Key Technologies and Application Key Points for Fastening Systems
- How to select the strength grade of bolts in the fastening system, and what is the relationship with track types and loads?
For ordinary railways (speed ≤120km/h), 8.8 - grade bolts are generally selected. Their tensile strength is 800MPa and yield strength is 640MPa, which can withstand the loads of ordinary trains. For high - speed railways (speed ≥250km/h), due to the high speed and large vibration of trains, 10.9 - grade or higher - grade bolts are mostly used. The tensile strength of 10.9 - grade bolts is 1000MPa and yield strength is 900MPa, meeting the needs of high - speed operation. For heavy - haul railways (axle load ≥25t), which need to bear huge loads, 12.9 - grade bolts are selected. Their tensile strength is 1200MPa and yield strength is 1080MPa, ensuring the stability of the track structure.
- The anti - loosening performance of nuts is crucial to the fastening system. What are the common types of anti - loosening nuts and what are their principles?
Common anti - loosening nuts include nylon - locked nuts. A nylon ring is embedded in the nut. When tightened, the nylon ring closely fits the bolt thread to generate friction for anti - loosening. There are also flange - faced nuts, which increase the contact area between the nut and the connected part, disperse the pressure, and improve the anti - loosening effect. In addition, there are slotted nuts with split pins for anti - loosening. After the nut is slotted, a split pin is inserted to prevent the nut from rotating, which is suitable for environments with large vibrations and ensures the long - term stability of the fastening system.
- What role do washers play in the fastening system, and what are the differences in the application scenarios of different types of washers (flat washers, spring washers, etc.)?
Flat washers can increase the contact area between the nut and the connected part, disperse the pressure, and protect the surface of the connected part to prevent scratching when tightening the nut. They are suitable for general fastening scenarios. Spring washers use the reaction force generated by their own elastic deformation for anti - loosening and are used in parts with vibration but relatively small vibration. Wave washers can provide a large elastic deformation amount and are suitable for occasions where a large pre - tightening force is required and there is a certain vibration. Different washers are reasonably selected according to actual needs to improve the performance of the fastening system.
- During the installation of the fastening system, how to ensure that the tightening torque of bolts meets the requirements, and what are the detection methods?
During installation, a torque wrench is used to set the tightening torque value according to the design requirements. For example, when M24 bolts are used for ordinary railways, the torque is controlled at 300 - 350N·m. Detection methods include the torque method, directly using a torque wrench to detect whether the tightening torque meets the standard; and the marking method, making a mark at the connection between the bolt and the nut and regularly checking the position of the mark to determine whether the nut is loose, ensuring the installation quality of the fastening system.
- During long - term use, what problems will the fastening system face, and how to carry out maintenance and replacement?
During long - term use, problems such as bolt loosening, nut thread stripping, and washer damage may occur. During maintenance, regularly check the tightening torque and retighten the loose bolts with a torque wrench. Replace the stripped nuts and damaged washers in a timely manner. When replacing, select components of the same specification and model and operate according to the standard installation process to ensure the normal operation of the fastening system and maintain the stability of the track structure.