Basics of MIG Welding: MIG Gun Liners
Have you ever encountered feeding problems in MIG Welding? MIG Gun Liners can help.
With the right equipment knowledge and maintenance, you can prevent feeding problems.
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. 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.
Common Wire Feeding Issues
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 used 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, as gravity pulls the insulation downward, it becomes bent at a more substantial angle.
The size of the liners typically matches both the diameter of the wire and the length of the gun cable. There is some margin of error on both accounts.
You can move up one or two sizes on the diameter of a liner without impeding proper feeding (example: a .045” liner 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.
People are most likely to run into problems when trying to squeeze a larger diameter wire through a small liner (such as .035” wire through a .030” liner).
Liners are usually 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. You can accomplish this by keeping your wire feeder closed or off the floor and blowing out your liner with compressed air.
Best practices recommend blowing out your liner with compressed air every time you install a new roll of wire 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. Bending a MIG gun cable too sharply can cause kinks in the liner. Although the rest of the components inside the cable will return to shape, you should replace a kinked coiled steel liner 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. Improper installation may damage the liners, and trimming a liner too short can cause 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.
- Shut off the shielding gas and purge any remaining gas from your system. Turn off your machine and unplug it.
- 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.
- If the power pin has a guide cap or threaded nut, loosen it by turning it counterclockwise. If the liner is retained with a set screw, loosen it with a hex key.
- Grip the liner from the rear with a pair of pliers and remove it from the MIG gun.
- Feed the new liner into the MIG gun from the rear, being careful to avoid kinking. Twist the liner clockwise if needed.
- 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 it while making sure that the o-ring is fully seated in the bore of the power pin.
- 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.
- Reinstall the diffuser, contact tip, and nozzle. Reinstall the MIG gun on the feeder and make sure that the power pin is fully seated.
- 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!
If you want to learn more about welding equipment & maintenance, we have plenty of material just for you!
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