CA1177419A

CA1177419A - Method of producing container bodies and container bodies produced thereby

Info

Publication number: CA1177419A
Application number: CA000395851A
Authority: CA
Inventors: Edward P. Spencer; Gordon L. Peters
Original assignee: NATIONAL STEEL Corp
Current assignee: NATIONAL STEEL Corp
Priority date: 1981-02-11
Filing date: 1982-02-09
Publication date: 1984-11-06
Also published as: ES8304457A1; GB2108412B; WO1982002697A1; EP0070900A4; GB2108412A; IT8247771A0; ES509474A0; NL8220067A; EP0070900A1; AU8208782A; BR8206157A; JPS58500056A; DE3231643A1

Abstract

METHOD OF PRODUCING CONTAINER BODIES
AND CONTAINER BODIES PRODUCED THEREBY

ABSTRACT OF THE DISCLOSURE

Cylindrical container bodies, or cans, having welded sideseams are formed from sheet steel blanks having a thin coating of nickel, or a coating of nickel containing up to about 12 percent zinc, on each side.
The nickel coating extends completely to the edges of the blanks which are formed into a cylindrical configuration with the side edges slightly overlapping. The overlapped edges of the respective blanks are then welded, preferably by a wire mash welding process, to produce a welded seam having a thickness substantially less than twice -the thickness of the metal blank. Prior to welding, the nickel plated steel may be chemically treated in a dichromate or chromic acid solution, with the chemical treatment also extending completely to the edges to be welded. Power requirements for welding the material are substantially less than for tin plate.
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Description

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BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to a process for forming can bodies from -tinfree steel and more particularly to the high-speed sideseam welding of tlnfree steel to form can bodies, and to can bodies formed by the process.

Description of the Prior Art It is well known to form can bodies from sheet steel container stock by initially cutting the steel sheet - 10 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. Tin plate can be welded by such an operation without edge preparation and billions of welded sideseam cans have been produced from tin plate. 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 wel.ding.
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A number of high-s~eed seam welding bodymakers are available commercially for automatically shaping steel can body blanks in-to 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 approxi-mately 0.040 inches 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 tin plate container stock, there is a tendency for the tin to build up on the rolling electrode wheel surfaces and `. increase the resis-tance of the contact points leading eventually to unacceptable welding conditions.

Another commercially available high-speed side-seam 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 . . .

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coil so -that a clean electrode c;ontact surface is continuous-ly presented at the point of contact with the container stock. This continuously replaced electrode enables high-speed welding of tin plate, but again edge cleaning has been required for the welding of tinfree container stock.
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The overlap of the edges to be welded with currently available wire mash welders can be as small as 0.012 inches 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 sicleseam is compared with ~` a soldered sideseam of the type widely used in three-piece cans.

The inability of the commercial 19 available body-makers 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. Thls excess stripping presents problems _ a~ _ ~ '7~

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 the edye surface of container blanks for welding. Brochures and publications 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 attach-ments 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.

SUMMARY OF THE INVENTION
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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 withou-t re~uiring edge s-tripping of `

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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 reguired to form ~uch a seam utilizing ; tin-plated container stock.
, 10 - In the attainment of the foregolng.and other objects and advantages of the invention, an important feature resides in provlding a coating of nickel on each surface of a steel sheet such as blackplate having a thick-ness and temper suitable for use as contalner stock. The ` 15 nickel coating may contain up to about 12 percent zinc and may be as thin as about 1/2 microinch. A chemical treatment, for example a cathodic dichromate or chromic acit 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 un-lacquered along the edges which are to be joined by welding.

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The flat sheet steel ls cut into can bodv 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 ` 5 treated (but unlacqured) 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 substantially less than twice the thickness of the steel ?
,` ` sheet. The welded seam may be striped for anticorrosiveness~'` 10 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 utllizing conven-tional apparatus.

DESCRIPTION OF THE DRAWINGS
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The foregoing and other objects and advantages of the inventlon will be apparent from the detalled des-cription 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 . . . ~ , , : ; . . :
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in accordance with the present inventioni FIG. 3 is an enlarged schematic view showing the electrode positions emp~oyed in the apparatus of FIG. 2;

FIG. 4 is a further enlarged fragmentary sec-tional vlew showing the seam being weldedi and FIG. 5 is a fragmentary sectional view of a welded seam formed in accordance with -the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In its broadest aspects, the present invention involves the formation of a can body from tinfree steel contalner stoek 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 stoek in the form of thin sheet steel such as blackplate having a very thin coating of nickel plated on its surfaces.
The niekel may contain up to abou-t 12 percent zinc. The eontainer stoek is cut into blanks which are formed into a eylindrical configuration with the edges to be joined re-tained in overlapping relation with the nickel coated sur-. faces in direct contact. Pressure is applied by rolling ~` ; ' ```: ` :
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electrodes which supply the necessary energy to produce a high-strength fusion bond at the overlapping surfaces.

The container stoc,k employed in the present '' invention is illustrated in FIG, 1 and comprises a sheet ~ 5 lO of mild steel such as blackplate haviny a thickness '`~ suitable for use as container stock. The steel substrate lO has its outer surfaces coated with a layer 12 of nickel, '' which may contain up to about 12 percent zinc, by an electro-plating process. The nickel coating may be'very thin and preferably is within the.range of about 1/2 to 5 microinches in thickness. Thicker coatings can also be used, but generally are not considered economical, and excessively thick coatings may result in only the nickel coatings being welded or fused.

The zinc 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. l, which will form the side edges of-container blanks 17 to be joined by welding.

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Surprisin~ly, 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 determi~ed that substantially less welding current may be employed than is required for welding tin pla-te of the same thickness. Further, a good weld can be obtained while utilizing substantially less pressure on the electrodes than is normally required ~or wel~ing tin pla-te. 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 inven-tion;
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 .

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and then moved therealong through a welding station by ~`` suitable feed mechanism, not shown. The side edges of the blank 17 are brought toyether 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 respectively, 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 sur:Eace of the overlapped portion of the cylinder. Electrical energy is applied to the electrodes rom a suitable source indicated at 27, and pressure is simultaneously applied through the elec-trodes 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 circumfrentially 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 ~ha-t a solid fusion join-t . 25 is-formed. Pressure applied by the electrodes during the . ~ .

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fusion process substan-tially eliminates sharp edyes and burrs. Preferably, a narrow strip or oryanic coating material is applied to the welded seam and overlapping the ed~es of the lacquer coating 15 in a conventional manner.

Experiments conducted using nickel coated black-plate as described above show that 15 to 24 percent less welding curr~nt may be re~uired than is necessary to provide an equivalent weld joint utilizing ~ tin coated container stock formed from the same base steel material.
Further, pressures applied by the electrode wheels may be reduced by as much as 25 percent, 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 -~ 20 we do not intend to be restricted solely there-to, but ~:` rather that we do intend to include all embodiments thereof which would be appa;rent to one skilled in the art and which come within the spirit and scope of our invention.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of forming can bodies having a welded sideseam comprising, providing a base steel sheet of suitable thickness to be formed to can bodies, electrically plating a thin nickel coating to 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 0.5 to about 6.0 microinches.

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

6. The method defined in claim 1 wherein the electroplated nickel coating has a thickness within the range of about 0.5 to about 6.0 microinches.

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

8. The method defined in claim 1 wherein the electroplated nickel coating contains up to about 12 percent 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 nickel-plated 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 percent 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.