Heat Treat Oven Project

P

Plas62

Well-Known Member
I picked up this older Paragon E14A on Craiglist for $100 from a nice fellow that use to make knives. I haven't hooked it up yet to test it, but he told me that the last time he used it several years ago that it worked and that the heating elements had been replaced not long before he stopped using it.

Paragon E14A
240 vac
13 amps
3120 Watts
Max Temp 2000 deg f
Chamber Width:13.00 IN
Chamber Depth: 13.50 IN
Chamber Height: 8.75 IN






I plan to clean it up, repaint, probably make heavier duty door hinges for it and add a PID controller with T/C.

I had found a link to Auber Instruments when I did a Google search and they had these recommendations for upgrading a kiln to pid a controller.

http://www.auberins.com/index.php?main_page=page&id=20

Does anyone have any other suggestions for a PID upgrade for my oven?

Since I will be mainly heat treating folder blades and springs. I was thinking about ordering some refractory bricks to take up some of the volume in the interior. My thinking is that it would reduce heat up time and possibly help to stabilize temperature. Does anyone else do this or is it not really necessary when using an oven that is over sized for the job?

The max temp on the oven is 2000 degree f. I will be heat treating stainless CPM154 and CPM154CM. From the HT data I found it looks like I need to be at 1900 to 1950 degrees on this material. Hopefully the oven will reach it's rated temp. Is it possible to replace the heating elements with a higher wattage to increase the max temp to 2350 degrees.

I will post updates to this thread as I make progress on this project.
 
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Paragon is a good oven. Don't replace the controls if it works. Don't fill the oven with refractory bricks,that will increase the time it takes to get to temp and stabilize and increase the time it takes to cool off to the temp you need to temper your springs.If it's working properly it will reach the 2000 degrees it is rated for.
 
Similar to Cal's comment, but for a different reason - consider carefully before changing manufacturer's specs. It will invalidate your UL listing and if - God forbid - your place ever burns down, it would present insurance and liability problems. I know - people build ovens from scratch too. Just sayin' that UL label is a valuable 'feature'. Don't throw it away lightly.

In particular, I'm thinking about your plans to raise max temperature. The Evenheat oven that goes to 2400 uses thicker fire brick. That may be more change than you want to undertake.

Rob!
 
As the guys have said, filling it with bricks will just increase the thermal mass and slow things down.

I can't make out the markings on the control knob from the photos, but assume they are power increments. These are unlikely to relate in any meaningful way to actual temperature. To get decent performance out of the steels you mention, you will need pretty good temperature control.

You will need to buy a suitable high-temperature type K thermocouple as the first step. Personally, I'd also buy a TM902C pyrometer from ebay first and see if it's possible to calibrate the dial for the temperatures you need. You can also see what temperature it will reach at full power. At around 5 bucks delivered, the TM902C is too cheap to be without in my opinion. You'll also need a miniature type K plug and suitable cable to connect the thermocouple to the TM902C.

If you cannot realistically calibrate the dial, but make the necessary temperature, going to PID control will be the next step.

The Auber SYL 2352P seems to be used successfully by a lot of folk on your side of the pond. It has Ramp/Soak capability which is very nice to have and Auber seem to provide good customer support.

Auber do not have a UK presence, so I use either the Omega CN7823 or AutomationDirect SL4848VR. These two seem to be the same controller with different branding. Both AutomationDirect and Omega have very good customer support.

http://www.omega.com/pptst/CN7800.html

http://www.automationdirect.com/adc...ers/1-z-16_DIN_Size_(SL4848_Series)/SL4848-VR

These are also ramp/soak controllers. One advantage they have over the Auber is the ability to hold up to 4 sets of PID terms at different autotune temperatures and automatically choose the one that was tuned closest to the setpoint.

This probably does not make much difference for most users. If you go with the Auber and will be using the same oven for Austenitizing and tempering, it is best do the autotune at the lowest tempering temperature you will ever use. When I did some testing, I found that tuning at Austenitizing temperature would tend to give overshoot at tempering temperatures that would be big enough to lose over a Rockwell point with O1. Tuning at tempering temperatures would tend to give a slightly slower final approach to temperature. The latter was not even noticeable unless the datalogger traces were compared directly.

I use a separate control box for my homebuilt HT ovens, and will eventually get around to building a tempering-only oven. If I tune the Omega for the lowest tempering temperature and the highest tempering temperature with the tempering-only oven, then tune for one degree above the highest tempering temperature and a realistic Austenitizing temperature on the Austenitizing oven, I can just unplug one, plug in the other and set the target temperature or ramp/soak profile, without having to change PID terms.
 
Thanks for the advise everyone. I'll will keep the oven at it's rated temp. I didn't think about the possible insurance liability.

I definitely want to upgrade it though to a PID control. The existing control is a voltage control only and there is no T/C.

Tim - I checked out the controller at Automation Direct that you recommended and it looks like a nice unit. Do you use the downloadable software for? It looks like you can configure the controller and possibly enter set points on your PC with the software

What SSR's and T/C did you buy to go with the SL4848VR?
 
A question for you - how often will you be using the ramp function of a PID controller? Auber has the cheaper PID for around $40 or so that does a good job, but does NOT have the ramp function. There are 25 amp SSR's for around $5/$6 or so. For a 220vac system you should use two of them to break BOTH hot legs of the circuit. The McMaster.com site has the TC with #8 wire that would work nice for $16 and their shipping is very reasonable. BUT, Auber has the extension wire and all for around $30 and shipping would be included with the PID. All parts considered, perhaps a tad less than $100 for the full PID setup on your oven. "IF" you do need the ramp function, then add the $40 to the package for the $80 PID.

You did good with that purchase.

Ken H>
 
I really don't know if I need the ramp function as I don't have any experience heat treating.

For those of you that heat treat do you use the ramp function? If so what are the advantages of ramping?
 
I use ramp when tempering blades that are straight out of cryo -just a few minutes to warm them gently. Probably not necessary, but I do. I also use it for annealing. (slow cool). Pretty much everything else is ramp full speed.
 
In working with carbon steel, there are a few heat treating formulas that use the ramp, and annealing carbon steels can use the ramp to slow cool. I'm not really aware of any stainless steels that do make use of ramp - other than perhaps someone's personal method of heat to xxºF and hold for y minutes, then heat up to xxxxºF and hold.

Goodl luck, Ken H>
 
Ramp is useful when the HT recipe calls for it, but also has a role to play when tempering. Using a slow ramp can dramatically redice temperature overshoot as a result of direct radiative heating.

When heating to a setpoint, the controller runs the elements at full power until the thermocouple temperature is close to the setpoint and then trims back the heating to slow the rate-of-approach and, ideally, reach setpoint without overshooting.

The temperature of the thermocouple "should" precisely match the temperature of the workpiece at all times, but this does not necessarily happen in the real world.

Often the workpiece is heated faster than the thermocouple because it has a large surface area exposed to the radiated heat from the elements. In this case, the workpiece will get hotter than the main structure of the oven during the full-power heating, then will cool to match the temperature of the oven when the power input is cut back by the controller.

The effect is not unlike the hood of a car reaching a much higher temperature than ambient on a sunny day.

I did some fairly geeky testing of my first ovens, in an attempt to get the control "good enough". I lost most of the data in a hard-drive failure, but posted screenshots of one of the tests, so that one is still around.

I logged the temperature of the control thermocouple, along with several other thermocouples of reducing diameters, to try to simulate the effect of the bevels. I was using what I had available and cannot claim a high standard of scientific rigour, but I was sufficiently convinced to buy ramp/soak controllers thereafter, even though I had access to basic controllers for free.



In this graph, the controller was set to 250 degC (482 degF), no ramp, and the oven was started from cold.

The peak temperature seen on my "simulated blade" thermocouples was 369 degC (696 degF). An overshoot of 119 degC (214 degF).



On the next run, the controller was set to ramp up (probably from 0 deg) to 250 degC over one hour.

The peak temperature seen on the simulated blade thermocouples was 269 degF An overshoot of 19 degC (34 degF)

In terms of Rockwell points on O1, the second, ramped, run would have lost a point vs the 250 degC setpoint. The first, unramped, run would have lost five.

As I said above, I was using what I had available and the control thermocouple was a 6mm (1/4") diameter Mineral Insulated type K with an insulated junction. Nobody is going to have a setup that is as bad as this one was at the time (it was greatly improved by a faster-responding control thermocouple shortly afterwards), but I am sure the effect will be there to some degree in almost every HT oven.

There are other ways to overcome the radiative heating, so ramp is not essential, but I am convinced it is worth having.
 
In that case ramp is surelly good. I usually don't put the blade in oven until temp as stabilized past that "peak".
 
Here it is painted, with High Heat semi- gloss and reassembled.





Best of all the wires get hot!!



So far, I've got about $150 in it with the paint and the stainless steel sheet metal screws, I bought to replace all the old screws with.

It will probably be a awhile before I can afford to purchase the parts for the PID control upgrade. I'll update this thread once I get the control upgrade installed.
 
I'm staying tuned on this one! I am in the same boat as you Plas... I picked up a gen 1 (it seems) paragon ht oven but mine has a bad control board. They want $300 for another one but I am thinking of going digital w/ the PID, so thanks for posting the link in the OP.

Let us know which PID you end up going with... I may go with the one recommended in the link you posted. I will update here and maybe we can share ideas and figure out how to wire everything up (wiring isn't my specialty lol). but i have already wired one PID for my cerakote oven, so I think I can do it again - auber has a great manual!
 
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