Physical Finishing (Mechanical)

1 Introduction
The term finishing includes all the mechanical and chemical processes employed commercially to improve the acceptability of the product, except those procedures directly concerned with colouring. The objective of the various finishing processes is to make fabric from the loom or knitting frame more acceptable to the consumer. Finishing processes include preparatory treatments used before additional treatment

2 Finishing
Any operation (other than preparation or dyeing) in the manufacture of textiles to improve the appearance and imparts useful characteristics to the fabric. May gives same basic fabric multiple uses to over market versatility.

2.1 Terms Used to Categorize Finishes
1. Chemical finishing
2. Physical (Mechanical) finishing
3. Wet
4. Dry
5. Durable
6. Non-durable

3 Physical finishing
Physical (Mechanical) finishes usually involved specific physical treatment to fabric surface to causes change in fabric appearance. This is also known as dry finish.

4 Types Physical Finishing (Mechanical)
a. Heat Setting
b. Raising
c. Milling
d. Sanforising
e. Shearing
f. Calendaring
g. Decatizing
h. Compacting
i. Relaxation Drying

4.1 Heat setting
• Process for stabilizing polyester and nylon fabrics by heating at 350-4000F for 20-60 seconds.
• Uneven moisture causes the fabric to dry unevenly and therefore be subjected to uneven heat setting.
• Not effective on cotton or rayon.
• May be performed in fabric or garment form.
• Differential dyeing, bow-bias and yellowing can result.
• May cause shade variation from side-to-side if done prior to dyeing.
• May cause variations in shrinkage.

4.2 Raising
Two main types
4.2.1 Napping
a. Using wire-covered rolls to "dig out" individual fiber ends to the surface
b. Fabric construction and yarn has big effect on the pile.
c. Important to have a napping lu B ricant on the fabric toaid in pile raising.
4.2.2 Sueding
a. Using abrasive-covered rolls (sandpaper, emery cloth, etc.) to produce shorter pile surface - does cause an apparent shade change
b. Special type of raised surface fabric is corduroy
c. Purpose is to cut surface fibers and produce a fuzz, a suede-like surface on the fabric.
d. Fabric is abraded with sandpaper covered rolls (emery cloth, etc.)
e. Course paper gives heavier pile whereas fine grit papergives a light pile.
Fig: Sueding finishing
4.2.2.1 Types of Machines:
1. Large single roll
2. Series of smaller diameter rolls

4.2.2.2 Variables:
a. Grit of sandpaper
b. Speed of the fabric
c. Speed of the sanding roll
d. Pressure of the sandpaper on the cloth
e. Number and direction of passes through process

4.2.2.3 Problems Are Caused By:
a. Folds and creases which give obvious defects.
b. Too much softener loads up sandpaper. Causes shiny appearance.
c. Slubs, knots and heavy selvages cause holes in the fabric.
d. Paper needs to be changed at the proper time to give a uniform product.
e. Multirole machine allows for continuous replacement of roll covers over a preprogrammed schedule.

4.3 Shearing

• Napped fabrics may be sheared to give a fabric of uniform height and even pile.
• Smooth fabrics may be sheared to make smoother fabric.
• Pilling of some fabrics may be improved by shearing.
• Hi-Lo patterns can be created by going over a solid bar. Random patterns are created by using rubber blankets.
• Shearing defects are caused by folds creases and heavy edges.
• Misaligned blades cause uneven shearing.
• Sewn seams must be jumped otherwise the shearer will destroy the seam and damage the blades.
• Foreign metallic objects will damage the blades.
• Use of rotary blade(s) to trim raised surfaces, primarily napped fabrics, to a uniform height.
• This reduces the tendency of the fabric surface to mat and also reduces the pilling tendency.
• Special types of blades and conveyor belts can produce pattern effects on the surface.

Fig: Shearing finishing
4.4 Calendaring
Calendaring may be defined as the modification of the surface of a fabric by action of heat and pressure. The finish is obtained by passing the fabric between heated rotating rollers when both speed of rotation and pressure applied are variable. The surface of roller can be either smooth of engraved to provide the appropriate finish to fabric.
The rollers may be made of various materials from hardened steel to elastic thermoplastic.

4.4.1 Objective of Calendaring

• To improve the fabric handle and to impart a smooth silky touch to the fabric
• To compress the fabric and reduce its thickness.
• To reduce the air permeability by closing the threads.
• To increase the luster.
• To reduce the yarn slippage.
• To increase the opacity of the fabric
• Surface patterning by embossing

4.4.2 Process of calendaring

• Fabric is passed between rolls under heavy pressure. Calendaring machine
• One roll is usually metal and the other is usually covered with paper or fabric.
• The temperature ranges from cold to 500oF, while pressure may range from 200 lbs/in2 to 2500 lbs / in2.
• Moisture in the form of water or steam may be used to achieve a desired luster.

4.4.3 Key Components of calendaring

• Composition of calendar roll
• Pressure
• Heat
• Moisture

4.4.4 Fabric Characteristics after calendaring
- Becomes thinner, less permeable, has more cover and luster.
- Too much pressure makes the fabric papery.
- Excessive heat and pressure will cause too much luster.
- Scarred surface rolls will imprint the defect onto the fabric.
- Effect is usually permanent on thermoplastic fibers.
- Resins required to be used to make calendaring durable on cellulosic fabrics. Without the resin the effect lasts only one laundering.

4.4.5 Types of calendaring
a. Friction calendaring
b. Schreiner calendaring
c. Embossing calendaring
d. Swissing or normal gloss or simple calendaring
e. Cire calendaring

4.5 Friction Calendaring

• Usually 3 roll process
• B central cotton fabric or paper roll is sandwiched between two metal rolls which are turned at very fast speeds as compared to the cotton roll.
• The fabric to be calendared is laced between the metal rolls and the cotton roll, and the surface of this cloth is brought to a highly polished state.
• Starches and waxes give a temporary glaze, while durable glazes are generated from fabrics treated with resins.

Fig: Friction calendaring

4.6 Schreinering

• Large metal roll engraved at a 260 angle with fine lines (250-300/in.) presses on the fabric surface.
• Result is a soft, silk-like luster on cotton and linen. Soft, opaque lingerie fabrics are produced from tricot knits by Schreinering.

Fig: Schreiner calendaring
4.7 Embossing:

• Usually a two roll special calendar.
• Uses a heated metal roll with an engraved pattern surface and a paper roll with the "negative" of the pattern on the metal or without a pattern.
• Fabric is passed between these rolls and the pattern is set into the fabric by heat and pressure. Thermoplastic fibers can be set by heat.
• Cotton fabrics must have a resin finish to give a durable effect.

Diagram of Embossing Rolls for raised designs

5 Conclusion
Physical (Mechanical) finishing is very important to improve fabric handle properties, silky touch effect, and air permeability and increase fabric luster. Physical finishing is less expensive than chemical finishing. In this case of physical finishing does not use any chemical to improve fabric properties without any hazards.


6 Source of information
1. Textile finishing
2. www.scribd.com
3. www.wikipedia.com
4.