This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Riser Placement”.
1. The presence of chills in the mould does not have any affects on the riser mechanism.
a) True
b) False
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: 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
View Answer
Explanation: In tedious calculation for a complex casting, a method is used which gives different risering curve than the conventional method of area to volume ratio. In this method, the shape factor (l + w)/h is used instead of (A/V), where l, w, and h denotes the maximum length, maximum width and the maximum thickness of the casting respectively.
8. The allowable thermal gradient generally depends on the shape and size of a cross-section of the casting.
a) True
b) False
View Answer
Explanation: The thermal gradient within the casting is the most important factor during the last stage of cooling of casting. The minimum allowable thermal gradient generally depends on the shape and size of a cross-section of the casting. So to set up the risers in the casting system, area to volume (A/V) ratio of the casting is considered.
9. It is always desirable to have a large volume of molten metal in the riser to make casting products.
a) True
b) False
View Answer
Explanation: The riser basically represents waste metal that is to be separated from the casted part and re-melted to make other castings. It is always desirable to have a minimum volume of molten metal in the riser to make efficient production of castings. This increases the casting yield which saves metal and reduces the time of production too.
10. In casting system, the riser is generally placed at the heaviest section to avoid defects from the casting.
a) True
b) False
View Answer
Explanation: In the casting system, the risers must be placed at the heaviest sections to obtain better casting free from defects. And because the heavier sections, themselves act as feeders for the thin sections of the casting, and variations in the volume of riser should be done if the shape and size of casting sections also vary.
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