Oven and process to control the air-flow over the belt width in a spiral oven

The present invention relates to an oven comprising: a first chamber, conveyor means with a width for guiding products from the inlet through this chambers to the outlet, whereas the conveyor means are at least partially arranged in a helical path, temperature control means for controlling the temperature and/or humidity in the chamber using a fluid, which comprise a heater to heat the fluid and a duct to introduce the heated fluid into the chamber,

The present invention further relates to a process how to operate this oven.

An oven of this type is for example known from EP 1 221 575 and EP 0 558 151 and is suitable for the complete or partial cooking of edible products, especially protein containing products, like chicken, hamburgers, cordon bleu etc.. The above mentioned patent applications are herewith included by reference and are therefore part of the disclosure of the present patent application. The temperature and humidity can be set such, that during the residence time in the oven, which is dependent on the length and velocity of the conveyor belt, the desired cooking and, if needed, browning is effected.

The spiral ovens known from the state of the art have the potential risk, that there are conditions in the oven, resulting in differences in temperature, color and/or yield. The consequences are products with differences in temperature, color and/or moisture content. Differences in one of these parameters will result in unequal and lower quality of the products.

It is therefore an objective of the present invention to provide an oven and a process that leads to uniform, high quality products.

The problem is solved by an oven according to claims 1 or 2.

Due to the adjustment of the fluid flow over the width of the conveyor means, the resulting products are much more uniform and have thus a higher quality. The inventive oven is easily operated.

The oven according to the present invention comprises at least one chamber. The inventive oven further comprises conveyor means for guiding products from the inlet through this chamber to the outlet. The conveyor means are at least partially arranged in a helical path. The conveyor means are preferably an endless conveyor belt, which more preferably is at least partially permeable for the process fluid. Additionally, the inventive oven comprises temperature control means for controlling the temperature and/or humidity in the chamber using a fluid, which is normally a mixture of air and steam. The temperature of the fluid is adjusted by a heater. The humidity of the fluid is adjusted by adding steam or for example air with a low humidity. Preferably, the fluid is circulated in the chamber, preferably by a fan, which extracts the fluid out of the chamber at one end and reintroduces the fluid at another end. Due to this recirculation, there is a fluid-motion in the chamber that improves the heat-transfer from the fluid to the product and/or reduces temperature differences in the chamber.

Furthermore, the oven comprises means to adjust the flow-rate-distribution over the width of the conveyor means depending on at least one process parameter and/or a recipe.

Conveyor means-width according to the present invention means the width at a discrete point or in a discrete region of the conveyor means. Normally, the width is uniform over its entire length. The width is the extension of the conveyor means perpendicular to its direction of motion.

The flow-rate- distribution can be adjusted to any desired pattern over the width. A certain recipe can require a certain flow-rate-distribution, which is e.g. stored in computer means associated with the inventive oven and can be downloaded. The desired flow-rate-distribution can be constant over time or can be changed for example according to a recurrent pattern.

The means adjust the flow-rate-distribution over the width of the conveyor means according to a certain recipe or based on a certain parameter. As soon as the recipe, e.g. the product to be cooked and/or the degree of cooking and/or browning or a parameter changes, the flow pattern is adjusted. A preferred pattern is a uniform flow-rate over the width of the conveyor means.

Preferably, the means to adjust the flow-rate-distribution over the width of the conveyor means extend or are moveable over essentially the entire width of the conveyor means.

A process parameter is for example the product temperature and/or the moisture content of the product before it enters the oven and/or after it leaves the oven, respectively, the product color after it leaves the oven, the seize of the products and/or whether the product comprises bones or not. Other parameters are the temperature and/or humidity of the process-fluid and/or its distribution, especially over the width of the conveyor means and/or in the chamber. Another parameter is the flow-rate at which the process fluid is recycled.

The means to adjust the flow-rate-distribution can be operated manually or automatically. Preferably, they are automatically controlled by computer means, for example a PLC, which receives information about the actual flow pattern over the width and/or data of at least one parameter. If the flow pattern and/or the parameter is not in the desired range, the distribution of the flow-rate over the width will be adjusted.

The parameter(s) can be measured manually or automatically, inline and/or offline.

Preferably, the inventive oven comprises temperature-measuring-means, like a thermocouple or an infrared camera, optical means to measure the size of the product and/or to inspect the color of the products, means to measure the moisture of the products and/or means to measure the a volume-flow-rate, fluid-velocities, the relative humidity of the process fluid and/or velocity-distributions. These measurements can be executed before, in and/or after the oven.

Preferably, the flow-rate-distribution is not only adjusted at a discrete point along the conveyor means, but over a certain length. This length is preferably the length of a 90° radius of the helical part and/or the length of the straight part. Preferably, the length is between one and 6 meters for one chamber.

Preferably, the means to adjust the flow-rate distribution over the width is a flow- divider and/or a flow-guider. This means spreads the fluid-flow such, that the desired flow-pattern over the belt-width is achieved.

In a preferred embodiment of the present invention, the means to adjust the flow-rate is at least one plate, which is preferably pivotable around a bearing and which is more preferably motor-driven. Most preferably, the plate is oriented parallel or tangentially to the conveyor-means.

Preferably, the means adjust the flow-rate over the entire width of the conveyor means, i.e. since the entire volume-flow-rate is preferably not or only very little influenced by adjustment-means, the adjustment means increase the flow-rate in one section of the width, while simultaneously reducing the flow-rate in another section of the width. Only the distribution of the flow-rate is altered, while its integral over the width remains essentially the same.

Preferably, the means to adjust the flow-rate-distribution over the width are located in the area where the heated fluid is introduced into the chamber. Here the process fluid has its highest temperature and consequently influences the outcome of the product most.

Preferably, the adjustment means are located over a part, more preferably of the top turn, of the top turn of the helical path. More preferably, the adjustment means extent over 120°, even more preferably over 90°

Additionally and/or in another preferred embodiment of the present invention, the means to adjust the flow-rate-distribution over the width of the conveyor means are located in the straight conveyor means section.

Preferably, the overall magnitude of the volume-flow-rate can be increased, due to a better distribution of the process fluid over the width. This normally results in an improved cooking result.

In a preferred embodiment of the present invention, the oven comprises a second chamber with a second helical path of the conveyor means. The two chambers are separated by a partition. The two helical paths are preferably connected by a straight conveyor means section. The partition preferably comprises a passage through which the straight conveyor means section extends. Detail about ovens with two chambers are given in the above mentioned patent application. This disclosure is explicitly included by reference and thus part of the present disclosure.

Preferably, the adjustment means are located over a part, more preferably of the top turn, of the helical path. More preferably, the adjustment means extent over 120°, even more preferably over 90°. In a preferred embodiment of the present invention, the control means over the top turn of the helical path are located just before and/or just after the straight conveyor means between the helical paths.

Preferably, the adjustment means is a plate with one or more holes, whose size varies over the width of the conveyor means and/or the quantity of holes per unit of area of the plate varies over the width of the conveyor means. The plates can be manually exchanged and/or adjusted.

Additionally or in another preferred embodiment flow guiding means like for example a deflector plate is utilized to the flow-rate-distribution over the width of the helical path of the conveyor means. This can be done manually and/or automatically.

Additionally and/or in another preferred embodiment of the present invention, the means to adjust the flow-rate-distribution over the width of the conveyor means are located in the straight conveyor means section.

In a preferred combination, the flow-rate-distribution-adjustment is done by a plate and by the flow guiding means, which are preferably at least partially automated. The plate and the adjustment means can be arranged parallel or in series.

Preferably, the inventive oven comprises means to equalize the fluid-flow, which are more preferably located downstream of the means to adjust the flow-rate-distribution over the width of the conveyor means. Most preferably, this means to equalize the fluid-flow is a perforated plate.

Additionally or in yet another preferred embodiment, uniform cooking and/or browning of the products on the conveyor means, especially uniform cooking and browning over the width of the conveyor means can be achieved means of fluctuating the volume-flow of the heated fluid, its temperature, its humidity and/or its velocity with time. More preferably, the fluid is passed through a fixed plate with at least one fixed hole. This plate with the at least one hole is preferably located above the conveyor means. Preferably, the fluid flow will be ejected from a fixed spot.

The above made disclosure also applies to the subsequent inventive process and vice versa.

Another subject-matter of the present invention is a process according to claims 15 or 16.

Preferably, the flow-rate distribution is adjusted over the entire width of the conveyor means, i.e. the flow-rate is increased in one part of the belt-width and simultaneously decreased in another part of belt-width, while the integral over the width remains essentially unchanged

Preferably the means to adjust the flow-rate over the width of the conveyor means are controlled based on a measurement. This measurement can be done manually, visually and/or automatically, inline and/or offline.

Preferably, the means to adjust the flow-rate over the width of the conveyor means guide and/or divide the flow according to the desired flow-pattern.

Preferably, the means to adjust the flow-rate over the width of the conveyor means are adjusted automatically, most preferably according to measured or preset parameters.

Subsequently, the inventions are explained according to the attached figures. These explanations do not limit the scope of protection.

Figure 1 shows one embodiment of the inventive oven.

Figure 2 is a top view of the oven according to figure 1.

Figure 3 shows the adjustment means.

Figure 4 shows even another embodiment of the adjustment means.

Figure 5, 6 show a third embodiment of the adjustment means.

Figure 7 shows flow pattern

Figure 8 shows four examples of the plate above the helical part.

Figure 9 shows an embodiment according to figure 8 with a deflector plate.

Figures 1 and 2 show the inventive oven. The oven 1 comprises a first chamber 3 and a second chamber 4. The chambers are divided by means of a partition 2. A rotatable drum 5, 6 is arranged in each of these chambers, around which the conveyor belt 7 is guided along two helical paths 8, 9. The endless conveyor belt enters the oven 1 via the entrance 10 by a straight conveyor belt section 11 and leaves the oven 1 via the exit 12, likewise by means of a straight section 13. The two helical sections 8, 9 are connected by the straight conveyor belt section 14, which lies at the top. The belt is permeable to the process fluid, e.g. air and steam. The partition means 2 comprise a passage 2.1 for the belt section 14. This passage 2.1 is

larger than the conveyor belt 14. The person skilled in the art understands that the oven needs not necessarily comprise two chambers.

The heating means, which are overall denoted by 15, are arranged in the top of the housing. These heating means 15 each comprise a fan 16 with a spiral casing 17, which opens into a duct 18. The heating elements 34 are situated in the ducts 18, respectively. The process fluid, e.g. air and steam, is sucked up by the fans 16 out of chambers 3, 4 via inlet 24 and is forced into the duct 18 via the spiral casing 17, respectively. The process fluid 31 flows past the heating elements 34 and is then recycled into the respective chamber 3, 4. Arrow 23, according to figure 3, depicts the fluid flow in the chamber 3, 4. The motion of the products (not depicted) to be cooked in the oven is depicted by arrows 29.

Figure 3 shows a first embodiment of the adjustment means, which is, in the present example a plate 19. This plate 19 is located in the straight part 14 of the conveyor belt 7 and extends over the length L, as can be seen in figure 2. The plate 19 is partially located in the duct 18 and extends into a control area 21. The plate 19 pivots around an axis 26. The degree of deflection relative to its vertical position is depicted by double-arrow α. The plate 19 guides and splits the fluid flow 31 after it has passed the heating means, so that the desired flow pattern over the width of the conveyor belt is achieved. By means of the plate 19, the flow 31 can be split and guided from the outside 7 ^" of belt 7 to the inside 7 ^' and vice versa. Every desired fluid-flow distribution over the width W can be achieved by means of plate 19. Examples for fluid-flow distributions are shown in Figure 7. The desired fluid-flow distribution is achieved over the entire length L of plate 19. Equalization means 20, here a perforated plate, are located at the bottom of the control area 21 to support the flow- distribution of plate 19 and/or increase the pressure in the control area. After the fluid flow has heated products 25, it passes through the permeable belt 7 and is the deflected by an inclined plate 22. The flow 23 inside chamber 3 flows past the helical path 8 and is then sucked up again by fan 16 via inlet 24. Plate 19 is motor driven (not depicted). The motor itself is connected to a PLC-controller or adjusted by an operator. The position of the plate can be maintained in the same position throughout the entire process or altered in case the cooked products are not as desired and/or the recipe or the incoming product changes. The PLC-controller can be additionally

connected to a measurement device which measures certain parameters. Based on these measurements, the position of the plate 19 is adjusted automatically. Figure 2 also shows the position and extension of the adjustment means in the chamber 4.

Figure 4 shows another embodiment of the inventive oven, whereas the adjustment means comprise two plates 19, 28. Plate 19 is pivotable as described according to figure 3. Plate 28, which is similarly built and operated as plate 19, is pivotable around axis 27. The degree of its defection relative to the horizontal is depicted by arrow β. The two plates allow an even improved control of the flow-rate-distribution over the belt width W.

Figures 5 and 6 show yet another embodiment of the adjustment means. It comprises two plates 31 , 30, each having a multitude of parallel, equidistant slots. The slots in plate 31 are larger than the slots in plate 30 and are slightly tilted. The plates 31 , 30 extend over the entire width W of the belt 7 and have a length L. The number of slots needed is dependant from the length L over which the flow rate distribution shall be controlled. As can be seen from Figure 6, plate 31 is placed on top of plate 30 and is, as depicted by arrow 33, shiftable relative to plate 30 and preferably parallel to the motion 32 of the belt 7. Arrow 32 depicts the direction of motion of belt 7. The slots in the two plates define a passage 34 for the fluid flow. By shifting the at least one plate 31 relative to the other plate 30, the distribution of the flow rate over the belt width can be adjusted. Figure 6a shows the two plates 30, 31 in a neutral position. The seize of the passage 34 is essentially uniform over the width W of the belt 7. Figure 6b depicts a position of the plates, in which the fluid flow is directed to the outside 7 ^" of belt 7 ^' , while Figure 6c shows a position of the plates 30,31 , which directs the flow to the inside 7 ^' . The plate 31 can be actuated automatically, for example by a motor, which is connected to PLC-controller. Based on a set value or on measured parameters, the position of plate 31 is set.

Figure 7 shows three examples of flow rate distributions, i.e. flow pattern, over the belt width. The length of the arrows is proportional to the local velocity, respectively. Figure 7a shows a uniform flow rate over the belt width. In Figure 7b, the velocity is higher at the outside 7 ^" of belt 7 than at the inside 7 ^' and in Figure 7c the other way round. The integral of the local velocities over the width W is in all cases the same.

The person skilled in the art understands, however, that due to a better distribution of the flow rate over the belt width, for example a uniform distribution, the overall flow rate can be increased and thus the cooking can be improved without damaging the resulting products.

Figure 8 shows four embodiments of a plate 35 above the helical section 8, 9. The plate 35 extends over an angle of 90° and is locate right upstream and/or right downstream of the straight connecting section between the helical sections 8, 9. In the embodiment according to figure 8a, the plate comprises a multitude of rectangular holes, which are oriented essentially perpendicular to the motion of the conveyor belt 7. In the embodiment according to figure 8b, the holes are not rectangular, but decrease in width from the inside to the outside. The embodiment according to figure 8c shows a multitude of holes, whereas the number and/or the size of the holes at the inside of the plate is larger than at the outside. In figure 8d, there is only one hole, which is located at the inner side of the plate and which has a constant width. The plates can be exchanged manually.

In figure 9, the embodiments according to figure 8a is shown with two deflector plates 37, which can be rotated around pivot 38 in order to direct more or less fluid-flow to the inside or the outside. The person skilled in the art understands that movement of the deflector plate can also be a pure translational movement or any combination of a translational and a rotational movement. Figure 9b shows the embodiment according to figure 9a, whereas in this case, the holes 36 have a different shape, i.e. their width increase from the inside to the outside.

Reference signs:

1 oven

2 separation means, partition

2.1 passage from first- to second chamber

3 first chamber

4 second chamber

5 drum

6 drum

7 conveyor means, conveyor belt 7 ^' inside of the conveyor means 7 ^" outside of the conveyor means

8 helical section first chamber

9 helical section second chamber

10 inlet

11 straight conveyor means

12 outlet

13 straight conveyor means

14 connecting conveyor means section

15 temperature control means, heating means

16 fan

17 spiral casing

18 air duct

19 control means, valve 0 equalization means 1 control area, box 2 guiding means 3 flow of the fluid 4 inlet 5 product 6 pivot 7 pivot 8 control means, valve 9 arrow

30 bottom plate

31 top plate

32 motion direction of the belt 7

33 movement of the top plate 31

34 passage for the fluid flow

35 adjustment means above the helical part, plate

36 hole

37 deflector plate

38 pivot

W width of the conveyor means

L Length over which the air flow is controlled α angel β angel