A METHOD AND OVEN FOR PROCESSING PRODUCTS WITH A HEATED AIR-FLOW

Abstract: In an oven for baking, grilling or drying products by means of a heated air-flow there are used two fans (10, 11) arranged in the upper part of the oven (1) and having mutually adjacent fan wheels (10a, 11a) and vertical shafts. Accommodated in a space (12) beneath the fan wheels (10a; 11a) is a heating battery (14). Located at a distance from two opposing oven sides is a guiding and deflecting plate (15; 16) for circulating hot air. The plates are provided with slot-like openings (15a; 16a) and optionally also with separate deflecting means (15b; 16b) arranged in connection with the slot-like openings. Co-acting with the heat battery (14) is a vapour-generating means (19; 17). One of the fans is driven in one direction for a given interval of time, whereupon a heated flow is caused to pass downwardly along one oven side and is deflected horizontally inwardly through slot-like openings of a corresponding plate. When a given period of time has lapsed - for example from one to two minutes - the firstmentioned fan is disconnected and the other fan connected and driven in the opposite direction. In this way the whole of the oven space is heated in an even and uniform manner - optionally with vapourized air.

Description: A method and oven for processing products with a heated air-flow Field of invention The present invention relates to a method for pro¬ ducing an even and uniform air-flow throughout the whole of the cooking space of an oven when processing products with the aid of a heated air-flow in said oven, in order to bake, grill, cook or dry said products, or to process the same in some other way. According to another aspect the invention also refers to an oven for practising said method. A serious problem encountered when processing pro¬ ducts in this way in air-flow ovens, is one of producing an even and uniform flow of air in all parts of the oven space, and therewith uniform heat transfer to all the products in the oven. State of the art Various measures have been proposed for obtaining such uniform air-flow. One common, technical solution to the problem is to place the products on a rack which is caused to rotate in the oven. This solution is relatively complicated, and requires the presence of drive means, which can give rise to operational disturbances and which, among other things, make servicing and cleaning of the oven space difficult. Such rotating racks also require a large oven space. Other solutions involve guiding the circulating hot air with the aid of throttle-valve devices arranged to cause the air to change direction. One problem with this solution is that of sealing and journalling the valve arrangement in a satisfactory manner. Other known solutions to the problem of reversing the air-flow include the use of vertically mounted cross- flow fans having a height corresponding to the oven space. OMPI An example of the first mentioned solution, utilizing a rotatable rack, is described in SE-B-7504080-8 (AB Svenska Bakugnsfabriken) . This arrangement is encumbered with the disadvantages afore-mentioned. Ovens equipped with various kinds of air-guiding throttle-valve constructions are described in NO-B-117,196 (Electrolux) and DE-A-28 04 545 (Werner & Pfleiderer) . The first arrangement requires progressive throttling, while the second arrangement incorporates the use of separate closure means. Both types of oven are technically complicated and result in an irregular flow of air in the oven space. Another design of oven is described in SE-A-7514334-7 (Electrolux) . The conventional oven described in this application also generates an irregular air-flow. SE-B-369,828 and SE-B-391,110 (both Tipe Revent) describe baking ovens equipped with two cross-flow fans having vertical shafts which extend throughout the entire height of the oven space and are driven simultaneously in mutually the same direction, the direction of rotation of the fans being reversible. The major drawback with this type of cross-flow arrangement is that the hot air will not be mixed in vertical direction which results in substantially lower temperature in the bottom part than in the top part of the oven. Further the arrangements are relatively space-consuming and expensive; they also present certain problems when desiring to generate vapour in the oven space, to improve the heat-transfer effect. Similar cross-flow arrangements having the same drawbacks are described in FR-B-2,390 ,102 and CH-A-532,363 (both Debag) . Brief presentation of the invention The method according to the invention is mainly characterized by initially driving in one direction one of two radial fans having vertical shafts and being OMPI located in the upper part of the oven, while holding the other fan disconnected; by causing the flow generated by said one fan to pass a heating battery located in the region of the fans in the upper part of the oven; by guiding the generated, heated flow verti¬ cally downwardly along at least one of the sides of the oven and to deflect said flow inwardly at different levels, and thereafter horizontally upwardly at the opposite side of the oven; and by disconnecting said one fan and connecting the other fan at given time intervals, so as to reverse the direction of flow. The method according to the invention provides • a reversal in the direction of air-flow without requiring the provision of movable throttle-valve arrangements, which can readily give rise to operational disturbances. Because cooler air from. the oven space is drawn through . the stationary fan, the fan will be cooled during the stationary periods. The heating batteries will also be cooled effectively, since the air changes direction in the space in which the batteries are located. The method according to the invention permits the oven construction to be extremely compact, with all electrical components, such as motors and electric batteries, positioned above the actual oven space, i.e. cooking area. This enables the oven space to be cleaned by, for example, rinsing or flushing the same with water, even with water under high pressure, without the risk of the water coming into contact with the electircal installations. In practice, it is preferred that the heated air¬ flow is guided downwardly along the sides of the oven by means of a guiding and deflecting plate having perfora¬ tions or slot-like openings located at different levels. Such an arrangement will cause the air to be supplied to the oven space via one side wall and to be drawn out by suction at the opposite side wall, after having first come into contact with the products located in the oven. When wishing to generate vapour in the oven, the heating batteries are caused to heat a tray which is placed beneath the fans and on which liquid is sprayed, to generate vapour which is conveyed to the oven space by the circulating air-flow. One important advantage afforded hereby is that vapour is effectively generated even when the temperature in the actual oven space is relatively low (100-150°C), such as when baking products. Another important advantage is that all lime deposits originating from the water supplied are deposited on the bottom of the tray. The tray is arranged so that it can be readily drawn out and cleaned, as opposed to conventional spray nozzles provided with small orifices, which readily become blocked. The underside of the tray is suitably insulated, so that the upper side of the tray can be heated to very high surface temperatures, for example temperatures of 400-600°C, thereby providing highly effective vapour generation. The invention also relates to an oven, for example for baking, grilling, cooking, drying or the like, the essential characteristics of the oven being set forth in the claims. The guiding and deflecting means of the oven include stepped plates located preferably at opposite sides of the oven and having slot-like openings positioned at different levels, and deflecting means which are located transversely of the flow direction immediately downstream of the slot-like openings, and which project into the path of the flow through a distance which corresponds at least to the height of the slot-like openings parallel with the flow. Such flow-guiding and flow-deflecting means have an extremely purposeful form and can be manufactured cheaply OMH and obtain satisfactory rigidity even when the plate is comparatively thin. Efficient deflection of the air¬ flow is obtained, and also uniform distribution of the flow through the whole of the oven space, despite the fact that the plates lack movable throttle-valves or the like. The heating battery is preferably located beneath the fans, in a defined area having an insulated bottom surface. In this way, in the region of one half of the heating battery air will be drawn in via the stationary fan, which as a result of the subpressure generated will subsequently be caused to co-rotate with the other fan. Subsequent to being heated, the air-flow will pass the driven fan, which pressurizes the flow. The air-flow can then - if so desired - be caused to pass further heating coils. Alternatively, or in addition, it is possible to use different types of one-way butterfly- or throttle- valves for guiding the air-flow,- particularly the air- flow drawn-in to the driven fan. This air-flow can, for example, be guided so as not to pass the stationary fan, but so as to be conducted directly to the suction side of the driven fan. Such one-way valves are of extremely simple design, and the particular advantage characteristic of the invention, namely that butterfly- or throttle- valves are normally not required, is ' not impaired by using .one or more valves of the afore-mentioned kind. A number of embodiments of the invention will now be described in more detail with reference to the accompanying schematic drawings. Brief description of the drawings Figure 1 is a partially sectional front view of a simple kind of oven not provided with vapour-generating means; Figure 2 is a similar view of a modified oven having O PI vapour-generating means and also flow-distributing and flow-deflecting plates of a particular design; Figure 3 is a cross-sectional view of the upper part of a relative to Figure 2 modified embodiment when the left fan is rotating; and Figure 4 is a similar view of the Figure 3 embodi¬ ment when the right fan is rotating. Description of preferred embodiments Referring first to Figure 1 , the numeral 1 identifies a baking oven having an insulated oven space 2, in which there is arranged a stand 3 which supports a plurality of plates 4 on which are placed loaves or buns 5 to be baked in the oven. Arranged in the upper part of the oven are two radial fans 10, 11 having vertical shafts. The fan wheels 10a and 11a, respectively, are located immediately beneath the ceiling of the oven space. Located beneath the fan wheels 10a and J1a is a space 12 which is defined by walls 13 and which accommo¬ dates a heating battery 14 having the form of electric heating filaments. The fan drive motors are located externally of the oven space, together with guide means (not shown) for alternate driving of the fans, first one fan in one direction and then the other fan in an opposite direction during given time intervals. Arranged within the oven space on each side of the oven is a deflecting and distributing plate 15 and 16, respectively, by means of which heated air is conducted downwardly along the sides of the oven and is deflected, via perforations 15a, 16a, horizontally so as to come into contact with the products located in the oven. In the embodiment illustrated in Figure 1 there are used smooth plates 15, 16 provided with a suitable number of perforations of suitable shape and form. As will be seen from the illustrated flow pattern, air is drawn in through the fan wheel 11a to the right- hand fan 11 , from where it moves downwardly to the space 12 accommodating the heating battery 14. The fan wheel 11a is, in this way, caused to co-rotate by the air stream drawn thereinto, this stream being heated by the heating battery and drawn out through the opening located beneath the fan wheel 10a. The heated and inwardly drawn air-flow is pressurized by the fan wheel 10a and is then forced downwardly in the space between the left-hand side of the oven and the distributing plate 15, where the flow is deflected in horizontally directed part flows, which pass the products 5 in the oven space while transferring their heat content to said products. When a given period of time has lapsed - for example from one to- two minutes - the flow direction is reversed, by disconnecting the fan 10 and connecting the fan 11. In this way, heat is uniformly transferred readily to all products present in the oven. With the aid of simple one-way butterfly-valves (Figs. 3 and 4) the major part of the air under suction can be guided so as to be conducted directly to the space 12 accommodating the heating battery 14. Only a small part of the flow will then -pass the "stationary" fan wheel 11a. Although not shown, additional heating coils can be located externally of the space 12. The bottom defining wall 17 of the space 12 is normally heated to very high temperatures, for example 400-600 C, and is therefore suitably provided with an underlying insulation 18. The embodiment illustrated in Figure 2 corresponds to the embodiment illustrated in Figure 1 , with exception that the laterally located flow-distributing and flow- deflecting plates have a different form, and that the oven is provided with vapour-generating means. In this embodiment, the' oven space is also larger, and two rows of plates 4 are located side-by-side on the same level. In this embodiment, the guiding and deflecting plates 15 are stepped and include approximately horizon¬ tally extending shoulders 15b, which are located immediately downstream of slot-like openings 15a and project into the path of the air-flow through a distance which at least corresponds to the height of the slot-like openings, parallel with the flow. Despite its thinness, such a guide and deflecting plate is sufficiently rigid and provides for an effective and uniform deflection .and flow-distribution within the oven space. The bottom 17 of the space 12 accommodating the heating means 14 has the form of a tray. Water is sprayed onto the bottom 17 of the tray through a pipe 19. The high temperature of the tray causes the water to be - effectively vapourized, the vapour being carried by the air-flow as it circulates within the oven. A vapour-generating means of the described simple kind is extremely effective, due to being positioned immediately beneath the fan wheels 10a, 11a. Several of the various components of the ovens illustrated in Figure 1 and Figure 2, respectively, can be removable and exchangeable. This greatly facilitates cleaning of the oven, and it is also possible, in certain instances, to exchange, for example, the deflecting and flow-distributing plates 15, depending upon how the products are to be processed in the oven from case to case. Figs. 3 and 4 illustrate the upper part of a modi¬ fication of the Figure 2 embodiment. A simple one-way butterfly-valve 20, 21 is positioned at each end of the space 12 accommodating the heating battery 14. Each butterfly-disc 20a, 21a coacts with a wing or shovel 20b, 21b positioned in the air stream from the respective fan 10 or 11 which is rotating in each instance. A rod 22 connects the butterfly-discs 20a and 21a, so that when the disc 2θa is in closed position disc 21a is open and vice versa. In Figure 3 the left fan 10 is rotating and the left valve 20 accordingly closed whereas valve 21 is open. Figure 4 illustrates the reverse situation, i.e. when the right fan 11 is rotating and valve 21 accordingly closed. Pipe 19 and tray 17 may also be present. This embodiment has the advantage that the heat exchange within chamber 12 is improved. Further, at the suction side of each fan 10, 11 there will automatically be less resistance to the flow which will result in improved behaviour of the oven. The drawing figures show that only a small part of the flow will find its way through the in each instance "stationary" fan 11 or 10, respectively. Technical applicability An oven according to the invention can be used in a variety of different contexts. In addition to different kinds of baking and food-preparing processes , the oven can also be used in connection with different industrial processes, such as drying processes for example. Various kinds of auxilliary arrangements are also possible within the scope of the invention as defined in the accompanying claims. The flow generated by either fan may optionally be conducted to one or to two adjacent sides of the oven and may be supplied to the whole of the oven space or to a part thereof, so that mutually intersecting flows occur in said oven space or said parts thereof. In certain cases, the turbulent part flows obtained in this way can contribute to improving the efficiency of the oven. OMP

Claims: CLAIMS 1. A method for producing an even, uniform flow throughout the whole of the oven space of an oven when processing products with the aid of a heated flow in said oven, in order to bake, grill or dry the products, or to process the same in some other way, comprising the steps of initially driving in one direction one of two radial fans having vertical shafts and being located in the upper part of the oven, while holding the other fan disconnected; causing the flow generated by said one fan to pass a heating battery arranged in the vicinity of the fans in the upper regions of the oven; guiding the generated, heated flow vertically downwardly along at least one of the sides of the oven and to deflect said flow inwardly at different levels, and thereafter hori- zontally upwardly at the opposite side of the oven; and disconnecting- said one fan and connecting the other fan at given time intervals, so as to reverse the direction of flow. 2. A method according to claim 1, c h a r a c t e r - i z e d by passing the heated flow downwardly on said oven side by means of a guiding and deflecting plate having slot-like openings or perforations located at different levels. 3. A method according to claim 1 or claim 2, c h a r - a c t e r i z e d by causing the heating battery to heat a tray placed beneath the fan, spraying liquid onto said tray so as to generate vapour and carrying said vapour to the oven space by the circulating air-flow. 4. A method according to anyone of claims 1-3, c h a r - a c t e r i z e d by drawing the flow by suction through the disconnected fan, so as to cause said fan to co-rotate, and at least partially heating said flow by the heating battery prior to put it under pressure by the driven fan. 5. A method according to any of claims 1-4, c h a r ¬ a c t e r i z e d by guiding a substantial part of the flow at the suction side of the rotating fan directly to the heating battery by means of two coacting valves , one at each end of a chamber housing said heating battery. 6. An oven, for example for baking, cooking, grilling, drying or like process, comprising means for circulating and heating the flows in various directions through the oven, c h a r a c t e r i z e d in that the circulating means comprises a) two radial fans (10, 10a; 11 , 11a) having vertical shafts and being mounted in the upper part of the oven; b) guiding and deflecting means (15; 16) arranged on two mutually opposing sides of the oven for co-action with the flows generated by the fans, said means being arranged to conduct the flows downwardly along either oven side and to deflect said flows horizontally inwardly at different levels; and c) means for alternately driving each fan in one direction and the other fan in the opposite direction over a given period of time; and in that the heating means includes a heating battery (14) located in the vicinity of the fans. 7. An oven according to claim 6, in which the guiding and deflecting means include plates (15; 16) which are located on opposite oven sides and which have slot-like openings located at different levels, c h a r a c t e r ¬ i z e d in that the plates (15; 16) are provided imme¬ diately downstream of the slot-like openings (15a; 16a) with step-like deflecting means (15b; 16b) which project into the path of the downwardly directed flow through a distance which at least corresponds to the height of the slot-like openings (15a; 16a) parallel with said flow, for dividing the flow and deflecting the same horizon- tally through the slot-like openings into the oven space. OMPI W 8. An oven according to claim 6 or claim 7, c h a r ¬ a c t e r i z e d in that the heating battery (14) is located in a confined space (12) having an insulated undersurface and being located beneath the fans (10, 10a; 11, 11a). 9. An oven according to claim 8, c h a r a c t e r ¬ i z e d in that said space accommodates a tray (17) together with means (19) for spraying liquid onto, the tray, so as to generate vapour which is entrained by the circulating flows. 10. An oven according to claim 8 or claim 9, c h a r ¬ a c t e r i z e d by a one-way valve (20; 21) at each end of said confined space (12) each said valve coacting with a wing or- shovel ('20b; 21b) exposed to the flow from one of said fans (10; 11) to keep the corresponding valve shut, a bar (22) connecting said two valves (20; 21) so that when one is shut the other is open and vice versa.

Inventors: LIND LEIF, LIND, LEIF
Applicants: PRO TECH AB, PRO-TECH PROGRESSIVE TECHNIC AB
Application year: 1983
Main classification: A21B1
IPC codes: A21B1