Tool, tools runner system

The mould bolster comprises the bulk of the moulding tool and forms the matrix that supports and locates the cavity inserts. The bolster block also encompasses the runner system. The metal of construction must reflect the working needs of the mould. 

Multicavity tools can be built to make over 100 parts per cycle. These are complex molds that can cost hundreds of thousands of dollars. The cold runner systems in multicavity tools can be extensive, wasting plastic. The runner has to be separated from the part, handled, discarded, or reground for reuse if possible. An alternative to cold runners and a trend in the molding industry are hot runners or runnerless molds. Hot runners serve the same purpose as cold runners, ie. 

Dropik M. Isolation of True Runner System Behavior in Simulation Tools for Injection Molding, ANTEC, 2006... 

One development for coinjection equipment was the inclusion of separate hot-runner temperature control systems for the different resins, for example, in order to allow an EVOH core layer to be processed at a temperature 70 C lower than the PET skin layers. Another development was the use of computer simulation to design tooling that manipulates the barrier resin distribution to fortify critical areas such as wall sections. Both wide mouth and narrow neck coinjection stretch blow molded bottles are available. 

---