One of the guys in our bow building group started using a small radiant heater to heat treat the limbs on his all wood bows. He is getting excellent results without the drawbacks we have using heat guns that will very often go around the bow limb and scorch the back of the bow. I know absolutely nothing about radiant heat, I can’t find much on line about building one but if one could be built flexible enough to conform to the shape of a bow limb it would be perfect. Any suggestions?
RV water line heaters are flexible and heat up, but they’re designed to heat the water lines to above freezing. I don’t know what they’d do if you used them in a room-temperature environment. The manufacturers may make something to deliver the heat you need without catching fire, which I’m assuming is a priority.
Just get a piece of NiChrome wire and bend it into the shape you need.
Metal rod or long rectangle is flexible.
Radiant heat is specifically what I was looking for
Right. Heat the rod or plate, like by passing an electric current through it, and it radiates heat.
Industrial Rods for Industrial Heating Applications is a quick example of a commercial source.
Yes, Nichrome wire will glow when it is hot enough. And it can be thick enough to be stiff enough to hold it’s shape, even when red hot. You can buy it on the internet, or you can disassemble it from a dryer, or heater, or heat gun.
The problem with disassembling from a fan heater or heat gun is that the wire is probably to thin to hold it’s own shape without the framework.
I don’t think it will solve your problem: radiant heat burns just as much as hot air: if you can’t control your hot air you probably aren’t going to be any better at controlling your radiant heat.
FWIW, I actually have a couple of small loops of wire downstairs in a test system, that are heating up and glowing on about a 2 second cycle, as we check the operation of a thermostat for a solar-powered hot water system.
The type I am talking about does not heat the air between the heater and the object, only the object gets hot. It will only heat where it’s light hits.
Reptile heater pads are flexible pads, but possibly don’t get hot enough for your needs.
HoneyBadgerDC - long time no posts. I see others have proposed using nichrome wires, but my personal experience from metal working, is that nichrome wires do not hold up at high temperatures for long times. I have used kanthal wire with better results. Kanthal wire can be purchased online from vendors like amazon and you can make a coil from them.
I would recommend that you instead get commercially available radiant / personal heaters like this one https://www.amazon.com/COSTWAY-Infrared-Electric-Heating-Radiant/dp/B01N4GUXTM?ref_=fsclp_pl_dp_8
May be put two or three of these small heaters facing outside at the center of a circle. Then have your bow limb go around in a circle (like on a toy train on toy train tracks) around the radiant heaters. You can then change the diameter of the train circle depending on how much heat / drying you need.
That might work but I am looking for something like infra red where the space is not heated only the area where the light actually hits is heated.
I don’t understand; why do you want the radiant heater to conform to the shape of the bow if it never touches it?
For one reason even heat, for another reason once the limb reaches temperature we start bending it and ideally would be able to readjust the lamps after each bend. We are toying around with different heat treating methods and temperatures looking for maximum performance from the wood as well as making the wood less hydroscopic.
You mean something like this : https://www.costco.com/Presto-HeatDish-Plus-Parabolic-Heater.product.100505979.html
?
Well then you need a metal frame in the same shape as your target object, run electric heater wire through the frame and the line them up. Old electrical heaters had a coiled element that you could probably use.
Maybe… Silicone. You might be able to make a mold of the bow in it’s initial shape. Make the mold fairly thick. An inch? The silicone can be heated by various means, but should conduct that heat fairly uniformly to the bow. It comes in various formulations for stiffness. Silicone can survive a lot of heat. It would be reusable. Maybe you could embed heating elements in it. Or use radiant heat on it.
The easiest way to get a bunch of IR light is by heating up a wire/resistor. Radiative heat transfer scales by 1/(distance)^2, so you want your item to be as close to the wire/resistor as possible. Unfortunately the really hot wire will also heat up the air immediately around it via conduction & convection, and the only way to get reduce this component is to either:
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[li]put an insulator between the two, that is also mostly transparent to IR (clear glass, for example)[/li][li]concentrate and reflect IR so that you can place the receiving object out of the immediate air around the wires without significantly weakening IR from the abovementioned distance^2.[/li][li]put the whole thing in a vacuum chamber. [/li][/ul]
Heat lamps? Mount a few in gooseneck fixtures and aim them to give fairly even coverage. Use a little fan to keep the air moving around them if necessary. They don’t heat the air much from the light, but the bulb gets very hot.
I think this is a better approach them most heating elements.
When I worked in a lab, they had some kind of flexible metal “fabric” that they would wrap around pipes to heat gas for experiments. It looked like woven metal strands. It was hooked up to a massive variable resistor so they could dial how hot they wanted it to be. Although it wouldn’t be radiant heat, you could lay the fabric along the bow and set the dial for how hot you wanted it to get. Does that kind of heating fabric ring a bell for anyone in a scientific environment? I don’t know what it was called, but I can try to look it up if you want.
I don’t know what it’s called but it sounds like what I have for a plastic sheet bender, and there are similar things for heating/thawing water pipes. It can get very hot but spreads the heat out instead of concentrating it in a thin wire.
ETA: I think it is metal wire sheathed in some kind of wrapping, then woven together.