Analysis of Bearings in Mine Truck Application

In recent years, under the background of tight international energy supply, China has increased investment in new energy fields represented by wind energy, which has gradually increased the output of new energy. However, for a long time, China’s coal-based energy sources The structure will continue. Compared with underground coal mining, open-pit coal mining has high productivity, low accident rate, and easy equipment maintenance and other objective advantages. Whether at home or internationally, vigorous development of open pit mining is a major trend. Mine trucks, one of the important equipment necessary for open pit mining, will also have a bright future with the development of open pit mines.

The tapered roller bearings produced by TIMKEN Bearings have decades of application history in mining trucks and have accumulated considerable application experience. This article will briefly analyze the problems that should be paid attention to when using tapered roller bearings for mining trucks. It is hoped that it will help the majority of mine truck designers and users to better select and use bearings and improve the reliability of mining trucks.

In addition to the factors of system design matching and installation adjustment, there are three main factors that determine the performance of tapered roller bearings: 1) the material of the bearing 2) the roughness of the bearing raceway 3) the surface modification of the bearing raceway . Next, a detailed analysis of the factors that should be considered in these three aspects of bearing selection during mine truck conditions.

First, the material of the bearing

Two considerations are taken into account when considering the material of the bearing: the purity of the steel and the heat treatment process of the steel.

The time it takes for the bearing to run is its fatigue life. The occurrence of spalling is mainly due to the presence of non-metallic inclusions inside the bearing steel. When the bearing is working, non-metallic inclusions will cause stress concentration inside the steel, resulting in weak points. As the bearing runs day after day, these weak points gradually develop into fine cracks, which eventually cause the surface of the raceway to peel off. Therefore, the purity of the steel is critical to the bearing. The smaller the particle size of the inclusions inside the steel, the smaller the number of particles, the smaller the probability of crack occurrence and the higher the fatigue life of the bearing.

With the development of modern smelting technology, the bearing manufacturers of world-class brands have reached a very high level in the purity of bearing steel. In addition to bearing materials that meet ISO and ABMA standards, they also use materials that are cleaner than pure steel to improve the reliability of bearings under high loads. With the hub bearing application in a mining truck, the bearing carries a very high force. Taking the load of 200 tons as an example, the whole vehicle is about 350 tons after full load, and the force of the one-side rear wheel hub bearing reaches about 120 tons. Therefore, if a standard material bearing is selected, its size will be very large. In order to minimize the size of the hub and make the design more compact, bearings with high purity precision materials are often used in this position. Even so, the inner diameter of the bearing is about 500mm.

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The importance of bearing grease stability

Proper use of bearing grease requires knowledge of the movement of the grease in the bearing. Guarantee the stability of the grease. The movement of the grease filled in the rolling bearing can be roughly divided into two stages as the SKF bearing rotates.

By the way, by the way, when lubricating the bearing, pay attention to the amount of grease. For details, please refer to the article "Introduction of the amount of grease used in lubrication of SKF bearings".

In general, the amount of grease in the SKF bearing always exceeds the actual amount of lubrication directly involved in the lubrication, on the frame and in the cavity of the bearing cover, and forms a contour on the periphery of the rolling element. In this process, the bearing temperature rises rapidly due to the resistance of excess grease. Although most of the excess grease is squeezed out at the beginning of the run, the grease that is squeezed into the raceway attachment may still be carried by the rolling element into the raceway. In the initial stage of the bearing crucible, most of the grease is squeezed out of the raceway very quickly (less than one minute), and the accumulated grease is discharged a small amount while circulating along with the bearing rotating body. At this time, the bearing temperature continues to rise until the excess bearing grease is completely discharged, which can be called the walking phase of the grease. According to the grease quality and filling amount in the bearing structure, this time may last for more than ten. Minutes, even hours.

After the remaining bearing grease is completely discharged, the remaining small amount of grease forms a thin layer of grease film on the mutual contact surface of the rolling element, the raceway and the cage, thereby entering the normal bearing of the bearing. stage. At this time, the temperature gradually drops and reaches equilibrium. In other words, long-term lubrication is mainly borne by this layer of grease film. In addition, during the long-term operation of the bearing, the contour of the rolling element and the raceway and the grease on the cage are shrunk to separate a part of the base oil, and after flowing into the raceway, the lubrication is also supplemented. .

Different bearing greases are not the same in the contours of the bearings. It is necessary to form a contour that is relatively straightforward. The running time is short. In the long-term operation, the bearing temperature is low and stable. This is an ideal one. Grease is especially important for grease channeling.

Some so-called eddy-flow greases are not easy to form contours, and even if they are contoured, they are easy to collapse. At this time, the excess grease repeatedly returned to the raceway is in a state of being strongly stirred for a long time, and the bearing torque is large and the temperature is high. Unbalanced, noise may also be generated, and grease is also prone to deterioration and loss.

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Reasons for affecting the circularity of the inner ring of a rolling bearing

1. The circularity of the inner ring of the rolling bearing is an important quality index, which directly affects the working accuracy, stability and service life of the bearing. Grinding is usually a semi-finishing or finishing process of the inner ring channel, which plays a decisive role in the roundness of the inner ring channel. The roundness of the inner ring channel grinding depends on the accuracy and dynamics of the grinding process system. In addition to the characteristics, it is also closely related to the process parameters of the grinding. The former has been valued by many scholars and has carried out a lot of research, which has greatly improved the roundness of the inner ring of the grinding inner ring. With the improvement of the precision of the grinding process system and the improvement of the dynamic characteristics, the grinding process parameters become the main factors affecting the roundness. Therefore, the influence of the grinding process parameters on the roundness is studied, and the process parameters are ensured to ensure the bearing channel. The grinding roundness and the optimization of the process parameters for grinding the bearing channel are of great significance.

2. The inner ring of the bearing is usually cut into the grinding mode by variable feed rate. The grinding cycle can be divided into four stages: rapid approach, coarse feed, fine feed and no feed grinding. The main factors affecting the roundness of the grinding bearing channel can be summarized as: (1) the accuracy of the process system during the grinding process, which depends on the accuracy of the grinding machine and the positioning principle of the fixture, structural parameters and accuracy: (2) the process system Dynamic characteristics, especially the balance of the grinding wheel: During the dressing and grinding process, the grinding wheel is unbalanced, which will cause forced vibration. The relative position of the dresser and the grinding wheel and the relative position of the workpiece and the grinding wheel during grinding are different due to the dressing of the grinding wheel. And the difference in the stiffness of the process system in these two different cases makes the surface of the workpiece caused by vibration not round: the grinding process parameters will affect the contact stiffness between the grinding wheel and the workpiece, the wear process of the grinding wheel and the damping characteristics of the vibration of the process system. Therefore, the vibration characteristics of the grinding process are affected, which is ultimately reflected in the geometry (ie roundness) and other surface quality of the grinding workpiece: (3) The original error of the workpiece caused by the elastic deformation of the process system: analysis of the grinding cycle workpiece The variation law of geometric shape error shows that the geometric error of the workpiece after grinding is mainly determined by the stiffness of the process system and grinding. Cutting process parameters, grinding wheel wear speed and original workpiece error? Considering the above influencing factors, when the stiffness and dynamic characteristics of the process system are constant (especially the grinding wheel must be well balanced), the roundness error of the grinding workpiece depends mainly on the grinding process parameters, so the roundness test data can be passed. The stepwise regression modeling, selecting important parameters from multiple process parameters, and gradually introducing regression equations, to establish an optimal regression equation for the relationship between grinding roundness and process parameters.

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Bearing speed limit index

In the general bearing model table, there will be a speed limit indicator. What does it mean?

When the bearing exceeds a certain operating speed, it will begin to generate uncontrolled internal heat.

The speed limit varies with bearing type, size, lubrication system, bearing internal design, and operating load. In addition, the speed limit will vary depending on the type of composite seal used (depending on the speed of the seal contact zone).

The term "speed limit" generally refers to the estimated speed, the number of revolutions per minute at which the bearing will remain operational.

The limit speeds for grease lubrication and oil lubrication are given in the general dimensions table. This value is based on bearings that are mounted on a horizontal shaft, suitable for lubrication operation, and light loads.

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Some knowledge of bearing heating failure

Bearing consultation to form a knowledge of bearing heating failure

The bearing is a fixed part of the machine and is the main body of the machine. Its function is basically to maintain the center position of the shaft and the mechanism for controlling the movement. Bearings play a decisive role in any machine. If there are no imported bearings, the machine will not work.

Many users have reported that when using bearings, the failure of bearing heating is the most common, and this failure will also affect the life and performance of the bearing. So how is this failure formed? Below, is the knowledge that is summarized for everyone.

1. The oil level is too low and the lubricant is lost from the oil seal;

2. The grease in the bearing housing is completely filled or the oil level is too high. This can lead to excessive lubrication, high temperature or oil leakage;

3. The contact type (friction) oil seal is too dry or the spring is too tight;

4. The inner hole of the bearing box is not round; the bearing box is twisted and deformed; the bearing surface is not flat; the inner diameter of the box hole is too small;

5. The contact type (friction) oil seal is too dry or the spring is too tight.

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Type of needle bearing

Type of needle bearing:

In addition to the catalogue, it can be used for general engineering bearings, such as: open drawn cup needle roller bearings (1), closed cup needle roller bearings (2), needle roller bearings with inner ring (3) and Inner ring needle roller bearings (4) SKF can also supply various types of needle roller bearings, 1, needle roller cage assembly 2, non-ribbed needle roller bearings 3, self-aligning needle roller bearings 4, combined needle roller / ball Bearing 5, combined needle roller / thrust ball bearing 6, combined needle roller / cylindrical roller thrust bearing

Drawn cup needle roller bearings

The drawn cup needle roller bearings are needle bearings with a thin stamped outer ring. Its main features are low cross-section height and high load carrying capacity. Mainly used for bearing arrangements that are compact, inexpensive, and the bore of the bearing housing cannot be used as the raceway for the needle roller cage assembly. The bearing and bearing housing must be installed in an interference fit. If the axial positioning function such as the box shoulder and the stop ring can be omitted, the inner hole of the bearing housing can be made extremely simple and economical.

The drawn cup needle roller bearings mounted on the shaft end are open on both sides (1) and closed on one side (2). The base end face of the closed stamped outer ring can withstand small axial guiding forces.

Drawn cup needle roller bearings generally do not have an inner ring. In the case where the journal cannot be hardened and ground, the inner ring listed in the table can be used.

The hardened steel outer ring of the drawn cup needle roller bearing is inseparable from the needle roller cage assembly. The free space to store the lubricant can extend the relubrication interval. Bearings are generally designed in a single row. Except for the wider series of bearings 1522, 1622, 2030, 2538 and 3038, they are equipped with two needle retainer assemblies. The outer ring of the bearing has a lubrication hole. All single row drawn cup needle roller bearings with a shaft diameter greater than or equal to 7 mm can be equipped with an outer ring with a lubrication hole (code suffix AS1), depending on the user's needs.

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Problems that should be paid attention to when using variable speed INA self-aligning ball bearings

1. Understand the shape and connection dimensions of the variable speed drive INA self-aligning ball bearing.
2. Variable speed drive INA self-aligning ball bearings can be placed horizontally or vertically or tilted. Can be rotated forward and backward. Positive and negative input and output power.
3, variable speed drive INA self-aligning ball bearings regardless of the installation method, and its couplings have size requirements.
Recommended:
The inner ring hole d and the shaft are matched by H7/h6;
The pin hole do of the middle ring and the transmission are matched by H7/r6;
The outer ring D and the housing are matched by H8/h7;
The gear is matched with the hole on the output shaft by a clearance fit, and the gap is 0.2~0.5mm.
4. Axial positioning of the variable speed drive INA self-aligning ball bearing: After any three turns of the ring are axially positioned, the other two axes do not need to be axially positioned.
5. Positioning in the direction of rotation; both the outer ring and the inner ring are flat key positions. The middle circle is positioned by the drive.
6. Variable speed drive INA self-aligning ball bearings can withstand small external forces in the radial direction, but should not withstand large working loads.
7. Transmission ratio is the transmission ratio according to the first installation method. If other installation methods are used, the gear ratio should be calculated.
8. At the rated speed (1500 rpm), select the variable speed drive INA self-aligning ball bearing model according to the transmission ratio and the required power (Kw).
9. When based on the working torque, the model number should be selected accordingly.
10. The selection of the reducer model should be consistent with the model of the variable speed drive INA self-aligning ball bearing.

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