Painting method for a ship hull block or the like

Abstract: The painting method comprises a baking process in which electrostatic painting powder is scattered uniformly on both surfaces of a steel plate, which is subjected to shop primer painting or chemical conversion coating treatment after being shotblasted or pickled, the unnecessary portions of scattered electrostatic painting powder on the steel plate is removed by means of a suction nozzle moving under numerical control, and thereafter the scattered electrostatic painting powder on both surfaces of the steel plate is baked by the high-frequency baking method; an intermediate assembly block process in which the baked steel plate is cut into a predetermined shape under numerical control, and a related steel plate is welded to the unpainted portion to form an intermediate assembly block; a major assembly block process in which a plurality of intermediate assembly blocks are welded to each other to form a major assembly block; and an integrated assembly block process in which the major assembly block is subjected to secondary surface treatment by pickling, and thereafter secondary painting is performed on the major assembly block before forming an integrated assembly block.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT Ships are usually built through various main processes as shown in Fig.4. As indicated in Fig.4, (1) steel plates used for a ship are subjected to (2) primary surface treatment by shotblasting and then to (3) shop primer painting. The steel plates are (4) cut and bent, and (5) a block assembly step is performed comprising intermediate and major assemblies. In this process, secondary surface treatment, block painting, and unit painting are performed. In (6) an outfit work step, secondary surface treatment, inside painting, and bottom shell painting are performed. Then, the ship is (7) launched. Considering the painting work in the above main processes, rust occurring in the ship building process is prevented by (3) shop primer applied to the entire surface of the steel plates, and then block painting and unit painting is carried out in (5) the block assembly step and secondary surface treatment, inside painting, and bottom shell painting are performed in (6) the outfit work step. However, after the welding operation in (5) block assembly step and (6) outfit work step performed after shop primer painting, the shop primer coating damaged in (4) cutting and bending steel plates must be treated and painting after welding has been performed. Such work requires not only very high cost but also heavy labor involving danger and dirt. It is therefore said that the biggest problem in securing workers and reducing cost is to improve the work of this kind in the future ship building operation. This is true for bridges and offshore structures in addition to ships. From British patent specification 1 465 146, an electrostatic powder-coating method for selectively coating a pattern on the surface of steel plate and an apparatus for carrying out the method is known which comprises the steps of the pre-characterizing clause of claim 1. It comprises depositing coating powders uniformly on the surface of a steel plate and arranging that the coating powders adhere electrostatically to the article surface, and selectively removing the deposited powders from the surface of areas not requiring any powder coating using a force stronger than the adhesive force between the coated powders and the steel plate surface. Subsequently, the surface of the steel plate is heated to form the coating film on the surface areas containing deposited powders. The coating powders may be scattered uniformly on the surface and then charged or vice versa. Those portions of the powder on areas which do not require a coating treatment may be removed by using an air-stream or using suction, so that a pattern-like coating of the surface can be obtained. Thereby, those portions from which the powder has been removed have the charges left unerased. OBJECT AND SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an economical painting method for a ship hull block or the like, which provides labor and manpower saving, shortened work period, and reduced cost due to an improvement of work environment, safety of work, and lightening of labor. To achieve the above object, the first mode of the present invention wherein the painting method comprises a baking step in which electrostatic painting powder is scattered uniformly on both surfaces of a steel plate, which is subjected to shop primer painting or chemical conversion coating treatment after being shotblasted or pickled, the unnecessary portions of scattered electrostatic painting powder on the steel plate is removed by means of a suction nozzle moving under numerical control, and thereafter the scattered electrostatic painting powder on both surfaces of the steel plate is baked by the high-frequency baking method; an intermediate assembly block step in which the baked steel plate is cut into a predetermined shape under numerical control, and a related steel plate is welded to the unpainted portion to form an intermediate assembly block, is characterised by a major assembly block step in which a plurality of intermediate assembly blocks are welded to each other to form a major assembly block; and an integrated assembly block step in which the major assembly block is subjected to secondary surface treatment by pickling, and thereafter secondary painting is performed on the major assembly block before forming an integrated assembly block. Next, in a second mode of the present invention the painting method comprises the steps of independent claim 2, and in a third mode of the present invention the painting method for a ship hull block or the like comprises the steps of independent claim 3. Further, a preferred mode of the present invention is characterized in that, in the painting method for a ship hull block or the like according to claim 2, the remaining electrostatic painting powder on said steel member having a required sectional area is baked by the infrared ray baking method in addition to the high-frequency baking method. According to the first mode of the present invention, as shown in Process A in Fig.1, after a regular-size steel plate, which has been shotblasted or pickled, is subjected to shop primer painting or chemical conversion coating treatment, electrostatic painting powder is scattered uniformly. Then, the electrostatic painting powder at portions of cutting, welding, and burning for bending, which is performed in the subsequent process, is selectively removed by means of a suction nozzle moved under numerical control. The electrostatic painting powder remaining on the regular-size steel plate is baked into a predetermined shape on the regular-size steel plate, which is cut into a predetermined shape and marked with part number, etc. under numerical control. After major assembly is completed via intermediate assembly, second surface treatment by pickling is performed. In this process, the unpainted portions are cleaned by pickling, and high-performance painting is performed as the secondary painting before integrated assembly is performed. According to the second mode of the present invention, as shown in Process B in Fig.1, a steel plate which is subjected to shop primer painting or chemical conversion coating treatment as described in claim 1 is cut and marked under numerical control. After welding assembly, the surface treatment by pickling and the scattering of electrostatic painting powder are performed, and thereafter the electrostatic painting powder at the unnecessary portions is selectively removed under numerical control or by masking before applying the powder. After being baked by the high-frequency baking method, the welded member enters Process A at the intermediate assembly for subsequent processes. Therefore, this mode is also suitable for the assembly and painting of sections and straight pipes. According to the third mode of the present invention, as shown in Process C in Fig.1, a steel plate which is subjected to shop primer painting or chemical conversion coating treatment as described in claim 1 is cut and marked under numerical control. After welding assembly, the surface treatment by pickling is performed and then the scattering of electrostatic painting powder is performed; thereafter, the electrostatic painting powder at the unnecessary portions is selectively removed under numerical control or by masking before applying the powder. After that, the welded member is baked by the far infrared ray or near infrared ray baking method. Therefore, this mode is suitable for the assembly and painting of subassembled members, outfittings, and deformed pipes. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, Fig.1 is a flowchart showing the entire process of one embodiment of the present invention, Fig.2 is a block diagram showing Process A in Fig.1, Fig.3 is a temperature distribution diagram for steel plate and paint coating in high-frequency baking and far/near infrared ray baking in Fig.1, and Fig.4 is a block diagram showing the conventional process for ship building. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. Fig.1 is a flowchart showing the entire process of the embodiment, and Fig.2 is a block diagram showing Process A in Fig.1. In Fig.1, the present invention consists of a steel plate precoating process with numerical control unpainted portions shown on the left half of the figure, a block painting process on the upper right half, and an on-berth painting process on the lower right half. Process A indicates the method described in claim 1, Process B indicates the method described in claim 2, and Process C indicates the method described in claim 3. Incidentally, the on-berth painting process is publicly known. Process A is the basic process. A regular-size steel plate 1, which has been shotblasted or pickled, is subjected to shop primer painting or chemical conversion coating treatment 1a. Then, electrostatic painting powder 2 is uniformly scattered on the entire surface of plate. The electrostatic painting powder applied to the portions which are cut, welded, or burnt for bending in the following process is selectively removed by means of a numerically controlled suction nozzle 3, that is, unpainted portions 4 are formed. The electrostatic painting powder 5 remaining on the regular-size steel plate is baked in a predetermined shape 7 on the steel plate by high-frequency baking 6. The steel plate is cut by an numerically controlled cutter 8 into a predetermined shape 7, and part number, etc. are marked under numerical control. After that, intermediate assembly 9 and major assembly 10 are performed. After the major assembly is completed, secondary surface preparation 11 by pickling is further performed, where the unpainted portions 4 are cleaned by pickling. Thereafter, high-performance painting is carried out as secondary painting 12 before integrated assembly 13 is performed. After the integrated assembly 13 is completed, the block is erected on the berth 14 in the conventional manner. Afterwards, block joint painting and finish painting are performed by conventional methods. Thus, the ship is completed and delivered. This basic process A offers the following effects by the process in which electrostatic painting powder 2 is scattered and unnecessary powder is removed under numerical control, that is, by forming unpainted portions 4 on both surfaces. (1) The conventional image of painting work that the work is dirty, heavy, and unhealthy can be eliminated. (2) The use of numerical control provides full mechanization of painting work, resulting in significant labor saving and reduction in manpower. (3) A solventless system is used, and more than 90% of electrostatic paining powder is recovered for reuse. Therefore, the waste of painting powder is almost eliminated. The high-frequency baking 6 of the electrostatic painting powder 2 offers the following effects: (1) Full mechanization provides significant labor saving and reduction in manpower. (2) The use of high-performance paint such as epoxy resin paint upgrades the quality of paint coating. (3) According to the high-frequency baking, the heating is performed from the surface of steel plate, that is, the back surface of the coating as indicated by the solid line in Fig.3(A); therefore, the baking surface of steel plate can be mainly heated by the skin effect. As a result, the powder paint does not contain air bubbles, and high-temperature and short-time baking also achieves energy saving. Further, in the intermediate assembly 9 and the major assembly 10, the paint coating is less prone to be damaged mechanically and thermally during numerically controlled cutting, assembly, and welding. The high-frequency baking achieves energy saving due to short-time heating. However, uniform heating sometimes cannot be effected in the thickness direction due to the temperature distribution shown in Fig.3(A) when a thick paint film is heated in a very short time because the back surface side of the coating is heated. For far infrared ray heating, the coating is heated from the top surface side, so that the temperature distribution is as shown in Fig.3(B). Therefore, by combining the high-frequency baking and the far infrared ray heating, the temperature distribution shown in Fig.3(C) is attained, thereby effecting heating which is uniform in the film thickness direction. Further, the secondary surface treatment by pickling offers the following effects: (1) Full mechanization provides significant reduction in manpower. (2) Pickling can treat the unpainted portions at low cost, and the recovery percentage of acid amounts to 90% or more. (3) The surface treatment by pickling greatly upgrades the quality. Finally, the secondary painting offers the following effects: (1) Since the painting areas are limited to linear shape, labor saving by using a robot becomes relatively easy. (2) The cold fast-drying system shortens the painting process. (3) The use of high-performance paint such as urethane resin paint upgrades the quality of paint coating. The blocks of intermediate assembly with a somewhat complicated shape and construction are painted by Process B in Fig.1. The steel plate, which is subjected to shop primer painting or chemical conversion coating treatment 1a at the initial stage of Process A, undergoes numerically controlled cutting 8 and part number is marked on each part. After welding assembly 15 is completed, surface treatment 16 by pickling is performed and electrostatic painting powder 2 is scattered. Thereafter, selective removal 3 of electrostatic painting powder at the unnecessary portions is performed under numerical control or by masking before applying the powder. Baking is completed by high-frequency baking 6, and the subassembled member enters the aforesaid Process A at the intermediate assembly 9 for subsequent processes. Therefore, Process B is suitable for the assembly and painting of sections, straight pipes and so forth. In this case, pre-painting heat baking 17 or fluidized-bed coating powder painting 18 may be performed in place of high-frequency baking 6. According to pre-painting heating, the object to be painted is heated before painting, and the painting film can be formed by spraying paint by the electrostatic method or by the fluidized-bed coating (immersion in paint floated by air) method. In this case, the unpainted portions are masked or removed after film formation. If full curing is not achieved, heating is further performed subsequently. Subassembled members and the like are processed as shown in Process C in Fig.1. The steel plate, which is subjected to shop primer painting or chemical conversion coating treatment 1a at the initial stage of Process A, undergoes numerically controlled cutting 8 and part number is marked on each part. After welding assembly 15 is completed, surface treatment 16 by pickling is performed and electrostatic painting powder is scattered. After selective removal 4 of electrostatic painting powder at the unnecessary portions being performed under numerical control or by masking before applying the powder, far infrared ray baking 19 is performed. Since the paint coating is widely heated in far infrared ray baking or near infrared ray baking, objects of somewhat complicated shape can be baked effectively. Therefore, Process C is suitable for the assembly and painting of not only subassembled members but also outfittings and deformed pipes. In this case, pre-painting heat baking 17 or fluidized-bed coating powder painting 18 may be performed in place of far/near infrared ray baking.

Claims: A painting method for a ship hull block or the like comprising the following steps: a baking step in which electrostatic painting powder (2) is scattered uniformly on both surfaces of a steel plate (1), which was subjected to shop primer painting or chemical conversion coating treatment after being shotblasted or pickled, any unnecessary portion of electrostatic painting powder scattered on the steel plate is removed by means of a suction nozzle (3) moving under numerical control, and thereafter the electrostatic powder (5) scattered on both surfaces of the steel plate is baked by a high-frequency baking method (6); and an intermediate assembly block step in which the baked steel plate (1) is cut into a predetermined shape (7) under numerical control, and a related steel plate is welded to the unpainted portion (4) of the cut steel plate so as to form an intermediate assembly block (9); characterized by a major assembly block step in which a plurality of intermediate assembly blocks (9) are welded to each other to form a major assembly block (10); and an integrated assembly block step in which the major assembly block (10) is subjected to secondary surface treatment (11) by pickling and thereafter to secondary painting (12) before forming an integrated assembly block (13). A painting method for a ship hull block or the like comprising the following steps: a welding assembly step in which a steel member having a required sectional area is formed by appropriately assembling a plurality of strip-shaped steel plates, which are cut and marked under numerical control, the strip-shaped steel plates being cut from a steel plate which was subjected to shop primer painting or chemical conversion coating treatment after having been shotblasted or pickled; an electrostatic painting powder scattering step in which the steel member having a required sectional area is subjected to surface treatment by pickling, and thereafter electrostatic painting powder is uniformly scattered on the entire surface of the steel member; an unpainted portion forming step in which any unnecessary portion of the electrostatic painting powder on the steel member having a required sectional area is removed by means of a suction nozzle (3) moving under numerical control or by leaving an unpainted portion (4) on the steel member by masking, a baking step in which the remaining electrostatic painting powder (5) on the steel member having a required sectional area is baked by high-frequency baking or by prepainting heat-baking, a further welding step by which a related steel plate is welded to said unpainted portion of the steel member so as to form an intermediate assembly block (9), and welding a plurality of the intermediate assembly blocks (9) together so as to form a major assembly block (10), subjecting the major assembly block (10) to secondary surface treatment (11) by pickling and thereafter performing secondary painting (12) on the major assembly block so as to form an integrated assembly block (13). A painting method for a ship hull block or the like comprising the following steps: a welding assembly step in which a steel member having a required sectional area is formed by appropriately assembling a plurality of strip-shaped steel plates, which are cut and marked under numerical control, the strip-shaped steel plates being cut from a steel plate which was subjected to shop primer painting or chemical conversion coating treatment after having been shotblasted or pickled; an electrostatic painting powder scattering step in which the steel member having a required sectional area is subjected to surface treatment by pickling, and thereafter electrostatic painting powder is uniformly scattered on the entire surface of the steel member; an unpainted portion forming step in which any unnecessary portion of the electrostatic painting powder on the steel member having a required sectional area is removed by means of a suction nozzle (3) moving under numerical control or by leaving an unpainted portion (4) on the steel member by masking, a baking step in which the remaining electrostatic painting powder (5) on the steel member having a required sectional area is baked by far infrared ray baking or near infrared ray baking, a further welding step by which a related steel plate is welded to said unpainted portion of the steel member so as to form an intermediate assembly block (9), and welding a plurality of the intermediate assembly blocks (9) together so as to form a major assembly block (10), subjecting the major assembly block (10) to secondary surface treatment (11) by pickling and thereafter performing secondary painting (12) on the major assembly block so as to form an integrated assembly block (13). The painting method for a ship hull block or the like, according to claim 2, in which the remaining electrostatic painting powder on the steel member having a required sectional area is baked by infrared ray baking in addition to the highfrequency baking.

Inventors: HIBI TERUMI, MATSUDA KENICHIRO, SHIBATA AKIO, HIBI, TERUMI, MATSUDA, KENICHIRO, SHIBATA, AKIO, Hibi, Terumi, c/o Mitsubishi Jukogyo K.K., Matsuda, Kenichiro, c/o Nagasaki Shipyard &amp; Mach., Shibata, Akio, c/o Nagasaki Res. &amp; Develop. Center
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1993
Main classification: B05D1
IPC codes: B23K9, B05D3, B05D7, B05D1, B63B9, B63B59