Solving Common Plasma Cutting Mistakes

Do you find yourself being told by customers that they are not getting the perceived life out of their replacement plasma cutting consumables?

Operators, maintenance men, shop foremen and production managers have expectations that their equipment will perform at a high level. Once your customers ask you how to improve the performance of their system, taking a look at a few basic steps can help improve on the cut quality and life of the replacement consumables.

Read the Owner’s Manual
Most people don’t take the time to read their owner’s manual before using their equipment. The owner’s manual is the bible for settings, trouble-shooting and performance indicators. Understanding how the equipment works and the pitfalls to avoid can prevent a catastrophic failure.

Plasma nozzle with circular carbon arc trails

Plasma consumables contaminated by moisture will show circular carbon arc trails on the electrodes and nozzles.

Proper Parts Assembly
The owner’s manual provides references and charts to help maximize performance of the equipment based upon the type of material being cut, thickness, amperage and gas selection. The manual provides a baseline on how to achieve maximum performance of a cutting system. Based upon these performance charts, can you determine if the correct series of consumables are assembled at the proper settings?  Variances from factory settings or changes to the parts assembly will negatively affect parts life and cut quality.

Once the correct series of parts are realized, proper assembly is required. Parts should fit snugly together and not over-tightened. By creating a snug fit and not over-tightening, a sound electrical connection and proper flow of gas and coolant is ensured.

Often overlooked is the cleanliness during a parts change out. Prevent putting contaminated parts in a torch by placing the consumables to be assembled on a clean shop rag to eliminate dirt or dust metal from contacting any new series of parts assembled into the torch.

Maintaining Clean Shop Air
When you fill your tires at a local gas station, do you ever notice the moisture in the lines before adding air to your tires?  Over 90 percent of shop compressed air systems contain moisture within the air lines. Clean shop air is critical to the performance of plasma cutting consumables. Torches can last for extended periods of time or even years with proper care. However, if a preventive maintenance program isn’t in place to eliminate moisture, expect premature failure of the replacement consumables and torch head. Installing a filtration system that connects the air line to the power supply is the first step in eliminating moisture within the compressed air system. Once the system is installed, a routine maintenance schedule is required; otherwise moisture will continue to cause problems. Moisture can also build in the lead sets that connect between the power supply and torch head. Most plasma air-cooled systems feature a purging option that allows the maintenance of clean shop air within the replacement leads.

Maximizing Consumable Life
With experience, a well-trained plasma operator can often tell by the sound or color of the arc the wear of parts life and cut quality. The most effective method of judging parts life is to check the cut quality of the material being cut; as the cut quality deteriorates, so will the parts life.

Operators must be careful not to over-extend the life of the consumables as severely worn consumables can cause damage to the material being cut, consumables or torch failure. Over-use of consumables is easily avoidable. The work horse consumable for any plasma cutting system is the electrode. For electrodes, the pit depth of the hafnium (insert held in the center of the electrode) should not exceed a 2/32-inch for air or oxygen and 1/8-inch for nitrogen or argon-hydrogen. To understand and recognize the proper pit depth of an electrode is extremely important to maximizing the life of electrodes. The electrode’s hafnium erodes from the starting and stopping in the cutting process. Materials that require a tremendous amount of starts and stops will have a shorter electrode life.

The orifice of a “nozzle” or “tip” should remain centered. Once the hole becomes distorted, it’s time for a change out. A “swirl ring” or “gas distributor” will require less change outs than the electrodes or nozzles/tips. A swirl ring should only be changed if it shows containment in the holes, burns or cracks. Does the electrode slide easily inside the swirl ring?  If no, it’s also another indication that the swirl ring or gas distributor should be changed. The holes in shields should also remain centered and not distorted. Like swirl ring/gas distributor, if the shield shows containments in the holes, burns, cracks, etc., it’s time for a change.

Different Types of Dross
Maintaining the correct cutting speed is critical to the cutting process. Little to no dross will result in a clean edge cut. Cutting too fast or too slow will create cut quality problems and will require a rework or grinding of the material and can add additional labor and manufacturing costs to the finished products. “Low speed dross” creates an accumulation of molten material along the bottom edge of the cut. If the plasma arc is straight down, the cut speed is too slow. If the arc sprays back, the speed is too fast and there will be a small hard bead of dross along the bottom edge of the cutting edge. Ideally, the arc should exit the material at roughly a 15-degree angle.

These basic trouble shooting tips are simple and can be often overlooked.

When customers are experiencing problems with the life of their plasma cutting consumables or cut quality, use the check list in the Sidebar to make sure these initial steps are addressed before trying to dig into a more complex issue.

Troubleshooting Checklist

When customers are experiencing problems with the life of their plasma cutting consumables or cut quality, address the steps below before trying to dig into a more complex issue.

Verify from the owner’s manual that proper machine settings and consumables are being used specific to the material being cut. If the settings are not to the manual, re-adjust and use the manual settings as the starting point to determine the best performance for the material being cut.

Do a visual check to make sure the consumables are not being over used, nozzle holes are not distorted, and there are no visual cracks or breaks to any ceramic materials. If any of the consumables show distortion from original appearance, it’s time to change them.

Does the plasma arc sputter or hiss? If yes, check the filter elements, look to see if the consumables are worn, or consumables are improperly installed.

Does the customer use a filtration system at the power supply? If no, there is a risk of moisture within the gas lines when cutting with shop air.

Look at the used consumables for any discoloration of the copper or carbon arc trails. If yes, these are tell-tale indicators of too much heat from improper gas flow or moisture within the torch lines.

Does the torch arc, only to have the arc blow out and, trying to re-ignite, experience the same problem?  If yes, check gas pressures for improper settings, parts are worn out, or filter element needs to be changed.

    Gases and Welding Distributors Association
    Kevin Bonneau Meet the Author
    Kevin Bonneau is president and general manager at Thermacut Inc., headquartered in Claremont, New Hampshire, and on the Web at www.thermacut.com.