Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/878969
22 AGGREGATES MANAGER / September 2017 EQUIPMENT MANAGEMENT problems, as initial set up takes finesse, and glands have a higher 'start-up failure' rate. Always check the quality, pressure, and flow of any lubrication water. Bearings in slurry pumps mostly have B10 lives in excess of 50,000 hours and should, if properly lubricated, provide years of service before failure. However, if the pump is cavitating (poor design) or running on 'snore' (low sump level causing vortexing), bearing and gland life can diminish to weeks, so main- taining make-up water valves is instru- mental in assuring pump life. Failure of 'wet-end' bearings can also be caused by gland failure. V-belt tension can factor into 'drive-end' bearing and motor bear- ing failure, so belt tension should be rou- tinely checked. Hydrocyclones — These have no moving parts, but there are two failure modes, delamination and wear, that af- fect performance. Liners coming loose (due to wear or adhesion) cause disrup- tion of flow inside the unit, and poor per- formance with misplaced particles is the result. Checking the internal lining of a cyclone should be done at least season- ally; this is particularly important when dealing with siphon (vacuum)-assisted cyclones/separators. The apex (spigot) is the fastest wearing component; they are sized based on mass-flow, so, as they wear, the underflow becomes more di- lute and more fines will bypass into that stream affecting the wash-out of delete- rious fines. If your product is getting dirt- ier, check the apex. Worn vortex finders can allow coarse fractions to short-cir- cuit to the overflow and fill the ponds or contaminate the next stage of production. Worst case is wear can cause the pipe to detach from the plate, causing significant damage. Separators or 'siphon-assisted' cy- clones can be affected by holes worn in the overflow piping, which de- feats control, and flushing will occur. Unfortunately, symptoms such as uncon- trolled flushing are insidious and hard to trace. Close annual inspection for thin pipe sections should be carried out. Dewatering screens — Dewatering screens typically have a very long service life, but there are some areas to watch. Side plate cracks (as with sizing screens) can occur. If noticed, trace the crack to its end with dye penetrant and drill a 1/8- inch to 3/16-inch hole. This ususally takes care of the problem, and the side-plate will last the life of the screen. Cracks in cross members or the bridge should be referred to the manufacturer immediately, as should any bolt breakage. The prob- lem with cracking in dewatering screens is frequently the support structure rather than machine integrity. Lubrication is a general maintenance activity, but take extra care as some vibrator motor man- ufacturers use specialized grease that, if not used, voids the warranty. Often, motor wiring gets draped across from the motor to the side of the screen and vibrates against adjacent sur- faces — this is a very dangerous condi- tion. Check this and replace the wiring as needed. Always check direction of motor rotation on restarting after electri- cal work. It is not uncommon to see sideways tracking of material on a lightly loaded screen, this is typically not of concern, but springs or rubber buffers should be checked once a month. At rest, mea- sure the height of each buffer and con- firm with the O&M manual that it is within tolerance. The screen should sit square; any sideways deformation at rest should be investigated, as should sideways motion greater than 1/16-inch during operation. Record and refer this to the manufacturer. If the screen has an unusual action (non-linear), check the motor counterweights for settings — all four locations should be consistent — and On vibrating equipment, re-torqueing bolts can be critical. Repeated dismantling and reassembly to inspect a pump gland may end up causing higher failure rates.