Page 67 - Injection Molding Advanced Troubleshooting Guide
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50 6 Mold Texture and Polish
When running glass-filled materials, gloss will change over time from erosion of
the surface finish of the texture or eroding the texture itself. So in this case con-
sider using hardened tool steel, coatings, or surface treatments.
For visual defects or cosmetic issues typically a higher gloss level on textured parts
will produce a better looking part. When gloss levels get low (for instance under
3 on a 60° gloss reading) the dullness of the molded part will tend to magnify
defects.
6.2 Mold Polish
Molds can be polished to a wide variety of levels depending on the requirements of
the finished part. Polishing is conducted in a series of increasingly fine grit levels
to achieve the desired results up to an A1 mirror finish (see polish chart in Table
6.1).
Table 6.1 Polish Chart
Finish Polishing medium
A1 #3 diamond
A2 #6 diamond
A3 #15 diamond
B1 600 grit paper
B2 400 grit paper
B3 320 grit paper
C1 600 stone
C2 400 stone
C3 320 stone
D1 #11 glass bead
D2 240 aluminum oxide blast
D3 #24 aluminum oxide blast
It is vital to keep in mind that not all materials will interact well with a polished
surface. For instance, materials such as thermoplastic polyurethane and thermo-
plastic elastomers will often stick hard to polished surfaces and even polypropyl-
ene will show a tendency to stick when exposed to highly polished surfaces. When
dealing with sticky materials like those mentioned, often times a blasted surface
will be required to help break the vacuum of the part sticking to the mold. In cases
where a glossy finish is desired a 320 paper finish will often work well as a com-
promise that provides adequate release.
