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Mold casting of silver


#1

Dear members:

Although I am not new to the jewellery trade, I am indeed new to
the question that I want to put forth today.

I have recently purchased a rolling mill in the hopes of being
able to melt and reuse all the silver scraps that I have piling up
in my studio… Well, then I had decided to go and purchase a
steel flat plate mold and a crucible and a handle that all nicely
fits together to allow one to pour directly from the crucible to
the mold, I proceded to prime said mold as directed, and prime the
crucible with borax, and then the moment of truth. The melting and
pouring of the silver…all the metal that I chose for the melt
was clean cutaway scraps.

Then the worst…I had the metal at the pouring consistency and
the mold warmed as best as possible and when I proceeded to pour
the metal it just kinda decided that it would congeal at the
opening of the mold and not slide in nice and smooth as I would
have expected.

Hmmmmm, and so now I am at a loss as to what to do…Do I have to
have a second friend beside me with a second torch, just to keep
heating the mold, or is there a trick to this that I am just not
getting?

I constantly watch the responses in here from all of you and I
know that someone must have a fail safe method for this
dilemma…I have read Oppi’s book, but still feel the complete
idiot as of late.

thanks and hoping for some help!
smartdog@msn.com
Metalogic


#2

Bryna,

You need to slightly over-heat the metal. Make sure that the
surface is really ‘spinning’ before you pour and keep the flame
playing on the metal in the crucible as you pour it.

I have to say that I always use flat, open ingot moulds, although
I know that the metal quality from the closed moulds is said to be
better.

Yours aye,
Dauvit Alexander,
Glasgow, Scotland.


#3

Hello Bryna: It is important that the mold be hot. It is important
that you pour the metal without ever covering the entire hole. The
metal must flow down the inside of the mold allowing air to escape
past it or it will seal the top and will not fill. I put my ingot
mold on a charcoal block so that the heat does not sink away very
fast. Try tilting the mold slightly and pouring slower.

Michael Mathews Victoria,Texas USA


#4

Dear Bryna,

You are not alone in this very irritating problem; the friend with
another torch is a good one but the friend might not be available
when you need to work. What I do to solve this is to heat my mold
200 degrees F higher than melting point of my metal. Then very
quickly pour the said molten metal. Now, don’t get in such a hurry
that you slosh some of it out… that can be a sad thing too. good
luck. Denise Jenkins


#5

Dear Tracy,

I may have a solution to your problem. I too used to warm the
mold (as I was trained) and suffered the same difficulty.

Here’s what works: forget heating the mold! Apply 3-in-1 oil
liberally to the mold. Keep the torch on the lip of the crucible,
AS WELL AS the metal, in order to keep the “pouring path” hot. Pour
in one quick continuous movement. The oil should help prevent the
metal from congealing at the opening of the ingot mold. The oil will
smoke off.

Good luck

Eben-


#6

Bryna, sounds like one or two things are wrong.

  1. did you coat the mold with carbon soot or oil. this helps the
    metal slide over the surface instead of sticking.

  2. your mold was not hot enough. very common when you are first
    starting to pour ingots. heat the mold before yyou start to melt
    and then rest the crucible against the ingot as you melt letting
    the flame bleed over the edge of the crucible a little and keep
    the mold hot. mabe three!

  3. practice! it is something i miss every now and again and have
    to go back for a second melt and pour. I’ve been doing this for 25
    yrs, so don’t get discouraged.

Frank Houston, Tx.


#7

Bryna, Hi,

I can discern 2 possibles here. The mold seems to have been too
cool. Not hot enough. Did you use an oil or wax coating on the
mold? You should’ve, and it’s a good indication of mold readiness
when the wax/oil fumes or smokes.

Plus maybe the metal was not hot enough. … nah, on second
thoughts, I’d go for the mold too cold option. Yoursilver seems to
have been only just molten (not superheated very much) but that’s a
good temp to pour.

Keep the flame on the metal as it pours.

Regards,
Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT ONE - Queenstown Mar11 to Mar18 '98
http://www.adam.co.nz/ruthbaird/ across the bench from me


#8
Here's what works:  forget heating the mold! 

This advice is somewhat misleading, Eben, as you go on to say you
do in fact heat the mold, although indirectly while heating the
silver. I’d hate someone forget about heating the mold and to pour
molten silver into a cold mold. The water content in the steel may
not have evaporated off and will turn to steam and expel silver at
a great rate into the air.

Regards
Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT ONE - Queenstown Mar11 to Mar18 '98
http://www.adam.co.nz/ruthbaird/ across the bench from me


#9
    Hello Bryna: It is important that the mold be hot. It is
important that you pour the metal without ever covering the
entire hole. The metal must flow down the inside of the mold
allowing air to escape past it or it will seal the top and will
not fill. I put my ingot mold on a charcoal block so that the
heat does not sink away very fast. Try tilting the mold slightly
and pouring slower.

I agree. Pour like you’re pouring beer! (down the side of the
mold). Til you learn a quick and smooth action I suggest you learn
a slow and smooth action.

I have the whole deal on a steel tray to catch any clumsy
over-shoots.

Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT ONE - Queenstown Mar11 to Mar18 '98
http://www.adam.co.nz/ruthbaird/ across the bench from me


#10
   ...I had the metal at the pouring consistency and the mold
warmed as best as possible and when I proceeded to pour the metal
it just kinda decided that it would congeal at the opening of the
mold and not slide in nice and smooth as I would have expected.

G’day Bryna; I always recycle my scrap sterling using the same
process as you, but I use one of the flat, shallow crucibles in a
home-made holder. I hold the torch on the silver in my left hand -
fairly soft, reducing flame - add a sprinkle of flux (put the
crucible on a pumice hearth for a moment) and then keep the flame
on the molten silver whilst pouring into the heated moulds. Pickle
the rods/slab, dip in baking soda, wash, dry, then roll out the
surface imperfections - there will be some; you just expect that as
you aren’t vacuum or centrifugal casting, and they don’t matter
usually.

If you heat the silver for too long, oxygen will dissolve in the
melt, causing tiny voids in the cast as the metal cools. These
will show up as tiny spiky tags when you draw your rolled rods into
smaller wire. I know! Quoth he, wryly :frowning: Many happy
recyclings and Cheers,

        /\
       / /    John Burgess, Nelson, New Zealand
      / /
     / //\    @John_Burgess2
    / / \ \
   / (___) \
  (_________)

#11
   I'd hate someone forget about heating the mold and to pour
molten silver into a cold mold. The water content in the steel
may not have evaporated off and will turn to steam and expel
silver at a great rate into the air.

G’day; I saw a good mate - a very experienced jeweller - do just
that. I was peering over his other shoulder, (good, eh?) and then
we both spent the rest of the afternoon scraping 18carat gold off
the wall, floor, etc. “It shouldn’t happen”, mumbled my mate. Among
other

words.

        /\
       / /    John Burgess, Nelson, New Zealand
      / /
     / //\    @John_Burgess2
    / / \ \
   / (___) \
  (_________)

#12
Then the worst...I had the metal at the pouring consistency and
the mold warmed as best as possible and when I proceeded to pour
the metal it just kinda decided that it would congeal at the
opening of the mold and not slide in nice and smooth as I would
have expected.

This may be a stupid question, but was the mold adequately vented?
I.e: small troughs carved into the mold leading away from the main
cavity to the outside of the mold allowing the trapped, heated air
to escape? Lisa


#13

This advice is somewhat misleading, Eben, as you go on to say you
do in fact heat the mold, although indirectly while heating the
silver. I’d hate someone forget about heating the mold and to pour
molten silver into a cold mold. The water content in the steel may
not have evaporated off and will turn to steam and expel silver at
a great rate into the air.

I did not wish to mislead anyone, but I do not heat the mold at
all. In fact, I only heat the crucible and it’s “pouring path”.
The mold barely receives any heat during this process. My
suspicion is that the mold does not get heated to any more than 100
Fahrenheit. I can touch the mold immediately after my pour with my
bare hands. The only preparation to the mold that I do, is to
generously oil it. I suspect that any water in the mold get
displaced by the oil.

I’ve used this technique, successfully, in excess of 10 years.

If in doubt, give it a try.

Eben Lenz


#14
This may be a stupid question, but was the mold adequately vented?
 I.e: small troughs carved into the mold leading away from the main
cavity to the outside of the mold allowing the trapped, heated air
to escape? 

Good point. My molds are homemade and consist of two heavy plates
of steel clamped with square-section steel rod bent in a square U
shape. The sandwich when tightly clamped has a few imperfections to
allow for the escape of gases ets when I pour. But then I also pour
down one end of the opening.

If your ingot mold is a new product, either it should have vent
channels and that’s ok, or it doesn’t and it fits TOO well - better
file some small grooves in the mating surfaces with the edge of a
square file.

Hmmm, I seem to have typed ‘square’ a lot in this email…

Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT ONE - Queenstown Mar11 to Mar18 '98
http://www.adam.co.nz/ruthbaird/ across the bench from me


#15

Bryna…

You’ve received some good advice… I’d add that melting and
pouring metals is a lesson in physics/thermodynamics. Don’t be
afraid just think of all the things you already know about. How fast
a liquid turns to solid depends upon … amongst other
things… how much colder the mold is than the metal. Yes the mold
should be preheated to about 300-400 F after being coated with a
layer of oil. DO NOT use a synthetic oil. POUR IN A WELL
VENTILATED AREA. The oil layer acts in a number of ways not the
least significant is that it generates carbon which creates a nice
reducing atmosphere minimizing oxides and giving you a nice bar to
roll out. In addition, if you don’t pre-heat the mold you risk -
big time - an explosion of any water/moisture that may be on the
mold surface. It’s not a pretty sight.

You’ll have lots of small bubbles on the surface which can be
removed by scalping (sanding or grinding the surface) to get the
best possible results from your rolled material.

Metal temperature can be gaged by eye. The metal should be very
shiny and bright. The surface should appear to be moving quickly.
You should flux the melt well with anhydrous borax or boric acid
and remove as much of the flux before pouring as possible with a
graphite or quartz rod. You’ll have to develop a feel for the
pouring rate. Have fun.


#16
    My molds are homemade and consist of two heavy plates of
steel clamped with square-section steel rod bent in a square U
shape. 

G’day; I think we must have the same dreams - my ‘ingot’ sterling
mould is exactly as Brian described though with the slight mod
that I filed a sort of flat funnel so it’s easier to pour into.

For rod moulds I got a strip of 1cm x 5cm steel, and had the
village garage cut two pieces about 9cms long (their mechanical
hacksaw saves sweat!) and in one of these I drilled two 3mm dia
holes on a centre line, one at each end. I clamped the plates
together face-to-face, and using the holes to guide the drill, made
the holes in the other plate about 6mm deep. I found a nail which
was a tight (drive-fit) into the part-drilled holes, and used emery
paper to make it a slide fit into the holes in the other plate. The
nail/s were cut off flush with the surface of the ‘slide-fit
plate’. The nail studs are to keep the plates in registration. I
clamped the plates face-to-face vertically in a vice and drilled
two holes down the length of the plates with a 6mm drill, - but
NOT of course, out the other end, frequently pulling it out to get
rid of the swarf, and using CRC as a drill lubricant. I used a
large countersink and round file to create funnel shapes at the
open end of the holes.

I have used this cheap rod mould for around 10 years, and do find
I get a better pour if I heat it a bit first. And no, I don’t use
oil. I use a small clamp to hold the two pieces together which acts
as a rest to tilt the mould towards the flat-type crucible, and
mind you, I stand the moulds in a shallow tin - I don’t trust
myself to pour perfectly every time! And I’d better come clean
and tell you that my flat ‘ingot’ mould is simply the rod mould
pieces back-to-back, with the U-shaped piece of 3mm square steel
clamped between them. The registration studs are not needed for
this operation. Oh, in case you are interested, each rod plus the
bit forming the funnel weighs 15 grams in sterling.

Now all I need is a rolling mill, but can’t think how to make one
from the junk I have around. So I borrow my mate’s from down the
road a bit, in exchange for our erudite(?) conversation over a
couple of my home-brews. It’s 7.5%, so we have to ration it
though. ;-D Cheers - and happy recycling.

        /\
       / /    John Burgess, Nelson, New Zealand
      / /
     / //\    @John_Burgess2
    / / \ \
   / (___) \
  (_________)