Oven heating element ?

Mark Williams

Mark Williams

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I've got to build a tempering oven for a sword. I'm using the shell from a discarded water heater for the body of the oven. I was planning on using the heating element from a regular oven and just bend the element into an elongated loop to fit inside. Does anyone see anything wrong with this plan? I'm wondering if the element will bend without breaking.Its trash pickup day near my house so i'll be perrusing the hood for a discarded one. (Sanford and son theme plays in background)

Water heaters are a great source for nice tanks also. I'm using the inside tank to hold the quenchant. I guess if the heating element inside the tank was still okay, they could actually be used to heat your oil up to proper temp.

Mark
 
When I was in college, a fire started in my apartment building from a cracked heating element from a stove. They caught it early, but what I learned is that stresses on these things can cause them to basically start burning rather than just heating. From what I understand, they can't be bent or they will crack and burn (this may be the issue with only a single model or could be the advice of a nervous firefighter). I wonder if they make heating elements for commercial bakery ovens that are elongated and may serve you better? They gotta cook that whole baguette somehow...

Tim
 
Mark what if you put a shelf between the heating element and where you are going to put the sword, that way there is only indirect heat, wouldnt that make the temp spread more evenly over the whole sword? that way it wouldnt matter what shape the element was.
 
Terry,
What I have planned is to bend the elemnt into a loop and attach it to one end of the shell so that it is near the bottom. I guess I could lay it on some scrap pieces of fire brick for support. I was going to just make a few holes going through the shell to put in some pieces of round rod to hold the sword up and act as the cooking shelf. If I can bend the element without it breaking it may hold up for its one time use. I'll give it a shot. No more expensive than the heating elements are, I may just get a new one in hopes that it would bend easier from less scale and thermal abuse than a used one.

Mark
 
Mark

You will not be able to bend or straighten out the elements from a stove or oven. The resistive element is encased in some kind of ceramic material. A crack in the ceramic coating will cause the resistive element to oxidize rapidly when hot and "burn open". This will probably cause a hot spot and may lead to a fire. The ceramic coating also acts as an electrical insulator, for safety. I have used straight versions of these things as resistive loads at work but they are expensive and only available from specialty suppliers.

How about finding a range with an oven that still works, removing the door and adding an extension cut from a hot water heater so that it becomes big enough to fit your sword. The oven will have a thermostat to control the heat as well as an easy and SAFE way to connect to your electrical supply. As with when using the oven for baking, do not rely on the built-in oven control for accurate temperature control. Use a separate oven thermometer. Variations in the mains voltage may cause the temperature to fluctuate.

It would probably be good to use a convection oven since it would have a fan that would stir the air and eliminate hot spots. Do not use fans like the one on the power supply for your computer or that you can buy from an electronics supplier since they are rated for a maximum of smething like 80C, or so. All have parts, inside and out, that will melt/burn at the temperatures that you require.

Hope this helps.

Phil
 
Thanks Phil,

I thought the elements were just inconel. Learn something new every day. I like the extended oven idea, that just might be the ticket.

Crap, we threw away a big old resistive load unit not too long ago:(


Mark
 
I think Phil has an excellent idea. What I would do is take the water heater tank and split it in half. Then take the glass out of the door and welding one half of the tank onto the door. Then cut a large round section in the back of the oven to match the second half of the tank. Weld that on. Insulate where necessary.

Maybe you could rig up a shelf inside and line it with firebrick to really retain and reflect the heat?
 
I mentioned the load resistors because they are similar but not the same. I don't think that they would withstand running for long periods of time at the temperatures that would be required. We just bought a 100kVA load to test the UPS' that we make.

I had originally thought of cutting off one end the hot water heater and mounting it on a stand with casters (how long do you want your sword to be? ;)). It would then be pushed up against the front of the oven, with the glass removed. That would not require any welding,especially if the hot water heater is bigger than the hole for the glass. Some latches could be used to hold the extension in place. The sword would just rest on the oven racks. It would not be as quick to remove the sword but this set up is for tempering not hardening so it should not matter. A fan would be needed to blow the heat into the hot water heater extension. It would probably be a good idea to add extra insulation in the hot water heater and oven.

Phil
 
I just told Deb about Your idea Phil and she asked, " Does he know you have a wife?":D . She's a trooper though. I guess a knife makers wife or GF has to be to put up with some of the unusual stuff we do.

Mark
 
Hello Mark

I did not consider whether you had a wife, GF, spousal unit or SO when making my suggestions since it seemed that you would be scrounging for the materials and leaving the "basic household infrastructure" alone. I get the impression that some of the contributors to this forum don't work that way and do things such as set up grinders in their living room. I am sure that my wife would freak out if she caught me violating her oven in the way I had described in previous posts. I do suspect that once she got over it, she would be Ooohhing and Aaahhing over the results, though. You see, both the knives that I have made so far have been for her, the latest being her own design... ;) This may help explain why the townhouse she picked for our current residence is less than a mile and a half from TKS :D Yes, I am very thankful that she participates in some of my hobbies.

Phil
 
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