This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Riser Design – 1”.
1. How can we eliminate the shrinkage cavity?
a) By increasing riser height
b) By reducing riser height
c) Reducing the number of risers
d) By using an open riser
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.
2. Which of the following can be used for increasing feeding distance?
a) Uniform temperature gradient
b) Negative temperature gradient towards the riser
c) No temperature gradient
d) Positive temperature gradient towards the riser
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.
3. What will be the feeding distance (in inches) without using chill for a plate of thickness T?
a) 4.5√T + 2
Explanation: Feeding distance will be equal to 4.5√T + 2 if we are using chill for a plate. For a bar, feeding distance will be 6√T without chill and 6√T +2 with chill. Thus, feeding distance will be equal to 4.5√T if we are not using chill during casting a plate.
4. How can we enhance the feeding distance during casting?
a) Reducing molten metal temperature
b) Increase fluidity
c) By using low thermal conductivity mold
d) Using sand mold
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.
5. When do we need more number of risers during casting?
a) Feeding distance is low
b) Feeding distance is high
c) Thermal conductivity of mold is high
d) Fluidity of molten metal is high
Explanation: If feeding distance is high, number of the isolated zone in casting will be less thus less number of risers required. For high thermal conductivity, the metal will solidify faster and high fluidity molten metal will flow over a long distance which will result in less number of risers. If feeding distance is low, we have to use more risers to overcome isolated liquid pools.
6. How can we calculate the solidification time?
a) Shrinkage volume consideration method
b) Modulus method
c) Novel research method
d) Chvorinov’s rule
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.
7. Which of the following is a key parameter when we design a riser using Novel research method?
b) Freezing ratio
c) Shape factor
d) Shrinkage volume
Explanation: Modulus is used for designing of riser using modulus method. The freezing ratio is a key parameter when we design riser using Caine’s method. Shrinkage volume is used when we use the shrinkage volume method. For Novel research method, we use shape factor and corresponding to this we find Y from casting databook which is the ratio of the volume of casting to the volume of the riser.
Explanation: If we are not using any chills, number of risers without end effect will be L⁄4T and with end wall effect it will be . If we are using chills at center as well as end, number of risers will be . In case if we are using chills only at the ends number of risers required will be .
9. Modulus method can be used for determining the dimensions of the riser.
Explanation: Yes, Modulus method can be used for determining height and diameter of the riser. In this method, we find modulus of casting and riser which is the ratio of volume and area. The ratio of modulus of the riser to that of casting is 1.2, and the ratio of riser height to its diameter is 1.5. By using these two equations dimension of the riser is estimated.
10. If feeding distance is more, the number of risers required will be more.
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.
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