Patent Application
20150014238
The present embodiments generally relate to a device for filtering a fluid.
Devices for filtering a fluid are commonly referred to in the art as screen changers. Screen changers are used, for example, to filter foreign particles from a fluid, such as from molten plastic in the form of its polymer melt.
Large quantities of contaminants may arise, for example, in recycled material. In the course of filtering, it is obvious that the filter or filter unit will sooner or later become clogged with residues, and must be cleaned.
It is desirable for an efficient and versatile device to filter fluids that can be easily taken off line for cleaning and placed back in service.
There is a further need for a device that can quickly be cleaned and placed in service with minimal down time.
The present embodiments meet these needs.
The detailed description will be better understood in conjunction with the accompanying drawings as follows:
The present embodiments are detailed below with reference to the listed Figures.
Before explaining the present apparatus in detail, it is to be understood that the apparatus is not limited to the particular embodiments and that it can be practiced or carried out in various ways.
Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis of the claims and as a representative basis for teaching persons having ordinary skill in the art to variously employ the present invention.
The invention relates to a device for filtering a fluid, more particularly for filtering a thermoplastic polymer melt. The device comprises a housing having at least one fluid feed channel and at least one fluid discharge channel and having at least two mutually parallel and interspaced bores in respective fluid communication with the fluid feed channel and the fluid discharge channel.
Each of the bores houses in a fluid-tight manner, an axially displaceable and/or radially rotatable bolt. Each displaceable bolt comprises a filter unit having an inflow side and an outflow side, wherein each of said bolts can be moved at least between a first, filtering position, in which the inflow and outflow sides of the filter unit are in respective fluid communication with the fluid feed channel and the fluid discharge channel, and a second, back-flushing position, in which the inflow side of the filter unit is in fluid communication with at least one back-flushing channel in the housing.
Devices for filtering a fluid are commonly referred to in the art as screen changers. Screen changers are used, for example, to filter foreign particles from a fluid, such as from molten plastic in the form of its polymer melt. Large quantities of such contaminants may arise, for example, in recycled material. In the course of filtering, it is obvious that the filter or filter unit will sooner or later become clogged with residues, and must be cleaned.
It is preferably the case that two filter systems are configured in parallel, thus making it possible for one filter system to remain in operation while the other undergoes cleaning. One method of cleaning a filter is by back-flushing with a previously filtered fluid in a direction opposite the filtering flow direction of the fluid. Devices incorporating this methodology are referred to in the art as back-flush screen changers.
Such filter devices are often used in applications that are highly critical with respect to the mass flow of the fluid, such as in the production of thin plastic films. It is desirable to be able to guarantee the continuous flow of filtered fluid without variations of particulate concentrations, even when a filter needs cleaning or replacing.
The Applicant's German utility model DE 20 2010 017 247 U1 provides such a device for filtering a fluid in which various bolts are ingeniously arranged in a multi-part housing. Some bolts serve to hold the screens, while other bolts are movable to create separate cavities that can be filled with previously filtered fluid. With the movable bolts and screen-holding bolts in the back-flushing position, said fluid is then used to clean the screen surfaces by back-flushing. The therein-employed division between functionally separate bolt arrangements serves to maintain a constant melt flow, including when a filter is replaced or during back-flushing to clean an individual filter.
The Applicant's German Patent DE 196 12 790 C2 describes a device for filtering a fluid in which two filters are arranged in a common bolt, with the result that, depending on the position of the axially displaceable and radially rotatable bolt, the flow can be directed through different cavities in the axially displaceable and radially rotatable bolt in different side-streams.
European patent specification EP 1 778 379 B1 describes a device and method for filtering a fluid, more especially for plastics-processing machines, said device and/or method likewise being intended to maintain a constant flow rate also during back-flushing. Said device employs an additional movable bolt in a melt channel downstream of a filter unit. With the filter unit suitably positioned, said movable bolt is able to press previously filtered melt through the filter in a direction opposite to the production direction in a back-flushing operation. Once again in said device, the multi-part configuration in combination with a functional separation into different bolts, a filter-carrying bolt and a movable bolt, makes it possible to maintain a generally continuous flow of melt, including during cleaning.
European patent specification EP 0 577 680 B1 describes a filtering device for fluids to be cleaned in which disposed within a piston carrying the filter is another piston that, whenever back-flushing is required, is capable of pressing previously filtered material through the filter in a counter-flow. Once again, the functions of filter-carrying piston and additional movable piston are separately configured and implemented.
The publication WO 98/47688 describes a filter for viscous masses in which, once again, previously filtered fluid can be pressed by an additional movable piston in a melt channel through the suitably positioned filter in a back-flushing operation to suitably clean the filter. Said device, too, provides a functional separation between screen carrier and movable piston.
The object of the present invention, therefore, is to provide a device for filtering a fluid, and more particularly for filtering a thermoplastic polymer melt material, in which filter cleaning by back-flushing is made possible by simple design means. A particular object of the invention is to allow back-flushing of the fluid without disruptions or mass losses in the main stream during back-flushing. A further object of the invention is to prevent material from collecting in the region of the device and thus from solidifying and causing disruptions during back-flushing.
The device for filtering a fluid, such as a thermoplastic polymer melt, comprises a housing having at least one fluid feed channel and at least one fluid discharge channel and having at least two mutually parallel and interspaced bores in respective fluid communication with the fluid feed channel and the fluid discharge channel, wherein each of the bores houses in fluid-tight manner a therein axially displaceable and radially rotatable bolt, each of said bolts being provided with a filter unit having an inflow side and an outflow side.
Each of the bolts can be moved at least between a first, filtering position, in which the inflow and outflow sides of the filter unit are in respective fluid communication with the fluid feed channel and the fluid discharge channel, and a second, back-flushing position, in which the inflow side of the filter unit is in fluid communication with at least one back-flushing channel in the housing.
According to the invention, each of the axially displaceable and radially rotatable bolts can be moved into a third, filling position, in which fluid flows, through a clean-fluid channel in the axially displaceable and radially rotatable bolt, from the outflow side of the filter unit to a storage cavity formed in the bore by the movement of the axially displaceable and radially rotatable bolt, wherein, when the axially displaceable and radially rotatable bolt moves into the second position, said fluid then again flows through the filter unit to the at least one back-flushing channel and thus escapes from the housing.
In the course of the entire corresponding inventive movement of the axially displaceable and radially rotatable bolt during filling (third position) and during back-flushing (second position), therefore, the creation/enlargement and filling with fluid of the storage cavity (collectively referred to as the third position) and the reduction in size or, ultimately, disappearance and back-pressing of the fluid of the storage cavity (collectively referred to as the second position) takes place while the axially displaceable and radially rotatable bolt is correspondingly moved axially backwards and forwards, similarly to a syringe.
Therefore, the invention makes it possible for the function of creating a cavity to receive previously filtered fluid from production to be combined in one component with the correspondingly possible back-flushing by movement of the axially displaceable and radially rotatable bolt, this allowing the previously collected fluid to be back-flushed through the corresponding filter in the same bolt.
In addition, the appropriate provision of two parallel bolt arrangements guarantees the continuous melt flow of filtered fluid during the production process of a complete system. In contrast to the prior art, therefore, it is not necessary according to the invention to provide a separate displacement piston, which would additionally necessitate separate movement mechanisms.
In a single arrangement with just one bolt and just one suitably assigned actuator, the axially displaceable and radially rotatable bolt, which also houses the screening surface, can simply not only provide the corresponding volume for holding filtered fluid, but can also displace said fluid in the back-flushing position during back-flushing through the screening surface. This results in an especially simple design that can also be integrated in compact and space-saving manner into larger complete production systems.
According to the described and claimed device of the invention, therefore, the “positions” are to be understood in the sense of variable positions with respect to the position of the axially displaceable and radially rotatable bolt, said positions additionally including a movement of the axially displaceable and radially rotatable bolt and not being limited to static “end points” of corresponding movements. This applies in particular to the second and third positions, which include a corresponding movement of the axially displaceable and radially rotatable bolt according to the invention to create/fill and to compress/expel the fluid in/from the storage cavity during the filling and back-flushing operations, respectively.
According to a preferred embodiment of invention, with the axially displaceable and radially rotatable bolt in the first position, the outflow side of the filter unit is in communication with the at least one fluid discharge channel through the intermediary of the clean-fluid channel and through the intermediary of a radial groove disposed on the end face of the axially displaceable and radially rotatable bolt and extending only over some of the circumference of one end face of the axially displaceable and radially rotatable bolt and through the intermediary of an axially extending longitudinal groove of the axially displaceable and radially rotatable bolt.
The preferred provision of radial and longitudinal grooves according to the invention makes it especially reliably possible in every case to guarantee a constant flow of fluid, including when the axially displaceable and radially rotatable bolt is in the first position. Consequently, there is no clogging with melt, which might otherwise collect and solidify in dead spaces.
According to a preferred embodiment of the invention, the longitudinal groove extends only over some of the axial length of the axially displaceable and radially rotatable bolt.
In a preferred embodiment of the invention, the radial groove on one end face of the axially displaceable and radially rotatable bolt is covered there by a cover plate, said cover plate being provided with a therethrough extending through-opening to create a fluid communication between the radial groove and the storage cavity during the movement of the axially displaceable and radially rotatable bolt, especially during the axial displacement of the axially displaceable and radially rotatable bolt in a forward or backward direction.
Also the cover plate preferably provided according to the invention ensures that the fluid does not collect there during filling and is able to continue to be back-flushed in the back-flushing position without a tendency to solidify.
In another preferred embodiment of the invention, the axial movement of the axially displaceable and radially rotatable bolt from the first position into the third position results at the end face of said bolt in the formation of the storage cavity for filtered fluid, wherein, over the entire distance of said axial movement, the outflow side of the filter unit is in communication with the at least one fluid discharge channel through the intermediary of the clean-fluid channel, the radial groove and the longitudinal groove.
This preferred design according to the invention guarantees in especially reliable manner a constant flow of fluid, with the result that the solidification of fluid in any otherwise occurring cavities or dead spaces is not to be feared.
In a further preferred embodiment of the invention, the axially displaceable and radially rotatable bolt is movable from the first position by radial rotation into a first intermediate position, wherein, depending on the magnitude of the rotation angle, the fluid discharge channel is partially or completely sealed by the wall of the axially displaceable and radially rotatable bolt, such that, in case of complete sealing, the axially extending longitudinal groove of the axially displaceable and radially rotatable bolt is no longer in communication with the at least one fluid discharge channel.
A further preferred embodiment of the invention provides that, with the axially displaceable and radially rotatable bolt in a second intermediate position and depending on the magnitude of the rotation angle, the fluid feed channel is partially or completely sealed by the wall of the axially displaceable and radially rotatable bolt, such that, in case of complete sealing, the inflow side of the filter unit of the axially displaceable and radially rotatable bolt is no longer in communication with the at least one fluid feed channel.
The appropriate use of the lateral surface of the axially displaceable and radially rotatable bolt to seal corresponding openings in the housing allows an especially simple design for melt flow control in the filter. More particularly, this makes it possible for the dimensions of the axially displaceable and radially rotatable bolt to be kept very compact without additional need for complex valves or sealing arrangements.
In an advantageous embodiment of the invention, the axially displaceable and radially rotatable bolt is preferably so movable that it is simultaneously both in the second position and in the first intermediate position.
In a further advantageous embodiment of the invention, the axially displaceable and radially rotatable bolt is preferably so movable that it is simultaneously both in the third position and in the second intermediate position.
In yet a further advantageous embodiment of the invention, the axially displaceable and radially rotatable bolt is preferably so movable that it is simultaneously both in the first and second intermediate positions and/or in the second and third positions.
Sealing by the axially displaceable and radially rotatable bolt itself can thus be provided in especially effective manner and with simplicity of design by means of contact of the lateral surface of the axially displaceable and radially rotatable bolt to seal the corresponding openings of the housing.
In a further preferred embodiment of the invention, each filter unit is associated with at least one back-flushing channel.
The provision of a plurality of bores and back-flushing channels makes it possible for the continuous flow of melt to be realized in especially simple manner also during back-flushing of the screens in one of the axially displaceable and radially rotatable bolts.
In a preferred embodiment of the invention, the axially displaceable and radially rotatable bolt is provided with an outlet channel, wherein, with the axially displaceable and radially rotatable bolt in a fourth, starting position, said outlet channel can be brought into fluid communication with the fluid feed channel and has an opening to the surrounding area of the device, such that fluid can be discharged from the device through said opening.
The housing of the invention preferably consists of one or more parts, preferably of two parts, each housing part having a bore, a fluid feed channel and a fluid discharge channel as well as a bolt with a filter unit, a back-flushing channel and an outlet channel.
In a further preferred embodiment of the invention, the axially displaceable and radially rotatable bolt can be moved into a fifth, screen-changing position, in which the filter unit is outside of the housing to allow replacement of the filter unit in said position, said fifth position being in the opposite direction to the end face of the axially displaceable and radially rotatable bolt.
Consequently, in the fifth position, if a change of screen is required, this can easily be accomplished without the need for the entire device to be completely disassembled. More particularly, it is not necessary, when a screen is being changed, for the sealing end face region of the axially displaceable and radially rotatable bolt to be completely removed from the bore of the housing. Under certain physical conditions, however, an end-face screen change may also be advantageous if the available space at the opposite end of the filter device is insufficient to change the filter at that end. In such a case, the fifth position can alternatively be realized with a bolt adapted to be pulled out from the end face after removal of a cover plate there.
In an especially preferred embodiment, the axially displaceable and radially rotatable bolt is so long and movable that, in the fifth position, the at least one fluid feed channel and the at least one fluid discharge channel are completely sealed by the wall of the axially displaceable and radially rotatable bolt.
In a preferred embodiment of the invention, shut-off valves are provided upstream of the at least one fluid feed channel and downstream of the at least one fluid discharge channel, wherein, with the axially displaceable and radially rotatable bolt in the fifth position, said shut-off valves allow the respective channels to be sealed.
In an advantageous, extremely simple preferred embodiment of the invention, the design of the axially displaceable and radially rotatable bolts is such that the starting position of the axially displaceable and radially rotatable bolt, i.e. the above-described fourth position, is identical to the above-described fifth, screen-changing position.
To make the axially displaceable and radially rotatable bolt as compact of construction as possible, so that, in case of a change of screen, there are no sealing bolt surfaces that can cover the corresponding openings in the housing, the embodiment with the aforementioned shut-off valves nonetheless allows the melt flow to be shut off in relatively simple manner. This makes it possible for the axially displaceable and radially rotatable bolt to be of a shorter axial length, which can be advantageous under certain physical conditions of a complete system.
In a preferred embodiment of the invention, the device comprises two bolts, said bolts being movable independently of each other between the first position, the second position, the third position, the fourth position, the fifth position and the first and second intermediate positions and being held in the housing by corresponding bores, wherein, with the axially displaceable and radially rotatable bolt in the first position, the fluid to be filtered is filtered and, with the axially displaceable and radially rotatable bolt in the second position, fluid to be filtered does not flow through the filter unit of said bolt, said filter unit instead being subjected to a flow, opposite to the filtering direction, of filtered fluid supplied from the storage cavity associated with said bolt, wherein, during filtering by the other bolt, the storage cavity associated with the one bolt is filled with filtered fluid through axial movement of the one bolt from the first position into the third position or into the third and simultaneously intermediate position, wherein at least some of the thus stored fluid is then supplied to the filter unit of the one bolt through the movement of the one bolt when the one bolt is moved from the third position or the third position and simultaneously second intermediate position into the second position or the second position and simultaneously first intermediate position.
Consequently, operation of the complete machine can be continuously accomplished in alternation by suitably intermittent movements of the respective bolts according to the invention.
In the described manner with a simplicity of design, therefore, the invention allows a continuous productive operation without major variations in the production flow of the filtered melt, it being simultaneously possible for individual filter elements to be suitably cleaned by back-flushing.
Hereinbelow, a non-limiting example embodiment of the invention will be more fully explained and described reference to the drawings, in which:
In the drawings, identical components are identified by identical reference characters, the reference characters being omitted in some drawings in the interests of clarity. The individual described components according to the preferred embodiments of the present invention can be combined at will in a manner familiar to the person skilled in the art. The presented embodiments are non-limiting with regard to the respective combinations.
The actuators 26, 27 shown in
The only difference between
Such sealing elements are shown in a schematic sectional view in
Each of the bores 4, 5 houses a bolt 6, 7, which is axially movable and radially rotatable therein in fluid-tight manner. Movement of the axially displaceable and radially rotatable bolts can be accomplished by the actuators 26, 27 (see e.g.
In
As shown in
The states of movement of the axially displaceable and radially rotatable bolts 6, 7 are in all cases visualized by corresponding arrows in the drawings.
With the upper bolt 6 in the position shown in
Back-flushing of the filter unit 8 of the axially displaceable and radially rotatable bolt 6 can now take place. With reference to
Similarly to the sequence presented in
With the invention, it is possible, using just the axially displaceable and radially rotatable bolt, which carries the filter unit, i.e. simply through corresponding movement of said bolt, to obtain back-flushing fluid, which can then be back-flushed through the filter unit of the axially displaceable and radially rotatable bolt by movement of the axially displaceable and radially rotatable bolt itself. Consequently, elaborate prior-art solutions employing several additional bolts and additional fluid connections are not necessary according to the invention.
The invention is capable, therefore, of allowing a simple and compact design for reliable back-flushing and, therefore, cleaning of the corresponding filter device. Consequently, the invention provides a filter device of simple design without high constructional complexity that is reliable in use, easy to operate and quick to clean by back-flushing.
While these embodiments have been described with emphasis on the embodiments, it should be understood that within the scope of the appended claims, the embodiments might be practiced other than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012006563.9 | Mar 2012 | DE | national |
| PCT/EP2013/000886 | Mar 2013 | EP | regional |
The present patent application is a Continuation Application that claims priority to and the benefit of co-pending International Patent Application No. PCT/EP2013/000886, filed Mar. 22, 2013, entitled “DEVICE FOR FILTERING A THERMOPLASTIC MELT”, which claims priority to DE Application No. 102012006563.9 filed Mar. 30, 2012, entitled “DEVICE FOR FILTERING A THERMOPLASTIC MELT”. These references are incorporated in their entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2013/000886 | Mar 2013 | US |
| Child | 14502553 | US |
