Pressure vessel having pressure releasing mechanism

A can has a cylindrical metal can body having a bottom and a metal upper lid double-seamed thereto. It also has a recess for the engagement of a seaming chuck which is formed in the upper surface of the upper lid, and which is made to project into the interior of the can body by the seaming to make a cavity thereinto. The bottom of the recess has a plurality of score lines extending in the circumferential direction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a pressure vessel having a pressure 
releasing mechanism which allows the pressure in the vessel to escape by 
itself when the internal pressure thereof has increased to such an extent 
as to blow off the lid of the vessel. 
A pressure vessel mentioned herein refers to a vessel containing a quick 
lime which reacts exothermically with water when brought into contact 
therewith so as to heat a food or a pharmaceutical product separately 
accommodated in the vessel by the heat generated by the contact between 
the quick lime and water, or an aerosol vessel containing a cosmetic 
preparation and a liquefied gas. 
Such a pressure vessel generally has a pressure releasing mechanism to 
prevent any explosion that would occur if an excessive exothermic reaction 
takes place in the former type of vessel, or if the internal pressure is 
excessively increased because the latter type of vessel has been thrown 
into a fire. 
2. Description of the Prior Art 
A conventional pressure releasing construction for a pressure vessel of 
this type has been disclosed in the specification of Canadian Patent No. 
957,628. 
In this pressure releasing construction, a metal upper lid b is 
double-seamed to a metal can body a of an aerosol vessel, as shown in 
FIGS. 10 and 11. A vertical lid plate portion c of the metal upper lid b 
which abuts against the inner wall of the can body has a large number of 
score lines d extending in the radial direction, each starting from 
halfway down the vertical lid plate portion c and extending over the top 
of the seaming. If the upper lid b is deformed from the state shown in 
FIG. 10 to the state shown in FIG. 11 by an increase in the internal 
pressure, the score lines d are broken so as to release the internal 
pressure therethrough, thereby preventing blow-off of the upper lid b. In 
such a construction, however, since the score lines d are provided over 
the seamed portion of the lid, they cannot be broken until the vertical 
lid plate portion c of the upper lid b and the top portion extending 
therefrom have been deformed to such an extent that they have risen. This 
means that there is the danger of a time lag between the excessive rise of 
the internal pressure and the escape of the pressure. In addition, it is 
illogical in terms of the function originally required of the internal 
pressure vessel to provide the score lines d in the portion of the lid 
which is to be firmly seamed to make the vessel completely air-tight. 
SUMMARY OF THE INVENTION 
In the present invention it is noted that an engagement recess for a 
seaming chuck which is formed in the upper surface of the upper lid is 
made to project into the interior of the can body to form a cavity 
thereinto by the seaming of the upper lid to the can body and is subjected 
to pressure, and is considered releasing the internal pressure by 
providing score lines in the bottom of the recess and by allowing these 
score lines to break immediately once the internal pressure rises 
excessively. 
To accomplish the object of the present invention, there is provided a 
pressure vessel having a pressure escaping mechanism, the pressure vessel 
including a cylindrical metal can body having a bottom, a metal upper lid 
which is double-seamed to the can body, and an engagement recess for a 
seaming chuck which is formed in the upper surface of the upper lid and 
which is made owing to the seaming to project into the interior of the can 
body to form a cavity thereinto, wherein the pressure vessel is 
characterized by comprising a plurality of score lines formed on the 
bottom of the recess and extending in the circumferential direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described hereinunder 
with reference to FIGS. 1 to 6. 
In the first embodiment of the pressure vessel, a metal upper lid 3 is 
double-seamed to a cylindrical metal can body 2 having a bottom 1. This 
leaves a space 13' between the can body 2 and the cylindrical wall 
defining the recess 10, the space 13' extending approximately halfway to 
the bottom 1 of the can body 2. 
The construction of this seaming is as follows. The can body 2 has an 
overhanging flange 4 at the edge of an upper opening thereof, as shown in 
FIG. 3, while the upper lid 3 has a flange 5 which is to be seamed 
together with the flange 4. Inside the flange 5, an engagement recess 8 
for a seaming chuck is formed beforehand by both a side plate 6 extending 
vertically, as viewed in the cross-section, and a bottom plate 7 provided 
at the bottom of the side plate 6 and extending therefrom in the 
horizontal direction. When the chuck is engaged in the recess 8, and the 
flange 4 of the can body 2 and the flange 5 of the upper lid 3 are seamed 
together by means of the chuck and an external roller by a usual method, 
the recess 8 is inevitably made to protrude thereby into the interior of 
the can body 2, as shown in FIG. 4 
The first embodiment of the present invention is characterized by the 
provision of a plurality of score lines 9 on the bottom plate 7 of the 
recess 8, extending in the circumferential direction. The score lines 9 
are preferably provided as close to the vertical plate portion 6 as 
possible, as shown in the drawing. It is also preferable for them to be 
provided on the lower surface of the bottom plate 7, as shown in FIG. 4. 
However, they may be formed on the upper surface thereof, as shown in FIG. 
6. 
The thus-arranged pressure vessel is a pharmaceutical vessel. It has a 
recess 10 formed in the upper lid 3 for accommodating a pharmaceutical, 
holes 11 formed in the bottom lid 1 of the can body 2 through which can 
water enter the can body, and a water absorption member 12 which blocks 
each hole 11. When the bottom of the can body 2 is placed on an article 
such as a dish filled with water in a state wherein an interior 13 of the 
can body 2 contains quick lime, water enters through the holes 11 and 
comes into contact with the quick lime contained in the can body, 
generating an exothermic reaction. The heat generated by this reaction 
then causes the pharmaceutical contained in the recess 10 to spray 
outward. 
Consequently, the pressure in the can body 2 will greatly increase if the 
amount of water which makes contact with the quick lime is excessive. 
If an excessive rise in the internal pressure occurs, the pressure acts on 
the weakened portions of the upper lid which constitute the score lines 9, 
breaking them and escaping outward therethrough. 
A second embodiment of the present invention will be described hereinunder 
with reference to FIGS. 7 to 9. 
The internal pressure vessel of this embodiment is an aerosol vessel. 
Therefore, in this vessel, the upper lid 3 has a dome-like configuration, 
and the recess 8 for chuck engagement which is provided to enable the 
seaming of the upper lid 3 and the can body 2 takes the form of a groove, 
as viewed at the cross section, which is formed along the inner periphery 
of the can body 2. This recess also projects into the interior of the can 
body 2 to form a cavity thereinto, like that of the first embodiment. 
The pressure vessel of this embodiment has a plurality of score lines 9 
formed in the bottom of the groove-like recess 8 in such a manner that 
they extend in the circumferential direction. 
The score lines 9 are preferably formed in the lower surface of the recess 
8, as shown in FIG. 8. However, they may be provided on the upper surface, 
as shown in FIG. 9. 
Consequently, if the aerosol vessel is thrown into a fire, an increased 
pressure acts on the weakened portions of the lid which constitute the 
score lines 9, breaking them and releasing the pressure outward 
therethrough. 
In accordance with the present invention, the score lines through which the 
internal pressure is released are not formed in the seamed portion but in 
a portion which is not related thereto, i.e., in the recess for the 
engagement of the seaming chuck which must be provided for the seaming and 
which is made to project into the interior of the can body by the seaming 
to form a cavity thereinto. Consequently, the score lines can be broken in 
the initial stages of the generation of the pressure, when the generated 
pressure does not yet affect the seamed portion, thereby eliminating the 
possibility of exploding the vessel.