To establish and maintain a controllable arc it is important that the wire feed

To establish and maintain a controllable arc it is

This preview shows page 39 - 42 out of 92 pages.

To establish and maintain a controllable arc, it is important that the wire feed speed and voltage settings are proportionally increased or decreased at the same time, in order to produce acceptable weld deposits. More modern machines have a switch will automatically adjust both. Inch switch This switch is generally used when changing electrode (placing a new roll of GMAW wire) onto the wire feed unit, or when there has been a jam at the feed unit end. It passed the wire through liner at max speed thus reducing wasted time. Burnback time switch When the trigger on the torch is released, the welding current, wire feed and gas flow are deactivated. If these things were to happen at the same time, the wire would stick to the work piece. The burnback timing switch overcomes this problem by allowing a variable time delay to take place so the arc continues for a fraction of a second after the wire has stopped. Gas purge switch This switch is used to adjust and set the gas reading on the flow meter. The switch activates the gas solenoid mechanism within the wire feed unit without the operator having to press the trigger on the welding torch. Some of the older machines do not have this function, so you need to waste a little wire to adjust the gas to the correct setting.
Image of page 39
Baxter Institute | MEM05018C Perform advanced welding using gas metal arc welding process P a g e | 39 MEM05018C Learner Guide V6.5 Spot weld timer switch Spot welds can be made by turning the panel switch on to the spot mode. The timer is then adjusted to allow the arc to operate for the duration of the weld. The timer is activated by the trigger on the torch and is automatically switched off after the pre-set spot welding time has elapsed. A special nozzle with a castellated effect is used to allow the hot gases to escape. Braking device An adjustable braking device is incorporated into the spool hub to prevent an overrun. Carbon Equivalent The carbon equivalent is a calculation used to determine the weldability of low alloy steel compared to the weldability of plain carbon steel. There is a difference between the weldability of low carbon and low alloy steels. The hardening effects of the alloying elements in low alloy steels must be considered. Steels containing less than 2% alloying elements indicate: These percentage comparisons can be used in a calculation to find the weldability of low alloy steels. Manganese, Chromium, Nickel, Molybdenum & Copper Relationship between carbon equivalent and the group number Carbon equivalent Group number 0.30 1 ≥0.30 to 0.35 2 ≥0.35 to 0.40 3 ≥0.40 to 0.45 4 ≥0.45 to 0.50 5 ≥0.50 to 0.55 6 ≥0.55 to 0..60 7 ≥0.60 to 0.65 8 ≥0.65 to 0.70 9 ≥0.70 to 0.75 10 ≥0.75 to 0.80 11 ≥0.80 12 Machine configuration GMAW is extremely fast and economical. This process is easily used for welding on thin gauge metal as well as on heavy plate. The high welding rate and reduced post-weld clean-up are making GMAW an outstanding welding process
Image of page 40
Baxter Institute | MEM05018C Perform advanced welding using gas metal arc welding process P a g e | 40 MEM05018C Learner Guide V6.5 GMAW machine
Image of page 41
Image of page 42

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture