Holes from abrasion and normal wear and tear typically appear in the upper outside casing, inside drum, and upper and lower tailings cones. Patch it with steel, and you’re back in business. In extreme conditions, parts or wear liner replacement becomes necessary.

5  Surface moisture content.

Under normal operation, this must be 1.5 percent or less. If the moisture content is any higher, the finer particles will cling to larger ones, making it difficult to get a good quality classification. If the moisture content, whether it comes from rainfall or dust suppression spraying, is very high, the water is centrifuged out, resulting in equipment clogging. Natural inherent or internal moisture content usually has no effect on air classifier performance.

6  Vibration.

Always check for vibration. Excessive vibration could cause the classifier’s structural integrity to fail prematurely. Vibration will also put undue stress on the gear unit bearings and seals.

7  Proper lubrication.

It’s important to maintain the proper oil level and drip setting for the lower bearing and proper interval greasing of the upper bearings. The gear unit oil should also be drained and replaced after the recommended hours of operation. Consult your owner’s manual for recommended lubrication practices.

8  Belt tension.

The belt tension should be checked periodically to maintain belt life and power transmission. Over-tightened belts could be the cause of vibration. Always follow your manufacturer recommended intervals when it comes to checking belts.

9  Gear unit backlash in 90-degree gear drives.

Gear backlash is the amount of clearance between the ring gear and pinion gear. Maintaining the proper amount of backlash is important. If it is too tight, you’ll wear the gears out, which will not only reduce the lifespan of the gears, but it also can result in top bearing problems in the gear unit. An annual check of the backlash in the gears is imperative to maximize the life of the gears. Again, consult your owner’s manual for proper backlash amounts and procedures.

10  Bearing temperature.

High bearing temperatures and wear are generally not an issue because classifiers are relatively slow-speed machines and don’t handle the aggressive work of pulverizers. However, a high bearing temperature can be an indication of an impending bearing failure and could save you from having a major failure. Bearings have been known to fail simply because they were not properly monitored.

As part of an expanded preventive maintenance program, a vibration analysis expert can take a vibration reading as a baseline and then compare it to annual readings. They can identify and isolate any suspect bearings.

Remember, wear and tear is based on the characteristics of your specific material. For instance, silica sand applications may have to be inspected every 30 to 60 days to troubleshoot any wear problems, whereas soft limestone-like materials will give you a much more generous maintenance schedule. Each deposit from each territory is different depending on the chemical property of the material, so always be aware of the silica or quartz content.

Keep on top of your maintenance schedule and your air classifier will earn its keep, doing what it was designed to do — turning common stone into common currency. 

William Chapman is lab manager and William MacNeil is lab service technician, both with Sturtevant Inc.