JPS6121400B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a plasma arc torch, and more specifically to a plasma arc torch provided with two or more mantles having narrow holes around a center electrode (hereinafter referred to as "mantle-type plasma arc torch"). The purpose of the present invention is to provide an operation method that improves the stability of the arc column of the .) and significantly improves the performance such as current density and output.

In a plasma arc torch, an arc column is passed through a narrow hole with an air flow (inert gas such as argon, helium, or active gas such as air or oxygen), the workpiece is used as one electrode, and the electricity generated on the workpiece is It uses concentrated energy to weld, cut, etc. various metal materials. This concentration of electrical energy is limited by the double arc created in the constricted hole of the torch. The generation of double arcs depends on the stability of the arc column within the torch.

For example, even if the tip of the center electrode (cathode rod) is offset by about 0.1 mm from the center axis of the torch, the arc current value (maximum allowable current value) that can pass through the narrowed hole will drop by more than 10%. and the degree of concentration of electrical energy decreases. For this reason, many methods and jigs have been devised to accurately set the electrode position. In addition, a method has been developed to improve the stabilization of the arc column including the cathode spot by flowing an air flow in a swirling manner, thereby improving the degree of concentration of electrical energy in the plasma arc torch.

In this way, various technologies related to plasma arc torches have been developed in the past, but the ultimate technology for all of them is arc stabilization, and the performance of the torch is influenced by the quality of stabilization of the arc column within the torch. It is no exaggeration to say that this determines the value of industrial equipment.

As a result of extensive research and development into stabilizing the arc column of a plasma arc torch, the inventor of the present invention found that, in a jacket-type plasma arc torch, by dividing gas at an appropriate ratio into at least two annular channels formed inside the torch. It was discovered that the stability of the arc column was significantly improved and a high degree of energy concentration, which had not been possible before, could be obtained. In other words, it has been found that there is a region in which the arc column is significantly stabilized in the split ratio of the gas flowing through at least two annular channels of a jacket-type plasma arc torch.

The present invention is based on the above knowledge, and is based on the positive polarity (center electrode (electrode with an arc column)) to be operated.
This is a jacket-type plasma arc torch with a negative polarity (polarity of the torch is negative), and due to the bias of the airflow path of the outer channel, which is the airflow path of a conventional torch, the presence of an external magnetic field, and the arrangement of the reverse polarity torch, which will be described later, the arc column inside the torch is centered. Off-axis heat loss increases in the outermost mantle. The present invention addresses such arc column deviations by operating the gas at a flow rate substantially equal to or greater than the flow rate at the extreme value coordinate of the characteristic curve of the heat loss of the outermost mantle versus the inner annular channel. It is characterized by correcting the bias of the arc column and improving the concentration of energy by flowing it through the inner channel of the torch. Here, the inner channel refers to the channel on the center electrode side when the jacket-type plasma arc torch has two annular channels, and refers to the two channels on the center electrode side when there are three annular channels.

Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings.

The method of arranging a reverse polarity plasma arc torch described in detail here is based on the above-mentioned shunting method that corrects the unavoidable deviation of the arc column within the torch that occurs when a positive polarity plasma arc torch is used for cutting, welding, etc. This is an appropriate example for finding a ratio.

FIG. 1 shows an example of a positive-polarity jacket-type plasma arc torch used in the operating method of the present invention, which has two jackets. This torch has cathode rod 1
a holder 2 holding the cathode rod and a first mantle 4 defining a first annular channel 3 surrounding this cathode rod.
and a second mantle 6 defining a second annular channel 5 surrounding this mantle. Argon is supplied to the first annular channel 3 from the gas supply port 7;
A first gas 8, which is an inert gas such as helium, is supplied to the electrode and discharged from the narrowed holes 9 and 10.
A second gas 12, which is an inert substance, is supplied to the second annular channel 5 from the gas supply port 11 and is discharged from the narrowed hole 10. Holder 2, first mantle 4,
The second mantles 6 are each electrically insulated by an insulator 13. The holder 2 is connected to the negative terminal of the power source 15 by a conductor 14, and the first jacket 4 and the second jacket 6 are connected to the positive terminal of the power source 15 via switches 16 and 17, respectively. The water-cooled rod-shaped electrode 18 is connected to the positive terminal of the power source 15 by a conductor 19.

The positive jacket type plasma arc torch constructed as described above is normally operated as follows.

First, the first gas 8 is caused to flow, and an arc 20' is generated between the cathode rod 1 and the first mantle 4 by the high frequency power source built in the power source 15, and the switches 16,1
7 are sequentially opened, the arc 20' moves to the electrode 18 and becomes an arc 20. At this point, the second gas 12 is made to flow, the supply of the first gas 8 is stopped, and the arc current is increased and adjusted by the power source 15. Various types of processing are performed through such operations.

As mentioned above, the method of stopping the first gas 8 in the operating state and operating with no gas present in the first annular channel 3 is based on the cathode envelope type plasma previously developed by the present inventor. This is a method of operating an arc torch (Patent No. 663311), which eliminates arc instability caused by the cathode.

In contrast, the operating method of the present invention is characterized by operating the above-mentioned positive-polarity jacket type plasma arc torch by flowing gas through the first and second annular channels 3 and 5 at an appropriate split flow ratio. In some cases, such a shunt ratio is specified by the method described below, but the shunt ratio specified there is a region that significantly stabilizes the arc column, causing the arc column to move straight, increasing the current density (maximum allowable current value) (due to an increase in torch pressure), it brings about remarkable effects such as an increase in output due to an increase in pressure inside the torch.
It is possible to dramatically increase the concentration of electrical energy.

In Fig. 2, a reverse polarity mantle type plasma arc torch is used in place of the water-cooled rod-shaped electrode 18 shown in Fig. 1, and the reverse polarity is applied in the direction crossing the positive polarity mantle type plasma arc torch A to be operated. A cloaked plasma arc torch B is installed. Torch A
The configuration is the same as in FIG. The torch B includes a holder 22 holding an auxiliary cathode rod 21, a first mantle 24 defining a first annular channel 23 surrounding this auxiliary cathode rod 21, and a second mantle surrounding this mantle.
a second mantle 26 defining an annular channel 25 of the
It is made up of. first annular channel 23
A first gas 28, which is an inert gas, is supplied from the gas supply port 27 and released from the narrow holes 29 and 30. A second gas 32, which is an inert gas, is supplied to the second annular channel 25 from the gas supply port 31 and is discharged from the narrowed hole 30. holder 22,
The first mantle 24 and the second mantle 26 each have an insulator 3
3 and is electrically insulated. The holder 22 is connected to the negative terminal of the auxiliary power source 35 by a conductor 34, and the first
The jacket 24 is connected to the positive terminal of the power source 15 by a conductor 19 and is also connected to the positive terminal of an auxiliary power source 35 via a switch 36.

In addition, the first and second mantles 4 and 6 holder 2 of torch A and the first and second mantles 24 and 26 of torch B,
The holders 22 each have a structure in which cooling water flows back, but are not shown for convenience of explanation.

Torch A and torch B having the above configuration are operated as follows.

(1) In the torch A, the first gas 8 is caused to flow, and an arc is generated between the cathode rod 1 and the first mantle 4 using a high frequency power source built in the power source 15,
Next, the switch 16 is opened, and while the switch 17 is kept closed, the arc 20' is transferred between the second jackets 6 to operate as a so-called non-transition type plasma jet device.

(2) In the torch B, the switch 36 is closed, the first gas 28 is caused to flow, and the auxiliary power source 35 generates a non-transfer type arc 40' between the auxiliary cathode rod 21 and the first mantle 24, and the plasma air flow is is emitted toward the intersection 37 of the central axes of the two torches. In this state, (3) when the switch 17 is opened, hairpin arcs shown at 20 and 40 are formed between the cathode rod 1 of the torch A and the first jacket 24 of the torch B; Here, (4) After flowing the second gas 12 of torch A, stop the first gas 8. Also, after flowing the second gas 32 of the torch B, the first gas 28 is stopped, and the switch 36 is turned on.
is opened and the auxiliary arc 40' is also stopped. Next, the arc current is increased by the power supply 15.

Now, here, the total gas flow rate Q of the torch A is the sum of the flow rate Q ₁ of the first gas 8 and the flow rate Q ₂ of the second gas 12, and it is assumed to be constant (Q = Q ₁ + Q ₂ ... constant), and Q ₁ When increasing from 0 (Q ₂ decreases accordingly) and measuring the heat loss L of the second jacket 6 from the rising temperature of the cooling water, the characteristic curve (a) of Q ₁ vs. L in Figure 3 is obtained. It will be done.
As is clear from the characteristic curve (a) in Figure 3, Q ₁
As L increases from 0, L decreases, reaches the minimum value at the extreme value coordinate point A, and then increases again.

The main specifications of this measurement are as follows.

Narrow hole in the first mantle of torch A 9: Diameter 3.0mm,
Length 3.0mm.

〃 2nd 〃 10: Diameter 1.0mm, length 0.8mm.

Narrow hole 29 in the first mantle of torch B: diameter 2.0 mm, length 2.0 mm.

〃 2nd 〃 30: Diameter 3.0mm, length 4.0mm.

Distance between the intersection point 37 of the central axes of both torches and the tip of each torch: 10 mm each.

Intersection angle of the central axes of both torches: 100° Q of torch A: Argon, Q ₁ + Q ₂ = 2.0/min (reading of atmospheric pressure scale flowmeter) Flow rate of second gas 32 of torch B Q ₃ : Argon, 1.0/min min (reading on an atmospheric pressure scale flow meter) Note that if the 6th end of the second mantle of the torch A is brought too close to the intersection 37, the value of L increases although the position of the point A with respect to Q ₁ does not change. Also, if it is too far away, the hairpin arc will become unstable. Usually, when measuring in the range of 5 to 15 mm and also measuring the intersection angle of both torches in the range of 90 to 114 degrees, the same value of Q ₁ at point A is obtained. However, the distance between the intersection 37 and the end of the second jacket 26 of the torch B is arbitrary within the range permitted by the power supply voltage.

Also, the characteristic curve (b) is shown in Fig. 3, but this shows that when torch A is operated alone, that is, using the torch shown in Fig. 1, Q = Q ₁ + Q ₂ as in the above measurement.
This is a characteristic curve obtained by measuring L of the second mantle 6 while keeping Q 1 constant and increasing Q ₁ from 0 (Q ₂ decreases accordingly). Curve (b) shows the characteristic that L increases as Q ₁ increases from 0, but the increasing characteristic almost coincides with curve (a) above Q ₁ at point A of curve (a). Shows increasing properties.

Now, considering both characteristic curves (a) and (b), in the region of Q ₄ to the left of point A, the two curves are largely separated, and in the region to the right, they almost match. When an external magnetic field is applied, both curves change in the left region, but there is almost no change in the right region. In other words, regarding curve (a), under the influence of the magnetic field generated by the hairpin arc formed between both torches, the arc column on the torch A side will move as shown by the broken line in Figure 2. It is deviated from the central axis (this deviation can be observed when the narrowing hole is enlarged), and as Q ₁ increases from 0, the deviation of the arc column 20 decreases, so L decreases,
When the flow rate is substantially the same as or higher than the flow rate at point A (0.3/min), the arc column moves straight regardless of the influence of the magnetic field and is stabilized on the central axis within the narrowed holes 9 and 10, The degree of stabilization can be said to be such that it is hardly affected by the application of an external magnetic field. On the other hand, regarding curve (b), even in the operating state of a single torch in Fig. 1, the left side of point A
The Q ₁ region is an unstable region where the arc column moves straight and L is small, but it is biased due to the influence of the external magnetic field.The Q ₁ region on the right is an unstable region where the arc column moves straight without being biased even when affected by the external magnetic field. It can be said that this is a stable area.

As is clear from the above measurement results and their discussion, even if the Q flowing to the torch to be operated (Fig. 1) is constant, by dividing a part of it into the inner channel (first annular channel 3) as _Q1 , , the arc column within the torch is significantly stabilized. This stabilized splitting ratio is determined by forming a hairpin arc between both torches as shown in Fig. 2 to keep Q constant, and _Q1 is determined from point A of the characteristic curve of _Q1 vs. L. is specified as a flow rate that is the same or higher than the actual flow rate.

Note that the point A for specifying the split flow ratio obtained as described above is important for the following reasons.

(1) The operating state in which a hairpin arc is formed between two torches as shown in FIG. 2 also occurs in the actual operation of the single torch shown in FIG. 1 to be operated. That is, at the beginning or end of operations such as welding, cutting, etc., hairpin arcs are often formed between the workpiece and the torch. Therefore, the conditions for stable operation of the torch as an industrial device must be sufficiently satisfied even under operating conditions where a hairpin arc is formed (for example, the maximum allowable current value of the torch is also (The value shall be acceptable under the operating conditions in which the arc was formed.) For this reason, the A point determined in the operating state where a hairpin arc is formed has an important meaning.

(2) When operating a single torch as shown in Figure 1, when operating in a flow rate range of Q ₁ or more specified by point A, the pressure increase effect within the torch will be applied as described later. As a result, the allowable current value can be significantly increased.

FIGS. 4 and 5 show characteristic curves of Q ₁ versus L, respectively, using the apparatus shown in FIG. 2 and using Q and arc current 1 as parameters. In both cases, the A point for specifying the diversion ratio was obtained.

Figures 6 and 7 show how to use the device shown in Figure 2 to
Similarly to Fig. 5, with 1 and Q as parameters,
The pressure in the second annular channel 5 of the torch A, that is, the torch internal pressure P _N with respect to Q ₁ is measured.

In either case, P _N increases with Q ₁ , and the increasing characteristic is remarkable up to the vicinity of Q ₁ specified at point A. Note that an increase in P _N means an increase in the enthalpy of the gas flowing out from the torch, that is, an increase in the output of the torch, and when the shape of the narrow hole, Q, and 1 are constant, P _N is directly proportional to the output. Therefore, the output of the torch can be significantly increased by diverting a portion of the Q flowing into the torch as Q ₁ to the inner channel, particularly at a flow rate substantially equal to or greater than Q ₁ determined from point A. It is understood that

Figure 8 uses the device shown in Figure 2, Q = 2.0/pin
The dividing ratio _Q2 : _Q1 is 2.0:0, 1.8:0.2,
The relationship between P _N and 1 was measured by changing the readings of 1.6: 0.4, 1.4: 0.6, and 1.2: 0.8 (atmospheric pressure scale flow meter).

However, a plurality of second mantles 6 were used to avoid damage caused by double arcing, and the diameter of the narrowed hole 10 was 1.0 mm, and the length was approximately 1.0 mm. When the current splitting ratio is 1 = 100 A or more and P _N = 4.0 Kg/cm ³ or more, no double arc occurs. When the splitting ratio is , a double arc occurs at the point marked with an x. As is clear from these results, when the flow rate is substantially the same as or greater than Q ₁ determined from point A of the characteristic curve (a) of Q ₁ vs. The current value Ic has increased significantly. However, as can be seen from the tendency when the splitting ratio is , if Q ₁ is increased too much, L increases and Ic decreases, and eventually Q ₁ = 0, that is, the Ic obtained when no gas is split into the inner channel. It will decrease more than that. Therefore, it will be lower than the Ic obtained when not dividing the flow in this way.
The value of Q ₁ indicates the upper limit of the splitting ratio of the present invention.

Furthermore, using the apparatus shown in Fig. 1, Q ₂ :Q ₁ =2.0:
0, the diameter of the narrowing hole 10 of the second mantle is 1.0 mm,
If the length is shortened by processing from the outside, a characteristic curve of P _N vs. I that is almost the same as the splitting ratio shown in FIG. 8 can be obtained. However, a double arc occurs at I=65A (that is, Ic=65A). In other words, it is understood that when gas is caused to flow through the inner channel of the torch at a specific split flow ratio as in the operating method of the present invention, an Ic that is about 1.5 times larger can be obtained with the same P _N vs. I characteristic curve. . Conventionally, in order to increase P _N in order to increase the output of the torch, the length of the narrowed hole had to be increased, and when the length was increased, Ic suddenly decreased. However, as can be seen from the above results, it is understood that such problems can be solved by the operating method of the present invention.

As is clear from the above measurement results and explanations, when operating torch A, a hairpin arc is formed between torch A and torch B, and the sum (Q) of Q ₁ and Q ₂ of torch A is By flowing gas into the inner channel of torch A at a flow rate substantially equal to or greater than Q ₁ determined from point A of the characteristic curve of Q ₁ vs. L, As a result, the arc column is significantly stabilized, resulting in remarkable effects such as the arc column moving straight, an increase in current density due to an increase in Ic, and an increase in output due to an increase in P _N .

In addition, in the Q ₁ vs. L characteristic curves in Figures 3, 4, and 5, point A, which shows the minimum value of L, is the point where L due to the bias of the arc column in the torch is completely eliminated. It is difficult to define. but,
Q ₁ identified from point A significantly stabilizes the arc column in the torch, causing the arc column to move straight, increasing Ic,
It is understood that this has the effect of increasing P _N . It is also understood that point A is the only extreme value for determining an appropriate Q ₁ for the operating method of the present invention from the characteristic curve of Q ₁ vs. L.

FIG. 9 shows an example of another torch A used in the operating method of the present invention, which consists of three mantles and is configured to produce an active gas plasma arc. In the figure, the same components as in the torch of FIG. 1 are designated by the same reference numerals. The configuration of the torch shown in FIG.
An annular channel 42 and its gas supply port 43 are provided, and an electric circuit having an arc transition switch 44 is provided.

The torch A in FIG. 9 is operated as follows. First, an inert gas is used as the third gas 45, the first gas 8, and the second gas 12 flowing through the torch.

(1) Similar to the operation shown in Figure 1, flow the third gas 45, open the switches 44 and 16, and switch the arc to the second
Move to cloak 6.

(2) Here, the third, first and second gases 43, 8, 12
After adjusting the flow rates Q ₁₂ , Q ₁₁ , Q ₂ and I, the switch 17 is opened to generate the arc 20.

(3) Then, the first gas 8 and the second gas 12 are switched to active gas.

By the above operating procedure, an active gas plasma arc is generated from the torch A in FIG.

Here, torch B is combined as in the case of Figure 2, Q = Q ₁₂ + Q ₁₁ + Q ₂ is constant, and Q ₁₂ (inert gas) necessary to protect the cathode rod is also constant, When Q ₁₁ is increased from 0 and L of the second mantle 6 is measured from the rising temperature of the cooling water, the characteristic curve (a) in Figure 3 is obtained.
Similarly, point A of the characteristic curve of Q ₁ (=Q ₁₁ +Q ₁₂ ) versus L is found. In other words, _Q1 , which is the gas flow rate that stabilizes the arc column found from point A, is the sum of _Q11 , which is an active gas, and _Q12 , which is an inert gas.
Since Q ₁₂ is constant, Q ₁₁ is obtained by dividing a part of Q ₂ , which is an active gas.

That is, the third inner channel of torch A
and the first annular channel 42, 3, the third annular channel 42 is supplied with an inert gas having a constant Q ₁₂ necessary to protect the cathode rod, and the first annular channel 3 is supplied with an inert gas having a constant Q 12 necessary to protect the cathode rod. By flowing active gas at a flow rate substantially equal to or higher than _Q11 determined from point A, the arc column within the torch is stabilized, and a plasma arc with a high active gas concentration can be obtained as the current density increases. .

For example, when cutting mild steel by generating an active gas plasma arc with the torch shown in Fig. 1 using an inert gas (argon) as the first gas 8 and an active gas (air, oxygen) as the second gas 12, the cutting speed is If you try to increase the active gas concentration in the plasma arc (reducing _Q1 ) in order to increase the However, there was a problem that the arc voltage also decreased.

However, such problems can be solved by the above-described operating method of the present invention using the torch shown in FIG.

Example The test was carried out using the torch shown in FIG. 9 under the following conditions.

Narrow hole 46 in the third mantle: diameter 26 mm, length 2.0 mm 1st 9: 4.0, 3.0 2nd 10: 1.0, 0.7 Q ₁₂ : Argon 0.25/min (atmospheric pressure scale) Flow meter reading) Q ₁₁ : Air 0.15/min (〃
) Q ₂ : Air 5.6/min (
) As a result, stable operation was possible at P _N =5 Kg/cm ² and I = 90 A, that is, current density 115 A/mm ² and air concentration 96%.

The torch shown in FIG. 9 is constructed by constructing the inner channel of the torch shown in FIG. 1 into two annular channels, a third and a first, so that the gas flowing through the inner channel is divided. Therefore, when an inert gas is caused to flow through all channels, this corresponds to the torch shown in FIG. 1, and the same effects as in FIG. 1 can be obtained.

As detailed above, in operating the torch A, the operating method of the present invention significantly stabilizes the arc column within the torch by flowing gas at an appropriate flow rate from at least two annular channels of the torch. The current density of the generated plasma arc,
It has a remarkable effect of significantly improving performance such as output, and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a positive-polarity jacket-type plasma arc torch used in the operating method of the present invention, and FIG. 2 is a cross-sectional view showing an example of a combination of a positive-polarity jacket-type plasma arc torch and a reverse-polarity jacket-type plasma arc torch. The cross-sectional view shown in FIG. 3 shows an example of a characteristic curve of gas flow rate versus heat loss obtained using the torch of FIGS. 1 and 2. FIGS. 4 and 5 respectively show examples of characteristic curves of gas flow rate versus heat loss obtained using the torch of FIG. 6 and 7 show examples of characteristic curves of gas flow rate versus torch internal pressure obtained using the torch of FIG. 2. FIG. 8 shows an example of a characteristic curve of arc current versus torch internal pressure for each branch ratio obtained using the torch shown in FIG. FIG. 9 is a sectional view showing an example of another positive-polarity jacket type plasma arc torch used in the operating method of the present invention. Codes in the diagram: 1...Cathode rod, 3...First annular channel, 4...First mantle, 5...Second annular channel,
6... Second mantle, 8... First gas, 9, 10... Narrow hole, 12... Second gas, 20... Arc column, 40... Arc column, 41... Third mantle, 42... Third annular channel, 45 ...Third gas, 46...Narrowed hole.

Claims (1)

[Scope of Claims] 1. A hairpin arc is formed between a positive-polarity jacket-type plasma arc torch to be operated and another jacket-type plasma arc torch of opposite polarity disposed in a direction crossing this torch, and the positive-polarity Substantially the same as the flow rate at the extreme value coordinates of the characteristic curve of gas flow rate vs. heat loss of the inner annular channel obtained by flowing gas with a constant total flow rate through the inner annular channel and the outer annular channel of the shroud type plasma arc torch. A method of operating a shrouded plasma arc torch, the method comprising: flowing a gas flow rate of 1,000 or more into the inner annular channel of the positive polarity torch when the torch is operated as a single torch. 2. Said torch to be operated comprises a cathode rod, a first mantle defining a first annular channel surrounding said mantle, and a second mantle defining a second annular channel surrounding said mantle. 2. The method of operating a shroud plasma arc torch according to claim 1, wherein said inner channel is said first annular channel. 3. The torch to be operated has a cathode rod, a third mantle defining a third annular channel surrounding the cathode rod, and a first annular channel surrounding the third mantle. and a second mantle defining a second annular channel surrounding the first mantle, said inner channel being said third and first annular channels. A method of operating a jacket-type plasma arc torch according to claim 1. 4. Operation of the jacket-type plasma arc torch according to claim 2, characterized in that an inert gas is flowed through the first annular channel and an inert gas is flowed through the second annular channel. Method. 5. The method according to claim 3, wherein an inert gas is caused to flow through the third annular channel, and an inert gas or an active gas is caused to flow through the first and second annular channels. How to operate a cloak-type plasma arc torch.