The conditions at which compounds are molded are known to influence the properties of the specimens. The degree of cure, elimination of knit-lines between particles, density of the part, and degradation of the polymer are among those factors which will be affected by the molding conditions. Thus it is important to hold to a standard set of conditions in order to have a valid comparison of properties between different compounds and different batches of the same compound.

If the molded specimens show evidence of low-density areas due to trapped gases, they should be discarded. A breathe step may be necessary to eliminate this situation. It is critical that the breathe step be as brief as possible to avoid precuring of the compound before full pressure is applied. This would lead to poorly “knitted” areas and lower strength in the molded specimen.

1.1 This practice covers the general principles to be followed when compression molding test specimens of thermosetting molding compounds, such as phenolics, aminoplastics, melamine phenolics, epoxies, and unsaturated polyesters.

Note 1—This standard is similar in content (but not technically equivalent) to ISO 295-1974 (E).

1.2 Molding conditions are given for amino, phenolic, and allyl molding compounds. Materials specification standards should always be consulted to determine whether the material to be molded has any special requirements.

1.3 The values stated in SI units are to be regarded as standard. The values in brackets are given for information only.

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.