Pit & Quarry, May 2018

CRUSHING HYDRAULIC BREAKING THE BASICS OF CRUSHING Bring the new hire of your crushing operation up to speed with these introductory level pointers EDITED BY ZACH MENTZ N o matter where an operation is located or what geologic material is available the goal is always the same produce required aggregate sizes at the lowest cost per ton To do that an operation must be organized and efficient especially when it comes to the crushing process Crushing is at the heart of every aggregate operation Put simply crushing aggregate is the process of making little ones out of big ones Mark Krause managing director of North America for McLanahan Corp recently explained the basics of crushing in an introductory level webinar Presented here are some key points from the presentation TYPES OF OPERATIONS There are two types of aggregate operations open circuit and closed circuit An open circuit operation is where feed material is only run through the crusher once This usually occurs in a primary and sometimes secondary operation where uniformity of product size is not as critical A closed circuit operation is where material is continuously returned to the crusher until its of a size that will pass through the product screen TYPES OF CRUSHERS The two most common types of crushers are compression crushers and impact crushers The four factors affecting the crusher type be it compression or impact for an aggregate operation are Type of material abrasiveness Hardness of material friability Density toughness Fragmentation particle shape Condition Compression crushing is when material is squeezed between two surfaces The crusher reduces the material as it advances downward through the chamber by means of squeezing the material between moving and stationary pieces of steel These include gyratory crushers jaw crushers roll crushers and cone crushers COMPRESSION CRUSHING QUICK FACTS 1 The output is changed by adjusting the gap setting at the discharge point of the crusher 2 Rule of thumb Twice the setting is the top size discharging from the crusher 3 The tighter the setting the lower the throughput 4 Material breaks to fill the air pockets or voids in the crushing chamber IMPACT CRUSHING Impact crushing is when the material is hit or thrown This crushing process uses the theory of mass and velocity to reduce the feed material Therefore the faster the speed of the crusher means the finer the output However the faster the speed also means exponential wear on the machine The first break of the feed will occur along the natural fracture line while the second break will be perpendicular to the first These include horizontal shaft impactors vertical shaft impactors cage mill and hammermills IMPACT CRUSHING QUICK FACTS 1 The faster the speed the finer the gradation 2 Setting has some effect on gradation and throughput but speed is by far the most important factor 3 Rotor penetration is critical for best performance 4 Double the speed equals four times the wear CRUSHING EFFICIENCY There are four factors that most affect the crushing process S12 PIT QUARRY May 2018 pitandquarry com PHOTO COURTESY OF MCLANAHAN CORP A compression crusher reduces material by squeezing the material between moving and stationary pieces of steel Crushing is at the heart of every aggregate operation Put simply crushing aggregate is the process of making little ones out of big ones