Cast Master

[savarin]

I have found a tin can works for one only melt of aluminium and dont hold it in there once melted but dont use stainless containers, they dissolve.I use a simple sheet steel flare on the end to help with holding the flame that I replace as needed (when its burnt through) but once the kiln is hot (red) the flare isnt required.The burner is also placed in at an angle to swirl around the inside and I have a steel baffle to prevent the flame from impinging directly on the crucible.The clay graphite crucibles are very good albeit a tad expensive but in the long run well worth it.I think I need a couple of full days casting to convert all my ally and brass scrap into ingots to move to my new shed.

[woodchucker]

they disolve?  I always used SS because I thought it was capable of higher temps... When I built waste oil heaters for friends I used Stainless because it lasted. I used regular oil burner, fire bricks, and SS in the burn area.

[savarin]

I tried to melt some ally in a stainless bowel, it dissolved a heap of holes right through.
The only saving grace was I turned off the gas and it solidified quick enough that I only lost about a cup.
Also it wasnt quite hot enough to totally liquify the complete mass and the resulting lump was virtually porosity free.
This led to experimenting with casting the ingots then re melting them just barely hot enough to pour which to date has produced very good solid casts with no pinholes or porisity.
I'm wondering if we all have different results due to the variety of burners and gas pressures.

[PJB]

Ya  molten aluminum will dissolve bare steel/stainless steel rapidly.   You can do it but need to spray with a clay or talc mold wash as a barrier.
I make disposable furnace rakes for the guys in the foundry to skim slag and they last maybe a week.   

[woodchucker]

Ya  molten aluminum will dissolve bare steel/stainless steel rapidly.   You can do it but need to spray with a clay or talc mold wash as a barrier.
I make disposable furnace rakes for the guys in the foundry to skim slag and they last maybe a week.

it's not just a thermal reaction then, since aluminum melts at a much lower temp than SS. There must be a chemical component in the reaction.

[PJB]

I remeber years ago when I naively used 304 SS tube for a stalk tube on an experimental miniature low pressure casting furnace I built.  That wasn’t the only blunder either but it was pretty funny after one shot of blowing air we pulled the stalk out from the crucible and it was literally almost gone.   
ZYP makes a boron nitride refractory coating you can get in rattle cans but not sure how long it would work in a crucible application.   We use it more as a release/topcoating on permanent molds.   

[savarin]

I've read about boron nitride as a release agent and protecting layer but didnt know it was available in rattle cans.
I must search for some.

[woodchucker]

check welding stores for the boron nitride. it's used in welding too.

[PJB]

We resell it as an accessory item to our products.   $45 US a can.   
Not exactly inexpensive stuff.   I’m sure its available cheaper we obviously mark it up.
Other thing to note is its more of a release coat than a base refractory material.   Aside from using a proper clay graphite or silicon carbide crucible, to coat a steel vessel I would look into more of a clay vermiculite material that provides a heavier/ insulating barrier.
Foseco and Pyrotech are a few mfg’s
To get good adhesion the vessel needs to be sandblasted, roughened surface, preheated to 650-700ish F then sprayed.   

[jpigg55]

We resell it as an accessory item to our products.   $45 US a can.   
Not exactly inexpensive stuff.   I’m sure its available cheaper we obviously mark it up.

You weren't kidding. Just took a look on Amazon: https://www.amazon.com/Aerosol-Lubricoat-can-oz-High-Temperature/dp/B013X7D25G/ref=sr_1_2?crid=3P9IGS4BXBLW9&dchild=1&keywords=boron+nitride+mold+release+spray&qid=1596479957&sprefix=boron+nitride+m%2Caps%2C195&sr=8-2

There were cheaper options, but had less than stellar reviews.

[woodchucker]

I think mcmaster and grainger have boron nitride for less.