This paper analyzes the performance and applicable working conditions of four commonly used sealing materials such as nitrile rubber and polyurethane, expounds their impact on the service life of hydraulic rotary actuators, and emphasizes that scientific material selection combined with working conditions can extend the service life of the actuator and control maintenance costs.

In the power transmission and motion control links of hydraulic systems, hydraulic rotary actuators play a core executive role. As key components of hydraulic rotary actuators, the rationality of sealing material selection directly determines the sealing effect and operational stability of the actuator, thereby affecting the overall service life of the equipment. In practical applications, if the sealing material is not matched with the working conditions, it is very easy to cause problems such as hydraulic oil leakage and accelerated wear of the sealing parts, which will eventually shorten the service life of the hydraulic rotary actuator. Therefore, systematically analyzing the performance characteristics of common sealing materials and scientifically selecting materials according to working conditions is of great significance for improving the long-term operational reliability of hydraulic rotary actuators.
I. The Core Role of Sealing Materials in Hydraulic Rotary Actuators
The seals of hydraulic rotary actuators assume three key missions: first, to prevent hydraulic oil leakage, ensure stable system pressure, and avoid power loss; second, to block external dust, impurities, etc. from entering the interior of the actuator, preventing wear of core components such as the cylinder barrel and piston rod; third, to maintain a stable sealing state during the reciprocating swing of the actuator to ensure motion accuracy. This requires the sealing material to maintain good elasticity, wear resistance and structural stability for a long time under the combined action of working pressure, ambient temperature, reciprocating friction and hydraulic medium. The rate of its performance attenuation is directly related to the wear degree of the internal components of the actuator, as well as the maintenance frequency and cycle of the equipment.
II. Common Sealing Materials for Hydraulic Rotary Actuators and Their Performance Analysis
At present, in hydraulic systems, the commonly used sealing materials for hydraulic rotary actuators mainly include four types: nitrile rubber (NBR), polyurethane (PU), fluororubber (FKM) and polytetrafluoroethylene (PTFE). The performance characteristics of various materials are significantly different, and their applicable working conditions also have their own focuses, which are specifically as follows:
(I) Nitrile Rubber (NBR)
Nitrile rubber is one of the most widely used sealing materials in hydraulic systems. Its core advantage is excellent hydraulic oil resistance and a certain degree of mechanical strength, with low processing cost. It is suitable for hydraulic rotary actuator working conditions with medium and low pressure and conventional temperature (-20℃~80℃). However, this material has obvious limitations. Under long-term high-temperature environment or working conditions with frequent impact loads, its elasticity will gradually attenuate and harden, and the sealing performance will decrease accordingly, which will lead to hydraulic oil leakage, accelerate the wear of internal components of the actuator, and indirectly shorten the service life of the hydraulic rotary actuator.
(II) Polyurethane (PU)
The prominent characteristics of polyurethane seals are strong wear resistance, excellent tear resistance, and good resilience. They perform particularly stably in hydraulic rotary actuator working conditions with frequent reciprocating swings and large load fluctuations. Its excellent resilience can effectively compensate for the sealing gap, reduce internal leakage, thereby reducing the abnormal wear of key components such as the cylinder barrel and piston rod, and playing a positive role in extending the service life of the hydraulic rotary actuator. However, this material has general high-temperature resistance and is not suitable for long-term high-temperature working conditions.
(III) Fluororubber (FKM)
Fluororubber has outstanding performance in high-temperature resistance and chemical medium resistance. It can adapt to a wide temperature range of -20℃~200℃ and can withstand a variety of corrosive hydraulic media. It is suitable for hydraulic rotary actuator working conditions with large temperature fluctuations and complex medium conditions. Seals made of fluororubber can maintain stable structure and sealing performance for a long time under harsh working conditions, effectively reducing the performance attenuation of the actuator caused by seal aging and failure, and significantly extending the service life of the hydraulic rotary actuator. However, its processing cost is relatively high, and its elasticity is slightly inferior to that of nitrile rubber and polyurethane.
(IV) Polytetrafluoroethylene (PTFE)
The core advantage of polytetrafluoroethylene seals is extremely low friction coefficient, which generates little resistance during operation, and can effectively reduce the wear of the piston rod surface. It is suitable for hydraulic rotary actuators that require high motion stability and precision. However, this material itself has poor elasticity and cannot achieve good sealing alone. It usually needs to be used in combination with elastic materials such as nitrile rubber and polyurethane to compensate for the gap changes during installation and operation and avoid seal failure.
III. Core Influencing Factors of Sealing Material Selection on the Service Life of Hydraulic Rotary Actuators
The impact of sealing materials on the service life of hydraulic rotary actuators is mainly concentrated in three core dimensions: first, wear resistance. The wear resistance of the seal directly determines its service life. If the wear resistance is insufficient, it will quickly wear and fail, leading to leakage and accelerating the loss of components such as the cylinder barrel and piston rod; second, pressure resistance. The pressure resistance of the material needs to match the working pressure of the actuator. If the pressure resistance is insufficient, the seal is prone to deformation and rupture, resulting in seal failure; third, working condition adaptability. The temperature resistance and medium resistance of the material need to be consistent with the actual working environment, otherwise aging, hardening and other problems will occur, shortening the service life of the seal and indirectly affecting the overall service life of the actuator.
In different application scenarios, the working conditions of hydraulic rotary actuators vary greatly: for working conditions with high-frequency reciprocating swings, materials with strong wear resistance (such as polyurethane) should be preferred; for high-temperature and corrosive medium working conditions, fluororubber should be focused on; for medium and low pressure and conventional working conditions, nitrile rubber can meet the needs; for working conditions requiring high motion precision, PTFE combined seals are suitable. Therefore, comprehensive evaluation combined with actual working conditions during the material selection stage is the key to ensuring the long-term stable operation of hydraulic rotary actuators.
IV. The Indirect Impact of Rational Material Selection on Actuator Maintenance Costs
From the perspective of the economy of long-term equipment operation, rational selection of sealing materials can not only extend the service life of hydraulic rotary actuators, but also effectively control maintenance costs. Stable performance of seals can reduce hydraulic oil leakage loss, reduce the number of unplanned shutdowns for maintenance, shorten the maintenance cycle, thereby reducing related costs such as seal replacement, hydraulic oil supplement and manual maintenance, and improve the operational reliability of the entire hydraulic system, avoiding chain equipment problems caused by actuator failures.
In summary, different sealing materials have their own advantages and disadvantages in the application of hydraulic rotary actuators. Their impact on the service life of the actuator is the result of the combined effect of material performance and working condition adaptability. Combining the working pressure, ambient temperature, motion mode and medium characteristics of the hydraulic rotary actuator, scientifically selecting suitable sealing materials can not only give full play to the performance advantages of the seals, but also maximize the service life of the hydraulic rotary actuator, providing a reliable guarantee for the continuous and stable operation of the hydraulic system.