A hot runner system is an assembly of heated components used in plastic injection molds that inject molten plastic into the cavities of the mold. The runner is hot to maitain the plastic material molten. The molten plastic is injected into the hot runner and flow from the heated manifold into the cavity through the heated nozzles. Here we list some advantages and disadvantages of hot runner mould compare with cold runner system.
Shorter cycle time:The plastic flows faster than the cold runner, and it has no need to wait the cooling of the runner section. The part can be ejected when solidified. The part with thin wall thickness can have the circle time less than five seconds.
Saving cost:In cold runner mould, the solidified runner section is ejected out together with the part. It wastes the raw plastic material. Hot runner system can help to save the cost of this section. If the plastic is expensive, the economic effect is not small.
Higher quality：The heat can be controlled uniformly in the runner, molten plastic flow into the cavity symmetrically. The finished part has better comestic finish, less sink marks and less warpage.
Advanced technology：Many advanced technologies are developed based on hot runner system, like the PET pre-formed precess, multi-color shot, multi-material shot and stack mould.
Other benefits of hot runners:
- hot runners available for both single cavity and multi cavity moulds
- can be used with most plastic materials and part designs
- are easy to maintain
- reduce the number of moving plates in a mold
- gives good gate vestige
- can use with close pitch mold designs
Higher tooling cost：The components of hot runner are much more expensive than cold runner. It may be not economic when quantity is not large.
Difficult maching processes：Hot runner system require high accuracy of tooling components. Most of the tooling parts have to be machines precisionly.
Complicated operation and repairment：Compare with the cold runner mould, hot runner is hard to operate and repaire. It is easy for the new users to break the mould due to the incorrect operation.