Filtering device and method for operating same

Abstract

The invention relates to a filtering device for filtering a fluid, and in particular a liquefied plastic. The filtering device includes a control unit to control the position of a screen carrier by generating control signals such that the fluid pressure in a fluid inlet channel and/or in a fluid outlet channel remains within definable pressure ranges while a cavity is being filled.

Claims

1. A filtering device for filtering a fluid, the filtering device comprising: a housing having a receptacle, a fluid inlet channel, and a fluid outlet channel; a screen carrier movable inside said receptacle, the screen carrier having at least one cavity for receiving a screen support plate having a filter element, wherein the screen carrier is movable from a filtering position into a screen replacement position, wherein the screen carrier and/or the receptacle has a filling recess for filling the at least one cavity with fluid, which releases a flow cross-section having a size dependent on a position of the screen carrier in the receptacle to feed fluid from the fluid inlet channel and/or the fluid outlet channel into the at least one cavity, and wherein the screen carrier has at least one ventilation recess for releasing any air which is in the at least one cavity during filling; and a control unit configured to change the position and/or a feed speed of the screen carrier such that a fluid pressure in the fluid inlet channel and/or in the fluid outlet channel remains within predetermined pressure ranges while the at least one cavity is being filled, wherein the control unit is configured to change the position and/or the feed speed of the screen carrier in steps and repeatedly, or continuously, by means of control signals.

2. The filtering device of claim 1, wherein the fluid is a liquefied plastic.

3. The filtering device of claim 1, further comprising at least one pressure sensor configured to measure the fluid pressure in the fluid inlet channel and/or in the fluid outlet channel.

4. The filtering device of claim 1, wherein the screen carrier is axially movable inside the receptacle, and the filling recess extends substantially parallel to a longitudinal axis of the screen carrier.

5. The filtering device of claim 1, wherein the filling recess is a groove that has a change in cross-section in a direction of a longitudinal axis of the screen carrier and/or has a substantially triangular cross-section.

6. The filtering device of claim 1, wherein the screen carrier is driven by a linear motor or a stepper motor.

7. The filtering device of claim 1, wherein the screen carrier has a position sensor configured to determine the position of the screen carrier.

8. The filtering device of claim 7, wherein the position sensor is an ultrasonic transducer.

9. The filtering device of claim 1, wherein the control unit has a memory and the control unit is configured to adjust control parameters based on stored sensor data from previous filling operations.

10. The filtering device of claim 9, wherein the stored sensor data from previous filling operations comprise filling positions and feed speeds of the screen carrier and/or filling times for the at least one cavity.

11. The filtering device of claim 1, wherein the control unit comprises a user control panel and/or a touch-sensitive display.

12. The filtering device of claim 3, wherein the fluid is a liquefied plastic.

13. The filtering device of claim 3, wherein the screen carrier is axially movable inside the receptacle, and the filling recess extends substantially parallel to a longitudinal axis of the screen carrier.

14. The filtering device of claim 3, wherein the filling recess is a groove that has a change in cross-section in a direction of a longitudinal axis of the screen carrier and/or has a substantially triangular cross-section.

15. The filtering device of claim 3, wherein the screen carrier is driven by a linear motor or a stepper motor.

16. The filtering device of claim 3, wherein the screen carrier has a position sensor configured to determine the position of the screen carrier.

17. The filtering device of claim 16, wherein the position sensor is an ultrasonic transducer.

18. The filtering device of claim 3, wherein the control unit has a memory and the control unit is configured to adjust control parameters based on stored sensor data from previous filling operations.

19. The filtering device of claim 18, wherein the stored sensor data from previous filling operations comprise filling positions and feed speeds of the screen carrier and/or filling times for the at least one cavity.

20. The filtering device of claim 1, wherein the control unit is configured to change the position and the feed speed of the screen carrier such that the fluid pressure in the fluid inlet channel and/or in the fluid outlet channel remains within predetermined pressure ranges while the at least one cavity is being filled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the Figures:

(2) FIG. 1 shows a first embodiment of a filtering device according to the invention, in a cross-sectional view;

(3) FIG. 2 shows the embodiment of the filtering device according to the invention, in a further cross-sectional view;

(4) FIGS. 3a-d show the embodiment of the filtering device according to the invention in cross-sectional views relative to the longitudinal axis of the screen carrier, with different steps in the process of filling the screen plug being shown;

(5) FIGS. 4a-c show the embodiment of the filtering device according to the invention in cross-sectional views, with different steps in the process of advancing the screen plug being shown;

(6) FIG. 5 shows the embodiment of the filtering device according to the invention in a hot melt adhesive application system;

(7) FIG. 6 shows the embodiment of the filtering device according to the invention in a hot melt adhesive application system, in which one of the screen carriers has been removed from the arrangement;

(8) FIG. 7 shows a flow diagram of the method according to the invention for operating a filtering device;

(9) FIG. 8 shows a block diagram of a control unit according to the invention; and

(10) FIGS. 9 and 10 show block diagrams of alternative embodiments of control units according to the invention, for an alternative embodiment of a filtering device according to the invention.

DETAILED DESCRIPTION

(11) FIG. 1 shows a filtering device 2 which has a housing 8. Housing 8 has a receptacle 12 for receiving a screen carrier 10 which is provided in the form of a screen plug 10, in the Figures that follow.

(12) It should be noted that alternative designs of a screen carrier, for example a plate-shaped screen carrier and the like, are explicitly included in the extent of protection.

(13) A filter element 11 is disposed in screen plug 10. Screen plug 10 also has ventilation recesses 4. Screen plug 10 also has a filling recess 6. It is possible by means of filling recess 6 to fill screen plug 10, or the cavity arranged inside it (cavity 18, see FIG. 2), by selectively connecting it to fluid inlet channel 14. During the filling operation, ventilation recess 4 is used to release air to the surroundings. The fluid required to fill the cavity is taken from fluid inlet channel 14. In the Figures, both fluid inlet channel 14 and fluid outlet channel 16 are designed so that they are in fluid communication with the top receptacle 12 and the bottom receptacle 12 when there is a screen plug 10 in the respective receptacle 12. In FIG. 2, filtering device 2 is shown in a cross-section perpendicular to the longitudinal axis of screen plug 10. Housing 8 has a total of two receptacles 12 for receiving screen plugs 10. In the example shown, however, only one screen plug 10 is inserted in the upper receptacle 12.

(14) The upper screen plug 10 has a screen plate 20 having a filter element 11. Ventilation recesses 4 can be seen, as can filling recess 6 which can be brought into fluid communication with fluid inlet channel 14, depending on the axial position of screen plug 10.

(15) The cavity 18 in screen plug 10 can also be seen in FIG. 2. During the filling operation, more particularly, said cavity 18 is filled with fluid via filling recess 6, and any air initially found in cavity 18 is released to the surroundings via ventilation recesses 4.

(16) When screen plug 10 is in a filtering position, the fluid flows from fluid inlet channel 14 into screen plug 10, is filtered by filter element 11 and subsequently flows out of filtering device 2 via fluid outlet channel 16, for example in the direction of an applicator (not shown, see FIGS. 5 and 6).

(17) The filling operation and the steps necessary to perform it are shown in more detail in FIGS. 3a-3d. In FIG. 3a, screen plug 10 is initially in a starting position in housing 8. As can be seen from FIG. 3a, filling recess 6 is already in fluid communication with fluid inlet channel 14 to a slight degree. This has the consequence that small amounts of fluid flow into the cavity 18 of screen plug 10. The air trapped in cavity 18 can be released to the surroundings via ventilation recesses 4.

(18) In FIG. 3b, screen plug 10 has been advanced so far to the right that a larger opening is provided between fluid inlet channel 14 and cavity 18. The consequence is an increase in the mass flow of the fluid in the direction of the cavity, with the result that the latter is filled more rapidly. Finally, after cavity 18 has been completely filled, screen plug 10 is advanced via intermediate step 3c further to the right and is brought into its filtering position in step 3d.

(19) FIG. 4a shows screen plug 10 with filter element 11, in the familiar manner. Filling recess 6 can also be seen, as can fluid inlet channel 14.

(20) As can be seen from FIG. 4b, the control process involves screen plug 10 being advanced in discrete clock steps 22 in the direction of fluid inlet channel 14 to the right in the present Figure. Control unit 30 is responsible for controlling the forward movement of screen plug 10 in such a way that the cavity is adequately filled by connecting filling recess 6 to fluid inlet channel 14, but keeping the overall system pressure within predefined limits.

(21) FIG. 4c shows a ventilation stop position, by way of example. This is the position of screen plug 10 relative to the surrounding housing 8, in which position filling recess 6 is in fluid communication with fluid inlet channel 14 such that cavity 18 is filled and the system pressure remains within predefined threshold values. This position is dependent on the fluid, in particular, and needs to be determined anew each time the cycle is performed.

(22) FIG. 5 shows filtering device 2 embedded in a hot melt adhesive application system 31. Hot melt adhesive application system 31 has a liquefying and conveying means 24. Solid plastic, mostly in the form of granulate, is liquefied therein by heating it, after which it is conveyed by a pump integrated into the liquefying and conveying means 24 in the direction of an applicator 25. A line 32 is arranged between liquefying and conveying means 24 and fluid inlet channel 14.

(23) To ensure that the fluid reaches applicator 25 in high quality and without any solid material trapped therein, the fluid passes through filtering device 2. In a familiar manner, filtering device 2 has a housing 8 which has two screen plug receptacles 12. As FIG. 5 shows, both screen plugs 10 are in a filtering position and filter the fluid. The filtered fluid now flows via a line 34 to applicator 25.

(24) There are also pressure sensors 26, 28 arranged in lines 32 and 34: input pressure sensor 26 in line 32 and output pressure sensor 28 in line 34. The system pressure is monitored by means of pressure sensors 26 and 28.

(25) FIG. 6, finally, shows the same hot melt adhesive application system 31, in which the bottom screen plug 10 is not shown in the Figure in question.

(26) FIG. 7 shows a flow diagram 36 for operating a filtering device 2. The point of departure is screen replacement position 38. Screen plug 10 is located here in a position that allows filter element 11 to be replaced. In this position, screen plug 10 is not used to filter the fluid.

(27) After filter element 11 has been replaced, screen plug 10 is now moved partially into the corresponding screen plug receptacle 12. Before a first ventilation clock position is reached, pressure P1 is measured (step 40). In principle, said pressure P1 may include not only measurement of the input pressure of the filtering device by means of input pressure sensor 26, but also measurement of the output pressure of the filtering device by means of output pressure sensor 28, or a combination of both.

(28) After the ventilation clock position has been reached (step 42), the process is paused. Screen plug 10 is then advanced by a further incremental amount with clock step 22, which corresponds to a predefined insertion distance. After this clock position 44 has been reached and a pause has elapsed, pressure P2 is subsequently measured anew (step 46). This pressure may relate to the input pressure of the filtering device (input pressure sensor 26) and/or to the output pressure of the filtering device (output pressure sensor 28). This pressure P2 which has now been measured is now subtracted in step 48 from the pressure P1 measured in step 40.

(29) Depending on the result of subtraction, a distinction is made between three cases:

(30) In a first case, no drop in pressure has occurred after performing clock step 22, which means that P1 is equal to P2 or that the pressure difference measured is less than a threshold value to be defined. In this case, it is necessary to continue inserting screen plug 10, and the method restarts with step 43. In relation to screen plug 10, the advancement of screen plug 10 was still not sufficient at this point to connect filling recess 6 with fluid inlet channel 14 in such a way that a sufficient amount of fluid flows into cavity 18.

(31) In a second case, the pressure difference measured in step 48 is greater than a total permissible pressure drop Pm in the system. In this case, screen plug 10 has been advanced so far forward that the cavity is filled so quickly that the pressure drop is greater than threshold value Pm. As a consequence, screen plug 10 is retracted a distance d in step 52, and subsequently moved in again in step 43, but with a halved clock step 22. Thus, by halving clock step 22, the ventilation stop position is approached with tighter control.

(32) A third case is one in which the difference between pressures P1 and P2 is greater than zero (or greater than a minimum pressure difference), but less than Pm. In this case, ventilation stop 50 is reached. Screen plug 10 now remains in this position until it has been completely filled. Operating parameters, such as the momentary position of screen plug 10 in the ventilation stop position, the type of fluid, and the system operating pressure, are subsequently stored in step 50.

(33) For subsequent filling operations, it is now possible, depending on the fluid being used, either to move directly to the ventilation stop position identified as the optimal position, or to approach it in a targeted manner in order to speed up and optimize the process by means of these self-learning functions.

(34) FIG. 8 shows in more detail the structure of control unit 30 and its interfaces. As already shown in FIGS. 5 and 6, control unit 30 receives pressure measurements from input pressure sensor 26 and/or from output pressure sensor 28. There is also a user interface 54 coupled to control unit 30. User interface 54 is connected bidirectionally to control unit 30, which is thus configured to receive data from user interface 54 and also to transfer data to the latter.

(35) Control unit 30 controls drive means 60 by taking into account pressure measurements 26, 28 and user input entered at user interface 54. Said drive means 60 is coupled to screen plug 10 and is adapted to selectively influence the position of screen plug 10 relative to the surrounding housing 8. Screen plug 10 can thus be moved with the aid of drive means 60 into the screen replacement position, the filtering position and any other clock positions, for example to fill cavity 18 after a screen replacement.

(36) The position of screen plug 10 is monitored by means of position sensor 58. The position of screen plug 10 is transferred to control unit 30 with the aid of position sensor 58.

(37) Control unit 30 is specifically configured to carry out method 36. Control unit 30 also has a memory, in particular for storing parameters from method 36 and making them available for subsequent cycles.

(38) FIG. 9 shows an alternative embodiment of a flow diagram 61 for operating a filtering device 2. Once again, screen replacement position 38 forms a starting point for the method. Screen plug 10 is located here in a position that allows filter element 11 to be replaced. In this position, screen plug 10 is not used to filter the fluid.

(39) After filter element 11 has been replaced, screen plug 10 is moved partially into the corresponding screen plug receptacle 12. Before a first ventilation position 62 is reached, pressure P1 is measured in step 40. As already noted, said pressure P1 may include not only measurement of the input pressure of the filtering device by means of input pressure sensor 26, but also measurement of the output pressure of the filtering device by means of output pressure sensor 28, or a combination of both.

(40) After ventilation position 1 has been reached (step 62), the screen plug is inserted continuously at a first feed speed in step 64. During insertion, pressure P2 is continuously measured in step 66. Pressure P2 may relate to the input pressure of the filtering device (input pressure sensor 26) and/or to the output pressure of the filtering device (output pressure sensor 28). This measured pressure P2 is subtracted in step 48 from the pressure P1 measured in step 40. Unlike the embodiment shown in FIG. 7, this occurs continuously while screen plug 10 is being inserted.

(41) Depending on the result of subtraction in step 48, a distinction is made between three cases:

(42) In a first case, no drop in pressure or minimum pressure drop Pmin has occurred yet during continuous insertion of screen plug 10, so screen plug 10 is inserted further in step 68. If, in contrast, the drop in pressure exceeds a maximum value Pm, the screen plug is retracted by a specific distance d in step 70 and is subsequently inserted again at a reduced feed speed. In this case, the method is performed anew, commencing with step 66. If the pressure drop calculated in step 48 is within a range which is greater than the minimum pressure drop Pmin and less than the maximum pressure drop Pm, then the ventilation stop position has been reached in step 50 and screen plug 10 remains in the respective position; cavity 18 is flooded.

(43) FIG. 10 shows another alternative embodiment of a flow diagram 71 for operating an alternative filtering device 2. According to this alternative embodiment, a pressure sensor is not necessary in order to carry out the method, or for the alternative filtering device 2 according to the invention.

(44) Proceeding from screen replacement position 38, screen plug 10 is moved partially into the respective screen plug receptacle 12 and reaches a ventilation position 1 (step 62). Proceeding from this ventilation position 1, screen plug 10 is now inserted further, continuously or in step, with a defined, preferably slow feed speed. This is carried out until a ventilation stop position is reached in step 72. In this method, the screen plug 10 is inserted so slowly, using an appropriate definition of the insertion speed, that the respective pressure drop in the system is guaranteed not to exceed a defined maximum pressure drop. In this alternatively preferred method, there is no monitoring of pressure.

LIST OF REFERENCE SIGNS USED

(45) 2 Filtering device 4 Ventilation recess 6 Filling recess 8 Housing 10 Screen plug (screen carrier) 11 Filter element 12 Receptacle 14 Fluid inlet channel 16 Fluid outlet channel 18 Cavity 20 Screen plate 22 Clock step 24 Liquefying and conveying device 25 Applicator 26 Input pressure sensor 28 Output pressure sensor 30 Control unit 31 Hot melt adhesive application system 32 Input line 34 Output line 36 Flow diagram of the method 38 Screen replacement position 40 Pressure sensing P1 42 Reaching ventilation clock position 1, pause 44 Clock position 46 Pressure sensing P2 48 Comparison of pressures 50 Ventilation stop reached, storage of parameters for subsequent operations 52 Retracting the screen plug, halving the clock step 54 User interface 56 Memory 58 Position sensor 60 Drive means 61 Second flow diagram 62 Reaching ventilation position 1 64 Inserting the screen plug with a first feed speed 66 Determining P2 continuously 68 Further insertion of the screen plug 70 Retract screen plug distance d, reduce feed speed 74 Third flow diagram 72 Ventilation stop reached