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    [Technology] Frequently Asked Questions! Summary of the attributes of excavator support wheels and analysis of the causes of damage---Quanzhou excavator guide wheels

    * : * : admin * : 2021-11-10 16:10:16 * : 24
    [Technology] Frequently Asked Questions! Summary of the attributes of excavator support wheels and analysis of the causes of damage---Quanzhou excavator guide wheels

    Excavator rollers carry the excavator's own quality and operating load. The attribute of the roller is an important criterion to measure its quality. This article analyzes the attribute, damage and cause of the roller. ---Quanzhou excavator guide wheel

    1. The attributes of the supporting wheels

    (1) Structure

    The structure of the supporting wheel is shown in Figure 1. The outer cover 2 and inner cover 8 at both ends of the supporting wheel spindle 7 are fixed on the lower part of the crawler frame of the excavator. After the outer cover 2 and the inner cover 8 are fixed, the spindle 7 can be prevented from axial movement and rotation. There are flanges on both sides of the wheel body 5, which can clamp the crawler chain track to prevent the crawler from derailing and ensure that the excavator runs along the crawler.

    The outer cover 2 and the inner cover 8 are respectively provided with a pair of floating seal rings 4 and a floating seal rubber ring 3. After the outer cover 2 and the inner cover 8 are fixed, the floating seal rubber ring 3 and the floating seal ring 4 are pressed against each other. The opposing contact surfaces of the two floating seal rings 4 are smooth and hard to form a sealing surface. When the wheel body rotates, the two floating seal rings 4 rotate relatively to form a floating seal. The O-ring seal 9 is used to seal between the main shaft 7 and the outer cover 2 and the inner cover 8. The floating seal and the O-ring seal 9 can prevent the leakage of lubricating oil in the rollers and prevent muddy water from entering the rollers. internal. The oil hole in the screw plug 1 is used to fill the lubricating oil into the roller. ---Quanzhou excavator guide wheel

    (2) Force condition

    The excavator wheel body is supported by the upward supporting force of the track chain rail, and the two ends of the main shaft bear the excavator's gravity, as shown in Figure 2.

    The gravity of the excavator is transmitted to the main shaft 7 through the crawler frame, the outer cover 2, the inner cover 8, and is transmitted to the sleeve 6 and the wheel body 5 through the main shaft 7, and then transmitted to the chain rail and the crawler shoe through the wheel body 5 (see Figure 1) . When the excavator is working on uneven ground, it is easy to cause the track shoe to tilt, leading to the tilt of the chain track. When the excavator makes a steering action, an axial movement force will be generated between the main shaft and the wheel body. Due to the complex force of the supporting wheel, its structure must be reasonable, and the main shaft, wheel body and bushing need to have relatively high strength, toughness, wear resistance and sealing.

    (3) Technical requirements

    Spindle spindle material is 50Mn high quality carbon structural steel, C content is 0.48%~0.56%, Si content is 0.17%~0.37%, Mn content is 0.7%~1.0%, S content is less than 0.035%, P content is less than 0.035% , Cr content is less than 0.25%, Ni content is less than 0.30%, Cu content is less than 0.25%. Among them, Mn is an important element in alloy steel, which can improve the forgeability and plasticity of steel, and can ensure that the material has sufficient toughness and wear resistance. After heat treatment, 50Mn steel has higher strength and hardness, excellent hardenability, deeper hardened layer, finer pearlite structure and better mechanical properties. ---Quanzhou excavator guide wheel


    The spindle design standard requires that the depth T of the hardened layer is 2~7mm, and the quenching hardness is 50~62HRC, as shown in Figure 3.


    The wheel track surface of the wheel body support wheel is subjected to frequent impact loads and is prone to extrusion deformation, which makes the wheel body track surface extend into a conical shape. In order to improve the stress condition, we have lengthened the track surface of the wheel body, and designed the transition between the track surface and the wheel waist as an inclined surface to improve the supporting capacity of the track surface. The shaded part shown in Figure 4 is the extended track surface and transition Incline.


    In order to improve the wear resistance of the roller body, the wheel body material is 40Mn2 alloy structural steel. The C content is 0.37% to 0.44%, the Si content is 0.17% to 0.37%, the Mn content is 1.4% to 1.8%, the P content is less than 0.030%, and the S content is less than 0.030%.


    The wheel body is formed by forging, and the roughness of the wheel body is quenched and tempered after forming, with a hardness of 26~32HRC, in order to maintain the high strength, plasticity, toughness and comprehensive mechanical properties of the wheel body. The surface of the wheel body is quenched to improve the hardness and wear resistance of the track surface of the roller. The quenching hardness is 50~58HRC, and the depth of the hardened layer is 6~12mm, so that the rail surface hardness is basically close to the chain rail link hardness (48~58HRC). ---Quanzhou excavator guide wheel


    The size and surface roughness of the ring groove of the sealing O-ring should meet the design requirements, the mating surface should be chamfered, and the burrs and sharp edges should be cleaned.


    Floating seal rubber ring and O-shaped sealing ring should be made of high-quality nitrile rubber. The inner diameter, wire diameter, elasticity, hardness (Shore), and surface finish should meet the standards. Before assembly, the above items should be inspected one by one before they are qualified. Put into assembly.


    If the floating seal ring does not cover the ring groove of the floating seal ring, or does not adhere to the floating seal ring, the floating seal ring will exert uneven pressure on the floating seal ring. Uneven pressure will increase local blade surface wear when the floating seal ring rotates, resulting in oil leakage of the floating seal ring. If the edge of the O-ring seal is cut badly when assembling the inner and outer covers, the half of the O-ring is stuck outside the ring groove, or is twisted when installed in the ring groove, the sealing performance or service life of the O-ring seal will be reduced. Sometimes, if the airtightness check pressure does not reach a certain value, no leakage will be detected, and no leakage will occur after oil filling. However, after the excavator has been working for a certain period of time, the friction of the various components of the roller will increase, and the internal cavity pressure will rise to a certain value. , There will be leakage. If you continue to use it after a leak occurs, the floating oil seal will leak seriously. ---Quanzhou excavator guide wheel


    Clearance The gap between the main shaft of the roller and the sleeve on the wheel body is 0.2~0.4mm, there should be no blocking when rotating, the sealing performance is good, and there is no oil leakage.


    For lubrication, use an oiler to fill the roller with gear oil, and if necessary, increase the viscosity of the lubricating oil. Before adding gear oil, drain the failed gear oil first, and then add new gear oil into the oil plug hole until the oil flows out. When adding lubricating oil, unscrew the screw plug at the shaft end, put the end of the lubricating nozzle of the lubricator against the inner shoulder of the oil passage, and inject oil into the oil passage. When installing the oil plug, a torque wrench is required to control the tightening torque of the oil plug within the range of 157~255Nm.


    2. Analysis of the cause of damage


    This article takes a 20t excavator from a certain manufacturer as an example to analyze the cause of damage to its supporting wheels. We inspected the partially damaged support wheels of the excavator and found that the main faults were mainly damage to the main shaft and wheel body and oil leakage. Among them, the heavy-damaged main shaft of the supporting wheel appears to hold the shaft, causing the entire supporting wheel to be unable to rotate. Now we will analyze it separately. ---Quanzhou excavator guide wheel


    (1) Spindle damage


    The material is unqualified. We use a spectrometer to detect the content of each element in the damaged spindle of the supporting wheel. The measured content of Mn element is 0.59%, which is much different from the standard content (0.7%~1.0%). This seriously affects the mechanical properties of the spindle.

    The unqualified heat treatment measures the surface hardness of the damaged spindle and the depth of the hardened layer, as shown in Table 1. The test data shows that the surface quenching hardness of the spindle and the depth of the hardened layer do not meet the design requirements, which seriously affects the strength, rigidity and wear resistance of the spindle.

    Severe abrasion After testing, it is found that the main shaft is bent, and the mating parts of the main shaft diameter and the shaft sleeve are severely worn, as shown in Figure 5. After measurement, the clearance between the main shaft and the shaft sleeve is greater than 0.3mm (the gap should be less than 0.2mm), and the main shaft and shaft sleeve need to be updated. ---Quanzhou excavator guide wheel

    (2) Wheel body damage

    Check the damaged support roller wheel body, found that the wheel body track surface is deformed, cracked, and broken. Figure 6 shows that the track surface of the support roller extends into a conical shape after being impacted.

    Severe wear and tear of the wheel body is mainly manifested in the track surface, the guide cam flange and the shaft sleeve seat hole. This is because excavators often work in sandy, muddy, and gravel sites. A large amount of abrasive enters the track surface of the rollers and the chain rail, forming strong abrasive wear, and these sands affect the track surface and flanges and the track chain track. Larger extrusion stress is generated between the nodes, resulting in a lot of micro-extrusion deformation and dry friction. These dry frictions include rolling friction and sliding friction, which cause severe wear on the track surface of the wheel body, resulting in a decrease in the rigidity and strength of the wheel body. After the flange is severely worn, it is easy to derail the rollers.

    Unqualified heat treatment, measured roller damage, hard surface of wheel body

    The test results are shown in Table 2. The measured data shows that the quenching hardness of the wheel body surface and the depth of the quenching hardness layer do not meet the design requirements. ---Quanzhou excavator guide wheel

    Dissecting the wheel body with the problematic material, it was found that there were cracks inside, as shown in Figure 7. This shows that the wheel body blank forging is unqualified, and the wheel body forging process needs to be improved to prevent coarse grains and abnormal structure.

    (3) Oil leakage

    Check that the O-ring seal groove dimensions (groove width, groove depth, O-shaped groove roundness, etc.) of the supporting wheel spindle are within the design tolerance range and meet the technical requirements. Detection of floating seal rubber ring, O-shaped sealing ring wire diameter and inner diameter are out of tolerance, and the surface is damaged. The reason for the damage is the unqualified material of the sealing ring, which is reflected in the expansion and deformation, loss of elasticity, early aging, hardness (Shore) not meeting the design requirements after contact with lubricating oil, and oil leakage due to inadequate sealing.

    There are two reasons for the analysis of the oil leakage of the supporting roller: one is that the supporting roller is soaked in water for a long time during the operation of the excavator, causing the floating seal ring and the O-ring ring groove to be corroded; the second is the construction in muddy water in winter. Cause the floating seal ring to freeze and fail. ---Quanzhou excavator guide wheel

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