Fishplate and Bolt Connection Matching and Reliability Assurance
Why is it necessary to match the material selection of fish plates and bolts?
Fish plates are mostly made of alloy steel treated by quenching and tempering, with a hardness controlled between HB220-260, having both strength and toughness. Bolt materials need to be selected according to the strength of fish plates; Grade 8.8 or 10.9 high-strength bolts are common choices. Material mismatch will lead to uneven force distribution, either the bolts break first or the fish plates are damaged prematurely. High-strength fish plates need to be matched with high-strength bolts of the same grade to exert the overall connection effect. Material matching is the basic premise to ensure connection strength.
What impact does the positional accuracy of the bolt holes in fish plates have on the connection effect?
The positional deviation of the bolt holes in fish plates must be controlled within ±0.3mm to ensure accurate alignment with the rail bolt holes. Excessive positional deviation will make bolt installation difficult or even impossible. Even if installed reluctantly, the bolts will bear additional shear force, reducing connection reliability. High-precision bolt holes can ensure uniform force bearing and avoid local stress concentration. Positional accuracy is a key guarantee for the smooth connection between fish plates and rails.
What is the significance of controlling the torque coefficient of bolts for connection reliability?
The torque coefficient of bolts needs to be controlled between 0.12-0.18 to ensure that the tightening torque is converted into effective preload. Excessively large torque coefficient increases the required tightening torque, which is likely to cause bolt overload; excessively small torque coefficient results in insufficient preload, which is prone to loosening. Unstable torque coefficient will lead to large differences in preload among bolts of the same batch, affecting connection consistency. The torque coefficient can be stabilized by strictly controlling thread processing accuracy and surface treatment processes. Appropriate torque coefficient is the core to ensure firm bolt connection.
What are the requirements for the contact surface flatness of fish plates? Why is it important?
The contact surface flatness error of fish plates must be ≤0.2mm to ensure tight fit with the rail contact surface. Insufficient flatness will reduce the contact area, concentrating pressure in local areas. Under long-term operation, local high pressure will cause deformation of the rail or fish plate, affecting connection stability. High-precision contact surfaces can make load transfer evenly and reduce fatigue damage. Contact surface flatness is an important factor to ensure uniform force transfer.
How to test the reliability of the connection between fish plates and bolts?
Finished fish plates need to undergo ultrasonic flaw detection to check for internal defects such as cracks and ensure the material is intact. Bolts need to be tested for tensile strength and torque coefficient to meet the corresponding grade standards. After assembly, it is necessary to check whether the bolt preload meets the standard to ensure a firm connection. During regular operation and maintenance, it is necessary to detect whether the bolts are loose and whether the fish plates are deformed or cracked. Multi-link detection can fully guarantee the reliability and safety of the connection.