Forced convection ovens for cooking food.

Abstract: IMPROVEMENT OF THE COMBUSTION CHAMBER, PARTICULARLY IN FORCED CONVECTION FOOD OVENS, of the type essentially comprising: a control panel and the relative electrical and electronic components, an external parallelepiped containment structure with at least one cooking chamber, to which access is possible by an oven door, and a heating unit with a fan surrounded by bands of heat exchange piping located in an intercommunicating ventilation antechamber which is part of the cooking chamber, while below the oven in correspondence to the pipe bands there is a gas burner housed inside a combustion chamber; characterised by the fact that the said combustion chamber has two spaces in correspondence with at least a part of the base of the cooking chamber, the first of which contains insulating material and the second the end(s) of at least one manifold pipe which is dissociated and coaxial with respect to each pipe in the bands of pipes, and is partly inserted in correspondence with the opening.

Description: The object of this invention is to improve the combustion chamber, with particular reference to forced convection food ovens. The innovation has a particular, but not exclusive, application in industrial kitchens. In the prior art various types of ovens available for large kitchens are known, but recently demand has generally centred on three models: the first provides heat to the cooking chamber by steam, the second by convection (both electrical and by a burner) and the third is a combination that operates like the first, the second, or in both modes at the same time. Schematically, an oven can be composed of the control panel and the relative electrical and electronic components, together with an external parallelepiped containment structure with at least one cooking chamber, to which access is possible by a traditional oven door. The heating of the cooking chamber can also be provided by one of three means: by steam, in which case a traditional type boiler is used, with a steam emission pipe directed into the chamber; by convection, or rather, by a fan placed in a space intercommunicating with the cooking chamber, and conveniently surrounded by bundles of thermal exchange tubing; by both steam and convection at the same time. In the second case, the lower part of the oven also contains a gas burner and an associated combustion chamber. The current applicant also holds the Italian patent No.1158054 of 15.01.1982, the subject of which is a forced convection oven for cooking foods. In particular, in the lower part of the oven, or rather in a space below the bottom of the cooking chamber, there is a combustion chamber, essentially delimited by a parallelepiped structure with a "U" configuration conveniently fixed from below to the base of the cooking chamber, and inside which, with various connections, there is at least one burner arranged longitudinally, so that the flames are directed upwards in direct contact with the lower surface of the cooking chamber's base. The openings of the heat exchange tube bundles are welded to the bottom of the cooking chamber and in logical correspondence with the underlying burner. These remove the combustion gases and are in direct communication with the combustion chamber. The oven base is made of steel plate and is formed to contact the other sides of the oven and thus define the cooking chamber. EP-A-0 344 743 discloses a forced-convention gas cooking oven comprising a fan and a heat exchanger to circulate hot air around foods placed in the cooking chamber of the oven, the heat exchanger being composed of a plurality of U-shaped pipes distributed concentrically about the periphery of the fan in a symmetrical and uniform manner, the ends of the pipes communicating with ctwo oncentric collectors which in turn communicate with a burner and a combustion gas outlet port respectively. Several drawbacks can be deduced from the above solutions. The most important of these is the fact that the high temperatures commonly reached in the combustion chamber lead to overheating of the overlying area of the base of the cooking chamber, causing surface deformations which can lead to serious structural changes. This problem is most common near the openings of the tube bundles which, being welded directly to the metal base plating, suffer from expansion also caused by the constant pressure from the flames, eventually leading to the joints breaking. The influence of the frequency and the conditions of use of the oven will affect its durability, in that there is a progressive loss in the oven's cooking capacity due to the slow but relentless loss of efficiency by the heat exchanger. The aim of the present invention is to prevent the above mentioned drawbacks. This and other aims are met by innovations which are cited in the claims section and which will now be described. The problems described above are solved by the oven according to claim 1. Further advantageous embodiments of the oven are claimed in the dependent claims. Immediate technical progress results from these creative modifications, leading to several advantages: the efficient insulation of the base of the cooking chamber, thus avoiding deformations and, secondly, a definite reinforcement close to the junctions of the ends of the tube bundles with the base, at the same time allowing for the necessary expansion and avoiding damage. These and other advantages appear from the following detailed description of the preferred solution, which also makes use of schematic diagrams, the details of which are not intended to be exhaustive but rather examples. Figure 1 represents an enlarged detail of the barrier wall of the cooking chamber seen close to the openings of the tube bundles. Figure 2 represents a frontal view of a forced convection food oven, in which the base and a section of the base can be seen. Figure 3 shows a cut away view from the front of a convection oven's combustion chamber, in which the arrangement of the burners and their respective distribution nozzles with respect to the overlying tube bundles can be seen. Figure 4 represents a side view of a combustion chamber as in the preceding Figure. From the figures, it can be seen that a logically controlled forced convection oven (A), particularly one for cooking food, is essentially composed of an external parallelepiped covering (1) and a cooking chamber (2), the inside of which is accessed by a traditional oven door which, in this case, is located at the front of the oven (A). At the back of the said oven (A), being a part of the cooking chamber (2), there is an intercommunicating ventilation antechamber, inside which there is a fan (3) surrounded by a mass tube bundles (4) which, comprising the heat exchanger, rise from the base (5) of the cooking chamber (2) until at the top of the oven they are carried to a waste device. Beneath the barrier wall (5, 8, 9, 9', 10, 11') of the oven (A) and in correspondence with the said ventilation antechamber, there is a traditionally connected burner (6), which in this case comprises two transverse pipes (6', 6''), each having groups of distribution nozzles (12) above and along their length to direct the flame upwards in correspondence with the openings (4') of the tube bundles (4). In this way, the base (5), particularly in the area between the openings (4') of the groups of tube bundles (4), is not directly in contact with the flame, as the nozzles are arranged approximately opposite the ends of the burners (6) in correspondence, as stated above, with the openings (4') of the the tube bundles (4). These are welded to a first metal plate (5) which is also the base of the cooking chamber(2). Immediately below this first base metal plate (5) and covering at least the entire area of the combustion chamber (7), there is a layer of insulating material, in this case made of "armaflex" (commercial name of a common heat resistant insulating material) (8), which is supported by a second metal plate (9) which, together with a third (9'), suitably separated, allows a second space to be obtained (10). A manifold pipe (11) is fitted so as to be dissociated and coaxial to the opening (4') of each pipe (4) in the tube bundle and extends several centimetres into the pipe. The lower part of the manifold pipe has a round disc flange (11') which extends and moves freely in the respective lower interspace (10). In this way, particularly the ends of the tube bundles (4-4') are conveniently protected by the coaxial pipe (11) which can efficiently absorb both its own deformations independently of the remaining structure and expansion of the metal plates without causing breaking points.

Claims: An oven of the type essentially comprising: a control panel and the relative electrical and electronic components, an external parallelepiped containment structure with at least one cooking chamber (2), to which access is possible by an oven door, and a heating unit with a fan surrounded by heat exchange tube bundles (4-4') located in an intercommunicating ventilation antechamber which is part of the cooking chamber (2), while below the oven in correspondence to the said tube bundles (4-4') there is a gas burner, housed inside a combustion chamber (7) which is divided by a barrier wall from said cooking chamber and wherein from said barrier wall departs said heat exchange tube bundles (4-4') to remove the burnt gases from the burners of said combustion chamber; characterised by the fact that: said barrier wall dividing said combustion chamber from said cooking chamber, has at least two superimposed interspaces (8,10), placed at least in correspondence with the wall's connection with said heat exchange tube bundles (4-4'), the first in the upper position (8) containing insulating material and the second in the lower position (10), which contains the end(s) of an external disc flange extention (11') of a manifold pipe which is dissociated and coaxially inserted into the lower openings of each pipe of said heat exchange tube bundle (4-4'). An oven, according to claim 1, characterised by the fact that above the burner (6) in the oven's combustion chamber (7), and involving at least part of the barrier wall (5,8,9,10,9',11') of the oven's (A) cooking chamber (2) corresponding to the area concerning the said ventilation antechamber, there is a metal plate (5) below which is a layer of insulating material (8) supported by a second metal plate (9) which, together with a third (9') suitably spaced forms said second interspace (10). An oven, according to the previous claims, characterised by the fact that a manifold pipe (11) is fitted so as to be dissociated and coaxial to the opening (4') of each pipe (4), and extends several centimetres into the respective pipe, and wherein the lower part of the manifold pipe has a round disc flange (11') which extends into and moves freely in the respective lower interspace (10). An oven, according to the previous claims, characterised by the fact that the burners (6) have flame distribution nozzles (12) arranged exclusively in correspondence with the area immediately below the openings (4'') of each pipe of the heat exchange tube bundle (4).

Inventors: LAZZER NATALINO, LAZZER, NATALINO
Applicants: LAINOX SRL, LAINOX S.R.L.
Application year: 1993
Main classification: F24C15
IPC codes: F24C15