Basics of MIG Welding: MIG Gun Liners

MIG Welding Gun liner

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 MIG Gun Liners
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.

What’s the Function of a MIG Gun Liner?

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.

How to Change a MIG Gun Liner

Proper installation is critical to the liner function. Liners may be damaged during installation and trimming a liner too short is a sure way to encounter feeding issues. Any burrs left from a poorly cut liner will catch your wire and may shave off metal or even cut through the wire entirely. To properly change a MIG gun liner, you will need the following: A new replacement liner of the appropriate diameter and length, a clean area long enough to lay your MIG gun out with the cable straight, a tool for clipping the liner, pliers, and a liner gauge or ruler. Some designs may also require a 5/64” hex key or a 10mm wrench. Here are a few key steps you need to take to change a MIG Gun Liner.
  1. Shut off the shielding gas and purge any remaining gas from your system. Turn off your machine and unplug it.
  2. Remove the MIG gun from the feeder and lay it out straight on a table or the floor. Remove the nozzle, contact tip, and diffuser.
  3. If the power pin has a guide cap or threaded nut, loosen it by turning it counter-clockwise. If the liner is retained with a set screw, loosen it with a hex key.
  4. Grip the liner from the rear with a pair of pliers and remove it from the MIG gun.
  5. Feed the new liner into the MIG gun from the rear, being careful to avoid kinking. Twist the liner clockwise if needed.
  6. If your power pin is threaded, tighten the liner collet with the 10mm wrench. If your power pin uses a guide cap, install it at this time. If your power pin uses a set screw, tighten while making sure that the o-ring is fully seated in the bore of the power pin.
  7. Trim the front end of the liner to the proper length according to the manufacturer’s guidelines. This distance may vary from 3/8” to ¾” depending on the design. Do not use helpers! A cutoff wheel or diagonal cutting pliers are the best choices. If there are any burrs, dress the end of the liner with a small round file.
  8. Reinstall the diffuser, contact tip, and nozzle. Reinstall the MIG gun on the feeder, making sure that the power pin is fully seated.
  9. Feed the wire into the MIG gun and set your drive roll tension.

MIG Gun Liners

If you take care of your liner, it’ll take care of you!

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