Regrind can be a source of contamination. If a part or runner of another material is dropped into a grinder the result will be contaminated regrind. Contaminated regrind could degrade due to differing melt temperatures, which then can lead to buildup. See Figure 19.3 for an example of contaminated regrind. If contamination is suspected take some material and spread it out across a table sorting through the pellets looking for contamination.