ELASTOMER INJECTION MOLDING AND INJECTION TOOLS – EXACTLY ACCORDING TO YOUR REQUIREMENTS
FOR ECONOMIC, LONG-LASTING AND RIGHT-RESISTANT FORM PARTS
For the cost-effective production of large quantities of elastic components such as seals or dampers, the rubber or elastomer injection molding process is very well suited. Customerspecific injection molding tools are designed by SPT and equipped with the right injection molding machine for elastomers. The process is run in by experienced technicians and the parameters for series production in elastomer injection molding are specified. This gives our customers quality molded parts over the entire project period – shot by shot – including the corresponding care and maintenance of the tools.
THE PROCESS IN ELASTOMER INJECTION:
Elastomers such as natural rubber or synthetic rubber vulcanize due to the influence of heat. The tools or injection molds for the elastomers are hotter tempered than the rubber compound during injection.
- The mixture is drawn in by a special screw, which introduces little shear into the plasticized mass. The temperature of the cylinder around the screw is about 70 – 80 ° C, so that the mass does not overheat and premature vulcanization is prevented.
- In the screw, the mixture is kneaded and thereby processed homogeneously.
- At the injection molding machine, the dosage for filling the cavities in the tool incl. The sprue channels and, if necessary, groove grooves is determined. During the injection process or flow of the elastomer mixture in the nozzle and the sprue channels generates frictional heat, which shortens the vulcanization time compared to conventional presses (compression molding).
- When the tool is filled and the closing pressure is established, the heating time starts. This is always dependent on the polymer base or rubber mixture, cross sections of the sprue channels, injection parameters and ultimately on the wall thickness of the molded articles. The vulcanization occurs at mold temperatures between 170 ° C and 195 ° C. While the parts are vulcanizing in the mold, the injection molding machine starts in parallel the dosage for the next shot.
- The press operator or robot demolds the parts after the tool automatically opens after the heating time has elapsed. After demolding, the cavities are cleaned and the next cycle is started. If the moldings are not yet 100% vulcanized on the injection molding machine, they can be post-annealed in an oven.
THE USE OF COLD RUNNERS IN RUBBER INJECTION MOLDING
Due to the use of cold runners, elastomer injection molding can save a lot of material depending on the tool concept. The cold channels are tempered separately and sit on the mold tops. The mixture remains free-flowing in the cold runner and does not cure. Due to the nozzle distribution of the cold runner, the cavities in the tool can be filled directly (needle valve cold runner) or placed as close to the cavity as possible with a small residual injection.
ELASTOMER INJECTION FOR REALLY FORMABLE PARTS
Once the molded rubber parts have been cross-linked after elastomer injection, the condition can not be reversed. The molded rubber parts retain their properties through the chemical, mechanical cross-linking process even under the most severe conditions.
Rubber profile with molded part
Rubber profiles made of EPDM are also part of our product range, as well as coex-profiles made of EPDM + EPDM sponge rubber with special anti-friction coatings and adhesive tape applications. The yard goods can also be further processed on specially developed punching equipment or by water jet cutting. Finally, we also inject moldings directly onto the profiles, thus providing a perfect connection between the extrudate cross-section and the molded part.
Elastomer injection molding automation handling systems
An alternative to industrial robots are linear handling systems. These are usually less variable, but also cheaper to buy. With linear handling systems, we remove multi-cavity injection molds with one stroke and can also position inserts in the tool for the next cycle.