COTTON AND RAYON LOOMS:-

COTTON AND RAYON LOOMS:-

A comparative study of a cotton and  rayon or silk loom is always useful to the texile students and supervisory staff of the textile Mills. Acetate, nylon and other synthetic yarns may also be woven in the same manner in rayon looms. An ordinary cotton weaving loom may be converted into a rayon or silk loom with the following modification:-

(1) SHEDDING:-

In cotton weaving the back rest is raised and the top line of shed is made slack and small : thus, the bottom line gets bigger and is more strained giving better 'cover' in cloth. But in a rayon loom the depth of shed in the top as well as in the bottom line is equal, so that equal strain is put upon the warp threads when the shed is open.

(2) Shed timing:-

In a cotton loom, healds are level at the top center of crank : whereas , healds are level between the top and front centres of crank in case of a silk or rayon loom. In highly picked rayon looms the shed is mafe ablityle early. In some silk and rayon weaves heallds are also level when the crank is at front centre.

(3) Shuttle:-

(a) In a cotton loom, an ordinary shuttle is used, and when well-formed cops of cotton yarn may be wound to its cilnging and adhesive nature . In cotton looms the picking motion is overpick ,excepting in wide looms : whereas the picking motion in underpick in case of silk or rayon looms.

(b) In a rayon looms the size of shuttle being smaller , lesser depth shed produced which puts less strain on the warp. Rayon yarns bring slippery, well formed bobbins cannot be made  without proper tension. The rayon shuttle lined with furs is smoothened and polished it will catch the ends. The rayon shuttle eye heve been develope to render uniform tension. An under pick loom is generally provided with a parallel motion in case of rayon or silk weaving to obtain smooth pick.

(4) SLEY:-

The cotton loom sley is used unprotected or sometimes protected with a metal plate or race plate , whereas , the rayon loom sley is surfaced with felt , corduroy or a similar material to protect the warp yarns , and the bottom lone of shef must be embedded on the sley.

(5) Healds:- Cotto , steel or cadmium plated healds are used for cotton weaving: whereas , flat healds with slightly small eye allows less movement of the rayon ends and less abrasion when the healds moves up and down to produce a shed. Rayon healds are made of specially rolled high carboned steel wire with high polish.

(6) Reed:-

 Fast and loose reed motions are used for weaving heavy and light cotton fabrics respectively: whereas , all metal or soldered loose reed is generally used in rayon or silk weaving, and the reed wires are more flexible. The front fender the shuttle box is covered with felt to minimise friction and abrasion of rayon weft when the shuttle enters the box. 

(7) Warp Stop Drop Wires:-

Ordinary, open or closed-endrd steel drop wires are used in cotton weaving: whereas sharp edge, rusted , bent or rough drop wires should be smoothened to minimise abrasion and cutting of rayon warp ends. Again, overcrowding of drop wires on a slide bar should also be avoided in rayon weaving : the number of slide bars should therefore, be increased in case of rayon or silk weaving.

(8) Take-up Motion:-

An emery or sometimes a sand roller of 15.05" or 38.22 cm. or 16" or 40.64 cm. diameter with  a press roller is provided on a cotton loom. Rayon is a slippery material: hence large frictional surface should be about double the circumference is, therefore used . A special covering for cloth roller viz. rubber , hard felt, cork composition etc. and 2" or 5.08cm , solid steel guide or press roller with a thick felt coating have been developed. If the back rest of small radius, rayon cloths are  strained during weaving and give rise to 'cracks' or 'splits', owing to the reason that the surface contact of warp is less.

(9) Let-off Motion:-

 Rope or chain , lever and weight or positive geared let-off motion is used in a cotton loom: whereas frictional negative let-off motion is preferred to a rayon loom . A positive let-off motion is seldom used in rayon or silk weaving.

(10) Temples:-

Pin type temple rollers are mostly used for cotton weaving but they injure the rayon fabrics. Temples of different widths  to suit weaving a variety of fabrics are composed of rubber , cork and dyntld. In case of high  contraction in a rayon cloth, long temple rollers are used.

(11) Lease Rods:-

In a rayon or silk loom small and smooth lease are placed near the back rest to prevent the warp from getting entangled.

Cotton and rayon Mixture Fabrics:-

In cotton and Rayon Mixture fabrics  , coton is commonly used as warp and rayon as weft . 

RAYON AND CREPE WEAVING:-

Most rayon yarns are woven dry, as wet decreases their strenght . For weaving rayon Crepes, the setting of various loom parts do not follow ordinary fixing, for if so, they would not produce the desires effects in the finished fabrics. In some rayon loms, parts are made by and act for crepes, but in others , the adjustments are made by the overlookers or jobbers.

The plain weave is commonly used to produced the bulk of rayon and worsted crepes. These may be produced as:- (a) The first method is the use of both right and left-hand twits in making chifon and georgettes in plain weaving, and (b) In a drop box loom the reverse twist is placed in the first box and other boxes are used when weft mixing is desired.

Loom setting in Rayon Crepe Weaving:-

The following special setting of the loom parts are required to produce the desired effects in finishe rayon crepe fabrics:-

(1) Drafting of HEALDS:-

The ends may drawn through heald eyes as, 1, 2, 3, 4, or 1, 3, 2, 4. In the former method, the pairs one two, and three and four healds rise and fall together. In the latter method , the pairs one end three healds, and two and four headls rise and fall together but in a contrary manner. When weaving the first two shafts rise and fall together, as the second pair vice versa. The first heald is actuated by the first tappet, the second by the third tappet, the third Heald by the second tappet, and the fourth heald by the fourth tappet. Accordingly connecting rods have to be adjusted . An open shed with lease rods in weaving rayon crepe fafrics is shown in fig. 231.

Image Fig. 231. (Top) Fig. 232 (Bottom)

(1) (a) In fig.231, at A is the sley sword: B the going part: C the crank arm at the back center E : and D is the circle described by the crank . At F is the tilted breast beam and the cloth is at G. At H is the front shed fully open, and the healds are placed 1, 2, 3 and 4 . Here the warp is leased two and two : but the warp can be leased one and one . At N is the back rest, and at P is the thick lease rod.

(b) To set for rayon crepe weaving , band or cord is passed over the back rail N from the breast beam F, with a weight at the end. The black rail is then raised until the band is from 1, 1/8 inches to 1, 1/4 inches, or 2.85 cm. to 3.18 cm. above the shuttle race, when the crank is at the top centre . This tightens the bottom shed and slackens the top shed , and imparts a good 'cover' to the cloth (fig. 231).

(2) Shedding Tappets:-

Shedding Tappets constructed for rayon crepe weaving have longer dwell, say, two thirds of a pick and shorter changing period of healds. The longer dwell allows more time for the passage of the shuttle and no friction marks made by the top of the shuttle are perceptible after finishing. The tappets are cast in pairs and are negative. Sometimes they are used to impart an over motion to healds, the undermotion in that case being controlled by springs and quadrant, bolted to cross rails with hooks at the bottom of the loom.

(3) Picking : The picking motion is underpick and is provided with the parallel motion. By moving the picking stick parallel to the shuttle box , the chance of the shuttle flying-out of shed are minimised.

(4) Back and Front Rests:-

 In rayon crepe weaving the back rest is raised and the front rest is sloped. The sloping of the warp is generally to the extent of the same angle as the shuttle race, when the crank is at the top or bottom centre . The tilted front rest has a flat top and a curved front. This setting assists in spreading the warp ends and minimise crease in fabrics, and also allows the bottom line of shed to bed on the velvet or corduroy on the race board, and decreases shuttle friction on the top shed . A 'tugger cord' is also used to impart a good cover to the rayon crepe cloth.

(5) Lease Rods:-

The warp is leased two, or one and one. The back lease rod  is thick and is inserted when two back healds are down. The thin  front lease rod is inserted when two front healds are down. This applies more tension on two front shafts which smaller sheds.

Timing of Poplin and Rayon Crepe Weaving Looms:-

(1) In weaving high grade poplins and rayon cerpes , the Shedding Tappets are so timed that the healds have not to cross each other at the same time. The second and the fourth healds are level when the cranks are at the top cetre, and the first and third healds are level when the cranks are just before the front centre, or 1/2 inch or 1.27 cm. away from the cloth fell. Accordingly, tappets must be set on the countershaft . Such timing is considered very essential in weaving these classes of fabrics owing to the reason that in 44 inches or about a112 cm. wide loom there are from 8000 to 14000 ends . This provides more space for the bulkier heald eyes and prevents many warp breakages. 

(2) Crossing of HEALDS:- The figure 232 shows the crossing of healds with the loom cranks at the top center . The warp threads do not cross each other the same time , and this is done by timing the shedding tappets.

(3) In the figure, the crankshaft E is at the top center. In this position, the tappets are set so that the second and the fourth healds are level. The first and the third shafts are level when the crank is within half an inch or 1.27 cm. of the cloth fell. This is very important in weaving high grade poplins and rayon crepes. The back rest N is also raised as usual.

NYLON WEAVING:-

Nylon is a strong yarn. It therefore, has a cutting action on parts over or through which it passes. A wooden back rest and the wooden lease rods would soon be grooved . The particulars of the loom weaving nulon fabrics are as following:-

(i) A hardened steel roller , whose gudgeons turn in ball bearing,and tin-cover lease rods are used.

(ii) Healds-eyes should be made of metal and not wire.

(iii) To prevent the grooving of the sley race, it should be covere with corduroy.

(iv) Nylon fabrics being slippery, the take-up roller is covered with the coarse emery cloth for better grip. The cloth beam should be turned by sprocket wheel and link chain , provided with a clip motion.

Take-up Motion: The take-up of nylon cloth is explained in fig. 233.

At A is the take-up roller, B the shaft, D is the sprocket wheel and the link chain E is connecting it to the sprocket F, fixed to sleeve that carries friction pulley G. The friction clip H, carruong pin I , that penetrates s note on the cloth beam flange J , on the pulley G . The wing screw K tegulates cloth winding on the beam L , and is at the base of yje the friction clip.

Fig. 233 take-up motion.

To assist grip of cloth, a felt-covered roller is placed at M, on the top of take-up rollerA. The cloth over M on way to the cloth beam L.

Lupton's Nylon Temples:-

In Nylon weaving the interior of shuttle is lined with fur. Lupton's Nylon temples, two for narrow looms or mote for wider looms , are usually made the width of the reed space . The front of the Temples must be free if reed when the cranks are at the front center , and the under-sides must be clear of the shuttle race.

Ref ;- Weaving Mechanism Book Vol. 2 by Prof. N.N. Banerjee.