Electric Kiln

[Mcgyver]

Jo, show us how its done!

I bought the same pid, arrived before Christmas.  Cheap. <$20 cdn.  Much to my surprise it arrived with the SCR and thermocoupler!

[propforward]

You could get a bottle of forming gas and have a go at some brazing.

Good for heat treating too - you only need a small percentage of hydrogen to get a nice reducing atmosphere.

[Jo]

You could get a bottle of forming gas and have a go at some brazing.

  I am not sure what you mean by forming gas. Could you explain.

Jo

[propforward]

Sorry about that. Forming gas is a mix of hydrogen and nitrogen. 5% hydrogen in balance N2 is typical(although other mixes are used), and as a result a very safe mixture. It’s just enough to produce the reducing / cleaning effects from heating in Hydrogen, without the safety (BOOM!) risk. Your furnace runs hot enough to melt quite a range of braze alloys, but you need the reducing atmosphere of the forming gas to do it without flux. Reducing atmosphere just means that the hydrogen removes / prevents surface oxides forming.

But admittedly it’s a lot more messing about. Since you have to continuously purge the oven during the run it can use a lot of gas - and I’m not sure what it even costs these days. But I thought - food for thought maybe. Just another way such a kiln could be useful. In reality a lot of faffing about for the home user, but it’s fun to think of the possibilities anyway.

[Jo]

This is all new to me    Maybe that accounts for why there is a hole in the back as well as the front of the kiln.


China post has successfully delivered me all the gadgets I ordered: The correct temperature range controller, which came with a spare thermocouple of a different range, the required relay and two 1250 degree K type 100mm long thermocouples which are long enough that the body can sit outside the kiln and not melt 

The instructions for the controller are in Chinese and some sort of English that is not any more understandable 

So I decided to remove the back of the Kiln to see what it has: It has two separate heating elements and a device for reducing the power to the heater. So first up remove the controller as I am going for electronic temperature control a I also need to look at how that hole in the back could be used to support the thermocouple.

The two power wires for the heaters will need to go to the output on the relay and the entire unit will also require earthing 

Jo

[gerritv]

Would one of these manuals be better suited to your controller? Same model number.

Gerrit

[Jo]

Thanks Gerrit, much better  .

I had read as far as the bit on the instructions that said "Speech inverse action " and "play a positive action" and decided that their translation leaved a bit to be desired 

Jo

[Don1966]

Jo the controller use two devices and RTD OR THERMOCOUPLE tie your thermocouple TO 9 & 10.  Your kiln has two elements in series should be easy enough and the controller has The SSR output well labeled. RTD stands for Resistive temperature device.


Don

[Admiral_dk]

I do really NOT like the fact that the manual from Gerit and the label (second picture) on the unit itself has very different connections   

Especially the fact that the mains is connected to Pins 1 & 2 on the label and Pin 6 & 7 in the manual.

Is there a wrong label on the box itself or is the manual to a different version of the controller ?

Best wishes

Per

[Jo]

Don I was wondering about that as the pin out does not match the pin out on the previous circuit diagrams I will have to do a bit of further reading.

Thanks for pointing that out Per: The manual that Gerrit kindly provided is for units with more pins on the back than the one I have purchased. The important bit is how to program it is in English 

Jo

[jadge]

The acronym RTD stands for resistance temperature detector. Platinum is normally used as the element, although copper and nickel are also used. The coefficient of resistance with temperature is almost, but not quite, linear. Platinum RTDs are limited to around 600°C, above that the platinum tends to get contaminated. Since RTDs are a resistance device they need an accurate voltage or current source in order to work. Whereas thermocouples are inherently a voltage source.

Most standard ovens, including mine, go to about 1100°C. This is limited by the heating element. Before I bought mine (secondhand on Ebay) I looked at ones that would get hot enough to melt iron. That would require a silicon carbide heating element. The problem with SiC elements is that they're not generally used much below 600°C. So I stuck to a standard kiln.

My oven takes several hours to get up to 800°C or so. Although that can include heating the several kilograms of steel in the cavity. For a heating cycle for annealing, or hardening and tempering, I reckon on about 12kWh of electricity.

Andrew

[Jo]

My oven takes several hours to get up to 800°C or so. Although that can include heating the several kilograms of steel in the cavity. For a heating cycle for annealing, or hardening and tempering, I reckon on about 12kWh of electricity.

So best done on a sunny day then 

Jo

[Admiral_dk]

Your comment about the number of pins Jo, made me realize that this is probably yet one of those projects somebody posted on the net in the public domain => a number of Chinese (might be others too) decides to put it into production as their own .... So you're probably also right about the Firmware being the same => same way to operate the units = manual can be shared for almost all parts 

I have other products from China that are copies too - even to the degree that you have to download the drivers from the original maker / company, for it to work 

[Vixen]

Hi Jo,

If you have a generic controller clone, made in China, there may well be some "How to do it" videos on Youtube. It's worth a quick look to check.

Mike

[Mcgyver]

So...I don't think the REX C100 is the right contoller for this, well at least for me.   afaik it doesn't offer ramp and soak programs, the adverts all call it programmable but it looks like that just means you get to set the temp.

something like this might do the trick:

http://www.thermomart.com/index.php?route=product/product&product_id=222

Anyone have a suggestion on whats the best low cost RS (ramp soak) PID?  Or maybe the REX has it and I've missed it?