If You Can’t Take the Heat

Published On: January 9th, 2014|Categories: Blog|

Mold temperature control

Molders talk about injection molding your parts and the process is all about balancing time, temperature, and pressure. That concerns the first half of the process, making the shot. The back end of the process, cooling the shot in the mold is also of critical concern. The purpose of the mold is not just to establish the end shape of the part, but to remove heat while the plastic returns from liquid into solid. How that mold removes the heat, or more accurately how efficiently or consistently heat is removed has a large bearing on the end part meeting print dimensionally and cosmetically.

Cooling issues tend to rear their head in three ways, at the beginning of a production run, in a very dramatic appearance or through gradual effects that mount up over time. All three manifest themselves due to either under-cooling or over-cooling taking place.

Over-cooling usually results in the material not being able to flow (transition too fast) and not filling out the mold. You may also see surface irregularities or imperfections as a result of over-cooling. Under-cooling means resin stays liquid state longer and as such may not be solidified enough for ejection. Under-cooled parts may stick in the mold or are manhandled by the ejection system.

As a supplier evaluator, look for systems that ensure the cooling will and is operating as planned. Mold lines are maintained and clear. Instruction on connecting hoses properly for flow. Has the cooling need been assessed for what type of temperature control unit should be used and are they maintained and working correctly?

All of these would be issues regardless of whether your problem was from initiation, a catastrophic mid-run failure, or a gradual trend toward unacceptable parts. One of those failure modes would have you looking to these same components. Look for troubleshooting systems that would systematically assess what a where the technicians should look.

When the cooling system is used correctly and maintained, a molder should be able to repetitively shoot parts and extract them from the mold adhering to print throughout the run. This is assuming of course that the molder can keep cool but not too cool!


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