As anyone working with automated plasma cutting systems can tell you, plasma shops spend a lot of time and money correcting and cleaning up from the results of bad plasma cuts. Whether they're grinding off excessive dross from the finished work or even having to recut pieces altogether because the cut results didn’t meet the job’s intended specifications. The result is a financial hit to the operation, because there’s nothing but resource drains in cleanup or re-cutting. There’s only a negative cost, both in hours and materials. One of the key issues plasma torch operators encounter is unintended bevel introduced into a plasma cut. To better understand the causes and cures for unintended bevel, here are a couple of things to consider.
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What is Plasma Bevel?
“Bevel” is the angle of the cut edge. For instance, a cut with a bevel of 0º is a straight cut that runs perpendicular to the workpiece. In plasma cutting, at least one side of the cut will always have a bevel. This side of the cut is often referred to as the “bad side,” and is the result of the actions of the plasma gas, which swirls in a circular motion (“vortex”) inside the torch nozzle. Most torches will produce anywhere from 1 to 3 degrees bevel on the “good side” and from 3 to 6 degrees on the “bad side” of a cut. To reduce unintended bevel, the torch must travel in the correct direction in relation to the direction of the gas swirl. In most torches, the “good side” is on the right side of the torch as it moves away from the operator.
There’s always an angle
Several things can affect bevel angle, including correct torch height and proper torch squaring.
The shape of a plasma arc is actually oval, so it widens as gas escapes from the nozzle, then the arc tapers at the
bottom. If the torch is set too low for the intended cut, the result will be a negative bevel. If it’s set too high, you’ll get a positive bevel.
The torch should always be squared to the plate. A torch that isn’t squared will produce irregular, uneven bevel angles on each side of the cut.
Unintended bevel is one of many causes to poor cut quality. You may find yourself experiencing problems like this. If so – we want to offer a solution: