JPH10251882A - Surface cleaning method by vacuum arc, and deivce therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely remove contamination on the metal surface and to obtain a clean surface by preparing an oxidative vacuum atmosphere for opeartion while varying the arc current as a pulse current when org. compd.- based contamination on the metal surface is removed by vacuum arc method. SOLUTION: A vacuum camber 1 equipped with an anode for vacuum arc and with a member 5 having org. compd.-based contamination to be treated for the cleaning treatment as a cathode is evacuated by a vacuum pump 2, while a power supply 3 for vacuum arc which enables pulse modification of the arc current is controlled by a controller 8 to produce arc discharge by the pulse current between the abode 4 and the cathode 5. At the same time, an oxidative gas such as oxygen and air is introduced through an inlet valve 7 which can control the leak amt. into the vacuum chamber 1. The org. contamination on the surface of a metal material 5 is decomposed by the effect of arc and the produced carbon is oxidized and removed as CO or CO2 gas by the oxidative gas. Thus, the surface residue as a solid carbon can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for obtaining a clean surface by removing dirt and impurities on the surface of a conductive material represented by metal. For example, it is a technique applied to surface cleaning or surface activation as a pretreatment when performing plating, thermal spraying or other surface coating treatment or painting treatment, or surface modification.

[0002]

2. Description of the Related Art As a method for removing surface dirt or a coating film, there is a method of mechanical removal by grinder grinding or shot blast, a method of chemical reaction using an acid or alkali solution, or a method of dissolving and washing with an organic solvent. There are methods and the like, which have been selected and used depending on the case.

[0003] The mechanical method has problems that the working environment is not good due to the generation of dust and noise and that it takes time and labor, and the method using an acid or alkali solution or the method using an organic solvent has a problem in the working environment. In addition to the poor quality, there were problems such as the generation of harmful waste liquid and its treatment.

As a technique for avoiding these problems, for example, a method utilizing a cathode spot effect of a vacuum arc as disclosed in Japanese Patent Application Laid-Open No. 5-86451 has been devised.
However, the conventional vacuum arc cleaning method is mainly used to remove the oxide film present on the metal surface, and is recognized as a method that can remove a small amount of dirt other than the oxide film accompanying the removal of the oxide film. It has been.

Conventionally, in this method, the arc operation is performed by a direct current and a constant current operation. The composition of the arcing atmosphere was not controlled, and the inside of the vacuum chamber was simply evacuated by a vacuum pump. An oil rotary pump is generally used as a vacuum pump, and the atmospheric pressure is 100
It is often performed at Pa or lower.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a technique for solving a problem in a surface treatment method utilizing a cathode spot action of a vacuum arc. That is, in the conventional method of removing surface contamination using the cathode spot action of a vacuum arc, particularly when the contamination is an organic compound, after the organic substance is decomposed, part of carbon is solidified on the surface. Problems such as the remaining surface not being cleaned and the presence of carbon on the surface lowering the action of cleaning the cathode spot occur.

When the organic compound is decomposed and vaporized, a large amount of gas is released, so that the degree of vacuum in the atmosphere is remarkably reduced, and there is also a problem that the characteristics of the vacuum arc cannot be maintained. The conventional vacuum arc method, which mainly removes oxide films, does not pose a problem.However, there is a special problem when removing organic compounds, especially when a large amount of organic compounds is present on the surface. Was not available.

[0008]

In order to solve the above-mentioned problems, in a method of removing an organic compound present on the surface of a metal substrate by a vacuum arc, an oxidizing gas is introduced into the atmosphere to reduce the oxidizing atmosphere of the vacuum arc. Or fluctuate the arc current in a pulsed manner, or perform these two things simultaneously.

In order to realize these methods, at least a DC power supply capable of pulsing an arc current, a vacuum chamber, a vacuum exhaust device, a gas introduction valve capable of controlling a flow rate, and a pressure in the vacuum chamber are detected. An apparatus having a pressure sensor, a mechanism for feeding back a pressure signal of a pressure sensor in a vacuum chamber to an arc power supply, and automatically controlling a pulse operation of an arc so that a predetermined atmospheric pressure is maintained. Is used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As disclosed in Japanese Patent Application Laid-Open No. 5-86451, there is a technique called vacuum arc descaling for removing an oxide film on a metal surface by utilizing the cathode spot action of a vacuum arc. The cathode point of the vacuum arc has a high energy density, and once the cathode point is formed, the surface of the cathode is instantaneously evaporated and vaporized, thereby removing the oxide film.
Even if oxide film and dirt other than oxide film are present at the same time,
Both vacuum arc cathode spots can be removed.

The removal of an oxide film and dirt on the surface by a vacuum arc is hereinafter collectively referred to as vacuum arc cleaning. In vacuum arc cleaning, a member to be cleaned is connected to a negative electrode of an arc power supply, acts as a cathode, and generates an arc between the anode and a separately installed anode.

In vacuum arc cleaning, in particular, when the dirt is an organic compound such as oils and fats or a coating film, when these organic compounds are decomposed, part of the carbon remains on the surface as a solid, or carbon once vaporized. But,
It is deposited on the surface of the surrounding low-temperature member.

It takes time to remove the carbon layer on the surface by the action of the cathode spot, and there is a problem that the surface cannot be cleaned. Furthermore, since the decomposition of organic substances involves generation of a large amount of gas, the degree of vacuum in the atmosphere is significantly reduced, and the characteristics of the vacuum arc cannot be maintained.

The present invention is directed to a method for solving these problems. The method of the invention will be described with reference to FIG. A vacuum exhaust pump 2 is connected to a vacuum chamber 1 for creating a reduced-pressure atmosphere.

A DC arc power supply 3 for generating an arc in the vacuum chamber 1 has a function capable of pulsing an arc current. The positive electrode of the arc power supply is connected to an anode 4 installed in a vacuum chamber, and the negative electrode is connected to a cleaning processing member 5 installed in the vacuum chamber.

The vacuum chamber 1 is provided with a pressure sensor 6 for measuring atmospheric pressure, and further has a leak valve 7 for introducing gas into the vacuum chamber. When a vacuum arc is generated at a constant current in a vacuum chamber by a conventional method, dirt on the surface of the processing member 5 is decomposed and turned into a gas, which is released into the vacuum chamber and the pressure in the vacuum chamber increases.

The first aspect of the present invention relates to prevention of residual carbon on the surface, and is characterized by introducing a small amount of oxygen into the atmosphere. By adjusting the opening of the leak valve 7, pure oxygen or a gas containing oxygen, for example, air is introduced. The presence of oxygen in the atmosphere causes the carbon of the organic compound to react with the oxygen, resulting in a carbon monoxide gas or a carbon dioxide gas, thereby suppressing the surface residue as solid carbon.

When the removal of the organic compound is completed, the leak valve is closed, the supply of oxygen is stopped, and the metal oxide formed by the supply of oxygen is removed by a vacuum arc to complete the cleaning process. The flow rate of the introduced gas may be determined by operating the evacuation pump and determining that the pressure in the vacuum chamber does not exceed 100 Pa.

A second aspect of the present invention is to make the arc operation pulse-like in order to suppress an excessive rise in the atmospheric pressure. The arc current operation mode of the power supply 3 is set to the pulse mode, and the arc current is varied in a pulsed manner. The pulse-like variation of the arc current means that the arc current is repeatedly turned on and off at a constant cycle.

However, if the current is completely reduced to zero in the off state, it becomes difficult to re-ignite the arc. Therefore, it is necessary to keep flowing a small arc current to such an extent that the arc becomes unstable and does not disappear. Is also often done. In the specification of the present invention, such a small current state for maintaining the arc, including the small current state, is turned off, and the arc current is repeatedly turned on and off.

The pulse operation of the arc is widely performed in arc welding for the purpose of improving the shape of a weld bead, and the pulse operation in a vacuum arc can be easily realized by employing a known technique. The arc pulse operation causes intermittent gas release and suppresses an increase in ambient pressure.

For efficient vacuum arc cleaning, the atmospheric pressure is desirably 1000 Pa or less, more preferably 10 to 2 × 100 Pa. The degree of increase in the atmospheric pressure in the vacuum arc cleaning according to the conventional method differs depending on the degree of surface contamination and the type of substance constituting the contamination, and also varies depending on the vacuum arc current. It also depends on the volume of the vacuum chamber and the capacity of the exhaust pump.

The pressure in the vacuum vessel where a vacuum arc is formed is 1000 Pa or less, preferably 10 to 2 × 100 Pa
The pulse operation of the arc current is controlled so as not to be out of the range. The control parameter of the pulse operation is the time ratio between the ON state and the OFF state. The absolute value of the pulse cycle time has little relation to the pressure adjustment, but if the cycle time is too long, the atmospheric pressure will fluctuate greatly within the ON state time, and the vacuum arc cleaning action will not be uniform.

It is preferable that the fluctuation of the atmospheric pressure be suppressed within 20% of the average pressure. Since the pulse cycle within 20% differs depending on the amount of gas decomposed and released, the capacity of the vacuum chamber, and the pumping speed of the vacuum pump, the upper limit of the pulse cycle is determined while observing the pressure fluctuation width. The arc current value for vacuum arc cleaning is from 100 A to 2
00A is desirable. If necessary, the first invention and the second invention can be combined.

FIG. 2 is a block diagram of an apparatus for detecting the atmospheric pressure in the vacuum chamber and automatically controlling the arc current pulse operation so that the pressure becomes a predetermined value. The output signal of the pressure sensor 6 becomes an input to the pulse controller 8 of the arc power supply and is compared with a preset value. The ON / OFF time ratio of the pulse operation is adjusted by a logic circuit in the controller so that the pressure approaches the set value. Is output to the arc power supply 3.

In response to this signal, the pulse operation condition of the arc power supply is changed. The exchange of these signals and the change of the pulse operation are repeated until the pressure reaches the set value.
The construction and realization of such a logic mechanism and a control mechanism for automatic adjustment are well-known technologies, and thus the details thereof are omitted.

[0027]

【Example】

(Example 1) A vacuum arc cleaning was performed under the conditions shown in Table 1 using a steel material covered with an oxide scale and having a surface contaminated with machine oil as a cathode. In Table 1, condition 1 is a conventional vacuum arc cleaning method, the arc current value is constant at 100 A, and no external air is introduced during the arc processing. When the surface was observed after the arc treatment for 20 seconds, a black portion remained on the surface. Under these conditions, a clean surface could not be obtained.

Condition 2 is the air-introduced vacuum arc cleaning method of the present invention. The arc current was 100 as in condition 1.
A. Immediately after arc ignition, 5 Ncm ³ per second
Air into the atmosphere through a leak valve,
After maintaining that state for a second, the air introduction was stopped. 5 more
After a second, the arc was stopped and the vacuum arc cleaning was completed. When the surface was observed after completion, it was confirmed that the entire surface had a metallic color and a clean surface was obtained.

[0029]

[Table 1]

(Example 2) A steel sheet having a surface coated with an oil paint was used as a cathode, and surface cleaning was performed by vacuum arc under various conditions shown in Table 2. Condition 1 was a conventional vacuum arc cleaning method, in which air was not introduced into the atmosphere and the arc current was constant at 200 A. After arc ignition, the pressure in the vacuum chamber increased with time, and the arc was extinguished 6 seconds later. The surface of the sample had a metal-colored part, but most of the surface had carbonized paint and remained.

In condition 2, air is not introduced, but the arc current is pulsed. The on state is 200A and is 0.
The pulse operation was repeated for 5 seconds, and the off state was repeated at 0.5 A for 20 seconds at 20A. By performing pulse operation,
The pressure in the vacuum chamber was kept almost constant at 180 Pa. Although the surface after the treatment had many metallic portions, a black portion where the coating was partially carbonized remained.

Condition 3 is that the current is pulsed and air is introduced. Since there is a gas introduced from the outside in addition to the release of the decomposition gas, the on / off time ratio of the pulse operation is changed from the condition 2 to increase the off time, and the on state is 2
00A, 0.5 seconds, and the off state was repeated at 20A, 1.0 seconds. The air introduction rate was set to 5 Ncm ³ / sec.

Under these conditions, the pressure value was 170 Pa. After stopping the air introduction, perform arc cleaning 7 more times.
After continuing the arc for a second, the arc was stopped, and the surface was observed. As a result, it was confirmed that a clean surface with a metallic color was obtained over the entire surface.

[0034]

[Table 2]

[0035]

According to the present invention, in vacuum arc cleaning for removing an organic compound from a metal surface, by setting the arc current to a pulse mode, a rise in the pressure of the atmosphere can be suppressed and stable cleaning can be continuously performed. Further, by introducing an oxidizing gas such as air into the vacuum arc atmosphere, a clean surface having no carbon residue on the metal surface was obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conventional vacuum arc cleaning device.

FIG. 2 is a diagram showing one embodiment of a vacuum arc cleaning device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Vacuum chamber 2; Vacuum pump 3; Vacuum arc power supply which can modulate pulse of arc current 4; Vacuum arc anode 5; Member to be cleaned 6; Pressure sensor 7; Valve 8: Power control controller

Claims (4)

[Claims] 1. A method for removing an organic compound present on a surface of a metal substrate by a vacuum arc, wherein an oxidizing gas is introduced into the atmosphere to make the vacuum arc operating atmosphere oxidizing. By surface cleaning method. 2. A method for removing organic compounds present on a surface of a metal substrate by a vacuum arc, wherein the arc current is varied in a pulsed manner. 3. A method for removing an organic compound present on the surface of a metal substrate by a vacuum arc, wherein an oxidizing gas is introduced into the atmosphere, the vacuum arc operating atmosphere is oxidized, and the arc current is pulsed. A method for cleaning a surface by a vacuum arc, wherein the method is varied. 4. An apparatus for removing an organic compound present on a surface of a metal substrate by a vacuum arc, comprising:
It has a DC power supply capable of pulse operation of arc current, a vacuum chamber, a vacuum exhaust device, a gas introduction valve capable of controlling a flow rate, and a pressure sensor for detecting a pressure in the vacuum chamber. A vacuum arc descaling apparatus having a mechanism for feeding back a signal to an arc power source and automatically controlling an arc pulse operation so that a pressure in a vacuum chamber is maintained at a predetermined value.