Deep Groove Ball Bearings For Centrifugal Pumps

NSK has introduced a range of high load capacity deep groove ball bearings for centrifugal pumps. The basic dynamic load rating of these bearings has been improved by about 10%, and their fatigue life by around 30%, without any changes to the standard bearing dimensions. These improvements have been achieved via a combination of a heat treatment process and enlarged ball diameters, and by optimising the interior design of the bearing cages. The UR heat treatment process is effective in alleviating the stress concentrations that cause surface originated flaking on bearing material. Surface originated flaking tends to occur under contaminated lubricating conditions. Stress concentrations develop immediately around indentations formed by foreign particles. The process prevents this from happening by increasing the amount of retained austenite within the bearing material. As a result, bearing durability is improved in contaminated environments. Another problem is creep. This is the name given to wear that may occur between the bearing outside surface and housing bore due to low speed sliding. It is the result of loads becoming excessively high on the driving shaft of a pump. If not addressed, creep causes excessive shaft vibration, which can trigger abnormal oscillation and lead to impeller damage. Common measures against creep include an interference fit between bearing and housing. For pumps, however, a tight fit is not practical, as it makes pump assembly more difficult and does not allow for additional loading caused by an increase in the shaft length due to heat generation. A better method, developed by NSK in its range of anti-creep bearings, is to install O rings into the two grooves on the bearing outer ring. The frictional force of the O rings helps prevent the occurrence of creep. The launch of the high-load capacity bearings follows that of the BMPC series of bearings, designed to provide greater reliability and longer life in harsh centrifugal pump applications, in pulp and paper, waste-water treatment, steel mills, irrigation, mining and other demanding industries. The series exceeds the API 610 standard. The standard calls for angular contact ball bearings, with a 40deg contact angle, arranged in a back-to-back configuration, and giving a minimum life expectancy of 25,000 hours (three years) continuous running, or 16,000 hours at maximum radial and axial loads. The BMPC series surpasses API 610 by incorporating a strong machined brass cage, providing more reliability in harsh applications. The bearings also achieve longer service life, through smoother running, reduced levels of friction and lower temperature rise: the latter as a result of the better heat dissipation of the brass cage material. The design is an amalgam of high strength materials technology, ABEC3 (P6) manufacturing tolerances and pump specific axial internal clearances. It delivers higher running accuracy, plus optimum levels of bearing stiffness, shaft positioning accuracy, load sharing and cooler running. In addition, the combination of finished raceways, low inner ring run out and high ball grade contribute to reduced levels of ball skidding and hence smoother operation.