Vacuum packaging

In a vacuum packaging machine there is provided the combination of a sealing unit and vacuum unit. The sealing unit comprises first and second sealing dies and the vacuum unit comprises a primary spacer located adjacent the input end of the sealing dies. The primary spacer is spaced from the first die to form a first web feeding passage therebetween and is spaced from the second die to form a second web feeding passage therebetween. The vacuum unit also includes a secondary spacer located adjacent the input end of the dies and mounted for movement between a retracted position permitting closure of the dies to effect sealing and an extended position maintaining at least a portion of the webs which passed through the first and second web feeding passages, in a spaced relationship to permit evacuation of the container space formed between the webs. A drive mechanism is provided for driving the secondary spacer to and fro between the retracted and extended positions and vacuum passages are provided in the vacuum drawing unit opening towards the sealing dies for communicating with the interior of a packaging space when the secondary spacers are in the extended position to maintain the webs in a spaced relationship whereby atmosphere from the container space may be withdrawn through the vacuum passage means prior to sealing of the webs.

FIELD OF INVENTION 
This invention relates to vacuum packaging machines. In particular, this 
invention relates to improvements in a vacuum packaging machine which 
serve to permit a direct evacuation of the container space. 
PRIOR ART 
Considerable difficulty has been experienced in attempting to vacuum-pack 
food products because the reduction in pressure in the container space can 
adversely affect the character of the product during the packaging 
operation. If, for example, a cheese product is to be vacuum packaged in a 
container, the reduction in pressure in the space around the cheese 
product, during the packaging operation, may be such that the cheese 
product may explode. This is particularly true in cheese products where 
there are voids in the body of the cheese which are filled with air or 
other gases. The gases which are trapped within the cheese are at a higher 
pressure than the vacuum pressure within the container space with the 
result that the trapped gases can cause the body of cheese to explode. 
Similarly, the reduction in pressure in the vacuum packaging of meats can 
cause the juices within the meat to be forced to the surface of the meat 
so that the meat has an oily appearance and texture. 
In the widely used vacuum packaging processes in which a pocket is formed 
in one web of material and a second web is placed over the open end of the 
pocket, it is customary to locate both webs between a pair of sealing dies 
during the sealing operation and to locate a vacuum chamber about the 
outer face of each web and to draw a vacuum in this chamber to prevent 
inward collapsing of the webs when a vacuum is drawn in the container 
space between the webs. 
I have found that many of the difficulties associated with the damage to 
products such as cheese and meat can be overcome by permitting the webs to 
collapse inwardly to physically support the product when a vacuum is drawn 
in the container space formed between the webs. The inward collapsing of 
the webs serves to physically support the product thus preventing 
explosions and preventing the migration of juices to the surface of the 
product. This can, however, only be achieved by providing for the physical 
spacing apart of the webs to provide a vacuum passage communicating with 
the container space between the webs during the vacuum packaging 
operation. 
SUMMARY OF INVENTION 
It is an object of the present invention to provide a spacer mechanism for 
positively spacing the webs from one another to provide access to the 
container space formed therebetween during the time that a vacuum is drawn 
in the vacuum space. 
According to one aspect of the present invention, there is provided in 
combination a sealing unit and a vacuum unit for use in a vacuum packaging 
machine in which a container space formed between oppositely disposed 
sealing faces of a pair of sealable webs is to be evacuated before the 
webs are sealed together about the periphery of the container space. The 
sealing unit comprises first and second sealing dies mounted one on either 
side of a sealing plane for movement relative to one another between an 
open position to permit movement of a package forming web assembly 
therebetween and a closed position for engaging and sealing said web 
assembly. The sealing unit has an input end for receiving web to be sealed 
between said dies and an output end through which sealed packages are 
discharged. The vacuum unit comprises primary spacer means located 
adjacent said input end of said sealing dies, said primary spacer means 
being spaced from said first die to form a first web feeding passage 
therebetween and spaced from said second die to form a second web feeding 
passage therebetween whereby said primary spacer means is located between 
oppositely disposed sealing faces of webs being fed into said dies through 
said first and second web feeding passages, secondary spacer means located 
adjacent said input end of said dies and mounted for movement between a 
retracted position permitting closure of the dies to effect sealing and an 
extended position maintaining at least a portion of the webs in a spaced 
relationship to permit evacuation of the container space formed 
therebetween, means for driving said secondary spacer means to and fro 
between said retracted and extended positions, vacuum passage means in 
said vacuum drawing unit opening towards said sealing dies for 
communicating with the interior of a packaging space when said secondary 
spacer means is in said extended position to maintain said webs in a 
spaced relationship whereby atmosphere from the container space may be 
withdrawn through said vacuum passage means prior to sealing of the webs. 
According to a further aspect of the present invention there is provided a 
combination described in the preceding paragraph wherein the first sealing 
die has a chamber formed therein to accommodate the protrusion formed in 
the first web to form the container space, the chamber being isolated from 
the vacuum passage means by the first web in use such that the first web 
is free to collapse inwardly about the product located within the 
container space as the vacuum is drawn within the container space thereby 
to physically support the article.

With reference to FIG. 1 of the drawings, the reference numeral 10 refers 
generally to a first web of heat sealable plastics material of the type 
commonly used in the manufacture of vacuum packaged articles and in which 
a plurality of article receiving compartments 12 have been previously 
formed and loaded with an article 14 which is to be vacuum packaged. A 
sealing flange 16 extends continuously about the periphery of each 
compartment 12. The web 10 has wall portions projecting downwardly from 
the flange 16 which, together with a bottom wall, collectively form a 
protrusion 18. 
A second web 20 of heat sealable plastics material is located in an 
overlying relationship with respect to the sealing flanges 16 and is 
heat-sealed to the sealing flanges 16 about the periphery of each 
compartment 12 in the vacuum packaging process described hereinafter. The 
support rails 22 serve to support the web 10 in its passage through the 
vacuum packaging station. 
Vacuum packaging machines which incorporate a mechanism for forming the 
article receiving compartments in the web 10 immediately before the vacuum 
packaging during operation are well known and may be incorporated into the 
apparatus of the present invention. 
In FIGS. 1, 3 and 4 of the drawings, the reference numeral 24 refers 
generally to the sealing unit and the reference numeral 26 refers 
generally to the vacuum unit. 
SEALING UNIT 
The sealing unit 24 consists of a first sealing die 28 in which a plurality 
of pockets 30 are formed, each pocket 30 forming a corresponding 
protrusion 18 in the opposite face of the web. The first die 28 has a 
resilient gasket 32 extending about the periphery of each pocket 30. The 
first die housing 28 is mounted on a shaft 34 which is reciprocally driven 
by a drive unit 36 so that the housing 28 may be moved to and fro between 
the raised position shown in solid lines and the lowered position shown in 
broken lines in FIG. 3 of the drawings. In the raised position, the gasket 
32 underlies a marginal edge portion of the flange 16 formed about each 
compartment 12 as shown in FIGS. 3 and 4 of the drawings. It will be noted 
that the pockets 30 formed in the die 28 are not placed in communication 
with any source of vacuum. 
The second die 24 includes a housing 40 within which a vacuum chamber 42 is 
formed. A heated sealing plate 44 is located within the vacuum chamber 42 
and has a recess 46 formed in the lower face thereof about which a sealing 
flange 48 extends. The end face of the flange 48 is disposed directly 
opposite the gasket 32 of the lower sealing die 28. A plate 50 is 
supported on shoulders 52 and extends across the open end of the recess 46 
in a spaced relationship with respect to the sealing flange 48 so that 
heat is not transmitted from the sealing flanges 48 to the plate 50. 
Heating elements 54 are embedded in the sealing plate 44 and are connected 
to a source of electrical energy through terminals 56. Sealing plate 54 is 
mounted on a pair of shafts 58 which are coupled to shafts 60 of 
reciprocating drive units 62 which are supported by the frame member 64. 
(FIG. 1). Shafts 58 extend through passages 66 formed in the upper wall of 
the housing 40. A collar 68 is located between the shafts 58 and 60 and 
serves as a stop limiting the downward movement of the shaft 58 with 
respect to the housing 40. A plurality of guide pins 70 are mounted in the 
upper wall of the housing 40 and extend downwardly therefrom through guide 
passages formed in the sealing plate 44 and terminate in heads 72 which 
serve to limit the downward movement of the sealing plate 44 with respect 
to the housing 40. A vacuum passage 74 opens through the upper wall of the 
housing 40 and is coupled to a source of vacuum through a conduit 76. The 
die unit 24 has an input passage 78 formed at one end thereof and an 
output passage 80 formed at the other end thereof. 
VACUUM UNIT 
The vacuum unit consists of a head 84 which is mounted on a pair of arms 82 
which are secured at one end to the housing 40 and which project 
rearwardly therefrom. As shown in FIG. 2 of the drawings, the arms 82 have 
a threaded passage 86 at the outer end thereof within which a bushing 
member 88 is threadably mounted. The bushing member 88 having a passage 90 
therein. A short stub-shaft 82 projects outwardly from each end of the 
head 84 to be slidably received within the passage 90 of the bush 88 in a 
close fitting relationship so that the head 84 may rock about the axis 94. 
The head 84 has lower face 96 which rests on the sealing flanges 16 of the 
web 10 in use. The head 84 also has an upper face 98 which is inclined 
downwardly toward the lower face 96 in a direction toward the sealing die 
assembly to form a support face for supporting the web 20 in a spaced 
relationship with respect to the web 10 prior to entry into the sealing 
station. The head 84 also has a forward end face 100, short triangular 
shaped wedges 102 project forwardly from the front face 100 and serve as 
side closures for the vacuum passage which is formed between the webs in 
use. A chamber 104 is located within the head 84 and a pusher bar 106 is 
mounted in the chamber 104. The pusher bar 106 is mounted on a shaft 108 
of a reciprocating drive unit 110 for movement within the chamber 104 
toward and away from the forward end 100 of the head. A plurality of 
passages 112 extend from the chamber 104 and opens through the forward end 
face 100 of the head. A plurality of spacer rods 114 have their inner end 
mounted on the bar 106 and project through selected passages 112. By 
activating the reciprocating drive mechanism 110, the spacer rods 114 can 
be moved between the extended position shown in FIGS. 2 and 3 of the 
drawings and the retracted position shown in FIG. 4 of the drawings. A 
detector 116 is provided for detecting the location of the bar 106 in the 
position which it assumes when the rods 114 are fully retracted. The 
detector 116 is wired to a suitable control circuit which serves to 
prevent closure of the dies to the heat sealing position until after the 
spacer rods 114 have been fully withdrawn. The chamber 104 is connected to 
a source of vacuum through a conduit 118 so that a vacuum may be drawn 
through the passages 112 which are not restricted spacer rods 114. 
METHOD OF OPERATION 
In use, an article 14 such as a portion of cheese or meat is loaded into 
each of the compartments 12 of the lower web 10. Before the webs 10 and 20 
are advanced into the sealing station, the housing 28 is located in its 
lowered position and the housing 40 is located in its raised position and 
the rods 114 are located in their extended position. Thus, when the webs 
10 and 20 are advanced toward the sealing station, they pass over the 
surfaces 96 and 98 respectively of the head 80 so that when the article 
storing compartments 12 are located in alignment with the pockets 30 of 
the housing 28, the spacer rods 114 project into the compartment 12 which 
is to be evacuated and serve to maintain a spaced relationship between the 
web 20 and the flange 16 of the web 10 at the input end of the sealing 
dies. The reciprocating drive unit 36 is activated to raise the housing 28 
until the gasket 32 engages the sealing flange 36 extending around the 
compartments 12 and lifts the sealing flange 16 into engagement with the 
lower face of the housing 20 about each edge except the edge formed at the 
input end of the housing 40 where it raises the forward end of the head 80 
into wedging engagement with the inclined front face 78 of the housing 40. 
A vacuum is then drawn in the chamber 104 of the head which in turn draws 
a vacuum in each of the compartments 12 located within the sealing head 
through passages 112. The lower web 10, being made from a flexible 
material, collapses inwardly around each compartment 12 to physically 
support the article 14 which is located therein. The collapsing of the 
webs 10 and 20 will be prevented in the area of the input end of the dies 
by the presence of the spacer rods 114 so that an adequate vacuum can be 
drawn within each compartment 12. The spacer rods 114 are then withdrawn 
and the heat sealing plate 44 is lowered to the position shown in FIG. 4 
to press the webs 10 and 12 together to form a heat-seal about the 
peripheral edge of each compartment. 
From the aforegoing, it will be apparent that the present invention 
provides a simple and efficient mechanism for permitting the vacuum 
packaging of articles while also providing the inward collapsing of the 
web in which the article supporting compartment is formed so that it 
supports the article which is located within the package.