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MIG Gun Liner Types & Best Practices

Posted by Paul Pfingston on Jul 22, 2019 9:57:00 AM
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In today’s environment it is absolutely critical to minimize downtime and operate in the most efficient manner. Reasons for downtime are many and varied, particularly in the welding fabrication field. Grounding problems, gas leaks, contaminated material, machinery malfunction and worn components represent a few of the many issues confronted. In MIG welding, one of the most frustrating is wire feed problems and MIG gun liner issues in general.

Feeding problems are marked by erratic wire feeding, wire burnback and, in some cases, birdnesting. Causes are typically the result of worn or incorrect drive rolls, clogged liners, wrong tip size, incorrect installation of wire liner, among others. One of the most overlooked causes is the use of incorrect wire liners. The MIG gun liner is often thought of as the simplest component in the MIG gun assembly but can often prove to be the most important and has a dramatic effect on welding fabrication downtime.

A MIG gun liner is either a tube or helically wound wire which acts as a conduit to guide the welding wire through the MIG gun to the contact tip. It is important to match the type and size of the MIG gun liner to the type and size of the welding wire consumed. In other words, identifying and supplying the right tool for the job.

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MIG Gun Liner Diameter Size

There is some debate within the industry as to how to match the MIG gun liner size to the wire size. Some welders prefer using larger diameter liners because they believe the extra space can collect more debris without impeding wire feeding. They also believe that larger diameter MIG gun liners offer less resistance. Bouncing between different wire sizes allows some to use one liner for each, which influences their choice to go with larger liners. Although the latter may have some merit, it is important to proceed with caution.

As a general rule, smaller diameter welding wires possess less column strength and can have a tendency to wander and buckle inside the MIG gun liner, especially when there is any increased resistance. This leads to premature wear as the welding wire is rubbing excessively. It also can lead to serious feeding problems resulting in birdnesting or jamming inside the liner. Birdnesting is a tangling of the welding wire between the drive roll and end of the torch often caused by using an incorrect MIG gun liner size or an improperly cut liner. Not only does birdnesting waste wire, but is also very time consuming to correct.

Large diameter MIG gun liners (.052 and larger), on the other hand, have greater column strength. Using larger diameter wires should be no problem. If oversized MIG gun liners are going to be used for these applications, pay attention to the outer diameter of the liner, particularly in relation to the inner diameter of the MIG gun's inner tube. Too large a liner outer diameter can impede gas flow inside the torch. This can result in poor welds. Flat wound liners can be used to fit the limited space in the MIG gun and accommodate large gauge welding wire.

If you or your customer insists on using a larger MIG gun liner, then it is strongly encouraged to have diligent preventative maintenance procedures in place. Regularly blowing out the MIG gun liner and replacing the liner at an increased frequency will minimize some of these potential large diameter liner problems.

We recommend blowing the MIG gun liner out after every spool change. When taking the welding gun offline to perform the spool switch, remove the wire from inside the wire liner as well as the contact tip and the diffuser from the front end of the torch. Use a compressed air liner and put it up against the collet to blow out debris from the wire liner and increase it's service life.

All MIG gun manufacturers make liners to match specific welding wire sizes. As a general rule, it is best to follow the manufacturer’s recommendations.

Steel MIG Gun Liners

The traditional steel wound MIG gun liner has widespread use. These liners have a good balance of rigidity and flexibility and performance and cost effectiveness. Most standard mild steel welding wire (ER70S-3, ER70S-6, etc.) works well with these liners. Problems can arise when these liners are used for other types of wires.

Some filler metals, like stainless steel and chrome moly alloys, have rough surfaces which result in increased resistance and excess wear. Many times, the operator tries to overcome the resistance by clamping the drive rolls tighter on the wire. This tends to only make the problem worse by not only distorting the wire, but also forcing the wire too much instead of slipping. This leads to an increased risk in birdnesting.

Steel liners are naturally more resistant and are abrasive on the softer wires like aluminum, silicone bronze, and cored wire. There is also the risk of the steel MIG gun liners introducing contaminants into the weld itself when using softer filler metals with a steel liner. This makes steel liners poor choices for these types of filler metals.

There are also insulated steel liners that can be used on your MIG gun. Using an insulated steel MIG gun liner compared to a normal steel MIG gun liner is entirely dependent on how the welding gas is introduced into the MIG gun. If your MIG gun uses a dedicated gas line from the rear connect to the front end, a regular steel liner will be sufficient. But if you use a MIG gun that introduces gas through your cable and around the wire liner (i.e., not channeling it through a dedicated line), then you'll need an insulated steel liner. The insulation of the MIG gun liner around the collet keeps the gas from seeping through the coils and purging out the back of the MIG gun. Depending on your welding gun's make, it will be pretty clear which type of liner you need. But as always, check with your welding gun manufacturer to verify if need be.

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Plastic MIG Gun Liners

Beyond steel MIG gun liners, which are very cost effective and popular among welders and welding shops, there are a variety of plastic liners you can use as well. Most plastic liners look very similar but have different properties to them that make them more durable or better fits for certain types of filler metal and MIG weld processes:

  • Polyamide (PA) is a carbon filled nylon liner designed to be used in low temperature applications in a variety of wire types. It is a low cost alternative and a good choice for low duty cycle air-cooled, push-pull applications for smaller gauge aluminum, stainless steel and silicon bronze welding wires.
  • Combi-PA contains the addition of a short brass spiral wound liner attached to the front which enables this MIG gun liner to be used in higher temperature applications. The brass jumper aids in transferring current to the weld wire, and for this reason, Combi-PA liners are often used with soft wires such as aluminum silicone broze. This enables low melting plastic  MIG gun liners to be used in high amperage/duty-cycle applications where they would otherwise melt.
  • Polyethylene (PE) MIG gun liners are for soft wires with poor column strength like aluminum bronze and 4000 series aluminum. The interiors of these liners are smooth and provide stable wire feeding, especially on small diameter welding wire. Polyethylene has a low melting temperature so they are best used in low heat MIG welding applications.
  • Teflon® (PTFE) has a higher melting temperature than polyethylene but generally is not recommended for high heat applications in an air-cooled MIG gun because of the high direct heat. Teflon MIG gun liners can be good for higher heat applications that utilize water-cooled torches and brass neck liners. Teflon has good abrasion resistance characteristics and can be used with a variety of wire types. Recommend careful inspection on the welding wire prior to insertion. Burrs can scar the inside of the liner and accelerate the liner's wear. While this is exceptionally important for the teflon liner, welding wire should be inspected prior to insertion into any plastic liner.
  • Carbon Teflon (C-TFE) MIG gun liners are ideally suited for wires that are difficult to feed due to either the composition of the wire (soft) or the outside characteristics of the wire. This makes it well suited for stainless steel (ER308, ER309, ER409Cb etc) or flux-cored wire. It also performs well with some aluminum (such as ER5356). The teflon material is impregnated with carbon leading to better wear characteristics compared to other plastic MIG gun liners. It also has good temperature resistance compared to other plastic liners.
  • High Density Teflon (High Density PTFE) liners, also known as high molecular weight Teflon, have a similar melting point to that of carbon Teflon liners while providing longer service life. These MIG gun liners work well with a range of wires from soft wires to stiff wires and abrasive wires.

Neck Liners (Jump Liners)

Beyond the wire liner itself, neck liners are great tools to help extend the life of your wire liner. Neck liners, also called Jump Liners, are short liners with a small collet that sit in the welding torch swanneck and are far easier to replace should the liner fail. Typically, the most common location for MIG gun liner failure in at the bend of the gun's neck, so using a neck liner is not only a convenient time saving option, but also presents a lot of cost-savings because it uses less material, not to mention it is more ecologically-friendly.

Neck liners, pictured below on a robotic MIG gun, are able to be used for robotic and manual welding applications. Much like with the wire liner itself, it's important to match the neck liner size to the wire in use as make sure the neck liner material is a good fit for the wire, as well.

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Which MIG Gun Liner is Right For Me?

The best wire liner for your operation is going to depend on three main things:  the parameters you're welding with, the filler metal you're using to weld, and your MIG gun liner size.

The key is to make sure you're doing the basics really well. This includes:

  • Marrying up your wire size to your wire liner size
  • Looking at your wire liner material compared to the liner material you're using (or welding gun build if it requires an insulated steel liner)
  • Regularly blowing out the wire liner during spool changes to get debris out and ensure a smooth feed
  • Using neck liners when appropriate and advantageous 

Getting these four items correct will be what gets your the most life out of your MIG gun liner and all of your welding consumables in general. This includes the diffusor, contact tip, nozzle, and your torch cable. 

More MIG Gun Liner Tips

Affixing all plastic liners with a brass wound jumper or neck liner will always increase the working temperature of a MIG gun liner.

It is very important to stress that every liner be cut to the correct length. The right MIG gun liner will not help feeding ability if the length is improperly cut. Any gaps between the liner and tip holder/contact tip or back end of liner and the drive rolls can cause wire feeding issues.

Also, always be mindful that burrs from cutting the liner and/or wire can cause feeding issues. The brief reminder to make sure any burrs are filed away before installation may make a world of difference for the welder. Lastly, always check manufacturer’s guidelines on how to properly cut and install a MIG gun liner.

As you can see, there are many liner choices. By researching various liner materials, you can find the best possible recommendation for your customer’s application resulting in decreased downtime and improved quality and a great reputation for you. Work always goes smoother with the right tool. 

This article originally appeared in Welding and Gases Today Online and has since been updated.

Topics: MIG Guns & Torches, Welding Consumables