Filter device for a plastic melt or another highly viscous fluid

Abstract

The invention relates to a filter device for a plastic melt or another highly viscous fluid, comprising a housing with an inlet plate and a discharge plate. At least one spacing element and a screen wheel which can be rotated by a drive device are arranged between the inlet plate and the discharge plate. The inlet plate and the discharge plate are clamped against each other with the inclusion of the spacing element via at least three housing clamping elements. An engagement point of the drive device on the screen wheel is arranged outside of the pretensioning surface. When viewed in the rotational direction, an angle α larger than 110° and smaller than 160° is formed on the screen wheel between a first line that extends between the pretensioning surface centroid on which a resulting frictional force F.sub.R acts and the center of the screen wheel and a second line between the center and the engagement point on which an advancing force Fv acts.

Claims

1. A filter device for a plastic melt or another highly viscous fluid, comprising: a housing having at least: an inlet plate with at least one inlet channel, a discharge plate with at least one discharge channel; spacer elements arranged between the inlet plate and the discharge plate; and at least three housing clamping elements, with which the inlet plate and the discharge plate are braced against one another, enclosing the spacer elements; a screen wheel rotatably supported in the housing between the inlet plate and the discharge plate, the screen wheel having of screen sections which can each be positioned and flowed through between the inlet channel and the discharge channel, wherein regions of the screen wheel which can be flowed through and to which fluid pressure can be applied lie within a pretensioned area which is spanned by the housing clamping elements; and a drive device having a drive element which exerts a feed force Fv on the screen wheel at an engagement point; wherein the engagement point of the drive device on the screen wheel is arranged outside the pretensioned area, wherein, when viewed in a direction of rotation of the screen wheel, an angle α greater than 90° and less than 160° is included on the screen wheel between a first line which extends between a surface center of gravity of the pretensioned area, at which a resulting frictional force F.sub.R acts, and the center of the screen wheel, and a second line between the center of the screen wheel and the engagement point, at which the feed force Fv acts, and wherein the screen wheel is surrounded by the spacer elements across more than 80% of a circumference of the screen wheel.

2. The filter device of claim 1, wherein a support point of the drive device and the engagement point are each arranged in an upper corner region of the housing.

3. The filter device of claim 2, wherein a vector of the feed force Fv exerted by the drive device on the screen wheel is outside the pretensioned area .

4. The filter device of claim 1, wherein a vector of the feed force Fv exerted by the drive device on the screen wheel is outside the pretensioned area .

5. The filter device of claim 1, wherein an outer circumference of the screen wheel is provided with at least one toothing and a feed ram of the drive device engages positively in the toothing at the engagement point.

6. The filter device of claim 5, wherein the toothing on the screen wheel is designed as a symmetrical toothing and the feed ram is a rotatably mounted pinion.

7. The filter device of claim 5, wherein the drive device is designed as a ratchet drive, and wherein the toothing on the screen wheel has flanks which are inclined in the direction of the feed ram.

8. The filter device of claim 5, wherein the drive element is connected to the feed ram via at least one transfer element.

9. The filter device of claim 1, wherein the spacer elements include two spacer elements which are spaced apart from one another on an underside of the filter device and form a discharge channel therebetween.

10. The filter device of claim 8, wherein the transfer element is mounted at a support point of the drive device in an axis extending through the inlet plate and the discharge plate.

11. The filter device of claim 10, wherein the spacer elements include two spacer elements which are spaced apart from one another on an underside of the filter device and form a discharge channel therebetween.

12. The filter device of claim 10, wherein with respect to the regions of the screen wheel that lie within the pretensioned area, more than 90% of a circumference of the screen wheel is surrounded by the spacer elements.

13. The filter device of claim 1, wherein the spacer elements include two spacer elements are provided which are separated from one another in an upper half of the filter device in a region of a support point and the engagement point.

14. The filter device of claim 13, wherein a support point of the drive device and the engagement point are each arranged in an upper corner region of the housing.

15. A filter device for a plastic melt or another highly viscous fluid, comprising: a housing having at least: an inlet plate with at least one inlet channel, a discharge plate with at least one discharge channel; spacer elements arranged between the inlet plate and the discharge plate; and at least three housing clamping elements, with which the inlet plate and the discharge plate are braced against one another, enclosing the spacer elements; a screen wheel rotatably supported in the housing between the inlet plate and the discharge plate, the screen wheel having screen sections which can each be positioned and flowed through between the inlet channel and the discharge channel, wherein regions of the screen wheel which can be flowed through and to which fluid pressure can be applied lie within a pretensioned area which is spanned by the housing clamping elements; and a drive device having a drive element which exerts a feed force Fv on the screen wheel at an engagement point; wherein the engagement point of the drive device on the screen wheel is arranged outside the pretensioned area, wherein, when viewed in a direction of rotation of the screen wheel, an angle a greater than 90° and less than 160° is included on the screen wheel between a first line which extends between a surface center of gravity of the pretensioned area, at which a resulting frictional force FR acts, and the center of the screen wheel, and a second line between the center of the screen wheel and the engagement point, at which the feed force Fv acts, and wherein with respect to the part regions of the screen wheel situated that lie within the pretensioned area surface, more than 90% of a circumference of the screen wheel is surrounded by the spacer elements.

16. The filter device of claim 15, wherein the spacer elements include two spacer elements are provided which are separated from one another in an upper half of the filter device in a region of a support point and the engagement point.

17. The filter device of claim 15, wherein an angle β of less than 60° is included between respective vectors of the resulting frictional force F.sub.R acting in the pretensioned area and the feed force Fv acting at the engagement point and straight lines leading through the respective vectors intersect outside the housing.

18. A filter device for a plastic melt or another highly viscous fluid, comprising: a housing having at least: an inlet plate with at least one inlet channel, a discharge plate with at least one discharge channel; spacer elements arranged between the inlet plate and the discharge plate; and at least three housing clamping elements, with which the inlet plate and the discharge plate are braced against one another, enclosing the spacer elements; a screen wheel rotatably supported in the housing between the inlet plate and the discharge plate, the screen wheel having screen sections which can each be positioned and flowed through between the inlet channel and the discharge channel, wherein regions of the screen wheel which can be flowed through and to which fluid pressure can be applied lie within a pretensioned area which is spanned by the housing clamping elements; and a drive device having a drive element which exerts a feed force Fv on the screen wheel at an engagement point; wherein the engagement point of the drive device on the screen wheel is arranged outside the pretensioned area, wherein, when viewed in a direction of rotation of the screen wheel, an angle α greater than 90° and less than 160° is included on the screen wheel between a first line which extends between a surface center of gravity of the pretensioned area, at which a resulting frictional force FR acts, and the center of the screen wheel, and a second line between the center of the screen wheel and the engagement point, at which the feed force Fv acts, and wherein an angle β of less than 60° is included between respective vectors of the resulting frictional force F.sub.R acting in the pretensioned area and the feed force Fv acting at the engagement point and straight lines leading through the respective vectors intersect outside the housing.

19. The filter device of claim 18, wherein the spacer elements include two spacer elements which are spaced apart from one another on an underside of the filter device and form a discharge channel therebetween.

Description

(1) The invention is described in more detail below with reference to the exemplary embodiments illustrated in the drawings. The Figures show in detail:

(2) FIG. 1 a perspective view of a housing of a filter device,

(3) FIG. 2a a filter device in plan view;

(4) FIG. 2b parts of the filtration device in perspective view; and

(5) FIGS. 3a, 3b each a schematic illustration of the forces acting on the filter device during operation.

(6) FIG. 1 shows a perspective view of a housing 10 of a filter device on the side of a discharge plate 12. FIG. 1 shows only the plane of the so-called inner pairing in full lines, which includes spacer elements 15, 16 and a screen wheel 20. The intermediate plane is enclosed between an inlet plate 11 and a discharge plate 12, both of which are shown as illustrated as imaginary or hidden lines.

(7) All three adjacent elements, i.e. the inlet plate 11, the spacer elements 15, 16 and the discharge plate 12, are connected via a total of six housing clamping elements 17.1 . . . 17.6 and braced against each other with a pretension designed for the operating pressure. The intermediate plane has only two interruptions on the outer circumference of the screen wheel 20: In the upper right corner, where a free space 41 is kept free for the arrangement of a drive or feed element, and on the underside, where a narrow discharge channel 42 is formed between the spacer elements 15, 16 to be able to discharge the fluid accumulating at the lower low point from the housing 10.

(8) The screen wheel 20 is designed in a basically known manner with a large number of screen sections 22, each of which is delimited by an inner annular sealing web 23, an outer annular sealing web 24 and webs 25 extending between them, which run from the inside to the outside. A hub 26 is provided in the middle to accommodate an axle or shaft to support the screen wheel 20 in the plates 11, 12 of the housing 10. Hub 26 can be used as an additional pretensioning element.

(9) The outer circumference of the screen wheel 20 has a ratchet toothing 21 with flanks that drop flat in one direction and jump back in the other.

(10) The housing clamping elements 17.1 to 17.6 cause a compression of the housing elements within a pretensioning area 40, in which the housing elements 11, 12, 15 and parts of the element 16 are strongly pressed against each other, thereby reducing the distance between the inlet and discharge plates 11, 12 and the screen wheel 20 enclosed between them. Beyond the imaginary line between the housing clamping elements 17.4, 17.5, i.e. laterally and below the free space 41 for the drive, there is no strong pretension, so that at this point, where no tightness is required, the friction between the housing plates 11, 12 and the screen wheel 20 is reduced.

(11) The circle designated by 14 indicates the position of the inlet and discharge channels and corresponds to the flow channel with direct flow at the screen wheel 20, which, however, as is basically known, is considerably widened immediately in front of and behind the screen area in order to make better use of the available screen area. Nevertheless, the region of the inlet or discharge channel or the flow channel 14 can be regarded as the position of the surface center of gravity of the pressurizable region. This pressurizable region is completely, or almost completely, within the preload area 40.

(12) An imaginary line between the pretensioning elements 17.3, 17.6 leads directly through the region of the flow channel 14. The connecting line between elements 17.1, 17.2 runs almost parallel to it. A deviation exists only in the position of the last two housing clamping elements 17.4, 17.5, since the lower housing clamping element 17.5 must be shifted further outwards to keep the discharge channel 42 free.

(13) FIG. 2a shows a mounted filter device 100 in plan view on the discharge side. A region 44 corresponds to the flow and pressure region, which is extended from the diameter of the inlet channel 13 or the discharge channel. It is symmetrically constructed, with its center of gravity in the region of the flow channel 14, which in turn is arranged slightly above a horizontal center axis in the housing 10. Accordingly, the direction of the restraining force F.sub.R is not entirely vertical but perpendicular to a radial connecting line between the center of the flow channel 14 and the center axis 18.

(14) A further line 46 represents the connecting line between the center 18 and an engagement point 32 of a feed ram 31 into the external toothing 21 of the screen wheel 20. A drive device 30 is formed by a drive element 34 in the form of a hydraulic cylinder that is supported on a bearing element 35, which in this design is mounted directly with the spacer element 15 in the intermediate plane between the plate elements 11, 12. The drive element 34, with its extendable piston, is connected via a first joint 36.1 to a transfer element in the form of a transfer lever 36, which is mounted at a support point 33 in the housing 10, namely on an axle that bridges the free space 41, and at the same time is mounted in both plate elements 11, 12, so that the drive forces act only exactly perpendicularly to the axis of rotation of the screen wheel 20 and asymmetrical distortion of the housing by insertion of the drive is avoided.

(15) A feed element is movably supported on the transfer lever 36 via a further joint 36.2 and is designed in the form of a feed ram 31 which engages with its tip in the toothing 21 at the engagement point 32 and exerts a feed force F.sub.V directed outwards from the housing 10 and, above all, away from the pretensioning region 40.

(16) FIG. 2b shows the filter device 100 in a perspective view on the discharge side, whereby both the screen wheel and the discharge plate have been removed for clarification in this illustration. The inlet plate 11 and the spacer elements 15, 16 as well as the complete drive device 30 of the housing are visible. When looking into the interior of the housing, first the inlet channel 13 in the inlet plate is visible, which expands into an annular segment that encompasses about 120°. The fluid, which exits through the inlet channel 13, can therefore spread unhindered in the pressurizable region 44 and flow through several screen sections of the screen wheel.

(17) This main filter region, in which the inlet channel 13 lies approximately in the center, is supplemented by two further segments 48.1, 48.2 above and below the center axis 18, which in the side view resemble the shape of a coffee filter. These segments 48.1, 48.2 are pressurized by projecting one of the cavities of the screen wheel 20 into the region 44 and pressurizing it from the intersection with the region 44.

(18) The lower segment 48.1 is a preflow area, i.e. the screen section entering there with the clockwise rotation of the screen wheel are pre-flooded with the fluid as soon as a screen section overlaps with region 44, especially if the screen at the relevant screen section has previously been replaced at a screen change position 49.

(19) The pretensioned surface region 44 indicated by the dashed line does not completely enclose the upper segment 48.2, so that a small region of the pressurizable area 44 protrudes. Apart from the fact that the pressure there is reduced in relation to the flow pressure in the region 44, because it is built up only indirectly by a slowed flow within a cavity when the cavity partially overlaps with the region 44, and that the real pretensioned surface extends outwards beyond the polygon course 44, which in the figures represents the pretensioned region, the small protruding region is also advantageous, so that air trapped there can escape if necessary after a screen change.

(20) FIG. 3a is a schematic illustration of the force relations and an explanation of the principle of the so-called “breathing deformation”. When the drive starts the continued rotation of the screen wheel 20—and only then—does a feed force F.sub.V act via a lever arm corresponding to line 46 in relation to the center 18. Due to the friction, the feed force F.sub.V counteracts a restraining force F.sub.R which varies slightly in location, direction and size depending on where the webs 23, 24, 25 of a screen section are located in the region of the flow channel at a point 43. The levers of both forces F.sub.R, F.sub.V include an angle α, which must be significantly larger than 90° and significantly smaller than 180°, otherwise the described elongation effects in the relevant sector of the screen wheel 20 between lines 45 and 46 cannot occur. Preferably the angle α is more than 110° and especially at 135°.

(21) If the force vectors F.sub.R, F.sub.V are extended backwards against their orientation, the lines of force intersect at a point outside the housing 10 at an acute angle β of more than 20° and less than 70°. The spring 47 symbolically represents the flexible sector of the screen wheel 20. As already described above, the force vector F.sub.R is to be assumed as always perpendicular to the effective lever length in the form of line 45, since point 43 moves during operation, depending on the momentary flow and pressure conditions, and the lever 45 thus lies on a radius. On the other hand, the force vector F.sub.V acts at a fixed engagement point 32 on the housing, so that the lever arm is firmly defined in the form of lines 46. However, depending on the direction of action of the drive, F.sub.V is not exactly perpendicular to line 46, as also illustrated in FIG. 3a. Thus, the relationship β=180°−α does not apply inevitably.

(22) Also, because of the temporarily variable point 43 as the assumed point of action of a resulting restraining force F.sub.R, it must be taken into account that the preferred angular dimension for α=110° . . . 135° is to be regarded as an average value, and that according to the “breathing deformation” an instantaneous angle α(t) is reduced or increased by a few degrees wave-like.

(23) If the drive stops again in order o carry out the retraction movement of the ram 31 and the transfer lever 36 or simply to pause until a new contamination of the screen area is registered, there is no longer any feed force F.sub.V and also no restraining force F.sub.R as a reaction force. This situation is shown in FIG. 3b. During this time interval, the screen wheel 20 can relax in the previously elongated, upper sector and thereby take on its original shape, increasing the width of the screen wheel 20, temporarily reducing the gap width and thus increasing the sealing effect.