Heat Treat Furnace Build

[jbolt]

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.

Thanks Linghunt. I appreciate all your help!

 

[jbolt]

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



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,

 

[Linghunt]

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.

 

[jbolt]

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

Inside the oven or the electronics enclosure?

 

[Linghunt]

Inside the oven or the electronics enclosure?

Inside the oven.

 

[jbolt]

Not sure how I could do that.

 

[Linghunt]

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]

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]

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]

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.