Monday, March 30, 2015

What is Heat Setting?

Heat Setting

Heat-setting can be defined as a treatment by which shape retention, crease resistance, elasticity etc. is given to the fibres. It also changes the strength, softness and dye-ability of the material. All these changes are directly connected with the structural and chemical modifications occurring in the fibre.

The heat-setting process is mainly used for thermoplastic fibres to improve their dimensional stability in washing and drying. It could also be done for woolen fabric. The chief processes for imparting permanent set to wool are (a) Crabbing (b) Blowing (c) Potting or roll boiling
Fig: Stenter machine to apply heat seat
Heat-setting temperature for thermoplastic fibres varies depending on the type of fibre and their melting point. Normally heat-setting is done at a temperature above glass transition temperature polymer molecules vibrates vigorously, higher the temperature higher the vibration and greater the possibility or better relaxation of molecules in the fibres. Treatment time depends on setting temperature, fibre type and method of heat setting process. Heat setting colud be done by:
  • Dry heat (Stenter)
  • Super Heated Steam (Stenter)
  • Saturated steam (Pressure Stenter)

Stenter heat-setting is the most common method. In most modern stenter there are sophisticated arrangements for example, over feed, edge curling straightener etc. In the stenter, hot air alone could be used or super heated steam could be injected in hot air. Setting in presence of steam gives good dimensional stability in wet processing. Setting temperature for Nylon and Polyester is 200 to 2250C for 10 to 30 seconds. At the end of stenter, the temperature of the fabric must be cooled down below glass transition temperature using cool air. Garments could be heat set in pressurize steamer using saturated steam.
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