What effect does the internal clearance of deep groove ball bearings have on bearing performance

Deep groove ball bearings are the most widely used rolling bearings in mechanical equipment. Their performance directly impacts the reliability, efficiency, and lifespan of the equipment. Among the many factors influencing bearing performance, internal clearance is undoubtedly one of the key parameters determining bearing performance. Internal clearance, also known as radial clearance, refers to the maximum radial and axial movement of the bearing's inner and outer rings when no load is applied. This seemingly simple clearance actually has a profound impact on a range of performance indicators, including bearing temperature rise, noise, vibration, lifespan, and stiffness.

The Impact of Clearance on Bearing Temperature Rise
During bearing operation, rolling and sliding friction between the rolling elements and raceways generates heat, causing a temperature increase. Internal clearance has a crucial impact on bearing temperature rise.
If clearance is too small, the bearing's rolling elements and raceways will experience preload or an overtight fit. This significantly increases the frictional torque of the rolling elements, generating significant heat. Excessive temperature rise not only accelerates grease aging and failure but also causes thermal expansion of the bearing material. Unsynchronized thermal expansion of the inner and outer rings can further reduce or even eliminate clearance, creating a vicious cycle that can ultimately lead to bearing seizure or premature failure. When clearance is too large, the movement of the rolling elements in the bearing raceways becomes unstable. When the bearing is under load, the contact area between the rolling elements and the raceways decreases, leading to contact stress concentration. At the same time, rolling element sliding and friction increase. While not as severe as friction caused by too little clearance, it can still cause temperature rise under high-speed and high-load conditions. Furthermore, excessive clearance can cause shock during radial runout, further increasing temperature.

The ideal clearance is to maintain a slight positive clearance after the bearing is installed and reaches thermal equilibrium. This ensures smooth operation of the rolling elements while effectively reducing friction, thereby keeping temperature rise within acceptable limits.

The Impact of Clearance on Bearing Noise and Vibration
Bearing noise and vibration are important indicators of smooth operation. Internal clearance directly affects the dynamic performance of a bearing.

Excessive clearance can cause rolling elements to produce a "banging" sound during operation. When a bearing is subjected to fluctuating loads, the rolling elements bounce back and forth between the inner and outer rings. This unstable motion can cause noticeable vibration and noise. Especially in high-speed applications such as motors and spindles, excessive clearance can cause severe vibration, impacting the equipment's machining accuracy and operational stability.

Although excessively small clearance reduces rolling element runout, it also generates high-frequency vibration and high-pitched noise due to increased frictional torque. This noise is often directly related to the bearing's preload: the higher the preload, the higher the noise. For example, in applications requiring high stiffness and precision, such as precision machine tool spindles, bearings with low or even negative clearance are often chosen, but the preload must be precisely controlled to balance stiffness and noise.

Appropriate clearance ensures smooth and continuous rolling of the rolling elements in the raceways, reducing impact and slippage, thereby minimizing vibration and noise. This is crucial for equipment requiring extremely smooth operation, such as household appliances and medical devices.

The Impact of Clearance on Bearing Life and Stiffness

Bearing life is generally determined by fatigue life, and clearance is one of the key factors influencing fatigue life.

Excessive clearance significantly increases the contact stress between the rolling elements and raceways. According to Hertz contact theory, excessive contact stress can cause premature material fatigue, shortening the bearing's fatigue life. Furthermore, the temperature rise caused by excessive clearance can accelerate grease failure, further shortening bearing life.
Excessive clearance can also shorten bearing life. When bearing loads are applied, excessive clearance reduces the number of rolling elements, concentrating the load on a few. This causes a sharp increase in contact stress on these rolling elements, leading to localized fatigue and reducing the overall bearing life.
Appropriate clearance can evenly distribute the load across more rolling elements, effectively reducing contact stress and maximizing bearing fatigue life.
Bearing stiffness is an important indicator of its resistance to deformation. Clearance has a direct impact on stiffness. The smaller the clearance, the less deformation the bearing experiences under load, resulting in higher stiffness. In applications requiring high stiffness, such as machine tool spindles and automotive wheel hubs, bearings with low clearance or even negative clearance (preload) are often selected to improve the overall stiffness of the system.

Selecting Clearance Grades
To accommodate diverse application requirements, deep groove ball bearings typically offer multiple clearance grades, such as C2, CN (or C0), C3, C4, and C5. CN represents standard clearance, C3, C4, and C5 represent high clearance, and C2 represents low clearance.

Standard clearance (CN) is suitable for most general industrial applications, such as electric motors and pumps.

High clearance (C3 and C4) is suitable for applications with large mounting interference and drastic temperature fluctuations, such as rolling mills and high-temperature fans, to compensate for the clearance reduction caused by thermal expansion.

Low clearance (C2) is suitable for applications requiring high operating precision and low noise, such as precision instruments and small motors.

Therefore, when selecting deep groove ball bearings, focusing solely on size and model is insufficient. A thorough understanding of the comprehensive impact of internal clearance on bearing performance and selecting the appropriate clearance grade based on specific operating conditions are key to ensuring long-term stable and reliable operation of your equipment. The correct selection maximizes bearing performance, extends its service life, and ultimately reduces maintenance costs.