I have recently had 2 questions asked of me regarding very bad
silver castings. Both cases are from the same country but different
customers. The silver castings are incomplete, at first yes you
think of short filling. But it clearly is not short filling, it
looks like there has been a very violent reaction in the silver when
it has entered the flask (almost as if it exploded). I was told by
both people concerned that the fine silver used was 99.9, this got
me to wondering what trace elements were in the 99.9 fine silver. I
am sure the fine was taken from photographic plates and perhaps
x-ray plates. I know both of these contain many other alloys other
than silver, i was wondering if anyone can help me by explaining the
effect that maybe Lead can have when melting silver and casting, i
am clear on the effect of Boron and others but Lead i am not sure
about other than of course its poisonous. Can it cause a violent
reaction or not, does the silver become unstable when entering the
flask?
I hope someone can help me,
Thanks much,
Pete Croton
Pete,
I once used a sterling supplier who used fine silver from reclaimed
film. I believe one batch was not refined correctly and I lost 9 3 x
7 flasks, 450 pieces. They all cast, however they snapped like dry
pasta when any pressure was applied.
Contacting many different people trying to find out what was wrong,
the most common comment was that lead contamination could be the
problem.
I noticed that the metal when melted was like bubbling lava, not the
shiney puddle I was used to. I was casting centrifically. If it is
not casting completely can I venture that you are using vacuum
casting? Hope this helps.
Richard Hart
am clear on the effect of Boron and others but Lead i am not sure
about other than of course its poisonous. Can it cause a violent
reaction or not, does the silver become unstable when entering the
flask?
I too have done castings in fine silver, and the castings have no
problem.
I think the trace elements will not effect much even if it is lead,
the reason i think may be incomplete bunout in both the cases. Due
to incomplete burnout the trace elements may have reacted and caused
the trouble that is due to carbon film remaining in the cavity of
the mould it must have prevented the air to escape through the mold
cavity when the metal is injected in to the mould,and this is known
as back pressure porosity,even if the metal has no trace elements as
lead or other elements.
Ask the casters that the burnout was perfectly done or not?
Hope this will give you some idea to think about the problem in one
direction of many causes.
Wishing all my Orchidian friends a total health Physical, Mental,
Spiritual and Social.
Srrive to be Happy
Umesh