This article relates to my previous article “choosing a Gas Metal Arc Welding Machine for home use”.
Displayed below in figure 1 is a typical wire feed unit that is found on a Gas Metal Arc Welding (GMAW) or Flux Cored Arc Welding (FCAW) plant. The photo identity’s the Gun cable assembly as well as the drive roller location.
Note; I am in Australia so terminology may vary from your region. For instance MIG / MAG welding is referred to GMAW in Australia
The GMAW & FCAW welding processes use 3 different methods to get the electrode wire from the wire spool to the welding gun.
For the push system to work the electrode wire needs to be stable and hard enough to be able to be pushed from the drive rollers to the welding gun. Typically solid wire used in the GMAW process such as mild steel and stainless steel suit the push system. The FCAW process also uses the push system.
Note on the difference between GMAW and FCAW electrode wire.
GMAW – This wire is a solid mild steel wire with a copper coating to assist in electrical connection at the copper contact tip (where wire exits the gun) as well as to reduce corrosion.
FCAW – This wire is tubular, the centre is filled with a flux which protects the arc from the atmosphere (as opposed to GMAW which uses a shielding gas to protect the arc from the atmosphere). FCAW wire often has a bare metal finish but also comes with a copper coating.
Drive rollers - 2 rollers or 4 rollers set up (Push system)
Inside the wire feed section of each GMAW or FCAW machine there will be a 2 drive or 4 drive roller set up.
Figure 1.1 below shows a wire feed unit with 2roller set up - most commonly found in cheaper single phase machines, used on short welding hand piece’s to push the electrode wire up to the welding hand piece.
Figure 1.2 below shows a wire feed unit with 4roller set up - most commonly found in 3 phase machines and higher end single phase machines. The 4roller set up provides a more constant feed capable of pushing the wire over a further distance.
The pull system
The pull system has a small spool of electrode wire built into a gun (refer to image 1.3 below) along with drive rollers & drive motor. This system is used to pull soft wire such as aluminium across the short distance from the small spool to the tip of the welding gun. The drive rollers in the gun are the only drive rollers used in the pull system.
The push / pull system
This system uses the rollers in the wire feed unit along with a second set of rollers driven by a motor which are located inside the welding gun. Unlike the pull system the push/pull system wire obtains its wire from the spool of electrode wire in the wire feed unit. Image 1.4 below shows a typical push/pull gun and figure 1.5 shows the internal feed roller mechanism of a push/pull gun.
Drive rollers used for wire type
Note that the following the figure’s 2.1, 2.2 & 2.3 are sketches of various types of drive rollers. The view is drawn as if standing in front of the machine looking at the rollers front on. Also note it is common practise for the bottom rollers to be fixed and the top roller has a spring tensioned adjustment which can be altered to adjust the tension placed on the wire.
Solid hard wire GMAW
Figure 2.1 below shows the top roller has no groove and the bottom roller has a V groove for solid hard wire’s such as mild steel and stainless steel.
Solid soft wire GMAW
Figure 2.2 below shows the top roller has no groove and the bottom roller has a U groove for solid soft wire such as aluminium.
Tubular wire FCAW
Figure 2.3 below shows V grooves in both top and bottom rollers. These rollers are also serrated, the additional groove and serrations are in place because the FCAW wire is tubular and requires additional grip to push the wire up the liner to the hand piece.
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Metal Design, Industrial design
Freestyle Metal (FMA) Artis - Glen Jones Designer and Fabricator of unique metal products..