Looking for ideas for a propane burner design

[Omaha]

TL;DR Summary

Need to design a custom burner for a "sandbox" used to hold ceramic shells in a bronze casting operation

I make custom cast bronze decorative motorcycle parts using lost wax investment casting. I'm looking to improve the precision and reliability of my casting process (currently getting maybe 25% duds over time). My current initiative is to improve my temperature control on the shells prior to pouring in the bronze.

Toward that end, I fabricated this "sandbox":

There is a floor in the box at the 13" mark, and then a 4" air chamber underneath. (The box has a bottom plate that is not shown here.)

My original idea was to just stick the business end of a propane weed burner into the port (shown on the right of the image). That works, but there isn't enough combustion oxygen in the air chamber, and I have to position the burner outside of the chamber, and only blow in the flame.

Here is a short video showing a pour. You can see the shells getting pre-heated, then filled after they are loaded into the sandbox. In case you're wondering, the sand used is just plain play sand like you can buy at any Home Depot. It is just there to make sure the shells don't split open.

In a perfect world, I'd have the shells at 1000F for the pour. I'm not sure that is feasible, but I'd like to get as close to that as possible.

What I need to do is design a burner so as to get more heat into the air chamber, and consequently more heat into the sand and the shells. The fuel is ordinary, 20# propane tanks.

Anyone have any experience with something like that who could point me in a particular direction?

 

[Arjan82]

Why not just drill some appropriate sized holes to mitigate the oxygen problem? You need to think about the airflow. Probably some holes behind the burner and some exit holes at the far end.

 

[Omaha]

What I'm thinking is that there's no way to have the combustion oxygen be drawn from inside the chamber. It has to come from outside, either via some sort of venturi setup, or perhaps even a forced air fan.

 

[Baluncore]

Maybe you could build an outer stove box that surrounds the sandbox, but with a 2" gap. Inject the flame from the burner into the gap between the walls, from low-down, to heat the sandbox and contents. The hot gasses should flow around the sandbox several times before being exhausted at the top. That will heat-soak the contents of the sandbox, from the outside in to the shells. Any vapour products of the heated sand will flow up through the sand, to be vented at the top. Once the sand has dried, you can pour the

 

[Tom.G]

Look at the burners on a gas stove or furnace. They typically have air intake thru an adjustable vent before the burner. This also allows the gas and air to mix before it gets to the burner itself. The small holes of the burner block the flame from getting inside the burner. Propane torches and Oxy-Acetylene Welding torches use the same approach.

Cheers,
Tom