LGK-100.160.200IGBT OPERATOR’S MANUAL
18
material under the same thickness, the parameter should also be different.
z
Nozzle selection
The three main dimension of nozzle are the diameter of nozzle
φ
, the hole pass length
ι
and
the compacted angle
α
, they all can affect the cutting. There should be a certain proportion
between
ι
and
φ
, the value is usually lower than 2, and it usually takes
ι
= 1.5 ∼1.8
Φ
, the
compact angle usually takes
α
＝
30°
～
60°, and now it usually takes
α
＝
30°.
z
Cutting current and arc voltage
The selection of cutting current should be according to the diameter of the nozzle, the
relationship between the two should be as: I(current A)
＝
(70
～
100)×
φ
(mm). As the increase of
the metal thickness, the influence of arc current to the cutting speed will become less. But as
the increase of current, the burning damage will be worse for the electrode and the nozzle. So
when cutting a thick metal workpiece, usually the increase of cutting speed is made by
increasing arc voltage. The actual arc voltage is decided not only by the gas type but also by the
air flux and nozzle shape. Working voltage increases with the increase of gas flux.
z
Gas flow Q
The arc voltage increases as the increase of air flow, that is, the arc power, the cutting speed,
as well as the cutting capacity and quality is improved accordingly. Because the arc
compression level increases, the energy is more concentrated, the arc beam temperature, the arc
spraying speed, as well as the arc current impulsion increases. But overlarge current may cause
the instability of the plasma arc. Usually no change is made to air flow for one torch. But it can
be adjusted a little when the cutting torch or cutting thickness is different.
z
Electrode inner contraction
Δ
L
y
When electrode inner contraction
Δ
L
y
is so small that electrode extends into spray hole,
electrode is damaged seriously by air flow impact and the combination function between high
temperature gas and electrode. This leads to the instability of plasma arc, weak compression
effect, and weak cutting penetration ability that cutting cannot be proceeded. If
Δ
L
y
is too big,
the arc is so unstable that the cutting ability is weakened. The electrode end should be placed
within siphoning zone of gas current under a relative vacuum condition, and it will difficult to
damage electrode by burning, as well as this is beneficial for compression of arc.
Δ
L
y
is about
2-4mm.
z
The distance between the nozzle and the workpiece (d)
If the d is too big, the blow power of plasma arc for molten metal decreases, so does the
cutting ability, and the burr on the bottom increases, meanwhile the instability of the arc
increases. However, if the d is too small, it increases the possibility of short circuit between the
nozzle and the workpiece. Usually d should be as small as possible on condition that no short
circuit is caused between nozzle and workpiece. The d under normal cutting of air plasma is
usually 2
～
5mm. The workpiece can also contact with the nozzle during air plasma cutting,
that is, the nozzle glide on the surface of the workpiece. This cutting method is called contact
cutting, and the cutting thickness is the half as the ordinary cutting.
z
Open circuit voltage
The power source with high open circuit voltage is required for cutting thick workpiece.
The open circuit voltage is related with air type, for example, by using argon the open circuit
voltage may be lower, while it is higher by using air, nitrogen, hydrogen.
z
Cutting speed
The cutting speed is related with many parameters. The main parameters determining
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