Topics: Calendering TARIQUL ISLAM
Wet Processing Lecturer (TECN)
Calendering:
Calendering is a process where fabric is compressed by passing it between two or more
rollers under controlled conditions of time, temp. & pressure.
It is a type of mechanical finish.
Objectives of Calendering:
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 yarn slippage.
To increase the opacity of the fabric.
Surface patterning by embossing.
Working Principle of Calendering:
The fabric is run through the rollers that polish surface &
make fabric smoother & more lustrous.
The rollers may be highly polished, friction or engraved.
High temp. & pressure is used as well.
The durability of finish depends on the proportion of
synthetic fibre component, finishing additives & process
condition.
Controlling parameters are: Pressure, Temp. & Speed.
Factors/Controlling Parameters of Calendering:
1. Pressure into the nip:
a. Lever or screw system: Allow very high ‘dead-set’ pressures that has greater risk
of fabric or bowl damage.
b. Pneumatic system: Modern & more resilient system.
c. Hydraulic pressure system: Raise the bottom bowls to give contact with a fixed
top bowl.
2. Temperature of the metal bowl: Temperature is achieved by gas, electric, thermal fluid
or steam heating. Gas & electric heating need very accurate control whereas steam or
fluid heating gives level heating profiles.
3. Speed of the bowls: The slower the speed, the longer the fabric is in the Calender nip &
the greater the effect on the fabric. Modern thyristor motor controls give highly accurate
speed control.
Types/effects of Calendering:
1. Swizzing or normal or simple Calendering
2. Chasing Calenders
3. Glazed or friction Calendering
4. Ciŕe Calendering
5. Embossed Calendering
6. Moiré Calendering
7. Schreiner Calendering.
01. Simple/Swizzing Calendering:
Swizzing is a British term used to denote that the fabric runs
through all nips at same surface speed as the rolls.
Swizzing Calenders usually consists of 7-10 bowls.
Fabric effect is closed interstices, a smooth appearance &
gloss without high glaze characteristic of friction Calender.
It applies high speed & high pressure, at room temp.
High pressure flattens the yarn, smoothen & weaken the
fabric, increases luster.
Used for woven plain or twill weaves.
It is a temporary finish, return to its natural cross-section after
first laundering.
02. Chasing Calender:
Chasing calenders are very similar to swizzing calenders.
In chasing Calender, the cloth passes through the nips of 7-
bowl Calender, then over the chasing rollers.
The cloth is then fed back again into the nip of the Calender
such that layer of cloths lies one over another & repeated
several passes before it exits to a take-up roll.
The cloth is compressed against itself with as many as 5 to 6
layers being in a nip. This gives the cloth a thready-linen
appearance and a soft special feel.
Sometime a water mangle precedes the Calender.
03. Glazed/Friction Calendering:
It is a Calendering finish to produce highly glazed/shined
polished cotton.
One cylinder of highly polished steel cylinder rotating at
speed much higher than the fabric passing through it.
Fabrics are first treated with starches or resins before
Calendering to make more durable.
The spaces between the yarns are thus filled up and glazed
appearance is obtained.
Glazed Calendering using starch are semidurable & using
resins are durable.
04. Cire Calendering:
It is a type of glazed Calendering where friction roller rotates at speed much greater
than ordinary friction Calendering.
The fabric become highly lustrous and takes on a wet look.
Cotton, rayon, polyester, nylon & blends can be given cire finish.
Fabrics are treated with waxes & resins before Calendering.
Highly polished effect is produced.
When thermoplastic fabrics are ciŕe finished, they becomes moderately water-repellent
due to flattening or partially fusing of fibres.
05. Embossed Calendering:
It is a Calendering in which a three dimensional design is
created on a fabric.
This is done on a special embossing Calender in which the
roller cylinder is engraved with the embossing design.
The pattern is then pushed or shaped into the cloth when the
fabric passes between the rollers.
Some embossed fabrics are made to imitate more costly
woven jacquard or dobby designs.
Embossed patterns of fabrics treated with resins and cured
after embossing are durable.
Embossing of fabrics of thermoplastic fibres are permanent
because the heated metal roll heatset the design.
06. Moire Calendering:
The moiré finish produces a watermark effect on fabric.
It can be temporary, durable or permanent.
Durable moiré finish requires initial resin treatment for cotton or rayon & use of
heated roller for thermoplastic fiber fabrics.
Methods of producing moiŕe:
Using engraved cylinder: Engraved cylinder causes different light reflectance &
creat moire effect.
Using smooth Calender roller: Two fabrics are fed through smooth Calender,
high pressure on Calender rolls causes fabric to squeeze into each other in certain
areas & create light reflectance.
07. Schreiner Calendering:
Schreiner Calendering produces a low, soft key luster on
fabric distinct from high glaze of the glazing Calender.
To produce this effect, one of the steel cylinders of the
Calender is embossed with fine diagonal lines.
Widely used on cotton & cotton/polyester sateen.
Schreiner Calendering may be permanent, durable or
temporary finish, as follows-
Permanent: if the fibre is thermoplastic.
Durable: if the fabric is resin treated but not cured.
Temporary: if the fibre is non-thermoplastic and not
treated with resin.
