Key points for selecting fishplates (joint clamps)
ⅠWhat is the core difference between insulated fishplates and ordinary fishplates?
Insulated fishplates embed insulating gaskets (e.g., phenolic resin plates) between the and rail, with insulation resistance ≥1MΩ, used in automatic block sections to prevent track circuit short circuits. Their bolt holes are insulated (nylon sleeves + rubber washers), and materials are mostly QT450 ductile iron (ordinary fishplates use Q235B steel). Avoid gasket damage during installation, as it can cause signal false alarms.
ⅡWhy do African customers often require Dacromet treatment for fishplates?
Dacromet (zinc-chromium coating) offers salt spray corrosion resistance exceeding 1,000 hours, suitable for Africa's hot and humid climate. Thinner (6-8μm) than hot-dip galvanizing, it has no hydrogen embrittlement and withstands 200℃. However, its surface hardness is low (HV≤200), so avoid scratches during handling, which can initiate corrosion.
Ⅲ What problems can "bolt hole misalignment" in fishplates cause?
Hole pitch deviations over ±1mm can prevent bolt insertion or create additional stress when forced. A batch of exported fishplates with loose hole pitch tolerance (+1.5mm) required on-site reaming, incurring $50,000 extra labor costs. Use CNC drilling machines to control hole pitch within ±0.5mm and inspect each piece with a gauge.
Ⅳ How to determine if a fishplate's "fitness" is (qualified)?
Place the fishplate on the rail joint and check the contact surface with a 0.3mm feeler gauge, with insertion depth ≤15mm. Poor fit reduces joint resistance, causing "clanking" noises when trains pass and accelerating bolt loosening. In one case, 30% of fishplates failed fitness tests due to un-machined bottom surfaces, increasing rework costs by 12%.
ⅤHow to set the "pre-tightening torque" for fishplate bolts?
For 60kg/m rail fishplates, M24 bolts require 400-500N・m to ensure joint resistance ≥100kN. Under-tightening causes 夹板 displacement; over-tightening may break bolts (M24 yield strength ≥600MPa). Use torque-sensitive wrenches, tightening in two steps: first to 50% torque, then to standard, and mark with anti-loosening paint lines.