*it does seem like it would be a rather simple process : * which
comprises a step involving fabrication of a first hollow element in
tubular form, made of precious metal or a precious metal alloy and
intended to act as" a lining;and then preparation of a second element
in cylindrical form made of metal or metal alloy, or precious metal"
in your case and " intended to act as a core for said first element
in tubular form; a step involving coaxial combining together of the
two elements by interposing a layer of solder in between so as to
obtain a tubular assembly which is then subject to a first drawing
step aimed at compressing the first element onto the second element;
Followed by a step involving brazing of the tubular assembly so as to
melt the layer of solder and fix together the two elements before a
second drawing step for reducing the thickness of the brazed tubular
assembly to the desired value is reached…"
But its not as simple as it sounds and requires more specialized
equipment than a drawbench and furnace /kiln along with some
calculations based on the liquidus properties of each to prevent a
meltdown of the silver - or rather the silver seemingly 'absorbing"
the gold layer before even adding a metal alloy /solder layer between
the two to help prevent this. All to make a relatively small amount
of stock. and that’s just the most immediately probable issue you’d
experience at the cost of a fair amount of gold and silver sheet.
Even if you used lengths of tubing of gold and added a layer of
powdered solder suspended in a gum or other binder and then a length
of silver as an “insertion wire” with a graphite or otherwise
non-conductive material as a core to keep it all from collapsing when
heated and hoping at the precise temperature the solder melts and
bonds the gold that is no where near liquidus, but has heated enough
to bond to the silver insertion tube, which couldn’t be as thin as
the O. D. normally supplied by vendor and finding the right i. d.
graphite, magnesium, or some ceramic composite rod ( imagine a long
length of mechanical pencil lead in the exact core size and length
necessary to fit the assembly which is now four layers that all have
to remain perfectly intact, not move and - well, stay put in the kiln
perhaps in a pile of alumina to prevent movement…) You would need to
buy a fair amount of it for the trial and error it will surely
require.!.
It would be far easier to simply purchase bi-metal sheet, anneal it
very carefully (math required or a conversation with the tech person
at the manufacturer that sells you their bi-metal sheet as to the
annealing time at x temp for x gauge and in your case without
coaxial pressure)…Then forming it into a tube and then drawing the
tube to the desired thickness and length. the bi-metal sheet would
already be bonded., and joining the seam straightforward if gold,
rather yellow silver solder is used to close the seam as the gold
temp. wouldn’t be an issue if you carved the metal sheet into a lap
joint (removing with a sharp graver or other tooling the gold on a
bevel to have a silver to silver seam which could be closed with
yellow silver solder and the tube resulting appearing all gold on the
outside and silver inside…
If 40 cm is needed you could probably triple that amount of raw
materials just for the trial and error experimentation of making
your tubing in the small studio.
i don’t quite understand why the id has to be silver though unless
you are going to engrave it, or carve, etc. If it’s for slicing off
some pieces for tube settings there are easier ways to do that too! I
suggest your looking at the patent info and equipment that you would
need access to to accomplish it successfully. patent. EP 1679015 A1.
- pertains to the methodology involved in and problems related to
making tubular bi-metal for jewellery. it may seem technical but many
questions you ask are answered in the application’s abstract…
It is not that it is impossible but that you could far more easily
buy 40cm + of bi-metal sheet than finding the **equipment necessary
to make the metals bond to the core and then convincing the equipment
owner(s) to let you have a go at it on their equipment in their
space/factory. and where is that factorye there are a lot of things
you perhaps haven’t thought of ! At least, if you have strong hands,
a decent drawbench set-up (or an electric winch) and some bi metal
sheet, you could draw down the tubing. But the process isn’t
something i’d let even an intermediate student attempt- particularly
if I had to watch! You can do it- I can’t figure out why you’d need
silver as an lining unless you’ll embellish the tube once drawn…
I also don’t want to discourage your experimentation, but perhaps
you have available funds and money isn’t an issue- in which case, a
bi-metal sheet is generally supplied in 12 inch (one measurement) or
6 inch size **s and working with the bond already done seems like the
right way to start. Good luck. rer