Lesson 2/Learning Event 1
problems quickly in order to minimize downtime due to maintenance problems. Blasting! Blasting times must be
established so personnel in the quarry and rock crushing area close to the blast can be evacuated before the blast.
These are only a few of the areas to be coordinated by the commander. Experience and attention will reveal many
VARIABLE PRODUCTION RATES
Remember, you should not use the tonnage nomenclature of the rock crushing plant to estimate production rates.
Three variables that influence production rates are the type of rock being crushed, the feed size of the raw
material, and the size of the finished product desired. These variables are discussed below.
Type of Rock Being Crushed. The harder the rock is the longer it will take the crusher to reduce its size. For
instance, it takes more time to crush basalt than limestone. Table 6 gives the production factors for various types
Feed Size of Raw Material. Production will be increased as the feed size of the raw material is decreased. This
is because it takes less time to crush the smaller rocks in the crushing components than the rocks that approach
maximum feed size.
Size of Finished Product Desired. The size of the finished product is the most important factor to consider when
determining production rates. It takes more time to crush rock down to 1-inch size than down to 2-inch size. It
should be remembered that when the product must meet graded size specifications, production may be less than
the tons per hour (tph) nomenclature of the plant. Although the plant may be able to process 80 tph of quarry
rock, only 50 tph may be in the desired product range with the remaining 30 tph being too small to meet
specifications. In some cases, the 30 tph of by-product may be of value in other construction operations, but for
planning purposes when aggregate is crushed to graded size specifications there will be product and a by-product.
Priorities should be established as to what size aggregate will be produced and for which construction projects it
will be produced. Where several projects are under way that require crushed rock, priorities must be established
at a high level to insure that the crushed aggregate goes to the right job. Avoid changing specifications or desired
product sizes where possible. For example, one battalion produces 1-inch minus and 1/2-inch minus for its
construction projects, and another battalion of the group produces the same two sizes for its projects. It would be
better to have one battalion produce all the 1-inch minus rock and the other battalion produce all the 1/2-inch
minus rock. This