By Neil Hise
When you’re in the crushing game, you need equipment that can optimize efficiencies while reducing maintenance and overhead costs. A vertical shaft impact (VSI) crusher is one of the best ways to do that, and understanding the different configurations will help you get one that scores big for your operation.
|An anvil system can reach up to 97 percent gradation in the first pass, nearly eliminating recirculation and increasing efficiency over a rock shelf system.||Rotor diameter, number of ports and speed all affect the size and shape of the final product.|
|Rock shelf units can recirculate nearly 30 percent of material, which reduces efficiency.||The material collects in a rock shelf system to create a wall. Additional material is hurled at high speeds and with great force to break or fracture the minerals.|
Breaking It Down
VSI crushers have two main sections – the component that hurls material, which can either be a closed rotor or an open shoe table, and the fracturing surface at which rocks or minerals are hurled, which is either a rock shelf or anvil ring.
Rotor: An Open and Closed Decision
An open shoe table works best for processing soft materials, such as slate or limestone. When processing materials that are around 26 or 32 on the L.A. abrasion spectrum, the shoes can last 30 hours or more, and the results are low maintenance and associated costs. But run more abrasive materials through an open shoe table, and you could be replacing shoes as often as every six hours.
For extremely abrasive materials such as gold ore or granites that register 17 or lower, a closed rotor system will be far more effective and require less maintenance. Many units feature heavy-duty tungsten carbide pins that trap material to build up their own internal shoe systems. Since there are no shoes to replace, these machines don’t need as much maintenance. Some crushers also include bolted-on components that can be replaced on site to minimize downtime.
Choosing between a closed rotor or open shoe table can be as simple as knowing the material you’re processing, but selecting the right fracturing surface involves a more economics-based approach.
|With a VSI crusher, material is fed through the hopper to the rotor impact system that does the fracturing.|
Fracturing Surface: The Heart of the Matter
In a rock shelf system, the rocks or minerals the unit is crushing build up to form a shelf on an open ring. The biggest downfall of this design is that, when material impacts the shelf it too moves, shifts and absorbs energy that could otherwise be used for breaking.
The results can be gradation of only 54 percent in a single pass and the need to recirculate nearly 50 percent or more of the material. Rock shelves also require high rpms to operate, and adding a larger motor and more kilowatts can increase production costs by as much as $2-3/ton.
A more economical option is an anvil ring that features a series of heavy-duty, 28 percent chrome white-iron stationary anvils. Nearly all of the energy goes into fracturing or crushing the material that is propelled at the anvils, so there is very little energy absorption or material rolling.
Anvil units can reach 97 percent gradation in the first pass, and they require only 1.5 hp/ton versus 3.0 hp/ton on a rock shelf system. In addition, users can sometimes rotate and reuse the entire face of the anvil before it needs to be replaced, which significantly extends the wear life.
With increased productivity, efficiency and energy savings, most applications with an anvil unit will result in a 30 percent increase in profits.
Finding the right VSI crusher configuration for your operation can put you way ahead in terms of efficiency, productivity and profits. And when you have exactly the right one, you’re sure to have a winning score.
Neil Hise is president of CEMCO Inc.