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Processing of Thermosetting Molding Compounds

MC Plant Baumgarten2

Molding compounds are processed to molded parts through the combined forces of pressure and temperature. The following methods are used in processing:

  • Compression molding
  • Transfer molding
  • Injection molding
  • Injection compression molding

1.

Compression Molding – The molding compound, fed volumetrically or by weight, is filled into the (typically) electrically heated mold, either loosely or pelletized, preheated or preplasticized. Upon closing the mold, the molding compound softens and fills the mold. The molding can be removed after a sufficient curing period, which will depend on the reactivity of the molding compound, its prior treatment, the mold temperature and the wall thickness of the mold profile.

 

Advantages:

  • Minor processing and post shrinkage
  • Minor warpage of molded part
  • Minor damage of reinforcing filters

Disadvantage:

  • Cycle times depend on maximum wall thickness

2.

Transfer Molding – Technically, transfer molding is a process between the compression molding and the injection molding process. Here, the pelletized and preheated or preplasticized molding compound is pushed by a plunger from an antechamber in the mold via a runner and gate system into the cavity where the material cures. Three plate molds with the plunger working from the top can be built into conventional presses. From the perspective of process technology, single split molds are easier – the plunger works from below or horizontally from the side and requires a press with two hydraulic plungers.

 

Advantages:

  • Shorter cycle times, compared with compression molding
  • Minimal flash since form filling occurs in the closed mold

Disadvantage:

  • More warpage, compared with compression molding (due to anisotropy)

3.

Transfer Systems with Screw Preplastification and Plunger Feeding – These systems are an obvious choice for manufacturing items that are subjected to stress and good dimensional tolerances. Using this method, a more reactive molding compound can be used in suitable applications. The benefit is relatively short cycle times and accurate shot weights.

4.

Injection Molding – Due to its high efficiency, injection molding is the most widely used processing method today. Here, one unit automatically performs all the required operational steps. The screw feeds and homogenizes the molding compound – having melted it through friction and heat conduction – and acts as a plunger during the injection process. Because of high material inlet temperature, very little energy needs to be introduced through heat conduction for curing the molded part, resulting in short cycle times.

5.

Hot Cone Process – Also known as the HTM process, this method can reduce the curing times required for a molded part by up to 50%, while simultaneously improving the physical properties of the molded part. Before the molding compound reaches the cavity, it flows over a cone heated up to 280°C, which is built into the mold with thermal insulation. The higher temperature of the molding compound, increased via heat conduction, will reduce the required curing time especially for thick-walled molded parts.

Contacts

Contacts for Americas
Hexion GmbH
Gennaer Str. 2-4 Germany 58642 Iserlohn-Letmathe Postfach 7154 Germany 58609 Iserlohn-Letmathe

Technical Inquiries

+1 614 225 2076
moulding-compounds@hexion.com