What Is a Steel Rail?
Steel rails are the main components of the track. The function of the rail is to guide the wheels of the locomotive vehicle forward, directly withstand various forces from the wheel and other aspects, transmit them to the under-rail foundation, and provide a continuous and smooth surface for the rolling of the wheel. The rail must be strong enough to carry the axle load, tough enough to resist impact, and wear-resistant enough to give a long service life.
Rail Types by Mass per Metre
Steel rail types are customarily expressed in kilograms of the mass per metre of rail. Chinas rail standard includes 75 kg per metre, 60, 50, 43 and 38 kg per metre heavy rails. In the international market there are AREMA, BS, JIS, UIC, DIN and other standard rails. The table below shows the dimensions of common rail sections.
| Classification | Rail | Height in mm | Head in mm | Bottom in mm | Web thickness in mm | Weight in kg per metre |
|---|---|---|---|---|---|---|
| Light rail | 8 kg | 65 | 25 | 54 | 7 | 8.42 |
| Light rail | 9 kg | 63.5 | 32.1 | 63.5 | 5.9 | 8.94 |
| Light rail | 12 kg | 69.85 | 38.1 | 69.85 | 7.54 | 12.2 |
| Light rail | 15 kg | 79.37 | 42.86 | 79.37 | 8.33 | 15.2 |
| Light rail | 18 kg | 80 | 40 | 80 | 10 | 18.06 |
| Light rail | 22 kg | 93.66 | 50.8 | 93.66 | 10.72 | 22.3 |
| Light rail | 24 kg | 107 | 51 | 90 | 10.9 | 24.46 |
| Light rail | 30 kg | 107.95 | 60.33 | 107.95 | 12.3 | 30.1 |
| Heavy rail | 38 kg | 134 | 68 | 114 | 13 | 38.733 |
| Heavy rail | 43 kg | 140 | 70 | 114 | 14.5 | 44.653 |
| Heavy rail | 45 kg | 145 | 67 | 126 | 14.5 | 45.546 |
| Heavy rail | 50 kg | 152 | 70 | 132 | 15.5 | 51.514 |
| Heavy rail | 60 kg | 176 | 73 | 150 | 16.5 | 60.64 |
| Crane rail | QU70 | 120 | 70 | 120 | 28 | 52.8 |
| Crane rail | QU80 | 130 | 80 | 130 | 32 | 63.69 |
| Crane rail | QU100 | 150 | 100 | 150 | 38 | 88.96 |
| Crane rail | QU120 | 170 | 120 | 170 | 44 | 118.1 |
How to Select the Rail Type
The type of rail should be adapted to the traffic volume, the allowable speed and the axle weight. Technically, it is necessary to ensure sufficient strength, toughness, wear resistance and stability; economically, it is necessary to ensure a reasonable overhaul cycle and reduce maintenance. The main factors for determining the mass of the rail are as follows. First, the rail quality must match the axle load of the locomotive; the axle ratio is generally above 2.75, and the rail quality is increased to match the axle load. Second, under the condition of a certain speed, the impact of the wheel on the rail and the vibration of the rail components and the track bed are inversely proportional to the quality of the rail, so improving speed requires improving rail quality. Third, the greater the total mass passed, the more easily it causes fatigue damage of the track components and geometric transformation of the track, so the rail must be selected according to the annual total mass.
Shape and Size of the Rail Section
In a straight section, the force on the rail is primarily a vertical force, which results in deflection of the rail. Since the rail is considered to be an infinitely long beam supported on a continuous elastic foundation, the optimum cross-section of the beam against deflection is an I-shape. Therefore the rail adopts an I-shaped section, which is composed of a rail head, a rail waist and a rail bottom. The rail head is the part directly contacting the wheel. In order to improve the contact condition of the wheel and rail and improve its resistance to indentation and wear, the rail head should be large and thick, and it should have a tread surface with an adapted shape and sufficient area for wear.
Rail Damage Classification, Inspection and Maintenance
Rail damage refers to rail breakage, rail cracks and other damage that affects and limits the performance of the rail during use. Rail damage is classified into three categories: light injury, serious injury and fracture. Rail breakage refers to one of the following conditions: the full section of the rail is broken; the crack penetrates the entire rail head section; the crack penetrates the entire rail bottom section; or, for an allowable speed of not more than 160 km per hour, the top surface of the section rail has a block with a length greater than 50 mm and a depth greater than 10 mm. For an allowable speed greater than 160 km per hour, the criterion is a block with a length greater than 30 mm and a depth greater than 5 mm.
Regular rail inspection should look for surface defects such as cracks, crusting and scratches, as well as head checking, squats and corrugation. Measure the rail wear at the gauge corner and the rail head, and check the rail for bending and twisting at the ends. When damage approaches the fracture criteria, the rail must be replaced or repaired in time. Keep the fastening system properly maintained so that the rail is held securely and the load is distributed evenly to the track bed.
A common misconception is that a heavier rail is always the right choice. The rail type must match the axle load, speed and traffic volume; a heavier rail costs more and requires stronger track structures. Another misconception is that rail damage always starts at the surface; internal defects such as shatter cracks and transverse defects can also develop inside the head. It is also wrongly assumed that crane rails are the same as standard rails; crane rails have a much wider head and web for the concentrated wheel loads of cranes.
Frequently Asked Questions
What is the function of a steel rail? The rail guides the wheels, withstands the wheel loads, transmits them to the track bed and provides a smooth rolling surface.
How are rail types expressed? Rail types are expressed in kilograms of mass per metre, such as 50 kg per metre or 60 kg per metre rail.
Why is the rail section I-shaped? The I-shape is the optimum cross-section for a beam on an elastic foundation resisting vertical deflection.
What is the difference between light rail and heavy rail? Light rail from 8 to 30 kg per metre suits industrial and mine lines, while heavy rail from 38 to 75 kg per metre is used for mainline traffic.
What are the three categories of rail damage? Light injury, serious injury and fracture.
What is a crane rail? crane rail such as QU70 to QU120 is a wide-head rail designed for the concentrated wheel loads of cranes on runways.
