ASTM D955-00

Injection Molding—In injection molding, the difference between the dimensions of a mold cavity and of the molded specimen may vary according to the design of the mold and operation of the molding process. Factors such as mold and melt temperature, fill times, and packing conditions are known to affect shrinkage significantly. Adherence to the specified mold design (see 7.1) and specifications outlined in Practice D 3641 or ISO 294-4 or the appropriate material will improve the reproducibility of the test.

Compression Molding—In compression molding, the difference between the dimensions of a mold cavity and of the molded specimen may vary according to the design of the mold and operation of the molding process. Factors, such as the amount of material in charge, cooling time, and pressure application are known to affect shrinkage significantly. Adherence to the specified mold design (see 7.2) and specifications outlined in Practice D 4703 or ISO 293 or the appropriate material specifications will improve the reproducibility of the test.

1.1 This test method is intended to measure shrinkage from mold cavity to molded dimensions of thermoplastics when molded by compression or injection processes with specified process conditions.

1.2 This test method covers initial shrinkage measurements. The method also accommodates shrinkage at 24 and 48 h, which may be critical for some materials.

1.3 This method will give comparable data based on standard specimens and can not predict absolute values in actual molded parts with varying flow paths, wall thicknesses, pressure gradients and process conditions. Differences in mold shrinkage may also be observed between the three specimen geometries described in this test method.

1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are given for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Note 1--This test method is technically identical to ISO 294-4 where Type D2 specimens are used except that pressure transducers are an option in this test method and required in ISO 294-4.