Finite element analysis of the magnitude and distr

2022-09-22
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Finite element analysis of the magnitude and distribution of oil seal lip pressure

oil seal is a high-tech precision rubber part, which prevents the leakage of lubricating oil or other media through the contact between flexible rubber (or leather, plastic, etc.) seals and shafts. Many experts and scholars have studied the sealing mechanism of oil seals, and put forward the surface tension theory, adsorption theory, and some have put forward the boundary lubrication theory. No matter which theory, its foundation is that there is an oil film between the shaft and the oil seal lip. The existence of oil film directly affects the sealing effect and the service life of oil seal. The following conditions may occur during the use of oil seals, namely: dry friction, boundary lubrication, boundary lubrication, fluid lubrication, and massive leakage. Its oil film status is: no oil film (thousand friction state), boundary lubrication film (boundary lubrication state), fluid lubrication film (boundary lubrication state), oil film damage (fluid lubrication state), oil film disappearance (massive leakage). The thickness of oil film and how to distinguish whether it is qualified polyurethane insulation material have become the urgent position of enterprises, management departments, design units and law enforcement departments at all levels. It is the key to whether the skeleton oil seal can have good initial sealing effect and lasting service life When the oil seal is in the boundary lubrication state, the lip of the oil seal has good contact with the shaft, and the surface contact stress is concentrated on the contact belt with a width of m~0.25mm. Figure 1 (a) shows the boundary lubrication state, the contact stress PR is centrally distributed, and the oil film is thin and triangular distributed on the air side, so it has good adsorption capacity and sealing effect. Figure 1 (b) shows the boundary lubrication state, and the contact stress distribution is relatively dispersed. The oil film is thick and distributed on the air side and oil case under the lip (belonging to fluid lubrication film), so the adsorption capacity is very poor, and leakage is easy to occur. Figure 1 (c) shows the fluid lubrication state, and the contact stress p: is seriously dispersed. The oil film is thick and unevenly distributed, so the adsorption capacity is lost and serious leakage occurs

it can be seen from the previous study of oil seal mechanism that the sealing performance of oil seal mainly depends on the thickness of oil film between oil seal lip and shaft diameter and the distribution of contact stress. The thickness of oil film is directly related to the contact pressure, so it can be said that the sealing performance and service life of oil seal largely depend on the size and distribution of oil seal lip pressure. In this paper, the finite element model of the oil seal is established and simulated by using the large-scale finite element analysis software ANSYS, so as to investigate some structural parameters of the oil seal and the influence of the spring force of the oil seal on the magnitude and distribution of the lip pressure of the oil seal, which lays a foundation for the structural optimization and fatigue analysis of the oil seal

1 calculation model

due to the complexity of the mechanism of the oil seal, for the convenience of modeling and analysis, the shape of the oil seal is simplified during modeling, and some structural details that will not have a great impact on the results are omitted. Moreover, considering the complete axisymmetry of the oil seal during assembly, we use the two-dimensional axisymmetric model to simulate the three-dimensional problems in practice. This simplification will not affect the analysis results, but will greatly reduce the modeling and analysis time. The two-dimensional axisymmetric model of the oil seal is shown in Figure 2 Model 50x70 X8 (mm). The material is butadiene rubber (NBR). En route β It is the vertical distance between the center of the oil seal spring and the lip of the oil seal, also known as the theoretical contact width. A and β They are the included angles between the oil side and the air side of the oil seal lip and the shaft, also known as the front lip angle and the rear lip angle

2 finite element model

in the static analysis carried out in this paper, the superelastic characteristics of oil seal material (rubber) and the large deformation and contact problems existing in the analysis make the analysis include material nonlinearity, contact nonlinearity and large deformation (structure) nonlinearity. These nonlinearity often make the analysis difficult to converge, so for the convenience of analysis, the author puts forward some assumptions without affecting the analysis results

(1) the oil seal material has a determined elastic modulus E and Poisson's ratio μ;

(2) the rigidity of the shaft and oil seal fixing sleeve made of steel is tens of thousands of times that of rubber, and its deformation can be ignored, that is, it is regarded as the constraint boundary when the oil seal is deformed

in this paper, the simplified Mooney revlin model is used to describe the strain energy function of rubber materials:

w=c1 (I) + C2 (I)

the stress-strain relationship is:

in this paper, C1 and c21.87 and 0.47 are used respectively

in the analysis model, the rubber element adopts hyper74, the spring and skeleton adopt linear solid element plane82, and the model also includes contact elements targe169 and conta172 automatically generated when ANSYS establishes contact pairs. There is only one load step in the solution - the displacement in the X direction applied by the shaft as the interference

3 analysis of calculation results

this paper analyzes the factors affecting the size and distribution of the contact pressure of the oil seal lip under static conditions. The analysis results and analysis are as follows

(1) the influence of the lip contact width r value (as shown in Figure 2) on the magnitude and distribution of oil seal lip pressure

Figure 2 oil seal set model

Figure 3 finite element model of oil seal

the contact width r of oil seal lip refers to the axial distance between the oil seal lip and the center of spring groove. Its existence makes the measurement process contact pressure mainly distributed on the air side of the oil seal. It can be seen from the references that the value of R directly affects the distribution of lip pressure and also has a certain impact on the contact pressure of oil seal lip. In this paper, the influence of R value on the distribution and size of the contact pressure at the lip of oil seal is analyzed by changing only the R value with other parameters unchanged. Fig. 4 and Fig. 5 show the changes of the maximum contact pressure at the lip and the contact width at the front and rear lip angles with R value respectively. Figure 6 shows the lip contact pressure distribution when r=0.6mm

Fig. 4 change of maximum contact pressure of oil seal with R value

Fig. 5 change of contact width of front and rear corners of oil seal with R value

from the analysis results, it is not difficult to see that with the increase of R value, the maximum contact pressure at the lip will decrease to a certain extent due to the weakening of spring effect, but the impact is not great. The contact width of the front lip angle decreases significantly with the increase of R value, which also proves that the existence of R can make the contact mainly exist on the air side. However, different from the previous theoretical views, the contact width of the rear lip angle (i.e. the contact width of the air side) also decreases when the R value increases. This paper believes that the reason for the decrease of the contact width of the rear lip angle is the weakening of the spring effect. The analysis method and results have certain guiding significance for designing or selecting the contact width r of oil seal lip

(2) the influence of interference on the pressure of oil seal lip

interference refers to the difference between lip diameter and shaft diameter in free state (without spring). It can generate the radial force when there is no spring at the lip and compensate the eccentricity of the shaft. The interference is too small, which will cause leakage and reduce the tightness when the installation eccentricity and shaft jump are large; Too much interference makes the lip close to the shaft, the gap between the lip and the shaft is too small, and there is a "dry contact" between the lip and the shaft. Under high-speed rotation, high temperature will quickly occur between the lip and the shaft surface, accelerating the aging and cracking of the lip, and even burning the sealing lip, making the seal ineffective. Therefore, it is very important to choose the appropriate interference amount. This paper analyzes the influence of interference on contact pressure by changing interference alone. Since springs are mostly used in practice, the analysis is carried out with springs. This paper analyzes the gradual change of interference from 0.2mm to 0.8mm. Fig. 7 and Fig. 8 respectively depict the changes of the maximum contact pressure and the contact width of the lip with the interference amount. Figure 9 and figure 10 show the lip contact pressure distribution when the interference is 0.2mm and 0.8mm

Fig. 7 Variation of the maximum contact pressure of the lip with the interference amount

Fig. 8 variation of the contact width of the lip with the interference amount

Fig. 9 distribution of the lip pressure when the interference amount is 0.2mm

Fig. 1 Distribution of the lip pressure when the interference amount is 0.8mm on the operation site of the pressure testing machine

the results of the analysis prove the previous empirical conclusions, and the analysis method can be used to determine the selection of the interference amount according to the pressure needs

(3) simulation of the effect of spring stiffness on the pressure of oil seal lip

the effect of oil seal spring can improve the contact pressure and the follow-up of oil seal lip to the shaft. In this paper, the influence of oil seal spring stiffness on the magnitude and distribution of oil seal lip contact pressure is simulated and analyzed. Analysis at r=0 6mm, interference is 4mm The analysis results are shown in Figure 12 and figure 13 From the analysis results shown in the figure, it can be seen that the front corner contact width changes little, while the maximum contact pressure and rear corner contact width increase with the increase of spring stiffness. These analyses are consistent with the actual situation, and have certain guiding significance for users to select the spring stiffness according to the pressure needs

Fig. 11 change of maximum contact pressure of lip with spring stiffness

Fig. 12 change of lip contact width with spring stiffness

(4) influence of rear lip angle on the size and distribution of oil seal contact pressure

it can be seen from the references that the difference between the front and rear lip angles of the oil seal has a great influence on the pumping effect of the oil seal. Choosing the appropriate size of the front and rear lip angles has a very important impact on the sealing performance of the oil seal. This paper believes that the front and rear lip angles of the oil seal lip, especially the rear lip angle, will also have a great influence on the size and distribution of the lip contact pressure Therefore, this paper analyzes the influence of the rear lip angle on the distribution and size of contact pressure under static conditions. Analysis at r=0 6mm, interference is 0 4mm, and the spring stiffness is 3142n/m. The results are shown in figures 13 and 14. From the results given in the figure, it can be seen that with the increase of the rear lip angle, the contact width decreases significantly, and the decrease of the contact width increases the maximum contact pressure at the lip. This analysis method can be used to select the size of the rear lip angle according to the needs of contact pressure and contact width, which has a certain guiding significance for product design

Fig. 13 the maximum contact pressure of the lip changes with the size of the lip angle

Fig. 14 the contact width of the rear lip and the subsequent change of the size of the lip angle

in addition to the typical parameters analyzed above, the surface roughness of the shaft, installation error, coaxiality, rubber material parameters for oil seal and movement conditions all have an impact on the pressure size and distribution of the oil seal lip, that is, they all have an impact on the sealing performance of the oil seal

4 conclusion

1) the finite element analysis of static nonlinear analysis with seals is successfully realized by using ANSYS; The experience of many years has been verified, which provides theoretical guidance for the design and selection of oil seals

2) the influence of the contact width of the oil seal lip, the interference amount, the spring stiffness and the size of the rear angle of the oil seal on the size and distribution of the contact pressure of the oil seal lip is analyzed and calculated. The lip contact width has little effect on the contact pressure of the oil seal lip, but with the increase of the lip contact width R, the contact begins mainly on the air side, which just reflects the significance of the existence of R. The interference amount is the only way for the oil seal without pre tightening of the spring to produce lip pressure. From the analysis, it can be seen that with the increase of the interference amount, the rear corner contact width increases significantly. Due to the increase of the contact width, the increase of lip contact pressure is relatively slow. The increase of spring stiffness makes the lip contact width and the maximum contact pressure increase slowly. The contact width of the rear lip angle decreases obviously with the increase of the lip angle, while the maximum contact pressure increases slowly with the increase of the lip angle. These analyses and the results obtained in this paper are of great significance to

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