CALENDeRING

Calendering is a process where fabric is compressed by passing it between two or more rolls under controlled conditions of time, temperature and pressure.

Calender is a machine consisting of two or more massive rolls which are compressed by means of hydraulic cylinders applying pressure at the journals

One roll is considered the pattern roll and is responsible for the finished appearance of the fabric

The other roll is called a bowl and serves as the pressure back-up for the pattern roll and also serves to transports the fabric through the machine.

The composition of the rolls, number of passes, temperature controls, moisture control , fabric speed, number of bowls, arrangement of bowls,and pressure can vary to fit the desired effect

The temperature ranges from cold to 500°F, while pressure may range from 200 psi to 2500 psi.

Moisture in the form of water or steam may be used to achieve a desired luster.

The reason fabrics are calendered is to improve aesthetics. The major fabric

changes are:

1.To compress the fabric and Reduced fabric thickness.

2.Increased fabric luster,

3.Increased fabric cover,

4. To up grade the fabric and impart Smooth silky surface feel,

5. Reduced air porosity and

6.Reduced yarn slippage.

Types of Calenders

The type of calendar used depends on the type of cloth to be run and what the desired effect is to be. There are

Embossing calenders,

Friction calenders,

Swizzing calenders,

Chase calenders, and

Compaction calenders.

Schreiner Calender

The difference between them is the number of rolls and the drive system.

The use of different types of calenders gives different effects such as:

Sheen appearance: it can be obtained by smoothing the cloth surface, which ensures a better reflection of light.

Better coverage: it is due to the compression of the cloth, which generates a flattening of each single yarn.

Softer hand: it is obtained thanks to a slight ironing effect, which produces a smoother, and softer cloth surface.

Surface patterns: they can be obtained by means of special effects ("embossing" for example) for decorative purposes or to modify the surface smoothness.

Yarn swelling and rounding effect: they give a modest glaze finishing to the fabric, a surface smoothness and above all a full and soft hand.

UNIVERSAL CALENDERS:

These calenders, equipped with 3-5-7 or even more rollers, are referred to as universal calenders. They can give the fabric different effects; some of them are detailed below:

roll effect: flattened fabric, high coverage ratio, soft hand and moderate glaze;

matt effect: high coverage ratio, soft hand and matt effect;

Lustrous effect: this effect originates from friction created during the passage between a smooth and a steel roller.

1. Swizzing Calenders

Swizzing is a British term used to denote that the fabric runs through all of

the nips at the same surface speed as the rolls. Swizzing calenders usually consists of seven to ten bowls and are run at ambient temperatures. The fabric effect is closed interstices, a smooth appearance and gloss without the high glaze characteristic of a friction calender. Hot roller- more lusture and smoothness

7- Closed-grained iron bowl

6- Compressed cotton bowl

5- Highly polished, chilled iron,

steam – heated bowl

4- Compressed cotton bowl

3- Compressed cotton bowl

2- Highly polished, chilled iron,

steam – heated bowl

1- Compressed cotton bowl

Friction calendaring• Usually a three roll process

– A 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 calendered is laced between the metal rolls and the cotton roll, and the surface of this cloth is brought to a very highly polished state.

• Starches and waxes give a temporary glaze, while durable glazes are generated from fabrics treated with resins

• It’s produces high degree of lusture on one side of the fabric and also closing up the interlacing threads

• Third roll – polished chilled iron bowl with steam and surface speed is double that of the fabric and those lower two bowl. Speed variation b/w first and trird rolls is one and half time higher than lowest bowl.

• Friction effect is exerted on the fabric due to different speed level of bowl

• Speed – 30m/mins for friction , 60m/mins for with out fiction. 7bowl roller run at 80m/mins, light finish – 130-230m/mins

5 Roll Universal Calender with 2 Fabric Webs

CHASING CALENDER

The cotton fabric passes normally through the nips of a 7-bowl calender, then chasing rollers. The cloth is then fed again into the cotton nip of the calender .

Chasing gives the cloth a thready –linen appearance and a special handle

WITH WATER MANGLE

Under high pressure, threads are well flattened and the spaces b/w them are closed

Different effects comes from different bowl

Hollow , steam-heated chilled iron rolls provide hard surface --- lusture produced

Two cotton rolls in contact with each other ( nip ) – flat, soft effect

Steam calendering

the chilled iron roll, which is a hollow cylinder, is usually heated by using high-pressure steam. This calender roller called steam calendering

Chasing calendering

SCHREINER CALENDERThe schreiner finish can be imparted to textile fabric by means of schreiner calender

PURPOSE

It’s gives silk-like brilliance to cotton fabric.

It’s gives the nearest possible resemblance to silk when produced on meccerised fabric,

Uses

Cotton linings, sateen and printed fabric

Mechanism

The silk like finish due to the fine lines engraved on the steel roller of the schreiner calender

Lines – 5 to 20 lines/mm

Lines are at small angle with respect to the direction of the warp and weft threads in the fabric.

Weft sateen – angle of about 20° to the weft and in directions of the twist.

Plain weave – course line ( 6-7/mm)

Bowl

Dia – 7.5 cm for both bowl

Top bowl – Special, Fine grained steel and gas heated from the inside

Wide – 325 cm

Pressure – up to 140 tonnes

EMBOSSING CALENDER

Usually a two roll special calender.

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 two 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.

To produce a damask effect on cotton fabric but the effect is temporary

THREE BOWL ROLLER