Aggregates Manager Digital Magazine
Issue link: https://read.dmtmag.com/i/93285
EQUIPMENT MANAGEMENT effective. However, large particles with low density can have a similar mass and weight as some small particles with high density. This can reduce the effectiveness of an air classifier's density separation. Even though air classifiers are rugged by design, they do require a degree of maintenance to keep them running at peak performance. Here are 10 items to look at that will enable a technician to better identify any problems being experienced or allow for an in-house fix. properly vented? Plenty of dust to contend with results from improper venting. The fines side of the classifier has positive air pressure, so you want to be able to vent or remove it to prevent dust- ing. In quarry applications, the venting can be eliminated, because dusting can be controlled with fine water mist. selector blades and the inside drum cover correct to specifications in the owner's manual? It is one of the most common problems encountered by service techni- cians. It is very important to maintain a proper gap between the top of the selector blades and the underside of the drum cov- er; the general rule of thumb is 1/4 inch or as close as you can get without contact. An excessive gap will result in unwanted oversize particles in the fines fraction. 1 2 Are you over feeding or under feeding the classifier? Whether you employ inclined belts, screw feeders, or air slides, it is important to maintain relative consistency in the feed rate. 3 Feed rate. Selector blade adjustment. Is the clearance between the Proper venting. Is the "fines" side of the classifier Maintain a proper gap between the top of the selector blades and the underside of the drum cover; the general rule of thumb is 1/4 inch or as close as you can get without contact. the classifier for wear. If you discover any holes, then your material could start to migrate between the fines and coarse side of the classifier by sheer gravity. This will obviously throw your product out of spec. 4 Under normal operation, this must be 1.5 percent or less. If the mois- ture content is any higher, the finer particles will cling to larger ones, making it difficult to get a good quality classifica- tion. If the moisture content, whether it comes from rainfall or dust suppres- sion spraying, is very high, the water is centrifuged out, resulting in equipment 5 Surface moisture content. 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. Material-to-air-flow ratio can have dra- matic effects on classifier efficiency. Excessive wear. Check the internal areas of clogging. Natural inherent or internal moisture content usually has no effect on air classifier performance. Always check for vibration. Ex- cessive vibration could cause the classifier's structural integrity to fail pre- maturely. Vibration will also put undue stress on the gear unit bearings and seals. It's important to maintain the proper oil level and drip setting for the lower bearing and proper interval greas- ing of the upper bearings. The gear unit oil should also be drained and replaced after the recommended hours of opera- tion. Consult your owner's manual for recommended lubrication practices. 6 7 checked periodically to main- tain belt life and power transmission. Over-tightened belts could be the cause of vibration. Always follow your manu- facturer recommended intervals when it comes to checking belts. 8 AGGREGATES MANAGER October 2012 23 lubrication. Proper Belt tension. The belt tension should be Vibration.