Sealing unit and method and production device for a hot air sealing process

Abstract

The invention relates to a sealing unit (2) for a hot air sealing process, having a heating device (4) for generating a hot air flow (H), a nozzle (6) for controlledly discharging the hot air flow (H), an outlet (8) for discharging the hot air flow (H), and a movable switching element (10) for switching the hot air flow (H) between the nozzle (6) and the outlet (8), wherein the switching element (10) is provided within a housing (12), the switching element (10) supplies the hot air flow (H) to a nozzle channel (14) of the nozzle (6) in a first switching position and to an outlet channel (16) of the outlet (6) in a second switching position, and the housing (12) and the switching element (10) exterior (18), which faces the housing (12), delimit a flow channel (20) for supplying the hot air flow (H) generated by the heating device (4) to the outlet (8) and to the nozzle (6).

Description

[0001] Windmöller & Hölscher SE & Co. KG

[0002] Münsterstraße 50

[0003] 49525 Lengerich / Westphalia

[0004] December 17, 2025

[0005] Our reference number: 9581 WO - SCHN

[0006] Sealing unit, process and manufacturing equipment for hot air sealing

[0007] The present invention relates to a sealing unit for hot air sealing, comprising a heating device for generating a hot air stream, a nozzle for directed the hot air stream, an outlet for discharging the hot air stream, and a movable switching element for switching the hot air stream between the nozzle and the outlet, wherein the switching element is arranged within a housing, wherein the switching element directs the hot air stream to a nozzle channel in a first switching position and the switching element directs the hot air stream to an outlet channel in a second switching position. The invention further relates to a method and a manufacturing device for hot air sealing with such a sealing unit.

[0008] A sealing unit as described above is used, for example, for welding the bottoms of cross-bottom bags. Document DE 195 02 255 A1 describes a device for applying sheet-shaped bottom layers made of plastic film to flat tubular layers made of plastic film.

[0009] The quality of the bond between the plastic layers to be welded depends significantly on the control of the hot air flow. The hot air flow is pulsed, meaning it is alternately directed towards the sealing point and bypassed via the outlet.

[0010] The hot air flow is switched by a mechanism subjected to very high dynamic and thermal loads. On the one hand, the large number of switching operations must be taken into account, as several hundred welds per minute are required. On the other hand, the temperature of the hot air flow used to seal the plastic layers reaches up to 750°C. Further requirements for such a sealing unit include minimizing the amount of leakage. "Leakage" refers to the portion of the hot air flow that, for each switching position, bypasses the switching element and enters the unswitched channel. This means that for the first switching position, as much of the hot air flow as possible should be directed to the nozzle channel to ensure efficient sealing. The portion of hot air that nevertheless reaches the outlet channel for the first switching position is the leakage.The proportion of hot air flowing through the nozzle is the amount of excess air. Conversely, in the second switching position, the entire hot air flow should be discharged through the outlet to prevent heating of areas of the product that are not to be sealed. Therefore, in the second switching position, the portion of hot air that nevertheless reaches the nozzle channel is the excess air, or the excess air component of the hot air flow.

[0011] The amount of air trapped within a sealing unit can increase over its service life, particularly due to changes in the shape and position of the individual mechanical components of the sealing unit caused by wear or temperature fluctuations. Therefore, maintaining consistent dimensional stability under temperature influence is another important quality criterion for a sealing unit.

[0012] The sealing unit should therefore withstand high dynamic and thermal loads overall, have a long service life and be designed in such a way that it is insensitive to temperature expansions or has a thermal expansion behavior that is as symmetrical as possible in order to switch reliably and with a low proportion of false air.

[0013] Against this background, the present invention addresses the technical problem of providing a sealing unit of the type mentioned above that enables reliable switching of hot air, particularly with a low amount of air leakage and low wear. Furthermore, a method and a manufacturing apparatus for hot air sealing are to be described.

[0014] The technical problem described above is solved by the features of the independent claim. Further embodiments of the invention are described in the dependent claims and the following description.

[0015] According to a first aspect, the invention relates to a sealing unit for hot air sealing, comprising a heating device for generating a hot air stream, a nozzle for directed the hot air stream, an outlet for discharging the hot air stream, and a movable switching element for switching the hot air stream between the nozzle and the outlet, wherein the switching element is arranged within a housing, wherein the switching element, in a first switching position, directs the hot air stream to a nozzle channel of the nozzle, and, in a second switching position, the switching element directs the hot air stream to an outlet channel of the outlet. The sealing unit is characterized in that the housing and an outer surface of the switching element facing the housing define a flow channel for directing the hot air stream generated by the heating device to the outlet and the nozzle.

[0016] The formation of the flow channel between the outside of the switching element and the surrounding housing enables uniform heating of the switching element by the hot air surrounding the switching element.

[0017] Furthermore, the switching element, which is at least partially enclosed around the flow channel, can enable precise switching between the outlet and the nozzle, similar to a diverter valve, since a seal can be created directly and precisely in the area of ​​the nozzle and the outlet. This reduces the amount of air entering the system.

[0018] The flow channel can have a gap width of several millimeters or centimeters, and the flow channel can be designed in particular to guide the entire volume of hot air generated by the heating device.

[0019] In particular, it may be provided that the flow channel is not a sealing gap, and / or that the switching element does not have a through-opening penetrating the switching element that allows hot air to flow through the switching element.

[0020] The switching element can be moved about a rotational axis by a rotary actuation movement, wherein a rotary swivel range of the switching element for switching the hot air flow can be less than or equal to 30°, in particular less than or equal to 25°, and further, in particular less than or equal to 20°. The rotary actuation movement, together with a small swivel range, enables rapid switching between the nozzle and the outlet.

[0021] The switching element can be assigned a servomotor for moving the switching element, wherein the servomotor can in particular be configured to set a plurality of switching positions of the switching element, wherein the switching positions have end positions and intermediate positions for fully or partially opening and closing the nozzle and outlet.

[0022] For example, a control device of the sealing unit may be configured to operate a temperature profile for sealing, in which different switching positions of the switching element are set by means of the servomotor during each sealing operation. Within the scope of this patent application, a temperature profile is understood to mean a variable temperature of the hot air volume flow, but also more generally a heat flow and / or energy profile.

[0023] For example, the control device may be configured to operate with a temperature profile that exhibits a higher temperature at the beginning and end of the sealing process than at a point in the middle of the sealing process located between the beginning and end. To achieve this, the control device may be configured to supply a larger volume of hot air to the nozzle for a predetermined duration at the beginning and end of the sealing process than during a period when a lower volume of hot air is supplied to the middle of the sealing process.

[0024] The first switching position of the switching element, for which the hot air is supplied to the nozzle, can therefore be part of a switching position profile that allows different hot air volume flows for sealing and thus enables sealing with a temperature profile.

[0025] The switching element can have a shaft, wherein the outside of the switching element is an outer circumferential surface of the shaft and wherein the shaft has, in particular, at least partially, a circular cylindrical shape, especially in the area of ​​bearing points of the shaft.

[0026] The at least partially circular-cylindrical shape of the wave promotes symmetrical expansion behavior under the influence of temperature. In particular, the wave can be essentially circular-cylindrical overall.

[0027] The shaft can have different diameters along its length, i.e., across the width of the nozzle. The shaft can also have a cross-sectional shape other than a circular cylinder in certain sections. This allows for different heat flows across the nozzle width. For example, sensitive areas of the bags, such as around folded edges, can be exposed to a lower heat flow compared to other areas, thus preventing damage.

[0028] The nozzle channel can be completely closed by means of the movable switching element, and in particular, closed virtually without gaps. This allows the occurrence of air leaks to be virtually completely prevented.

[0029] The outlet channel of the exhaust can be completely closed by means of the movable switching element, and in particular, closed virtually without gaps. This allows the occurrence of air leaks to be virtually completely prevented.

[0030] It may be provided that the movable switching element has a first sealing element associated with the nozzle, which projects into the nozzle channel and which, in the first switching position, releases a connection between the flow channel and the nozzle channel and, in the second switching position, at least partially or completely blocks the connection between the flow channel and the nozzle channel, and that the movable switching element has a second sealing element associated with the outlet, which projects into the outlet channel of the outlet and which, in the first switching position, at least partially or completely blocks a connection between the flow channel and the outlet channel and, in the second switching position, releases the connection between the flow channel and the outlet channel.

[0031] The movable switching element, with the aid of the sealing elements, allows for the adjustment of the sealing gap formed between the switching element and the nozzle channel or the outlet channel. This enables the compensation of deviations in the shape and position of the housing, the nozzle channel, the outlet channel, and / or other components of the sealing unit, which can arise, for example, from manufacturing tolerances, wear, or temperature-related distortion and which may lead to an increase in the amount of excess air. These deviations can be compensated for by readjusting the switching positions of the element.The arrangement of the flow channel between the outside and the housing therefore enables an adjustable sealing of the nozzle channel and the outlet channel by means of the movable switching element, in which a first sealing element projecting at least partially into the nozzle channel and a second sealing element projecting at least partially into the outlet channel are provided as part of the movable switching element.

[0032] The first and second sealing elements can form an angle of 90° or less with each other. This allows hot air to flow around the switching element on its outer surface over an angle of 270° or more. This promotes even heating of the switching element.

[0033] The first sealing element can form a sealing gap with a wall of the nozzle channel for the respective first and second switching positions of the switching element, whereby a gap width of the respective sealing gap is predetermined and adjustable by the respective first and second switching positions of the switching element.

[0034] The gap width of the sealing gap can be adjusted within a range of 0 mm or greater than or equal to 0.2 mm, and in particular within a range of 0 mm or greater than or equal to 0.1 mm. A gap width of 0 mm means that the sealing gap is essentially completely closed, although a 100% seal can only be achieved in exceptional cases due to manufacturing tolerances and thermal influences.

[0035] The second sealing element can form a sealing gap with a wall of the outlet channel for the respective first and second switching positions of the switching element, i.e., for the first switching position and / or the second switching position, whereby a gap width of the respective sealing gap is predetermined and adjustable by the respective switching position of the switching element.

[0036] The gap width of the sealing gap can be adjusted within a range of 0 mm or greater than or equal to 0.5 mm or less than or equal to 0.2 mm, and in particular within a range of 0 mm or greater than or equal to 0.1 mm or less than or equal to 0.1 mm. A gap width of 0 mm means that the sealing gap is essentially completely closed, although a 100% seal can only be achieved in exceptional cases due to manufacturing tolerances and thermal influences.

[0037] For a sealing gap width of 0 mm or greater than or equal to 0.2 mm, the connection between the flow channel and the outlet channel is considered closed according to the first switching position, since essentially no hot air is released into the environment via the outlet. For a sealing gap width of 0 mm or greater than or equal to 0.2 mm, the connection between the flow channel and the nozzle channel is considered fully open according to the first switching position, since essentially all the hot air is released via the nozzle channel towards the product to be sealed. The above applies analogously to the second switching position.

[0038] The first sealing element can be a projecting web. The second sealing element can be a projecting web.

[0039] The first sealing element can be tapered at its end in a wedge shape. The second sealing element can also be tapered at its end in a wedge shape.

[0040] The first sealing element can be a radially projecting web and, viewed in a cross-section perpendicular to the axis of rotation of the shaft, can in particular be extended essentially perpendicular to the axis of rotation.

[0041] According to alternative designs, the sealing gaps of the first and second sealing elements can be adjusted separately and independently of each other, whereby the first and second sealing elements can be moved separately and independently of each other.

[0042] The second sealing element can be a radially projecting web and, viewed in a cross-section perpendicular to the axis of rotation of the shaft, can in particular be extended essentially perpendicular to the axis of rotation.

[0043] The first sealing element and / or the second sealing element may be made of or consist of a steel material. The first sealing element and / or the second sealing element may have a coating that prevents adhesion to adjacent components upon contact, such as a PVD coating or a CVD coating. The first sealing element and / or the second sealing element may be made of or consist of a ceramic material.

[0044] According to a second aspect, the invention relates to a method comprising the following process steps: generating a hot air stream by means of a sealing unit according to the invention; directing the hot air stream towards flat products to be sealed, which are conveyed by means of a conveying device.

[0045] It may be provided that a temperature profile or heat flow and / or energy profile is operated by means of the sealing unit during the sealing process, whereby an adjustment of a hot air volume flow applied via the nozzle is made by adjusting the position of the switching element.

[0046] Furthermore, it may be provided that at the beginning of the sealing process, a higher sealing temperature or a higher heat flow and / or energy flow is set for a first period than for a subsequent second period.

[0047] Alternatively or additionally, it may be provided that at the end of the sealing process, a higher sealing temperature or a higher heat flow and / or a higher energy flow is set for a third period following the second period than for the second period.

[0048] For example, the sealing temperature for the second time period can be set to be 80% of the sealing temperature, or a higher heat flow and / or energy flow, of the first time period and / or the third time period. If, for example, a sealing temperature of approximately 750 °C is set for the first and / or third time period, a sealing temperature of approximately 600 °C can be set for the second time period.

[0049] According to a third aspect, the invention relates to a manufacturing device for hot air sealing, comprising a conveying device for conveying products to be sealed and a sealing unit according to the invention.

[0050] The products to be sealed can be, for example, cross-bottom bags or valve bags.

[0051] The production equipment can be configured to apply two or more cover sheets to different locations on the products by hot air sealing. For this purpose, the production equipment can have two or more hot air sealing units.

[0052] The invention is described in more detail below with reference to an exemplary embodiment shown in a drawing. The drawing schematically depicts:

[0053] Fig. 1 shows a sealing unit according to the invention in a first switching position;

[0054] Fig. 2 shows the sealing unit from Fig. 1 in a second switching position;

[0055] Fig. 3A is an enlarged view according to detail Z from Fig. 1;

[0056] Fig. 3B shows an adjustable sealing gap in the area of ​​the nozzle channel;

[0057] Fig. 4 shows a temperature profile for a seal;

[0058] Fig. 5 shows a manufacturing device for hot air sealing;

[0059] Fig. 6 shows a temperature profile for individual length sections of a seal;

[0060] Fig. 7 Examples of sealing products;

[0061] Fig. 8 Process steps of a process according to the invention.

[0062] Fig. 1 shows a sealing unit 2 for hot air sealing. The sealing unit 2 has a heating device 4 for generating a hot air stream H.

[0063] The sealing unit 2 has a nozzle 6 for the directed application of the hot air stream H.

[0064] The sealing unit 2 has an outlet 8 for discharging the hot air flow H into an environment U.

[0065] The sealing unit 2 has a movable switching element 10 for switching the hot air flow H between the nozzle 6 and the outlet 8. The switching element 10 is arranged inside a housing 12.

[0066] In a first switching position, the switching element 10 directs the hot air flow H to a nozzle channel 14 of the nozzle 6. The first switching position is shown in Fig. 1. In a second switching position, the switching element 10 directs the hot air flow H to an outlet channel 16 of the outlet 8. The second switching position is shown in Fig. 2.

[0067] The housing 12 and an outer surface 18 of the switching element 10 facing the housing 12 define a flow channel 20 for supplying the hot air flow H generated by the heating device 4 to the outlet 8 and to the nozzle 6.

[0068] The flow channel 20 has a gap width S of several millimeters. The flow channel 20 is designed to guide the entire hot air volume flow H generated by the heating device.

[0069] The flow channel 20 is not a sealing gap. The switching element 10 does not have a through-opening that would allow hot air H to flow through the switching element 10.

[0070] The switching element 10 is movable by a rotary positioning movement about a rotational axis 22, wherein a rotary swivel range B of the switching element 10 for switching the hot air flow H is less than or equal to 30°. The rotational axis 22 is oriented perpendicular to the drawing plane.

[0071] A servomotor 24 is assigned to the switching element 10 for moving the switching element 10. The servomotor 24 is a rotary servomotor.

[0072] The servomotor 24 is configured to set a plurality of switching positions of the switching element 10, wherein the switching positions represent end positions and intermediate positions for fully or partially opening and closing the nozzle 6 and the outlet 8.

[0073] The servomotor 24 is located on the outside of the housing 12 and can be connected to the switching element 10 via a cardan shaft or directly.

[0074] The switching element 10 has a shaft 26, wherein the outer surface 18 of the switching element 10 is an outer circumferential surface of the shaft 26. The shaft 26 has a circular cylindrical shape.

[0075] The nozzle channel 14 of the nozzle 6 can be completely closed by means of the movable switching element 10 – and indeed, closed essentially without a gap. The outlet channel 16 of the outlet 8 can also be completely closed by means of the movable switching element 10 – and indeed, closed essentially without a gap.

[0076] The movable switching element 10 has a first sealing element 28 associated with the nozzle 6. The sealing element 28 projects into the nozzle channel 14. In this case, the sealing element 28 projects into a widened section 30 of the nozzle channel 14, the widened section 30 of the nozzle channel 14 opening into the flow channel 20.

[0077] In the first switching position of the switching element 10, the first sealing element 28 opens a connection between the flow channel 20 and the nozzle channel 14 (Fig. 1). In this case, the hot air H is directed through the nozzle 6 towards the product to be sealed.

[0078] In the second switching position of the switching element 10, the first sealing element 28 blocks the connection between the flow channel 20 and the nozzle channel 14 (Fig. 2). In this case, the hot air H is not discharged via the nozzle 6 towards a product to be sealed.

[0079] The movable switching element 10 has a second sealing element 32 associated with the outlet 8. The second sealing element 32 projects into the outlet channel 16 of the outlet 8.

[0080] In the first switching position of the switching element 10, the second sealing element 32 blocks a connection between the flow channel 20 and the outlet channel 16 (Fig. 1). No hot air H is released into the environment U via the outlet 8.

[0081] In the second switching position of the switching element 10, the second sealing element 32 opens a connection between the flow channel 20 and the outlet channel 16 (Fig. 2). In this case, the hot air H is discharged into the environment U via the outlet 8 (Fig. 2).

[0082] The first sealing element 28 and the second sealing element 32 form an angle W of approximately 90° to each other.

[0083] Fig. 3A shows an exemplary and schematic enlarged view of one end of the second sealing element 32 according to detail Z from Fig. 1. For the first switching position of the switching element 10, the second sealing element 32 forms a sealing gap 34 with a wall 36 of the outlet channel 16. A gap width 38 of the sealing gap 34 is determined by the switching position of the switching element 10.

[0084] The gap width 38 of the sealing gap 34 is adjustable for the first switching position within a range of greater than or equal to 0 mm to less than or equal to 0.2 mm. This means that for a gap width 38 of the sealing gap 34 of greater than or equal to 0 mm to less than or equal to 0.2 mm, the connection between the flow channel 20 and the outlet channel 16 is considered closed, since essentially no hot air H is discharged into the environment U via the outlet 6.

[0085] For the second switching position of the switching element 10, the sealing gap is formed accordingly between the second sealing element 32 and the opposite area of ​​the wall 36. This design and definition of sealing gaps 34 applies analogously to the first switching element 28 and an associated wall 40 of the nozzle channel 14 for the respective first and second switching positions (see Fig. 3B).

[0086] The first sealing element 28 is a radially projecting web. The first sealing element 28 extends perpendicular to the axis of rotation 22 in the cross-section shown in Fig. 1 and Fig. 2.

[0087] The second sealing element 32 is a radially projecting web. The second sealing element 32 extends perpendicular to the axis of rotation 22 in the cross-section shown in Fig. 1 and Fig. 2.

[0088] The hot air stream H, which is discharged via the nozzle 6 in the direction of a product or item to be sealed, can be adjusted by means of the servomotor 24.

[0089] Fig. 4 shows an exemplary and schematic temperature profile for a sealing process. The temperature T in degrees Celsius [°C] is plotted against the time t in seconds [s]. The profile can be the same if a heat flow or energy flow is used instead of temperature.

[0090] At the start of the sealing process, the maximum available hot air volume flow rate H is applied via the nozzle 6 for a period t0 to t1, so that a maximum sealing temperature or a maximum heat flow and / or energy flow is achieved, e.g. up to 750°C. The switching element 10 is in the first switching position during this time – forming the sealing gap described above.

[0091] Subsequently, for a period t1 to t2, the nozzle 6 is partially closed by moving the actuating element 10 to an intermediate position by means of the servomotor 24, as shown schematically in Fig. 4. This reduces the hot air volume flow rate H discharged through the nozzle 6, thus also reducing the sealing temperature, heat flow, and / or energy flow at the product to be sealed to a lower temperature T2, or a lower heat flow and / or energy flow. This is because the reduced hot air volume flow rate H results in a lower heat input per second and per unit area into the product to be sealed.

[0092] At the end of the sealing process, nozzle 6 is fully opened again and sealed with maximum energy input - as can be seen for the period t2 to t3.

[0093] By regulating the hot air volume flow using the servomotor 24, temperature profiles can be applied to optimize the sealing process. The temperature profile shown in Fig. 4 can be useful, for example, if the wall thickness of the product to be sealed, as it passes the nozzle 6, is greater at the beginning and end of the sealing process than in the middle. Temporarily reducing the sealing temperature can therefore prevent excessive heat input into a thinner wall area of ​​the product being sealed.

[0094] Fig. 5 shows an exemplary and schematic representation of a manufacturing device 42 with a sealing unit 2 according to the invention. The sealing unit 2 is stationary.

[0095] Products 44 to be sealed are conveyed by a conveying device 45 at a speed f along a longitudinal direction L past the sealing unit 2 and locally heated. Simultaneously, cover sheets 46 are fed from a direction V and also heated by the sealing unit 2. The cover sheets 46 are pressed onto the products 44 and welded to them.

[0096] For each sealing operation, the temperature profile shown in Fig. 4 is used. This means that different length sections L1, L2, L3 of the cover sheets 46 are sealed at different temperatures T1 and T2. Fig. 6 schematically shows the length sections L1, L2, and L3, sealed at different temperatures, corresponding to the time intervals t0-t1, t1-t2, and t2-t3, which result from the velocity f in the longitudinal direction L.

[0097] The products 44 to be sealed can be, for example, cross-bottom bags or valve bags (Fig. 7). Two or more cover sheets can be applied to different locations on the products 44. For this purpose, the manufacturing device 42 can have two or more sealing units 2 for hot air sealing.

[0098] According to the invention, a method for hot air sealing is therefore specified, comprising the following process steps: generating a hot air stream H by means of the sealing unit 2 according to process step 100 from Fig. 8; applying the hot air stream H in the direction of the planar products 44 to be sealed, which are conveyed by means of a conveying device 45, according to process step 200 from Fig. 8.

[0099] Reference sign

[0100] 2 victory units

[0101] 4 Heating system

[0102] 6 nozzle

[0103] 8 Outlet

[0104] 10 switching element

[0105] 12 cases

[0106] 14 nozzle channel

[0107] 16 Outlet channel

[0108] 18 Outside

[0109] 20 Flow channel

[0110] 22 Rotation axis

[0111] 24 servo motor

[0112] 26 wave

[0113] 28 first sealing element

[0114] 30 widened area

[0115] 32 second sealing element

[0116] 34 Sealing gap

[0117] 36 wall

[0118] 38 gap width

[0119] 40 wall

[0120] 42 Manufacturing facility

[0121] 44 Product

[0122] 45 Conveyor system 46 Cover sheet

[0123] 100th process step

[0124] 200 process step

[0125] B Swivel range

[0126] Hot air flow / hot air volume flow

[0127] L direction

[0128] S gap width U surroundings

[0129] V direction

[0130] W angle f velocity tO temperature

Claims

Windmöller & Hölscher SE & Co. KG Münsterstraße 50 49525 Lengerich / Westphalia Our reference number: 9581 WO - SCHN Sealing unit, process and manufacturing equipment for hot air sealing Patent claims 1. Sealing unit for hot air sealing, comprising a heating device (4) for generating a hot air flow (H), a nozzle (6) for directing the hot air flow (H), an outlet (8) for discharging the hot air flow (H), and a movable switching element (10) for switching the hot air flow (H) between the nozzle (6) and the outlet (8), wherein the switching element (10) is arranged within a housing (12), wherein the switching element (10) supplies the hot air flow (H) in a first switching position to a nozzle channel (14) of the nozzle (6) and the switching element supplies the hot air flow (H) in a second switching position to an outlet channel (16) of the outlet (6), characterized in that the housing (12) and an outer surface (18) of the switching element (10) facing the housing (12) form a flow channel (20) for supplying the hot air flow generated by the heating device (4). Limit the hot air flow (H) to the outlet (8) and to the nozzle (6).

2. Sealing unit according to claim 1 , characterized in that the flow channel (20) has a gap width (S) of several millimeters or centimeters, wherein the flow channel (20) is designed to guide an entire hot air flow (H) generated by the heating device (4).

3. Sealing unit according to one of the preceding claims, characterized in that the flow channel (20) is not a sealing gap and / or the switching element (10) does not have a through-opening penetrating the switching element (10) that allows hot air (H) to flow through the switching element (10).

4. Sealing unit according to one of the preceding claims, characterized in that the switching element (10) is movable by a rotary positioning movement about a rotation axis (22), wherein a rotary pivoting range of the switching element (10) for switching the hot air flow (H) is less than or equal to 30°, in particular less than or equal to 25°, and further in particular less than or equal to 20°.

5. Sealing unit according to one of the preceding claims, characterized in that a servomotor (24) for moving the switching element (10) is assigned to the switching element (10), wherein the servomotor (24) is in particular configured to set a plurality of switching positions of the switching element (10), wherein the switching positions have end positions and intermediate positions for fully or partially opening and closing the nozzle (6) and the outlet (8).

6. Sealing unit according to one of the preceding claims, characterized in that the switching element (10) has a shaft (26), wherein the outer surface (18) of the switching element (10) is an outer circumferential surface of the shaft (26) and wherein the shaft (26) has, in particular, at least partially, a circular cylindrical shape, especially in the area of ​​bearing points of the shaft (26).

7. Sealing unit according to one of the preceding claims, characterized in that the nozzle channel (14) of the nozzle (6) can be completely closed by means of the movable switching element (10), in particular can be closed substantially without gaps, and / or the outlet channel (16) of the outlet (8) can be completely closed by means of the movable switching element (10), in particular can be closed substantially without gaps.

8. Sealing unit according to one of the preceding claims, characterized in that the movable switching element (10) has a first sealing element (28) associated with the nozzle (6), which projects into the nozzle channel (14) and which, in the first switching position, opens a connection between the flow channel (20) and the nozzle channel (14) and, in the second switching position, at least partially or completely blocks the connection between the flow channel (20) and the nozzle channel (14), and that the movable switching element (10) has a second sealing element (32) associated with the outlet (8), which projects into the outlet channel (16) of the outlet (8) and, in the first switching position, opens a connection between at least partially or completely blocks the flow channel (20) and the outlet channel (16) and in the second switching position releases the connection between the flow channel (20) and the outlet channel (16).

9. Sealing unit according to claim 8, characterized in that the first sealing element (28) and the second sealing element (32) enclose an angle of 90° or less to each other.

10. Sealing unit according to claim 8 or claim 9, characterized in that the first sealing element (28) forms a sealing gap (34) with a wall (40) of the nozzle channel (14) for the respective first and second switching positions of the switching element (10), wherein a gap width (38) of the respective sealing gap (34) is predetermined and adjustable by the respective first and second switching positions of the switching element, in particular that the gap width (38) of the sealing gap (34) is adjustable in a range from greater than or equal to 0 mm to less than or equal to 0.2 mm, in particular in a range from greater than or equal to 0 mm to less than or equal to 0.1 mm, and / or the second sealing element (32) forms a sealing gap (34) with a wall (36) of the outlet channel (16) for the respective first and second switching positions of the switching element (10).wherein a gap width (38) of the respective sealing gap (34) is predetermined and adjustable by the respective first and second switching positions of the switching element, in particular that the gap width (38) of the sealing gap (34) is adjustable in a range from greater than or equal to 0 mm to less than or equal to 0.2 mm, in particular in a range from greater than or equal to 0 mm to less than or equal to 0.1 mm.

11. Sealing unit according to one of claims 8 - 10, characterized in that the first sealing element (28) is a projecting web and / or the second sealing element (32) is a projecting web.

12. Sealing unit according to claim 4, claim 6 and one of claims 8-11, characterized in that the first sealing element (28) is a radially projecting web and, viewed in a cross-section perpendicular to the axis of rotation (22) of the shaft (26), is in particular substantially perpendicular to the axis of rotation (22) and / or the second sealing element (32) is a radially projecting web and, viewed in a cross-section perpendicular to the axis of rotation (22) of the shaft (26), is in particular substantially perpendicular to the axis of rotation (22).

13. Hot air sealing process, comprising the following process steps: Generating a hot air stream (H) by means of a sealing unit (2) according to one of the preceding claims; Direction of the hot air stream (H) towards flat products (44) to be sealed, which are conveyed by means of a conveying device (45).

14. Method according to claim 13, characterized in that a temperature profile and / or a heat flow profile and / or an energy flow profile is operated by means of the sealing unit (10) during sealing, wherein an adjustment of a hot air volume applied via the nozzle (6) menstroms (H) is achieved by adjusting the position of the switching element (10).

15. Method according to claim 14, characterized in that at the beginning of the sealing process, a higher sealing temperature and / or a higher heat flow and / or a higher energy flow is set for a first time period than for a subsequent second time period, and / or at the end of the sealing process, a higher sealing temperature and / or a higher heat flow and / or a higher energy flow is set for a third time period following the second time period than for the second time period.

16. Manufacturing device for hot air sealing, comprising a conveying device (45) for conveying products (44) to be sealed, comprising a sealing unit (2) according to any one of the preceding claims 1 - 14.

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