Heating Elements and Forges

[Rogue]

Nichrome alloys such as this one have maximum operating temperatures up to 1922F, well over the critical temp for forging.

Is it feasible to build an electric forge or would the power requirements for this kind of element cause problems - including running costs?

[narsil]

The important thing would be to cosider the mechanism of heat transfer. In a soild fuel forge itis primarily by conduction, with the metal being in direct contact with the hot embers which are at a similar temperature to the steel. In a gas forge there is a combination of convection and radiation which means that the flame temperature fo the burner needs to be considerably hotter than the forging temperature to work effectively.

A gas burner is effective because it produces large volumes of hot gas which can circulate through the forge space and also evenly heat the lining which then transfers more heat to the blade by radiation.

If you were to make an electric forge based on teh gas pattern than it would need to be able to heat a similar volume of air at a similar rate, possibly fan assistance would help.

I've never actually come across an electric forge (heat treat oven yes) except for induction forges which are bit different.

[APG1961]

I would seriously re think your idea of an electric forge. The only way you will heat up your steel to forging temp is with the door closed. Most electric furnaces take to long to heat the steel. You will spend more time waiting for the steel to heat up than forging.

A gas forge will heat up VERY fast and you can keep an eye on the steel through the front of the forge. Judging the temperature of the steel by eye is the secret to successful forging.

Andy..

[Rogue]

I would seriously re think your idea of an electric forge...

I *knew* there would be a flaw in the idea That's why I ask! I suppose the principle could instead be applied to a heat-treating oven which I believe already exist.

[APG1961]

Check out the information in my tutorial..read the book quoted in the tutorial. This gives all the calculations you need.

I dont know how you calculated the cost of your heating element £395-33400 but my HT furnace cost less than £100 to build and it reaches a temp of 1100 oC using Kanthal elements.

http://budgetcastingsupply.com/Heati...l#7101-WARNING

There is nothing wrong in thinking outside the box, but remember don't try to re-invent the wheel.

Gas for forging...Electric for heat treating.

Andy..

[Rogue]

I was pulling the numbers off a single supplier without reading the specs to see which one was correct, so I quoted from the top and bottom of the range. The numbers came from assuming you needed an awful lot of wire, compared to the (hopefully) more realistic £50 I anticipated a little further on.

I never agreed with the shape of wheels, that's my problem. I'm more comfortable with electrickery and electronikery than gas plumbing so the natural instinct is to try and redesign to fit one's own area of knowledge. Realistically I should get off my lazy backside and learn a little more about gas/solid fuel designs

Many thanks for the input.

[Rogue]

If you were to make an electric forge based on the gas pattern then it would need to be able to heat a similar volume of air at a similar rate, possibly fan assistance would help..

I was thinking along the lines of the narrowest cylindrical area possible, with the element running as a relatively tight coil along the cylinder space, heavily insulated as with any other forge design. I say cylinder, maybe eliptical or rectangular, worth thinking about. Bad things about this idea include (i) second guessing the maximum size blade that will be made and (ii) increasing the length of wire needed, in turn increasing cost and power requirements. As a knife-only forge this problem could be reduced of course, maybe a diameter of 7-8cm, length 30cm max. This would take approx. 25cm wire per turn, say 2 turns per cm plus say 2cm(?) per cm of cylinder length for the spiral. 30cm length x 52 cm would make in the region of 15.6 meters of element needed. Based on how I'm reading the charts that could put the cost somewhere between £395 and £3,400! I'm making up the coil requirements through guesswork, I hope it is complete overkill to have such a large element (not to mention the power source to heat it). Just bouncing ideas around while I investigate further. If we started stretching (say) 30cm of coil over 5cm of cylinder, making 1 turn per 5cm, we would need less than 2m to cover a 30cm cylinder. Could enough heat be generated with this or even less? I find it an interesting thought.

I understand how fan assistance would help a gas/solid fuel burner as they require oxygen. Would it be as beneficial for this kind of heating? Would there be a risk of the fan preventing the even and consistent heating of the air space?

I'm off in the clouds right now but I think it is an interesting concept that could give you an electronically controllable heating unit. On the grounds that they are not more commonplace I assume there is a massive flaw in the theory and I suspect that, rather than cost, it is power requirements!

[imagedude]

The only way I can see electricity being used to heat steel (other than by induction) is via salt pots. I wouldn't want to forge steel covered in molten salt though! I know of a local factory that uses a large electrical furnace for melting aluminium but that takes hours to reach working temperature. Stick to 'raw' fossil fuels for the rapid heating of steel.

[ZDP-189]

This is an interesting topic for me. I have been considering making a pre-heat oven which would ideally double as an indoor mini-forge, because I am tired of CO headaches and too lazy to go up to the roof for small jobs.

One reason gas forges and coal forges are so effective is that they dump massive amounts of heat energy into the forge. The other, as you say, is convective heat transfer. I was hoping that a small cavity and possibly an internal air circulation fan would give adequate heat transfer for my purposes.

I know there are electric forges (not furnaces or kilns). Farriers have used them for years.

[ZDP-189]

Way OT, but very cool: http://www.richieburnett.co.uk/indheat.html

[Iron_Heinie]

I recomend going with gas..... I have never had luck with my electric kiln. After the second pair of coils burnt out I said to heck with it. The gas is offers more rapid heating, and having an open door is good.

Way OT, but very cool: http://www.richieburnett.co.uk/indheat.html

Now having said my bit for gas..... That is pretty sweet! I wonder how even the heating is and if thickness plays a part?

The bit about how heating slows after a piece of steel reaches critical tempature is very interesting.

[Rogue]

"This means that above 700°C there can be no heating of the material due to hysteresis losses. Any further heating of the material must be due to induced eddy currents alone. This makes heating steel above 700°C more of a challenge for the induction heating systems..."
(taken from http://www.richieburnett.co.uk/indheat.html)

So it naturally slows down/stops heating at the critical temp?

And this has to be faster than a gas forge...

Excellent and informative link, ZDP! Are you planning something that you'd like to tell us about?

[shing]

Electric furnaces are not powerful enough to heat steel quickly if ventilated to the atmosphere. My electric furnace is rated at 3.6kw and reaches 1200C. That is about as powerful as an ordinary blow torch but the furnace is well insulated and lets very little heat out. A forge to heat steel for forging will have to be open to let you see the steel colour and will loose a lot of heat as a result. A small gas forge produces several times the power output of the electric version so you would need to multiply the power of an electric furnace 5 or 6 times. In addition a gas forge can be set to burn rich so making the steel oxidise less while its heating up minimising scaling.

[shing]

http://www.farriersupplies.co.uk/Forges_Sterling.html

[jackal]

Nichrome alloys such as this one have maximum operating temperatures up to 1922F, well over the critical temp for forging.

Is it feasible to build an electric forge or would the power requirements for this kind of element cause problems - including running costs?

I can get hold of various gauges of Nichrome resistance wire if anyone is after any, as I was trying to use it to build a heating element for my project.

Unfortunatly I had issues with electrically instualling it from what I was heating.

I know a fair bit about what current to use to get what temp. with various gauges as well if thats any help.