Fishplate and Fishbolt Matching and Installation Specifications
What are the key points of structural matching between fishplates and fish bolts?
The tail of the fish bolt is designed with an elliptical protrusion, which needs to be accurately matched with the elliptical hole on the fishplate to prevent the bolt from rotating during tightening. The diameter and length of the bolt must match the thickness of the fishplate and the specification of the rail. For example, bolts of Φ24×135 specification are usually suitable for thick fishplates and heavy rail connections. The thread accuracy must meet the standard, and the bolt with half-thread design must ensure the effective engagement length to ensure the connection strength. The hole diameter tolerance of the fishplate should be controlled within ±0.1mm to avoid bolt shaking caused by excessive hole diameter or installation difficulty caused by too small hole diameter. In addition, the curvature of the contact surface between the fishplate and the rail must be consistent with the curvature of the rail base to ensure tight fit and uniform clamping with the bolt.
What are the correct installation sequence and operation steps of fish bolts?
Before installation, it is necessary to clean the connecting holes of the fishplate and the rail, remove internal debris, rust and oil to ensure that the bolt can be smoothly inserted and the contact is good. Apply lubricating oil to the contact part between the fishplate and the rail and the surface of the bolt, which can not only reduce installation resistance but also play a rust-proof role. When inserting the bolt, align the elliptical protrusion at the tail of the bolt with the elliptical hole of the fishplate. For four-hole fishplates, insert the middle two holes first, then the two sides, and the nuts should be arranged alternately inside and outside. When tightening the bolt, use a special wrench with a length of about 55 cm, and avoid using overlong tools or two people operating at the same time to cause excessive force. The tightening sequence is to first tighten the middle bolts, then the two sides, and finally retighten the middle bolts to ensure uniform force on the fishplate and avoid local stress concentration.
What are the key requirements for controlling the tightening torque of fish bolts?
The tightening torque of fish bolts should be moderate. Too loose will lead to unstable joint connection, vibration during train operation, and possible loosening and falling off of bolts in the long term; too tight will cause plastic deformation of bolts and fishplates, affect service life, and even lead to thread damage. The tightening torque of fish bolts for ordinary lines is usually controlled at 300-400N·m, and for heavy-haul lines, it needs to be increased to 450-550N·m. The specific value should be determined according to the bolt material and specification. A torque wrench should be used for control during tightening to ensure that the tightening torque of each bolt is consistent and avoid uneven force. After installation, check the height of the bolt head above the rail platform, which is usually controlled at 1-6 mm. Too high or too low will affect the connection effect. During long-term operation, regular retightening is required to make up for the torque loss caused by vibration.
What are the differences in material requirements for fish bolts in different line types?
For fish bolts of ordinary branch railways and yard lines, the material can be Q235 steel or 45# steel. These materials can meet the requirements of light to medium loads and medium and low-speed operation, with relatively low cost. Fish bolts for conventional mainline railways need to be made of 20 manganese titanium boron steel, whose strength and toughness are better than ordinary steel, and can resist large vibration and impact loads, adapting to operating speeds below 200km/h. High-speed railways and heavy-haul railways have the highest material requirements for fish bolts, which need to be made of high-strength alloy steel such as 35CrMoA, with a tensile strength of ≥1080MPa and a yield strength of ≥930MPa, which can meet the long-term stable operation under high-speed and heavy-haul conditions. In corrosive environments such as coastal and chemical park lines, regardless of the line type, fish bolts made of galvanized or stainless steel should be selected to enhance corrosion resistance.
What are the key points of regular maintenance for fishplates and fish bolts?
Regularly check the tightening status of fish bolts, use a torque wrench to detect the tightening torque, and retighten in time if it is lower than 80% of the standard value to prevent loosening. Check whether there is rust, wear or cracks on the surface of fishplates and bolts. Those with severe rust need to be derusted, and those with excessive wear need to be replaced in time. Observe the displacement of the rail joint. If there is an abnormal gap or step, it may be caused by fishplate deformation or bolt failure, and disassembly inspection is required. For heavy-haul and high-speed lines, the joint connection quality should be sampled and inspected every quarter, and a comprehensive inspection should be carried out every year; for ordinary lines, sampling inspection can be carried out every six months, and comprehensive inspection every two years. If the bolt is difficult to disassemble during maintenance, violent knocking is strictly prohibited. Special loosening agent can be applied to assist disassembly to avoid damaging the thread and fishplate.