New Vacuum Furnace Control Information

ceilingwalker

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ceilingwalker
Join Date
Mar 2010
Location
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Posts
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Good day all. I have been tasked with automating a vacuum furnace and unfortunately, I have no experience with vacuum furnaces. Would anyone happen to know what all is needed for such a system. I know of the diffusion pump, vacuum control and sensors and that is about it. I need to take a manual system that is in place now and move it all over to a SLC 500 control. Any information that anyone can offer would be greatly appreciated. I'm kind of partial to the SLC 500, that was my call. The environment the control will be placed in is not something I would put a micro logix nor a Compact Logix in. Control Logix is to pricey. Also will be using Factory Talk for HMI. So that reminds me of another question: for all the analog sensors and valves I will need, if anyone knows of manufacturers that their hardware will interface with a particular SLC 500 module, I would appreciate that info, as well as the specific SLC 500 modules that are used. Thank you for your time.
 
I would use either a Micrologix or a CompactLogix 10 times before I bought a soon to be silver series product like the SLC.
What makes you think the compact or micro can't handle something and the SLC could?
What vacuum range are you planning on using? How does the system work currently? Can you just take that sequence and automate it?
 
I've done several vacuum furnaces, both in medium vac (10-3) and high vac (10-7) vacuums.

It is not a project that I recommend for someone who has no experience with vacuum furnaces.

I don't understand why you are using a SLC500 as opposed to a CompactLogix or a MicroLogix, especially since looking at your posts it appears you do have Logix5000 and have used the CompactLogix hardware. A CompactLogix is cheaper than a SLC. A MicroLogix 1400 is as powerful as a SLC5/05 except for IO count. The ML also supports more data types, including a dedicated PID file type.

Search the forum for vacuum furnace. There have been a few threads (Including one started by you). Some more specifics on the furnace and exactly what kinds of sensors and how many you need will be helpful.

A few questions that you need to answer for yourself before you begin:
  • What is being processed? (helps determine instruments)
  • What volatiles will off gas from product? (determines vacuum instruments)
  • What is the vacuum range? (determines instruments)
  • Is there a process gas or sweep gas? If so what? (determines instruments)
  • Does your chamber backfill with any gas besides nitrogen or air? (dictates instruments)
  • Are you controlling vacuum or pumping to ultimate vacuum and holding as low as the pumps can go?
  • Are you controlling pumping speed at any point, such as when pumping from atmosphere or when using a process gas?
  • What are the vacuum pump types? Be specific.
  • What temperature range?
  • What is the heating power supply?
  • Three phase or single phase elements?
  • What heating power parameters do you want to monitor. I recommend at least monitoring current but I instrument for voltage, current, and true power.
  • How many heating zones?
  • Are the elements graphite or alloy (most elements require different PID parameters when cold -vs- hot)
  • How big is the chamber? (helps determine instruments)
  • Do you need a ramp/soak setpoint profile? If so how many do you need to store? (If the answer to this question is yes then I recommend that you stop thinking about anything except Logix5000 family controllers - UDTs will make life a lot easier for this)
  • Is there a gas quench at the end of the cycle?
  • Does the vacuum furnace have a cold trap? If so how is it chilled and does that need a controller?
  • How many cooling loops does the chamber have? (flow interlocking)
  • Is the power supply water cooled? (flow interlocking)
  • Is there a volatile compound condenser? If so how is it chilled? How is it heated for regeneration?
 
Last edited:
I agree with the other guys and recommend you go with MicroLogix or Compactlogix (my preference is the CompactLogix). No reason I can see why either of these won't withstand any environment that the SLC will.

As for the overall project, do yourself a favor and spend what feels like way too much time learning how the system works today, how it should work but doesn't, and how they would like it to work - new features and improvements. Get close to all the machine operators and maintenance folks. Let them know you want to deliver the machine they want and that you want to know what they know. You will never regret spending the extra up-front time but you will regret it if you short-cut this step or make assumptions. Chances are your maintenance folks can tell you exactly what you need, part numbers and all.

Steve
 
The reason I believed the SLC would be better is because it is a dusty dirty environment and the Compat Logix I have running another system has had modules fail because of that environment, as well at the Micro Logix. All 17 of my SLC's are in areas as bad or worse, and have not failed me. All except for the one that is exposed to toxic acid gases. Even my PLC-5's hold up well in the toxic gas area's. Robust I believe is the word I would use to describe the PLC-5 and SLC's.
 
I never design a panel that will allow the uncontrolled environment inside it. I built a few positive pressure enclosures in high dust applications.
Sorry I don't think that is a good argument, but then again it is your system.
 
Assuming you have one roughing pump. This pump is used mainly for backing the diffusion pump (DP). You "borrow" it to pump the chamber.

Components (outputs):
Foreline valve. From pump to DP.
Roughing valve. From pump to oven chamber.
Gate Valve. Isolates DP and chamber.
Vent valve. Brings oven back up to atmosphere.
High vacuum gauge filament (HV if Cold Cathode).

Inputs:
Foreline pressure
Chamber pressure
Atmosphere (ATM) switch.
Door closed switch.
Start, Vent. Could be on HMI.
Timer if using a timer.
Overtemp if using a temp controller.

Sequence:
Don't allow Start if Door not closed.
1) Close Foreline. Wait 2 seconds.
2) Open Roughing. Pump down to 100 millitorr (mT).
While roughing, monitor DP foreline. Repump if it rises above 1000 mT.
3) Close Roughing. Wait 5 seconds.
3A)Option - check rate of rise. Rerough if needed.
4) Open Foreline valve. Waits until 100 mT, or 5 seconds.
5) Open gate valve.
Wait 10 seconds, then turn on High Vacuum gauge.
6) Start heating.
7) Start timer.

Vent:
1) Turn off heat and High Vacuum gauge.
2) Close gate valve.
Wait for cooldown. Flow gas to aid cooldown if you have option.
3) Open vent valve. Wait for ATM switch.
Vent for additional 10 seconds. ATM switches are never accurate.

Interlock all but Foreline with Door.
Interlock Vent, Gate with Rough.

A diffusion pump uses oil and a heater. If you dump the DP to atmosphere, you blow the oil into the rough pump. The remainder burns onto the surface of the heater. A nightmare to clean.
There's so much I haven't told you. All of Tconnolly's questions are valid.
Reconsider your choice of the SLC platform. That's fine if you said you have several on the shelf.
I agree 100% will all posts above. Fix the contamination problem. Proper enclosure with fan and filter, or sealed with positive pressure (dry air or N2 purge).
 
keithkyll said:
Assuming you have one roughing pump. This pump is used mainly for backing the diffusion pump (DP). You "borrow" it to pump the chamber.

Components (outputs):
Foreline valve. From pump to DP.
Roughing valve. From pump to oven chamber.
Gate Valve. Isolates DP and chamber.
Vent valve. Brings oven back up to atmosphere.
High vacuum gauge filament (HV if Cold Cathode).

Inputs:
Foreline pressure
Chamber pressure
Atmosphere (ATM) switch.
Door closed switch.
Start, Vent. Could be on HMI.
Timer if using a timer.
Overtemp if using a temp controller.

Sequence:
Don't allow Start if Door not closed.
1) Close Foreline. Wait 2 seconds.
2) Open Roughing. Pump down to 100 millitorr (mT).
While roughing, monitor DP foreline. Repump if it rises above 1000 mT.
3) Close Roughing. Wait 5 seconds.
3A)Option - check rate of rise. Rerough if needed.
4) Open Foreline valve. Waits until 100 mT, or 5 seconds.
5) Open gate valve.
Wait 10 seconds, then turn on High Vacuum gauge.
6) Start heating.
7) Start timer.

Vent:
1) Turn off heat and High Vacuum gauge.
2) Close gate valve.
Wait for cooldown. Flow gas to aid cooldown if you have option.
3) Open vent valve. Wait for ATM switch.
Vent for additional 10 seconds. ATM switches are never accurate.

Interlock all but Foreline with Door.
Interlock Vent, Gate with Rough.

A diffusion pump uses oil and a heater. If you dump the DP to atmosphere, you blow the oil into the rough pump. The remainder burns onto the surface of the heater. A nightmare to clean.
There's so much I haven't told you. All of Tconnolly's questions are valid.
Reconsider your choice of the SLC platform. That's fine if you said you have several on the shelf.
I agree 100% will all posts above. Fix the contamination problem. Proper enclosure with fan and filter, or sealed with positive pressure (dry air or N2 purge).
Click to expand...

Very detailed, thank you much.
 

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