Hi guys,
Having spent most of my life working with plastics, let me repeat what I said on another post about warped records/plastic. A record is made by placing a small, heated wafer of plastic on top of the record mold. High pressure is then applied to spread the plastic into the mold, after a controlled time the mold is opened and the record is removed. When plastic is pressed into the mold, it creates stresses internally in the plastic, ie record. As long as the 'record' stays at a reasonable temperature, the stress forces are neutralized. When a record is subjected to higher heat, it allows the stresses in the plastic to have an effect on the shape of the record, thus warping it. To remove the effects of the warp is near impossible as the material has been stretched. You may get them flat again; but, that does not mean that they are back to its original integrity.
Papajoe