Textile Finishing: Different Types of Mechanical Finishes for Textiles

In the previous post, the classification of textile finishes and treatment are listed. This post will cover those treatments?

1. Calendering

A simple device which simulates the effects of calendaring is the domestic iron. Hot ironing makes garment smooth flat by removing its crinkles and creases. Besides making the fabrics free from creases by calendaring,

• it is possible to raise the luster of the fabric, 
• make it compact by closing the threads, 
• impart a soft feel and ‘thready’ or 
• linen like appearance to it

It reduces the yarn slippage as well as thickness of the fabric by varying the calendaring operation.

The need of calendaring arises mainly because the fabric when it is wet processed and dried, is in the least lustrous state and its surface is not smooth because of presence of highly crimped and wavy threads. To meet this need the fabric is passed between the rollers or bawls of a machine termed ‘Calender’ and this mechanical process is called calendering.

Different types of calenders:

Ordinary Calender: An ordinary calender consists of a series of hard and soft rollers or bawls mounted vertically in a robust frame and the fabric is passed between the rollers. Hard bawls are made of polished metal and soft bawls are made of compressed cotton or paper or wood.

Swizzing calender: This is an ordinary calender usually with 7 bawls which run at the same peripheral speed so that there is no slip between them.

Friction calender: When maximum increase of luster, higher gloss and greater closing up of the fabric is desired, a calender in which one bawl is made to rotate faster than the other and which is heated and polished, is used. Friction calendars are used for finishing lining, shirting, and printed clothes.

Chasing Calender: In this calender five bawls are used. All bawls run at a same speed. This operation of chasing produces a ‘thready’ or linen-like appearance together with a soft fell.

Embossing Calender: In embossing calender fine lines are embossed on the cloth. Embossing brings about a high degree of luster on the cloth, makes it smooth and flattens it. Damask effect can also be produced on cotton cloth by this process, but effect of embossing is temporary.

2. Sanforising

A method of producing unshrinkable cotton fabric is to give it a thorough wash in a washing machine so as to allow it to shrink freely and then dry and finish it without stretching. This method however is not reliable and not suitable for commercial production.

3. Raising

Raising is a process of lifting of a layer of fibres from the surface of the fabric so as to form a hairy surface or pile. The process imparts a warm and soft handle to both on the woven and knitted fabrics; in fact, the formation of a pile on the fabric can make it exceptionally soft. The pile also includes a large amount of air and since air is a bad conductor of the heat, the raised fabrics feel vary warm as well as soft.

In the early days, only cotton and woolen fabrics were raised, but now besides these fabrics, man-made fibre fabrics also raised. If the fabric contains a woven or coloured pattern, the weave and pattern get subdued on raising and various colour blends.

It is easier to raise the fabric in the wet state than in dry state. Therefore, moist raising is most widely adopted.

4. Napping

In napping the surface of the cloth is raised, cut even and smoothed by a napping machine known as planetary napper.

5. Shearing

Shearing means removing or taking off fibre ends by cutting. It is carried out to cut fibres of random length to produce a level pile and prevent pilling in case of synthetic fibres by resulting of the height of the fibres particularly to produce clean staple fibre fabrics. Napped fabrics are mostly sheared.

Knitted fabrics are sheared on a machine having a single cutting head per unit where in case of woven fabrics multiple sheared are used. The pile heights are regulated by adjusting the distance between the cloth rest and rotary blade.

6. Sueding

When a vary mild effect of raising is required a special type of machine called sueding machine is used. This consists of a vertical set of small diameter rotating rollers covered with an abrasive surface such as sand paper or emery cloth. There is a rubber covered pressure roll which presses the fabric against the abrasive covered cylinder. The abrasion of the fabric surface takes place when the fabric is open width presses between the pressure roller and abrasive covered cylinder. A vary sort pile thus raised according to the pressure of the fabric against these rollers which rotate in a direction of opposite to that of the fabric.

6. Setting and Heat-setting

During manufacturing processes like spinning, weaving or knitting, the fabric is subjected to stresses and strains and release of these distortions in fabric leads to distortions in fabric structure and woven design and also uneven shrinkage. The purpose of the setting is to stabilize the woven structure of the fabric in a regular and permanent manner by relaxing the stresses. The effect is bought about by agencies like heat, moisture, and pressure and generally no chemicals are used in the process.