FILTERING DEVICE FOR THE LARGE-AREA FILTRATION OF FLUIDS

A filtering device (100′) for the large-area filtration of polymer melts comprises at least: a housing (20; 20′) with at least one inlet channel (23; 71′) and at least one outlet channel (26; 61′) and a filter carrier element (40, 40′), which can be moved longitudinally in relation to a housing bore and has at least one filter insert (10; 10′), which in a production position can be arranged in a filter chamber (24; 24′) between the inlet channel (23; 71′) and the outlet channel (26; 61′) of the housing (20; 20′), wherein the filter insert (10, 10′) has a main element (12, 12′) through which the flow can pass, and from which a fluid stream branches off to multiple individual filter elements (11, 11′) or in which multiple fluid streams from the individual filter elements are combined. The filter insert (10, 10′) is arranged on an end face of the filter carrier element (40, 40′). The filter chamber (24, 24) is formed by a housing bore, which extends up to a mouth (25) on an outer side of the housing and into which the filter insert (10, 10′) can be pushed by moving the filter carrier element (40, 40′), and a closure element (41, 41′), which can be placed onto the mouth (25) of the housing bore and/or can be inserted therein when the filter carrier element (40, 40′) is lowered into the housing bore or thereafter.

The invention relates to a filtering device for the large-area filtration of fluids, which consists of at least:a housing with at least one inlet channel and at least one outlet channel anda filter carrier element which can be moved longitudinally in relation to a housing bore consisting of at least one filter insert, which is to be allocated in a filter chamber that is located between the inlet channel and the outlet channel of the housing in a production position,wherein the filter insert has a main element through which the flow can pass, and from which a fluid stream branches off into multiple individual filter elements or into which multiple fluid streams from the individual filter elements are joined.

In filtering devices of the mentioned kind, polymer melts flow through a filter insert element which is located inside of a cylindrical filtering housing, which is constructed as a large-area filter in form of a disc- or cartridge filter, at temperatures reaching up to 350° C. and with pressures reaching up to 300 bar.

Such large-area filters in form of double filters are know from DE-C-19823765 or DE-A-102005061770. In these embodiments, each individual filter with its cylinder tube shaped filter housing can be swung out of its working position, in order to pull out the filter inserts upwards for a filter replacement. In these embodiments, both filters are mounted to a carrying die set or are solidly interconnected via the switching valves. The filter housings are interconnected via the valves or a carrying die set. Therefore, a replacement or a cleaning of the filter insert is difficult, since the temperature of the filter housing as well as of the remaining device cannot be maintained.

When polymer melts are filtered, the high processing temperatures lead to significant thermal expansions within the filter elements. By means of this, pressures and displacements occur within the modular embodiment of suchlike double filters with the danger of leakage at the junctions of the flow channels in various elements. This basic problem cannot be solved with the solution suggested in DE-A-102005061770, because it is important that there always is a heated filter insert for a filter change, which consists of the same temperature as that of the housing. If this is not the case, it will not be possible to perfectly align the flow channel junctions of the filter insert to the flow channels of the housing and to connect them in a way that they are fully sealed, due to the thermal expansion.

Thus, the present invention has the objective to produce a filtering device for the large-area filtration of polymer melts in particular, which can be cleaned easily and where a filter insert can be replaced in a quick and safe manner. The filtering device further has to consist of a construction which can be homogeneously heated, in order to prevent mounting- and leakage problems due to different thermal expansions.

The objectives are accomplished by means of a filtering device for the large-area filtration of fluids, in particular of polymer melts, by means of the characteristics of claim1.

It is fundamental that the filtering device consists of at least one drive unit and a solid filter housing with a filter chamber, whereby the filter insert can be inserted into a bore of the housing by means of a translational movement, and where a closure element on the filter insert seals the bore hole, by means of which a fully sealed filter chamber is formed.

By means of the drive unit, a simple maintenance and cleaning of the filter insert is possible. In this way, the filter insert can be installed and removed, and the filter chamber can be cleaned without having to reduce the temperature in the solid housing.

The temperature of the housing is preferably homogeneously controllable. In a preferred embodiment, heating-cooling channels for a homogeneous heating are intended in the solid housing. The heating can be accomplished in a hydraulic- or electric way as well as by means of a steam heating.

The filtering device according to the invention is preferably suited for polymer melts, e.g. for polyester, polyether or polyamide.

The filtering device according to the invention is suited for melts within a temperature range of up to 350° C., preferably from 10° C. to 350° C., preferred from 10° C. to 300° C.

In a preferred embodiment, the invention consists of switching valves that can be screwed onto the filtering housing or that can be built into the housing, by means of which the flow of the melt to the filter via the flow channel junctions can be released or stopped. They are aligned to the respective inlet- or outlet channel.

In a preferred embodiment, the valves are designed in such a way, that the filter insert can be cleaned by means of a backflush function with a flow reversal in the filter insert. For this reason, backflush channels are arranged in the switching valve and in the housing, by means of which the filter cake can be discharged from the filter medium towards the outside.

The filtering device according to the invention can be used in a continuous as well as in a discontinuous operating mode.

In a first preferred embodiment, the filtering device can work as a simple, discontinuously operating filter, in that the filter housing is designed as a solid housing with only one filter chamber for one single filter insert as well as with an attached drive unit for a simple filter replacement. This construction form allows for a construction without the use of valves for stopping or releasing the melt flow through the filter, as long as the device can be turned off for the filter replacement.

In a further preferred embodiment, the filtering device can be made in form of a continuously operating multiple filter, in particular in form of a double filter, and can consist of a simple, solid construction that can be heated very homogeneously, in order to prevent mounting- and leakage problems due to differing thermal expansions.

In a preferred embodiment, such a double filter is operated in a parallel arrangement of two filter inserts, in order to be able to operate without any production interruption while one filter insert is being replaced.

In a further embodiment, a parallel arrangement of two or more filters is possible as well, in order to e.g. accomplish a stage filtering, in which there is a coarse filtering in a first filter insert and a fine filtering in a second filtering insert.

The construction type of such double- and multiple filters is a subsequent arrangement of filtering devices according to the invention in the previously mentioned basic way of construction, but which consist of a common housing.

The multiple filtering devices preferably consist of switching valves, which enable a distribution of the fluid flows according to the desired operation mode.

A double filter can be operated as a continuous filtering system in two different functions with two filtering inserts that are arranged parallel:

On the one hand it is basically possible that both filter inserts are used for the filtration during production. If these have to be replaced after a certain time due to dirt in the filter elements, one filter insert is first disconnected from the inflow and outflow of the melt by means of the valves, while the other one is kept in production. In this way the first filter insert can be replaced without any production interruption. After the filter replacement is accomplished, the new filter insert is put into production by means of the valves, the second used insert is disconnected from the production in the same way, in order that it can be replaced as well. After both filter elements have been replaced, the production can again be performed by means of both filter inserts.

On the other hand, it is possible that only one of the filter inserts of a double filtering device is used for the filtration. The second filter insert is in a waiting position in the second filter chamber without being used. As soon as the filter insert that is in production is soiled and has to be replaced, it is possible to switch to the second filter insert of the double filtering device which is in a waiting position, ready for use, by means of the valves.

Since the housings of a discontinuously operating single filter as well as of a continuously operating multiple filter, in particularly of a double filter, are designed in a solid way and are equipped with a suitable heating for a permanent homogeneous temperature control during the filtering of polymer melts, a replacement of the filter inserts can be performed at any time. Thus, there are no waiting periods for heating up certain parts of the housing, in order that they can be subsequently interconnected in a precise manner.

The removal or replacement of a filter insert can be arranged in a very simple way, since it is only necessary that the filter carrier element with the filter insert is moved out of the housing by means of a drive unit, e.g. a hydraulic cylinder.

The axes of the filter carrier element, of the filter insert that is attached to it and of the filter chamber, are preferably aligned in the same direction. The operation of the drive unit thus allows for a removal of the filter insert without having to produce any transverse forces for it, since the drag force issues in longitudinal direction of the filter insert. In known large-area filters on the other hand, filter inserts are general lifted out of the housing by means of a crane, which leads to forces that issue in a slanting way which may include the danger of damage to the filter insert.

It is further possible that the motion of the filter carrier element is used in order to clean the filter chamber of the melt. In order to accomplish this, cleaning scrapers, brushes or other possible cleaning tools can be attached to the drive unit and can be moved up and down with it inside the filter chamber. This allows the operating personnel to clean the bore in a simple, efficient and safe way, since it can be performed inside the hot housing by the machine.

The function of the valves, which can advantageously be mounted to a multiple filter, e.g. to a double filter or which can be integrated into the solid housing in a different construction type, is to release the melt inlet or outlet of the one of the other filter chamber of the housing, whichever is selected. In a middle position of the valve, the flow of the material can be directed via both filter chambers of the housing.

A special form of the switching valve can be intended to perform a backflush function for a self-cleaning of the filtering device by means of additional channels inside the valve pistons and inside the housing. In order to accomplish this, the inlet valve is set in a position, where the inflow of the material into the filter chamber, that is to be backflushed, is interrupted. Instead, the backflush channel within the inlet valve is set in a hydraulic connection with this filter chamber while at the same time the connection to the outlet channel on the outlet side is maintained. By means of this, a flow reversal is accomplished inside the filter chamber that is to be backflushed, where the melt is flowing from the clean side of the filter insert through the filter medium towards the dirt side of the filter insert, where it lifts the filter cake off the filter medium and discharges it via the backflush channel in the inlet valve toward the outside of the housing.

The same backflush procedure can advantageously be designed in such a way, that a backflush channel is directly inserted into the filter chamber, which can be sealed with a plug or a simple stop valve, instead of a backflush channel inside the inlet valve. In order to perform a backflush, the inflow to the filter chamber has to be stopped by means of such a simple inlet valve and the flow connection on the outlet side has to be maintained. An opening of the backflush channel of the filter chamber by means of a removal of the plug or by means of opening the simple valve accomplishes the flow reversal inside the filter chamber along with the cleaning effect of the filter medium.

The flowing direction of the filtering device according to the invention is solely determined by the kind of filter insert. Stacked disc filters are usually flown through from the outside towards the inside, in order to prevent an expansion resulting from the existing high pressure. Apart from that, the mentioned flowing directions of the embodiments which are described in the following are also reversible.

A simple filtering device100according to the invention, which is operated discontinuously, is depicted inFIG. 1.

It features a filtering housing20with one inlet channel23, one outlet channel26and a filter chamber that is located on the inside. Heating-cooling channels are arranged within housing20for holding electric heating cartridges, in order to achieve a homogeneous temperature control of the overall housing20.

An attached drive unit45consists of a hydraulically operated cylinder, by means of which a filter carrier element40can be axially moved.

In the depicted embodiment, filter carrier element40consists of a filter insert10, which is attached to its lower end face, which is created like a pyramid cake with a support profile12that is flown through centrally and a plurality of disc filter elements11, so called leaf-disc-filter element, which are stacked on top of it. The individual disc filter elements11consist of a respective encasements that are made of a metal filter fabric, which is spanned by means of a support frame, so that a hollow space is created. The fluid that has passed the filter fabric, flows out of the spanned hollow space into the central support profile12, as it is generally know.

Essential for the invention is, that above filter insert10, there is a closure element41which is attached onto filter carrier element40. It consists of a radial flow channel43, which is directed downwards and which leads into support profile12of the filter insert.

FIG. 2depicts the same filtering device100in cross section. The design of drive unit45is clearly detectable in the upper section. The upper end of filter carrier element40is designed as piston46.

Also detectable inFIG. 2are the paths of the flow inside of closure element41with an axial flow channel42and a radial flow channel43, which overlaps with outlet channel26on the housing side when filter insert10is pushed into filter chamber24. The position of closure element41in production position is suggested by the dotdashed rectangle.

Filter chamber24is created by means of a bore in housing20, which first of all, has to be produced all the way through, due to technical reasons, and which was then tightly sealed by means of insert element21. An axial flow channel22within the closure element is in connection with inlet channel23of housing20and leads into filter chamber24.

The mouth25of the housing bore or of filter chamber24toward the upper side is open, when filter insert10is pulled out.

It is further essential for the invention, that support profile12of filter insert10is arranged in a parallel way towards the center axis of filter carrier element40and towards its sliding direction, in particular that they are aligned in the same direction.

Filter carrier element40with filter insert10are lowered into filter chamber24along with closure element41, so that closure element41tightly seals mouth25of the bore that is open on the upper side and thus a closed filter chamber24is formed.

In production position, filter insert10is located inside of filter chamber24and can be freely flown through. The fluid reaches through the filter fabric of the individual disc filter elements11, from there into the central support profile12and then, via flow channels42,43to the outlet channel26in housing20.

After the production has ended, or when a replacement of filter insert10is necessary, filter carrier element40with the closure element41and filter insert10is again pulled out of filter chamber24, so that its mouth25is open again. In the pulled out state, as depicted inFIGS. 1 and 2, filter insert10is freely accessible and can be replaced or serviced.

Instead of filter insert10, a mechanical cleaning element, like a scraper or a wire brush, can be attached to filter carrier element40as well, in order to enable a cleaning of the filter chamber.

FIG. 3depicts a double filtering device100′, which basically consists of two partial filtering devices100according to the embodiment that has been described with reference toFIGS. 1 and 2, whereby these are here connected by means on a common housing20′.

Filter carrier elements40,40′ of double filtering device100′ can be moved individually, so that e.g. one of the filter inserts10′ can be moved out of filter chamber24′, while the other one remains in production operation.

In order to perform the distribution of the fluids to the individual partial filtering devices, the double filtering device100′ consists of additional switching valves60′,70′.

The lower switching valve70′ is used to distribute the fluid that is supplied at inlet channel71′ to the respective filter chambers. At switching valve60′, the individual flow paths from the filter chambers to an outlet channel61′ can also be closed in such a way, that one filter chamber can remain open while the other one is used for the production operation.

The exact function of the filtering device100′ results from the sectional view according toFIG. 4:

The left partial filtering device is depicted here in production operation. Filter insert10is lowered into filter chamber24. Closure element41at filter carrier element40closes the upper section of the left bore in housing20′, by means of which a sealed filter chamber24is formed.

The fluid enters through an inlet sub-channel23.1, which is fed via switching valve70′, into flow channel22and into filter chamber24, which is located above it. There, it enters through the individual disc filter elements11of filter insert10into the central support profile12and via flow channel42inside of closure element41into outlet channel26.1.

The right partial filtering device is set in waiting position. Filter chamber24′ is open at the top. Appropriate switching positions at switching valves60′,70′ ensure that no melt or any other filtered fluid can leak out of filter chamber24′ at the inlet- and outlet channels23.2,26.2.

FIG. 5depicts a section through the lower switching valve70′ for the incoming stream and the flow channels in the base of filtering device100′.

In the upper part ofFIG. 5, the base area of housing20is cut. The round elements are the closure elements21,21′ (compareFIG. 4), which allow that filter chambers24,24′ are created by one respective bore all the way through housing20′ in a simple way and then to seal the one end permanently by means of the inserted closure elements21,21′.

The actual switching valve70′ consists of two parallel plates72′,74′ and a slider element73′ which is located in between, and which can be shifted by means of a hydraulic or pneumatic drive76′.

Plate72′ consists of two pairs of angular sub-channels, where each pair is joined to the inlet sub-channels23.1,23.2, respectively. The central inlet channel71′ is arranged within plate74′, which is located opposite of it. Slider element73′ consists of a central recess75′, which is rectangular in the sectional view according toFIG. 5and which allows for different switching positions. In a top view onto inlet channel71′, the recess would have the shape of a horizontal eight. The three parallel, slot-shaped channels, which are connected via common areas on the plate surfaces, enable a deliberate connection of the paired slot channels which jointly lead into one inlet channel. Backflush bore holes77′ in slider element73′ enable a backflush of the filter insert by means of a flow reversal and the discharge of the melt cake towards the outside of the housing.

The upper switching valve60′ is constructed in the same way, but without any backflush bore holes.

The most important switching positions of the double filtering device100′ are depicted in the sectional views according toFIGS. 6ato6d, whereby the outlet valve60′ is always depicted on the left and the inlet valve70′ on the right.

In the position according toFIG. 6a, the right partial filtering device is fed by establishing a flow path from inlet channel71′ towards the right sub-channel23.1. The same can be said for the switching valve at outlet channel61′ which is depicted on the left: A connection to the left outlet sub-channel26.2is established via recess65′ inside of the slider element, which is connected to the right filter chamber24.

In the position according toFIG. 6b, both sub-channels23.1,23.2at switching valve70′ are fed from inlet channel71′, and at switching valve60′, both sub-channels26.1,26.2are connected to outlet channel61′. This position shows the parallel operation of both partial filtering devices, or it depicts the moment, when one partial filtering device is switched to the other partial filtering device.

The position according toFIG. 6conly allows a supply to the left inlet sub-channel23.2at switching valve70′ on the inlet side, and thus results in the operation of only the left partial filtering device. Also at switching valve60′ on the outlet side, only the left partial filtering device is connected to outlet channel61′ via the left outlet sub-channel26.2.

In the position according toFIG. 6d, the backflush for the filter insert in the right filter chamber24is performed while the production is maintained via the filter insert in the left filter chamber24′. The melt flows from inlet channel71′ via switching valve70into the left inlet sub-channel23.2and via the left filter chamber24towards the slider element of the upper switching valve60′, which leads to outlet channel61′. Slider element63′ is positioned in such a way, that its recess65′ is connected to both outlet sub-channels26.1,26.2at the same time, by means of the respective inner one of the two slot channels which strut apart in V-shape, which both form the outlet channels26.1,26.2and which can be seen in the exemplified switching valve70′ inFIG. 5.

With the main flow direction through the left filter chamber24′, there is a connection of the recess65′ inside of slider element63′ to the right filter chamber24, so that the melt does not only stream directly to the outlet channel61′, but that a transverse flow towards sub-channel26.1is formed as well. This flow runs opposite to the common flow direction in production operation through filter chamber24according toFIG. 6aand runs through the filter insert which is located there into the right inlet channel23.1.

At the lower switching valve70′, the melt can be discharged along with the removed dirt from the filter insert via the outer one of the two slot channels of inlet sub-channel23.1into the backflush bore hole77′ and through it towards the outside of switching valve70′.