Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/945822
AGGREGATES MANAGER / March 2018 35 to install an OEM-designed bushing to en- sure proper oil fi lm is maintained around the bearing surface. The upper bearing, or spider bushing, also needs to be checked regularly. Whether oil or grease lubricated, there will always be some level of leakage in this area. The proper lubricant level needs to be maintained or there is a risk of high heat generation at the upper journal that can eventually lead to mainshaft damage. The spider bushing also maintains proper pitch of the mainshaft during crushing and idling, and, at times, there can be damage to the eccentric or bottomshell bushing from misalignment caused by an excessively worn spider bushing. Spider bushing wear can be measured directly, but it can also be monitored by changes in oil/grease leakage, increased no load head spin over time, or even by hearing a knocking sound when shifting from idle to crushing to idle again. Operating practices have a large infl uence on crusher reliability. It goes without saying, but tramp events such as large bucket teeth can cause signifi - cant stress and damage. Most gyratory crushers today have tramp relief in the form of a lowering head as the force in the chamber exceeds the pressure of the hydraulic oil supporting the mainshaft; however, there will still be some level of overload, and particles too large to pass will invariably stall out the crusher and put heavy stress on the bearings. Stress can also be put on the crusher if oversize boulders are frequently encountered, and a rock hammer is used to break the boulders while they sit on or inside the crusher, as every impact from the hammer that does not break the boulder gets transferred directly to the crusher. It is impossible to completely avoid all of these events, but minimizing the over- loads that you can control will go a long way to improving crusher reliability. Another operating practice that can be a detriment to component life in a gyratory is making trucks/loaders wait to dump their load until the chamber of the crusher has emptied. Gyratory crushers are designed to be "buried" with material well above the spider arms, and dumping a truck onto a full chamber helps to cushion and absorb the high impact energy from fast-falling large boulders. There is less stress on the spider, less impingement on the mainshaft, lower wear rate on the wear liners, and less risk of cracking and knocking out a concave when dumping in to a full chamber. Of course, it is important to ensure that there is adequate surge capacity/space under the crusher so that all of the material in and above the crusher has a place to go if the takeaway feeder or conveyor should be tripped. When operated and maintained properly, a primary gyratory should last for decades. Using best practice operation and maintenance will ensure it does so trouble free. AM This article is courtesy of Metso Minerals. We've got it. Rockability. Experience Knowledge Service Rock Solid Solutions Built on Experience since 1977…. Proud Distributor of Aggregate Material Handling Systems 323 Energy Way • Bridgeport, TX www.crispindustries.com 800.315.0871