<strong>NTN</strong> TECHNICAL REVIEW No.742006 contact ball bearing used was a standard HTA020ADB, and the bearing used on the rear side was the N1016 single row cylindrical roller bearing. Deflections occurring on the front end of the spindle when pure axial loads and pure radial loads are applied to the front end are plotted in Figs. 9(a) and (b). For example, when an axial load of 4 kN is applied to the front end, the axial deflection on the authors’ bearing is approximately 50% less than with the conventional bearing arrangement. When a radial load of 4kN is applied to the front end, the radial deflection on the authors’ bearing is approximately 80% less than the conventional bearing arrangement even though the front side bearing span with the authors’ tapered roller bearing is approximately 30% smaller than the conventional bearing arrangement. More specifically, it has been confirmed that the authors’ bearing has high rigidity against both axial and radial loads. Bearing deflection m 16 14 12 10 8 6 4 2 0 0 Conventional bearing arrangement Authors’ tapered roller bearing 1 2 3 4 5 6 Axial load kN Calculated axial deflection As mentioned in the first section of this report, the high-speed rotation per<strong>for</strong>mance of the axial-load carrying angular contact ball bearing within the conventional bearing arrangement shown in Fig. 8(b) is insufficient, and this bearing arrangement is capable of only 1 million dmn with air-oil lubrication. In contrast, in terms of both high-speed per<strong>for</strong>mance and rigidity, a spindle supported by the authors’ tapered roller bearing excels over spindles supported by a conventional bearing arrangement that consists of a double row cylindrical roller bearing and an axial-load carrying angular contact ball bearing. 4. Conclusion By using their unique tapered roller bearing that boasts greater rigidity <strong>for</strong> machine tool main spindles, the authors have invented a novel bearing construction and a novel air-oil lubrication mechanism to address the issue of unsatisfactory high-speed per<strong>for</strong>mance, which is a drawback of conventional tapered roller bearings. As a result of testing the authors’ tapered roller bearing with an inner bore diameter of 100 mm, this bearing achieved unprecedentedly high dmn of 1.25 million with air-oil lubrication. For bearings that support machine tool main spindles, higher running speed and greater rigidity are challenges to be addressed in achieving better surface finish quality <strong>for</strong> workpieces and improved machining efficiency. <strong>NTN</strong> will remain committed to addressing these technical challenges by pursuing further advances in its bearing technology. Bearing deflection m 5 Conventional bearing arrangement 4.5 Authors’ tapered roller bearing 4 3.5 3 2.5 2 1.5 1 0.5 0 0 1 2 3 4 5 6 Radial load kN Calculated radial deflection References 1) T. Miki: Per<strong>for</strong>mance and Application of Ultra-High Speed HA-Type Tapered Roller Bearings, Mechanical Design 26, 10 (1982) pp. 109-114. (In Japanese) 2) N. Soda: Bearings, Iwanami Shoten (1964). (In Japanese) 3) H. Fujiwara, K. Fujii: Rolling bearing torque in oil bath lubrication, Japan Society <strong>for</strong> Precision Engineering Spring Conference Academic Lecture Proceedings (2002), p. 219. (In Japanese) 4) Zhou, R. S. and Hoeprich, M. R.: Torque of Tapered Roller Bearings, ASME J. of Tribology, 113, 3 (1991) 590-597. 5) Gadallah, N. and Dalmaz, G.: Hydrodynamic Lubrication of the Rib-Roller End Contact of a Tapered Roller Bearing, ASME J. of Tribology, 106, 2 (1984) 265-274. Fig. 9 Comparison of spindle end deflections between developed bearing and conventional bearing arrangements -22-
High-Speed Tapered Roller Bearing <strong>for</strong> Machine Tool Main Spindles Photos of authors Masatsugu MORI Elemental Technological R&D Center Takuji KOBAYASHI Elemental Technological R&D Center -23-
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