billyO

PID (or thermostat) controlled forge

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Hello all.  I couldn't find anything on iforgeiron about this when I tried searching multiple phrase combinations, which kinda surprises me.  If there are threads about doing this, feel free to redirect me. 

Is this something that the community would be interested in following and willing to help me with my design?

Thanks and happy new year.

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There are a few threads scattered throughout the forum on this topic.  For the most part we see PIDs used on electric ovens and kilns rather than used on gas forges.  In principle it can still work, but you most likely will not be able to keep a gas forge within a few degrees as well as you can with an electric oven.  Personally I'm not sure it's worth the hassle.  If you need accurate ramp and soak times for certain alloys then electric is the way to go for the heat treating.    For forging you can get by with a thermocouple and readout if judging by color isn't close enough.  Once you have it set where you want it you just wait for the steel color to match the forge interior color and go to work.

Having said all that, here's one of the threads on the topic and Wayne Coe gives his pyrometer setup.

 

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OK, it seems as if there is at least a passing interest from some folks, so I'll go ahead.

53 minutes ago, Mikey98118 said:

The control you're thinking about was designed for electrical heating--not gas,

I'm aware of that but I've seen and used a few forges over the past 5-6 years with this kind of set-up.  

 

51 minutes ago, Buzzkill said:

...you most likely will not be able to keep a gas forge within a few degrees as well as you can with an electric oven.  Personally I'm not sure it's worth the hassle.  If you need accurate ramp and soak times for certain alloys then electric is the way to go for the heat treating.    For forging you can get by with a thermocouple and readout if judging by color isn't close enough.  Once you have it set where you want it you just wait for the steel color to match the forge interior color and go to work.

Having said all that, here's one of the threads on the topic and Wayne Coe gives his pyrometer setup.

Thanks for the link, Buzzkill, I had already seen that thread.   My main reason is not necessarily to hit and maintain a specific, tight temp range, but rather to help conserve fuel.  John Emmerling has a forge with a similar set-up and when I was at his shop a few years ago, I noticed that his gas solenoid was cycling on/off every 1-2 seconds while at a welding heat, and I thought to myself that he must be using almost 1/2 the propane that I use with my burners running 100% of the time. 

From what I've read on other knifemaking and blacksmithing forums is that folks say that with this set-up, they are able to maintain a relatively tight temp range (+/10 deg F) which will come in handy if I decide to break away from my current 1080/O1/15N20 damascus  focus and start forging blades with other steels that require tighter heat control.  And hopefully it will be effective in the 650-700F range for forging aluminum so that I don't have to keep checking the stock with a stick. (say that 5 times fast...)  And finally, folks claim that they use this type of system for more accurate heat treating and while I have a JenKen Fiber Front Loader 24 HT oven, it might be nice to have a backup, just in case.

 

Here's a rough schematic of what I'm thinking:

1639786449_Basicschematic.thumb.jpg.3c401d10209efea35ac68d37377b29c7.jpg

 

Since doing this sketch, I've decided that the first green box (NC solenoid) is a bit overkill because the blue box (which should be labeled PID controlled solenoid) will also be a NC valve wired in parallel with the blower so that if the blower stops, so does the gas flow. 

 

On point that has been raised on one of the other forums was that a PID controller might not be the best thing, because during operation, the solenoid is either fully open to the low flow or high flow branches and not the best for the varying output from the PID controller (sorry if my electrical vocabulary is inaccurate) and one party suggested using a simple thermostat instead of PID controller.  


Again, thanks for the thoughts.

 

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As noted on other fora, I still see a couple of issues with your design. Ideally for PID burner control you want both the air and gas to modulate together to keep the correct mixture proportion.   You also want the gas air mixture to range between a minimum and maximum, but not shut off.  The former can be accomplished in a couple of different ways.  You can source a ECM fan from a condensing furnace or boiler and wire it to the output of your controller.  You can get a modulating air valve for the air supply. You can use a zero pressure regulator to meter the gas proportionately with the air.  I did the last on my glass furnace gas train build.

If your 3 way valve is modulating, you should still use a NC main gas safety valve.  The modulating valve most likely will not be rated for shut off service.  If not modulating ,  I would substitute a 2 way valve in the high fire side and run the low manually to act as a pilot.  Note if modulating you don't really need a high/low seperation.

Perhaps you should consider just modulating the mixture?

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Thanks for the ideas, Latticino.  From all the conversations I've had over the past year or so, both online and in person, modulating the air-flow, while great in theory, doesn't seem to be worth the hassle. 

Also, my brain finally decided to engage after a number of folks suggested that instead of having a 3-way solenoid choosing between HIGH and LOW flow lines, I'm going to have a LOW (or Idle) flow line that's always open and use a 2-way solenoid (MUCH less expensive, btw) to open/close a second, HIGH flow line that will merely allow more propane to be added to the mix.  Here's the new schematic:1806234694_Basicschematic2.thumb.jpg.4bdb410eea76f7c0c32dae41ed36eeb0.jpg

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Hello all.  I hope the new year finds everyone healthy and safe.

 

After quite a bit of reading, research, and numerous drafts, here's my final wiring diagram:Wiringschem1.jpg.01a7c1cbac473f99f6c6a74362bbb043.jpg

 

I'm now waiting for all the components to arrive and hopefully will get this plumbed in and fired up next week.

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That looks very good to me, a nice blue print to deserve:D. Searching the schema for hose brake protection and flame arrestor (despite of the discussion if there are necessary for Propene or not, -in the EU they are still common practice and I use them on my gassers and furnaces<_<) Good luck and Cheers, Hans    

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Hello Hans.  Thanks.  While I can't see how either of those would be a bad idea, I don't think they are necessary for my application.  (Well, at least in regards to the break protection, as I strap my 100# tank to the shop wall to prevent accidental tipping or moving.)

And I think the flame arrestor is taken care of through the NC valves.  As long as the blower is operational, (keeping the gas supply valve open) there should be no risk for a backflash to occur?  (I am thinking about trying to figure out how to wire the NC valves in such a way that if the blower fan stops working for some other reason than loss of power, they close.  But so far, everyone I've talked to has said this would involve adding some sort of flow meter to the blower output, and that will have to be a future project for me.)

 

 

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I think it's simpler than that billy.  All you need is an arm in the air flow with a paddle on it that will move with even light air flow.  That goes to a switch or relay.  If the air is flowing it moves the paddle and closes the circuit.  If there is no air flow the paddle will drop and open the circuit.  It just has to be sensitive (light) enough at the low end.  You don't care exactly how much air is flowing, just that it is flowing - a flow indicator rather than a flow meter.

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57 minutes ago, Buzzkill said:

All you need is an arm in the air flow with a paddle on it that will move with even light air flow

Now that's an intriguing thought...  Thanks Buzzkill!  I'll start looking into it.

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Of course you will need a way to start the blower with that circuit open.  You can put in a momentary switch to bypass it on start up or manually hold the switch that your flow indicator will operate when you start the blower, but it should be fairly easy to do.

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If the paddle switch is wired only to the main NC valve, will this be an issue?  The SPST main power switch starts the blower, so as long as that's working,  the gas solenoid should open, no?

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I've read about a number of forges that use PID control.  Why don't you use a Naturally Aspirated (venturi) burner?  With forced air, the air will be cooling off the forge when the gas is off creating more temperature fluctuation, and introducing oxygen to the forge - increasing scaling.  With NA burner, it just shuts off and on - no air blowing in oxidizing the metal.  I've looked into this for my forge, but haven't got around to it.  Mine is a NARB and I can turn it down to a steady 1500F or less, so I haven't had much motivation to do this project.

DanR

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11 hours ago, billyO said:

If the paddle switch is wired only to the main NC valve, will this be an issue?  The SPST main power switch starts the blower, so as long as that's working,  the gas solenoid should open, no?

Sure.  you probably just wouldn't want the blower on full blast at startup, which is what would tend to happen with a simple on/off PID setup.   It might be ok though. Certainly once you get the temperature up past the point of the FA ignition then both the air and the gas could be cut simultaneously.  I'd probably want to leave the blower running and have a NC solenoid controlling the air flow for safety reasons, but then my paddle idea might not work.  A 3 way valve could solve that problem though. Dan brings up some good points if the blower continues to push air into the forge without any fuel.  It would be desirable when you shut down for the day, but maybe not while trying to maintain a specific temperature and forge atmosphere simultaneously.

A NARB setup would certainly be simpler/safer from that point of view.  Any time the gas is flowing through the jet orifice you have air induction too so there's only one thing to control.  However, if it was set up to be all on or all off you'd potentially get backfiring every time the gas shut off.  That type of system would probably be better off set up with an "always on" idle circuit with the main gas supply controlled by the PID using a NC solenoid for the gas line.

I've only used a PID setup for a DIY heat treat oven, but the cycle times can be very short as you approach the desired temperature, so I don't think I'd want a NARB cycling completely off and on repeatedly with those durations.

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11 hours ago, D.Rotblatt said:

Why don't you use a Naturally Aspirated (venturi) burner?  With forced air, the air will be cooling off the forge when the gas is off creating more temperature fluctuation, and introducing oxygen to the forge - increasing scaling.  

Hi Dan.  Thanks for the thoughts.  You do realize you're opening a can of worms when bringing up the venturi/ribbon burner question, right?:huh::)  But I won't go there....

Yes, I think you're right about having cold air entering the forge without fuel, which is why I'm having in a Low flow (or idle, if you will) line that will allow a minimum amount of fuel to keep the flame going and the PID will add more fuel through the Hi flow line to increase the temp as needed.

 

1 hour ago, Buzzkill said:

Sure.  you probably just wouldn't want the blower on full blast at startup, which is what would tend to happen with a simple on/off PID setup.   It might be ok though.

I think it will be OK, because over the past number of years that I've been using my forge, I've pretty much left the air flow alone, unless when welding Damascus billets, then I cut the flow enough to create a reducing atmosphere. 

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