The maintenance cost is a little higher than a jaw. But the impact crusher gives us greater efficiency and a better, more cubical product with no slivers. We can reduce 24-inch limestone down to six inch minus in one step. From there it goes to secondary and tertiary cone crushers for final processing.
In less than seven years, we’ve crushed about nine million tons of shot limestone and had no unplanned downtime, just simple maintenance as we go. We operate the quarry all year, but shut down the crushing operation for three months in winter. That’s when we do our most thorough service work and make any repairs, such as belts, replacing or welding the wear liners or rotor to build it up — hard face it — things our regular work force can do. We have no mechanics on staff, so we rely heavily on durable, dependable equipment that runs and runs and runs with minimum maintenance. That kind of quality is absolutely essential.
We crush 10 hours a day, five days a week. We have three difference grades (hardness) of limestone in our quarry; so replacement of wear parts varies according to the hardness of the material we’re crushing at the time. We use four blow bars in our crusher and flip the bars about every two weeks. That equates to a high of approximately 80,000 to 100,000 tons per flip down to a low of 60,000 to 80,000 tons per flip. So a set of blow bars will last from about 240,000 to 400,000 tons before replacement.
With good maintenance practices, a good quality crushing plant will perform well for a long, long time. We’ve gotten about seven very good years from ours. I look for at least 10 more.
Butch Cherrington, vice president, Complete Resources, Columbus, OH
Complete Resources is a contract crushing company that processes concrete and asphalt rubble and aggregates with several Grasan road-portable and pit-portable impactor plants of various sizes ranging from KR1013 to KR1315. All are diesel-powered plants. Cherrington says:
We have a three-pronged approach to maintenance and downtime prevention. First, we make the plant operator responsible for regular equipment maintenance. In our case, that person is the foreman. We feel that’s better than a committee responsibility with a lot of ‘who, me?’ and finger pointing. Second, we employ several full time mechanic-welders who take care of heavy and non-scheduled repairs. Third, we try to perform maintenance as much as possible when moving equipment from one crushing site to another. That works very well for us.
A balance needs to be struck between running the plants till they break and maintaining them as good as new, because neither is profitable. If left up to production people, plants would be run into the ground in short order. If my maintenance people had the say, I would have plants in “as new” condition; but I couldn’t afford to operate them.
With diesel-powered units, make sure connections between the engine and air cleaner are tight. And run a duct from the air intake to a clean area 20 or 30 feet away — maybe more, if necessary — dust ingestion is a big problem! Without proper filtration, you can ruin an engine in days or even hours.
An oil-sample analysis program can save you a lot of engine grief. The analysis will expose air cleaner problems by identifying any high silica content or other contaminants in the oil. We have virtually no unexpected engine downtime. Some people just expect engine problems and live with them. Not us. That’s too costly and profit-killing.
You can go to electric-motor power instead of diesel to eliminate dust damage. But you have to change pulley sheaves to change speeds. Diesel power gives you instant speed variation.
Make sure you keep wear parts — especially crusher wear liners and blow bars — in stock so you won’t have delays when you need to replace them. We’re usually into the crusher once a week to check on whether blow bars or liners need replacement, and whether anything else needs to be done. When we change blow bars, we generally also change liners if they’re fairly worn, so we won’t have to shut down again soon. Leaving a little metal on the liner is less costly than another shut down.