Simple Solutions That Work! Issue 13

DEFECT PREVENTION 29 GATE AND FEEDER BAR DESIGN Gate and Feeder Bar sizes for each feeding zone are calculated using the thermal modulus. This takes into account not only casting alloy and shell material, but also the solidification dynamics of the specific situation, including the use of insulating materials such as Kaowool or Fiberfrax wrapping. Guidelines for gate and feeder bar sizing are given in Figure 4 . Once we know the maximum modulus in the feeding zone, we can calculate the appropriate size for a tapered gate, as well as feeder bar dimensions that will adequately feed that part of the casting. This calculation Figure 2: Feeding Zone #1 Figure 3: Feeding Zone #2 Last point to freeze on the zone Last point to freeze on the zone is done in the Riser Design Wizard, which was originally developed to calculate cylindrical risers for the sand- casting process. However, it provides good information for investment castings, too. An example of the wizard screen is shown in Figure 5 . Figure 5: Modulus data is used to size both the tapered gate and the feeder bar. Continued on next page Figure 4: Gate and Feeder Bar Sizing