QUESTION:Find the weights that need to be kept to compensate for the forces during the pouring in a sandcasting of a cast-iron pipe of 12.5cm OD and 10cm ID with a length of 180cm. The metal head is to be about 20cm, while the molding flask used for the purposes is 200 X 25 X 20 cm in size. Take the density of the core sand to be 0.0165 N/cm3 and the liquid metal density to be 0.0771 N/cm3.

ANSWER:

OD = 12.5 cm ID = 10 cm = 0.0771 N/cm3 d = 0.0165 N/cm3 H = 20 cm size : 200 X 25 X 20 cmVolume of core = = 14137.2 cm3Buoyancy force = V ( d) = 14137.2(0.0771 0.01650) = 856.7 NProjected area of the casting = 180 X 12.5 = 2250 cm2Upward metallostatic force = 2250 X 0.0771 X 20 = 3469.5 NThe total upward force = 3469.5 + 856.7 = 4326.7 NVolume of sand in the cope = 200 X 25 X 20 = 100000 cm3Weight of the cope = 100000 X 0.0165 = 1650 NNet upward force acting = 4326.7 1650 = 2676.7 N The foundry has to keep a total weight of about 2700 N to compensate for this upward thrust exerted by the core and the metallostatic forces.