Patent Application
20190119824
The present invention relates to a technique for preventing foreign materials from adhering to a roll surface of an electroplating conductor roll.
In the electroplating line of cold-rolled steel sheets, the plating treatment is performed through a series of processes including an alkali cleaning process, a pickling process, a plating process, a cleaning process, and a chemical treatment process while conveying the cold-rolled steel sheet.
In the plating process, a plurality of conductor rolls is installed. Here, the conductor roll is to energize the cold-rolled steel sheet conveyed in a plating bath. Metal, which is a component of the plating liquid, or its oxide easily adheres to the conductor roll as a foreign material. This is because the plating liquid adhering to the conductor roll is electrodeposited by electroplating, and the plating liquid is dried and solidified on the surface of the conductor roll. As another cause, it is conceivable that the plated metal of the steel sheet or the oxide of the plated metal adheres and is fixed to the conductor roll due to the contact and friction between the plated steel sheet and the conductor roll.
An asperity portion is formed on the roll surface of the conductor roll in order to obtain a frictional force necessary for conveying the cold-rolled steel sheet. Therefore, the asperity portion of the roll surface may be worn by the foreign materials that adheres at the time of conveyance of the cold-rolled steel sheet, whereby the cold-rolled steel sheet may slip.
When the cold-rolled steel sheet slips, the cold-rolled steel sheet bends due to an impact at the time of slipping, and a gap is formed between the cold-rolled steel sheet and the conductor roll. When a gap is formed between the cold-rolled steel sheet and the conductor roll, the contact area of the cold-rolled steel sheet and the conductor roll is reduced. Therefore, abnormal discharge may occur, and the life of the conductor roll may be shortened.
Patent Literature 1 discloses a doctoring device for a conductor roll which is used to scrape off foreign materials that adheres to a roll surface, by pressing a cutting edge, which is formed on a front edge of a doctoring blade, against a roll surface of a rotating conductor roll. Patent Literature 2 discloses a method of removing attached metal by reverse electrolysis or the like. Patent Literature 3 discloses a method of preventing energization to a conductor roll by a shield plate or the like.
Patent Literature 4 discloses a method of forming a composite coating film having corrosion resistance and withstanding long-term use, which is characterized by forming a glassy surface layer film, although the technique belongs to a technical field different from that of a conductor roll. The glassy surface film is formed by the following method: A single metal, alloy, cermet or ceramic is sprayed onto a substrate surface having been pre-processed for thermal spraying. After that, a pore-sealing liquid having a good permeability for forming a pore-sealing substance in pores in the thermal spray coating film is applied or impregnated, and then aged or heat-treated to perform a sealing treatment. After that, a solution in which a glassy material forming component is dissolved or suspended is applied by brushing or spraying. The resulting article is dried at room temperature or baked at a temperature of 900° C. or lower to form the glassy surface layer film. Further, as a pore-sealing agent, there has been disclosed those containing an inorganic colloidal liquid containing SiO2 and the like, and a phosphate-based inorganic binder.
Patent Literature 5 discloses a surface hardening treatment method, which is characterized by performing a pore-sealing treatment, although it belongs to a technical field different from that of a conductor roll. The pore-sealing treatment is performed by forming a porous coating film on a sliding portion of a nuclear power equipment or the like by a thermal spraying method, applying a graphite-containing liquid to the porous coating film, and baking the porous coating film.
Patent Literature 1: JP2013-151716
Patent Literature 2: JPH1-162798
Patent Literature 3: JPS63-50495
Patent Literature 4: JP2001-152307
Patent Literature 5: JPH2-298587
However, in the configuration of Patent Literature 1, a doctoring device for scraping off foreign materials is required. This configuration thus complicates the plating line and increases the costs. Further, the doctoring device is exposed to a large amount of plating liquid vapor or the like. Therefore, there is a problem that the maintenance is difficult and the replacement frequency of parts is high as compared with a doctoring device used for a roll for iron making, a roll for a paper machine, or the like. In addition, the thermal spray layer may be damaged and have to be re-sprayed when the cutting edge impinges on the surface of the conductor roll (e.g., the thermal spray layer).
Further, in Patent Literatures 2 and 3, during removal of the attached foreign materials, the use of the conductor roll must be temporarily interrupted. Therefore, the productivity of the plated steel sheets is lowered.
In Patent Literature 4, it is described that a thermal spray coating film is subjected to a pore-sealing treatment and the surface layer thereof is coated with a glassy film to close through pores and obtain excellent corrosion resistance against molten metal, acid, alkali, or corrosive gas. However, the above-mentioned problem of the conductor roll (i.e., the adhesion of foreign materials) is not considered. In addition, the specification in paragraph 0001 describes “a method of manufacturing a coating film that has a high voltage resistance and is unlikely to generate a corona discharge”. As can be seen from this description, the technique of Patent Literature 4 also aims to insulate the coating film, and does not target conductor rolls having conductivity in the first place.
Further, Patent Literature 5 describes that wear resistance can be enhanced, and the friction coefficient can be lowered and seizing can be prevented by applying a graphite-containing liquid as a lubricant to a porous coating film, and baking it to perform a pore-sealing treatment. However, the above-mentioned problem of the conductor roll (i.e., the adhesion of foreign materials) is not considered.
In order to solve the above-described problems, the inventors of the present application has found that a conductor roll is subjected to a surface treatment using a mixed aqueous solution containing 3 to 14 mass % of aluminum phosphate, 7 to 37 mass % of silica, and 4 mass % or more of graphite, so that a conductive property and an effect of preventing adhesion of foreign materials can be imparted to the outermost layer of the conductor roll. The present invention has thus been completed.
According to the present invention, foreign materials derived from the plating liquid, metal derived from the plated steel sheet, and oxide of the metal can be prevented from adhering to the surface of the conductor roll.
A conductor roll 14 is disposed between adjacent plating tanks 11. The conveying direction of the metal strip S is changed from the upward direction to the downward direction by the conductor roll 14. Here, the plating liquid M adheres to the metal strip S discharged from the plating tank 11. Therefore, when the metal strip S reaches the conductor roll 14, the plating liquid M adheres to the roll surface of the conductor roll 14.
An anode of a not-illustrated DC power source is connected to the electrode plate 13, and a cathode thereof is connected to the conductor roll 14, and a voltage is applied to these electrode plates to energize between the electrode plate 13 and the strip S. As a result, the surface of the strip S conveyed in the plating tank 11 can be continuously subjected to a plating treatment. However, the present invention can also be applied to a horizontal continuous electroplating cell in which the conductor roll 14 is constantly immersed in the plating liquid M.
A surface treatment layer 14c (which corresponds to a foreign material adhesion prevention layer) is formed on the surface of the thermal spray coating film 14b. The surface treatment layer 14c is formed by applying a predetermined surface treatment liquid to the thermal spray coating film 14b and baking the same. The application method may be brushing or spray coating. The baking treatment can be performed in an electric furnace. The baking temperature is preferably 150° C. or lower. The surface treatment liquid is obtained by dispersing graphite particles in a mixed solution of an aluminum phosphate aqueous solution and colloidal silica. However, the surface treatment layer 14c may be formed directly on a base material of the conductor roll 14. That is, the surface treatment layer 14c of the present invention can also be applied to the conductor roll 14 without the thermal spray coating film 14b.
(Aluminum Phosphate Aqueous Solution)
When the entire amount of the surface treatment liquid is 100 mass %, the concentration of aluminum phosphate is 3 mass % or more and 14 mass % or less, and preferably 6 mass % or more and 11 mass % or less. If the content of aluminum phosphate is less than 3 mass %, colloidal silica cannot be sufficiently gelled. As a result, dripping may occur on the surface of the conductor roll and the distribution of graphite may become uneven. If the content of aluminum phosphate exceeds 14 mass %, colloidal silica gels before being applied to the thermal spray coating film 14b (i.e., gels at an early stage) and cannot be applied.
As aluminum phosphate, one kind or two or more kinds of aluminum dihydrogen phosphate (Al(H2PO4)3), aluminum hydrogen phosphate (Al2(HPO4)3), and monomethyl aluminum phosphate (Al[(O)P(O)OH(OCH3)]3) and an aluminum phosphate ester may be used.
However, when the amount of aluminum phosphate is 100 mass %, it is preferable to contain at least 70 mass % or more of aluminum dihydrogen phosphate (Al(H2PO4)3) or at least 70 mass % or more of monomethyl aluminum phosphate (Al[(O)P(O)OH(OCH3)]3).
The present inventor also conducted an experiment of surface treatment of the thermal spray coating film 14b using a surface treatment liquid in which graphite is dispersed in a mixed solution of an aqueous solution containing a phosphate compound (for example, sodium metaphosphate (NaPO3)) other than aluminum phosphate and colloidal silica. However, a high effect of preventing adhesion of foreign materials could not be obtained. Although the mechanism is not clear, a high effect of preventing adhesion of foreign materials was not obtained unless the surface treatment liquid prepared by dispersing graphite in a mixed solution of an aluminum phosphate aqueous solution and colloidal silica was used. This issue will be clarified in examples described later.
(Colloidal Silica)
The colloidal silica is obtained by dispersing fine particles of silica (SiO2) in water, and may contain a small amount of a dispersant or the like as required. When the entire amount of the surface treatment liquid is 100 mass %, the concentration of silica (SiO2) is 7 mass % or more and 37 mass % or less, and preferably 15 mass % or more and 25 mass % or less. Silica (SiO2) functions as an aggregate for the surface treatment layer 14c, and gels to fix graphite in the surface treatment layer 14c. If the content of silica (SiO2) is less than 7 mass %, the effect of fixing graphite in the surface treatment layer 14c is reduced. If the content of silica (SiO2) exceeds 37 mass %, many cracks are generated in the surface treatment layer 14c and the surface treatment layer 14c would be peeled off.
The present inventor also conducted an experiment of surface treatment of the thermal spray coating film 14b using a surface treatment liquid in which graphite is dispersed in a mixed solution of colloids other than colloidal silica and an aluminum phosphate aqueous solution. However, in the formed surface treatment coating film, many cracks were generated, the film quality of the coating film was poor, and the problem of delamination occurred. In addition, since the dispersion of graphite did not proceed uniformly in the process of solating colloids other than colloidal silica and aluminum phosphate, a high effect of preventing adhesion of foreign materials could not be obtained. Although the mechanism is not clear, a high effect of preventing adhesion of foreign materials was not obtained unless a surface treatment liquid prepared by dispersing graphite in a mixed solution of an aluminum phosphate aqueous solution and colloidal silica was used. This issue will be clarified in the examples described later.
(Graphite)
When the entire amount of the surface treatment liquid is 100 mass %, the concentration of graphite is 4 mass % or more, and preferably 6 mass % or more. Graphite prevents adhesion of foreign materials and imparts conductivity to the surface treatment layer 14c. If the concentration of graphite is less than 4 mass %, foreign materials may adhere to the surface treatment layer 14c, and the conductor roll 14 may not be used at an early stage.
The upper limit value of the concentration of graphite is not particularly defined, but is preferably 14 mass % or less, and more preferably 11 mass % or less. If the concentration of graphite exceeds 14 mass %, the contents of aluminum phosphate and silica (Si) are lowered, so that there is a possibility that the surface treatment layer 14c cannot be formed.
The above-mentioned surface treatment liquid is applied to the thermal spray coating film 14b of the conductor roll 14 and baked to form the surface treatment layer 14c containing alumina (Al2O3), diphosphorus pentaoxide (P2O5), silicon dioxide (SiO2), and graphite. Incidentally, the surface treatment layer 14c may contain impurities other than the above-mentioned components (for example, solid substances generated when a dispersant added to colloidal silica is baked). However, since the amount thereof is negligibly small, a detailed description thereof is omitted.
Here, alumina (Al2O3) and diphosphorus pentaoxide (P2O5) are compounds derived from the aluminum phosphate solution. When the concentration of aluminum phosphate with respect to the surface treatment liquid is adjusted to 3 mass % or more and 14 mass % or less, the content of alumina (Al2O3) in the surface treatment layer 14c becomes 1.5 mass % or more and 6.8 mass % or less, and the content of diphosphorus pentaoxide (P2O5) becomes 6 mass % or more and 27.3 mass % or less. In addition, when the concentration of aluminum phosphate with respect to the surface treatment liquid is adjusted to 6 mass % or more and 11 mass % or less, the content of alumina (Al2O3) in the surface treatment layer 14c is 3 mass % or more and 5.5 mass % or less, and the content of diphosphorus pentaoxide (P2O5) is 13 mass % or more and 23 mass % or less.
Silicon dioxide (SiO2) is a compound derived from colloidal silica. When the concentration of silica with respect to the surface treatment liquid is adjusted to 7 mass % or more and 37 mass % or less, the content of silicon dioxide (SiO2) in the surface treatment layer 14c becomes 18 mass % or more and 80% or less. Further, when the concentration of silica with respect to the surface treatment liquid is adjusted to 15 mass % or more and 25 mass % or less, the content of silicon dioxide (SiO2) in the surface treatment layer 14c becomes 37 mass % or more and 65 mass % or less.
When the concentration of graphite with respect to the surface treatment liquid is adjusted to 4 mass % or more and 14 mass % or less, the content of graphite in the surface treatment layer 14c becomes 10.2 mass % or more and 36 mass % or less. When the concentration of graphite with respect to the surface treatment liquid is adjusted to 6 mass % or more and 11 mass % or less, the content of graphite in the surface treatment layer 14c becomes 17 mass % or more and 27 mass % or less.
A more specific description regarding the present invention will now be given by showing examples.
(Evaluation Test for Effect of Preventing Adhesion of Foreign Materials)
A predetermined sample was prepared, and the state in which foreign materials were attached and the amount of foreign materials attached were measured to evaluate the effect of preventing adhesion of foreign materials.
The thermal spray surfaces A to C were formed by a WC—Cr2C3—WNiCr-based (67% W-13% Cr-14.2% Ni-5.8% C by mass) cermet thermal spray coating film. The composition of the surface treatment liquid applied to the thermal spray surfaces A to C was changed variously. As the aluminum phosphate aqueous solution, a mixed solution in which aluminum dihydrogen phosphate and aluminum hydrogen phosphate were mixed was used. When the amount of aluminum phosphate was 100 mass %, the content of aluminum hydrogen phosphate was limited to 20 mass % or less, and the remainder was aluminum dihydrogen phosphate.
In the evaluation, a score was assigned to each of the thermal spray surfaces A to C according to the attachment state of the foreign materials, and the effect of preventing adhesion of foreign materials was evaluated on the basis of the total number of points (MN number). When the foreign material powder 2 was dropped off with the thermal spray test pieces 1 and 1′ directed vertical, the effect of preventing adhesion of foreign materials was very good and three points were given. When the foreign material powder 2 was dropped off by rubbing with gauze, the effect of preventing adhesion of foreign materials was generally good and two points were given. When the foreign material powder 2 was dropped off by rubbing with tweezers, the effect of preventing adhesion of foreign materials was poor and one point was given. When the foreign material powder 2 was not dropped off even by the above-mentioned methods, the effect of preventing adhesion of foreign materials was extremely poor and 0 points were given.
After the reciprocating motion of the half-moon-shaped roll 3 described above, the amount (mass %) of Sn adhering to the thermal spray surfaces A to C (the amount (mass %) of Ni) was measured using an X-ray fluorescence measuring apparatus. These averages were calculated. The test results are shown in Tables 1 to 4. When the MN value was more than 7 and the Sn adhesion amount (Ni adhesion amount) was 2 mass % or less, the effect of preventing adhesion of foreign materials was evaluated as extremely good and the evaluation “AA” was assigned. When the MN value was 5 or more and 7 or less and the Sn adhesion amount (Ni adhesion amount) was 5 mass % or less, the effect of preventing adhesion of foreign materials was evaluated as good and the evaluation “A” was assigned. When the MN value was 3 or more and less than 5 and the Sn adhesion amount (Ni adhesion amount) was more than 5 mass % and 8 mass % or less, the effect of preventing adhesion of foreign materials was evaluated as fault and the evaluation “B” was assigned. When the MN value was less than 3, regardless of the Sn adhesion amount (Ni adhesion amount), the evaluation “C” was assigned as having no effect of preventing adhesion of foreign materials. In Table 1, the numerical values expressed with “mass %” are the concentration of aluminum phosphate, the concentration of silica (SiO2), and the concentration of graphite when the entire amount of the surface treatment liquid is 100 mass %.
It was found that Examples 1 to 11 and Examples 12 to 22 were excellent in the effect of preventing adhesion of foreign materials to tin (Sn) and nickel (Ni). In addition, it was found that the effect of preventing adhesion of foreign materials to tin (Sn) was particularly high. In Example 2, since the concentration of aluminum phosphate was slightly low, the dispersion of graphite was slightly insufficient, and the overall evaluation was not AA but A. In Example 6, since the concentration of silica contained in colloidal silica with respect to the surface treatment liquid was slightly low, the effect of fixing graphite was slightly lowered, and the evaluation on the effect of preventing adhesion of foreign materials was not AA but A. In Example 7, since the concentration of silica contained in colloidal silica with respect to the surface treatment liquid was slightly high, slight cracking was generated in a part of the thermal spray coating film, and the evaluation on the effect of preventing adhesion of foreign materials was not AA but A. In Example 10, since the content of graphite was slightly low, the evaluation on the effect of preventing adhesion of foreign materials was not AA but A.
With reference to Comparative Example 1 and Example 1 for comparison, by changing the aluminum phosphate aqueous solution to a sodium metaphosphate aqueous solution, the evaluation on the effect of preventing adhesion of foreign materials became B. With reference to Comparative Example 11 and Example 12 for comparison, by changing the aluminum phosphate aqueous solution to the sodium metaphosphate aqueous solution, the evaluation on the effect of preventing adhesion of foreign materials became C. With reference to Comparative Example 2 and Example 1 for comparison, by changing the colloidal silica to colloidal alumina, the evaluation on the effect of preventing adhesion of foreign materials became C. With reference to Comparative Example 12 and Example 12 for comparison, by changing the colloidal silica to colloidal alumina, the evaluation on the effect of preventing adhesion of foreign materials became C. With reference to Comparative Example 3 and Example 1 for comparison, by changing the colloidal silica to colloidal titanium, the evaluation on the effect of preventing adhesion of foreign materials became C. With reference to Comparative Example 13 and Example 12, by changing the colloidal silica to colloidal titanium, the evaluation on the effect of preventing adhesion of foreign materials became C.
With reference to Comparative Example 4 and Example 1 for comparison, by changing the colloidal silica to a mixture of colloidal alumina and colloidal titanium, the evaluation on the effect of preventing adhesion of foreign materials became C. With reference to Comparative Example 14 and Example 12 for comparison, by changing the colloidal silica to a mixture of colloidal alumina and colloidal titanium, the evaluation on the effect of preventing adhesion of foreign materials became C. In Comparative Example 5 and Comparative Example 15, since graphite was not contained, the evaluation on the effect of preventing adhesion of foreign materials became C.
In Comparative Examples 6 and 16, since the concentration of aluminum phosphate contained in the aluminum phosphate aqueous solution with respect to the surface treatment liquid was too low, the colloidal silica could not be gelled. Therefore, the effect of preventing adhesion of foreign materials could not be evaluated. In Comparative Examples 7 and 17, since the concentration of aluminum phosphate contained in the aluminum phosphate aqueous solution with respect to the surface treatment liquid was too high, the surface treatment liquid gelled before being applied to the thermal spray coating film. Therefore, since the surface treatment liquid could not be applied to the thermal spray coating film, the effect of preventing adhesion of foreign materials could not be evaluated.
In Comparative Example 8, since the concentration of silica contained in colloidal silica with respect to the surface treatment liquid was too low, the effect of fixing graphite was greatly lowered, and the evaluation on the effect of preventing adhesion of foreign materials became B. In Comparative Example 18, since the concentration of silica contained in colloidal silica with respect to the surface treatment liquid was too low, the effect of fixing graphite was greatly lowered, and the evaluation on the effect of preventing adhesion of foreign materials became C.
In Comparative Examples 9 and 19, since the concentration of silica contained in colloidal silica with respect to the surface treatment liquid was too high, the effect of fixing graphite was greatly lowered, and the evaluation on the effect of preventing adhesion of foreign materials became B. In Comparative Example 10, since the content of graphite contained in the surface treatment liquid was too small, the evaluation on the effect of preventing adhesion of foreign materials became B. In Comparative Example 20, since the content of graphite contained in the surface treatment liquid was too small, the evaluation on the effect of preventing adhesion of foreign materials became C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-136328 | Jul 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/018506 | 5/17/2017 | WO | 00 |
