Plastic injection molding has many variables involved that affect the quality and consistency of a produced part. Thermal energy transfer is one of these variables, and with lower mold temperatures (under 80 C) it is relatively easy to manage, but at higher temperatures it can become problematic.
In modern plastics manufacturing, there are many polymers that have high mold temperature requirements. If the thermal energy created when working with these polymers is not properly managed there can be a significant impact on the integrity of the production equipment.
Some polymers require processing temperatures as high as 300 C with mold temperatures 80 C or higher along with other special drying and cooling regimens. When working with these polymers, it’s essential to keep the mold at the appropriate temperature and carefully manage their special production requirements while ensuring that the platens and other parts of the production equipment are protected from excess heat transfer.
Heat Transfer to Platens Can Lead to Production Problems
At first glance it does not seem like a major issue, but excess heat transfer to the platens when producing a part with a mold temperature requirement over 80 C can cause several issues with part production quality and consistency.
Platens expand as they heat up, and the resulting expansion can cause the tie-bars to spread apart and cause resistance when the mold closes. This can cause excess wear on the platens, tie-bars, and the mold which is undesirable. The entire production process can be significantly affected by heat transfer, and as a result it needs to be managed.
Insulator Plates Are Used to Reduce Thermal Energy Transfer
In order to reduce thermal energy transfer to the platens, an insulator plate is often placed between the platen and the mold clamping plate. This type of insulator plate reduces the rate of heat transfer, but it still occurs.
Even with these insulator plates, the platens can get so hot that they cannot be touched or worked on. After about an hour or more of production, problems can start to develop. Because of this, additional cooling and insulation techniques are beneficial for high mold temperature part production.
John Klees Suggests Water Cooled Clamping Plates
To further protect the production equipment from thermal energy transfer, additional insulator plates can be placed between the clamping plate and the mold, as suggested by mold designer John Klees. He also recommends that the clamping plates are gun drilled for cooling, and that water should be run through them at 65 C in order to cool the machine, mold and platen.
Recommended for Molds that Run at 80 C or Hotter
Klees’ approach further reduces excess heat transfer to the platens, creates a more stable production process that will require fewer alterations, a shorter wait time before the mold can be handled, and platens that are not too hot to be touched or worked on. His heat management technique is recommended for any mold that needs to be run at 80 C or higher, and the improved production efficiency and equipment protection is well worth the installation cost and time.