Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title~ U OF N~r~Tr~ 7 AN I~PACT
METAL CO~I~ATNI;~
FIELD O~ THE lNv~ lON
This invention relates to a method of forming a
narrowed, elongated neck on an impact extruded cont A i ner .
RA~RG~OUND OF q~HE lNVl!;h~ lON
Impact extrusion is a well-known process, in
which a slug of metal (usually aluminum or an aluminum
alloy) is placed in a cylindrical die and struck with a
punch at high speed and high pressure. The metal of the
slug then flows upwardly to form a thin-wall open ended
container. Such containers are commonly used in numerous
applications, e.g. as beverage containers, aerosol
containers, and to hold various other products.
After the container has been formed, the open
end is usually formed into a narrowed neck, and a top
(e.g. a spray valve) is applied to the container.
Until the present time, the extent to which the
neck has been narrowed has been limited, and the narrowed
neck of the container has been of relatively short axial
dimension. It has not been easily possible to form a long
neck of greatly reduced diameter on one piece impact
extruded containers, because of the difficulties
encountered when forming the material of the neck.
Because the material tends to wrinkle and split when being
formed, the reject rate has been unacceptably high.
Therefore, when containers having elongated narrow necks
have been needed, e.g. to contain liquids to be added to
automotive fuel or oil, such containers have usually been
made from plastic. Plastic containers have the
disadvantage that they may be permeable to compounds in
the liquids which they are to contain, and they may even
be attacked by such liquids.
-
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BRIEF SU~QL~RY OF I~IE lN~ oN
Therefore, it is an object of the invention to
provide a method and apparatus for providing an elongated
reduced diameter neck on a one piece metal container. In
one of its aspects the invention provides a method of
forming a metal container of predetermined diameter and
having an elongated, narrowed neck, said method
comprising:
~a) impact extruding a slug to form a container
having an open end, said open end being
defined by an encircling first edge,
(b) trimming a portion from the length of said
container at said open end to define a
second encircling edge, said portion being
longer than that necessary merely to
produce a straight unwrinkled edge and
being sufficiently long that the metal of
said container at said second edge
comprises metal which is substantially more
formable than the metal of said container
at said first edge,
(c) inserting said container sequentially into
a series of necking dies to form said
elongated, narrowed neck at said open end.
In another aspect the invention provides a
method of forming a long-necked metal container of
predetermined diameter, comprising:
(a) impact extruding a slug to form a container
having an open end defined by a first
encircling edge,
(b) trimming a portion from the length of said
container at said open end to form a second
encircling edge,
(c) inserting said container sequentially into
a series of necking dies to form an
elongated neck of diameter less than said
predeter~ined diameter at said open end,
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(d) said necking dies comprising a first
plurality of necking dies for partially
forming said neck and a second plurality of
necking dies for completing the forming of
said neck,
(e) and after said neck has been partially
formed in said first plurality of necking
dies but before said neck has been
completely formed in said second series of
necking dies, trimming a further portion
from the open end of said neck to form a
straight smooth edge thereat.
In another aspect the invention provides a
method of forming a long-necked metal container of
predetermined diameter, comprising:
(a) impact extruding a slug to form a container
having an open end defined by a first
encircling edge,
(b) trimming a portion from the length of said
container at said open end to form a second
encircling edge,
(c) inserting said container sequentially into
a series of necking dies to form an
elongated neck of diameter less than said
predetermined diameter at said open end,
(d) and after said container is inserted into
each necking die and formed therein,
ejecting said container from such necking
die, and including the step of injecting
compressed air into said container through
at least some of said necking dies to
assist in ejecting said container from such
necking dies.
Further objects and advantages of the invention
will appear from the following description, taken together
with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 is a perspective view of a typical slug
used to form a container according to the invention;
Fig. 2 is a diagrammatic sectional view showing
conventional impact extrusion apparatus used to form an
open ended container from the slug of Fig. l;
Figs. 3A and 3B are side views of cont~iners
produced by the apparatus of Fig. 2;
Fig. 4 is a diagrammatic view showing a trimmer,
and a necking machine used to form necks in the containers
of Figs. 3A, 3B;
Fig. 5 is a graph showing hardness plotted
against distance from the open end of the containers of
Figs. 3A, 3B;
Fig. 6 is a photomicrograph showing metal
structure at the free edge of the container of Fig. 3B;
Fig. 7 is a photomicrograph showing metal
structure 8 to 10 mm from the free edge of the Fig. 3B
container;
Fig. 8 is a photomicrograph showing metal
structure approximately 30 mm from the free edge of the
Fig. 3B container;
Fig. 9 is a side view, partly in section,
showing outer and inner die parts mounted on a die holder
for necking a container, and showing a container in
position between the die parts;
Fig. 10 is a side view of a guide shaft used in
the Fig. 7 apparatus;
Fig. 11 is an end view of the guide shaft of
Fig. 10;
Fig. 12 is a side view, dimensioned, of a
finished threaded container formed by the method of the
invention;
Fig. 13 is a side view, dimensioned, of a
modified threaded container formed by the method of the
invention;
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Figs. 14 to 21 are each side sectional views of
respective progressive outer dies used with the apparatus
of ~ig. 9;
Figs. 22 to 29 are side sectional views of
progressive internal guides used respectively with the
external dies of Figs. 14 to 21; and
Figs. 30 to 47 are side views of a contAin~r as
it is processed through the respective stations to produce
a narrowed elongated neck.
DE~ATT~ DESCRIPTION OF PREFERRED EMBODIMENT
Reference is first made to Fig. 1, which shows
a typical slug 100 used in the impact extrusion process.
Slug 100 is formed of aluminum with suitable alloying
materials added, e.g. trace amounts of boron and titanium.
The slugs 100 are available from various commercial
suppliers.
In the impact extrusion process, a slug 100 of
suitable dimensions is placed in the cylindrical opening
102 of a hollow die 104 (Fig. 2). A punch 106 impacts the
slug at very high speed and pressure, causing the metal of
the slug to flow upwardly in the interstitial space
defined between the punch outer diameter and the die inner
diameter. This forms a thin wall container 108a, 108b as
shown in Figs. 3A, 3~.
The dimensions of the slug 100 will vary
depending on the size container which is to be formed.
Typically, for a container having its outer diameter 66
mm, a slug of 65.7 mm diameter is used (just undersized to
fit the die), and of thickness varying between about 5.6
mm (to produce a container 135 mm long) to about 8.5 mm
(to produce a container 235 mm long). It will be
understood that while various dimensions are given
throughout this description, all such dimensions are
illustrative and other suitable dimensions may be used
depending on the container size, wall thickness and length
of neck desired.
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After the container 108a, 108b has been formed,
it is cleaned, and if desired painted or lacquered. After
this process, a neck is formed on the container in what
is commonly called a necking process.
In a conventional manufacturing process, the
open edge portions llla, lllb of the container 108a, 108b
(which edges are usually somewhat uneven after the
extrusion process) are trimmed, to provide a straight,
smooth edge 112a or 112b. The trimmed contAinPr is then
thrust sequentially into a set of forming or necking dies,
to form a reduced diameter neck on the container.
StAn~rd necking machines for this purpose are sold by
various suppliers, e.g. Nussbaum AG of Matzingen,
Switzerland as its model EM-38. This machine has 28
stations, at each of which a necking or other operation
may be performed.
Fig. 4 diagrammatically shows a necking machine
120 for performing a method according to the invention.
The necking machine 120 is the stAn~Ard Nussbaum A~
machine model EM-38, but much of the tooling on the
machine (at its various stations) has been modified or
replaced, as will be described. Before containers 108a,
108b are processed in the necking machine 120, they are
first trimmed in a standard trimming machine 122. In
trimming machine 122 the container rotates and a knife
engages the contAiner to cut off a desired circumferential
portion, to provide the smooth, straight cut edge 112a or
112b.
Because the metal used to form the containers
108a, 108b is expensive, it is normally desired to trim as
little as possible from the end of each container.
Conventional practice in the industry is to trim about 8
to 10 mm from the free end of the container. This is
usually sufficient to remove the wavy and uneven free edge
portions llla, lllb produced by the impact extrusion
process and to permit normal necking of the cont~i~ers.
However when the conventional necking method was
used in an attempt to produce containers having a long
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narrow neck, the method worked poorly. It was found that
the reject rate caused by split or wavy ends was about 30%
to 40% or higher. It was found, as mentioned, that many
of the container edges 112a would split or wrinkle during
the necking process, producing a frayed edge during
reduction. The contAiners would not pass through the
complete set of dies in this condition. In addition, even
when the containers did pass through the dies, splitting
would occur during the thread forming stage. It therefore
proved difficult or impossible consistently to produce a
container having a long, narrowed neck.
The problem was largely solved by trimming much
more than the usual 10 mm from the open end of the
container. While this is directly contrary to the normal
practice of trimming as little material as possible, it
was found that trimming a larger amount of material before
beginning the necking process greatly reduced the extent
of wrinkling and splitting of the container end or edge
during the reduction process, and during thread forming.
Typically at least 20 mm of metal is trimmed from the
container end, and preferably 25, or 28, or 30 mm (or
more) is trimmed. The precise amount trimmed will depend
(as will be explained) on the container dimensions, the
length and diameter required for the container neck, and
the nature of the material used. It was found that with
the l'deeper trimming, used with the other features to be
described, the reject rate due to split or wavy ends
dropped from 30% to 40~ to about 2% to 4%.
The reasons why the increased amount trimmed
reduces the extent to which the container edge 112
wrinkles and splits during the necking process are not
fully understood. Initially it was believed that the
reason was that there may be a difference in hardness at
the free end of the container, as compared with the
hardness of the cont~iner wall further toward the closed
end of the container. However tests were conducted on the
container 108a, 108b shown in Figs. 3A, 3B. Container
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108a was of ~st~n~Ard~ length, i.e. 225 mm (for a trim
length of 215 mm) while container 108b was extruded to be
considerably longer, e.g. 243 mm (again for a trim length
of 215 mm)~
Longitudinal sections were taken from the walls
of the contAiners 108a, 108b and Rnoop microhardness
measurements were made at the midwalls of the sections
every 2 mm beginning at the top of the containers (i.e.
edge llla, lllb) to the end of the sections, as shown in
Fig. 5. In Fig. 5, curve 126 shows the hardness as a
function of distance from the open edge llla of the
standard height container 108a, while curve 128 shows the
hardness as a function of distance from the edge lllb of
longer container 108b. The point on curve 126 at which
the standard height container 108a was trimmed is
indicated at 130 (approximately 10 mm from its open edge
lllb), and the point on curve 128 at which the longer
container was trimmed is indicated at 132 (approximately
28 mm from its open edge lllb). It will be seen that the
hardness at point 132 is greater than that at point 130.
As shown, there was a slight increase in the hardness
~cold working) of the metal with increasing distance from
the open edge llla, lllb of each container. Since a
material having a higher level of cold working hardness is
less formable, therefore the degree of hardness or cold
working does not account for the difference in behaviour
observed when a larger amount of metal is trimmed.
Next, photomicrographs were taken of the
sections taken from container 108b. Fig. 6 is a
photomicrograph of a sample from container 108b (100 times
magnification) at the open edge lllb of the container.
Fig. 7 is a similar photomicrograph taken about 10 mm from
the open edge lllb of the same container 108b, while Fig.
8 is a photomicrograph taken about 28 mm from the open
edge lllb of the container 108b.
It will be seen in Fig. 6 that adjacent the open
edge llla, there are numerous precipitates 134 in the
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metal which form nearly continuous lines 136 on the
photomicrographs. It is believed that these abundant
precipitates, and perhaps a higher degree of irregularity
in the metal structure, can create weaknesses in the
microstructure of the metal, resulting in poor formability
in the dies.
In Fig. 7 (showing where st~Ard trimming in
effect occurs), it will be seen that the precipitates 134
are still abundant, although slightly less so than in Fig.
6, and that they still form nearly continuous lines 136.
In Fig. 8, about 28 mm from the edge llla of the
container 108b there are fewer precipitates than in Fig.
7, and the continuous lines formed by them are less
marked. It is believed that the reduction in precipitates
or cont~m;nAnts is an important reason for the improved
formability.
It is believed that the cont~inA~ts or
impurities occur in the slugs during their forming and
preparation. In the production of slugs, aluminum with
appropriate additives is liquified and fed down a trough
through rollers in a type of continuous casting process,
to form aluminum strips. The strips when cast may
initially be 4 inches wide and 2 inches high but when they
are rolled, they are reduced greatly in thickness, to
between 4 and 12 mm depending on the thickness of slug
required. They are then usually rolled for storage, and
later unrolled and stamped to form the slugs, although
they can also go directly from forming to stamping.
During this manufacturing process, the exterior surfaces
of the aluminum are exposed to the rollers and to the air
and may accumulate impurities.
In addition, after the slugs are stamped, they
are normally pre-tumbled by their manufacturer to roughen
their surfaces, so that lubricant will adhere evenly to
them. The pre-tumbling creates major surface
irregularities. The slugs are then again tumbled (usually
by the container manufacturer) in grease (e.g. zinc
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stearate) to coat them with a lubricant which permits the
material to flow through the impact extrusion tools
without scratching the tools. Without the lubricant, the
aluminum (which is very abrasive) tends to scratch the
tools. ~he lubricant may add further impurities to the
surface of the aluminum slug.
It is k~own that when a slug is impacted by an
impact extrusion punch, the first metal to flow comes from
the impacted side of the slug and from the exterior
circumference of the slug. It therefore appears that the
contaminants on the surfaces, and perhaps some surface
irregularities, are the first to move from the slug and
thereby position themselves at or near the leading edge
llla, lllb of the extruded container. It appears that
this is the reason why the cont~minA~t levels reduce in a
direction away from the open or leading edge llla, lllb of
the extruded container, and why a deeper trim than normal
permits formation of a long, narrow neck without a high
reject rate. In effect the deeper trim exposes metal at
the open edge which is substantially more formable than
that exposed by a normal (less deep) trim.
The method of making a long, narrow neck
container will next be described. Reference is made to
Fig. 9, which shows an outer die 140 and an internal guide
142 in position on a die holder 144. As shown, the outer
die 140 includes a cylindrical outer surface 146 having an
enlarged lip 148 at its rear end. The lip 148 is received
in an opening 150 in die holder 144, with a rear clearance
space 152 to accommodate dirt particles and the like. Die
holder 144 has an outer thread 154 which receives a die
locking nut 156 to hold the outer die 140 in position.
Die holder 144 also includes a rear stem 158 having a rear
surface 159 and which has an outer thread 160 to permit it
to be locked into a necking machine such as the Nussbaum
AG necking machine referred to above.
The outer die 140 also has an inwardly curving
surface or lead profile 164. Lead profile 164 blends
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smoothly into a forming radius or surface 165, which is
the surface that actually works the metal of the
container. Forming radius 165 blends smoothly into a
generally cylindrical inner surface 166 (which in fact
tapers slightly outwardly toward the rear of the outer
die).
The internal guide 142 has an outer cylindrical
surface 167 which is positioned within the cylindrical
surface 166 with a small annular space between them,
sufficient to accommodate the metal of the container end
with very narrow clearances (to limit and control
undesired waviness and splitting of the metal). The
internal guide 142 includes at its rear end a lip 168
which serves as a stop for the free edge of the container.
The internal guide 142 is mounted on a guide
shaft 170 (also shown in Figs. 10, 11). Shaft 170 extends
through the center of internal guide 142 and is held
thereto by a locking bolt 172 accommodated in an internal
threaded recess 174 in the front end of guide shaft 170.
A coil spring 176 encircles the guide shaft 170
behind the internal guide 142 and abuts against the rear
end 178 of the inner guide. The spring 176 is received in
a recess 180 in die holder 144.
Internal guide shaft 170 extends through recess
180 and through an axial opening 182 in the rear stem 158
of die holder 144 and has an enlarged end 184. End 184
has a first surface 186, a threaded outer surface 188, and
a rear flat 190 (Fig. 11) to permit gripping of end 186 by
a wrench (not shown). An axial opening 192 extends
entirely through the guide shaft 170, from enlarged end
184 and through the locking bolt 172. The opening 192
permits compressed air from a source 194 to be introduced
via flexible hose 196 into the container to help eject the
container, as will be described. Hose 196 is connected to
guide shaft 184 by a fitting 198 threaded into opening 200
in the enlarged end 184.
In use, before the container is introduced into
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the die 140 of Fig. 9, the guide shaft 170 normally
assumes a position in which the front surface 186 of
enlarged end 184 contacts the rear surface 159 of the die
holder stem 158, and the enlarged rear lip 168 of the
internal guide 142 is positioned adjacent the position
where the outer die inner surfaces 165, 166 join. When a
container 108b is thrust into the die 140 by the necking
machine, the free edge of the contA; ner contacts lead
surface profile 166 and is guided into the forming radius
165, beginning the forming process. Once through the
forming radius, the free edge contacts lip 168 and forces
the internal guide 142 rearwardly (to the right as drawn
in Fig. 9), against the pressure of spring 176. As the
container is forced against the forming radius 165, the
. 15 metal of the open end of the container is deformed thus
performing one step in the necking process. As the
internal guide 142 is forced rearwardly or to the right as
drawn in Fig. 9, the metal ring 201 mounted on the
enlarged end 184 moves to the right, away from a proximity
switch 202 which is mounted on the necking machine. If
the guide shaft sticks and fails to return to its original
position, the switch will detect the absence of a target
and the machine will shut off.
After the container has been partially formed in
die 140, it must be ejected so that it can move to the
next forming station on the necking machine. Because the
clearances between the metal of the container and internal
guide 142 and the outer die 140 are so small at least in
the initial die stations (as will be explained), it is
found that the force of spring 176 is not sufficient to
eject the container in at least the first few forming
stations. Therefore, in at least the first three or four
forming stations, compressed air from source 194
(typically at about 100 psi pressure) helps to eject the
container during the ejection step. It is found that
without the compressed air, the contA;ners may stick in
the dies and are ruined when the machine tries to move
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them to the next forming station. In addition the air
helps to cool the contAiners, dies and guides, removing
heat added by the aggressive forming (the necking machine
typically forms about 100 containers per minute).
A typical container having a long, narrow neck
which may be formed by the method of the invention is
shown at 210 in Fig. 12. ContAiner 210 has the usual
cylindrical body 212 and is (in the illustrative
embodiment described) 228.3 mm long, of which the neck 214
is in total 102.5771 mm long. The neck 214 includes a
first curved portion 216, a cylindrical narrowed portion
218 (diameter 34.0 mm) extending from curved portion 216,
a second curved portion 220 extending from portion 218, a
second cylindrical narrowed portion 222 extending from
curved portion 220 (diameter 22.0 mm), and a thread 224 at
the end of portion 222. Other profiles can of course be
made, e.g. as shown at 210a in Fig. 13, where portions
216, 218, 220 are formed as a single straight, conical
taper 225.
Figs. 14 to 21 are dimensioned drawings of the
outer dies 140-1 to 140-8 used in the first eight forming
or necking stations 230-1 to 230-8 (Fig. 4) of a necking
machine 120 for producing containers of the kind shown in
Fig. 12. Reference numerals followed by the suffix -1"
to "-8" indicate parts corresponding to those of Figs. 9
and 10 and/or located at the first eight forming stations.
It will be seen that the inner curved surfaces 164-1 to
164-8 of the outer dies become progressively more arcuate,
and longer, as the dies progress from stations 230-1 to
230-8 (as the neck of the container is progressively
narrowed).
Figs. 22 to 29 show the internal guides 142-1 to
142-8 used with the outer dies 140-1 to 140-8
respectively. The internal guides are all of the same
general shape, but their particular dimensions vary as
shown depending on the die with which they are used.
Figs. 30 to 37 show the container 210-1 to 210-8
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after it has passed through each of the first eight
stations (cont~; ni ng the dies and internal guides shown in
Figs. 14 to 29). The length of the container is also
shown. It will be seen by comparing Figs. 30 and 12 that
at the first necking station 230-1, the neck has been
reduced in diameter from 66.0 to 60.26 mm and the
cont~; ner has been reduced slightly in length from 215 to
213.3 mm. The reason for the shortening in length is that
the aggressive curvature 216-1 of the neck has absorbed
what would otherwise be an increase in length. However it
will be seen from Figs. 31 to 37 that at each successive
necking station, as the neck becomes smaller in diameter,
the length of the container (specifically of the neck
portion) increases.
To allow for the changes in container length and
also for the various dies used, the length of the guide
shaft 170 is made shorter at each successive station. In
the embodiment with the dimensions shown, the guide shaft
170 lengths at the first eight stations were:
Length L (total Length Q (length of
Station length of guide shaft portion supporting
170 (mm) inter~l guide
142 (mm)
230-1 319.75 56.27
230-2 315.55 54.13
230-3 312.26 52.78
230-4 30g.67 51.55
230-5 307.87 51.45
230-6 306.34 51.52
230-7 304.12 51.40
230-8 303.51 52.48
It is also noted that the wall thickness of the
container neck increases during the necking process.
Therefore the thickness of the annular space between outer
dies 140 and internal guide 142 is increased at each
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necking station. The thickness of each annular space can
be seen from the dimensions in the drawings. For example
at the first station 230-1 the internal diameter of
surface 166-1 in die 140-1 is 60.2619 mm, while the
external diameter of corresponding guide 142-1 is 59.30
mm, leaYing an annular space between them of 0.9619 mm.
At station 230-8 the internal diameter of surface 166-8 is
34.0 mm and the external diameter of guide 142-8 is 32.62
mm, leaving an annular space between them of 1.38 mm,
which is considerably thicker.
It is also noted that the annular space between
each die and its internal guide is sufficiently wide to
accommodate not only the wall thickness of the container
at that stage, but also a clearance. In many common
necking processes the clearance is between 0.11 and 0.15
mm, but with the process of the invention the clearance
has been reduced to 0.04 to 0.06 mm (preferably 0.04 mm).
(The clearance of 0.04 mm is a total clearance, i.e. 0.02
mm clearance from each surface of the container neck
wall.)
The very small clearance helps to control the
flow of material and prevent splitting and wrinkling, and
in addition the tight clearance causes "ironing" of the
material to occur during the necking steps. During the
ironing, the metal surface is smoothed and actually
reformed as it lengthens. However ~ecause of the friction
created by the narrow clearances, the compressed air from
source 194 is needed as mentioned to help eject the
containers, at least in the-first few stations.
With the container profile shown in Fig. 12, the
most aggressive forming occurs in stations 230-1 to 230-8,
where the neck is rapidly narrowed from 66 to 34 mm. In
the next set of forming stations 230-9 to 230-14, the neck
is further naLLowed to 22 mm. This is a lesser degree of
necking and therefore compressed air ejection assist is
not normally needed. The cont~iner as it passes through
stations 230-9 to 230-14 is shown in Figs. 38 to 43.
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These stations 230-9 through 23-14 contain dies and
internal guides as previously described, with appropriate
dimensions.
It is found that even with the steps described
above, the integrity of the cut edge 112b of the container
cannot be preserved throughout the entire necking process.
Even with removing a much larger than normal portion of
the open end of the contAiner before beginning the necking
process, to reduce impurities at the free end, and even
with the very tight clearances used, the cut edge of the
container tended to split, wrinkle and become uneven to
some extent during the reduction process. The uneven edge
is indicated at 112-14 in Fig. 43. This caused fractures
to occur when applying the thread in the threading station
234 (Fig. 4).
Therefore a mid-station trimmer 236 is added, as
shown in Fig. 4. The trimmer 236 is a conventional
trimmer, like trimmer 122, and simply cuts off a small
section of the free end of the container between forming
stations 230-14 and 230-lS, to eliminate the edge which
may contain splits and wrinkles. It is normally necessary
to remove only about 3 mm for this purpose.
After the contA i ner leaves the mid-station
trimmer 236, it has a cut edge 112-15 which is straight
and smooth (Fig. 44). The container then passes through
three additional (and conventional) forming stations 230-
16 to 230-18 which reduce the top of the neck to a shape
suitable for a thread. The shaped top portion is shown at
240-16 to 240-18.
The container then moves to the threading
station 234, where the thread 224 (Fig. 12) is applied.
Despite the aggressiveness of the thread forming, it is
found as mentioned that very little splitting occurs, and
that the reject rate due to splitting or wrinkling is now
only 2% to 4%.
After threading, the contA;ner moves to a final
trimming station 238 where its open edge is again trimmed,
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to regulate the height of the container. This final
trimming is conventional.
While specific dimensions have been given by way
of example, it will be understood as previously mentioned
that the ~imensions may be changed depending on the
ions of the particular cont~ r and neck being
formed, and on the extent of impurities present in the
slug used to form the container. For example, instead of
pre-tumbling the slug twhich tends to create large scale
surface irregularities which may increase the precipitates
found in the open end of the container), the slug can be
sandblasted (to create a more controlled textured surface)
and lubricant then applied. With the sandblasting, the
lubricant adheres more evenly, with no need for the harsh
pre-tumbling, and it may then be possible to cut off less
from the open end of the cont~;n~r in order to reach a
metal region which produces better formability. In
addition, if more care is taken in the production of
slugs, so that they pick up fewer cont~ nts from the
air, the rollers, and generally from handling during their
production, then a less deep trim will be needed. However
the initial trim will normally always be deeper than that
needed simply to achieve a straight, smooth edge.
The deep trim is particularly useful when the
reduction in the neck diameter must be large (e.g. as
here, from 66 mm to 22 mm, and then to 19.45 mm, or by
more than 44 mm, i.e. two thirds) and where the neck is to
be elongated. (For automotive applications preferably the
neck is at least 75 mm long, and desirably at leat lO0 mm
long.) If the neck reduction were smaller, again a less
deep trim would be needed.
While preferred embodiments of the invention
have been described, it will be appreciated that various
changes may be made within the spirit of the invention and
all such changes are intended to be included within the
scope of the attached claims.
