CRUSHING
TIPS FOR MAINTAINING EFFICIENCY IN CRUSHING CIRCUITS
Today, the demand for highly specified aggregates means smaller top-sized products are finer than in the past. This means the crushing application has to be just as precise. What are the best tips for crushing materials at the first go, without resizing or stockpiling oversized products?
E
fficiency can be defined by the ratio of work done by a machine to the energy supplied to it. To apply what this means to your crusher, in your reduction process you are producing exactly the sizes your market is demanding. In the past, quarries produced a range of single-size aggregate products up to 40mm in size. However, the trend for highly specified aggregate has meant products have become increasingly finer. Currently, many quarries do not produce significant quantities of aggregate coarser than 20mm; it is not unusual for material coarser than 10mm to be stockpiled for further crushing. The following are tips and best practices to keep your site crushing efficiently and reduce the number of fines produced.
JAW CRUSHERS A jaw crusher is a compression-type of crusher. Material is reduced by squeezing the feed material between a moving piece of steel and a stationary piece. The setting or the space between those two pieces of steel controls the discharge size. The tighter the setting, the smaller the output size and the lower the throughput capacity. Jaw crushers are mainly used in primary crushing; they are rarely used as a secondary crusher. As compression crusher, jaws generally produce the coarsest material because they break the rock by the natural inherent lines of weakness. A jaw crusher can be an excellent primary crusher when used to prepare rock for subsequent processing stages such as washing, classifying or a secondary crusher. General efficiency tips • Grease lubrication systems are preferred over an oil-lubricated system. • An annual radial clearance check of the mainframe bearing should be recorded to track bearing wear. • Minimum discharge setting should not exceed full load amps. 18
Quarry April 2019
A jaw crusher can be an excellent primary crusher when used to prepare rock for subsequent processing stages.
• Do not crush oversize material against the barrel of the jaw. That area is not considered part of the crushing chamber. • Periodic oil sampling of the bearings is advised, when oil lube is used. • The discharge conveyor and under crusher hopper should be wider than the discharge width of the crusher. • Sufficient tension must be placed on the toggle plate to ensure proper alignment.
Efficiency tip Try to choke-feed any compression-type crusher. Remember, we are using gravity and the weight of the material to push or force material through the chamber. Since in a compression machine the material breaks to fill the air pockets or voids in the chamber, a non-choke chamber will produce a slabbier output than a choke-fed chamber. Feeding for efficiency Jaw crushers are routinely choke-fed, as this
maximises production capacity and ensures particles are uniformly broken. This promotes stone-on-stone crushing, which breaks up flaky or slabbier particles. If you are seeking fewer fines, trickle-feeding material into the jaw crusher could achieve this; however, this would have an adverse effect on particle shape and would also reduce throughput capacity, hindering the crusher’s efficiency. Ideally, the feed rate should not be switched from choke to non-choke, as this would cause problems downstream at the secondary processing plant. In practice, many jaw crushers are fed in this intermittent fashion due to gaps in the delivery of feed material from the quarry. Jaw crusher feed should be pre-screened using a grizzly screen prior to crushing, to remove material finer than the closed side setting (CSS).
Efficiency tips In practice, many jaw crushers are not fed to their design capacity; this is because the
