**Machine Tool Spindle and Bearing**
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*Created on 2018/5/16*
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In recent years, the function of the machine tool spindle has evolved towards higher speed, precision, and rigidity. Meeting these demands also requires a focus on environmental protection and addressing global warming concerns.
One unique approach is NSK’s bearing depiction based on conflict learning. Their four intermediate skills—analytical, assessment, slick, and data skills—are centered around conflicts. This is especially relevant when describing machine tool spindle bearings. NSK introduced long-life, high-performance bearing data using advanced techniques. Regarding the rolling body, they developed ceramic materials that perform exceptionally in high-speed and ultra-high-speed environments, enabling ultra-high-speed and ultra-precision rotation for metal tumblers, which received widespread user approval.
NSK also designed a resin cage with a common layout shape, allowing smooth grease running-in in a short time, stable temperature rise, low friction, and noise. These features make it ideal for use under grease-smooth conditions. Additionally, they used PPS and PEEK resin materials for fine cylindrical roller bearings, offering superior speed and heat resistance.
Mr. Chen Shizhen emphasized that radial runout, face runout, and inconsistent roll diameter can severely impact the accuracy of the spindle system and its machined parts. Therefore, the bearing accuracy on precision machine tools should be at least P5. For high-speed, high-precision machine tools like CNC machines, bearings must be P4 or higher.
The high-speed adaptability of spindle bearings is crucial. As machining speeds continue to increase, so does the need for high-speed spindles, including electric spindles. Poor high-speed adaptability leads to severe temperature rises in the spindle system.
Mr. Ye Jun explained that as the core component of the machine tool, the spindle bearing is the foundation of precision. Modern machine tools are moving toward higher precision, speed, and reliability, placing greater demands on spindle bearings. While traditional machinery operates at hundreds to thousands of RPM, modern high-speed machining tools require tens of thousands to hundreds of thousands of RPM. The dmN value (diameter × speed) is used to measure high-speed performance, with machine tool spindles typically targeting up to 4 million.
To meet these demands, bearings must be re-evaluated. For example, angular contact ball bearings require detailed analysis of data selection, layout design, guidance methods, lubrication techniques, and groove curvature coefficients.
Mr. Ye Jun also mentioned that spindle bearings for machine tools have special data requirements. Ferrule data is often made from high-quality refined steel, and some foreign countries use special steels, copper, plastic, and self-lubricating materials. Rolling bodies are typically made from bearing steel or ceramic materials.
Ceramic materials have revolutionized bearing technology by breaking through the limitations of traditional steel bearings, such as high speed, wear resistance, insulation, and heat resistance. Silicon nitride ceramics, for instance, are only one-third the weight of steel, reducing stress on the raceway at high speeds and increasing bearing speed. With a hardness of 1500 HV, double that of bearing steel, and heat resistance up to 1200°C, ceramic bearings offer significant advantages over traditional materials.
Ceramic bearings are increasingly used in high-speed applications. However, due to the difficulty in processing ceramic materials, most fine ceramic bearings are ceramic ball bearings with steel inner rings.
Mr. Yu Wei highlighted that as CNC machine tool spindles develop at high speed, there is a growing need for bearings with high rigidity, low temperature rise, and long life. Ceramic materials, particularly Si₃N₄ engineering ceramics, offer small density, high stiffness, low thermal expansion, wear resistance, heat resistance, and corrosion resistance, making them ideal for high-speed precision bearings.
Compared to steel balls, ceramic components are 40% lighter, reducing centrifugal force. This leads to lower friction and better performance at high speeds.
In addition to ceramic rolling elements, NSK has focused on long-life technologies, introducing high-performance spindle bearings such as SHX materials for ultra-high-speed environments, EP steel for high-load scenarios, and Z steel for long life in normal conditions.
Mr. Chen Shizhen pointed out that aligning spindle bearings is essential to achieve high guiding precision and speed. FAG’s treatment plan involves selecting new materials, optimizing product design, and ensuring and improving machining quality.
Through continuous theoretical analysis, experimentation, and anti-happiness measures, FAG’s TX series spindle bearings reduce temperature rise by 10% during high-speed operation and can increase speed by up to 10% under the same clearance conditions.
In electric spindles, large temperature gradients exist between bearings, causing uneven loads on axial and radial directions, affecting stiffness and bearing set lifespan. FAG offers optional bearing sets that significantly reduce these issues.
Mr. Ye Jun noted that Axis Research Technology provides comprehensive processing solutions for spindle bearings from P4 to P2. They developed high-speed plastic safety frames, ceramic rolling elements, high-definition bearing assembly techniques, and overall matching skills. Their precision machine tool spindle bearings have won national high-tech awards.
Regarding wear and heat problems, Mr. Yu Yu mentioned that NSK has developed high-strength, long-life steel and high-precision ceramic rolling elements that effectively handle wear and heat during operation. They also improved cage layout and materials to minimize grease degradation, enhance lubrication, and improve heat resistance.
To ensure smooth bearing operation and prevent dust intrusion, NSK continuously improved lubrication methods. They pioneered oil-gas lubrication, which is now widely adopted. In the environmental protection era, NSK introduced a grease replenishment system for high-speed spindles, intermittently adding trace amounts of grease. Using the best spacer design, used grease is drained into a storage tank within the bearing housing, marking the first successful implementation of high-speed grease lubrication worldwide.
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Machine Tool Spindle and Bearing
Source: Bearing Network | Time: 2013-03-08
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