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DIY Vacuum heat treatment oven

Any hints and tops for building a DIY heat treatment oven

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IanH26/12/2010 14:12:38
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129 forum posts
72 photos
Hi,
 
Just wondering idly over the Christmas break abou the practicality of making a DIY vacuum heat t reatment oven. I saw one recently in another workshop based on a gas cylinder lying on its side - the "top" of the cylinder had been removed and flanges welded on the cylinder body and on the remains of the top. It was hinged to form a door and although there was a clamping arrangement - the vacuum kept it shut and sealed - there was an O ring seal in the flange.
 
Inside there were refractory bricks and some electrical elements - and there was also a control system.
 
Anyone have any ideas - how many KW woud I need to heat treat steel  - the actual chamber needs to be no bigger than a coupe of house bricks. Sources of heating elements and refractory bricks etc etc?
 
Ian

Edited By IanH on 26/12/2010 14:13:32

Peter G. Shaw30/12/2010 20:40:33
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1531 forum posts
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Not sure I understand what you are getting at here, but anyway a few suggestions based on what I think you are saying:
 
I've never heard of vacuum heat treatment (but that doesn't mean anything - I don't know much about anything!). In respect of heat treatment of steel, may I suggest Workshop Practice Series No. 1 by Tubal Cain. Titled Hardening, Tempering & Heat Treatment it will tell you all you need to know, and possibly more!
 
Refractory bricks should be available from any good builders merchants although I'm not too sure about what they may be called. The first lot I bought came from Uriah Woodhead in Bradford and worked extremely well. I recently bought some more from there, but I'm not at all sure what I've got and I haven't yet tried them. The invoice describes them as Firebrick.
 
I did also find a firm, in Nottingham I think, who seemed very knowledgable about them and were prepared to sell them singly and either post them (!) or I could collect. I found them by a roundabout way involving tracing Fossalcil bricks. Apparently the original maker of these had been taken over. Price wise these were about the same as the Woodhead ones.
 
Anyway, suggest the book first, and then take it from there.
 
Regards,
 
Peter G. Shaw
Keith Long30/12/2010 21:41:27
883 forum posts
11 photos

Hi Ian

You might try doing a search for pottery kiln materials suppliers - most likely (still) to be around the Stoke area. You should be able to source all the materials you need from them, refractories, element wire, controllers, pyrometers etc. Pottery isn't usually dealt with under vac but they will have knowledge about both oxidising and reducing atmospheres in kilns and be able to tell you which element wires will be suitable. Temperature wise a pottery kiln can melt steel if you want to go that high.

Keith

Terryd31/12/2010 00:36:15
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1946 forum posts
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Hi Ian,
 
We used to use a pottery firm called Wengers, as Keith said they are in the potteries.  you can calculate the size of elements necessary for a given volume and buy Kanthal wire which is a resistance wire made for elements.  Knowing the length you need you can then wind your own elements (the wire is annealed) and by using soft refactories you can file and drill tracks to locate them.
 
Terry
Les Jones 131/12/2010 10:09:00
2292 forum posts
159 photos
Hi Ian,
               Here are two other places you could try for refractory brick.
 
Refractory brick is easy to work. It can be cut with a wood saw.
Do not be tempted to use castable refractory  as this is not a good insulator.  It is suitable for lining a furnace but needs insulating fibre surrounding  it. I have seen wire suitable for heating elements advertised on ebay from time to time.  If you do not need very high temperatures you can make a DIY castable refractory that is insulating using a mixture of perlite,  clay and cement. I made a small furnace for melting aluminium using this and it works very well. It is only suitable for up to about 600 to 700Deg C If you are interested in this let me know and I will try to find the recipe again. I bought insulating refractory brick from a place near Liverpool airport. (Which may be close enough for you to collect,) But his website is not working so he may have stopped trading. I probably have his email address and phone number so you could contact him to see if he has what you need. Again let me know if you want this information.
Les.
 
 
Howard Jones31/12/2010 14:17:02
70 forum posts
112 photos
  can I pass on a piece of experience from another model engineer.
he found that when the wire element was heated it expanded.
suggestion was then made that coiling it would keep the wire respectable when hot, but it didnt.
what was needed was to coil the wire into a long tight coil then coil this into a bigger coil,
the compination of the coiled coiled wire allowed it to go somewhere without sproinging out of the holder and making a nuisance of itself. this nuisance usually involved shorting on the job being heated.
 
if the heating in a vacuum idea is to get rid of surface scale can I relate that a very good heat treaters in melbourne (which I suspect was the ansett setup) actually does its work in an argon environment.
David Colwill31/12/2010 15:59:09
782 forum posts
40 photos
I fed argo shield into my muffle oven for a job I did once and it worked ok. If you feed the gas in at a fairly high pressure to get rid of the air initially you can then turn the flow right down and maintain the shield. It didn't use that much gas overall.
IanH02/01/2011 18:57:23
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129 forum posts
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Thanks very much for all this information - I don't live far from Stoke so I guess I have no excuse but to make some contacts and see what I can find out there, I will post progress as it happens.....
Thanks again
 
Ian

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