Kiln temperature controllers

[youngdylan]

I've just bought this kiln to try to get to grips with proper heat treating. Not blades but jigs, PH and other tooling. Mostly 4340

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110563439221&ssPageName=STRK:MEWAX:IT

There's no temperature controller with it but there's plenty of VERY cheap ones on ebay. They're almost too cheap. Does anyone have any experience of them. Or has anyone got any advice on temepertaure controllers/thermocouples in general. Maybe I should go for a programable controller, eg with times, ramp up ramp down etc?

[ciladog]

Youngdylan,

I built a digital control for my propane forge from plans posted on the internet by Whitney Potter. This was a few years ago and they were downloaded as a pdf file. Well, Mr. Potter has now published a book on the subject and the pdf file is no longer found for download. This is the link to the book.

I’m posting a pic of one of the pages from the file with the assumption that what I have posted was not copyright protected since it was available before Mr. Potter published his book and nothing in the document says it is copyright. ADMINISTRATOR: Please delete the pic if my assumption is incorrect.

Now with that being said, I have replaced the blower in the diagram with a power relay (both 120 V and 220 V) that I can either plug my forge blower or my kiln into. The connection to the thermocouple has a plug connector so I just unplug the forge thermocouple and plug in the kiln thermocouple. It works very well for both.

A type “k” thermocouple will take you up to 2300 F. If you use it in a forge, I suggest it be 8 gauge. I don’t think it matters what gauge you use in a kiln. And be suspicious of used thermocouples; they wear out.

[NeatGuy]

I've just bought this kiln to try to get to grips with proper heat treating. Not blades but jigs, PH and other tooling. Mostly 4340

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110563439221&ssPageName=STRK:MEWAX:IT

There's no temperature controller with it but there's plenty of VERY cheap ones on ebay. They're almost too cheap. Does anyone have any experience of them. Or has anyone got any advice on temepertaure controllers/thermocouples in general. Maybe I should go for a programable controller, eg with times, ramp up ramp down etc?

Make sure that the controller can operate a solid state relay (ssr), these can also be purchased on ebay. Choose a ssr that matches you kilns current draw and voltage requirement (if your kiln is 3 phase you will need three ssrs). A controller that does not have a ssr output can be used with the controllers internal mechanical relays but then you will need an extra power supply to power a mechanical relay for the kiln.

The controller should be a pid controller so it will automagicaly adjust itself to your kiln. If you buy a controller with ramp and soak you can then fuse and slump glass which is nice if you make architectural lighting. In fact I think that glass and iron work well together. If you get a controller with ramp/soak features you can also do controlled anneals. I like Honeywell and Omron controllers.

Get a type "K" thermocouple they are made in different lengths to reach the interior of you kiln, you should also get a ceramic sleeve to protect the thermocouple. I get my thermocouples from a ceramic/pottery supply but they are also available on ebay.

If you choose to use a Honeywell or Omron contoller use there web sites to help decode the product feature codes that are on the controllers.

One last thing get a fan or small blower to keep your ssr cool.

I hope this helps a little.

brad

[youngdylan]

Ciladog,

thanks for the diagram. I was vaguely aware of the book but think I'll get it now. Guess it's the same principle for a forge or kiln, instead of switching an electrical element on/ off you switch a gas valve on/off .... with a lot more sfety features. It would be useful for the forge cos I just tend to run it full tilt a lot and 3 burners gets unbearable in my shoebox of a workshop. I also want to get into forging bronze.

Brad

good point about the 3 ssr's and cooling fan. It's wired for sigle phase now but I might replace the elemnts for 3 phase wiring. It's a 6KW so thats a relatively large current draw on just one phase, better to spread the load over all 3 phases. A full set of new heating elemnts is only about £140 direct from the manufacture, seems pretty reasonabl all things considered.

Yeah, I gues I'll go for a named brand controller, Even with postage a controller from YingTongTiddleEyePo is just too cheap at £4.95

http://cgi.ebay.co.u...=item335fcd9b82

Actually I've nothing against buying Chinese as long as the quality control is there. I've had an Anyang 40kg hammer for 5 faultless years now and I've got an induction heater on it's way. It's just that £5 is just too cheap.

It's a long term project, Kilns just sat on my trailer buried in my garage till I find time to reorganise my workshop but I'm quite exicited about doing proper heat treating, no more looking at chicken blood under the light of a full moon.

Controlled ramp would be good for annealing things like h13