Case Study: Fill Pressure Increase with Barrel Size ChangeThis particular case was molding a PC/ABS part in a 170-ton press with a small barrel. The mold was moved into a 330-ton press to evaluate flash.Even though all the process documentation was followed for barrel temperatures, recovery time, etc., the fill pressure was substantially higher in the larger machine barrel. All intensification ratios were taken into account but the fill pressure was still higher in the larger machine. Further investigation showed that due to the shear rate during plastication the material was not achieving the same viscosity from barrel to barrel. The larger screw wasturning slower and not generating as much shear heating during recovery.Remember that it is important to account for shear differences between different screw sizes.