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Old September 15th 06, 03:22 AM posted to rec.crafts.jewelry
Peter W.. Rowe,
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Posts: 355
Default rolling mill questions

On Thu, 14 Sep 2006 18:41:26 -0700, in rec.crafts.jewelry "br"
wrote:

Hello all,
I've been a lost-wax caster for over thirty years, and I never really
learned to use a rolling mill. I never even bought one, because I could
always figure out how to get along without it. I have several questions for
you bench experts concerning rolling gold wire. For an upcoming line, I need
long bands of 18K yellow gold to then have disks punched out, 1/10th. of a
millimetre thick and 8mm in diameter. How many operations/reductions am I
looking at to roll down a 1.2mm wire to a 0.1mm x 10mm ribbon?


three comments.

First, one tenth of a millimeter is quite thin stock. not all rolling mills
will give you uniform thickness at this thin guage. You'll need a good quality
mill to get that. Some of the cheaper mills simply won't be a uniform enough
thickness at that thin guage.

Second, your understanding of what to start with, is wrong. Assuming you wish
to roll the wire in a continuous length so it passes straight through the mill,
if you want to end up with ten millimeters wide, you need to start with square
wire stock not a whole lot narrower than that. I'd run a few tests to find the
exact needed starting stock, but I'd hazard a rough guess you'll need to start
with stock roughly six millmeters square, maybe a bit more, from a square wire
rolling mill. Remember that rolling mills mostly elongate the stock. Only a
little of the spreading out is laterally, so the stock gets thinner and longer
as it goes through the mill, but only a little bit wider. If you started with a
round or square 1.2 millimeter wire and rolled it to a tenth of a millimeter,
you'd end up with somewhere in the area of 1.5 mm wide, not ten millimeters.
Now, if you roll the piece of wire crosswise through the mill, you'll get to the
width you wish, but this then limits the length of your strips to the width of
the rolls, and is not likely to give you a uniform and straight strip either. It
will have some random and annoying bends in it... probably, even rolling it the
long way through most mills, you'll end up with a few wobbles and bends, but not
to the same degree, and for punching your disks, unless it's being done on an
autmated machine that's very picky about starting stock (some are), you should
be OK.

Third, with 18K yellow golds, you generally can roll the metal out to about a 90
percent reduction in cross sectional area between annealing operations. The
number of passes through the mill as you go from starting to ending operations
will vary depending on the type of of mill and power source, and whether it's
geared down, etc.


Is this too
thin to be done reasonably?


No, but you'll need a quality mill.

Could I do this, with good repeatability
(thickness-wise I'd like to stay between 0.09mm and 0.11mm), using an off
the shelf rolling mill?


Maybe. Again, you'll need a good quality mill. The problem is not whether YOU
can do it, but whether the rolls of the mill are concentric enough and uniform
enough that the stock they produce meets your standards.

Do standard mills have well polished rollers


No. Most rolling mills are sold with a finely ground finish, not polished. A
good machine shop can polish them for you, or perhaps some manufacturers would
supply that as special order. Highly polished rollers are harder to care for,
and since they don't grab the metal as much, sometimes a little harder to use.
And in use, you need to be much more careful to keep the rolls, and the metal
going through them, very clean too. Even an oil film on the rolls will change
the polish you get on the metal being rolled. Certainly, it's possible to have
polished rolls produce polished metal. The industrial level users of rolling
mills do this routinely. But it's not such standard practice for studo
craftspeople or for the hand operated mills generally sold to craftspeople.

, and will I have a problem getting an easy polish on the ribbon after the final
reduction?


At that guage, yes. If you need an actually polished ribbon, your best bet is
indeed to use a fully polished rolling mill to do it.

I'm hoping to need about 10 meters a year, lets say 1000 pieces.
What are the do's and don'ts for doing these myself? Perhaps I'd be better
off getting them made? I have kilns and temp. control for annealing. That's
no problem. I'd appreciate any and all ideas, comments, etc. B.RANDALL
http://www.srdfrance.com


Are your kilns also atmosphere controlled to elimiate fire scaling? If not,
you'll have to take steps to preserve that polish you wanted.

Normally, because of the difficulty in rolling thin strips and getting them
really straight sided and all, the standard practice at the industry level
(refiners, metals suppliers, larger manufacturfers, etc) would be to start with
a wider sheet, and run it through a slitter that gives you your end strip cut to
precise width with straight edges. Better product, better for punching machines
that want to start with a coil of strip, but additional waste to deal with if
you're running it through a slitter yourself.

Frankly, I'd suggest ordering the stock already rolled and slit to the
dimensions you need. Your needs are for a fairly small amount of material
According to my quick rough calculations, your ten meters of this stock should
end up being only about 3/4 of an ounce of 18K gold, something less than 400
dollars worth at todays prices. Thoughj ordering this stock made for you might
as much as double that cost, you're then still looking at a total figure for
that years worth of not all that much more than just a good manual rolling mill
would cost, not to mention the value of the time needed to produce your stock.

Given that, the cost and effort of doing this yourself might not be easy to
justify, especially given the difficulty of getting the level of quality you
could get from a decent metals supplier. I'd suggest, franly, placing an order
for several years worth at a time, if you order the stock.. Ten meters of this
thin stock simply isn't all that much, given how thin it is. Order more, and
any special order charges get spread out over a larger oder.

Frankly, I'd consider ordering the fully cut disks, not the slit stock. With
the slit stock, you end up with the waste that then needs to be reprocessed.
More time and fuss, and again, considering the very thin stock involved, not
such a large amount of money in the metal, even with gold's current prices.


Peter
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