Note: Descriptions are shown in the official language in which they were submitted.
BACK(iROUND ` (~F' " 'r~lF~ :rNVl~`N'l':lON
Various techniques haye ln the past been employed
to coat the i`nteriors of hollow articles and, more particularly,
the shell or body of two--piece metal cans. Typically, such
coatings are applied from a spray nozzle, which is positioned
adjacent the open end of the can shell for delivery of the
coating material thereinto. I~owever, the spray patterns of
co.lventional spray nozzles are such that the resul-tant coatings
tend to be nonuniform, thus requiring the over-spraying of certain
areas of the can so as to provide a necessary minimum coating on ~ :
other areas. The problem is particularly acu-te in tlle case of
can bodies made by drawing and ironing either tinp].ated or tin-
frce steel and in-tended for ùse with carbonated beverages, since
they require especially heavy, uniform, void-free coatings to
prevent corrosion and product contamination.
While attampts have been made to improve upon the ~:
aforementioned spray pattern deficiencies (see for example, the
spray nozzle described in United States pa-tent No. 3, 737,108),
so far as is known no presently available nozzle provides a
2U spray pattern wnich is capa~le of uniformly covering, in a single :.
operation, the interior surfaces of a can body having one open
and one closed end. Consequently, it has been found necessary to
apply the spray coating i.n -two applications, with the initial
coating being cured prior to the second spray applica-tion;
without such curing, the combined weigllts of the two coatings,
as here-tofore applied, would cause them to run and sag, and to
accumulate in the corners of the can.
Whil.e entirely satisfactory from the standpoiIlt of
produciIlg good quality coatings within the can shell, sucll a
"double coat" -techIlicfue i.s rather inefficient, ;n requiri.llg
either two passes of tlle can shell through -the spraying and
curiIlg apparatus, or a single _ass througll two spraying ~d curing
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stations. ~rhus, Lhe tcchnique is disadvantacJcous in Ihat it
cntails hic31~ capita] expcllditures for ecluipmc?n-t, cxcessive pian-t
spaee, energy, manpower and materials; moreover, the can she]ls
are subjectc?d to possible abuse as a result of -the amount of
handlillg wllich the double-coat process may invo]ve.
Accordingly, it is an object of this invention to
provide a novel method for producing a relatively heavy, uniform
and eontinuous eoating on the interior surfaces of ho]low ar-ticles.
It is also an object of the invention to provide such
a me-thod wherein the effieieney of the eoating opera-tion is
maximized.
~ nother object of the invention is to provide such a
method wherein eapital expenditures, and rccllliremen-ts of spaee,
energy, manpower and materials are minimized, withou-t saerifiee
to the quali-ty of the eoating produecd.
A more speeifie object of the invention is to provide
a novel method having the foregoing features and advantages,
whieh method is partieularly benefieial for -the coating of ean
shells fabrieated by drawing and ironing steel blanks.
SUMMARY OF THE INVENTION
It has IIOW been found that the foregoing and related
objeets of the invention are readily attained in a method of
eoating the interior surfaees of a hollow article, comprised OL
a siclewall having one end open and an end wall closing the
opposite end thereof, which method includes two spraying s-tcps.
In aceordanee therewith, a lic~uid coating material is sprayed into
the ar-tiele through the open end thcreof to produce one deposit
-therewitllin, which is confined substan-tially to the cn-tire
inside surface of the sidewall. ~nother deposi-t is produced
within the article by spraying a lic~uid coating material therein-to
throuc3h tlle open end thereof, so as to cover substan-tially the
entire inside surface of both tlle sidewall and also the end wal].
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Finally, the initi~1 solidificat~on of both of t-he deposits is
simultaneously effected.
Preferably, the "onet' deposit is applied prior -to the
"anotller" deposit, and the spraying steps are effected while the
article is rotated about its lonyitudinal axis, most desirably at
a rate of rotation of about 1000 to 3000 revolutions per minute.
It is hiyhly advan-tageous that the sprayin~ steps be of a duration
of about 1 to 4 revolutions of the article, and that the temp~
eratures of tne coating rnaterial, as applied, be betwecn about
20 and 85 Celsius. Generally each of tile sprays will have a
sector-shaped confiyuration, wherein the rates of material
delivery will preferably vary from minimum values at the margins
of the sector to a maximum value -therebetween, with the maximum
value o~ material delivery occurring along a radius which lies at
a point which is about 65 to 95 percent of the total arc distance
.. ~,
between the margins.
In the particularly preferred embodiments, the article
~ employed is the body or shell for a two-piece drawn and ironed
; ~ metal can, fabricated from steel and having a cylindrical side-
wall. In such a method, the total weigh-ts of the coating
material applied to produce the "one" deposit and the "another"
deposit are desirably within the ranges of about 120 to 200
milligrams and 80 to ]50 milligrams, respectively, with no more
than about 10 percent of the total weight of the ma-terial applied
to produce the "one" deposit being applied to the end wall of
the body. Most advantageously, the combination of the "one"
~eposit and the "another"~deposit will produce a substantially
uniEorm and void-free coating having an average distribution of
from about 5 to 8 mil]igrams of coating material per square
inch. Finally, the coating materials applied should have a
viscosity of about 10 to 250 centipoises, and preferably about 15
to 50 centipoises, at the temperature of application.
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BRIEE D~SCRIP'l'IO~ OF_TI~E D AWING
Figure 1 is a diagrammatical representation of the first
spraying step of the method of thepresent invention, showing
a spray nozzle and a can shell, -the shell being in cross section
and disposed to receive coating material from the nozzle; and
Fiyure 2 is a view similar to that of Figure 1, showing
the second spraying step of the method.
: DETAILED DESCRIPTION_OF THE ILLUST~ATED EMBODIMENT
Turning now in detail to the appended drawing, therein
shown are the two spraying steps of the novel method embodying
the present invention. Referring to Figure 1, which illus-trates
the spraying step which is preferably effected first, a hori-
zontally disposed, open-ended can body or shell, generally ~ -
~esignated by the number 10, comprised of a generally cylindrical
sidewall 12 and an integral end wall 14, is rotated about its
longitudinal axis (by means not shown). Ilhile the shell 10
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is~rotated at least once, and preferably between one and four
revolutions, a spray nozzle 18, positioned adjacent the open end
of the shell 10, directs a spray of a liquid coating material into
the open end of the can shell 10 to form a deposit which is
confined substantially to the entire interior surface of the
sidewall 12 of the shell 10.
Following the application of the first deposit, and
; while the shell 10 lS still rotating, a second spray (of similar
duration to that of the first application) is applied over the
still wet or uncured first deposit. As illustrated in Figure 2
the spray is directed into the open end of the can shell 10 from
a second spray nozzle 18l to produce a second deposit which
encompasses the entire interior surface of the shell 10 including
both the sidewall 12 and also the end wall 14 thereof.
Finally, following the two spraying operations, the
co-mingled "wet" coatings are cured, such as by subjecting the
~
sllell to elevated temperatures in all oven. It slloul.d be pointed
out that, while there may be some casual drying of the coatings
following each of the spray applications, there is no appreciable
curing thereof prlor to their exposure to the oven. Accordinyly,
their initial solidification may be regarded to be simultaneously
effected, as a practical matter~ :~
For each of the spraying operations depicted in the
figures the fan- or sector-shaped spray patterns of two preferred
conventional spray nozzle orifices are illus-trated, that of the
controlled-distribution nozzle, i.n full line AC, A'C', and of the
drumhead nozzle, in phantom line AB, A'BI. The drumhead nozzle ;
orifice is designed to provide a fan-shaped spray pattern which
has a maximum flow rate of coating material at (ideally) or
closely adjacent one margin of the fan which decreases generally ~;
linearly to a point of minimum output at the other end or margin ::
of the fani the point of maximum flow is generally along a radius
of the fan which is located at a point approximately 95 percent
of the fan width or arc distance from one of the margins thereof
: and 5 percent from the other maryin thereof. In contrast, the
:20 controlled-distribution nozæle provides a fan-shaped pattern having
a maximum rate of flow at a point approximately 75 percent of the
distance from one end of the fan and 25 percent from its other
end; again, the flow rate decreases generally linearly from the
point of maximum flow to the poin-ts of minimum flow, at each margin
of the spray fan. The orifice designs and distribution patterns ;^--
~:~ of -these nozzles are more fully described and illustrated in
United States patent No. 3,737,108.
Regardless of whether the drumhead or controlled-
distribution nozzle is emplyed in the first spraying step
(Figure 1), each nozzle is oriented, relative to the can shell
10, such that the radius of their spray fan defining the point
of ma~imum flow output is directed at the corner 13 of the can
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shell; this generally compensates, al-though not perfectly, for
the increased distance the spray must travel to reach -the corner
13. As a result of these nozzle orientations (mostly notably
that of the controlled-dis-tribution nozzle), parts of their
spray fan will be directed at the annular flat surface 15 o~ the
end wall 14. Mowever, in nèi-ther case is there any appreciable
coating accumulation on the end wall 14; generally, no more -than
about lO percen-t of -the total weight of the coating material
applied in the first step.
0 : FOI the second spraying step (Figure 2), if a drur;1llead
; ~ nozzle is employed, it is disposed relative to the she]:l lO,
so as to produce a spray defined by margins A'B', which spray ex- ~
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tends from the rim ll of the shell lO along the entire length of
the sidewall 12 and onto the end wall 14 to a point sligh-tly
beyond the center of the central dome or dimple 16 -thereof
(to ensure its full coverage). Alterna-tively, if a con-trolled
distribution nozzle is used, it is preferred that it be disposed
; ~ ralative to the can shell lO such that its spray A'C' extends
beyond that of the drumhead pattern A~s~, encompassing the entire
end wall 1~ as well as a portion of the opposite side of the
;~ ~ sidewall 12 adjacent the corner 13. As can be appreciated, this
provides added coverage to the bottom portion of the sidewall,
an area of the can shell 10~ which, regardless of whether the
spray is directed at only the sidewall (i.e., AB or AC), or at
the entire can interior (i.e., A'B' or A'C'), typically receives
; at least amount of spray coverage. Accordingly, a more uniform
~: ~ coating distribution is achieved.
Usually, each of the spraying steps will be completed
in a single pass through a spraying machine. This may
appropriately ~e accomplislled by feeding a multiplicity of uncoated
can shells to successiv~ can~receiving pockets of a rotatable
turret, which intermittently inde~es the shells to a first and
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th~n to a second spray sta-tion, whereat -they are rotated (such
as by belts) while they receive the sprays from separ~te]y
mounted nozæles. Thereafter, the coated shells are removed from
the turret at a discharge station, Eor transfer -to an oven in
whicll curing of the coa-t;.ngs is effected.
In such a machine, the cans are preferably coated at
the rate of 150 to 325 per rninute, and are rotated at relatively
high speeds, typically on the order of about 1000 to 3000
revolutions per minute, wi-th the duration of each of the spraying
steps being in the range of about 50 to 120 milliseconds and ~ :
the duration between each of the spraying steps being in -the :
range of about 75 to 250 milliseconds. Generally,.the spray
nozzles used will have a flow rate oE about 0.09 to 0.16 gallons
of water per minute at a pressure of 500 pounds per square inch,
and the coating materials will normally be applied ullder a hy-
draulic pressure in the range of about 500 to 1200 pounds per
square inch. Preferably, the first gun will apply a total weight ~ ;~
of 120 to 200 milligrams of coating material, with the second
gun app~ying a total weight of about 80 to 150 milligrams, so as
to achieve an average distribution of between about five and
eigllt milligrams per square inch~over the entire interior surface
of the shell.
Suitable coating materials for drawn and ironed
container can shell fabricated from steel and intended for cax-
bonated beverage use include~ among other types of resins,
epoxies, acrylics, and polyesters. 'rhese materials are prefera~ly
applied at a temperature within the range of about 20 to 85
Celsius, and they will normally have a viscosity in the range ::
of about 10 to 250 centipoises at the temperature of applicat;on;
preferably, they will exhibit viscosities of about 15 to 50
centipoises under the condition.
As a specific example~ a shell for a two~piece drawn
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and ironed can, fabricated from -ti.np]atean~.having an outsi.de
diameter of about two and eleven~sixteentlls;nches and a helc3ht of
about four and thirteen-sixteenths inches, was coated in
accordance with the instant method using two controlled- -
distribution nozzles employed in apparatus of the sort previously
described. The first gun, used to apply the "sidewa]l" coat,
:
was oriented downwardly at an angle of about thir-ty-five degrees
relative to the horizontally disposed can shell, and was positioned
at a dlstance of about one and one-~uarter inches from the opening
of the can shell with its orifice about one-half inch radially
inward from the uppermost point of the can sidewall; its spray
pa-ttern was about seven inches wide, i.e., from margin to margin, ;
measured at a poin-t ten inches frorn the nozzle. The second
gun, used to apply the "ful]." coat, was oriented downwardly at
an angle of about twenty~five degrees from t.he horizontal and
:~ positioned at a distance of about one inch from the opening of
: the can shell with its orifice about three-quarters of an inch
radially inward from the uppermost point of the can sidewall;
its~:spray pattern was about ten inches wide, measured as described
above. Each of the nozzles' flow rate was rated at 0.12 gallons
.
per minute of water at 500 pounds per square inch and operated
at a pressure o~ 800 pounds per square inch.
An epoxy-urea formaldehyde resin having a viscosity
of:about 20 centipoises was applied by each spray gun at a tem- :
perature of about 52C. As the cans were rotated at about 180Q .
~ ~ revolutions per minute, each coating was applied for about 100
: ~ milliseconds, or for about two and one-half revolutions of the
can sllell and the time between sprays was about 100 m.illiseconds.
The first gun applied a total of about 180 milligrams, which
3D provided an average distributi.on of about 5 milligrams per square
; inch on the in-teri.or surface of the side ~all and about 0.5
milligrams per square inch on the annular flat interior surface 15
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of the end wall 14. The second gun applied a total weiyht of ahout
120 milligrams, which provided an average dis-tribution of about
2.5 milligrams per square inch on the sidewall, and about 7
milligrams per square inch and 7.5 milligrams per s~uare inch
respectively, on the annular flat surEace 15 and the cenkral
dome 16 of the end wall 1~; this resulted in a combined total
weight for the two spray coatings of about 7.5 milligrarns per ~:
square inch for the entire interior surface of both the sidewall
12 and the end wall 14. The can shell was then baked at about :; :
216C for about two minutes.
.
While the instant.method has been described in relation .~
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to the illustrated and preferred embodiment, it should be under- .
stood that modification may be made, as will be apparent to -those `
skilled in the art. For example~ while mcst advantageously the ~
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"sidewall" coat is applied prior to the "full" coat, their order
may be~reversed. It should also be mentioned that, although the .
fan-shaped spray patterns of nozzles having either a 75:25 or
95:5 flow distribution, are.preferred, the rnaximum rate of material
delivery may occur along a radius which lies at a point which is
about 65 to 95 percent of the total arc distance between the
fan margins.
It should be pointed out that, although i.t is preferred
that the time between sprays be relatively brief, i.e. 75 to
:~ 250 milliseconds, considerably longer periods of time may be
tolerated and, in fact, may be advantageous for certain applica~
tions. In addition, the coating materials applied in each spray
need not necessarily be the same. Finally, it should be noted
that, although the instant method is especially valuable for
:~ coating the inside surface of one-piece cylind~ical shells or
bodies Lor two-piece cans~ and particularly for such shells
fa~ricated from either tinplated or tin~free steel and intended
to bè filled with carbonated beverages, it may advantageously be
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cmployed for coating virtually ally hollow article having a closed
end.
Thus it can be seen that the present invention provides
a novel method for producing a uniform and continuous coating
on the interior surfaces of hollow articles. In the rnethod, the
efficiency of the coating operation is maxirnized, and capital
expenditures and requirements of space, energy, manpower and
materials are minimized, without sacrifice to the quality of the
coating produced. In particular~ a novel method is provided
having the foregoing features and advantages, which method is
particularly beneficial for the coating of can shells fabricated
: by drawing and lroning steel blanksA
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