Moulding Compound
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Moulding compound
Definition
The main tasks of polymer testing involve the examination, evaluation and characterisation of different materials, and the specification of characteristic values (see: material value) along with the associated measurement uncertainty. The plastics to be tested may take the form of powder, granules, test specimens, semi-finished products, finished products or components. By definition, the term ‘moulding compound’ refers to unformed or preformed materials which are processed into semi-finished products or finished parts by means of mechanical force and elevated temperatures through a non-cutting moulding process. In this process, the moulding compound becomes the moulded material. Moulded parts are products that can be manufactured from moulding compounds, e.g. by pressing, injection pressing or injection moulding in fully enclosed moulds, followed by cooling [1–3].
Types of moulding compounds
In polymer processing, various moulding compounds are used, which either exhibit the properties of solids as bulk materials (see: bulk density) or exist as liquids in the form of polymer dispersions or solutions. These are essentially:
- Granules
- Cylindrical granules from extrusion granulation
- Cubical granules from band granulation
- Cylindrical granules from underwater pelletisation
- Lenticular granules from underwater pelletisation
- Splinter granules from cut pelletisation
- Powders
- Spherical powders from synthesis
- Powders from grinding processes with an irregular surface
- Pastes
- Dispersions and
- Solutions.
Technological and processing-specific properties
In the case of solid moulding compounds, differences in the bulk properties arise due to the varying size, geometry and surface topography of the granules or powders. Knowledge of these bulk properties is essential for the optimal design of dosing and conveying systems in processing machinery, as well as for the geometry of the screw or mould.
In the case of dispersions and solutions, the concentration of the polymer in the solvent or dispersing medium determines the rheological behaviour and thus the processing properties.
Ultimately, it is the properties of the polymer melt—that is, the state of the highly viscous liquid in which the polymer exists during processing—that determine the effectiveness of the processing operation and the quality of the resulting product.
The need for a precise understanding of processing-specific properties results from the requirement to design optimal processing procedures and to optimise materials from a processing perspective. This necessitates, on the one hand, the use of processing-relevant testing methods and, on the other hand, the precise characterisation and testing of polymer materials from a processing-specific perspective [4].
See also
References
| [1] | Woebcken, W., Stoeckert, K.: Kunststoff Lexikon. Carl Hanser, Munich Vienna (1998) (ISBN 3-446-17969-0; see AMK-Library under G 3) |
| [2] | Orthmann, H. J., Mair, H. J.: Die Prüfung thermoplastischer Kunststoffe. Carl Hanser, Munich Vienna (1971) (ISBN 978-3-446-10318-4) |
| [3] | Bierögel, C.: Preparation of Specimens. In: Grellmann, W., Seidler, S.: Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 15–38 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22) |
| [4] | Radusch, H.-J.: Bestimmung verarbeitungsrelevanter Eigenschaften. In: Grellmann, W., Seidler, S.: Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 41/42 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23) |