Oven

Abstract

Provided is an oven comprising a heating structure for enhancing heating efficiency.　An oven according to the present invention is characterized by comprising: a plurality of linear burners that are placed in the oven or horizontally juxtaposed above a food moving within the oven, the linear burners each being provided with a combustion port in one horizontal direction; and a plurality of far-infrared generation plates that are composed of thin metal plates provided with ceramic coating layers on only the lower surfaces thereof, the far-infrared generation plates being provided, at positions that are above respective burners and are separated from the ceiling surface of the oven and from the burners, so as to cover the respective burners, flames that are blown out in the one horizontal direction from the burners, and heating zones at the ends of the flames.

Description

oven

[0001] The present invention relates to an oven, and more particularly to an oven equipped with a heating structure that enhances heating efficiency by providing a far-infrared ray generating plate based on a thin metal plate above a burner, which is an upper heat source, so as to cover the burner and the heating zone ahead of the burner flame.

[0002] Ovens used to heat food, especially industrial ovens used to heat large quantities of food, typically have heating devices such as gas burners above and below the food. The food is heated from above and below as it is placed between the upper and lower heating devices or transported between them by a conveying device. When the heating device is a burner, heat is transferred below the food to the tray or conveyor belt supporting the food through radiation from the burner flame and the rising currents of high-temperature exhaust gases and heated surrounding air generated by combustion. Meanwhile, above the food, the food is heated primarily by radiant heat from the burner flame. Because the high-temperature exhaust gases and heated surrounding air generated by the upper burner rise, some are expelled from the oven, while the rest contributes to heating the food through convection within the oven, but this is an inefficient use of heat. Furthermore, the effectiveness of radiant heat differs between the area directly below the burner flame and areas not covered by the flame, such as the gaps between the burners, leading to uneven heating of the food. Therefore, a structure has been put into practical use in which a far-infrared generating plate is combined with the upper burner to achieve uniformity.

[0003] Patent Document 1 describes a tunnel oven that includes a baking furnace, a radiation panel that is capable of emitting radiant heat when heated and has multiple air vents, dividing the interior of the baking furnace into upper and lower sections, a baking chamber located below the radiation panel, a combustion chamber located above the radiation panel and equipped with a burner inside, and a conveyor for transporting the material to be baked to the baking chamber.

[0004] Patent Document 2 describes a tunnel oven that can use superheated steam or heated air in combination with a burner, in which multiple burner units are arranged above and below a conveyor that transports trays carrying baked goods, and in which far-infrared radiation plates are provided above and between the burner units arranged above the conveyor in correspondence with the burner units.

[0005] According to the tunnel oven of Patent Document 1, the baking chamber into which the baked goods, such as confectionery dough, are transported has an upper surface that is almost uniformly covered by a radiant panel, which allows radiant heat to be applied appropriately to the goods, and is expected to result in baking products of uniform quality. However, because the radiant panel of the tunnel oven of Patent Document 1 is located between the upper burner and the goods to be baked, the heat generated by the upper burner is temporarily blocked by the radiant panel, and the goods to be baked are mainly heated by the radiant heat emitted from the radiant panel, which has been heated by the radiant heat of the upper burner. For this reason, the heat efficiency is not necessarily good.

[0006] In addition, in the tunnel oven of Patent Document 2, the far-infrared radiation plate is installed between the burner units near the top, so it does not block the heat radiation from the burner units to the baked goods, and because it is installed between burner units where no burner units exist, it is expected to reduce the variation in the radiant heat radiated to the baked goods. However, there is a gap between the burner units and the far-infrared radiation plate, and the heat from the burner units escapes upward through this gap, so the problem remains that the heat generated by the burner units is not necessarily used effectively.

[0007] Far-infrared generating plates, also known as radiant panels or far-infrared radiating plates, emit stronger radiant heat as their temperature increases, so using the heat generated by the burner to raise the temperature as much as possible is an effective way to increase thermal efficiency.Therefore, it is desirable to provide an oven that is useful for industrial use, which uses a far-infrared generating plate to effectively utilize the heat generated by the burner, has a heating structure that is uniform and has good thermal efficiency, and does not block the heat generated by the burner.

[0008] JP 2012-000033 A Japanese Patent No. 5545422 A

[0009] The present invention has been made in consideration of the problems with conventional ovens described above, and an object of the present invention is to provide an oven with a heating structure that improves heating efficiency by providing a far-infrared generating plate based on a thin metal plate above the burner, which is the upper heat source, so as to cover the burner and the heating zone ahead of the burner flame.

[0010] The oven of the present invention, which has been made to achieve the above-mentioned object, comprises a plurality of linear burners which are placed in the oven or arranged horizontally side by side above food which is moving through the oven and which have combustion ports on one horizontal direction, and a plurality of far-infrared generating plates which consist of thin metal plates with a ceramic coating layer only on their undersides and which are provided at positions above each burner and spaced apart from the burners and the oven ceiling so as to cover each burner, the flames which blow out in one horizontal direction from the burners and the heating zone beyond the flames, and each of the far-infrared generating plates is rectangular in shape with two end faces parallel to the longitudinal direction of the burners bent downwards.

[0011] The thickness of the metal plate of the far-infrared ray generating plate is preferably 2±0.5 mm.

[0012] In the oven of the present invention, the far-infrared generating plate is located above the burner above the food, covering the burner, the flame emitted horizontally from one side of the burner, and the heating zone beyond the flame. Furthermore, the two end faces parallel to the longitudinal direction of the burner are bent downward, facilitating heat transfer to the far-infrared generating plate, which in turn raises the temperature of the far-infrared generating plate and allows for efficient generation of radiant heat. Because the far-infrared generating plate is installed to cover a wide area above the burner, it also effectively distributes radiant heat uniformly within the oven. At the same time, because there is no obstruction between the burner and the food being heated, convection heat generated by the burner unit within the oven can be transferred to the food without loss. This allows for efficient use of the generated heat without loss, as in Patent Document 1, resulting in the efficient use of not only radiant heat but also the heat within the oven for heating.

[0013] Furthermore, in the oven according to the present invention, the far-infrared generating plate has two end faces folded downward, allowing for a thickness of 2±0.5 mm. This reduces the heat capacity of the far-infrared generating plate, allowing it to be efficiently heated to a high temperature using the heat generated by the burner, while minimizing heat storage in the plate itself, minimizing the loss of heat that would otherwise be used for heating food trapped within the plate. Because the far-infrared generating plate is made of a thin metal plate with a ceramic coating layer only on the underside, heat radiation from the heated far-infrared generating plate occurs primarily from the underside, with radiation to the metal upper surface suppressed. This results in more efficient food heating, allowing food to be baked well even with reduced burner power.

[0014] Furthermore, with the oven according to the present invention, the heat capacity of the far-infrared generating plate is kept low, so the time it takes for the temperature to stabilize in response to a temperature change is shortened, and when changing the temperature distribution setting of the oven, the time required to change the setting can also be shortened. Generally, when heating food at multiple different temperature settings in an oven, it takes a long time to change the setting, which leads to a decrease in production efficiency and energy loss, so a significant reduction in time also increases production efficiency and has an energy-saving effect, which are also CO２ This also leads to reduced emissions and running costs, which is a major benefit for industrial use. Furthermore, with the oven of the present invention, there is no obstruction between the burner located below the carrier and the carrier, making it possible to efficiently use heat to heat food. Even without an obstruction between the burner and the carrier, the insulating structure of the oven's furnace body, the air intake and exhaust adjustment function, and the internal structure that controls the flow of heat generated by the lower burner make it possible to heat the carrier so that the heat generated by the burner unit is evenly transferred to the food.

[0015] Fig. 1 is a diagram schematically showing the overall structure of an oven according to an embodiment of the present invention; Fig. 2 is a diagram schematically showing the heating structure of an oven according to an embodiment of the present invention; Fig. 3 is a diagram showing the structure of a far-infrared ray generating plate according to an embodiment of the present invention; Fig. 4 is a diagram showing an attachment structure of a far-infrared ray generating plate according to an embodiment of the present invention; Fig. 5 is a diagram schematically showing the heating structure of an oven according to another embodiment of the present invention; Fig. 6 is a diagram schematically showing a modified example of the heating structure of an oven according to another embodiment of the present invention; Fig. 7 is a diagram showing the structure of a far-infrared ray generating plate according to another embodiment of the present invention; Fig. 8 is a diagram showing the baking state of food depending on the heating structure.

[0016] Next, specific examples of embodiments of the oven according to the present invention will be described in detail with reference to the drawings. Figure 1 is a diagram showing the overall structure of an oven according to an embodiment of the present invention. Referring to Figure 1, the oven 1 according to the embodiment of the present invention is a tunnel oven 2 for baking food, and has an upper baking section 14 that heats the food from above, a lower baking section 15 that heats the food from below, and a conveying device 11.

[0017] The conveying device 11 is equipped with a conveying body 12 that travels in a circulating manner within the tunnel oven 2, folding back at folding sections 13 provided at the entrance and exit sides of the tunnel oven 2, and conveys food such as dough from the entrance to the exit of the tunnel oven 2 by the conveying body 12. The conveying body 12 may be a caterpillar-shaped body driven by a chain that circulates multiple baking plates, or an endless steel belt-like body. The conveying speed of the conveying device 11 can be adjusted by the operation panel 10.

[0018] The upper baking section 14 and the lower baking section 15 each include a plurality of burners 16 arranged along the conveying direction of the conveying device 11. In the embodiment shown in FIG. 1 , the plurality of burners 16 are divided into three zones, A, B, and C, from the entrance side to the exit side of the tunnel oven 2, and temperature control is performed for each zone. Each zone is provided with a viewing window 19 so that the heating status of the food can be confirmed. In this embodiment, the burners 16 are gas burners. The food is placed on the conveying body 12 and is heated and baked by the upper baking section 14 and the lower baking section 15 while being conveyed from upstream to downstream.

[0019] An exhaust fan 18 is provided at the top of the tunnel oven 2, and discharges the burned gas generated by the burner 16 as exhaust. Although not shown in Figure 1, an air intake port with an automatic opening and closing shutter is provided at the bottom of the tunnel oven 2, and by controlling the amount of air taken in from the air intake port and the amount of air exhausted by the exhaust fan 18 with a control device, not only can the oven simply exhaust the burned exhaust gas, but also convection can be generated within the tunnel through which the food is transported, thereby reducing temperature variations from place to place within the tunnel.

[0020] As will be described below with reference to Figure 2, the oven 1 according to the embodiment of the present invention is characterized by its heating structure, and is not limited to the tunnel oven 2. In other embodiments, the oven may be a batch oven that does not have a conveying device 11. However, in this specification, the tunnel oven 2 will be described as a representative example.

[0021] Fig. 2 is a schematic diagram illustrating the heating structure of an oven according to an embodiment of the present invention. Food items 60 to be baked are placed at regular intervals on a circulating conveyor 12 and transported through the tunnel oven 2 in the x-axis direction from the upstream right to the downstream left, where they are heated and baked by the upper baking section 14 and the lower baking section 15.

[0022] Both the upper baking section 14 and the lower baking section 15 include linear gas burners 20, each extending in the y-axis direction perpendicular to the conveyance direction of the food 60, with a plurality of gas burners 20 arranged along the conveyance direction of the food 60. Each gas burner 20 is placed horizontally, but is provided with a plurality of combustion ports 21 along the longitudinal direction of the gas burner 20 on one side of the gas burner 20, i.e., in one horizontal direction. Combustion gas supplied from one end of the gas burner 20 is ejected and burned from the plurality of combustion ports 21, generating a horizontal flame 22. Therefore, a heating zone 23 containing high-temperature exhaust gas generated by the gas burner 20 and heated ambient air exists at the tip of the flame 22.

[0023] The gas burners 20 themselves are common to the upper baking section 14 and the lower baking section 15, but the upper baking section 14 is provided with a far-infrared generating plate 30 so as to cover each gas burner 20, the flame 22 blowing out horizontally from one side of the gas burner 20, and the heating zone 23 beyond the flame 22.

[0024] The far-infrared ray generating plate 30 is made of a thin rectangular metal plate 32 with a ceramic coating layer 33 only on its underside. When heated by the heat generated by the gas burner 20, the plate 30 emits far-infrared rays 34 from the ceramic coating layer 33 formed on its underside. Examples of ceramics include silicon carbide, silicon nitride, and titanium dioxide, and the ceramic coating layer 33 can be formed by thermal spraying of a ceramic material or by applying and baking a ceramic coating agent. The emitted far-infrared rays 34 are irradiated onto food 60 moving below, contributing to the heating of the food 60 as radiant heat.

[0025] The total amount of heat energy Q radiated by radiation from a flat plate with a radiation surface area A is expressed by the following equation (1): Q = σεT [Equation 1] ４ A (1) where, σ is the Stefan-Boltzmann constant, ε is the emissivity of the radiation surface, and T is the absolute temperature of the radiation surface.

[0026] Thus, the higher the emissivity of the radiation surface and the higher the absolute temperature of the radiation surface, the greater the amount of heat energy released. For this reason, the lower surface of the far-infrared generating plate 30, which faces the food 60 and contributes to heating the food 60, is coated with ceramic, a material with high emissivity. Conversely, the upper surface of the far-infrared generating plate 30, which does not contribute to heating the food 60, is not provided with the ceramic coating layer 33.

[0027] On the other hand, in terms of increasing the absolute temperature of the radiation surface, it is effective to keep the heat capacity of the far-infrared generating plate 30 as low as possible so that the temperature can easily rise by receiving the heat generated by the gas burner 20. Furthermore, in order to efficiently utilize the heat generated by the gas burner 20, the far-infrared generating plate 30 is preferably shaped to easily retain high-temperature exhaust gas and heated surrounding air.

[0028] 3 is a diagram showing the structure of a far-infrared ray generating plate according to an embodiment of the present invention. Referring to FIG. 3, the far-infrared ray generating plate 30 according to an embodiment of the present invention has a rectangular shape with a length L in the y-axis direction, which is the same as the longitudinal direction of the gas burner 20, and a width W. Two end faces parallel to the longitudinal direction of the gas burner 20 are bent to form bent portions 31 with a height H.

[0029] The far-infrared generating plate 30 is formed by bending a metal plate 32 having a thickness t. In Fig. 3, the underside facing the food 60 is shown facing upward, and the bent portion 31 is also shown facing upward, but when actually installed in the oven 1, the bent portion 31 is formed into a downward-facing U-shape. As mentioned above, it is preferable that the heat capacity of the far-infrared generating plate 30 is low, and to achieve this, it is effective to reduce the thickness t of the metal plate 32. In this embodiment, the metal plate 32 is made of heat-resistant and strong stainless steel, and has a thickness t of 2 ± 0.5 mm.

[0030] On the other hand, in the embodiment, the far-infrared generating plate 30 may be used with a side exceeding several hundred mm, and although a thin plate would be prone to bending deformation in the longitudinal direction, forming the bent portions 31 at the widthwise ends improves the bending rigidity in the longitudinal direction, and this poses no practical problem. The far-infrared generating plate 30, which has a low heat capacity due to being made thin with such a shape, has the effect of making the temperature rise more easily even with the same amount of heat and shortening the time until the temperature stabilizes. Therefore, for example, when changing the set temperature of the tunnel oven 2 to switch to another food 60 with different baking conditions after baking the food 60, the preparation time required for the changeover can be shortened.

[0031] As described above, the bent portions 31 are effective in improving the rigidity of the far-infrared generating plate 30, and also have the effect of increasing interaction with the high-temperature exhaust gas and heated surrounding air generated by the gas burner 20. As shown in FIG. 2, a flame 22 extends horizontally from one side of the gas burner 20, and a heating zone 23 extends beyond the flame 22, through which the high-temperature exhaust gas and heated surrounding air flow. The bent portions 31 are bent to block the flow of the high-temperature exhaust gas and heated surrounding air, thereby increasing interaction with the gas on the underside of the far-infrared generating plate 30. In this embodiment, the height H of the bent portions 31 is 30 to 50 mm, but is not limited to this.

[0032] The far-infrared ray generating plate 30 according to the embodiment of the present invention has a structure that retains heat and allows the temperature to rise easily by forming a thin metal plate with bent portions 31. In addition, the far-infrared ray generating plate 30 has a ceramic coating layer 33 on the underside with a high emissivity ε of approximately 0.9, which allows the plate to radiate far-infrared rays 34 more efficiently.

[0033] On the other hand, the upper surface of the far-infrared generating plate 30 is not provided with a ceramic coating layer 33, and the metal surface of the metal plate 32 is exposed as is. The metal surface has an emissivity of approximately 0.1 or less, preventing heat loss from the upper surface, where heat radiation is not required. Even for the same metal, the emissivity differs between a mirror-finished surface and a roughened surface, with the roughened surface having a higher emissivity. Therefore, the metal plate 32 of the far-infrared generating plate 30 has a flat rolled surface. However, in some embodiments, a metal plate 32 with a mirror-polished upper surface may be used. Since the folding portion 31 does not face the food 60, even if the folding portion 31 is provided with a ceramic coating layer 33, the far-infrared rays 34 emitted from the folding portion 31 do not contribute significantly to heating the food 60. Therefore, the folding portion 31 does not need to have a ceramic coating layer 33.

[0034] 4 is a diagram showing a mounting structure of the far-infrared ray generating plate according to the embodiment of the present invention. Referring to FIG. 4, the frame 40 to which the far-infrared ray generating plate 30 according to the embodiment of the present invention is mounted includes two main frames 41 extending in the x-axis direction, which is the conveying direction of the conveying device 11, and a plurality of side frames 42 orthogonal to the main frames 41 and provided to connect the two main frames 41.

[0035] The side frames 42 have an L-shaped cross section, and two adjacent side frames 42 are arranged opposite each other. The two main frames 41 and the two opposing side frames 42 form a rectangular frame 44 that is open at the top and bottom and is used to attach one far-infrared ray generating plate 30. As a result, the lower side of the L-shaped side frame 42 forms a flange 43 located below the bent portion 31 of the far-infrared ray generating plate 30.

[0036] In the embodiment of Fig. 4, the frame body 40 has four side frames 42, which form two rectangular frames 44 for mounting two far-infrared ray generating plates 30 at a distance. The gap between the two rectangular frames 44 serves as a passage for exhaust gas from the combustion using heat to be vented to the exhaust fan. In other embodiments, the frame body 40 may have more side frames 42 and may be configured to mount three or more far-infrared ray generating plates 30.

[0037] The main frame 41 is provided with support protrusions 45 that protrude toward the rectangular opening. The support protrusions 45 are provided at four locations, two on each of the two opposing main frames 41 for one rectangular frame 44. The support protrusions 45 support the underside of the far-infrared ray generating plate 30. The position and arrangement of the support protrusions 45 are not limited to the example shown in Fig. 4. They can be changed as long as the far-infrared ray generating plate 30 is stably supported.

[0038] When the far-infrared generating plate 30 is placed from above so as to fit into the rectangular frame 44, it is supported by the small support protrusions 45, and therefore the amount of heat escaping from the far-infrared generating plate 30, which has been heated to a high temperature by the heat generated by the gas burner 20, to the frame 40 is negligibly small. In Fig. 4, the support protrusions 45 are shown as extending horizontally, but in other embodiments, they may be provided so as to extend in the yz plane along the vertical direction. In this way, the contact area with the far-infrared generating plate 30 can be reduced while ensuring the strength to support the far-infrared generating plate 30, thereby further suppressing the outflow of heat from the far-infrared generating plate 30.

[0039] The frame 40 on which the far-infrared ray generating plates 30 are mounted is placed on a frame support rail 51 provided on the inner side wall of the tunnel oven 2, and is then moved and installed at a position corresponding to the gas burners 20 of the tunnel oven 2. The position corresponding to the gas burners 20 is a position where each far-infrared ray generating plate 30 covers the gas burner 20, the flame 22 generated by the gas burner 20, and the heating zone 23 ahead of the flame 22. This allows the far-infrared ray generating plate 30 to efficiently receive the heat generated by the gas burner 20 and easily reach a high temperature.

[0040] The high-temperature exhaust gas and heated surrounding air generated by the gas burner 20 transfer heat to the far-infrared generating plate 30, are pushed out by the exhaust gas generated later, and pass upward between the adjacent far-infrared generating plates 30, and finally most of them are discharged to the outside through the exhaust fan 18. However, the exhaust gas and heated surrounding air still have a sufficiently high temperature even when passing upward between the adjacent far-infrared generating plates 30, and this temperature can be used to maintain the high temperature of the far-infrared generating plate 30.

[0041] Fig. 5 is a schematic diagram illustrating the heating structure of an oven according to another embodiment of the present invention. Referring to Fig. 5, the food 60 to be baked is transported by a circulating carrier 12 and baked in an upper baking section 14 and a lower baking section 15, each equipped with a gas burner 20, and the upper baking section 14 is equipped with a far-infrared ray generating plate 30 covering the gas burner 20. The basic heating structure is the same as the heating structure described with reference to Fig. 2. However, the embodiment of Fig. 5 differs in that a cover plate 37 is provided above the far-infrared ray generating plate 30 at a certain distance.

[0042] The cover plate 37 is provided so as to cover at least the gap between adjacent far-infrared generating plates 30 from above. The cover plate 37 is also installed so as to partially or entirely cover the upper portion of at least one of the adjacent far-infrared generating plates 30. With this structure, the exhaust gas and heated surrounding air passing upward between the adjacent far-infrared generating plates 30 are prevented from rising by the cover plate 37 and flow and spread horizontally along the cover plate 37. The cover plate 37 may be provided with a folded portion in which the end in the width direction is folded downward, similar to the far-infrared generating plate 30. The cover plate 37 may be a common element with the far-infrared generating plate 30, rather than being manufactured as a dedicated element.

[0043] With the above-described structure, a state is created in which the space defined by the upper surface of the far-infrared generating plate 30 and the lower surface of the cover plate 37 is filled with relatively high-temperature exhaust gas and heated surrounding air. As combustion occurs in the gas burner 20, relatively high-temperature exhaust gas and heated surrounding air are continuously supplied to this space, so the temperature within this space is kept relatively high, and the upper surface of the far-infrared generating plate 30 can maintain a higher temperature than in the case where the cover plate 37 is not provided. If the temperature within this space is higher than that of the upper surface of the far-infrared generating plate 30, this also contributes to further increasing the temperature of the far-infrared generating plate 30.

[0044] Incidentally, it is also known that, when viewed in a direction perpendicular to the conveying direction of the conveying device 11, the temperature of the food 60 near the center of the tunnel oven 2 tends to be higher than the temperature of the food 60 at both ends near the side walls of the tunnel oven 2, which is a technical issue. To address this issue, a linear gas burner 20 has been installed with its length perpendicular to the conveying direction of the conveying device 11, and is divided into three sections along its length: a central section and both ends, allowing for adjustment of heat output depending on the section. However, it is also possible to improve the temperature distribution issue by using a far-infrared emitting plate 30 without using such a special gas burner 20.

[0045] 6 is a schematic diagram illustrating a modified heating structure of an oven according to another embodiment of the present invention. Referring to FIG. 6, a cover plate 37 is installed above the gap between adjacent far-infrared ray generating plates 30 and straddles the adjacent far-infrared ray generating plates 30. The length of the cover plate 37 in the y-axis direction, i.e., the length in the direction perpendicular to the conveying direction of the conveying device 11, is shorter than the length of the far-infrared ray generating plate 30 in the y-axis direction. Two cover plates 37 are installed at both ends of the far-infrared ray generating plate 30, with a central gap between them.

[0046] The exhaust gas and heated surrounding air passing upward between adjacent far-infrared generating plates 30 are unobstructed in the center of the far-infrared generating plate 30 where no cover plate 37 is provided, and so rise and escape unimpeded. However, at both ends where the cover plate 37 is provided, they are blocked by the cover plate 37 and spread in the space between the upper surface of the far-infrared generating plate 30 and the lower surface of the cover plate 37. As a result, when viewed along the y-axis direction, the temperature of the both ends of the far-infrared generating plate 30 is higher than that of the center, and the radiant heat radiated from both ends is greater than that of the center. The both ends of the far-infrared generating plate 30 are close to the side walls of the tunnel oven 2, and correspond to areas where the temperature of the products 60 flowing underneath is less likely to rise. However, the installation of the cover plate 37 increases the radiant heat from these areas, making it possible to reduce uneven baking of the products 60.

[0047] The variation in temperature distribution when viewed in a direction perpendicular to the conveying direction of the conveying device 11 can be reduced by changing the structure of the far-infrared ray generating plate 30, without using the cover plate 37 as shown in Fig. 6. Fig. 7 is a diagram showing the structure of a far-infrared ray generating plate according to another embodiment of the present invention.

[0048] 7, the fundamental shape of a far-infrared ray generating plate 35 according to another embodiment of the present invention is the same as that of the far-infrared ray generating plate 30 shown in FIG. 3, but the state of the ceramic coating layer 33 formed on the underside is different. While the far-infrared ray generating plate 30 is shown as having a uniform ceramic coating layer 33 formed on the entire underside, the far-infrared ray generating plate 35 has an exposed metal portion 36 formed by masking or the like in a portion of the underside near the center of the tunnel oven 2 where the temperature of the food 60 is likely to rise as described above, where the ceramic coating layer 33 is not formed.

[0049] By providing portions where the ceramic coating layer 33 is not formed by masking or the like, the amount of far-infrared rays 34 radiated from the far-infrared generating plate 35 varies between the center in the longitudinal direction and both ends even at the same temperature, thereby reducing the temperature variation between food 60 conveyed to both ends close to the side walls of the tunnel oven 2 and food 60 conveyed to the center where the temperature tends to rise.

[0050] 7, the exposed metal portions 36 where the ceramic coating layer 33 is not to be formed are shown as five thick lines along the longitudinal direction, but the shape of the portions where the ceramic coating layer 33 is not to be formed is not limited to this and may be a pattern shape perpendicular to the longitudinal direction, a pattern shape tilted relative to the longitudinal direction, or a lattice pattern. Furthermore, the ceramic coating layer 33 may not be formed over the entire central portion in the longitudinal direction.

[0051] Alternatively, the ceramic coating layer 33 may be formed on the entire lower surface, but the density of the applied ceramic may be varied so that it is low in the center so that the underlying metal plate 32 is partially exposed, and high at both ends. After the ceramic coating layer 33 is formed on the entire lower surface, the ceramic coating layer 33 may be partially removed by mechanical grinding or the like to form exposed metal portions 36, so that the amount of far infrared rays 34 generated varies depending on the location.

[0052] In any case, by using the above-described method, the ceramic coating layer 33 is provided so that the amount of far-infrared rays 34 generated varies depending on the part of the tunnel oven 2 where the temperature rises easily and the part where the temperature rises slowly, and thus it is possible to realize a far-infrared ray generating plate 35 that suppresses temperature variations depending on the location of the food 60, even when using a normal linear gas burner 20. The far-infrared ray generating plate 35 may be used in combination with the modified heating structure shown in Figure 6.

[0053] Figure 8 shows the toasted state of food depending on the heating structure, with Figure 8(a) showing the toasted state of food when toasted in a tunnel oven with heating structure A according to the prior art as described in Patent Document 2, and Figure 8(b) showing the toasted state of food when toasted in a tunnel oven with heating structure B according to an embodiment of the present invention.

[0054] In the heating structure A, the basic configuration in which the product 60 is transported between upper and lower gas burners 20 is similar to that of the heating structure shown in FIG. 2 . However, unlike the far-infrared generating plate 30 according to the embodiment of the present invention, the far-infrared generating plate 70 in the heating structure A does not cover the gas burners 20 and the flames generated horizontally from the gas burners 20, but is instead placed between adjacent gas burners 20. The far-infrared generating plate 70 is formed by bending a metal plate, but is bent upward in the opposite direction to the far-infrared generating plate 30. The metal plate has a thickness of 3±0.5 mm, and a ceramic coating layer 33 is formed on both the upper and lower surfaces of the far-infrared generating plate 70. Therefore, far-infrared rays 34 are emitted from the upper surface as well as the lower surface of the far-infrared generating plate 70. In the heating structure A, a cover cap 71 is provided on the upper gas burner 20, but the cover cap 71 does not have a ceramic coating layer 33, and therefore emits almost no far-infrared rays for heating food. The heating structure B is a structure including the far-infrared ray generating plate 30 according to the embodiment of the present invention described with reference to FIG.

[0055] In the example shown in Figure 8, the baked state of food 60 is compared when croissant dough is used as food 60 in tunnel ovens 2 having heating structures A and B as described above, baked at the same conveying speed and the same set temperature. It was confirmed that the baked state of the croissant dough was clearly stronger when baked using heating structure B than when baked using heating structure A. This result indicates improved thermal efficiency, and demonstrates that by using the thin far-infrared generating plate 30 according to the embodiment of the present invention, the required baked state can be obtained even if the set temperature is lowered.

[0056] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the technical scope of the present invention.

[0057] REFERENCE SIGNS LIST 1 Oven 2 Tunnel oven 10 Control panel 11 Conveyor device 12 Conveyor 13 Folding section 14 Upper baking section 15 Lower baking section 16 Burner 17 Turbo blower 18 Exhaust fan 19 Sight window 20 Gas burner 21 Combustion port 22 Flame 23 Heating zone 30, 35, 70 Far-infrared ray generating plate 31 Folding section 32 Metal plate 33 Ceramic coating layer 34 Far-infrared ray 36 Exposed metal portion 37 Cover plate 40 Frame 41 Main frame 42 Side frame 43 Flange 44 Rectangular frame 45 Support protrusion 50 Ceiling surface 51 Frame support rail 60 Food 71 Cover cap

Claims

1. An oven comprising: a number of linear burners arranged horizontally side by side above food that is placed in the oven or that moves through the oven, and each having a combustion port in one horizontal direction; and a number of far-infrared generating plates made of thin metal plates with a ceramic coating layer only on their undersides, which are provided at positions above each burner and away from the burners and the oven ceiling so as to cover each burner, the flames blowing out in one horizontal direction from the burners, and the heating zone beyond the flames, said far-infrared generating plates being rectangular in shape, with the two end faces parallel to the longitudinal direction of the burners bent downwards.

2. The oven according to claim 1, wherein the thickness of the metal plate of the far-infrared radiation generating plate is 2±0.5 mm.

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