Release mold, performance requirements

This moldable material primarily consists of TS polyester resin, glass fiber reinforcement, and filler. Additional ingredients, such as low-profile additives, cure initiators, thickeners, and mold-release agents are used to enhance the performance or processing of the material. As with any material, such as metallics and plastics, SMC can be formulated in-house or by compounders to meet performance requirements of a particular application such as tensile properties or Class A surface finish. Varying the type and percentage of the composition will result in variations in mechanical properties and processability. 

Tool coatings/platings are typically used to enhance tool performance in one or more of the following areas wear resistance, corrosion resistance, improved tool release, resizes components, and/or their combination. No single treatment is ideal for solving all these problems. Treatments are used that resist the corrosion damage inflicted by chemicals such as hydrochloric acid when processing PVC, formic acid or formaldehyde with acetals, and oxidation caused by interaction between tools and moisture in the plant atmosphere. Release problems require treatments that decrease friction and increase lubricity in mold cavities.3... 

Viscosity is an important factor. Standard PDMS oils spread well and form an efficient release film on the mold surface, but they do not perform in this application when paintability of the demolded articles is required. 

Productivity factors are shown 1n Table IIWith today s technology, 1t 1s possible to operate both SMC and Injection molding clamps during an entire shift. However, because RIM requires frequent application of an external mold release, approximately one hour per shift 1s required to perform both major and minor cleaning of the tool. Thus for RIM, only an 87.51 process efficiency was assumed. 

Air can be entrapped in the melt during processing. This can happen when plastic (pellets, flakes, etc.) is melted in a normal air environment (as in a plasticating extrusion process or in an injection barrel, compression mold, casting form, spray system, etc.), and the air cannot escape. Generally the melt is subject to a compression load, or even a vacuum, which causes release of air but in some cases the air is trapped. If air entrapment is acceptable, no further action is required. However, it is usually unacceptable, for reasons of both performance and aesthetics. 

A major development has been to provide easy release of parts from the mold. Special mold treatments and careful physical removal of parts were required, increasing the cost. PURs now incorporate an internal mold release (IMR) agent that improves part performance and process economics. However, thin-walled, complex parts may require the use of release agents on the mold. Material developments are under way to rectify this situation. 

Vapor degreasing equipment using trichloroethylene vapor is very effective in eliminating mold release. This operation, however, is performed at a high temperature, thus requiring the substrate to be thermally stable. 

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