Jaw crushers resemble a giant jaw chewing the stone into gravel. One plate is mounted on the base of the machine and remains static. The other plate, or jaw, is mounted on a wheel. The hinged jaw mechanically opens and closes against the static jaw. The distance of the mobile jaw from the bottom of the static plate is adjustable. The size of that gap is set to the desired diameter of the gravel. When the jaws are open, the crushed pieces that are small enough fall through the gap as finished gravel.
Impact crushers apply the same principle that people used before machines to break rocks. They used a bigger, harder rock to smash into the smaller, softer rock.. Impact crushers mount wide, flat steel paddles on a rotating axis. Think of a steamboat paddle. These paddles turn at high speed and hit -- or impact -- the stone that is fed into the machine. The paddles are set at a chosen distance from the sloping shelf where the stone is fed into the machine. That gap between the impact paddles and the sloping shelf determines the diameter of the gravel that falls through.
A standard cone crusher has a cone-shaped receptacle with an outlet at the bottom. Mounted on the underside of the cone-shaped receptacle is a cone-shaped, vertical shaft -- or spindle -- that resembles a large toy spinning top, with the point up. The spindle is smaller than the lower aperture of the shaft. The spindle is attached to a wheel that moves it back and forth over the bottom aperture of the shaft, crushing stone that falls into the gap.
The gyratory crusher is a cone crusher that makes a finer, more consistent gravel than the standard cone crusher. Like the cone crusher, the gyratory crusher has a vertical axis -- or spindle -- in the receptacle that looks like a giant metal top with the point up. The spindle in the gyratory crusher is longer and extends farther up into the cone-shaped receptacle than the standard cone crusher. The gyratory crusher is set for finer gravel than a standard cone crusher. Gyratory crushers are frequently used after rock has been crushed once or twice by coarser methods.