Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) on “Riser Placement”.
1. The presence of chills in the mould does not have any affects on the riser mechanism.
a) True
b) False
Answer: b
Clarification: The presence of chills in the moulding system greatly affects the riser mechanism. Chills in the mould increase the feeding distance of the riser, which is basically achieved by providing a sharp thermal gradient with the consequent decrease in the feeding resistance of the riser mechanism.
2. For a single riser in the casting system, the chill should be placed at the ends of the riser.
a) True
b) False
Answer: a
Clarification: To have proper directional solidification and to maintain the riser mechanism, the chill used should be placed at the ends of the riser. When more than one riser is used in the casting system then the chill should be placed at the midway between the two risers to have accurate and systematic solidification.
3. Which of the following equations defines the form of risering curve in the riser mechanism?
a) x = a*(y-b) + c
b) x = a/(y+b) + c
c) x = a/(y-b) + c
d) x = a*(y+b) + c
Answer: c
Clarification: The equation for a risering curve in the riser system is given by: x = a/(y-b) + c, where a is the freezing constant for the molten metal, b is the contraction ratio from liquid phase to the solid phase and c is a constant depending on the different media around the riser and the casting.
4. For a casting with a high area to volume (A/V) ratio, one central riser can be enough to feed the entire casting.
a) True
b) False
Answer: b
Clarification: Normally, for casting with a high area to volume (A/V) ratio (for example, for a plate and a bar), usually more than one riser is required. And for the low area to volume (A/V) ratio casting like cube and sphere, one central riser can be used to feed the entire casting. In such cases, the proper location of the riser is decided.
5. Placing of riser at the correct location is necessary to feed the melt to the desired locations within the casting.
a) True
b) False
Answer: a
Clarification: In casting system, riser is provided to compensate the liquid and solidification shrinkage during solidification of the casting in the mould. But to feed the melt at desired locations within the casting, it is very important to identify the correct location on the casting system to set up the riser mechanism.
6. A large size of riser should be placed on the casting system to compensate the solid shrinkage of the casting.
a) True
b) False
Answer: b
Clarification: In the solid shrinkage of the casting, casting cannot take any molten metal from the riser, as the casting is almost solidified. So, riser has no application for the solid shrinkage of the casting. To compensate the solid shrinkage, pattern of large size is placed in the mould which called a pattern with shrinkage allowance.
7. Which of the following formulas is used for the calculation of shape factor for complex casting in risering system?
a) (l – w)/h
b) (l2 + w)/h
c) (l2– w)/h
d) (l + w)/h