Shrinkage dimension control

The rate and uniformity of cooling are important for dimension control because of shrinkage and distortion in hot extrusion. 

In general, more highly oriented and therefore higher modulus fibers tend to exhibit lower shrinkage and less creep. Creep is an important factor in the control of tire dimensions during service and in certain aspects of tire appearance (30). 

In chain mercerising, the weft threads of the fabric are kept under tension on a clip stenter. In a chainless merceriser the fabric dimensions are controlled by a series of rollers. The fabric is usually woven slightly wider to allow for some weft shrinkage. Yarn is mercerised in hanks between two movable rollers which create the required tension whilst knitted constructions may be mercerised in either slit or tubular forms. Chain and chainless mercerising have been compared [276]. 

Ebonite compounds shrinks to about 6% during cure and as such due allowance for a change of dimensions has to be made for this during manufacture. The ebonite dust and the mineral fillers added for controlling the exothermic reaction serves to reduce this shrinkage. 

Pyrolysis yield affects the density of the final ceramic products. Typical pyrolysis yields of carbon-based polymers are 40-60%. The change from starting polymer densities of about 1 g/cm to final densities of 2 g/cm or more commonly results in about 30% porosity. Thus, unless there is substantial shrinkage as a result of sintering or plastic deformation, a substantial amount of porosity is generated. Any densification is counterbalanced to some extent by outgassing pressure, which is determined by pyrolysis conditions, especially the rate of heating and the cross-sectional dimension, that control the rate of... 

Sanforizing, a complementary operation for stabilizing the dimensions of cellulose fabrics, is an induced shrinkage of cotton fabric achieved by controlled dampening and drying of the relaxed fabric to remove any tensions and distortions which have appeared as a result of other processing. It does not produce pollutants. 

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