Realize sealing with oil seals and short axial length of journal bearing units

NTN Corporation (hereafter, NTN) has developed “Short Type Sealed Journal Bearing Unit” for rolling stocks that have approximately 15% shorter axial length compared to conventional journal bearing units.

Journal bearing units, which support train operations, need to be reliable so that it is maintenance-free for operation of 600,000 km or more. In the case of lower rigidity of axles, the axle bending under the axle load may lead to fretting wear*1 of the journal bearing unit components. Contamination by the fretting wear particles may lead to poor lubrication, wear, flaking and other defects inside the bearing. The axial length of journal bearing units need to be shortened in order to reduce journal bending that could potentially cause defects in the journal bearing.

Oil seals of sealed journal bearing unit are fitted to the outer ring in order to prevent grease leakage. For effective sealing, space between oil seals and rotating parts of the journal bearing (inner ring, roller and cage) used to be necessary. This places the oil seals on the outside of the bearing width and limits the shortening of the axial length of the journal bearing unit. Alternatively, a simpler sealing structure such as a shield-plate can be used to shorten the axial length. However, journal bearings with shield-plates tend to suffer from grease leakage more often, compared to journal bearings with oil seals.

The newly developed “Short Type Sealed Journal Bearing Unit” has the flanged-tip sleeve, which prevents the grease flow toward oil seal lips, as well as the newly designed oil seals with the optimized seal lip shape and interferences. This improves grease sealing and allows the oil seals to be placed within the bearing width, making the axial length of the journal bearing unit shorter. The journal bearing unit has the equivalent load capacity, high-speed rotational performance*2, and grease sealing performance to conventional products. Axial length of which are approximately 15% shorter reduces the journal bending by around 30% and the fretting wear, which contributes to the journal bearing durability.

NTN will propose the developed product to customers who need to shorten the journal length or are suffering from grease leakage issues with shield plates, contributing to an even safer and more comfortable operation of railway vehicles.