**Bearing Ferrule Grinding and Superfinishing: New Skills and Developments (1)**
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Source: Bearing Network | Time: May 1, 2013
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Grinding and superfinishing are essential steps in the manufacturing of mechanical components, particularly in the bearing industry. These processes are crucial for achieving high precision, ensuring product quality, and enhancing performance. In the case of bearings, the grinding of the ferrule is a critical step that directly affects the accuracy of the entire bearing. Similarly, the superfinishing of the raceway significantly influences the bearing’s lifespan, as well as its noise and vibration characteristics.
In the 1960s, foreign bearing industries had already established a stable process for ferrule grinding and superfinishing. This involved double-face grinding, centerless cylindrical grinding, and subsequent superfinishing. While this process has remained largely unchanged over decades, it doesn’t mean that no advancements have been made. In the 1960s, the "double-end centerless grinding and superfinishing" process was introduced, along with specialized machines that achieved part machining accuracy of 3–5 μm, with processing times around 13–18 seconds for small to medium-sized parts.
By the 1970s, the use of high-speed grinding at 60 m/s became more common, and digital control systems based on integrated circuits began to be widely adopted. This improved machine stability and process consistency, allowing part accuracy to reach 1–3 μm, with processing times reduced to 10–12 seconds. In the 1980s, the focus shifted toward increasing productivity, improving convenience, and implementing numerical control and automated systems, while maintaining stable quality.
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In the production of bearings, grinding accounts for approximately 60% of the total labor and 60% of all metal-cutting machines. The cost of grinding also represents more than 15% of the total bearing cost. For high-precision bearings, the grinding process becomes even more significant. Despite being one of the most complex and costly operations, grinding remains a key challenge due to the numerous factors affecting machining accuracy and the difficulty of online monitoring.
One of the main goals in modern bearing manufacturing is to adopt new technologies and techniques that enable high-precision, high-efficiency, and low-cost grinding. High-speed grinding is one such technology that improves both product quality and production efficiency. Increasing the grinding speed from 35 m/s to 50–60 m/s can boost productivity by 30–60%, extend the life of the grinding wheel by 0.7–1 times, and reduce surface roughness by about 50%.
High-speed grinding is generally defined as a process where the grinding speed exceeds 45 m/s. Machines like the ZYS 811 automatic internal grinding machine developed in the 1980s were among the first to introduce high-speed grinding in China. These machines featured high-rigidity spindles and high-speed grinding wheels, enabling better performance and efficiency. Today, high-speed grinding is widely used internationally, with grinding speeds reaching up to 80–120 m/s. Companies like Mikrosa (Germany), KOYO (Japan), and TOYO (Japan) have implemented such technologies in their bearing manufacturing processes.
To achieve high-speed grinding, it's essential to enhance the power of the grinding wheel drive system and increase the rigidity of the machine tool. The high-speed spindle unit is the most critical component in these machines. Additionally, the grinding wheel must not only be strong but also capable of delivering excellent grinding performance. Cooling systems also play a vital role in ensuring the effectiveness of high-speed grinding.
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Another important development in bearing grinding is the use of Cubic Boron Nitride (CBN) grinding wheels. CBN is a super-hard abrasive known for its high hardness, thermal conductivity, and thermal stability, which allows it to withstand temperatures up to 1300–1500°C. CBN grinding wheels have a much higher grinding ratio compared to conventional corundum wheels—ranging from 4,000 to 10,000, versus just 50–80 for standard wheels. This means they last longer and require less frequent dressing or replacement.
The application of CBN grinding wheels in the bearing industry is still relatively new in China, but it holds great potential. Challenges include developing CBN wheel production techniques, finishing methods, and specialized grinding machines. However, globally, CBN grinding has been widely adopted, especially in Japan since 1982, and is considered a major breakthrough in manufacturing technology.
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