Injection molding is a cost-effective process used to produce plastic parts at scale. There are two main types of mold systems: hot runner and cold runner. Each
system has its own mechanism with difference in terms of cost, speed, and accuracy of the molded parts. This article will make a detailed comparison between
hot runner and cold runner.
What is Hot Runner?
A hot runner system is a heating component system used in injection molds to inject molten plastic into the cavity of the mold. Hot runner mold is a new structure that heats the sprues and runners of traditional molds or three-plate molds, so that there is no need to remove the runners and sprues during each molding process.
Advantages of Hot Runner Compared to Cold Runner Molds
Easier to start
There is no need to remove runners, and auto cycle occurs faster and more frequently.
Design flexibility
The gate can be located at many points on the part, which can further improve the aesthetics of the part and optimize the filling effect of the mold cavity during the injection.
More precise
Hot runner molds can produce more precise parts with tighter tolerances in a short lead time.
Production of Larger volumes and sizes of parts
Hot runner molds also can produce large volumes and sizes of parts when compared with cold runner molds .
Balanced melt flow
Separate melt channels are in externally heated manifolds that are insulated from mold plates surrounding them.
Shorter cycle time
There is no need to separate the runner from the part for hot runner molds. The plastic is kept at optimum temperature, which allows for faster processing of materials. Therefore, their cycle time can be shorter than cold runner molds.
Reduced material wastage
The mold system generates little to no material waste.
Fewer sink marks and under-filled parts
It is helpful to achieve the highest levels of quality and part volume at the lowest part cost due to the fewer sink marks and under-filled parts.
Disadvantages of Hot Runner Compared to Cold Runner Molds
Higher initial investment and maintenance costs
Hot runner molds have higher initial investment and maintenance costs than cold runner molds because of the more complex and sophisticated components.
Fail to accommodate some heat-sensitive thermoplastic materials
Compared with cold runner molds, hot runner molds are not suitable for certain heat-sensitive thermoplastic materials.
High requirement for precision in the equipment
High-end equipment is required due to the accuracy requirements of the hot runner molds. Otherwise, defects may occur because of machine failure.
Have difficulty in making color changes in hot runner molds
Require more technical skill and experience
Compared to cold runner systems,hot runner systems require more technical skill and experience to operate and optimize, affecting the quality control of the process.
Application of Hot Runner Systems
Cell phone cases
Bottle caps
Projects that require a high volume of inexpensive parts
Other high-volume items
What is Cold Runner?
A cold runner is simply a channel formed between the two halves of the mold, which is used to carry molten thermoplastic material from the injection molding machine nozzle to the cavities. A cold runner mold is more popular for its lower setup and maintenance cost. However, it can produce more waste than a hot runner mold.
Advantages of Cold Runner Compared to Hot Runner Molds
Cost-effective
Cold runner molds are cost-effective for their lower tooling cost, less inspection and maintenance cost because they are not complex.
Suit a variety of thermoplastics
Cold runner molds suit a variety of thermoplastics, even some thermally sensitive polymers.
Allow for quick changes in design or color
Disadvantages of Cold Runner Compared to Hot Runner Molds
More waste
Cold runner molds generate more waste than hot runner molds, which need further trimming.
Lower tolerances
Compared with hot runner molds, cold runner molds tend to produce parts with lower tolerances.
Slower production process
Cold runner molds have a slower production process because of the need to remove the runner and sprue and the reduced plastic flowability. The slower cycle time leads to the production of fewer parts.
Application of Cold Runner Systems
Electronic housings and coverings where blemishes
can be hidden
Keyboards
Lower volume production
Differences Between Hot Runner and Cold Runner

  • Hot Runner vs. Cold Runner: Cost Comparison

    • Hot runner molds are more expensive to set up and maintain when compared with cold runner molds.

  • Hot Runner vs. Cold Runner: Speed Comparison

    • Hot runner molds produce more parts per unit time and have a shorter lead time than their cold runner counterparts. This is because the hot runner molds don’t need to separate the runner from the mold like cold runner molds. As a result, hot runner molds can reduce the cycle time.

  • Hot Runner vs. Cold Runner: Materials Comparison

    • Hot runner molds are not compatible with some heat-sensitive thermoplastic materials whereas cold runner molds can work with a variety of polymers or thermoplastics. It means that cold runner molds suit heat-sensitive types.

  • Hot Runner vs. Cold Runner: Tolerance Comparison

    • Hot runner molds produce parts with a higher degree of tolerance compared to cold runner molds.
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