom Timings

By stating the crank position in terms of degrees, the mechanisms like shedding, picking, etc. can be set and studied without any difficulty. The timings are graduated on a wheel fixed to the crank shaft in degrees and a fixed pointer enables settings to be made in relation to the angular position of the crank shaft.

In a plain power loom the heald shafts, shuttle and sley are operated by mechanisms that are set in motion by a motor through a crankshaft and a bottom shaft. The heald shafts move up and down by the shedding mechanism. The motion is obtained from the bottom shaft or counter shaft that carries the tappets. So the warp sheet is divided into two layers and it forms a shed. The shuttle is pushed into the warp shed by a picker that gets activated by a picking mechanism. Normally the shuttle is kept in a shuttle box. When the shuttle is pushed, it reaches the opposite box. The arrival of the shuttle in the opposite box is confirmed by shuttle checking devices. The picking mechanism is set in motion by the bottom shaft. The crankshaft operates the sley through the crank and crank arms. The sley gets a to and -fro motion. As the sley reciprocates, the reed, which is fixed to the sley, also gets a to and fro motion. The reed thus beats up the weft into the fell of the cloth.

  • Warp and Cloth Control

The shuttle is pushed into the warp shed by a picker that gets activated by a picking After beating up the weft into the fell of the cloth, a take-up motion draws the cloth forward and winds it on to a cloth roller. At the same time the warp is delivered from the weaver’s beam by a let-off motion. These two motions are operated simultaneously and at a constant rate. i.e. the rate of cloth take-up is so set as to be equal to the rate of warp let-off. The take-up motion is operated through a sley stud and gear mechanism. The let-off motion operates by the pulling action of the cloth. The two temple pieces located at the selvedges of the cloth control width.

  • Stop Motions

To ensure good productivity and quality of cloth, the following stop motions are used: The warp protector mechanism protects the warp from breakages during shuttle trap and stops the loom immediately. The weft stop motion stops the loom if a weft thread breaks or the weft yarn gets exhausted, and thereby prevents the formation of weft-way cracks in the fabric. The brake stops the loom instantaneously at any desired moment. The warp stop motion stops the loom when a warp thread breaks during weaving.

Digg This

Methods of Driving a Plain Power Loom


Power loom are driven by the following types of drives :

a. Individual drive

b. Group drive

  • Individual Drive

 

In this method, each power loom is driven by an individual motor. The power required to drive a plain power loom is 0.75 HP. Figure 1.2 shows a simple driving arrangement commonly found in mills. A single motor is used to drive the loom. Motor A, via motor pulley B and loom pulley or fast and loose pulley C and D, drives the top shaft or crank shaft E. A crank shaft gear wheel F and a bottom shaft gear wheel G drive the bottom shaft H. By means of a starting handle, a belt fork can be used to change the position of the belt on the fast-and-loose pulley arrangement. When the belt is on the loose pulley D the pulley will rotate but the crank shaft will not rotate. Therefore the machine can be stopped. By moving the belt to the fast pulley C the loom can be started or stopped at any time. In the latest looms, a motor with an electro-magnetic clutch drive is used. This is more reliable and stops the loom instantaneously by a push-button control system.

Figure 1.2 Individual drive in a loom

From the figure, it is clear that : 1) Speed of the crank shaft = motor speed x = 960 x = 120 revolutions per minute (rpm) 2) Speed of the bottom shaft = Speed of the crank shaft x = 120 x = 60 rpm

Note

1. The ratio of the number of teeth on the gear wheels i.e. the ratio of the number of teeth on the crank shaft gear wheel to that on the bottom shaft gear wheel is 1:2. The actual number of teeth in the two gear wheels could be 36:72, 45:90, etc.

2. Since the ratio of the number of teeth on the gear wheels is 1:2, the ratio of the speeds of the crank shaft and the bottom shaft will be 2:1. If the crank shaft has a speed of 50 rpm, the bottom shaft will have a speed of 25 rpm.

3. When the crank shaft makes one revolution, one pick is inserted. If it has a speed of 75 rpm, 75 picks will be inserted in a minute. Therefore the crank shaft speed in rpm also indicates the picks per minute (ppm), i.e. a crank shaft speed of 75 rpm indicates a pick insertion rate of 75 ppm.

4. Crank shaft speed indicates the loom speed.

  • The advantages of individual drive are listed below :

1. In case the motor of any particular loom fails, that loom alone will stop running, while all the other loom keep running.

2. Power losses in individual loom drive are much less than the losses in a group drive system. There is therefore a considerable saving in power.

3. The life of the transmission belt is comparatively greater in individual drive.

4. In the individual drive system, there will be a clear view of all the looms in the shed. Due to the absence of a overhead shafts and moving belts, the lighting in the shed will be brighter and more uniform.

5. The possibility of accidents is considerably minimised in the individual drive system as each loom and its drive is compactly arranged, without any interloom connection.

6. The shed plan and layout of looms is neat and easy.

  • The disadvantages of individual drive are :

1. Initial cost is high.

2. High maintenance cost.

 

  • Group Drive

 

In the de-centralised weaving sectors, a group of looms is driven by means of a common motor and an overhead shaft and belt-drive arrangement.

Figure 1.3 Group drive in a loom shed

This method of driving power looms is found in the de-centralised weaving sectors, It can be seen in Figure 1.3 that in this system, a common motor A drives an overhead shaft D via pulleys B and C, which is in fact the main shaft of the system. The main shaft runs from one end of the loom shed to the other. A number of pulleys E, are fixed on this shaft, one for each loom. Each loom has a fast-and-loose pulley G which is connected to the corresponding main shaft pulley by means of a belt F. The belts can be shifted on the corresponding fast-and-loose pulley, either to run the loom or to stop it.

  • Advantages of group drive :

1. Initial cost is low.

2. High maintenance cost.

  • Disadvantages of group drive ;

1. Higher power consumption.

2. One motor drives a number of looms. So, if it fails, all the looms it drives are affected. This results in poor loom-shed efficiency.

3. There are greater chances of accidents due to the overhead and other interloom connections

4. The large number of pulleys and belts in the loom shed will reduce the effective amount of light in the loom shed.

5. The layout for a group-drive system is complicated and presents a clumsy overall appearance.

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Basic Motions (Mechanisms) of Weaving


1.1 Introduction

The process of producing a fabric by interlacing warp and weft threads is known as weaving. The machine used for weaving is known as weaving machine or loom. Weaving is an art that has been practiced for thousands of years. The earliest application of weaving dates back to the Egyptian civilization. Over the years, both the process as well as the machine have undergone phenomenal changes. As of today, there is a wide range of looms being used, right from the simplest handloom to the most sophisticated loom. In this rang, the most widely prevalent loom, especially with reference to India, is the ubiquitous “plain power loom”. In this and in the chapters that follow, the various mechanisms associated with the plain power loom are discussed in elaborate detail.

1.2 Basic Mechanisms in a Plain Power Loom

In order to interlace wrap and weft threads to produce a fabric, the following mechanisms are necessary on any type of loom: 1. Primary mechanisms 2. Secondary mechanisms 3. Auxillary mechanisms

1.2.1 Primary Mechanisms These are fundamental or essential mechanisms. Without these mechanisms, it is practically impossible to produce a fabric. It is for this reason that these mechanisms are called ‘primary’ mechanisms. The primary mechanisms are three in number. a. Shedding mechanism b. Picking mechanism c. Beat-up mechanism

Primary Motions

a. Shedding mechanism

The shedding mechanism separates the warp threads into two layers or divisions to form a tunnel known as ‘shed’

b. Picking mechanism

The picking mechanism passes weft thread from one selvedge of the fabric to the other through the shed by means of a shuttle, a projectile, a rapier, a needle, an air-jet or a water-jet. The inserted weft thread is known as “pick”.

c. Beat-up mechanism

The beat-up mechanism beats or pushes the newly inserted length of weft thread (pick) into the already woven fabric at a point known as “fell of the cloth”. These three mechanisms namely shedding, picking and then beat-up are done in sequence.

1.2.2 Secondary Mechanisms

These mechanisms are next in importance to the primary mechanisms. If weaving is to be continuous, these mechanisms are essential. So they are called the ‘secondary’ mechanisms. They are: a. Take-up motion b. Let-off motion

a. Take-up motion

The take-up motion withdraws the cloth from the weaving area at a constant rate so as to give the required pick-spacing (in picks/inch or picks/cm) and then winds it on to a cloth roller.

b. Let-off motion.

The let-off motion delivers the warp to the weaving area at the required rate and at constant tension by unwinding it from the weaver’s beam. The secondary motions are carried out simultaneously.

1.2.3 Auxillary Mechanisms

To get high productivity and good quality of fabric, additional mechanisms, called auxillary mechanisms, are added to a plain power loom. The auxillary mechanisms are useful but not absolutely essential. This is why they are called the ‘auxillary’ mechanisms. These are listed below. a. Warp protector mechanism b. Weft stop motion c. Temples d. Brake e. Warp stop motion (Predominantly found in automatic looms)

a. Warp protector mechanism

The warp protector mechanism will stop the loom if the shuttle gets trapped between the top and bottom layers of the shed. It thus prevents excessive damage to the warp threads, reed wires and shuttle.

b. Weft stop motion

The object of the weft stop motion is to stop the loom when a weft thread breaks or gets exhausted. This motion helps to avoid cracks in a fabric.

c. Temples

The function of the temples is to grip the cloth and hold it at the same width as the warp in the reed, before it is taken up.

d. Brake

The brake stops the loom immediately whenever required. The weaver uses it to stop the loom to repair broken ends and picks.

e. Warp stop motion

The object of the warp stop motion is to stop the loom immediately when a warp thread breaks during the weaving process.

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