Weight measurement weighing unit

Abstract

The present invention relates to a gravimetric weighing unit for bulk materials comprising a weighing means (2) having a container (8) for the bulk material to be weighed, and a base unit (4) having a conveying path which is fed to an outlet line of the weighing unit (1) via a connecting device having a flexible sealing element, via which the conveying path can be operably connected to the outlet line and detached again from the outlet line, the connecting device having a magnetic fastening arrangement for operably connecting the sealing element at least to either the outlet line or the conveying path, or to both.

Description

[Technical Field]

[0001] The present invention relates to a gravimetric weighing unit according to the preamble of claim 1 .

[0002] Gravimetric weighing means, also known as loss-in-weight feeders, are widely used in many sectors of industry for any kind of flowable or bulk material, i.e., bulk material that can be conveyed by the gravimetric weighing means at all. In this case, the bulk material is dispensed into a container, from the container to a base unit located below it, and from the weighing means to an outlet line by a conveyor located in the base unit. Because the weighing means is installed above a weighing scale, the weight recorded by the weighing scale is the total weight, i.e., the known constant weight (tare weight) of the components of the weighing device plus the variable weight (net weight) of the bulk material currently present in the container and in the base unit.

[0003] In this way, the weighing scale continuously records the weight loss of the entire weighing means during operation, and therefore the weight loss of the bulk material present in the weighing device, since the weight of the weighing means is constant, so that the control device of the weighing means can determine the actual mass flow rate of the dispensed bulk material from the weight loss, compare it with a predetermined target mass flow rate, and control the dispensing conveyor accordingly to minimize the difference between the actual mass flow rate and the target mass flow rate.

[0004] Very precise control of the output mass flow rate may be required, for example, in the pharmaceutical sector or when adding color pigments in industrial production. Furthermore, the target mass flow rate may be small (e.g., less than a few kilograms per hour) in the production of the aforementioned color pigments or pharmaceuticals, or large (e.g., more than one tonne per hour) in, for example, plastics production or mining, and precise metering may also be required for such transportable volumes. Furthermore, different batches may be introduced one after the other, which may require regular maintenance as well as additional thorough cleaning depending on the bulk material.

[0005] The most commonly used weighing scales are precision weighing scales with a resolution of 1:100,000 or greater, such as Coperion K-Tron's vibrating wire scales known as the SFT-III, SFT-II-M, and SFT-II-L. These scales have a resolution of up to 1:4,000,000, allowing for accurate weighing even at container capacities of hundreds of kilograms and conveying speeds of several tons per hour. For example, a 1:1,000,000 resolution scale with a 100 kg container capacity can record weights to an accuracy of 1 / 10 g and be used for weighing.

[0006] To take advantage of the accuracy of the weighing scale for metering, the connection to the outlet line must be designed so that forces are not transmitted from the outlet line to the metering means by weight-directed components of the metering means, as otherwise the weighing scale would measure such forces in addition to the actual weight loss, resulting in the control device using an erroneous weight change of the metering means to adjust the actual mass flow rate.

[0007] In many cases, non-vertical conveyors, i.e., horizontal or inclined conveyors, are preferred, since gravity does not act in the conveying direction and therefore does not interfere with the conveying direction, allowing for somewhat better control of the hydrodynamic behavior of the bulk material. For example, a longer screw conveyor is well suited as a horizontal conveyor, since, when properly driven, the actual flow rate can be changed very easily and without delay depending on its rotation speed, and the mass flow from the hopper to a collection container located outside the metering unit can be properly connected without any adverse effect on the actual mass flow rate itself. In many cases, such conveyors in the aforementioned types of metering means are fixed at the end of their shafts in holders that support the conveyor in a precisely aligned position within its conveyor tube, thereby forming a conveying path.

[0008] To connect the conveying channel to the outlet line, a connecting device is often provided, which has a flexible sealing element that, due to its mobility, allows relative movements between the conveying channel (and thus the metering means) and the outlet line and isolates the metering means from the forces resulting from these movements. These relative movements can be very small depending on the type of weighing scale used, but are still relevant. The connecting device must be suitable for the aforementioned bulk materials, and therefore is, for example, of a dust-tight design, i.e., it is usually connected to the conveying channel and the outlet line via a threaded connection with a seal or via a clamping ring. As mentioned above, when changing batches or when handling sensitive bulk materials, the flexible sealing element (and the entire connecting device) must be cleaned or replaced.

[0009] For example, as shown in the brochure for "K4G-L Group / K-Tron Product Information, K4G Continuous Gravimetric Blender," when multiple weighing units are grouped in one location in a spoke-like fashion around a common outlet line, the design not only requires a relatively high level of maintenance effort, but also makes the outlet line cramped, making it difficult for installers to access, which increases maintenance time. As a result, it is often necessary to provide additional space for maintenance work when assembling the weighing units.

[0010] It is therefore an object of the present invention to provide a conveying device for a weighing unit or weighing means which saves maintenance time and can be easily assembled and disassembled even in limited spaces.

[0011] This object is solved by a metering unit having the features of claim 1.

[0012] By providing a magnetic connection, known detachable connections such as screw connections are not required, thereby eliminating the space required to apply tools (and the movement of the tool required). Furthermore, the magnetic connection is essentially a snap connection that can be released with a gentle pull anywhere, even on the back of the metering means, and automatically clicks back into place when replaced, eliminating the time required to fasten and unscrew the connection.

[0013] Further preferred embodiments include the features of the dependent claims.

[0014] The present invention will now be described in more detail with reference to the drawings.

[0015] In the figure, FIG. 1 shows a schematic representation of a metering unit according to the prior art. FIG. 2 shows an embodiment of a metering unit according to the invention; FIG. 3 is a diagram of a bellows with a retaining ring.

[0016] Figure 1 shows diagrammatically a prior art gravimetric weighing unit (1) for bulk materials of the type mentioned above, in which a weighing means (2) comprising a hopper (3) and a base unit (4) is suspended above a weighing scale (5) in a frame (6).

[0017] During operation, the hopper (3) is filled with bulk material, from which it drops via a transfer hopper (7) in the base unit (4) (which can be omitted) into the conveyor receptacle (8). A screw conveyor (9) protrudes from the conveyor receptacle (8), which transports the bulk material from right to left to the output line (10). Via the output line (10), the bulk material reaches the subsequent conveyor section (11) (shown in dashed lines) for further processing. The hopper is refilled before emptying.

[0018] In addition to the conveyor housing 8, the base unit 4 comprises a drive motor 12 with a gear 13 and a screw conveyor 9 driven by the drive motor. The screw conveyor 9 is mounted on a mandrel in a holder 14 and extends from the conveyor housing 8 through a conveying path 15, which also belongs to the base unit, to an outlet line 10. The base unit 4 or the conveying path 15 is mechanically decoupled from the outlet line 10 via a flexible sealing element, here designated as a bellows 17, which completely seals off the powdered bulk material, ensuring that the metering of the metering unit 2 is not influenced by the outlet line 10. The bellows 17, together with the associated screw connections on the outlet line 10 and the conveying path 15, form a connecting device 17 for connecting the conveying path 15 to the outlet line 10.

[0019] The weighing means (2) rests on the weighing scale (5) via the support (19), which records the weight of the weighing means (2) and the weight of the bulk material in the hopper (3) (and in the base unit (4)). During the weighing operation of the weighing device (2), as the screw conveyor (9) rotates and discharges the bulk material into the subsequent conveyor section (11), its weight is correspondingly reduced. This weight is recorded on the weighing scale (5) and then evaluated by a control device (not shown to reduce the complexity of the diagram). The weight reduction corresponds to the actual mass flow rate of the discharged bulk material, which must be adjusted to the target mass flow rate. For this purpose, the control device continuously corrects the speed of the screw conveyor (9) by means of the drive motor (12) according to a control algorithm known to those skilled in the art.

[0020] For example, if several weighing units (1) are grouped around a common outlet line (10), maintenance or cleaning of the bellows (16) must be performed from the right side, passing through the motor (12), the conveyor housing (8) and the conveying path (15), which is tedious and makes it difficult to use tools, especially if the space at the location of the bellows (16) is limited.

[0021] Figure 2 shows a portion of a base unit (20) of a metering unit according to the invention, corresponding to the dashed area (18) of the metering unit (1) in Figure 1. In this figure, one-third of the components shown have been cut away, with the upper half of the figure shown in cross section (the cutting plane is in the plane of the drawing) and the lower half of the figure shown in cross section, cut obliquely from below, with the cutting plane inclined at approximately 30 degrees to the plane of the drawing.

[0022] A conveyor receptacle (21) is visible, into which protrudes a screw conveyor (22), which extends further to the left next to the conveyor receptacle (21) through the conveying path (23) to the outlet line (24), into which it now protrudes freely suspended and therefore without contact. In operation, conveyed bulk material leaves the conveyor receptacle (21) via the rotating screw conveyor (22) into the outlet line (24) on the left, where it falls below the subsequent conveyor section (11) (Fig. 1), not shown in Fig. 2.

[0023] According to the invention, the connection device (17) comprises a flexible sealing element, which in the illustrated embodiment is designed as a bellows (25), as well as a connecting piece (26) and a carrier (27) for the bellows (25). Instead of a bellows, a person skilled in the art can also provide another suitable flexible connection in a particular case. For example, in the case of short conveying paths, instead of a separate carrier (27), the wall of the conveyor container (21) (or another component of the metering means (2) in FIG. 1) can also be designed as the carrier. Likewise, for example, depending on the design of the base unit (4) in a particular case, the connecting piece can also be formed by the outlet line (24) itself.

[0024] At this point, it should be noted that Figure 2 also shows that, in one embodiment, the conveying channel (23) is horizontally positioned. Figure 2 also shows that the conveying channel (23) projects beyond the bellows (25) or flexible sealing element in the conveying direction (i.e., from right to left in the figure toward the outlet line (24)). Therefore, the bulk material discharged therefrom falls directly into the outlet line (24) and possibly onto the connecting piece (26), but not into or onto the bellows (25). When the bulk material falls onto the bellows (25), the impact and its mass exert a load on the bellows (25). These forces necessarily also act on the carrier (27) supporting the bellows (25), resulting in the weighing scale (5) (Figure 1) recording an additional weight that erroneously measures the bulk material. The connecting device (17) is therefore designed so that the dispensed bulk material does not interfere with the weighing by the scale (5) and thus with the gravimetric metering of the bulk material. Preferably, the end of the sealing element facing the outlet line (24) is arranged in the conveying direction at or behind the end of the conveying path (23) facing the outlet line (24), so that the flow of bulk material discharged from the conveying path (23) during operation does not reach the sealing element.

[0025] A magnetic safety device (28) provided on the connecting device (17) ensures a detachable and reconnectable connection of the flexible sealing element or bellows (25) with the outlet line (24) (via the outlet connecting piece (26)) on the one hand and with the conveying path (23) (via the carrier (27)) on the other hand. The magnetic safety device (28) comprises, on the one hand, a mechanical positioning device (29) for mechanically positioning the bellows (25) in the connecting device (17) in its working position, and, on the other hand, a magnetic fixing device (30) for magnetically fixing the bellows (25) in its (mechanically designated) working position.

[0026] The mechanical positioning device (29) has a stop element on the bellows (25) and opposing stop elements on the outlet connecting piece (26) and on the carrier (27). In the illustrated embodiment, the stop element on the bellows (25) is designed as an opening (31, 31') and the opposing stop element is designed as a magnet (the magnetic properties are not important for the mechanical positioning device) with the geometry of a positioning pin; therefore, the opposing stop elements here are positioning magnets (32, 32'), which are arranged on the outlet connecting piece (26) and on the carrier (27) and mechanically engage with the openings (31, 31').

[0027] The openings (31, 31') are arranged in the safety portion of the bellows (25), here in the radially protruding flanges (33, 33'). However, the safety portion can also be designed as a tongue suitably arranged on the flexible sealing element with the opening, or any other suitable area of ​​the flexible sealing element can be provided as the safety portion. It is clear that the flexible sealing element has a safety portion with an opening for the locating pin. Furthermore, the safety portion is preferably designed as a flange protruding radially from the bellows, which flange is provided at at least one or both ends of the bellows. Figure 3 shows the bellows (25) of Figure 2 in more detail.

[0028] The mechanical positioning device (29) also preferably has a stop element on the flexible sealing element and a further stop element opposite to the stop element on the connecting piece (26) arranged on the outlet line or on the carrier (27) arranged on the base unit (4), to determine the relative position of the flexible sealing element on the connecting piece (26) or on the carrier (27) during operation.

[0029] It should be noted that "opposing" does not necessarily mean that the interacting stop surfaces are perfectly aligned. From Figure 2, for example, it can be seen that the positioning magnets 32 and 32' precisely position the bellows 25 radially, but the precise angular position of the bellows is not critical. Therefore, the openings 31 and 31' can also be designed as slots, since the ferromagnetic rings 34 and 34' will be uniformly intimately attached to the positioning magnets 32 and 32' at any angular position. Therefore, "opposing" means that the stop surfaces are perfectly aligned, or at least as aligned as necessary for perfect operational positioning, depending on the specific design of the magnetic safety device 28.

[0030] In addition to the positioning magnets 32, 32', which are arranged, for example glued, on the connecting piece 26 and the carrier 27, respectively, the magnetic fixing device 30 also comprises a magnetic ring 34, 34', which is designed, for example, as a ferromagnetic ring and which magnetically interacts with the positioning magnets 32, 32'. However, the rings 34, 34' can also be made of plastic or another non-magnetic material with a magnet. In the embodiment shown in Figure 2, the positioning magnets 32, 32' have both a mechanical function (positioning, see above) and a magnetic function: they attract the magnetic rings 34, 34' and fix them in their position.

[0031] As a result, each ring (34, 34'), held in place by the magnets (32, 32'), traps the flange (33, 33') of the bellows (25) between the ring and the connecting piece (26) or carrier (27), preventing the bellows (25) from lifting off the connecting piece (26) or carrier (27), thus fixing the flange (33, 33') and thus the bellows (25) in their relative positions (determined by the stop elements) in an operational manner. In this context, "operational" means maintaining its intended function under all conditions occurring during operation of the metering unit, such as movement and the bulk material used. Therefore, regardless of its specific design, the ring (34) is a magnetically effective fixing element that can be designed as a fixing ring or in any other suitable form. Figure 3 shows the bellows (25) and magnetic ring (34) of Figure 2 in more detail.

[0032] The ferromagnetic rings (34, 34') provide a magnetically effective area on the bellows (25), and the positioning magnets (32, 32') position the magnetically effective areas opposite each other on the outlet connection piece (26) or carrier (27), allowing these magnetically effective areas to interact with each other.

[0033] As a result, the magnetic fixing device (30) preferably has a magnetically effective area on the flexible sealing element (here designed as a bellows) and a magnetically effective area arranged oppositely (in terms of position) on the connecting piece (26) arranged on the outlet line (24) or on the carrier (27) arranged on the base unit (4), which effective areas operably fix the operative relative position of the flexible sealing element on the connecting piece (26) or on the carrier (27).

[0034] In the embodiment shown in Fig. 2, the positioning magnets (32, 32') act on the one hand as stops for the openings (31, 31') and on the other hand as magnets for fixing the magnetic rings (34, 34'). It is clear that one magnetic effective area is preferably formed by a positioning pin designed as a magnet, in the embodiment of Fig. 2 by the positioning magnets (32, 32').

[0035] FIG. 3 shows an exploded view of the bellows (25) and magnetic rings (34, 34'). To reduce the complexity of the illustration, the connecting piece (26) and carrier (27) (FIG. 2) have been omitted, while the positioning magnets (32, 32') (FIG. 2) are indicated by dashed lines (35, 35'). In the assembled state, as indicated by the dashed arrows, ring (34) is located inside flange (33), and ring (34') is located inside flange (33'). Each ring (34, 34') preferably has a handle (36, 36'). The fixing element, here designated as the fixing ring (34, 34'), preferably has a handle (36) and is particularly preferably made of a ferromagnetic material. However, as mentioned above, it can also be made of, for example, a non-magnetic material or can contain a magnet or ferromagnetic material.

[0036] This allows the installer to pull out the weighing unit (1), which has been assembled in a ready-to-operate state using the base unit (4) designed, for example, as shown in Figure 2, to the right with a slight pull, and the magnetic connection between the outlet line (24) and the conveying path (23) is released without the need for tools, labor, or time, even in limited space.

[0037] To reconnect the removed base unit 4 to the outlet line 26, simply press the bellows 25 against the positioning magnet 32' on the carrier 27 and place the ring 34 on it, and the bellows will be locked in place on the carrier 27. The base unit 4 is then moved along its length from right to left into its operating position, where the installer simply reaches the connecting piece 26 at the rear of the conveyor container 21, grabs the loose ring 34 with the handle 36 between his thumb and fingers, and places it on the connecting piece 26. The opening 31 is already positioned at the position of the positioning magnet 32, because the fringe 34' has already been correctly positioned by the positioning magnet 32'. No tools are required, and the installation requires a relatively small amount of space, so limited space is not an issue. The installation process takes very little time.

[0038] In a further embodiment not shown, the bellows 25 or flexible sealing element is provided with a magnetic fastening device on only one side, the other side being conventionally fastened to a connecting piece or carrier. In this case, the base unit 4 can be removed (or attached) as described, with the advantage that the conventional fastening to the removed base unit 4 can be removed or connected more easily and quickly. Conversely, if the conventional fastening is on the side of the connecting piece, the flexible sealing element can also be disassembled or assembled more easily, since the disassembled base unit is less in the way and therefore takes up less space.

[0039] In a further embodiment not shown, the mechanical positioning device and the magnetic fixing device are separate from each other and the stop element does not produce a magnetic effect.

[0040] However, preferably, as in the case of the positioning magnets (32, 32'), the stop element comprises a positioning pin and the opposing stop element comprises an opening facing the positioning pin, and more preferably, the stop element comprises an opening in the flexible sealing element and the opposing stop element comprises a positioning pin fixed relative to the connecting piece (26) or the carrier (27).

[0041] Whether the mechanical positioning device and the magnetic fixing device are separate or not, preferably the flexible sealing element has a safety portion, and the magnetically effective area on the flexible sealing element is formed by at least one magnetic fixing element, which, in the operative position, encloses the safety portion between itself and either the connecting piece or the carrier, thereby operably fixing the flexible sealing element in the operative position, and the fixing element is then magnetically held in that position.

[0042] In the embodiment shown in FIG. 2, a positioning pin designed as a magnet is arranged on at least one of the connecting piece (26) or the carrier (27), or both, and extends from one side through an opening (31, 31′) provided in the flexible sealing element for the positioning pin, and at least one magnetic fixing element is further provided on the other side of the opening (31, 31′), which seals the safety part of the flexible sealing element between itself and the connecting piece (26) or between itself and the carrier (27) and fixes the flexible sealing element in an operative position by being magnetically fixed to the magnet.

[0043] Although not shown in the figures, there are embodiments in which instead of the connecting piece (26) or carrier (27), the fixing ring or fixing element has a magnetic positioning pin, and for example the connecting piece (26) or carrier (27) is made of a ferromagnetic material and has openings for the positioning pin.

[0044] Next, a positioning pin, preferably designed as a magnet, is placed on the fixing element and extends from one side through an opening for the positioning pin provided on the flexible sealing element, and on the other side a magnetically active opening is provided in the connecting piece or carrier, the fixing element enclosing the safety part of the flexible sealing element between itself and the connecting piece or carrier and being magnetically fixed in the opening, fixing the flexible sealing element in the operating position.

[0045] As mentioned above, the situation is different if the mechanical positioning device and the magnetic fixing device are separate from each other and therefore the stop element is not magnetically active. In that case, for example, a magnet can be arranged on the connecting piece (26) or on the carrier (27) separately from the stop element, and said magnet interacts with a ferromagnetic fixing ring or fixing element that is provided with a magnet. The connecting piece (26) or the carrier (27) is a ferromagnetic material and interacts with the magnet arranged on the fixing element.

[0046] As a result, the magnetic fixing device is preferably separate from the mechanical positioning device and comprises a magnet arranged in the connecting piece or carrier, the fixing element being designed to be magnetically effective and enclosing the safety part of the flexible sealing element between itself and the connecting piece or between itself and the carrier, and being magnetically fixed to the magnet, thereby fixing the flexible sealing element in its working position.

[0047] Common to all described embodiments is a gravimetric weighing unit for bulk materials, comprising a weighing means (2) having a container (8) for the bulk material to be weighed and a base unit (4), the base unit (4) having a conveying path which opens into an outlet line of the metering unit (1) through a connecting device having a flexible sealing element, the conveying path being operably connected to the outlet line via the connecting device and detachable again from the outlet line, the connecting device further comprising a magnetic fastening device for operably connecting the sealing element to at least either the outlet line or the conveying path, or both.

Claims

1. A gravimetric weighing unit for bulk materials, comprising a weighing means (2) having a container (8) for the bulk material to be weighed and a base unit (4), said base unit (4) comprising a conveying path (23) feeding into an outlet line (24) of said weighing unit (1) through a connecting device (17) having a flexible sealing element, said conveying path (23) being operatively connected to said outlet line (24) via said connecting device (17) and being detachable from said outlet line (24) again; 1. A gravimetric weighing unit, characterized in that the connecting device (17) comprises a magnetic safety device (28) for operatively connecting the flexible sealing element to at least one of the outlet line (24) and the conveying path (23), or both.

2. 2. A weighing and measuring unit according to claim 1, wherein the magnetic safety device (27) comprises a mechanical positioning device (29) for positioning the flexible sealing element in the connecting device (17) in an operating position, and a magnetic fixing device (30) for magnetically fixing the flexible sealing element in the operating position.

3. 3. A gravimetric measuring and weighing unit according to claim 2, wherein the mechanical positioning device (29) has a stop element on the flexible sealing element and a further stop element designed to face a stop element on a connecting piece (26) arranged on the outlet line or on a carrier (27) arranged on the base unit (4), and these stop elements determine the relative operating position of the flexible sealing element on the connecting piece (26) or on the carrier (27).

4. 4. A weighing and measuring unit according to claim 3, wherein the stop element has a positioning pin and the opposing stop element has an opening designed to face the positioning pin.

5. 4. A weighing and measuring unit according to claim 3, wherein the stop element has an opening provided in the flexible sealing element and the opposing stop element has a positioning pin fixed relative to the connecting piece or the carrier.

6. 5. A weighing and measuring unit according to claim 4, wherein the flexible sealing element has a safety portion with an opening for a locating pin.

7. 2. A weighing and measuring unit according to claim 1, characterized in that the flexible sealing element is designed as a bellows (25).

8. 7. A weighing and measuring unit according to claim 6, wherein the flexible sealing element is designed as a bellows (25), and the safety part is designed as a flange (33, 33') protruding radially from the bellows, the flange (33, 33') being provided at least at one or both ends of the bellows (25, 25').

9. 3. A gravimetric measuring and weighing unit as claimed in claim 2, wherein the magnetic fixing device (30) has a magnetic effective area on the flexible sealing element and, opposite to the magnetic effective area, on a connecting piece (26) arranged on the outlet line or on a carrier (27) arranged on the base unit (4), which effective areas operably fix the operative relative position of the flexible sealing element on the connecting piece (26) or on the carrier (27).

10. 10. A gravimetric measuring and weighing unit according to claim 9, wherein the flexible sealing element has a safety portion, the magnetically effective area on the flexible sealing element being formed by at least one magnetic fixing element, which in an operating position encloses the safety portion between itself and either the connecting piece or the carrier, thereby operably fixing the flexible sealing element in an operating position, and the magnetic fixing element is then magnetically held in the operating position.

11. A weighing unit according to claims 4 and 9, wherein one magnetically effective area is formed by a positioning pin (32, 32') designed as a magnet.

12. 7. A gravimetric measuring and weighing unit according to claim 6, wherein one magnetic effective area is formed by a locating pin (32, 32') designed as a magnet, which locating pin (32, 32') is arranged at least on the connecting piece (26) or on the carrier (27) or both, and extends from one side through the opening (31, 31') provided in the flexible sealing element for said locating pin (32, 32'), and on the opposite side of said opening (31, 31') there is provided at least one magnetic fastening element, which seals the safety part of the flexible sealing element between itself and the connecting piece (26) or between itself and the carrier, is magnetically fastened to a magnet, and in turn fastens the flexible sealing element in an operating position.

13. 7. A weighing and measuring unit according to claim 6, wherein one magnetically effective area is formed by a locating pin (32, 32') designed as a magnet, said locating pin (32, 32') being arranged on a magnetic fixing element and extending from one side through a locating pin opening in the flexible sealing element, and on the other side a magnetically effective opening is provided in the connecting piece or carrier, said magnetic fixing element sealing the safety part of the flexible sealing element between itself and the connecting piece or carrier and being magnetically fixed in said opening and fixing the flexible sealing element in an operating position.

14. 7. A gravimetric measuring and weighing unit according to claim 6, wherein the magnetic fixing device is separate from the mechanical positioning device and comprises a magnet arranged in the connecting piece or in the carrier, the magnetic fixing element being designed to be magnetically effective, the magnetic fixing element enclosing the safety portion of the flexible sealing element between itself and the connecting piece or between itself and the carrier and being magnetically fixed to the magnet to fix the flexible sealing element in an operational position.

15. 13. A weighing unit according to claim 10 or 12, wherein the magnetic fastening element is designed as a ferromagnetic ring (34, 34').

16. 13. A gravimetric weighing unit according to claim 10 or 12, wherein the magnetic fastening element comprises a magnet.

17. A weighing unit according to claim 10 or 12, wherein the magnetic fastening element comprises a handle (36).

18. 2. A weighing unit according to claim 1, characterized in that the conveying path (23) is arranged horizontally.

19. 20. A gravimetric weighing unit according to claim 1 or 18, characterized in that the end of the flexible sealing element facing the outlet line (24) is arranged at the same position as or further back than the end of the conveying path (23) facing the outlet line (24) in the conveying direction, so that the flow of bulk material leaving the conveying path (23) during operation does not reach the flexible sealing element.

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