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220 23 Contamination
removed, trapped metal was found in the nozzle and tip. Using the STOP pro-
cess led to observation of parts being reground with metal inserts resulting
in contaminated regrind.
Extra care must be taken if running regrind on parts that have inserts or
assembly. Magnets will help catch ferrous metals but any non-ferrous metals
such as brass will pass right through a magnet.
23.3.4.3 Material: Incoming Contamination
Every material has a level of “contamination” as produced. Most of the time the
level of incoming material contamination is at levels that do not affect part quality.
For some fine-level molding applications materials are screened after manufactur-
ing with a gel tape analysis (see Figure 23.9 for an example). Gel tape analysis can
highlight if there are large or excessive contaminants in a material.
Figure 23.9 Gel tape
Contaminants that can be found in incoming material include:
Rubber gels
Agglomerates of ingredients
Foreign material such as dirt, pollen, wood, or cardboard
Carbon specks from degraded material occurring during the extrusion process
