Posted in Fabric

Processofcotton( Fibre to Fabric )

Processing of Cotton
Cotton is the world’s most important natural fibre. In the year 2007, the global yield was 25 million tons from 35 million hectares cultivated in more than 50 countries.[1]
There are five stages
1. Cultivating and Harvesting
2. Preparatory Processes
3. Spinning
4. Weaving
5. Finishing
Cultivating and harvesting
Cotton is grown anywhere with long, hot dry summers with plenty of sunshine and low humidity. Indian cotton, gossypium arboreum is finer but the staple is only suitable for hand processing. American cotton, gossypium hirsutum produces the longer staple needed for machine production.[3] Planting is from September to mid November and the crop is harvested between March and May. The cotton bolls are harvested by stripper harvesters and spindle pickers, that remove the entire boll from the plant. The cotton boll is the seed pod of the cotton plant, attached to each of the thousands of seeds are fibres about 2.5 cm long.[4]
Ginning
The seed cotton goes in to a Cotton Gin. The cotton gin separates the seeds and removes the “trash” (dirt, stems and leaves) from the fibre. In a saw gin, circular saw grab the fibre and pull it through a grating that is too narrow for he seeds to pass. A roller gin is used with longer staple cotton,. Here a leather roller captures the cotton. A knife blade, set close to the roller detaches the seed. by drawing them through teeth in circular saws and revolving brushes which clean them away.[5]
The ginned cotton fibre, known as lint, is then compressed into bales which are about 1.5m tall and weigh almost 220 kg. Only 33% of the crop is usable lint. Commercial cotton is priced by quality, and that broadly relates to the average length of the staple, and the variety of the plant. Longer staple cotton ( 2 1/2 in to 1 1/4 in) is called Egyptian, medium staple ( 1 1/4 in to 3/4 in) is called American upland and short staple ( less than 3/4 in) is called Indian.
[6]
The cotton seed is pressed into a cooking oil. The husks and meal are processed into animal feed, and the stems into paper.
Issues
Cotton is farmed intensively and uses large amounts of fertiliser and 25% of the worlds insecticide. Native Indian variety were rainwater fed, but modern hybrids used for the mills need irrigation, which spreads pests. The 5% of cotton bearing land in India uses 55% of all pesticides.[3] Before mechanisation, cotton was havested manually and this unpleasant task was done by the lower castes, and in the United States by slaves of African origin.
Preparatory Processes- Preparation of yarn
1. Ginning, bale-making and transportation is done in the country of origin.
2. Opening and cleaning
Cotton mills get the cotton shipped to them in large, 500 pound bales. When the cotton comes out of a bale, it is all packed together and still contains vegetable matter. The bale is broken open using a machine with large spikes. It is called an Opener.In order to fluff up the cotton and remove the vegetable matter, the cotton is sent through a picker, or similar machines. A picker looks similar to the carding machine and the cotton gin, but is slightly different. The cotton is fed into the machine and gets beaten with a beater bar, to loosen it up. It is fed through various rollers, which serve to remove the vegetable matter. The cotton, aided by fans, then collects on a screen and gets fed through more rollers till it emerges as a continuous soft fleecy sheet, known as a lap. [7][8]
3. Blending,
Mixing & Scutching 4.Carding
the fibres are separated and then assembled into a loose strand (sliver or tow) at the conclusion of this stage. The cotton comes off of the picking machine in laps, and is then taken to carding machines. The carders line up the fibres nicely to make them easier to spin. The carding machine consists mainly of one big roller with smaller ones surrounding it. All of the rollers are covered in small teeth, and as the cotton progresses further on the teeth get finer (i.e. closer together). The cotton leaves the carding machine in the form of a sliver; a large rope of fibres.[9]
Note: In a wider sense Carding can refer to these four processes: Willowing- loosening the fibres; Lapping- removing the dust to create a flat sheet or lap of cotton; Carding- combing the tangled lap into a thick rope of 1/2 in in diameter, a sliver; and Drawing- where a drawing frame combines 4 slivers into one- repeated for increased quality.
5. Combing is optional,but is used to remove the shorter fibres, creating a stronger yarn.
6. Drawing the fibres are straightened
Several slivers are combined. Each sliver will have thin and thick spots, and by combining several slivers together a more consistent size can be reached. Since combining several slivers produces a very thick rope of cotton fibres, directly after being combined the slivers are separated into rovings. These rovings are then what are used in the spinning process. Generally speaking, for machine processing a roving is about the width of a pencil.Next, several slivers are combined. Each sliver will have thin and thick spots, and by combining several slivers together a more consistent size can be reached. Since combining several slivers produces a very thick rope of cotton fibres, directly after being combined the slivers are separated into rovings. These rovings (or slubbings) are then what are used in the spinning process. [11]
Generally speaking, for machine processing, a roving is about the width of a pencil.
Drawing frame: Draws the strand out
Slubbing Frame: adds twist, and winds on to bobbins
Intermediate Frames: are used to repeat the slubbing process to produce a finer yarn.
Roving frames: reduces to a finer thread, gives more twist, makes more regular and even in thickness, and winds on to a smaller tube.
[12]
Spinning- Yarn manufacture
The spinning machines take the roving, thins it and twists it, creating yarn which it winds onto a bobbin.In mule spinning he roving is pulled off a bobbin and fed through some rollers, which are feeding at several different speeds.This thins the roving at a consistent rate. If the roving was not a consistent size, then this step could cause a break in the yarn, or could jam the machine. The yarn is twisted through the spinning of the bobbin as the carriage moves out, and is rolled onto a cop as the carriage returns. Mule spinning produces a finer thread than the less skilled ring spinning.The mule was an intermittent process, as the frame advanced and returned a distance of 5ft.It was the descendant of 1779 Crompton device. It produces a softer less twisted thread that was favoured for fines and for weft. It requires considerable skill, so was womens work. The ring was a descendant of the Arkwright water Frame 1769. It was a continuous process, the yard was coarser, had a greater twist and was stronger so was suited to be warp. Requiring less skill it was mens work. Ring spinning is slow due to the distance the thread must pass around the ring, other methods have been introduced. These are collectively known as Break or Open-end spinning.[15]
Sewing thread, was made of several threads twisted together, or doubled.
Checking
This is the process where each of the bobbins is rewound to give a tighter bobbin.
Folding and twisting
Plying is done by pulling yarn from two or more bobbins and twisting it together, in the opposite direction that that in which it was spun. Depending on the weight desired, the cotton may or may not be plied, and the number of strands twisted together varies.[16]
Gassing
Gassing is the process of passing yarn, as distinct from fabric very rapidly through a series of Bunsen gas flames in a gassing frame, in order to burn off the projecting fibres and make the thread round and smooth and also brighter. Only the better qualities of yarn are gassed, such as that used for voiles, poplins, venetians, gabardines, many Egyptian qualities, etc. There is a loss of weight in gassing, which varies’ about 5 to 8 per cent., so that if a 2/60’s yarn is required 2/56’s would be used. The gassed yarn is darker in shade afterwards, but should not be scorched.
Measurements
1. Cotton Counts: The number of pieces of thread, 840 yards long needed to make up 1 lb weight. 10 count cotton means that 10×840 yds weighs 1lb. This is coarser than 20 count cotton where 20×840 yards are needed.
2. Hank: A length of 7 leas or 840 yards
3,Thread: A length of 54 in (the circumference of a warp beam)
4.Bundle: Usually 10 lbs
5.Lea: A length of 80 threads or 120 yards
[18]
6.Denier: this is an alternative method. It is defined as a number that is equivalent to the weight in grams of 9000m of a single yarn. 15 denier is finer than 30 denier.
7.Tex: is the weight in grams of 1km of yarn.
[19]
Weaving-Fabric manufacture
The weaving process uses a loom. The lengthway threads are known as the warp, and the cross way threads are known as the weft. The warp which must be strong needs to be presented to loom on a warp beam. The weft, passes across the loom in a shuttle, that carries the yarn on a pirn. These pirns are automatically changed by the loom. Thus, the yarn needs to be wrapped onto a beam, and onto pirns before weaving can commence. [20]
Winding
After being spun and plied, the cotton thread is taken to a warping room where the winding machine takes the required length of yarn and winds it onto warpers bobbins
Warping or beaming
Racks of bobbins are set up to hold the thread while it is rolled onto the warp bar of a loom. Because the thread is fine, often three of these would be combined to get the desired thread count.[citation needed].
Sizing
Slasher sizing machine needed for strengthening the warp by adding starch.
Drawing in, Looming
The process of drawing each end of the warp separately through the dents of the reed and the eyes of the healds, in the order indicated by the draft.
Pirning (Processing the weft)
Pirn winding frame was used to transfer the weft from cheeses of yarn onto the pirns that would fit into the shuttle
Weaving
At this point, the thread is woven. Depending on the era, one person could manage anywhere from 3 to 100 machines. In the mid nineteenth century, four was the standard number. A skilled weaver in 1925 would run 6 Lancashire Looms. As time progressed new mechanisms were added that stopped the loom any time something went wrong. The mechanisms checked for such things as a broken warp thread, broken weft thread, the shuttle going straight across, and if the shuttle was empty. Forty of these Northrop Looms or automatic looms could be operated by one skilled worker.[21]

The three primary movements of a loom are shedding, picking, and beating-up.
Shedding:
The operation of dividing the warp into two lines, so that the shuttle can pass between these lines. There are two general kinds of sheds-“open” and “closed.” Open Shed-The warp threads are moved when the pattern requires it-from one line to the other. Closed Shed-The warp threads are all placed level in one line after each pick.
Picking:The operation of projecting the shuttle from side to side of the loom through the division in the warp threads. This is done by the overpick or underpick motions. The overpick is suitable for quick-running looms, whereas the underpick is best for heavy or slow looms.
Beating-up: The third primary movement of the loom when making cloth, and is the action of the reed as it drives each pick of weft to the fell of the cloth. [22]
A
Cartwright Loom was an early power loom, that stopped each time the pirn was empty are needed an operative to replace the shuttle. Jacquard Looms and Dobby Looms are looms that have sophisticated methods of shedding. They may be separate looms, or mechanisms added to a plain loom.
Measurements
Ends and Picks: Picks refer to the weft, ends refer to the warp. The coarseness of the cloth can be expressed as the number of picks and ends per quarter inch square , or per inch square. Ends is always written first. For example: Heavy domestics are made from coarse yarns, such as 10’s to 14’s warp and weft, and about 48 ends and 52 picks.[23]

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