GQZ Technology Knowledge: Control Method of Preload for Rolling Bearing Installation

Empirical test method,method of measuring rotating moment,preload method, measurement and control method of bearing deformation, use a constant torque wrench and sensor method.




Abstract: The preload of bearing can eliminate the axial clearance, reduce the reverse error and improve the rotation accuracy of shafting. Axial pre tightening can be achieved by adjusting the size of bushing or gasket, or by means of spiral spring, constant torque wrench, etc. In the process of preloading, the methods of experience detection, rotation moment measurement and sensor detection can be used to control the preload of the bearing.


Keywords: preload; friction moment; clearance dimension; torque wrench


After the installation of the rolling bearing, the rolling element and the ring raceway are properly pre compacted, which is called the pre tightening of the rolling bearing. The purpose of bearing preloading is to improve the rotation accuracy and support stiffness during operation, reduce vibration and noise, and reduce the relative sliding of the bearing rolling element relative to the inner and outer raceways of the bearing caused by inertia torque and other factors. The preloading method is usually used in angular contact bearings and shafting with high requirements for rotation accuracy and stiffness.


The preload is to use the external force applied during the assembly process to give the bearing an appropriate preload. If the preload is too small, there will be clearance when the bearing works, which will reduce the support stiffness and rotation accuracy, and cause vibration and noise. Excessive preload will increase the friction between the rolling element and the inner and outer race raceways, and the temperature will rise too fast during operation, reducing the transmission efficiency and bearing life. Only by applying appropriate preload can axial clearance be eliminated, reverse error be reduced, shafting rotation accuracy be improved, and vibration and noise be reduced. Give the bearing proper preload. Even if the relative position of the bearing changes slightly after a certain period of operation, the preload can still keep the positions of the inner and outer rings of the bearing stable. Therefore, the control of preload during installation is very important.


The commonly used axial preloading method can obtain the appropriate preload by adjusting the size of the bushing or gasket. The appropriate preload can also be obtained by controlling the starting friction torque. It is also possible to use a pair of tandem bearings with a pre adjusted fixed preload. After the axial preload is applied to the bearing, its relative position will remain unchanged during use. The bearing can also be preloaded properly with spiral spring, constant torque wrench, etc. Determination method of pre tightening force during assembly:


1) Empirical test method

The empirical test method is to judge the bearing preload by virtue of the technical workers' ability to feel the torque in practice. In the process of shafting assembly, preload the bearing, rotate the main shaft manually, or put the shafting into the low-speed transmission test system. The flexibility of spindle rotation can be sensed through the resistance moment of both hands. The resistance moment of both hands is the pre tightening moment of the bearing on the shaft. Although this method is rough, it is simple to use. It has been adopted by a large number of experienced assembly workers and can be used as a primary test method for product assembly accuracy. However, this method has low efficiency and high labor intensity, so it is not suitable for occasions with high accuracy requirements, and the maximum load on the shaft cannot be determined. This method is only suitable for experienced operators.


2) Method of measuring rotating moment

Use a spring scale or simple dynamometer. During assembly, fix the bearing and the rotating shaft, and ensure that the shaft can rotate, and then install the spring scale or simple Dynamometer on the shaft. Use the spring scale to apply tension along the tangent direction of the shaft, and the inner ring and the shaft rotate together. When the reading is in a stable state, it is the final measurement result. The measured force is multiplied by the distance from the tangent to the axis, which is the preload torque value of the bearing on the main shaft.


The matched angular contact ball bearings have friction torque requirements. Under certain conditions such as bearing form, internal parameters and lubrication mode, the friction torque of the bearing has a certain corresponding relationship with the axial load, so the preload can be determined by referring to the friction torque of the bearing. Therefore, by calculating the friction torque of the paired bearings bearing the preload, the calculated results are compared with the measured value of the actual friction torque to judge whether the preload inside the bearing meets the requirements.


3) Preload method

Before the installation of the bearing, a test system similar to the actual installation is used to pre install the bearing, install the bearing in the mechanism, apply the axial preload f required after conversion, and measure the actual distance D of the bearing. The measured value is the actual size required in the assembly after the preload is applied to the bearing, which includes the actual distance of the bearing and the clearance adjustment size after the preload is applied to the bearing. The spacer length is processed according to d.


In the actual installation process, the fit between the bearing inner hole and the shaft shall be strictly controlled, and the fit of the bearing inner ring at the journal shall not be loose, but also can move flexibly along the axial direction. When the inner and outer rings are required to be assembled, it is most appropriate to just push the thumb of both hands into the shaft journal and bearing seat hole. Then, the actual assembly dimension D can be ensured by adjusting the sleeve dimension and the outer end bearing cover dimension. If necessary, a fixed size adjusting shim can be added in the dimension adjustment process to ensure that the bearing preload value is close to the predicted value.


4) Measurement and control method of bearing deformation

Measure the relationship between the bearing friction torque and axial load in advance, place the bearing on the circular seat, and apply a given load on the inner ring of the bearing by gravity or spring pressure through formula conversion. After the bearing bears the force, there are axial dimension differences  K1 and  K2 between the inner and outer rings, and use a lever dial indicator for numerical measurement. When assembling the bearing, the preload of each assembled transmission shaft bearing shall be checked with a special dial indicator. If the preload applied is insufficient, a washer can be added for adjustment to fix the clearance size of the bearing, so as to ensure that the preload is within a fixed range.


5) Use a constant torque wrench

In order to eliminate the clearance between the inner and outer rings of the bearing, the bearing, which is axially fixed by the nut, can compress the inner ring of the bearing axially by twisting the nut, so as to achieve the goal of bearing pre tightening. This method is a general method with simple structure and strong applicability. In this way, the preload of the preloaded bearing is easy to control, and the defect is that there is no quantitative data. However, the preload can be adjusted by measuring the final assembly axial dimension and adding appropriate gaskets. In order to improve the production efficiency and assembly accuracy, the assembly is usually completed with the help of a constant torque wrench in production. The main feature of the constant torque wrench is that the torque can be set and adjusted. The constant torque wrench can be used for initial tightening and final tightening. Its use is to adjust the torque first, and then tighten the bolts. During the assembly of the bearing, pre assembly can be carried out to obtain the tightening torque required by the pre tightening force, and then assembly can be carried out.


6) Sensor method

In the assembly process with high requirements, we can use sensors to realize measurement and control. With the rapid development of modern sensor technology, measurement becomes more and more simple. Torque sensor can be selected in the assembly process of bearing. The torque sensor pastes the special strain gauge for measuring torsion on the measured elastic shaft with strain glue and forms a strain bridge. The electric signal of the elastic shaft under torsion can be measured by supplying current to the strain bridge. After amplifying the strain signal, it is converted into a frequency signal proportional to the torsion. The obtained signal can be processed by relevant instruments or computers to display the torque value. Using the previous installation method for reference, fix the shaft rotating bearing seat for measurement. Using the special mechanical fixture with torque sensor to clamp, the bearing pedestal rotates with the measuring machine under the drive of the driving equipment, and the reaction torque value of the fixture, that is, the bearing pre tightening torque value, can be measured. Common drive motors can act as drive equipment to provide power. The control method of bearing installation preload discussed in this paper has practical significance for bearing installation. The adjusted spindle can be inspected through the test run method until it meets the requirements.


More about GQZ Cylindrical Roller Bearing

GQZ precious-quality cylindrical roller bearing with reasonable price for customers all over the world and first-class service and unrivaled products.


GQZ Cylindrical roller bearings are available in a wide range of designs, series, variants and sizes. The main design differences are the number of roller rows and the inner/outer ring flanges as well as cage designs and materials.


The bearings can meet the challenges of applications faced with heavy radial loads and high speeds. Accommodating axial displacement (except for bearings with flanges on both the inner and outer rings), they offer high stiffness, low friction and long service life.


Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life. Split bearings are intended primarily for bearing arrangements which are difficult to access, such as crank shafts, where they simplify maintenance and replacements.