Method for freezing food products in containers, and an automatic plate freezer for implementing the method

A method and an automatic plate freezer for freezing food products in boxes or trays, or in containers of low mechanical strength and therefore being deformable, or of nonparallelepiped shape. Such boxes or containers are frozen in a plate freezer within which a moisture-free atmosphere is maintained together with dehumidified cold air circulation. Jets of dehumidified cold air are fed under the base of the containers in the container loading/discharge station to form an air cushion between the upper surface of the plate at rest in the station and the base of the containers, which can thus be easily thrust forward directly by other successively loaded containers insofar as the resistance to the movement of the containers along the plate is very low.

Background of the Invention 
1. Field of the Invention 
This invention relates to a method for freezing food products packaged in 
boxes, trays, dishes, bags and the like, and to an automatic plate freezer 
for implementing the method. 
2. Discussion of the Background 
Food products for freezing can be considered to form part of two large 
groups. The first group comprises those products which are frozen in 
parallelepiped containers having such a consistency or strength as to 
withstand the mechanical stresses to which they are subjected during their 
insertion and movement within the freezer. The second group comprises 
those products which are frozen after being packaged in bags or in trays 
of low mechanical strength or of non-parallelepiped shape such as trays 
with their side walls diverging outwards from their base. 
The products of the first group are frozen in automatic plate freezers, 
i.e. of the type comprising a plurality of superposed spaced-apart plates 
through which a refrigerant fluid circulates. The products to be frozen, 
enclosed in their respective strong parallelepiped containers and arriving 
from a conveyor belt, are loaded onto a plate positioned in a loading 
station and spaced apart from the immediately overlying plate. A number of 
such containers are loaded simultaneously side by side to form a row 
substantially equal to the plate width. When the next row of containers is 
loaded, the containers of this second row rest against the containers of 
the first row and push them forward. This is repeated until the plate is 
completely loaded, during which a large number of rows move along the 
plate, each row being pushed forward by the next row and itself pushing 
the previous row forward. 
Such a procedure can be followed only if the products to be frozen are 
enclosed in strong parallelepiped containers. 
If the products to be frozen are enclosed in containers in the form of 
bags, boxes without strength or trays with their side walls inclined to 
the base, a procedure involving container movement by mutual pushing 
cannot be used because the containers could undergo compression or 
deformation, with the danger of damaging not only the container but also 
the wrapping of the food products, which could escape from the container 
before being frozen. In this respect, it must be taken into consideration 
that the containers pushed along the plates must withstand considerable 
stresses depending on the plate length, the number of containers present 
in the length direction of the plate to be moved along it, the presence of 
frost or ice on the plate, possible adherence of the food product to the 
plate, and the weight of the container, and thus the overall resistance to 
be overcome in order to move the containers. 
To obviate the aforesaid drawbacks, such containers are currently frozen on 
a different type of freezer, i.e., they are loaded onto an endless 
conveyor belt driven within a large refrigerated compartment in which fans 
blow very cold air over the containers until the products contained in 
them are frozen. These types of freezers have very low efficiency and the 
time required for freezing the food products is excessively long, with the 
result that the freezer volume must be excessively large. 
The efficiency of plate freezers is much higher than that of the aforesaid 
cold air freezers, and because of this plate freezers are in fact also 
used for products enclosed in boxes of low mechanical strength or in bags, 
dishes, trays or the like of non-parallelepiped shape. For this purpose, 
at the loading station for the plate freezer, each row of containers 
(originating from a conveyor belt) is pushed forward onto the plate by an 
automatic pusher substantially consisting of a long transverse bar which 
rests against the upstream side of all the containers of the considered 
row and pushes them forward onto the freezer plate. The next container row 
is pushed onto the plate by another pusher identical to the first and 
which simultaneously pushes the first pusher forward along the plate 
together with the first container row. 
Thus a plurality of container rows builds up on the plate, each row being 
moved forward along the plate by a respective pusher (possibly shaped to 
accommodate the container shape), so that a plurality of pushers is also 
present on the plate. 
As the freezer comprises a plurality of freezer plates, it is apparent that 
this method requires a very large number of pushers, itself representing a 
considerable problem in that when the pushers emerge from the discharge 
station at which they push the frozen products out, the pushers have to be 
recovered and returned to the loading station. 
Plate freezers are well known and various types are described in the 
patents: U.S. Pat. Nos. 2,882,697, 3,271,973, 4,240,270, 4,423,604, 
4,432,214, GB-A-2,041,313, GB-A-2,120,776 and FR-A-2,531,522. 
Spacer devices for the plates of plate freezers at a controlled distance 
apart are described in the patents: U.S. Pat. Nos. 4,240,270, 4,423,604, 
4,841,881 and GB-A-2,195,429. 
Automatic pushers for pushing container rows forward on the loading plate 
of a plate freezer are described in the patents: U.S. Pat. Nos. 3,271,973, 
3,557,975, 4,432,214, GB-B-1,259,073, GB-A-2,041,313 and FR-A-2,531,522. 
It has also been proposed to insert low-strength or non-parallelepiped 
containers into suitable seats provided in strong parallelepiped frames 
which are rested on and made to move along the plate surface in the same 
manner as normal strong parallelepiped containers. However, such frames 
have obvious drawbacks such as the fact that their presence necessarily 
reduces the number of containers which can be housed on each plate, the 
fact that the frames have to be returned to the loading station after 
being pushed out of the freezer discharge station, and the fact that the 
seats provided in them are unable to receive and move containers having a 
shape different from that of the seats or such that two or more containers 
cannot be housed in the same seat. 
Thus, plate freezers have the highest efficiency but have considerable 
drawbacks when used for freezing food products enclosed in boxes of low 
mechanical strength, in bags, or in dishes or trays of non-parallelepiped 
shape, and in particular with side walls which diverge upwards from the 
tray base. As stated, these drawbacks are due to the fact that a large 
number of pushers together with complicated automatic systems for 
returning the pushers leaving the discharge station to the loading station 
are required, or supplementary frames with seats for housing the 
containers are necessary. 
SUMMARY OF THE INVENTION 
The main object of the present invention is to provide an automatic plate 
freezer for deep-freezing food products packaged in boxes, bags or trays 
of any shape but with a flat base, the freezer being of reliable and 
simple operation, of relatively simple and compact structure, and allowing 
effective freezing of food products without damage to the containers in 
which they are enclosed. 
This and further objects are attained by a method by which the containers 
for food products to be deep-frozen are loaded into and frozen in a plate 
freezer within which a substantially moisture-free atmosphere is 
maintained together with dehumidified cold air circulation. Preferably, 
jets of dehumidified cold air are fed under the base of the containers 
located on the plate positioned in the container loading station to lift 
the containers from the plate surface. 
In this manner, as freezing is effected in a substantially dry atmosphere 
there is no formation of frost which could hinder the movement of the 
containers along the freezer plates and reduce heat transfer, the 
dehumidified cold air circulation within the freezer increasing heat 
transfer from the product to be frozen as it acts over all surfaces not in 
contact with the plates, whereas the dehumidified air jets fed under the 
base of the containers in the loading/discharge station create practically 
an air cushion between the container base and the adjacent surface of the 
underlying plate, so that the containers can be easily pushed forward and 
thus move along the plate, practically without friction. The result is 
that the row of containers being loaded into the freezer can be allowed to 
come into contact with and act directly on the containers of the row 
previously inserted into the freezer, which then undergo easy movement 
along the plate without suffering damage. 
The automatic plate freezer for implementing the aforesaid method is 
characterized by comprising means for cooling and dehumidifying the air 
present within the freezer and for maintaining it at low temperature and 
dehumidified, and means for generating and maintaining a cold dehumidified 
air stream between the plates within the freezer. 
The plates of the automatic freezer preferably comprise a plurality of 
channels in which holes are provided opening into the upper surface of 
each plate, means being provided for feeding cold dehumidified air into 
said channels of that plate positioned at the loading station for the 
products to be frozen in the freezer. 
The method and the structure and characteristics of the freezer according 
to the present invention will be more apparent from the description given 
hereinafter by way of nonlimiting example with reference to the 
accompanying drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 to 4 show an automatic freezer comprising an insulated housing 1, 
described hereinafter, containing a plurality of refrigeration plates 19, 
also described hereinafter and shown in detail in FIGS. 5, 6 and 7 and 
devices for moving them and positioning them one at a time at the correct 
level in a loading station to be loaded with or unloading packages or 
containers enclosing the food products to be frozen, these devices not 
being described nor shown on the drawings as they comprise the normal 
frames, hydraulic cylinders and other parts used in this type of freezer 
and illustrated in the previous patents cited in the introduction to the 
present description. 
The freezer also comprises a loading device 2 for the packages or 
containers 22, which is also of well known type and commonly used in such 
freezers, for example of the types described in the patents U.S. Pat. No. 
3,557,975 and GB-B-1,259,073, with the difference being that in the case 
of the present invention, it is totally ducted and isolated from the 
outside environment. A conveyor belt 6 for the packages arriving at the 
housing 1 and a conveyor belt 7 for the packages leaving at the housing 1 
are provided at the front and rear of the freezer respectively, these 
belts having that portion close to the the housing enclosed within ducts 3 
and 4 which are connected together by a channel 5 to isolate the areas in 
which the packages are introduced into the housing 1 and discharged from 
it, so that the only apertures through which air can enter and leave are 
apertures 3a and 4a, which have cross-sections slightly greater than that 
of the packages 22, these apertures being provided with closure devices of 
known structure, which are normally closed and open only when the packages 
have to pass through them. In the embodiment shown on the drawings, a 
self-contained unit 8 is shown schematically for refrigerating and 
dehumidifying the air contained in the housing 1 and in the ducts 3 and 4 
connected to it, the refrigeration unit 8 being connected to the housing 1 
by connectors and ducting 9 and 10 and being connected to ducts 3 and 4 by 
means of the connection branch 11. 
The purpose of the unit 8 is to cool to a temperature similar to that of 
the refrigeration plates 19 and to continuously dehumidify both the air 
present within the freezer and the air which enters through the ducts 3 
and 4 together with the product to be frozen. or from other sources. 
The refrigeration and dehumidification unit 8 is put into operation before 
operating the freezer, i.e., before feeding the refrigerant fluid into the 
plates, in order to prevent frost forming on them, the unit also 
circulating the cold dehumidified air within the freezer so that it aids 
heat transfer with the product to be frozen. 
A device 12 is provided to cool and dehumidify air withdrawn from the 
interior of the housing 1 (instead, but less advantageously, the air fed 
by the device 12 could be taken from the compressed air main of the 
factory in which the freezer operates), compress it, remove any traces of 
impurities and feed it to a device described hereinafter and shown in FIG. 
8, which then feeds it to the plate 19 which is at rest in the position 
for loading, and only to that plate. This air traverses channels provided 
in each plate but separate from those through which the refrigerant fluid 
circulates, to feed the holes provided in the upper surface of each plate, 
through which the air is expelled in the form of jets which create air 
cushions able to lift the packages of products to be frozen and allow them 
to be moved by the loading device 2 under zero or nearly zero friction 
conditions. 
A fundamental characteristic of the described freezer is that it operates 
under zero humidity conditions within the housing 1, and thus with the 
plates cold but dry, without frost, and with heat transfer of a mixed 
type, i.e., by direct contact between the packages and plates and by 
conduction to the cold air circulating within the housing 1. 
The freezer is suitable for freezing food products enclosed in 
parallelepiped packages (freezing being improved by the absence of frost 
on the plates, i.e. by improved contact between the plates and packages) 
and products enclosed in trays either of non-parallelepiped shape or of 
low mechanical strength (it allowing the latter to be loaded, as loading 
is facilitated by the absence of friction and of adhesion with the plate, 
which if present result in forces which usually cause deformation of the 
packages when they are pushed in order to move along the plates). 
The housing 1 of the freezer according to the present invention is shown in 
vertical section in FIG. 3 and in horizontal section in FIG. 4. 
The front end wall 1a and the rear end wall 1b, the term "front" meaning 
the end in which the product enters and the term "rear" meaning the end 
from which the product leaves, are both provided with inner backing walls 
13a and 13b respectively, which form a front interspace 1c and a rear 
interspace 1d. These two interspaces are divided into two parts by the 
product entry mouth 14 and product exit mouth 15, namely an upper part and 
a lower part, which are connected together by lateral ducts 16 and 17 
respectively. 
On that face facing the interior of the housing 1, the backing walls 13a, 
13b are provided with holes suitably distributed over their entire 
surface, through which a number of small air jets pass, these being 
indicated by small curved arrows in FIG. 3. The interspace 1c is connected 
to the air refrigeration and dehumidification unit 8 by the ducts 9, the 
interspace 1d being connected to the same unit by the ducts 18 and 10. 
In the normal manner for this type of known freezer, the housing 1 houses a 
certain number of plates 19 in a superposed arrangement spaced apart by 
spacers of adequate height for the product to be frozen, with refrigerant 
fluid circulating through each plate, and means for raising the plates, 
lowering them, moving them to the level of the mouths 14 and 15, spacing 
them apart for the introduction of the product to be frozen, and making 
them approach each other again after the product has been loaded, which 
means will, as stated, not be described as they are of a usual type and 
are amply described in detail in the previous patents cited in the 
introduction to the present description. 
The loading device 2 (which as stated is totally housed and isolated from 
the outside) is located outside the housing 1, and is of the type usually 
used in such freezers (see for example the patents U.S. Pat. Nos. 
3,557,975, 4,432,214, GB-B-1,259,073 etc.) but of which the drawings show 
only the loading bar 20 and a small portion of the chains 21 which move 
the bar 20 forwards and backwards. 
The purpose of the loading device is to transfer a row of packages 22, 
carried by the belt 6 and abutting against the stop element 23 (FIG. 4) 
onto the plate 19 at a rest position in front of the loading mouth 14. The 
unit 8 is able to circulate the air which it has previously dehumidified 
and cooled to a temperature similar to that of the plates 19, by feeding 
it through the channels 9 into the lower part of the interspace 1c and 
from here into the upper part of the interspace 1c via the lateral 
channels 16, and to draw said air from the lower and upper parts of the 
interspace 14, connected together by the lateral channels 17, via return 
channels 18 and 10 which again feed it to said unit 8. 
The air is obliged to pass through the housing 1 and, in the region in 
which the plates 19 are located, to infiltrate between them and into the 
spaces left free by the packages 22, such air being at a temperature 
similar to the plates participates in the cooling of the product, to 
provide the same effect as that due to direct contact between the packages 
and the plates. It can be noted that this refrigerant effect due to the 
air is particularly important when the products have only one flat 
surface, such as when they are enclosed in plastic bags, because in this 
case the contact area between the packages and the plate above that onto 
which they are loaded is generally small, whereas the heat transfer due to 
the air is generally increased because the product is exposed to the air 
not only perimetrally but also on its top. 
The dehumidified air circulation is metered by the unit 8, and is 
controlled so as to occur essentially between those plates 19 not in front 
of the moths 14 and 15, at a rate which does not cause the packages to 
move along the respective support plates towards the wall 13b, which is 
extremely close to the rear edge of the plates 19 so as not to allow the 
packages to fall from the plates. 
The plates 19 of the freezer according to the present invention are shown 
in FIGS. 5, 6 and 7. 
FIG. 5 shows two spacers one above the other and separated by spacers 24 of 
height which matches the height of the product to be frozen. Said spacers 
can provide different distances between the plates if constructed in 
accordance with the patent: U.S. Pat. No. 4,841,881. Hoses 25, 26 connect 
each plate 19 to manifolds (not shown on the drawings) for the circulation 
of the refrigerant fluid through the plates. 
Guides 27 are fixed on the upper surface of each plate to prevent the 
packages 22 of a product to be frozen from falling off the plate 
positioned at the mouths 14, 15 during the plate loading and discharge. 
FIG. 6 is an exploded view of one of the plates 19. The central region of 
the plate consists of a series of central elements 28 joined together 
usually by welding, to form a continuous plate traversed by channels 28a 
and 28b (FIG. 6), channels 28a being used to circulate the refrigerant 
fluid and channels 28b being used to feed air to small holes 28c provided 
along channels 28b through the upper surface of elements 28. 
On the lateral ends of the elements 28 there are provided headers 30 which 
are fixed to the central elements 28 by welding and are each traversed by 
two longitudinal channels 30a and 30b. The headers 30 positioned to the 
left in FIGS. 5 and 6 feed compressed air (via the channels 30b) to the 
channels 28b and from these to the holes 28c, and collect the refrigerant 
fluid leaving the channels 28a of the central plate elements 28, this 
fluid leaving through the hoses 26 to be conveyed to a discharge manifold 
(not shown). 
The headers 30 positioned to the right in FIGS. 5 and 6 have their channels 
30a connected via a hose 25 to a manifold (not shown) for feeding 
refrigerant fluid to the channels 28a of each plate element 28, their 
channel 30b feeding refrigerated and dehumidified compressed air to the 
channels 28b of said elements 28. 
As the channels 28b are closed at their ends and are connected to the 
channels 30b of the two lateral manifolds 30 only via external tubes 31 
(FIG. 7), the refrigerant fluid circuit and the compressed air circuit can 
operate independently. 
FIG. 7 represents an enlarged partial sectional view through a plate 
portion 19, this section being taken of channel 28b to show the air path 
from the channel 30b, through the external tubes 32 and into the channel 
28b, to then emerge from the holes 28c. 
The ends of the headers 30 are closed at the channels 30a so that the 
refrigerant fluid flows through the elements 28 of each plate but is 
connected to them only via the hoses 25 and 26 of FIG. 5. 
The air channels 30b are open at both ends to receive air when the plate to 
which they are connected is at the discharge level in front of the mouth 
14, as shown in FIG. 8. 
The unit 12 for drying, filtering and possibly removing oil from the 
compressed air is of a known type and provides an adequate quantity of air 
which after cooling in the unit 8, in which the air passes through a 
separate circuit, is fed to four devices 31 (FIG. 8) provided one at each 
open end of the channels 30b of the two headers 30 of the plate at rest in 
the loading station. 
The devices 31 are therefore located at the mouths 14 and 15 where the 
plate 19 to be loaded with or unloaded of packages 22 stops. For 
simplicity, the devices 31 are not shown in FIGS. 3 and 4, and it should 
be noted that in FIG. 8 the plate 19 at rest in front of device 31 is 
represented in simplified section, i.e., showing only that part relative 
to the channel 30b of one of the headers 30. 
FIG. 8 is therefore a schematic representation showing the inlet mouth 14 
for the product 22 to be frozen and the location of the device 31. 
Each of the four devices 31 consists of a normal cylinder containing a 
piston driven by compressed air fed through the connector 40 or 41 
respectively, the piston rod 31a having its free end facing the relative 
header 30 and carrying a hollow connector 31c, the hollow portion being 
fed via a hose 31b with the air delivered by the unit 12. 
The connector 31c is shaped to mate with the front and rear apertures of 
the channels 30b of each header 30 forming part of the plate 19 at rest in 
front of the mouth 14. 
Consequently, only the plate 19 to be loaded is connected, when correctly 
positioned, by operating the air cylinder 31 which moves the rod 31a to 
cause it to emerge (towards the right in FIG. 8) and engage the connector 
31c, usually of rubber material to facilitate sealing, against the 
adjacent open end of the channel 30b of the header 30. 
When engagement has taken place, valves (not shown for simplicity) provided 
in the circuit containing the air fed by the unit 12 to the hose 31b, 
allow the compressed air to pass so that it enters the channels 30b of the 
headers 30, to then pass into the plate channels 28b and emerge from the 
holes 28c to lift the food product packages 22, which thus become 
suspended on a cushion of air formed between the base of the packages and 
the upper surface of the plates, so that the pusher 20 can push the row of 
packages adjacent to it into the freezer, these packages themselves easily 
pushing the previous row of packages forwards as there is practically no 
resistance to movement, with the result being that even extremely light 
and thus deformable packages can be used without such packages suffering 
any damage. 
The independent unit for cooling and dehumidifying the air circulating 
within the housing 1 and directly associated with the latter need not be 
provided if the required air can be cooled by the general refrigeration 
plant of the factory in which the freezer is installed and operating. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.