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Standards
for Finish and Appearance |
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- Introduction
- The purpose of this section is to list and discuss some of the factors that have an
effect on the finish and appearance of molded products and to present standards covering
four classes of finish.
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- FACTORS AFFECTING FINISH AND APPEARANCE
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- Machined Finish of Mold
- The machined finish of the mold has considerable effect on the surface finish or
appearance of a rubber product.
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- The best finish can be obtained from a highly polished steel mold, free from all tool
marks or other imperfections. Naturally, this type of mold is quite expensive to construct
and maintain and is not generally required unless surface finish is of paramount
importance from either an appearance or functional standpoint. In addition, it may be
desirable in some cases to chrome plate the mold in order to maintain the required surface
finish under production conditions.
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- The commercial type mold is a machined steel mold made to conform to good machine shop
practice. Machine tool marks will not ordinarily be polished out of this type of mold. It
should be noted that regardless of how highly the mold itself is polished, the appearance
of the rubber surface will depend to a large extent upon the factors outlined in the
following paragraphs.
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- Type of Rubber Material Used
- The type of rubber material used can greatly affect the appearance of the rubber
product. Some compounds lend themselves to a bright glossy surface while others may be
dull as molded or become dulled very easily during handling or storage. Also, there are
some rubber compounds to which antiozonants are added to impede attack from ozone. As
these compounds age, the antiozonants "bleed out," giving the product a colored
or waxy surface. This is a common practice and the product should not be considered
imperfect or defective in any way. This or other specification requirements may make it
impossible to produce a product with a glossy surface.
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- Mold Release Used
- There are certain compounds that can be removed from the mold with the use of little or
no mold release lubricant, while others require the use of considerable quantity of mold
release lubricant. The latter may have the appearance of being oily.
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- If the surface of the rubber product is to be bonded to other materials in its
application or is to be painted, the designer should designate this on the drawing so that
the manufacturer may use a mold release lubricant that will not impair adhesion quality
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- Flash Removal Method
- Some of the many methods used to remove flash from rubber parts may affect the
appearance of the finished product. As an example, hand trimming will ordinarily have no
effect, while tumbling may result in a dull surface.
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- Method of Designation of Finish
- The symbol "F" followed with an appropriate number selected from table 5 shall
be used to designate the type of finish required.
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- An arc enclosing the actual are included by this designation and a leader to the finish
number designates the type of finish desired. The use of a finish symbol on the surface
does not preclude the possibility that other surfaces may require different finishes.
However, the use of a standard notation is desirable wherever possible to eliminate the
repetition of finish symbols and maintain simplicity. Always permit "Commercial
Finish" (F-3) whenever possible.
Table 5
Drawing Designation |
F1 |
A smooth, polished and uniform finish completely free of tool marks,
dents, nicks and scratches, as produced from a highly polished steel mold. Finish of 10
microns. |
F2 |
A uniform finish as produced from a polished steel mold. Finish of 32
microns. |
F3 |
Surfaces of the mold will conform to good machine shop practice. No
micron finish is specified. A "Commercial Finish" |
F4 |
Satin Finish |
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