So what do I need ?

Just bought meself a small muffle furnace seeing as winter is coming and need to keep warm.

It's only a tiny thing 6" x 6" x 5" approx and rated at 1200W 240 v, just a plug and a switch but would be handy to have it temperature controlled.

Seen loads of digital displays on Ebay with thermocouples but have no idea just what I need. Any pointers please guys ? I'd like it to be able to melt tiny amounts of brass around 940 degrees if it will go that high, not checked it yet but many of the thermocouples max out at 800 from what I have seen.

Some fairly exotic, high temperature, thermocouples listed here

But optical thermometry, or even the 'bending' cones used in kilns, may be more appropriate

... Does the furnace have a viewing window?

MichaelG.

Edited By Michael Gilligan on 21/10/2015 23:13:29

Edited By Michael Gilligan on 21/10/2015 23:15:14

Most of the temperature controllers/indicators can take a type K (chromel\alumel) thermocouple. These go up to 1300C. However, the stated range usually depends on the type of Insulation on the wires. Providing you don't mind the plastic melting or the fibre glass fusing, the actual wires will be fine. For the higher temperature work it is usual to insulate the wires with ceramic tubes or fishbones in the hot zone. The important thing is to make that the wires only touch at the point where you want to measure the temperature. The cheap Chinese PID controllers on eBay seem to work fine in my experience, just as good as the Eurotherm ones I used to use in my professional life.

HTH

Rod

Edited By Roderick Jenkins on 21/10/2015 23:32:08

An old model engineer magazine gave details of a small furnace. He used K type, the fibre glass covered ones which are cheap and allowed it to burn/melt off.. K is ok up to about 1300C and it's usually the casing that limits it. You might find some enclosed in ceramic that can go to 1300. The ones in a stainless tube are limited to 1250C.

There is plenty of info on the wiki about thermocouple materials.

Actually I would suspect your furnace uses nichrome elements and gets to about 1100C -1200C. It needs to be kanthal a1 to be able to get a furnace to 1300C and more exotic material to go higher - graphite for instance.

K is usually the thermocouple that the controllers are intended to work with. No harm at looking for ones that can be used with a selection of thermocouples but take care that it's not an option when bought. The data sheets can be confusing in that respect as can ebay listings. Some times used controllers with a high temperature thermocouple crop up on ebay in the pottery section. They tend to fetch pretty high prices.

Myfordboy on youtube has done a video of brass casting using a small furnace.

I have the materials about me to cast my own furnace. On my list of things to do.

John

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Not something I've any experience of myself, but it's probably worth looking around on the British Blades Forum

I've got a PR electronics 5514 controller and a cheapo k type thermocouple here. I'm not sure if they will fit together but if you are willing to have a go.......

David.

John W1 came close with the reference to Myfordboy.

Watched the video and I had seen these on ebay but they now make sense and armed with this knowledge found a hand held unit with two thermocouples for £14.50 from a UK seller.

**LINK**

And an extra K type thermocouple that can go up to 1250 degrees C as the supplied ones are only good for 400 degrees but would come in handy for hand held use like checking bearings.

**LINK**

Anyone see any problems with this idea. The thermocouple could be fitted to the furnace permanently and just plugged in when needed.

All looks good. Should be fine.

is there any sort of energy controller with the muffle? One of these **LINK**

would enable you to set the required temperature and give you read out of current temp. Might need an additional higher current relay, controlled by the in built one, to pass the max current of the furnace.

Rod

I had to google muffle furnace to see what you guys were talking about.

We had one of those at work, I though they were just for heat treating etc, I didn't realise you could melt brass in them.

I did use it once but for the life of me I can't remember what for!

I've had one for ages. I was given it as the temperature control was bust. I spent some time and quite a bit of cash fitting it up with a modern controller and thermocouple. Result I've never used it since. Would I sell it? NO NO NO it's MINE!

At some point I'd like to do case hardening in it. When that will be is anybodies guess.

David.

If anyone is interested in smelting / casting etc the myfordboy video's are well worth watching. His rolls and power hacksaw are worth a look too. The rolls appeared in model engineer some time ago.

He tales a dim view of me trying to do an electric furnace for aluminium, probably right too but .......... I suspect he had to use electric for brass because of temperature control. Electric is slower than propane or waste oil but easier to control.

There is also a very good video on a propane torch on youtube. For a forge but burns well into enclosed spaces so should be ok for furnaces too. It's a bit of a black art. Very slowly explained so easy to tell which one it is. Source north america.

I did know some one who managed to do cast iron. Charcoal and a hair drier for the draught. It doesn't need to be too close to the hole in the furnace for heat to be a problem. He also used an oil sand to get a better finish.

John

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John S,

You might want to look at these people http://www.west-cs.co.uk/products-uk/categories-uk/single-loop-temp-and-process-controllers/ for control (also Eurotherm but they are pricey) and a firm I can recommend for thermocouples https://www.sterlingsensors.co.uk/

Sterling sensors are particularly helpful.

Mark

Edited By Mark C on 22/10/2015 17:41:41