Advanced-design bearings can keep vibrating screens operating longerTake a tour through a mining or quarry operation and you’ll witness one of the harshest industrial environments. You might assume that the equipment used in these industries could withstand just about anything. But even in these rugged environments, equipment can fail suddenly and catastrophically as a result of a relatively small particle of dirt, a minor increase in operating temperature, or a little too much vibration.

In the mining industry–as with many others–vibrating equipment is particularly at high risk of operating problems that have the potential to cause an unplanned shutdown. One of the most critical pieces of vibrating equipment in a mining or quarry operation is the vibrating screen, which is used to sort and separate rock and other materials, typically by size. As the material passes through the vibrating screen, smaller particles drop through the screen while larger pieces continue on for further processing. The process enables the mine or quarry to turn out stone or other material of a specified size, as required by customers.

The many environmental forces that impact vibrating screens can pose significant operating challenges. In these applications, operating speeds can be very high, lubrication runs the risk of contamination from the ever-present dust and debris, and premature wear of key components is always a possibility.

Recognizing the unique issues at work in these environments, SKF developed bearings specifically designed for the unique operating environment of a vibrating screen. These bearings–which meet the new SKF Explorer quality standard –are designed to last significantly longer than other bearings on the market today.

No small task

By its very nature, a vibrating screen is subject to tremendous stress and a host of harsh conditions that can be very taxing on the screen’s bearings. First, to generate the level of vibration needed, the screen is equipped with large weights that are mounted off-center of the shaft and swung with tremendous force in a circular motion.

“The rotating weight essentially produces a different type of loading situation, for which the standard spherical roller bearing configuration isn’t sufficient,” explains Keith Meyers, SKF Global Engineering Manager, Mining and Construction Segment. “In most typical bearing arrangements, the bearing inner ring has a tight fit on the shaft while the outer ring is fixed in its housing. But the vibrating screen’s operation requires just the opposite.” Unfortunately, movement of the inner ring can result in fretting corrosion, which can lead to premature bearing failure.

At the same time, the environment in most mining and quarry operations creates potential lubrication problems for the vibrating screen’s bearings. With rock constantly being pulverized, the air is continually bombarded with dust and debris that can easily make its way into the seal of the bearing’s housing. This type of contamination frequently causes a high percentage of premature bearing failures.

Up to the challenge

SKF Explorer spherical roller bearings have a unique and advanced design that allows them to run cooler, quieter and longer than their standard counterparts. Within the Explorer line, three bearings were designed specifically to meet the particular challenges of vibrating equipment: the VA405, VA406 and a new Explorer quality CARB™ bearing.

According to Meyers, Explorer bearings are the result of many years of research and development at the SKF Engineering & Research Centre in the Netherlands – along with intensive testing at a combination of SKF facilities and customer sites. The mission of the development effort was to create bearing performance meeting customer requests that would minimize the negative effects of wear, contamination and friction and maximize the positive effects of lubrication.

“Beyond the new bearing designs, the Explorer initiative also involved the development of new manufacturing processes and standards for the consistent production of these new components,” Meyers notes.

One of the key features of the SKF bearings for vibrating screens is their hardened steel cage, a major factor in their performance. SKF has 10 years of operating experience in the U.S. and other customer locations around the world. While many bearing cages in the industry are made of soft materials, SKF’s Explorer bearings for vibrating screens use hardened steel cages. This steel construction makes them lightweight, rugged and extremely resistant to wear.

Installed in vibrating screens–in both clean and contaminated environments–the Explorer bearings are demonstrating an operating life that is many times the expected life of standard spherical roller bearings. The longer bearing service life can be evaluated using the SKF Life Method. At one U.S. test site, the bearings were successfully operated for over two years with complete satisfaction.

The Explorer quality VA406 bearing features a PTFE-lined bore, designed to help prevent fretting corrosion. Fretting corrosion is particularly common in vibrating screens, as a result of the movement that occurs between the shaft and the bearing’s inner ring. The PTFE-coated bore helps to reduce the incidence of fretting and the resulting potential for bearing failure and shaft damage.
Not only do the new Explorer designs enable bearings to operate longer in vibrating screens and other vibrating equipment; they also allow them to run cooler and quieter than conventional spherical roller bearings. Test sites have demonstrated temperature reductions of up to 10° C (18° F) when compared to standard bearings in the same applications.

“SKF’s extensive experience indicates that lower operating temperatures have a significant impact on a bearing’s performance and its service life,” Meyers says. The reductions in vibration and friction made possible by the Explorer design also translate to reductions in noise, which may be critical in some applications.

Service life gains

The three Explorer quality bearings for vibrating applications offer a number of very positive service life gains. In some applications, the screen manufacturer may be able to use a smaller Explorer bearing to do the same job as a larger conventional bearing. As a result, the Explorer bearings open the door to new product designs that may be lighter, faster and require less power.

“Manufacturers can incorporate an Explorer bearing of equal size into an existing product design–providing increased output and capacity without the costs associated with product redesigns,” Meyers notes.

The superior design and performance of SKF’s new Explorer bearings offer noticeable improvements for customers that operate vibrating screens or other vibrating equipment, as well as the original equipment manufacturers that produce them.

“Our new Explorer bearings literally redefine the design limits of spherical roller bearings, resulting in many tangible benefits that can impact the bottom line,” Meyers says. “By improving the reliability of vibrating equipment and helping to minimize unplanned downtime, the Explorer bearings can help to increase throughput and, ultimately, customer profitability.
For more
information
about the entire Explorer line–including the VA405, VA406 and CARB bearings for vibrating applications –visit the SKF Web site at skf.com or
call 215-513-4400 for new literature on our Explorer bearings.