GB2166536A - Plate freezers - Google Patents

Abstract

The invention relates to a method for operating a plate freezer comprising a stack (1) of pairs of freezing plates (2) each defining between them a freezing zone (A,B,C,D,E,F) in which method the freezing zones are successively brought into register with a feed station (7) from which articles are fed to the freezing zones to fill the zones in a spaced sequence so as to leave one or more empty zones between the filled zones on the rising stroke of the freezer. These empty zones are then filled on the fall stroke of the freezer so that at the end of the filling cycle the last zone to be filled is adjacent the first zone to be filled. Discharge of the freezer can be carried out by raising or lowering of the zones through only one zone to bring that first zone into register with the feed/discharge station (7, 8). The invention also provides a plate freezer in which the stack of plates is moved by means of a screw actuated mechanism (10), notably by means of screw jacks located at or adjacent each corner of the stack of plates. <IMAGE>

Description

SPECIFICATION Device and method for feeding articles The present invention relates to a device and to a method for feeding articles, notables articles which are to be chilled or frozen in a plate freezer.

A conventional plate freezer comprises a number of substantially parallel and horizontal cooling plates arranged as a stack and defining between adjacent pairs of plates a series of superimposed freezing zones. The stack of plates is housed within a thermally insulated casing having an opening in a side wall thereof with which successive freezing zones can be brought into register by moving the stack up or down by a zone at a time. Articles, notably foodstuffs, e.g. food portions or slabs of meat or fish, are fed into a freezing zone via the opening from a feeding station at one side of the freezer. When the zone is filled, the stack is moved up or down one zone to bring the next empty zone into register with the feed station. This cycle of moving a zone and filling it is repeated until all the zones in the stack have been filled.

At this point, the articles in the first zone will have been held in the freezer for the desired time to chill or freeze the articles, The stack is then raised or lowered through the full extent of its travel until that zone again registers with the feed/discharge station so that the frozen articles can be discharged through a discharging station on the opposite side of the freezer. However, during the moving of the stack at the end of the filling cycle, articles can not be fed to the freezing zones.

Provision therefore has to be made in the mechanism feeding articles to the feed station to accommodate the articles during the lowering stage, or the feed of articles has to be interrupted. The delay can often be of a minute or more and this can impose severe problems in the operation of a large scale food processing line.

We have now devised a form of operation of a plate freezer or chiller which reduces these problems and a new design of plate freezer for use in the method of the invention.

Accordingly, the present invention provides a method for operating a plate freezer having a plurality of superimposed cooling zones defined by upper and lower substantially parallel and horizontal cooling plate members the zones being adapted to receive articles to be cooled, which zones are adapted to be moved in and out of register with a feeding station whereby articles can be fed to a succession of the zones, which method comprises the cycle of:: a). feeding articles via the feed station of the freezer to a first cooling zone in register therewith; b). moving the cooling zone out of register with the feeding station in an upward or downward sense with respect to the feeding station and by at least two cooling zones so as to bring a second cooling zone into register with the feeding station and so that there is an interval of one or more zones between the said second zone and the first said zone; c). feeding articles from the feeding station to that second zone; d). moving the said second zone out of register with the feeding station by at least two zones and in the same sense as the first movement so as to bring a third zone into register with the feeding station with an interval of at least on zone between the second and third zones and feeding articles to that third zone;; e). if necessary repeating the moving and feeding operations until the final or penultimate zone in the direction of movement is fed with articles; e). moving the cooling zones up or down one zone to bring whichever of said penultimate zone or final zone is adjacent to the zone to which articles were last fed in step e) into register with the feeding station and feeding articles to that zone; f). subsequently moving the zones in the opposite sense to the first direction of movement with respect to the feeding station so as to bring zones not fed with articles on the first direction of travel successively into register with the feeding zone and feeding articles to those zones as in steps a) to e) above until the final zone in this direction of movement has been fed with articles;; g). moving the zones up or down to bring the said first zone of step a) above into register with the feeding station for feeding articles to said zone and for discharging cooled articles from that zone; h). and repeating the cycle of steps a) to g).

In the method of the invention, the freezing zones between adjacent plates of the freezer are filled both on the upward stroke of the freezer and on the downward stroke and the filling cycle is completed in the zone immediately or closely adjacent the first zone of the filling cycle. The travel required to bring the first zone into register with the feed/discharge point is thus only one or two zones. This avoids the prolonged delay between the completion of one filling cycle and the start of the next cycle inherent in the need to lower the freezer through its full travel with conventional operating methods. The invention can be applied to the chilling of articles as well as to the freezing of those articles and the term cooling is used herein to denote both chilling and freezing where the context permits.

The method of the invention can be applied to conventional plate freezers whose control systems, for example those controlling the rise and fall mechanism of the plates, have been modified to achieve the new sequence of zone registers with the feeding station. It is also within the scope of the present invention to raise or lower the feed station output into the freezer in the required sequence or to commence the cycle by lowering the plates into register with the feed opening in the housing rather than raising them.

However, we have found that hydraulic systems as used in conventional plate freezers give problems in securing accurate register of the feed station and the desired cooling zone and in maintaining accurate alignment of the plates in the stack during the rise and fall of the stack, especially with plates having a dimension greater than about 2.5 metres. Surprisingly, screw actuated rise and fall mechanisms provide a simple and effective means for securing accurate registration of the feed station with the freezing zones, even where the freezer plates are being moved through more than two zones between successive filling steps.Such mechanisms have not hitherto been used in plate freezers and the invention therefore provides a plate freezer comprising a number of substantially parallel and horizontal cooling plates arranged as a stack and defining between adjacent pairs of plates a series of cooling zones; the stack of plates being housed within a thermally insulated casing having an opening in a side wall thereof into which successive cooling zones can be brought into register by moving the stack up or down, characterised in that the stack is moved by means of a screw actuated rise and fall mechanism.

The screw actuated mechanism can take a number of forms, eg. a series of screw threaded pillars arranged substantially symmetrically around the periphery of the stack of said plates and each engaging a co-operating threaded sleeve carried by a member supporting the stack of plates, eg. a bottom or top frame upon which the stack of plates is carried. Rotation of the pillars will cause the stack to rise and fall in an accurately controlled manner. Alternatively, the stack can be mounted on one or more screw operated scissor jacks.

The use of a number of screw actuated mechanisms located substantially symmetrically around the stack has the advantage that their operation can be interlinked with one another to ensure uniform vertical movement of the plates by each screw mechanism to give accurate control of the rise and fall of the stack and the orientation of the stack can be held steady, even where the freezer has been unevenly loaded. This enables the size of the plates to be increased over that which can be handled using hydraulic systems. Thus, the freezers of the invention can have plates with a plan dimension of 3 metres or more. The use of screw actuated mechanisms also overcomes the problems of leakage of hydraulic fluid or freezing of water within the hydraulic lines or control valves with hydraulic systems.

The invention will now be described with particular reference to a preferred form thereof as shown in the acoompanying drawings in which: Figure 1 is a diagrammatic vertical sectional view of the freezer; and Figure 2 is a diagrammatic representation of the order of feeding of articles to the plates in the stack in the device of Figure 1.

A plate freezer comprises a stack 1 of a series of substantially parallel plates 2 defining freezing zones A,B, etc. between them. The plates 2 are separated by spacer members 3 which correspond to the height of the articles to be loaded onto the plates so that the articles in a freezing zone are contacted by cooling surfaces both from above and from below.

Preferably, the spacers 3 are demountable so that they can be interchanged so that the freezer can accept articles of a variety of heights.

The stack of plates is carried by a top frame 4 from which is suspended a bottom frame 5 by vertical tie bars 6. The individual plates 2 are vertically moveable within the framework formed by the top frame, the tie bars and the bottom frame so that a plate can be supported as described below whilst the remainder of the stack below it is lowered to create a bigger spacing between the plates for ease of loading of articles into the cooling zones between plates. Preferably, the length of the tie bars is adjustable to accomodate different spacings between the plates.

The stack 1 is housed in a thermally insu lated housing 3 having a feed station opening 7 in one side wall with a discharge station opening 8 at the directly opposed side of the housing. Articles to be cooled are fed by a conveyor 9 to the feed station 7 and into the cooling zone (A) registering with the feed station. Where a zone is already charged with cooled articles, the feed of further articles to that zone will displace the cooled articles from the zone through the discharge opening 8.

The stack 1 is mounted on one or more screw jacks 10, preferably one to each corner of the stack and inter-linked by gears or other drive means 11 to a motor or other means 12 to drive the jacks 10. The operation of the jacks is oontrolled by a suitable control mechanism which can incorporate sensors and the like to detect when a given zone is in register with the feed station 7 and when each cooling zone contains the desired weight of material to be cooled. Thus, the level reached by a plate can be detected by the tripping of a stationary contact or proximity switch as the plate passes the switch. Alternatively, the level of the plate can be detected by monitoring the rotation of the screw jacks, the number of turns in either direction giving the extent to which the plate has been raised or lowered from a given starting position.

Opposed to the stack adjacent the upper level of the side opening 7 are a series of pawls 20 which are actuated to engage with the under surface of the upper plate of a cool ing zone and to support that plate and those above it whilst the plate below it is lowered into register with the feed opening 7 to ac cept articles fed through the opening 7. In this way the spacing between the plates is increased so that the plates are no longer in close proximity to the articles to be fed into or discharged from the cooling zone. When the pawls are released to allow the plates to close up again so that they come into close proximity with the articles therebetween, thus aiding cooling of the articles. The pawls 20 are actuated by any suitable mechanism which is preferably interlinked with the operation of the screw jacks 10.

Initially, the stack will be in its lowered position with zone A in register with the feed station 7 and the upper plate 2a supported by the pawls 20 so that there is an increased gap between that plate and the plate 2b in register with the feed opening 7.

Articles are fed to the zone to charge it with the desired number of articles. The jacks 10 are then actuated to lift the stack to raise plate 2b so that the spacer member 3 thereon abuts plate 2a and releases the pawl 20. The stack is lifted further to bring the upper plate of another zone into register with the pawl 20 which engages that plate. The stack is then lowered to bring the lower plate of that zone into register with the feed station 7. Usually, it will desired to raise the stack through two zones so that one zone is left empty between each of the filled zones. However, it is within the scope of this invention to raise or lower the stack through more than two zones and the rise or fall need not be the same for each movement.However, with the freezer shown, it is preferred to actuate it so that the order of registration of the zones with station 7 on the upward stroke are A, C, B and F; and D then B on the downward stroke.

When the stack has zone B in register with the feed station 7 and the zone is charged with articles, the freezer has completed its charging cycle. The articles in zone A have been frozen to the desired extent and the stack is moved, in this case lowered, to bring zone A into register with feed station 7 so that fresh articles can be fed to zone A and frozen articles displaced via discharge opening 8. The stack moves through only one zone and hence the delay between the end of one charging cycle and the start of the next charging/discharging cycle is no more than that between steps within a cycle. Thus, the delay does not cause any significant bottle-neck in the operation of the freezer and it is not necessary to provide means to interrupt or to store the feed of articles during the change from one cycle to the next as hitherto.

Claims (12)

1. A method for operating a plate freezer having a plurality of superimposed cooling zones defined by upper and lower substantially parallel and horizontal cooling plate members the zones being adapted to receive articles to be cooled, which zones are adapted to be moved in and out of register with a feeding station whereby articles can be fed to a succession of the zones, which method comprises the cycle of:: a). feeding articles via the feed station of the freezer to a first cooling zone in register therewith; b). moving the cooling zone out of register with the feeding station in an upward or downward sense with respect to the feeding station and by at least two cooling zones so as to bring a second cooling zone into register with the feeding station and so that there is an interval of one or more zones between the said second zone and the first said zone; c). feeding articles from the feeding station to that second zone; d). moving the said second zone out of register with the feeding station by at least two zones and in the same sense as the first movement so as to bring a third zone into register with the feeding station with an interval of at least on zone between the second and third zones and feeding articles to that third zone; e). repeating the moving and feeding operations until the final or penultimate zone in the direction of movement is fed with articles; f). moving the cooling zones up or down one zone to bring whichever of said penultimate zone or final zone is adjacent to the zone to which articles were last fed in step e) into register with the feeding station and feeding articles to that zone;; g). subsequently moving the zones in the opposite sense to the first direction of movement with respect to the feeding station so as to bring zones not fed with articles on the first direction of travel successively into register with the feeding zone and feeding articles to those zones as in steps a) to e)above until the final zone in this direction of movement has been fed with articles; h). moving the zones up or down to bring the said first zone of step a) above into register with the feeding station for feeding articles to said zone and for discharging cooled articles from that zone; i). and repeating the cycle of steps a) to h).

2. A method as claimed in claim 1 wherein each of said cooling zones is substantially filled with articles at each feeding step; and discharge of cooled articles from each zone is achieved simultaneously by displacement of the cooled articles from the cooling zone by the infeed of articles from the feeding station.

3. A method as claimed in either of claims 1 or 2 wherein the articles are of foodstuff.

4. A method as claimed in any one of the preceding claims wherein the zones are moved out of register by two zones so as to provide an interval of one zone between the zones brought into register with the feeding station on each direction of movement.

5. A method as claimed in claim 1 substantially as hereinbefore described with respect to the accompanying drawings.

6. A plate freezer comprising a number of substantially parallel and horizontal cooling plates arranged as a stack and defining between adjacent pairs of said plates a series of cooling zones; the stack of plates being housed within a thermally insulated casing having an opening in a side wall thereof with which successive cooling zones can be brought into register by moving the stack up or down, characterised in that the stack is moved by means of a screw actuated rise and fall mechanism.

7. A plate freezer as claimed in claim 6 wherein a series of screw threaded pillars is arranged substantially symmetrically around the periphery of the stack of said plates, each engaging a co-operating threaded sleeve carried by a member supporting the stack of plates, whereby rotation of said pillars causes the support member to rise or fall and carry the stack of plates relative to said opening.

8. A plate freezer as claimed in either of claims 6 or 7 wherein the operation of the screw actuated rise and fall mechanisms is interlinked.

9. A plate freezer as claimed in any one of claims 6 to 8 wherein the cooling plates have a plan dimension of 3 metres or more.

10. A plate freezer as claimed in any one of claims 6 to 9 wherein the spacing between the plates in the stack is achieved by means of demountable spacer members.

11. A plate freezer as claimed in any one of claims 6 to 10 wherein the plates are vertically moveable within the stack and pawl means are provided to engage and support the plate immediately above the opening and those carried upon that plate whilst the remainder of the stack of plates is lowered to bring the plate next below that said plate into register with the opening so as to increase the spacing between said plates.

12. A plate freezer as claimed in claim 6 substantially as hereinbefore described with resect to the accompanying drawings.