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

-2- 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 appa¬

ratus. Successful use of the apparatus in the past to weld

can bodies from tinfree steel has required the edge sur¬

faces of the blanks to be cleaned by mechanical abrasion immediately prior to welding to insure uniform clean steei- 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 side- seam welding bodymaker employs a so-called wire mash elec¬

trode 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

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 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. 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 resis¬

tance 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. 2,305,6 ^* 55 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 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.

It is an object of the present invention to pro¬ vide a method of forming a container body with a welded

sideseam from tinfree steel container stock in a.high-speed automatic body a ing 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 fea- ture resides in providing a coating of nickel on each sur¬

face 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 pre¬ ferably applied to the nickel-coated steel to increase its corrosion resistance and enhance lacquer adhesion charac¬

teristics. After chemical treatment, a coating of lacquer is preferably applied, leaving a narrow strip unlacquere ^' d

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 opera¬

tion in the conventional manner and utilizing conventional apparatus.

T e foregoing and other objects and advantages of the invention will be apparent .from the detailed 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 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 contai¬ ner stock. More -specifically, the invention involves forming a sideseam welded, container body from steel con¬

tainer stock in the form of thin sheet steel such as black- plate 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 eleσtro- plating 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 deter- mined that substantially less welding current may be

employed than is required for weldin _^ iinplate 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 contac as illustrated in FIG. 4. The overlapped edges are then fe between a pair of copper wire electrodes 20, 22 respect- tively, 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 sur¬

face 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 simul¬ taneously applied through the electrodes to overlapped

portions of the container blank to simultaneously heat and mash, or flatten the overlapped edges and form .flattened fused weld joint as illustrated at 28 in FIG. 5. ^' The com¬ pleted 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 σircumferentially 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 pro- cess substantially eliminates sharp edges and burrs. Pre¬ ferably, 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 black- plate 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.