Basics of MIG Welding: MIG Gun Liners
Have you ever encountered feeding problems in MIG Welding? MIG Gun Liners can help.
Oftentimes, feeding problems can be prevented with the right equipment maintenance.
Welding problems are a mild inconvenience at their least. At their worst, they contribute substantially to lost productivity and cause delays in the fabrication process.
MIG gun liners tend to have some kind of mysterious aura surrounding them and even some veteran MIG welders don’t fully understand the design, function, and replacement process of their liners.
However, we’re here to simplify the use of MIG gun liners and provide you with a more in-depth understanding of their role.
The basic function of a liner is to act as a guide for the wire electrode from the drive rolls to the contact tip. Sounds simple, right? Well, yes and no.
While the job of a liner is pretty straightforward, the dynamics of a MIG gun and wire feeding system present a unique set of challenges. When the wire encounters resistance on its journey from the spool to the pool, a myriad of problems may occur.
The most common symptoms of a wire feeding issue are erratic wire feeding, burn back, and bird nesting (this can occur at either end of the liner). Consequently, you should carefully choose liners to fit the application.
Most liners are manufactured from carbon steel wire (also called music wire or piano wire), which is tightly wound in a coil to allow for a balance of rigidity and flexibility. The profile of the wire can be round, oval-shaped, or flat, with each shape lending itself to the optimum function of its design.
Liners for use with stainless steel, flux-cored, or aluminum wire will often be coated with a polymer such as Teflon to reduce drag, wear, and contamination. Tightly fitted insulation wrapped around the base of the liner prevents shielding gas from seeping through where the gun cable exits the feeder. Additionally, the insulation is often bent at a more substantial angle as gravity pulls it downward.
Liners are typically sized to match both the diameter of the wire and the length of the gun cable. There is some margin of error on both accounts.
Typically, moving up one or two sizes on the diameter of a liner will not impede proper feeding (example: a .045” liner being used with .035” wire). The fit is more critical with smaller diameter wire than with larger sizes. A.023” wire may not feed properly through a .035” liner.
Where you are likely to run into problems is trying to squeeze a larger diameter wire through a liner that is not designed for it(such as .035” wire through a .030” liner).
Liners are typically a foot or so longer than the gun and cable assembly, which allows the operator to trim it to the proper length.
When should you change a MIG Gun Liner?
Liners don’t get the attention they deserve. They sit silent, ignored, and unmaintained until a problem happens. Truth be told, they don’t need a lot of attention, but a little bit of love goes a long way. The single most important measure a welder can take to prolong the service life of their liner is to keep contaminants out of it. This can be accomplished by keeping your wire feeder closed or off the floor and blowing out your liner with compressed air. It is generally recommended that the latter be done every time a new roll of wire is installed in the feeder. Simply remove all wire from the MIG gun, remove the contact tip, remove the MIG gun, and shoot a few blasts of clean compressed air from the power pin end. You should be able to feel the air pressure at the front end of the MIG gun. When the liner inevitably does reach the end of its life, you will likely encounter feeding issues. If a MIG gun cable is bent too sharply, the liner may become kinked. While the rest of the components inside the cable will return to shape, a coiled steel liner that has become kinked must be replaced immediately. If you take care to keep contaminants out of your liner and not abuse your MIG gun, you can expect an average of 6-12 months of service life.