ASTM D6289-13 Test for Measuring Shrinkage from Mold Dimensions of Molded Thermosetting Plastics

Scope:

ASTM D6289-13 test method is used to measure molding shrinkage and post shrinkage. Molding shrinkage (initial shrinkage) is the difference in dimensions between the molding and the mold cavity in which it was molded. Post-shrinkage is the shrinkage of a plastic product after molding, during post-treatment, storage, or use. Measurement of batch-to-batch consistency in initial shrinkage from mold to molded dimensions is useful for evaluating the quality of thermosetting plastics. The data on the initial shrinkage of plastics is important for the construction of molds, and the data on post-molding shrinkage is important for determining the suitability of the molding material for manufacturing thermosetting plastic components. 

This test provides comparable data based on standard specimens and not absolute values.

Test Procedure:

At least two specimens are molded to shape using compression Molding, injection molding, or transfer molding. The specimens are removed from the mold. They are allowed to cool to room temperature. Before measuring their lengths, they are placed on a flat surface to determine any distortion. Any test specimen that has a warp exceeding 1 % of its length is discarded.  To determine molding shrinkage, the lengths of the bar specimens are measured. The plaque specimens are measured at a distance of 20 mm from the corners, two measurements in the same direction. To determine post-shrinkage, the test specimens are heated in an oven at a specific temperature. After the heating period, they are removed from the oven and allowed to cool in a standard atmosphere for at least three hours. After that, the specimens are examined for any distortion and then measured again at a specific temperature.

Specimen Size: 

Different molding procedures require different sample sizes. 

• Compression-Molding Materials: For mold shrinkage of compression-molding materials, the test specimens should be bars 120 by 15 by 10 mm, bars 12.7 by 12.7 by 127 mm, or disks 3.2 mm in thickness and 102 mm in diameter. 
• Injection-Molding Materials: For mold shrinkage of injection-molding materials, the test specimens should be bars 12.7 by 3.2 by 127 mm, bars 12.7 by 12.7 by 127 mm, disks 3.2 mm in thickness, and 102 mm in diameter gated radially at a single point in the edge, plaques 120 by 120 by 4 mm, or plaques 60 by 60 by 2 mm gated with a full edge gate. 

• Transfer-Molding Materials: For shrinkage of transfer molding materials, specimens 12.7 by 12.7 by 127 mm gated at the end or at the top near one end to provide flow throughout their entire length, or disk specimen 3.2 mm in thickness and 102 mm in diameter gated radically at a single point in the edge.

Data:

Percentage of molding shrinkage and Post-shrinkage is reported.