A hot runner system is an assembly of heated components used in plastic

injection mold Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

s that inject molten

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

into the cavities of the mold. (The cavities are the part of the mold shaped like the parts to be produced.) By contrast, a cold runner is simply a channel formed between the two halves of the mold, for the purpose of carrying plastic from the

injection molding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

machine nozzle to the cavities. Each time the mold opens to eject the newly formed plastic parts, the material in the runner is ejected as well, resulting in waste. A hot runner system usually includes a heated

manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a n ...

and a number of heated

nozzles A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, a ...

. The main task of the manifold is to distribute the plastic entering the mold to the various nozzles which then meter it precisely to the injection points in the cavities.

Hot runner advantages

* Shorter cycle time: No runner controlling the cooling time * Easier to start: Without runners to remove, and auto cycle occurs faster and more frequently * Fewer sink marks and under-filled parts: Unlike when plastic flows through a cold runner and loses heat to mold plates * Design flexibility: Can locate the gate at many points on the part * Balanced melt flow: Separate melt channels are in externally heated manifolds that are insulated from mold plates surrounding them. Hot runner systems were first developed and came into sporadic use in the early 60s with generally negative results. They gained popularity in the 80s and 90s as technological advancements allowed improved reliability and the escalation of plastic materials prices made hot runner systems more desirable and

cost effective Cost-effectiveness analysis (CEA) is a form of economic analysis that compares the relative costs and outcomes (effects) of different courses of action. Cost-effectiveness analysis is distinct from cost–benefit analysis, which assigns a monetar ...

. Hot runners are fairly complicated systems, they have to maintain the plastic material within them heated uniformly, while the rest of the injection mold is being cooled in order to solidify the product quickly. For this reason they are usually assembled from components pre manufactured by specialized companies. A hot runner controller is a temperature controller used to control the temperature in the hot runner. This helps create the most consistent part(s). Hot runners usually make the mold more expensive to manufacture and run, but allow savings by reducing

plastic waste Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are catego ...

and by reducing the cycle time. (do not have to wait until the conventional runners freeze).

References

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Hot runner advantages

References

See also