Hot VS. Cold Runner Molding Systems

With the increasing cost of steel and raw materials, supply chain professionals are often looking for options to reduce part prices, cycle times, and material waste. Cold runner systems may be a cost saving solution in contrast to typical hot runner systems for the right application.

Hot runner vs Cold Runner - Sprue Waste

Difference Between Cold Runner & Hot Runner

Hot runner systems, a.k.a. “hot sprues,” are molding systems where the molten raw material is physically heated as it is being transferred from the machine’s nozzle into the mold cavity.

Cold runner systems, on the other hand, use unheated channels to direct the molten raw material into the mold cavity. Cold runners keep the rubber compound from curing while within the cold runner unit extending from the molding machine’s injection chamber.

Advantages/Disadvantages of Hot Runner Systems

Hot runners are the commonly used system for high volume runs and ensures high quality parts will be produced. Parts with complex geometries will do well with hot runners. Hot runner systems also have lower overhead costs compared to cold runners.

The downside to hot runner systems is the higher set up cost and higher material waste compared to cold runner systems.

Advantages/Disadvantages of Cold Runner Systems

Cold runner systems have shorter set-up times and lower set-up costs than hot runners. Due to its ease of automation, cold runners can be set up to have fast cycle times. The cold system also produce less material waste, saving material cost for each run. Parts having several different color options may benefit from using cold runners for their ease of swapping out colors during production runs.

One disadvantage is the increased maintenance cost required for the tool. Cold runner units have parts which need to be replaced such as the individual nozzles, seals, and valve gate pins. Additionally, the higher pressures required by cold runner systems can create more wear and tear on the molding machine as well as increase energy consumption.

Should I Use Hot or Cold Runner?

Cold runners are a good choice for small volume runs with applications in prototyping and testing color options.

Hot runners tend to be more cost-effective for medium to high volume runs with high repeatability.

Which runner system to choose would usually be decided by the volume of the project. Hot runner systems are the go-to for most injection molding projects due to its reliability and low overhead costs. However, cold runner systems may be more cost effective for smaller quantity projects thanks to its low set-up cost and set-up time.

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