i have a strange problem - i have thin copper sheets (about 0.020" thick) that have paint on them. they are somewhat warped.
my challenge is that i need to flatten them. normally i would just clamp them between two pieces of steel and heat them up in a kiln at about 500-600 C for about an hour or so and they’d become flat.
the problem is that this process will damage the paint. i tried lowering the temp to 300 C and it still damages it. at 250 C is doesn’t damage it, but it doesn’t flatten the metal, even after 8 hours of heating.
i have a roller, but i have not had any luck rolling them without having them come out with a curve to them.
any ideas?
When you say paint, do you mean flame paint or just paint?..Rob
it’s literally just a thin layer of paint (it’s a painting.) removing the paint is easy of course, but unfortunately it’s not something i can do in this situation - i need to figure out how to flatten the sheets with the paint on.
Without damaging the painting? If the painting is what you want to preserve, you might talk to an art conservator. They may have a way to remove the copper and save the painting. It would be very expensive…Rob
the goal is to flatten the copper plate while preserving the painting. i think this is a “metal problem” not an art problem. just not sure how to solve this puzzle.
All cold metal need to be pushed further than the end form during forming.
Some metals more than others.
Are you in position to “over” bending it or will that destroy the painting.
Are the painting what you want to preserve?
the sheet is about 4x4 inches, and it has warps in it from annealing and rolling. the metal is not in a relaxed state. if there was simply a bend in it then perhaps i could counter the bend - but this is just random warpage. and yes, i want to preserve the painting. the goal is to get the sheet back into a flat state w/ the painting undamaged.
This is definitely an art conservation problem. Keep in mind that art conservation doesn’t deal only with paintings on canvas or drawings on paper. Art conservation includes conserving and repairing metal sculpture, painted tinware, painted sheet metal on antique furniture, even antique arms and armor. There are plenty of metal objects which are treated by specialist conservators.
If you are in a city with a big museum get in touch with the appropriate conservation department. They won’d do the job for you, but they will likely look at the pieces and offer some guidance. Perhaps they may explain a process. At least they’ll be able to point to someone who can help, or perhaps a private conservator who will take on the job, for a fee of course.
Where I live in New England a lot of buildings have copper roofs. After 20-40 years New England roofing copper gets an amazing green patina that is incredibly durable. I’ve been lucky to have talked my way into getting some old roofing copper when local building are getting reroofed.
It comes in very mangled 2’ x 8’-12’ sections that cannot be heated or annealed at all. I’ve discovered that I can flatten small sections with minimal damage using a hydraulic press.
Most Bonny Doon presses have 6" x 6" platens. I don’t know all press platen sizes, but you should be able to flatten a 4"x4" piece. Remember that your platen must be perfectly clean. If there’s a divet or a piece of debris on the platen, that’s going to be pressed into your metal. Also, you want to use the least amount of pressure necessary to flatten the metal.
If you don’t have a hydraulic press or can’t gain access to one, you might be able to do something similar by firmly clamping your metal sandwiched between wood and a vise.
Also, as pretty much everyone is describing paint on metal is very delicate. You run the risk of damaging the paint with whatever you do to flatten the metal. I’m amazed that you heated this metal at all. That was very brave! I can’t believe that even low heat didn’t damage the paint.
Anyway, I’d try a hydraulic press. Hope that helps!!
Jeff
Jeff…Our Dad collected roofing copper for its scrap value and some of it made its way into our shops. I have a piece that I use on my soldering bench as a fire break around the wooden top and soldering pads. I was going to suggest a press, but am worried that any texture on the plattens will be transfered to the surface of the painting or copper. The poster might want to sandwich the copper and painted surface between thin pieces of cardboard first. If it would fit, this same sandwich could go through a flat rolling mill closed just tight enough take away the irregular surface, but not stretch the metal. This is a tough one. Maybe a planishing hammer…Rob
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thanks. i actually have tried a hydraulic press and the warps in the copper plate just sort of spring back - but i was just applying about 6,000 lbs of pressure. perhaps i should try out a 20 ton bonny doon press. i also like the idea of trying some wood to offer some protection to the paint.
(also, the paint isn’t particularly delicate - it just needs to be survive the process of straightening the plate.)
i think my plan is to try a 20 ton press, and if that fails, then i will take your suggestion of trying a planishing hammer, or perhaps a rolling mill set to not stretch by testing with the plate sheathed first. great ideas.
6,000 psi is a lot. I only go there when I am trying to push a piece of maybe 22 gauge annealed silver into a complicated impression die with small urethane pushers. Maybe you could try using pushers on just the warped spots. Again, I have no ideas what you painted image would do in the process. You might set it up and take a series of really nice pictures of the painted image before you try any of this. Good luck…Rob
Could you glue each to a thicker flat piece of metal (copper for matching thermal expansion)?
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Hi,
ok, i am now so curious!
4x4 square of copper
work hardened springy and warped
painted surface
what is the end use?
like the previous poster, i was just going to suggest a solution that would physically restrain the metal…
ie:
securing it to a backplate…metal…wood…acrylic…
via rivets…a bezel- like frame…brackets…
or physically relieve the metal…maybe pierce interesting patterns, radiating outward…
hmmm….
julie