Title of Invention

"PLATING APPARATUS AND PLATING METHOD FOR CONTINUOUSLY PLATING STEEL SHEET"

Abstract

A plating equipment for continuously plating a steel sheet S. The plating equipment has an acid-pickling unit (4) for pickling a steel sheet (S) with an acid solution, a cold-rolling mill (5) for cold-rolling the steel sheet (S) and a plating unit (7) for plating the steel sheet (S), disposed below the acid pickling unit (4) and the cold-rolling mill (5) with respect to a moving direction of the steel sheet (S). The acid-pickling unit (4), the cold-rolling mill (5) and the plating unit (7) are arranged in a single line for continuously plating the steel sheet (S). A steel sheet of a desired quality can be manufactured by passing the steel sheet S only through the single line provided with the acid-pickling unit (4), the cold-rolling mill (5) and the plating unit (7). The plating equipment does not need to be arranged in a plurality of lines. The plating equipment can manufacture plated steel sheets in a small investment in equipment, at a small floor space for installation, at low, running costs in a short manufacturing time, and at very low manufacturing costs.

Full Text

DESCRIPTION PLATING EQUIPMENT AND PLATING METHOD FOR CONTINUOUSLY PLATING STEEL SHEET TECHNICAL FIELD The present invention relates to a plating apparapus for continuously plating a steel sheet and a method for continuously plating a steel sheet. More particularly, the present invention relates to a plating equipment and a plating method for continuously producing a plated steel sheet of a thickness in the range of about 0.6 to about 1.0 nun. BACKGROUND ART Galvanized steel sheets of a thickness smaller than or equal to 1 mm are manufactured by the following process. A hot-rolled steel sheet of a thickness in the range of 2.0 to 4.0 mm is formed by hot-rolling work. The hot-rolled steel sheet is processed by an acid pickling line. The acid-pickled steel sheet is sent to a cold-rolling line that is independent of the acid pickling line. The cold-rolled steel sheet is processed by a zinc-plating line. Referring to Fig. 2 showing a conventional zinc-plating equipment of a general construction, a welder 2, loopers 3 and 15, an annealing furnace 6 and a molten zinc pot 7, i.e., a plating means, are arranged between feed reels 1 and a take-up reel 17. When necessary, a galvannealing unit 9, a skin pass mill 12, a tension leveler, not shown, and a chemical conversion treatment unit, not shown, are arranged below the molten zinc pot 7. The cold-rolling line that rolls the steel sheet before subjecting the steel sheet to a zinc-plating process is an independent line separate from a acid pickling line and a plating line. The cold-rolling line rolls a hot-rolled steel sheets of a thickness in the range of 2.0 to 4.0 mm into a steel sheet of a thickness in the range of 0.2 to 1.2 mm by a plurality of passes by a reversing mill or a tandem mill. Generally, a hot-rolled steel sheet of a thickness in the range of 2.0 to 4.0 mm is produced by hot-rolling a slab of a thickness in the range of about 200 to about 250 mm which is produced by a continuous casting process. The recent progress in the development of techniques for producing thin slabs by continuous casting has made it possible to manufacture hot-rolled steel sheets by hot-rolling thin slabs of about 50 mm thick which is produced in a continuous casting line and is directly fed to a hot-rolling line. However, even in the conventional method using continuous casting of thin slabs, when a plated steel sheet is manufactured, a hot-rolled steel sheet of a thickness in the range of 2.0 to 4.0 mm is produced first. Then, the hot-rolled steel sheet is processed by an independent acid pickling line, an independent cold-rolling line and an independent plating line. The foregoing processes for forming the zinc-plated steel sheet from the slab manufactured by continuous casting are shownj in "Kaitei Usuita Manyuaru", Shadan Hojin Nippon Tekko Kyokai Kohan-bukai Hen, p. 5, Fig. 2.1. The zinc-plating line is shown in "Yoyuu Aen Mekki Kohan Seizou Gijutu no Shimpo", Nishiyama Kinen Gijutus Koza, 106th/107th, Shadan Hojin Tekko Kyokai, p. 4, Fig. 3. Techniques relating to the manufacture of thin slabs by continuous casting are mentioned in "Production of 1 mm Thick Hot Rolled Steel Strip:, MPT International, 1/1998, pp. 50 to 51. As mentioned above, the conventional zinc-plated steel sheet manufacturing method must pass a hot-rolled steel sheet through three independent lines, i.e., an acid pickling line, a cold-rolling line and a plating line. The conventional zinc-plated steel sheet manufacturing method that needs a plurality of lines has the following problems. The number of necessary pieces of equipment is equal to that of lines and the zinc-plated steel sheet manufacturing method needs a large investment in plant and equipment and a large space for installing the pieces of equipment in a steel works. The greater the number of lines the greater the running cost because leading and trailing edges of the steel sheets are liable to be damaged in each line, defects are liable to be formed in the steel sheet and the transportation of the steel sheet from line to line needs transportation costs. It is difficult to transfer the steel sheet that has been processed by a line immediately to the next line because each line takes time for completing arrangements. Consequently, a long time is necessary to pass the steel sheet through all the lines to manufacture the zinc-plated steel sheet. The present invention has been made in view of those problems and it is therefore an object of the present invention to provide a plating equipment and a plating method for continuously plating a steel sheet that is capable of manufacturing a plated steel sheet by processing a hot-rolled steel sheet by a single line. DISCLOSURE OF THE INVENTION To achieve the object, according to a first aspect of the present invention, a plating apparatus for continuously plating a steel sheet comprises: an acid-pickling unit for pickling a steel sheet with an acid solution; a cold-rolling mill for cold-rolling the steel sheet; and a plating unit for plating the steel sheet by a plating process, disposed below the acid pickling unit and the cold-rolling mill with respect to a moving direction of the steel sheet. The acid-pickling unit, the cold-rolling mill and the plating unit are arranged in a single line for continuously plating the steel sheet. Preferably, the steel sheet to be subjected to the plating process is a hot-rolled steel sheet of a thickness smaller than or equal to 1.2 mm. Preferably, the hot-rolled steel sheet has a thickness in a range of 1.0 to 1.2 mm. Preferably, a plated steel sheet obtained by plating the steel sheet by the plating process has a thickness in a range of 0.6 to 1.0 mm. Preferably, the hot-rolled steel sheet is obtained by hot-rolling a thin slab produced by a continuous casting. Preferably, the cold-rolling mill has one stand. Preferably, the single line includes below the plating unit at least one of a gal annealing unit, a skin pass mill, a tension leveler, and a chemical conversion treatment unit. Preferably, the plating unit has a pot for storing a molten metal therein. The plating apparatus of the present invention is capable of manufacturing a desired plated steel sheet by processing the steel sheet only through the single line provided with the acid-pickling unit, the cold rolling mill and the plating unit. The plating equipment does not need a plurality of lines that are inevitable for the conventional plating equipment. The plating equipment can manufacture plated steel sheets at a small investment in equipment, in a small floor space for installation, at low running costs in a short manufacturing time and at very low manufacturing costs. Those advantageous effects can be exercised by the arrangement of the acid-pickling unit, the cold-rolling mill and the plating unit in the single line. To achieve arranging the acid-pickling unit, the cold-rolling mill and the plating unit in the single line, the cold-rolling mill must be able to cold-roll the steel sheet by one or two passes. Recently developed techniques has made it possible to commercially produce hot-rolled steel sheets of a thickness in the range of 1.0 to 1.2 mm. As a result, it has become possible to form a single line including a plating unit and a cold-rolling mill in combination and to dispose an acid-pickling unit above the cold-rolling mill. According to a second aspect of the present invention, a plating method for continuously plating a steel sheet comprises the steps of: an acid-pickling step for cleaning a steel sheet with an acid solution; a cold-rolling step for cold-rolling the steel sheet; and a plating step for plating the steel sheet after the acid-pickling step and the cold-rolling step. The acid-pickling step, the cold-rolling step and the plating step form a single continuous steel sheet plating line. Preferably, the steel sheet to be subjected to the plating step is a hot-rolled steel sheet of a thickness smaller than or equal to 1.2 mm. Preferably, the hot-rolled steel sheet has a thickness in a range of 1.0 to 1.2 mm. Preferably, a plated steel sheet obtained by plating the steel sheet by the plating step has a thickness in a range of 0.6 to 1.0 nun. Preferably, the hot-rolled steel sheet is obtained by hot-rolling a thin slab produced by a continuous casting. Preferably, the cold-rolling step is carried out by a cold-rolling mill having one stand. Preferably, the single line includes a predetermined process for processing the steel sheet after the plating step by at least one of a galvannealing unit, a skin pass mill, a tension leveler and a chemical conversion treatment unit. Preferably, in the plating step, the steel sheet is immersed in a molten metal stored in a pot. The plating method of the present invention is capable of manufacturing a desired plated steel sheet by processing the steel sheet only through the single line of the acid-pickling step, the cold-rolling step and the plating step. The plating method does not need a plurality of lines that are inevitable for the conventional plating method. The plating method can manufacture plated steel sheets at a small investment in equipment, in a small floor space for installation, at low running costs in a short manufacturing time and at very low manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a typical view of an upper section of a plating equipment for continuously plating a steel sheet in a preferred embodiment according to the present invention; Fig. 1B is a typical view of a middle section of the plating equipment for continuously plating a steel sheet in the preferred embodiment according to the present invention; Fig. 1C is a typical view of a lower section of the plating equipment for continuously plating a steel sheet in the preferred embodiment according to the present invention; and Fig. 2 is a typical view of a conventional steel sheet plating equipment. BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment according to the present invention will be described with reference to the accompanying drawings. Figs. 1A, 1B and 1C are typical views of an upper section, a middle section and a lower section, respectively, of a plating equipment for continuously plating a steel sheet (hereinafter referred to simply as "plating equipment") in a preferred embodiment according to the present invention. Figs. 1A, 1B and 1C show a series of sequential processes by which a steel sheet is processed. The plating equipment is intended for the zinc-plating of the steel sheet. As shown in Fig. 1A, the upper section of the plating equipment includes unwinding reels 1, a welder 2, an entrance looper 3, an acid-pickling tank (acid-pickling unit) 4 and a cold-rolling mill 5, which are arranged sequentially in that order. Two steel sheet coils each of a steel sheet S can be supported on the unwinding reels 1. The steel sheet S is unwound from the steel sheet coil supported on one of the reels 1 after all the steel sheet S has been unwound from the coil supported on the other reel 1 to feed the steel sheets S continuously. When changing the steel sheet coils, the trailing edge of the steel sheet S and the leading edge of the other steel sheet S are welded together by the welder 2 to connect the steel sheets S. The looper 3 has a plurality of movable rolls, whose positions are variable. The steel sheet S is extended around the plurality of rolls. The positions of the rolls vary to absorb the difference of the speed of the steel sheet S on the upper side of the looper 3 and that of the same on the lower side of the looper 3. For example, the steel sheet S can be fed from the looper 3 at a fixed speed while the two steel sheets S are being welded together by the welder 2. The acid-pickling tank 4 disposed below the looper 3 removes scales (iron oxide films) from the surfaces of the steel sheets S before rolling. The acid-pickling tank 4 has an acid-pickling section, a rinsing section and a drying section, which are not shown. The cold-rolling mill 5 disposed below the acid-pickling tank 4 has a pair of work rolls 5a and 5b and back-up rolls pressing the work rolls 5a and 5b toward each other. The cold-rolling mill 5 has one six-high nonreversing rolling stand, and pairs of bridle rolls 5c and 5d disposed on the opposite sides of the rolling stand, respectively. The cold-rolling mill 5 having the single rolling stand reduces the equipment costs of the plating equipment and the space necessary for the installation of the plating equipment. As shown in Fig. 1B, the middle section of the plating equipment includes an annealing furnace 6, a zinc bath pot (plating unit) 7, an air knife 8, a galvannealing unit 9, an air-cooling unit 10 and a water-cooling unit 11, which are arranged sequentially in that order. The annealing furnace 6 has a heating zone 6a, a reducing zone 6b and a cooling zone 6c arranged in that order from the upper side downward. The annealing furnace 6 is capable of heating the steel sheet S for annealing without oxidizing the same immediately before plating. The zinc bath pot 7, i.e., the plating unit, stores molten zinc in which the steel sheet S is immersed for plating. The air knife 8 is disposed above the zinc bath pot 7 to regulating the thickness of zinc layers formed on the surfaces of the steel sheet S. The galvannealing unit 9 is a heating device that heats the steel sheet S to reduce the porosity of the zinc layers coating the surfaces of the steel sheet S. The steel sheet S heated by the galvannealing unit 9 is cooled by the air-cooling unit 10 and the water-cooling unit 11 disposed below the galvannealing unit 9. As shown in Fig. 1C, the lower section of the plating equipment includes a skin pass mill 12, tension leveler 13, a chemical conversion treatment unit 14, an exit looper 15, an oiling unit 16 and a take-up reel 17, which are arranged sequentially in that order from the upper side downward. A shearing machine may be disposed in front of the take-up reel 17. The skin pass mill 12 rolls the plated steel sheet S lightly at a rolling reduction in the range of 1% to 3% to eliminate yield elongation and to smooth the surfaces of the steel sheet S. The tension leveler 13 tensions the steel sheet S to improve the flatness of the steel sheet S by straightening center waves and edge waves formed in the steel sheet S. The chemical conversion treatment unit 14 processes the steel sheet S by a chromate coating process or the like. The steel sheet S processed by the zinc-plating line of the plating apparatus is a hot-rolled steel sheet (hot coil) of a thickness in the range of 1.0 to 1.2 mm. Preferably, the hot-rolled steel sheet of a thickness in the range of 1.0 to 1.2 mm is formed by rolling a thin slab of about 50 mm in thickness which is manufactured by continuous thin slab casting. If the steel sheet of such a thickness is to be manufactured by hot-rolling a thick slab of a thickness exceeding 200 mm manufactured by ordinary continuous casting, a special hot-rolling mill will be necessary, which increases the cost of the hot-rolled steel sheet greatly and such processes are hardly commercially and economically feasible. Commercial production of thin slabs by casting, which has been started in recent years, needs casting apparatus which is less expensive than ordinary continuous casting apparatus . The casting equipment includes a tunnel furnace disposed on the upper side of a finish mill to maintain a high rolling temperature to make possible the commercial production of 1 mm thick steel sheets . Although thin slabs for manufacturing the steel sheet S are not limited to those of about 50 mm in thickness, it is preferable to use thin slabs which can be easily hot-rolled into steel sheets of a thickness of 1.2 mm or below. The hot-rolled steel sheet S of a thickness in the range of 1.0 to 1.2 mm is passed through the zinc plating line of the plating equipment to pickle the surfaces of the steel sheet S in the acid-pickling tank 4. The pickled steel sheet S is rinsed with water and the rinsed steel sheet S is dried. The steel sheet S thus cleared of scales is cold-rolled by the cold-rolling mill 5, the rolled steel sheet S is annealed in the annealing furnace 6 and is plated with zinc in the zinc bath pot 7. The zinc-plated steel sheet S is subjected to a galvannealing process by the galvannealing unit 9, the galvannealed steel sheet S is passed through the skin pass mill 12 and the tension leveler 13 to improve the smoothness and flatness of the surfaces of the steel sheet S. The zinc-plated steel sheet S thus manufactured is taken up by the take-up reel 17 after being processed by a necessary process by the chemical conversion treatment unit 14 or the like. As mentioned above, the cold-rolling mill 5 of the plating apparatus has a single stand and is of a nonreversing type. Therefore, the steel sheet S can be passed through the cold-rolling mill 5 only once and the plating apparatus has a simple construction. A rolling reduction at which the cold-rolling mill 5 is able to roll the steel sheet S is as low as about 40% or below. However, since the hot-relled steel sheet S of a thickness in the range of 1.0 to 1.2 mm is fed to the plating equipment, the plating equipment provided with the cold-rolling mill 5 having a single stand is able to manufacture a cold-rolled plated steel sheet of a thickness in the range of about 0.6 to about 0.8 mm. Since the cold-rolled plated steel sheet is rolled at a low rolling reduction, the cold-rolled plated steel sheet is somewhat inferior in drawability (r value) to conventional plated steel sheets which are rolled at a rolling reduction in the range of 70% to 80%. However, the cold-rolled plated steel sheets manufactured by the plating apparatus of the present invention can be used as steel sheets for light working that are not expected to be processed by deep drawing and can be used for various purposes. Products that can be manufactured by the continuous plating line of the plating apparatus of the present invention are not limited to cold-rolled zinc-plated steel sheets. The plating apparatus is able to manufacture various products by the following methods. A first method passes a steel sheet S through the cold-rolling mill 5 with the opened working rollers 5a and 5b in order to manufacture a hot-rolled zinc-plated steel sheet. A second method stores a molten metal other than molten zinc, such as molten aluminum, in the pot 7 to manufacture a steel sheet S placed with a metal, such as aluminum. A third method keeps the pot 7 empty to manufacture an annealed, nonplated cold-rolled steel sheet. If the third method skips cold-rolling as the first method does, an acid-pickled hot-rolled steel sheet can be manufactured. A fourth method uses the galvannealing unit 8, the skin pass mill 12, the tension leveler 13 and the chemical conversion treatment unit 14 selectively to manufacture steel sheets of a desired quality at proper manufacturing costs. Thus, the plating apparatus embodying the present invention is capable of manufacturing a product of a desired quality by an economically reasonable, optimum manufacturing method according to the desired product quality. A plating apparatus in a modification of, the foregoing embodiment may be provided with a cold-rolling mill having two or more stands instead of the cold-rolling mill 5 having one stand. The rolling reduction at which the steel sheet S is rolled can be increased and thinner steel sheets can be manufactured by increasing the number of stands of the cold-rolling mill 5. INDUSTRIAL APPLICABILITY The plating apparatus and the plating method according to the present invention is prevalently applicable to the continuous manufacture of plated steel sheets of a thickness in the range of about 0.6 to about 1.0 mm. We claim: 1. A plating apparatus for continuously plating a steel sheet comprising: an acid-pickling unit for pickling a steel sheet with an acid solution; a cold-rolling mill for cold-rolling the steel sheet; the cold rolling mill having a single stand; and a plating unit for plating the steel sheet by a plating process, disposed below the acid pickling unit and the cold-rolling mill with respect to a moving direction of the steel sheet; wherein the acid-pickling unit, the cold-rolling mill and the plating unit are arranged in a single line for continuously plating the steel sheet, wherein the steel sheet to be supplied to the plating equipment is hot-rolled steel sheet of a thickness in a range of 1.0 to 1.2 mm and wherein a cold rolled and plated steel sheet produced by the plating equipment has a thickness in a range of 0.6 to 1.0 mm. 2. The plating equipment as claimed in claim 1, wherein the hot-rolled steel sheet is obtained by hot-rolling a thin slab produced by a continuous casting. 3. A plating method for continuously plating a steel sheet comprising the steps of: an acid-pickling step of cleaning a steel sheet with an acid solution; a cold-rolling step of cold-rolling the steel sheet , the cold rolling step being carried out by a cold rolling mill having a single stand ; and a plating step of plating the steel sheet after the acid-pickling step and the cold-rolling step; wherein the acid-pickling step, the cold-rolling step and the plating step form a single continuous steel sheet plating line; wherein the steel sheet to be processed by the plating method is a hot-rolled steel sheet of a thickness in a range of 1.0 to 1.2 mm and wherein a cold rolled and plated steel sheet produced by the plating method has a thickness in a range of 0.6 to 1.0 mm.

Documents:

in-pct-2001-00034-del-abstract.pdf

in-pct-2001-00034-del-claims.pdf

in-pct-2001-00034-del-correspondence-others.pdf

in-pct-2001-00034-del-correspondence-po.pdf

in-pct-2001-00034-del-description (complete).pdf

in-pct-2001-00034-del-drawings.pdf

in-pct-2001-00034-del-form-1.pdf

in-pct-2001-00034-del-form-13.pdf

in-pct-2001-00034-del-form-19.pdf

in-pct-2001-00034-del-form-2.pdf

in-pct-2001-00034-del-form-3.pdf

in-pct-2001-00034-del-form-5.pdf

in-pct-2001-00034-del-gpa.pdf

in-pct-2001-00034-del-pct-210.pdf

in-pct-2001-00034-del-pct-304.pdf

in-pct-2001-00034-del-pct-409.pdf

in-pct-2001-00034-del-petition-137.pdf