26. Plastics offer designers a number of unique material properties, including light weight, corrosion resistance, good thermal and electrical insulation, and the possibility of integral color. Some of the design limitations of plastics include” the inability to perform at elevated temperature of operation, poor dimensional stability, and the deterioration of properties with age. 27. When selecting a molding process for forming plastics, one should consider the advantages and limitations of each alternative, followed by the optimization of the selected process. Concerns might include the amount of material introduced into the mold cavity, its flow into the cavity, and venting of the air that previously occupied the space. Shrinkage concerns and part cooling should be considered. Product properties can be affected by melt temperature, material flow, pressure during molding, thermal degradation and cooling rate. 33. Since the mold is the reverse of the product, depressed letters or designs would require these features to be raised above the mold. This would require the entire remainder of the mold to be cut away at a considerable expense. If the details were raised, only these details would have to be machined. 41. By rapidly cooling the surfaces of hot glass, a residual stress pattern of surface compression can be induced. The resulting glass is stronger and more fracture resistant. Annealing operations can be used to relieve unfavorable residual stresses when they exist.
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unfavorable residual stresses, unique material properties