www.engineeringnews.co.nz 45 Bearing reliability is a crucial component of productivity and uptime in expensive machinery and plant throughout industries such as mining, manufacturing, bulk handling and primary production. If a bearing fails, production can grind to a halt. Bearing failures can be caused by a number of factors. They include: 1. Fatigue, which can occur naturally over time, but also occurs prematurely if the incorrect bearing is chosen for the task. 2. Incorrect installation or mounting, which can lead to significantly higher wear and tear and ultimately premature failure. Examples include misalignment, incorrect fits – too loose or too tight, out-of-roundness in shafts or housings. About 25% of bearing failures occur because of incorrect mounting. 3. Lubrication problems, which can occur if too little, too much or incorrect lubrication is applied to the bearing. Incorrect or insufficient lubrication is the single biggest cause of bearing failure, accounting for more than 45% of problems. 4. Poor maintenance or monitoring, because even the best precision bearings are not ‘set-and-forget’ technologies. Their maintenance needs change with service and local conditions, so good monitoring and suitable maintenance is vital. 5. Contamination, which can occur when foreign substances enter the bearing. It is often considered to be the major component of lubrication problems. Contamination is particularly prevalent in aggressive process and manufacturing environments, such as mining, primary production and bulk handling. Bearing contamination challenges “Despite it being an eminently preventable problem, a staggering 25% of all bearing failures are caused by contamination,” says Martin Grosvenor, industrial sector manager, Schaeffler Australia. “Contaminants can include airborne dust, dirt or any abrasive substance that finds its way into the bearing. The main sources of these contaminants are dirty tools, contaminated work areas, dirty hands and foreign matter in lubricants or cleaning solutions,” explains Mr Grosvenor. Symptoms of a contaminated bearing include excessive vibration and wear, which is best detected before it becomes expensively obvious in the form of unscheduled maintenance, or worse, production breakdown. Schaeffler solution In challenging environments or operations where the risk of contamination is high, such as continuous casting plant, conveyor belts, elevator plant or food industry applications, Schaeffler’s FAG sealed spherical roller bearing (SRB) is ideally suited to the task. FAG SRBs are a special rolling bearing design where the inner ring runs inside the outer ring on two rows of rollers. The bearings have an angular adjustment of up to 2° and are not only designed for high load carrying capacity but can also compensate misalignments, due to the fact that the symmetrical barrel rollers orient themselves freely on the concave outer ring raceway. FAG Sealed SRBs offer the same benefits as open SRBs, but with seals typically consisting of nitrile rubber or, high performance fluoro rubber depending on the application and operating conditions. FAG Sealed SRB’s are available to suit a wide range of common applications in heavy industries such as pulp & paper, mining, minerals processing, wood products, power generation “The seals effectively close off the bearings, giving them an increased operating life compared with open bearings, because they are protected from contaminants. Additionally, they require significantly lower quantities of grease to keep them lubricated (up to 80% less in some applications), which means they can assist in reducing environmental impacts too,” says Mr Grosvenor. Other features of Sealed SRBs include: • Very high basic dynamic and static load ratings • Environmentally friendly characteristics • Lower grease consumption and disposal costs • No requirement for expensive relubrication systems • Reduced maintenance outlay • Simple reconditioning X-life sealed SRBs Schaeffler’s FAG Sealed SRBs are also available in X-life ranges (marked by the suffix E1), which have improved kinematics, optimised surfaces, are made from higher performance materials and do not have a rigid central rib. These enhanced characteristics of the premium X-life range mean that under identical operating conditions, basic dynamic and static load ratings as well as the basic rating life of the bearing is significantly improved. In certain applications, this means that a smaller bearing arrangement can be designed. Schaeffler introduces largest ever sealed SRB Designed to help industry reduce costs and boost efficiency, Schaeffler has developed the world’s first sealed 241/1250 spherical roller bearing for high-pressure grinding roll crusher applications. It is an engineering milestone that is expected to offer significant cost savings to mining and bulk materials handling companies throughout the world. Featuring an outside diameter of nearly two metres, the ultra-large 241/1250 bearing was specifically designed for the highest-capacity high pressure grinding roll crushers (HPGRs) used by the mining industry. Previously only available in an open configuration (i.e., without seals), Schaeffler’s new sealed version of this massive roll support bearing is designed to prevent the crushing materials from contaminating its internal components. Schaeffler developed the sealed 241/1250 bearing to help the mining industry cut costs and boost efficiency. Until now, miners have typically been forced to inject high quantities of grease into the bearings to prevent contamination. While necessary, this practice wastes resources and significantly increases a mine’s preventive maintenance expenditures. By introducing a sealed bearing for this challenging application, Schaeffler’s innovation promises to also increase mining productivity. The bearing’s sheer mass – as evidenced by a total weight of approximately eight metric tons, including rolling elements that weigh 60 kg each – presented an engineering challenge that very few companies are able to master, even before the complex sealing arrangement is factored in. The outside diameter of the moulded seal, which features unique design elements that were first developed for marine applications, measures approximately 1.4 metres. The state-of-the-art sealing properties are provided by metal shields installed on both of the bearing’s side faces, each of which features an optimised polymer seal that prevents the ingress of crushing material. According to
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