CA1058454A - Drawn and ironed containers and method of manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Drawn and ironed containers and method for manufacturing the same from metal stock having an organic resin applied to its surfaces are provided. The resin is retained on the metal surfaces during the drawing and ironing procedure, resists break down at points of high stress, functions to effect a lowered coefficient of friction and exhibits plastic flow under high stress during the forming operation and serves as a base coat on the formed container.

Description

BACKGROU~D O~ TIIE: INVENTION
Metal containers may be formed by any of various tech-niques including drawing and ironing, drawing or multiple draw techniques.
Drawn containers are manufactured by forcing a metal blank into a die while the blank is prevented from ~inkling by pressure exerted on a clamp plate. The clearance between the punch and die is such that the metal is not pinched or thinned, i.e. the drawing operation changes a flat blank into a hollow vessel with littie change in its thickness.
Drawn cups can be redrawn when taller cups are desired. A
typical operation would involve the steps of blanking and drawing metal into a shallow cup and feeding the cup into another die of smaller diameter to make it taller, these steps being repeated as desired. Through all of such s$eps although the metal has changed shape several times, the sidewall and bottom of the shells are essentially the same thickness as that of the original blank with a substantial reduction in the inside diameter of the cup.

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1 As use~ herein, ~he t~rnl "~lrawing" is used relative to the can-making industry and is ~efined as the forming of recessed parts by forming me~als in dies and refers to the operations wherein a peripheral rnargin of flat stock is turned inwardly and simultaneously smoothed by means of a punch and drawing die to form a cup having a wrinkle-free sidewall the thickness of which is neither substantially less than nor substantially greater than the thickness of the original blank.
In contrast to drawn cups including deep draw or multiple draw procedures, manufacture of containers by a drawing and ironing procedure forming a Cllp from a relatively thick sheet of metal and then reducing the thickness of the sidewall of the cup by pushing it on a cylindrical punch or mandrel through a series of ring-like ironing dies. Each of these ironing dies has a slightly smaller inside diameter than the preceding one in the series. The metal is squeezed or ironed between the punch and the ironing rings and is forced up the punch to form a tall cylindrical shell with walls - 20 - thinned or reduced substantially from the original thickness of the metal stock.
As used herein, 'tironing" will designate the forming of a thin walled wrinkle-free-cylindrical structure with sidewalls thinned from the original thickness without substantially reducing the inside diameter of the cup.
-~ Such drawing and ironing, procedures, hereafter referred to as D & I, are accompanied by several problems of manufac-ture usually associated with the high radial surface pressure exerted on the dies. Because of this pressure, it is necessary to use materials of very high strength and having a high ~o5a~54 modulus of elasticit~ for the production of the dies and tooling.
The high radial sur~ace pressure also results in a considerable frictional force between the body of the container and the ironing dies, necessitating that provision be made for a lowered coefficient of friction. This has generally been accomplished by providing a polished die surface together with intensive lubrication using oily, greasy lubricants together with intensive cooling of the dies and/or punch. Chemical roughening and mechanical roughening have also been proposed methods to deform the workpiece surfaces so that lubricant can be retained to aid in lubrication.
The workpiece itself may be steel, aluminum, tinplate, etc. and the manufacturing process may involve either blank-fed or cup-fed ironing depending on the metal. With tinplate, for example, it is possible to form a D & I container shell directly from a flat blank of metal from a single stroke of a punch. In this procedure, circular blanks are cut from lubricated coil or sheet and fed directly into an ironing press. The first die in ` the press forms a cup around the punch and irons the cup wall slightly. The punch then continues down through a series of dies which thin the sidewall to its final thickness. Such a procedure is possible with tinplate because of the great strength and drawability of steel. However, because of the high tensile and yield strength, variations in sheet thickness and lower ductility of steel, many problems are associated with the extreme mechanical deformation encountered during D & I procedures involving this metal, particularly extensiVe galling and die wear due to metal-to-metal contact, unless tin is present on the surface.

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1 Most aluminum contaitlers are made by a cup-fed procedure which involves a separate cupping press for for~ning a cup.
The cup-fed ironer has a die stack similar to that employed for the blank-fed process except that it is preferably turned 90 degrees so tha~ the punch moves in a horizontal plane and gravity can be used to assist cup-feeding. Cups are generally relubricated after forming and prior to ironing.
Aside from the different feed mechanisms dictated by the particular metal, there are problems met in providing D
& I containers which, although comrnon in many respects, have been different in specific ways that relate to the specific metal. It is customary to change the ironing dies, coatings, decorating, bake temperat~lres, etc. to accomodate the proper-ties of the metals. With any of the metals however, pro-vision of lowered frictional forces during the operation has been a major problem. Oily, greasy lubricants, though effective, have been less than ideal since they ~ust be removed and add to the expense of the operation. Because of low viscosity, such films breakdown at localized, highly stressed points resulting in a chain reaction of galling of both tools and product.
Various organic coatings have been used in drawing, multiple draw or deep draw operations wherein blanks are precoated with various substances and then formed. U.S.
Patent 3,206,848 to K. R. Rentrneester issued September 21, - 1965 and commonly assigned herewith, proposes deep drawn containers produced from metal stock precoated with organic coatings by a method of essentially baking the coating, - drawing the metal, rebaking the coating, redrawing the metal, etc. Attempts to utili~e similar and other prior ... . .

procedures utilizing ~reco~ted stock ~n a D & ~ operation have not been success~ul particularl~ because of the extreme stxesses imposed on the coating during the ironing operation, the buildup of heat in the apparatus which often leads to the thermal break-down of the coating and the frictional forces exerted which tend to exfoliate the coating.
In U.S. Patent 3,577,753 to Shah, it has been proposed that dry film lubricants precoated on metal stock could be utilized in a D & I procedure by modifying the apparatus employed to provide an internally fluid-cooled punch while circulating cool air over the dies and metal blanks. In such an apparatus, the surface temperature of the blank, punch and dies is maintained at 50F or below to avoid decomposition of the lubricant. Such method and apparatus is obviously not the solution to the major and diverse problems encountered in the drawing and ironing of precoated metal stock, particularly since it introduces the need to circulate cold fluid with attendant means for circulating and - cooling the fluid, adding to the expense of the procedure.
Additionally, it introduces the need for constant monitoring to assure that the temperature of either the punch, die or workpiece does not exceed 50F to prevent decomposition of the film lubricant.
A method of forming D & I containers from precoated metal stock, suitable for application to steel or aluminum, employable in either a sheet or cup-fed process, would be a highly desired and much needed tool in the can-making industry. It is to this need that this invention is directed.
It is a primary object of this invention to provide a method of forming coated thin-walled cup-shaped metal containers of the drawn and ironed t~pe fro~ precoated metal stock.

lOS~3454 ~ nothe~ ob~ect ~s to provide ~ ~eth~d ~oX drawin~ and i~oning a seamless container fro~ ~etal stock havin~ an organic resin applied thereto.
Another object is to provide a method whereby an organic resin is applied to metal sheet and is retained on the metal during and after the metal is subjected to a drawing and ironing operation.
Another object of the invention is to provide an organic resin film, bonded to the metal, having suitable viscoelastic properties to permit plastic flow of the resin at the stress levels necessary to cause plastic flow in the metal.
Another objec_ of the invention is to provide a method, applicable to steel and aluminum, of forming a coated seamless - container from metal having an organic resin applied thereto without substantial exfoliation or decomposition of the resin film during drawing and ironin~.
It is another object of this invention to provide a method for forming a drawn and ironed container from metal stock having an organic resin film on its surfaces wherein it is ~-- 20 possible to eliminate or substantially reduce subsequent manufacturing steps.
These and other objects and advantages of the invention will be apparent as the~ are better understood from the following description which, when taken in connection with the accompanying drawings, discloses a preferred embodiment hereof.
DESCRIP$ION OF $HE DR~WINGS

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Referring to the Drawings:

Figure 1 is a schematic sectional view of a D ~ I die 3~ ;

1058~54 stack, showing the workpiece~ cup ~ed, in the various stages of progression through the dies, Figure 2 is a schematic sectional view of a D & I die stack showing the workpiece, blank fed, in the various stages of progression through the dies.
Figure 3 is a perspective view of a formed container of the invention with bottom profiling, after necking-in and flang-ing, with an organic resin applied thereto.
Figure 4 is a graph showing the relationship between cure temperature and ironing forces exerted as determined by a screening procedure when forming metal stock carrying an organic resin according to the invention.
Figure 5 is a graph showing the relationship between the cure temperature and stripping ~orce required with metal stock carrying an organic resin according to the invention as deter-mined by the screening procedure.
Detailed Description of the Inve-ntion .. ..
The method of forming D & I containers according to the invention broadly comprises the steps of: a) applying an organic resin to the surfaces of flat metal sheet; b) subjecting said sheet carrying said resin to an elevated temperature for a period of time sufficient to effect adhesion to the metal and a partial curing of said resin; c) forming a workpiece from said organic resin-carrying metal sheet; d) forcing said workpiece through a series of drawing and ironin~ dies on a punch to form an elongated cylindrical article, the sidewalls o~ which are substantiall~ reduced in thickness, and e) removing said article from said punch; said resin being cured in step b~ to the extent that it is retained on said metal surfaces, is capable of effecting a lowered coefficient of ~
friction, and exhibits plastic flow with respect to the metal and tooling at high stress levels during steps c), d) and e).
More specifically, an organic resin is applied to metal sheet, which may be steel, including blackplate, tinplate or other chemically treated steel, aluminum including alodine treat-ed aluminum; after which the resin~carrying metal sheet issubjected to an elevated temperature, for example by baking in an oven, for a time sufficient to effect curing of the resin to the extent that it is capable of functioning as a film lubricant, - e.g., it effects a lowered coefficient of friction between the workpiece and the ironing dies under loading up to about 500F.
Because of the resin's viscoelastic properties, it prevents metal-to-metal contact at surface asperities while the workpiece-is forced through a series of drawing and ironing dies. Prefer--; ably, the resin is cured to the extent that it is capable of exhibiting the following characteristics during the drawings and ironing steps:
1) it will require exertion of an ironing force of less than about 10,000 pounds and a stripping force of less than about 1200 pounds as determined by a screening technique set ; forth later hereinbelow:

2) it will exhibit good elongation, compression and plastic flow under loading at temperatures up to about 500F;

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3) it exhibits ~alle~bilit~ with good adhesion to metal stock without adhesion to tooling;

4) it will be abrasion resistant;

5) it will be capable of reflow at temperatures up to about 500F;

6) it will be capable of maintaining adhesion to the substrate as it is drawn and ironed without severe exfoliation;

7) it will be capable of being cleaned, topcoated and rebaked without decomposition or loss of adhesion;

8) it will prevent rust or corrosion of formed contain-ers during storage prior to subsequent operations such as decoration or topcoat spraying;

9) it will not impart off-flavor or odor to products packed in the container and will act as a barrier to metal ion dissolution of the container metal into the product; and

10) it will be capable of withstanding subsequent metal forming operations such as bottom doming and top necking-in ~nd flanging.
The stripping and ironing forces recited herein are those obtained on a cup-fed Stolle bodymaker, Model No. HX50-20, Serial No. 561190-2, (Stolle Corp,, Sidney, Ohio) for a 211 diameter can with a five die stack. Strain gauges on the ironing ram were employed to determine peak ironing force by measuring the compressive loading of the ram during ironing and the nega-tive compressive forces, i.e. elongation, as the ram withdraws and the formed shell is stripped therefrom. While the forces recited have been found to be reasonably consistent when employing various types of bodymakers, to the extent that it is possible that these values may vary "

utilizing different apparatus, tooling, etc., they are ~iewed as a screening techni~ue for evaluating cure conditions and the ability of specific resins to function in the D & I process and are given for purposes of illustration only. Curing of the coating to the extent that it is capable of exhibiting plastic flow with respect to the metal and tooling at high stress levels, of lowering the coefficient of friction during the forming operation and of being retained on the workpiece surfaces is the essential criterion for reasons discussed further hereinbelow.
The resins utilized herein may be any thermoplastic or thermosetting resin capable of exhibiting the characteristics above defined. A varied and diverse selection of resins is possible ïncIudingresins selected from the classes ofepox~-phenolic, epoxy-urea formaldehyde,uinyl organosol, and solution vinyls.
The applicability of these resins in a D & I procedure is surprising and unexpected due to their diversity in type and particularly since attempts to utilize other types of resins have resulted in exfoliation and/or total removal of the resin or in the resin becoming liquid and exhibiting "run-off" with little or no effect, resulting in galling, die wear, tensile failure and "earing" of the workpiece during forming. While the exact phys-ical and/or chemical phenomena that are responsible for the results obtained are not known~ one very important function of - the bonded resin is believed to be in its behaviour as a film lubricant, i.e., as a "plastic solid" material interposed between ; the workpiece metal and the tooling which serves to lower the coefficient of friction .

; 30 1(~584S4 permitting a lower punch force ~nd lower stress levels in the container wall. However, many failures in the drawing and ironing process are triggered by "stress risers"~ i.e.~ highly localized points of weakness caused by metal flaws or metal to metal contact between the workpiece and tooling which are not ` necessarily eliminated by placement of a lubricant to lower the coefficient of friction between the workpiece and tooling. For example, the metal exhibits plastic flow in the dies at a stress level beyond the yield point defining the onset of plastic flow in the metal. At that stress level, a localized breakdown of the film or films separating surface asperities on the workpiece and tooling could lead to a stress riser for any of the following reasons: metal to metal contact causing a "stick-slip" dis-ruption of plastic flow; metal to metal contact causing spalling of surface asperities generating particulate abrasive material to damage films, workpiece walls and tooling; welding of foreign particles to previously smooth tooling surfaces; and/or localized heat generation sufficient to change the properties of the films or metals involved.
It is believed that the resin films of this invention, in addition to lowering the coefficient of friction, also tend to distribute high stresses due to surface irregularities over a wider area through the plastic flow of the film which is control-led by the stress state present as the container passes through the different operations of the D & I process. In contrast to Newtonian fluids such as water~ oils, etc., which show a direct proportionality between stress and shearing velocity whereby in-ternal slippage will occur in the film at any stress level, the plastic films of the invention a~pe~ to xes~st flo~ until a certain yield shearing stress is imposed, This yield stress is construed as the stress that must be exceeded before the cured~
bonded film begins to flow. The distinction is believed to be a significant one, since the resin film at a high stress level will be capable of functioning as a high viscosity "filler" thereby minimizing the effect of surface irregularities and resisting breakdown, yet below that stress level, resists flow and serves--as a film lubricant, characteristics that Newtonian fluids can not exhibit. Moreover, since in the D & I process, radial compressive stresses imposed by the tooling are transmitted to the metal through whatever resin or lubricant films are present, it is essential, if the effect of the film is to be maintained throughout the process, that the plastic flow characteristics of the resin be compatible with the flow characteristics of the metal and that the film permit the development of higher stress levels without film failure. The D & I process involves at least four -distinctly different operations, namely: blanking or cupping, redrawing, ironing and stripping; the film re~uirements beiny different for each operatîon because of variations in stresses inherent to each. The processr increases the surface area of the metal so that elongation characteristics of the film are important if a major portion is to remain bonded to the metal surface.
Additionall~, localized compression of the film, which may affect film adhesion even more than elongation, is necessarily present in the cupping and redraw operations with the effect being most pronounced at the open end of the shell where the metal has moved through the greatest radial displacement from the flat blank cutedge. It has been found that the shearing stress history of the film ~0584S4 varies with location depending upon which of the four operations and which portion of the container wall is under consideration.
The requirements therefoxe for a film applied on flat metal which will be functional in all the operations are much more stringent than those for any one of the operations alone.
The resin films of the present invention are believed to satisfactorily combine the necessar~ viscoelastic properties including suitable contraction, elongationi the ability to effect a lowered coefficient of friction as well as the ability to resist plastic flow until a yield stress is imposed after which the resin flows distributing and minimizing the stresses during the process.
Measuremen~ of the punch force required to move the work-piece through the diestack is used to show apparent changes in the coefficient of friction due to the presence of the resin film on the metal surfaces by the screening technique discussed hereinabove and provides significant information from a few samples for evaluating resins.
The successful operation of the resin types above enumerated and the characteristics exhibited are believed to be a function of the degree of curing to which the resin is sub-- jected prior to forming. It has been found that there is a direct relationship between the extent of cure in terms of temp-erature and time and the characteristics exhibited by the resin as well as the forces that are exerted during the forming steps.
It has been found, for example with the epoxy-phenolics, that short high bakes, for example 400-425F for 5 seconds are equal to a bake of six minutes at 300F in terms of the ironing and stripping forces exerted during the operation. High bakes for longer times, e.~. 400-425~ for six minutes~ result in considerably higher forces that lead to det~imental results in the pxocedure It has been found, maintainin~ the time, apparatust i.e. punch and dies, metal, resin weight and resin as constants, that;
1) as the bake temperature increases, the ironing forces generated during forming increases. During ironing, the resin film is su~jected to hi~h radial stresses inside the die stack.
~lastic flow of the resin during this stage is believed to be beneficial and a function of the high stress level.
2) as the bake temperature increases, the stripping force decreases. The stripping action takes place outside the diestack and in this state, the stress level is a function of the strength of the can wall. Here, sprin~back and resistance to plastic flow are beneficial in resisting drag caused by surface asperities on the punch; and 3) as the bake temperature increases, the integrity of the film on the formed container becomes less than optimum.
The different curing temperatures appear to influence the film properties necessary for successful functioning herein.
A high baking temperature for a period of time sufficient to ~0 fully cure the resin leads to a harder, more brittle film having flow properties that are other than characterized above and such a hard or brittle film may lead to a scraping action in the tooling which removes portions of the film from the metal~surface and requires a higher punch force to move the workpiece often with galling and exfoliation of the film.
Graphical representation of these relationships may be seen in Fi~ures 4 and 5 which were taken employing CMQ (Can Makin~
Quality) steel precoated with an epoxy~phenolic resin and baked for six minutes at the temperatures illustrated.
- 30 The optimum conditions herein are thus those wherein the resin ..

is cured to the extent that it i~ non tacky, capable of effecting a lowered coefficient of friction~ exhibiting plastic flow, and resisting breakdown at point of high stress during the D & I
forming steps. Preferably, the resin is also cured to the extent that it does not generate ironing forces substantially in excess of 10,000 pounds nor stripping forces substantially great-er than 1200 pounds when employing the screening technique dis-closed hereinabove.
Optimum and preferred conditions for the classes of resins listed above have been found to be a cure of about 270 -380F for about 6 to 8 minutes at a weight of about 5 to 30 milligrams.
~ hile full curing of the resin is undesirable in the process, under curing of the resin is likewise unsatisfactory.
When tacky, the resin film sticks to tooling and stripping forces are so high as to prevent successful practice of the process.
For example, with an epoxy-phenolic resin applied as a coating and baked for six minutes at 240F, the resin fails by sticking in the cupping press and requires a stripping force that is undesirable. Partial curing of the resin is indicated to be essential and such curing must be sufficient to prevent tack, to permit stripping and also to permit the resin to exhibit the viscoelastic properties and plastic flow necessary for its successful function during the forming steps.
Epoxy-phenolic resins suitable for use herein include ~ reaction products of the classic epoxy resin obtained by reaction - of epichlorohydrin and bisphenol A, known in the art as digly-cidyl ethers of ~,:

bisphenol A, also re~er~ed to in the art as P~EBA resins, and other resins of this type derived ~rom reaction o~ polyhydric phenols and epihalohydrins with phenol-formaldehyde type resins.
Preferred DGEBA reactants are diglycidyl ethers of bisphenol A
having average molecular weiyhts of from about 1,000 to about 4,000 and epoxide equivalents of about 425 to about 6,000. In addition to the DGEBA resins, a variety of other epoxides may be employed including epoxidized novolacs. The phenolic component of the reaction product may be methylol phenyl ethers in which the H of the hydroxyl grou attached to the phenyl group is substituted by an alkyl, alkenyl or cycloalkyl group, or by an aralkyl or aralkenyl group, as well as the halogenated derivatives thereof. These resins are A-stage methylol-phenol resins, i.e., soluble and fusible, and are disclosed and described in U.S.
Patent 2,579,330. The preferred resin from this class is 1-allyloxy 2,4-trimethylol benzene. A preferred epoxy-phenolic resin, which also constitutes the preferred class of resin, preferably employed with suitable solvents, catalysts, etc., may be illustrated by a formulation comprising about 50 to 90~, preferably 70% Epon 1007! a DGEBA type epoxy resin having an epox~ equivalent weight of about 2000-2500, about 5-50%, pre-ferably about 25% 1-allyloxy-2,4,6-trimethylolbenzene and about 1 to 8%, preferably 4%, polyvinyl butyral.
Epoxy urea formaldehydes are epoxyamino resins, derived by reaction of epoxy ethers such as DGEBA having an aver-age molecular weight of about 900 to 4000, with the product of condensation of urea and formaldehyde in relative proportions varying from about 95 to S0 parts epoxide to about 5 to 50 parts urea-formaldehyde. Such resins likewise will have average molecular wei~hts rangin~ ~rom about 1~000 to 4~000 and epoxide equivalents of about 425 to about 6~000. A preferred resin, preferabl~ applied as a coating, may be illustrated by a mixture 1~5~454 of DER667, a DGEBA e~oxy resin ha~ing an epoxy equivalent weight of 1,600-2,000, and Plaskon (a trademark~ 3300~ a urea-formal-dehyde resin.
Vinyl orqanosols are well known compositions comprising polyvinyl chloride resins of relatively high molecular weight, usually at least about 15,000, which resins are relatively insoluble in the usual solvents and are designed to be dispersed in the liquid ingredients of the organosol. The high molecular weight resins are in a finely divided state, generally of a particle size of less than 5 microns. "Vinyl organosol" as employed herein indicates dispersions of particles of vinyl chloride resins including not only the homopolymer but also copolymers of vinyl chloride with a vinyl carboxylate including vinyl acetate, vinyl butyrate, etc., usually containing at least 50% vinyl chloride in the vinyl copolymer structure. Dispersants include oxygen-containing polar solvents including ketones, e.g.
diisobutyl ketone, isophorone; ether alcohols, e.g. 2-butoxy ethanol; other glycol ethers, e.g. diethylene glycol monobutyl ether; esters, e.g. ethyl acetate as well as hydrocarbons, e.g.
benzene, toluene and mixtures thereof. Also suitable as adhesion promoting solution resins are other resins including epoxy resins, melamines, acrylic acid resins, phenol formaldehydes, etc. A
preferred composition containing this resin type may be illustrated by a dispersion comprising about 80% polyvinyl chloride with a 20% solution resin mixture comprising epoxy, acrylic and urea-formaldehyde resins.
Solution vinyls are also a well known class of resin compositions and include vinyl chloride polymers, t~e homopolymer as well as copolymers of vinyl chloride with vinyl acetate or other vinyl carboxylates, dissolved in suitable solvents includ-ing those mentioned above used as dispersants for the organosols and particularly ketones such as methyl ethyl ketone, hydrocar-~058454 bons such as benzene~ toluene~ and mixtures of such solvents.Additionally, the vinyl resins, whlch are of low molecular weight, usually below about 15,000, may be dissolved in or contain other resins in the solution including epoxides, melamine, phenol~formaldehydes, etc. A preferred composition containing this resin type may be illustrated by vinyl chloride-vinyl acetate copolymer containing about 1~ maleic anhydride.
The organic resins identified above may be formulated in suitable solvents or dispersants with pigments and/or fillers and/or internal lubricants, as desired, by means well known in the art. The particular additives, whether solvents or disper-sants, etc., are not especially critical. It is necessary, how-ever, that the solvents or dispersants be volatile at the baking temperatures indicated and that they be compatible with all ingredients of the composition in their useful concentration.

The above classes of organic resins appear to be unique in their ability to meet the criteria above discussed.

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lOS8454 Attempts to utilize other t~pes of resins includin~ phenolics~
polybutadiene~ oleoreslnous~ acr~lic~ ! ultxa-~iolet (U.~ cured pol~esters and others were not successful, in the absence o~ at least one of the epoxy-phenolic, vinyl organosols, etc. listed above, these other resins bein~ ineffective to lower the coefficient of friction and exhibit suitable viscoelastic properties at ~raduated bake temperatures between 200F to about 500F, and in most cases were unable to withstand the forces generated in the initial cup forming step. None of these other resins were satisfactory for forming the ironed shell.
The fullowing examples will serve to further illustrate the invention.
Example 1:
With reference to Figures 1 and 2, which are schematics of a D & I die stack showing the workpiece, cup and blank, respectively, as it progresses through the steps of the process, - CMQ steel is coated on both sides with an epoxy phenolic resin composition at a coating weight of about 10 mg./4 in. and cured by baking in an oven at 300F for about 6 minutes. After drying, a 2.610 in. diameter x 0.0113 in. thick x 2.250 in. in height cup or a 5.694 in. x .0145 in. to .0150 in. thick blank was placed over the respective die assembly, schematically illus-trated, in either a cup-fed Stolle or Standun B-l bodymaker ;(Standun, Inc., Compton, California), or a blank-fed XBB press ~-~(American Can Company). Coolant comprising an emulsion of 95%
water and 5% commercially available mineral oil, Prosol (a trade-m~rk, Mobil Oil Company), circulates through the die assembly, and contacts the workpiece. In the cup~fed procedure, a punch then forces the cup through the ironin~ dies, which progressively result in drawin~ the cup into a shallow . . .

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seamless cu~ hav~ng ~ sidewall thickness o~ 0.0102 inch in the first die and 0.0062 inch in the second die. As the punch continues to force the metal workpiece through the die assembly~
the sh~llow cup is elongated and the side walls are ironed through passage through the ironing dies to a final elongated, thin-walled 5 inch container, having a sidewall thickness of about 0.0038 inch and a bottom wall thickness of 0.0113 inch which corresponds to the thickness of th~ ori~inal blank, that is subsequently removed from the ironing punch by a stripping operation. In the blank-fed procedure, the blank is forced through the drawing and ironing dies which result in a shallow seamless cup having a sidewall thickness of 0.0125 inch in the first die, 0.0108 inch in the second die, and 0.0055 inch in the third die, resulting in a final elongated, thin-walled 5 inch container having a sidewall thickness of 0.0055 inch and a bottom wall thickness of about 0.0145 inch. Ironing forces exerted during the procedures were as indicated in Figure 4, about 8,000 pounds, and stripping forces (Figure 5) were about 950 pounds.
The container, with bottom profile imparted, is now ready for subsequent treatment as desired, including washing, decorating, coating, necking~in and flanging to produce a container, for example, as illustrated in Figure 3. In the preferred embodiment, the desired bottom profile is also formed by the ironing punch. It is to be understood, however, that - while this example and the schematics employ a three-die stack, the number of dies may be varied as desired to produce the container.
The above example has been run on a 2400 can lot and has been found to be remarkably free from failures.

~ hen the above example was ~epeated with blackplate, but omitting application of the resin, only 1 out of 12 cans could be run successfully because of broken cans due to galling.
When the example was repeated with epox~-phenolic-coated tinplate on either a cup-fed or blank-fed Stolle bodymaker, with either matte or bright tinplate, the results were substantially the same as those achieved with precoated steel.
The most striking effect of the resin film may be seen in the attempts to draw and iron uncoated, unplated steel.
Drawing and ironing of this material with various and extensive oily type lubricants has resulted in a frequency of ironing failures triggered by localized breakdown of the lubricant that is intolerable for an efficient, economical high-speed commercial process. Locali~ed failure of lubricants has caused galling which leads to rapid and progressive deterioration of tooling and workpieces. For example, for 211 x 413 drawn and ironed cans - with similar steel, tooling and lubricants, only 2 cans out of a 24-can lot could be run successfully, corresponding to a 92% wall failure, while with precoated steel according to the invention, 20 only 1 wall failure was experienced with 3,200 cans run, corresponding to a wall failure rate of 0.031~.
Examples 2 to 10:
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The procedure of Example 1 was repeated using the Stolle bodymaker and a cup-fed procedure employing the .' ~: '.

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epoxy-phenolic resin ~f Exa~ple 1 as the inside coating and various organic resins as outside coatin~s. Bake tem~eratures, time and resin weights were varied as indicated, and the outside coating evaluated for integrity. The results were as obtained in the Table which follows;

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O ~ ~al O :~ Z o 1l1 5 ~ g ~ ~ _ ~ 4 . ___ ~
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tq~ U s~ ~:1 ~JO U~ ~1 ~ O a? '1 ~ rl O ~ U~
rI ~ k I ~ ~ ~ h ~ 111 ~ ~ ~ p ~0 ~ ~ O ~ ~ ~ O
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u~ 1 u~ ~ ~ ~ ~ u~
~ p O ~ al rl P~ ~~ E~
14 ~ e = ~ ~ 4~ 1 ~ o . ~
o 0 ~ O 0 ~ ~ q~0 ~ ) O -I
Ou~ 1; 6 U~ O ~ )~ 0 U O uq e ~
o o ~ ~ o ~ 0 ~ ~ O 0 o ~ ~ ~ 0 P C~ ~ C,) P~_ D Z ~-1 u~ U ~ ~ 4~ 3 O 1~; 3 .Y~ ~
s~ a0)~
a~ a) Ll 0_1 e ~ ~ a~

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P P o P~ o ~
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1058~54 In the table, the results ~re reported indicate the following: (a) "Unsatisfactory on Cup" indicates the resin was ineffective to withstand the forces ~enerated in the first drawing die, resulting in earing, galling and poor integrity where sufficient coating remains to evaluate this property. (b) "Un-satisfactory on Shell" indicates the resin was effective through the first drawing die but ineffective to withstand the forces generated in the first ironing die. (c) "No cup" indicates that metal containing the resin could not be formed into a cup in the first die.
Example 9:
The procedure of Example 1 was repeated except that blanks were cut from sheet coated with a solution vinyl resin at 10 mgs~/4 in , cured at 340F for six minutes and utilized in a blank-fed procedure on an XBB bodymaker. Results were substan-tially the same as achieved in Example 1.
Example 10:
The procedure of Example 1 was repeated except that a blank-fed procedure was employed using the XBB bodymaker and an epoxy-urea Pormaldehyde resin was applied at 12 mgs./4 in. and cured for 6 minutes at 400~F. Results were substantially the same as achieved in Example 1.
Example 11:
The procedure ofExample 1 was repeated except that a blank-fed procedure was employed using the XBB bodymaker. In this run, the outside of the metal sheet was coated with a vinyl organosol at 30 mgs./4 in and cured at 380F for 6 minutes, after which the inside was coated with an epoxy-phenolic ~t 15 mgs/4 in. and cured for six minutes at 300~F. The results were substantially the same as obtained in Example 1.
Example 12:

Example 1 was repeated except that aluminum was the .

1~)5845~
metal e~ployed, the procedure was cup-fed, and a Standun B-l body-maker was the apparatus used After drying the epoxy-phenolic coating, a 5.280 inch diameter x 0.0145 inch thick aluminum blank, with dioctyl sebacate as the lubricant, was fed to a cupping die to form a 3.50 inch diameter x 1.188 inch in height seamless cup. Cups were run on the Standun B-1 bodymaker using a 4 die stack with the coolant of Example 1, resulting in a 5 inch seamless cup having a sidewall thickness of 0.005 inch and a bottom wall thickness of 0.0145 inch. Forces exerted in the Stolle screening technique were substantially less than those in Example 1.
It will be apparent from these experiments that the classes of resins suitable for use herein are unique. It will be - obvious also from Example S, which employs an epoxy resin cured by U.V. lamps and yet was unsatisfactory, that the degree of curing is a critical feature in this invention.
Variations in the procedure above described may be practiced as desired. ~or example, combinations of the resins may be employed. In a preferred embodiment, the side of the blank that is to form the inside of the container is coated with epoxy-phenolic resin while the outside surface is coated with a vinyl organosol. Additionally, the same resin may be applied at dif-ferent weights; for example, a polyvinyl chloride organosol may be applied at 30 mgs on the outside and 8 mgs on the inside, both with a 380~ bake.
Various lubricants known in the art may be employed to aid in lowering the coefficient of friction between the workpiece and the apparatus, if desired. It will be understood, however, that such auxiliary lubricants, whether external or internal, ; 30 are optional and are not necessary, since it is a ~eature of this invention that the organic resin functions effectively for this purpose in the absence of additional compounds. AuxiIlary lubri-cants suitable for use herein may include any of conventional compounds, as long as such compound does not soften or tackify the resin film applied to the metal or otherwise affect its flow properties during the process. Examples of suitable external lubricants include dioctyl sebacate, dibutyl sebacate, mineral oil, acetylated tributyl citrate, deionized water, Prosol, ete.
Dioctyl sebacate, acetylated tributyl citrate and/or water are especially preferred as the auxiliary external lubricant herein, since it has been found that use of such compounds is effective to eliminate or at least simplify subsequent washing steps. For example, the containers may be cleansed merely by baking in an oven at a temperature sufficient to remove the dioctyl sebacate, when dioctyl sebacate is the auxiliary lubricant, without the necessity for further washin~.
Examples of suitable internal lubricants include amide type waxes, e.g. ethylene bis stearamide; alkyl aryl siloxanes; -~
ester type lubricants, e.g. dioctyl sebacate, acetylated tributyl ~ ~ -; citrate, tallow; glyeol fatty acid esters; hydrocarbon type lubricants, e.g., mineral oil, higher molecular weight waxes;
lanolin, spermaceti, polyolefin based lubricants, polytetrafluoro-ethylene lubricants, etc.
When sueh auxiliary lubrieants, either internal or - external, are employed, they may be used in proportions ranging from 1 to 15% by weight of the dry film.
Example 13:
. .
Example 1 was repeated employing a horizontal wall ironer - HWI (Ameriean Can Company), using a tin-free CMQ steel cup, the coating of Example 1 having been applied and baked prior to forming the cup, and the cup having been washed to remove any residual oil whieh might be present from the eupping press.
Normal eoolant (95% water and 5~ Prosol) employed in Example 1 was eompletely removed from the HWIand the system was ~ 058454 flushed with water. The system, withoùt the use of any lubricant or coolant whatsoever, was then employed to form several D 6 I
containers as in Example 1. The resin film had good integrity both lnside and outside the ironed shell, and was satisfactory through all of the ironing dies. There were no unusual effects noted during this experiment run without coolant or auxiliary lubricant, although an extensive run without coolant would be expected to generate excessive heat after an extended period. The experiment is indicative, however, of the uniqueness and special properties of the resin film and its ability to effect a lowered coefficient of friction, resist breakdown at localized points of high stress, and exhibit plastic flow during the D ~ I process, and also of its ability to withstand the effects of ironing and stripping forces generated without decomposition and exfoliation.
The present invention provides a ready means for simplifying the conventional steps involved in manufacture of a D & I container. These steps, afterforming, normally involve trimming, washing, decorating, interior coating, necking, flanging : `
and palletizing.
Throu~hout thc hcretofore convcntional mctal-forming and trimming operations, for example, the container shell is -~ normally covered by a film of oily lubricant which must be removed prior to decorating by cleaning, usually with heated aqueous detergent sprays. In a typical washer, cans are con-veyed through a series of cleaning and treating zones. After cleaning, the surfaces of ironed metal, especially tinplate or blackplate, must be chemically passivated to prevent darkening during baking and to prevent loss of enamel adhesion. The final step in a washer is usually a deionized water rinse to eliminate residues from the spray solutions. The ecological and economical importance of this invention becomes readily apparent when it is considered that the resins utilized and preapplied include many of the coatings normally applied to containers after forming for decoration, as size coats for protection against corrosion, etc. With tinplate and blackplate particularly, conventionally the entire bottom end must be sprayed with organic coating or otherwise treated to prevent rusting. The container of this invention, as formed already has present on its surfaces a protective and/or decoratable coating which protects against corrosion and makes it possible to eliminate the necessity to apply a size coating a~ter forming. The container as formed provi~des a base for applying decorative top coats and the problem bottom end, which is particularly hard to protect by conventional means, is protected as formed. Moreover, oily lubricants are not necessary in forming and thus do not have to be removed, or if a lubricant is employed, it can be selected to be a volatile one, for example, the dioctyl sebacate above described, which can be baked off, virtually eliminating the need for multiple washing steps and washing equipment. Elimination of large numbers of heated a~ueous spray applications would result in substantial energy savings, which is an increasingly significant feature and advantage.
Additionally, containers derived from stock carrying organic resins appear to exhibit better adhesion to a wider variety of inks, and coatings and topcoats, where utilized, may be applied at reduced weights. The adhesion to a variety of inks is particularly important, since currently only a few inks and varnishes are satisfactory for use with unsized tinplate because of poor adhesion. The present invention provides a greater variety in the selection of such inks. Another advantage is in the techni~u~,of film labeling wherein decorated labels of plastic film are adhered to the container surface. Adhesion of such labels to containers having organic resin film applied, as formed herein, has been found easier to obtain and greatly simplifies film labeling procedures.

.' ~

~058454 Reflow of the coating which may occur during forming or subsequently during washin~, decorating or interior coating, may effectively heal and eliminate metal exposure both on the inte~ior surfaces, thereby preventing metal ion dissolution into products, and on the exterior surfaces, resulting in a container having a glossy surface finish. Such reflow of the coating further improves adhesion and serves to remove any flaws in the resin film that may result from the forming operation.
Another advantage of this invention is that aluminum and steel may be utilized interchangeably, as a result of the resin film, permitting great flexibility and substantial savings with -only a changeover of ironing dies being needed to accommodate the different metals.
Specific problems associated with forming aluminum D & I
containers, such as difficulty in handling due to its light weight and the tendency to anneal during high temperature oven bakes necessary to dry standard top coats suitable for use with aluminum, are eliminated. Since the container as formed contains an organic ; film, it is possible to apply a low curing top coat, thus eliminating the problem of accidentally annealing and weakening the container. It is also possible that such a container would perform well without the need for applying alodine treatment to the formed container, as is currently conventional practice, since the combination of a precoat and a topcoat would perform as well as the present commercial single spray coat on bare cans which normally require the alodine treatment for adequate adhesion and performance, particularly with carbonated beverages. Where the container is intended for use with mild, non-corrosive products such as beer, it is possible to eliminate the spray topcoat completely, since a reflowed precoat functions to prevent metal dissolution into the product. Since galling is substantially eliminated, higher speeds are possible and die wear is minimized.
It is apparent from the foregoing description of the process that the organic resin films on the interior and exteriorsidewall surEaces of the drawn and ironed container are subjected to extreme and varying mechanical actions. The internal sidewall surface is forced to undergo a 90 compressive bend around a punch and a tensional force during ironing,whereas the exterior sidewall ` surface undergoes the 90 tensional bend in the drawing and is then exposed to an extrusion or "squeezing" action when passing through the forming dies. The bottom end of the container has not been essentially deformed. It is apparent that the exterior resin film on the container has undergone a deformation and change different from that of the interior resin film. With each ironing step, the interior resin film undergoes severe deformation as it is squeezed between the partic~ar ironing face and the mandrel or punch. On the other hand, the organic resin film on the exterior surface of the container is thinned by each succeeding ironing die which reduces the thickness of the sidewall and increases its height, so that-the resin film on the exterior sidewall of the container has been forced to undergo a 90 tensional bend in the drawing operation and then elongation or stretching during the ironing.
It should be noted that both the interior and exterior surfaces of the bottom end of the container retain the as-deposited ; organic resin films.
It should be obvious from the foregoing description that it was extremely surprising that organic resins could be found which were able to withstand the extreme stresses and conditions involved in drawing and ironing operations resulting in the pre-vention of galling of the metal substrate on the drawing and ironing dies while providing a virtually continuous film.
It is thought that the invention and man~ of its attendant advantages will be understood from th~ foregoing description and it will be apparent that various changes will be made in the form, construction, and arrangement of the parts and in the steps of the method described and their order of accomplish-ment, without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form herein-before described being merely a preferred embodiment.

Claims (22)

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

1. A method of drawing and ironing thin-walled cylindrical articles from flat metal sheet comprising the steps of: a) applying a composition comprising an organic resin to at least one surface of metal sheet; b) subjecting said sheet carrying said resin to an elevated temperature for a period of time sufficient to effect adhesion to the metal and a partial curing of the resin; c) forming a workpiece from said resin-carrying sheet; d) forcing the workpiece on a punch through a series of drawing and ironing dies without actively heating the workpiece between the drawing and ironing operations to form an elongated cylindrical article the sidewalls of which are sub-stantially reduced in thickness; and e) removing said article from said punch; said resin being cured in step b) to the extent that it is retained on said metal surfaces and exhibits the visco-elastic properties necessary to effect a lowered coefficient of friction and to exhibit plastic flow at high stress levels during the drawing and ironing steps.

2. The method of Claim 1, wherein the metal is steel.

3. The method of Claim 2, wherein the workpiece is a circular metal blank.

4. The method of Claim 1, wherein the metal is aluminum.

5. The method of Claim 1, wherein the workpiece is a seamless cup which is forced through a series of ironing dies,

6. The method of Claim 1, wherein the resin is selected from the group consisting of epoxy-phenolic, epoxy-urea formaldehyde, vinyl organosol and solution vinyl.

7. The method of Claim 1, wherein said resin composition includes a lubricant.

8. The method of Claim 1, wherein a lubricant is applied to said resin-carrying sheet after step b).

9. The method of Claim 8, wherein said lubricant is selected from the group consisting of dioctyl sebacate, acetylated tributyl citrate, mineral oil and water, and mixtures thereof.

10. The method of Claim 1, wherein said resin is an epoxy-phenolic.

11. The method of Claim 1, wherein said resin is a vinyl-organosol.

12. The method of Claim 1, wherein an epoxy-phenolic resin is applied to the interior surface of said sheet and a vinyl organosol resin is applied to the exterior surface of said sheet.

13. A method of drawing and ironing thin-walled cylindrical metal containers comprising the steps of: a) applying an organic resin to the surfaces of steel sheet; b) subjecting said sheet carrying said resin to an elevated temperature for a period of time sufficient to effect adhesion to the steel and a partial curing of the resin; c) forming a seamless drawn cup from the resin-carrying sheet; d) placing said seamless drawn cup over axially aligned drawing and ironing dies and forcing said cup through said dies with a reciprocal punch without actively heating the cup between the drawing and ironing operations to form an elongated cylindrical container having sidewalls substantially reduced from its original thickness, and e) removing said container from the punch; said resin being cured in step b) to the extent that it is retained on said metal surfaces, exhibits plastic flow at high stress levels, and effects a lowered coefficient of friction during the drawing and ironing steps.

14. The method of Claim 13, wherein the resin is selected from the group consisting of epoxy-phenolic, epoxy-urea formaldehyde, vinyl organosol, and solution vinyl coatings.

15, A method of drawing and ironing thin-walled cylindrical metal containers comprising the steps of: a) apply-ing an organic resin to the surfaces of aluminum sheet; b) sub-jecting the resin-carrying sheet to an elevated temperature for a period of time sufficient to effect adhesion to the aluminum and a partial curing of the resin; c) forming a seamless drawn cup from the resin-carrying sheet; d) placing said cup over axially aligned drawing and ironing dies and forcing said cup through said dies with a reciprocal punch without actively heating the cup between the drawing and ironing operations to form an elongated cylin-drical container having sidewalls reduced substantially from its original thickness, and e) removing said container from the punch; said resin being cured in step b) to the extent that it is retained on said metal surfaces, exhibits plastic flow at high stress levels, and effects a lowered coefficient of friction during the drawing and ironing steps.

16. The method of Claim 15, wherein the resin is selected from group consisting of epoxy-phenolic, epoxy-urea formaldehyde, vinyl organosol, and solution vinyl coatings.

17. A drawn and ironed metal container having an organic resin film on the bottom end and sidewalls thereof, the film on the bottom end being as deposited prior to forming the container, the film on the sidewalls having been subjected to the drawing and ironing steps of Claim 1.

18. A drawn and ironed metal container as claimed in Claim 17, wherein the metal is steel.

19. A drawn and ironed metal container as claimed in Claim 17, wherein the metal is aluminum.

20. A drawn and ironed metal container as claimed in Claim 17, wherein the resin is selected from the group consisting of epoxyphenolic, epoxy-urea formaldehyde, vinyl organosol and solution vinyl coatings.

21. A drawn and ironed metal container having an organ-ic resin film on the bottom end and sidewalls thereof, the film on the bottom end being as deposited prior to forming the container, the film on the sidewalls having been subjected to the drawing and ironing steps of Claim 13.

22. A drawn and ironed container having an organic resin film on the bottom end and sidewalls thereof, the film on the bottom end being as deposited prior to forming the container, the film on the sidewalls having been subjected to the drawing and ironing steps of Claim 15.