Vacuforming acrylic

[jaysteel]

I'm having a problem I hope you can help. I'm trying to thermoform acrylic. I am using less than 1/8 inch extruded acrylic instead of cast acrylic to keep costs down until I have the application system completed. I am heating the material in a convection oven and vacuuming. The problem is I keep getting blisters. I've gotten blisters as low as 175 degrees - and of course at all higher temperatures. I've been told to preheat the stuff at 100 degrees for 24 hours to correct the problem. Any thoughts? Thanks

[spektr]

I think whats happening is that you have a problem measuring the sheet temperature. Assuming you are measuring it with an infared temp gage, you
could very easily overtemp the sheet surface without getting the core temps to a moldable number. Acrylic will only accept so much energy per unit time per unit area. If you exceed that number, you blister the surface before you can mold it because the core will still be too cool to mold.

A second consideration is residue from the masking. What was it masked with and how did you clean it?

Scott.