3.48 Cast iron or steelmolds are used in a horizontal-spindlemachine to make tubular castings such as liners and tubes. A charge of molten metal is poured into the spinning mold. The radial acceleration permits nearly uniformly thick wall sections to form. A steel liner, of length L=6 ft, outer radius ro =6 in , and inner radius ri =4 in , is to be formed by this process. To attain nearly uniform thickness, the angular velocity should be at least 300 rpm. Determine

(a) the resulting radial acceleration on the inside surface of the liner and

(b) the maximum and minimum pressures on the surface of the mold.