In crushing energy calculations, a crushability index $($impact work index, $W_i)$ which can be

determined by laboratory tests, is used. Now consider a hard rock ore being crushed in two different

size ranges, a coarse crushing range and a fine crushing range, for the same reduction ratio of about

$3\mathrm{.}5$:$1.$

a$)$ Determine the work input required for the two cases of size reduction, given the following data:

Impact work index of the material, $W_i$ is $15kW\frac{h}{?}$ tonne; $80$ percent passing sizes for the feed to

the coarse crushing and fine crushing stages are $350mm$ and $35mm,$ respectively. Determine

the product size for the coarse and fine crushing cases and comment on the comparative results

of crushing energy.

b$)$ Suppose that the coarse crushing case above is to handle $10,000$ tonnes of a massive sulphide

ore per day. What is the net power $($in horsepower$)$ required for the crusher to be used before

any safety factor applies? Assume that the crusher is operated two shifts out of three $($i$.$e$.,16$

hours per day$).$