EP0070900A1

EP0070900A1 - Method of producing container bodies and container bodies produced thereby

Info

Publication number: EP0070900A1
Application number: EP82900895A
Authority: EP
Inventors: Edward P. Spencer; Gordon L. Peters
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1981-02-11
Filing date: 1982-02-11
Publication date: 1983-02-09
Also published as: ES8304457A1; CA1177419A; WO1982002697A1; EP0070900A4; DE3231643A1; GB2108412B; AU8208782A; ES509474A0; GB2108412A; IT8247771A0; NL8220067A; JPS58500056A; BR8206157A

Abstract

Des corps de conteneurs cylindriques, ou boites, ayant des joints lateraux soudees sont formes a partir de flans en tole d'acier (17) ayant un revetement fin (12) de nickel, ou un revetement de nickel contenant jusqu'a environ 12% de zinc, de chaque cote. Le revetement de nickel (12) s'etend completement jusqu'aux bords des flans (17) qui sont formes avec une configuration cylindrique, les bords lateraux se chevauchant legerement. Les bords de chevauchement des flans respectifs sont alors soudes, de preference par un procede de soudage continu avec un fil metallique pour produire un cordon de soudage (28) ayant une epaisseur sensiblement inferieure a deux fois l'epaisseur du flan metallique. Avant le soudage, l'acier plaque au nickel peut etre traite chimiquement dans une solution d'acide chromique ou de bichromate, le traitement chimique (14) s'etendant entierement jusqu'aux bords a souder. Les besoins en energie electrique pour souder le materiau sont sensiblement inferieurs a ceux utilises pour le fer blanc.Cylindrical container bodies, or boxes, having welded side seals are formed from sheet steel blanks (17) having a thin coating (12) of nickel, or a nickel coating containing up to about 12% zinc, on each side. The nickel coating (12) extends completely to the edges of the blanks (17) which are formed with a cylindrical configuration, the lateral edges slightly overlapping. The overlapping edges of the respective blanks are then welded, preferably by a continuous welding process with a metal wire to produce a weld bead (28) having a thickness substantially less than twice the thickness of the metal blank. Before welding, the nickel-plated steel can be chemically treated in a chromic acid or dichromate solution, the chemical treatment (14) extending entirely to the edges to be welded. The electrical energy requirements for welding the material are significantly lower than those used for tinplate.

Description

METHOD OF PRODUCING CONTAINER BODIES AND CONTAINER BODIES PRODUCED THEREBY

This invention relates to a process for forming can bodies from tinfree steel and more particularly to the high-speed sideseam welding of tinfree steel to form can bodies, and to can bodies formed by the process. It is well known to form can bodies from sheet steel container stock by initially cutting the steel sheet into generally rectangular blanks and then shaping the blanks into a cylindrical configuration with the side edges of the blanks in overlapping relation to be joined by resistance welding. Tinplate can be welded by such an operation without edge preparation and billions of welded sideseam cans have been produced from tinplate. However, due to the resistance of oxide coating normally present on tinfree steel and to the fact that the steel is very thin, it has generally not been considered possible to reliably sideseam weld can bodies from tinfree steel, including chrome-chrome oxide coated steel, in a high-speed commercial operation without first stripping any oxide or other coating from the edges to be joined by welding. A number of high-speed seam welding bodymakers are available commercially for automatically shaping steel can body blanks into cylindrical form and welding the sideseam. One such machine employs welding electrodes in the form of two opposed copper or copper alloy wheels, one inside and one outside the can body, for rolling along and welding the overlapped edges. An overlap of approximately 0.102 centimeters is required to form a seam in this apparatus. Successful use of the apparatus in the past to weld can bodies from tinfree steel has required the edge surfaces of the blanks to be cleaned by mechanical abrasion immediately prior to welding to insure uniform clean steel-to-steel contact of the overlapped edges at the welding station. When such apparatus is employed to weld tinplate container stock, there is a tendency for the tin to build up on the rolling electrode wheel surfaces and increase the resistance of the contact points leading eventually to unacceptable welding conditions.

Another commercially available high-speed sideseam welding bodymaker employs a so-called wire mash electrode wherein a formed copper wire is carried in a track or groove in the periphery of the electrode wheels. The copper wire is continuously replaced from a spool or coil so that a clean electrode contact surface is continuously presented at the point of contact with, the container stock. This continuously replaced electrode enables high-speed welding of tinplate, but again edge cleaning has been required for the welding of tinfree container stock. The overlap of the edges to be welded with currently available wire mash welders can be as small as

0.030 centimeters which, when welded, produces a sideseam which is only approximately 1.2 times the thickness of the original container stock. A welded seam of this thickness can readily be accommodated when the can end is double seamed onto the can body. Thus, the use of such bodymakers is highly advantageous when the sideseam is compared with a soldered sideseam of the type widely used in three-piece cans.

The inability of the commercially available bodymakers to successfully weld tinfree stock without the necessity of edge cleaning has greatly limited their use. Further, when the side edges of tinfree container stock are mechanically stripped to enable welding on such apparatus the side edges are necessarily cleaned or stripped over a width greater than that actually incorporated into the welded seam. This excess stripping presents problems both in appearance of the can and in the necessity of covering the stripped area by an organic strip for corrosion resistance both on the inner and outer surfaces of the can body. Examples of the difficulties encountered in sideseam welding of tinfree steel container stock may be found in U.S. Patent Nos. 2,305,655 and 2,326,814 each of which discloses a process for stripping in the edge surface of container blanks for welding. Brochures and publication of the bodymaking machine manufacturers also acknowledge the inability of the commercial apparatus to reliably weld tinfree steel without prior edge cleaning, and most such machine manufacturers have developed abrasion type attachments for their machines to adapt them for welding tinfree steel. Such edge cleaning apparatus removes oxide and other coatings which normally prevent the reliable welding of the extremely thin container stock in a continuous high-speed operation.

It is an object of the present invention to provide a method of forming a container body with a welded sideseam from tinfree steel container stock in a. high-speed automatic bodymaking apparatus without requiring edge stripping of the container blanks.

Another object of the invention is to provide an improved welded sideseam container formed from tinfree container stock. Another object of the invention is to provide a method of forming a welded sideseam in a container body which requires less energy and less electrode pressure than normally required to form such a seam utilizing tin-plated container stock. In the attainment of the foregoing and other objects and advantages of the invention, an important featu-e resides in providing a coating of nickel on each surface of a steel sheet such as blackplate having a thickness and temper suitable for use as container stock. The nickel coating may contain up to about 12% zinc and may be as thin as about 0.013 microns. A chemical treatment, for example a cathodic dichromate or chromic acid treatment, is preferably applied to the nickel-coated steel to increase its corrosion resistance and enhance lacquer adhesion characteristics. After chemical treatment, a coating of lacquer is preferably applied, leaving a narrow strip unlacquered along the edges which are to be joined by welding.

The flat sheet steel is cut into can body blanks which are formed into a cylindrical configuration with the side edges overlapping so that the nickel-plated. surfaces are in direct contact. The overlapping coated and treated (but unlacquered) surfaces are then welded by a high-speed sideseam welding bodymaker to produce a completed can body having a welded sideseam which has a thickness substantiall less than twice the thickness of the steel sheet. The welded seam may be striped for anticorrosiveness in the conventional manner, and can ends may be attached. to the completed cylindrical body utilizing a double seam operation in the conventional manner and utilizing conventional apparatus. The foregoing and other objects and advantages of the invention will be apparent .from the detailed description contained hereinbelow, taken in conjunction with the drawings, in which:

FIG. 1 is a fragmentary sectional view, on an enlarged scale, illustrating a coated steel sheet suitable for use in the present invention; FIG. 2 is a schematic illustration of a welded sideseam being formed on an automatic bodymaking machine in accordance with the present invention;

FIG. 3 is an enlarged schematic view showing the electrode positions employed in the apparatus of FIG. 2;

FIG. 4 is a further enlarged fragmentary sectional view showing the seam being welded; and

FIG. 5 is a fragmentary sectional view of a welded seam formed in accordance with the invention. In its broadest aspects, the present invention involves the formation of a can body from tinfree steel container stock in a high-speed sideseam welding bodymaker without requiring edge stripping or cleaning of the container stock. More specifically, the invention involves forming a sideseam welded, container body from steel container stock in the form of thin sheet steel such as blackplate having a very thin coating of nickel plated on its surfaces. The nickel may contain up to about 12% zinc. The container stock is cut into blanks which are formed into a cylindrical configuration with the edges to be joined retained in overlapping relation with the nickel-coated surfaces in direct contact. Pressure is applied by rolling electrodes which supply the necessary energy to produce a high-strength fusion bond at the overlapping surfaces. The container stock employed in the present invention is illustrated in FIG. 1 and comprises a sheet 10 of mild steel such as blackplate having a thickness suitable for use as container stock. The steel substrate 10 has its outer surfaces coated with a layer 12 of nickel, which may contain up to about 12% zinc, by an electroplating process. The nickel coating may be very thin and preferably is within the range of about 0.013 to 0.125 microns in thickness. Thicker coatings can also be used, but generally are not considered economical, and excessivel thick coatings may result in only the nickel coatings being welded or fused.

The nickel coating 12 preferably has a thin layer 14, of an anticorrosive chemical treating solution applied to its outer surface. Chemical layer 14 may be applied by subjecting the plated steel to a cathodic dichromate or chromic acid treatment in a manner conventional in treating chrome-plated, container stock. The treated, plated steel is then preferably coated with a layer 15 of a suitable can lacquer except for a narrow strip, indicated at 16 in FIG. 1, which will form the side edges of container blanks 17 to be joined by welding.

Surprisingly, the chemically treated nickel-plated steel can not only be welded without the necessity of stripping either the chromate chemical treatment or the nickel plating from the side edges, but it has been determined that substantially less welding current may be employed than is required for welding tinplate of the same thickness. Further, a good weld can be obtained while utilizing substantially less pressure on the electrodes than is normally required for welding tin plate. The very thin nickel coating and the oxide coating resulting from the chemical treatment are diffused in the joint and a strong fusion bond is produced.

Various commercial sideseam welding bodymakers may be employed in the practice of the present invention; however, the preferred apparatus utilizes the so-called wire mash technique. One such apparatus is the Super WIMA automatic bodymaker, manufactured by Soudronic AG, of Bergdietikon, Switzerland, and the operation of which is illustrated schematically in FIGS. 2-4. The nickel-coated container stock illustrated in FIG. 1 is initially cut into generally rectangular blanks of the appropriate size and supplied to the bodymaker to be processed automatically by the apparatus. The individual blanks 17 are formed into a cylindrical configuration around a hollow mandrel 18 and then moved therealong through a welding station by suitable feed mechanism, not shown. The side edges of the blank 17 are brought together in overlapping relation with the nickel-plated, chemically treated surfaces in direct contact as illustrated in FIG. 4. The overlapped edges are then fed between a pair of copper wire electrodes 20, 22 respecttively, supported within grooves on electrode wheels 24, 26 respectively. Electrode 22 and electrode wheel 26 are supported within the mandrel 18 and contact the inner surface of the formed cylinder while wire electrode 20 and electrode wheel 24 are positioned outside and contact the outer surface of the overlapped portion of the cylinder. Electrical energy is applied to the electrodes from a suitable source indicated at 27, and pressure is simultaneously applied through the electrodes to overlapped portions of the container blank to simultaneously heat and mash, or flatten the overlapped edges and form a flattened fused weld joint as illustrated at 28 in FIG. 5. The completed weld joint may be from about 1.2 to about 1.3 times the thickness of the coated container stock and the total length d, measured circumferentially of the formed can body, may be substantially less than twice the thickness t of the original container stock. Metallurgical analysis of weld joints thus formed show that a solid fusion joint is formed. Pressure applied by the electrodes during the fusion process substantially eliminates sharp edges and burrs. Preferably, a narrow strip of organic coating material is applied to the welded seam and overlapping the edges of the lacquer coating 15 in a conventional manner.

Experiments conducted using nickel-coated blackplate as described above show that 15% to 24% less welding current may be required than is necessary to provide an equivalent weld joint utilizing a tin coated container stock formed from the same base steel material. Further, pres sures applied by the electrode wheels may be reduced by as much as 25%, thereby substantially increasing the life expectancy of the electrode wheels. The reduced electrical current required for welding the nickel-plated stock not only enables a substantial energy saving, but also reduces spatter which can occur during forming of such welds.

While we have disclosed and described preferred embodiments of our invention, we wish it understood that we do not intend to be restricted solely thereto, but rather that we do intend to include all embodiments thereof which would be apparent to one skilled in the art and which come within the spirit and scope of our invention.

Claims

1. A method of forming can bodies having a welded sideseam comprising, providing a base steel sheet of suitable thickness to be formed into can bodies, electrically plating a thin nickel coating onto both surfaces of the base steel sheet, cutting the plated steel sheet into blanks of suitable size to form a can body, forming the blanks into a cylindrical configuration with two edges in parallel overlapping relation and with the opposing nickel-plated surfaces adjacent the overlapping edges being in contact with one another, and passing the overlapped edges between a pair of electrodes and simultaneously applying pressure and electrical current to the overlapped edges through the electrodes to fuse and flatten the nickel-plated overlapped edges.

2. The method as defined in claim 1 further comprising the step of treating the nickel-plated surfaces with a dichromate or chromic acid solution prior to the step of forming the blanks into a cylindrical configuration,

3. The method as defined in claim 2 further comprising the step of applying a lacquer coating to said plated and chemically treated surfaces while leaving a narrow strip adjacent said two edges lacquer-free.

4. The method as defined in claim 3 wherein the nickel coating has a thickness within the range of about 0.013 to about 0.125 microns.

5. The method defined in claim 4 wherein the electroplated nickel coating contains up to about 12% by weight of zinc.

6. The method defined in claim 1 wherein the electroplated nickel coating has a thickness within the range of about 0.013 to about 0.125 microns.

7. The method defined in claim 5 wherein said electroplated nickel coating contains up to about 12% by weight of zinc.

8. The method defined in claim 1 wherein the electroplated nickel coating contains up to about 12% by weight of zinc.

9. A cylindrical can body comprising a base steel sheet having a thin coating of nickel electroplated on both surfaces and a welded sideseam, the sideseam being formed by positioning opposing edge surfaces of the nickel-coated plate in parallel overlapping relation with the nickelplated surfaces in contact with one another and welded by simultaneously applying pressure and electric current to the overlapped edges to form a hermetically fused seam having a thickness substantially less than twice the thickness of the base steel sheet.

10. The can body defined in claim 9 wherein the nickel-plated base steel sheet further comprises a dichromate or chromic acid chemical treatment applied to the nickel-plated surfaces prior to being formed into the cylindrical configuration, the contacting chemically treated nickel-plated surfaces being fused into the weld seam.

11. The can body defined in claim 10 wherein the plated nickel coating includes up to about 12% by weight of zinc.

12. The can body defined in claim 11 further comprising a lacquer coating extending over the plated and chemically treated surfaces except in the area of said fused seam, and a layer of organic material covering said fused, seam and overlapping the adjacent portions of the lacquer coating.