Processing of wool fibre - from fibre to woollen fabric

Wool fibre


Wool is a fibre that is obtained from the fleece of a domestic sheep. It is a natural, protein multicellular, staple fibre. It has a complex and unique structure covered with tiny overlapping scales, all pointing in the same direction. 

Its ability to trap air and provide warmth to the wearer makes it one of the best choices for making winter garments. Each wool fibre consists of three parts namely, cuticle, cortex, and medulla.

Wool fibres go through a series of manufacturing steps in order to produce the woollen fabric that are later converted into various apparel items and clothes. Here I will show you the processing steps of processing wool fibre.

Wool processing steps

  1. Shearing
  2. Grading and sorting
  3. Scouring
  4. Carbonising
  5. Neutralization
  6. Carding
  7. Backwashing
  8. Gilling and Combing
  9. Drawing
  10. Spinning
  11. Steaming
  12. Weaving
  13. Finishing
Wool processing steps are shown in the flow chart. 

Process flow chart of woollen fabric manufacturing


1. Shearing

It is a process where the fleece of the sheep is cut to obtain the wool fibres. One Sheep is sheared once a year by an expert shearer, who shears many shears per day. The fleece of an average sheep roughly ways around 6 to 18 pounds. Most of the sheep are sheared by hand, however, modern technologies have enabled us to shear sheep with computers and robot-controlled arms which are more comfortable to the animal.

2. Grading and sorting

Grading is the breaking up of fleece based on its quality. It is then sorted into different sections depending on its quality and the body part from which it has been obtained. The best wool fibres are obtained from the shoulder and sides of the sheep and the lowest fibres are obtained from the lower leg of the sheep.

3. Scouring

Wool consists of a greasy substance which makes it impure. This greasy substance mainly formed by lanolin, dirt, suint, and sand must be removed to get the pure wool fibres. 

This process of removal of this greasy impurity is known as Scouring. In order to do so, the greasy wool is passed through a series of bowls containing was liquor. The initial 2 to 3 bowls are filled with warm water containing detergent and alkali as these help in removing the major portion of impurities present in the wool fibre. 

The remaining bowls contain freshwater which is used to rinse the fibre. The wool is then passed through a continuous drier followed by a machine that mechanically removes the sand and other insoluble impurities. 

Then the wool fibres are transferred to a bin where it is blended and is conditioned.

4. Carbonising

Carbonising of wool is done to remove the vegetable matter present in it such as seeds, burs and grass. As most of the vegetable impurities are cellulosic in nature, they can be easily removed by dissolving them in a strong solution of sulphuric acid followed by baking in a dryer set. 

After that, the wool fibres pass through a dryer at 95 to 120 degrees centigrade. Then the fibres are passed through fluted rollers which crush carbonised burs. The dust is then removed by the de-dusting roller.

5. Neutralization

The sulphuric acid present in the wool fibre after carbonization is removed by the process of neutralization. The wool fibres are passed through a cold water rinse bowl and subsequently passed through a squeeze roller. 

The fibres are then passed through a soda bath at 37 degrees Celsius followed by an ionic wash. The process of neutralization occurs for around 12 minutes at a pH of about 6.5. The fibres are then dried and passed to the next zone.

6. Carding

After that, the woollen fibres are passed through metal teeth which separate and blend into slivers. This is known as the carding process. This also removes any residual dirt particle as it opens the fibre strand to its individual fibre. 

Carding may be done by hand carders or by drum carders to produce fibres for spinning felting, or other fabric- or cloth-making activities. The carding process hence produces a thin sheet of fibres of uniform thickness which forms a thick strand of untwisted fibres known as a sliver.

7. Backwashing

An additional scouring treatment is performed on the wool slivers after carding to remove any unwanted dirt or impurities picked up by the sliver during carding process. This process is known as Backwashing.

8. Gilling and Combing

Gilling is the process of aligning the wool fibres such that they can lie parallel to each other.

The combing process is generally done to eliminate the short fibres present in the wool fibres.

These two additional process after carding makes the fibres straight, uniform, and unidirectional. Thus making the sliver finer by reducing the weight per unit length of the fibres.

9. Drawing

Here the fibre tops are drawn to thoroughly blend into one. This results in the evenness and regularity of roving material. The top is passed through rollers which reduces the slivers to a definite thickness. A small amount of twist is imparted into the slivers to increase their strength of it.

10. Spinning

One strand of yarn is formed by spinning the fibres together. The fibres cling and stick to one another making it fairly simple to spin wool yarn. 

The spinning of woollen yarn is generally done by mule spinning whereas spinning of worsted yarns is done by any number of the spinning machine. The yarn is then wrapped around a bobbin, cones or drums and transported to the next process.

11. Steaming

To eliminate the snarling effect on yarn, steaming of yarns is done after the Ringframe process. This sets the twist imparted to it and prevents it from snarling. 

The steamed yarn is kept in cool condition for 8 hours such that the yarns can retain the moisture and gets stabilized thus helping the winding process.

12. Weaving of woollen fabric

Finally, the woollen yarn is woven into fabric. Generally, two types of weave are done to weave wool fabrics namely – plain weave and twill weave. Mostly plain weave is used produces which produces fabric of looser weave and gives a soft structure. 

This soft structure is formed due to napping. Although napping reduces the lustre of the fabric still it largely helps in concealing the flaws in the fabric. 

Twill weave is generally used to perform exquisite designs on fine fabric. Worsted yarns are more durable than woollen yarns and hence are much more expensive.

13. Finishing

Finishing is the last step of processing woollen fabric. After the weaving of the woollen fabric, it undergoes a series of finishing processes. Some of these are -
  • Fulling - Here the fabric is immersed in water to make fibre interlock.
  • Crabbing – In this process, the interlock formed is permanently set.
  • Decorating – This is done to add lustre to the fabric.

Wool fibres can be dyed before the carding process but it is generally done after the wool is woven into fabric.


Related post: 8 Uses of wool fibre

References

http://www.madehow.com/Volume-1/Wool.html
https://www.woolmark.com/industry/use-wool/wool-processing/woollen-scouring-carbonising
https://www.britannica.com/technology/carding
Fibre to fabric manufacturing process of wool (Fibre2Fashion)

Image source: www.pexels.com

About the Author: Agniv Chatterjee is pursuing his graduate degree from the Department of Textile Technology, Government College of Engineering and Textile Technology, Serampore.

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