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Analysis of Bearings in the Application of Mine Trucks
Source: China Bearing Network Time: 2018-03-31
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The tapered roller bearings produced by Timken have decades of application history in mining trucks, and they have accumulated appropriate and rich experience. This paper briefly analyzes the problems that should be paid attention to in the use of tapered roller bearings in mining trucks. Expect to be able to assist the vast mine truck descriptors and users to better select and use bearings; improve the reliability of mining trucks.
In addition to the elements of its own system depicting matching and device adjustment; the following three aspects of the function of the tapered roller bearing are as follows: 1) bearing data 2) bearing race roughness 3) bearing raceway appearance modification Next, a detailed analysis of the mining trucks under the conditions; bearing selection in these three aspects should not be considered elements.
One. Bearing information In the thinking of the bearing information, the first two points to consider: the purity of steel and the heat treatment process of steel.
The bearing is in normal working condition; when the outer surface of the raceway appears 6mm2 off (as shown in Figure 1); we say that the bearing is invalid; the moment of operation of this bearing is its fatigue life. The main reason for the seizure is because There are non-metallic inclusions inside the bearing steel. When the bearing is working, non-metallic inclusions will attract the internal stress of the steel; the shortcomings of the attack; follow the bearing day after day; these thin defects gradually develop into slender cracks; The appearance of the raceway is detached. Therefore, the purity of the steel is very important for the bearing; the volume of the inclusions in the steel is the more the volume. The Pa å å ä¼² ä¼² ä¼² 蛄 蛄 æ¯ æ¯ æ¯ æ¯ æ¯ è¯• 试 试 试 试 试 试 @ @ @ @ @ @ @ @ @
Figure 1 bearing surface shedding follows the development of modern exercise skills; bearing manufacturers of world-class brands have reached an appropriate level in terms of bearing steel purity. They have not only bearing the ISO and ABMA specifications, but also More reliable steel than the material; to improve the reliability of the bearing under high load. Take the wheel bearing in the mine truck for use; the bearing bearing force is very high. Take 200 tons of load as an example; after the vehicle is fully loaded About 350 tons; the force of the one-side rear wheel hub bearing reaches about 120 tons. Therefore, if the bearing is selected, the scale will be very large. In order to reduce the hub size as much as possible, the drawing is more compact; Bearings with high purity and precision data. Even so; the inner diameter of the bearing is about 500mm.
In addition to the purity of the bearing steel; the heat treatment process of the bearing also has a moderately large effect on the function of the bearing. Today, there are two main heat treatment processes for the bearing on the market: full hardening and external carburizing. The original data is high carbon steel; after full heat treatment; the internal and external hardness of the steel reaches 58-64HRC; the tensile stress of the steel appearance; when encountering a large impact load; simple attack crack; Or direct fragmentation. The original data for carburizing heat treatment is low carbon steel; the selected heat treatment process is external carburizing; such information is characterized by the appearance of 58-64HRC strong wear resistance; and the internal soft 30-35HRC; steel appearance The compressive stress; the shock load that can be buffered; the ability to reduce the impact crack.
Figure 2 Tapered roller bearings used in carburized steel outer hard and soft mine trucks are mainly used in bridge and wheel ends; these two local operating environments are very harsh; often accompanied by impact loads and heavy loads. Plus castings It is impossible to prevent the abrasive particles from attacking; and the external pollution caused by the failure of the oil seal; these have brought great detection to the bearing itself. Under the condition of abrasive particles and heavy load; the raceway appearance of the bearing cannot prevent the ground attack. Pit; if it is a fully-hardened bearing; under the influence of two layers of brittleness and external tensile stress; the development of this pit will be more agile; the bearing will fail early without reaching the fatigue life. Carburized bearings; because the material itself has resistance and external compressive stress; the pit is not easy to expand; so that the bearing can still reach a good fatigue life. Timken has experimented to simulate the full hardened bearing and carburized bearing in the rolling The bearing life ratio under the condition of damage to the outer surface of the road is compared; the results show that the outer carburizing bearing can reach a higher fatigue life than the fully hardened bearing. According to the above reasons; we are choosing When Hill truck bearings used; we should try to use carburizing bearing.
two. The appearance of the bearing raceway and the roller affects the function of the bearing in addition to the data elements just mentioned; there is also a large factor that is smooth. According to statistics; 70-80% of the bearings fail early because the bearing is not smooth Generally formed, we use oil or grease to smooth the bearing. The smooth system works in the bearing; it will attack the metal surface with a layer of oil film. If we use a high magnification magnifying glass to investigate the bearing raceway; we can see that the raceway appearance is not Smooth; there are many small metal high points; like a "mountain peak". If it is in the bearing operation; the "mountain peak" between the raceway and the raceway is touched; then the "mountain peak" will crack; The outer surface of the raceway is slightly detached; the end of the bearing forms the bearing damage (Fig. 3). The intention of the oil film is to make the small "mountain peak" between the raceway and the roller not touch directly. To achieve such effect; the thickness of the oil film It is necessary to go beyond the sum of the roughness of the two touches. When we find that the film thickness is not enough to separate the two metal faces; there are two choices: use a more viscous smooth oil or grease, roll down Appearance roughness. Because mine trucks generally use SAE80W-90 oil bath in the bridge package to be smooth; and the second smooth grease with EP additive is smooth at the wheel end. It is affected by heavy load and low speed; The condition. If the viscosity of the gear oil cannot be changed, we can improve the bearing function by improving the appearance of the raceway and the roller.
Figure 3 operates in a poorly sturdy condition; the bearing has the ability to cause damage. Bearing raceway appearance modification Now let's look at another important factor affecting the bearing function. The tracker's external stress can be imagined here. A bearing should not exceed its extra load; the stress on the raceway surface should be It is not a problem. If there is a problem; clarify that the bearing's own additional load data is elevated. This understanding is negligent; the bearing is under stress; its outer and inner ring centerlines can not be in a straight line; Angle (Figure 4);
Inconsistent bearing operation, this misalignment can be caused by improper installation of the device; it can also be caused by slight deformation of the shaft or the bearing seat under heavy load conditions; it can be the error of the shaft and the bearing seat during processing. Inferred; or the induction of the above elements. The additional load of the tapered roller bearing on the sample refers to the bearing operation; this angle is less than 0. 0005 radians. When the misalignment is less than 5/10,000 arc Time; does not affect the life and function of the bearing; but when this angle exceeds five thousandths of a degree of arc; it will have an impact on the function of the bearing. This misalignment will lead to bearing raceway stress gathering; Unable to reach the depicted fatigue life and fail early. This failure mode is shown in Figure 6; the general attack occurs at the edge of the raceway; and the diagonal form appears in the upper and lower 180 degrees.
Figure 5 Bearing failure caused by misalignment The bearing damage caused by this misalignment is very common in the bearing application of mine trucks; the first is because the load of the mining truck is too large; the formation of the shaft deformation is formed. When bearing damage occurs; if it is not carefully analyzed, it can not be attributed to the bearing load; it can only be perfuncated by the scale of the progressive bearing; the result is often not ambition. Timken is aiming at the raceway to exceed the allowable stress. The end of the operation leads to the low bearing life, the introduction of the bearing with the raceway shape modification; the ability to deal with the marginal stress gathering of the raceway without having to improve the bearing scale; the stress on the raceway surface is always in the data. Within the scale.
In the selection and accounting of mine truck bearings; relying on the accounting machine; input working conditions using professional software can simulate the bearing can have the problem of excessive raceway stress. In theory, such a case; Large-tonnage mine truck bearing selection; in the life cycle accounting, it is found that the bearing life of the front wheel hub is better than that. 在. Check the stress level of the bearing roller often; found that there is a high raceway stress under one working condition. Figure 6 shows; the groove stress of the roller has exceeded the required stress of the data; and some of the stress in the center of the raceway is better than that of the 啬芰 å²¢ æŸ . .. On the basis of the bearing, the raceway is modified; the loading software is calculated from the beginning; then the stress is found under the same working conditions; the stress distribution of the same roller is shown in Fig. 7; the bearing life is also appropriately improved.
Figure 6: General bearing raceway chasm stress is too large Figure 7 raceway repair bearing stress spread four. Summarize the above-mentioned application characteristics of the primary trucks; the paper analyzes the problems of bearing selection and analysis in terms of bearing data, bearing race roughness and raceway stress and shape modification. It is expected to pass the above Treatment method; improve the reliability of mine trucks; then reduce the time of parking protection; improve mining power.
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