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rolling mill questions



 
 
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  #1  
Old September 15th 06, 02:41 AM posted to rec.crafts.jewelry
br
external usenet poster
 
Posts: 11
Default rolling mill questions

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? Is this too
thin to be done reasonably? 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? Do standard mills have well polished rollers, and
will I have a problem getting an easy polish on the ribbon after the final
reduction? 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



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  #2  
Old September 15th 06, 03:22 AM posted to rec.crafts.jewelry
Peter W.. Rowe,
external usenet poster
 
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
  #3  
Old September 15th 06, 09:17 AM posted to rec.crafts.jewelry
lemel_man
external usenet poster
 
Posts: 22
Default rolling mill questions

Peter W.. Rowe, wrote:

...snip
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.



I'd say Peter was pretty much spot-on concerning the practicalities of
making your own 0.1mm strip and punching the discs. 0.1mm is pretty thin.
I tend to make quite a lot of strip in the work I do; usually 0.2mm up
to 1mm thick, and 1 to 5mm wide. The requirements are such that it is
completely impractical for me to stock all the strips I might need, so I
have to make my own. I have to anneal frequently and try to make the
minimum number of passes. Getting straight strip is a problem. I've
found that the first pass of the square wire is critical: if that
results in straight strip then its likely to continue that way. Best
results are obtained by making sure the wire enters the rolls at right
angles and by maintaining a slight tension on it. ie, forcing the mill
to pull the wire.
I often want to end up with strip of a particular thickness and width
and to that end ran a series of experiments to see how the width was
affected when rolling wire. The result was surprising: the width
increased rather more than I expected and more than Peter suggested.
Basically, when you roll a wire or strip the width increase depends on
the ratio of the previous width to thickness. The bigger the ratio the
smaller the increase, but its not linear. I worked out some sort of
correlation between the ratio and percentage increase and found I could
get pretty accurate results, especially for ratios smaller than about
10:1. Based on that work, I would say that 1.2mm square wire rolled down
to 0.1mm would end up close to 4mm wide.
For what its worth, my calculations suggest that 2.2mm square wire
rolled to 0.1mm would end up around 10mm wide. But as said above, the
accuracy at a ratio of 100:1 is not good. With more work it could
probably be improved, but in my case its just not worth it.

--
Regards, Gary Wooding
(To reply by email, change feet to foot in my address)

  #4  
Old September 15th 06, 04:08 PM posted to rec.crafts.jewelry
br
external usenet poster
 
Posts: 11
Default rolling mill questions


"lemel_man" a écrit dans le message de news:
...
Peter W.. Rowe, wrote:

...snip
you'd end up with somewhere in the area of 1.5 mm wide, not ten
millimeters.

snip With more work it could

probably be improved, but in my case its just not worth it.

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)


Thank you both for your very informative and pertinent replies. Only one of
my suppliers (I'm in France) will even consider doing this for me, and won't
give me a quote for at least a week, so I'd like to continue with a few
questions about rolling these pieces myself, although I'm already shying
away from that idea. My decision will, of course, depend on the quote(s) I
get back from my supplier, but at least I will have learned a lot more than
I knew before about rolling mills. I hope your patience won't wear out
before my questions do! Indeed, my calculation of the diameter of wire
(1.2mm) needed was based solely on the cross-sectional surface area, and
didn't take into account the differences between lateral spreading and
elongation. Perhaps starting out with 0.5mm thick by 2 or 3mm wide would be
easier? I doubt that "wobbles and bends" would be a big problem as the disks
will be hand-punched. Am I correct in assuming that the "straightness" of
the ribbon depends on the parallelism of the two rollers? Concerning a
polished surface (only one side needs to be polished); would it be feasible
to use a long strip of highly polished spring steel, run through the mill at
the same time as the gold ribbon, to polish the surface? My kilns have an
argon injection system to reduce oxygen content in our flasks. I could
easily (I hope) avoid the firescale from annealing. Thanks again for the
help. If ever I start to make these myself, I'll be back with a few more
questions!
B.RANDALL
http://www.srdfrance.com



  #5  
Old September 16th 06, 04:58 AM posted to rec.crafts.jewelry
Carl
external usenet poster
 
Posts: 38
Default rolling mill questions

When lemel_man put fingers to keys it was 9/15/06 4:17 AM...

....
Basically, when you roll a wire or strip the width increase depends on
the ratio of the previous width to thickness. The bigger the ratio the
smaller the increase, but its not linear. I worked out some sort of
correlation between the ratio and percentage increase and found I could
get pretty accurate results, especially for ratios smaller than about
10:1. Based on that work, I would say that 1.2mm square wire rolled down
to 0.1mm would end up close to 4mm wide.
For what its worth, my calculations suggest that 2.2mm square wire
rolled to 0.1mm would end up around 10mm wide. But as said above, the
accuracy at a ratio of 100:1 is not good. With more work it could
probably be improved, but in my case its just not worth it.


Hmmm...

http://c-24-63-36-176.hsd1.ma.comcas...llingChart.gif

Add some more points and it could be useful, Yes?

There has _got_ to be something like this out there in the literature.

- CW

  #6  
Old September 16th 06, 04:58 AM posted to rec.crafts.jewelry
lemel_man
external usenet poster
 
Posts: 22
Default rolling mill questions

br wrote:


Indeed, my calculation of the diameter of wire
(1.2mm) needed was based solely on the cross-sectional surface area, and
didn't take into account the differences between lateral spreading and
elongation. Perhaps starting out with 0.5mm thick by 2 or 3mm wide would be
easier?

The wire gets longer and wider when you roll it. The textbooks usually
state that the width doesn't alter much, but I've found that it does.
According to my calculations, if you roll 1.65mm square wire down to
0.5mm thick it will spread to be about 3mm wide. The volume remains
constant of course.

I doubt that "wobbles and bends" would be a big problem as the disks
will be hand-punched. Am I correct in assuming that the "straightness" of
the ribbon depends on the parallelism of the two rollers?


If the rolls aren't parallel you will start to roll an arc and when you
try to correct it it will start to go wrong. If the rolls are truly
parallel _and_ you keep the straight wire at right angles to the rolls
you will produce a nice straight strip, but its harder to do than to say.

Letting the wire enter the rolls at other than right angles is the most
common cause of a curved strip. Allowing the wire to wander sideways
causes it to enter the rolls at less than 90 degrees, thus again
creating a wiggle.

I've found that holding the wire in some thick smooth faced pliers,
right up close to the rolls so that they actually rub (being thick there
is no chance of the rolls grabbing them), keeping them at right angles,
and squeezing them gently while rolling works pretty well for me.
Squeezing the wire with the pliers ensures that the rolls actually pull
the wire, thus tending to keep it straight.

Once you get a wobble on the strip its almost impossible to remove it.
If its not too severe you can sometimes rescue it by winding the strip
into a tight whirl, holding it together with binding wire, annealing it,
removing the binding wire and gently hammering the whirl flat.
Unfortunately its not a guaranteed cure 'cos the parts of the strip on
the outside of a curve will get hammered the most and will therefore be
a little thicker; when they get rolled they get spread a little more and
tend to be on the outside of the curve again. But sometimes it works.

Concerning a
polished surface (only one side needs to be polished); would it be feasible
to use a long strip of highly polished spring steel, run through the mill at
the same time as the gold ribbon, to polish the surface?


Most good rolls have nicely polished hardened rollers which impart a
pretty good surface ready for polishing. If you take care of them they
last a long time.


--
Regards, Gary Wooding
(To reply by email, change feet to foot in my address)

  #7  
Old September 16th 06, 05:13 AM posted to rec.crafts.jewelry
ted frater
external usenet poster
 
Posts: 133
Default rolling mill questions

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? Is this too
thin to be done reasonably? 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? Do standard mills have well polished rollers, and
will I have a problem getting an easy polish on the ribbon after the final
reduction? 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



This one is something I can help you with.
Putting it simply, a rolling mill makes metal thinner IN the direction
of the rolling.
IE your 1.2mm wire will go down to the thinness you want BUT wont get
any wider!!.( ok I know there will be someone who will say it actually
does get wider by about 2/4 %)
If you want to go wider IE to make the ribbon you describe you will
have to cross roll the wire. the length you can do this with is the
width of the rolls.
so if yor mill rolls are say 5in wide, youll be able to work a 4.5in
length of your wire. This is going to be difficult in handling and
placing the wire just right so it gets nipped by the rolls and flattened
across its width.
not the way to go
Now to produce the width you want youll need to buy a 10mm wide piece of
gold and roll that. NOT wire
I say 10mm wide ans youll need a bit of spare each side of the punch dia.
also your punch and die tolerances will have to virtually zero and
sharp. also youll need to punch it hard not annealed.
Youll need a good quality mill.Because the thinner you go the greater
any lack of parrallelness will show up on the rolled metal. ie it will
come out curved. so you then have to turn it over to get it straight again.
If you take all this learning curve into account, the cost of the mill
setting it up etc youll find it cheaper to buy it in from the bullion
dealer already rolled, assuming it is listed in his catalogue.
As for the finish. Rolling to a high finish is also difficult. Most
rolls are grouind finish not mirror.
Hope this helps.


..


  #8  
Old September 16th 06, 08:48 AM posted to rec.crafts.jewelry
Carl
external usenet poster
 
Posts: 38
Default rolling mill questions

When br put fingers to keys it was 9/15/06 11:08 AM...

...I doubt that "wobbles and bends" would be a big problem as the disks
will be hand-punched.


Hmmm... why the strip then? Surely it's possible to find a sheet that's
0.1mm thick, polish it and punch it. You'd be able to pack the holes
more efficiently on a larger sheet and have less scrap when you're done.

For your volume, you can probably find someone to make the discs for you
at a reasonable price compared to your cost for equipment, space,
learning, and time.

- CW

  #9  
Old September 16th 06, 08:48 AM posted to rec.crafts.jewelry
lemel_man
external usenet poster
 
Posts: 22
Default rolling mill questions

ted frater wrote:
...snip...
This one is something I can help you with.
Putting it simply, a rolling mill makes metal thinner IN the direction
of the rolling.
IE your 1.2mm wire will go down to the thinness you want BUT wont get
any wider!!.( ok I know there will be someone who will say it actually
does get wider by about 2/4 %)


I am surprised that this myth continues to be preached. Its simply not
true. I found that out when I wanted a 100mm 0.25mm x 1mm strip. I took
a 25mm length of 1mm square wire and rolled it down to 0.25mm. That
should do it, right? Wrong. I got a 50mm strip 2mm wide. That's when I
did the experiments. I did lots, plotted the results on a graph, applied
some curve fitting algorithms and came up with a pretty nasty equation.
I simplified it a bit and wrote a program that I've been using for a
number of years. Its not 100% accurate, but close enough to be extremely
useful. It also varies a little with the metal being rolled. I feed in
the width and thickness of the strip I need and it tells me the size of
the square or round wire I need.
For example, suppose I want a 3 by 0.2 strip 400mm long. It tells me I
need to start with 161.25mm of 1.22mm square wire, or 162.81mm of 1.37
diam round wire, and it will weigh 2.688gm in 9ct yellow gold.

You don't believe me? try it yourself. You must start with well annealed
wire and roll it aggressively, ie. minimise the number of passes and
anneal frequently. In the example I would set the roll to give 0.2mm
thickness in one pass, measure the result, adjust for the error (its
never too thin), and do the correction pass.
I can't believe I've got the only magic rolling mill in the world.


--
Regards, Gary Wooding
(To reply by email, change feet to foot in my address)

  #10  
Old September 17th 06, 03:52 PM posted to rec.crafts.jewelry
Abrasha
external usenet poster
 
Posts: 298
Default rolling mill questions

ted frater wrote:



This one is something I can help you with.
Putting it simply, a rolling mill makes metal thinner IN the direction
of the rolling.
IE your 1.2mm wire will go down to the thinness you want BUT wont get
any wider!!.( ok I know there will be someone who will say it actually
does get wider by about 2/4 %)



Not true! Ted, there you go again! Once again you speak of things you do not
know about, a bit too soon. Why don't you do a test and roll down a piece of
1.2 mm wire and roll it down to .2 mm (you probably do not have a mill that will
do .1 mm accurately) for instance, and see for yourself what happens. 2 to 4%?
I don't think so.

Precious metal wire that gets rolled down in thickness will widen considerably.
I do it all the time for a number of my production pieces, where I make
rectangular cross section wire from square wire. For one particular piece I
start with 1.5 mm square wire, and end up with wire that is approximately 1.15 x
1.8 mm. By my calculation, that is a 20% increase in width!

I have a table in a German training book for goldsmiths, that lists the
thicknesses and widths one will end up with for a number of square starting
stock. Comes in very handy from time to time. If there is interest, I can scan
the page, and put it on my site for a few days.

--
Abrasha
http://www.abrasha.com

 




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