Hydrodynamic Composite Bushings and Plain Bearings in Wind Turbine Gearbox Rotor Shafts: Improving Efficiency with the Right Lubricant and Overcoming Challenges

Wind turbine gearboxes are crucial components of wind energy systems, responsible for converting the low-speed rotation of the rotor blades into high-speed rotation suitable for generating electricity. The use of hydrodynamic composite bushings and plain bearings in the gearbox rotor shaft can significantly improve the efficiency and reliability of wind turbines. In this article, we’ll explore the benefits of using these bearings, the importance of choosing the right lubricant, and the challenges associated with hydrodynamic plain bearings in wind turbine gearboxes.

1. Hydrodynamic Composite Bushings and Plain Bearings in Wind Turbine Gearboxes

Hydrodynamic composite bushings and plain bearings are designed to support the rotor shaft in wind turbine gearboxes, reducing friction and wear. These bearings utilize a layer of fluid, such as oil or grease, to create a thin film between the bearing surfaces. This fluid film allows for smooth, efficient operation, minimizing friction and enabling the bearing to handle heavy loads and high speeds.

2. The Importance of the Right Lubricant for Wind Turbine Gearboxes

Choosing the right lubricant for wind turbine gearboxes is essential for ensuring optimal performance, longevity, and efficiency. A high-quality lubricant can:

• Minimize friction and wear, prolonging the life of the bearings and gearbox components.
• Protect against corrosion and other forms of damage, reducing maintenance requirements and costs.
• Enhance heat dissipation, preventing overheating and maintaining consistent performance even under harsh conditions.

3. Challenges for Hydrodynamic Plain Bearings in Wind Turbine Gearboxes

Despite their many benefits, hydrodynamic plain bearings in wind turbine gearboxes can face several challenges, including:

• Varying loads and speeds: Wind turbines are subject to fluctuating wind speeds, which can cause variations in the load and speed experienced by the bearings. This can make it challenging to maintain a consistent fluid film thickness, potentially leading to increased wear and reduced efficiency.
• Contamination: Dirt and debris can enter the lubrication system and cause damage to the bearings and other gearbox components. Proper sealing and filtration are critical to preventing contamination and ensuring smooth operation.
• Temperature fluctuations: Wind turbines often operate in extreme temperatures, which can impact the viscosity and performance of the lubricant. Choosing a lubricant with a wide operating temperature range is essential for maintaining optimal performance.

Hydrodynamic composite bushings and plain bearings play a vital role in the performance and efficiency of wind turbine gearboxes. By selecting the right lubricant and addressing the challenges associated with these bearings, wind turbine operators can enhance the performance, reliability, and longevity of their gearboxes. Companies like Bronzelube (www.bronzelube.com) specialize in the development and manufacturing of high-quality hydrodynamic plain bearings for wind turbine applications, helping to promote the growth and success of the renewable energy industry.

Hydrodynamic Plain Bearings in Wind Turbine Gearboxes: Requirements for High-Performance Oil and Characteristics

Hydrodynamic plain bearings have long been used in applications such as turbomachines and marine drives, demonstrating their reliability and effectiveness. A more recent application is their use in wind turbine gearboxes, where they offer excellent resistance to shock, dirt particles, and vibration. In this article, we will discuss the requirements of a high-performance oil for hydrodynamic plain bearings in wind turbine gearboxes and the characteristics of these bearings.

1. Requirements for High-Performance Oil in Hydrodynamic Plain Bearings

To ensure optimal performance of hydrodynamic plain bearings in wind turbine gearboxes, it is crucial to select a high-quality lubricating oil that meets the following requirements:

• Compatibility: The chosen oil should be compatible with the plain bearing materials, such as white metal alloys. This compatibility ensures that one oil can be used for both gears and bearings without compromising functionality or service life.
• Viscosity: The oil should maintain an appropriate viscosity over a wide temperature range, ensuring consistent performance even under extreme conditions.
• Wear protection: High-performance oil should provide excellent wear protection to minimize friction and prolong bearing life.
• Corrosion resistance: The oil should protect the bearings from corrosion, which can result from moisture or contaminants.
• Oxidation stability: High-performance oil should have excellent oxidation stability, preventing the formation of sludge and other harmful deposits that can impede bearing performance.

2. Characteristics of Hydrodynamic Plain Bearings in Wind Turbine Gearboxes

Hydrodynamic plain bearings offer several key characteristics that make them well-suited for use in wind turbine gearboxes:

• Maintenance-free: These bearings do not require regular maintenance or additional lubrication, reducing downtime and maintenance costs.
• Protection from tribo-chemical corrosion: High-performance oil and the bearings’ design protect the components from corrosion caused by the interaction between the bearing materials and the lubricant.
• Low operating bearing clearance: Hydrodynamic plain bearings have a low bearing clearance, ensuring minimal shaft movement and accurate alignment of gearbox components.
• Low wear: These bearings exhibit low wear, even under fluctuating stresses, contributing to their longevity and reliable performance.
• Low friction coefficient: Hydrodynamic plain bearings have a low friction coefficient, enhancing the efficiency of the wind turbine gearbox and reducing energy loss.

Hydrodynamic plain bearings are an effective solution for wind turbine gearboxes, offering excellent resistance to various challenges such as shock, dirt particles, and vibration. By selecting a high-performance oil that meets the necessary requirements, wind turbine operators can maximize the performance, reliability, and service life of their gearboxes. These bearings’ characteristics, such as their maintenance-free nature and low friction coefficient, make them an attractive choice for use in wind energy systems.

Hydrodynamic Self-Lubricant Bush Bearings: Environmental and Economic Advantages of High-Performance Lubricants

Hydrodynamic self-lubricant bush bearings are designed to offer continuous operation with minimal wear and friction during start-up and deceleration. The selection of the correct lubricant and maintaining the required viscosity is essential for these bearings to achieve their specified service life. In this article, we will discuss the environmental and economic advantages offered by high-performance lubricants in hydrodynamic self-lubricant bush bearings.

1. Environmental Advantages of High-Performance Lubricants

• Reduced pollution: High-performance lubricants can minimize the need for frequent oil changes, reducing waste oil disposal and the risk of oil leaks that can harm the environment.
• Lower energy consumption: Lubricants that minimize friction help to improve the efficiency of the bearing, reducing energy consumption and the associated greenhouse gas emissions.
• Biodegradable options: Some high-performance lubricants are formulated using biodegradable base oils, which break down more readily in the environment, reducing their environmental impact.

2. Economic Advantages of High-Performance Lubricants

• Extended service life: High-quality lubricants can help prolong the life of hydrodynamic self-lubricant bush bearings by minimizing wear and maintaining the proper viscosity, reducing the need for frequent replacements and associated costs.
• Reduced maintenance costs: Using high-performance lubricants can lead to longer intervals between oil changes and lower maintenance requirements, resulting in cost savings for the user.
• Improved efficiency: Lubricants that reduce friction can enhance the overall efficiency of the bearings, leading to lower energy costs and improved performance.

3. Selecting the Optimal Lubricant for Hydrodynamic Self-Lubricant Bush Bearings

To choose the best lubricant for a specific application, it is important to consider the following operational technical requirements:

• Sliding speeds: Different lubricants may be more suitable for high or low sliding speeds, so it’s essential to select a lubricant that can perform well under the specific operating conditions.
• Loads: The lubricant should be capable of withstanding the loads experienced by the bearing, ensuring proper lubrication and minimal wear.
• Temperatures: The lubricant should maintain its performance across a wide temperature range, ensuring consistent operation even under extreme conditions.

Various types of oils, including mineral oils and synthetic oils, are available in different viscosities to cater to individual application requirements. By carefully assessing these factors, users can select the optimal lubricant to maximize the environmental and economic benefits of hydrodynamic self-lubricant bush bearings.

Hydrodynamic Plain Bearing Bushes Applications: Industrial Machinery, Engines, and Power Plants

Hydrodynamic Plain PTFE Bushing Bearings in Wind Turbine Gearboxes

Hydrodynamic plain PTFE bushing bearings offer several benefits for use in wind turbine gearboxes, including self-lubrication, resistance to harsh environments, low wear, and compatibility with various materials. By incorporating these bearings into wind turbine gearbox designs, operators can improve the performance, reliability, and longevity of their systems.

Self-lubricating properties

One of the key advantages of PTFE bushing bearings is their self-lubricating properties. PTFE has an extremely low coefficient of friction, which allows the bearings to operate smoothly without the need for additional lubrication. This reduces maintenance requirements and helps to ensure consistent performance, even under harsh conditions.

2. Resistance to harsh environments

PTFE bushing bearings are highly resistant to extreme temperatures, chemicals, and moisture. This makes them well-suited for use in wind turbine gearboxes, which are often exposed to harsh environmental conditions. The ability of PTFE bearings to withstand these conditions helps to prolong their service life and maintain optimal performance.

3. Low wear and long service life

PTFE bushing bearings exhibit low wear rates, even under high loads and varying operating conditions. This contributes to a longer service life, reducing the need for frequent bearing replacements and associated maintenance costs. In wind turbine gearboxes, this can lead to improved overall efficiency and reduced downtime.

4. Compatibility with other materials

PTFE bushing bearings are compatible with a wide range of materials, including metals, composites, and plastics. This allows for greater design flexibility in wind turbine gearboxes, enabling the use of various materials to optimize performance and durability.

5. Hydrodynamic operation

When used in a hydrodynamic configuration, plain PTFE bushing bearings create a fluid film between the bearing surfaces, reducing friction and wear. This fluid film enables the bearings to handle heavy loads and high speeds, making them an effective solution for wind turbine gearbox applications.

Hydrodynamic bearings are widely used in machines, particularly in engines and power plants.

A, a rich variety of sliding bearings, foreign dominated the global market

1.1, sliding bearings are widely used, the market space of more than $ 14 billion

Sliding bearings are mainly divided into two categories: fluid-lubricated bearings and self-lubricated bearings. Bearing is an important basic component in contemporary mechanical equipment, the main function is to support the rotating shaft or other moving body, while ensuring the accuracy of its movement. Depending on the structure and working principle, bearings can be divided into two categories: “rolling bearings” and “sliding bearings”. Rolling bearings are bearings that contain rolling bodies for rolling motion between parts, while sliding bearings are bearings that work without rolling bodies and only under sliding friction. Depending on the friction state between the sleeve and journal surface during operation, sliding bearings can be divided into fluid-lubricated bearings (such as dynamic pressure bearings, hydrostatic bearings), non-completely fluid-lubricated bearings and non-lubricated bearings, the latter two generally belong to self-lubricated bearings.

The latter two are generally self-lubricating bearings. There are a variety of technical routes of plain bearings, and the diverse principles and structures are suitable for different application scenarios. Although fluid-lubricated bearings and self-lubricated bearings belong to the same subdivision of sliding bearing track, there are big differences in the principle, structure and downstream applications. (1) fluid lubrication bearing: there are mainly two types of liquid lubrication and gas lubrication, according to the lubrication principle can be divided into dynamic pressure lubrication and static pressure lubrication. Liquid dynamic pressure lubrication bearings rely on the journal rotation of the fluid dynamic pressure to form the appropriate pressure oil film will be bearing and journal surface separation, so that the metal and metal does not occur in direct contact; liquid hydrostatic lubrication bearings rely on the external supply of pressure oil, the establishment of hydrostatic bearing oil film in the bearing to achieve liquid lubrication; gas dynamic pressure / hydrostatic lubrication bearings with gas as the lubricant, the principle is similar to liquid lubrication.

(2) self-lubricating bearings: generally contains non-complete liquid lubrication bearings (such as oil bearings, etc.) and solid lubrication bearings. Oil bearing is powder metallurgy bearing, is made of metal powder and other friction reducing material powder pressing, sintering, shaping and oil dipping, with porous structure, in the hot oil after wetting, the pores are filled with lubricating oil. When working, due to the suction effect of journal rotation and friction heat, the metal and oil heat expansion, the oil out of the pores, and then the friction surface lubrication, bearing cooling, oil is sucked back into the pores; solid lubrication bearings with graphite, molybdenum disulfide, phthalocyanine dye, polytetrafluoroethylene and other solid lubricants lubrication, the formation of permanent lubrication film, can adapt to extreme working conditions.

Sliding bearings are in a period of rapid development, the global market size has exceeded $ 14 billion. From the overall perspective of the bearing industry, the global market size has exceeded 100 billion U.S. dollars, the global bearing market size of about 120 billion U.S. dollars in 2021, 2016-2021 CAGR of 4.4%; China’s bearing market size of about 227.8 billion yuan in 2021, 2016-2021 CAGR of 7.0%. From the sliding bearing market segments, compared with the standardized rolling bearings, sliding bearings are currently in the rapid development period of application expansion and category enhancement, the global sliding bearing market size is about 14.1 billion USD in 2020, and the sliding bearing market size in China is about 13.7 billion RMB in the same year, the global and China sliding bearing market size CAGR is 12.8% and 13.2% respectively in 2016-2020. 12.8%, 13.2%, are higher than the overall growth rate of the bearing industry.

1.2, foreign capital dominates the global market, domestic enterprises are taking shape

Fluid lubrication bearing pattern: five multinational groups have the leading advantage, the global CR5 is about 18.86%. At present, the sliding bearing industry is basically dominated by large multinational groups, such as Kingsbury, Michell, RENK, Waukesha and Miba. The sliding bearing industry in developed countries has a long history and has formed a comprehensive technology system, accumulated rich research and engineering application experience, mastered a number of high precision manufacturing process, and has established a few leading enterprises as the head of the sliding bearing supply system, so the world’s important equipment, key supporting fluid lubrication slide bearing basically from the above large slide bearing manufacturers. In 2020, the top five companies in the global market share of dynamic oil film plain bearings, for example, will have a combined market share of about 18.86%. The domestic dynamic oil film sliding bearing market competition pattern is relatively fragmented, including the global dynamic oil film sliding bearing market share of 1.31%, ranked sixth, in the domestic market share of about 5.57%, ranked first.

Self-lubricating bearing pattern: the global market is dominated by foreign investors, the domestic high-end market concentration is high. Compared with rolling bearings, self-lubricating bearing sub-industry specialization division of labor is obvious, different applications of self-lubricating bearings in the varieties and specifications of the large differences in material selection, technical path and other requirements are different, so self-lubricating bearing industry is unique, the formation of the United States GGB company, Japan Oiles company, France Stain-Gobain and other professional self-lubricating bearing enterprises as the leading competition. The pattern. The domestic self-lubricating bearing industry has been developed for many years with a certain scale, and formed a clear industry cluster in Jiashan, Zhejiang. The domestic pattern, the low-end market more small and medium-sized enterprises, most small and medium-sized production level is not high, the high-end market is occupied by Changsheng bearings, Shuangfei shares, Zhongda precision and a few enterprises, a high degree of concentration.

1.3, self-lubricating bearings in many areas to replace the traditional program, the material is the core barrier

Self-lubricating bearing is a new type of bearing, the global promotion of the use of history only 50 years. In 1956, the world’s first self-lubricating DU bearing with PTFE as the liner and steel plate as the support was put on the market. In the late 1960s, self-lubricating bearings began to enter the aerospace and other cutting-edge technology applications. In the late 1960s, self-lubricating bearings were introduced into the aerospace industry and other advanced technology applications. From the 1970s, British self-lubricating bearing manufacturers licensed their technology to French, German, Japanese and American companies.

In terms of application areas, self-lubricating bearings for automobiles are spreading rapidly, and product and technology penetration is accelerating. Self-lubricating bearings are lightweight, low-noise, oil-free, and flexible, so their use in automobiles is spreading rapidly. (1) The number of self-lubricating bearings per passenger car has increased from 30 to more than 100, and they are replacing needle roller and powder bearings and generating new applications. (2) In addition to bearings, the use of self-lubricating technology in non-bearing areas is also increasing, such as self-lubricating coating for air conditioning compressors, swash plates, polymer engineering plastics with self-lubricating properties, etc.

The excellent performance of self-lubricating bearings also makes it in the construction machinery, general industry and other fields to expand the application. 1) construction machinery: general with low speed, heavy load characteristics, and harsh working conditions, and self-lubricating bearings with no oil, impact resistance, dust resistance, high strength and other characteristics, in the solution to the lubrication problem at the same time to reduce the noise, extend the service life, especially suitable for the harsh mine, field operations equipment (2) General industry: maintenance-free self-lubricating bearings have excellent wear resistance and anti-seize in the continuous operation of high-speed and high-precision industrial equipment, in injection molding machines, hydraulic equipment, stamping equipment, ferrous metallurgy, textile machinery, furnaces, canned food, industrial robots, pharmaceutical machinery, etc. In the fields of injection molding machines, hydraulic equipment, stamping equipment, ferrous metallurgy, textile machinery, melting furnaces, cans and foodstuffs, industrial robots, pharmaceutical machinery, etc. are gradually replacing conventional bearing solutions and expanding their applications.

The barriers to self-lubricating bearings are high, and material development is the core. The technology of self-lubricating bearings is mainly reflected in the research and development of self-lubricating materials. At present, self-lubricating materials are mostly composite materials, such as PTFE, POM, PA, PI, phenolic resin, PEEK and other high fraction composite materials, as well as bimetallic/multimetallic composites, high-performance copper alloy composites, metal matrix composites and other metal matrix materials and friction reducing materials. The development and industrialization of composite materials require deep technical accumulation and long-term repeated tests, so the development of self-lubricating materials requires a high-quality R & D team with a good theoretical foundation and rich practical experience, and has a simulation for different working conditions to test the product load capacity, service life, limit temperature and speed and other performance testing equipment.

At present, the production and processing technology of high-performance plain bearing materials is mainly in the hands of a few large enterprises, new entrants lack sufficient R & D capabilities, and can only buy high-performance bearing materials from advanced enterprises, or use some low-grade materials to produce low-end bearing products. The lack of research and development capabilities of high-end products has hindered the development of new enterprises in the industry, but also formed the main barriers to self-lubricating bearing industry.

Second, in line with industry trends, sliding bearing solutions to help solve the problem of wind power cost reduction

2.1, wind power sliding bearing with the feasibility of “to slide instead of roll” program has been verified by domestic and foreign OEMs

Wind power bearing is a high barrier to the core components, the current rolling bearing is the main. Wind power bearings generally include pitch bearings, yaw bearings, drive train bearings (spindle bearings, gearbox bearings, generator bearings). Bearings are the core components of wind power equipment and need to meet the harsh working conditions and long life and high reliability requirements of wind power equipment, so they have high technical barriers. Generally speaking, a direct-drive wind turbine requires one to two sets of main shaft bearings, one set of yaw bearings, and three sets of pitch bearings, while a double-fed or semi-direct-drive wind turbine requires multiple sets of gearbox bearings due to the addition of a gearbox on top of the direct-drive type. At present, wind turbine bearings are mainly rolling bearings, and because the working conditions and design requirements of different types of bearings are different, the wind turbine bearings are highly customized.

Wind power bearings use different types of bearings according to the design requirements. Rolling bearings can be divided into different types according to the differences in structure, rolling elements and function, and can be divided into radial bearings (radially stressed)/thrust bearings (axially stressed) according to the load bearing aspect or nominal contact angle; spherical bearings/non-spherical bearings according to whether they can be aligned; ball bearings/roller bearings according to the type of rolling elements; single row bearings/double row bearings/multiple row bearings according to the number of rolling elements.

In the typical wind power rolling bearing design, yaw bearings generally choose single row ball bearings, double row ball bearings; variable pitch bearings mostly use double row ball bearings, in recent years there is a trend to replace the ball bearings with roller bearings (overseas to replace 30%, domestic about 15%); spindle bearings according to the power and design of different, in the spherical roller bearings, single row tapered roller bearings, cylindrical roller bearings, double row tapered roller bearings, three rows of cylindrical roller bearings among the choice of the bearing. The bearings used in the low-speed, intermediate and output shafts of the gearbox bearing are different. The low-speed shaft is usually spherical roller bearing, cylindrical roller bearing, tapered roller bearing, etc. The output shaft can also use four-point contact ball bearing as thrust bearing; the generator bearing has more forms of combination, the most common is the combination of deep groove ball bearing and cylindrical roller bearing. The most common form is the combination of deep groove ball bearings and cylindrical roller bearings.

Slippery bearings have a variety of excellent properties to meet the requirements of wind power operating conditions, and self-lubricating bearings also have significant cost advantages. Sliding bearings and rolling bearings have their own advantages and disadvantages in terms of performance indicators. Specifically, rolling bearings have a lower coefficient of friction and higher transmission efficiency (generally 0.08-0.12 for sliding bearings and 0.001-0.005 for rolling bearings). Due to the large contact area, the load carrying capacity, impact resistance and smooth running of sliding bearings are significantly higher than those of sliding bearings, and due to the elimination of rolling elements, the radial dimensions of sliding bearings are smaller and suitable for applications with compact structure requirements. Therefore, the excellent bearing performance and environmental adaptability of sliding bearings are very suitable for wind power, nuclear power and other large equipment. In addition, in the sliding bearing category, the environmental adaptability and motion adaptability of self-lubricating bearings are significantly better than those of fluid-lubricated bearings, and the manufacturing and maintenance costs of self-lubricating bearings have significant advantages due to their simple structure and maintenance-free or low maintenance.

Main shaft bearings: Theoretically, they can all be replaced by plain bearings. In wind turbines, the main shaft system is connected to the gearbox and hub respectively, which plays a fundamental role in supporting the turbine blades and transferring the blade load to the gearbox. About 80% of horizontal axis wind turbines use the spindle support principle, where the spindle needs to withstand axial forces, radial forces and overturning moments at the same time, and therefore needs to have good alignment performance, vibration resistance and operational stability. The spindle support method is divided into “three-point support”, “two-point support” and “one-point support”, of which three-point support is the common arrangement for double-fed models, consisting of The three-point bearing is a common arrangement for double-fed models, consisting of “main shaft bearing + bearing in the gearbox”, which is generally used for smaller MW fans; the two-point bearing is a double-row tapered roller bearing + cylindrical roller bearing”, which is suitable for large MW fans; the one-point bearing is usually a double-row tapered roller bearing + cylindrical roller bearing.

One-point bearing usually uses double-row tapered roller bearings, the advantage is easy to install, but with the increase in bearing diameter, bearing costs will greatly increase, for direct-drive models more than 6MW is difficult to use a single bearing. From the point of view of sliding bearings, anti-vibration performance and operational stability are the advantages of sliding bearings, while there are “spherical plain bearings” and other types of bearings with excellent alignment performance. The possibility of replacing the sliding bearings.

Gearbox bearings: In theory, all low and medium speed gearboxes can be replaced by sliding bearings, while the low and medium speed shafts of high speed gearboxes can be replaced by sliding bearings. In doubly-fed and semi-direct-drive models, due to the small number of pole pairs in the generator, the wind turbine impeller speed is far from the rated speed of the generator, so the gearbox must increase speed to achieve power generation. The working conditions and transmission ratios of different models of gearboxes are different, so the structure varies greatly: 1) doubly-fed models generally adopt a high-speed gearbox with planetary wheel system + parallel shaft drive, and the most widely used is a three-stage drive structure, mainly “one-stage planetary + two-stage parallel shaft” and “two-stage planetary + one-stage parallel shaft”. One-stage planetary two-stage parallel shaft is mostly used for wind turbines of 2MW and below, which is more reliable but also larger in size; two-stage planetary one-stage parallel shaft is mainly used for wind turbines above 2.5MW, which has the advantages of strong bearing capacity, high efficiency of variable speed and small size.

(2) Semi-direct-drive models generally use a low-speed gearbox with one or two stages of transmission, which has a lower transmission than doubly-fed models, but is relatively compact and more reliable. In terms of bearing performance, the low-speed and medium-speed shafts of the gearbox of the double-fed model can use sliding bearings, while the high-speed shaft is not suitable for sliding bearings due to the high speed; for the semi-direct drive model with medium and low-speed gearbox, all the bearings of the gearbox can theoretically use sliding bearings.