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Rolling mill "rules of thumb"


#1

I’ve been searching the Orchid archives for some guidelines while
learning to use my new Durston DRM130 rolling mill (yahoo!). The
recommendations include, “take small bites,” “don’t take too small
bites,” “anneal frequently,” “don’t anneal too often,” etc. It’s
confusing and too general for someone without a good frame of
reference.

However, there were bits and pieces of specificity in the archives
that I’ve cobbled together as follows. I don’t want to start out by
causing myself problems, so I’m asking if these guidelines make
sense as a starting point for someone who is new to a quality
rolling mill:

Anneal when sheet is reduced by 30% for hard alloys.
Anneal when sheet is reduced by 70% for soft alloys.

Reduce by.25mm (1/4 wheel turn) on each pass for hard alloys
Reduce by.50mm (1/2 wheel turn) on each pass for soft alloys

One more question. Would guidelines be the same for wire as for
sheet?

Thanks so much for your advice,
Jamie


#2

Using rolling mills correctly is surprisingly complicated. All the
different rules of thumb were created as an attempt to simplify.
Sometimes they work and sometimes they do not, because there is no
real substitute for knowledge.

There are two type of damage that can be produced, - damage to mills,
and damage to ingot. Let’s take damage to mills first:

The maximum amount of bite should be stated in documentation that
come with the mill. If it not there make an effort to find out. If
maximum is exceeded, the gears will be damaged. Some say it can be
estimated depending on roll diameter, but in our corner cutting
world, good rolls can have crappy gears, just to save a cent or two.

Maximum amount of bite also depends on condition of rolls surface.
Maintaining pristine polish is very important. Metal that touches
surface of rolls moves at different speeds as compared to rolls.
There will be a point, where speed of rolls and metal will be the
same. Metal prior to this point moves slower, and metal past the
point moves faster. There is great deal of friction between metal
that moves slower and the rolls. Rolls have to slide past this metal
and if surface looses it’s polish, the forces acting on gears can
exceed original design specifications, with subsequent damage not far
behind.

Let’s deal with ingot damage. On first pass through rolls, bite must
be as large as possible. 30% reduction in thickness in one pass is
recommended. This is necessary to engage the core of ingot.
Otherwise, rolling will only affect outside layers, leaving core
untouched. Unless you have a motorized mill capable of such bite,
this is an impossible task. Therefore, ingot must be forged prior to
milling. After forging small bites are not ideal, but with hand mill
there is no other choice.

Theoretically, milling should continue until 70% of original
thickness is reduced. I said theoretically, because in practice it
would require ingot to be perfect. I am quite happy to anneal after
50% reduction, If 50% percent cannot be achieved, the ingot should be
recast.

It is advisable not to anneal at theoretical annealing temperature
if maximum deformation of 70% has not been reached. There is definite
relationship between amount of deformation and annealing temperature.
However, to practice this theory requires great deal of experience
and the damage may not even be noticeable, unless whatever you doing
requires a lot of annealing and deformation.

To summarize: Large bites are better than small and try to achieve
at least 50% of deformation. If you can do more even better, but do
not exceed %70. Do not anneal unless absolutely necessary and if
deformation is less than 70%, use slightly less temperature.
Deviations from recommendations are not deadly and only show up in
projects with many annealing/deformation cycles.

Leonid Surpin
www.studioarete.com


#3

Ive had my durston mill for some 35 yrs. Same roll size as the 130,
tho an earlier model.

to get to know what is possible and what is not, I ran lots of
trials with copper, brass iron etc so expensive silver etc wasnt
screwed up. do the same, and youll soon find out what is too thick to
mill. Make sure you bolt it to a strong bench with room all around
like a pedestal bolted to the floor. also get a strong lad or lass to
turn the handle for you so you can guide the metal
properly.,especially whan your down to 1mm or less. then youll find
that the metal will do all sorts of funny things.

As to damaging the gearing you wont do that, it will lock up before
that happens.

I motorised mine tho kept the handle for a specific job where I have
to roll so far then back off, alter the thickness then repeat. Ie to
make a tapered section piece of metal. Otherwise it is production
rolling mill for strip.

I had a job where the metal supplied by the customer wasnt enough
for the total of 2500 plaques ordered.

So I cut 36in strips off the rolls, at 36,/I000 in thick, and rolled
it down to 29/1000.in. to 48 in long, did the job fine, however that
was on another powered mill somewhat bigger.

dont be afraid to experiment. for example twist 3 1/8in copper wires
together really tightly. then put through the groves of the mill.
Makes an interesting section.

Repeat in silver and youve a section to make a nice torque. Also do
put good oil on the bearings such as ep 90. Let us know how you get
on.


#4
There is definite relationship between amount of deformation and
annealing temperature. However, to practice this theory requires
great deal of experience and the damage may not even be noticeable,
unless whatever you doing requires a lot of annealing and
deformation. 

Yes there is a relationship

Do not anneal unless absolutely necessary and if deformation is
less than 70%, use slightly less temperature. 

And from this statement you clearly don’t understand it. The greater
the strain on the metal/alloy crystal lattice i.e. the deformation
from applied stress, the lower the annealing (recrystalazation)
temperature is for that piece of metal. So your advise in regards to
annealing is incorrect. You cannot specify a precise annealing
temperature without knowing how much cold work the item has
undergone since the last annealing so recommended annealing
temperatures are just ball park figures that may or may not be
correct for a particular operation. And given most readers on this
list are going to be using a torch to anneal the idea of precise
temperature control of the annealing process is not really
applicable.

A 70 % reduction will be fine for some metals/alloys but in others
will be too much. It all depends on the particular alloy but as a
rule of thumb a reduction of 50-70% is a reasonable target range.

James Binnion
James Binnion Metal Arts


#5

Jamie,

The people who manufacture rolling mills often don’t know how to
actually use the machines they make. Several years ago, I taught
Matthew and Sara Durston how to make their own wedding rings on one
of their 120 mm Durston D2 rolling mills. They were delighted with
their finished rings.

In my studio, our main concern is the maintenance and preservation
of our mills. At the end of our day, we wipe our mill’s rollers with
oil, and cover each mill with a cover, to keep dust out. Mills get
wiped clean each day before use.

I try to prevent the rollers from coming all the way together
(touching). Any grit or small pieces of metal that may be on the flat
rollers could tend to pit the rollers if they were tight together
when rolled. If you do need to roll the rollers all the way together
( like when using the side rollers), then make sure the flat rollers
are absolutely clean.

When rolling square wire in the grooved rollers, you won’t want the
rollers touching together when rolling down ingots. The wire ingots
push outward from the force of the rollers, and they tend to need a
bit of room between the rollers to do this. This will also prevent
thin “fins” from being extruded onto the square wire when rolling.

Each type of metal and the form it is in helps dictate how much
force is used to roll out a sheet or wire. If you are needing to
almost stand on the mill’s handle to get the metal to roll through,
then you are applying way too much force and effort. Don’t break
either yourself or the mill’s gears by trying to be macho. Take
smaller “bites” and don’t beat yourself up making stock.

Oh, and make really sure your metal is CLEAN and DRY before rolling
in your mill. Rust spots happen quickly, and are no fun to polish out
with 1500 sandpaper.

Good luck with your new Durston. You couldn’t have made a better
choice in rolling mills.

Jay Whaley


#6

Looks like good advice from Leonid.Be very careful when rolling wire
not to over compress so as to produce a protruding edge on each side.
If you do file it off, dont compress it back into the octagonal wire
as you will have problems later. I made a table showing the start and
finish limits for each set of grooves and how much to compress the
wire for each pass through the rollers. Use the sliding marker in the
groove your material is in. And learn your table by heart and stick
to it religiously. ie:

groove 7 = 3.5mm > (reduce) by 5 degrees > / finish = 3mm
groove 8 = 3 mm > 2.5 > = 2.7

And if I am going to want to produce a particular measurement
repeatedly for a job, the job card will have all the necessary
both for wire sizes and sheet thicknesses, and
subsequent wire drawings and proceses. The rolling mills can be used
in many different ways,see: Ganoksin: On Your Metal. Forging a Heavy
signet ring using the Rolling Mills, where I produce two reverse
tapers and then cross roll. I have produced paper knives using a
similar method.

David Cruickshank (Australia)
jewellerydavidcruickshank.com.au


#7
And from this statement you clearly don't understand it. 

Really?

The greater the strain on the metal/alloy crystal lattice i.e. the
deformation from applied stress, the lower the annealing
(recrystalazation) temperature is for that piece of metal. So your
advise in regards to annealing is incorrect. 

Strain can be caused by different factors. Displacement of atoms from
their positions in lattice is much better measure. The larger the
displacement, the more work atoms have to perform while returning to
their original positions, and therefore the more energy they require.
The energy is supplied by source of heat during annealing and amount
depends on temperature and length of application.

You cannot specify a precise annealing temperature without knowing
how much cold work the item has undergone since the last annealing
so recommended annealing temperatures are just ball park figures
that may or may not be correct for a particular operation. 

Since I am the one who is applying cold work to the item, I
definitely know the amount of it, and therefore I can estimate
annealing temperature and time required. As far as been "ball park"
that is stating the obvious. I do not remember suggesting some hard
numbers.

And given most readers on this list are going to be using a torch
to anneal the idea of precise temperature control of the annealing
process is not really applicable. 

How could this be true? We solder using torches. We solder next to
soldering seams; next to next to small parts than can be
melted in a blink of an eye. If we can do that, we can definitely
have precise temperature control with the torch.

Leonid Surpin
www.studioarete.com


#8
Really? 

Yes, really

Strain can be caused by different factors. Displacement of atoms
from their positions in lattice is much better measure. The larger
the displacement, the more work atoms have to perform while
returning to their original positions, and therefore the more
energy they require. The energy is supplied by source of heat
during annealing and amount depends on temperature and length of
application. 

Strain is the displacement of atoms in the lattice caused by applied
stress exceeding the metals elastic deformation limit, that is its
definition. The greater the strain the more energy stored in the
lattice which translates to a lower amount of energy (temperature)
required to release the strain. When enough strain is accumulated in
the lattice the lowest energy transformation when heat is applied is
to form several new smaller crystals from the distorted parent
crystal rather than try to move the great distance that would be
required to return to original position and shape. This is called
recrystalazation or annealing. If there is no recrystalazation then
all one is doing is strain relief.

How could this be true? We solder using torches. We solder next to
soldering seams; next to next to small parts than can
be melted in a blink of an eye. If we can do that, we can
definitely have precise temperature control with the torch. 

In soldering you have the advantage of many visual clues for the the
correct temperature not the least of which is the melting of the
solder. Annealing is a product of temperature and time and if done
at optimum temperatures there is not going to be much in the way of
visual clues to overheating as the temperatures are lower than
solder melting temperatures and the light from the torch makes
reading the metal color quite difficult. It is highly improbable
that one could hold the correct temperature for the required
duration (10 - 30 min) with a torch without over heating and
certainly not possible with a torch to hold a given temperature for
optimum annealing. So in annealing with a torch you substitute
higher temperatures in an attempt to deal with the short time period
that is possible in torch annealing.

James Binnion
James Binnion Metal Arts


#9

Regarding keeping mills clean… We keep a large chunks of sponge
rubber saturated with oil jammed in at the top and bottom of our
rolls. They clean and oil the rolls as we use them.

Have fun and make lots of jewelry.
Jo Haemer
www.timothywgreen.com


#10

Jay,

I am pleased to hear of your care for the tools you have…I am not
so thoughtful. Most of my shop has a light coating of grit and oil
which is rarely wiped clean…I swept up 25 pounds of floor grit
yesterday and, to my surprise, I have proof that there is actually a
floor.

As to rolling mills:

I have two, but I have not cold rolled anything in months… unless
you count tongs.

All my work from steel to copper to titanium is hot rolled with
water coolant at about 33 feet per minute. I try to take only 1/16"
reductions (on stock from 2" down to 1/2" thick and then less for
the thinner sheet), but some materials can handle quite a bit
more…more than my mill can deliver in fact. I have a 7.5hp motor
on one and 40 hp on the other (both with rather large gear
reductions) and I have stalled the smaller mill trying to find its
limits…I have a loose belt drive so the belt slips before the
gears take the ultimate force.

I feel that the occasional re-heat and smaller bite extends the life
of the tool so I gladly work that way. Thus far no particular job
was worth the replacement of the rolls. Some jobs I roll 200 pounds
of material a day.

I have run from one ounce billets up to 25 pounds in steel in
lengths of four foot…the rule of thumb I have is to try very
hard to keep my thumbs. Your milage may differ.

Ric Furrer
www.doorcountyforgeworks.com
Sturgeon Bay,WI


#11
Strain can be caused by different factors. Displacement of atoms
from their positions in lattice is much better measure. 

I’m not sure that’s possible Leonid, maybe you meant molecules, or
grains?

And given most readers on this list are going to be using a torch
to anneal the idea of precise temperature control of the annealing
process is not really applicable.

How could this be true? We solder using torches. We solder next to
soldering seams; next to next to small parts than can
be melted in a blink of an eye. If we can do that, we can
definitely have precise temperature control with the torch. 

I think what James means is that we use a flame to anneal, as
opposed to a kiln with an inert atmosphere.

Using a flame is not precise, you can get close, but it will never
be precise, due to the nature of flames.

Added to this you have fluctuations in the gasses that you use,
maybe there’s an air current in the workshop.

You have to have skill to use a torch, there’s an art to it,
otherwise anyone could pick up a torch and use it straight away.

Anyone can use an atmosphere controlled kiln, by pressing a couple
of buttons and setting a few dials. It will be precise.

When I anneal precious metal I watch the colour of the flame change
to tell me the metal is in an annealed state, other people watch the
colour of the metal… both of these methods rely on your eye, and a
judgement. A judgement is not precision, it’s an estimate.

Regards Charles A.


#12
I think what James means is that we use a flame to anneal, as
opposed to a kiln with an inert atmosphere. Using a flame is not
precise, you can get close, but it will never be precise, due to
the nature of flames. 

There are 2 kinds of craftsmen. One kind ( I call them technocrats )
are totally enslaved by machinery. Take from them their mechanical
toys, and they are lost. Cannot do anything without gadgets. Another
kind are trained to use their senses and intelligence in their work
and have no need for technological crutches. Back in Russia, I was
making a living by doing architectural scale repousse. We were using
Aluminum sheets 12 x 9 feet, which had to be annealed prior to work
and as required during the work. By it’s nature, repousse is very
unforgiven if material is not uniform, and annealing Aluminum is
much trickier than Gold or Silver. As a source of heat, we used
kerosine lamps, which is as far from precise heat source as one can
get. Never the less, we did it and did it successfully.

Leonid Surpin
www.studioarete.com


#13

Hi Leonid,

Jim was talking about metallurgically ideal technique, which is
flatly unobtainable by hand, with a torch. Just can’t be done, so
there’s no point wasting time trying.

You’re talking about how hard aluminum was to torch anneal, but your
skill made it possible. Well…not exactly. Aluminum’s not really
all that hard to torch anneal, as long as you know what you’re
doing, and don’t treat it like anything other than aluminum. It’s
nastier than silver, or gold, but so are a lot of metals. (A2
anyone?) The window of acceptable results is pretty wide. Anything
that gets you anywhere in the window will work out well enough, which
is really all any of us need for hand work. So long as you’re in the
window, you probably won’t notice much of a difference one way or the
other, even though you may be a long way from the “ideal” of maximum
softness. Your reflexes, honed over years of dealing with hand
annealed stock, will stop you long before you shatter the material.
Even though “perfectly” annealed stock could have been pushed much
further. The costs of blowing up a handmade part vastly outweigh the
gain of pushing as hard as is metallurgically possible. So our
trained skill makes us stop short, before there’s much risk of the
part cracking.

On the other hand, if you’re feeding raw billet stock into a rolling
mill, and trying to get 5 km of sheet rolled today, you need to
make sure you are pushing the material as far and as fast as you
possibly can. That’s where it becomes critical to make sure you’re
getting every last bit of anneal you can, and every last bit of
deformation you possibly can before failure. That sort of work pushes
the metal much, much farther than we ever do by hand.

It’s not a case of skill versus technological crutches, it’s two
entirely different processes, for entirely different goals.

FWIW,
Brian


#14
The window of acceptable results is pretty wide. Anything that gets
you anywhere in the window will work out well enough, which is
really all any of us need for hand work. 

That is fine when piece of aluminum is small, but when it is 12 x 9
feet, it is not that simple. We put a sheet against the wall and
starting at one corner, standing on a ladder, annealing commences one
small area at a time. When you done, softness must be uniform, or
your work will have cracks. Problems with cracks are not only visual.
Cracks can happen after installation, especially if it a sunny side
of building. Hot during the day, cold at night, expansion and
contraction all the time. If metal is not uniform, it does not take
long. Once cracks appear, water get’s in, freezes, and what had
installation weight of few pounds, now weigh a ton. You see the
problem. So the window that your are talking about is very, very
narrow.

Leonid Surpin
www.studioarete.com


#15
 Aluminum sheets 12 x 9 feet, which had to be annealed prior to work
 and as required during the work. By it's nature, repousse is very
 unforgiven if material is not uniform, and annealing Aluminum is
 much trickier than Gold or Silver. As a source of heat, we used
 kerosine lamps, which is as far from precise heat source as one can
 get. Never the less, we did it and did it successfully.

Well that wasn’t really what I was driving at.

A job, even a complex one, can be completed without precision. This
is what you’ve just described with your example above.

He’s a better example that I’m hoping will let me explain myself a
little better.

Annealing 18k yellow gold.

One gold supplier states the the correct way to anneal 18k yellow
gold is for 18 minutes in an inert atmosphere, then quenched
immediately in water.

I don’t know anyone that does this, they all use a torch to anneal.

Getting the job done, and precision operations are very different
things.

Experience is not to be confused with precision either.

I can make a knife blade that will have excellent edge holding
capabilities, you wont need to sharpen it much, and depending on the
application you may never need to sharpen it. My knife making peers
have their own chosen method for tempering a knife. Some use
temperature controlled kilns, some use their forge, I use a hand
held propane torch.

My method is not precise at all, but it creates a superior blade. I
use my experience, and literally paint where I want the blade to be
hard or flexible. This is getting the job done.

Regards Charles A.


#16
When I anneal precious metal I watch the colour of the flame
change to tell me the metal is in an annealed state, other people
watch the colour of the metal... 

I’ve always watched the color of the metal…Could you tell us
about watching the color of the flame… Never heard of
that…:-)…!

Janet in Jerusalem


#17

Janet,

Flame can be used as an indicator of annealed state by watching for
the flame to change to yellow. When the flame that bounces off of any
metal, it will change to yellow when the metal is annealed. Don’t
know why, maybe off gassing of an oxide. But they say it works that
way for ALL metals, I have only used it for silver and copper.

Tom Paris


#18
But they say it works that way for ALL metals, I have only used it
for silver and copper. 

I am not going to agree with you here. This is a metalsmiths
equivalent of an urban legend. Just for one counter example platinum
will not be annealed using this method.

James Binnion
James Binnion Metal Arts