JPH026071A - Air plasma cutting machine - Google Patents

Abstract

PURPOSE:To make the arc of the title cutter longer so that a rugged steel sheet can be cut smoothly by controlling the output frequency of an inverter in the inductive area of a frequency band within the crest of the resonance characteristics of the load circuit of the inverter and making the operating voltage of the output frequency higher than the operating voltage obtained when the output frequency is in an inductive area outside the crest. CONSTITUTION:The frequency (fz) produced by an inverter 55 is set a little higher than the resonance frequency (fo) in dependence of L and C on the load side. The conventional resonance frequency is (fo) which is much lower than the output frequency (fz) of the inverter and exists in the L area where the crest of resonance characteristics K2 practically ends. On the contrary, the resonance frequency (fo) is close to the output frequency (fz) and the frequency (fz) is in the L area of the resonance characteristics K1 or their crest. Moreover, in the case where the frequency is controlled in the C area, the current also becomes 0A when the voltage becomes 0V and no plasma arc can be maintained. In the L area, a stable plasma arc is obtained, since the current tends to flow even when the voltage becomes 0V.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an air plasma cutting machine that can easily cut a material to be cut that has irregularities.

[Conventional technology]

As shown in FIG. 7, there is a floor deck made by bending a thin steel plate 10. The thin steel plate that will be used as the flooring material needs to be cut out at the column 12 to match the outer shape of the column, and if the floor has an oblique side, the end of the thin steel plate must be cut to match the oblique side. Must be. The dotted line 14 in FIG. 4(b) is
An example of a cutting line of the thin steel plate 10 is shown.

Conventionally, gas cutting has been mainly used to cut steel plates.

However, gas cutting is not suitable for cutting thin plates, and there are problems such as the cut surface is messy, and if the tip of the gas torch comes into contact with the steel plate, it may cause a misfire, requiring skill. Additionally, since flammable gas is used, there are safety issues.

Another cutting method is plasma cutting. There are two methods for cutting thin steel sheets: small current air plasma cutting and oxygen plasma cutting, and an example of the former is shown in FIG. In this figure, 20 is a compressor unit, which includes a motor 21, a compressor 22, and an air tank 23. 24 is a pressure detector, 2
-5 is an air intake port. Further, 26 is an air unit, which includes a drain tank 27 and a pressure regulator 28 .

Further, 30 is a plasma power supply, which includes a rectifier 31, a transistor 38 for oscillating a transformer 3211, and a high frequency generator 33.
, a coupling coil 34 and a capacitor 35 for introducing the high frequency generated by the generator into the power supply circuit, and a solenoid valve 36 and a pressure switch 37 for the air supplied from the compressor. Further, 40 is a plasma torch, 41 is its electrode, and 42 is a tip. Electric power and air are supplied to the plasma torch 40 through a cable 43. This generates a plasma flame 44, which cuts the material to be cut 46, which is the thin steel plate 10 in the above example. 45 is air for cooling.

The compressor operates until the pressure in the air tank 23 reaches a predetermined value, stops operating at the predetermined value, and resumes operation when the pressure decreases due to the use of air. As shown in FIG. 9(a), the compressor operates with air pressure. Stop, repeat.

As shown in (b), (c), and (d) of the same figure, when the torch switch (not shown but attached to the torch 40) is turned on, air is immediately supplied, and after preflowing for a certain amount of time, the plasma arc is ignited. do. As soon as the torch switch is turned off, the plasma arc is extinguished, after which the air afterflows for a time tz, and then the supply is stopped.

[Problem to be solved by the invention]

When cutting thin steel plates, it is common to move the tip of the torch of a small current plasma cutting machine into contact with the thin steel plate. Because of this, the tip of the torch tends to separate from the thin steel plate, causing frequent arc breaks and making it impossible to cut smoothly. That is, the torch is moved up and down to maintain close contact with the floor deck 10, which has a trapezoidal wave-like cutting surface, and furthermore, the torch is moved along the line 14 while changing the torch angle so that the cutting surface is always perpendicular to the steel plate surface. In the concave portions 10a and convex portions 10b carved in the floor deck 10, the tip of the torch does not fit into the concave portions or the corners of the convex portions, but there are places where the torch tip cannot enter the concave portions or the corners of the convex portions, and has no choice but to separate. In such places, the arc length becomes long, the arc becomes unstable, and arc breakage is likely to occur.

It is an object of the present invention to improve this point and provide a small current air plasma cutting machine that can smoothly cut uneven thin steel plates without making the arc unstable even if a close contact state cannot be maintained. It is.

[Means to solve the problem]

FIG. 1 shows the basic configuration of the air plasma cutting machine of the present invention. 51 is a DC power supply, which is usually obtained by rectifying a commercial power supply. An inverter 55 includes a switching element 56 and a transformer 57, and generates alternating current at a frequency f2. The output frequency f2 is 2f. The switching element 56 is a transistor or a thyristor, and can control the output voltage by controlling the on period, thereby also performing constant current control. A full-wave rectifier 58 converts the alternating current generated by the inverter 55 into direct current. L and C are smoothing inductances and capacitances inserted into the output circuit of the rectifier 58, and these include inductances and capacitances in the power supply cables f, f, etc. Power supply cable f,, II! , corresponds to the cable 43 in FIG. 8, and is usually integrated with an air supply hose. This power supply cable l.

A plasma torch is connected to the tip of 2. A shows the arc originating from the torch.

A cable connecting the power supply device (55, 58, etc.) 50 and the plasma torch 402. ．． If a relay box 60 is installed between 22 as shown in FIG. 1(b) and a high-frequency generator 33 using spark discharge is housed in the box, the work site will be wide such as a deck floor, and therefore the cables f,, fz will be long. Suitable for cases where

In the present invention, as shown in FIG. 2, the frequency f2 generated by the inverter 55 is set to be slightly higher than the resonant frequency f0 determined by the load side coefficient C. The conventional resonant frequency is f0! So, it is warmly lower than the inverter's output frequency f2, and has resonance characteristics! The frequency f2 is located in the L-type region where the peak of . On the other hand, in the present invention, the resonant frequency f0
is close to the output frequency f2, and the resonance characteristic is still in the +Yamauchi L-type region. Further, when the frequency is set in the C region, when the voltage becomes 0 volts, the current also becomes 0 ampere, and the plasma arc is not maintained.

In the L-type region, even if the voltage drops to 0 volts, the current tends to continue flowing, so the plasma arc becomes extremely stable. [Function] The air plasma cutting machine shown in Fig. The operation is similar to that shown in FIG. 8, but arc breakage does not occur even if the tip of the torch is slightly heated by the material to be cut. This will be explained below.

Since the output frequency f2 of the inverter 55 is set as shown in FIG. 2 with respect to the resonance frequency f0 on the load side, the highest voltage (hereinafter referred to as operating voltage) during plasma arc cutting (hereinafter referred to as operating voltage) is expressed by rectifier output voltage, etc. becomes ■2. On the other hand, the operating voltage of the conventional system is 1, and VZ>L.

The voltage-current characteristics of such a power supply device are as shown in FIG. K3 is the characteristic of the present invention, K4 is the characteristic of the conventional method, and Vo
is the no-load voltage. This power supply device performs constant current control, and the cutting operation is performed in a portion P of the constant current region.

As shown in Fig. 4, the cutting area P is divided into a contact cutting area P1 and a non-contact cutting area P2, but in the conventional method b), the operating voltage ■1
Since the arc length is low, the non-contact cutting area P2 is narrow, which means that the arc length cannot be increased, and arc breakage is likely to occur when the material to be cut has irregularities. On the other hand, in method (a) of the present invention, since the operating voltage (2) is high, the non-contact cutting area P2 is wide, which means that the arc length can be increased, and even when the material to be cut has irregularities, the arc There is little risk of cutting. Moreover, the no-load voltage is vo, which is the same as in the conventional system, so there is no need to make the voltage particularly high.

〔Example〕

5 and 6 show examples of voltage-current characteristics of the power supply device of the present invention. As shown in curve 3 in FIG. 5, the operating voltage (horizontal voltage in the figure) of the present invention is nearly 180V, whereas in the conventional system shown in curve 4, this is about 140V. The no-load voltage is a little less than 240V in both cases. In the present invention, the constant current can be maintained up to about 160V, and the arc length is 20m.
About m is possible. On the other hand, in the conventional and conventional methods, the constant current can only be maintained up to about 115V, and the arc length is 3 to 3.
The limit is four cabinets.

Figure 6 shows the AC voltage (inverter output voltage) Vac at 24
The voltage-current characteristics are shown when the voltage is changed to 0V, 220V, 200V, and 190V, and the constant current characteristics are set to IOA, 2OA, and 30A. Increasing the voltage will widen the constant current range, but the no-load voltage will also increase.

〔Effect of the invention〕

As explained above, in the present invention, the arc length can be increased with the same power supply capacity, so even uneven thin steel plates can be cut smoothly with a small current air plasma cutting machine. It is also highly safe because it does not use

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Figs. 2 to 4 are explanatory diagrams of the operation and effect, Figs. 5 and 6 are graphs showing the characteristics of the embodiment of the present invention, and Fig. 7 is a floor deck. FIG. 8 is an explanatory diagram of the configuration of a conventional air plasma cutting machine, and FIG. 9 is an explanatory diagram of the operation of FIG. 8. zI figure ta1 present invention (bl conventional ° also silkworm pe(bl /

Claims (1)

[Claims] 1. In an air plasma cutting machine equipped with an inverter and using a power supply device with constant current characteristics, the output frequency of the inverter is in the inductive region of the frequency band within the peak of the resonance characteristics of the load circuit of the inverter; An air plasma cutting machine characterized in that the operating voltage is higher than that in the inductive region outside the machine.