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Abstract: The article mainly analyzes the development of self-lubricating joint bearings for key nodes of the spatial self anchored suspension bridge of Hangzhou Jiangdong Bridge.
Keywords: radial joint bearings; Array arrangement of self-lubricating materials; Self anchored suspension bridge
1. Project Background
The Hangzhou Jiangdong Bridge is an important component of the Hangzhou Qiantang River Crossing Project. As a bridge with a novel structure and high construction difficulty on the Qiantang River, the Jiangdong Bridge has the national spatial cable self anchored suspension bridge and prestressed concrete continuous beam combination system as its structural form. The bridge has a unique structure, multiple types of bridges, complex craftsmanship, and high technical difficulty, while requiring the application of a large number of new technologies. Among them, the main navigation hole self anchored suspension bridge has a unique shape and is a three span space cable self anchored suspension bridge. The main span of the suspension bridge is 260 meters, using single column bridge towers, separated steel box stiffening beams, space cables, and no suspension cables on the side spans. This form of suspension bridge is unprecedented in China. The space self anchored suspension bridge requires the suspension cables to adapt to longitudinal and transverse bi-directional deformation during the completion stage, with a large slope of about 2.9:1. The traditional pin joint suspension cables of suspension bridges can only adapt to unidirectional deformation, so this bridge must undergo innovative design and develop new types of suspension ball joints. The main design personnel of the project design unit Shanghai Engineering Design and Research Institute and Shanghai Materials Research Institute have visited our company multiple times for discussions and entrusted our company to develop the joint bearings used in ball joints.
2. Project Implementation Plan
2.1 Preliminary work situation of the project
Through technical exchanges with the main design personnel of Shanghai Engineering Design and Research Institute in the early stage, it is preliminarily envisioned that the upper end of the suspension cable will be connected to the main cable clamp using radial joint bearings, and the lower end will be connected to the steel box girder using angular contact joint bearings. This way, the suspension cable can adapt to both longitudinal and transverse deformation of the bridge. For the engineering requirement of ensuring a service life of 50 years, it is preliminarily determined to use self-lubricating joint bearings and stainless steel materials, and it is determined to conduct full-scale tests on trial production samples first.
2.2 Main content and objectives of project research and development or construction
Characteristics (technical indicators) of pin on type suspension: able to adapt to longitudinal and transverse bi-directional deformation, low friction coefficient of upper and lower joint nodes (fixed index value), and able to adapt to ± 6 ° angle.
2.2.1 Basic project requirements: The bearings of this project must meet the requirements of aging corrosion resistance, self-lubricating, wear resistance, and long service life under harsh working conditions. At the same time, they must have performance such as adjusting deviation, buffering vibration, and no maintenance required. To meet these requirements, the self-lubricating radial joint bearings of the key nodes of the self anchored suspension bridge of Jiangdong Bridge adopt the following structural form:
The outer ring is made of stainless steel 4Cr13, quenched, split into outer rings, and the inner spherical surface is chrome plated. It is fixed with a locking ring, and the outer ring end face is embedded with a sealing ring material made of PTFE; The inner ring is made of stainless steel 4Cr13, and the spherical surface is embedded with uniform solid self-lubricating material. The main technical key points that need to be addressed for this type of bearing are:
(1) Research on the frictional properties of spherical embedded solid self-lubricating materials; (2) Research on the process of embedding solid self-lubricating materials into spherical surfaces; (3) Research on the process performance of PTFE sealing rings; (4) Research on the manufacturing process of the inner and outer rings; (5) Research on the matching technology of inner and outer rings.
2.2.2 The product structure diagram is shown in Figure 1. This type of bearing structure breaks through the limit of the service life of general radial joint bearings with sealing rings, which is 20-30 years, and reaches the requirement of a service life of 50 years; At the same time, it can withstand large radial loads, especially suitable for special working conditions such as high radial loads, small swing angles, self-lubricating, maintenance free, and wear resistance, such as space cable self anchored suspension bridges.
2.2.3 Key technology research content: (1) Product structure design research (maintenance free self-lubricating structure design); (2) Study the friction and wear performance of solid self-lubricating materials under low speed and heavy load; (3) Study the lubrication principle of solid self-lubricating materials with uniform stainless steel inlay; (4) Research on the uniform embedding processing technology of solid self-lubricating materials; (5) Study the processing technology and usage status of PTFE sealing rings; (6) Chromium plating process for stainless steel outer ring spherical surface.
2.2.4 Key technical principles: Dry wear mechanism. When two non lubricated surfaces rub against each other, the uneven peaks on both surfaces are subjected to shear, local adhesion, and plastic deformation, resulting in friction and wear. Traditional lubricants can significantly reduce these effects, however, during pauses, especially under high load conditions, lubricating oil and grease are squeezed out, leaving behind non lubricated bearings that often exhibit high static friction coefficients in the next movement. The solid self-lubricating material embedded in the inner ring of the radial joint bearing will not move under these conditions, so the material will not increase the friction coefficient in subsequent motion. This type of bearing always provides a lubricating film on the surface of the bearing, ensuring low friction and wear. Even under high static load conditions, the solid lubricant film remains on the bearing surface. When wear occurs, more solid lubricant will be released to the bearing surface of the required lubricant.
2.3 Product Innovation Points
Therefore, the innovation of this project's product lies in:
2.3.1 Structural Innovation:
(1) The product of this project adopts stainless steel embedded solid self-lubricating material and spherical chrome plating to replace the original friction pair form of steel to steel or steel to copper. In addition to high load-bearing, impact resistance, wear resistance, and long service life characteristics, it also has maintenance free self-lubricating function, thereby achieving zero failure of key nodes of space self anchored suspension bridges and avoiding environmental pollution caused by original lubrication. Meanwhile, the use of stainless steel inner rings instead of copper inner rings can significantly save copper materials, improve the overall strength of the inner rings, and achieve sustainable innovative development.
(2) PTFE sealing ring is used to replace the traditional graphite nylon or polyurethane sealing ring, so that the service life of the sealing ring is increased to 50 years, and the operating temperature is expanded from -30 ℃~130 ℃ to -50 ℃~200 ℃, greatly enhancing the anti-aging and corrosion resistance characteristics.
2.3.2 Technological Innovation:
(1) The machining of uniformly embedded solid self-lubricating materials on the inner ring spherical surface is currently a difficult problem in the machining of domestic joint bearings. Our company has basically overcome this problem and specially designed and equipped such specialized machine tools; This technology can exponentially improve the machining specifications and capabilities of uniformly embedded solid self-lubricating materials on the inner ring spherical surface.
(2) A self-lubricating material with a coverage rate of Z% can effectively reduce wear, friction, and prevent bite, and significantly improve the service life of bearings during operation. It can gradually distribute the solid lubricant to the friction surface to achieve the effect of small friction coefficient and good wear resistance under oil-free condition by generating heat through friction. In terms of uniform array layout: all mounting holes are arranged in a cross pattern along the direction of motion, and the distance between the holes in the axial or radial direction (based on the direction of motion) should be kept in a close proportion to ensure that lubrication covers the entire sliding direction, forming a complete solid lubrication film.
Due to the use of PTFE sealing rings in this project, it is difficult to accurately process and control the spherical interference, in order to achieve the sealing effect inside the bearing;
2.4 Comparison of product technical performance with similar domestic and foreign products
There are currently no similar product manufacturers domestically or internationally, so the products of this project have originality both domestically and internationally. The progressiveness of its product technical performance is reflected in:
2.4.1 progressiveness of the product: the product of this project needs to pass the comprehensive performance assessment test of the upper and lower joints of the sling under fatigue load and the 1 million swing test of the upper and lower joints of the sling and other system tests of Shanghai Materials Research Institute, and the overall performance can reach the domestic leading level.
2.4.2 Structural progressiveness: the product of this project has maintenance free progressiveness due to its self-lubricating structure. At the same time, it saves copper resources and achieves sustainable development.
2.4.3 Process progressiveness: the processing technology of evenly inlaying solid self-lubricating materials on the spherical surface of the inner ring and the control technology of PTFE sealing ring adopted by the project products are at the leading and advanced level in China.
3. Project maturity level
(1) The self-lubricating joint bearing of the key node of the space self anchored suspension bridge has passed the pilot test and formed a small-scale production process technology. The research and application of solid self-lubricating materials and PTFE sealing ring control technology have been successful, making the bearing not only have high strength and wear resistance, but also high impact resistance, ensuring that the joint bearing can still be intact and undamaged under large radial and axial combined loads, Compared with the original bearings, it saves a lot of non-ferrous metals and solves the installation and maintenance problems of bearings.
(2) The product of this project has been appraised by the company's technical appraisal committee and has originality both domestically and internationally. Due to our strong R&D team, complete production equipment, process tooling, and testing methods, we have established a quality and environmental system in accordance with ISO/TS16949 and ISO14001, which can meet the requirements of mass production and product quality and environmental protection. The product quality is stable and reliable; The product of this project has been tested by the Shanghai Materials Research Institute and its performance indicators have been recognized. At the same time, the company has always been guided by value engineering in the process of transforming technical achievements, striving to improve the cost-effectiveness of the product and receiving unanimous praise from users.
(3) Intellectual property situation of core technology: The core technology of this project is independently developed and mastered by the company. For the self-lubricating joint bearings of key nodes in space self anchored suspension bridges, the company has applied for relevant patent technology protection. Due to the company's leading position and advanced level in joint bearing technology in China, one of the main research projects of the doctoral program at the company's postdoctoral workstation is the research and development of solid self-lubricating materials, which has a strong ability for continuous innovation and improvement. Therefore, it can meet the diverse needs of users in different usage scenarios, making our project bearings always at a high level in the same industry in China, And strive to surpass advanced levels.
4. Achievements
The prototype has been completed and passed the performance assessment test of the upper and lower nodes of the suspension cable under fatigue load and one million swing tests of the upper and lower nodes of the suspension cable at the Shanghai Institute of Materials Research; The service life of PTFE sealing rings can meet the requirement of 50 years; The operating temperature of the bearing reaches and meets the requirements of -50 ℃~200 ℃.
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2024-01-12