Speck (plastic)
A speck is a surface defect on an injection molded part .
definition
There are two types of specks, organic and inorganic. Organic specks consist of a cracked, ie thermally decomposed polymer and have a brownish inherent color, whereas the inorganic specks usually consist of metallic abrasion that got into the injection molding process. These specks usually have a black or grayish color of their own. In contrast to burners, specks do not occur continuously, but form a statistical problem that is often difficult to avoid. The main factors influencing the formation of specks are the quality of the plastic granulate , the type of conveyance and storage, and the correct setting of the processing parameters .
Emergence
Three main topics are responsible for the formation of specks.
The raw material, the extraction and the transport, as well as the injection molding process as such.
This results in the following picture for the error distribution according to an FMEA :
- 62% of all errors are based on the raw material. High levels of dust, contaminated material, or abrasion from the extruder due to wear and tear can cause specks.
- 33% of all errors arise from improper storage, which can lead to contamination of the material, and from unsuitable conveying.
- 5% of the remaining defects result from thermally damaged material or flaking coating elements from the screw or the cylinder wall.
Individual evidence
- ↑ E. Bürkle, B. Klotz, P. Lichtinger: Perspective in injection molding. In: plastics. Issue 11 2001, p. 56.