How many types of molded parts are there

Molding compound

Molding compound


The main tasks of the plastics test consist in the investigation, evaluation and labeling of the different materials and the specification of characteristic values ​​(see material characteristic value) with the associated measurement uncertainty. The plastics to be tested can be in the form of powder, granulate, test specimen, semi-finished product, finished product or component. According to the definition, the term molding compound is understood to mean unformed or preformed materials that are processed into semi-finished or finished parts by means of mechanical forces and increased temperatures through non-cutting shaping. The molding compound becomes a molding material. Molded parts are products made from molding compounds such. B. can be produced by pressing, transfer molding or injection molding in tools closed on all sides and subsequent cooling [1–3].

Types of molding compounds

In plastics processing, different molding compounds are used, which either have solid properties as bulk goods (see: bulk density) or are in the form of liquids as a polymer dispersion or solution. These are essentially:

  • granules
    • Cylinder pellets from strand pelletizing
    • Cube granulate from belt granulation
    • Cylinder granulate from underwater granulation
    • Lentil granules from underwater granulation
    • Splinter granulate from cutting granulation
  • powder
    • Spherical powder from synthesis
    • Powder from grinding processes with an irregular surface
  • Pastes
  • Dispersions and
  • Solutions.

Technological and processing-specific properties

In the case of solid molding compounds, due to the different size, geometry and surface topology of the granulates or powders, there are differences in their bulk material properties. The knowledge of the bulk material properties is essential for the optimal design of dosing and conveying devices of processing machines as well as the screw or tool geometry.
In the case of dispersions and solutions, the concentration of the polymer in the solvent or dispersion medium determines the rheological behavior and thus the processing properties.
After all, it is the properties of the polymer melt; H. the state of the highly viscous liquid in which the polymer is during its processing, which determine the effectiveness of the processing process and the quality of the resulting product.

The need for precise knowledge of the processing-specific properties results from the requirement for optimal processing design and material optimization from the processing point of view. This requires, on the one hand, the use of processing-relevant test methods and, on the other hand, precise description and testing of the polymer materials from a processing-specific point of view [4].


[1] Woebcken, W .; Stoeckert, K ​​.: Plastic Lexicon. Carl Hanser Verlag, Munich Vienna (1998) (ISBN 3-446-17969-0; see AMK book collection under G 3)
[2] Orthmann, H. J .; Mair, H. J .: The testing of thermoplastics. Carl Hanser Verlag, Munich Vienna (1985)
[3] Bierögel, C .: Manufacture of test specimens. In: Grellmann, W., Seidler, S .: Kunststoffprüfung. Carl Hanser Verlag, Munich (2015) 3rd edition, p. 17 (ISBN 978-3-446-44350-1; see AMK book collection under A 18)
[4] Radusch, H.-J .: Determination of processing-relevant properties. In: Grellmann, W., Seidler, S .: Kunststoffprüfung. Carl Hanser Verlag, Munich (2015) 3rd edition, p. 43/44 (ISBN 978-3-446-44350-1; see AMK book collection under A 18)