Numerical Simulation Analysis and Experimental Verification of Pressure-resistant Self-compensating Oil Seal

The glyd ring of the transmission device is prone to wear and leakage, which causes the sealing failure to cause the failure of the transmission device. Therefore, a pressure-resistant self-compensating oil seal is proposed in this research. The influence of working conditions such as pressure and rotational speed on its temperature is studied by the numerical simulation method. An experiment bench for oil seals is constructed and utilized to validate the simulation findings. The above research results can ensure the safe and stable operation of the transmission device seal for a long period. In this research, the effect of working conditions such as pressure and rotational speed on its temperature of the glyd ring and the pressure-resistant self-compensating oil seal is compared, and it is verified by the experiment results. The research results show that with the increase of pressure and rotational speed, the temperature of the two seals also increases. Under the same condition, the temperature of the pressure-resistant self-compensating oil seal is significantly lower than that of the glyd ring. The temperature rise of the pressure-resistant self-compensating oil seal can be reduced by about 27 % compared with the glyd ring.


Introduction
Leakage caused by sealing failure is one of the main problems faced by transmission devices in construction machinery, and sealing life is an important index to measure the quality of transmission devices.The glyd ring is commonly used in the transmission device seal.The glyd ring is a combined seal composed of O-ring and polytetrafluoroethylene slip ring, which is widely used in industries such as aerospace, construction, mining [1,2].The rapid growth of the machinery industry has also put forward higher requirements for the operating parameters of transmission devices.Due to the serious friction, high temperature rise, O-ring elastic failure and slip ring wear, the leakage is large and the service life is short, which can not meet the needs of higher parameters of the transmission device.
A large number of scholars have studied the rubber ring and the glyd ring.Nikas et al. [3][4][5][6][7] studied the tribological characteristics of seal rings with rectangular cross section and their influence on leakage through numerical simulation and experiment.Mazza and Belforte [8] proposed a model that can solve the friction of lip-shaped seal ring, and verified it by experiments.Kaneta et al. [9] measured the friction force and oil film thickness of the D-shaped seal ring by optical interference method, and gave the oil distribution in the sealing area.Wang et al. [10] studied the resistance caused by rotary seal, and the experimental results of rotation torque were consistent with the numerical simulation results.Pan et al. [11] studied the effect of sealing types on the friction force of hydraulic cylinders.
The research results reveal that compared with the glyd ring and U-ring seal, the combined sealing hydraulic actuator has the largest friction force and is insensitive to load changes.Huang and Salant [12,13] studied the friction and pressure distribution of the U-ring seal.Song et al. [14] conducted research on the friction and wear properties of O-ring, stepped ring, and glyd ring through analysis and experimental testing.Nikas and Sayles [15] constructed a model of slip-ring combined seal, analyzed the parameters such as leakage, dynamic friction and film thickness, and optimized the sealing structure.Yu et al. [16] conducted research on O-ring and sliding ring combination seals, and the results showed that compared to sliding ring combination seals, O-rings are more prone to damage and have higher power losses.Heipl et al. [17] studied the effects of oil pressure and temperature on polytetrafluoroethylene slip-ring combined seal.Wei et al. [18] studied the effects of fluid pressure and temperature on the contact stress of the glyd ring.By analyzing these literature, it can be concluded that most of the research on rubber ring and glyd ring focus on sealing performance, and there are few studies on the improvement of sealing structure.Therefore, this research improves the glyd ring and proposes a pressure-resistant self-compensating oil seal.Compared with the glyd ring, the surface temperature of this seal is lower, thereby prolonging the service life of the seal and ensuring that the transmission device in engineering machinery can work normally for a long time under high parameters.
In this research, a pressure-resistant self-compensating oil seal is first proposed, and then the influence of working conditions such as pressure and rotational speed on the temperature of pressureresistant self-compensating oil seal and glyd ring is studied by numerical simulation.Finally, an oil seal experiment bench is built and used to verify the previous results.The above research results can provide theoretical support for the optimization of glyd ring and the normal operation of transmission device in construction machinery under high parameters.

Introduction of Pressure-resistant Self-compensating Oil Seal
In response to the problems of serious friction and large temperature rise of the glyd ring, a pressureresistant self-compensating oil seal is proposed in this research, and its working principle is shown in figure 1.On the right side of the diagram is high pressure oil.The function of the pressure-resistant self-compensating oil seal is to prevent the high-pressure oil from leaking outward, and to avoid the oil pressure of the transmission device in the construction machinery being lower than the oil pressure required for normal operation, resulting in the failure of the transmission device.The orange line part is the friction area of the pressure-resistant self-compensating oil seal and the shaft.The increase of the sealing temperature is caused by friction heat generation in this area.During the working process of the transmission device, the pressure-resistant self-compensating oil seal and the shaft are in a state of interference fit.The elasticity of the O-ring after wear in the sealing friction area can realize realtime automatic compensation after wear.

Seal lip
Compared with the glyd ring, the pressure-resistant self-compensating oil seal proposed in this research uses the seal lip to contact the shaft, which greatly reduces the friction area and can significantly reduce the temperature rise caused by friction heat generation.Therefore, under the same conditions, the temperature rise energy of the pressure-resistant self-compensating oil seal is much lower than that of the glyd ring, which extends the seal life.And under the pressure of the oil, the sealing lip will be closer to the shaft, making its leakage less.In summary, the pressure-resistant selfcompensating oil seal proposed in this research can not only reduce the temperature and prolong the service life, but also reduce the leakage, so as to ensure that the transmission device in construction machinery can work normally for a long time under high parameters.The pressure-resistant self-compensating oil seal is shown in figure 2. Its inner diameter is 38 mm, outer diameter is 55 mm, and axial thickness is 8 mm.

Numerical Simulation Model of Pressure-resistant Self-compensating Oil Seal
Because the spending time of the numerical simulation model established completely according to the actual situation is too long, the simplified analysis of the pressure-resistant self-compensating oil seal and glyd ring is carried out [19].The simplified numerical simulation model of the pressure-resistant self-compensating oil seal is shown in figure 3, and the O-ring is ignored.This is because the interference fit between the shaft and the seal caused by the extrusion of the O-ring during actual work can achieve the same effect by setting the seal interference.The main material of the pressure-resistant self-compensating oil seal is modified polytetrafluoroethylene, and the material of the shaft is 45 steel.The physical parameters of the two materials are shown in table 1.In the process of numerical simulation, the shaft speed ranges from 500-3000 rpm, and the initial environment temperature is set to 20 °C.Due to the self-lubricating characteristics of polytetrafluoroethylene, the friction coefficient between the pressure-resistant selfcompensating oil seal and the shaft is set to 0.05, and the interference of the pressure-resistant selfcompensating oil seal is set to 0.8 mm.After consulting the relevant literature [20], the convective heat transfer coefficient between the pressure-resistant self-compensating oil seal and the oil is 530 W/(m 2 • K), and the convective heat transfer coefficient between the oil and the air is 40 W/(m 2 • K).

Numerical Simulation Results Analysis
Figure 4 and figure 5 show the temperature contours of the glyd ring and the pressure-resistant selfcompensating oil seal at different rotational speeds.The temperature of the glyd ring and the pressureresistant self-compensating oil seal increases with the increase of the rotational speed, and the highest sealing temperature is located in the friction area between the seal and the shaft.This is because the heat is due to the friction between the seal and the shaft, the higher the speed, the more serious the friction between the seal and the shaft, and the friction generated by the friction area is transferred to the outside of the seal, so the higher the speed, the higher the temperature of the seal surface, and the highest temperature in the friction area of the seal, the lowest temperature outside the seal.Figure 6 and 7 show the temperature contours of the pressure-resistant self-compensating oil seal and the glyd ring under different pressures.The temperature of the glyd ring and the pressure-resistant self-compensating oil seal increases with the increase of the pressure, and the highest sealing temperature is located in the friction area between the seal and the shaft.This is because the heat is due to the friction between the shaft and the seal, the higher the pressure, the tighter the seal and the shaft, the more serious the friction between the seal and the shaft, and the friction generated by the friction area is transferred to the outer side of the seal, so the higher the speed, the higher the temperature of the seal surface, and the highest temperature in the friction area of the seal, the lowest temperature outside the seal.
According to the temperature contours of t the pressure-resistant self-compensating oil seal and the glyd ring, the maximum temperature of the glyd ring and the pressure-resistant self-compensating oil seal is basically the same under the same conditions.This is because the two sealing materials are polytetrafluoroethylene, so the physical parameters and working conditions are the same in numerical simulation, resulting in the same maximum temperature of the two seals.However, the temperature of most areas of the glyd ring is significantly higher than that of the pressure-resistant self-compensating oil seal.When the rotational speed is 3000 rpm and the oil pressure is 3 MPa, most of the surface of the temperature cloud of the glyd ring is green, the temperature is 48.310-49.262°C, and the average value is 48.786 °C.Most of the surface of the temperature cloud of the pressure-resistant self-compensating oil seal is blue, the temperature is 28.846-32.153°C, and the average value is 30.4995°C.The temperature of the pressure-resistant selfcompensating oil seal is nearly 20 °C lower than that of the glyd ring.The temperature of the pressureresistant self-compensating oil seal is significantly lower than that of the glyd ring.This is because the pressure-resistant self-compensating oil seal only has the seal lip part to rub with the shaft, while the glyd ring is the entire slip ring.The friction area of the glyd ring is much larger than that of the pressure-resistant self-compensating oil seal.Under the same conditions, the pressure-resistant selfcompensating oil seal generates less heat, so its temperature is lower.In summary, compared with the glyd ring, the pressure-resistant self-compensating oil seal has a lower temperature and a longer service life.Therefore, after using the pressure-resistant selfcompensating oil seal, the transmission device in the construction machinery can operate safely and stably for a longer time.

Experiment Bench Introduction
As shown in figure 8, the previous oil seal experiment bench was improved [21] so that the temperature experiments of the pressure-resistant self-compensating oil seal and the glyd ring could be carried out.The oil enters the seal experiment device from the oil station.The spindle rotates with the motor, and the seal temperature rise is measured by the temperature sensor.And the temperature

Experiment Results of Rotational Speed Influence
When the oil pressure in the seal experiment device is 2.5 MPa, the temperature rise of the pressureresistant self-compensating oil seal and the glyd ring with respect to the rotational speed is shown in figure 10.The sealing temperature rise is the result of the sealing measurement temperature minus the sealing ambient temperature.The experimental results of the temperature rise of the glyd ring are basically consistent with the simulation results, verifying the accuracy of the previous results.
The temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring increases with the increase of the rotational speed.When the rotational speed increases by 1000 rpm, the temperature rise of the pressure-resistant self-compensating oil seal increases by about 5.4 °C, and the temperature rise of the glyd ring increases by about 7.4 °C.The temperature rise of the pressureresistant self-compensating oil seal is reduced by about 27 % when compared to the glyd ring.As the rotational speed is 3000 rpm, the increase rate of temperature rise of the pressure-resistant selfcompensating oil seal can be reduced by about 33 % compared with the glyd ring.
From figure 10, the partial experimental results of the temperature rise in the glyd ring are slightly lower than the numerical simulation results.This is because the experiment ambient temperature set in the numerical simulation process is 20 °C, and sometimes the actual experiment ambient temperature is lower than 20 °C, which increases the heat dissipation of the glyd ring, resulting in the occurrence of this phenomenon.

Experiment Results of Pressure Influence
The temperature rise changes of the pressure-resistant self-compensating oil seal and the glyd ring under different pressures at a rotational speed of 3000 rpm are shown in figure 11.The experimental results of the temperature rise of the glyd ring are basically consistent with the simulation results, verifying the accuracy of the previous results.
The temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring increases when the pressure increases.When the pressure increases by 1 MPa, the temperature rise of the pressure-resistant self-compensating oil seal increases by about 6.7 °C, and the temperature rise of the glyd ring increases by about 8.0 °C.The temperature rise of the pressure-resistant self-compensating oil seal is reduced by about 16 % when compared to the glyd ring.When the pressure is 3 MPa, the increase rate of temperature rise of the pressure-resistant self-compensating oil seal can be reduced by about 29 % compared with the glyd ring.
From figure 10, the partial experimental results of the temperature rise in the glyd ring are slightly lower than the numerical simulation results, and the reason is the same as that described in section 4.2.

Comparison Results of Temperature Rise in Sealing Experiment
The temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring when the rotational speed is 3000 rpm and the oil pressure is 2.5 MPa is shown in figure 12.As time goes on, the temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring increases first and then tends to be stable.However, the temperature rise experiment result of the pressure-resistant self-compensating oil seal is significantly lower than those of the glyd ring.The temperature rise result of the pressure-resistant self-compensating oil seal is reduced by about 27 % when compared to the glyd ring.
The comparison results of this experiment are consistent with the previous numerical simulation results, indicating that the pressure-resistant self-compensating oil seal proposed in this research can significantly reduce the sealing temperature rise, thereby prolonging the seal service life and ensuring the long-term safe and stable operation of the transmission device seal.

Conclusion
In this research, the simulation analysis and experimental verification of the pressure-resistant selfcompensating oil seal are carried out.The relevant conclusions are as follows: (1) The temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring increases with the increase of the rotational speed.When the rotational speed increases by 1000 rpm, the temperature rise of the pressure-resistant self-compensating oil seal and glyd ring increases by about 5.4 °C and 7.4 °C, respectively.The increase rate of temperature rise of the pressure-resistant self-compensating oil seal is reduced by about 27 % when compared to the glyd ring.
(2) The temperature rise of the pressure-resistant self-compensating oil seal and the glyd ring increases when the pressure increases.When the pressure increases by 1 MPa, the temperature rise of the pressure-resistant self-compensating oil seal and glyd ring increases by about 6.7 °C and 8.0 °C, respectively.The increase rate of temperature rise of the pressure-resistant self-compensating oil seal is reduced by about 16 % when compared to the glyd ring (3) The temperature rise experiment result of the pressure-resistant self-compensating oil seal is reduced by about 27 % compared with the glyd ring when the rotational speed is 3000 rpm and the oil pressure is 2.5 MPa.

Figure 4 .
Figure 4.The temperature cloud diagram of the glyd ring under different rotational speeds (pressure is 2.5 MPa).

Figure 5 .Figure 6 .
Figure 5.The temperature cloud diagram of the pressure-resistant self-compensating oil seal under different rotational speeds (pressure is 2.5 MPa).

Figure 7 .
Figure 7.The temperature cloud diagram of the pressure-resistant self-compensating oil seal under different pressures (rotational speed is 3000 rpm).
measurement point of the sensor is close to the friction area between the shaft and the seal, as shown in figure9.

Figure 9 .
Figure 9.The temperature measurement point of the sensor.

Figure 10 .
Figure 10.The results of seal temperature rise at different rotational speeds.

Figure 11 .
Figure 11.The results of seal temperature rise at different pressures.

Figure 12 .
Figure 12.The comparison results of seal experiment temperature rise.