Detailed explanation of bearing clearance

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Clearance adjustment is a key technique in bearing installation, as it affects the operating condition of the bearings and thus of the entire equipment. The method of adjusting clearance demonstrates the true expertise of bearing manufacturers in every millimeter. This article provides a detailed introduction to the definition, types, influencing factors, and adjustment methods of bearing clearance. Let’s learn about it now. What is bearing clearance? Simply put, bearing clearance refers to the gap (or interference) inside a single bearing, or within a system composed of several bearings. Clearance can be divided into axial clearance and radial clearance, depending on the type of bearing and the measurement method. https://mmbiz.qpic.cn/mmbiz_png/vVRn3EfibM2HOKyHvfNrXwzxhibD6*yKib2j5PXe6MvXMVLkRx76ttW54Awe0aE9FJYY6xMKKhFr7TeQvYFjTUxw/640?wx_fmt=png Why is it necessary to adjust the bearing clearance? For example, using too much or too little water when cooking rice can affect its texture. Similarly, if the bearing clearance is too large or too small, the service life of the bearing as well as the stability of the entire equipment’s operation will be reduced. https://mmbiz.qpic.cn/mmbiz_gif/vVRn3EfibM2EFnVrlp71OXC1bcicIyWLzA8ZiajSpGvsVDIZ2mclI4tFHLnMa5UOWicl9XwEx1TLSszMfMf89ial6ibg/640?wx_fmt=gif Types of bearings suitable for different adjustment methods. The method of adjusting the clearance depends on the type of bearing; generally, bearings can be categorized into those with non-adjustable clearance and those with adjustable clearance. Non-adjustable clearance bearings are those in which the bearing clearance is determined after the bearing leaves the factory. The deep groove ball bearings, self-aligning bearings, and cylindrical roller bearings that we’re familiar with all fall into this category. Bears with adjustable clearance are those in which the relative axial position of the bearing races can be changed to achieve the desired clearance; cone bearings, angular contact ball bearings, and some thrust bearings fall into this category. ▲Tapered roller bearings ▲ Angular contact bearings. Classification of bearing clearance adjustment: For bearings with fixed clearance, the industry provides standard values (CN, C3, C4, etc.), and it is also possible to specify a particular clearance range. Once the dimensions of the shaft and bearing housing are known, the fit between the inner and outer rings is determined, and the clearance after installation cannot be changed. Since the amount of fit during the design phase is a range, the final clearance also falls within a range; therefore, it is not suitable for applications requiring high clearance precision. Adjustable bearings effectively solve this problem; by changing the relative axial position of the raceways, we can obtain a definite clearance value. As shown in the figure below, when moving the position of the inner ring, we can generally obtain two types of play: positive and negative. https://mmbiz.qpic.cn/mmbiz_gif/vVRn3EfibM2EFnVrlp71OXC1bcicIyWLzA8RXb8jY4U9RtL5h1eQrVj7GcdKF1WjTZMY9yd5UShO3rw98dT7ic3Kg/640?wx_fmt=gif Factors affecting bearing clearance. The selection of the optimal operating clearance is determined by the application conditions (load, speed, design parameters) and the desired operating characteristics (maximum lifespan, optimal stiffness, minimal heat generation, ease of maintenance, etc.). However, in most applications, we cannot directly adjust the operating clearance. This necessitates calculating the appropriate post-installation clearance value based on an analysis of the application and our experience. Methods for adjusting the clearance of tapered roller bearings: The post-installation clearance of non-adjustable bearings is primarily influenced by the fit, so the following focuses on the methods for adjusting the clearance of adjustable bearings, taking tapered roller bearings that can operate over a wide range of speeds and withstand both axial and radial forces as examples. 1. The push-pull method is generally used for positive clearance, where the axial gap between the bearing race and the rolling elements can be measured. A force is applied to the shaft or bearing housing in one direction; once it has been pushed to the extreme, the dial indicator is set to zero as a reference. Then, a force is applied in the opposite direction, and the amount of movement of the pointer on the dial indicator at that point represents the clearance value. During measurement, the roller should be rotated slowly back and forth to ensure that it is properly positioned on the large ridge of the inner ring. https://mmbiz.qpic.cn/mmbiz_jpg/vVRn3EfibM2EFnVrlp71OXC1bcicIyWLzAiaZka3cHO0o0f9haF0JNBaFsz06jUOk2tjak32KIgnVR9RAKzibAQNKw/640?wx_fmt=jpeg2、The Acro-SetTM method is based on Hooke’s law, according to which the degree of elastic deformation of an object is proportional to the external force applied to it. Under a certain installation force, the gap of the measuring gasket or spacer ring is measured to obtain the correct clearance. Read the required correct gasket or spacer size directly from a chart created during preliminary testing. This method is suitable for normal clearance and preloading; operators need to be trained to create the charts. 3. Torque-SetTM method: The principle of Torque-Set is that, under preloading, the rotational torque of the bearing increases as a function of the bearing’s preloading force. The experimental results show that for a set of new bearings of the same model, under a given preload, the variation in the rotational torque of the bearings is very small. Therefore, the preload can be estimated using the torque. The principle of this method is to establish a conversion relationship between the rotational torque of the bearing and its preload, which needs to be determined through testing. During actual installation, the thickness of the gasket can then be determined by measuring the torque. 4. Projecta-SetTM method: Projecta-Set involves projecting or converting the thickness of gaskets or spacers that cannot be measured directly to a location where it can be easily measured. A specially designed gauge sleeve and spacer ring can achieve this effect. When both the inner and outer rings of the bearing are in a tight fit, removing and adjusting the bearing becomes difficult and time-consuming; this is where Projecta-Set proves its advantages. This method requires separate gauges for different series of bearings, resulting in relatively high costs. But when installed in large quantities, the average cost per installation becomes very reasonable. It has proven to be an effective method, especially in the field of automation. https://mmbiz.qpic.cn/mmbiz_jpg/vVRn3EfibM2EFnVrlp71OXC1bcicIyWLzA2WrGVZkvYlMGYmAjvX5BCnIwtXbyOPEGPYpjzPAib7mcWuz0R7ia8qbw/640?wx_fmt=jpeg5、The Set-RightTM method employs probability-based approaches and controls the dimensional tolerances of related components to ensure that 99.73% of the bearing clearances in all assemblies fall within acceptable ranges. This is a mathematical prediction derived from a combination of random variables, namely the tolerances of the bearings and those of the mounting components such as shafts and bearing housings. This method requires no installation or adjustment; the application components can be simply assembled and clamped, making it very convenient for large-scale installation. However, a clearance range is ultimately obtained (around 0.25 mm), and it must be decided at the design stage whether Set-Right can be used in certain applications. For many years, the Set-Right method has been successfully used in both the industrial and automotive sectors. https://mmbiz.qpic.cn/mmbiz_jpg/vVRn3EfibM2EFnVrlp71OXC1bcicIyWLzAQcVcSsPBNv7Pay2y9RtGJ6RgxCDf1iaD3yjQW2rGpuibwWQkLvJzncYg/640?wx_fmt=jpeg