So-called manually operated plate freezers are known. Such freezers comprise a stack of horizontally arranged freezing plates and means for step-wise lifting of the stack. After the termination of a freezing period followed by a thawing loose period the stack in question is lifted and the uppermost freezing plate of the stack is supported, whereafter the lowermost part of the stack is lowered until an interspace is achieved between the uppermost plate and the plate next to the uppermost, which is sufficient for removing the frozen product and inserting the product to be frozen. Now the lowermost part of the stack is again lifted whereby the uppermost plate of the lowermost part of the stack, which has now been refilled, lifts the plate positioned there above and the uppermost plate now lifted is supported, whereafter the lowermost part of the stack is lowered, whereafter the next plate interspace will now be emptied and filled. The operation continues in this way until the interspaces between the plates of the plate freezer in question have been emptied for frozen products and filled with product to be frozen. Then the stack is lowered, and a pressure is applied to the stack, whereafter a freezing period is initiated during which the product is frozen followed by a thawing loose period, whereafter the emptying and filling operations are repeated. Such manually operated plate freezer has the advantage that since pressure is applied to the product to be frozen during the freezing period, a compact structure of the frozen material is achieved and, accordingly, air pockets and uneven surfaces are avoided. However, such plate freezer suffers from the drawback that the feeding of the product to be frozen to the plate freezer and the removal of the product must be carried out intermittently because the feeding of the product to and the removal of the frozen product from the plate freezer must be stopped during the freezing period and the thawing loose period.

Moreover, so-called automatic plate freezers are known which allow generally continuos feeding of the product to be frozen to the freezer and generally continuous removal of the product. As regards the emptying and the filling, such plate freezer operates in the way explained above. However, cooling medium is fed to the plates all

the time, and when an emptying/filling cycle has been terminated the whole stack is lowered, whereafter the emptying/filling cycle is repeated immediately. During the freezing the product is not subjected to other pressure forces than the pressure forces which the plates apply to each other. The plate, which at any time forms "ceiling" above the emptying/freezing interspace will be subjected to the pressure from the plates positioned there above, and the plate which at any time is positioned at the bottom of the stack will be subjected to the pressure from the plates arranged there above inclusive the plate which forms "floor" of the emptying/filling interspace. Accordingly, the product positioned below the uppermost plate will at the maximum be subjected to the pressure from this plate and parts which may be connected thereto, if any. Furthermore, since the plate freezer does not have any thawing loose period it may be necessary to use violence upon the frozen product when this is to be removed.

It is the object of the present invention to provide a freezing plant which may operate continuously without the drawbacks connected with the automatic plate freezer, and which, accordingly, results in the advantages which are achieved by means of the manually operated plate freezer, and this object is according to the invention achieved in that the freezing plant comprises a series of plate freezers and a conveyor system for feeding the products to be frozen to each of the plate freezers and for removing the frozen products from each of the plate freezers, that each of the plate freezers is provided with a stack of freezing pjates, means for lifting the stack stepwise, whereby each lifting step corresponds to or is higher than the height of the interspace between two freezing plates necessary for filling and emptying, respectively, such interspace; disengageable supporting means for supporting the at any time lowermost plate of the upper part of the stack at the upper limit of the interspace and releasable supporting means for supporting the at any time uppermost plate of the lower part of the stack at the lower limit of the interspace; the disengaging and the releasable supporting means being adapted to release the stack for lowering the stack after positioning of the product to be frozen upon each freezing plate; each of the plate freezers, moreover, comprising means for applying pressure upon the stack of freezing plates after

filling and lowering the stack, the plate freezers, moreover, being adapted so that the plates of each plate freezer have a freezing period during at least part of the time during which pressure is applied to the stack during which freezing period freezing medium is fed to the plates; a thawing period following the freezing period for thawing loose the product and during which thawing period thawing-up medium is fed to the plates, and an inactive period following the period of thawing loose the product for emptying and filling the plate freezer; the number of plate freezers belonging to the series being equal to at least one plus the sum of the freezing period and the thawing loose period of a plate freezer divided by the inactive period of the plate freezer. Hereby it is achieved that the freezing plant in question can operate continuously because one plate freezer may be emptied and filled while the other freezers freeze the product in question and provide for thawing the product loose, but in such a way that the next plate freezer is available for emptying and filling immediately after the beforegoing plate freezer has been emptied and filled. Accordingly, it is achieved that the series may be fed with the product to be frozen in a continuous way and the product may also continuously be removed from the series and an exellent product is achieved, because pressure is applied to the product during the freezing period, and due to the thawing loose period the withdrawal of the frozen product causes no difficulties.

The invention will hereinafter be further explained with reference to the drawing, on which

Fig. 1 schematically shows a top view of an embodiment of the freezing plant according to the invention,

Fig. 2 shows a side view of a plate freezer belonging to the plant in Fig. 1, wherein, however, some parts have been omitted for the sake of clarity,

Fig. 3 shows the plate freezer shown in Fig. 2 from the left hand side of Fig. 2,

Fig. 4 shows a picture corresponding to Fig. 2 for illustrating the

plate freezer during a first step during an emptying/filling opera¬ tion, and

Fig. 5 shows a picture corresponding to Fig. 4 for illustrating a final step after an emptying/filling cycle.

The freezing plant shown in Fig. 1 consists of four plate freezers 1, 2, 3 and 4 and a conveyor system which according to the embodiment shown consists of a feeding conveyor 5 and a removing conveyor 6. The plate freezers 1, 2, 3 and 4 constitute a series and are according to the embodiment shown aligned with each other in such a way that the feeding conveyor 5 and the removing conveyor 6 may serve all the plate freezers.

As it appears from Figs. 2-5 each plate freezer, e.g. the plate freezer 1 on Fig. 1, comprises a stack of freezing plates 7 of which seven are provided according to the embodiment schematically shown on Figs. 1-5.

The uppermost freezing plate 7a is supported by means of a cross beam 8 which at each end of the plate freezer has an outwardly extending end 8a and 8b, respectively, and between each of the ends and a basis 9 for the frame 10 of the plate freezer a double acting hydraulic cylinder 11 and 11a, respectively, is arranged.

The cylinders are arranged outside end frame parts each consisting of two columns 12,13 and 14,15, respectively. Within each end frame part 12,13 and 14,15, respectively, the corresponding end of the cross beam 8 carries an end beam 15a extending crosswise with respect to the cross beam, and of which only one is visible in Fig. 3. Each of these end beams is by means of bolts.16 and 17, connected with a supporting plate 18 for the lowermost freezing plate. The upper ends of the bolts extend with clearance through a bracket 19 and 20, respectively, supported by the corresponding end beam 15a. The upper ends of the bolts extend with a surplus length up over the corresponding holes and a stop in the form of a nut 22 and 23, respectively, is arranged at the upper end of each bolt.

At each end frame part two pawls 24,25 and 26,27, respectively, are

arranged and each set of pawls is supported by a pawl arm 28 and 29, respectively. The pawl arms are pivotally supported at their lower ends with respect to the basis 9, and the bearing for the pawl arm 28 is shown in Fig. 3 and is designated 30. Accordingly, each pawl arm 28 and 29 may make a small pivot movement as indicated by means of the double arrow 32 in Fig. 4.

As it appears from Fig. 3 the plate freezer shown has a feeding device 33 consisting of two horizontal arms of which only one 34 is shown in Fig. 3. Each of the arms is supported by one of the columns 12. and 14, respectively _, . This feeding device has been omitted in Figs. 2, 4 and 5 for the sake of clarity. Between the arms 34 a pushing plate 35 is suspended by means of a pair of chains (not shown) which by means of a motor 36 arranged above the pair of chains may be moved to and fro as indicated by means of the double arrow 37 in Fig. 3. The pushing plate 35 has a length which generally corresponds to the length of the freezing plates 7. In Fig. 3 the pushing plate 35 is shown in its outermost position, wherein it is positioned above the edge of the feeding conveyor 5, indicated by means of a broken line, facing away from the plate freezer. Also the removing conveyor 6 is indicated by means of a broken line, and accordingly it will be understood from Fig. 3 that the two conveyors are arranged in the same level as the lowermost pawls 25,27.

As indicated above each of the pawl arms 28 and 29 are pivotable in the direction of the double arrow 32. Their pivoting in the inward direction is limited by a stop 40 and 41, respectively, and moreover each of the pawl arms are biased by a pressure spring 42 and 43, respectively, which keep the pawl arms in the positions shown in Fig. 2, but which permit the pawls 24,25 and 26,27, respectively, of the pawl arms to pivot outwardly while compressing the springs in question and provided solenoides 44 and 45, respectively, which are arranged one between each of the cylinders 11,11a and the corresponding pawl arm 28 and 29, respectively, are activated by the activation of a contact 46 carried by the uppermost cross beam 47 of the frame 10.

Each of the four plate freezers shown in Fig. 1 is provided with

manifolds 48,49; 50,51; 52,53 and 54,55, respectively, which by means of conduits are connected with a distributor 56 arranged in such a way that it can conduct cooling medium to the manifolds 49,51,53 and 55 and cause exit of cooling medium from the manifolds 48,50,52 and 54 in a controlled way. Moreover, the distributor 56 may conduct thawing up medium, e.g. hot gas to the manifolds 49,51,53 and 55 and provide exit for such thawing up medium via the manifolds 48.50,52 and 54 also in a controlled way.

Each of the manifolds is connected with each of the plates of the corresponding plate freezer for feeding said plates with cooling medium/thawing loose medium and for removal of cooling medi¬ um/thawing up medium. Such connections, preferably, are constituted by flexible reinforced tubes which allow the movement of the freezing plates.

The operation of the plant shown will be further explained below:

It is supposed that the plant shown in Fig. 1 is in operation and that a freezing operation and a thawing loose operation have just taken place as regards the plate freezer 1, and that the plates thereof thereafter have been made inactive controlled by the distributor 36. Now the hydraulic cylinders 11,11a of the plate freezer in question are activated by means of a control system 63 schematically shown in Fig. 2, whereby the cross beam 8 is lifted. Thereby also the uppermost plate 7a is lifted, viz. corresponding to the surplus lengths of the bolts lδ-,17. Thereafter the remaining plates in the stack are lifted. When the uppermost plate 7a passes the pawls 24,26 the pawl arms 28 and 29 are pivoted outwardly by cooperation between inclined surfaces 60,61 on the pawls and the plate, respectively. After the passage the pawl arms pivot back to the positions shown in Fig. 2. When the next plate passes the lowermost pawls 25,27 the same operation occurs. The plate freezer is provided with means (not shown) which when the two uppermost plates have passed each set of pawls operate the control system 63, which now reverses the hydraulic cylinders 11,11a for lowering until the two uppermost plates occupy the positions shown in Fig. 4. A well defined interspace is now provided between the two plates and this interspace is higher than the height of the interspace which

the plates had during the freezing due to the surplus lengths of the bolts 16,17 shown exaggerated in Fig. 3 for the sake of clarity. Accordingly, it will be understood that this surplus movement does not need to be considerably greater than the increase of the interspace to be provided between the plates for emptying and filling thereof. Now the feeding device 33 is activated whereby the corresponding pushing plate 35 pushes a product, which in the meantime has been fed by means of the feeding conveyor 5 and stopped by means of the movable stop 65, Fig. 1, sideways into the interspace provided between the two uppermost plates. This pushing-in movement will simultaneously result in pushing at least a part of the frozen product in the interspace in question out upon the moving conveyor 6, because the two conveyors as previously explained and as it appears from Fig. 3 are arranged exactly aligned with the plate supported by means of the pawls 25 and 27. Now the feeding device 33 by reversing the motor 36 moves the pushing plate 35 back to the position shown in Fig. 3, whereafter a new transfer to the interspace of product which has been fed towards the stop 65 takes place. These operations continue until the frozen product in the interspace concerned has been transferred to the conveyor 6 and product to be frozen has been inserted into the interspace in question from the feeding conveyor 5.

Now the cylinders 11,11a are again activated and in the way explained above the second plate from the top will now be brought to rest upon the pawls 24 and 26, whereas the third plate from the top will be brought to rest upon the pawls 25,27. Now a new feeding/emptying interspace will be arranged opposite the conveyors and filling and emptying of this interspace is now carried out in the same way as previously explained. These operations continue until the product in the whole stack has been exchanged. At the final lifting step the contact 46 is activated whereby the two solenoids 44 and 45 are activated whereby the pawl arms 28 and 29 are pivoted away from each other to the position shown in Fig. 5. These movements simultaneously affect the control system 63 which reverses the cylinders 11,11a for lowering the whole stack until the stack occupies the position shown in Fig. 2. After this position has been reached the control system 63 will arrange for the applying of a downwardly extending force upon the cross beam 8 by means of the

cylinders 11,11a and, accordingly, upon the plate stack in such a way that the product will be put under compression for driving air, if any, out. Then the distributor 56 serves for feeding the freezing plates of the plate freezer in question with cooling medium.

During at least the last part of the exchange cycle explained above thawing loose is arranged for as regards the product frozen in the plate freezer 2 controlled by means of the distributor 56. Now the plate freezer 2 is refilled because the stop 65 is lifted by means of the corresponding solenoid 65a, Fig. 3, and the product fed is now stopped by means of the second stop 66. The cycle explained above as regards the plate freezer 1 is now repeated as regards the plate freezer 2, and in this way the operation continues as regards the plate freezers 3 and 4, because also these freezers are provided with movable stops 67 and 68, respectively, corresponding to the stops 65 and 66.

The number of plate freezers belonging to the line in question is equal to one plus the sum of the freezing period and the thawing loose period of a plate freezer divided by the inactive period of the plate freezer. Hereby it is achieved that the plant in question can operate continuously, because one plate freezer always undergoes an emptying/filling cycle while the other operate for freezing and the next plate freezer to be subjected the filling/emptying cycle undergoes the thawing loose step.

According to the example illustrated on the drawing four plate freezers are provided. The freezing time plus the thawing loose time according to the example shown for one of the plate freezers is approximately one hour and an emptying/filling cycle takes approximately twenty minutes.

Accordingly, on the drawing a series of plate freezers is shown wherein the number of the plate freezers is at a minimum. However, it may be appropriate to provide the series with one or more further plate freezers in case of shifting over to the freezing of another product or in order to be able to operate the plant in case one or more of the plate freezers should brake down.