Fishplate Connection Reliability and Maintenance
- What are the structural types of fishplates, and what are the application scenarios of different structures?
Fishplates are mainly divided into ordinary fishplates, special-shaped fishplates, and insulated fishplates. Ordinary fishplates have a symmetrical structure with evenly distributed bolt holes, suitable for rail connections in straight sections. For example, ordinary fishplates matching 60kg/m rails are easy to install; special-shaped fishplates are designed according to the rail section, with one side adapting to standard rails and the other to switch rails, suitable for rail joints in turnout areas to ensure smooth transition of the track; insulated fishplates use insulating materials (such as glass fiber reinforced plastic) or add insulating layers in metal fishplates, used in track circuit sections to prevent current leakage and ensure normal operation of the signal system, suitable for electrified railways.
- How to determine the number and diameter of bolt holes in fishplates, and what is the relationship with rail specifications?
The number and diameter of bolt holes in fishplates must strictly match the rail specifications. Fishplates matching 43kg/m rails have 4 bolt holes per end with a diameter of 24mm; fishplates for 50kg/m and 60kg/m rails have 4-6 bolt holes per end with a diameter of 26mm; fishplates for 75kg/m heavy-haul rails have 6 bolt holes per end with a diameter of 28mm. The number of bolt holes increases with the increase of rail weight, and the diameter increases accordingly. This is because heavier rails need to bear greater loads, and more bolts and larger diameters can disperse stress, ensure the connection strength of the joint, and avoid cracking of bolt holes due to stress concentration. For example, 75kg/m rails are used in heavy-haul railways with an axle load of more than 30t, and the design of 6 bolts can evenly transmit the load and reduce the stress burden of a single bolt.
- What is the standard for reserved rail gaps when installing fishplates, and why is it important?
The reserved rail gaps when installing fishplates need to be adjusted according to the ambient temperature: for ordinary railways, the gap is ≥10mm in summer and ≤18mm in winter; for seamless track sections, the gap is ≤6mm; for alpine regions, the gap is ≤15mm in winter. The core function of reserved gaps is to compensate for the thermal expansion and contraction of the rail: when the temperature rises, the rail expands, and the gap can absorb the deformation to avoid excessive stress and rail buckling; when the temperature drops, the rail contracts, and the gap can prevent the rail from being pulled apart. If the gap is too small, the rail is easy to be "locked" in high temperature, leading to track arching and affecting driving safety; if the gap is too large, the train will produce greater impact when passing, increasing the wear of fishplates and bolts, while increasing noise and vibration, shortening the service life of components.
- What are the common damage forms of fishplates, and how to detect them?
Common damages of fishplates include bolt hole cracks, wear at the rail head contact part, surface corrosion, and overall deformation. Bolt hole cracks mostly extend from the edge of the hole to both ends, which can be found by visual inspection combined with magnetic particle testing. Magnetic particle testing can detect tiny cracks (≥0.2mm) that are difficult to see with the naked eye; the wear of the rail head contact part can be measured with a vernier caliper, and the fishplate needs to be replaced if the wear exceeds 3mm; surface corrosion can be observed by appearance, and rust removal is required if the corrosion area exceeds 20%; overall deformation needs to be detected with a straightedge for flatness, and a deviation of more than 1mm/m is unqualified. For example, on busy freight lines, the contact part of fishplates wears quickly due to long-term bearing of wheel impact force, so special wear detection is required every quarter.
- How to extend the service life of fishplates through maintenance?
Extending the service life of fishplates requires efforts from installation, daily maintenance, and regular maintenance: during installation, ensure that the bolts are tightened according to the standard torque (such as 300-350N·m for 60kg/m fishplate bolts) to avoid looseness or over-tightening; in daily inspections, timely clean the debris at the contact part between the fishplate and the rail to prevent wear by foreign objects; derust and paint the fishplates every six months, and galvanizing or Dacromet coating can be used in coastal areas to enhance corrosion resistance; retighten the bolts once a year to prevent loosening due to vibration; for fishplates with severe wear, surfacing repair technology can be used to restore the flatness of the contact surface, but the surfacing thickness shall not exceed 2mm to avoid affecting the overall strength. In addition, installing wear-resistant gaskets on the outer fishplates of curve sections can reduce the wear rate and extend the service life by 3-5 years.