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Square lil bertha

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shipto:
I wasnt going to bother showing this but it seems to me its going to work so here it is.
After my posts about getting my casting sand issue sorted out I decided that my old coal furnace was far too much hassle to do on a regular basis so started looking up electric furnaces and found a few copies of Dave Gingery's lil bertha.

I already had most of the bits needed so decided to give it a go, the fire brick I had was salvaged from a fire proof safe I had to get open when someone at worked locked it without realising the key was lost years ago and it was all in bits which meant I had to cut and shape the 4 sides and cement it all together like 4 crazy paving fire bricks  :lol:.

The elements are from a dismantled convection heater and if I had been more confident I would have brought some slightly thicker nichrome wire but thats still a option.

I got the controller for a good price from ebay along with the SSR and a thermocouple which unfortunatly is only good for 400C so rs supplied me with some that are rated for 1100C, Actually got 2 sets of controllers etc so need a project for the second one now  :coffee:.

so as it stands now I plug it into the supply and the power goes to the 24v transformer to feed the controller and the top switch which when on activates the isolating relay and allows power to go to the bottom element via the SSR the other 2 switches activate the second and third elements. When I first started it all was good so gradually raised the temp until the rcd tripped and at first I couldnt understand why then I felt the second layer of insulation and it was wet. I had let it dry for 3 days before starting it but it obviously wasnt enough so I am currently doing a naughty thing  :wack: I have taken the earth off and running it at 225C to dry it out. The voltage going to "ground is currently at 3.5VAC so it still has a little moisture there.

shipto:
So had a slight change of plan as I wasnt happy with the salvaged nichrome wire it broke a few times and I ordered some thicker stuff. Had the new stuff come on saturday I probably would have done the element the same as before but it didnt so my mind wandered to the old oven/grill we replaced a while ago. there was a total of 3 elements 2 of them where approximatly 1.5kw but the main grill one is about 2.5kw so decided to give that a go.
After bending it to the desired shape to fit into the furnace I wired it up and melted my first bit of alluminium :ddb: it took around 30 minute to get this melted I reckon somewhere in the region of 50 to 60cc.

Manxmodder:
Really impressed with your efforts here, shipto  :clap: .

I have also been pondering for some time if domestic oven elements could be suitable to build an electric furnace capable of ally melting.

The other thing that occurs is an electric furnace is more thermally efficient than gas as there is no constant flow of heat escaping through an exhaust vent/chimney.

Even at 6kw for a couple of hours use the cost of running would seem quite economical compared to gas with the added bonus of no noise.

Watching this one with great interest.

OZ.

shipto:
Thanks manxmodder I think the controller makes all the difference regarding efficiency as I dont know about others but the ones I brought bring the temperature up to 2/3 of set point then allow it to cool for x amount of time and from that it figures out how much is being lost and works out how long it needs to keep element on to keep heat around the level required, pretty clever stuff.
I still have a few things to work through on it but its all looking very good now.
by next weekend I hope to have it completed.

shipto:
I have got the cradle done for the melting pot now but might have to expand it a little as it got stuck once it was hot, I thought I had left enough room for expansion but maybe not.
The temperature is transferring nicely to the pot the picture shown is about 10 minutes after start up by the time I turned it off the pid was showing 500C and the meter was showing 410C thats when I discovered the pot wouldnt come out. it might be fine once the temperature has stablised I will see once I have made the lid.

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