Simple Solutions That Work! Issue 15

CASE STUDIES volumetric demand of the casting is not satisfied by the feeder(s), a void will appear somewhere in the casting. As it is nearly impossible to feed 100% of the riser volume into the casting, the riser volume must be appropriately larger than the volumetric demand of the casting. There are feeding aid products available that can provide between 20% to 50% of the contained metal in the riser to the casting. A feeder with a volume of 10 in³ would be capable of delivering somewhere between 2 in³ and 5 in³ to the casting depending on the performance level of the feeding aid product(s) used. That means a riser head with the remaining volume is destined for the return pile. Foundries using much larger risers see this effect in an exponentially larger fashion. More efficient feeding aid products will deliver yield improvement, reduced riser removal times, reduced foundry returns, increased production capacity and lower overall costs. MODULUS CONSIDERATION Modulus is the ratio of the volume of the casting divided by the area of the cooling surfaces. Castings having relatively low volume and high surface area correlates to low modulus values (like short solidification times). A casting with a very high volume and low surface area correlates to high modulus values (like longer solidifications times). Once the modulus of a casting (or section of a casting) is determined, we simply use a feeder that has a slightly larger modulus than the casting section to be fed. This ensures the riser solidifies after the section it is intended to feed. We also take into consideration the volume requirements as described above. With these two steps complete, the foundry personnel can accurately select a feeding aid which should perform optimally. Calculation of Casting Modulus and Section Modulus for Hub Casting Surface Equation Surface Area A π DH 3.141 x 13.79 x 4.54 = 196.65 in² B π R^2 (2) 3.141 x (2.065)² x 2 = 26.79 in² C π DH (2) 3.141 x 10.13 x 1.27 x 2 = 80.82 in² D ( π R^2- π R^2) (2) 3.141 x (5.065)² = 80.58 - 3.141 x (2.065)² = 13.39 = 67.19 x 2 = 134.38 in² E ( π R^2- π R^2) (2) 3.141 x (6.895)² = 149.33 - 3.141 x (5.065)² = 80.58 = 68.75 x 2 = 137.50 in² F π DH (2) 3.141 x 4.13 x 1.27 x 2 = 32.95 in² Total Surface Area = 609.10 in² Section Equation Volume X π R^2 H 3.141 x (2.065)² x 4.54 = 60.81 in³ Y π R^2 H- π R^2 H 3.141 x (5.065)² x 2 = 161.16 in³ - 3.141 x (2.065)² x 2 = - 26.79 in³ 134.37 in³ Z π R^2 H- π R^2 H 3.141 x (6.895)² x 4.54 = 677.95 in³ - 3.141 x (5.065)² x 4.54 = -365.83 in³ 312.12 in³ Total Volume = 507.30 in³ Total Casting Modulus: Volume/Cooling Surface Area = 507.30 in³/609.10 in² = 0.833 in. Modulus of Section X – Center Hub Volume Section X / Cooling Surface Area of Section X 60.81/ (B+F) = 60.81/59.74 = M = 1.018 in. Modulus of Section Y – Web Volume Section Y / Cooling Surface Area of Section Y 134.37/D = 134.37/134.38 = M = 0.9999 in. Modulus of Section Z – Outer Rim Volume of Section Z / Cooling Surface Area of Section Z 312.12/ C+E+A = 312.12/ (80.82+137.50+196.65) = M = 0.752 EXAMPLE: • Generic 130 lb. ductile iron hub • 65-45-12 Ductile Iron • No-bake molding Continued on next page 17