Hot air circulating baking oven - with steam generator and valves for air and steam discharge

Holder: Idem ni

Agent: Cabinet Plasseraud.

Sale of fescicutes at IMPRlMERIE NATIONALE, 27, rue de la Convention - 75732 PARIS CEDEX 15

The invention, due to Ludwig SGHW0K, relates to a baking oven comprising a cooking chamber, delimited by an insulating enclosure and capable of being closed by a door, a heating device and a closed-circuit stirring device i ntended to create and stirring the cooking atmosphere inside the cooking chamber, a steam generator device, disposed in the region of the heating device, and at least one valve provided on the cooking chamber.

Such an oven is known from Austrian Patent No. 324,988.

For the baking of various bakery and biscuit products, a steam atmosphere must be maintained in the baking chamber for a short time, but possibly also throughout the baking, so that the product has, for example, a surface rough and shiny exterior. However, this atmosphere may have to be removed after a certain time. In this regard the German patent. No. 1,103,112 describes a process for removing steam from the circulation circuit - Forced from a bakery oven.

According to the Austrian patent n ° 324 988, in the part, located between two blowers of the blowing device and containing the heating device, of the forced circulation circuit of the oven is provided an exhaust device provided with a valve which can be consisting of either a manually operated valve or a pressure relief valve. This particular arrangement of a valve serves to quickly evacuate the cooking atmosphere from the forced circulation circuit. However, when the steam is produced in the steam generating device, the entire cooking chamber must be uniformly filled with steam as quickly as possible so that the items to be cooked in the oven are reached. more simultaneously possible by water vapor. This method of contact of uncooked items with steam affects the volume, the shiny appearance and the staying power of the breads produced.

the invention therefore aims to provide a baking oven of the kind described in the preamble, in which the valve is arranged so as to allow optimai optim adjust the baking process, in particular during the initial application phase steam items to be cooked.

To solve this problem, according to the invention, the valve is arranged at a location remote from the steam generator device, so that at the time of steam production, the air contained in the cooking chamber can be expelled with the minimum possible loss of steam and that it can be distributed uniformly, in the minimum time, throughout the cooking chamber.

Such an arrangement of the valve has the advantage that, when the steam is produced, the air contained in the cooking chamber, expelled by the propagation of the steam, can leave the cooking chamber at a location distant from that or. steam is produced. Under these conditions the steam can spread evenly throughout the baking chamber and on all the items to be baked, which ensures a regular volume, uniform shine and impeccable resistance of the breads produced.

To further improve this effect of air movement, in order to obtain a uniform and rapid filling of steam from the cooking chamber, the valve can be placed at the location as far as possible from the steam generating device. Under these conditions, the valve can be produced either as a pressure relief valve opening from the inside of the cooking chamber towards the outside, or as a manually operated valve.

For the escape of steam from the cooking chamber, a second valve can be placed in the brewing circuit in a closed circuit, at the location where the pressure is maximum. Advantageously, this second valve can be produced in the form of a manually operated valve, so that it can be closed during the production of steam.

The two valves can be coupled in such a way that when the first valve opens for expelling air from the cooking chamber, the second valve is closed.

To allow the steam to escape very quickly and efficiently, a ventilation gap can be formed along the door when the second valve is open.

In a bakery oven where the heating device and the closed-circuit stirring device are arranged above the baking chamber and where, on each side wall of this chamber, a distribution duct is provided, connected to the stirring in a closed circuit and extending essentially over the entire side wall of the cooking chamber, the cooking atmosphere flowing transversely with respect to the cooking chamber of a distribution duct from one side wall to the distribution duct of the other wall, the first valve can be arranged in the lower region of the chamber Cooking.

More particularly still, the first valve can be placed at the deepest location of the cooking chamber.

In addition to the advantages already mentioned, this arrangement of the valve at the lowest location of the oven offers the advantage that at this location there is always a flow and that the lower part of the oven can be heated. Heating the lower part of the oven has the effect of preventing puddles from occurring at the bottom of the cooking chamber, which is normally the case, because in the case where the bottom is not not directly heated, the wall thereof, as a result of heat losses by thermal radiation, more intense at the bottom, of the space where the oven is erected, has a lower temperature than that of the other regions of the cooking.

In the case where the closed-circuit stirring device comprises two blowers with transverse flow and where the heating device is arranged between these blowers, the second valve can also be disposed between the two blowers with transverse flow.

According to a particularly advantageous development of the invention, the first valve can be constituted by a pressure relief valve whose resistance to opening is adjustable. This possibility of adjusting the resistance to opening the overpressure valve has the essential advantage that the flow conditions inside the cooking chamber can be varied by opening this valve more or less.

The invention is explained in more detail below using some of its embodiments, taken by way of illustration but in no way limiting, with reference to the appended drawings in which:

FIG. 1 is a cross section of a bakery oven along line II of FIG. 2,

- Figure 2 is a longitudinal section along the line II-II of Figure 1 without shelving and

- Figure 3 is a longitudinal section along line III-III of Figure 1.

] ja figure 1 schematically represents the essential elements of a bakery oven 10. In the middle of the oven is a baking chamber 12, not subdivided into separate shelves but on the contrary forming a single cavity, which is delimited laterally by perforated sheets 14. The bottom 16 of the cooking chamber 12 is at ground level 18 on which the oven 10 is placed. The cooking chamber 12 is housed in an enclosure 20, the walls of which are lined with insulating material to prevent any heat leaking out.

Above the cooking chamber 12, also inside the enclosure 20, there is provided a heating device 24, comprising a heating tube 26 and a burner 28 disposed at one end thereof. At the opposite end to the burner 28 of the heating tube 26, the latter has an opening / exhaust of the combustion gas. As can be seen more particularly in FIG. 1, on each side of the heating tube 26 is arranged a blower with transverse flow 32 and 34. The axes of these blowers 32 and 34 are essentially parallel to the longitudinal axis of the heating tube 26. Below the heating tube 26 are arranged evaporator plates 36, arranged in a V, above which are arranged spray nozzles water 38. Below the evaporator plates 36 is provided a water evacuation gutter 40. The evaporator plates 36 and the nozzles for spraying water 3θ constitute a steam generating device.

Below each blower with transverse flow, to the left and to the right, and 34 is provided / a distribution duct 42, 44, is arranged between the enclosure 20 and the perforated plate 14. These ducts 42 and 44, on the side of enclosure 20, are delimited by external walls

46, directed obliquely from top to bottom while approaching the perforated sheet 14 "which go to the bottom 48 of the corresponding distribution duct 42, 44. Due to the inclination of these outer walls 46, the distribution conduits 42 and 44 are narrowed downward. As can be seen in FIG. 1 where the direction of flow of the oven's cooking atmosphere has been indicated by arrows, the left distribution duct 42, with the cross-flow blower 32, constitutes the delivery side and the right distribution duct 44 "with the cross-flow blower 34, the suction side of the closed-circuit stirring device.

Inside the cooking chamber is disposed a rack 50 mounted on wheels 51 which occupies essentially the entire volume of the cooking chamber 12 and is composed of a number of superimposed shelves 52, intended to receive the articles to be cook and the bottoms, individually removable, are perforated. So that, the shelving 50 being stationary inside the cooking chamber, there is obtained a regularly golden surface of the cooked articles and that there is practically no diagonal flow in the closed-circuit brewing system. the cooking atmosphere, in particular from the lower end of the left distribution duct 42 to the upper end of the right distribution duct 44 "in each of these ducts, the perforated sheets 14 carry perforated deflecting sheets 54, directed obliquely downwards inside the duct. As can be seen in FIG. 3, the perforations of these deflecting sheets 54 are alternated, along the length of these sheets, that is to say according to the depth of the furnace 10. The deflecting sheets 54 therefore have regions alternately perforated and solid regions.

The perforated regions 63 are provided with square perforations 65.

The deflector plates 54 have essentially all the same dimensions, their free lower edge being in the same horizontal plane as the edge fixed to the perforated plate 14 of the immediately lower deflector plate 54, the deflector plates 54 form with the side wall 14 of the cooking chamber an acute angle of 20 * to 70 °, preferably from 30 ° to 50 °. From the intersection ridge of the outer wall 46 of each duct and of the bottom 48 of this distribution duct 42, 44 leaves a deflected sheet metal 56, non-perforated and directed obliquely upwards inside the duct, which constitutes the lower part of the lower perforated deflected plate 54.

As can be seen in FIG. 2, the cooking chamber 12 can be closed, at the front, by a door 58. It can also be seen in FIG. 3 that the cross-flow blowers 32 and 34 each protrude on each side of the corresponding distribution duct 42 and 43. To produce a regular and non-turbulent air flow between each blower and the distribution duct, between the wall 60 on which the blower is mounted and the posterior 62 or anterior wall 64 of the distrihutinn duct is disposed an oblique connection wall 66 .

The loading and operation of the oven are as follows. When the door 58 opens, the cross-flow blowers 32 and 34 stop automatically or start to rotate at reduced speed so that in the door open position there is no longer any circulation in the circuit closed with hot air. Then the rack 50 carrying the articles to be cooked is brought to the floor 18 of the bakery to the oven 10 and is introduced directly into the baking chamber 12, the bottom 16 of which is at ground level 18. Then the door 58 is closed and the cross flow blowers 32 and 34 restart. For the baking of rolls for example, the articles are immediately subjected to the steam produced by the spraying of water, by, the nozzles 38, on the evaporator plates 36 which are heated by the heating tube 26. Because when the door is open it does not brew in a closed circuit, the article to be cooked is first of all relatively cold, so that at the beginning of the production of steam, it condenses on the surface of the articles . This gives a shiny appearance to the exterior surface of the baked items. Cross flow blowers 32 and 34 are arranged such that their flow direction varies periodically, as described in German Patent No. 1,206,824. Air thus flows from the delivery side of the distribution duct, traverses transversely, in a substantially uniform manner, the cooking chamber 12 passing over the articles to be cooked therein, and reaches the duct. located on the opposite suction side. During the entire cooking operation, the directions of rotation of the blowers 32 and 34 are frequently reversed, so that the resulting inversion of the discharge and suction sides results in an inversion of the transverse flow direction through the cooking chamber. Because the distribution conduits are equipped with deflector plates, for a regular flow field along the height of the cooking chamber 12, a relatively low flow speed is obtained in alternating directions, so that after the baking all buns are evenly browned.

At the location which, in the cooking chamber 12, is furthest from the steam generating device, that is to say the evaporator plates 36, namely at the lower end of the cooking chamber 12 is provided a first valve 11 which passes through the wall 22 of the casing 20. Above the steam generator device * preferably at the location where the pressure of the closed-circuit brewing circuit is highest, between the two cross-flow blowers 32 and 34, a second valve 13 is provided which passes through the wall of the enclosure 20, the valve valves 11 and 13 are preferably not placed directly in the oven, but are connected to the latter by a pipe, the two valves can be produced both in the form of manually operated valves and in the form of pressure relief valves. More particularly, however, the first valve, or. lower valve 11 is produced in the form of a pressure relief valve and the second valve, or upper valve 13, is produced in the form of a manually operated valve. To show that the lower valve 11 is overpressure, there is shown at the outer end thereof, a closing weight 15, but this representation is not limiting and one can use as pressure relief valve any this type usual in the technique.

the second valve or upper valve 13 is used to evacuate the steam and the first valve or lower valve 11 is mainly used to evacuate the air contained in the cooking chamber.

As explained above, after the door 58 of the cooking chamber has closed, water is sprayed onto the evaporator plates 36, so that these are the seat of a sudden release of steam. Because during this release of steam the air which is inside the cooking chamber, below the evaporator plates 36 can leave the cooking chamber at the lower end thereof, it that is to say at the location which is furthest from the steam generating device, the vapor which forms in the region of the evaporating plates, at the top of the cooking chamber, can spread quickly and evenly throughout the entire cooking chamber, which ensures regular application of steam to all items to be cooked and gives them a homogeneous volume, an even shine and impeccable hold.

During the operation of the cooking chamber, that is to say during the stirring in a closed circuit of the atmosphere of the oven, the latter can escape into the region of the bottom of the cooking chamber, by the pressure relief valve 11, which ensures, on the one hand, a more regular transverse flow through the cooking chamber and, on the other hand, a direct licking by the flow of the bottom of this chamber. Direct heating of the bottom 16 of the cooking chamber 12 is thus obtained, which prevents puddles from forming therein, the first valve or lower valve preferably has an adjustable opening resistance, which makes it possible to make vary the exhaust air flow rate produced in the lower region of the cooking chamber 12.

We can thus act on the flow conditions in the baking chamber, so that, on the one hand, for baking elongated breads, we can create a flow component from bottom to top through the baking chamber. baking to brown the underside of the bread more strongly, and that, on the other hand, an essentially horizontal transverse flow can be established through the chamber when, for example for baking rolls, the article must be browned uniformly over its entire outer surface.

To quickly and evenly distribute the steam in the cooking chamber 12, the second valve or upper valve 13 is closed to prevent steam escaping from above.

When steam has to be escaped during the cooking process, the second valve or upper valve 13 is opened. To obtain an impeccable and efficient exhaust of steam, it is necessary either to open the first valve or lower valve, provided that it is manually controlled, or still open, so as to form a small ventilation gap, the door 58 of the oven. For this purpose the door 58 can be provided with a snap which immobilizes the door in a position where it leaves a small gap for the passage of air.

As goes without saying and as it already follows from the foregoing, the invention is in no way limited to that of its modes of application, no more than to those of the embodiments of its various parts, having have been more particularly envisaged; on the contrary, it embraces all its variants.

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