Hot runner tools use a temperature-controlled manifold to greatly reduce or eliminate runner scrap from the cycle. Injection points can be outside the part or directly into the part. This can greatly improve cycle times, as a sprue or runner system is often a determining factor on the mold cycle. And, eliminating the runner saves expensive wasted material.
Hot runner molds require a temperature controller for the press they run in, with the controller being sized to match the manifold in the mold. Some mold maintenance costs are higher on a hot runner tool, but they often pay for themselves in the long run through material and cycle time savings. This is particularly true of applications that require expensive engineering grade resins or high annual volumes.