Line Them Up

Torch liners can have dramatic impact on fabrication downtime.

Torch LinersIn today’s environment it is absolutely critical to help your customers 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/MAG welding, one of the most frustrating is wire feed problems.

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 wire 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.

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

Liner Diameter Size
There is some debate within the industry as to how to match the 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 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 wires possess less column strength and can have a tendency to wander and buckle inside the liner, especially when there is any increased resistance. This leads to premature wear as the wire is rubbing excessively. It also can lead to serious feeding problems resulting in birdnesting. Birdnesting is a tangling of the welding wire between the drive roll and end of the torch. It not only wastes wire, but is very time consuming to correct. If your customer insists on using a larger liner, then you must encourage them to be more diligent in preventative maintenance. Regularly blowing out the liner and replacing the liner at an increased frequency will minimize some of these potential large diameter liner problems.

Large diameter liners (.052 and larger), on the other hand, have stronger column strength. Using larger diameter wires should be no problem. If oversized liners are going to be used for these applications, pay attention to the outer diameter of the liner, particularly in relation to the I.D of the MIG torch inner tube. Too large a liner OD (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 torch and accommodate large gauge welding wire.

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

Steel Liners
The traditional steel wound liner has widespread use. These liners have a good balance of rigidity and flexibility and performance and price. 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 wires, 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 potentially distorting the wire, but can also force the wire too much instead of slipping. This leads to an increase in birdnesting.

Steel liners naturally offer more resistance and are abrasive on the softer wires like aluminum and cored wire. This makes steel liners poor choices for these.

Plastic Liners
There are a variety of plastic liners for use in varied applications.

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 contain an addition of a short brass spiral wound liner attached to the front which enables this 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. This enables such low melting plastic liners to be used in high amperage/duty-cycle applications where they would otherwise melt.

Polyethylene (PE) 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 feedability, especially on small diameter welding wire. Polyethylene has a low melting temperature so they are best used in low heat applications.

Teflon (TFE) has a higher melting temperature than PE but generally is not recommended for high heat applications in an air-cooled torch because of the high direct heat. TFE can be good for higher heat applications that utilize water-cooled torches and brass neck liners. TFE 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 score the inside of the liner and lead to accelerated wear. While this is exceptionally important for the TFE liner, welding wire should be inspected prior to insertion into any plastic liner.

Carbon Teflon (C-TFE) 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 liners. It also has good temperature resistance compared to other plastic liners.

High Density Teflon liners, also referred to as high molecular weight Teflon, have a similar melting point to that of carbon Teflon liners while providing longer service life. These liners work well with a range of wires from soft wires to stiff wires and abrasive wires.

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

It is very important to stress that every liner be cut to the correct length. The right liner will not help feedability 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 remind your customer 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 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.

Gases and Welding Distributors Association
Paul Pfingston Meet the Author
Paul Pfingston is director of marketing and sales, and Jim DiLeo is regional sales manager-Canada at ABICOR Binzel, headquartered in Frederick, Maryland, and on the Web at www.binzel-abicor.com.
Jim DiLeo