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Compression machine oven temp control

This topic contains 4 replies, has 2 voices, and was last updated by  Wes 2 months ago.

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Wes superduperwesman

Compression machine oven temp control

05/01/2019 at 22:31

Why not utilize the existing oven temperature control? Is the extra precisions of the PID controller and new thermocouple required? If it’s precise enough for baking why would it not be sufficient for the plastic.. I feel like baking would require more precision but thought I’d ask to understand further.

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starter
06/01/2019 at 04:59
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Analog oven controls can only do 100% on or 0% off. This leads to overshooting of the desired temperatures and no control of the band around your desired temperature. Typical oven controllers hold +-5 degrees. PID Controllers can hold +-1 to +-2 degrees with no overshoot for many reasons you can look up on Wikipedia. One main reason is PID Controllers can apply a percentage of power any where from 0-100%. This is important when you get close to your desired temperature that is when you want to apply 10-20% power to “glide” right to your temperature set point.

new
06/01/2019 at 05:45
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Thanks for clarifying. That does make sense. So the plastic is that sensitive to temperature that the overshoot can make the difference between getting a nice workable plastic vs… burning it?

starter
06/01/2019 at 06:00
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It depends on the plastic you are using…pvc yes. It also depends on where u r are in the operating range for the plastic you are using. Let’s say your range is 450-550 degrees F. If your part dictates a lower viscosity and you are running 550 degrees then a few degrees can make a difference. If you are using a screw for injection or a screw for extrusion then yes as the screw in parts shear heat to the plastic. If you are plungering for injection then pid is probably not necessary.

new
06/01/2019 at 06:14
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Yeah I could see how you’d want finer control for extrusion or injection. I wasn’t sure if it would matter as much for the compression molds. In the videos the plastic seemed quite “liquid” I just wasn’t sure if you would undershoot a little and then just use a bit more pressure. It’s all very new to me. I guess you could try it without and then add the PID control later?

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