Injection Molding - HEAT/COOL advice wanted

Plastic

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Join Date
Feb 2009
Location
Michigan
Posts
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Heat/Cool – First Experience

Although we have extensive PID heating experience for thermoplastic injection molding, today we are faced with a welcome, new, challenge of alternate media injection.

The media is staged in a vertical tank that is staged in vertical temperature zones where the top zones are at a higher liquid temperature, and the lower zones are cooler.

We have NO empirical data collected yet.

We are confident with PID set-up for electric heating of the zones, but do not have any COOLING PID experience.

We speculate that the heat/cool would not be a balanced slope, therefore, we speculated that two separate PID loops would be required. One loop tuned for the HEATING gains, and a secondary LOOP set up for cooling.

We will have thermocouples in the process media, we have electric resistance heating for the the heating PID, and we have digital on/off solenoid valve for cooling of the same zone.

Again, embarrassed that we have been around thermoplastic extruders with this heat/cool scenario, this is our first actual implementation.

Questions:
Should we use a single, bi-polar PID for heat/cool…

OR

Should we use two separate PID controllers, one for heating, and another for cooling.

Thank You for your input.
Plastic
 
At my work there are 5 or 6 plastic injection machines, they don't have a cooling temperature regulation, they just open the solenoid valve and wait for the temperature to descent to some level.
And the older machines cool down during a prefixed time that need to be changed from summer to winter
 
No experience whatsoever with injection molding. But in cases where we have two controllers, controlling the opposite effect, we usually use two controllers. The heating controller setpoint would be slightly higher than the cooling one, so that they don't interfere with each-other.


Alternatively, you could set up a controller that works from -100 to +100%, where negative would be cooling and positive would be heating. (I guess that would be one of the options you already mentioned :) )
 
As far as I know it the objective is to cool the mold as fast as possible and for that it does not need any PDI, just let the water circulate and wait
 
better to use separate control processes (many controllers can do both and have 2 outputs )
keep in mind the big difference in lagtime, as the cooler is a lot slower.
 
Hi

Here is a tech note that may help.


There is also an Add ON instruction you can find at the AB sample code website
P_TempIntg
I have over 250 loops running with this instruction about 50-60 are Heat/cool
 
Thank you rkukl

We are currently running satisfactorily with PID for heat when below setpoint, and on/off for cool when above setpoint.

Your attached Rockwell article points us in a good direction using a bi-polar SRTP, we may elect to spend efforts to enhance utilizing the referenced article.

Thank you :)
 

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