Vacuum-packing method and apparatus

In a vacuum-sealing method and apparatus for various articles to be packed under vacuum, the improvement consisting in that a hot-air circulating closed-loop path is provided within the vacuum-packaging enclosure, so as to have hot air circulating unidirectionally in order to sweep the package virtually concurrently with the evacuation and autogenous welding stage. A swingable flap valve inserted in the hot-air path upstream of the specially provided heating means ensures such a unidirectional hot air flow. By so doing, the vacuum-packing operations can be more efficiently and quickly completed. The package wrappers are made of a thermoplastics, heat-shrinkable material.

This invention relates to a method and an apparatus for vacuum-packing 
miscellaneous goods in thermoplastic material packagings and for the 
simultaneous heat treatment of the latter material. 
Methods are known which comprise the steps of placing one or more products 
in the interior of a preshaped package, introducing the package assembly 
in a hermetically sealed enclosure, withdrawing air from the interior of 
the enclosure and thus concurrently from the interior of the package, 
permanently sealing the open end of the package by heat-welding or any 
other method and, after having restored in the interior of the enclosure 
the atmospherical pressure, opening the enclosure to remove the finished 
package. The vacuum-packs thus obtained are often subjected, in a 
subsequent step, to a heat treatment in specially provided ovens to order 
to melt-weld the inner surfaces of the used thermoplastic material over 
all the points in which they contact one another, or also in order to 
bring about the heat-shrinking of such material: by so doing, it becomes 
possible to have the material better adherent to the goods concerned and 
to improve the seal. The ovens which are used for this purpose are usually 
of the hot-air circulation type, combined with a continuously moving 
conveyor mechanism to forward the packed goods. The defect of such ovens 
is that they are considerably bulky and expensive. In addition, the 
dumping of the packet product takes place at a spot which is away of the 
station at which the enclosure operator stands for the vacuum-packing, so 
that an additional operator is required to discharge the product at the 
outlet end of the plant. 
An object of the instant method is to make it possible to overcome the 
defects enumerated above by carrying out the heat-treatment in the very 
interior of the vacuum-enclosure and concurrently with the air-evacuation, 
package welding and atmospherical pressure restoring operations. 
It is known that certain conventional plants afford the possibility of 
carrying out the heat-shrinking of a package placed in the interior of an 
enclosure, by forced circulation of hot air in the enclosure, hot air 
being drawn from a specially provided heat source. In such cases, however, 
no possibility had been provided for carrying out simultaneously the 
evacuation of the enclosure and the vacuum-sealing of the package. It has 
now been found, as will be detailed hereinafter, that these two steps can 
be coextensive. In practice, once a package has been placed in the 
enclosure and the latter has been closed, air evacuation is immediately 
started: even though the air grows progressively thinner, it is 
nevertheless sufficient, if heated to an appropriate temperature and 
caused to be forcibly circulated, to transfer congrous quantity of heat to 
the package, heat being derived from an appropriate source. It is likewise 
possible, in order that the transferred quantity of heat might be 
increased, to feed the enclosure anew with hot air under atmospherical 
pressures as soon as the welding cycle is started and until such times as 
the welding step has been completed: if so, such air can be heated by 
causing it to flow through the same heat source prior to feeding said air 
into the vacuum enclosure, or even by taking heat from an external source. 
Obviously, it is possible to extend the hot air flow also to the stage 
preceding the start of the evacuation, or to the stage which follows the 
completion of the welding operation, but in such cases the total duration 
of the vacuum-packing operation is longer. As a rule, these precautions 
are not always required. It is possible, moreover, to assist the action of 
hot air by the provision of infrared heating bodies arranged in the 
interior of the vacuum-enclosure. 
The device which permits to reduce the instant method to practice is, under 
many respects, not dissimilar from the conventional ones. The device has 
as its basic component part an enclosure which can be opened in order to 
introduce thereinto one or more products which have been placed beforehand 
in their packaging wrappers, such as puches or bags, or sandwiched between 
previously provided films of a heat-sealable material. The open side(s) of 
the packaging is so arranged as to facilitate the action of the 
package-sealing mechanism. At a subsequent time, the enclosure is closed 
and air is removed by opening a communication valve connected to a 
vacuum-pump. The package-sealing mechanism is usually composed by two or 
more bars which are spaced apart from each other when in the at rest 
position. One or more bars can be heated so as to effect a heat-welding 
operation over the open side of the packaging. The autogeneous welding is 
obtained by actuating one bar which, being pushed against the other, 
causes the two flaps of the package in the sealing area to become squeezed 
therebetween. Autogenous welding thus takes place by the mere coaction of 
heat and pressure. A second valve then enables air under atmospherical 
pressure to be introduced into the enclosure. In addition to the 
conventional devices enumerated above, this invention provides for a 
system adapted to heat the air contained in the interior of the 
vacuum-enclosure, along with a system for causing the forced circulation 
of said air. Such a heat treatment, coacting with the atmospherical 
pressure, enables the sealing of the package to be effected also with cold 
bars and the latter, in this case, have a mere function of pressers. The 
heating device can be an electrically heated body which is so positioned 
as to have the forcibly circulated air sweeping thereover. Such heating 
body can be properly gilled so as to improve heat transfer. Usually, 
bodies having a high thermal inertia have given the best performance, but 
it is likewise possible to use exposed electric resistors made of a 
nickel-chromium alloy which can be energized only when necessary. The 
heating bodies can be in number of one or more and can be directly 
arranged within the vacuum-enclosure, or in a second chamber which can be 
connected to such enclosure either permanently or by operating a specially 
provided valve. If the resistors are arranged in a second chamber, the 
latter can be a suitable hot air storage room from which hot air can be 
drawn when appropriate. At any rate, it is necessary that a blower or any 
other equivalent contrivance ensures the circulation of air from the 
heating chamber to the vacuum-enclosure, and viceversa. 
The circulation of hot air can be effected before, or during, the 
evacuation stage, during autogenous welding and restoring the 
atmospherical pressure or also during a portion only of the latter stage: 
this can be obtained by merely stopping the blower or also by closing by 
the agency of a valve the communication between the heating chamber and 
the vacuum enclosure. The feeding of air for restoring the atmospherical 
pressure in the vacuum enclosure can also be effected by causing air first 
to flow through the heating chamber, or over the heating bodies, that 
which can be obtained by properly positioning the air feeding valve.

In FIG. 1, the two half-shells 1 and 2, which are the walls of the vacuum 
enclosure 20 are shown in explosion view and are spread apart from one 
another, so that the device is ready to receive one or more products. The 
valve 3 for communication with the vacuum-pump and the valve 4 for 
communication with the atmosphere are closed. The blower 5 and its driving 
motor 6 are motionless. The heating body 7 is continuously energized: it 
has a high thermal mass and is gilled so as to improve heat transfer. 
Under these conditions, the air in the space 8 (heating chamber) stores 
heat. 
FIG. 2 illustrates the same device after that a package 9 containing a 
product 10 has been manually, or automatically, placed in the vacuum 
enclosure, the latter having been closed. The seal between the two 
half-shells of the enclosure is provided by a gasket 11. The open side of 
the package 12, is arranged between a top welding bar 13 and a bottom bar 
14, which are conventional welding elements. 
The top bar 13 is parallel to the bottom bar 14 and there is a gap 
therebetween which permits that air may be drawn from the interior of the 
package. The package rests on a few rods 15 which allow air to sweep also 
the bottom face of the package. As soon as the enclosure has been sealed, 
the blower 5, driven by the motor 6, starts its motion and conveys hot air 
from the chamber 8 to the interior of the vacuum enclosure 20. The air 
sweeps the outer surface of the package and then is brought back along the 
channel 16 to the chamber 8 and so forth. A swinging flap 17, the purpose 
of which will be illustrated hereinafter, is lifted by the air thrust so 
as to leave the passage free. The opening or gap 18 permits an easier 
circulation or air. Of course, also the air in the ecnlosure 20 is driven 
on and is, in its turn, heated by the heater 7. Concurrently with the 
sealing of the enclosure 20, or with a certain adjustable delay with 
respect to it, the valve 3 is opened and air is gradually drawn 
therethrough by a vacuum-pump, not shown. As the pressure of air in the 
enclosure is decreased, also the air contained in the package 19 is 
exhausted. Also the transfer of heat towards the package is gradually 
decreased due to the effect of air rarefaction so that very low values of 
heat transfer are attained. This notwithstanding, the welding of the 
package can be started and the atmospherical pressure restored in the 
enclosure 20 and the heating chamber 8. 
This stage is shown in FIG. 3. It can be seen that the top bar 13 is 
pressed against the bottom bar 14 to start the welding step. The exact 
configuration of the bar 13 and its actuation device 21 are not shown 
since they are conventional. As soon as the open side 12 of the package 9 
has been pinched between the bars 13 and 14, the suction valve 3 is closed 
while the valve 4 is concurrently opened, which permits the outside 
atmospherical air to enter. Meanwhile, due to the lack of an adequate 
thrust, the flap 17 was closed and air, by breaking through, is compelled 
to sweep the heater 7 prior to entering the enclosure 20. The blower 5 
provides to the continuous circulation of air so that the heat treatment 
of the package can be proceeded with. On completion of the welding cycle, 
or at a subsequent stage, the blower 5 is stopped, the valve 4 is closed, 
the shell 1 of the enclosure is lifted and the bar 13 is brought back to 
its inoperative position. The package is thus finished and can be removed 
from the enclosure. 
The packaged product could be removed also automatically if the rods 15 
were appropriately driven or replaced by a suitable conveyor belt system. 
Such a possibility can be provided but it has not been shown in order not 
to overcrowd the drawings. 
The device shown in FIGS. 1, 2 and 3 is but an example since the possible 
embodiments of this invention are countless. 
For example, it is possible, instead of evacuating the entire enclosure, to 
restrict the evacuation to the interior of the package and this can be 
obtained, of course, by the agency of appropriate suction nozzles to be 
inserted through the open sides of the package. If so, it is possible to 
carry out the heat treatment by forced circulation of hot air during the 
evacuation of the package interior. It is obviously possible, moreover, to 
arrange in the interior of the wrapper a plurality of articles which, once 
the package has been sealed, will be separated from each other by severing 
the package.