Mold shrinkage

Apparatus for the measurement of this property according to DIN 53464 [56] are available from ATS FAAR (Table 2.6). Beracchi and coworkers [60] reported on computer-simulatedmoldshrinkage studies on talc-filled polypropylene, glass-reinforced polyamide, and polycarbonate/acrylonitrile-butadiene-styrene blends. 

Mold shrinkage injection compression injection compression and postshrinkage 

Test Suitable for Meeting the Units Following Standards 

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Noryl is a rigid dimensionally stable material. Dimensional stabiUty results from a combination of low mold shrinkage, low coefficient of thermal expansion (5.9 x 10 per° C), good creep resistance (0.6—0.8% in 300 h at 13.8 MPa (2000 psi)), and the lowest water absorption rate of any of the engineering thermoplastics (0.07% in 24 h at room temperature). Noryl resins are completely stable to hydrolysis. They are not affected by aqueous acids or bases and have good resistance to some organic solvents, but they are attacked by aromatic or chlorinated aUphatic compounds. 

Physical Properties. Physical properties include specific gravity, water absorption, mold shrinkage, transmittance, ha2e, and refractive index. Specific gravity affects performance and has commercial implications. The price of the material divided by the specific gravity gives the yield in cost per unit volume. Comparison of yields gives an evaluation of raw material costs. 

MoldShrinka.ge. Mold shrinkage of unreinforced crystalline plastics is high. This is critical in part and mold design, especially for large... 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Amorphous nylons are transparent. Heat-deflection temperatures are lower than those of filled crystalline nylon resins, and melt flow is stiffer hence, they are more difficult to process. Mold shrinkage is lower and they absorb less water. Warpage is reduced and dimensional stabiUty less of a problem than with crystalline products. Chemical and hydrolytic stabiUty are excellent. Amorphous nylons can be made by using monomer combinations that result in highly asymmetric stmctures which crystalline with difficulty or by adding crystallization inhibitors to crystalline resins such as nylon-6 (61). 

Mold shrinkage determined on 0.125 X 3 X 6 in molded plaques actual shrinkage will vary with part size and design. Mold shrinkage values for pellethane ... 

As a first approximation, a superposition method has been used that can provide a guide to predicting mold shrinkage (Fig. 3-27). However, problems arise in measuring the influencing variables, because they... 

Reduced Mold Shrinkage (Increased mold-to-size capability) Glass fibers Carbon fibers Fillers Ductility, cost Ductility, cost Tensile strength, ductility, cost Ductility, cost Ductility, cost Tensile strength, ductility, cost... 

Resin Material Flammability, in. /min Specific Gravity Mold Shrinkage, in./in. Clarity... 

Polyphenylene sulfide PPS is able to resist 450°F (232° C), and has good low temperature strength as well. It has low warpage, good dimensional stability, low mold shrinkage. Use includes hair dryers, cooking appliances, and critical under-the-hood automotive and military parts. 

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

Besides high mechanical strength, polyester LCPs exhibit excellent thermal and chemical resistance, high heat deflection temperature, low mold shrinkage,... 

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