Hydraulic Slip Ring

In hydraulic transmission systems, the Hydraulic Slip Ring is a critical component responsible for transmitting hydraulic fluid between rotating and stationary parts. As the working medium of hydraulic systems, the performance of hydraulic oil directly affects the stability and reliability of the entire system operation. Among them, the viscosity of hydraulic oil is a crucial parameter, and its changes will have multiple impacts on the performance of hydraulic slip rings. It is of great significance to have a deep understanding of these impacts and take effective measures to ensure the normal operation of hydraulic systems and extend the service life of equipment.

Basic concepts of hydraulic oil viscosity

Definition and expression method of viscosity

Viscosity is a physical quantity that measures the ability of a fluid to resist flow, reflecting the internal friction between fluid molecules. In hydraulic systems, commonly used viscosity representation methods include dynamic viscosity, kinematic viscosity, and Engler viscosity. Dynamic viscosity refers to the internal friction force per unit area experienced by a fluid flowing at a unit velocity gradient, measured in pascals per second (Pa · s). Kinematic viscosity is the ratio of dynamic viscosity to fluid density, measured in square meters per second (m ²/s). In practical applications, the commonly used unit of kinematic viscosity is square millimeters per second (mm ²/s). Ennian viscosity is the ratio of the time required for a certain volume of test oil to flow out of 200ml of Ennian viscosity meter at a certain temperature under specified conditions to the time required for distilled water to flow out of the same volume at 20 ℃.

Factors affecting the viscosity of hydraulic oil

Temperature: Temperature is the most important factor affecting the viscosity of hydraulic oil. Generally speaking, the viscosity of hydraulic oil decreases with increasing temperature and increases with decreasing temperature. This viscosity temperature characteristic can be represented by a viscosity temperature curve, and different types of hydraulic oil have different viscosity temperature curves. For example, the viscosity of mineral oil hydraulic oil varies significantly with temperature, while synthetic hydraulic oil has relatively better viscosity temperature performance.

Pressure: Within the general pressure range, the effect of pressure on the viscosity of hydraulic oil is relatively small and can be ignored. But when the pressure exceeds a certain value (usually above 10MPa), the viscosity of hydraulic oil will increase with the increase of pressure. This is because an increase in pressure reduces the distance between oil molecules, increases internal friction, and leads to an increase in viscosity.

Additives: In order to improve the performance of hydraulic oil, various additives such as anti-wear agents, antioxidants, rust inhibitors, etc. are usually added to the base oil. Some additives can also affect the viscosity of hydraulic oil, for example, thickeners can increase the viscosity of hydraulic oil and improve its viscosity temperature performance.

The Influence of Hydraulic Oil Viscosity Changes on the Performance of Hydraulic Slip Ring

The impact on sealing performance

Leakage problem caused by viscosity reduction

When the viscosity of hydraulic oil decreases, the oil film between the seal and the rotating parts will become thinner. As an important component of sealing, the oil film plays a role in preventing hydraulic oil leakage. After the oil film becomes thinner, its load-bearing capacity decreases, making it difficult to effectively fill the sealing gap, which can easily lead to leakage. Leakage not only causes waste of hydraulic oil, but also makes it difficult to maintain stable system pressure, affecting the efficiency of the system. For example, in some hydraulic control systems that require high pressure accuracy, even slight leaks can lead to increased control errors and fail to meet operational requirements.

Seal damage caused by increased viscosity

On the contrary, when the viscosity of hydraulic oil increases, the fluidity of the oil decreases. During the operation of the Hydraulic Slip Ring, the seal needs to continuously deform with the movement of the rotating components to maintain good sealing performance. However, high viscosity oil can cause greater resistance to the seal during movement, resulting in uneven force distribution on the seal. Long term exposure to such uneven stress can lead to damage such as wear and tear of the seals, resulting in leakage. In addition, an increase in viscosity may make the installation and disassembly of seals more difficult, increasing maintenance costs and equipment downtime.

Influence on torque characteristics

Slip phenomenon at low viscosity

When the viscosity of hydraulic oil is low, the internal friction of the oil is small, which reduces the torque of the Hydraulic Slip Ring during rotation. Lower torque is beneficial for achieving high-speed rotation. In some equipment that requires high-speed operation, such as the hydraulic drive system of high-speed centrifuges, low viscosity hydraulic oil can reduce energy loss and improve equipment operating efficiency. However, during power transmission, slippage may occur due to insufficient internal friction of the oil. Slipping can cause unstable power transmission, making it difficult to accurately transfer power to the load and affecting the normal operation of the equipment. For example, in the hydraulic drive system of industrial robotic arms, if slippage occurs, the accuracy of the robotic arm's movements will be seriously affected, making it impossible to complete precise grasping and placement tasks.

Motor load increases when viscosity is high

When the viscosity of hydraulic oil increases, the torque required for the rotation of the Hydraulic Slip Ring will increase. This is because high viscosity oil generates greater resistance during the flow process, requiring greater driving force to rotate the slip ring. The increase in torque directly increases the load on the drive motor, and the motor needs to output greater power to overcome this resistance. If the power reserve of the motor is insufficient and it operates under high load for a long time, the motor may overheat or even burn out. In addition, high torque can also lead to a decrease in the system's response speed and slow equipment movement. For example, in the hydraulic control system of an injection molding machine, a decrease in response speed can affect the quality and production efficiency of injection molding.

The impact on the degree of wear and tear

Insufficient lubrication caused by low viscosity

Lubrication is an important means of reducing component wear, and hydraulic oil plays a lubricating role in the Hydraulic Slip Ring. When the viscosity of hydraulic oil decreases, its lubrication performance will decrease. The decrease in lubrication performance increases the probability of direct contact between rotating and stationary components, thereby accelerating component wear. Wear and tear can lead to a decrease in the dimensional accuracy of components, an increase in surface roughness, and further affect the performance of Hydraulic Slip Rings. For example, wear between the rotor and stator of a slip ring can lead to increased clearance, intensified leakage, and ultimately shorten the service life of the equipment.

Local high temperature caused by high viscosity

When the viscosity of hydraulic oil is high, the flow of the oil is difficult, and local oil stagnation zones are easily formed in the narrow gaps and complex flow channels of the Hydraulic Slip Ring. The oil is constantly subjected to shear and compression in the stagnant zone, converting mechanical energy into thermal energy, resulting in a local temperature increase. High temperatures can degrade the performance of hydraulic oil, accelerate oxidation and decomposition, and generate acidic substances and deposits that further exacerbate component wear. At the same time, high temperatures can also cause changes in the material properties of seals, reducing their sealing performance. For example, in some hydraulic systems operating in high-temperature environments, if the viscosity of the hydraulic oil is not properly selected, the problem of local high temperature will become more severe and the harm to the equipment will be greater.

Measures to deal with changes in hydraulic oil viscosity

Choose the appropriate hydraulic oil

Select hydraulic oil type based on work environment and working conditions

Different working environments and conditions have different performance requirements for hydraulic oil, so it is necessary to choose the appropriate type of hydraulic oil according to the actual situation. Hydraulic Slip Rings working in high-temperature environments should choose hydraulic oil with good thermal stability and high-temperature oxidation resistance, such as composite hydraulic oil. Synthetic hydraulic oil usually uses chemically synthesized base oil and adds high-performance additives to maintain stable performance at high temperatures. In low-temperature environments, hydraulic oil with good low-temperature fluidity and low pour point should be selected to ensure that it can quickly reach various lubrication parts during low-temperature start-up and avoid equipment damage caused by poor lubrication. In working environments with corrosive media, it is also necessary to choose hydraulic oil with good rust and corrosion resistance properties.

Pay attention to the viscosity index and viscosity temperature performance of hydraulic oil

The viscosity index is an important indicator for measuring the viscosity temperature performance of hydraulic oil. The higher the viscosity index, the less the viscosity of hydraulic oil changes with temperature, and the better the viscosity temperature performance. When selecting hydraulic oil, it is advisable to choose products with high viscosity index to ensure that the viscosity of the hydraulic oil can be maintained within a reasonable range at different operating temperatures. For example, some high-performance hydraulic oils can have a viscosity index of over 150, providing stable lubrication and sealing performance for hydraulic slip rings over a wide temperature range. In addition, one can also refer to the viscosity temperature curve of hydraulic oil to understand its viscosity changes at different temperatures, in order to more accurately select hydraulic oil suitable for working conditions.

Install oil temperature regulating device

Working principle and application of cooler

The cooler is one of the commonly used oil temperature regulating devices, and its working principle is to transfer the heat in the hydraulic oil to the cooling medium (usually water or air) through heat exchange, thereby reducing the temperature of the hydraulic oil. During the operation of the Hydraulic Slip Ring, the oil temperature gradually increases due to the circulation of hydraulic oil and mechanical friction. When the oil temperature exceeds the allowable range, the cooler starts to work, taking away excess heat and keeping the oil temperature at a suitable level. For example, in the hydraulic system of large hydraulic presses, plate coolers or tube coolers are usually installed. Based on the system's heat generation and working requirements, the type and specifications of the cooler are reasonably selected to ensure effective control of oil temperature.

The function and usage of the heater

At low temperatures, the viscosity of hydraulic oil will significantly increase, affecting the normal start-up and operation of the Hydraulic Slip Ring. At this point, a heater is needed to increase the temperature of the hydraulic oil. The working principle of a heater is to transfer heat to hydraulic oil through methods such as electric heating or steam heating, reducing its viscosity. Heaters are usually installed in hydraulic oil tanks or oil pipelines. Before starting the equipment, turn on the heater to heat the hydraulic oil to the appropriate temperature, and then start the equipment. When using a heater, it is important to control the heating temperature to avoid deterioration of hydraulic oil performance caused by excessive oil temperature. At the same time, a temperature protection device should be installed to automatically cut off the power supply of the heater when the oil temperature reaches the set upper limit, ensuring equipment safety.

Regularly inspect and replace hydraulic oil

Methods and frequencies for detecting hydraulic oil viscosity and contamination level

Regularly testing the viscosity and contamination level of hydraulic oil is an important measure to ensure the normal operation of the Hydraulic Slip Ring. The viscosity of hydraulic oil can be measured using a viscometer according to the methods specified in relevant standards. Commonly used viscometers include capillary viscometers, rotational viscometers, etc. Particle counting method, spectral analysis method, etc. can be used to detect the degree of hydraulic oil contamination. The particle counting method evaluates the degree of oil contamination by measuring the number and size of particles in the oil; Spectral analysis method determines the presence of pollutants such as wear particles, moisture, and impurities in oil by analyzing the elemental composition of the oil. The frequency of testing should be determined based on factors such as the operating conditions and running time of the equipment. Generally, for frequently used hydraulic equipment, it is recommended to test the viscosity and pollution level of the hydraulic oil every 1-3 months; For devices with low usage frequency, the detection cycle can be appropriately extended.

Standards and precautions for replacing hydraulic oil

When the viscosity of the hydraulic oil exceeds the allowable range or the degree of contamination reaches a certain level during testing, it is necessary to replace the hydraulic oil in a timely manner. When replacing hydraulic oil, it is recommended to choose products of the same brand, model, and specification as the original hydraulic oil to avoid mixing different brands or models of hydraulic oil to prevent chemical reactions that may affect the performance of the hydraulic oil. Before replacing hydraulic oil, the old oil in the hydraulic system should be drained completely, and then the system should be cleaned with a cleaning agent to remove residual impurities and pollutants. After cleaning, add new hydraulic oil. Meanwhile, it is also necessary to pay attention to replacing the hydraulic oil filter to ensure the cleanliness of the newly added hydraulic oil. In addition, during the process of replacing hydraulic oil, it is necessary to strictly follow the operating procedures to prevent safety accidents such as leakage and fire.

Optimize structural design

Improve sealing structure and materials

In order to improve the sealing performance of Hydraulic Slip Ring during changes in hydraulic oil viscosity, improvements can be made to the sealing structure and materials. In terms of sealing structure, new sealing forms can be adopted, such as combination seals, labyrinth seals, etc. Combination sealing is the process of combining multiple sealing components together, utilizing their respective advantages to improve sealing performance. For example, combining rubber sealing rings with metal sealing rings can improve the wear resistance and corrosion resistance of the seals while ensuring good sealing performance. Maze sealing is achieved by setting up complex maze channels to increase the length and resistance of the leakage path, thus achieving the purpose of sealing. In terms of sealing materials, materials with good oil resistance, wear resistance, and adaptability to hydraulic oils of different viscosities should be selected. For example, high-performance rubber materials such as fluororubber and nitrile rubber are used, which can maintain good elasticity and sealing performance in hydraulic oils of different viscosities.

Increase lubrication channels and adopt special lubrication methods

In order to improve the lubrication conditions of the Hydraulic Slip Ring and reduce wear caused by changes in hydraulic oil viscosity, lubrication channels can be increased and special lubrication methods can be used. Increasing lubrication channels can distribute hydraulic oil more evenly to various lubrication parts, improving lubrication effectiveness. For example, multiple lubrication holes are set between the rotor and stator of the slip ring to allow hydraulic oil to directly enter the friction surface and form a good lubrication film. Special lubrication methods such as oil air lubrication, solid lubrication, etc. can also effectively improve lubrication performance. Oil air lubrication is the process of mixing compressed air with a small amount of lubricating oil and delivering it to the lubrication area to form a gas-liquid two-phase lubrication film. This lubrication method has the advantages of good lubrication effect and low pollution. Solid lubrication is the use of solid lubricants (such as graphite, molybdenum disulfide, etc.) to form a solid lubricating film on the friction surface, which plays a role in reducing friction and wear resistance, especially suitable for lubrication under special working conditions such as high temperature and high load.

Conclusion

The change in hydraulic oil viscosity has a significant impact on the performance of Hydraulic Slip Rings, involving multiple aspects such as sealing performance, torque characteristics, and wear degree. By deeply understanding these impacts and taking effective measures such as selecting appropriate hydraulic oil, installing oil temperature regulating devices, regularly testing and replacing hydraulic oil, and optimizing structural design, the adverse effects of hydraulic oil viscosity changes on the performance of Hydraulic Slip Rings can be minimized, ensuring the stable operation of hydraulic systems, extending the service life of equipment, and improving production efficiency and economic benefits. In practical applications, it is necessary to comprehensively consider various factors based on the specific working environment and conditions, develop reasonable solutions, and continuously optimize the performance and reliability of the Hydraulic Slip Ring.