Here is a quote from a Chemical Engineering manual called "Practical Guide to Polyethylene" that talks about the conditions necessary to cause a permanent vs temporary change in shape. Polyethylene acts like an extremely thick liquid, and will "flow" permanently into a new shape, but the rate this occurs depends on the temperature, pressure, and time. You might try again slightly increasing those variables (too much will destroy it). "Like other viscoelastic materials, PE exhibits creep (or cold flow). Creep is the deformation (or total strain) that occurs after a stress as been applied. Its extent depends on the magnitude and nature of the stress, the temperature, and the time for which the stress is applied. Over a period of time, PE undergoes deformation even at room temperature and under relatively slow stress. After the removal of the stress, a moulding more or less regains its original shape, depending on the time under stress and magnitude of the stress. Recoverable deformation is known as elastic deformation and permanent deformation as plastic deformation." Tyler Davis, CA M15 #157 "Defiant"
On Oct 23, 2015, at 5:35 AM, Rick Davies <jdavies104@gmail.com> wrote:
Gary,
I was interested in your comment that your plastic rudder doesn't warp. I have a Ruddercraft retractable rudder that has a plastic blade, and it took a warp during its first season that I've not been able to permanently fix. Joel at Ruddercraft suggested bending it in the opposite direction and clamping it for several days. This did straighten it, but the fix was temporary and within a few days on the boat it was back to the same warped shape again. Any ideas?
Thanks,
Rick M17 #633 Lynne L