Analysis of the sealing leakage of the Idler wheel

The heavy wheel is an important load-bearing component of crawler construction machinery (commonly known as the "lower roller"), which is composed of the support wheel body, support shaft, left and right support seats and sealing assembly and other parts. The support shaft is fixed on the trolley frame through the left and right support seats. The inner hole of the wheel body has a press-fitted shaft sleeve that rotates in coordination with the support shaft. Between the rotating wheel body and the fixed left and right support seats, there is a sealing assembly to maintain the sealing of the lubricating oil in the support shaft, shaft sleeve and other parts. This sealing assembly consists of a pair of double-conical metal material sealing rings and two nitrile rubber fixed compression rings. The rubber rings are respectively installed in the sealing seat openings of the wheel body and the support seat. As the metal sealing ring bears the squeezing support of the rubber ring, it ensures that the annular edge band meshes closely during rotation. Therefore, this seal belongs to the floating sealing type.

Analysis of the sealing leakage of the Idler wheel

The idler wheel is an important load-bearing component of crawler construction machinery (commonly known as "lower roller"), which is composed of idler wheel body, support shaft, left and right support seats and sealing assembly and other parts. The support shaft is fixed on the trolley frame through the left and right support seats. The inner hole of the wheel body has a press-fitted shaft sleeve that rotates in coordination with the support shaft. Between the rotating wheel body and the fixed left and right support seats, there is a sealing assembly to maintain the sealing of the lubricating oil in the support shaft, shaft sleeve and other parts. This sealing assembly consists of a pair of double-conical metal material sealing rings and two nitrile rubber fixed compression rings. The rubber rings are respectively installed in the sealing seat openings of the wheel body and the support seat. As the metal sealing ring bears the squeezing support of the rubber ring, it ensures that the annular edge band meshes closely during rotation. Therefore, this seal belongs to the floating sealing type.

In 1995, our factory produced idler wheels for excavators of a certain company. The company provided production drawings from abroad, and the floating oil seal assembly was imported from abroad. During the installation test, it was found that some idler wheels were leaking oil at the floating oil seal. After multiple tests, analyses and experiments, it was ultimately discovered that the conical surface bevel Angle of the floating seal assembly and the seat ring mouth that matches it of this company was significantly smaller than that of other types of oil seals produced by our factory. Through graphical calculation, it is known that the compression amount of its rubber ring is relatively large.

We believe that the small bevel Angle of the conical surface of the floating oil seal is beneficial for reducing the runout of the meshing ring band of the floating sealing ring caused by the external impact of the idler wheel, improving the axial force on the sealing meshing surface, and maintaining its axial force from changing sharply due to the increase of the axial clearance of the system. However, when the sealing cone Angle becomes smaller, it is prone to cause the rubber ring to be skewed on the conical surface during the assembly of the idler wheel. Moreover, the compression of the rubber ring by the sealing seat opening increases, making it even more difficult to ensure the correct position of the sealing meshing blade during assembly. An analysis of the relevant data of some advanced international companies reveals that the reduction of the bevel Angle of the conical surface of floating oil seals is a trend in design development.

Based on the above analysis, we have taken two measures:

(1) The parameters of the original design, such as the taper of the floating oil seal sealing ring and the cone Angle of the rubber ring seat opening, remain unchanged. The compression of the sealing rubber ring is appropriately adjusted with the simplest design changes.

(2) Improve the assembly process, add special tools, and ensure the correct position of the rubber ring of the floating oil seal on the conical surface of the sealing ring and its correct position when installed into the sealing seat opening, so as to ensure the correct meshing of the cutting edges of the two sealing rings.

After strict assembly in accordance with the above measures, no leakage was found either during testing or in installation and use.

We believe that in order to increase the service life of the floating sealing components of the idler wheels in the traveling mechanism of construction machinery, foreign companies have reduced the conical surface bevel Angle of the sealing ring and the conical surface bevel Angle of the rubber ring seat opening. This is beneficial both theoretically and in practice. However, if the assembly cannot be ensured to be accurate and in place during manufacturing, it will backfire.

If the floating seal assembly is assembled incorrectly, although the factory needs to conduct an air tightness check at the static original position, due to the elastic effect of the rubber ring, the air tightness check cannot be detected when the pressure does not reach a certain value. After oiling, there will be no leakage. After working for a certain period of time, due to the friction and temperature rise of each component, the internal cavity pressure will increase to a certain value. At the rotating meshing point, due to the elastic force of the rubber ring, the axial contact force of the blade band at this point is the smallest, resulting in intermittent instantaneous leakage. If the rotation stops under such circumstances, the leakage at the meshing point will not be instantaneous but severe oil leakage, which will continue until the inner cavity pressure drops to a certain value and the elastic force of the rubber ring reaches a new equilibrium, at which point the leakage will cease.

When assembly is incorrect, during operation, local cutting edges may experience intensified friction and wear due to high pressure, and at the same time, heat is generated rapidly, causing the viscosity of the lubricating oil to decrease and the wear of each rotating pair to increase.

The above analysis indicates that for a high-quality component, in addition to advanced design and high-quality parts processing and manufacturing, correct and perfect assembly is of great significance.