Elettro 455 Manuel D'instructions page 14

6. HOW TO USE THE MACHINE TORCH
The information in the following sections can help you to
optimize cut quality and maximize consumable parts life.
6.1. Ensure the torch and table are set up correctly
Align the torch at a right angle to the workpiece.
•
The torch may travel more smoothly if you clean, check, and
•
"tune" the rails and drive system on the cutting table. Unsteady
machine motion can cause a regular, wavy pattern on the cut
surface.
Ensure that the torch does not touch the workpiece during
•
cutting. Contact with the workpiece can damage the shield and
nozzle and affect the cut surface.
Problem
Negative cut angle
Cut OK
Positive cut angle
Notes: the right cut angle will be on the right side with respect to the forward motion of the torch. The left side will always have
some degree of bevel.
2) Dross
Some amount of dross will always be present when cutting
with air plasma. However, you can minimize the amount and
type of dross by adjusting your system correctly for your
application.
Dross appears on the top edge of both pieces of the plate
when the torch is too low (or voltage is too high if using a torch
height control). Adjust the torch or the voltage in small
increments until the dross is reduced.
Low-speed dross forms when the torch's cutting speed is too
slow and the arc shoots ahead. It forms as a heavy, bubbly
deposit at the bottom of the cut and can be removed easily.
Increase the speed to reduce this type of dross.
High-speed dross forms when the cutting speed is too fast and
the arc lags behind. It forms as a thin, linear bead of solid
metal attached very close to the cut. It is welded to the bottom
of the cut and is difficult to remove. To reduce high-speed
dross:
• Decrease the cutting speed.
• Decrease the torch-to-work distance.
6.2. Understand and optimize cut quality
There are several factors to consider in cut quality:
1) Cut angle: the degree of angularity of the cut edge.
2) Dross: the molten material that solidifies on the top or
bottom of the workpiece.
3) Straightness of the cut surface: the cut surface can be
concave or convex.
The following sections explain how these factors can affect cut
quality.
1) Cut or bevel angle
A positive cut angle results when more material is removed
•
from the top of the cut than from the bottom.
A negative cut angle results when more material is removed
•
from the bottom of the cut.
Cause
The torch is too low.
The torch is too high
3) Straightness of the cut surface
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Solution
Raise the torch; or if you are using a torch
height control, increase the arc voltage.
Lower the torch; or if you are using a torch height
control, decrease the arc voltage.
A typical plasma cut surface is slightly concave.
The cut surface may become more concave or
convex. Correct torch height is required to keep
the cut surface acceptably close to straight. Worn
consumables also affect the straightness of the
cut.
A strongly concave cut surface occurs when the
torch-to-work distance is too low. Increase the
torch-to-work distance to straighten the cut
surface.
A convex cut surface occurs when the torch-to-
work distance is too great or the cutting current is
too high. First, try lowering the torch, then reduce
the cutting current.