Page 32 - ITA Journal 3-2018

Technical Papers
Fig. 3: Standard Argweld® radiused and at Trailing Shield®.
Flat trailing shields for plate, sheet and rectangular tanks are availa- ble in small lightweight versions for manual welders or, like the radi- used versions, larger, more robust, versions for attaching to automatic/ mechanised welding systems.
Argweld® Trailing Shields® have been designed speci cally for use with GTAW (TIG) or PAW (plasma) welding torches and provide a high level of additional inert gas shielding to supplement that supplied by the basic torch.
Pipe and tube purging
Systems for weld root protection are based on sealing the inside of a pipe on either side of the weld zone then displacing air with an inert gas. The seals must be reliable and leak tight, effective and easy to insert and remove. The inert gas must be of a quality commensurate with the need to protect the molten metal.
Gas ow should be laminar to maintain a high level of protection and pressure controlled to offer adequate coverage but without expel- ling molten metal from the joint. Early, and with hindsight, primi- tive systems, mostly home made and individually fashioned at great expense, involved the use of paper, card, wood and polystyrene discs. Often these provided at best poor sealing and on occasions burst into ames – satisfactory removal after welding presented challenges.
Ensuring that all oxygen had been removed during purging was left entirely to the skill and experience of the operator.
There were regular incidences where protection proved to be inade- quate and the joint had to be re-made with consequent expense and loss of time. It comes as a surprise that these practices are still used, even by prominent fabrication companies across the world.
Fig. 4: Pipe and tube purging concept
Argweld® systems have been developed to help speed up the welding of pipes. This has been realised using a design, which allows for easy and positive insertion into position and by limiting the purge volume.
Home made purge dam set
ITAtube Journal No3/October 2018
32