What is the difference between part removal in medical silicone injection molding vs. medical plastic injection molding?

Question: What is the difference between part removal in medical silicone injection molding vs. medical plastic injection molding?

Answer: Part removal is dictated by the size, shape, geometry, material, and surface finish. In both processes the use of an automated handler or manual handling can be used to pull some types of parts directly from the mold.

Plastics tend to be significantly more rigid and lower elasticity than silicones. So plastic often requires drafted sides to prevent binding and undercuts in most plastics are not possible without actions. In silicone, the rigidity does not generally allow the use of knockout pins inside the cavity to push the part out. Silicone can often deflect or stretch during removal and then snap back to original shape meaning that draft is usually not needed and parts can often have undercuts without needing actions. The drawback is that knockout pins may cut or fail to remove parts since they stretch around pins. Compressed air, external brush, or sometimes push plates that contact a greater surface area than knockout pins can be used to remove silicone parts. High hardness, low tear strength parts tend to have more issues in release than those parts with high tear strength and high elongation. Silicone release generally improves with a sand blasted finish while the release may be more difficult with highly polished surfaces.

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About Matt

Matt is a project engineer at Albright Technologies, Inc. After interning for two years and earning a Bachelors of Science in Mechanical Engineering from Western New England College Class of 2009, Matt joined Albright Technologies full time.