How to reduce residual stress in polycarbonate?

[6373]

Hello,

I am currently working on a project which involved a lens (injection-molded,polycarbonate). It has a lot of residual stress in it and is causing alot of problem for my optical application.

I read (from other source) that annealing will reduce the stress, and I had performed the annealing test on the lens. The lens was heat up to 135degC for 3hrs and then gradually cooled down in the oven till room temperature. I tested with my optical application and there is a lot of improvement.However, after two days, I discovered that the lens is back to its original form.

Does anyone has experience on this issue. Please advice me on this problem?

Regards,

 

[TheAnswerGuy]

6373,

You are not giving enough information to make an assement of the cause. But the most common causes of molded stress are:

- Improper gate location
- Improper gate design
- Improper venting
- Improper part design
- Improper material choice

I will add, that since you are annealing the parts and the same condition is showing up days later. The first thing I would check is that you have good gate design. I have found the "Fan chisel gate" to work best for lenses.

Again, this is only speculation into the cause of your problem.