Determination of the Degree of Heat Setting
Sunman Textile Mills Ltd. Chittagong
Heat setting is a thermal process which is applied in textile industry. Which fabrics produced from synthetic fibers or from blends containing large proportion of such fibers are normally heat-set to stabilize them. It is done for shape retention, crease resistance, resilience and elasticity are imparted to the fibers. The effect of the process gives fibers, yarns or fabric dimensional stability and, very often, other desirable attributes like higher volume, wrinkle resistance or temperature resistance. It also brings changes in strength, stretch ability, softness, dye ability and sometimes on the color of the material.
Heat-setting can be carried out at three different stages in a processing sequence i.e. in grey condition; after scouring; and after dyeing. The stage of heat-setting depends on extent of contaminations and types of fibers or yams present in the fabric.
Although heat setting is usually considered a finishing process, often specific fabrics are heat set during preparation to control shrinkage during processing. The fabrics are heated while held under tension in a stenter machine to maintain the desired fabric dimensions.
Heat setting of lycra knitted fabric or elastomeric fabric is a very critical process. During heat setting process the fabric is passed through heated chambers of 2000C for achieving the desired property of the Lycra knitted fabric. If the parameters like over feed, temperature, speed etc. suddenly changed, the fabric quality like GSM, width, dimensional stability of the knitted fabric also change, thus resulting in variation between and within fabrics.
Determination of the Degree of Heat Setting:
By the following process heat setting is measured:
1. Shrinkage test:
Normally a square area is drawn on the heat-set material and measured. The marked cloth is boiled in soft water in the washing wheel for 30 min, centrifuged and air dried. The dimensions of the square are measured without ironing the dried fabric and the shrinkage is determined. A well set fabric should not show more than 1% residual shrinkage.
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2. Crease-recovery angle:
The determination of crease recovery angle before and after heat-setting of the fabric is done. The extent of crease-recovery of heat-set fabric before and after setting at and above 170-175~ will give idea of the degree of heat-setting.
3. Assessment of handle:
Assessment of handle before and after setting gives an idea of the degree of heat-setting. In general, fabric becomes stiff after heat-setting. Stiffness is measured by bending length and compared with that of the unset fabric. The narrower the difference of bending length between the set and unset fabrics, the better the setting.
4. Iodine absorption method:
The degree of heat-setting of polyester fabrics can be correlated with their iodine absorption value. Heat-setting under industrial conditions in a taut form reduces the amorphous content of synthetic fibers. So, there will be a decrease in iodine sorption and increase in critical dissolution value.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.