rigid pvc running on higher capacity presses

By futuremolding
Published: February 19th, 2013

Hi all, 
Is ther any trick to run RPVC on higher shotweight presses ,avoiding yellow burnmarks and other aesthetic problems . Here i just want to use the 30% of the machine shot weight. We are stuck and unable to move the die to alow capacity press.

The trick to running PVC (or

The trick to running PVC (or any plastic) in any machine, is residence time and shot capacity. PVC tends to soak up heat. The longer it sits in a machine (even at 200F) the more likely it is to degrade. when going to a larger machine calculate the shot capacity (PVC runs well at 60+%). Calculate the residence time - PVC tends to degrade if it's cooking for longer than a few minutes.

PVC likes low compression screws. You'll have difficulty running it in a high compression screw. A GP screw - 10-5-5 is OK for PVC.

Hope this helps.

Bill Tobin

If you know the actual melt

If you know the actual melt temp in the current press; you just need to find the settings to mimic the other machine. You can do so by reducing the barrel temp settings say from center of barrel back towards the feed throat. How much you can and still fill and pack the part will take some time.
There are two other items you didn't mention that will preclude you being successful with this task. 1-Will the larger screw size lower the cavity pressure to the point you can't fill the mold? 2-Do both machines have injection units in good shape, with approximately the same compression ratio?
I've moved POM and PVC molds in the past. My success rate was good; only two couldn't make the move because the shot size was too small and/or the residence time too long and melt began to yellow.
Rick.

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