Crushers

The first step in transforming large particles into small pieces is running them through a primary crusher – a crusher that takes raw material and crushes it smaller. The material can be virgin material or recycled material that has been prepared to a size that the crusher can handle. Sizing can involve the loading machine simply picking through oversize pieces or having a rock breaker on site that attaches to an excavator to reduce the size of the larger pieces. Both Impact Crushers and Jaw Crushers can be used as primary crushers. Here’s how each works:

Our Impact Crushers feature a four-bar rotor inside a large crusher chamber. The rotor typically has two “blow bars” that strike the raw material and knock it against aprons inside the chamber. Two “inactive bars” typically counterbalance the blow bars and help maintain the speed of the rotor. The raw material continues to be impacted within the chamber until is it sized to escape through the gap between the rotor bars and the chamber.

Impact Crushers are best used with softer rock, such as limestone and sandstone, and for recycling processed materials like concrete and asphalt. Impact crushers tend to produce more “fines” than Jaw crushers.

Jaw Crushers have two opposing ribbed panels, or jaws, with one jaw moving forward and back to crush raw material against the fixed jaw. Only material that has been crushed to a size equivalent to the opening at the bottom of the jaws falls through the bottom of the machine. This sizing is determined by the closed side setting of the jaw panels.

Jaw Crushers exert more crushing power and are the best choice for very hard rock like granite and abrasive rock.

A secondary crusher is one that takes crushed material out of a primary crusher and reduces the product further.  An impactor or a cone crusher can be used as a secondary crusher. (6-8” feed size to ½” to 2” finished product).

Cone Crushers are typically used as secondary crushers. Cone Crushers feature a large circular chamber with a manganese cone or head inside. The stationary chamber is referred to as the concave and the moving cone inside is referred to as the head. The head moves in an elliptical motion and crushes material against the liner wall of the concave. When the material has been crushed to a size that allows it to escape the crushing chamber, it falls through the bottom.

Crushers are heavy-duty equipment that perform a difficult job very efficiently. Wear parts on all three types of crushers – blow bars, jaw plates and “heads and concaves” in cones – will become worn over time and require replacement. The frequency of the replacement depends on the hardness of the material being run through the machine and the amount crushed.

Fine materials also contribute to the wear of the crushing parts. Sand and fine pieces of material will slow production (because they don’t need further crushing) and they will increase wear. It’s important to remove as many fines as possible before proceeding with crushing. Also a large amount of “fines” or “wet and soggy” material will tend to build up in a crusher. This will significantly affect the crusher operation, create maintenance problems and in some cases make the crusher inoperable.

Important note: To attain accurately sized product, a screening plant should be used after the material has been run through a crusher. Crushing plants can get within a range of sizing, but screening plants are designed to separate material to a specific size.