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Mold Shrinkage - ASTM D955

ABIS Mold Technology Co.,Ltd Updated: Jul 18, 2016

This standard covers the measurement of specimen shrinkage for injection and compression molding. Data for mold shrinkage should be
used for material comparison. Actual mold shrinkage values are highly dependant on part geometry, mold configuration, and processing
Mold shrinkage for many materials differs for flow and transverse (or across flow) directions. Flow direction is taken as the direction the
molten material is traveling when it exits the gate and enters the mold.

Measurement Orientation
Three specimen types may be used to determine mold shrinkage, Type A, Type B, and Type D2. Mold shrinkage is expressed as a percent
change in dimension of a specimen in relation to mold dimensions.

Mold shrinkage in the flow direction is calculated by:
SFlow = 100 * (LM - LS) / LM
where LM is the length of the test section of the mold cavity and LS is the corresponding length of the test specimen after it has cooled.
Mold shrinkage in the transverse direction is calculated by:
STransverse = 100 * (WM - WS) / WM M is the width of the test section of the mold cavity and WS is the corresponding width of the test specimen
after it has cooled.
Similar Standards:
• ISO 294-4

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