Runners—Cold and Hot

The runner size depends on the material being processed and whether it is a TS cold or hot runner. As reviewed in Chapter 2 and Fig. 2-7, with TPs a hot runner solidifies with the injection molded part. If a cold runner is used (with TP), only the molded parts solidifies there is no runner scrap. 

With TS closed molds (TM, IM, etc.), the complete mold can be at the maximum heat, which cures and solidifies both the runner and the molded parts. With TSs, this runner is called a hot runner. If the mold is designed so that the maximum heat surrounds only the cavity and the lower heat (similar to the lower pot heat) surrounds the runner, that is called a cold 

Unfortunately, solidified TS runners, flash, and defective parts cannot be recycled as they are with TPs. Some operations can use this material as a filler after it has been granulated but in practically all molding plants using TS, the material is lost and has to be considered in the part cost. One should consider using cold runners with TSs. Materials must be of a type that will permit their use for example, the time cycle should permit material to remain in the fluid state. As different hardeners, accelerators, and so on, can be used, it is practical to use cold runners. They have limited use in TM but are used more widely in IM. 

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