JPH07278862A - Continuous cleaning method by high-boiling-point hydrocarbon - Google Patents

Abstract

PURPOSE:To reduce environmental pollution and to improve cleaning efficiency by using a high-b.p. hydrocarbon such as NMP in the continuous cleaning of a strip or wire metal in the working stage, recovering the cleaning soln. by distillation after use and recycling the cleaning soln. CONSTITUTION:A strip metal 1 is preheated in a cleaning soln. storage tank 5 of a first cleaning tower 2 and cleaned with the cleaning soln. ejected from a spray nozzle 4. The metal is then spray-cleaned in a second cleaning tower 3, passed through a vacuum drying zone 6, dried and sent to the succeeding stage. In this case, a fresh cleaning soln. is supplied to the second cleaning tower 3 from a cleaning soln. storage tank 15 and then successively sent to the first cleaning tower 2. The cleaning soln. in the first cleaning tower 2 with the oil content increased to a specified value is sent to a sludge separation tank 8 to separate sludge 9, introduced into a condensor 12 from the evaporator 10 of a vacuum distillation device, cleaned and again stored in the tank 5 through a receiver 13. The sludge 9 in the evaporator 10 is discharged outside the system and incinerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method applicable to continuous cleaning in the metalworking industry, and in particular, continuous cleaning performed as a pretreatment such as plating of strip-shaped and linear metal materials, bright annealing, and chemical conversion treatment. It is intended to provide an effective method for the process.

[0002]

2. Description of the Related Art In the process of degreasing and cleaning cold rolled steel in the steel industry, conventionally, a method of electrolysis using a sodium silicate aqueous solution or an aqueous solution containing a surfactant and an alkali is mainly used. The method of brushing was adopted. When performing degreasing cleaning as a pretreatment of the plating process,
Particularly strict cleanliness is required, and the residual oil content is 3 to 10 m.
The target is g / m ² , and a method called finish cleaning is used. Following the wash treatment, it was rinsed with a large amount of hot water and dried. Further, the contaminated and aged cleaning liquid and the water used for rinsing were detoxified and discharged through a wastewater treatment device.

In the electrolytic cleaning method using sodium silicate, the amount of residual oil can be extremely reduced, but silicon in the cleaning liquid is adsorbed on the surface of the steel sheet, which causes deterioration of plating quality.
There was a situation where the measures are being considered. In addition, there are drawbacks such as large energy consumption during electrolysis, heavy consumption of the electrode, and troublesome handling of the electrode, and a large-scale wastewater treatment device required because a large amount of wastewater is generated.

The method of brushing with an aqueous solution containing an alkaline shaving and alkali has an advantage of less energy loss during cleaning as compared with the electrolytic cleaning method, but has a disadvantage of poor plating quality due to poor cleanliness. there were. In addition, there are drawbacks such as the exhaustion of the brush being severe and the waste water being a very troublesome waste water treatment because it requires treatment of COD and bubbles.

In the bright annealing process for stainless steel and the like,
In addition to silicic acid electrolytic cleaning, degreasing cleaning with Freon 113 or trichlorethane has been adopted, but it has been revealed that these cleaning agents destroy the ozone layer and cause global pollution. . Its use, manufacturing and sales are regulated by the CFC Regulation Act and the Water Pollution Control Act based on the Montreal Protocol, and its manufacture and sale is prohibited by the end of 1995.

[0006]

According to the present invention, a cleaning method applicable to a continuous process in the metalworking industry can achieve a degree of cleanliness that does not hinder processes such as plating and chemical conversion treatment in an extremely short time, No need for wastewater treatment,
It is an object of the present invention to provide a continuous cleaning method that satisfies the conditions that there is no danger of ozone layer depletion and that it is highly safe, and solves the aforementioned problems.

[0007]

In the present invention, NMP (n-methyl-2-pyrrolidone), which is a high boiling point hydrocarbon as a cleaning liquid, and NS Clean (paraffin thread hydrocarbon cleaning agent manufactured by Nikko Petrochemical Co., Ltd.) are used. ), Naphthezol (a cleaning agent containing naphthene-based hydrocarbons manufactured by Nippon Petrochemical Co., Ltd.), etc., or those obtained by adding water to these hydrocarbons, etc. To do.

Using a high boiling point hydrocarbon such as NMP added with water, the hydrocarbon remaining on the surface of the object to be cleaned after cleaning is removed by immersion cleaning by batch operation and vacuum drying, and the aging cleaning liquid is vacuum distilled. The inventors of the present invention have reported a method of recovering and recycling hydrocarbons (Japanese Patent Application No. 43158/1993). However, this method cannot be applied to a continuous cleaning process in which the line speed reaches several hundred m / min because the cleaning time is long and requires several minutes. The present invention is based on this method and is improved so that the cleaning time is several seconds or less so that it can be applied to continuous cleaning.

[0009]

The main factors that control the cleaning speed are the type and condition of dirt, the shape of the object to be cleaned, the type of cleaning liquid and the cleaning conditions. In this case, the shape of the strip-shaped or linear metal body is simple, there are few irregularities on the surface, and the contamination is due to the adhesion of rolling oil (adsorption due to intermolecular attraction), and its thickness is 1
The cleaning rate can be controlled mainly by the type of the cleaning liquid and the cleaning conditions because the amount is less than μm and the amount is relatively small, and the variation in the adhered amount is small.

It is said that the cleaning power of the cleaning liquid generally increases exponentially with an increase in the temperature, and when the cleaning mechanism does not change, the cleaning power is approximately doubled by the temperature increase of 10 ° C. Taking NMP as an example, the boiling point is 204 ° C, so even if it is used in an open state up to about 150 ° C, which is about 50 ° C lower than the boiling point, the vapor pressure is low and evaporation loss can be almost ignored. Also, it has little effect on the work environment.

On the other hand, it is known that the detergency can degrease stains caused by ordinary cutting oil to a cleanliness level of 3 mg / m ² required for the plating step by immersion washing at 60 ° C. for 5 minutes. If the above-mentioned assumption is applied, the cleaning time required to obtain the cleanliness required for the plating pretreatment is less than 1 second at 140 ° C. In particular, in a high temperature range of 100 ° C. or higher, it is difficult to stably use a solution containing water in a liquid state due to evaporation of water, but in the case of a high boiling point hydrocarbon, use it stably. Therefore, it is possible to significantly increase the cleaning ability in combination with the stirring action described later.

Factors that should be taken into consideration in such extremely short-time cleaning are that there is a delay of several tens to several hundreds of seconds from the time when the object to be cleaned is immersed in the cleaning liquid until the predetermined temperature is reached,
Also, the concentration of contaminants in the cleaning liquid near the surface of the body to be cleaned becomes higher than the average concentration in the cleaning liquid, and desorption of contaminants is impeded.

The former heating delay effect can be prevented by heating the strip-shaped or linear metal body to a predetermined temperature before cleaning, and steam or hot air can be used for heating.
The latter effect of diffusion control can be eliminated by imparting a mechanical stirring effect at the time of cleaning, and, for example, a method of bringing the cleaning liquid into contact with the object to be cleaned in the form of a jet flow, a spray flow or the like can be used. Further, in the case of an aqueous solution, a very large stirring effect can be imparted by generating bubbles of oxygen and hydrogen on the surface of the object to be cleaned by electrolysis.

Following the cleaning step, the cleaning liquid remaining on the surface of the object to be cleaned is removed under reduced pressure and dried. In the case of NMP, the degree of vacuum is 40 torr, the temperature is 110 ° C., and the degree of vacuum is 10 t.
Since the boiling point is reached at a temperature of 80 ° C. at orr, it is possible to easily remove in a short time by slightly reducing the pressure by utilizing the residual heat at the time of cleaning. Further, local depressurization by a continuous method can be solved by adopting these methods, since they are usually carried out in a line such as vacuum plating and vacuum deposition in the iron making process.

As a factor controlling the cleanliness, the concentration of the oil component (contaminant) in the final cleaning liquid is also important, and the oil component in the cleaning liquid adhering to the surface of the object to be cleaned is hardly removed in the drying step. Therefore, it is necessary to make the oil content in the final cleaning liquid as low as possible. When the thickness of the adhered liquid film is 20 μm,
It is necessary to keep the oil content in the final cleaning solution at about 200 ppm or less. For this reason, it is desirable to divide the washing tank into multiple tanks and arrange them in series, which makes it easy to keep the oil content in the washing liquid in the final washing tank low.

In FIG. 1, the strip-shaped metal body 1 is preheated in the cleaning liquid storage tank portion 5 of the first cleaning tower 2 and cleaned with the cleaning liquid ejected from the spray nozzle 4. Subsequently, the second cleaning tower 3 is also similarly spray-cleaned, dried through the vacuum drying zone 6 and guided to the next processing step. Clean cleaning liquid is cleaning liquid storage tank 15
To the second washing tower, and then sent to the first washing tower in this order. When the oil content in the first cleaning tower is C ₁ and the oil content in the second cleaning tower is C ₂ , the liquid that moves from the first cleaning tower to the second cleaning tower is limited to that attached to the surface of the strip-shaped metal body. Since it is small in quantity, there is a relationship of C ₁ >> C ₂ even if it is operated for a considerably long time, and the oil content in the second washing tower is reduced until the oil content in the first washing tower becomes 1 to 2%. It is possible to maintain the content at 200 ppm or less. In the case of NMP, the saturated dissolution concentration is about 10% at room temperature, although it varies depending on the type of oil.

(FIG. 1)

When the cleaning liquid in the first cleaning tower is contaminated until its oil content reaches a predetermined value, sludge 9 is separated via a sludge separation tank 8 and then sent to an evaporator 10 of a vacuum distillation apparatus. The cleaning liquid cleaned by vacuum distillation is stored in the cleaning liquid storage tank 15 via the condenser 12 and the receiver 13, and is circulated and used as the cleaning liquid. Since oil and other additives for processing oil are concentrated in the residual liquid of the evaporator, a part of the oil is blown and contaminants such as oil are discarded out of the system. Since the blow liquid 11 can be incinerated, a wastewater treatment device is unnecessary.

In FIG. 2, the strip-shaped metal body 1 is preheated in the preheating zone 2 with steam, hot air or the like, and the electrode 6 is placed in the first cleaning tank 3.
To carry out electrolytic cleaning. Subsequently, in the second cleaning tank and the third cleaning tank, electrolytic cleaning is performed in the same manner, drying is performed through the vacuum drying zone 7, and the next processing step is performed. The electrolysis is performed by an indirect energization method using a cleaning solution containing water. The strip-shaped metal body is alternately charged by the positive electrode and the negative electrode to generate hydrogen and oxygen on the surface, thereby removing the contaminants adhering to the surface by peeling and alternately changing the polarity. It prevents a decrease in electrolysis efficiency due to the formation of a polarized film on the surface. The clean cleaning liquid is supplied from the cleaning liquid storage tank 16 to the third cleaning tank, and then sent to the second cleaning tank and the first cleaning tank in this order.

When the oil content in the first cleaning tank is C ₁ , the oil content in the second cleaning tank is C ₂ , and the oil content in the third cleaning tank is C ₃ , the first cleaning tank to the second cleaning tank The amount of oil that moves from the 2nd cleaning tank to the 3rd cleaning tank is small because it is limited to that attached to the surface of the strip-shaped metal body, and C ₁
As described above, the relationship of >> C ₂ >> C ₃ and the oil content in the final cleaning liquid can be suppressed to a low value. Furthermore, dividing the cleaning tank into a plurality of parts and lining them is effective for improving the electrolytic efficiency together with the above-mentioned electrode arrangement, because the generation of stray current is suppressed.

If the cleaning liquid in the first cleaning tank is contaminated until its oil content reaches a predetermined value, the sludge 10 is separated via the sludge separation tank 9 and then sent to the evaporator 11 of the vacuum distillation apparatus. The cleaning liquid cleaned by vacuum distillation is cooled by the condenser 13, stored in the cleaning liquid storage tank 16 via the receiver 14, and is circulated and used as the cleaning liquid. Since oil etc. is concentrated in the residual liquid of the evaporator, a part of it is blown and the contaminants are discarded to the outside of the system. Since the blow liquid 12 can be incinerated, a wastewater treatment device is not required, which is very effective in reducing the device construction cost and operating cost.

(FIG. 2)

[0023]

Example 1 Table 1 shows the results of high temperature cleaning tests carried out on a bench scale. A 10% aqueous solution of a water-soluble rolling oil (A3K-100) made by Daido Oil Co., Ltd. was applied to a test piece by dipping and dried, and used as a sample, and an NMP solution was sprayed and washed with an airless nozzle. Prior to the washing operation, hot water of 90 ° C. was sprayed and preheated. In addition,
The spray nozzle was placed 15 cm away from the sample, and spraying was performed at a spray pressure of 1 kgf / cm ² G and a spray liquid amount of 1 l / min · dm ² . After washing, place in a vacuum dryer at a temperature of 80
It was dried under reduced pressure at 10 ° C. until it became 10 torr. The residual oil was extracted with carbon tetrachloride and then measured with an infrared spectrophotometer.

[0024]

[Table 1]

From Table 1, it was observed that the cleanliness became 1 mg / m ² or less by the spray cleaning at a temperature of 140 ° C. for 1 second, and it could be used as a pretreatment for plating, and it can be applied to the continuous cleaning process. It is shown.

[0026]

Example 2 Table 2 shows the results of electrolytic cleaning tests on a bench scale. The method for preparing the sample is the same as in the case of Example 1, in which the sample is immersed in a 70% aqueous solution of NMP, and the sample is used as an anode in a direct electrolysis system to produce an electrolytic current density of 20 mA / cm ^2.
Electrolytically cleaned. Sodium sulfate was added to the electrolyte to increase the electrical conductivity, and the anode part had a peripheral speed of 15 m /
It was rotated in minutes, which also added a mechanical stirring effect. Table 2
From this, it is observed that at the temperature of 90 ° C., the target cleaning value is reached by electrolytic cleaning for 0.1 second.

[0027]

[Table 2]

[0028]

According to the present invention, a cleaning method using a high boiling point hydrocarbon such as NMP or the one obtained by adding water to the cleaning solution is used to preheat the strip-shaped or linear metal body by using the cleaning solution at a high temperature. By combining the mechanical stirring action or the electrolytic action, and dividing the washing tank into series, the washing time can be shortened and the cleanliness can be improved. It has the following advantages and is extremely useful in industry. 1. The cleaning ability is comparable to that of the conventional alkaline electrolytic treatment, and it is possible to prevent the deterioration of the plating quality due to the adsorption of silicon, which has been a difficulty in the conventional method. 2. The cleaning liquid can be regenerated by vacuum distillation and reused, and wastewater treatment is not required, so the operating cost can be greatly reduced. 3. The toxicity of the cleaning solution is low, and the impact on the working environment is low. 4. The flash point is high and there is little danger of fire. 5. There is no danger of ozone layer depletion.

[Brief description of drawings]

FIG. 1 is a flow sheet of a spray-type continuous cleaning apparatus showing an outline of the flow of a continuous cleaning method according to the present invention by a spray method.

[Explanation of symbols]

1 strip-shaped metal body 2 1st washing tower 3 2nd washing tower 4 spray nozzle 5 washing liquid storage tank 6 vacuum drying zone 7 vacuum pump 8 sludge separation tank 9 sludge 10 evaporation can 11 blow liquid 12 condenser 13 receiver 14 vacuum pump 15 regenerated cleaning liquid Storage tank 16 Replenisher

FIG. 2 is a flow sheet of a continuous cleaning apparatus of an electrolytic system, showing a flow outline of a continuous cleaning method of the present invention which is of an electrolytic system.

[Explanation of symbols]

1 strip metal body 2 residual heat zone 3 1st washing tank 4 2nd washing tank 5 3rd washing tank 6 electrode 7 vacuum drying zone 8 vacuum pump 9 sludge separation tank 10 sludge 11 evaporating can 12 blow liquid 13 condenser 14 receiver 15 vacuum Pump 16 Regeneration cleaning liquid storage tank 17 Replenishing liquid

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location C25D 5/34 // C23C 22/78 (72) Inventor Takeo Fukushima 2-5 Marunouchi, Chiyoda-ku, Tokyo No. 1 Mitsubishi Heavy Industries Co. Ltd. (72) Inventor Shigeo Itano 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries Ltd. (72) Inventor Nobuhiro Shibatomi 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries Stock Company

Claims (2)

[Claims] 1. A continuous cleaning method in a metal working process, comprising: 1. A step of washing using a high-boiling point hydrocarbon as a washing liquid, and removing the high-boiling point hydrocarbon and the like remaining on the surface of the object to be washed by vacuum drying after washing. A continuous cleaning method using high-boiling hydrocarbons, which comprises a step of recovering the high-boiling hydrocarbons by vacuum distillation of the used cleaning liquid, and recycling the high-boiling hydrocarbons. 2. A continuous cleaning method in a metal working process, comprising: Using high boiling hydrocarbons with water added as a cleaning liquid, electrolytic cleaning is performed using multiple tanks by the indirect energization method, and after cleaning, the high boiling hydrocarbons remaining on the surface of the object to be cleaned are dried by vacuum drying. Step of removing 2. A continuous cleaning method using high-boiling hydrocarbons, which comprises a step of recovering the high-boiling hydrocarbons by vacuum distillation of the used cleaning liquid, and recycling the high-boiling hydrocarbons.