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Heat Treat Furnace Build

ezduzit

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#33
Almost like a professional job. :) Seriously, I'm green with envy; would love to have this.
 

jbolt

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#36
A little more progress now that the bathroom remodel is done.

I did the enclosure cutouts today on the CNC mill. Always fun to do setups on enclosures. This enclosure is small enough I could get it rigid enough to cut full depth with a 1/8" carbide end mill.

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I used some of the left over ceramic tile from the bath remodel to cover the back of the heat box where the elements terminate. The area around the tiled area will get a 1" layer of ceramic blanket.

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jbolt

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#37
Here is the back panel construction and installation.

Back panel cutout on the CNC mill.

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The only brake I have access to does not have any dies narrow enough to do the bend so I made up a redneck bender using angle iron and some door hinges. I used a crescent wrench has a handle. Worked perfect!

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One layer of 1" ceramic blanket, back panel and the 1" angle iron retaining frame. The frame locks in with set screws in the corners.

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To terminate and secure the ends of the heating elements I modified some 5/16" stainless steel bolts. The element passes through the middle of the bolt and is captured by the grooves. I put kinks in the pig tails of the element wire to create positive contact inside the hole to avoid potential arching. I don't know if that would have been an issue but the instructions for the heating elements required that the coils be stretched to create a gap between the coils to prevent arcing so I figured this was a good idea.

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Heating elements and thermocouple installed.

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Here is my first wiring configuration. I originally had the heating element setup with a SSR on each end of the element so it would be fully disconnected when off. I had a problem with the Auber PID controller. It would not give a consistent reading from the thermocouple and after a day and a half of trouble shooting I determined the unit was bad.

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I called Auber on the PID issue and they agreed it was faulty and sent me a return shipping label. That PID has been sent back for replacement. I posted about the PID issue in the electrical forum looking for troubleshooting help and during those conversations another forum member, who has been an incredible help, suggested I use a single SSR and a double pole contactor. Apparently SSRs still leak some voltage when off. I also liked the idea of being able to switch the contactor to turn off the elements and still keep the PID under power for setups, troubleshooting etc. I also decided to order another PID from automation Direct. It has the ability to be programmed from a PC.

Here is the revised electrical with a contactor, single SSR and a Solo SL4848-VR PID controller. The contactor is the type use in air conditioners. This one is 40 amp with a 240vac coil. The whole system is run on 3-wire 240vac. The PID provides up to 14vdc to trigger the SSR.

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Here is a quick shot of the back panel with the elements terminated and hooked up. Last thing to make is a protective cage for the termination area.

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Today I powered it up and setup the PID. I did the initial setup with the elements disconnected and with a 75w light buld hooked up to the SSR. The PID manual is not very intuitive so it took some trial and error to figure out the settings. I'm not the sharpest tool in the shed when it comes to things like this but after pushing buttons for a while it starts to make more sense.

After I was comfortable that the PID was operating correctly I hooked up the heating elements. The PID has 4 modes, PID, Manual, On/Off and Ramp/Soak. In PID mode you can auto tune the system to set the PID parameters. Currently the oven is on and set at 200 degs for the first part of the break in. The auto tune took about 10 minutes but once done the temp is holding rock steady. I will keep it at 200 overnight to burn off any excess moisture that may still be in the brick and then do the element break in and install the door gasket tomorrow.

Up and running!

The toggle switch is for the contactor, the green light is on when the contacor is energized. The amber light shows when the SSR is on and the elements are heating. The two red indicators are lighted buzzers for Hi/Low alarms.

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extropic

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#38
Just read this thread.

Nice work jbolt. Looking great.

Wondering if you're going to post a wiring diagram? It would be a help to the electronically challenged, like me.

I'm subscribing so I won't miss the Christening.
 

Linghunt

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#39
Very nice. I might have to try something like that for a long 6 foot furnace. Low on my project list with so many things to do.
 

jbolt

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#42
I installed the door gasket and did the burn in today.

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The oven heats up very quickly. Took about 20 minutes to go from 200 to 1200. It could go faster but the controller starts pulsing before the set temp to not over shoot. I'm really pleased how well it works and how stable the temps are. Once up to temp the temp never varies more than a degree.

I did the burn-in outside under shade. The electrical enclosure started to get warm at the end of the 1200 deg period so I took the side panel off. I was concerned the controller might over heat. Factory spec is 122 deg F operating temp. I'm going to add a stand-off between the enclosure and the frame to give it a little more air space and since I am only using one SSR I will use the other SSR cutout for a case fan.

For those interested in the outside temps I recorded them at each setting at the end of each soak period. I took measurements at several locations. The door has the least amount of insulation with only 3 layers of 1 mm ceramic paper between the brick and frame. The highest temps were at the back of the oven at the ceramic tile back in the area around the upper heating element terminations.

Ambient Temp, deg F 87, 90, 93, 93, 93, 92,
Oven Temp, deg F 1200 , 1300, 1400, 1500, 1600, 1700,
Soak Time, Hrs 2, 1, 1, 1, 1, 1,
Temp Readings
Top, 159, 185, 193, 198, 213, 222,
Upper right front corner of frame, 164, 195, 205, 215, 236, 244,
Face of door, 164, 184, 192, 199, 212, 216,
At upper element termination bolt, 229, 248, 271, 262, 312, 321,
At tile between upper element terminations, 238, 259, 301, 313, 336, 406,
At PID case, (rated to 122 F) 114, 110, 111, 105, 106, 105,
 
Last edited:

Linghunt

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#43
Add a vent for the fan, think about a filter for the fan and suck in air . You don't want the enclosure to be a vacuum cleaner so pressure inside should be higher than outside. You could make some little pagoda type top vent. maybe a little screen or lip so bolts don't fall in, from future clutter.

Example picture.
http://www.newark.com/hoffman-enclosures/p2tp88/pagoda-top-800-x-800mm-grey/dp/79Y3261

Standoff as you said is great idea.

Use second measurement tool to profile different spots inside for temperature gradients.
 

Linghunt

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#47
Not sure how I could do that.
Small gauged T / C wire thru the door seal , just for test. Strip the insulation off and separate via air gap. make T/C on end by twisting them together. ( it actually works that way, but has hillbilly look to it. )

You could do a few and then swap meter from pair to pair. perhaps one to a piece of scrape metal.

Take some measurements, get a feel for how the Oven heats parts. then pull all it off. and call it done. Don't go crazy on it.

Going crazy example:

I rented a datalogger deal with like 20 channels and used this to profile baffling designs and adjustments in a forced air annealing oven. If you want to get fancier and think of a Ballast on the T/C.

Not saying to do this, but just Food for thought.

Heating in done by 3 methods: Convection, Radiation, Conduction.

Convection for this oven is main heat transfer method.

To mimic the actual part temperature You add a ballast part to the T/C. This will help display the actual part temperature vs air temperature inside the oven at one location.

Think of the Ballast part as a small piece of metal (same as what you heat treating ) with a hole in it slid over T/C. This part will get scaling etc and mess up radiation heating and just be a mess.

The Ballast concept is useful for heating in a vacuum chamber where all you got is radiation heat transfer method. Different materials heat differently , so the Ballast is same as part. Dig into black body radiation if you want more.

I left out a lot.

I stuck a big chunk of SS in my little oven. It's like 4"x4"x2". ( thermal mass that will not change in temperature much form Oven heaters cycling on and off). Setpoint at 900 and 990 F for the most part.

I sit my parts on top of it in a SS basket I made. I used the thick Foil that you seal the parts in with some paper to prevent scaling.

If I wanted a better system, I would buy an isolated T/C install it in that chunk of SS with a setscrew and hole. But when I do larger parts I take it out so then I would have to mess with T/C location. Takes you back to KISS method, and don't go crazy.
 

Groundhog

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#48
I hope this thread doesn't go away. I really want to build an oven but it will be awhile. Although I haven't read this through from end to end yet there seems to be a lot of useful info here. Looks like an exact copy might be an easy (for me) way to go (especially if you keep tweaking it).
I know pictures and write-ups along the way are a real pain. Thanks so much for sharing.
 

dulltool17

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#49
I gotta build one! I see you bought from Automation Direct....it's a pleasure working with these folks.
Actually, we build ovens where I work, but he chances of acquiring one "on the cheap" are nil.
 

Linghunt

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#50
I gotta build one! I see you bought from Automation Direct....it's a pleasure working with these folks.
Actually, we build ovens where I work, but the chances of acquiring one "on the cheap" are nil.
What company and size of Ovens? Do they sell scratch and dents maybe? Looking for a long 6 footer x 5" x 5" for treating long rods. I'm limited to 37 inches now.
 

dulltool17

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#51
Thermo Fisher SCIENTIFIC. I'm the Manufacturing Engineer for Chiller Production, but spent a bit of time this afternoon with the MFE for the Furnace line. They build a long one with a chamber I'd estimate at 6" diameter x 50" long. It has three separate elements. I have no idea what the specs are or pricing. I was told that the smallest, with about a 5 x 5 x 5 interior goes for a grand. I've not seen Scratch & Dent items. YOu might find one on E-bay.

If you're going for 6' long, maybe the JBolt route would be viable. Definitely needs multiple elements, probably with independent control. Not an undertaking for the faint of heart...
 

Linghunt

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#52
Thermo Fisher SCIENTIFIC. I'm the Manufacturing Engineer for Chiller Production, but spent a bit of time this afternoon with the MFE for the Furnace line. They build a long one with a chamber I'd estimate at 6" diameter x 50" long. It has three separate elements. I have no idea what the specs are or pricing. I was told that the smallest, with about a 5 x 5 x 5 interior goes for a grand. I've not seen Scratch & Dent items. You might find one on E-bay.

If you're going for 6' long, maybe the JBolt route would be viable. Definitely needs multiple elements, probably with independent control. Not an undertaking for the faint of heart...
Thanks for the info. The JBolt direction is probably the most economical method. I keep an eye out on used equipment site when I remember. That is how I got my current tube furnace that is 37" length capacity x 3 inch diameter. I recall getting it for about $1K without controls. This one has 3 thermocouples, but only need to control off of one from measurements and testing. I had the controls already from my attempt to building one from an old tool box inside a salvaged Hoffman cabinet.

Multi-section ovens and controls can be tricky. I had project with an inline continuous feed 3 section furnace used to heat large glass circles around 24 inch diameter that were pressed to a spherical curves for computer monitors. This was pre autotune days. I sure learned a lot about PID loops on that job. I bought and studied a book just on PID's. The biggest fix I did was changing out the K thermocouple wiring. I discovered they used multiple types of wire and also aluminum terminal box in various locations. It was a great learning project, but a nightmare of a job. I was total cherry back then too that didn't help.

Today's controls are so much better. I got stuck with a PID tuning application that other engineers gave up on. I messed with it for a while and didn't get anywhere. I figured I needed to try anything as long with it was different. My fix was to make the bandwidth ranges of the PID variables vs constants and I changed those at diffferent stages of the ramp and steady state. It worked and surprised them that I fixed it.
 

jbolt

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#53
I did a few more tweaks to help with the electronics enclosure cooling.

I added 1" standoffs between the enclosure and the enclosure mounting straps.

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I also added a 60mm 220vac fan to the bottom of the enclosure. A 80mm fan filter cover covers the 70mm x 50mm cutout for the SSR I did not use. The fan comes on with the contactor.
I got the fan from mouser electronics. p/n OA60AP-22-1WB

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jbolt

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#54
Attached is an initial setup and quick start guide for the SOLO SL4848-VR controller. I didn't find the manual very intuitive for someone not familiar with PID controllers so I'm passing along what took me a few sessions to figure out.
 

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Linghunt

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#55
Is the fan blowing out of the box or sucking air in?

My "general" picky thought process for cooling fans: Suck air into the enclosure, you now have a slight pressure gradient in the box, cracks or gaps from different holes or the door will have air flow out of these. Most of the air will go out the vent, so this is being real picky. Filter the fan so you don't suck "dirty" air into box. Heat rises, so fan on bottom, vent on top. Don't forget to change filter or blow it out on some schedule.

What you have here is more than good enough. My Oven has no filter , and the vent is on the side, I built with what I had. My box does collects dirt, I blow it out when I remember

Aside: I got an extra cooling fan on my phase perfect converter and no filter. I didn't have one to fit the fan I had from salvage and just went with it. Manufacturer has a fan as well hooked to a thermal switch, and no filter.
 

jbolt

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#56
The fan draws air into the enclosure.

Sent from my SM-G955U using Tapatalk
 

Linghunt

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#59
Is it a book you'd recommend?
Or do you have other resources you could point to?
Thanks,
-brino
If you have a technical background and understand Laplace transforms etc, then it's good. Without the a high level of mathematics it will read Greek. The Math is not hard and illustrated well, but without having seen them before is the point.

Here are some samples of the authors writing style. There are 4 old controller referenced in the book, That section is interesting but junk. Book is 1988.
















Found this one , (my 1st EE boss gave it to me when he retired) This is a small handbook from 1980. Still good today since math and physics doesn't change. I took one internal page picture. This type stuff is hard to read.







I think I have some other material not so Math based. Let me know how this reads for you.
 

brino

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#60
Thanks @Linghunt
Electromagnetics was my most difficult class.
PID looks interesting. I wish I knew more control systems theory.
-brino
 
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