The Purpose of Cushion

I just received this question regarding a recent posting on my blog…

Blog Reader
You mentioned pressure loss with respect to the importance of maintaining a consistent cushion, could you quickly expand that thought?

My Response
All plastics are compressible… therefore there is a compression that takes place with the polymer in front of the screw. There needs to be a cushion to compensate for variability, but too much cushion results in too much pressure loss before the nozzle.
Additional Thoughts
Although a consistent cushion will help ensure a more reliable process… cushion control is not a reliable method of achieving this. You are best to monitor the cushion and adjust the shot size and transfer yourself when necessary.

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