Gunner wrote:

A young entrepreneur friend of mine makes spear guns, spears, etc. He
has been getting his spears heat treated at a commercial treater, but
the costs are eating him up.

Here is the requirements... a stack of 6 foot long spear blanks has to
be kept at 925F for 2 hours. They are about .30 in diameter.

Pretty simple.

Now the problem...making an oven 6+ feet long that will reach that
temp fairly uniformly over the entire length.

Propane is probably the cheapest way, or even city gas.

We were thinking of a 7' length of 6" Sched 40, slid into a 7' lenght
of 12" Sched 40, using either ribs welded to the outside of the 6"
pipe to keep it centered, or something similar.

Now the big issue...how to make a burner(s) that will uniformly heat
the inner pipe.

I recall seeing a set up many years ago, that somehow managed to get a
spiral of flame down the inside of the outer pipe that actually
wrapped around the inner pipe. It was fascinating to see. But we
would be happy to get any sort of unifiorm flame...G

Anyone with any hints, links ideas on how to accomplish this task?

I do have a 350' roll of .065 x .125 nickle flat resistance
ribbon..but think it would be a bitch to make this thing run on
electricity, and expensive to operate.

Help!

Unless there is a compelling reason to go with gas, go electric. No way
you can run a gas heater and control the temps to the level you want as
easy or as cheap as electricity.

This is for heat treating aluminum right?

A single coil type element on a controller, and a motorized impeller
inside the furnace (motor outside, impeller inside, think convection
oven) to keep the air moving and , thusly, the heat even throughout the
interior.

Works for the heat treating furnace at work.

Cheers
Trevor Jones