Can Low Melt Temperature Cause Flash?

Yesterday, I was asked this question…

My tech told me that we were getting flash as a result of a low barrel temperature. An increase in barrel temperature fixed the problem, but I don’t know why, could you explain?

My Response
It may seem counter-intuitive, but flash could be the result of a low melt temperature or a high melt temperature.
If the temperature of the melt is too low, the viscosity will increase and the pressures required to fill the mold may be too high. This high pressure can exceed the clamp tonnage resulting in flash near the center of the mold or near the gate.
If the temperature of the melt is too high, the melt viscosity will drop – especially if the material degrades. This drop in viscosity may allow too much material to enter the mold during 1st stage fill, resulting in flash. A decrease in melt viscosity may also cause the material to flash during 2nd stage packing.
Additional Thoughts
Keep in mind, the focus should be on the actual melt temperature, which is a process output, instead of barrel temperature settings, which is a process input.

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