Page 32 - MetalForming-Sep-2018-issue

Welding Well
By Doug Smith
Choosing an Air-Cooled GMAW Gun
and Consumables
Many welding systems and wire feeders come bundled with a gas-metal-arc welding (GMAW) gun and consumables. However, welders and shop owners often discard bundled items and request the gun and consumables of their choice. Their decisions are typically driven by choos- ing a gun with a rating more suited to their application and consumables that enhance performance and lower oper- ating costs.
Use Enough Gun
The GMAW gun and consumables serve as the contact point for transfer- ring electric current from the tip to the welding wire, as well as to direct the welding wire and shielding gas (if required) to the workpiece. They also dissipate the heat generated by the welding process and the electrical resistance in the system.
Like power sources, guns have ther- mal duty-cycle ratings, governed by IEC 60974-7, Standard for Arc Welding Equipment. The standard requires (among other things) temperature-rise tests for the gun handle and cable. Based on how well their construction dissi- pates heat, GMAW guns and consum- ables are classified as light-, medium- and heavy-duty. Respective examples of duty-cycle ratings would be 180 A at 40 percent, 250 A at 60 percent and 400 A at 60 percent.
How hard a gun works depends on
Doug Smith, product business manager--arc equipment, Esab Welding & Cutting Products, shares his arc-welding insights in MetalForming magazine’s new Welding Well column every-other month.
Doug Smith
Product Business Manager- Arc Equipment, Esab Welding & Cutting Products
dsmith@esab.com
The larger the welding cable, the more heat it dissipates. These guns have the same handle diameter but use different size cables. The top gun has a rating of 250 A at 60-percent duty cycle while the bottom gun with its larger cable yields a rating of 450 A at 60-percent duty cycle.
wire diameter, welding parameters, and process and service conditions such as arc-on time and environmental conditions. Short-circuit GMAW with a 0.030-in. wire in a muffler shop would be considered light-duty work. Pulsed GMAW with a 0.035-in. wire would be medium- to heavy-duty work, and spray-transfer GMAW welding or flux- cored with a 0.045-in. wire or larg-
er would be heavy-duty work. “For anything surpassing
sheetmetal work with a 0.030-in. wire, I rec- ommend at least
a medium-
duty setup
that has a 250-
or 350-A rating at 60-percent duty cycle. The larger cable will keep
the gun cooler and lower pri-
mary power draw, plus it
will come with a bet-
ter set of consum-
ables com-
pared to a light-duty gun,” says Galen Johnson, senior lab technician at Esab’s Welding & Cutting Products’ test lab in Denton, TX, and a professional welder since 1968.
Johnson also reminds welders that guns have different ratings when used
30 MetalForming/September 2018
www.metalformingmagazine.com
Threaded consumables use a brass-to-copper connection that increases resistance. They also require a welper to unscrew the tip in the event of a burnback.