Got a Halogen Oven to work for HT ?

[SniderBoomer]

Why? Money, I'm broke but I got one of these Halogen oven things already.

Wondered if I could get it to HT my cast boolits.

The oven manual says it gets to 482F, but at 61F shed temp it only got to 423F.

So I lined the glass dish with rockwool, this proved good to heat to 500F

http://i41.tinypic.com/2cql1mb.jpg

Now thinking I was good to go, I placed some 30-30 boolits I cast with a good hardball/arsenic bearing lead that water dropped to settle at BHN 19 or so.

So I started to heat em, with the oven set for 430F - which goes to 482F according to my German oven thermometer probe.

However... at just 374F by the thermometer, I noticed the first sign of the boolits leaning over...


At just 410F by the thermometer, more boolits are melting over under their own gravity...

http://i40.tinypic.com/8ziwpy.jpg

And by an indicated 474F, I am starting to more or less see all my soldiers keel over... oh the tragedy...

http://i42.tinypic.com/295qq8j.jpg


Rats. Well, that was interesting. I think these little Halogen ovens heat differently, am I right in assuming the halogen heat ring is blasting the boolits with too much 'direct' heat leading to hot spots?

You reckon if I set a cast metal plate barrier on a grill cage between the halogen ring and the boolits to act as a heat-dispersal shield, I might get an even oven heat so that the probe temperature and boolit temperatures match?

Will try this next unless someone has already tried a different way with a halogen.

[Hip's Ax]

I think your suspicions are correct. The radiant portion of the heat generated is obviously large in this type of oven. Making the temperature homogenous throughout the oven would be the answer I think.

[SniderBoomer]

Thanks, will try and get a nice fitting metal plate in between boolits and heat, recast the metal and see how it goes next...

[bangerjim]

That is why we use convection ovens rather than heat lamps.

bangerjim

[SniderBoomer]

That is why we use convection ovens rather than heat lamps.

bangerjim


Yep, but I don't have use of one right now Jim, so trying to fumble a way to use this halogen.

It would be a handy little thing if I can get success with stabilizing and equalizing the heat to the boolits.

[bangerjim]

Well,you can go the route of an ACCURATE "K" thermocouple laying right in with the boolits to measure in-situ temp and read it out with a temp meter. COST.....You are talking more money than buying a cheap convection oven at WalFart. I would suggest that temperature thing you are currently using for your measurements is totally off base.

Or you can try the "hunt & peck" method of trying different layers and types of insulation and baffles and playing around with that mix. COST......your time.

Radiant heating, which I have never used for anything, obviously must be different than convection heating, as you are melting your slugs. I have never melted slugs in my correctly operating convection ovens, even when I tried to.....just to test them. I have an old one that the thermostat is shot and I jumpered it out. It did start making slugs sag. I was using an IR temp gun to check it and it was around 520F.

Good luck!

bangerjim

[Dale in Louisiana]

You could try covering your slugs with a single layer of aluminum foil. Its reflective properties will take the radiant heat out of the picture. You then need to monitor for the temperature under the layer of foil to make sure that you reach the proper temperature there.

dale in Louisiana

[el34]

Radiant heat doesn't heat air. It heats objects that absorb its energy. Shiny stuff will reflect it back, flat black items absorb all of it and will heat the air in contact. If you can think of a way to let it hit something black that won't melt or smoke, and how to stir the air around, you'd have a convection oven. Kind of a big if though.

[SniderBoomer]

Radiant heat doesn't heat air. It heats objects that absorb its energy. Shiny stuff will reflect it back, flat black items absorb all of it and will heat the air in contact. If you can think of a way to let it hit something black that won't melt or smoke, and how to stir the air around, you'd have a convection oven. Kind of a big if though.


Dale - I tried a tripple-layer of aluminum foil 3 inches over the booiuts between the halogen ring. Sadly I got a full melt of all boolits (same alloy) even thought the tray (at boolit level) was only at 410C. Clearly that expensive temperature probe is no good for 'open' Radiant Heat.

El34 - yep, this is my next step, going to try to get a full round disc of mild steel between the boolits and halogen ring, and use matte black HT exhaust paint on both sides to increase even heat transmit. Your post was very educational.

Will report back - not givin up just yet. Though Grandma now has her eye on this oven for her chicken -)

[bangerjim]

Temp measurements are somewhat unique. "Black body radiation" measurements are different than standard or shiny surface.

Example: My laser IR temp guns will NOT measure the temp of the surface of a lead pot due to the reflectivity. Yet I use them to monitor very accurately the temp of my matte black boolits while baking in my convection oven.

As you have seen, radiant heating differs greatly to convection heating, as proven by your puddles of "soup" in your halogen thingy.

I have not read on here where anyone has ever attempted to do what you are doing. You are pioneering the technique!

Keep us informed.

bangerjim:guntootsmiley:
"inquiring minds want to know"

[Dale in Louisiana]

Dale - I tried a tripple-layer of aluminum foil 3 inches over the booiuts between the halogen ring. Sadly I got a full melt of all boolits (same alloy) even thought the tray (at boolit level) was only at 410C. Clearly that expensive temperature probe is no good for 'open' Radiant Heat.

El34 - yep, this is my next step, going to try to get a full round disc of mild steel between the boolits and halogen ring, and use matte black HT exhaust paint on both sides to increase even heat transmit. Your post was very educational.

Will report back - not givin up just yet. Though Grandma now has her eye on this oven for her chicken -)
Uh, 410 C is 770 F. Lead is supposed to be melted by then. I think you should be shooting for 400 F.

Put the temperature probe UNDER the foil, alongside the bullets. It doesn't work if it's catching radiant heat.

dale in Louisiana

[el34]

I think you'll need to arrange stuff so that the radiant heat doesn't directly hit the boolits. Give it the black target in your idea, and try hard to think of a way to cause air movement in the bowl. It doesn't have to blow hard, just a gentle 'stirring' of the air will spread the heat around. But don't suck in outside air, your hot air will escape the system.

The black target will be the heat generator, the air contacting it will heat up, the air movement will transfer heat to the boolis. That's what convection is- transferring heat with air. A fan easily comes to mind but it and its wiring would need to be okay at high temp. Maybe some paddles or a fan blade mechanically powered from outside. Good engineering challenge!