Introduction of Calendering Finishing | Working Process of Calendering Finishing

Calendering is a mechanical finishing process used on cloth where fabric is folded in half and passed under rollers at high temperatures and pressures. Calendering is used on fabrics such as moire to produce its watered effect and also on cambric and some types of sateens.

Calendaring is a high speed ironing process that primarily imparts lustre and is usually the final treatment for the fabrics in the finishing sequence. The basic principle of calendaring is to expose the cloth to the combined effect of moisture, heat and pressure until the fabric acquires a very smooth and light reflecting surface and gets a good lustre. The calendaring effect on the fabric is usually temporary and disappears after first washing. Semi permanent lustre is sometimes achieved by padding fabric in a sparingly soluble polyvinyl acetate emulsion before calendaring, where the solution acts as a binding agent. More permanent finish can be obtained by treating fabric with a solution of crease recovery reagent, followed by drying, calendaring and curing the fabric at about 150 ÂșC. The calendars are basically an assembly of heavy rolls, alternatively of iron and paper or cotton that are normally mounted in vertical frames. The rolls are bearing one on the other under a high pressure that is applied by compound levers or hydraulic or pneumatic equipment. 

Paper or cotton rolls are made by compressing sheets of paper and cotton under heavy pressure of hundreds of tons and then finely turned to produce a smooth surface. The iron rolls are also called chilled rolls because these are hardened by sudden chilling of the red-hot rolls. These are hollow so as to allow passage of steam or sometimes gas-fire to heat these to different temperatures.

Nipco-Flex Calender
The pressure application concept of this calender is different from the conventional calendering system. The pressing roller consists of a rotating shell that is covered with a highly elastic plastic material named as RACOLAN. The roller has fixed axels on which hydrostatic support elements are mounted that press the racolan shell against either steel or a cotton/paper roller. The hydrostatic pressure is applied with oil and is adjustable according to width of the cloth. The NIPCO roller can be arranged in vertical position or in L shape with a hot steel roller at top and a cotton bowl in front of it.

The main advantages of NIPCO calender over a conventional calender are;

  1. Attainment of very high pressure.
  2. Adjustment of pressure line according to width of cloth.
  3. No over load at the fabric selvedge.
  4. Easy installation and removal of the rollers.
Felt Calender
Felt calenders are mainly used for imparting lustre and smoothness to silk, rayon and cotton knitwear materials. These work at low pressure and temperature than used for cotton. The cloth is pressed between an endless felt blanket and a hot steel cylinder at a speed of 20 to 40 meters/minutes. By adjusting speeds of the feed and take up rollers the tubular knitwear can be compacted to some extent on this calender.
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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