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.docAutomatic welding
Automatic welding, by MIG, pulse and C02 processes, now plays an important part in welding fabrication practice. It enables welds of consistently high quality and accuracy to radiographic standard to be performed at high welding speeds because of the close degree of control over the rate of travel and nozzle-to-work distance. It is less tolerant than semi-automatic welding to variations of root gap and fit-up but reduces the number of start-stop breaks in long sequences. The choice between semiautomatic and automatic process becomes a question of economics, involving the length of runs, number involved, volume of deposited metal if the sections are thick, method of mechanization and set-up time. The torches are now usually air cooled even for currents up to 450 A and are carried on welding heads fitted with controls similar to those used for semiautomatic welding, and may be remote controlled (Fig, 2.20).
The head may be: (1) fixed, with the work arranged to move or be rotated beneath it, (2) mounted on a boom and column which can either be of the
Fig. 2.19. (a) Unprepared fillets, {b) multi-run prepared fillets in thick plate, (c) \ deep preparation fillets, (d) multi-run unprepared fillet. CO, welding.
positioning type in which the work moves, or the boom can traverse over the work (Figs. 2.2 la and b), (3) gantry mounted so as to traverse over the stationary work, (4) tractor mounted, running on guide rails to move over the fixed work, (5) mounted on a special machine or fixture designed for a specific production. A head may carry two torches arranged to weld simultaneously, thus greatly reducing the welding time.
For the C02 process in steel a typical example would be with wire of 1.2 mm diameter using 150-170 A on thinner sections and multiple passes up to 30 on thicknesses up to 75 mm with current in the 400-500 A range and 2.4 mm wire. With automatic surge (pulse) arc welding on stainless steel, accurate control of the underbead is achieved, obviating the necessity for back-chipping and sealing run. In the case of aluminium welding on plate above 10 mm thickness the accuracy of the underbead produced with the MIG automatic process results in more economical welding than by the double-operator vertical TIG method. In general the full automation of these processes results in greater productivity with high-quality welds.
ФЕДЕРАЛЬНОЕ АГЕНСТВО ПО ОБРАЗОВАНИЮ
Государственное образовательное учреждение высшего профессионального образования
«ТОМСКИЙ ПОЛИТЕХНИЧЕСКИЙ УНИВЕРСИТЕТ»
Реферат по английскому языку
Выполнил: студент гр. 4В41
Евдакимов Д.С.
Проверил: преподаватель
Земляницына А.П.
Томск 2007