Heat Treat Oven...

[Ray C]

Hi All,

I'm going to start a heat treating oven project over the next few weeks so, I'll post the developments here.

The goal is to have something that can handle up to 2200F with soak times not much longer than 2-3 hours and inside cavity dimensions of roughly 16"W x 24"D x 18"H.

One of the suppliers I called was from a place that specializes in foundry equpment and the guy was a ceramics engineer. Much to my surprise, I don't need expensive insulating bricks but will use a blanket material instead. The fellow gave me verbal instructions on what to make and he said he'd answer any questions as I go. With the blanket material, he estimates the cavity can get to full temperature in 15-20 minutes instead of 45-90 (although a gradual warming of the part is desirable in many cases).

Anyhow, just about all the parts are ordered and so far, it's only running about $350. The remaining stuff (8 ga wire, electrical plug, a little bit of angle iron etc) will probably be another 50 or so. I happen to have several sheets of 20ga stainless steel laying around to cover the outside but, cement board could be used instead.


I'll be the guinea pig and see if this thing works... Given the holidays and all, this will drag on for a few weeks but, stay tuned.

Ray

 

[Bill Gruby]

This might be of some help along the way. I built one like this for a friend.

http://www.budgetcastingsupply.com/papers/HT-FURNACE.pdf

"Billy G" :whistle:

 

[pdentrem]

The ceramic blanket material is fantastic stuff.

We use the following Durablanket for insulation in our continuous caster, belt feed annealer, induction furnace and gas furnace application.

http://www.fiberfrax.com/

 

[Ray C]

Bill,

Yes, the setup I'm after is about the same dims as the one you showed. Matter of fact, while reading-up on this, I do believe I recently came across that link. Did you ever use the one you made and if so, how's it working out?


pdentrum,

From the description the fellow gave me, it sounds a lot like the link you pointed me to. With that blanket material, I'm hoping to have a lighter setup and with the minimum quantity (at 65 bucks) the fellow claims I can probably build about 5 ovens of the desired size even if I double or triple-up the material. I'm guessing it's a little more fragile though... Curious to see how it all turns out.

 

[pdentrem]

How would you support the blanket? I agree that the thermal mass is less than regular fire brick and will allow to get to set temp much quicker.

We do have a heat treatment oven of about the size you are planning, same one sold by Brownells. I installed a clock timer to start it up a couple hrs prior to our arriving in the morning other wise we have to wait a good long time to get to temps. This is one reason I am currently building a new one. It starts with a ceramic tube that has the heater wire wrapped around the exterior, the interior is 7" wide by 5" high and 40" deep. It gets to temp in about an hour, mind that it is 3 phase 220 volt 25 amp draw!

As for the insulation I use a straight edge and a razor knife to cut the material. A couple passes tends to work the best if the knife is a bit dull. The material will tear just like fiberglass insulation but has a stiffer and tighter weave, if one can call it woven.
With two layers one can see the glow of 1750 F but the heat is cut down a far bit.

For example on the top surface of the con caster, there are 5 layers under the lid which is 24" square 1/4" steel. With the Tempurature set at 2200F the steel lid is hot to the touch, likely too hot to handle but otherwise there is no indication of the internal temps.
At the cast die mould outlet, we use it as a packing around the die to contain the heat and the cover gas that is used to protect the carbon crucible, heater elements and the die from Oxygen in the air. The packing as about 3" in depth.

In time the heat does affect the Durablanket, it tends to stiffen and will crumble if handled roughly. In your case likely it will last a long time.

BTW wear a particle mask when cutting and handling the insulation. The fibers are floaters and irritate we air breathers!
Pierre

 

[Ray C]

pdentrem,

Here's what I'm thinking...

I'm planning to make a simple cage and wrap the insulation around it then, cover the exposed parts of the cage with an inner lining that's stitched with stainless steel wire. I'll probably make the cage out of stainless bar stock and 1/2" strips that I have around. That whole thing will then be encased in a simple angle iron frame that I'll cover with some 20ga stainless sheetmetal that is also laying around. I also ordered some type of fire block that sits at the bottom and is just laid in place. Need to figure-out how to suspend the kanthal wire around the sides... Need to dig-up some kind of ceramic insulator or possibly use some tungsten electrodes. -Plenty of those stumps around from the TIG welder. Tungsten laughs at temps up to 6000F.

I'm still thinking it through and in no hurry.

Ray

 

[Bill Gruby]

Yes Ray, my friend is a knife-maker. It is used every week. Next time I am there I will get pix.

"Billy G" )

 

[dennis98277]

i look forward to this because this is going to be one of my projects when we move in a couple of months.

 

[pdentrem]

I like that idea of placing your frame in a sandwich of insulation.

As for the support for the heaters, I can think of a couple ways. Use pieces of fire brick or modules which is softer than fire brick. Cut a slab and drill a hole for the wire to past through and wiring it to the sides of the oven. Maybe a dum idea, find some old knob and tube hardware?
Pierre

 

[Ray C]

Well then, stay tuned and don't touch that dial. You can learn from my mistakes -but with all the help here, I got a feeling it will turn out well....

One part of me was set to do this with the bricks but the blanket material sounded attractive because of the light weight, faster warming times and a heck of a lot less $$$. Anyhow, the sudden change of ideas has got me noodling a bit. On the plus side, the electronics are all the same and I've got a lot of drops SS laying around and if I can find it, a partial spool of SS mig wire to do the stitching.

BTW. I probably can't start working on this for at least a week when things start showing up and then the Holidays will be upon us... Also, I have a big brass lathe job to finish by 2nd week in Jan and another SS ornamental piece to do by Feb. There's going to be at least 40 hours in each one and I'll try to squeeze this furnace thing in between it all...

i look forward to this because this is going to be one of my projects when we move in a couple of months.