It's difficult to get through any construction project without the need for some sort of rocks or rock material. Usually rocks don't come in the exact size that's needed for a specific project. In the face of this problem, a machine was invented decades ago to help crush rock and make it more usable, and in some cases, make rock or concrete - reusable.
There are four different kinds of rock crushers - the cone crusher, jaw crusher, gyratory crusher, and the impact crusher. There are two types of impact crushers - the horizontal shaft impactor (HSI) and the vertical shaft impactor (VSI).
Cone rock crushers work very similarly to the gyratory rock crusher, whereby rock is fed and crushed through a gyrating spindle, except with the cone rock crusher, it is shorter on the feeding end and there is larger degree of a parallel zone between the crushing zones. 1
The jaw crusher works by crushing rock between two ridged surfaces that slope into a funnel. The funnel has a smaller opening at the bottom and rock that is too big to fit through this opening is crushed in the "jaw" of the rock crusher until the pieces are small enough to fit through the funnel's opening at the bottom. The basic design of the jaw crusher has remained the same for over sixty years.
A gyratory rock crusher works similar to the jaw crusher but there is a gyrating spindle that helps crush the rock. The rock is actually crushed twice - once when it first enters the machine and then again as it falls through until it is small enough to exit the bottom of the crusher.
Impact rock crushers come in two varieties - horizontal and vertical. HSI crushers use a simpler process than do VSI crushers. The HSI crusher uses hammers on a rotating shaft to crush the rock into smaller pieces, while VSI crushers uses swift force to break the rock apart by slamming it against an anvil, which causes the breaking force to be applied equally across the face of the rock and through the mass of the rock. 2
These various rock crushers help to crush rock to make aggregate and filler material for landscaping and to help prevent erosion. Crushed rock is also one of the main ingredients in road construction, and since it is a low-value commodity, companies are able to profit from producing it at a very high volume. Of course, profits are ultimately based on production costs such as: labor, the cost of the rock crusher, transportation of crushed rock, meeting safety regulations and the amount of construction demand. The more construction an economy sees, the more the demand for crushed rock and the need rock crushers.
1, 2 Wikipedia - http://en.wikipedia.org/wiki/Rock_crusher