One of the more frequent issues that is noticed within a rail environment is defects within the rail head.
These rail head flaws can become noticeable by either visual inspection or by ultrasonic analysis by approved vehicles (UTU). To help combat this, Thermit Welding with the support of Network Rail, has developed an aluminothermic weld repair process for the repair of rail head defects in plain line. This includes small isolated flaws.
This process has been fully approved by Network Rail.
During the approval process repairs were inspected by a process of radiography and ultrasonic inspection to test that all defects have been removed.
The process of head repair welding comprises 6 separate steps
- Preparation – the area for repair is marked on the rail, and excavated using a purpose designed flame cutting template and torch. The flame cut surface is then ground to prepare the surface for N.D.E (Non Destructive Examination). If any defects remain after grinding the rail is to be reported for repair and removal.
- Assembly of the welding equipment – Most of the used equipment is similar to that of the standard aluminothermic welding process. Either side of the rail is released from its fastenings, near the defect, and raised on wedges. A standard mounting or preheated mounting is finally fitted.
- Preheating preparation – The HR moulds are checked for fit, and inserted into their shoes. The moulds are sealed to the rail, with traditional luting material.
- Preheating – the mould is preheated with the preheater set at a fixed height above the defect, and the central plug is then installed.
- Welding – After the preheat, the burner is removed and using a single use crucible the portion is positioned above the mould shoe. The Thermit portion is then ignited and the Thermit steel is discharged into the mould.
- Solidification and profile finishing – The weld repair is allowed to cool for 6 – 6.5 mins, after which excess material is removed. After 50 min the rail is fastened down and the trimmed surface ground to profile.