KR101082698B1 - The water for removing the film of oxide or rust on metal, and the method for removing the film of oxide or rust on metal using this water - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to the use of acidic water obtained by electrolysis as an oxide film or rust removal water on a metal surface, and a method for removing an oxide film or rust on a metal surface using the water.

The present invention is water obtained by electrolysis of raw water containing sulfate ions or raw water added with a mixture containing sulfate or sulfate to raw water, wherein the concentration of sulfate ion is 20 to 20000 mg / l, and the pH of the water is 0.5. ~ 4.0, residual chlorine concentration of 10 mg / l or less, redox potential of 300 to 1150㎷, sulfate ion concentration of 30 to 30000 mg / l, chloride ion concentration of 3/4 or less of sulfate ion concentration or 50 mg / l Hereinafter, the present invention relates to an oxide film or rust removal water (hereinafter referred to as "oxide removal water") of a metal, which has an electrical conductivity of 10 S / m or less.

Description

The water for removing the film of oxide or rust on metal, and the method for removing the film of oxide or rust on metal using this water}

TECHNICAL FIELD The present invention relates to the use of acidic water obtained by electrolysis as an oxide film or rust removal water on a metal surface, and a method for removing an oxide film or rust on a metal surface using the water.

If the metal products (particularly steel alloys, copper and copper alloys) are left for a long time, an oxide film is formed on the surface, and adverse effects such as loss of metallic gloss, discoloration, deterioration of electrical properties, and deterioration of material strength occur. In addition, these oxide films are added to cause corrosion and proceed to the rust state.

In addition, when an operation involving heating such as gas welding, electric welding, spot welding, soldering, etc. is performed on a metal product, an oxide film is formed on the surface in the same shape as when left for a long time. In addition, when the heating time is long or when the heating temperature is high, a film-like oxide that is thicker than the oxide film called an oxide scale and is relatively hard adheres to the surface. This is an obstacle to coating or plating treatment, and also gradually peels off from vibration and the like, adheres to the periphery of the metal product or component, and if it is in a pipe, it is mixed inside a certain fluid and adversely affects the entire apparatus.

In order to remove the oxide film, rust, and oxidation scale of such metal, conventionally, a metal product is immersed or applied to high concentration (about 10% or more) of hydrochloric acid, sulfuric acid, acetic acid, and various strong acid-based medicines containing these as main components. The method is done.

However, these strong acids are designated as specific chemical substances under the Japanese Labor Safety Sanitation Act, and are required to reduce the amount of use in terms of the workplace environment. In addition, the adverse effects of being discharged to the surrounding environment due to steam, leakage, etc. are also large, and special care and care are required for use and storage of the waste liquid thereof.

Hydrochloric acid also generates hydrogen chloride, which is a corrosive and stimulating gas, which may corrode nearby metal machinery, buildings, and materials to be stored, or adversely affect the health of workers. Acetic acid also produces nitrogen oxides, which are corrosive and irritant gases, and have the same risk.

It is an object of the present invention to provide a water which can remove an oxide film or rust of a metal without using a specific chemical substance having high hazard, and a method of removing an oxide film or rust of a metal using the water.

In order to achieve the above object, the inventors of the present invention have intensively studied, and the electrolytic acid water of a specific ion composition obtained by electrolysis is exceptionally effective in removing an oxide film or rust of a metal. By adding a specific substance to the water, the surface condition after the removal of the oxide film can be improved. Furthermore, the ultrasonic vibration is applied to the oxidation water to find that the acidic film removal is performed in high quality in a short time.

In the first aspect of the present invention, the present invention provides a sulfate ion concentration of 20 to 20000 mg / L in raw water containing sulfate ions or raw water in which raw water is added a mixture containing sulfate or sulfate. Water obtained by electrolysis, wherein the pH of the water is 0.5 to 4.0, the residual chlorine concentration is 10 mg / l or less, the redox potential is 300 to 1150 kPa, the sulfate ion concentration is 30 to 30000 mg / l, and the chloride ion concentration is An oxide film or rust removal water (hereinafter referred to as "oxide removal water") of a metal, characterized by having a sulfuric acid ion concentration of 3/4 or less or 50 mg / l or less and an electrical conductivity of 10 S / m or less.

In a second aspect of the present invention, the present invention relates to an oxide film removing water characterized by using sodium sulfate or potassium sulfate or a mixture thereof as a sulfate added to raw water.

In the third aspect of the present invention, the present invention relates to an oxide film removing water, characterized in that the thiourea is added to the oxide film removing water.

According to a fourth aspect of the present invention, the present invention provides a rust removal water, characterized in that 0.01 to 1% of diethanolamine fatty acid ester and / or 0.01 to 1% of triethanolamine fatty acid ester are added to the oxide film removing water. It is about.                     

In a fifth aspect of the present invention, the present invention provides a method for removing an oxide film and rust of a metal, wherein the oxide film removal water is brought into contact with a metal surface to be treated to remove metal oxide or rust. Removal method ”.

According to a sixth aspect of the present invention, the present invention is filled with an oxide film removing water in a cleaning tank provided with an ultrasonic vibrator, immersed the metal to be treated therein, and in some or all of the immersion time, the ultrasonic vibrator provided in the cleaning tank It relates to an oxide film removing method characterized in that the oscillation causes the ultrasonic vibration to act on the metal to be treated.

In the seventh aspect of the present invention, the present invention provides a method for removing an oxide film, wherein the frequency of the ultrasonic wave acting on the metal to be treated is 20 to 45 kHz, and the output density obtained by dividing the output of the ultrasonic wave by the volume of water placed in the washing tank is It relates to an oxide film removal method, characterized in that the output per oscillation area of the ultrasonic vibrator is 3W / L or more, 0.15W / cm2 or more.

In the eighth aspect of the present invention, the present invention relates to an oxide film removing method characterized in that the temperature of the oxide film removing water is treated at 40 to 90 ° C.

In the ninth aspect of the present invention, the present invention provides an oxide film of a metal remaining on the surface of a metal to be treated by bringing alkaline electrolytic water obtained by electrolysis into contact with the surface of the metal to be treated after the treatment step according to the oxide film removal method. It is related with the oxide film removal method which has the process of neutralizing removal water.

According to a tenth aspect of the present invention, the present invention provides an alkaline electrolytic water for use in the neutralization step of the oxide film removal method of 8.5 to 13.0, a chloride ion concentration of 20 mg / l or less, and a sulfate ion concentration of 30 mg / l. Hereinafter, the present invention relates to a method for removing an oxide film, wherein the redox potential is from -850 to -50 mA.

According to an eleventh aspect of the present invention, in the method for removing an oxide film of the neutralization step, the present invention is characterized by placing alkaline electrolyzed water in a neutralization tank provided with an ultrasonic vibrator, and applying a temperature of 40 to 90 ° C. to the target metal. An oxide film removal method characterized in that the frequency is 20 to 45 kHz, the output density obtained by dividing the output of the ultrasonic wave into the volume of water in the cleaning tank is 3 W / l or more and the output per oscillation area of the ultrasonic vibrator is 0.15 W / cm 2 or more. It is about.

According to the first aspect of the present invention, oxides (oxides or rusts) formed on the metal surface react with sulfate ions contained in the oxide removal water to dissolve into soluble sulfates, thereby removing the oxides or rusts. Can be. At this time, in order to perform a practical treatment, water having a pH of 0.5 to 4.0 and a sulfate ion concentration of 30 to 30000 mg / L is required.

Here, when the chloride ion concentration is 3/4 or less or 50 mg / l or less of the sulfate ion concentration, the chloride ion proceeds to dissolve or oxidize the normal metal surface. For this reason, in steel alloys, components that do not dissolve in acids such as carbon, carbon compounds, and metal oxides in the steel are precipitated on the surface as smuts, causing the steel surface to turn black.

In addition, in copper and copper alloys (brass, bronze, etc.), oxidation gradually progresses after treatment, and discoloration starts to reddish brown. However, the chloride ion concentration is 3/4 or less or 50 mg / l or less. This can prevent these discolorations. Also in other metals (nickel alloy etc.), it was proved that the damage by excess oxidation can be prevented by reducing the chloride ion concentration.

This is because chloride ions are more chemically reactive to metal surfaces than sulfate ions.

So far, acid chloride having a pH of about 3 or less is produced in electrolysis. Sodium chloride is often used as an electrolyte to be added to raw water. However, in this case, the generated acidic water has a large amount of chloride ions. Not suitable for removing rust.

In addition, the discoloration prevention effect is related to the residual chlorine concentration of the oxide film removal water and the redox potential, the residual chlorine concentration is 10 mg / l or less, and the redox potential is 300 to 1150 Pa (preferably the residual chlorine concentration). Is less than 4 mg / l, and the redox potential is less than 1000 kPa), so that excessive dissolution, elution, and oxidation of the metal can be prevented. This is because the metal surface is prevented from corroding and discoloring due to the oxidizing power of hypochlorous acid measured as the residual chlorine concentration. The redox potential of the electrolyzed acidic water is high because it originates mainly in chlorine and hypochlorous acid. The redox potential is 1150 kPa or less (preferably less than 1000 kPa), but the metal oxide film or It is suitable for removing rust.

Furthermore, by setting the electrical conductivity to 10 S / m or less, it is possible to define the total amount of ions contained in the oxide film removing water and to prevent the promotion of oxidation by other anions.

According to the second aspect of the present invention, the amount of sulfate ions contained in the water used as raw water (do not bury water, industrial water, well water, etc.) is low, and an appropriate electrolytic acidic water cannot be obtained without an electrolyte added. If this is the case, it is possible to produce the oxide film removing water according to the first aspect of the present invention by adding these sulfates (sodium sulfate, potassium sulfate).

According to the third aspect of the present invention, since thiourea is selectively adsorbed to the newly formed surface obtained by removing the oxide film or rust with the metal to be treated, and further oxidation is prevented. It is possible to prevent anger synergistically. Adsorption of thiourea to other metals is not weaker than that of steel alloy, but the effect can be expected to some extent, and at least it does not adversely affect.

According to the fourth aspect of the present invention, in the same manner as in the third aspect, the diethanolamine fatty acid ester and / or the triethanolamine fatty acid ester are selectively adsorbed on the new surface which is obtained by removing the oxide film or rust with the metal to be treated. Since further oxidation is prevented, discoloration of the metal surface to be treated can be prevented. Since these additives can be used also for nonferrous metals, they are effective for a wide range of materials.

According to the fifth aspect of the present invention, in the metal oxide film removal operation or the rust removal operation, it is possible to provide a stable and eco-friendly method without the use of hydrochloric acid, sulfuric acid, sulfuric acid, or the like. It becomes possible.

According to the sixth aspect of the present invention, in the removal of the oxide film and the removal of rust, the effect of the oxide removal water and the ultrasonic vibration act synergistically, so that it is possible to shorten the time required for removal of the oxide film or removal of rust. Further, the treatment method combining the ultrasonic waves can perform the same amount of oxide film removal or rust removal in water having a higher pH or water having a lower sulfate ion concentration than in the case where no ultrasonic wave is used.

According to the seventh aspect of the present invention, in particular, the oscillation conditions of the ultrasonic waves specified herein can be performed to more effectively remove oxide film or remove rust. In particular, a relatively low frequency is appropriate for the frequency of the ultrasonic wave used when the oxide film or rust is removed. This is because the low frequency ultrasonic method has a strong effect on the surface of the metal to be treated and has a high effect of peeling off the oxide film and rust. In addition, although the improvement effect is obtained with respect to oxide film removal by making a certain output density and the output per oscillation area act, a sufficient improvement effect is not expected more than this.

According to the eighth aspect of the present invention, by raising the temperature of the oxide film removing water, it is possible to accelerate the chemical reaction with the metal to be treated and to shorten the time required for oxide film removal or rust removal. In addition, in the method of raising the treatment temperature, the oxide film removal or the rust removal can be performed with water having a higher pH or water having a lower sulfate ion concentration than in the case where the treatment temperature is not increased.

According to the ninth aspect of the present invention, if the film is left with the oxide film removing water attached thereto, the metal surface is excessively oxidized to cause discoloration or rust. It is possible to prevent alkaline electrolytic water from being brought into contact with the metal surface to be treated to neutralize it.                     

According to the tenth aspect of the present invention, in the neutralization by the alkaline electrolytic water, the pH, chloride ion concentration, sulfate ion concentration, and redox potential are specified, but it is effective to obtain subsequent rust prevention property. This is because if there are many chloride ions and sulfate ions contained in alkaline electrolytic water, discoloration or rust tends to occur in the metal to be treated even within a range defined by pH and redox potential.

According to the eleventh aspect of the present invention, in the neutralization by alkaline electrolytic water, ultrasonic vibration is combined to reliably strip off the oxide film removal water adhering to the metal surface to be treated and to neutralize it. As a result, subsequent discoloration and rust can be further prevented as compared with the case where it is simply immersed in alkaline electrolytic water and neutralized. In addition, it is possible to remove the fine oxides or stains generated on the surface of the metal to be treated by the oxide film removal process by ultrasonic vibration to clean the surface of the metal to be treated.

The conditions for generating ultrasonic waves at this time are defined herein, and more effective neutralization and removal of oxides and stains can be performed.

Embodiment of this invention is described based on an Example.

Examples 1-8

The water quality measurement of the electrolytic acid water obtained by performing electrolysis which adjusted the ion concentration in raw water was performed. The raw water was softened by tapping water from Biwa-cho, Shigaken Higashi-Azai-gun. Sodium sulfate, potassium sulfate, and sulfuric acid were used as the added electrolyte. The electrolyzed electrolytic cell was an open-type diaphragm electrolyzer, the anode of which was platinum-plated titanium, and the cathode of stainless steel (SUS 304). The electrode size was 50 mm x 100 mm for both the positive electrode and the negative electrode, and the thickness was 1 mm. The volume of the electrolytic cell was 4 L in both the anode chamber and the cathode chamber, and raw water was added thereto to perform electrolysis. The polyolefin neutral membrane was used for the diaphragm. As a power supply, a variable DC power supply was used to perform electrolysis while monitoring the electrolytic voltage and the electrolytic current. Using the electrolytic apparatus as described above, the water quality of the electrolytic acidic water (oxide film removal water) obtained by electrolyzing each raw water under the raw water and electrolytic conditions shown in Table 1 is as shown in Table 2. The pH of the electrolytic alkaline water obtained at the same time was also described. In addition, the concentration of chloride ion in raw water was adjusted by adding sodium chloride suitably.

As Comparative Example 1, electrolysis was performed by adding sodium sulfate and sodium chloride to raw water, and the chloride ion concentration of the electrolytic acidic water (oxide removal water) exceeded 3/4 of the sulfate ion concentration, and the residual chlorine concentration was 10 mg / L. And the redox potential exceeded 1150 mA. As Comparative Example 2, only sodium chloride was added to the raw water for electrolysis, and the chloride ion concentration of the resulting electrolytic acidic water (acidic film-removed water) was higher than the acidic ion concentration, and the redox potential exceeded 1150 kPa. Next, as Comparative Example 3, a pH exceeding 4 was produced.

The electrolytic acidic water obtained in Examples 1 to 8 and Comparative Examples 1 to 3 was oxidized film removing water, and the metals in the following examples were immersed in test pieces, and the degree of removal of the oxide film and rust on the surface, after treatment The discoloration of the metal surface was evaluated.

The test pieces were 100 mm x 50 mm in size and 1 mm in thickness.

In the immersion conditions, the temperature of the oxide film removing water was 60 ° C., and the immersion time was 3 minutes.

Example 9

Cold rolling copper plate (SPCC) left indoors to produce reddish-brown rust on its surface.

Example 10

Cold rolled copper plate (SPCC) heated with a gas burner for 10 seconds to form a black oxide film on the surface.

Example 11

A stainless steel plate (SUS 304) is heated with a gas burner for 10 seconds to form a dark brown oxide film on its surface.

Example 12

Pure copper plate left indoors to form a dark brown oxide film on its surface.

Example 13

Two pure copper plates were joined by soldering in 10 mm layers, and the black oxide scale was affixed by the heating at this time.

Example 14

The brass plate is left indoors to form a thin black oxide film on its surface.                     

Example 15

Two brass plates were joined in 10 mm layers by soldering, and a black oxide scale was attached by heating at this time.

Example 16

The bronze plate is left indoors to form a thin black oxide film on its surface.

Example 17

The bronze plate is heated on the gas burner for 10 seconds to form a dark brown oxide film on its surface.

Example 18

Nickel plating having a thickness of 20 μm on a cold rolled copper plate, and heated with a gas burner for 10 seconds to form an oxide film on the surface.

The results relating to the removal state of the oxide film or rust are shown in Table 3, and the discoloration of the surface of the metal to be treated after treatment is shown in Table 4. "Room 1" in the table represents "Example 1", and "ratio 1" represents "Comparative Example 1".                     

According to the results of Table 3 and Table 4, the electrolytic acid water having a high chloride ion concentration as shown in Comparative Example 1 and Comparative Example 2 and having a high redox potential is capable of removing oxide film and rust. Discoloration occurs on the metal surface. In addition, with the electrolytic acidic water having a pH of 4.0 or higher as in Comparative Example 3, a sufficient oxide film removing action cannot be obtained.

However, it is found that the electrolytic acidic water (oxidized film removing water) as in Examples 1 to 8 can achieve a sufficient oxide film removing and rust removing effect and a discoloration preventing effect on the metal surface after treatment.

Moreover, regarding the discoloration of the to-be-processed metal which arises when making the processing time of an oxide film removal long, evaluation of the additive which prevents it was performed in the following Example.

Example 19

The test pieces of Example 9, Example 12, and Example 15 were immersed by adding 0.01% and 3% of thiourea as an additive to the oxide film removing water of Examples 2, 4, and 6.

Example 20

0.01% and 3% of diethanolamine fatty acid ester was added to the oxide film removing water of Examples 2, 4 and 6 as additives to immerse the test pieces of Examples 9, 12 and 15.

Example 21

Triethanolamine fatty acid esters were added 0.01% and 3% as additives to the oxide film removing water of Examples 2, 4 and 6, and the test pieces of Examples 9, 12 and 15 were immersed.

Comparative Example 4

Also, the same was immersed in the oxide film removal water not added for comparison.

Table 5 shows the results of the presence or absence of discoloration of the metal surface produced when the treatment time was extended by immersing the treated metal in these oxide film removing water. The temperature of the oxide film removal water was 60 degreeC, and immersion time was 3 minutes and 5 minutes.                     

According to the results of Table 5, the oxide film removal water added with thiourea was found to have a significant discoloration prevention effect, especially in steel alloys. In addition, the copper alloy obtained a discoloration preventing effect of practically no problem.

Moreover, the diethanolamine fatty acid ester and the triethanolamine fatty acid ester obtained the discoloration prevention effect in all the metal which tested.

In addition, the ultrasonic vibration was applied to the oxide film removal treatment, and the ratio of the treatment time required for the oxide film removal was performed in Examples 22 to 32 shown in Table 6.

In addition, it was compared with the comparative example 5, the comparative example 6, and the comparative example 7, which did not apply ultrasonic vibration. The used washing tank was a square water tank made of stainless steel, its size was 500 mm x 500 mm, and the depth was 500 mm. The amount of water was 100 liters.                     

According to the result of Table 6, when ultrasonic vibration was applied, it was possible to shorten the processing time in all the Examples.

Example 32

Using the oxide film removal water produced in Example 4, the test piece rusted in Example 9 was immediately immersed in alkaline electrolyzed water obtained by electrolysis for 2 minutes and left in a neutralized room. The pH of the alkaline electrolyzed water was 8.9, the chloride ion concentration was 15 mg / l, the sulfate ion concentration was 26 mg / l, and the redox potential was -820 kPa.

Comparative Example 8

Immediately after treatment with the same oxide film removing water as in Example 32, the mixture was immersed in alkaline electrolytic water (pH 8.7, chloride ion concentration 38 mg / l, sulfate ion concentration 45 mg / l, redox potential -760 kPa) for 2 minutes and neutralized. One test piece was made and left indoors.

Comparative Example 9

Immediately after treating the same oxide film removing water as in Example 32, a test piece immersed in deionized water generated using an ion exchange resin for 2 minutes was prepared and left to stand indoors.

In each of the results, no rust or discoloration occurred even after 7 days in Example 32, but rust occurred after 2 days in Comparative Example 8 and after 1 day in Comparative Example 9.

Example 33

By the same neutralization method as in Example 32, neutralization was performed using alkaline electrolytic water having a pH of 8.8, a chloride ion concentration of 6.5 mg / l, a sulfate ion concentration of 15 mg / l, and a redox potential of -120 kPa, and left to stand indoors. This test piece did not develop rust or discoloration even after 7 days.

Example 34

By the same neutralization method as in Example 32, neutralization was carried out using alkaline electrolytic water having a pH of 11.8, a concentration of chloride ion of 18 mg / l, a concentration of sulfate ion of 25 mg / l, and a redox potential of -827 kPa, and left in the room. This test piece did not develop rust or discoloration even after 7 days.                     

Example 35

Ultrasonic vibration was applied to the neutralization treatment step performed in Example 32 to effect neutralization. The neutralization tank used was a square water tank made of stainless steel, and the size was 500 mm x 500 mm and the depth was 500 mm. The amount of water was 100 liters. The neutralized alkali electrolyzed water had a concentration of 40 ° C, the frequency of the ultrasonic wave acted on the metal to be treated was 25 kHz, the power density divided by the volume of the ultrasonic wave into the water bath was 6 W / l, and the output per blast area of the ultrasonic vibrator was 0.3. It was set as W / cm <2>.

The test pieces subjected to this treatment did not cause rust or discoloration even after standing indoors for 10 days. In addition, due to the scale generated immediately after the oxidation removal, very small black discoloration was removed by the ultrasonic vibration of the neutralization process, thereby improving the surface state.

According to the above description, if the present invention is used, there is no need to use a high concentration of hydrochloric acid or sulfuric acid for removing the oxide film or rust generated on the surface of the metal, and the working environment and the surrounding environment are improved. Furthermore, by applying the ultrasonic vibration, it is possible to shorten the processing time and to improve the oxide film removing effect. Further, by applying a neutralization step with alkaline electrolytic water, it is possible to prevent reoxidation of the oxide film or the metal from which the rust has been removed.

Claims (11)

Water obtained by electrolysis of water containing sulfate ions or a mixture containing sulfuric acid or sulfates or sulfates, having a sulfate ion concentration of 20 to 2000 mg / l, wherein the pH of the water is 0.5 to 4.0 Residual chlorine concentration of 10 mg / l or less, redox potential of 300-1150 ㎷, sulfate ion concentration of 30-30000 mg / l, chloride ion concentration of 3/4 or less of sulfate ion concentration or 50 mg / l, The oxide film or rust removal water of the metal, characterized in that the electrical conductivity is 10S / m or less. The oxide film or rust removal water according to claim 1, wherein sodium sulfate ions or potassium sulfate ions or a mixture thereof is used as the sulfate. The metal oxide film or rust removal water according to claim 1 or 2, wherein thiourea is added to the oxide film or rust removal water of the metal. The method of claim 1 or 2, wherein at least one selected from the group consisting of diethanolamine fatty acid esters and triethanolamine fatty acid esters is added to the oxide film or rust removal water of the metal by 0.01 to 1%. Oxide or rust removal water of metals. A method for removing an oxide film or rust from a metal according to claim 1 or 2, wherein the oxide film or rust removing water of the metal is brought into contact with the metal surface to be treated to remove the oxide film or rust from the metal. Filling the cleaning tank provided with the ultrasonic vibrator with the oxide film or rust removal water of the metal of claim 1 or 2, immersing the metal to be treated therein, and oscillating the ultrasonic vibrator installed in the cleaning tank at part or all of the immersion time. An oxide film or rust removal method of a metal, characterized by removing an oxide film or rust of a metal by applying ultrasonic vibration to the metal to be treated. The frequency of the ultrasonic wave applied to the metal to be processed is 20 to 45 kHz, the power density obtained by dividing the ultrasonic wave output by the volume of water placed in the washing tank is 3 W / l or more, and the output per oscillating area of the ultrasonic vibrator is 0.15. An oxide film or rust removal method of a metal, characterized in that more than W / ㎠. The metal oxide film or rust removal method according to claim 5, wherein the metal oxide film or rust removal water is treated at a temperature of 40 to 90 ° C. After the oxide film or the rust removal method of the metal according to claim 5, the alkaline electrolytic water obtained by electrolysis is brought into contact with the metal surface to be treated to remove the oxide film or rust removal water of the metal remaining on the metal surface. It has a process to neutralize, The oxide film and the rust removal method of metal. The pH of the alkaline electrolytic water is 8.5 to 13.0, the chloride ion concentration is 20 mg / l or less, the sulfate ion concentration is 30 mg / l or less, and the redox potential is -850 to 50 kPa. Method of removing oxide film and rust of metal. The alkaline electrolytic water is put into a neutralization tank provided with an ultrasonic vibrator, and the frequency of the ultrasonic wave which makes a temperature 40-90 degreeC and a to-be-processed metal is 20-45 Hz, and the volume of the water which put the output of an ultrasonic wave into the washing tank is 10%. An oxide film and rust removal method of a metal, characterized in that the neutralized by the output density divided by 3W / ℓ or more, the output per oscillation area of the ultrasonic vibrator is 0.15W / ㎠ or more.