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23.3 Contamination Troubleshooting 219
Figure 23.8 Contamination on gaylord lid
23.3.4.2 Material: Regrind
Regrind provides another source of potential contamination. There are many ways
that regrind can cause contamination including:
Allowing parts from the wrong material to be ground with other materials. This
can be avoided by either having people dedicated to grinding, or by only allowing
parts to be ground at the machine where they were molded. Way too often is the
case where an unaware operator throws a part into a grinder because the mate-
rial is black.
Regrind can become contaminated if it is stored before use. The same factors for
keeping material in enclosed containers apply to regrind.
When adding regrind to a process it is critical to make sure that everyone veri-
fies that the regrind is added to the correct material.
Contamination of the grinder itself whether from lack of cleaning or foreign ma-
terial contamination.
It is always best if regrind can be reused at the point of generation. By adding the
regrind back in at the molding machine many of the opportunities for contamina-
tion can be eliminated. Another advantage of point of use with regrind is that most
times redrying of the material can be avoided.
Case Study: Regrind Contamination
This example was an ABS part being molded in a 700-ton molding machine.
The machine was having problems with inconsistent shots that seemed to
point to the non-return valve. When the front of the nozzle and end cap were ▸
