Riser Design MCQ Questions - Casting

Explanation: If riser height is reduced, the pipe will extend to cast cavity. Similarly, if less no of the riser is used it will not satisfy feeding distance. Open riser alone can’t help in reduction of the cavity. But by increasing length of the riser, the pipe can be controlled in riser itself eliminating shrinkage cavity in casting.

Explanation: If the temperature gradient is not there, the metal will not solidify. Same will happen in case of the uniform temperature gradient. In case of the negative thermal gradient, the metal will first solidify near riser which results in unsound casting. Hence positive thermal gradient is required so that metal will solidify near walls first hence feeding distance will be increased.

Explanation: Feeding distance reduces by reducing molten metal temperature and using a low thermal conductive mold. For sand casting, feeding distance will be low because heat extracted by sand is very less compared to metals. By increasing fluidity, metal can flow over a long distance which results in higher feeding distance.

Explanation: Shrinkage volume consideration method, Modulus method, and Novel research method are used for riser design. For calculation of solidification time, Chvorinov’s Rule is used. The Same rule can be modified for riser design called as Caine’s method.

Explanation: Feeding distance is more implies molten metal can flow for a longer distance. This will result in very few mushy zones in the casting. Hence, if the mushy zone is less, the number of risers required will also be less.

Explanation: Different materials have different volumetric shrinkage, in which grey cast iron is the material which sometimes may have a negative shrinkage. This mainly occurs because of high carbon and silicon contents in the grey cast iron, which results in occurring of graphitization which increases the volume.

Explanation: Solidification is basically occurred by losing heat from the surfaces and the amount of the heat is given by the volume of the casting, and the cooling characteristics of casting are given by the surface area to volume ratio. Riser is also similar to the casting in its solidification nature; hence the riser characteristics can also be given by the ratio of its surface area to volume.

Explanation: In grey cast iron, while solidification the process of graphitization occurs, this increases the volume of the casting and counteracts the metal shrinkage, so risers can be eliminated for the casting of grey cast iron. But for some metals like aluminium and steel, the volumetric contraction is very high, so elaborate risering is required.

Explanation: For the chunky type castings like a cube, the volume component can be neglected, but for the rangy castings, like as plate-like casting, the influence of the volume part becomes increasingly significant. So, it is very useful to have a parameter called ranginess factor (R), to define the casting type.

Explanation: In the casting system, the risers should be located at the heaviest sections to achieve a better casting with fewer defects, and because the heavier sections, themselves act as feeders for the thin sections. And variations in volume of riser must be done if the size of casting sections also varies.