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Casting manganese bronze


#1

I love the color of manganese bronze. Supposedly your able to use
this alloy for a substitute for gold in sample mountings. I’ve not
been able to get it to work. I’ve had a lot of surface flaws and
haven’t been able to get it to melt or cast cleanly It leaves a lot
of dross and excess metal in the crucible. The best results I’ve had
to date were with my electomelter and vacuum caster, though I’ve
attempted to cast it centrifugally, too. The lowest flask temperature
I’ve cast the stuff in has been 900 degrees, thus far. I’m wondering
if I should lower it even further. The models are pretty thick. I’ve
cast the metal at 1900 on my last attempt with the electromelt, so I
think I’ll drop the next all the way down to 1700. Anyone here have
any experience with this alloy? My one source for bronze
casting advice has avoided manganese bronze for silicon bronze for
these very reasons, but he admitted he didn’t try to work out any of
the problems because silicon bronze was so easy to work with. I look
forward to any advice I can get.

Larry


#2

I have cast manganese bronze successfully in the centrifuge. You
might expect a larger percentage of failure from this metal but there
are several palliative steps you might take. You are already aware
that you must use flux in this process. Use powdered brazing flux
(from a welding shop). One of my solutions to the problem was to use
a lot of flux. Before the melt in the crucible put 1/2 teaspoon of
flux powder with the metal. As soon as the metal is well (!) melted
and swirling from the torch pressure, put more flux on the molten
bronze puddle and let the centrifuge spin. The metal will probably
cast well if you have it at the proper temperature. Your crucible
will have dross and of flux debris remaining in it and should only be
used for casting this metal. (When I first (50 yrs. ago) started
casting in the centrifuge I would wet small sheets of asbestos and
line the crucible with it to protect the crucible. DON’T do this. We
now know that asbestos paper is too dangerous to use. Besides mice
got in the drawer in which I kept it and used it to make nests.
Wonder what happened to them?)

Another potential problem is to make sure your casting material is
really manganese bronze. There are many bronze and brass alloys
suited for different purposes and you can’t distinguish them by
color. This is the problem with using scrap material from the
salvage yard. It is a rare scrap collector who knows what the metals
are that he has collected. I found this to be true the hard way with
my first foundry shop. I bought several hundred pounds of "bronze"
that was almost non-castable. Now I only use Si-bronze.

Another thing is that you should be careful remelting the sprues,
vents and scrap. Use fresh known metal for each run. (Si-bronze is
an exception in that you can remelt your scraps for casting)

Gerald Vaughan


#3

Hi Gerald, thanks for your input. I decided that the fail rate for
manganese bronze was too high. The piece I’m making has a large flat
area that shows pits very easily. The material I’m casting is a hard
plastic that doesn’t burn out well and is relatively thick. I solved
a few problems by making sure the investment sets up to it’s maximum
green strength before burnout. I also switched to silicon bronze.
The color isn’t as good but the client decided to have the part gold
plated, so it doesn’t matter as much what the alloy is. I may
eventually switch to silver if the bronze doesn’t gold plate well.
The big thing I have to figure out now is why detail near the casting
sprues gets deformed. It looks like the metal hits the detail and
breaks down the investment. I’m going to resprue away from the detail
and make the sprues thinner, but more abundant. Still have lots of
investigation yet to do. I’ve not given up on manganese bronze, but
it won’t work on this project. I’m pretty sure the metal I have is
manganese bronze because I bought it fresh from a trusted supply
house, not as scrap.

Larry