Leif, Pers
Nils
| 1. | A convection oven having an oven chamber (12) forming part of a closed circulation path for heated air and being bounded at one side by a vertical wall section (19) compris ing an air inlet (21) which opens into the oven chamber and extends over substantially the full height of the oven chamber, an air supply duct (20) , which is disposed on the side of the wall section (19) facing away from the oven chamber (12) and extends over substantially the full height of the oven chamber, the air supply duct being in open commu¬ nication with the air inlet and having its upper end con¬ nected to the outlet of a circulating fan (17) , characterised by a multiplicity of air deflecting elements (31A, 38) which are provided on the wall section (19) and distributed over substantially the full height of the oven chamber (12) . |
| 2. | A convection oven according to claim 1, characterised by the provision at the air inlet (21) , adjacent the deflect¬ ing elements (31, 38A) , of an air passage (29, 129) which extends over substantially the full height of the oven chamber (12) and is bounded by side walls (30, 36) that are substantially perpendicular to the plane of the wall section (19) , the horizontal dimension of the side walls of the air passage being small in relation to the height of the oven chamber, both transversely of and parallel to the plane of the wall section (19) . |
| 3. | A convection oven according to claim 1 or 2, characterised in that the horizontal dimension of the air passage (29, 129) transversely of the plane of the wall section (19) is at least twice as large as its horizontal dimension parallel to the plane of the wall section. |
| 4. | A convection oven according to claim 2 or 3, characterised in that the vertical distance between adjacent individual deflecting elements (31A, 38) is shorter than about 1.5 times the horizontal dimension of the air passage (29, 129) transversely of the wall section (19). |
| 5. | A convection oven according to any one of claims 2 to 4, characterised in that the deflecting members (31A, 38) are positioned at the the side of the air passage (29, 129) whic is remote from the wall section (19) . |
| 6. | A convection oven according to claim 5, characterise in that the air deflecting elements (31A) are provided by a strip (31) of expanded metal network. |
| 7. | A convection oven according to claim 6, characterise in that the ratio of the height (HI) of the bands (31AB) of the expanded metal strip (31) to the maximum height (H2) of the openings (31A) thereof, both heights being measured parallel to the main plane of the expanded metal strip, is a least 0.7 and preferably in the range of 0.8 to 1.2. |
| 8. | A convection oven according to any one of claims 2 to 5, characterised in that the air passage (129) is defined by a an elongate Uchannel member (131) which is secured to the side of the wall section (19) facing away from the oven chamber (12) and in that the deflecting elements are formed by lips (38) cut out of the web (35) of the channel member and bent at an angle to the web toward the oven chamber (12) . |
| 9. | A convection oven according to claim 8, characterised in that the channel member (131) comprises flange portions (37) provided at the end of the lateral flanges (36) of the channel member and extending away from the lateral flanges, the channel member being secured to the wall section (19) by said flange portions. |
| 10. | A convection oven according to any one of claims 2 to 9, characterised by the provision at the side of the wall section (19) which faces the oven chamber (12) of a pair of flanges (26, 27) which are directed inwardly towards the oven chamber which flanges define between them an air discharge slot (28) connected with the air passage (29, 129), the distance between the flanges being adjustable. |
This invention relates to a convection oven of the kind defined in the pre-characterising part of the independent claim, particularly a so-called rack oven, especially a rack oven for baking bread products.
Rack baking ovens are commercial cabinet-type baking ovens in which the bread products to be baked are carried on a stack of baking pans or plates or other supports positione in a rack which is usually provided with wheels. The rack, which is normally about the height of a man, is wheeled into and out of the the oven chamber through a doorway of almost the same height as the oven chamber.
During the baking hot air circulated at high velocity in a closed path flows over and around the bread products in th rack; the circulation path comprises the oven chamber, an ai heater and a circulating fan.
In order that the bread products in the rack may be evenly and properly baked over the full height of the rack, it is necessary for the heated air entering the oven chamber to be evenly distributed over the full oven chamber height. Moreover, the heated air must efficiently contact the bread products and also must be directed onto the lower face of th baking pans or plates in the rack to provide bottom heat for the bread products. In order to efficiently contact the lowe face of the pans or plates, the heated air has to flow into an ascending flow path when it enters the oven chamber.
It has been found to be very difficult to meet the above mentioned requirements for the distribution and flow direc¬ tion of the heated air. This is so particularly in the very common class of rack baking ovens in which for space-saving reasons the air circulation path is arranged so that the heated air enters the oven chamber from an air supply duct which is disposed outside one side-wall of the oven chamber and extends over the full height of the oven chamber. The air supply duct sometimes is divided into two or more vertical sub-ducts. The air supply duct or each sub-duct is supplied at the upper end thereof with heated air from the circulating fan and communicates with an inlet which is provided in the
side wall and extends over the entire height of the oven chamber. The air inlet may take the form of one or more slits or a large number of small openings.
When entering the oven chamber the heated air flowing downwardly at high velocity in the air supply duct according¬ ly has to be evenly distributed over the height of the oven chamber and evenly deflected more than 90°. As for space- saving reasons the supply duct is narrow, as measured transversely of the side wall, and the deflection therefore has to be rather abrupt, it is readily appreciated that it is difficult to provide for both an even distribution and a suitable direction of flow of the air entering the oven chamber.
An object of the invention is to provide in a convection oven of the aforesaid kind a simple structure by which an even distribution and a suitable direction of flow of the air entering the oven chamber can be accomplished.
To this end, the convection oven according to the inven¬ tion embodies the features set forth in the independent claim. Preferred embodiments include the features set forth in one or more of the dependent claims
The invention will now be described in greater detail with reference to the accompanying diagrammatic drawings in which: Fig. 1 is a vertical sectional view of a convection oven of the type with which the invention is concerned;
Fig. 2 is a horizontal sectional view of a portion of the oven shown in Fig. 1.
Fig. 3 is an enlarged sectional view on line III-III of Fig. 1;
Fig. 4 is a sectional view on line IV-IV of Fig. 3; Fig. 5 shows a portion of an air deflecting element as viewed in the direction indicated by an arrow V in Fig. 4; Fig. 5A is a sectional view on line VA-VA of Fig. 5; Fig. 6 shows a modified embodiment in a representation similar to that of Fig. 3;
Fig. 7 is an enlarged sectional view on line VII-VII of Fig. 6.
Apart from the portions described in greater detail below, the commercial convection oven diagrammatically shown in the drawings is essentially identical with that which is disclosed in US-A-3 954 053 and US-A-4 202 259. For a more detailed description of the portions not described here, reference is made to these patent specifications which are incorporated herein by reference.
As shown in the drawing, the oven comprises a heat-insu¬ lating enclosure, which is generally designated by 11 and in which an oven chamber 12 of about the height of a man and extending over the major portion of the height of the oven is provided. The oven chamber 12 is adapted to accommodate a rack trolley 13 comprising a number of superposed baking plates or other carriers for the goods, especially bread products, to be treated in the oven.
The rack trolley 13 is wheeled into and out of the oven chamber through a door 14 provided in the front wall of the oven enclosure (see Fig. 2) . Inside the oven chamber the rack trolley 13 is interconnected with a rotatable support 15 which is provided in the oven chamber and which can be raised and lowered; during the treatment the rack trolley is sus¬ pended in the support and rotates together with it.
During the treatment circulating heated air flows through the oven chamber 12. A heater 16 heats the air, which is circulated in the essentially closed circulation path by means of a circulating fan 17. From the outlet of the fan 17 the air flows through a passage 18 above the oven chamber to the upper end of an air supply duct 20 which is disposed at one side-wall 19 of the oven chamber 12 and extends over substantially the full height of the oven chamber. By way of one or more air inlets 21, symbolised in Fig. 1 by a number of openings in the side-wall 19, the air flows from the air supply duct 20 into the oven chamber 12 from which the air is then discharged through one or more air outlets in the oppos- ing side-wall 22 after it has passed through the rack trolley 13 and contacted the lower face of the baking plates and the bread products carried by the plates. The air is then
returned to the fan 17 through a steaming device 23 and a heater 16.
The air inlet or each air inlet 21 extends over substan¬ tially the full height of the oven chamber 12 so that the air entering the oven chamber is distributed over the entire portion of the height of the oven chamber over which bread products are loaded in the rack trolley.
The invention more particularly concerns the air inlet 21, and two embodiments of the air inlet are illustrated in Figs. 2 to 7 and described in greater detail with particular reference to these Figures.
As shown in Fig. 2 the oven comprises an air inlet which is subdivided into two horizontally spaced, substantially identical units, which for the sake of simplicity are also termed air inlets and designated by 21 and which are provided in respective portions or sections of the side-wall 19, the air supply duct being correspondingly subdivided into two parallel portions, both of which are designated by 20.
The aforesaid subdivision of the inlet into two units is based on practical considerations, primarily for reasons of space economy, and just as well as it is possible within the scope of the invention to concentrate the entire air inlet to one location in the side-wall, it is possible to subdivide the air inlet into more than two spaced units. The following description is limited to one of the two air inlets 21 illu¬ strated in Fig. 2 but naturally is applicable also to the other of these inlets.
In the side-wall 19, which is constructed from steel sheet, a slit 25 extending over substantially the full height of the oven chamber 12 is provided at the inlet 21. The part or section of the side-wall 19 in which the slit 25 is pro¬ vided is substantially perpendicular to a vertical plane through the slit and the axis of rotation of the rack trolley and forms part of the wall of the air supply duct 20. Provided on the face of the side-wall 19 directed towards the oven chamber 12 are a pair of parallel flanges 26, 27 which extend over the full height of the slit 25 and which project into the oven chamber 12 and define an air inlet gap
28 directed towards the centre of the oven chamber. One flange 26 is stationary while the other flange 27 is movable towards and away from the other flange to permit adjustment of the width of the gap; the adjustable flange is secured in a set position by means of screws (not shown) . The flanges are directed such that the extended centre line of the gap 28 is offset from the axis of rotation of the rack trolley 13.
At the face of the side-wall 19 facing away from the oven chamber 12 the gap 25 is connected with an air passage 29 which extends over the full height of the gap and the lateral walls of which are formed by a pair of parallel plates 30 mounted at right angles to the side-wall 19.
The length of the air passage 29, that is, the extent of the passage as measured at right angles to the side-wall 19, is a small fraction of the height of the passage but prefer¬ ably is at least twice as large as the width of the passage. The width of the passage suitably is chosen in dependence on the largest air flow to be conveyed through the air passage and the largest pressure drop across the air passage which can be accepted. It has been found in actual practice that a length of 3.5 to 5 cm and a width of 1.5 to 2 cm are pre¬ ferable. The length of the gap 28 suitably is about the same as the width of the air passage 29.
At the side or end of the air passage 29 remote from the oven chamber 12 an air deflecting member 31 is secured across the air passage, for example by welding or bolting. This air deflecting member 31 is in the form of a strip of expanded metal which extends of the full height of the air passage 29, see also Figs. 5 and 5A. The heated air flowing into the air passage 29 from the air supply duct 20 accordingly has to pass through the air deflecting member 31.
The air deflecting member 31 serves to effect a pressure drop from the air supply duct 20 to the air passage 29 which is of a suitable magnitude and substantially constant over the full height of the air passage 29, and to confer a suit¬ able upwardly directed flow component on the heated air flowing through the passage 29.
The dimensions of the openings 31A of the deflecting member 31 and the width of and inclination α of its indivi¬ dual bands 3IB which serve as air deflecting elements, are the factors which primarily determine the pressure drop across the air deflecting member 31 and the vertical flow component of the heated air entering the oven chamber 12. The exact dimensions are best determined by trial and error, but as a general rule the area of the openings as projected on a plane parallel to the main plane of the air deflecting member (the vertical plane) should be 30 to 60 percent of the total area of the air deflecting member projected on the same plane. Moreover, the angle α of inclination of the bands 3IB should be 30 to 45° to that plane, it being preferable that the ratio of the height HI of the band and the maximum height H2 of the openings 31A is at least 0.7 and preferably 0.8 to 1.2. Naturally, the above-mentioned relationships are valid for that portion of the air deflecting member 31 which is opposite to the air passage 29.
In the embodiment shown in Figs. 6 and 7 the air passage 129 and the air deflecting member 131 are formed by a single component, namely a ϋ-channel which is secured, e.g. welded, to the face of the side-wall 19 directed away from the oven chamber 12. For the attachment to the side-wall 19 the channel member 12 is provided with a pair of outwardly directed attachment flanges 37 at the end of the lateral flanges 36 which is remote from the web 35 of the channel member.
A large number of lips 38, which are uniformly spaced over the full height of the slit 25, that is, over the full length of the channel member, form air deflecting elements of the air deflecting member 131. The lips 38 are cut out of the web 35 of the channel member and bent inwardly towards the oven chamber 12 such that they are slightly inclined upwardly in the direction away from the web towards the free end of the lip; an inclination of 10-25° is generally preferable. In respect of the ratio of the width to depth of the channel member the preferred relationships which have been given above in respect of the air passage 29 in Figs. 2 to 5
apply. In order that the lips 38 may not need too steep an upward inclination, the vertical distance between adjacent lips should not be larger than 1.5 times the depth of the channel member, and preferably the just-mentioned distance should be substantially smaller.
As a separate inventive feature of the disclosed convec¬ tion oven, namely a feature which is applicable independently of the features recited in the claims, the side-wall 22 of the oven chamber 12 where the steaming device 23 is posi- tioned, that is, that portion of the side-wall which forms an outlet for the heated air, is formed by or covered by an expanded-metal perforated structure or network (indicated diagrammatically at K in Fig. 1) which is similar to the expanded-metal structure which forms the air deflecting member 31 in Figs. 2 to 5.
The expanded-metal structure K at the side-wall 22 has the same orientation as the expanded-metal structure at the side-wall 19, so that it deflects the air flowing out of the oven chamber through the side wall in the upward direction. However, the object of providing the side-wall 22 with an expanded-metal structure is not to bring about a deflection of the outflowing heated air; actually, the deflection which is brought about by the expanded-metal structure at the side-wall 22 does not produce any particular advantage. Instead, the expanded-metal structure K at the side-wall 22 is provided to promote the supply of steam to the lower portions of the rack trolley 13.
During a short period at the beginning of the baking of the bread products in the rack trolley 13 a large quantity of steam is produced with the aid of the steaming device 23. During this period the circulating fan 17 is passive. The steam fills the entire free space in the oven but is utilized in the oven chamber 12 to produce condensation of water on the still relatively cool bread. The steam entering the oven chamber 12 has a strong tendency to rise in the oven chamber and in known ovens it is therefore difficult to fill the lower portion of the oven chamber with a sufficient amount of steam. This problem is
obviated by the expanded-metal structure K in that this structure confers a downwardly directed flow component on the steam entering the oven chamber 12 through the side-wall 22 so that the steam initially flows downwardly in the oven chamber as is indicated by broken arrows in Fig. 1 and con¬ tacts the bread products on the lowermost plates in the rack trolley 13.
What has been mentioned above in respect of the charac¬ teristics of the expanded-metal structure or network which constitutes the air deflecting member 31 is also valid for the expanded-metal structure K at the side-wall 22.
Next Patent: FOUR A CONVECTION