Heat Treat Oven...

[Tony Wells]

CO2 is not an inert gas, and I don't believe it would be of any use in an atmosphere control furnace. Argon, sure. Helium, probably. Expensive....you bet. That's why I am leaning towards a vacuum furnace. Plus, you don't need any, or not as much gas at all, except for a flood when quench time comes. Plus, I believe I could gas nitride and possibly carburize as well.


No doubt it will be much more involved, but if your going to go first class..........

 

[pdentrem]

For gas atmosphere in the annealler, we use Nitrogen at a flow rate of +/- 70 cfm or cracked Ammonia at the same flow rate. Now this is a belt fed machine so the usage is more than what you would likely require for a some what closed furnace that you are building.
Pierre

 

[Tony Wells]

Pierre, what temperature do you that line furnace at? Don't you have to stay below a critical temp to avoid Nitrogen absorption?

 

[pdentrem]

Tony
Yes, temperature depends on what metal we are doing. As low as 250F for pure Au to as high as 1750F for Moly bonded to Cu. We also harden our tool steel after roughing, prior to Wire EDM and grinding to finish dimension. Mostly A2 for the tooling. When using pure Nitro you will get a bit of scale but that is removed during finishing. When cracked ammonia is used the steel has a silvery surface, problem there, is Hydrogen absorption. Cracked ammonia is 25% Nitrogen and 75% Hydrogen, but for what we use the tools for that has not been an issue. Naturally we burn off the Hydrogen as it leaves the muffle.
Pierre

 

[Ray C]

We're getting waaaarrrmmmerrrrr... Ok, just a couple more projects in the shop to clear-out and I'll soon start the heat-treating oven. Probably start on it next week.

And to really kicks things off, I just augmented my personal library with ASM's "Heat Treater's Guide: Practices and Procedures for Iron's and Steels". I've wanted that book for a while but couldn't bring myself to pulling the trigger on it. Had a weak moment and went for it. This is the definitive book on heat treating and as an aside, everything you ever wanted to know about chemical composition (and effects thereof) are covered.

Ray

 

[Ray C]

OK... Only 4 months and 1 week later, I got a start on this. It's going pretty quick so far. I decided to make a frame out of 3/8" diameter stainless rods and will line it with two layers of the "inswool". I'll hold the inswool in place with stainless steel MIG wire. Once that's done, I'll build an angle iron frame that will be attached to the corner protrusions and later on, I'll encase it in some appropriate covering -possibly stainless steel or concrete board. I'll do a test before encasing it to see how hot it feels. I still need to find some sort of ceramic posts to suspend the kanthal wire. I was thinking of using some ceramic TIG cups and come-up with some creative way of attaching them to the frame.

Only a little more welding to do. I'm going to put several more cross bars on the bottom and will weld some extra support legs as I expect it might sag a little.

It's been a fun project so far. Did all this in a few hours with a lot of screwing around in-between.

Here are some pics... There's not much more to be said as there's little to the imagination.

EDIT: BTW, the cavity dimensions will be 12x12x24 inches. The frame rods are all 15" long (centered at 13") and the four long corner rods are 26" long. Each corner protrusion is sticking-out 1". The inswool is approximately 7/8" wide uncompressed. The roll of inswool is 24" wide -and I'm not sure how long it is but, appears to be enough to make two units this size.

Ray

 

[pdentrem]

See your roll of wool. Identical to what we use. I don't know how many feet per roll but there is a fair length in the rolls we get from the place linked in my earlier post.

For the wire supports, if no success finding the softer insulating modules or knob and tube insulators, maybe make some from Fire able Modeling clay that you can get at art supply stores?

As for an aside. There is also a thinner product like the wool, that is more of a thick paper idea. It is 1/8" uncompressed and is a lot more forgiving when handled. I used it to partly insulate the die cooler blocks that are attached to the die mold. Hard to explain but instead of having full contact I place a piece of graphite paper on part of the surface and the rest covered with the insulate paper. I vary the amount of the two used to change the amount of cooling the blocks provide to the die.
Pierre

 

[Ray C]

Thanks, Pierre. I'll keep that up my sleeve just in case.

I'll say this with certainty... I'll wear a space suit when it comes time to wrap that insulation. Just pulling it out of the box had me itching and scratching despite not handling it directly. Nasty stuff.

I'm really wondering how hot it will get at the exterior with two layers. Trying to decide what the outer enclosure material should be. Any thoughts?


Ray

See your roll of wool. Identical to what we use. I don't know how many feet per roll but there is a fair length in the rolls we get from the place linked in my earlier post.

For the wire supports, if no success finding the softer insulating modules or knob and tube insulators, maybe make some from Fire able Modeling clay that you can get at art supply stores?

As for an aside. There is also a thinner product like the wool, that is more of a thick paper idea. It is 1/8" uncompressed and is a lot more forgiving when handled. I used it to partly insulate the die cooler blocks that are attached to the die mold. Hard to explain but instead of having full contact I place a piece of graphite paper on part of the surface and the rest covered with the insulate paper. I vary the amount of the two used to change the amount of cooling the blocks provide to the die.
Pierre

 

[pdentrem]

Yes it is itchy stuff, I do not notice too much but some co workers run and hide when I have to work with it. I do not remove it from the box. I just pull it out like shrink wrap and lay it flat to cut it. It reduces the fibers flying around.

Interesting question on the use of two layers. On the box that I have nearly finished building for the tool maker, I had two layers, 2" thick, as a temporary plug at the one end of the ceramic tube. Once the tube was up to over 1700F, I was curious on the amount of heat escaping through the wool. I naturally took a look, I could see the glow through the wool and heat as well. I should of measured it, I do have the equipment to do so but did not. It was not super hot but a third layer might be called for. On the con caster the front has approx 3 inches of wool depth and you can not see nor feel the +2200F on the other side.

As for the cover for the outside of the box, I would use a non rusting grade of stainless steel. What I see happening on our equipment is mild steel will rust on the inside surface as it collects the water being pushed away from the heat, and it builds a nasty looking flaky rust sheet that falls down behind it and this stuff breaks down and works it way into and through the wool over time. I would not want the rust flakes to get into the electrical and cause issues. Have you a sheet of Inconel 600/601 laying around that you could use? Not likely pretty pricy stuff!
Pierre

- - - Updated - - -

Just to add a thought, I would for sure have 3 layers on the top surface. Heat at the top will naturally be higher than on the sides.

What are you doing for the floor?
Pierre

 

[Ray C]

Pierre,

Oh, dawg gawn it! I had a whole bunch of that inconel laying around and I threw it out because it was taking-up too much space... :jester: Fortunately though, I do have a good supply of some 20 ga SS sheet.

Thanks for the insights on layers of insulation and external temperatures.

The base/floor will be two blocks of a fire brick material whose combined dimensions are 11 x 23". -Not sure what it's called but was recommended to me by the fellow who suggested using inswool. It's a white/gray color about 1" thick. I'm just going to lay it flat in there and it will be removable. I'm kinda building this thing as I go [in case you hadn't noticed ].

Ray