Filter wheel filtration device for high pressure filtration of molten plastics

Abstract

A filter wheel filter device for high-pressure filtration of molten plastics, comprising at least a casing, which comprises at least: an inlet plate with at least one inlet passage, an outlet plate with at least one inlet and outlet passage, at least one spacer element arranged between the inlet and outlet plates, as well as a bearing ring (18) on which a filter wheel (20) arranged between the inlet and outlet plates is rotatably supported, and clamping pins (19.1) guided through the bearing ring (18), via which the inlet plate together with the outlet plate is clamped surrounding the bearing ring (18) inserted between the inlet and outlet plates, and the filter wheel (20) can be arranged between the inlet and outlet passages, respectively. a flow-through area is formed between the openings of the inlet and outlet passages facing the filter wheel (20), and the surfaces of all filter locations (22.1...22.13) which at least partially overlap this flow-through area (40), projected onto the inlet and outlet plates, together form an active pressure surface area (44), and a lubrication gap is formed between the sealing surfaces (23, 24, 25) of the filter wheel (20) and the inner surfaces of the inlet and outlet plates, respectively, a filter wheel filtration device (100), characterized in that: the cross-sectional area A2 of the bearing ring (18) is at least 9 times the cross-sectional area A1 of the central tensioning pin (19.1), and the cross-sectional area A1 of the central tensioning pin (19.1) is 0.1 to 0.4 times the area A3 of the active pressure surface area (44).

Description

[Technical field]

[0001] The invention relates to a filter wheel filtration device for high-pressure filtration of molten plastics having the features of the preamble of claim 1. [Background technology]

[0002] When filtering molten plastics, agglomerates or solid particles must be screened out before the melt can be fed to a further processing device, such as an extrusion device with a nozzle. In order to allow uninterrupted production, various types of filter configurations are known in which the filter filter can be replaced during continuous operation by providing a new, uncontaminated filter in the flow path and removing the contaminated filter from the flow path. A particular difficulty in filtering molten plastics is that the filtering must be carried out at high temperatures and high pressures, which in normal use are already 250-300 bar.

[0003] The filter device of the type mentioned at the beginning is basically described in DE-A-3302343 and EP-A-0569866 and has been continuously improved on the basis of this. Such a filter device allows the filtration of molten plastics and other fluids of medium to high viscosity, the limitation to low-viscosity media being due to the type of construction, as explained below. The filter wheel carrying the individual filter elements is arranged between two casing plates which are held at a certain distance from each other, so that on the one hand the filter wheel is still able to rotate and on the other hand the gap between the sealing surface of the filter wheel and the adjacent sealing surface of the casing plate is so narrow that no leakage flows are formed in the gap open towards the outer surface, characteristic of the viscosity of the medium to be filtered. In short, in the filter wheel filter device of the type mentioned at the beginning, it is not possible to achieve an airtight seal towards the outer surface, but rather the gap width is kept so small that the medium cannot flow along the gap open towards the outside between the filter wheel and the casing as far as the outer surface due to its viscosity. In contrast, low-viscosity aqueous media cannot be processed on the basis of the open design of the filter wheel filtration system, since they would run off at the edges.

[0004] DE 33 41 508 A1 shows another filter device of the type mentioned at the beginning, which further discloses a drive device which consists of a drive element in the form of a hydraulic cylinder attached to the side edge of the housing, a transmission lever and a freewheel unit which consists of a pinion which meshes with the outer toothing of the filter wheel and a freewheel which allows a return movement of the transmission lever without displacing the filter discs.

[0005] DE 35 22 050 A1 shows a filter wheel filtering device which has a drive device via a ratchet tooth arrangement formed on the outer circumferential surface of the filter wheel and a feed rod which engages with the tooth arrangement in order to move the filter wheel in steps.

[0006] DE 299 08 735 A1 describes a filter wheel filtration device with a backwashing device. For the backwashing, a device is provided for increasing the pressure in the backwashing conduit. Operation of the filtration device at high pressure and means for preventing leakage flows are not disclosed.

[0007] DE 39 02 061 A1 likewise describes a filter wheel filtration device with a backwashing device which has no special suitability for high-pressure applications.

[0008] The filter wheel filtration apparatus shown in WO 2014 / 184220 is tuned to minimize pressure fluctuations, but is again not expressly specified or suitable for high pressure applications.

[0009] A particular advantage of the filter device of the type mentioned at the beginning is that a number of individual filters can be arranged on the filter wheel, which are passed through successively and can be easily moved to a position on the opposite side of the flow path in the casing for cleaning purposes or replaced. The construction of the filter device is also simple and inexpensive due to the layered construction of the casing.

[0010] The main difficulty, however, lies in the tightness between the outer casing plates and the filter wheel enclosed between them. The casing parts must be clamped against one another while surrounding the filter wheel such that the flow pressure does not cause excessive expansion of the casing and thus the formation of corresponding leak points through which the fluid can flow out excessively at the side edges of the casing. On the other hand, the mobility of the filter wheel must be permanently present, so that the filter wheel cannot rotate any further if it is excessively pinched. This means that in all operating states, a certain minimum gap width must be present between the sealing surfaces on the end faces of the filter wheel and the opposing contact surfaces of the inlet and outlet plates on the casing side. The required gap width depends in each case on the fluid to be processed and on its viscosity, the processing temperature and the flow pressure in the area of ​​the filter location. While there is a basic effort, i.e. tightness against leakage flows towards the edges, a sufficient gap width is always also required so that only a very small outflow of the fluid over the sealing webs remains possible and a kind of lubricating film is formed by the fluid itself on the two end faces of the filter wheel.

[0011] By correspondingly adapting the height of the filter wheel and the height of the spacer element surrounding the filter wheel, which is also arranged between the inflow plate and the outflow plate, a specific gap width can be adjusted for the intended processing process, but this gap width is in the range of several micrometers, so that the spacer element and the associated filter wheel, which form the so-called inner pair and are fitted together between the inflow plate and the outflow plate, are very difficult to manufacture.In practice, it has been shown that even when the gap width is calculated and manufactured very carefully, problems with the mobility of the filter wheel occur.This problem can only be eliminated by reducing the preload, but this also creates problems of non-tightness.

[0012] In the current state-of-the-art concepts of filter wheel filtering devices, at least two filter locations are simultaneously present in each case in the cross-section through which the flow passes, which is referred to below as the through-flow area. The through-flow area is the surface area available for filtering, which is entered from the front. Usually, the first filter location overlaps the through-flow area partially, so that an operating pressure is generated in the entering filter cavity. The other filter location is located completely or almost completely inside the through-flow area. Part of the second filter location or part of the third filter location overlaps the through-flow area partially at their upper edges, as viewed in the direction of rotation. However, the filter cavity which is separated from the through-flow area and moves into or out of the through-flow area is completely under the operating pressure, even if it overlaps the through-flow area only over a small area. Thus, a pressure area larger than the through-flow area exists, and since there are no angular positions of the filter wheel in which the flow path is completely or substantially interrupted, an approximately constant pressure operation of the filtering device is possible.

[0013] The plastic contained in such a blocked filter point is still under operating pressure of up to 500 bar. Therefore, not only the directly flowed-through area and the adjacent surface area of ​​the filter point that overlaps the flow-through area are under pressure, but also the filter cavity that has already been moved out of the pressure area that is actively flowed through. Assuming that there are usually at least 10 filter points on the filter wheel, in particular 13 filter points, the pressure-loaded area extends in the direction of rotation from the first filter point that is just beginning to overlap the flow-through area to the last filter point before entering the filter change position. Thus, more than half of the filter points arranged on the filter wheel are under high internal pressure, which contributes to the widening of the lubrication gap and causes leakage flows.

[0014] DE 10 2017100032 A1 describes the relationships that arise with respect to the geometry of the filter gap during operation. The gap width does not have a geometrically constant size during operation, because the gap widens due to the internal pressure during filtering operation, and by inserting a gap width adaptation layer between the spacer element and the adjacent casing plate, a given operating point can be adjusted so that, on the one hand, the gap is of sufficient size to fill with a fluid that also acts as a lubricant and to allow the movement of the filter wheel, and, on the other hand, the gap width is limited to a width such that no significant leakage flows occur with respect to the maximum internal pressure during operation. Uncontrolled leakage flows are desirable to be avoided, so that components arranged on the outer surface of the filtering device, such as measuring sensors, pivotable doors in the filter exchange station, or drives for the stepped rotation of the filter wheel, are damaged by fluids that run off and solidify on the outer surface. Such adjustment of the operating point is easily possible for normal operating pressures of approximately 250 bar, up to a maximum of 300 bar, in particular by inserting a gap width adaptation layer, in which case it is desirable that mobility of the filter wheel in an almost pressure-free state is also possible, and that leakage flows are prevented or reduced under the maximum operating pressure.

[0015] The difficulty in adapting to certain operating conditions is not at all to design the filter for a constant high operating point within a narrow range, but to ensure operation in almost pressure-free conditions as well as up to the maximum operating pressure, where known concepts reach their limits at the above-mentioned maximum pressures of 250 bar to 300 bar. Summary of the Invention [Problem to be solved by the invention]

[0016] The object of the present invention is therefore to provide a high-pressure filter wheel filtration device in which the functionality of the filtration device in the unpressurized state should be guaranteed as well as at other operating points where a fluid with a high pressure of 500 bar or more is pressed through the filtration device without having to individually adapt the preload of the casing parts before or during operation. [Means for solving the problem]

[0017] This problem is solved by a filter wheel filtration device for high-pressure filtration of molten plastics having the features of claim 1.

[0018] The concept according to the invention provides that the design of the filter wheel filter device remains unchanged in principle, but that the housing tension pins supporting the bearing ring, the bearing ring itself, as well as the area of ​​the flow-through filter points and the adjacent pressure-loaded filter points are coordinated to one another in a special way.

[0019] Overall, this adjustment for high pressure filtration of at least 500 bar results in the filter wheel having an outer diameter, which defines the filter cavity and where the ring-shaped outer sealing surface begins, that is approximately the same as in prior art filter wheel filtration devices, and therefore the casing is also approximately the same size.

[0020] However, according to the prior art, the diameter of the inner ring-shaped sealing surface that defines the filter cavity is selected as small as possible in order to increase the radial extension and thus the filter area available for filtering, whereas according to the present invention, the filter locations are pushed aside by the outer edge of the filter wheel. In this case, the inner bearing ring and / or the inner sealing surface on the filter wheel appear as a large surface area that appears to be wasted. That is to say, the present invention deliberately turns its attention away from the obvious approach of increasing the filter area available for filtering in the filter wheel with a given structural size of the filter device housing or reducing the structural size of the filter device housing with a given filter area. At first glance, the arrangement of relatively small filter locations at the outer edge of a filter wheel with a large diameter, as defined by the present invention, is misconstrued as irrational and economically disadvantageous.

[0021] The invention provides for a special geometrical adjustment of the bearing ring, the casing tension pin and the so-called active pressure surface area, which includes all the areas of the filter locations that are simultaneously under the operating pressure. The active pressure surface area is the surface that is projected onto the inlet and outlet plates, i.e. the surface that exerts an expansion force on the casing in relation to the internal operating pressure and thus expands the lubrication gap between the filter wheel and the adjacent surface of the casing.

[0022] The area of ​​the active pressure surface area is usually greater than the through-flow area, since the filter locations which only partially overlap in area with the through-flow area are still completely under the operating internal pressure. the cross-sectional area A2 of the bearing ring is at least 9 times, in particular 9 to 13 times, the cross-sectional area A1 of the central tensioning pin; - The cross-sectional area A1 of the central clamping pin is 0.1 to 0.4 times the area A3 of the active pressure surface area It is stipulated that:

[0023] Preferably, a predefined slenderness ratio of the active pressure surface area with area A3 is defined, in which the central length of the arcuate active pressure surface area is 1.9 to 2.5 times its radial width. The length is measured for this purpose along a central pitch circle passing through the center of the filter site. If the filter site does not have a symmetrical profile, the surface centroid of the filter site is instead selected as the reference point for the pitch circle. This defines, in addition to other geometric criteria, that the active area is long and thin rather than short and wide.

[0024] Taking into account the high preload forces and the resulting surface pressures, preferred embodiments provide that the thickness of the inlet and outlet blocks, respectively, is at least 2.5 to 3.5 times the thickness of the bearing rings and / or spacer elements inserted between them.

[0025] The active pressure surface area is preferably limited to the area adjacent to the openings of the inlet and outlet channels. In order to avoid the filter cavity remaining under pressure after being moved out of the through-flow area, it is advantageous for at least one pressure relief hole to be provided in the casing, which opens into the path traced by the filter points during the rotation of the filter wheel and is connected via a flow passage to lead the fluid to the outer surface of the casing. The area of ​​the pressure relief hole thus forms a pressure drop and a tangential flow passage is provided which extends from the closed filter cavity, which is substantially under pressure, in the direction of rotation.

[0026] As a result, the previously flowed-through filter cavity, which is still under pressure, is suddenly depressurized when it is moved out of the flow-through area. As a result, only by the directly flowed-through filter points does the expansion of the casing and the widening of the gap between the filter wheel and the adjacent casing plate occur. However, there are no longer any filter chambers under pressure that contribute to the expansion of the casing outside the pressure area and which can only be depressurized gradually by the leakage flow.

[0027] The tangential pressure relief defined according to the invention is achieved by the fact that the filter point located at the front upper side in the direction of rotation overlaps the opening of the pressure relief hole when the filter point has completely left the pressure area and is no longer in flow connection with the through-flow area. Furthermore, it is geometrically defined that the pressure relief hole opens into the path described by the filter point during the rotation of the filter wheel and is connected to the outer surface of the housing via a flow passage so as to lead the fluid. It is important in this case that the distance between the opening of the pressure relief hole and the front upper edge, viewed in the direction of rotation, of the funnel-shaped openings of the inlet and outlet channels is always greater than the maximum arc length of the filter point. As a result, the filter cavity is first completely separated from the through-flow area and then the filter wheel must be rotated some further until a flow connection can be established between the closed, but still pressured, filter cavity and the pressure relief hole.

[0028] Since the molten plastic is compressible, the pressure relief is carried out independently by the escape of a small amount of molten plastic at the pressure relief hole, When the pressure compensation is terminated, the escape of the molten plastic from the filter cavity stops again abruptly, i.e. the filter cavity remains filled.

[0029] According to the invention, during the intentional single relief of pressure at each contaminated filter location, the number of pressure-loaded filter cavities can be limited to a maximum of three, at least two of which during operation partially overlap the through-flow area and one of which is moved towards the relief hole.

[0030] For pressure relief, it is necessary to discharge a small amount of the compressed plastic fluid at the filter location, so that this discharge is preferably carried out through a pressure relief passage that starts from the pressure relief hole and leads mainly to a backwash area provided on the underside of the filter wheel filtering device. The backwash device can peel off the contaminant particles adhering to the filter element, and for this purpose, it is necessary to discharge the molten plastic containing the contaminant particles, so that the underside of the filtering device is separated from the other devices and a suitable collection device can be provided there.

[0031] In particular, the pressure relief holes are provided on the inlet plate side. The backwash channel and the pressure relief channel should preferably end in as similar an area of ​​the filter as possible, i.e. in the lower area, since then the material can be led from there by gravity directly to a collecting vessel arranged below the filter.

[0032] At least one pressure relief hole is provided on the outlet plate side, in which the washed melt is present, which can also be connected directly to the pressure-free part of the backwash passage in the outlet plate of the housing. This allows the backwashing of the filter insert elements in the filter cavity, which is necessary in any case, to be carried out at least partially by the amount of melt plastic discharged via the tangential flow path for pressure relief. An additional function can thus be added by the intermittent fluid discharge for pressure relief, and the power of the drive of the backwashing device, which, for example, moves a piston, can be reduced to carry out the backwashing. Furthermore, less melt needs to be diverted from the production stream for backwashing.

[0033] That is to say, in filter wheel filtration systems which are anyway provided with a backwashing device, the pressure relief according to the invention does not, in the balance, result in significant losses of filtered medium.

[0034] According to another preferred embodiment of the invention, it is additionally envisaged to enable at least one radial pressure relief channel.

[0035] "Radial" in this sense means flow inward toward the center or outward toward the outer circumferential surface starting from the location of the filter cavity in the filter wheel; the flow direction does not have to be strictly radial in the geometric sense.

[0036] In particular, the bearing ring, on which the filter wheel is supported in a sliding bearing, can be used for further pressure relief. The molten plastic flowing through the filter gap, which widens in the vicinity of the pressure area, reaches the bearing ring, which is basically intended for the purpose of forming a sliding bearing. However, at high pressure operation, more molten plastic reaches the area of ​​the bearing ring locally than is necessary here for lubrication. In order to prevent the formation of axial leakage flows along the bearing ring, which exit in front of the housing inlet or outlet plate, at least one additional pressure relief hole is preferably provided, which is located in an angular position located to the side of the through-flow area or below the through-flow area and reaches up to the lowest point of the bearing ring. If the through-flow filter point is located, for example, at 3 o'clock, with the housing top side at 12 o'clock and the housing bottom side at 6 o'clock, the radial pressure relief hole is preferably located between 2 o'clock and 6 o'clock.

[0037] In a further advantageous embodiment, it is provided for to also capture and divert leakage flows arising from the pressure region towards the outer circumference of the filter wheel, which reach the region of the outer teeth of the filter wheel, which are necessary for the drive. If the molten plastic were to stick there and be transported to the outer surface of the housing, it could solidify, which could possibly damage the drive after several revolutions of the filter wheel. To prevent this, the invention provides for a further pressure relief opening to be provided in the gap between the teeth on the outer surface of the filter wheel and the adjacent spacer element, so that any melt that may have entered the gap can be led outwards by gravity, in particular also to the lower region of the housing, from where it can flow off into a collection vessel arranged below.

[0038] It is advantageous to provide at least one tangential pressure relief passage on the side of the inlet plate, since on this side there is free access to the filter cavity, whereas on the opposite side, i.e. on the rear side of the filter wheel, the opening is partly covered by a perforated plate which supports the actual filter element inserted in the filter cavity.

[0039] The cross section preferably does not decrease in the flow direction, i.e. from the pressure relief hole to the discharge opening on the underside of the housing, but rather increases in the extension of the flow passage, so that it is prevented that foreign bodies or plastic plugs, e.g. from accumulated residual material from the previous production cycle, or deteriorated material, can cause retention in the passage, which would prevent pressure relief. Such an arrangement with an increasing passage cross section preferably applies to all passages for leading off the material from the casing to the collection vessel.

[0040] The invention will be explained in more detail below with reference to an illustrative embodiment, the drawings showing in detail: FIG. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 is a plan view showing the mid-plane of a filter wheel filtering device according to the prior art. [Diagram 2] FIG. 2 is a plan view showing a filter wheel of the filter wheel filtering device according to the present invention. [Diagram 3] FIG. 2 is a perspective view showing a casing of the filter wheel filtering device. [Figure 4] FIG. 2 is a perspective view of FIG. 1 with the inlet plate of the casing removed. [Diagram 5] FIG. 1 is a perspective view showing the filter wheel filtration device without the filter wheel, in the mid-plane. [Figure 6] FIG. 1 is a perspective view of a filter wheel filtration apparatus with an inflow plate shown partially cut away and in see-through view. [Figure 7] FIG. 2 is a perspective view of the filter wheel filtering device with the filter wheel in the mid-plane. [Figure 8] FIG. 2 is a perspective view showing a cross section passing through the rotation axis of the filter wheel. [Figure 9] FIG. 9 is an enlarged detail view of FIG. 8. [Figure 10] 1 is a tension graph for a portion of a filtration device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] FIG. 1 is a plan view of a filter wheel filter device 100' according to the prior art in the middle plane. In this case, the inlet plate, which guides the fluid to the filter locations 21' on the rotatable filter wheel 20', has been removed. Behind it, an outlet plate 12' is arranged, which guides the fluid from each filter location 21' to the outside. The filter locations 21' are each delimited by a ring-shaped inner sealing surface 23', a ring-shaped outer sealing surface 24' and a web 25' extending between the inner sealing surface 23' and the outer sealing surface 24'. The filter wheel is surrounded by two relatively small intermediate plates 13', 14' on the left and one relatively large intermediate plate 15' on the right. In the region of the intermediate plate 15', there is a pressure-loaded active pressure surface area 44', which is shown diagrammatically on the filter wheel 20' by a dashed line. A bearing ring 18' is also assigned to the middle plane, through which a housing tensioning pin 19 is guided. A filter wheel 20' is supported on the bearing ring 18', forming a plain bearing therebetween.

[0043] 2 shows a plan view of an optimal filter wheel 20 according to the invention with a total of thirteen filter locations 21. The outer seal area 24 and at the same time the outer diameter 3 of the outer edge of the filter locations 21 are unchanged with respect to the filter wheel 20' of FIG.

[0044] The outer diameter of the bearing ring 18 is significantly increased. For comparison, the circumference 1 indicates the outer circumference of the bearing ring 18' in FIG. 1. Accordingly, the inner sealing surface 23 and the inner defining lines of the filter locations 21 are also shifted outwards. For comparison, the circumference 2 indicates the corresponding circumference in FIG. 1.

[0045] In Fig. 10 the force F versus strain ε is shown for the system casing clamping pin-bearing ring-casing plate plotted as a tension graph, a qualitative diagram not to scale, on the basis of which the following example of the design according to the invention of a filter wheel filtration device is explained.

[0046] The area A3 of the active pressure surface area associated with the three filter locations 21 is A3 = 100 cm 2 10. The design for high pressure filtration assumes a maximum operating pressure of 500 bar. This pressure creates an opening force of 500 kN in the active pressure surface area, which corresponds to about 50 tons, causing the opening of the filter gap between the filter wheel 20 and the inlet plate 11 or between the filter wheel 20 and the outlet plate 12 and thus an enhanced leakage flow. The slope of the line 5 in FIG. 10 corresponds to the spring constant of the clamping pin 19 guided through the bearing ring 18.

[0047] The package consisting of the inlet plate 11, the bearing ring 18 and the outlet plate 12, preloaded by the casing clamping pin 19, can be regarded with sufficient accuracy as an integral flange with the cross section of the bearing ring 18, since the inlet plate 11 and the outlet plate 12 are very rigid, especially if the thickness of the inlet plate 11 and the outlet plate 12, respectively, is preferably set to be 2.5 to 3.5 times the height, i.e. the axial extension, of the bearing ring 18, respectively.

[0048] For example, the area of ​​the clamping pin is A1 = 33 cm 2 and the ring area is A2 = 357m 2 Since the cross-sectional area of ​​the bearing ring 18, i.e. minus the central hole for the clamping pin, is the ring surface A2, its value is preferably about ten times the cross-sectional area A1 of the clamping pin 19, the spring constant is about ten times greater. The slope of line 6 corresponds - qualitatively and not to scale - to this spring constant.

[0049] At operating point B, a preload force F V The maximum opening force F generated during operation is A partially unloads the compressed package, but in this case the preload is not completely removed.

[0050] The lines descending towards the horizontal axis show, on the one hand, the deformation when a preload force is applied - in the absence of any expansion force due to pressure flow - and, on the other hand, the deformation when pressure is applied during operation.

[0051] The preload is adjusted so that the lubrication gap between the inflow plate 11 and the filter wheel 20 and between the outflow plate 12 and the filter wheel 20 is minimal, or even so that no lubrication gap exists at all any more.

[0052] 10, it can be seen that the deformation changes during operation very little, because the area relationship between the areas A1 and A2 defined according to the invention is selected to be in a ratio of 1:9 to 1:13 and thus significantly different, which leads in the diagram to a significantly higher gradient of line 6 and to such a small change in strain during operation that excessive gap widening and, as a result, significant leakage flows are avoided.

[0053] In this case, this computational design results in the structural configuration described above in comparison with Figures 1 and 2, where the filter points according to the invention are thinner and visually moved further outwards with respect to the prior art, and in the center there is a bearing ring that appears to be over-dimensioned, which runs counter to the usual efforts to maximize the filter area.

[0054] FIG. 3 shows a perspective view of the casing 10 of the filter wheel filtering device 100, i.e., a view of the inlet plate 11 with the inlet passage 13. The outlet plate 12 is connected to the inlet plate 11 via spacer elements 15, 16, between which an intermediate space is formed in which the filter wheel is supported. All three adjacent elements of the casing 10, i.e. the inlet plate 11, the spacer elements 15, 16 and the outlet plate 12, are screwed together via a total of seven casing clamping pins 19.1, 19.2, 19.3 and are clamped together by a preload designed for the expected operating pressure. The central axis of the casing clamping pins 19.1 in the center of the casing simultaneously constitutes the axis of rotation of the filter wheel. The drive 30 for the filter wheel is arranged on the outer surface of the casing 10.

[0055] FIG. 4 shows a perspective view of the filter wheel filtering device 100 similar to FIG. 1, but with the inlet plate removed, so that the filter wheel 20 located inside can be seen. Furthermore, a further spacer element 17 can be seen, which connects the two lateral spacer elements 15, 16 to one another without gaps at the upper housing edge. This means that the filter wheel 20 is almost completely surrounded on the outer periphery. The openings in the casing 10 are therefore only present in the lower region in the form of discharge openings 48, which serve to allow the deliberate outflow of the melt into a collection vessel arranged below the filtering device. In the illustrated embodiment, the filtering device has a drive acting on the annular toothing 21 via a drive pinion 31. In the case of an alternative drive via a ratchet which engages with a suitable toothing on the outer periphery, the casing has at least one further opening in the upper region at the engagement point of the drive.

[0056] The filter wheel 20 is provided in a known manner with a number of filter locations 22.1...22.13, in the illustrated embodiment with thirteen filter locations. Each of the filter locations 22.1...22.13 is delimited by an inner ring-shaped sealing web 23 on the surface of the filter wheel 20, an outer ring-shaped sealing web 24 and a sealing web 25 extending between them and running from the inside to the outside. A stationary bearing ring 18 is arranged in the center, on which the filter wheel 20 is supported. A plain bearing is formed between the outer surface of the bearing ring and the inner surface of the central bore of the filter wheel 20. An annular toothing 21 is formed on the outer peripheral surface of the filter wheel 20.

[0057] The casing clamping pins 19.1, 19.2, 19.3 cause compression of the spacer elements 15, 16, 17 clamped between the outer casing plates on the inside of the preload surface, thereby reducing the spacing between the inlet plate 11 and the outlet plate 12 and the filter wheel 20 enclosed between these plates.

[0058] The dotted lines correspond to the contours of the funnel-shaped openings of the inlet and outlet channels of the filter wheel 20 and indicate the through-flow area 40 available for filtration. The filter wheel 20 rotates counterclockwise. In the angular position of the filter wheel 20 shown in FIG. 2, the filter point 22.1 overlaps the through-flow area 40 partially. As a result, the working pressure is established over the entire filter point 22.1. The filter point 22.2 is located completely in the through-flow area 40. The filter point 22.3 also overlaps the through-flow area 40 partially, so that the working pressure is also established here. The filter point 22.4 is rotated out of the through-flow area 40, in which case the fluid stored there is still under the working pressure.

[0059] FIG. 5 shows a perspective view of a filter wheel filtering device 100 similar to that of FIGS. 1 and 2, but with the filter wheel also removed. To give an idea of ​​the position of the filter wheel, only the annular teeth 21 of the filter wheel are shown. The contour of the funnel-shaped opening 14.1 of the outlet passage 14 corresponds to the through-flow area 40. A backwash passage starts from the lateral opening 12.2 of the outlet plate 12, which opens into an elongated slit-shaped backwash nozzle 49 in the lower area of ​​the filter wheel. The fluid resulting from the backwash flows out through the casing opening 48.

[0060] FIG. 6 shows the filtering device 100 including all the housing elements 11, 12, 15, 16, 17 and the filter wheel 20, in which the area to the right of the inlet plate 11 of the housing, in which the inlet passage 13 is arranged, is shown in a partially cut-out and transparent view. On the left side of the housing, a filter change position 10.1 is provided, in which the inlet plate 11 is opened so that the filter elements can be changed there. The filter change position 10.1 can be closed by a door, not shown. It can be clearly seen that the inlet passage 13 widens into a funnel-shaped opening 13.1, the position and shape of which are the same as the funnel-shaped opening 14.1 in the outlet plate 12 (see FIG. 3). Between these funnel-shaped openings, a through-flow area 40 is formed, outlined by a dotted line, in which the molten plastic flows through the filter elements arranged in the filter locations 22.1...22.13.

[0061] In the position of the filter wheel 20 in FIG. 6, the filter point 22.5 overlaps exactly with the pressure relief hole 41, which opens laterally into the filter wheel 20 and continues downwards in the pressure relief channel 41.1. The filter cavity at the filter point 22.5 is therefore already pressure-free. When rotating counterclockwise, the following filter point 22.4 is still under high internal pressure. The filter point 22.4 no longer overlaps the flow-through area 40 and is completely blocked off by the sealing web 25 from the next following filter point 22.3. The filter points 22.2, 22.3 are completely located in the flow-through area 40. The filter point 22.1 is just beginning to overlap the flow-through area 40. If a filter change has been carried out beforehand, a pre-fill takes place at this position and internal pressure is built up.

[0062] A further pressure relief hole 42 leads directly from the side into the plain bearing surface between the inner circumferential surface of the bearing bore of the filter wheel 20 and the bearing ring 18, which is firmly fastened to the housing. This pressure relief hole leads downwards into a further pressure relief channel 42.1.

[0063] 7 shows a vertical section through the casing 10 with the filter wheel 20, where the cutting plane is in the mid-plane in which the lubrication gap is formed and runs parallel to the plane of the filter wheel 20. The dotted arrows indicate the approximate flow directions of the molten plastic starting from the filter points 22.2, 22.3 in the through-flow area 40 or in the area adjacent thereto towards the pressure relief holes 41, 42. These flow directions differ in that the flow towards the first pressure relief hole 41 above takes place within the orbit of the filter points 22.1...22.13 of the filter wheel and is therefore approximately "tangential", whereas the flow towards the second pressure relief hole 42 below overcomes the inner ring-shaped sealing web 23 of the filter wheel 20 and is therefore called "radial".

[0064] 8 shows a perspective cross section through the axis of rotation of the filter wheel 20, which is the same as the central axis of the housing clamping pin 19.1 and the central axis of the bearing ring 18. In the cross section plane, the lower pressure relief hole 42 is arranged, which continues downwards in a pressure relief channel 42.1.

[0065] An important detail regarding the pressure relief caused by the second pressure relief hole 42, the so-called "radial" pressure relief, becomes clear for the first time from the enlarged view of a part of FIG. 8 shown in FIG. 9. Where the bearing ring 18 and the bore of the filter wheel 20 come into contact with each other to form a plain bearing, the bearing ring 18 and the filter wheel 20 are each provided with a chamfer on their edge sides, so that a ring passage 43 with a triangular cross section is formed by the adjacent double chamfers. The volume of this ring passage is significantly enlarged compared to the ring gap of the plain bearing 26, and the molten plastic can be discharged for pressure relief without having to modify the casing part or other parts of the pair filter wheel 20 and bearing ring 18. [Explanation of symbols]

[0066] 100,100' Filter wheel filtration device 10,10' casing 10.1 Filter replacement position 11,11' Inlet plate 12,12' spill plate 13,13' Inflow passage 13.1 Funnel-shaped opening 14,14' Outflow passage 14.1 Funnel-shaped opening 15,16,17;15',16',17' spacer elements 18,18' bearing ring 19, 19', 19.1...19.3 Casing fastening pin 20,20' filter wheel 21,21' Circular dentition 22', 22, 22.1... 22.13 Filter location 23,23' inner seal web 24,24' outer seal web 25,25' Seal Web 26,26' Plain bearing 30 Drive unit 40 Through-flow area 41 Pressure relief hole 41.1 Pressure relief passage 42 Pressure relief hole 42.1 Pressure relief passages 43 Ring Passage 44,44' Active pressure surface area 48 Release aperture 49 Backwash nozzle

Claims

1. A filter wheel filtration device (100) for high pressure filtration of molten plastics, comprising at least a casing (10), said casing comprising at least: an inlet plate (11) with at least one inlet passage (13), an outflow plate (12) provided with at least one outflow passage (14); at least one spacer element (15, 16, 17) arranged between said inflow plate (11) and said outflow plate (12) as well as a bearing ring (18) on which a filter wheel (20) arranged between said inflow plate (11) and said outflow plate (12) is rotatably supported, a central clamping pin (19.1) guided through said bearing ring (18), by means of which said inlet plate (11) together with said outlet plate (12) are clamped surrounding said bearing ring (18) inserted between said inlet and outlet plates; It has the filter wheel (20) has a number of filter locations (22.1...22.13) which can be arranged between the inlet channel (13) and the outlet channel (14) and through which a flow can pass, a through-flow area (40) is formed between the openings (13.1, 14.1) of the inlet channel (13) and the outlet channel (14) facing the filter wheel (20), - all filter locations (22.1...22.13) which at least partially overlap the throughflow area (40) are projected onto the inlet plate (11) and the outlet plate (12) together forming one active pressure surface area (44), a lubrication gap is formed between the sealing surfaces (23, 24, 25) of the sealing webs of the filter wheel (20) and the inner surface of the inlet plate (11) and the inner surface of the outlet plate (12), In the filter wheel filtration device (100), - the cross-sectional area A2 of said bearing ring (18) is at least 9 times the cross-sectional area A1 of said central tensioning pin (19.1); - the cross-sectional area A1 of the central clamping pin (19.1) is between 0.1 and 0.4 times the area A3 of the active pressure surface area (44); A filter wheel filtration device (100).

2. The filter wheel filtration apparatus (100) of any preceding claim, wherein the center length of the arcuate active pressure surface area (44) is between 1.9 and 2.5 times its width.

3. The filter wheel filtration device (100) according to claim 1 or 2, characterized in that the thickness of the inlet block (11) and the outlet block (12), respectively, is at least 2.5 to 3.5 times the diameter of the fastening pin (19.1).

4. - the inlet plate (11) and / or the outlet plate (12) are provided with at least one pressure relief hole (41) which opens into the path described by the filter locations (22.1...22.13) during the rotation of the filter wheel (20) and which is connected via a pressure relief channel (41.1) to the outer surface of the casing (10) in such a way that the fluid is led therethrough, - when a filter location (22.1...22.13) overlaps at least one pressure relief hole (41), said filter location (22.1...22.13) does not overlap the through-flow area (40); A filter wheel filtering device (100) according to any one of claims 1 to 3, characterized in that it comprises a filter wheel filtering device (100).

5. 5. The filter wheel filtering device (100) according to claim 4, characterized in that at least one tangential pressure relief channel is formed inside the at least one lubrication gap, which extends between one of the openings (13.1) of the inlet passage (13) or the openings (14.1) of the outlet passage (14) and at least one pressure relief hole (41) which opens in front of the through-flow area (40) in the direction of rotation.

6. 6. The filter wheel filtering device (100) according to claim 5, characterized in that the distance between the opening of the pressure relief hole (41) and the respective front edge in the direction of rotation of the through-flow area (40) is greater than the maximum extension of the filter points (22.1...22.13) in the direction of rotation.

7. 7. The filter wheel filtering device (100) according to claim 1, characterized in that at least one radial pressure relief channel is formed inside the at least one lubrication gap, which extends between the through-flow area (40) and at least one pressure relief hole (42) in the inlet plate (11) and / or the outlet plate (12), which pressure relief hole (42) opens into the bearing ring (18) and is connected via a pressure relief passage (42.1) formed in the casing (10) to the outer surface of the casing (10) in such a way that the fluid is conducted therethrough.

8. 8. The filter wheel filtering device (100) according to claim 7, characterized in that a ring passage (43) is formed in the filter wheel (20) and / or in the casing (10), which is flow-connected to a ring-shaped plain bearing (26) formed between the bearing ring (18) and the filter wheel (20).

9. The filter wheel filtering device (100) of claim 8, characterized in that the ring passage (43) is formed by a chamfer on the outer peripheral surface of the bearing ring (18) and on the inner peripheral surface of the hole of the filter wheel (20) that receives the bearing ring (18).

10. 10. The filter wheel filtering device (100) according to claim 1, wherein the cross-sectional area A2 of the bearing ring (18) is at most 13 times the cross-sectional area A1 of the clamping pin (19.1).

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