I need to confirm my suspicion with my problems melting silver. I
have a propane torch and am melting about 5 grams of silver leftover
small pieces (not bigger than 5mm wide). The metal forms a round
blob starts to spin, then I take the flame and nudge the blob over to
the edge of the crucible and pour…I get a blob in my open cast
mold.
How do I increase the metal fluidity?
Am I not getting the metal hot enough? i.e. it needs to be in a
liquid state. I am heating the mold. The size of the item is 20mm
tall x 2 mm deep.
Any comments are appreciated. Sorry to be such a newbie- Thanks!!!
If it was “spinning”, it’s fully molten, and as fluid as it’s going
to get. However, if the outside of the crucible isn’t as hot as the
area where you melted the metal first, then by the time you pour, the
cooler outside edge of the crucible could have chilled the metal a
bit. Make sure, while melting, that you’ve heated the pouring lip of
the crucible hot enough.
But 5 grams just isn’t very much. With an open faced mold, you have
to contend with normal surface tension, the same things that, when
you melt the metal, makes it ball up instead of just flowing out into
a thin sheet of liquid. You will always find, with an open mold, that
the top surface of the silver isn’t level, but curved, and the top
edges may not fully fit/fill the mold, as surface tension affects the
shape, and small quantities will make this more pronounced.
You might simply need to be melting a bit more metal, so the weight
of the metal itself forces it down into the mold, leaving excess on
top that you can file off. Or, with some sort of closed mold and a
sprue rising up, then the column of melted metal in the sprue pushes
down while the closed mold restricts the shape to the mold shape, so
once the metal is down into the mold, it has no choice but to take
the shape of the mold.
Pat, a problem those just beginning to pour metals have is they melt
the metal but forget to heat the pouring lip. After the metal is
liquid slightly tip it towards the pouring lip and move the flame to
the lip keeping the metal in the flame as it blows back into the
crucible. Then make a swift, smooth pour. Sometimes, depending on the
type of crucible and how thick it is, it can take come time to heat
the lip. If you do not do this, the metal begins cooling as it moves
over the lip and will not pour properly!
Keep your flame as you pour on the nudge of your crucible and on
your melt is one action that you have to concider.
You never mentioned anything concerning the temperature of your
crucible. It can happen that your metal freezes on top of your spreu
beeing to cold to accept the liquid metal.
The position of your flask i.e. your project -horizontal or
vertical- can be another cause for this issue. It’s much easier to
pour an object in a upright position due to the gravity of your
molten metal. Keep in mind that you are not using centrifugal force
or vacume system to pull that molten metal in your flask.
It’s a kind of hard to explain every detail by mail and not knowing
exactly in what position you are and under which conditions you’re
working. As far as I believe, Rio offers an very good video tape or
DVD showing how proper castings can be done. A good book is something
else to think of. Books are also available by Rio grande or other
suppliers.
By all means, I’m not making a commercial for Rio but I like the way
this company complete there business and all the effort they put to
keep their customers satisfied. Feel free to make your choice in any
supplier or manufacturer according your needs or location.
Do I understand correctly that you are pouring into an open, tray-
like mold? That will not work. It must be enclosed except for the
sprue (in) and possibly a vent (out) for gasses. If you are talking
about pouring into a proper mold with a cup on top and a sprue in to
the model, then maybe everything is just too cool, or else you need
more of an assist to get the metal forced in, either with steam,
vacuum, or centrifugal force. Get a book on jewelry casting and study
it. If I have misunderstood you, I apologize. Please give 3
dimensions of your mold, not just two, and maybe I will get what you
mean.
As I recall, Jay Whaley has a very good video posted somewhere on
melting/pouring from a crucible. I don’t remember if it’s on his web
site, Orchid, or YouTube. Jay, can you give us the link?
Yes Peter has reason as ever… and we should be sure that our metal
has to be some degrees over the melting point because the temperature
comes down quickly.
Are you using a flux like borax or auflux? Getting the metal hot
enough is obviously important, but keeping it hot is also important -
if it’s practical and not dangerous for you, try heating the crucible
and/or the silver during pouring. A 5gm blob of silver can lose it’s
heat very fast. Also try heating you mould ashot as you can - that
depends on the material the mould is made from, but the hotter the
better.
This note is tardy, but I have been pretty busy with orders, looking
for a job and troubleshooting my notebook issues. Anyway thanks for
all the great comments. I must have been just really, really lucky
when I poured my first cast, since the cross I did turned out pretty
ok. Then when I tried it again, again…could not get anything but a
blob.
Peter R: I think you solved over 50% of my problem- not melting and
pouring enough metal.
Jamie: I am not using borax or auflux- does it make a big
difference? Is the borax like the one in the green box from the
store?
Alfred, Pedro & Don: thanks- I do need to get the lip hot and the
mold hotter.
M’lou-Yes I am trying to pour just a two dimensional item. I had a
request for 20 tiny thin crosses and thought…I can do this. I ended
up soldering them.