Anealing PETG plastic 1

[emorsmor]

We MFG a clear plastic cyclone dust collection system for woodworking. We've had a problem with the PETG plastic cracking during shipping - especially in areas where we have heated the plastic with a torch for bending. My question is can PETG plastic be anealed? If so, how. This cyclone is 18" in diameter x about 48" long with a cone section on the bottom. It's make from 1/8" PETG, heated vertically in an oven and then formed over wood molds. Any help on the cracking and breakage would be greatly appreciated.

Thanks,
Ed Morgano

http://www.clearvuecyclones.com

 

[patprimmer]

Do you dry it before you heat it to form it. It is susceptible to hydrolysis and if heated to high while it contains absorbed moisture it will lose a lot of strength.

If you heat to the correct temperature to form and cool slowly, you should not induce any significant frozen in stress, so annealing will not help much.

Regards

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[dwightdixon]

You can easily observe the bent in stress by the use of polarized light. It may be that the material is not hot enough when you are actually bending it. It may be cooling down too much because of difficulties during fixturing. Use the polarizer to find a temperature and bending rate which will give you minimum stress. Also, use the polarizer to analyze where the crack has occurred and how the load got to the place it cracks. It may be that there are high loads during transportation. You may be able to change the packaging support to stop the problem. If all else fails, develop an anealing cycle. It will be dependent on the part geometry and processing. You will need to start at 165 F for a min. of one hour air time and then move the cycle up and longer, while analyzing the stress with the polarizer. You should also talk to the people supplying the PETG. Viscosity (solution) testing could easily be able to tell if you have degraded the polymer. Talk to the resin people to get the method. There are also a number of labs which will do your trouble shooting and testing for you, if you do not have the internal capability. Sometimes you must pay to play.