Roll Scars - Thermal ‘scars’ on rails

A rail of good quality requires not only internal purity, but also a smooth surface. However, rails need to go through multiple processes during the production process, especially due to improper operation or other accidental conditions during rolling, high-temperature transportation, etc. , will produce thermal damage defects on the rail surface, among which rolling scars are the most common defect. Statistics show that rolling scars account for 40% of rail surface quality defects. Today we will take a look at the rolling scar defect.

 

 

1.Characteristics

 

Rolling scars are the surface with traces of thermal processing caused by foreign objects (such as iron oxide scale sticking to the surface of the roll to form steel knobs) during the rolling process, scratches on the guide or roller table, defects in the surface quality of the roll, etc. Damage, some rolling scars have cyclical characteristics, and some rolling scars will form closed defects, which are difficult to identify.

 

2. Harm

 

The existence of rolling scars on the rails not only creates defects on the surface, but also seriously affects the mechanical properties of the rails. Especially under the dynamic load of high-speed operation of heavy-duty trains, stress concentration can easily occur in the defective parts of the rails, leading to crack sources in the rails and serious consequences. It may even cause breakage and endanger driving safety.

 

3. Inspection methods

 

Visually inspect and use a depth indicator to measure the depth. Before measuring, zero the depth indicator. When measuring, the reference plane of the depth indicator should be flush with the rail surface to avoid deviation in the measurement data caused by tilt.

 

4.Cause:

 

Foreign matter such as iron sheets and iron filings adhere to the surface of the roller, which can easily cause periodic rolling scar defects on the surface of the rail;

 

The iron oxide scale attached to the surface of the roll or steel billet is pressed into the surface of the rolled piece during the rolling process and falls off during the subsequent rolling process, causing irregular rolling scars on the rail surface;

 

Scratches on the rolled piece due to improper steel turning and steel shifting operations, as well as scratches on the rolled piece when it hits the guard plate or pass pattern when biting the steel, will cause rolling scars on the rolled piece during the subsequent rolling process;

 

Rolling with severely worn rollers can easily cause pits or pitting marks on the rail surface.

 

5. Treatment method

 

If the depth of the rolling scar does not exceed the standard requirements, it may not be processed or it may be ground according to the standard requirements. If the depth exceeds the standard requirements, the excessive parts shall be cut off and discarded.

 

6. Preventive measures

 

Ensure the descaling effect and reduce surface oxide scale;

 

Ensure that the rolling pass is not damaged, check the pass regularly, and repair or replace it in time if any damage occurs; ensure centered rolling, and the steel head is aligned with the pass when the rolled piece is fed into the pass to prevent bite deviation;

 

Do a good job in maintaining guides and other ancillary devices and equipment, and promptly adjust and deal with guide devices or mechanical equipment that cause damage to rolled parts.