Hot Runner Mold Design


There are numerous benefits of a hot runner mold design. It is these benefits that enable plastic injection molding companies to make better plastic part quicker and with less expense.

While it is true that the initial, up-front cost of an injection mold using a hot runner mold design exceeds that of a cold runner system, many times the ROI is easily realized over time.

Additionally, using a hot runner mold design is often a very good marketing tool to win contracts. The added value of the injection mold, together with the increased efficiency of the molding process can make for a very strong case for quoting purposes.


  • Lowered cycle time and increased production
  • Lower production costs
  • Better quality plastic molded parts
  • ¬†Lowered cycle time and increased production

In any plastic injection mold the cycle time is largely determined by the thickness of the part. In many cold runner systems, the runner thickness exceeds that of the molded part, slowing things down dramatically.

When the cold runner is eliminated, the cooling time is reduced by the difference in the cooling time of the part and the runner. Over time, this becomes quite significant.

Injection time is also dramatically reduced. As with the cooling time, the injection time is reduced by the difference in the time it takes to fill the runner compared to the plastic part.

Because there is no runner to deal with in a hot runner mold design, additional time is saved because there is no requirement for a sprue picker or robot to remove the runner. Also, costs are reduced because there is no need for any secondary operation to separate the runner or trim the gate vestige.


In the long run, a hot runner mold design saves money, despite the initial capital investment. The lower production costs also have a spill-over effect on other operations because of more machinery becoming available.

Molding machine costs are reduced because a mold with a hot runner mold design can usually be run in a smaller press than a cold runner mold. This is due to the fact that a cold runner simply requires higher tonnage due to the cooling of the runner during molding. More injection pressure is required and more clamping pressure as well.

Mold making costs may be reduced because less cavitation may be required. This is due to the efficiency of the hot runner mold design. More parts can be made with fewer cavities.

Labor is saved because there is no trimming, sorting, de-gating and so on.

Energy is saved due to the shorter cycle times, no regrinding of runners, and heating up resin to mold runners.

Resin savings can be huge. With no runner to mold, all the resin goes into the plastic part, saving money.


By using a hot runner mold design the molder will experience a higher level of quality in the final molded plastic part. The parts are consistently of higher quality compared to a cold runner system.

The mold design may need to be modified to accommodate the gating location of the hot runner system. This can present a challenge for the designer, but is typically not a deciding factor in the decision to use a hot runner mold design.

With a valve gate or thermal gate, mold fill is even, stresses are reduced in the part, gate vestige is minimal, and the molding process becomes easier to manage consistently.

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