Crane rail welding is a specialist process that must be undertaken by fully trained and competent engineers. Rapid rail supply welding engineers, supervision and /or training in either mma (puddle arc) or thermit/thermic welding
MMA Puddle Arc Welding is the process of joining carbon steel crane rails.
The rails to be joined together are aligned leaving a prescribed gap between their ends. Rail ends shall be smooth and free from defects and grease.
The rails are set with a slight camber at the joint to allow for weld contraction and copper moulds are placed around and under the joint.
Joints are pre-heated to prescribed temperature and confirmed using temperature indicators prior to welding.
Welding is carried out using low hydrogen electrodes to an approved working procedure by competent certified welders.
Using a specially designed burner, the moulds and the enclosed rail ends are pre-heated for a time, dependent upon the rail section, to achieve the correct welding temperature of 900 – 1000°C
When the correct degree of preheat has been achieved reaction is initiated in the crucible using a special igniter. Superheated molten steel is produced by an Aluminothermic reaction (the Thermit® reaction).Weld Forming
At the correct time the tapping system at the base of the crucible discharges the superheated molten Thermit® steel followed by the slag into moulds via the pouring cup.
After solidification, surplus Thermit® steel is removed from the rail head and following an appropriate cooling period, the railhead is ground to profile and the rail aligned and fastened.
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