Hot Forming Acrylic, Surfaces Not Smooth

[jjg1ttes]

Howdy -

Problem: acrylic sheet has pitted texture after hot forming in restraining mold.

We're making a curved acrylic window. Dimensions of the acrylic blank are roughly 7x 8 x 1/4 inches flat.

We've made a sandwich mold with a convex solid base (cast from epoxy i believe) and a thin sheet of titanium (it was handy) for restraining the form.

The acrylic blank goes into the oven for 10 minutes at 350, to make it soft. Then it goes into the restraining mold until it cools and holds its shape.

Dimension are a-ok, but the surfaces of the window look pretty awful now. It's still pretty smooth in general, but when you look closely it's loaded with surface imperfections that were not characteristic of the stock material. Every effort is made to clean the mold/fixture before introducing the warm blank, compressed air, damp or dry cloth... always the same when it comes out of the fixture.

any ideas?

Thanks,
Rob

 

[patprimmer]

Either it is reproducing the surface of the mould or it is out gassing on heating. Try heating it to an intermediate temperature of say 90 deg C, and hold it there for several hours before heating just enough to form it. Heat slowly so you don't degrade the surface.

Regards

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[jjg1ttes]

I'll pass that tip on to production and we'll see if we have any luck with it.

Thanks,
Rob