Pelletizing dies made from tools steel such as D2 (12% chromium) and H-13 ( 5% chromium) are used in under water polymer pelletizers. These steels provide abrasion resistance and withstand general wear from a cutting knife sliding over the surface at high speeds. A tungsten carbide finished coating layer of just .010” (surface ground and polished) can provide three times the wear resistance compared to these tool steels. In some cases it is possible to recoat a worn die or simply grind away the wear groove and continue using a tungsten carbide coated surface.
They simply soften as they heat up. These materials (PC, PVC) can be shear heat sensitive so feedscrew meter depths are usually greater to reduce the shear rates in this area. Compression rates are also lower to avoid high shear.
Crystalline or semi-crystalline materials must go through a heat of fusion to relax the crystalline regions before they will melt. (Ice for example must melt entirely before the temperature will rise). These materials (Nylon, PP, PE) require shear heat energy to facilitate melting. Feedscrew meter depths should be shallower to increase the shear and contact with the barrel. Compression rate is also higher to facilitate shear. If these resins contain glass fiber filers then the compression rate will decrease depending on loading to avoid breaking the glass fibers.