METHOD FOR FILLING A CONTAINER THAT IS AT LEAST PARTIALLY GAS-PERMEABLE

Description

[0001] The invention relates to a method for filling a container that is at least partially gas-permeable and to a filling device for carrying out this method.

[0002] For filling gas-permeable containers with free-flowing materials, it is state of the art to convey the material into the container using a stream of compressed air, whereby the compressed air passes through the gas-permeable wall of the container and the material remains inside. Such a pressure increase allows for the accelerated filling of materials with medium bulk density, as can be the case, for example, when filling FIBCs.

[0003] Especially for low-density, fine-grained materials, conveying the material by vacuum extraction is considered state of the art. When filling with vacuum packers such as those described in DE 10 2008 054 717 A1, the container to be filled, for example, a paper valve bag, is tightly placed onto a filling nozzle within an evacuable chamber. After opening the filling line and evacuating the chamber, the material is conveyed through the filling nozzle into the gas-permeable valve bag, and the air carried along with it passes through the bag wall into the valve chamber, where it is extracted. This chamber is pressurized with a vacuum pump during the filling process. To replace a filled container with one yet to be filled, the vacuum is broken and the chamber is opened.

[0004] Especially when filling highly dispersed substances, it is important to prevent the material from accumulating within the filling line. For this purpose, DE 10 2008 054 717 discloses the use of a pump supply in the filling line to convey the material.

[0005] Vacuum filling has proven particularly advantageous because it reliably ensures that no product escapes into the environment. This is because the container being filled is sealed within the vacuum chamber, and the air extracted from the chamber can be further purified by filters if necessary. The finer the material, the longer the filling process takes, as the gas permeability decreases with increasing fill level of the container, such as a valve bag. When such low-density, powdery material is drawn into the valve bag by vacuum, it compacts into a less gas-permeable mass. Furthermore, the remaining portion of the gas-permeable container can become clogged with the material, reducing gas permeability and thus slowing the filling rate.

[0006] Against this background, the invention aims to improve a method for filling a container that is at least partially gas-permeable, in particular a valve bag or an FIBC, with a bulk material, in such a way as to increase the filling speed. Furthermore, a filling device is to be provided with which such an improved method can be carried out.

[0007] The procedural part of this problem is solved by a method according to claim 1, and a filling device for carrying out this method is specified in claim 8. Advantageous embodiments of the method and the filling device are specified in the dependent claims, the following description, and the drawings.

[0008] The inventive method for filling a container that is at least partially gas-permeable, such as a valve bag or an FIBC, with a pourable filling material, in which the container is subjected to a negative pressure on the outside in order to generate a supply of filling material through a filling material line into the interior of the container, is characterized according to the invention in that, after a first filling time, the filling process is supported by pressurizing the filling material line.

[0009] The basic idea of ​​the filling method according to the invention is to provide a two-stage filling process. The first stage involves vacuum filling, as this is the most effective and fastest method for filling the container, particularly with low-density and fine-grained materials. However, if the filling speed decreases after the initial filling due to the problems described above, the invention provides support for the filling process by pressurizing the filling line, thus significantly accelerating it compared to pure vacuum or pure pressure filling. The pressurization is preferably not applied abruptly, but rather gradually, corresponding to the decrease in filling speed. Throughout the entire filling process, the operation must be controlled to prevent any overloading of the container wall.This is particularly important for paper containers, but also for containers made of fabric or similar materials. Pressure is applied, for example, by means of a pump that actively moves the contents, thereby creating the pressure.

[0010] With a suitable choice of parameters, an acceleration of the filling process by a factor of 2 or more compared to pure vacuum filling can be achieved in practice.

[0011] In the context of the present invention, negative pressure is a pressure below atmospheric pressure; such a negative pressure is also referred to as a vacuum in filling technology. It is understood that, therefore, vacuum in the context of the present invention is not the ideal vacuum pressure of 0, but rather any negative pressure between this pressure of 0 and atmospheric pressure. The terms vacuum and negative pressure are thus used synonymously.

[0012] According to an advantageous embodiment of the inventive method, the pressurization of the filling line, which is supported after the initial filling time, is maintained until the end or nearly the end of the filling process. It is understood that, advantageously, the external vacuum applied to the container is maintained throughout the entire filling process, whereby, after the pressurization of the filling line is initiated, the vacuum may be reduced, if necessary, to avoid exceeding the permissible load on the container. "Near the end" refers to a period within the last 5% to 10% of the total filling time. It may be advantageous to slow down the filling process shortly before its end to increase filling accuracy.This is then expediently achieved by ending the pressurization, i.e. the active filling by the pump, and completing the filling process only by means of vacuum filling.

[0013] In practice, it has proven advantageous if the duration of the initial filling phase, i.e., the time during which filling occurs exclusively under vacuum, is approximately half to two-thirds of the total filling time. For example, if the total filling time is 10 seconds, it has proven practical to fill the first five to seven seconds using only vacuum and only after five, or at the latest after seven, seconds to add pressurization to accelerate the filling process.

[0014] These values ​​may vary in individual cases, depending on the density of the filling material, the particle size of the filling material, the material of the container, especially the gas-permeable part of the container, and the volume of the container.

[0015] Since the filling rate decreases with increasing filling time during vacuum filling of the container, it is advantageous to determine the end of the initial filling phase—that is, the point at which supplementary pressurization of the filling line should begin—by ​​determining when the filling rate drops to a predetermined value. Such a determination is generally more advantageous than setting a fixed duration for the initial filling phase, as it better accommodates individual variations in each filling process.

[0016] Advantageously, the filling method according to the invention is carried out using a differential pressure control system, which regulates the differential pressure between the pressure inside the container and the pressure surrounding the container. Such a maximum differential pressure is generally determined by the container material and must not be exceeded to prevent damage to the container. This differential pressure is advantageously regulated to a constant value after the initial setup at the beginning of the filling process, for example, by a PID controller. Such a differential pressure control system also ensures that, if necessary, the vacuum applied to the filling line is reduced when pressure is applied to support the filling process, in order to keep the stress on the container material within permissible limits.

[0017] In practice, it has proven advantageous to regulate the differential pressure to a value between 300 mbar and 800 mbar, preferably between 500 mbar and 700 mbar. These values ​​are particularly suitable for filling valve bags and FIBCs.

[0018] The differential pressure control should be designed so that the vacuum is maintained throughout the entire filling process, i.e., until the end of the filling process. This advantageously ensures that no material escapes into the environment, but is instead discharged in a controlled manner.

[0019] A filling device according to the invention is defined in claim 8.

[0020] Crucially, the means for pressurizing the filling line must be designed to provide support during the filling process. Such means can be provided by suitable pumps, compressors in conjunction with jet pump-like jet guides, or preferably by a diaphragm pump, which introduces as little gas, especially air, as possible into the filling system.

[0021] From a machine perspective, it is advantageous to design the filling device with two delivery lines that feed into a common material line. One delivery line is for vacuum conveying, and the other for pressure conveying. The pressure conveying line is equipped with a pressure-boosting pump, specifically a diaphragm pump, while the vacuum conveying line has a valve that allows it to be partially or completely shut off. Towards the end of the filling process, when the supporting pressure in the delivery line is at its maximum, but the vacuum in the vacuum chamber still needs to be maintained, it is generally advisable to shut off the vacuum delivery line to maintain sufficient vacuum in the vacuum chamber.

[0022] According to the invention, the filling device includes a control and regulating unit designed and configured to regulate the differential pressure during the filling process between the interior of the container being filled and the surrounding space in the vacuum chamber. This control and regulating unit is connected to appropriate sensors, namely means for detecting the pressure in the vacuum chamber, the pressure inside the container being filled, and / or the pressure in the filling line. Pressure detection can be achieved using pressure sensors, with one pressure sensor advantageously located in the vacuum chamber and another at or near the end of the filling line to detect the internal pressure.The pressure at the end of the filling line, i.e. in the area of ​​the filling nozzle, is in a predetermined ratio to the pressure inside the container or corresponds to it, so that by arranging a pressure sensor in the area of ​​the filling nozzle, a complex pressure sensor arrangement inside the container is usually unnecessary.

[0023] To generate the vacuum in the vacuum chamber, the filling device advantageously includes a line connected to the vacuum chamber, which is connected to a vacuum pump. A vacuum control valve is integrated into the line and is part of the control system, i.e., controlled by the control unit. While controlling the vacuum pump directly is theoretically possible, controlling a vacuum control valve is usually simpler and faster in practice.

[0024] Furthermore, it is advantageous to provide a shut-off valve in the filling line so that the filling process can be interrupted or terminated by shutting off the filling line when a predetermined filling weight or volume is reached, while maintaining the negative pressure ensures that the filling material is completely introduced into the container to be filled and that the filling process is thus completed cleanly before the negative pressure chamber is opened to remove the filled container.

[0025] The invention is explained in more detail below with reference to an embodiment illustrated in the drawings. The drawings show... Figure 1 shows a highly schematic and simplified representation of the basic structure of a filling device according to the invention, Figure 2 shows a diagram relating to the filling process over time according to the methods according to the invention and according to the prior art, and Figure 3 shows the pressure profile during the filling process.

[0026] The based on Figure 1 The filling device shown is essentially designed in its mechanical structure in the same way as vacuum packers according to the state of the art; in this context, reference is made to a vacuum packer of type VeloVac from GREIF-VELOX Maschinenfabrik GmbH in Lübeck as an example.

[0027] The filling device has a storage container 1 for receiving material 2, which is connected via a conveying line 3 to a material line 4. At the end of the material line is a filling nozzle 5, which terminates within a vacuum chamber 6 designed to receive a container 7 to be filled. This vacuum chamber 6, which can be completely sealed off from the environment, is connected via a vacuum line 8, with a vacuum control valve 9 interposed, to a vacuum pump 10, the outlet line 11 of which may, if necessary, be filtered, leading to the outside atmosphere.

[0028] The vacuum chamber 6 is connected to the machine frame via a weighing device 12, which determines the filling weight of the container 7. A support body 13 is arranged inside the vacuum chamber 6, which serves to support the container 7 laterally and at the bottom during the filling process. This support body 13 has a grid-like design.

[0029] Furthermore, the filling device has a control and regulating unit 14, which is provided on the output side for controlling the vacuum control valve 9 and on the input side detects the pressure in the vacuum chamber 6 via a first pressure sensor 15 and the pressure inside the container 7 via a second pressure sensor 16. This second pressure sensor 16 is arranged at the end of the filling line 4 inside the filling nozzle 5.

[0030] A shut-off valve 17 is arranged in the filling line 4. This valve is controlled by the control unit 14 and is designed not only to open and close the filling line 14, but can also be moved to intermediate positions. A corresponding shut-off valve 18 is provided in the delivery line 3 from the storage container 1 to the filling line 4.

[0031] The vacuum chamber 6 can be opened for the purpose of removing a filled container 7 and inserting an empty container 7; the filling nozzle 5 is tightly guided into the vacuum chamber 6 and sealed against the container 7 by a seal 19. The setup described above corresponds to that of a vacuum packer according to the prior art.

[0032] In addition, the filling device has a second delivery line 20 running parallel to the delivery line 3. This second delivery line also connects the storage container 1 to the filling line 4 and incorporates a diaphragm pump 21, which is controlled by the control unit 14. Furthermore, the filling device has a third pressure sensor 22, which detects the pressure in the filling line 4 between the delivery lines 3, 20, and the shut-off valve 17. This sensor 22 is also connected to the control unit 14 via a signal.

[0033] The filling of a container 7 with the aforementioned filling device is carried out as follows: The container 7, for example a valve bag, is placed onto the filling nozzle 5 with the filling valve in the open vacuum chamber 6. The seal 19, which surrounds the filling nozzle 5 in an annular manner, is then pressurized with compressed air, thus sealing it against the interior of the valve bag 7. The valve bag is located inside the nozzle body 13 within the vacuum chamber 6, which is tightly closed after the valve bag 7 is placed on the filling chamber. The vacuum pump 10 is then switched on with the vacuum control valve 9 closed, and the filling process begins when the shut-off valves 17 and 18 are opened and the control valve 9 is opened at time t0.

[0034] When the control valve 9 is opened, the vacuum chamber 6 is pressurized, causing a flow of material 2 through the conveying line 3, the material line 4, and the filling nozzle 5 into the interior of the valve bag 7. The weight of the bag 7 is recorded by the weighing device 12. The profile of the product weight from the start of the filling process t0 until the target weight is reached at time t2 is shown in Figure 2 This is represented by the dashed curve 25. The filling of the valve bag 7 up to time t 1 occurs exclusively by negative pressure, just as in conventional vacuum filling technology. During this initial filling period, which lasts from t 0 to t 1, the filling of the container 7 occurs exclusively by negative pressure in the vacuum chamber 6. The dashed curve 26 in Figure 2This represents the product flow generated by negative pressure. The effect described at the beginning, whereby the product flow generated by negative pressure decreases more and more after an initially very high product flow, is clearly visible in curve 26.

[0035] When the product flow rate drops to a predetermined value, or when the rate of product weight increase, as shown in curve 25, drops to a specific value, then time t1 is reached, meaning the first filling phase, during which filling occurs exclusively by vacuum, is over. At time t1, the diaphragm pump 21 is activated to pump, and the shut-off valve 18 in the delivery line 3 is activated to close, so that now, in addition to the product weight generated by vacuum, which is shown in curve 27 (solid line), Figure 2As shown, a further product flow is added, which is caused by the pressure generated by the diaphragm pump 21 in the delivery line 20 and subsequently in the fill line 4. The additional fill weight generated by the delivery pump 21 is shown in curve 28. Figure 2 The curve is represented by a double-dotted line. Thus, after the initial filling time at time t1, until the end of the filling time at time t2, part of the product weight is generated by the negative pressure produced by pump 10, and part of the product weight is generated by the positive pressure produced by pump 21. The product weight generated by the respective flow rates adds up, so that curve 25 has already reached the target weight 23 at time t2, i.e., after the end of the filling time. Based on Figure 2 As can be seen from the example shown, the duration of the first filling time t 0 to t 1 is approximately half of the total filling time t 0 to t 2.

[0036] For comparison, in Figure 2 The diagram shows how long it would take to reach the target weight 23 using only vacuum filling. This would only be achieved at time t 3, whereby the filling time required with the combined vacuum-pressure filling (duration from t 0 to t 2) is only about half as long as the filling time required by pure vacuum filling (duration t 0 to t 3).

[0037] Like the in Figure 2As illustrated by the dotted curve 29, the control is based on the differential pressure between the inside of the bag and the environment within the vacuum chamber 6, i.e., on the differential pressure determined by sensors 15 and 16. After an initial build-up, this pressure should be kept as constant as possible. In practice, this means that when the conveying line 20 and the filling line 4 are pressurized, the vacuum control valve 9 must be retracted to maintain a constant differential pressure. Since the vacuum chamber 6 is to be maintained until the end of the filling time, i.e., until time t 2, the vacuum control valve 9 must be controlled so that the vacuum is reduced compared to the vacuum required during the initial filling time. This is achieved by... Figure 3 schematically represented, showing the pressure curve over time. The differential pressure is shown there as curve 29, corresponding to curve 29 in Figure 2The dashed curve 30 shows the pressure applied by the feed pump 21, whereas the solid curve 31 represents the pressure (vacuum) generated by the vacuum pump 10 in conjunction with the vacuum control valve 9. The differential pressure 29 results from the addition of the overpressure generated by pump 21 and the vacuum generated by pump 10 according to curve 31.

[0038] In principle, this multi-stage filling process can also take place at other pressure levels; the crucial point is that the permissible pressure difference is not exceeded, which also limits the speed of the filling process. Reference symbol list

[0039] 1 Storage container 2 Filling material 3 Conveying line 4 Filling material line 5 Filling nozzle 6 Vacuum chamber 7 Container 8 Vacuum line 9 Vacuum control valve 10 Vacuum pump 11 Outlet line 12 Weighing device 13 Nozzle 14 Control and regulating device 15 First pressure sensor 16 Second pressure sensor 17 Shut-off valve 18 Shut-off valve 19 Seal 20 Additional conveying line 21 Diaphragm pump 22 Third pressure sensor 23 Target weight 25 Dashed curve, time course of the product weight in container 7 26 Dashed curve, time course of the product flow generated by vacuum 27 Curve showing the time course of the product weight generated by vacuum in container 7 28 Dashed double-dotted curve showing the time course of the product weight generated by the conveying pump 29 Dotted Curve showing the differential pressure between the inside of the container and the inside of the vacuum chamber; 30 dashed curve showing the pressure generated by pump 21; 31 curvewhich shows the negative pressure generated by the vacuum pump 10,

Claims

1. A method for filling an at least partially gas-permeable container (7), in particular a valve bag or an FIBC, with free-flowing product (2), in which the container (7) is subjected to an external vacuum, so as to generate a supply of product through a product line (4) into the interior of the container (7), characterized in that, once a first filling time (t0-t1) has expired, the filling process is supported by pressurizing the product line (4).

2. The method according to claim 1, characterized in that the process of filling by pressurizing the product line (4) continues to be supported until the end or close to the end of the filling process (t2).

3. The method according to claim 1 or 2, characterized in that the duration of the first filling time (t0-t1) measures half to two thirds of the duration of the total filling time (t0-t2).

4. The method according to one of the preceding claims, characterized in that a drop in the filling speed to a predetermined value determines the end of the first filling time (t0-t1).

5. The method according to one of the preceding claims, characterized in that the differential pressure between the pressure prevailing in the container (7) and the pressure surrounding the container (7) is regulated.

6. The method according to claim 5, characterized in that the differential pressure is regulated to a value of between 300 mbar to 800 mbar, preferably of between 500 mbar and 700 mbar.

7. The method according to one of the preceding claims, characterized in that the exposure to a vacuum is continued until the end of the filling process.

8. A filling device for implementing the method according to one of the preceding claims, with a vacuum chamber (6) and a product line (4) that empties into the vacuum chamber (6) and is fed from a product container (1), wherein the vacuum chamber (6) is provided and designed for holding the container (7) to be filled, wherein in particular sealants are provided for sealing the product line (4) in relation to the container to be filled (7), into which the product line (4) empties, and further wherein means are provided for pressurizing the product line (4) during the filling process, characterized in that a control and regulation system (14) is provided, which is provided and designed for regulating a differential pressure during the filling process between the interior of the container (7) to be filled and the surrounding space in the vacuum chamber (6), and that means are provided for determining the pressure (15) in the vacuum chamber (6) and for determining the pressure in the interior (16) of the container (7) to be filled and / or for determining the pressure in the product line (4).

9. The filling device according to claim 8, characterized in that a membrane pump (21) is provided for pressurizing the product line (4).

10. The filling device according to one of claims 8 or 9, characterized in that two conveying lines (3, 20) that empty into the product line (4) are provided, of which one is provided for vacuum conveying, and the other for pressure conveying.

11. The filling device according to one of claims 8 to 10, characterized in that the vacuum chamber (6) is connected with a vacuum pump (10) via a line (8), wherein the line (8) integrates a vacuum control valve (9), which is controlled by the regulation system (14).

12. The filling device according to claim 10 or 11, characterized in that a shut-off valve (18) is integrated into the conveying line (3) for vacuum conveying.

13. The filling device according to one of claims 8 to 12, characterized in that a shut-off valve (17) is provided in the product line (4).