Yellow Brass sticking to investment


I’m pretty new to the casting world. Not a jewelry maker, but we are producing parts similar to typically jewelry with fine parts.

We have started working with Yellow Brass (using yellow brass casting chunks from Rio Grande). We wish to use this material as the parts we are producing will need to be soldered by our customers with questionable soldering skills. What we are finding is that the yellow brass tends to really want to stick to the investment, which is a bit of a challenge to remove. We can get it off in an ultrasonic cleaner, but then the finished parts have a pretty poor finish and color. (images below)

The images shown were cast at 1800 degrees in a 950 degree flask using a JR2 induction vacuum casting machine. Wax was steamed for an hour and burned out at 1350 over 3 hours.

Any suggestions as to what can be done to improve the finished casts?

I use Rio Grande’s Yellow Brass casting chunks to make parts like yours for bronze sculptures. I use an electric melting furnace and cast using jewellery vacuum casting equipment. I use a 12 hour burnout cycle with 4 hours at 732C (1350F).

I pour this material at 1040C (1900F). Try a hotter melt temperature?

Wow, I must have read your mind, I have a couple flasks burning out overnight that I intended on casting at 1900F to see if a hotter temperature would help. I’ll let you know how I make out with it.

Thanks for the input.

Yellow brass isn’t the easiest material to cast - or to solder. Its high zinc content makes it melt at lower temperatures than bronze, but the zinc also tends to volatilize as a white smoke when the brass is melted. This smoke isn’t good to breathe. Use a heavy flux coat over the metal as it gets up to temperature. Or better yet, switch to another metal that’s easier to deal with, like classic bronze (copper/tin) or silicon bronze (copper/silicon).

I don’t think it needed a higher melt temperature; that will make it smoke worse. The mold seemed to fill okay, even the thin sections, which would not happen if the metal was too cold. But the burnout does seem short; more time might help, particularly if you noticed any dark discoloration in the investment. The burnout temperature was a bit high; that can cause the investment to break down, leaving sulphur residues and a rough cast. 1250F should be sufficient, if you take enough time. Let the flask cool a little before pouring; 900F is about right for most things.

Did a cast at 1900F this morning and while still had the issue of the investment sticking to the metal, the cast was much better. Previous casts at 1800F didn’t fill completely, whereas this time all but one piece filled nicely. Still had lots of clean up though. Not sure what I should be expecting when casting Yellow Brass, but items I have seen cast by others seem to look nice and bright. Perhaps they are doing follow up work to them, but I suspect not as they are production parts.

Tim - this would be an ideal application for a tumbler to clean the casting. I’d run a midrange abrasive in a vibratory tumbler for 6 to 8 hours. It should take off the investment and start to smooth the parts. Then go to a fine abrasive for 4 to 6 hours and it should clean them up very well. Use a pyramid shape media to get into the little spaces.
Judy Hoch

awerby is correct, yellow brass smokes in the presence of oxygen because of the zinc. I hate zinc. I tried manganese bronze once and swore off ever using it again because of the boiling and sputtering and explosions in the crucible due to the high zinc content in the alloy.

My electric melter has a graphite crucible and a cap over the crucible which keeps the melt in an oxygen reduced environment. I only see the smoke with the yellow brass when I take the cap off my furnace to remove the crucible and pour. Use ventilation.

Silicon bronze might be an alternate. It’s less expensive, melts cleanly without smoke, and polishes to a yellow colour. I get my silicon bronze from Contenti as Bronze S Copper Casting grain. I pour this at 1070C. If you use this alloy be careful if you pour the casting grain into a hot crucible and one of the grains pops or explodes when it heats up. It can happen.

Good luck in your casting journey. It took me about a year to learn how to get good repeatable results.