12 Spindle Bearings.pptVIP

机械工程专业英语English In Mechanical Engineering Prepared by Xiaoping Pang From College of Mechanical Engineering Chongqing University 12 Spindle Bearings A machine tool(机床) spindle must provide rotational speed, transfer torque and power to the cutting tool, and have reasonable load carrying capacity and life. The bearing system, one of the most critical components of any high-speed spindle design, must be able to meet these demands or the spindle won’t perform. High-speed spindle bearing available today include roller, taper roller, and angular contact ball bearings. Selection criteria depend on the spindle specifications and the speed needed for metalcutting. Angular contact bearings are the type most commonly used in very high-speed spindle design. These bearings provide precision, load carrying capacity, and the speed needed for metalcutting. Angular contact ball bearings have a number of precision balls fitted into a precision steel race, and provide both axial and radial load carrying capacity when properly preloaded. 12 Spindle Bearings In some cases, tapered roller bearings are used because they offer higher load carrying capacity and greater stiffness than ball bearings. However, tapered roller bearings do not allow the high speeds required by many spindles. Angular contact ball bearings are available with a choice of preloading magnitude, typically designated as light, medium, and heavy. Light preloaded bearings allow maximum speed and less stiffness. These bearings are often used for very high-speed applications, where cutting loads are light. Heavy preloading allows less speed, but higher stiffness. To provide the required load carrying capacity for a metalcutting machine tool spindle, several angular contact ball bearings are used together. In this way, the bearings share the loads, and increase overall spindle stiffness. 12 Spindle Bearings Hybrid ceramic bearings are a recent development in bearing technology that uses ceramic (silicon nitride) material t