Changing mold inserts

For the production of mold inserts, the same possibilities and processes apply as in injection molds. The structures themselves are usually much easier to make and therefore cheaper. Other advantages are the simpler system and equipment technology and very short setup times - especially to change material, because no conversion and cleaning of machines (screw and nozzle) are required. 

FIGURE 2.34 Quick change mold system with interchangeable mold inserts... 

Compounds based on S—EB—S usually contain polypropylene, which improves solvent resistance and processibiUty and raises upper service temperatures. Compounds intended for use in the automotive industry are able to survive 1000 hours air exposure at temperatures of 125°C with only minor changes in properties (54). Very soft compounds have been developed to replace foam mbber for interior trim parts. In this and similar appHcations, these soft compounds are usually insert molded over polypropylene or metal and then coated with flexible polyurethane paint (55). Other automotive appHcations include products intended for sound deadening, flexible air ducts, and gear shifter boots, as weU as improving the properties of sheet mol ding compounds. 

The most common special feature of the mold is the quick change volume control insert. Rigid volume control is necessary for certain products, such as dairy containers. Here HDPE is used (for many excellent reasons), and the container slowly shrinks and changes in size for many hours after molding. Because of production volume control requirements, some dairies must fill containers molded half an hour before fill and then switch to filling containers molded several days previously. Volume-control inserts that displace the difference in volume between the two types are added to the mold, usually as a disc in the side wall, to ensure that the volume and fill levels are the same in both containers at the time of filling. The device works because HDPE shrinkage is reduced virtually to zero for the life of the container when filled with milk or juice and stored at cold temperatures. 

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