Foundry Practices

1. Design of casting
Unit III

2. Design Consideration for castings
• Variables in Casting process: characteristics of
the metals (or alloys) casts, method of casting,
mold/die materials, mold/die design.
• • The flow of the molten metal in the mold
cavities, the gating systems, the rateof cooling,
and the gases evolved all influence the quality
of a casting

3. Design Considerations in Casting
• Design the part so that the shape is cast easily.
• Select a casting process and material suitable for the
part, size, mechanical properties, etc.
• Locate the parting line of the mold in the part.
• Locate and design the gates to allow uniform feeding
of the mold cavity with molten metal.
• Select an appropriate runner geometry for the system.
• Locate mold features such as sprue, screens and risers,
as appropriate.
• Make sure proper controls and good practices are in
place

4. Design Considerations in Casting

5. Design Considerations in Casting

9. Design Consideration for castings
• Provision of Fillet Radius
Round All External Corners, it has two
advantages - it increases the endurance limit
of the component and reduces the formation
of brittle chilled edges. When the metal in the
corner cools faster than the metal adjacent to
the corner, brittle chilled edges are formed
due to iron carbide

10. Design Consideration for castings

11. Design Consideration for castings
• Avoid Concentration of Metal at the Junctions
• At the junction as shown there is a concentration
of metal. Even after the metal on the surface
solidifies, the central portion still remains in the
molten stage, with the result that a shrinkage
cavity or blowhole may appear at the centre as
shown in fig (a).
• There are two ways to avoid the concentration of
metal. One is to provide a cored opening in webs
and ribs, as shown in Fig. (b).

12. Design Consideration for castings
Alternatively, one can stagger the ribs and webs, as shown in Fig.(c)

13. Design Consideration for castings
Design of component in compression than in tension.
Always Keep the Stressed Areas of the Part in Compression Cast iron has more
compressive strength than its tensile strength. Hence, design the component such
that the stressed area become under compression for the better performance

14. Design Consideration for castings
Use of External devices for strengthen the part under tension:
When tensile stresses are unavoidable, a clamping device such as a tie rod or a
bearing cap as shown in Fig should be considered. The clamping device relieves
the cast iron components from tensile stresses