MX2008009372A - Method and apparatus for cleaning hot-dip galvanized steel sheet - Google Patents

Abstract

Disclosed is a method for cleaning a hot-dip galvanized steel sheet wherein a strip-shaped hot-dip galvanized steel sheet having been subjected to a surface oxidation treatment is brought into contact with a cleaning liquid for one or more seconds and then brought into contact with purified water, while being continuously conveyed. By this method, an acidic solution adhered to the surface of the hot-dip galvanized steel sheet after the surface oxidation treatment can be efficiently and sufficiently washed out. Also disclosed is an apparatus for cleaning a hot-dip galvanized steel sheet, which is used for carrying out such a method.

Description

METHOD FOR CLEANING GALVANIZED STEEL SHEET BY HOT IMMERSION AND CLEANING EQUIPMENT THEREOF TECHNICAL FIELD The present invention relates to a method and an apparatus for cleaning a steel sheet that was prepared by hot dip galvanization on a strip-shaped steel sheet, and applying alloy and tempering by rolling, further applying oxidation to the surface using the acid solution, (hereinafter referred to as "hot dipped galvanized steel sheet").

BACKGROUND OF THE INVENTION After applying hot-dip galvanization to a strip-shaped steel sheet, the steel sheet was treated by deoxidating treatment by surface deoxidation, followed by rolling in a rolling mill to a specific thickness and annealing in an annealing furnace, and is additionally transferred to a bath of molten zinc. Figure 3 illustrates the process of the hot dip galvanization line common in and after the bath of molten zinc. The steel plate moves in the direction of arrow "a". To apply galvanization by immersion in When heated to a sheet of steel, the steel sheet is submerged in a bath of molten zinc 2, as illustrated in FIG. 3. The zinc in the molten state is maintained in the bath of molten zinc 2, (hereinafter referred to as "the zinc bath"). During the displacement of the steel sheet in the zinc bath, the zinc adheres to both surfaces of the steel sheet. Then, the steel sheet is sent from the molten zinc bath 2 to an alloy furnace 3, where the steel sheet is subjected to alloy treatment. The alloy treatment is a heat treatment to allow the alloy reaction between the steel base material of the steel sheet and the zinc adhered to the steel sheet, thereby forming a zinc coating layer having excellent adhesion The steel sheet, after leaving the alloy furnace 3, is cooled before an interim linker 4 while the tension is adjusted thereon, and is further sent to a tempering rolling mill 5 to be tempered by rolling (which it is known as "movie step"). Lamination tempering is a lamination to apply a slight reduction of from about 0.6 to about 3% of the thickness to deform only in the vicinity of the surface of the steel sheet, thereby adjusting the Surface properties (such as surface roughness) of the steel sheet. The reduction in thickness is defined by the value derived from the equation (1): Reduction in thickness (%) = 100 x (ti - t2) / ti (1) where, ti is the thickness before tempering by rolling (mm), and t2 is the thickness after tempering by rolling ( mm). Then, the steel sheet is fed from the tempering rolling mill 5 to an oxidation apparatus of the surface 6 to receive an oxidation treatment of the surface. The oxidation treatment of the surface is provided by bringing both surfaces of the steel sheet into contact with an acid solution, to thereby form an oxide film on the surface of the coating layer. The steel sheet that was treated by the oxidation of the surface is hereinafter referred to as "the galvanized steel sheet by hot dip Ib". In this way covering the coating layer with the oxide film, the sliding property of the hot dip galvanized steel sheet Ib in work (for example in press forming) in products having varieties of shapes, improves. Market Stall that, however, the hot dip galvanized steel sheet Ib which is processed from the surface oxidation apparatus 6 has an acid solution adhered thereto, both surfaces of the hot-dip galvanized steel sheet Ib are cleaned in a rinse tank 7 washing the acid solution, and the hot-dip galvanized steel sheet Ib is further dried in a dryer 8. The hot-dip galvanized steel sheet Ib enters the outlet locker 9, where the tension on it is adjusted, and enters a oiler 10, where oxidation prevention is applied on the surfaces of the same, followed by cooling of the galvanized steel sheet by hot immersion Ib by a cooler 11. Then the conventional hot dip galvanization line described above, the Figure 4 shows a partially amplified view from the oxidation apparatus of the surface 6 to the rinsing tank 7. The hot dip galvanized steel sheet moves in the direction of the arrow "a". The surface oxidation apparatus 6 places the electroplating surface by hot immersion on the steel sheet in contact with the acid solution. As shown in Figure 4, for example, the Acid solution spray nozzles 12 for spraying the acid solution 13 are arranged there. The hot dip galvanized steel sheet Ib onto which the acid solution was sprayed into the surface oxidation apparatus 6 is sent to the rinse tank 7. To ensure a period of time necessary to form the oxide film on the surface of the coating layer to a sufficient thickness, the distance between the surface oxidation apparatus 6 and the rinse tank 7 is determined at a specific length. For example, by controlling the period of time of displacement between the surface oxidation apparatus 6 and the rinse tank 7, the thickness of the oxide film can reach up to 10 nm (nanometers) or more. Japanese Patent Laid-open Nos. 2002-256448 and 2003-306781 disclose that covering the coating layer with an oxide film having a thickness of 10 nm or more improves the sliding properties of the galvanized steel sheet by immersion in hot Ib, thereby preventing damage and detachment of the coating layer at work (forming in press and the like) in products having varieties of shapes. The rinse tank 7 arranges the nozzles in it to spray a cleaning water 14. Spraying the water of cleaning 14 to the galvanized steel sheet by hot immersion Ib, in the acid solution adhered to the galvanized steel sheet by hot immersion Ib is removed. With the single cleaning water spray 14 it is, however, difficult to completely wash the acid solution adhered to the hot dipped galvanized steel sheet Ib. Although research on the problem even gives the addition of chemical compounds to the cleaning water 14, the place to improve problems in terms of composition and quantity of chemical compounds added. The remaining acid solution on the surface of the hot-dip galvanized steel sheet Ib leads to corrosion of the coating layer by acid, which results not only in the deterioration of the appearance but also damage and detachment of the layer of coating, thus decreasing the performance of the product.

THE INVENTION An object of the present invention is to solve the above problems and provide a cleaning method and a cleaning apparatus to efficiently and completely wash the acid solution adhered to the surface of a hot dipped galvanized steel sheet that was treated by oxidation of the surface.

DESCRIPTION OF THE INVENTION The present invention provides a method for cleaning a galvanized steel sheet by hot dip by the steps of contacting a strip of galvanized steel by hot dip in the form of a strip, treated by oxidation of the surface in advance. , with a cleaning liquid for 1 second or more, and then put the galvanized steel sheet by hot dip in contact with pure water, while continuously transferring the galvanized steel sheet by hot dip. According to the cleaning method of the present invention, contact with the cleaning liquid and contact with pure water are preferably conducted in a single cleaning tank. In addition, it is preferable that a diluted cleaning liquid prepared by mixing the cleaning liquid with pure water in a single cleaning tank is stored in a tank with circulation, and that the hot-dip galvanized steel sheet is also put in contact with the diluted cleaning liquid in the circulation tank, while using the diluted cleaning liquid recirculating it. Furthermore, it is more preferable that the contact of the diluted cleaning liquid is provided in a position after a position of the beginning of the contact with the cleaning liquid and in a position before a position of the beginning of contact with pure water. For any of the previous cleaning methods, the cleaning liquid preferably contains P, and specifically the concentration of P in the cleaning liquid is preferably in the range of from 4 to 70 ppm by mass. The present invention provides an apparatus for cleaning a hot dip galvanized steel sheet, which has: cleaning liquid spray nozzles which spray a cleaning liquid to both surfaces of a hot dip galvanized steel sheet in strip form which was treated by oxidation of the surface and which is continuously displaced; and pure water spray nozzles which spray pure water to both surfaces of the hot dipped galvanized steel sheet in a position where the hot dipped galvanized steel sheet is moved 1 second or more after being sprayed with the cleaning fluid. The apparatus of the present invention preferably has an inverter roller to reverse the direction of travel of the galvanized steel sheet by hot dip, to a position between the spray position of the liquid spray nozzles of cleaning and the spray position of the pure water spray nozzles. Both of the above apparatuses preferably arrange both the cleaning fluid spray nozzles and the pure water spray nozzles in a single cleaning tank. Any of the above apparatuses preferably also has a circulation tank which stores a diluted cleaning liquid prepared by mixing the cleaning liquid with the pure water in the single cleaning tank, and diluted cleaning liquid spray nozzles, which spray The cleaning liquid diluted in the circulation tank to both surfaces of the galvanized steel sheet by hot dip. For these devices, it is preferable that the diluted cleaning fluid spray nozzles are located between a spray position of the cleaning liquid spray nozzles and the spray position of the pure water spray nozzles. The present invention provides a method for cleaning a galvanized steel sheet by hot dipping in the form of a strip while continuously transferring a galvanized steel sheet by hot dipping in the form of a strip which was treated by oxidation of the surface, which has the steps: put the galvanized steel sheet by hot dip in contact with the cleaning liquid for 1 second or more; and then put the galvanized steel sheet by hot dip in contact with pure water.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a cross-sectional view of an example of a cleaning apparatus according to the present invention. Figure 2 illustrates a cross-sectional view of another example of the cleaning apparatus according to the present invention. Figure 3 illustrates an arrangement of an example of the hot dip galvanization apparatus. Figure 4 illustrates a part of the conventional process going from the oxidation apparatus of the surface 6 to the cleaning tank 7.

BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 illustrates a cross-sectional view of an example of the cleaning apparatus according to the present invention. According to the present invention, it is possible that the tank where the cleaning liquid is sprayed and the tank where the water is sprayed that are installed separately to conduct the cleaning of a galvanized steel sheet by hot dip. The embodiment described here adopts an example of illustration in Figure 1, where the spray of cleaning fluid and the spray of pure water occur in a single tank, (hereinafter referred to as "the cleaning tank"). The hot-dip galvanized steel sheet once moves in the direction of arrow "a". Hot-dip galvanized steel sheet Ib prepared by hot-dip galvanizing on the strip-shaped steel sheet, applying alloy treatment and tempering by rolling, followed by oxidation of the surface using an acid solution is sent to a cleaning tank 15. The cleaning tank 15 has cleaning liquid spray nozzles 16 and pure water spray nozzles 17. The pure water nozzles 17 are located in a position where the hot-dip galvanized steel sheet moves 1 second or more after being sprayed with the cleaning liquid. The spray nozzles of the cleaning liquid 16 sprayed a cleaning liquid 18 having a cleaning function to both surfaces of the hot-dip galvanized steel sheet Ib, and the pure water spray nozzles 17 sprayed the pure water to both surfaces of the galvanized steel sheet by hot dip Ib. The pure water in the present immersion is distilled water, ion exchanged water, industrial cleaning water, and the like, which are free of P. The cleaning tank 15 preferably has an inversion roller 20 which reverses the direction of hot-dip galvanized steel sheet displacement Ib. The reversing roller 20 reverses the direction of travel of the galvanized steel sheet by hot dip Ib (in the bottom-up direction in the cleaning tank 15), after the cleaning liquid 18 is sprayed onto the hot dipped galvanized steel sheet Ib which travels up and down the cleaning tank 15, thereby allowing the cleaning liquid 18 in the lowermost position , (hereinafter referred to as "the lower end of the investment"), for immersing the galvanized steel sheet by hot dip Ib. Consequently, the hot-dip galvanized steel sheet Ib maintains contact with the cleaning liquid 18 during a period of displacement of the cleaning liquid mist 18 until it is immersed. According to the present invention, it is preferred that the central axes of the liquid spray nozzles 16 opposite cleaning (hereinafter referred to as "the cleaning fluid spray position") are aligned, and the reversing roller 20 is located in a position that ensures 1 second or more displacement time of the galvanized steel sheet by hot dip Ib from the spray liquid spray position to the lower end of the investment, thus ensuring 1 second or longer contact time of the hot-dip galvanized steel sheet Ib with the cleaning fluid 18. If the contact time is 1 second or more, the cleaning effect of the cleaning liquid 18 is completely achieved. It is preferred that the period of time for the hot dip galvanized steel sheet Ib to move from the spray position of the cleaning liquid to the lower reversing end (or the contact time with the cleaning liquid 18), 10 seconds or less. If the above time becomes excessively large, a large cleaning tank 15 is required, and the cleaning liquid 18 dries on the surface of the hot dipped galvanized steel sheet Ib to deposit the ingredients of the cleaning liquid, which deteriorates the appearance of the hot dip galvanized steel sheet Ib. Limiting the contact time of the sheet hot-dip galvanized steel Ib with cleaning liquid 18 to 1 second or more, preferably 1.5 to 8 seconds, the concentration of cleaning liquid 18 can decrease and the acid solution adhered to the galvanized steel sheet by immersion in Hot Ib can be washed. The type of cleaning fluid 18 is not specifically limited if it only has the cleaning function. However, it is preferred that the cleaning liquid 18 contains an alkaline ingredient to neutralize and wash acid solution adhered to the hot-dip galvanized steel sheet Ib, and specifically the preferred cleaning liquid 18 is that which contains P. For the cleaning liquid 18 containing P, a preferable concentration of P in the cleaning liquid 18 is from 4 to 70 ppm by mass. If the concentration of P is 4 ppm by mass or more, the acid solution adhered to the hot dip galvanized steel sheet Ib can be completely washed. The concentration of P of 70 ppm by mass or less considerably reduces the remaining amount of the ingredients of the cleaning liquid even after the pure water mist described above, and the appearance of the hot-dip galvanized steel sheet Ib is not deteriorates. After the steel sheet galvanized by hot dip Ib is brought into contact with the cleaning liquid 18, and the cleaning liquid 18 thereof drips in the lower end of the investment, the hot dip galvanized steel sheet Ib is brought into contact with the water pure 19 to remove the remaining cleaning liquid 18. According to the present invention, although the central axes of the opposed pure water spray nozzles 17 (hereinafter later referred to as "the pure water spray position"), are aligned , the displacement time period of the hot-dip galvanized steel sheet Ib from the lower end of the investment to the pure water spray position is not specifically limited. However, it is preferable that the pure water spray position is determined considering that the pure water 18 is sprayed before the cleaning liquid 18 remaining on the hot-dip galvanized steel sheet Ib is dried. The cleaning liquid 18 and the pure water 19, sprayed onto the hot dipped galvanized steel sheet Ib in the cleaning tank 15 drip on the bottom of the cleaning tank 15, which are then discharged successively to introduce an installed tank separately (hereinafter referred to as "the circulation tank"). That is, the liquid of cleaning 18 and pure water 19 are not kept in the cleaning tank 15 but are kept in the circulation tank as a mixture of cleaning liquid 18 diluted by pure water 19, (hereinafter referred to as "dilute cleaning liquid" ). If the diluted cleaning liquid is subjected to wastewater treatment to remove toxic substances before discharge, the environment is not contaminated. In addition, the inventors of the present invention derived a discovery that, after washing the acid solution adhered to the galvanized steel sheet by hot dip Ib, the reuse of the diluted cleaning solution improves the cleaning effect. An example of the cleaning apparatus is illustrated in Figure 2. The hot dipped galvanized steel sheet moves in the direction of arrow "a". As illustrated in Figure 2, as an example, the diluted cleaning liquid 22 maintained in the circulation tank 21 is recirculated by a pump 24 or the like, and is further sprayed onto both surfaces of the galvanized steel sheet by immersion in hot Ib in an interim position between the contact starting position with the cleaning liquid and the contact starting position with the pure water, thereby increasing the cleaning effect. That is, what to add to cleaning liquid ingredients existing in the cleaning liquid 18, the ingredients of the low concentration cleaning liquid that exist in the diluted cleaning liquid 22 is used to wash the acid solution adhered to the galvanized steel sheet by hot dip Ib . In the cleaning step, the diluted cleaning liquid spray nozzles 23 spraying the diluted cleaning liquid 22 are arranged to align their central axes in their opposite positions, hereinafter referred to as "the spray position of the diluted cleaning liquid. "). The spray position of the diluted cleaning liquid is preferably located between the position for spraying the cleaning liquid and the position for spraying the pure water, and the specifically preferable position is between the lower end of the inversion and the pure water spray position. , because the dilution of the diluted cleaning liquid 22 after the inversion of the cleaning liquid 18 effectively effects the cleaning effect of the cleaning liquid ingredients.

EXAMPLES The hot-dip galvanized steel sheet Ib was prepared by installing the cleaning tank 15 shown in Figure 1 instead of the rinsing tank. 7 in the hot dip galvanization line shown in Figure 3. The reversing roller 20 in the cleaning tank 15 was located so that the hot-dip galvanized steel sheet Ib took 2.5 seconds of displacement the spray position of the cleaning fluid to the lower end of the investment. The cleaning liquid 18 contained P at a P concentration of 14 ppm by mass, an injection pressure of 0.15 MPa, and a flow rate of 5m3 / hr. The pure water 19 was industrial cleaning water which was sprayed in a position so that the hot-dip galvanized steel sheet Ib took 2.5 seconds to move to a lower end of the investment to the pure water spray position. an injection pressure of 0.15 MPa and a flow rate of 10 m3 / hr. The example was named Example 1 of the Invention. The hot dip galvanized steel sheet Ib was prepared by installing the cleaning tank 15 shown in Figure 2 in place of the rinse tank 7 in the hot dip galvanization line shown in Figure 3. The roll positions of inversion 20, the spray nozzles of the cleaning liquid 16, and the pure water spray nozzles 17 in the cleaning tank 15, and the conditions for spraying the cleaning liquid and the pure water, were the same as those in Example 1, so that their descriptions are not given. Diluted cleaning liquid 22 was sprayed so that the hot-dip galvanized steel sheet Ib would take 2.1 seconds to move from the lower end of the investment to the spray position of the diluted cleaning liquid at an injection pressure of 0.20 Mpa and a flow velocity of 20 m3 / hr. The example was named Example 2 of the Invention. Conventionally, the hot-dip galvanized steel sheet Ib was made using the rinse tank 7 in the hot-dip galvanizing line given in Figure 3. The rinse tank 7 used industrial cleaning water as the cleaning water. 14 at the injection pressure 0.10 MPa and a flow rate of 10 m / hr. The example was named the conventional Example. For each of Examples 1 and 2 of the Invention and the Conventional Example, the cleaning status of the hot dip galvanized steel sheet Ib was determined. The calculated water moistening percentage of equation (2) was adopted as an index of cleanliness status. A higher value of the percentage of water moistening (%) indicates a better cleaning result.

Percentage of water wetting (%) = [Wetting surface area with water (mm2)] / (Sample surface area (mm2)] (2) The percentage of water moistening is defined by the following. oxidation (Nox-Rust 550KH, manufactured by Nihon Parkerizing Co., Ltd.) on a sample, after cleaning, at a rate of 1900 mg / m2. The sample was then immersed in a degreasing liquid (FC-E2011, manufactured by Nihon Parkerizing Co., Ltd.) for 2 minutes. In addition, the sample was cleaned by pure water. Then the percentage of the area of the moistened portion with water was determined by visual observation, percentage of area which was adopted as the percentage of water moistening. The observation gave a water moistening percentage of 80% for Example 1 of the Invention, 85% for Example 2 of the invention, still remaining 70% for the Conventional example.

INDUSTRIAL APPLICABILITY The present invention allows the efficient and complete washing of the acid solution adhered to the surface of the galvanized steel sheet by hot immersion after treatment by oxidation of the surface, in this way the present invention contributes to the industry.

Claims (12)

1. CLAIMS 1. Method for cleaning a hot dipped galvanized steel sheet comprising the steps of contacting a strip of galvanized steel by hot dipping in the form of a strip, treated by oxidation of the surface in advance, with a liquid of cleaning for 1 second or more, and then contacting the galvanized steel sheet by hot dip with pure water, while continuously transferring the galvanized steel sheet by hot dip. Method for cleaning a hot dip galvanized steel sheet according to claim 1, wherein contact with the cleaning liquid and contact with pure water are conducted in a single cleaning tank. Method for cleaning a hot-dip galvanized steel sheet according to claim 2, wherein the diluted cleaning liquid prepared by mixing the cleaning liquid with pure water in a single cleaning tank is stored in a circulation tank, and the Hot-dip galvanized steel sheet also comes in contact with the diluted cleaning liquid in a circulation tank, while using diluted cleaning liquid by recirculating it. 4. Method for cleaning a hot dipped galvanized steel sheet according to claim 3, wherein the contact of the diluted cleaning liquid is given in a position after the contacting position with the cleaning liquid and in a position before a contact start position with pure water. Method for cleaning a hot dip galvanized steel sheet in any of claims 1 to 4, wherein the cleaning liquid contains P. 6. Method for cleaning a hot-dip galvanized steel sheet according to claim 5, where the concentration of P in the cleaning liquid is in the range of 4 to 70 ppm by mass. 7. Apparatus for cleaning a hot dipped galvanized steel sheet comprising: a spray nozzle of the cleaning liquid which sprays a cleaning liquid to both surfaces of a strip of hot dipped galvanized steel strip; which was treated by oxidation of the surface and which is continuously displaced; and a water spray nozzle by which it sprays pure water to both surfaces of the galvanized steel sheet by hot dip in a position where the galvanized steel sheet Hot dip moves 1 second or more after being sprayed with the cleaning liquid. 8. Apparatus for cleaning a hot dipped galvanized steel sheet according to claim 7, further comprising an inversion roller for reversing a direction of travel of the galvanized steel sheet by hot dip, in a position between the spray position of the spray nozzle of the cleaning fluid and the spray position of the spray nozzle of pure water. 9. Apparatus for cleaning a hot dip galvanized steel sheet according to claim 7, wherein both of the cleaning fluid spray nozzles and the pure water spray nozzles are arranged in a single cleaning tank. Apparatus for cleaning a hot dipped galvanized steel sheet according to claim 9, further comprising: a circulation tank which stores a diluted cleaning liquid prepared by mixing the cleaning liquid with the pure water in the single tank of cleaning; and a spray nozzle of the diluted cleaning liquid which sprays the diluted cleaning liquid in a circulation tank to both surfaces of the hot dipped galvanized steel sheet. 11. Apparatus for cleaning a hot dipped galvanized steel sheet according to claim 10, wherein the spray nozzle of the diluted cleaning liquid is located between the spray position of the spray liquid spray nozzle and the spray position of the spray liquid. Pure water spray nozzle. 12. Method for cleaning a galvanized steel sheet by hot dipping in the form of a strip while continuously transferring a sheet of galvanized steel by hot dipping in the form of a strip as it was treated by oxidation of the surface, comprising the steps of: contacting the galvanized steel sheet by hot dip with a cleaning liquid for 1 second or more; Then contact the galvanized steel sheet by hot dip with pure water.