KR20070121062A - Apparatus and method for cutting with plasma - Google Patents

Abstract

In cutting soft steel or low-carbon steel with a plasma, the concentration of oxygen in an assist gas is controlled so as to diminish dross adhesion around the hole during piercing. As the plasma gas may be used oxygen, air, a gas mixture of oxygen and nitrogen, etc. As the assist gas may be used nitrogen, oxygen, air, a gas mixture of oxygen and air, etc. The oxygen concentration in the assist gas in the piercing step is regulated so as to be higher than in the cutting step. The oxygen concentration in the assist gas in the piercing step is 20 mol% or higher, preferably 100 mol% or a high concentration close to it, while that in the cutting step is 20% or higher and lower than the concentration in burning, e.g., about 40-80 mol%.

Description

Plasma cutting device and method {APPARATUS AND METHOD FOR CUTTING WITH PLASMA}

TECHNICAL FIELD The present invention relates to a plasma cutting apparatus and method, and more particularly, to an improvement in the composition of a gas supplied to a plasma torch.

As a plasma gas (also called working gas, main gas or primary gas), in a torch, in a plasma cutting in which mild steel, low alloy steel or low carbon steel is cut using oxygen, air, or a mixed gas of oxygen and nitrogen, etc. By supplying an auxiliary gas (also called a secondary gas) containing a significant proportion of oxygen around the ejecting plasma arc, cutting quality is improved, especially dross (melted metal that adheres to the back side of the workpiece). It is known that the thing which adheres and hardens to a workpiece | work) is reduced. The literature which discloses using an auxiliary gas containing oxygen has the following, for example.

Patent Document 1 discloses a gas having a relatively high oxygen concentration as a secondary gas around a plasma arc, and the oxygen purity of the secondary gas is 40% or more, and formed on the cut surface by the secondary gas rich in oxygen. It is disclosed that the nitride layer which inhibits welding to be reduced can be reduced.

In Patent Document 2, an oxygen curtain (pure oxygen secondary gas) is supplied around a plasma arc using oxygen as a plasma gas, and fluidity of the molten metal is increased by the secondary gas of oxygen, It is disclosed that the dross attached to the back side is reduced, and the participation of molten metal is promoted to improve the release agent of the dross.

Patent Literature 3 discloses using a mixed gas of a non-oxidizing gas and an oxidizing gas as a secondary gas, at least 40% or more of the oxidizing gas, and the non-oxidizing gas is nitrogen or argon, and the oxidizing gas is oxygen or air. Is disclosed.

Patent Document 4 discloses that a mixed gas of nitrogen gas and oxygen gas is used as the secondary gas, and at least the nitrogen ratio of oxygen gas is 25%.

Patent Document 5 uses a gas containing oxygen as the plasma gas (primary gas), secondary gas and tertiary gas, respectively, and the oxygen concentration of the plasma gas is Np, and the oxygen concentration of the secondary gas is N2, 3. When the oxygen concentration of the secondary gas is N 3, it is disclosed that Np> N 2 and N 2 <N 3.

In addition, plasma cutting is started from the process of punching a steel plate (also called a piercing process). In the piercing step, the steel sheet is melted by the plasma arc, and the liquid metal is sprayed up by the plasma airflow toward the plasma torch above the steel sheet until such a hole penetrates (the molten metal is called a sputter). The sputter ejected from the hole may cause the nozzle of the tip of the torch or the shield cap covering the nozzle to be melted. In addition, a part of the molten metal which spewed out from the hole adheres as a dross and solidifies and accumulates around the hole. When the torch returns to the cutting start position at the end of the cutting of the product, the torch tip contacts the dross accumulated around the hole at the cutting start position, so that the cutting operation may be interrupted. In order to avoid that, the position of the piercing may be separated from the product, but the cutting path is then extended. In connection with this problem, the following technique is known, for example.

Patent Document 6 discloses that the secondary gas flow rate during the piercing process is made larger than the secondary gas flow rate during the cutting process to protect the torch from sputters spouting out of the hole by the secondary gas having a large flow rate.

Patent Document 7 discloses reducing dross adhered to a periphery of a hole by spraying and applying a dross antifouling agent at a torch to a piercing scheduled point at a torch before the start of the piercing step.

In addition, in the piercing step in the plasma cutting and the subsequent cutting step, the plasma arc (also called the main arc) is formed by the arc discharge between the electrode (minus pole) and the steel plate (plus pole) in the plasma torch. The plasma arc is narrowly tightened by a nozzle to form a high temperature and high speed plasma jet, which is blown onto the steel sheet to melt the steel sheet. Prior to the start of the piercing process, a process (also called a pilot arc process) for igniting the arc is first performed. In a pilot arc process, an electrode turns into a negative electrode, a nozzle turns into a positive electrode, and arc discharge called a pilot arc is formed between an electrode and a nozzle. The pilot arc moves to the steel plate. After the pilot arc reaches the steel plate and shifts to the main arc, the electric circuit connected to the nozzle is cut off, only the steel plate becomes the positive pole, and the piercing process is started.

In the pilot arc process, the orifice exit of the nozzle is melted by the pilot arc. Since the time length of the pilot arc is short, from several msec to several tens of msec, the damage of the nozzle per one ignition process is small. However, as the number of ignitions increases, melting of the orifice outlet of the nozzle proceeds. After hundreds of ignition cycles are repeated, the damage at the orifice outlet of the nozzle is completely large, the state of the plasma arc changes, and the quality of cut is degraded. This ends the life of the nozzle.

In this regard, Patent Document 8 discloses that during the ignition of the pilot arc, a non-oxidizing gas flows into the plasma gas, a non-oxidizing gas also flows into the secondary gas, and the vicinity of the orifice exit of the nozzle is made into a non-oxidizing gas atmosphere. And substantially simultaneously with the transition of the pilot arc to the main arc, it is disclosed that the plasma gas is converted from a non-oxidizing gas into a gas containing oxygen or oxygen to enter the cutting process. By the non-oxidizing gas atmosphere in an ignition process, the damage of the orifice exit of a nozzle by a pilot arc is reduced.

Patent Document 1: Japanese Patent Application Laid-open No. 53-123349

Patent Document 2: Japanese Patent Application Laid-Open No. 59-229282

Patent Document 3: Japanese Patent Application Laid-open No. Hei 6-508793

Patent Document 4: Japanese Unexamined Patent Publication No. 7051861

Patent Document 5: Japanese Unexamined Patent Publication No. 2000-31293

Patent Document 6: Japanese Patent Application Laid-open No. Hei 2-504603

Patent Document 7: Japanese Unexamined Patent Publication No. 2004-188485

Patent Document 8: Japanese Patent Application Laid-Open No. 8-215856

Disclosure of the Invention

Problems to be Solved by the Invention

According to the above-mentioned prior art regarding plasma cutting in which mild steel, low alloyed steel, or low carbon steel is cut using oxygen or air, or a mixed gas of oxygen and nitrogen as the plasma gas, oxygen is used as the secondary gas in the cutting step. By using the gas contained in a considerable ratio, the dross adhered to the back surface of a steel plate can be reduced. However, in the piercing process, a problem arises that dross adheres and accumulates around the hole. In order to solve this problem, according to the prior art, in the piercing process, the flow rate of the secondary gas is increased, or the dross anti-sticking agent is applied before the piercing process is started.

Therefore, an object of the present invention is to reduce the adhesion of dross to the periphery of the hole in the piercing process in a manner different from the prior art.

Means to solve the problem

According to an aspect of the present invention, a plasma cutting device which performs a pilot arc process, a piercing process and a cutting process in sequence while ejecting a plasma gas flow from a plasma torch and spraying an auxiliary gas stream around the plasma gas flow. Is an auxiliary gas that supplies oxygen-containing gas as an auxiliary gas to the plasma torch in the piercing step and the cutting step, and controls the auxiliary gas oxygen concentration to a higher value than in the cutting step when all or part of the piercing step is performed. A supply control means.

According to this plasma cutting device, adhesion of dross to the periphery of the hole in a piercing process is reduced by making oxygen concentration of an auxiliary gas higher than a cutting process in all or part of a piercing process.

In a preferred embodiment, in the pilot arc process, an inert gas such as nitrogen that does not contain oxygen or a gas containing oxygen is used as the auxiliary gas, and the auxiliary gas oxygen concentration in the pilot arc process is lower than in the piercing process. Controlled by value. As a result, damage to the nozzle due to the pilot arc is reduced.

In a preferred embodiment, the auxiliary gas oxygen concentration in the piercing process is controlled in the range of 20 mol% to 100 mol%, and in the cutting process in the range of 20 mol% to 80 mol%. As a result, adhesion of the dross to the periphery of the hole is reduced in the piercing process, and adhesion of the dross to the back surface of the workpiece is also reduced while preventing the burning of the workpiece in the cutting process.

According to another aspect of the present invention, a plasma cutting device configured to transfer a pilot gas to a main arc after generating a pilot arc while ejecting an auxiliary gas stream around the plasma gas stream while ejecting the plasma gas stream from the plasma torch. While the main arc is maintained, the oxygen-containing gas is supplied to the plasma torch as an auxiliary gas, and the auxiliary gas oxygen concentration is higher than after the time interval has elapsed in a predetermined time interval immediately after the establishment of the main arc. An auxiliary gas supply control means for controlling the value is provided.

According to this plasma cutting device, the oxygen concentration of the auxiliary gas in the time interval immediately after the establishment of the main arc is higher than after the time interval, so that the circumference of the hole in the piercing process usually performed immediately after the establishment of the main arc is achieved. Adhesion of dross to is reduced.

Effects of the Invention

According to the present invention, adhesion of the dross to the periphery of the hole in the piercing process can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows schematic structure of the principal part of the plasma cutting device which concerns on one Embodiment of this invention.

2 is a time chart illustrating a method of controlling arc current, plasma gas 112 and auxiliary gas in the case of cutting a workpiece of mild steel, low alloy steel or low carbon steel.

3 is a piping diagram illustrating a configuration example of the auxiliary gas supply system 104.

4 is a time chart showing the operation of the auxiliary gas supply system 104 shown in FIG.

5 is a piping diagram illustrating another configuration example of the auxiliary gas supply system 104.

FIG. 6 is a time chart showing the operation of the auxiliary gas supply system 104 shown in FIG. 5.

Explanation of the sign

100 plasma cutting device

102 plasma torch

112 plasma gas

114 auxiliary gases

103 plasma gas supply system

104 Auxiliary Gas Supply System

106 power circuit

108 Chilled Water Circulation System

109 Control

140 workpiece

Implement the invention  Best form for

EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment of this invention is described with reference to drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic structure of the principal part of the plasma cutting device which concerns on one Embodiment of this invention is shown.

As shown in FIG. 1, this plasma cutting device 100 supplies a plasma gas 112, an auxiliary gas 114, an arc current, and a coolant 110 to the plasma torch 102 and the plasma torch 102, respectively. And a plasma gas supply system 103, an auxiliary gas supply system 104, a power supply circuit 106, and a coolant circulation system 108, and a controller 109 for controlling their operation.

The plasma torch 102 generally has a substantially cylindrical shape and faces downward, and in order from the center to the outside, the electrode 120, the nozzle 122, and the shield cap 124 are arranged on the same axis. Have The electrode 120 has an outer circumference surrounded by the nozzle 122. The nozzle 122 has an orifice for ejecting a jet of plasma gas at its tip. The nozzle 122 has an outer circumference surrounded by the shield cap 124. The shield cap 124 has an opening at its tip for passing a jet of plasma gas ejected from the nozzle 122.

The electrode 120 has an insert 126 made of a heat-resistant material, for example, hafnium, zirconium or an alloy thereof, at its distal end, and has a cooling water passage 128 therein. There is a plasma gas passage 130 between the electrode 120 and the nozzle 122. In the plasma gas passage 130, a plasma gas swirler 132 for forming swirl flow of plasma gas is provided. An auxiliary gas passage 134 exists between the nozzle 122 and the shield cap 124. The outlet of the auxiliary gas passage 134 is annular and surrounds the front of the orifice of the nozzle 122. In the auxiliary gas passage 134, an auxiliary gas swirler 136 for forming swirl flow of the auxiliary gas is provided.

The plasma gas 112 passes through the plasma gas passage 130 to become a swirl flow which turns in one direction, is supplied to the front of the tip of the electrode 120, and is rotated as an swirl flow from the orifice at the tip of the nozzle 122. Ejected downward. The auxiliary gas 114 passes through the auxiliary gas passage 134 and becomes a swirling flow that rotates in the same direction as the swing of the plasma gas 112 from the outlet, and around the plasma swirling jet from the nozzle 122. Squirt.

When the cutting of the sheet material (workpiece) 140 is performed, the plasma torch 102 is disposed with respect to the work piece 140 such that the work piece 140 is positioned near the bottom thereof. Immediately before the start of processing, a preflow step is performed, and the plasma gas 112 and the auxiliary gas 114 are ejected for a predetermined time until the flow rate is stabilized. Following the preflow step, a pilot arc step is performed, where the power supply circuit 106 applies a high voltage between the electrode 120 and the nozzle 122, whereby the tip of the electrode 120 and the nozzle 122 in the vicinity thereof. Generate a pilot arc between the inner surfaces of the. By the action of the pilot arc, the plasma gas 112 near the tip end of the electrode 120 is converted into plasma, and is ejected as a high speed jet stream downward from the orifice of the nozzle 122. Guided by the plasma jet stream, the pilot arc exits the orifice of the nozzle 122 and moves downward to reach the upper surface of the workpiece 140. This establishes a main arc (plasma arc) 138 integrated with the plasma jet stream between the electrode 120 and the workpiece 140. As soon as the establishment of the main arc 138 is detected, the power supply circuit 106 cuts the converter to the nozzle 122 and instead connects the converter to the workpiece 140. Thereby, an arc current path is formed between the electrode 120 and the workpiece 140, and then the main arc 138 is held until the arc current path is cut.

After the main arc 138 establishes, a piercing process is performed for the first time, in which a hole 142 is drilled in the workpiece 140 by the main arc 138. Until the hole 142 is penetrated, molten metal is ejected from the inlet above the hole 142 to solidify around the hole 142 to form the cumulative dross 144. After the hole 142 is penetrated, the cutting process is started. In the cutting step, the workpiece 140 is cut while the plasma torch 102 moves. When the cutting process is finished, the power supply circuit 106 cuts the current path of the main arc 138, and the main arc 138 is extinguished. Subsequently, an afterflow process is performed and the plasma gas 112 and the auxiliary gas 114 flow for a predetermined time.

In the series of processing steps in the order of the preflow process, pilot arc process, piercing process, cutting process, and afterflow process described above, the control device 109 includes the magnitude of the arc current, the plasma gas 112 and the auxiliary gas. Each composition, pressure and flow rate of 114 are controlled to be optimal. In the following, this control will be described in more detail. In particular, the control in the case of cutting the workpiece | work 140 made of materials, such as mild steel, a low alloy steel, or a low carbon steel, is demonstrated.

2 shows how the arc current, the plasma gas 112 and the auxiliary gas in the case of cutting the workpiece 140 of mild steel, low alloy steel or low carbon steel are controlled. FIG. 2 (a) shows the change in the magnitude of the arc current, FIG. 2 (b) shows the change in pressure and composition of the plasma gas 112, and FIG. 2 (c) shows the change in the flow rate and composition of the auxiliary gas 114. 2 (d) shows changes in the concentration of oxygen contained in the auxiliary gas 114, respectively.

As shown in Fig. 2A, the arc current flows from the pilot arc process to the cutting process. The arc current flows at a predetermined small pilot current value in the pilot arc process, gradually increases in the piercing process to reach a predetermined cutting current value, is constantly controlled by the cutting current value in the subsequent cutting process, and stops at the end of the cutting process. do.

As shown in FIG.2 (b), the plasma gas 112 continues to flow from a preflow process to an afterflow process. The pressure of the plasma gas 112 is controlled at a predetermined low preflow pressure from the preflow process to the pilot arc process, is rapidly increased to a predetermined high cutting pressure upon entering the piercing process, and is cut during the piercing process to the cutting process. It is constantly controlled by the pressure, and is drastically reduced when entering the afterflow process so as to be controlled at a predetermined low afterflow pressure.

As the plasma gas 112, nitrogen (inert gas), oxygen, air, or a mixed gas thereof can be used while changing the composition according to the process. In this embodiment, the composition of plasma gas 112 is 100 mol% nitrogen from a preflow process to a pilot arc process, and when it enters a piercing process, 80 mol of oxygen is mixed gas of oxygen and nitrogen, for example, by volume concentration. It transitions to an oxygen-rich composition with a% and 20 mol% nitrogen, is constantly controlled by the oxygen-rich composition from the piercing process to the cutting process, and is converted back to 100 mol% nitrogen after the afterflow process. . Alternatively, as a modification, the composition of the plasma gas 112 may include air (that is, about 20 mol% oxygen and about 80 mol% nitrogen in volume concentration) from the preflow process to the pilot arc process and the afterflow process, respectively. Or 100 mol% of oxygen during the piercing process to the cutting process.

As shown in Fig. 2C, the auxiliary gas 114 continues to flow from the preflow step to the beginning of the afterflow step, during which the flow rate is constantly controlled at a predetermined cutting flow rate, and the afterflow step Upon entering the auxiliary gas 114 is restrained. As the auxiliary gas 114, nitrogen (inert gas), oxygen, air, or a mixed gas thereof can be used while changing the composition according to the process. In this embodiment, the composition of the auxiliary gas 114 is 100 mol% of nitrogen from the preflow process to the pilot arc process, when entering the piercing process, the transition to 100 mol% of oxygen is maintained during the piercing process, and the cutting process Once in, it is converted into a composition containing oxygen and nitrogen, for example, a mixture of air and oxygen, which has a lower oxygen concentration than the piercing process, and remains there during the piercing process. Alternatively, as an alternative, the composition of the auxiliary gas 114 may include air (that is, about 20 mol% oxygen and about 80 mol% nitrogen in volume concentration) from the preflow process to the pilot arc process and the afterflow process, respectively. 100 mol% of oxygen may be sufficient from a piercing process to a cutting process, and air may be sufficient as an afterflow process.

It should be noted here that a change in the volume concentration of oxygen (hereinafter referred to as "secondary gas oxygen concentration") in the auxiliary gas 114 is made. That is, as shown in FIG.2 (d), the auxiliary gas oxygen concentration in a preflow process and a pilot arc process is D1, the auxiliary gas oxygen concentration in a piercing process is D2, and the auxiliary gas oxygen concentration in a cutting process is If it is set to D3, there exists a relationship that D1 <D3 <D2 between these process gas concentrations D1, D2, and D3. The auxiliary gas oxygen concentration for each process will be described in detail as follows.

Auxiliary gas oxygen concentration D1 in a preflow process and a pilot arc process is a low value of 20 mol% or less (that is, below the oxygen concentration of air). In particular, as the auxiliary gas oxygen concentration D1 in the pilot arc process is closer to 0 mol%, damage to the nozzle 122 due to the pilot arc is reduced.

The auxiliary gas oxygen concentration D2 in the piercing process is a high value of 20 mol% or more (that is, above the oxygen concentration of air), and is burned (e.g., excess in the cutting plane of the workpiece 140), for example, 80 mol% or more. What is necessary is just the density | concentration which an oxidation reaction) generate | occur | produces, and 100 mol% may be sufficient. As the auxiliary gas oxygen concentration D2 is closer to 100 mol%, the piercing ability is improved, and the amount of the dross 144 adhered to the periphery of the hole can be reduced. By this effect, the damage of the nozzle 122 and the shield cap 124 is reduced, the lifetime is extended, production efficiency improves, the maximum plate pressure which can be cut | disconnected, etc. can be expected. The auxiliary gas oxygen concentration D2 in this piercing step is higher than the auxiliary gas oxygen concentration D3 in the next cutting step.

Auxiliary gas oxygen concentration D3 in a cutting process is 120 mol% or more, and is a moderate value below the oxygen concentration (for example, 80 mol%) which burns. In the cutting step, unlike the piercing step, an auxiliary gas having 100 mol% of oxygen is not employed because burning occurs. The auxiliary gas oxygen concentration D3 in the cutting process is in the range of about 40 mol% to 80 mol%, for example 50 mol, for the purpose of reducing dross adhered to the back surface of the workpiece 140 without causing burning. Percent is appropriate.

FIG. 3 shows a configuration example of the auxiliary gas supply system 104 for supplying the auxiliary gas 114 whose oxygen concentration changes as described above.

As shown in FIG. 3, the auxiliary gas supply system 104 includes a nitrogen supply pipe 160 for flowing nitrogen gas from a nitrogen source, an air supply pipe 162 for flowing air from a source of air, and an oxygen source. Two oxygen supply pipes 164 and 166 are provided for flowing oxygen gas. The two oxygen supply pipes 164 and 166 have different flow rates of the oxygen gas flowing therethrough, hereinafter, the larger flow rate 164 is referred to as the "oxygen large supply pipe", and the smaller flow rate 166 is referred to as " Oxygen small supply pipe ”. Those four gas supply pipes 160, 162, 164, 166 are joined and connected to one auxiliary gas supply pipe 188, and the auxiliary gas supply pipe 188 is connected to the auxiliary gas passage 134 of the plasma torch 102. Connected. The four gas supply pipes 160, 162, 164, 166 mentioned above are provided with the solenoid valves 172, 176, 184, 186 for opening and closing each gas supply pipe. Hereinafter, the solenoid valve 172 of the nitrogen supply pipe 160 is a "nitrogen valve", the solenoid valve 176 of the air supply pipe 162 is an "air valve", and the solenoid valve 184 of the oxygen large supply pipe 164. The "oxygen large valve" and the solenoid valve 186 of the oxygen small supply pipe 166 are called "oxygen valve."

In the nitrogen supply pipe 160, upstream of the nitrogen valve 172, a flow regulating valve 170 is provided which constantly controls the nitrogen gas flow rate to a predetermined auxiliary gas flow rate value. In the oxygen large supply pipe 164, upstream of the oxygen large valve 182, a flow rate regulating valve 180 that controls the oxygen gas flow rate to a predetermined first oxygen flow rate value is provided. In the oxygen small supply pipe 166, upstream of the oxygen small valve 186, a flow regulating valve 184 is provided which constantly controls the oxygen gas flow rate to a predetermined second oxygen flow rate value smaller than the first oxygen flow rate value. do. Their addition value is slightly smaller than the auxiliary gas flow rate value (or, as a modification, may be equivalent to the auxiliary gas flow rate value). Further, in the air supply pipe 162, upstream of the air valve 176, the auxiliary gas pressure is set so that the flow rate of the auxiliary gas 114 in the state where the air valve 176 is opened is constant at the auxiliary gas flow rate value. A pressure reducing valve 174 is provided, and a check valve 178 is provided downstream of the air valve 176.

It is preferable that the confluence points of the four gas supply pipes 160, 162, 164, and 166 be disposed as close as possible to the plasma torch 102, and the auxiliary gas supply pipe 188 should be as short as possible. Thereby, when the gas flow control operation is performed upstream from the confluence point, the delay time until the control result is reflected in the plasma torch 102 is shortened, and the accuracy of gas control is improved.

4 shows the operation of the auxiliary gas supply system 104 shown in FIG. 3 in the series of processing steps described above. 4 (a) shows the change in the arc current in a series of processing steps, FIG. 4 (b) shows the opening and closing operation of the nitrogen valve 172, and FIG. 4 (c) shows the opening and closing operation of the air valve 176. 4 (d) shows the opening and closing operation of the oxygen large valve 182, FIG. 4 (e) shows the opening and closing operation of the oxygen small valve 186, and FIG. 4 (f) shows the auxiliary gas 114. Changes in the flow rate of nitrogen gas, oxygen gas and air contained

As shown in FIG. 4, in the preflow step and the pilot arc step, only the nitrogen valve 172 is opened, and the other gas valves 176, 182, and 186 are closed, and as shown in FIG. 4 (f), the auxiliary gas ( 114) only nitrogen gas flows. In the piercing process, the nitrogen valve 172 is closed, and instead, the air valve 176, the oxygen large valve 182, and the oxygen small valve 186 are opened, and thus the auxiliary gas 114 as shown in FIG. 4 (f). ), A mixed gas of oxygen-rich oxygen and air (or, as a modification, only oxygen gas) flows. In the cutting step, the air valve 176 and the oxygen small valve 186 are opened, the nitrogen valve 172 and the oxygen large valve 182 are closed, and as shown in FIG. 4 (f), therefore, as the auxiliary gas 114. A mixed gas of oxygen and air having a lower oxygen concentration than in the piercing step (or, alternatively, only air may be present) flows.

5 shows another configuration example of the auxiliary gas supply system 104. The structural example shown in FIG. 5 removes the nitrogen supply line 160 by the structural example shown in FIG.

FIG. 6 shows the operation of the auxiliary gas supply system 104 shown in FIG. 5 in the series of processing steps described above. Fig. 6 (a) shows the change in the arc current in a series of processing steps, Fig. 6 (b) shows the opening and closing operation of the air valve 176, and Fig. 6 (c) shows the opening and closing of the oxygen valve 182. 6 (d) shows the operation of opening and closing the oxygen small valve 186, and FIG. 6 (e) shows the change in the flow rates of air and oxygen gas contained in the auxiliary gas 114. FIG.

As shown in FIG. 6, in the preflow step and the pilot arc step, the air valve 176 is opened, and the oxygen main valve 182 and the oxygen small valve 186 are closed, and as shown in FIG. 6E. Air flows as auxiliary gas 114. In the piercing process, both the air valve 176, the oxygen main valve 182, and the oxygen small valve 186 are opened, and therefore, oxygen and air rich in oxygen as the auxiliary gas 114 as shown in Fig. 6E. Of mixed gas (or, as a modification, only oxygen gas) flows. In the cutting step, the air valve 176 and the oxygen small valve 186 are opened, and the oxygen large valve 182 is closed, and thus, as shown in FIG. 6E, as compared with the piercing step as the auxiliary gas 114. A mixed gas of oxygen and air having a low oxygen concentration (or, alternatively, only air may be present) flows.

According to the above-mentioned embodiment, the composition of the auxiliary gas 114 is optimized by the composition which is respectively different in a pilot arc process, a piercing process, and a cutting process. Thereby, the capability of piercing is improved and adhesion of dross to the periphery of the hole in a piercing process is reduced. As a result, the service life of the shield cap and the nozzle which are the consumable parts of the plasma torch is improved. In addition, the groove length from the position of the hole formed in the piercing process to the product can be shortened, and the production efficiency is improved. Also, by improving the piercing capability, the maximum cutting plate pressure, which is one of the basic performances of the cutting device, is increased. do.

By the way, in embodiment mentioned above, although the composition of the plasma gas 112 and the auxiliary gas 114 is switched in synchronization with the switching of a pilot arc process, a piercing process, and a cutting process, between the process switching and the gas composition switching. There may be a slight time difference within a certain allowable range. For example, the auxiliary gas oxygen concentration becomes the low concentration value D1 during the pilot arc process, and is converted to the high concentration value D2 suitable for the piercing process at the time when the pilot arc transitions to the main arc and the main arc is established, and immediately after that. The concentration value D2 may be maintained as high as the time interval of a predetermined length, and may be switched to the intermediate concentration value D3 suitable for the cutting step after the passage of the time interval. In this case, the point at which the auxiliary gas oxygen concentration is switched from the high concentration value D2 to the medium concentration value D3 may not necessarily be coincident with the time when the machining process is actually switched from the piercing process to the cutting process, for example, slightly faster than that. Or a little bit later. That is, even if the high concentration value D1 is not maintained continuously in all of the piercing processes, at least in part, if the high concentration value D2 (or a higher auxiliary gas concentration value than that in the cutting process) is provided, the piercing process is improved than before. In addition, even if the conversion from the high concentration value D2 to the medium concentration value D3 is not performed at the same time as the start of the cutting process, the gas composition conversion is performed while cutting the path from the hole drilled to the product in the piercing process, Or even if the gas composition change is performed slightly earlier than the end point of the piercing step, the cutting step can be performed satisfactorily.

As mentioned above, although embodiment of this invention was described, this embodiment is only the illustration for description of this invention, and it is not the meaning which limits the scope of this invention only to this embodiment. This invention can be implemented also in other various aspects, without deviating from the summary.

Claims (6)

In the plasma cutting device 100 which performs a pilot arc process, a piercing process, and a cutting process in order, while spraying a plasma gas flow from the plasma torch 102 and spraying an auxiliary gas flow around the plasma gas flow. In In the piercing step and the cutting step, a gas containing oxygen is supplied to the plasma torch as the auxiliary gas so that the auxiliary gas oxygen concentration is higher than that of the cutting step when all or part of the piercing step is performed. A plasma cutting device comprising auxiliary gas supply control means (104, 109) for controlling. The method of claim 1, In the pilot arc process, the auxiliary gas supply control means 104, 109 supplies a gas containing no or no oxygen as the auxiliary gas to the plasma torch, and supplies the auxiliary gas oxygen concentration to the pilot arc process. When the plasma cutting device is controlled to a lower value than when the piercing process. The method of claim 1, The auxiliary gas supply control means (104, 109) controls the auxiliary gas oxygen concentration within the range of 20 mol% to 100 mol% when all or part of the piercing process, and from 20 mol% to the cutting process Plasma cutting device to control in the range of 80 mol%. In the plasma cutting method of performing a pilot arc process, a piercing process, and a cutting process in order, while spraying a plasma gas flow from the plasma torch 102, and spraying an auxiliary gas stream around the plasma gas flow, A plasma cutting method in which the gas containing oxygen in the piercing step and the cutting step is used as the auxiliary gas to control the auxiliary gas oxygen concentration to a higher value than in the cutting step in the piercing step. Plasma cutting device 100 configured to transfer the pilot gas to the main arc after generating a pilot arc while ejecting an auxiliary gas stream around the plasma gas stream while ejecting a plasma gas stream from the plasma torch 102. To While the main arc is being maintained, a gas containing oxygen is supplied to the plasma torch as the auxiliary gas, and the auxiliary gas oxygen concentration is supplied after the passage of the time interval in a predetermined time interval immediately after the establishment of the main arc. A plasma cutting device comprising auxiliary gas supply control means (104, 109) for controlling to a higher value. A plasma cutting method in which a pilot arc is generated after a pilot arc is generated while ejecting a plasma gas flow from a plasma torch 102 and ejecting an auxiliary gas stream around the plasma gas stream. While the main arc is being held, a gas containing oxygen is used as the auxiliary gas, and the auxiliary gas oxygen concentration is higher in the predetermined time interval immediately after the main arc is established than after the elapse of the time interval. Plasma cutting method controlled by.

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