Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a nestable
can and a method of manufacturin~ such a nestable can.
The present invention is particularly useful
in providing a container of high integrity which is
suitable for packaging food products, such as fish.
One element of its utility is in providing a nestable
can that may be shipped to the user in packages of
high density.
Prior art can constructions currently in use
most commonly provide a three-piece soldered can compris-
ing a cylindrical can body and a pair of endsO The
can body is first made in a right cylindrical configura-
tion but then collapsed to increase shipping density.
Upon arrival at the packer's plant, the can body is
reformed to a round configuration and one end is seamed
on prior to filling. The operation of collapsing the
can and reforming them at the point of use is deleterious,
both to the can body seams and to the coating which is
conventionally applied during or prior to manufacture.
It has been recognized that a two-piece can
construction comprising a cup having an integral sidewall
and bottom is a preferred construction since it solves
problems of`seam leakage and coating removal. However,
conventional two-piece canshave not been made which
can be economically shipped and/or reassembled at the
packers' plantl although it is apparent that a tapered
nestable can may be made to increase shipping density.
The production of an acceptable two-piece
can has proven di~ficult using conventional drawing
methods, except for very shallow cups, since the cans
must be free of wrinkles and bulges and the coating
must be maintained when using precoated stock. It
is believed that the can industry generally considers
the manufacture of tapered two-piece containers to
be difficult to the point of impractical.
Notwithstanding, it is to be recognized that
two-piece cans comprised of a one-piece cup and closure
lid are known, and such cans have been made with nestable
tapered sidewalls, such as tau~ht in U.S. Patent 3,248,003.
It is to be further understood that the manufacture of
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nestable plastic containers and cups is well-known as
exemplified by the teaching conta.ined in United States
Patent Nos. 2,879,917; 3,091,360, and 3,139,213. The
present invention, however, differs from earlier teachings
both in the method of manufacture and in providing a cup
configuration which can be internested, stacked and
subsequently separated for process filling with conven-
tional machines.
The present invention comprises a method for
forming a tapered nestable can from sheet metal stock
comprising the steps: cutting a blank ~rom sheet metal
stock, and drawing the blank into a tapered die with a
tapered drawhorn while forming a first stage cup having a
bottom, a tapered cylindrical sidewall and a peripheral
flange, said blank being drawn with out coining said
sidewall and allowing wrinkles to form therein; and
reforming the first stage cup by expanding the diameter
of the tapered cylindrical sidewall to remove the wrinkles
while maintaining substantially the same taper, the diameter
20 of said sidewall after expanding being less than five
percent (5%) greater than the diameter of the sidewall
of the first state cup.
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The objects and advantages of this invention
will become apparent in view of the following detail~d
description and the accompanying drawings.
In the drawings forming a part of this applica-
tion and in which like parts are identified by likereference numerals throughout the same,
Fig. l is a vertical center section of a
plurality of nestable cans made in accordance wi-th
this invention;
Figs. 2, 3 and 4 illustrate sequential stages
of manufacturing each can; and
Fig. 5 is an enlarged vertical section taken
on the lines 5-5 of Fig. 1 showing structural relation-
ships of and between cans that are nested.
Referring to Fig. l of the drawings, there
is shown a plurality of internested cups C, each cup
being formed in essentially three stages as contemplated
by this invention. Figs 2-4 illustrate the three
stages of manufacture. First, as shown in Fi~. 2, a
circular blank (cut from precoated sheet metal stock)
is drawn into a tapered die with a tapered drawhorn,
froming a first stage cup having a bottom 10, a tapered
cylindrical sidewall ll, and a peripheral flange l~.
The preferred embodiment of can is made with a sidewall
that tapers upwardly from a bottom plane at an angle
of 87 ~3 taper relative to the vertical).
The first stage cup is formed without "coining"
the sidewaIl. (~he term "coining" as used herein is
defined as the stamping or extrusion of metal to change
its shape and thinness). To avoid "coining" during the
manufacture of the first stage cup a spacing is maintained
between surfaces of the die and drawhorn, and that
spacing should be equal to at least two metal
,
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thicknesses of the sheet metal stock from which the
blank is formed. For example 75# sheet steel stock of
.0083 inch thick is a suitable material/ and at least
twice that thick~ess (.0166 inch) should be used as
clearance when such material is used. As a consequence,
the first stage cup will possess longitudinal wrinkles
in the sidewall. Those wrinkles are then removed in
a reforming process wherein the first stage cup is
expanded or cylindrically enlarged using a tapered
drawhorn of increased size, but of substantially the
same taper as that used in the initial drawing opera-
tion. In the reforming process the sidewall of the
f~rst stage cup is diametrically enlarged, but the
finished diameter of the sidewall is less than five per-
cent (5%) greater than the diameter of the sidewallof the first stage cup. An increase of between two and
three percent (2-3%) has been found to produce smooth
sidewall surfaces while preserving the integrity o~
coatingsapplied to precoated metal stock. Expanding
the diameter size above five percent (5%) tends to
cause metal fractures and serious impairment of the
coating.
Fig. 3 illustrates the preferred shape of the
second stage cup having a sidewall lOa, a bottom lla
and an upper rim 13. In reforming~ both the upper end
and bottom wall of the first stage cup is reshaped and
profiled. It will be noted that rim 13 is laterally
and outwardly offset from the reformed sidewall lOa,
and the bottom is profiled to increase its strength.
3¢ Thereafter, the flange portion of the rim is trimmed
or cut to a precise diameter, as shown in Fig. 4, to
form the finished cup.
Fig. 5 illustrates details of a rim profile
which provides both the feature of nesting as well as
selected spacing of nested cans. More particularly,
rim 13 is f~rmed with first, second and third curvatures,
the first curvature being formed on a radius rl and
defining a first interior convex surface 15, the second
curvature being formed on a radius r2 and definin~ an
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exterior convex surface 16, and the third curvature
being formed on a radius r3 and defining a second
interior convex surface 17. The first curvature
projects the rim radially outward and of~set from
tapered sidewall lOa; the second curvature directs
a section o~ the rim vertically upward to support an
inner cup; and the third curvature connects to a radial
flange 18. The radii of the three convex surfaces are
selected and located one to another such that the
finished cups nest within another t the exterior convex
surface 16 of an inner cup resting upon the second
interior convex surface 17 of an outer cup and providing
a spacing between adjacent sidewalls (shown by the
letter "d'~ which is at least .0015 inch. The spacing
-between sidewalls is critical in that a spacing of side-
walls closer than .0015 may present problems in the
separation of nested cups. Closer spacings of side-
walls tend to result in vacuum type lock-ups and a
separation of such cups may cause scuffing of the coated
can surfaces.
It is also to be noted that the radius r2
forming convex surface 16 is substantially less than
the radius r3 forming convex surface 17, and contact
between nested cups occurs at a point of cotangency
whose vertical projected line image "b' is within the
concave profile of convex surface 17. Thus, once
contact is made between surfaces of nested cups, the
inner cup is supported on a circular ring of point
contacts within the outer cup.
Separation of cups is thereby inhanced by
virtue of the small area of surface contact and smooth-
ness of surfaces.
It will be apparent that the packing density
of nested cups increases in direct proportion to the
flange spacing "D" between cups. This follows since
the cup diameter and height are fixed. Therefore, the
closer the flange spacing, the more dense the pack.
Although a minimum flange spacing has not been established,
it has been determined that a flange spacing of .1~0 to
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.190 inch works well with standard processing equipment.
It may be noted that a geometric and dimen-
sional relationship exists in forming rim 13. The
flange space D is a linear distance function of flange
displacement distance S (a vertical distance from the
surface of one cup flange 18 to the corresponding surface
of a nested cup flange 18) and the flange thickness
T. (D = S-T). But displacement distance S is also a
function of the clearance spacing d between sidewalls,
the maximum thickness t of the sidewalls and the angle
of sidewall taper ~. This latter relationship may be
expressed by the formula S = dtan t~ , and that formula
may be used to determine or select flange spacing. As
an example, and assuming the following values by
engineering design, if d = .001~", t = .0083", and
~ = 3, then S = .1875". If engineering design also
suggests a flange thickness T of .0105", then flange
spacing D will be .177".
The distance S, it will be evident, also
describes or is equal to the axial distance between
the convex surfaces 16 and 17 at points of contact
with nested cups. Thus, once distance S is selected,
the locations of the convex surfaces (and the location
of the circular ring of contacts) become fixed; and
~the profile of rim 13 is then functionally de-termined.
Although a preferred embodiment of the invention
has been illustrated and described, various modifications
and changes may be resorted to without departing from
the spirit of the invention or the scope of the appended
claims, and each of such modifications and chang~s is
contemplated.
