The wheel-set axle box composition of rail transit vehicle is the core component of the high-performance bogie of rail transit vehicle, and many parts are bolted together during assembly, and the effect of bolt connection after assembly depends on the preload force achieved.
According to the bolt development and design process, the preload is composed of four parts: the minimum clamping load, the working load, the pre-added loss load caused by embedding and the temperature load.
Rail transit vehicles are subjected to complex, high-frequency, and high-amplitude impact loads during operation. As a result, the working load can adversely affect the breakage and loosening of the bolted joint.
Rail transit vehicles operate in the vast territory of China, and the obvious changes in ambient temperature and the temperature changes caused by the work of some structures will have a negative impact on the reliable operation of bolts.
01. Selection of bolt fasteners
The bolts in the design of rail transit vehicles should meet the requirements of GB T30981-2010、gb/t3098.2-2015、gb/t3098.Bolts and nuts made of steel or stainless steel according to 23-2020, ISO 898-1 and EN 20898-2 or EN ISO 3506-1 and EN ISO 3506-2.
Choose to execute TB T32461-2019 "Design Code for Bolted Joints of Locomotives and Rolling Stock Part 1: Classification of Bolted Joints", TB T32462-2019 "Design Code for Bolted Joints in Locomotive and Rolling Stock Part 2: Design for Mechanical Applications" and TB T32466-2019 "Design Guidelines for Bolted Connections of Locomotives and Rolling Stock Part 6: Connection Dimensions".
The bogie part comprises a frame, a wheelset, suspension, traction and braking system, and the main specifications of the connecting bolts are coarse teeth M12, M16, M20, M24, M30 and M36, and a small part of them are fine-tooth bolts.
According to the position of the bolt, the stress condition of the bolt is analyzed, and the appropriate strength grade is designed, which is mainly 8Level 8 and 10Level 9, for 12Grade 9 intensity is not used as much as possible, 12Grade 9 strength bolts are susceptible to delayed failure caused by hydrogen embrittlement.
Due to the large number of fasteners, in order to minimize the types of their use, the design stipulates that the use of hexagon head bolts, flat washers, double-stacked self-locking washers and hexagon nuts to cooperate with the components is the most basic installation method.
Screws will briefly introduce the design and progress of fastener anti-loosening.
02. Bolt anti-loosening design
1. Risk factors of bolted parts.
The load definition of static strength and fatigue strength of rail transit vehicles is according to TB T32461-2019 standard, the load of the bolted joint can be calculated by means of a limited FEM according to TB T32466-2019 Pre-selected dimensions for bolted joints. First of all, the risk level is defined according to the position of the bolted connection of the component, the size of the load and whether it affects the driving safety. tb/t3246.The 1-2019 standard classifies the risk level as high, medium, and low;Bolted joints, which are defined as high-risk levels, i.e. direct or indirect physical and life-threatening and/or operational hazards arising from the failure of bolted joints, must be stated in the drawings to ensure that the preload torque and its tolerances as well as post-tightening inspections are strictly controlled during the bolt tightening process.
For the function of bolting, TB T32462-2019 requires that a certain preload fm must be present. The preload can improve the reliability, anti-loosening ability and fatigue strength of the bolt joint, and enhance the tightness and rigidity of the connection. Generally, the torque method is used in the production and implementation of bolt connections, that is, a fixed torque wrench is used to control the torque of the bolt during assembly, so the elongation of the bolt must be within the elastic limit.
2. The method of bolt tightening.
The essence of bolt tightening is to control the preload of the threaded connection, and in order to ensure the quality of the assembly, the tightening state of the threaded pair must be controlled to avoid the combination of the bolt and the connected part and produce slippage or gap, which leads to the failure of the threaded pair.
Nowadays, there are four main methods used to control thread tightening: torque method, angle method, yield point method, and bolt elongation method. Depending on the bolt tightening assembly process, the preload is generated by the applied torque. The preload is affected by many complex factors such as lubrication of the contact surface, roughness of the contact surface, material of construction, thread shape and tolerance, tightening method and tightening tool.
Therefore, most of the current bolt tightening cannot directly monitor the bolt preload.
3. Bolt tightening characteristics.
There are various forms of bolt assemblies for the connection of the constituent parts of the wheel-to-axle box of rail transit vehicles, and the tightening of the bolt assemblies has the following characteristics: 1) The tightening control method is inconsistent.
The bolts of the parts with high connection reliability requirements are designed to be assembled using the angle control torque monitoring tightening control method, and the other part of the bolt assembly is designed to be tightened by the torque method.
2) There is a limit to the tightening work space.
The bogie component structure size is large, the mass is large, the assembly of the parts must be carried out in the appropriate working space, and the small working space of some parts must have higher requirements for the skills of the operator.
3) Tightening reliability is affected by many factors, bolt tightening reliability is affected by many factors such as the surface roughness of bolts and connected parts, the material of bolts and connected parts, and the lubrication of bolts, which has an adverse effect on tightening reliability.
4) Tightening importance high riskAccording to the normative tightening standard for the composition of wheelset bogies of rail transit vehicles, the bolt tightening level for component connection is a high-risk level, and the bolt tightening must be managed and controlled. 03. Anti-loosening design measures and progress
1. Establish a connector inspection and inspection plan.
According to the requirements of bolt tightening operation combined with the assembly of bogies of rail transit vehicles, the inspection and inspection plan mainly includes the following aspects: :
1) Bolts and other components should be inspected by incoming materials, including verification certificate, verification performance inspection certificate, sampling appearance and geometric dimensions to meet the requirements.
2) For bolts and other components involved in high-risk level connections, they need to be re-tested for mechanical properties and chemical composition in accordance with the technical documentation.
3) Bolts should be inspected before assembly, bolts with high importance level have clear and standardized batch information that can be recorded and traced, the bolts have no defects such as bumps, scratches and rust, and there are no defects such as oil, impurities and bumps in the matched parts of the connected parts.
4) After the bolt is tightened, the bolt head should expose the nut end face 2 3 pitches, and the bolt should be marked with a clear and standardized anti-loosening mark after tightening.
2. Adopt advanced tightening tools and equipment.
Bolt tightening tools and equipment have a great impact on the assembly quality and assembly efficiency of bolts, and the general enterprise selection from the quality, safety, efficiency and cost of four aspects of comprehensive consideration.
At present, the fixed torque tools on the market mainly include preset torque wrenches, hand-held electric sensor torque wrenches and fixed station electric sensor tightening shafts.
Among them, the tightening accuracy of the preset torque wrench is low, and there is generally no tightening data storage. Motorized transducer torque wrenches are the most advanced and reliable tightening tools available.
1) High tightening precision, stable performance, and less maintenance batches.
The tightening torque, angle and curve of the product can be stored and traced according to the product serial number, which is helpful for the analysis and improvement of product tightening quality.
2) A variety of tightening control strategies such as torque control, torque control angle monitoring and angle control torque monitoring can be adopted to realize real-time collection and judgment of tightening process curves.
For the quality problems in the bolt tightening process, such as stick-slip, jamming, thread damage, error-proofing, etc., it can be effectively monitored and fed back to the operator.
3. Adopt a scientific tightening strategy.
The tightening strategy of the bolt specifically involves the tightening control method, process parameters, etc., and the tightening strategy has an important impact on the preload of the bolt connection. According to the bolt performance quality level and connection risk level of the bolt, the assembly tightening control strategy designed for the assembly of the wheelset bogie assembly of rail transit vehicles is generally the torque method and the angle control torque monitoring method.
Comparison of the following three tightening processes (reference).
3.1 Torque method.
The torque method is based on the linear relationship between the tightening torque and the bolt preload when the bolt is deformed in the elastic area, generally 50% is consumed by the friction of the bolt head and the workpiece bearing surface, 40% is the friction consumption between the thread pair, and only about 10% of the tightening torque is converted into the preload of the bolt, which is not conducive to obtaining a more concentrated and consistent bolt preload.
Therefore, the tightening control strategy of the torque method should be used to comprehensively consider the size of the tightening torque, the tightening tool, the tightening strategy procedure and the risk level of the bolt connection.
1) Torque control step-by-step tightening.
The torque-controlled step-by-step tightening strategy refers to the target torque required by the process when the bolt is tightened in a single step, two or three steps.
In the actual tightening process, the general target torque is small and single-step tightening is adopted, the target torque is large, and the operator uses the manual tightening tool to adopt two-step tightening, and the target torque is large, and the automatic control tightening tool is used to tighten in three steps at the same time.
2) Torque control angle monitoring.
Torque control angle monitoring tightening strategy refers to controlling the tightening torque to reach the target value during the bolt tightening process, and monitoring the tightening angle to be within the set range, and the tightening angle is generally measured from the torque reaching the set tightening torque value.
This tightening strategy monitors for non-rejects such as missed screwing and seizure when bolts designed to be assembled using the torque method are tightened with a hand-held motorized sensor torque wrench.
3) Torque control, angle and gradient monitoring.
Torque control angle and gradient monitoring tightening strategy, refers to the control of tightening torque to reach the target value in the bolt tightening process, while monitoring the tightening angle and tightening gradient within the set range, tightening angle and tightening gradient generally from the torque to the set tightening torque value to start measurement, tightening the tightening strategy for the use of automatic tightening equipment for multi-axis tightening, can effectively monitor the bolt intermediate tightening process caused by the sleeve and bolt not effectively meshing the tightening tool idle problem.
3.2 Angle control torque monitoring method.
The angle control torque monitoring method is based on the bolt tightening and fitting, in the elastic area, the bolt preload force is proportional to the bolt elongation, and the elongation of the bolt is proportional to the rotation angle, the rotation angle in the tightening process is measured, and the following tightening measures are generally adopted according to the tightening tool tightening strategy program and the risk level of the bolt connection.
1) Rotation control torque monitoring method.
Angle control torque monitoring tightening strategy refers to controlling the tightening angle to reach the target value during the bolt tightening process, and monitoring the tightening torque within the set range, and the tightening angle is generally measured from the torque reaching the set tightening torque value.
This tightening strategy is widely used in bolt tightening operations with high importance levels, and most of the hand-held electric sensor torque wrenches and fixed electric tightening shafts have this tightening strategy, which has a significant effect on the preload of bolts after tightening.
2) Rotation control torque and gradient monitoring method.
Angle control torque and gradient monitoring tightening strategy refers to controlling the tightening angle to reach the target value during the bolt tightening process, while monitoring the tightening torque and tightening gradient within the set range, and optimizing the bolt tightening process parameters.
It mainly includes the following four aspects of monitoring and management:
1) Tighten the results of qualified management.
The tightening results of bolts are used as the direct basis for reliable tightening of bolts, and scientific and effective qualified management must be carried out. Generally, the torque, angle data and tightening curve of bolt tightening can rely on the tightening tool itself and the supporting tightening result management system to establish an automatic qualification judgment system, and monitor and manage the stick-slip, jamming, thread damage, part compression, wrong parts, sleeve detachment, torque out-of-tolerance and angle out-of-tolerance and other problems that occur in bolt tightening by using appropriate tightening strategies.
2) Stable management of tightening process.
According to the study, the operator, the tightening tool, the assembly method and the material of the connection and the connected part have a major impact on the quality of the threaded connection.
Rail transit vehicle bogie composition assembly workers after bolt tightening basic knowledge and product tightening skills training, enterprises use tightening tools with high tightening precision, stable performance, assembly methods need to be designed and calculated and batch verification before it can be implemented, bolts and connected parts adopt strict manufacturing process, its performance consistency is good, generally can ensure the quality of threaded connection.
However, in the long-term and long-lasting production process of the product, the stability of the tightening process also plays a very important role in the reliability of the threaded connection, if the tightening process is unstable, it will lead to unstable tightening quality output and affect the reliability of the product, so it is necessary to monitor and manage the stability of the tightening process.
The stability management of the tightening process generally relies on the tightening management system or other third-party software supporting the tightening tool to control the tightening data statistically.
3) Full life cycle management.
The bolted connection for the assembly of the wheelset bogie of rail transit vehicles is a high-risk level, and all tightening data needs to be stored until the end of the relevant component life according to customer requirements. At the same time, by analyzing the bolt tightening data of related components, it can also guide the optimization of the bolt tightening process. In the subsequent development of similar products, the bolt selection and design of the product can be guided through tightening data analysis.
4) Artificial intelligence tightening curve judgment system.
Because the bolt tightening curve has an important reference role for the bolt tightening quality, due to the complexity of the thread tightening fit, the bolt tightening curve morphology of the same assembly part presents complexity and diversity.
It is difficult to judge the shape of the tightening curve by the existing bolt tightening curve judgment system supporting the tightening tool, and an artificial intelligence Xi system can be established to judge the tightening curve shape.
04. Screw Jun's experience and summary
With the development of the economy, the speed of urbanization is accelerating, and the demand for urban rail transit is increasing.
The reliable bolt connection of rail transit vehicles ensures the safe operation of the train, adopts the new standard of TB T3246-2019, adopts the selection, design and anti-loosening of bolts, adopts scientific and reasonable bolt tightening strategy, and cooperates with the advanced and effective bolt tightening management and monitoring system, which will effectively improve the timeliness, accuracy and scientificity of bolt tightening quality assessment, and look forward to technological breakthroughs to solve the problems in development and make new and greater contributions to the realization of a transportation power.
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