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The symptoms (varying cut angle, nozzle with a "bad burn" on one side) indicate nozzle orifice damage that is almost always caused by pierce height being too close or pierce delay time being too short. One bad pierce on 3/8" plate can ruin a nozzle....good plate surface sensing and proper pierc height are the best ways to get maximum nozzle life.
The retaining cap on the Hypertherm torch has internal gas flow passages that route some of the air to the nozzle (plasma gas) as well as some of the air to the shield (shield gas). They are difficult to inspect.....the best troubleshooting method is to change the retaining cap and compare cut quality. A bad retaining cap almost always creates poor cut edge angularity and varying angularity.
The shield.....the center hole needs to be perfectly round and concentric. The small bleed holes need to be clear and unplugged. Do not use an oxy-fuel "tip cleaner" as this will change the size of the center and bleed holes...which will affect cut quality. The inside of the shield....especially in the area right around the orifice should be carefully inspected for steel blowback. If you see any signs of the material you are cutting inside the shield....then your pierce height and pierce delay times are incorrect. Material blown back between the shield an the nozzle will short these parts electrically....which will double arc the nozzle....which damages the orifice. If there is material inside the shield it often can be cleaned out and polished with scotchbrite.
Swirl rings wear out over time as well. The holes are drilled at tangental angles...and are very accurately sized. These holes can wear over time. The only good way to determine performance is to try a new swirl ring...and compare cut quality between new and old.
Typically when machine cutting with a properly functioning height control:
- The nozzle will wear out twice as fast as the electrode. Depending on the power level, duration of cut and the thickness......and assuming your pierce hieght and pierce delay is 100% correct....you can expect between 400 and 1500 starts on a nozzle.
-Shields get dirty and should be cleaned periodically as listed above. If the height control is operating 100%....they will last about 5x as long as the nozzle. Clean periodically with scotchbrite and use a small amount of mig welding anti spatter spray on the outside to minimize spatter buildup.
-Swirl rings and retaining caps should last 50x (or more....mine last about 100 times nozzle life) nozzle life before cut quality deteriation occurs.
When you do the math...these parts are a bit costly to purchase....but the ultimate cost per foot of cut works out to a few pennies. Typically on 3/8" steel cut with a Hypertherm air plasma the cut cost per foot...which includes consumable use only....is about 3 to 5 cents per foot. Many other brands claim lower cost consumables.....which is true if you only compare purchase price......when comparing cost per foot the Hypertherm systems win hands down.
Hope this helps,
Jim Colt
Originally Posted by Stout
