Fishplate Damage Types and Repair Methods
- What are the common damage types of fishplates?
Common damages of fishplates include: bolt hole wear, caused by long-term friction between bolts and hole walls leading to enlarged hole diameter; surface cracks, mostly around bolt holes caused by stress concentration; deformation, manifested as uneven fitting surface between fishplate and rail, affecting stress; corrosion, especially in bolt holes and edge parts, which will weaken structural strength; local wear, material loss at the rail head part in contact with the rail due to extrusion and friction.
- How to repair fishplates with worn bolt holes?
For fishplates with small wear (hole diameter enlargement ≤1mm), reaming repair can be used to expand the hole diameter to the next standard size (such as M24 to M25) and use bolts of corresponding size; for large wear, surfacing repair is adopted. Weld the hole wall with electrodes (such as J507) and then re-drill to ensure the hole diameter meets the requirements; after repair, check the perpendicularity of the bolt hole, the deviation should be ≤0.5mm/m to avoid additional stress during installation.
- What are the repair limitations for surface cracks of fishplates?
When the crack length is ≤10mm and does not extend to the edge, repair welding can be used. First, clean the rust and oil at the crack, grind a V-groove with an angle grinder, then weld. After welding, tempering at 200-300℃ is required to eliminate welding stress; fishplates with crack length >10mm or extending to the edge cannot guarantee strength after repair and must be replaced; all repaired fishplates must undergo magnetic particle flaw detection to ensure no residual cracks.
- How to straighten deformed fishplates?
For slightly deformed fishplates (flatness deviation ≤2mm/m), cold straightening can be used. Apply reverse force on the deformed part with a jack to straighten slowly. After straightening, keep warm for 2 hours to eliminate internal stress; for severely deformed fishplates (flatness deviation >2mm/m), hot straightening is adopted. Heat the fishplate to 600-700℃ (dark red), press and straighten with a special mold, and temper at 500-550℃ after cooling to prevent embrittlement; the straightened fishplate needs to recheck the fit with the rail, and the gap should be ≤0.3mm.
- Are severely rusted fishplates suitable for repair?
Fishplates with rust depth <1mm and area <30% can be repaired. First, remove the rust layer with a wire brush and rust remover, then spray anti-rust primer (such as epoxy primer) and topcoat (such as chlorinated rubber paint), with dry film thickness ≥80μm; fishplates with rust depth ≥1mm or area ≥30% should be directly replaced because the cross-section is weakened too much and the strength is insufficient after repair; repaired fishplates should be stored in a dry environment to avoid rapid re-rusting.