Can't believe I got this- (now what do I do with it?)

UPDATE: PID and Controller Refit

To keep the update on what the OP could accomplish on an updated DIY setup. Here is my completed unit all wired up. (finally!!!). It incorporates a few of the Original parts from the old 70's controller also. The Wood on the face came from a felled tree on the farm. I was tired of milling ALu or plastic stuff for bezels. I wanted a hunk of wood on it.

Will be running thru some basic ramp and soak time to cure the Mizzou side panels we cast and then into Steel HT tests.

The software for the unit is free from Automation Direct. It's simple and does the job. Thus far I like it!
.... And I'm a real newb here but the Son seems to really like working in this Venue and it's been a blast! Cannot wait to heat and quench (after reading the archives here too).

furnace0.jpg FURNACE3.JPG FurnAce1.JPG




countryguy said:
IT does not look all that big (as a unit) to me. My concern is the small work/heating chamber. I cannot tell the size but looks pretty small. I wonder if this is a High Temp item with all that insulating space? Anyway- To add some items to this thread related to making new encasedelements which seems to be a muffle furnace thing?

To take this and convert it into something more moden here are a few items from my own conversion going on right now:

Info on the overall build to the oven in the post above is finally to final phase.

The Soho PID temperature controller is in.($80 to 130) The TC (Thermocouple) probe is in($30-45). The TC wire obtained. ($35) The USB to 485 comms adapter ($13) is installed. Each are shown in the Circle's in the image below of the bench test setup. The new panels we poured are installed and connected. The way we hooked them up is shown in the hand drawn note (pic) below. I set it up for 24Amps. We have heated the new panels up to 500F on the bake cycle but need to get to 1200F which I could not do w/o this setup from Automation Direct. I must say I really like these guys! Great CS. No hassle on returns. Great docs and instructions (to me anyway).


To make this all work; I have 2 sets of 3A NO contacts on the SOLO PID controller. I'll use 1 set to trigger a 110VAc coil large contactor which will place the 240VAC & 24Amp draw on the coils. I know a lot of folks on the ebay PID sales use the Solid State's? I get that a mechanical & contacts will burn but is that all?

A few pics :
View attachment 55237 View attachment 55238 View attachment 55239
Click to expand...
 
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The big advantage of using SSRs for HT applications is the ability to run short output cycle times. When I did my initial testing on my first HT oven, a 2-second cycle time gave noticeably tighter temperature control than a 5-second cycle at tempering temperatures. At 30-second cycle, there was noticeable oscillation around the setpoint. I think the reason no improvement was measurable below 2seconds was probably down to the thermocouple and data logger I had available, but there was enough difference to persuade me that it was worth going for an AD Solo, or Omega equivalent, controller, instead of a more user-friendly kiln controller on subsequent builds. The available kiln controllers only allowed a 30-second cycle at that time and I felt that anything over 10 seconds would compromise performance.

It is only an issue at tempering temperatures, so there's nothing wrong with a cycle time of 10 seconds for Austenitizing, if you have some other means of tempering.
 
thanks Tim. The PID solo auto tune ran for almost 2 hours. The oven was 145F from an empty soak yesterday of 50 mins at 750. These are so neat to play with.
I am trying to cure the Mizzou cast side elements while getting used to the whole PID and settings goo. The auto tune seemed to work and hold me w/i 2 degrees. The ripple to temp was close to spot on and It held temp for the whole hour but I do see the point about the cycle times. Wow that contactor can get chatty.

So - I have the SSRs in my Amazon cart. I think it was fun to see it go. Time to make it right. Thanks for the help and encouragement.
 
A couple of things I'd suggest.

Run the oven for a maximum temperature cycle before your final autotune run. It gets a dark Oxide layer on the thermocouple and changes its response to radiated heat from the elements.

It's worth tuning at all 4 of the available temperature increments with the Solo. I think I used 100, 300, 750 & 1100 degC for mine. Start at the lowest and work up. It's one of the best autotunes I've come across and is both quick and effective.

If using a controller that can only store one set of PID terms, always tune at the lower end of your working range, especially if it will be used for tempering. Tuning hot tends to give overshoot at low temperatures.
 
Tim, THANK YOU for the notes And suggestions. Exactly what I need! So much to learn yet. I ran in ramp/soak today to 1250F and the data recorder from AD (freeware) crashed again. No real data to examine yet. I will follow your suggestions and rerun soon..


All; An added question if I may. The Son wants me to sell this muffle furnace and buy the evenheat KF 27". Q: How would you compare a muffle box to an evenheat furnace ? Both PID programmable. I just do not know why or which way to go? The experience and feature / benefit of each I simply do not know yet.

The son wants to do heat treat, anneal, temper type workloads. A few at a time. Maybe a longer sword type down the road. Oh what fun you guys have on this site! Thanks for all the help.
CG aka Jeff
 
Hey Guys-
I guess I started this thread- it sure escalated over my head in no time- due to my lack of knowledge and inexperience with these. I have been swamped with my job, and haven't had any time for knives, much less for the oven project. I appreciate the input from Country Guy and your project, and all the rest of you. The oven I got is still under tarps on the same truck I hauled it home on. But, I am very intrigued, and when I can get some time for what I want to be doing, instead of what I have to be doing, I will research, ask questions, and return to this thread, Lord willing. Thanks, too for the prices of some of those components-and I am anxious to see what some have to say about the muffled vs open elements.
Thx again,
Bill
 
I'm guessing that when you refer to muffled elements, you mean that they are embedded in the walls so that they are not visible from the chamber?

I had a small lab furnace a while back, made by Carbolite in the UK. Like yours, it had a large outer casing for its size, with a big air gap between the casing and the workings. There was a door safety switch as well, so I think it was basically designed to be as safe as anything that gets to 1100 degC (2012 degF) can possibly get: no way to touch the elements, enclosure surface temperature low enough to be safely touched, etc.

It was not working when I got it, so I changed the PID controller and thermocouple. The controller was not ramp/soak programmable and I could not get the temperature as stable as I would have liked. I changed the contactor for an SSR to see if shorter cycle times would help, but there was no real difference. I tried a ramp/soak controller temporarily and was able to get the temperature a bit more stable. It was fine while ramping and held soak temperature well, but still tended to go into oscillation if it was disturbed. Opening and closing the door would still cause enough of a disturbance to put it into oscillation. the oscillation was not particularly severe: perhaps plus/minus 10 degC from setpoint when at 825 deg C (about 1495-1535 degF on a setpoint of 1515 degF) and it did settle down again within 3 or 4 minutes.

I reverted to the simpler PID controller, because the ramp/soak one was expensive at the time.

Realistically, that might be about as good as temperature control got, back when many of the steels we still use were developed. It was certainly a lot better than no HT oven. However, I play with temperature and process control systems for a living and tend to get a little obsessive about such things, so I moved the Carbolite on and built the first of my scratch-built ovens with exposed elements.

Bottom line is that I think the muffled elements introduce a lag into the control which is difficult to overcome just by tuning the PID terms, but that they are probably not a deal-breaker.
 
Bill. I am here to help ya! When you can. Take some pics for me? Of the back where to elements come out. And if possible do you have am ohm meter? To check the elements is a very simply ohms check Check your PM As think I can Help ya out if/when this makes it up the list. A good winter project maybe.

Mr Gunn. Thanks. So muffle or lab furnace seem to be the same thing in many places. I like your reasoning on the muffle over open coil. Thanks for all the help.

Time to dig into all ya'lls other great writings in the other forums!

Again, Bill. Will PM you on my support and assistance.
Jeff.
 
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