GB1566799A

GB1566799A - Baking ovens

Info

Publication number: GB1566799A
Application number: GB43170/75A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-10-21
Filing date: 1975-10-21
Publication date: 1980-05-08
Also published as: NL7611643A; SE427888B; DE2647992A1; SE7611613L; DK469476A

Description

(54) IMPROVEMENTS IN OR RELATING TO BAKING OVENS (71) 1, PER ERIK MEINCKE, Hovedstensvej 33, 2650 Hvidovre, Denmark, of Danish nationality, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to industrial baking ovens.

In practice there is used two main types of baking ovens, viz. the tunnel oven and the socalled rack oven. Conventional tunnel ovens comprise a baking plate formed as an endless long conveyor belt, the upper run of which passes through a heat tunnel in which means are provided for producing a heat radiation against the products to be baked. In a house hold oven the air is heated so as to transfer its heat to the product, but the air layer adjacent the surface of the product forms a heat insula ting layer which prolongs the baking time to a degree which would be unacceptable in an industrial oven. The use of heat radiation over comes this problem, and the provision of the radiation is relatively simple, e.g. by means of open burners or a tube system carrying a hot medium; even electric heat radiators may be used.The radiation sources may be placed both above and underneath the baking plate, whereby it is possible to adjust the heat supply to the top and bottom side of the baking plate.

However, the heating of the products by means of heat radiation is disadvantageous in some respects, e.g. when the products are baked in metal foil trays, the material of which re flects the heat rays. The said rack ovens have been developed for overcoming these disadvan tages. They consist of an upright cylindric oven chamber having a door through which a movable multi shelf trolley holding a plurality of product loaded baking plates may be driven into the oven chamber, whereafter the door is closed.

Inside the oven chamber, adjacent the wall thereof, there is arranged a vertical tube provided with a row of nozzles for blowing hot air horizontally against the multi shelf trolley at all levels thereof, and the injected air is sucked out through an outlet opening located adjacent the bottom of the oven chamber diametrically opposite to the said injection tube. The bottom or top of the oven chamber is provided with means for engaging the multi shelf trolley and for rotating it slowly for ensuring that the hot air blast is not steadily directed towards the same area of the products, i.e. during the baking period the air blast is sent against all surface portions of the products to be baked.The transverse blast of hot air inside the restricted oven chamber sweeps across the products on the shelves and prevents the products from being heat insulated by any stationary air layer around them. In this manner a rapid and very even and well controlled baking is obtainable.

In fact for some products the baking is even to a degree higher than desired, and it is a general drawback of this type of oven that there is no possibility of separately adjusting the heat supply to the top and the bottom of the products on the various shelves, and, of course, also the non-continuous operation of the oven is a drawback thereof.

It is the purpose of this invention to provide an improved baking oven which is advantageous over both the said rack ovens and the tunnel ovens described above.

According to the invention there is provided an industrial baking oven of the tunnel type, comprising a baking plate constituted by an endless conveyor belt whose upper run passes through a baking tunnel, lower heating means for heating the said upper run from below, and upper heating means for heating the upper run from above, wherein the said upper heating means comprises a pressurised hot air supply system feeding a main duct communicating with a plurality of ducts extending transversely of the tunnel and spaced apart longitudinally thereof, the transverse ducts having nozzles and the air supply being operative to supply air under sufficient pressure to product jets of hot air from the said nozzles directed onto the upper surface of the said upper run, and wherein the main duct is situated below and close to the ceiling of the tunnel, and has a width less than width of the tunnel and extends both longitudinally and laterally of the tunnel.

It will be appreciated that the invention seeks to provide an oven combining the advantages of the conventional tunnel oven and the rack oven, and experiments with the improved oven according to the invention have shown remarkable results.

In the following the invention is described in more detail, by way of example, with reference to the accompanying drawing in which: Figure 1 is a perspective view of an oven according to the invention, Figure 2 is a schematic sectional side view thereof, Figure 3 is an end sectional view thereof, and Figure 4 is a perspective view, partly in section, of a detail thereof.

The oven shown in the drawing is basically constructed as an ordinary tunnel oven comprising a heat insulated tunnel tube 2 and an endless baking plate conveyor belt 4 passing around driven end rollers 6 outside the opposed ends of the tunnel 2 so as to have its upper run 8 passing through the tunnel 2 while the lower run 10 thereof is returned underneath the tunnel 2.

The ceiling of the tunnel is provided with an elongated, flat tube or main duct 12 extending almost along the entire length of the tunnel and communicating with a number of transversely arranged, flat tubes or ducts 14, the lower corners of which are made so as to constitute slot formed air nozzles, 16, see also Figure 4.

Pressurized, hot air is supplied to the main duct 12 from a heater and blower unit 18, 20 through a channel 22, and the air is blown out through the slot nozzles 16 downwardly against the top side of the baking plate 8, the air jets being inclined as most clearly shown in Figure 2 so as to be sent against the products on the baking plate partly against the front side thereof and partly against the rear side thereof.

As is well known, when the air velocity in the nozzles is high enough to produce real air jets these jets will not be disturbed by any general flow of air crosswise to the jets, i.e. through the tunnel 2, and the jets, therefore, will hit the products on the baking plate so as to effectively heat the products.

At the bottom side of the tunnel, below the baking plate 8, is provided suitable means for supplying bottom heat to the baking plate. In the drawing these heating means are shown as being similar to the top heating means, comprising an elongated flat channel or lower main duct 24 and a number of transverse channel members or ducts 26 provided with corner nozzles 28, the duct 24 being supplied with air from the heater and blower unit 18, 20 through a channel 30. Of course, the lower heating system can be arranged quite close to the lower side of the baking plate.As most clearly shown in Figure 3 the supply channels 22 and 30 are branched off from a main channel 32 downstream of the blower and heater unit 20, 18, and at the common branch point is mounted a switch over valve 34 which may be set in any intermediate position whereby it is easy to control the supply of hot air to the top and bottom heating systems, respectively, without substantially changing the total air flow.

It should be emphasized, however, that the bottom heating means may be of any convenient and even conventional type, because the heating of the bottom side of the products should take place by virtue of a heat transfer through the baking plate anyhow. Thus, the plate may be moved closely above a zig-zag heating duct system, or even be supported by such a system.

An important feature of the illustrated oven is the provision of means for directing the hot air jets against the products above the bottom surfaces thereof and the retained possibility of adjusting the top and bottom heat supply separately. The suction side of the blower 20 is connected to a wall opening 36 at a central portion of the tunnel through a suction channel 38, and experiments show that despite this central location of the suction opening in the tunnel, whereby the air is sucked back from both ends of the tunnel, the resulting general air flow through the tunnel does not disturb the air jets from the nozzles 16, and at the more or less open ends of the tunnel practically no resulting air flow is observed, so that the need to close the tunnel ends by suitable flap means is correspondingly small.

During the baking process, as well known, there is released a considerable amount of vapour from the products, and it is preferred, therefore, to arrange for a part of the recirculated air to escape to the atmosphere, e.g. through a chimney 40. It is possible hereby to obtain an equilibrium of the humidity of the air in the tunnel, and the escape of humid air is compensated by the vaporization of water from the products.

Experiments have shown that in the tunnel oven here disclosed it is very easy to secure a constant baking temperature and to adjust the nozzles 16 to produce a well defined or uniform air flow against the products. As well known it may be desirable in a tunnel oven to make use of different temperatures in consecutive sections of the oven, and it is a specific advantage of the illustrated oven, that a composite tunnel oven may be constructed as a number of tunnel portions each constituted by a unit as illustrated in the drawing arranged end to end, and all being passed by the same baking plate conveyor belt. Since the air will not be liable to be drawn or blown from one unit into the preceding or the following unit it will thus be easy to control the temperature in each of the units in the desired manner.

The nozzles 16, should extend across the full width of the tunnel (or the width of the baking plate), and it might appear obvious to provide the nozzles as slots in an overhead wide channel structure or intermediate top tunnel wall extending crosswise along the entire width of the tunnel. Such a construction, however, is thought to be disadvantageous with respect to the securing of a well defined air flow through the nozzles, especially if the nozzle plate is made of iron or steel plate, and the construction would tend to be rather heavy. The duct and nozzle system shown in the drawing is advantageous in these respects.

The duct 12, of course, might be placed on the top side of the tunnel 2, but would then in practice have to be heat insulated. When mounted inside the tunnel it needs no insulation, but with the use of an uninsulated channel of a crosswise extension smaller than the width of the tunnel, another problem might occur, viz. that the underside of the channel constitutes an elongated, narrow heat radiator which by heat radiation contributes to the supply of heat to the products in an uneven manner, because the radiation heat is supplied only to a partial wilth of the baking plate. The use of the additional radiation heat, also from the bottom sides of the transverse ducts 14, is advantageous, but as far as the main duct 12 is concerned it would of course not be advantageous if the products are not heated uniformly all over the width of the oven.

For this reason the main channel is mounted so as to extend diagonally across the rectangular ceiling of the oven, as clearly shown in Figure 1.

Though in each cross section of the oven the products are still not heated uniformly, this arrangement will ensure that all products receive substantially the same total amount of radiation heat during their travel through the entire oven. The products adjacent one edge of the baking plate will receive the radiation heat during the first part of their travel, while those adjacent the opposite edge will receive the same additional heat during the last part of their travel through the oven. Alternatively, the main duct may extend in zig-zag manner from side to side of the tunnel from one end to the other.

The air of the required temperature, e.g. up to some 300"C, may of course be admitted through nozzle means other than the slot nozzles shown, when it is only ensured that the air jets of the required relatively high velocity are distributed so as to cause the products to be heated in a uniform manner or rather so as to have heated the products uniformly when they leave the oven. The arrangement shown will normally be fully sufficient, but of course it will be within the scope of the invention to arrange for other types of nozzles, whether slot formed or tubular and whether stationary or movable, e.g. as rotary nozzle heads.

When a complete tunnel oven is made of two or more aligned oven units of the type shown it is of course not essential that each unit has its own separate blower and heater unit, but from several points of view it seems to be advantageous to make use of such complete tunnel sub units.

WHAT I CLAIM IS:- 1. An industrial baking oven of the tunnel type, comprising a baking plate constituted by an endless conveyor belt whose upper run passes through a baking tunnel, lower heating means for heating the said upper run from below, and upper heating means for heating the upper run from above, wherein the said upper heating means comprises a pressurised hot air supply system feeding a main duct communicating with a plurality of ducts extending transversely of the tunnel and spaced apart longitudinally thereof, the transverse ducts having nozzles and the air supply being operative to supply air under sufficient pressure to produce jets of hot air from the said nozzles directed onto the upper surface of the said upper run, and wherein the main duct is situa ted below and close to the ceiling of the tunnel, and has a width less than width of the tunnel and extends both longitudinally and laterally of the tunnel.

2. A braking oven according to Claim I, wherein the main duct extends diagonally of the tunnel from one side of the tunnel at the entrance cnd thereof to the opposite side of the tunnel at the exit end.

3. A baking oven according to Claim 1, wherein the main duct extends in zig-zag manner from side-to-side of the tunnel from one end to the other.

4. A baking oven according to Claim 1, 2 or 3, wherein some of the said nozzles are directed downwardly and forwardly with respect to the direction of the upper run, and other nozzles are directed downwardly and rearwardly.

5. A baking oven according to any preceding Claim, in which the lower heating means comprises a number of nozzles for directing jets of hot air against the lower surface of the upper run.

6. A baking oven according to Claim 5, wherein the lower heating means includes a lower main duct connected to the lower nozzles and extending both longitudinally and laterally of the tunnel.

7. A baking oven according to Claim 5 or 6 wherein the upper and lower heating means

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of different temperatures in consecutive sections of the oven, and it is a specific advantage of the illustrated oven, that a composite tunnel oven may be constructed as a number of tunnel portions each constituted by a unit as illustrated in the drawing arranged end to end, and all being passed by the same baking plate conveyor belt. Since the air will not be liable to be drawn or blown from one unit into the preceding or the following unit it will thus be easy to control the temperature in each of the units in the desired manner. The nozzles 16, should extend across the full width of the tunnel (or the width of the baking plate), and it might appear obvious to provide the nozzles as slots in an overhead wide channel structure or intermediate top tunnel wall extending crosswise along the entire width of the tunnel. Such a construction, however, is thought to be disadvantageous with respect to the securing of a well defined air flow through the nozzles, especially if the nozzle plate is made of iron or steel plate, and the construction would tend to be rather heavy. The duct and nozzle system shown in the drawing is advantageous in these respects. The duct 12, of course, might be placed on the top side of the tunnel 2, but would then in practice have to be heat insulated. When mounted inside the tunnel it needs no insulation, but with the use of an uninsulated channel of a crosswise extension smaller than the width of the tunnel, another problem might occur, viz. that the underside of the channel constitutes an elongated, narrow heat radiator which by heat radiation contributes to the supply of heat to the products in an uneven manner, because the radiation heat is supplied only to a partial wilth of the baking plate. The use of the additional radiation heat, also from the bottom sides of the transverse ducts 14, is advantageous, but as far as the main duct 12 is concerned it would of course not be advantageous if the products are not heated uniformly all over the width of the oven. For this reason the main channel is mounted so as to extend diagonally across the rectangular ceiling of the oven, as clearly shown in Figure 1. Though in each cross section of the oven the products are still not heated uniformly, this arrangement will ensure that all products receive substantially the same total amount of radiation heat during their travel through the entire oven. The products adjacent one edge of the baking plate will receive the radiation heat during the first part of their travel, while those adjacent the opposite edge will receive the same additional heat during the last part of their travel through the oven. Alternatively, the main duct may extend in zig-zag manner from side to side of the tunnel from one end to the other. The air of the required temperature, e.g. up to some 300"C, may of course be admitted through nozzle means other than the slot nozzles shown, when it is only ensured that the air jets of the required relatively high velocity are distributed so as to cause the products to be heated in a uniform manner or rather so as to have heated the products uniformly when they leave the oven. The arrangement shown will normally be fully sufficient, but of course it will be within the scope of the invention to arrange for other types of nozzles, whether slot formed or tubular and whether stationary or movable, e.g. as rotary nozzle heads. When a complete tunnel oven is made of two or more aligned oven units of the type shown it is of course not essential that each unit has its own separate blower and heater unit, but from several points of view it seems to be advantageous to make use of such complete tunnel sub units. WHAT I CLAIM IS:-

1. An industrial baking oven of the tunnel type, comprising a baking plate constituted by an endless conveyor belt whose upper run passes through a baking tunnel, lower heating means for heating the said upper run from below, and upper heating means for heating the upper run from above, wherein the said upper heating means comprises a pressurised hot air supply system feeding a main duct communicating with a plurality of ducts extending transversely of the tunnel and spaced apart longitudinally thereof, the transverse ducts having nozzles and the air supply being operative to supply air under sufficient pressure to produce jets of hot air from the said nozzles directed onto the upper surface of the said upper run, and wherein the main duct is situa ted below and close to the ceiling of the tunnel, and has a width less than width of the tunnel and extends both longitudinally and laterally of the tunnel.

include a common supply of hot air under pressure, and regulation valve means are pro vided for controlling the supply of hot air as between the nozzles of the respective upper and lower heating means.

8. A baking oven according to any preceding Claim in which the hot air supply comprises a heater and a fan the suction side of which is connected to a control portion of the tunnel.

9. A baking oven as claimed in any preceding Claim in which hot air is recirculated through the tunnel and means are provided for exhausting some of the hot air to atmosphere.

10. A baking oven including two or more ovens as defined in any preceding Claim arranged end to end and capable of operation at different temperatures.

11. A baking oven substantially as herein described with reference to the accompanying drawings.