1. As the size of feed increases, size of product ____
a) Remains same
b) Decreases
c) Increases
d) No effect
Answer
Answer: c [Reason:] The larger the size of the feed the larger will be the size of the product, a smaller size reduction is obtained with hard material.
2. For a ball mill, what will happen to product if the weight of ball increases?
a) Coarser
b) Finer
c) Bigger
d) No change
Answer
Answer: b [Reason:] If the mill is charged with heavy balls, the product will be finer, the weight can be increased or the number if ball can also be increased.
3. As the size of ball increase, the size of product ____
a) Remains same
b) Decreases
c) Increases
d) No effect
Answer
Answer: b [Reason:] Balls of smaller diameter give only fine product, but they do not deal effectively with larger particles in the feed.
4. Increasing the slope of the mill, product becomes ____
a) Coarser
b) Finer
c) Bigger
d) No change
Answer
Answer: a [Reason:] Increasing the slope of the mill increases the capacity of the mill because retention time reduced but a coarser product is obtained.
5. What does increased discharge freedom results in?
a) Coarser product
b) Finer product
c) Bigger product
d) No change
Answer
Answer: a [Reason:] Increasing the freedom of discharge of the product has the same effect as slope i.e. it results in coarser products.
6. At low speeds, ____ Crushing is obtained.
a) High
b) Low
c) Optimum
d) Total
Answer
Answer: b [Reason:] At low speeds, the balls simply roll over one another and little crushing is obtained, thus reducing the equality of product.
7. At high speed, Crushing obtained can be _____
a) Minimum
b) Maximum
c) No effect
d) Optimum
Answer
Answer: a [Reason:] At high speed, the balls present in the mills are carried over along the circumference of the mill and thus no crushing or minimum crushing is obtained.
8. What is the minimum speed at which ball mill operates called?
a) Cumulative speed
b) Threshold speed
c) Optimum speed
d) Critical speed
Answer
Answer: d [Reason:] The minimum speed at which ball mill operates is called Critical speed, under these conditions no resultant force acts on the mill and crushing is maximum.
9. What is the angular velocity We?
a) √(D/R)
b) g/R
c) √(g/R)
d) √(H/R)
Answer
Answer: c [Reason:] The angular velocity is defined as We = √(g/R) , where R is the radius of the mill less the radius of the critical speed.
10. As the level in the mill reduces, power consumption ____
a) Remains same
b) Decreases
c) Increases
d) No effect
Answer
Answer: b [Reason:] Power consumption is reduced by maintaining a low level of material in the mill, and this can be controlled using suitable discharge.
