What do you use for heat treatment?

I was hardening/tempering some small items last night.

With a small "mapp" gas torch.

I'm thinking about a small mini kiln, around £360, as these would have plenty room for the things I make and the temp can be set, which should make hitting correct temperature easier!

Has anyone used one of these for HT?

Thank you, Jim

I have used a slightly larger furnace whilst at work and had no problems with use as you can controle temperature to suit material and tempering is so much easier than trying to guess colour change for hardness. We used stainless steel foil to seal the parts in and that protects the part from scale etc.

David

Just picking up on the stainless foil comment. When idly exploring the idea of building a vacuum heat treatment oven in order to avoid scale, I came across the idea of putting a small piece of (brown) paper in the foil envelope along with the part. The idea is that the paper burns early on in the process and consumes any oxygen that there is in the envelope this avoiding oxidation of your component. The vacuum heat treatment oven didn’t get built.

i have a small gas lab type kiln in my workshop. It has been most useful for silver soldering when you have to silver solder something small onto something very big. With a gas torch it can be a struggle to get the bigger part hot enough without the smaller part getting too hot and killing the flux. Everything comes up to temp together in the oven.

Ian

If it is not a quick ‘heat and quench’ job, I use my Paragon SC2 kiln - originally bought for silver clay, lamp-work and enamelling (as well as case hardening). Very controllable with plenty of programming capability.

I cheat and take my heat treatment to my last employer to run in with their work. They always refuse payment so I put a few £ in the tea kitty.

Got a Tig unit but no Argon yet

They put energy in without any addition of weld material and may be handy for doing small parts

For quick 'n' dirty work I use a propane torch. But for bulk normalising, hardening and tempering of cutting tools and heating parts prior to hot forming I use a heat treatment oven by Carbolite. It has a PID controller that goes to 1100°C and is intended for heat treatment, it is not a kiln in the sense of pottery firing. New they cost a couple of thousand, but I bought mine secondhand on Ebay. Working area is 6" x 7" x 15" and I have had it full on some occasions. The downside is that a harden/temper cycle consumes a fair number of kWh.

Andrew

Not answering the question but on the topic of avoiding oxidation....my dad used to work for a company making high precision electron guns for electron microscopes. These has a number of components that needed brazing, which was done using induction heating in hydrogen. The hydrogen was contained in an inverted pyrex tube, open at the bottom, the gas rising to fill the tube and keep air out. The assembly with braze preforms was mounted near the top of the tube and heated by RF on a coil round the tube. This caused the assembly to get to red heat, melted the braze which would quickly flow since all the oxidation had been reduced by hot hydrogen. Result was a very clean and well-brazed assembly. Of course, having red hot metal around hydrogen and air wasn't without its hazards, and occasionally things went slightly awry and the gas ignited at the gas/air interface. But since the tube was open to the atmosphere at the bottom there would just be a loud whooping noise and a few red faces.

I’ve read that domestic ovens can be used for tempering but not tried it. Is this correct? Not sure how high my oven goes but I’m not sure it’s much above 220° - 240°C?

I’ve just used a gas torch for hardening stuff like O1.

I have considered buying an oven/kiln for many years but I don't know where I would put it in the workshop.

I do use my kitchen oven for tempering. For blacking very small steel nuts and screws a ring on the kitchen gas hob is used.

Otherwise I use a propane torch which is not ideal. I have case hardened successfully with it.

JA

Edited By JA on 12/12/2021 12:18:53

I have one of these small kilns - kiln. it has a stepped temperature controller and works well. The internal dimensions are 7" x 4" x 4", it is quite compact externally and sits out of the way on a top shelf when not in use. Cost about £300 at the time, Not quite as nice as a Paragon SC2 though.

I have used Brownell's ATP-641 anti-scale coating in the kiln with success, but it ain't cheap.

The kiln takes about 40 mins to reach hardening temperature for silver steel/gauge plate, with only a few degrees overshoot and maintains the temperature within 1 deg C for as long as necessary.

It is also useful for stress relief (of materials) and for dissolving the hard carbide inclusions often found in iron castings. The cooling rate can be controlled over many hours.

Often, however, I just use a propane torch for hardening and I can be done in a few minutes with good enough results.

Clive

Thank you for the feedback.

Clive,

Thank you for the information and link, this looks to be a better bet than the one I had seen.

I'll hopefully get something sorted this week.

Jim

I have successfully used a deep fat fryer with nominal 190 deg C max temp.

Jim

I have a small home built kiln/oven that I use for heat treatment and silver soldering items too large for my torch. Works very well. It is controlled by a home built controller which keeps the temp within about 10 deg which is OK more most uses (I have a PID controller which will keep it to much closer tolerances if I ever get around to installing it). Its rated at 660 watts @ 240 volts. Further pics in my album, including cutting diagrams for the insulating fire brick linings.

John

Edited By John Purdy on 12/12/2021 18:46:18

I've ordered one of these should be here tomorrow.

Thanks again for the feedback, it's much appreciated.

Jim

Jim,

Programming the kiln is actually pretty straightforward but it did get me scratching my head to start with. There are are a couple of youtube videos on the XMTG-7000 controller - XMTG-7000

The supplier sent me some useful tips on programming the unit too. I can email these to you if you don't have them together with the controller manual (unfortunately I can't seem to save pdfs to my album).

Clive

Clive,

Thank you for the offer.

I went for the basic one with just a temperature control.

It's arrived today and looks perfect for my "needs"

Jim

In one of his videos Dan Gelbart describes using a methanol drip into his furnace to maintain an ideal atmosphere for hardening.

I use my gas torch and always overdo it! Tubal Cain (TDWalshaw, not the American impostor) mentions tempering salts, but no idea where you'd get mall quantities.

He also mentions putting a bit of charcoal in an electrically heated furnace to mop up the oxygen, same idea as the paper mentioned by Ian H