3.3.3 Cutting performance
1 Amperage Standard rule of thumb is the thicker the material the more amperage required. On thick material, set
the machine to full output and vary your travel speed. On thinner material, you need to turn down the
amperage and change to a lower-amperage tip to maintain a narrow kerf. The kerf is the width of the
cut material that is removed during cutting.
2 Speed Amperage and speed are critical to producing a good quality cut. visually follow the arc that is coming
from the bottom of the cut. The arc should exit the material at a slight angle away from the direction of
travel. If it's going straight down, that means the speed is too slow, and IT will have an unnecessary
buildup of dross or slag. If the speed is too fast, it will start spraying back onto the surface of the
materia without cutting the workpiece completely. Because the arc trails at an angle, at the end of a
cut, slow your cutting speed and angle the torch in to cut through the last bit of metal.
3 Direction It is easier to pull the torch towards you than push it. The plasma stream swirls as it exits the tip, biting
one side and finishing off on the other leaving a bevelled edge and a straight edge. The bevel cut effect
is more noticeable on thicker material and needs to taken into consideration before starting your cut as
you want the straight side of the cut to be on the finished piece you keep.
4 Torch tip
height &
position
The distance and position of the plasma torch cutting tip has an affect on the quality of the cut and the
extent of the bevel of the cut. The easiest way to reduce bevel is by cutting at the proper speed and
height for the material and amperage that is being cut.
5 Tip size
and
condition
The tip orifices focus the plasma stream to the work piece. It is important to use the correct size tip for
the amperage being used,for example a tip with a 3/64" orifice is good for 0-40 amps whereas a 1/16"
orifice is better for 40-80 amps.
The low-amp tip has a smaller orifice which maintains a narrow plasma stream at lower settings for use
on thin-gauge material. Using a 25 amp tip at an 60 amp setting will blow out and distort the tip orifice
and require replacement.
Conversely, using an 80-amp tip on the lower settings will not allow you to focus the plasma stream as
well and creates a wide kerf.The condition of the tip orifice is critical to the quality of the cut result, a
worn or damaged tip orifice will produce a distorted plasma stream resulting in a poor cut quality.
6 Electrode
condition
A fixed gap is established between the electrode and the inside of the cutting tip. Electrons arc across
the gap, ionizing and super heating the air creating the plasma stream. The electrode contains an
insert in the end made of a highly conductive material called hafnium. This insert erodes with use and
develops a pit in the end of the electrode, when the pit becomes too much poor quality cuts will result
and necessitate replacement of the electrode.
7 Air quality,
Air
pressure
and
volume
Compressors take in air at atmospheric pressure and increase the pressure and store it in a tank.
Moisture that forms in air lines has a tendency to condense into larger drops when the air pressure
decreases as it is entering the plasma torch. When these droplets enter into the high temperatures in
the plenum of the torch, they immediately break down into oxygen and hydrogen, which alters the
normal chemical content of air in the torch. These elements will then dramatically change the plasma
arc which causes the torch consumable parts to wear very quickly, alters the shape of the nozzle
orifice, dramatically affecting cut quality in terms of edge squareness, dross formation, and edge
smoothness.Air pressure, flow rate and air quality are critical to quality plasma cutting and consumable
life span.Usually air pressure is preset at 60 psi . The volume capacity of your compressor is important,
If you are doing a lot of cutting, cutting thick plate (same air consumption but slower cut speeds =
longer cut time) then choose a compressor at 1.5 to 2 times the plasma system requirement.
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