I recently purchase my first ever rolling mill. I am finding pretty
much everything I roll, wire,sheet etc, that it ends up coming out
really wavey. Am I annealing improperly, or is something else going
on?
I recently purchase my first ever rolling mill. I am finding pretty much everything I roll, wire,sheet etc, that it ends up coming out really wavey. Am I annealing improperly, or is something else going on?
It could be annealing, or bad casting, or you trying to reduce to
much at one pass, or it could the the mill itself.
When you roll, reduce thickness a little at a time. Anneal very
carefully. Try to roll commercial plate. It it still wavy, contact
whoever sold you your mill. It could be rollers, or bearings, or
other defects.
Leonid Surpin
Hi Dave,
I recently purchase my first ever rolling mill. I am finding pretty much everything I roll, wire,sheet etc, that it ends up coming out really wavey. Am I annealing improperly, or is something else going on?
I find that I get a bit of deviation depending on the alloy and the
thickness of the ingot/sheet. I anneal my metal correctly, and when
necessary when rolling, so I can’t comment, if that’s what is
causing your problem.
It shouldn’t really matter if you are going to further work your
metal.
Regards Charles A.
I recently purchase my first ever rolling mill. I am finding pretty much everything I roll, wire,sheet etc, that it ends up coming out really wavey. Am I annealing improperly, or is something else going on?
That’s pretty much normal behavior for small rolling mills, which is
what virtually any hand rolling mill is. For one thing, we generally
are rolling metal that is not exactly uniform in structure and
internal stresses, be they from the prior pass through the mill or
defects or inclusions in the metal. But whatever the reason, the
compression of the metal may not be exactly uniform from one side to
the other, so the metal bends as it comes out of the mill. In
particular, with newly annealed sheet, the compressive force on the
metal is greatest right at the surface, which elongates a bit more
than the center (you easily see this at the ends, where the center
appears depressed compared to the edges or middle of a wire) So the
surface ends up more work hardened than the interior. With the next
pass, this results in more of the elongation and compression of the
metal happening closer to the center, which is still softer. This
progresses until the metal becomes uniformly compressed and work
hardened throughout it’s thickness. In practice, when rolling a
sheet, for example, right after annealing, you’ll see it curve or get
wavy as it leaves the mill, and this increases but changes a bit as
you continue with further passes. But about the time the internal
stresses in the metal become uniform, it pretty much straightens out
again. not usually perfectly flat, but a lot closer than it had been
before. This is a good clue to tell you it’s now time to anneal
again, since going further can overstress the metal and start it
cracking.
When you buy commercially prepared sheet metal, it’s flat in part
because the roll diameters used are a lot larger than the small
rolling mills we use. And generally those rolling mills are more
rigid and highly finished, so the variance in the metal is less, thus
the variance in stresses in the metal also is less. And such metal
usually is furnace annealed, which also contributes to more uniform
structure.
But basically, the effect you’re seeing is normal. If you need flat,
anneal the metal once it’s the thickness you wish, then gently mallet
it flat with a rawhide, rubber, or plastic (I like the lead weighted
dead blow types especially) mallets on a good flat steel block.
For wire, it’s easily straightened. Anneal it after you’ve drawn it
to size. Put one end in a vise, grab the other end with pliers or
draw tongs, and pull enough so you feel the wire slightly “give”,
stretching ever so little. That’s all it takes. Your wire will now be
dead straight.
Peter
Dave- I’m betting that you are taking too big a step down in the
rolls. I usually only take it down a tiny bit at a time. I also flip
the metal over for each roll. Don’t ever cross roll unless you have
annealed first.
I also like to keep a sponge soaked in oil wedged in at the top and
bottom between the frame and the rolls so that they are oiled and
cleaned every time you use it.
Have fun and make lots of jewelry.
Jo Haemer
www.timothywgreen.com
Thanks Peter for your excellent explanation as to why metal comes out
wavy when using a small rolling mill. My small mill does the same
thing and I have fussed fruitlessly trying to realign the rollers
thinking that they were the problem.
Alma
My small mill does the same thing and I have fussed fruitlessly trying to realign the rollers thinking that they were the problem.
Peter is correct in pointing out that warped metal could be simply
the function of roll diameter. But if this is the case there are
still remedies available.
What is the rolls diameter? It should be at least half of the
length. If it smaller, you are limited to very small increments.
Warped metal means uneven pressure of rollers on metal. It could be
caused by ingot defects ( areas of varying hardness ), uneven wear,
or engineering defects like rollers designed without any
consideration of roller flexing. If that been the case, just limit
yourself to 1/8 of the turn and see if it goes away.
There is one more thing I need to mention. At all costs avoid cross
rolling without annealing between directional changes. That will warp
the metal every time.
Leonid Surpin
Another thing to look for when your sheet stock has parallel
“stripes” on it coming out of the flat rollers.
Are you running the sheet through the mill in one continuous roll,
turning the handle without stopping, or are you having to stop the
mill periodically during the rolling process?
Often having to stop the handle while rolling metal through the
mill’s rollers can leave a noticeable mark on the stock. This is
especially true if you are putting too much pressure on the rollers,
and you just don’t have the strength to roll the metal through the
rollers without stopping a few times.
Sometimes I will see a student struggling to roll a sheet through
the mill, notice the stripes on the surface of the rolled sheet, and
then show them on the metal’s surface where they were stopping the
handle during the process.
Jay Whaley
Thank you all for your input. I am annealing evenly to the best of my
ability. I am using as pure a metal stock as I can, I am rolling as
smoothly and continuously as I can, and I am doing very little at a
time. One person told me I probably need to calibrate my rolls. Can
anyone tell me how to do that?
I am annealing evenly to the best of my ability. I am using as pure a metal stock as I can, I am rolling as smoothly and continuously as I can, and I am doing very little at a time. One person told me I probably need to calibrate my rolls. Can anyone tell me how to do that?
Take a piece of paper and oil slightly, then dust it with corn
starch or similar. Place the paper between rolls and close it down,
until contact with paper is made, NO FURTHER! Examine the print and
adjust screws until you can get an even print.
Leonid Surpin
Hi Dave
I am going to give you advice totally different than what you have
had. Everyone says adjust the mill slightly, the question is what is
slightly to one person is different to the other. I take the biggest
bite that I can without having to muscle the piece through. I still
have to put some force in it, but not all my weight. Basically
speaking, when you take too small a bite it moves the metal on the
outside but not the inside, which can cause waving and peeling.
Bill Wismar
Hi gang,
Someone asked about how to level out the rolls of their rolling
mill. The last time I had to reset the mill out at school, I took
pictures, and turned that into a “how to” web page.
http://www.ganoksin.com/gnkurl/33
Hope it helps,
Regards,
Brian.
I have to agree with Bill here. I was taught this 35 years ago and
it is how I have been rolling metal every since. This is especially
true with karat gold. If you want it flat and smooth take as big a
bite as you can roll through smoothly.
Frank
Take a piece of paper and oil slightly, then dust it with corn starch or similar. Place the paper between rolls and close it down, until contact with paper is made, NO FURTHER! Examine the print and adjust screws until you can get an even print.
Never heard of this technique for truing a mill Thanks Leonard I
will give it a try…
Frank
If you want it flat and smooth take as big a bite as you can roll through smoothly.
This is fine, except how do I know that I can roll a particular bite
smoothly?
It wold depend on roller diameter, mill construction, metal
condition, metal type, person’s physic, and etc… With experience we
come to know these things, but beginners should err on the side of
caution.
Leonid Surpin
Someone asked about how to level out the rolls of their rolling mill.
The easiest way to level the top and bottom rollers is to lower the
top, clean roller, to JUST before it touches the bottom one and then
look between them to see the very thin strip of light that shines
through. Very easy to see which side is higher and adjust
accordingly.
The easiest way to level the top and bottom rollers is to lower the top, clean roller, to JUST before it touches the bottom one and then look between them to see the very thin strip of light that shines through. Very easy to see which side is higher and adjust accordingly.
Hans, some mills have looser bearings, so the top roll drops down
slightly when not under load. With these, the visual only method
doesn’t work. Better to snug down the mill until a feeler guage, or
piece of sheet metal on one side, just is held. Then see if the other
side matches. This checks the adjustment of the actual bearings with
the roll riding on them, as they do in use.
Also, with regard to this whole thread, it should be noted that
“wavey” can refer to two different things. One is bending or
deformation of a piece of metal that is stretching/rolling more on
one side than the other, so it curves to the side in the horizontal
dimension. That is due to rolls not being adjusted right, or can be
to excessive wear on old rolls, so they are no longer truely
cylendars, instead being slightly concave in the middle, so the sides
of the rolls make the metal thinner than the middle of the rolls.
This can occur even with properly finished rolls, on mills with rolls
of too small a diameter. With the latter, simply taking smaller bites
fixes it. If the rolls are actually no longer true, then only having
them reground and if needed, rehardened, will help.
The second type of “wavey” is in the vertical dimension, so the
metal moves up and down, like a wave on water, but may still have
it’s edges straight and true as you look down on the sheet. it’s the
side/edge view that’s wavey. That is not due to rolls adjustment, but
as mentioned before, inconsistancies in the metal itself, or slight
variances in the concentricity of the rolls.
Peter
Take a piece of paper and oil slightly, then dust it with corn starch or similar. Place the paper between rolls and close it down, until contact with paper is made, NO FURTHER! Examine the print and adjust screws until you can get an even print.
The way I adjusted my rollers was to open the “jaws” up and slide a
sheet of paper as wide as the rollers, between them (I used regular
printer or typing paper), turn down the rollers until the paper is
snug but not smashed, remove the center gear from the mill, and while
pulling gently but firmly and evenly on the paper, slowly open the
individual gears until the paper comes out evenly. CAREFULLY put the
center gear back and use your superior jewelers skills to make
something to prevent that center gear from coming off accidently
(like if a friend comes into your shop and says, “Duh…what’s this
do?”…)
One practical measure that I haven’t seen mentioned is this:
Older (and or cheaper) mills will often have some minor
eccentricities. These imperfections have a periodicity, hence the
resultant waviness. The goal of this excercise is the spread the
imperfections around to reduce the waviness.
When rolling metal it is natural to just grab the handle (which is
usually hanging in the 6 O’clock position) and crank away. The
consequence is that on each pass through the mill, the same part of
the rollers touches the same part of the metal, reinforcing whatever
imperfections are in the mill.
When I am nearing my desired thickness of metal, I will take several
very shallow passes through the mill (about 0.1 mm each). On each
pass, I will vary the starting orientation of the handle (3 O’clock, 9
O’clock, etc) so that the same place in the rollers will be contacting
different places in the metal.
ed
some mills have looser bearings, so the top roll drops down slightly when not under load. With these, the visual only method doesn't work.
Peter, if your mill has “looser bearings” you will never get it
aligned for long. And if you got a mill that does not have a sprung
force upward, and hangs like a bunch of grapes in the wind, you got
to fix that. What I mean is that putting feeler gauges or pieces of
paper in between rollers to check their alignment is just plain
silly. Your average under ten years old mill will be just fine with
a visual. One tenth of a millimetre either way doesn’t matter much in
jewellery any which way. If you making space shuttle or moto GP
components, yes. For the rest, visual is just fine. The KISS
principle applies here.