Fishplate Radius Compatibility Requirements with Rail Head Jaw
How does a larger or smaller fish plate arc radius change its contact state with the rail head jaw?
When the arc radius is too small, the arc surface of the fish plate cannot fully fit the rail jaw, forming an "concave" gap, and the contact state changes from surface contact to line contact at upper and lower points, reducing the contact area by more than 80%. When the arc radius is too large, the fish plate can only contact the middle of the rail jaw, forming a "convex" single-point contact, with the contact area less than 10% of the normal state. Both deviations will cause a sharp increase in contact stress, far exceeding the material's allowable contact stress, laying hidden dangers for early cracking of the fish plate.
What is the core difference in the arc radius of fish plates matched with 60kg/m and 50kg/m rails?
The core difference stems from the different rail head cross-sectional sizes of the two types of rails. The arc radius of the jaw of the 60kg/m rail head is about 80mm, and the arc radius of the matched fish plate needs to be designed as 79.5-80mm to ensure a slight interference fit. The arc radius of the jaw of the 50kg/m rail head is about 60mm, and the arc radius of the matched fish plate is 59.5-60mm. This size difference is absolute; if a fish plate for 60kg/m rail is used for 50kg/m rail, severe point contact will occur, and vice versa, a large area of gap will appear, both of which cannot meet the joint force transmission requirements.
What impact does insufficient machining accuracy of the fish plate arc radius have on the dynamic smoothness of the rail joint?
Poor contact caused by insufficient arc radius accuracy will cause slight relative jumping of the rail joint under train loads. This jumping will be converted into dynamic impact loads, increasing the vertical acceleration of the wheel-rail in the joint area by more than 30% and deteriorating the dynamic smoothness of the line. After long-term service, the jumping will exacerbate the wear and deformation of the rail joint, making the vertical deviation of the rail surface at the joint quickly exceed the limit, becoming a "weak section" of the line. At the same time, dynamic impact will be transmitted to the sleepers and ballast, accelerating ballast consolidation and sleeper cracking, and increasing track maintenance costs.
What special considerations are there in the arc radius design of fish plates matched with international standard rails (such as UIC60, ASTM 136)?
The rail head jaw design of international standard rails pays more attention to streamlined transition, and its arc radius is usually larger and composed of multiple arc segments. The jaw of the UIC60 rail head adopts a double-arc design, and the matched fish plate also needs to adopt a corresponding double-arc structure instead of a single arc to ensure full fit. The arc radius of the jaw of ASTM 136 rail has slight changes with the rail length, and the matched fish plate needs to adopt an "adaptive" arc design to ensure the fit at different positions through precision machining. In addition, the arc surface of international standard fish plates is mostly hardened to improve the wear resistance of the contact area, matching the high load requirements of international standard rails.
How to quickly verify the adaptability of the fish plate arc radius to the rail on site?
The most intuitive method is the "prussian blue method": evenly apply a thin layer of prussian blue on the arc surface of the fish plate, fit it with the rail and press lightly, then remove it to observe the transfer of prussian blue. If the prussian blue covers more than 80% of the arc surface evenly, the adaptability is good; if the prussian blue marks only appear locally, the arc radius deviation exceeds the limit. A feeler gauge can also be used to measure the gap between the fish plate and the rail jaw; if the maximum gap exceeds 0.3mm and the distribution is uneven, the adaptability can be judged as unqualified, and the fish plate of the corresponding model must be replaced.