Note: Descriptions are shown in the official language in which they were submitted.
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
3C
reduction in the inside diameter of the cup.
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1058454
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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~05~
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
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1058454
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
.. .
Referring to the Drawings:
Figure 1 is a schematic sectional view of a D ~ I die
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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,
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1058454
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;
lOS8454
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
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1058454
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
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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
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1058454
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
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1058454
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
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1058454
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
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1058454
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
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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
-I9-
. . .
lOS8454 .
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.
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1058454
~ 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:
.
The procedure of Example 1 was repeated using the Stolle
bodymaker and a cup-fed procedure employing the
.' ~: '.
-21-
~: . , .
1058454
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;
;,'` .
-22-
~454
V~ --~o, ~ o
~ ~ g~
~J ~ : e ~ ::~ ,a ~0
d ~) ~ ~ P~ ~ ,1
O U~ ~ ~ .Y
O ~ ~al
O :~ Z o 1l1 5
~ g ~ ~ _ ~ 4 . ___ ~
~1~ `3 :~ O I P~
tq~ U s~ ~:1
~JO U~ ~1 ~ O a? '1 ~ rl O ~ U~
rI ~ k I ~ ~ ~ h ~ 111
~ ~ ~ p ~0 ~ ~ O ~ ~ ~ O
u~ a~ 4~ ~ ~ ~ P
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~
e~-n l l l u ~c~S~ .
P P o P~ o ~
_ * * o ~ o C) o
:~ s e ~ _ ~ .~
~ _ :,:
' ~ ~ ~ _
. o ~ C . ~ ~o
., .,~ . ~ u ~ ,t) ~ ~o : '
.; Z o ~ s~ ~ :~ a~ 'I a
O a~ ~_~ o s ~ o .-1 h d
. ~ ~ e~P~ ~o o ~: ~ ~ ~ 3 O
I 1~> I ~1 Irl Ir~ 1' 1` I'o ~
,~ --23--
.
.
~0584S4
r T~ ~T rl
~ Q. h : _ u~ ~ i
~ ~ ~ 1 l
O t~ ~ ,a ~)
oo ~ ~ ~ ~o ~
Ul O H D O u~ _ .
~ O 00 .
~ o ~0~
~ ~ h ~ ~ ~ l l
0~ ~ r~
~S U~ o-,l U~ o i
~ '~ ~ = ~ '~ l l l
O ~ ~ .~
, o ~ ~ ~ ~ ~
a) '~ O c~ H _ ~.) . ... ______
h ~1 'a tQ ~ 1 U~ S~
O h O ~ O ~ ~ ~ ~ O ~ ~) O O ,~
_~ a) t) o o Ll O :~ t) O ~ O ~ O o ~ ~:
~R ~ ~ ~ ~ ~ O ~ ~ 1 r~ ~ ~ ~ ~ ~ O
a) ~ Y-l ~ ~1 ~ + ~1 ~ .Y + ~ 4
lQ ~.rl U~ ~ ~ 1 ~
~E~ ~ c : ~ ~ ~ E~ o - ~ ~ 3
,~ a~ ~ ~ ~ ~ ~ u 4~ ~ U o u ~ u
. ~ ~ s~ o ~Q ~ ~n s~ u~ a) s~ ~ ~
t) ~ t~ O H ~ Z -O O ~ g ~ O O 1:: ~ -- O O ~ U~
. ' . . .
. ~ ~ ' .,
' ' ~ ~ _
:~ ~ U__ _ _ _ : =
= , '
~o .
a)~
. O 'a .,, h
O
z~7 ~ o o o~ ~ ~0~u
~ a) ~s ~ o ,¢ 1~:1 ~o ~3 a~
a ~ x ~ ~ ~ ~ ~ ~ _
tr;E~ W~ ~ ~r w I` ~ -
., .
-23A-
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
-24-
.
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-
-25-
1058454
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
-27-
1058454
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.
-28-
.' ~
~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
-29-
1058454
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
-30-
1058454
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.
-31-
