FandMmag.com |

A welder lays down a bead, then stops and bangs the nozzle against the workbench to release a ring of spatter buildup inside the gun.

Not a good idea.

The practice, among many others, can significantly reduce the life of some gas metal arc welding gun consumables, in this case the nozzle, explains Tom Jaeger, an engineering manager at Windsor, Ontario-based Tregaskiss.

A welding gun and cable assembly represents a complex yet elegantly simple piece of engineering, designed to carry the wire carefully and accurately from the spool, through the drive rolls, into the liner inside the power-cable assembly, then the diffuser/tip-holder/ retaining head (depending on the manufacturer design and naming conventions), and finally the contact tip. For the wire to have a smooth trip throughout, each connection must be clean and solid.

Debris is a welding gun's enemy; and in a dusty shop, such debris can easily get into any of these connections. It can, for instance, plug up the holes in the diffuser, hindering its ability to properly diffuse the shielding gas that surrounds the arc, causing weld porosity. Simply air-blowing or brushing off that debris can solve the problem.

"There are so many factors that contribute to an efficient welding operation," Jaeger adds. "If you do not take care of the simple basics of proper welding-gun care and consistent consumable service across your facility," it can just make all other potential welding problems—from improper welding procedure specifications to work fitup concerns—even worse.

GUN DISASSEMBLY AND ASSEMBLY

In recent years welding guns have become much easier to disassemble, through quick-connect couplings between the gun neck housing and diffuser, and the like. The ease of assembly makes it easier for the welder to ensure secure connections throughout the system: between the wire-feed system and cable, the cable and neck of the gun, the contact tip and diffuser, and so on. During assembly, a welder must clean the connection between the contact tip and diffuser to remove debris and ensure a tight connection.

Here, having the right tool at the welder workbench can be essential. Welpers, or welding pliers, can present great advantages, designed to do just about everything a welder needs to do to a manual welding gun with respect to placing consumables. It will properly loosen the contact tip, and a portion of it is specifically designed to take off the diffuser, depending on the diffuser design.

In most cases, simple pliers and a crescent wrench can work. Yet some welders, due to the lack of tools or a disorganized workbench, disassemble the gun with whatever tool may be available—perhaps employing the same side cutters used to cut the wire. This scores gun components and does not give suitable torque for the job. Suitable torque, specified by the gun supplier, ensures that components will not become loose when subjected to welding's dramatic heating and cooling effects. However, most welding operators do not have torque tooling available for everyday use. Suitable alternatives must be established.

"In the case of our diffuser and contact tips, we tell operators to spin the diffuser finger-tight and then tighten it with the proper wrench another half turn. For the contact tip, hand tighten, then tighten about another 15 degrees of rotation using a proper tool. We have collected data that supports this method, and found it to be very close to our standard torque specifications," Jaeger points out. "Here, each manufacturer is going to be different, depending on the type of connection they have."

Components that are over-tightened can have negative effects as well, making it impossible to get the components apart. Even worse, "if you over-torque that diffuser to the neck, you can damage the threads"—necessitating a costly replacement, Jaeger explains. These connections usually involve copper-alloy thread connections, which limits the amount of torque they can endure.

NOZZLES OR GAS SHIELDS

"Nozzles take a lot of abuse," Jaeger explains. And though most vendors offer a solid, durable design, a nozzle isn't a hammer. Knocking the nozzle, or gas shield, may remove some spatter; however, it significantly reduces the service life of the nozzle. The reason lies with basic physics of weld spatter; spatter has an easier time fusing to sharp, pointed surfaces—caused by the banging—simply because it requires less thermal energy to heat up a sharp edge and create a bond than it does to create a bond on a smooth surface. It also becomes increasingly difficult to remove the spatter from the nozzle. Every dent put near the arc zone creates another pocket that spatter can fuse to. The problem can become worse in a vicious circle of welding, banging, welding and fusing spatter to those newly created sharp edges, then more welding and more fusing of that spatter until, eventually, the gun becomes loose and full of spatter.

Using anti-spatter solution, either water- or oil-based, can help immensely, offering a coating to protect the nozzle as well as the diffuser from spatter buildup. When subjected to the heat of the arc, most water-based anti-spatter solutions harden slightly, forming a film on the nozzle and contact tip. The coating creates a barrier, making it difficult for spatter to adhere to the nozzle surface. The coating allows the spatter to easily fall out during cleaning—no banging required.

THE LINER

During GMA (MIG) welding, the liner — usually consisting of a tightly wound spring construction surrounding the welding wire — can wear from collected debris and the friction of the wire passing through it. "When wire-feed ability changes, the operator can see it and feel it right away," says Jaeger. When feedability deteriorates to the point where it's no longer reasonable to weld, it's time to replace the liner.

Most guns require disassembly to replace the liner, so when the new liner is inserted, a length of liner sticks out at the end of the gun. Once everything is secure on the back end and a welder is ready to cut the liner, he must pay special attention to the length of that stickout. Cut it too short, and the liner will "pull out of the seat and the diffuser, and you have feed issues right way," he says. "If you cut the liner too long, there is a potential for damage to occur to the diffuser/tip holder, when you thread them back on."

Again proper tools here matter, with side cutters giving a clean liner cut. A liner cut with a tool not designed for the job may give a poor cut, with a small piece of the liner hanging off to the side. If that piece of hanging liner, usually of hardened steel, is inserted into a copper-alloy or brass part, it will cut into the softer gun components. The same can happen if the liner is too long. In some cases, it can cut directly through the liner seat and emerge out of the front end of the diffuser.

Cut the liner too short, and the liner can pull back out of the liner seat, meaning there's nothing guiding the wire into the contact tip. Free to move, the liner's motion wears the lubricant and coating on the wire and, on the back side of the diffuser, it can create wear and debris inside, affecting wire feedability through the front end of the torch, ultimately affecting weld quality.

The proper length should be specified by the gun manufacturer, Jaeger explains, "depending on how the diffuser fits onto the back of the neck." Regardless, the length should be just enough to "allow compression of the liner, so when you coil the gun [cable] for some reason, the liner won't pull back."