Extruder

[SS ELEC]

Hello. I am programming an extruder for the first time and I'm not sure how to control the heat and cooling for the barrel. I want to use a PID but not have the heat and cool come on at the same time (or close to the same time). I'm using an AB SLC 504. Does anyone have any suggestions or examples?

 

[allscott]

Hello. I am programming an extruder for the first time and I'm not sure how to control the heat and cooling for the barrel. I want to use a PID but not have the heat and cool come on at the same time (or close to the same time). I'm using an AB SLC 504. Does anyone have any suggestions or examples?

If you want to do extruder temperature control with a SLC you will pretty much need a 1746 BTM (barrel temperature module). You really don't want to attempt to do a heat/cool PID in a SLC on your own (or at least I have never seen anyone do it and I wouldn't even try).

Alternatively you could use a process controller that will do this for you. I use Eurotherm products but there are many others. With your SLC you could communicate with these controllers with devicenet if you need to get the information into and out of the PLC.

 

[Passman]

Is it cooled with water and steam in the same chamber or air and electric heaters? I've used my own programming to accomplish both. I'm curious why it's not possible?

 

[Phrog30]

I'm using an AB SLC 504. Does anyone have any suggestions or examples?

Are you firm on using a SLC? I would suggest CLX/CpLX. Logix has SRTP instructions which work well. There is an example included in Logix software. I copied the instruction definition below:

Split Range Time Proportional (SRTP)
The SRTP instruction takes the 0-100% output of a PID loop and drives heating and cooling digital output contacts with a periodic pulse. This instruction controls applications such as barrel temperature control on extrusion machines.

James

 

[osmanmom]

Use Standard Temperature Controller

-honywell/omega/omron etc

if you use PLC then you need HMI for setting the SV

 

[SS ELEC]

It is electric heat and water cooled.

 

[SS ELEC]

Firm on using a PLC because we have one we're not using and we want to add it to our network

 

[robertkjonesjr]

I used to manage a few extruders; most of the older ones all had individual temperature controllers for each zone from, say, Eurotherm or whoever. There was one that was all PLC controller with SLC505, but we compromised: any new ones sourced all had individual controllers for each zone (the plastic engineers wanted this) but I would get the comms card option (usually Modbus with RS485) and then string them all together and feed them into a PLC. I would use the PLC for master functions only: setpoint changes, startup/shutdown procedures, data collection, alarming, etc. But individual zone PID control I just left to the experts - the little DIN mount temperature controllers.

If I had to do it again, this is the approach I would prefer - individual zone control, then all tied together through a fieldbus to a PLC/HMI/SCADA system.

 

[Helliana]

Controlling extruder heats work best with a 1746-BTM module. The regular PID loop in a SLC is not powerful enough to control effectively. Just a warning, setting up that module is not the easiest thing to do.

If you move away from the SLC and go with Compact/Controllogix, you can use the PIDE function block. It works rather well.

 

[snordvikqplas]

I am controlling heat and cooling on extrusion lines for plastic right now using PLCs. Compact, SLC, and Micro 1400.

All heat zones are controlled using Time based proportional control using mercury relays, there was a thread on here somewhere that explained it nicely, Ken Roach I believe. Power is 240V hence the need for the mercury relays and time proportional control, SCRs would be to costly. There is an HMI with each line allowing for adjustment of SP and PID values.

Anyways the heat zones here are somewhat slow on start, and any slight overshoot etc is acceptable. Once SP has been reached they hold temp rather well.

Cooling zones (water) are proportional valves controlled by compact logix analog output cards on larger lines while we do use seperate controllers for extruders that only have 1 or 2 cooling lines (nose cooling etc)

Look for the thread on Time Proportional control in the forum, this will allow for you to turn on and off your electric heaters as a percentage. Very affordable and is working well, (if you are allowed to use mercury relays)

 

[SS ELEC]

Thanks for the info. Are you using the BTM module in the SLC? Or are you controlling it with the regular PID instruction?

 

[SS ELEC]

Are you using a SLC to control it?

 

[iant]

Solid state relays are now very cheap. And environmentally safer than mercury switches. 240 v any current even 440 volt. No problems.

 

[snordvikqplas]

Using PID in the SLC. Time proportional control works well with this.

 

[iant]

One of the plants I service has two extrudes using compact logix
One using a Twido PLC
And the smallest one using an S7-300
The heating is a fairly standard PID, although the Twido is using standalone temperature controllers with Modbus comms.
The plant has a chilled water supply which is used to cool the barrel once the set point is reached. They achieve a fairly constant +\- 2.5 degrees C