Mold Shrinkage ASTM

Table 8-6 Guidelines for nominal TP mold shrinkage rates per ASTM Yt Yz in. thick test specimens...

Mold Shrinkage - The difference between the dimension(s) of the mold cavity at 23 °C and the dimension(s) of molded specimen. Measured for plastics after cooling the molding to room temperature according to ASTM D955. 

Table 9.59 Comparing unreinforced and reinforced thermoplastic mold shrinkage rates per ASTM D 955...

Thermal properties n. All properties of materials involving heat or changes in temperature. In Section 08 of ASTM s Annual Book of Standards ( Plastics ), tests listed under Thermal Properties include many properties, from brittleness temperature, coefficient of expansion, deflection temperature, etc., to heat of fusion, glass-transition temperature, thermal conductivity, heat capacity, mold shrinkage, flammability, and many more. 

ASTM D955 describes a method to measure mold shrinkage. Both the mold and the molding are at room temperature when the mold shrinkage is measured. The values of 0.022 in./in. in the flow direction and 0.018 in./in. in the transverse direction are typical for nnfilled crystalline thermoplastics. 

Mold shrinkage, cm/cm (injection-molded) ASTM D955 0.005-0.025... 

Table 7-4. Guidelines for Nominal TP Mold Shrinkage Rates Using ASTM V4- and... 

MSTM D955, Test Methodfor Measuring Shrinkage from Mold Dimensions ofMoldedPlastics, Vol. 8.01, ASTM, Philadelphia, Pa., 1989. 

To meet fabricated dimensional tolerances different approaches are used. They include use of specific fillers and reinforcements and process control (Chapter 3). Popular filler used is short glass fibers (Chapter 15). Over 50wt% of all types of glass fibers used with different plastics and by different processes are used in injection molding compounds. Table 2.2 shows the shrinkage of different unreinforced plastics ad glass fiber reinforced plastics based on ASTM testing procedures. 

ASTM D 955-96. Measuring shrinkage from mold dimensions of molded plastics. 

Measurement of shrinkage as a material property is covered by ASTM D955-89. In this test (which also covers transfer and compression molding), the shrinkage is derived from measurement of molded test pieces and the mold cavity dimensions. The moldings used are a bar 127 x 12.7 x 3.2mm and a disc 102mmdia x 3.2mm thick. 

Shrinkage allowance n. The dimensional allowance that must be made in molds to compensate for shrinkage of the plastic compound on cooling. The ASTM method for determining shrinkage from molded bars or disks and mold dimensions is D 955. This method does not provide for additional shrinkage that may occur as molded materials age beyond the first 48 h after removal from the mold. 

Shrinkage from mold cavity to molded dimensions of thermosetting plastics when molded by compression, injection, or transfer molding under specified conditions. ASTM D6289 specifies method of measurement. 

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