Recent Developments in Welding Techniques
The welding methods described above have been further improved in the recent past by employing new techniques and equipment. These techniques and equipment are described below in detail.
Automatic welding recorder The invention of a welding recorder, for controlling the quality of welding in the flash butt welding method is a recent development. The recorder is able to not only identify the defects in the flash butt welded joint, but also indicate the reasons for the same. A very sophisticated recording system has recently been developed by the German Railways with the help of Siemens. This system gives visible and audible indications whenever any parameter controlling the quality of the weld transgresses the predetermined limits. The recorder helps considerably in exercising proper control on the quality of welding.
Thermit welding without pre-heating A new method of thermit welding rails that does not involve preheating is currently being tested on German Railways. The necessary heat is produced by much larger quantities of a specially manufactured alumino-thermit mixture. This method also involves the use of special prefabricated moulds made from pure quartz sand. This method of welding requires considerably less amount of time due to the prior solidification of the material in the mould. A similar method is also being tried on Indian Railways on an experimental basis.
Flame cutting and welding technique A new flame cutting and welding technique is under trial on Northern Railways. It is proposed that this technique be implemented to get the desirable gap in a welded track or to repair welding where site conditions so warrant. The time taken in flame cutting is only 2 min. as against the 15-20 min. that it takes for cutting by hacksaw.
Welding with 50-mm gap A new technique of welding joints by introducing 50-mm gaps has recently been standardized on Indian Railways. In this technique, a gap of 50 mm is created by cutting the defective joint. The gap is held in position with the help of a tensor. This gap is fitted with a wider mould and heated for 20 min. The welding mixture is taken in much larger quantities and ignited, and after the reaction is complete, the same is poured into the mould. Demoulding is carried out after about 5 min. and a joint with a perfect tolerance is created.
Thermit welded joint with 50% decrease in height of collar At present, experiments are being conducted on Northern Railways to produce thermit welds with a reduction of 50% in the height of the collar. This will help in reducing the joggle in the joggled fish plate. The bottom collar is also likely to be designed as a plate rather than a curve. This will facilitate testing by ultrasonic rail flaw detection (USFD) equipment.
Mobile flash butt welding machines In order to produce good quality welded joints, Indian Railways has recently procured a few K335-type mobile flash welding machines manufactured by Messers Plasser and Theureri as shown in Fig. 16.8.
The new machine is self-propelled with a separate electric generator and can weld about 60 joints per day under field conditions. The approximate cost of welding comes to about Rs 500 per joint using this machine.