August 8, 2007
The FCAW process in the United States is currently estimated at more than 245 million pounds a year and still growing in popularity and use in all segments of the welding industry. One of the common issues often portrayed as a wire problem, commonly referred to as "birdnesting," is actually due to a lack of consistent wire feeding. This guide will address six areas that can adversely affect wire feeding. Attention to these areas will ensure consistent feeding and better welding results.
1. Improper Spool/Coil Brake Adjustment — If you are using spools or coils, they are mounted to a hub that can usually be adjusted. Adjust the hub so that the spool or coil"drifts" about one-eighth of a turn after welding is stopped. This enables optimization of the feed roll pressure adjustment.
2. Wire Guides — Wire guides need to be the correct size, not excessively worn, and set correctly. The wire guides should be as close to the drive rolls as possible without contacting them. You should never see wire shavings in or on the feed stand. If you do, the guide tubes could be the issue. If the wire guide tubes are excessively worn, or ovalled out, replace them.
3. Feed Rolls — Be sure the feed rolls are the correct size and type for the electrode diameter. For FCAW electrodes, knurled drive rolls are typically recommended by manufacturers. The wire diameter is usually stamped on the side of the drive rolls.
4. Feed Roll Pressure — Probably one of the biggest contributors to wire feeding and equipment failures is incorrect feed roll pressure adjustment. Excessive pressure actually notches the wire surface to the point that it acts like a file on the contact tip and causes the tip to wear prematurely. To set the drive roll pressure properly, begin with the torch as straight as possible and the feed roll pressure adjustment backed off completely. Start increasing the roll pressure until you can form a spring of four to eight inches by deflecting the wire off the floor (the larger the wire diameter, the larger the spring diameter). See Figure 1.
5. Torch/Gun Liner — Another major contributor to poor or inconsistent feeding is the torch liner. The correct liner size must be used. If the liner is clogged or kinked, replace it with a new one. If the liner has already been replaced, confirm that the replacement liner has been installed correctly. This can be checked by removing the gas diffuser and observing if the liner extends beyond the torch end. It should protrude beyond the end of the goose neck far enough to contact the inside end of the diffuser. If not, it should be replaced. When replacing the liner, before trimming the excess, roll the torch into a 12-in. circle and then push the excess liner back into the goose neck until it stops. Also be sure to remove any burr caused by trimming the liner. This could scratch the wire and create metal fillings in the gas diffuser.
6. Contact Tip/Nozzle — Finally, be sure to use the correct contact tip and nozzle. Use a contact tip and nozzle that will limit the recess inside the nozzle to no more than 3/8". The nozzle should also typically be no smaller than 1/2" diameter. If the contact tip is worn excessively, poor contact could reveal itself as a perceived feeding issue. Once the contact tip is ovalled out, replace it, as well as at any time the arc begins to start harshly or become erratic. (See Figure 2)
Flux cored wires create a high productivity process. By following these suggestions you should have many hours of trouble-free flux cored welding.
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