seamless line construction

How are seamless lines constructed?

Seamless line refers to a long rail line made by welding rails of standard length, also known as welded long rail line.

On ordinary lines, rail joints are one of the weak links of the track. Due to the existence of rail joints, impact and vibration occur when the train passes, accompanied by impact noise. The maximum impact load generated can reach more than 3 times of the non-joint area.

The seamless line eliminates rail joints over a considerable distance, so it has a series of advantages such as smooth driving, comfortable rides for passengers, low maintenance costs for rolling stock and tracks, and long service life.

1. Welded into a 500-meter long rail at the factory

First, the 100-meter-long rails that are not drilled or quenched are welded into 500-meter long rails at the base factory. The purpose is to reduce the number of joints welded on site, but it cannot be welded too long to cause inconvenience in transportation. Before rail welding, surface defect detection, rust removal and other processes must be carried out on the appearance of the rail base material before welding. The welding machine uses resistance heating to heat the adjacent ends of the two rails to about 1200°C, and then extrusion welds them. In order to ensure the quality of rail welding joints, the welded rail joints must be heat treated.

The straightness of the guide surface of the rail top running surface of the welded rail joint should be controlled between 0 and 0.2 mm, which means the error is equivalent to the diameter of 2 hairs. The drop weight test is an important part of welding quality inspection. The welded joint must be able to withstand the impact of a 1-ton hammer falling freely from a height of 5.2 meters. The welding head after hammering must ensure that it does not crack continuously.

2. Lay the rail and weld it into a rail without gaps

When laying the rail of the seamless line, two 500-meter-long steel rails are taxied to the corresponding position with the tractor, and dozens of engineering and technical personnel assist the tractor to unload the rail and accurately locate the rail. After the rail is laid, the locomotive can push a flat train consisting of flat cars along the top of the rail. After the tractor lays the rail on the ballastless track bed, another seamless line welding construction team will immediately weld the 500-meter-long rail laid in front of it into a rail without gaps with a special welding machine.

The stress release process in seamless line welding can prevent the thermal expansion and cold contraction of seamless line, that is, the stress inside the rail is evenly distributed to the rail, to prevent the rail from breaking when the temperature is too low, and the rail from expanding when the temperature is too high. Polish the joint and detect the flaw after welding. The technical requirements of the seamless line are extremely strict, and the flatness error within 1.5 meters of the rail interface of the seamless line cannot exceed 0.2 mm.

In this way, when the wheel goes to the joint of the two rails, a part of the wheel tread presses on the first rail at the same time, the other part of the wheel tread presses on the second rail at the same time, so that the two rails are stressed at the same time, so that the wheel smoothly passes through the joint of the two rails, without vibration.

3. Lock the rail onto the rail pillow

The last process of seamless line installation is locking, which is to fix all the long rail at one time under the temperature condition of the designed locking rail, install all the fasteners, and complete the job. Generally in the north, the temperature force inside a track will reach 50 to 100 tons, each fastener can provide about 1 ton of resistance, and it is necessary to use 100 fasteners to buckle the end of the rail and forcibly lock the rail on the rail pillow.

Seamless lines are the best choice for today’s track structures and are recognized by railways in various countries for their unobjectionable superiority. Because it not only eliminates a large number of joints, thereby providing smooth driving and passenger comfort, but also reducing maintenance costs for rolling stock and tracks.

Now Glory Rail has developed to be a leading and integrated steel rail supplier. We not only offer rails for the crane industry, but also provide various steel rails for the mining industry, railway transportation, steel industry, power plant, port, and metallurgy industry with strong R&D strength and reliable quality assurance capabilities. In order to provide diversified products for rail customers to meet the needs of different customers, Glory Rail actively negotiates cooperation with major steel rail mills and becomes a large agent of major steel rail mills in China, like Bao Steel, Yongyang Steel, Pan Steel, Anshan Steel, etc. We are committed to providing customers with comprehensive solutions for the whole rail system.