Rubber mold cold runner system

An injection block for the injection molding of thermoset polymers, such as rubber, formed from at least a pair of plates bolted or otherwise releasably held together and defining an improved runner system between the plates. Complimentary grooves formed in each plate substantially completely surrounding the portion of the runner system formed between the two plates to define, when the plates are mated together, a passage or enclosure constructed to receive a sealing member therein to prevent leakage of the material to be molded beyond the sealing member between the plates. Thus, the sealing member limits the leakage or creeping of the molding material from the runners. This is believed to limit the surface area over which the relatively high pressure under which the material is molded acts between the plates to limit the force tending to separate the plates. The plates may be releasably held together by a plurality of cap screws, bolts or screws without failure in use of the injection block. Bolting the plates together is desirable because it facilitates separating them to clean them, remove molding material, or otherwise service and maintain the injection molding block throughout its life.