Fastening Requirements on Heavy Steel Rail Track
Heavy steel rail systems carry higher axle loads and greater cumulative tonnage than light or industrial track, so every component between the rail foot and the sleeper is loaded harder and must be matched to the rail section. A heavy rail fastening assembly is made up of four working groups: joint bars that connect rail ends, clips that hold the rail down, bolts and nuts that close the joint, and elastic pads that sit between rail and sleeper. Each group has its own material options and inspection points, and a single failed component can interrupt traffic, so the four groups are treated as one system rather than as separate consumables.
Fish Plates and Rail Joint Bars
Fish plates, also called rail joint bars, connect the ends of two rails and distribute the wheel load across the joint so that the track stays stable. For P50 rails, joint bars are usually produced from Q235B structural steel or from 55Q rail steel, and both grades are covered by Chinese national standards for structural and rail steel. Common configurations are the 4-hole and 6-hole patterns, with a standard bar length of 610 mm for the 4-hole pattern; the number of holes is chosen to suit the drilling of the rail ends and the traffic level on the line.
Materials used for joint bars include rolled Q235 steel, ductile cast iron and forged steel. Rolled and forged bars give the highest fatigue resistance and are preferred on main line track, while ductile cast iron is used where a heavier section is needed at low cost. Whichever material is chosen, the bar must be free of laps, cracks and scale before it is installed, and bolt holes must be deburred so that the joint can be closed to the specified gap.
Rail Clips and Clamps
Rail clips hold the rail firmly on the sleeper, base plate or slab and prevent lateral displacement or loosening of the track under traffic. Because the base structure and the compression method differ from one track design to another, clips are supplied in families rather than as a single universal item. The 7216 rail clip and the WJK and WZ series of clips cover different installation environments and adapt to different rail base structures and clamping methods.
Toe load: the clamping force applied to the rail foot must be verified after installation, because an under-driven clip allows gauge widening and an over-driven clip can fatigue or crack.
Insulation: clips must work with insulating pads or insulators where track circuits require electrical separation between rail and sleeper.
Adjustability: on curves and transition zones, the clip family chosen must allow the gauge adjustment range required by the alignment design.
Bolts, Nuts and Joint Hardware
Fishplate bolts and nuts are essential for clamping joint bars to the rail web. For 43 kg/m and comparable heavy rail sections, M22 x 75 mm fishplate bolts are a standard size, supplied in property class 8.8 or in Q235 steel where a lower strength level is acceptable. Joint hardware has to be tightened to a controlled torque and re-checked after the first traffic passes, since a loose joint bolt allows impact loading that quickly damages both the bar and the rail ends.
| Component | Typical specification | Function |
|---|---|---|
| Fish plate (joint bar) | Q235B or 55Q, 4-hole or 6-hole, 610 mm bar length | Connects rail ends and distributes load |
| Rail clip | 7216, WJK series, WZ series | Holds rail foot to sleeper, plate or slab |
| Fishplate bolt and nut | M22 x 75 mm, class 8.8 or Q235 | Clamps the joint bar to the rail web |
| Rubber pad | Elastic natural rubber, typically 5 to 10 mm thick | Absorbs vibration, reduces noise, extends track life |
Rubber Pads and Rail Pads
Rubber pads are placed beneath the rail to absorb vibration and shock, to reduce rolling noise and to extend the service life of the sleeper and the ballast. For heavy railway track, highly elastic black natural rubber is the usual material, with the pad cut to match the rail foot dimensions and drilled or moulded to clear the clip shoulders. Pad thickness for heavy rail is normally in the range of 5 to 10 mm; the exact figure is set by the fastening system design, because pad thickness changes the installed toe load of the clip and must not be altered without re-checking the assembly.
Pads must be inspected for permanent set, tearing at the shoulder openings and loss of elasticity. A pad that has taken a permanent set no longer isolates vibration, and the resulting high-frequency loading is transferred into the sleeper and the ballast, where it accelerates deterioration.
Frequently Asked Questions
Q: What material is used for fish plates on P50 rails?
Joint bars for P50 rails are commonly produced from Q235B structural steel or 55Q rail steel, and ductile cast iron or forged steel is also used where a heavier or stronger section is required.
Q: What is the standard length of a 4-hole fish plate?
A 4-hole joint bar is normally supplied in a standard length of 610 mm; 6-hole bars are longer and are used where higher joint strength or heavier traffic demands it.
Q: What size are fishplate bolts for heavy rail joints?
M22 x 75 mm bolts are a standard size for 43 kg/m and comparable heavy rail sections, supplied in property class 8.8 or in Q235 steel depending on the joint design.
Q: How thick should a heavy rail rubber pad be?
Heavy rail pads are typically 5 to 10 mm thick. The value is fixed by the fastening system design, because a change in pad thickness changes the installed clip toe load.
Q: Why do rail clips come in several series?
Different clip series match different base structures and compression methods, so the correct series is chosen from the sleeper or slab design, the rail section and the required toe load.
Q: How is the quality of a heavy rail fastening system verified?
By material certificates against the referenced standards, dimensional checks on bar length, hole spacing and thread size, and toe load measurement on a sample assembly before the batch is released.