With diesel-powered units, make sure connections between the engine and air cleaner are tight. "Run a duct from the air intake to a clean area 20 or 30 ft. away - maybe more, if necessary," says Cherrington. "Dust ingestion is a big problem. Without proper filtration, you can ruin an engine in days or even hours."
Cherrington also emphasizes the importance of oil analysis. "An oil sample analysis program can save you a lot of engine grief," he states. "The analysis will expose air cleaner problems by identifying high silica content or other contaminants in the oil. We have virtually no unexpected engine downtime."
Of course, you could go with an electric motor instead of diesel to eliminate the risk of dust damage. "But you have to change pulley sheaves to change speeds. Diesel power gives you instant speed variation," says Cherrington.
Keeping common wear parts on hand will help to avoid delays when it's time for replacement. "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," Cherrington notes. "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."
While maintenance is important, Cherrington cautions against overdoing it. "Don't over-grease shaft bearings on your plant," he says. "Too much grease causes the bearings to overheat. Big bearings don't require as much grease as most people seem to think. Just follow the manufacturer's schedule - no more, no less."
Cherrington has found that turning the gearbox of stacking conveyors upside down for travel allows sediment and pieces of metal to fall down into the gears. "Until we figured this out, gearbox failures were a huge problem. Regular oil changes have eliminated it," he says.
Overall, Cherrington feels his company has a unique attitude when it comes to maintaining equipment. "We have no 'official directives' regarding maintenance - just smart people who need not be afraid to shut down to fix something that isn't totally broken," he says. "Scheduled downtime isn't really downtime. Downtime is when equipment isn't running outside of scheduled maintenance."
Weber Sand & Gravel, Lake Orion, MI, is a family-owned company formed in 1946. Contract crushing is a big part of its business. The company utilizes a custom-designed, diesel-powered Grasan KRH1515 primary impact crusher plant with an automatic hydraulic cylinder system.
Scott Weber, vice president, runs the crushing division, which operates from mid-March through mid-December. "We can crush as much as 900 tph of limestone or concrete rubble down to 1" x 3", or 500 tph of asphalt down to 5/8-in. minus while using only two blow bars of the possible four," he says.
The crushing operation includes the crusher plant, screening plant, return conveyor, radial stackers and a 30-ft. trailer with generator and controls. Weber Sand & Gravel is able to blow the equipment clean, move it 50 miles to a new site and be crushing again in about 12 hours.
"We pride ourselves on our production efficiency," says Weber. "Unplanned downtime is out of the question. So skimping on maintenance is equally out of the question."
The entire plant is inspected daily. Special attention is paid to the impactor, including checking the rotor, blow bars and side liners. "We adjust the aprons every day," says Weber. "And we change wear parts when needed, not when convenient."
When crushing concrete, the company normally uses high chrome blow bars, which are turned roughly every 25,000 tons, generating 100,000 tons before replacement. Manganese bars are used for limestone or for concrete in some situations. "Manganese is softer than high chrome; it's more 'forgiving' so the bars are less likely to break," says Weber. "But they do wear down faster, and we have to turn them more often."
For asphalt, high chrome bars are used. These are usually turned at 15,000 to 20,000 tons, depending on the material. "We replace blow bars when they're down to 1 1/4 in. from the rotor surface," Weber notes. "Some operators let their bars run down lower than that, but I don't advise it."