Pit & Quarry, March 2010

Jaw crushers are compression crushers designed for primary reduction of large feed materials such as concrete chunks A tracked jaw crusher has a typical feed opening of 26 in x 40 in up to 30 in x 55 in Larger jaw crushers are available on a wheel mounted chassis up to 44 in x 50 in With their adjustable crusher setting a jaw crusher can produce products up to 10 in or with a tighter adjustment produce products down to 3 in to create a coarse base type material Sometimes a jaw crusher is followed by a secondary crushing unit and a screen for the production of smaller final products Jaw crushers are suitable for processing concrete stone and demolition material such as brick and block and can produce larger products such as riprap Jaw crushers are not normally well suited for crushing asphalt as asphalt can bridge and stick inside the jaw crusher chamber Another popular crusher style is the horizontal shaft impact crusher HSI As the name implies impact crushers process via impaction and can be employed as a primary or secondary unit in recycling applications Compared to jaw crushers impact crushers produce smaller product sizes and often at higher tonnage rates They do have higher wear costs typically ranging from 20 cents to 50 cents per ton versus 10 cents per ton for a jaw crusher However impact crushers provide tremendous versatility effectively processing concrete limestone asphalt and most typical demolition materials Wear costs associated with impact crushers make them less feasible for processing harder granitetype stone Popular size impact crushers have 50 in x 42 in diameter rotors The most popular HSI crushers generally have three blow bars and two adjustable apron plates Impact crushers typically produce a good minus 1 1 2 in base material but can also produce larger products which can be screened to make some typical road materials or utility R E C Y C L I N G drainage materials Impact crushers are not well suited for producing larger products such as riprap A large track mounted impact crusher will generally accept a feed size up to 30 in with a thickness of 12 in depending on the crusher size However to maximize performance feed material should be prepped to an average size of 20 in x 20 in This guideline also applies to jaw crushers in recycling applications Properly sized feed is one of the most important factors in demolition recycling applications At the end of the day an operator with properly prepared feed will put more finished product on the ground Where necessary cone crushers can also be employed in a recycling system Designed as secondary or even tertiary units cone crushers operate by compression and can effectively process a screened 5 in feed to a final product of minus 1 in Information for this article courtesy of KPI JCI www pitandquarry com March 2010 PIT QUARRY 23