Special Issue; Products for Industrial Machinery - NTN

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NTN TECHNICAL REVIEW No.742006 New Product Development of New RCT Bearing for Axleboxes and Insulated Bearing with Shields Ryutaro OKA In recent years railroad carriages have been increasingly considered to be eco-friendly, energy efficient, and are viewed as a good means of transportation. Demand for railroad bearing business grows greatly in China and Europe. High reliability is sought after in a bearing for railroad applications because of public visibility. There is also a strong demand from the railroad companies for longer time between maintenance periods. Therefore the problems facing railroad bearings is how to effectively maintain reliability and extend the time between maintenance periods. NTN has developed an Insulated Bearing with shields and the new RCT Bearing, which could solve these problems and satisfy the Chinese and European markets. This report discusses laboratory evaluation test results concerning the performance of Insulated Bearings with shields and the new RCT Bearing. 1. Introduction Recently, the usefulness of rolling stock has been appreciated even more because trains are increasingly regarded as an eco-friendly means of transportation that excels in energy efficiency. In particular, there have been serious efforts for the construction of intercity railway infrastructure and the introduction of high-speed railway systems in China. Furthermore, in the European market, which accounts for 50% of the world’s railway equipment demand, higher train speeds are needed to accommodate the recent expansion of the EU. Thus, in these markets, the demands for rolling stock bearings have been increasing dramatically. The typical bearings for rolling stock include traction motor bearings for power transmission systems, drive system bearings used in the gearboxes (drives) that transmit the motor output to the axles, and axle bearings that support the weights of the train cars. Each of these bearings is a critical component whose performance directly affects the operation of railroads, and, therefore, they must all be highly reliable. At the same time, the end users who operate the trains are demanding longer maintenance intervals. Therefore, the manufacturers of bearings for rolling stock now have to address the challenge of realizing longer maintenance intervals while maintaining high levels of bearing reliability. Recently, we have developed unique bearing products to address these challenges and to fulfill the needs of the very promising Chinese and European markets. They are our new RCT bearings for axleboxes, which is a line of high performance axlebox bearings and our sealed insulated bearings for traction motors. This report describes the results of evaluation tests for our new RCT bearing for axleboxes and our sealed insulated bearings. 2. New RCT Bearings In the European rolling stock axlebox bearing market, metric-series bearings have been used commonly, and such bearings are also often adopted in the Chinese rolling stock market. We have recently developed a new line of RCT bearings for axleboxes that satisfy the EN standards, which are commonly adopted in the European and Chinese rolling stock markets. *RCT bearings: sealed double-row tapered roller bearings used on rolling stock axles. Industrial Engineering Dept. -84-
Development of New RCT Bearing for Axleboxes and Insulated Bearing with Shields 2.1 Development of the New RCT Bearing We incorporated the three new technologies below in a conventional RCT bearing to develop our new RCT bearing, and we subjected this new product line to evaluation tests according to the relevant EN standards. The features of the new technologies and the test results are provided below: 1) Adoption of a resin cage 2) Adoption of an anti-fretting plate 3) Adoption of a light contact seal 2.2 Resin cage The resin cage is made of a special resin material featuring impact resistance and is expected to provide longer lubrication life and boast better mechanical strength. Verification of the benefits of adopting a resin cage 1) Inhibition of the occurrence of wear dust (iron dust) The occurrence of iron dust from a steel cage in grease was compared with the occurrence from a resin cage. Consequently, we have verified that use of a resin cage can effectively inhibit the occurrence of ion dust on running bearings. Test bearing Double row tapered roller bearing (120 ID x 220 OD x 155/160mm) Test conditions Table 1 Condition of endurance test Bearing speed (min -1 ) Radial load (kN) Axial load (kN) Lubrication system Run duration Test results wt% 1.2 1.0 0.8 0.6 0.4 0.2 0 0.02 Run pattern at 2125 min -1 48.09.8 014.7 Grease lubrication Equivalent to 700,000 km of travel Standard value of the Railway Technical Research Institute of Japan (iron quantity 1.0%) Resin cage Iron quantity (wt%) 1.03 Sheet steel cage Fig. 2 Quantity of iron in grease after endurance test Resin cage Longer grease life and lighter weight Light contact seal Lower bearing temperature Soft, thin sheet (brass sheet with rubber lip) Fretting control Fig. 1 New RCT Bearing -85-
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