JPS637680B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to plasma technology, and more particularly to an arc plasma generator and a plasma arc apparatus equipped with the same for surface treatment of a workpiece.

The present invention has been found to be most useful for surface processing, cleaning and etching of metal surfaces in vacuum. In particular, vacuum condensation of metal plasmas can be used to create wear-resistant, corrosion-resistant, abrasion-resistant, heat-resistant, superconducting, optical, and other coatings.

Until now, the plasma flow generated by an arc plasma generator has a height of 0.025 or more.
Attempts have been made to treat metal surfaces with a roughness of 0.5 μm, but it is not possible to maintain such surface roughness values. This is because the plasma stream generated by the cathode spot is highly populated with large particles such as droplets and solid fragments of cathode material. Apart from impairing the surface finish of coatings deposited by plasma techniques, these large particles can form holes and bulges in the condensate that can cause mechanical, electrical, optical, and other damage to the coating. properties, so that the effects of applying the various coatings (abrasion resistance, good abrasion resistance, corrosion resistance, etc.) are practically not completely obtained.

A known arc plasma generator is covered by U.S. Patent No.
Disclosed in No. 3625848. The arc plasma generator includes a consumable cathode disposed within the anode in axial alignment with the anode, means for creating an arc between the cathode and the anode (igniting means), and an electrical connection between the anode and the cathode. It is equipped with a power supply device for arc maintenance which is connected to the mains. The ignition means initiates an arc discharge between the cathode and the anode. The cathode generates a plasma consisting of atoms and ions of the cathode material. As mentioned above, the plasma stream contains a significant number of large particles such as droplets and solid fragments of cathode material;
These are not desirable because they impair the quality of the coating.

Giant particles in the plasma stream result from local and general superheating of the active surface of the cathode by a strong, concentrated heat source, such as the cathode spot (the temperature of the spot is several thousand degrees, and the current The density is on the order of about 10 ⁶ to about 10 ⁷ A/cm ² ).

It also includes a consumable cathode disposed coaxially with the cylindrical anode, an ignition electrode connected to an ignition pulse generator for starting an arc between the cathode and the anode, and a power supply for maintaining the arc. An arc plasma generator is also known (1972,
ASGilmour, DL Lochuood, “Pulsed Metal-Plasma Generator” published in Proc. IEEE, Volume 60, No. 8, Page 977). The arc plasma generator also includes a focusing solenoid located on the anode.

This arc plasma generator is operated by applying an ignition pulse to an ignition electrode at a frequency on the order of tens of hertz. When a pulsed arc discharge occurs between the anode and the cathode, a plasma stream is generated at the above-mentioned frequency. Problems also arise with this arc plasma generator due to large particles in the metal plasma. By rotating the axis of the focusing solenoid at an angle relative to the axis of the device, the direction of the velocity vector of the charged component of the plasma stream can be changed. In this case, large numbers of large particles are removed from the plasma stream by spatially separating the large particles and charged components (ions and electrons) from the plasma stream to some extent. However, this known arc plasma generator is not able to remove all the large particles that reach its outlet and impinge on the workpiece. This is because in the range in which the focusing solenoid is rotated (15 degrees and above), giant particles rush in this direction, with a view from the cathode to the exit of the plasma generator.

The present invention relates to an arc plasma generator in which an electromagnetic system is configured to effectively remove giant particles from a plasma flow by spatially separating components of the plasma flow in a magnetic field, and a work piece equipped with the same. The present invention provides a plasma arc device for surface treatment.

The aim of the invention is to eliminate the above-mentioned drawbacks.

This object of the invention comprises a consumable cathode, a cylindrical anode, and a focusing solenoid, the anode and solenoid being disposed coaxially with the consumable cathode, and further providing electrical power to the consumable cathode and the anode. The arc plasma generator is also equipped with a power supply device for arc maintenance connected to the anode, and a tubular plasma guide is connected to the end face of the anode, and an electromagnet is arranged on the axis of the tubular plasma guide. the electromagnet is housed in a housing made of non-magnetic material and has a cross-sectional area sufficient to hide the cathode when viewed through the plasma guide in the direction of the cathode; This is achieved by providing an arc plasma generator characterized in that the solenoid is arranged on the tubular plasma guide and is connected in the opposite direction to the coil of the electromagnet.

In such a configuration, the giant particles fly out from the end face of the cathode, hit the wall of the electromagnet housing or the wall of the plasma guide, and do not reach the outlet of the plasma generator. On the other hand, the charged components (ions and electrons) of the plasma flow follow the path along the lines of magnetic force of the magnetic field induced by the focusing solenoid and electromagnet connected in opposite directions, fly around the electromagnet, and easily generate plasma. Reach the outlet of the vessel. Therefore, the output plasma is completely free of macroparticles and therefore treats the surface of the workpiece without deteriorating the surface finish with a roughness height of less than 0.025 to 0.05 μm (creating a coating). The arc plasma generator can be used for plasma cleaning, ion etching, etc.

Preferably, the plasma guide is insulated from the anode by an insulating liner, which increases the efficiency of plasma flow through the plasma guide.

It is known that charged particles follow magnetic field lines only when their Larmor radius is small compared to the size of the device. Most metal ions emitted from a cathode spot in vacuum have an energy of several tens of electron volts. Therefore, these ions can only pass through the plasma generator of the present invention, where the gap between the plasma guide and the electromagnet housing is 10 cm, when the magnetic field strength is several kiloersteds. Normally, it is difficult to induce such a magnetic field. However, this problem is overcome when the magnetic system is filled with vacuum plasma. This is because in this case a substantially small magnetizing force sufficient to magnetize the ions of the plasma is sufficient to pass the ionic components through the plasma generator of the present invention. In this case, the electronic conductivity of the plasma is maintained along the magnetic lines of force, but rapidly decreases in the lateral direction. The electric field penetrates the plasma. The electric field in this device is induced by the potential when electrons intersect magnetic field lines. When this occurs, the magnetic field lines acquire the potential of the electrodes or device walls they intersect. Therefore, when the plasma guide is at a positive potential with respect to the cathode,
An electric field is induced in the plasma stream in the direction of its axis.
This electric field constricts (focuses) the plasma stream, reducing the loss of positive ions at the walls of the plasma guide and increasing the number of ions that reach the exit, ie, pass through the annular gap between the plasma guide and the electromagnet. With an insulating liner between the plasma guide and the anode, the plasma guide gains a higher potential than the anode due to high velocity ion bombardment. The electric field near the walls of the plasma guide becomes stronger and the plasma flow along the plasma guide becomes more effective.

In order to prevent large particles bouncing off the walls of the plasma guide from reaching the outlet, the inner surface of the tubular plasma guide is preferably provided with ribs extending at an angle to the expected plasma flow.

Preferably, the electromagnet arranged in the plasma guide has an axially streamlined shape and its housing has a similar shape.
This facilitates the plasma flow to enter the annular gap between the plasma guide and the electromagnet, thus increasing the plasma flow reaching the outlet of the plasma generator.

The preferred shape of the housing and the solenoid therein is a cone, or two cones abutting each other at their bases.

Also, the number of turns per unit length of the focusing solenoid on the tubular plasma guide behind the electromagnet when viewed in the direction of the expected plasma flow is the number of turns per unit length of the focusing solenoid on the other part of the plasma guide. More is desirable. This results in
The incoming plasma stream can be focused, increasing its density and thus increasing the rate of film formation.

The present invention also provides an arc plasma generator and an assembly for holding a workpiece to be processed.
This is a plasma arc apparatus for treating the surface of a work piece, in which the arc plasma generator is configured as described above, and the assembly that holds the work piece is connected to the unsupported end face of the plasma guide. a lid fixed to the lid, the lid being made of non-magnetic material and having an opening for holding the workpiece to be processed; said lid having a disc coil mounted thereon and connected in auxiliary manner to a focusing solenoid; The present invention also relates to a plasma arc device characterized by:

As used herein, the term "disc coil" refers to a coil whose radial dimension is larger than its longitudinal (axial) dimension. The workpiece must be held on the axis of the plasma generator between the lid and the electromagnet housing. In this case, the magnetic field lines are sharply bent in front of the lid so as to approach the axis of the plasma generator. For this purpose, the plasma stream is also directed towards the axis of the plasma generator and follows a path through the annular gap between the plasma guide and the housing of the electromagnet and impinges on the side of the workpiece. This eliminates the need for axial rotation of the workpiece and therefore the need for forced cooling of the workpiece or the application of large currents to the workpiece as it undergoes ionic cleaning and surface machining. Considering this, the above technique considerably simplifies the structure of the plasma generator. Since the workpiece is fixed, it is also easier to extract the temperature when the workpiece undergoes surface processing.

The invention will now be described by way of example with reference to the accompanying drawings.

Referring to Figure 1, the arc plasma generator comprises a consumable cathode 1 and a cylindrical anode 2, the cathode 1 having a cylindrical shape with a diameter of 60 mm (this size is for illustrative purposes only). , and made of a plasma-forming material, for example titanium of grade BT-1, while the anode 2 is cup-shaped, with an opening arranged in the center of its bottom for axially mounting the cathode 1 into the anode 2. (The length of the anode is 200mm and the diameter is 260mm.
mm).

A tubular plasma guide 3 is attached to the unsupported end face of the anode 2, and this guide has a length of 360 mm.
mm, has a diameter of 260 mm, and is made of non-magnetic steel.

To enable an efficient flow of the plasma through the plasma guide 3, an insulating liner 4 is arranged between the plasma guide 3 and the anode 2 (this liner is made of acrylic plastic, for example). In this case, the plasma guide gains a higher potential than the anode since the highest velocity ions hit the plasma guide. The electric field near the walls of the plasma guide will be strong and the plasma flow along the plasma guide will be efficient.

The inner surface of the plasma guide 3 is preferably provided with ribs 5 extending at an angle to the expected plasma flow. This can prevent giant particles that have bounced off the walls of the plasma guide 3 from passing through to the exit. Most preferably, the ribs are formed in the form of rings arranged one behind the other in parallel planes perpendicular to the axis of the plasma guide 3.

Arranged axially within the plasma guide 3 is an electromagnet 6, which is housed in a housing 7 made of non-magnetic steel.

The electromagnet 6 and its housing 7 may be cylindrical, as shown in FIG. It may consist of two cones abutting each other at their bases (the diameter at the base of each cone is 100 mm and the height is 180 mm). It has been experimentally found that with an electromagnet having such a shape, the plasma flow easily enters the annular gap between the plasma guide 3 and the electromagnet 6, and as a result, the plasma flow reaching the outlet of the plasma generator increases.

The distance from the end face of the outlet of the plasma guide 3 to the center of the housing 7 is 175 mm. This particular structure as well as plasma guide 3, housing 7,
For the particular dimensions of the cathodes 1 and their relative positions, the housing 7 has a cross-sectional area sufficient to prevent the cathodes from being visible when looking through the plasma guide 3 in the direction of the cathodes 1.

The housing 7 is held in place by a hollow post 8, and current is supplied to the coil of the electromagnet 6 via a lead 9 and this post.

The cathode 1, anode 2, plasma guide 3, and electromagnet 6 are cooled with water (the cooling system is not shown).

Rod-shaped ignition electrode 1 made of molybdenum
1 abuts against the side surface of the cathode 1 via a ceramic connecting piece 10.

Reference numbers 12 and 13 in FIG.
This lead supplies the ignition pulse from the ignition pulse generator 14 to the spark gap between the ignition electrode 11 and the ignition electrode 11 .

It should be understood that the arc can be ignited between the anode and cathode by conventional means other than those shown here. Power supply device 1 that maintains the arc
one terminal of 5 is connected to the consumable cathode 1;
The other terminal is connected to the anode 2. Leads 12, 13 enter the anode 2 through openings in the bottom of the anode 2 and vacuum-tight insulating seals 16.

The plasma guide 3 is surrounded by a focusing solenoid 17. In this regard, the number of turns per unit length of the focusing solenoid 17 on the tubular plasma guide 3 behind the electromagnet 6 is greater than the number of turns per unit length of the focusing solenoid on other parts of the plasma guide. is preferable. This allows the incoming plasma stream to be focused most effectively and to increase its density, thus increasing the rate of coating formation when the plasma generator is used for surface processing of a workpiece.

Reference number 18 designates the workpiece to be processed (FIGS. 2 and 3). FIG. 3 shows a plasma arc apparatus for treating the surface of a workpiece, which apparatus comprises the arc plasma generator described above and an assembly for holding the workpiece to be treated. , this assembly is in the form of a lid 19 made of non-magnetic steel, which is connected to the plasma guide 3.
attached to the end of the The outer surface of this lid has a diameter
There is a disc coil 20 with a thickness of 260 mm and a thickness of 60 mm, which is connected in an auxiliary manner to a focusing solenoid. In this case, the workpiece carrier 22 is received into the plasma guide 3 via the central opening 19 and the insulating material 21.

In operation, the focusing solenoid 17 and the electromagnet 6
A power supply (not shown) is turned on to power the second
An electromagnetic field having a magnetic field line pattern as shown by dotted lines in the figure is induced.

Power supply 15 and pulse generator 14 are also turned on. When a high-voltage ignition pulse is delivered to the ignition electrode 11, a spark discharge occurs in the gap between the electrode 11 and the cathode 1 via the ceramic connection piece 10. This spark discharge initiates an arc discharge between the cathode 1 and the anode 2, and a cathode spot appears on the active surface of the cathode 1, which creates a plasma stream of the material of the cathode 1. The ions and electrons contained in this plasma flow follow the magnetic field lines, cross the housing 7 of the electromagnet 6, and reach the surface of the workpiece 18 through the outlet of the plasma guide 3. The arrows in FIG. 2 indicate the direction of the charged components (ions and electrons) of the plasma stream.

The neutral vapor and giant particles follow a straight path (dotted chain line in FIG. 2) and adhere to the surfaces of the plasma guide 3 and the housing 7. Therefore, near the exit of the plasma generator and thus the surface of the workpiece 18, there are no macroparticles in the plasma stream.

When processing the outer surface of a rotating body, the magnetic field lines are deflected by the disk coil 20 toward the surface of the workpiece (dotted line in FIG. 3). Therefore, the ionized components of the plasma stream are also deflected toward the axis of the apparatus and reach the surface of the work piece. The large particles are blocked by the housing 7 from their path to the surface of the workpiece.

Although the invention has been described in terms of its preferred embodiments, other embodiments are possible within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is an axial cross-sectional view of the arc plasma generator of the present invention, FIG. 2 is a diagram showing the principle of separating plasma flow components in the arc plasma generator of the present invention, and FIG. 1 is a longitudinal partial sectional view of a plasma arc apparatus for surface treatment of a workpiece, which is equipped with an arc plasma generator of the present invention; FIG. 1... Cathode, 2... Anode, 3... Plasma guide, 4... Insulating liner, 5... Plasma guide rib, 6... Electromagnet, 7... Electromagnet housing, 15... Power source for maintaining the arc. Device,
17... Focusing solenoid, 18... Work piece, 1
9...Plasma guide lid, 20...Disc coil.

Claims (1)

[Claims] 1. A consumable cathode 1, a cylindrical anode 2,
a focusing solenoid 17, the anode and the solenoid being arranged coaxially with the consumable cathode 1, and a power supply device 15 for arc maintenance electrically connected to the consumable cathode 1 and the anode 2. In this arc plasma generator, a tubular plasma guide 3 is connected to the end face of the anode 2, and an electromagnet 6 is arranged on the axis of the tubular plasma guide 3. The electromagnet is housed in a housing 7 made of material and has a cross-sectional area sufficient to prevent the cathode 1 from being visible when looking in the direction of the cathode 1 through the plasma guide 3, and the electromagnet is is arranged outside the tubular plasma guide 3 and connected in the opposite direction to the coil of the electromagnet 6 to generate a magnetic flux in the same direction as the magnetic flux generated by the electromagnet 6 in the gap between the solenoid 17 and the electromagnet 6. An arc plasma generator characterized by: 2 The tubular plasma guide 3 and the anode 2
The arc plasma generator according to claim 1, wherein an insulating liner 4 is arranged between. 3. The arc plasma generator according to claim 1 or 2, wherein the inner surface of the tubular plasma guide 3 is provided with a rib 5 extending at a certain angle with respect to the plasma flow. 4. The arc plasma generator according to claim 1, wherein the electromagnet 6 has a streamlined shape in the axial direction, and the housing 7 also has a similar shape. 5. The electromagnet 6 is in the shape of a cone with its apex facing the consumable cathode 1.
The arc plasma generator described in section. 6. The arc plasma generator according to claim 4, wherein the electromagnet 6 has a shape of two cones abutting each other at their bottoms. 7 The number of turns per unit length of the focusing solenoid 17 on the tubular plasma guide 3 behind the electromagnet 6 when viewed upstream of the expected plasma flow is equal to the unit length of the focusing solenoid on the other parts of the tubular plasma guide. The arc plasma generator according to any one of claims 1 to 6, wherein the number of turns is greater than the number of turns per round. 8. A plasma arc apparatus for treating the surface of a workpiece, comprising an arc plasma generator and an assembly holding the workpiece to be treated, the arc plasma generator comprising a consumable cathode 1 and a cylindrical an anode 2 and a focusing solenoid 17, the anode and the solenoid being arranged coaxially with the consumable cathode 1, and an arc maintenance power source electrically connected to the consumable cathode 1 and the anode 2. The arc plasma generator is also equipped with a device 15, in which a tubular plasma guide 3 is connected to the end face of the anode 2,
And within this tubular plasma guide 3 an electromagnet 6 is arranged on its axis, this electromagnet is housed in a housing 7 made of non-magnetic material, and this electromagnet looks through the plasma guide 3 in the direction of the cathode 1. The focusing solenoid 17 is arranged on the tubular plasma guide 3 and is connected in the opposite direction to the coil of the electromagnet 6 so that the solenoid 17 has a sufficient cross-sectional area so that the cathode 1 is not visible when It generates magnetic flux in the same direction as the magnetic flux generated by the electromagnet 6 in the gap between the electromagnet 6 and the work piece 18 to be processed.
The above assembly holding the lid 1 made of non-magnetic material
9, this lid has an opening for holding the work piece 18 and is fixed to the outlet end face of the tubular plasma guide 3, and the lid 19 has a disk coil 2.
0 is attached and connected to the focusing solenoid 17 in an auxiliary manner.