Above: Hypertherm shielded torches drag cut at up to 200 amps with no friction or double arcing. 

Here’s a question that equipment dealers commonly receive: How long should I expect the consumables to last on my air plasma system? Unfortunately, the answer isn’t all that simple, especially if the operator is cutting pieces by hand.

It’s difficult to give an exact (or even inexact) measurement because so many factors influence consumable life, including the operator’s experience, the type and age of the torch, the material and its gauge, and air quality. However, if the operator understands good piercing and edge starting techniques to keep molten metal from blowing back onto the torch nozzle (or tip if working with a system not built by Hypertherm) then consumable life can be extremely long.

Damage accumulates

Problems with plasma torches occur most often when hand cutting with an exposed (unshielded) nozzle. Ideally, the operator should hold a standoff with an unshielded setup at all electrical current flows greater than 30 amps or so. If the nozzle touches the plate during a cut, it creates a current path between the negative electrode, nozzle and positive plate. This causes a double arc between the electrode and nozzle, and the nozzle and plate, which damages the nozzle orifice.

When the orifice sustains a small amount of damage, poor angularity is the first thing a savvy operator will notice, followed by more double arcs and more damage. Eventually, the operator notices slower cut speeds and heavy dross, at which point it is time to change the nozzle.

It is recommended that shops keep a record of the average parts life for their consumables (in number of starts or arc-on time) and develop guidelines for expected parts life based on the amperage, material and thickness of the pieces being cut. Once average parts life is established, the operator will be able to determine when to check and or replace the parts, which goes a long way toward preventing a catastrophic failure.

Some people use a standoff device to hold the torch up off the metal. Unfortunately, molten metal can still blow back during piercing, once again creating a current path from the nozzle to the plate, and leading to double arcing. If you have used a handheld torch with an exposed nozzle at more than 30 amps while drag cutting, you’ve likely felt the torch “sticking” to the plate. This is a result of double arcing.

Shield technology

Hypertherm invented and patented the shielded torch technology in the 1980s, and has steadily improved it over time. The shield’s primary function is to electrically isolate (or insulate) the nozzle from the plate, totally eliminating double arcing. Hypertherm shielded torches drag cut at up to 200 amps with no friction or double arcing. This is great for easing the fatigue caused by holding a standoff and for dramatic improvement in consumable life and cut quality.

In the past 30-plus years, Hypertherm engineers made enormous strides in extending the life of these consumables. Each new iteration of the shield from Hypertherm seems to improve the capability (for both hand and machine cutting).

For example, the Duramax torches—which come standard with nearly all new Powermax systems and as a retrofit torch for most older Hypertherm systems—use the shield for more than just nozzle isolation. The shield and nozzle for these torches employ patented technology called Conical Flow to inject greater air flow around the perimeter of the arc. This increases the energy density of the arc and provides better cooling to the nozzle. The result is no sticking, no double arcing, faster cut speeds, thicker piercing capability, and dramatically longer nozzle life.

So, assuming a plasma cutting system operator uses a Duramax torch with the latest consumable technology, he or she would be expected to cut hundreds of feet of metal without changing nozzles.

In addition, the operator should be able to make between 600 and 1,200 pierces, after which time the electrode would need replacing. The remaining consumables would likely continue to work just fine. Put another way, a busy shop should be able to get between two and four full days of actual arc-on time before needing to replace any of their consumables.

Jim Colt is a strategic account manager for Hypertherm Inc.

Hypertherm Inc.
Hanover, New Hampshire
phone: 800/737-2978
www.hypertherm.com