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Warped Acrylic
We produced 19 outdoor signs for a heritage park. We used sheets of 5mm Acrylic with vinyl mounted to the rear. This was screwed into a metal frame tray (see attached file). The problem is that sometimes the acrylic becomes warped and the next day it may flatten out again. Any ideas why this problem occurs and how to modify the 19 signs without too much cost. Thanks in advance for any advice.[/img]
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11 Replies
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It has to be a heat-related (sun) issue.
I don’t know anything about laminates, but would it be possible to flood coat each sign face with some sort of optically clear UV laminate?
Love….Jill -
I would say the screws holes are to tight.
Did you oversize the holes when drilling so the acrylic could expand?
Acrylic should really go in a frame and not screwed to allow for movement. -
I would think heat also, but not dealt with acrylic much myself.
Maybe make the holes for the screws a little larger to allow movement, or use a rubber grommet in the hole.
How tight is the acrylic to the metal tray?
Looks like a tidy job though!
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As Jill says it is down to expansion of the acrylic sheet. You have probably fitted them to snugly into the metal trays & because the acrylic sheet expands more than the frame it causes them to bow. Easiest & simplest fix would be to take a shaving off the panels & enlarge the fixing holes a little so the panel has room to expand.
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Thanks for your suggestions. The signs were only installed about 4 weeks ago and the weather has not been too extreme (hot or cold). But I think the suggestion about the bolts been too tight is worth investigating. Our acrylic supplier suggested the product is for outdoor use and should not warp in our Irish climate. If anyone has ever encountered this specific problem, I would appreciate your feedback. Thanks.
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Thanks Martin. Your suggestion is worth a try.
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quote Noel Moore:Our acrylic supplier suggested the product is for outdoor use and should not warp in our Irish climate.
Only if it’s fitted correctly will it not warp. The best stuff in the world will still warp if not fitted right. It has to be allowed to expand. this is the problem your having.
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Differential expansion – one material expands/contracts more than, or at different rate than the other (acrylic and steel). I’d certainly make the holes slightly larger for a loose fit, but looking at the photo I think it’s fairly snugly nested into the steel frame. Perhaps worth trimming 3mm of the panel all around and filling the gap with something like silicon sealer – nice if you could get black stuff.
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I’m not sure if this information is a 100% accurate but I was once told that the expansion/contraction for 5mm acrylic is plus or minus 3mm per metre
I would say it’s a definite case of everything being fit a bit too tight
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I would say its sun heat expansion as we have had similiar problems here in spain! We use mushroom head fixings with large holes behind (the mushroom head hides the holes and allows for expansion when the sign is on it! hope thats clear?
cheers
Dan
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Looking at your photo in close up I see two problems as has been pointed out. Too tight in the frame and drill bigger screw holes, and don’t fit the screws to tight, back them off half a turn so they don’t pinch the acrylic.
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