Surface finish design features

Their weights can be very low to at least 16,000 lb. Diameters are at least up to 60 in. and widths at least up to 30 ft. Some rolls require roundness and surface finishes to be within 0.00005 in. (0.00127 mm). Many winders offer sophisticated features and are highly automated, but some are designed to answer the need for simplicity, versatility, and economy. There are surface winders with gap-winding ability for processing tacky films such as EVAs (ethylene vinyl alcohols) and the metallocene plastics. Information on these different types of rolls is provided in Table 18.1. 

A specification that identifies the basis on which a particular surface finish is selected will help the manufacturer to determine the appropriate construction, and provide some guidance on the method by which it is attained. Perhaps of equal importance, it will focus attention on details of the equipment design that are important to secure the objectives sought by the specification of a particular surface finish. The function of the designer is to match these attributes with other performance-related features of the equipment, and from these directions produce a blend of mechanical and geometric construction with a surface finish that meets the full requirements of the installation. 

Because most plated plastic parts are decorative rather than functional, appearance is extremely critical. For a smooth, even finish on a piece, the design of the part and molding process must be carefully considered. Mechanical welds are difficult to plate. If they are necessary, they should be hidden on a noncritical surface. Gates should be hidden on noncritical surfaces or should be disguised in a prominent feature. Gate design should minimize flow and stress lines, which may impair adhesion. 

As far as practicable, the packaging shall be so designed and finished that the external surfaces are free from protruding features and can be easily decontaminated. 

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