The problem for any pump manufacturer designing more compact pump systems is that any reduction in size cannot be at the expense of flow. What this means for key pump components such as bearings is that they, in- turn, must become more compact, but at the same time provide higher-load capacity to meet new operating demands. NSK has worked on this problem and the result is a new range of high-load capacity deep-groove ball bearings for centrifugal pumps. The basic dynamic load rating of these bearings has been improved by approximately 10%, and their fatigue life by around 30%, without any changes to the standard bearing dimensions.
One of the key factors in the longer life of the high-load capacity bearings is NSK's new UR heat treatment process, which 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, and stress concentrations develop immediately around indentations formed by foreign particles. The UR process prevents this from happening by increasing the amount of retained austenite within the bearing material. As a result, bearing durability is significantly improved in contaminated environments.
Another problem that NSK has addressed with its new pump bearing technology is creep. 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 solution, developed by NSK in its new 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 to prevent the occurrence of creep.
The launch of these high-load capacity bearings follows that of the BMPC series, the specification of which exceeds API 610, thanks to a strong, machined brass cage. BMPC series 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.