Heat Treatment Oven

[AjohnwParticipant @ajohnw51620]

Thanks for the info Jack. The burner shown in the video is stable in air and also when used in the forge he also shows but doesn't give any details on.

I'm hoping that the ceramic blanket material saves on the refractory needed. i'd guess that the volume of a bag of it is roughly equivalent to how much material can be cast. Some people seem to be using blanket for forges and nothing else so it should give pretty good heat insulation.

I have a couple of crucibles that were given to me some time ago which are probably a bit full with 2 lt in them but should be ok for 1 1/2. Not sure what to do size wise yet but I'm thinking in terms of going for kiln style with a front opening door probably with a plug in the top for adding more material. Not what most do but to me that gives a bit more flexibility size wise than looking for suitable barrels. So probably size it on a bigger crucible than I have.

Materials can be found here but I bought my bag off ebay.

**LINK**

Checking my ebay purchases I actually have the 1700C material but didn't pay that much for it. I also have a few insulating fire bricks that have been around for some time. They should be ok to make a base for it if I coat them with the high temperature stuff.

While electric makes temperature control easier it wont be easy to judge the wattage needed. I can get a rough idea by looking at various kilns especially glass furnaces at the sort of size I am likely to finish up with. Rather than go for one element I've gone for several of the same wattage so hopefully I can sort of tune it. eg 5 1kw elements worked out at £9 from a UK seller. 3 800w from the east £5. Should leave some spares. I'm almost bound to burn some out but a type of dimmer switch might prevent that happening while I'm messing about. The initial low resistance might blow these up but I can probably sort that out with a heftier triac.

John

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[jaCK HobsonParticipant @jackhobson50760]

I'm all for people experimenting and hopefully finding out something new (that's where the knowledge about Amal burners comes from).. So do it!

However, I'd suggest the current 'best practice' for DIY melting iron is blown burner into a top loading cylindrical furnace …. like a gas bottle lined with hard refractory. A cylinder of blanket, and nothing else, will do – seen it done – but you probably throw the blanket away afterwards.

[MuzzerParticipant @muzzer]

If you get one of those temperature controllers Rod linked to and a 50A SSR (eg Crydom from Farnell for instance), you have a >10kW digital, self-tuning controller for £50. You'd need a thermocouple admittedly but that's not going to be much more. If you are using 3-phase, you only need 2 SSRs, albeit it a higher voltage (500V instead of 240V)

If you are feeling a bit more adventurous, you could try an IR T/C which mimics the output of a thermocouple and allows non-contact temperature measurement. You may be able to get something similar from Ali Express or similar these days. The output characteristic isn't quite the same but for the range you are interested in it's generally not an issue. I used one of these in a furnace to control the temperature of PTFE hoses that we were convoluting and reinforcing and really there weren't many other options.

Merry

[Mark CParticipant @markc]

Merry,

You will need a high temp IR device as the cheap "normal" ones run out of range about 600/800 deg C

Mark

PS. For accurate heat treatment use we used to use optical hot wire pyrometers

[MuzzerParticipant @muzzer]

Never worked up there myself but that range extends up to 1100C, apparently ("the OS36-2 and OS36-5 models can be used to target temperatures of 1100°C&quot.

I would have thought the problem with hot wire pyrometers is that it's very difficult (expensive) to make them automatic ie provide a suitable signal for a process controller. The IRTC generates a simple voltage without any active circuitry.

Merry

[Mark CParticipant @markc]

Merry,

Yes, you are correct and there are IR devices that go way up. The bigger problem is probably matching the emissivity values and targeting accurately but these are all things that can be achieved with thought (they are done industrially, it is just a matter of scaling the cost I suppose to match DIY budgets and aspiration!).

The hot wire was used as a QC check as the furnaces all ran on TC probes which makes it easy to maintain the temperature and log furnace conditions.

I have never worked with steel beyond H/Treatment temperatures but have had some experience with automatic glass processing on optical glass moulding. I also got a a number of (very in-depth) visits to an optical glass production facility that was very interesting.

Mark

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