Annealing PC as a forming process?
Annealing PC as a forming process?
(OP)
We are manufacturing a curved face shield out of Polycarbonate. It is die cut from a flat sheet of Makrolon GP. The frame that it gets mounted in has a simple bend around 1 axis, forming a cylindrical shape. Easy enough shape to make. Is it possible to build a fixture which holds the flat blank in this simple curve and anneal the plastic to permanently set the curve? It appears to work, processing at 130C for 1.5 hours but I am concerned that this is an unconventional technique and problems will arise months later that we are missing today.
We have tried drape forming, but the process seems less reliable. The material cools so quickly, slight variations in handling time coming out of the oven cause varying results. We have limited resources for heating and forming.
Leaving the lens in the flat state and installing it stressed into the frame has shown much more sensitivity to environmental stress cracking. We need a way to effectively form.
Thank you for your help. I have enjoyed reading other posts on the subject of forming and ESC, you guys have the great knowledge base going.
Best regards,
We have tried drape forming, but the process seems less reliable. The material cools so quickly, slight variations in handling time coming out of the oven cause varying results. We have limited resources for heating and forming.
Leaving the lens in the flat state and installing it stressed into the frame has shown much more sensitivity to environmental stress cracking. We need a way to effectively form.
Thank you for your help. I have enjoyed reading other posts on the subject of forming and ESC, you guys have the great knowledge base going.
Best regards,






RE: Annealing PC as a forming process?
PC is hygroscopic, so I would guess the only thing to watch for is outgassing if a lot of moisture in it and heated too quickly.
Additional info: PC pellets for moulding are dried at 120C, so you're not much above that.
H
www.tynevalleyplastics.co.uk
It's ok to soar like an eagle, but weasels don't get sucked into jet engines.
RE: Annealing PC as a forming process?
Today we are noticing a few pock marks, much like a fish eye mark on a spray painted surface. I'm guessing this is moisture related, as you indicated. Since we do have 2 ovens available, we are going to try to pre-dry at 120C for an extended period, then process for stress relieving in a curved form at 130C.
RE: Annealing PC as a forming process?
Chris DeArmitt - PhD FRSC
Plastics & Materials Consulting
www.phantomplastics.com
Plastic Training Seminars
www.plastictraining.com
RE: Annealing PC as a forming process?
Do you have any idea when stress becomes an issue? If a part is effectively heated and formed to a 3" radius, but has to be installed in a 2.5" radius frame.... is this enough stress to have drastic ESC? Basically, How close is close enough?
RE: Annealing PC as a forming process?
The worse, absolute killer, problem with PC is that even a short exposure to a mild solvent, even if immediately wiped off and washed, will leave it substantially weakened, so much that even a small stress applied after exposure will shatter it.
I suggest you buy a sheet of ~.020" PC, shear it into small rectangles, and experiment with rapidly dipping it into common chemicals and then bending it with your fingers.
That's why I think it's criminally irresponsible to use PC for, e.g. helmets, and for face shields.
Mike Halloran
Pembroke Pines, FL, USA
RE: Annealing PC as a forming process?
Carbon tet probably banned now though...
H
www.tynevalleyplastics.co.uk
It's ok to soar like an eagle, but weasels don't get sucked into jet engines.
RE: Annealing PC as a forming process?
Thoughts on transparant ABS, Impact modified PMMA, or Styrolux?
considering that inevitably the end user might disregard warnings, and choose to use harsh cleaners or disinfectants.
RE: Annealing PC as a forming process?
Impact PMMA would be similar in mechanical performance. I suspect chemical resistance not as good as transparent ABS.
Styrolux is a block copolymer of styrene and butadience. Not as good chemical resistance as the transparent ABS.
Chris DeArmitt - PhD FRSC
Plastics & Materials Consulting
www.phantomplastics.com
Plastic Training Seminars
www.plastictraining.com
RE: Annealing PC as a forming process?
www.tynevalleyplastics.co.uk
It's ok to soar like an eagle, but weasels don't get sucked into jet engines.