The rotor spins so fast that the high bars are the ones that impact the incoming material to be crushed, and very little hits the low bars. When the high bars wear down to about the level of the low bars, you remove the most worn set and install new high blow bars. The worn-down bars now act as the dummies. The purpose of the low bars is to help balance the spinning rotor and to protect the rotor against any small amount of material that escapes the high bars.
Some impact crushers use a three-blow-bar rotor. The problem here is that if a partially worn bar breaks you have to replace all three, rather than just a set of two, to maintain balance, and that’s very costly. Blow bars are expensive, and you have to shut down longer to replace three than two. We’ve found that using two bars in a four-bar rotor gives us the combination of production efficiency and cost effectiveness that we need for our type of operation.
Another important wear part is the side liner. These are square plates bolted to the crusher inside walls on both sides of the rotor, which is mounted between them. Side liners inside the “rotor zone” are turned at about 50,000 to 75,000 tons, as a rule. By rotor zone, I mean the area where the rotor spins and puts the most wear on the liners. As the rotor spins it creates a circular wear pattern on the two side walls caused by crushed material getting between the wall and side of the rotor.
The wear pattern usually is such that you can unbolt the plates, turn them 90 to 180 degrees and keep using them, rather than replace them at that time. The wear plates outside the rotor zone will last longer and sometimes can be switched with rotor zone plates to get longer life from the whole set.
Our impact crushers each use four aprons, which are interchangeable. This allows us to stock fewer spare aprons and helps keep our parts inventory lower.
A good quality crushing plant like ours will last “forever” if you take care of it. If you don’t you’ll be amazed at how fast it becomes junk.
On the other hand, don’t over-maintain the equipment, either. It’s wasteful and can cause harm if you over-grease the bearings anywhere on your plant. It causes them to overheat and wear out faster.
We give all bearings (except the impactor) two to three pumps of grease in mid-March, when we begin our crushing season, and again in mid-September. We grease the impactor every 40 hours.
Sometimes you can cut down on maintenance and downtime by having the manufacturer custom design certain aspects of your plant. For example, I had Grasan engineer both the crushing and screening plants with quick-disconnect pins instead of bolts for almost anything we have to dismantle or take off for over-the-road travel. That saves a lot of time and hassle. It takes longer to work with bolts; the threads get worn after awhile so the bolts need to be replaced; and it’s easy to lose a nut or washer. The pins are quick, simple and chained to the equipment so you won’t lose them.