U.S. patent number 3,826,412 [Application Number 05/275,370] was granted by the patent office on 1974-07-30 for pressure release valves for aerosol cans.
This patent grant is currently assigned to Crown Cork & Seal Company, Inc.. Invention is credited to Raymond H. P. Kneusel.
United States Patent |
3,826,412 |
Kneusel |
July 30, 1974 |
PRESSURE RELEASE VALVES FOR AEROSOL CANS
Abstract
A pressure release valve is located in the domed bottom of an
aerosol can. A centrally located area in the domed bottom having a
lesser resistance to eversion than the peripheral area in the domed
bottom includes several score lines which meet at a common point in
a spoke-like configuration. The centrally located area of the
bottom will evert at a pressure of 170 to 200 p.s.i. so as to
rupture the bottom at the source lines before any substantial
eversion of the peripheral area occurs.
Inventors: |
Kneusel; Raymond H. P.
(Flourtown, PA) |
Assignee: |
Crown Cork & Seal Company,
Inc. (Philadelphia, PA)
|
Family
ID: |
26895302 |
Appl.
No.: |
05/275,370 |
Filed: |
July 26, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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199929 |
Nov 18, 1971 |
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Current U.S.
Class: |
222/397 |
Current CPC
Class: |
F17C
13/123 (20130101); B21D 51/24 (20130101); B65D
83/70 (20130101); F17C 2201/0109 (20130101); F17C
2205/0314 (20130101); F17C 2201/0114 (20130101); F17C
2205/0329 (20130101); F17C 2260/042 (20130101); F17C
2205/0394 (20130101); F17C 2205/0397 (20130101); F17C
2270/0718 (20130101); F17C 2201/058 (20130101); F17C
2205/0332 (20130101); F17C 2201/035 (20130101) |
Current International
Class: |
B21D
51/16 (20060101); B65D 83/14 (20060101); F17C
13/12 (20060101); F17C 13/00 (20060101); B21D
51/24 (20060101); B65d 083/14 () |
Field of
Search: |
;222/396,397,541
;220/89A,89B,44R,44D ;137/68-71 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Reeves; Robert B.
Assistant Examiner: Bartuska; Francis J.
Attorney, Agent or Firm: Woodcock, Washburn, Kurtz &
Mackiewicz
Parent Case Text
RELATED APPLICATION
This is a continuation-in-part of copending application Ser. No.
199,929 filed Nov. 18, 1971.
Claims
What is claimed is:
1. An aerosol can comprising a side wall portion, a top portion
adapted to receive a valve assembly including a valve cup, and a
steel bottom portion, said bottom portion having a peripheral
concave area, a centrally located substantially flat area connected
to and integrally formed therewith and substantially less resistant
to internal deforming pressures than said peripheral concave area,
and a pressure release valve formed by a plurality of intersecting
score lines located on said flat area, said flat area deforming
outwardly at a pressure in excess of 170 p.s.i., but below 200
p.s.i. with resulting rupturing of said bottom portion
substantially limited to a point of intersection of said score
lines located substantially centrally in said flat area so as to
release the contents of said can through a small opening created by
said rupturing, said flat area deforming outwardly before rupturing
at said point of intersection without substantial everting of said
concave area.
2. The aerosol can of claim 1 wherein each of said score lines is
linear.
3. The aerosol can of claim 2 wherein said score lines include
pairs of lines located on diametrically opposite sides of a point
on said flat area.
4. The aerosol can of claim 3 wherein said score lines are located
entirely within said flat area.
5. The aerosol can of claim 4 wherein said score lines consist of
six equally angularly spaced score lines.
6. The aerosol can of claim 4 wherein said score lines consist of
eight equally angularly spaced score lines.
7. The aerosol can of claim 1 wherein each said score line is a
compound score line including a rough score line and a finished
score line within said rough score line, said bottom portion having
a residual thickness of 0.002 to 0.005 inches at the base of said
fine score line.
8. The aerosol can of claim 1 wherein each of said score lines has
a lesser residual thickness near the center of the flat area than
at the edge of the flat area.
9. The aerosol can of claim 1 wherein the maximum diameter of said
flat area is less than one third the diameter of said bottom
portion.
10. The aerosol can of claim 2 comprising a series of arcuate score
lines located radially outwardly from said point of intersection in
a broken circular array, each of said arcuate score lines being
located between each adjacent pair of said linear score lines.
11. The aerosol can of claim 10 wherein the ends of said arcuate
score lines are spaced a substantial distance from each said
adjacent pair of said linear score lines.
12. The aerosol can of claim 11 wherein said arcuate score lines
are substantially aligned with the ends of said linear score
lines.
13. The aerosol can of claim 12 comprising five of said linear
score lines and five of said arcuate score lines.
14. An aerosol can comprising a side wall portion, a top portion
adapted to receive a valve assembly including a valve cup, and a
steel bottom portion, said bottom portion having a peripheral
concave area, a centrally located bubble-like area integrally
formed with said peripheral concave area and substantially
circumscribed by a score line, said buble-like area having a lesser
radius of curvature than said peripheral concave area, and a
pressure release valve formed by a plurality of intersecting score
lines located within said bubble-like area, said bubble-like area
everting at a pressure in excess of 170 p.s.i. with resulting
rupturing of said bottom portion at the intersection of said score
lines so as to release the contents of said can through an opening
created by said rupturing.
15. The aerosol can of claim 14 wherein said score lines consist of
eight equally angularly spaced score lines.
16. The aerosol can of claim 14 wherein said score line
circumscribing said bubble-like area is substantially circular.
17. The aerosol can of claim 16 wherein the maximum diameter of
said bubble-like area is less than one third the diameter of said
bottom portion.
18. An aerosol can comprising a steel side wall portion, a top
portion adapted to receive a valve assembly including a valve cup,
and a steel domed bottom portion, said bottom portion including a
steel concave peripheral area and a steel central area integral
with said peripheral area and having a lesser resistance to
internal deforming forces than said peripheral area, said central
area having score lines intersecting in a region located
substantially inwardly from said concave peripheral area, said
central area deforming outwardly at a predetermined pressure while
said peripheral area remains concave and substantially undeformed,
said scored region rupturing at a point of intersection of said
score lines after and as a result of the outward deformation of
said central area without any substantial rupturing along the
length of said score lines or substantial outward deformation of
said peripheral area.
19. An aerosol can comprising a side wall portion, a top portion
adapted to receive a valve assembly including a valve cup, and a
steel bottom portion, said bottom portion having a peripheral
concave area characterized by a first radius of curvature and a
centrally located concave valve area characterized by a second
radius of curvature different from said first radius of curvature,
said concave valve area comprising a plurality of intersecting
score lines everting at a pressure in excess of 170 p.s.i. and less
than 200 p.s.i. with resulting rupturing of said bottom portion at
the intersection of said score lines after said everting of said
concave valve area so as to release the contents of said can
through an opening created by said rupturing without substantial
everting of said peripheral concave area.
20. The aerosol can of claim 19 wherein said concave valve area and
said score lines substantially limit the rupturing of said score
lines to the intersection thereof.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Cans of the aerosol type having an internal propellant, such as
Freon, are potentially dangerous. When such a container is
subjected to excessive temperatures, dangerously high pressure
levels are generated within the container. Under these conditions,
the can bottom will evert and explode and portions of the can may
be propelled at dangerously high velocities. Such conditions may
occur when the can is incinerated and even during storage at high
temperatures. In order to provide for the safe release of a
pressure build-up within the can, a safety valve must be
provided.
2. The Prior Art
The prior art has suggested the use of scoring to provide pressure
release valves in various areas of an aerosol can. U.S. Pat. No.
3,074,602 -- Shillady et al. discloses a pressure release valve
which is formed by scoring the valve cup of an aerosol can. The
scoring supposedly occurs at a point of maximum deformation when
the can is subjected to abnormally high pressure levels within.
This distortion of the valve cup in the area of weakness is
intended to rupture the cup so as to safely release the pressure
build-up. A circular score line and a score point are disclosed in
two different embodiments of the Shillady et al. patent.
U.S. Pat. No. 3,292,826 -- Abplanalp discloses a pressure release
valve formed by at least partially circumscribing a line of
weakness, e.g., a score line, over a relatively large section of an
aerosol can wall. As suggested in the Abplanalp specification, the
line of weakness may be located at the various portions of the
container but should not be located on the bottom wall since the
discharge of pressure against the surface on which a conventional
can rests would, even with the Abplanalp valve, tend to displace
the can from that surface and this would be objectionable.
The particular pressure release valves described in the
above-discussed patents have a number of disadvantages. The failure
of the valves to release pressure build-ups within a narrow
pressure range of 170 p.s.i. to 200 p.s.i. is juat one of these
disadvantages. Although the Shillady et al patent does indicate an
effective range of 175 to 200 p.s.i. for the valve, such a valve is
not consistently effective in this range. The reason for this is in
large part due to the small size of the Shillady scored area which
requires a very small residual thickness and this small thickness
results in an unreliable release of pressure.
The Abplanalp circular score line which is located in the
cylindrical wall of the can body also requires a very small
residual thickness, e.g., 0.001 inches assuming a circular score
line diameter of one inch. This small residual thickness would be
required since there is little or no deformation of the cylindrical
wall outside the score line. However, such a small residual
thickness is difficult to achieve in commercial production due to
inclusions and variations in the metal thickness. The result is the
unreliable release of pressure from the can. Since pressure
approaching 200 p.s.i. will result in the eversion of most aerosol
can bottoms with the resulting unraveling of the double seam along
the periphery of the bottom, it is imperative that the pressure
release occur before this dangerously high pressure is reached.
It is of course just as important to avoid a premature release of
pressure; i.e., a release below the 170 p.s.i. level. This is
extremely important since a pressure of perhaps 160 p.s.i. may be
reached during normal operation without any real danger of
explosion at that pressure level. Therefore, any release of a
pressure build-up of 160 p.s.i. may result in the unnecessary
destruction of an aerosol can and its contents.
Another disadvantage of the prior art pressure release valves
relates to the aesthetic properties of the aerosol can. Readily
visible score lines which appear on the exterior of the can are not
pleasing to the eye. This is particularly true where the score line
is located on the exterior side of the can side wall and extends
over a large area as shown in Abplanalp patent.
The manufacturing technique which is utilized in making the
pressure release valves in the Shillady et al patent represnts a
further disadvantage. The Shillady et al patent discloses the use
of a tungsten inert gas shielded electric arc to score the valve
cup of the aerosol can. As the Shillady et al patent cautions, this
technique may result in excessive scoring so as to create a hole in
the valve cup. Furthermore, this method of scoring is relatively
costly and therefore not particularly suitable for the can industry
where low cost high speed production is required.
SUMMARY OF THE INVENTION
It is an object of this inventon to provide an aerosol can with a
safety valve which will reliably release a pressure build-up before
a dangerously high pressure level is reached.
It is another object of this invention to provide a safety valve
which will not prematurely release a pressure build-up.
It is a further object of this invention to provide a safety valve
in an aerosol can which does not adversely affect the aesthetic
properties of the can.
It is also an object of this invention to provide a safety valve
for an aerosol can which is inexpensive to manufacture.
It is still a further object of this invention to provide a safety
valve in an aerosol can bottom which does not result in the
propelling of the can upon release even when the can rests upon its
bottom.
In accordance with these and other objects of this invention, a
safety valve is located in the domed bottom wall of an aerosol can.
The valve comprises a central everting area having a resistance to
eversion less than that of the integral peripheral concave area
surrounding the everting area. By providing intersecting score
lines within the everting area and leaving a residual thickness
which is substantially less than the normal thickness of the domed
bottom, the valve will reliably release any pressure build-up at a
pressure within a range of 170 p.s.i. to 200 p.s.i. as the everting
area everts.
The scoring which may leave the bottom with a residual thickness of
0.002 to 0.005 inches may comprise several pairs of linear score
lines located on opposite sides of a point in a spoke-like
configuration. The score lines which are preferably located on the
exterior of the bottom may also be of the compound type.
In a first embodiment, the everting area of the can bottom is flat
to provide a lesser resistance to eversion. In a second embodiment,
the everting area has a different radius of curvature than the
surrounding area and is circumscribed by a line of weakness to
provide a lesser resistance to eversion.
In a third embodiment of the invention, the everting area includes
a plurality of arcuate score lines located between said linear
score lines but spaced therefrom.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of an aerosol can of the type
embodying the invention;
FIG. 2 is a sectional view of a domed bottom which may be double
seamed to the cylindrical side wall portion of the can of FIG. 1 in
accordance with one embodiment of this invention;
FIG. 3 is a plan view of the exterior side of the can bottom shown
in FIG. 2 showing the safety valve of this embodiment;
FIG. 4 is a sectional view of the can bottom of FIGS. 2 and 3 after
release by the valve;
FIG. 5 is a partial plan view of the exterior side of the can
bottom of FIGS. 2 and 3 after release by the valve;
FIG. 6 is a sectional view of a score line taken along line 6--6 in
FIG. 3;
FIG. 7 is a sectional view of another type of score line;
FIG. 8 is a plan view of the exterior side of a can bottom showing
a modified score line configuration;
FIGS. 9 (a-e) depict a method of making the safety valve in the
embodiment of FIGS. 1-6;
FIG. 10 is a plan view of the rough scoring taken along line 10--10
of FIG. 9b;
FIG. 11 is a plan view of the fine scoring punch taken along line
11--11 in FIG. 9d;
FIG. 12 is a plan view of the fine scoring anvil taken along line
12--12 of FIG. 9d;
FIG. 13 is a sectional view of a domed bottom which may be double
seamed to the cylindrical side wall portion of the can of FIG. 1 in
accordance with another embodiment of this invention;
FIG. 14 is a plan view of the exterior side of the can bottom shown
in FIG. 2 showing the safety valve of this invention; and
FIGS. 15 (a-e) depict a method of making the safety valve in the
embodiment of FIGS. 13 and 14;
FIG. 16 is a plan view of another can bottom with another safety
valve embodiment of the invention;
FIG. 17 is a partial sectional view of the can bottom shown in FIG.
16 taken along line 17--17;
FIG. 18 is a plan view of a scoring punch which may be utilized to
form the safety valve shown in FIGS. 16 and 17;
FIG. 19 is a sectional view of the scoring punch taken along line
19--19 and shown as engaging the can bottom of FIGS. 16 and 17;
and
FIG. 20 is a sectional view of the scoring punch of FIG. 18 taken
along line 20--20 and shown as engaging the can bottom of FIGS. 16
and 17.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
An aerosol can as shown in FIG. 1 comprises a side wall portion 10
and a top portion 12 receiving a valve assembly including a valve
cup 14, a valve stem 16, and a nozzle 18 adapted to be pushed by a
finger at a surface 20. A domed bottom wall portion 22 is double
seamed to the bottom edge of the side wall portion 10.
In accordance with one embodiment of this invention as shown in
FIGS. 2 and 3, the aerosol can of FIG. 1 is provided with a safety
valve comprising a scored flat area 24 which is centrally located
in the domed bottom 22 and surrounded by outwardly concave
peripheral area 26. The several score lines 28 (a-h) in the flat
area 24 meet at a common point 30 to form a spoke-like design. The
score line pairs 28a and 28e, 28b and 28f, 28c and 28g, and 28d and
28h are located on diametrically opposite sides of the point
30.
As may be seen by reference to FIGS. 4 and 5, the flat area 24 will
evert outwardly as a result of the pressure build-up so as to
rupture the bottom 22 at the point 30 thereby releasing the
pressure build-up. However, the peripheral concave area 26 of the
bottom 22 does not evert. Tests have revealed that the hole at 30
is so small, as to pass only 2.3 cubic feet per minute of air at
160 p.s.i. This is insufficient to significantly move the can on a
horizontal supporting surface. Also, the deformation which is shown
as exaggerated is such that the can will return substantially to
its undeformed position after pressure release thereby limiting
product spillage by substantial closing of the hole at 30.
In accordance with this invention, the bottom 22 will rupture at a
pressure no less than 170 p.s.i. and a pressure no greater than 200
p.s.i. In order to achieve pressure release, within this pressure
range, various aspects of the score lines 28 (a-h) and the flat
area 24 must be carefully controlled. For example, it has been
found that a residual scoring of 0.002 to 0.005 results in pressure
release in the range of 170 to 200 p.s.i. Actually, a scoring depth
in combination with a stepped circular indentation 25 leaving a
residual thickness of 0.004 inches in the region 27 of the spokes
28 and a residual thickness of 0.003 inches in the region 29 of the
spokes 28 which lies beneath the indentation 25 is preferred to
achieve a release pressure of 170 to 185 p.s.i. Preferably, the
diameter of the indentation 25 is 9/32 of an inch.
In order to assure the attainment of this appropriate residual
thickness, a compound score line as shown in FIG. 6 is preferred.
The flat area 24 is first rough scored to form a line 32 having a
base 34. The base 34 is then fine scored to the appropriate
residual thickness at the base 36 of a fine score line 38. It has
been found that a width of 0.002 to 0.004 inches (preferably 0.0025
inches) at the base 36 and an angle 40.degree. to 60.degree.
(preferably 50.degree.) between walls 40 of the lines 38 will
result in score lines which will reliably release the pressure at
the appropriate level.
Although the compound score line is preferred, a conventional score
line shown in FIG. 7 may be utilized if the appropriate residual
thickness can be achieved. Again, it has been found desirable to
provide a 40.degree. to 60.degree. angle between the walls 42 with
50.degree. preferred and a width of 0.002 to 0.004 inches with
0.0025 inches preferred at the base 44.
It is not only important to assure release before the pressure
build-up reaches a level at which the double seamed bottom may
unravel and evert, it is also important to avoid premature release
of pressure by the valve. In this connection, it has been found
that locating the score lines 28 on the exterior or outside of the
bottom 22 provides reliable release before the danger level is
reached while permitting the maximum residual thickness. Locating
the score lines on the exterior of the bottom may result in release
at a pressure of 20 p.s.i. lower than locating the same score lines
having the same residual thickness on the interior of the
bottom.
As shown in FIGS. 4 and 5, a very small opening is created at point
30 when the bottom 22 ruptures at the score lines 28. This is
extremely important since the score lines are located at the bottom
of the aerosol can and the bottom is usually used to support the
can on a horizontal surface. If the rate of flow through the
opening is excessive, the can will be upset or perhaps even
propelled off the horizontal surface. It has been found that the
spoke-like scoring on a flattened area of the aerosol can bottom
will produce an opening having a limited flow rate which is not
sufficient to upset the can on the horizontal surface since the
expelled fluid is able to seep between the horizontal surface and a
double seam of the bottom 22 at a sufficient rate to accommodate
the rate of flow through the opening.
The six spoke configuration for the valve of FIG. 8 is similar to
the eight spoke scoring configuration in FIG. 3. Preferably, the
flattened area 24' for the sixspoke valve and the flattened area 24
of the eight-spoke valve have 3/4 inch diameters where 135 lb. T-5
steel is utilized to achieve release at 180 p.s.i. The doming
radius is 2.319 in. .+-. 0.050 inches and the overall diameter of
the domed bottom as measured from the interior of the double seam
is approximately 2.553 inches for both embodiments so that the flat
area in both embodiments has a diameter of less than one third the
diameter of the bottom.
A method for making a safety valve comprising the compound score
lines 28 in the centrally located flat area 24 will now be
described with reference to FIGS. 9 (a-e). FIG. 9a shows a portion
of a domed bottom 22a prior to flattening and scoring. FIG. 9b
shows an anvil 50 in combination with a punch 52 for rough scoring
and simultaneously flattening the central area of the bottom 22a.
The bottom 22a is held between the supporting surface 54 of the
anvil 50 and the scoring surface 56 on the punch 52 to form the
rough scored and centrally flattened bottom 22b as shown in FIG.
9c. In some instances, it may be desirable to flatten and score the
spokes in separate steps.
The rough scored and flattened bottom 22b then assumes a position
between the fine scoring punch 60 and an anvil 58. When the fine
scoring surface 64 of the punch 60 closes on the bottom 22b which
rests on a stepped anvil surface 62 of the anvil 58, the fine
scored bottom 22c as shown in FIG. 9e is obtained.
An eight-spoke configuration for the rough scoring surface 56 is
shown in FIG. 10. Flats 68 form the base 34 of the rough score
lines while inclined surfaces 66 form the walls of the rough score
lines. An eight-spoke fine scoring surface 64 is shown in FIG. 11.
Flats 70 form the base 36 of the fine score line while inclined
surfaces 72 form the walls 40 of the fine score lines as shown in
FIG. 6. Finally, FIG. 12 shows a plan view of the stepped anvil 62.
The central stepped area 64 of the anvil 63 permits the residual
thickness of the score lines in the region 29 located beneath this
stepped area to have a lesser residual thickness than the area 27
of the score lines.
In accordance with another embodiment of this invention as shown in
FIGS. 13 and 14, the aerosol can of FIG. 1 is provided with a
safety valve comprising a bulging or bubble-like area 124 which is
centrally located in the domed bottom 22 and surrounded by an
outwardly concave peripheral area 126. The several score lines 128
(a-h) in the bubble-like area 124 meet at a common point 130 to
form a spoke-like design. The score line pairs 128a and 128e, 128b
and 128f, 128c and 128g, and 128d and 128h are located on
diametrically opposite sides of the point 130.
In order to render the area 124 less resistant to everting than the
surrounding area 126, the area 124 is circumscribed by a line of
weakness in the form of a circular score line 132. As the pressure
within the can builds up, the area 124 will evert outwardly as a
result of the pressure build-up as shown in phantom in FIG. 13 so
as to rupture the bottom 22 only at the point 130 thereby releasing
the pressure build-up. However, the surrounding area 126 at the
bottom 22 which is more resistant to everting than the area 124
will not evert.
Again, in accordance with this invention, the bottom 22 will
rupture at a pressure no less than 170 p.s.i. and a pressure no
greater than 200 p.s.i. In order to achieve the pressure release
within this pressure range, the various aspects of the valve must
be carefully controlled. For example, the residual thickness of the
score lines 128 (a-h) should be 0.002 to 0.005. Actually, it has
been found that a residual thickness of 0.004 inches in the region
127 of the spokes or lines 128 and a residual thickness of 0.003
inches in the region 129 of the spokes 128 which lies beneath a
9.32 diameter circular indentation 125 is preferred to achieve a
pressure release of 170 to 185 p.s.i. (see also FIG. 15c) The line
of weakness 132 circumscribing the area 124 is achieved by scoring
to a residual thickness of 0.010 inches. Thus the score line 132
has a greater residual thickness than the score lines 128 (a-h)
although this is not indicated in FIG. 15c or 15e.
Another critical aspect of the valve shown in FIGS. 13 and 14
involves the dimensions of the bubble-like area 124. It has been
found that an overall bubble diameter of 3/4 inch and a bubble
radius of one inch are particularly effective. This will leave an
overall bubble-height of approximately 1/16 inch. The foregoing
specifications apply to a bottom 22 of 135 lb. T-5 steel (0.015
inches thick). The doming radius is again 2.319 inch .+-. 0.050
inches and the overall diameter of the domed bottom as measured
from the interior of the double-seam is approximately 2.553
inches.
A method of making a safety valve comprising the bulging or
bubble-like area circumscribed by a line of weakness and having
score lines located inwardly of the line of weakness will now be
described with reference to FIGS. 15 (a-e). FIG. 15a shows a
portion of a domed bottom 122a before scoring. FIG. 15b shows a
flattening and scoring punch 152 having a scoring surface 153 in
combination with an anvil 150 having a stepped supporting surface
151 for scoring the bottom 122a to form score lines 128 a-h, 130
and 132 as shown in FIG. 15c. After scoring, the bottom 122c is
placed between a doming die 156 and an anvil 154 to form the
bulging area 124 as shown at FIG. 15e. Thus, the bottom is scored
in the flat initially and then domed to form the bulging area
124.
In accordance with yet another embodiment of the invention shown in
FIGS. 16 and 17, a flat area 224 having a 0.750 inch diameter is
scored on the exterior of the domed can bottom 222 so as to form
five substantially linear score lines 226 which extend radially
outwardly from a centrally located point 228. The flat area 224 is
also scored so as to form a plurality of arcuate score lines 230
located radially outwardly from the centrally located point 228 in
a broken circular array.
It can be seen that each of the arcuate score lines 230 is located
between an adjacent pair of linear score lines 226 at the radial
outward extremities of the linear score lines. It will also be seen
that the ends 232 of each arcuate score line 230 are spaced a
substantial distance from the adjacent linear score lines 226 as
contrasted with the embodiment shown in FIG. 14 wherein the
continuous circular score line 132 is joined with radially
extending score lines 128 (a-h).
A scoring punch configuration which may be utilized to form the
valve of FIGS. 16 and 17 is shown in FIGS. 18-20. The fine scoring
surface which may be substituted for the surface 64 in FIG. 9d
comprises flats 232 to form the base 234 of the score lines while
inclined surfaces 236 form the walls 238. By utilizing a stepped
supporting anvil having a 9/32 inch central pedestal, the central
area of the score line may be provided with a 0.003 inch residual
thickness while the residual thickness of the remainder of the
score line ranges from 0.005 to 0.006 inches. The scoring provides
flat area 224 with a fliplike action at pressures in the range of
172 to 200 p.s.i. This in turn will rupture the linear score line
226 within the 9/32 inch diameter.
Although a particular embodiment of the invention has been shown
and described, it will be understood that various modifications may
be made in that embodiment without departing from the true spirit
and scope of the invention as set forth in the appended claims. For
example the bottom of the can may be entirely flat.
* * * * *