1. Riser Design • Riser is a waste part, as it will be separated from the casting body after the mold is destroyed and reused for casting (for expandable mold casting). • To minimize the waste of material, it is desirable for the volume of the riser to be as small as possible. • But we want to have a large TST of riser, which then contradicts the small volume idea, as TST of a riser increases while the volume increases. • Therefore, design of the riser should make a trade-off between the large TST and small volume. This trade-off can be achieved by the surface area, that is, to design a riser so that its surface area is as small as possible. • Further, a riser can be in the following forms: • Side riser (to the side of the mold cavity), top riser (above the mold cavity) • Open riser (exposed to the outside of the mold) or blind riser (enclosed in mold)

2. Riser Design • For top riser, the area of the riser, which is connected with the casting or cavity, is not considered. • For open riser, the area of the riser needs to be multiplied by a coefficient, say C, so A’=C (A), where A’: the modified area, A: original area, and C>1.

3. Example 1. Riser Design Given: • Casting geometry: rectangular plate: length = 7.5 cm, width=12.5 cm, thickness=2.0 cm • TST of the casting itself: 1.6 min. • The riser is a cylinder with diameter/height=1.0. Design a riser: such that TST of the riser= 2.0 min

4. Determine V/A of plate • Given TST of plate, we determine Cm • We use the same Cm for riser design • Determine the volume of riser • Determine surface area of riser • As D/h=1, substitute D for h (1) Riser: • Side • Blind

5. Substitute • Now we have got for the riser Vr/Ar, Cm, TSTr (2 min) and we get the following equation • In (2), Cm is found from Eq. (1). From (2), we can determine D Vr/Ar = D/6 (2)