Process for the manufacture of a filter

Abstract

A process for manufacturing a filter composed of fibers for a filter element (38), comprising at least the following process steps: - forming a filter wall (34) having a gradually increasing wall thickness of a filter medium (35) by depositing the fibers from a suspension; - stopping the deposition operation no sooner than upon obtaining a hollow filter body (36) that is closed at one end and consists of the filter medium (35) having a specifiable wall thickness; - cutting off the closed end (20) of the filter body (36); and - placing the filter body (36) between two end caps (50).

Description

[0001] Method for producing a filter

[0002] The invention relates to a method for producing a filter. DE 10 2016 013 166 A1 discloses a filter element designed as a replacement element, the filter medium of which is formed as a hollow body and extends between two end parts, particularly in the form of end caps, and is pleated with individual filter folds. This filter medium comprises a filter material made of cellulose.

[0003] The filter medium consisting of cellulose material can be used with particular advantage in the known solution for separating water from hydraulic oils, whereby the filter medium increases the volume of the water droplets in the water-oil mixture, which sink due to the density difference between water and oil and under the effect of gravity, whereby a separation process takes place under the influence of gravity.

[0004] The cellulose filter medium has a uniform thickness of more than 2 mm, with filter pleats of equal height and identical bending or folding radii on the valley and peak sides. With this uniform thickness and the uniform pleat geometry, a strong coalescence effect can be achieved, enabling particularly effective water separation with the known filter body. To produce the cellulose filter body for a filter medium, a manufacturing process is used that includes at least the following manufacturing steps:

[0005] - Moistening a flat filter mat made of cellulose material, pleating the moistened filter mat using a pleating machine, forming a cylindrical hollow body,

[0006] - Joining the two long sides of the hollow body by means of a welding and / or gluing process, and

[0007] - Drying the cellulose filter body.

[0008] DE 696 24 632 T2 discloses a filter element and a method for its production. The filter element has a cylindrical section formed from a so-called slurry of main fibers and microfibers, of which the main fibers have a fiber diameter of at least five micrometers and microfibers have a fiber diameter of less than five micrometers. A plurality of longitudinal grooves are formed in an outer and / or inner surface of the cylindrical section, whereby the cylindrical section has thin and thick sections around its circumference. The cylindrical section has a fiber density gradient in its circumferential direction, such that the thick section has a low density and the thin section, in contrast, has a high density.

[0009] The known process for producing such a filter element is characterized by the following steps:

[0010] Feeding the slurry containing the main fibers and the microfibers into a liquid container and

[0011] Drawing the slurry into a suction unit which is immersed in the slurry and has an inner mold with openings formed on its surface and a star-shaped cross-section and a suction cylinder accommodated within the inner mold and formed with a plurality of suction openings, wherein the suction openings are arranged substantially uniformly over the entire cylinder surface and the opening rate of the suction cylinder is lower than that of the inner mold.

[0012] In this way, pressure losses during filtration are reduced and filter efficiency is increased accordingly.

[0013] US 201 7 / 0341004 A1 discloses a candle filter having a hollow cylindrical element body which is closed on one side in one piece by a curved dome part and has on its other, opposite side an annular extension relative to its other outer circumference, by means of which the respective candle filter can be suspended vertically in an exchangeable manner in a pot-shaped filter housing for the filtration of hot gas streams.

[0014] The known candle filter can be obtained by vacuum forming in a solid manufacturing mold adapted to the candle shape, into which a suspension is introduced, consisting of high-temperature-resistant inorganic fibers mixed with at least one binder and a carrier liquid, in order to obtain a green body as an intermediate product, which is then dried and further processed towards the finished filter product.

[0015] Based on this prior art, the object of the invention is to provide an alternative, improved manufacturing process compared to the known processes.

[0016] According to the content of patent claim 1, a method for producing a filter from fibers for a filter element is achieved, comprising at least the following method steps: - construction of a filter wall with gradually increasing wall thickness of a filter medium by precoating the fibers from a suspension, termination of the precoating at the earliest after receipt of a hollow filter body closed at one end consisting of the filter medium of a predetermined wall thickness,

[0017] - Detaching the closed end of the filter body, and

[0018] - The filter body is held between two end caps.

[0019] With the manufacturing process according to the invention, a largely undisturbed, successive build-up of the filter medium is achieved by the pre-coating of fiber material from the suspension, without the need to use fixed manufacturing molds that already define the geometry of the filter from the outset and thus restrict it.

[0020] By maintaining a closed end of the hollow filter body, it is already inherently stable during the precoating process, which benefits the further, process-reliable construction of the element material.

[0021] The inventive cutting process by separating the closed end of the filter body results in a clean end surface or cut edge geometry, which serves as a connection for an associated end cap, which can be permanently and reliably attached to the filter body, for example, using an adhesive bond. If the filter body is equipped with end caps on both sides, a tradable filter unit is created that can be easily replaced with a new element when it is worn out.

[0022] This allows for the creation of seamless or seamless filter bodies that are circumferentially closed and have a uniform wall thickness. Depending on the selected wall thickness for the filter body, both the mechanical load capacity during subsequent filtration operation and the strength required for stability can be specified. Depending on the wall thickness, filter bodies and later filter elements can be manufactured that can be adapted to a wide variety of filtration tasks. This has no equivalent in the state of the art.

[0023] In addition, the corresponding manufacturing process can be largely automated, so that additional cost-intensive manufacturing steps can be eliminated, such as the production of longitudinal seams for the purpose of closing a filter material forming a hollow cylinder.

[0024] The manufacturing process according to the invention can utilize a wide variety of fiber materials and need not be limited to cellulose fibers. Ultimately, any fiber material that can be suspended and meets the subsequent filtration requirements in practice is suitable.

[0025] In a preferred embodiment of the method according to the invention, the suspension is stored in a tank in which a separation device is accommodated below a liquid level in the tank, on which a pressure gradient is built up by means of a vacuum device such that the fibers are deposited by precoating, forming the filter wall. This results in a homogeneous filter mat structure with even fiber distribution, which allows presetting within the framework of the desired filtration performance. In particular, when the separation device is segmented into different pressure ranges, different pressure gradients can then be built up along the outer wall of the separation device using the vacuum device, so that a wide variety of geometries can be achieved for the filter body depending on the subsequent application.For example, a thicker wall thickness can be achieved in the base area of ​​the filter body than in the head area. In particular, the precoating of fiber material toward the inside of the filter body allows for a denser fiber material deposit than on the opposite outer side. This gradual buildup leads to favorable filtration behavior for fluid flows that pass through the element material from the outside to the inside.

[0026] In a further preferred embodiment of the method according to the invention, it is provided that the separation device remains in the tank and the filter body obtained is withdrawn from the separation device and removed from the tank, or that the separation device is designed in the manner of a support tube body and removed from the tank together with the filter body. Since the separation device to be arranged in the tank can be adapted in the manner of a manufacturing tool comparable to a conventional support tube body for filter element material, this opens up the possibility of leaving the separation device as a support tube body in the filter body in order to complete the process towards a complete filter element. On the other hand, keeping the separation device in the tank guarantees a rapid sequence of filter bodies to be produced within the framework of rationalized production.

[0027] In a further preferred embodiment of the method according to the invention, the hollow filter body is formed from a hollow cylinder having two opposing central openings, at least one of which is at least partially kept free by an assignable end cap, and each end cap is provided with an annular receptacle for receiving the end of the filter body. For certain filtration tasks, it can also be provided that only one end cap has a central opening for a fluid passage, whereas the other opposite end cap is designed to be completely closed. In a particularly preferred embodiment of the method according to the invention, the closed end of the filter body is formed from a dome, in particular in the form of a shell, preferably in the form of a hollow hemisphere.The bowl-shaped design leads to increased pressure stability of the filter body, even during the precoating process.

[0028] Preferably, it can further be provided that at least one end cap is provided with a sealing device arranged in the direction of the adjacent central opening of the filter body. Thanks to the sealing device, the filter element can be connected to third-party components, for example, fluid-carrying components, in a filter housing.

[0029] In addition to this solution, the method according to the invention can provide that the filter body constructed from fiber material is surrounded by a further filter medium, preferably in pleated form, in order to achieve effective particle cleaning in an unfiltered stream by means of the further filter medium, which passes through the filter body or the filter element, and the filter medium constructed from pre-wetted fibers can serve to separate so-called varnish or oil aging products from a fluid stream and / or, as already described in the prior art, support the water separation, with regard to the coalescence effect of the fiber material used.

[0030] It is particularly advantageous to use cellulose fibers suspended in a large amount of water to form a suspension. This suspension may be provided with additional components, such as fillers, additives, and filter aids. The manufacturing process according to the invention results in filter bodies and filter elements formed therefrom, whose filter medium can be seamlessly configured in a variety of geometric shapes.

[0031] In the following, the process according to the invention is explained in more detail using a manufacturing device and the products obtained therewith. The figures show, in a schematic and not to scale, the

[0032] Fig. 1 shows a highly simplified structure of the manufacturing device;

[0033] Fig. 2 shows a filter body as obtained with the manufacturing device according to Fig. 1;

[0034] Fig. 3 and 4 show the filter body according to Fig. 2, which in a further manufacturing step results in a hollow cylindrical filter body according to Fig. 4 by means of end cutting according to Fig. 3;

[0035] Fig. 5, 6 and 7 once in longitudinal section, once in bottom view and once in perspective top view the filter body according to Fig. 2 with inserted support tube body forming a filter element as a whole;

[0036] Fig. 8, 9 and 10 show, once in longitudinal section, once in bottom view and once in perspective top view, a filter element body according to Fig. 4 with inserted support tube body to form another type of filter element; and

[0037] 11, 12 and 13 show the filter element according to FIGS. 8 to 10 in a corresponding representation with additional filter medium arranged on the circumference. Figure 1 schematically shows a fluid tank 10 which is used to store a liquid suspension. A separating device 14 is accommodated below a predeterminable liquid level 12 in the tank 10. This separating device 14 has an outer wall 16 which is penetrated by a continuous perforation which, for the sake of simplicity, is not shown in Figure 1. This outer wall 16 has a hollow cylindrical wall part 18 and an adjoining, dome-shaped wall part 20. For stiffening, the outer wall 16 can have a support device 22 constructed from longitudinal and transverse bars.Furthermore, the hollow cylindrical separating device 14 with its outer wall 16, as viewed in the direction of Figure 1, is designed to be open towards the bottom and is firmly connected to the corresponding tank wall 24, in particular in the transition to the lower tank wall area.

[0038] A collecting container 28 is connected to the respective fluid tank 10 as part of a vacuum device 26, which is connected on the inlet side to the lower tank wall 24 via a connection 30. With a further connection 32 and connecting line 33, the collecting container 28 is connected to a vacuum pump (not shown in detail), which can generate a negative pressure in the collecting container 28 during operation, as well as on the inside of the outer wall 16 of the separating device 14, which opens with its interior into the media-carrying connection 30. The possible flow direction from the interior of the separating device 14 via the connection 30 to the collecting container 28 and via the further connection 32 and line 33 to a vacuum pump is indicated by arrows in Figure 1.

[0039] The suspension held in the eluid or storage tank 10 comprises a liquid, for example water, which contains individual fibers not shown in detail. In addition to the respective fiber material, for example made of cellulose, other substances can be part of the suspension. These include, for example, fillers such as silicates (e.g. kaolin), carbonates (e.g. chalk), sulfates (e.g. gypsum or barium sulfate), oxides (e.g. titanium dioxide) and other fiber material, for example in the form of aramid fibers, carbon fibers, etc. Furthermore, additives can be introduced into the suspension, such as sizing agents, binder systems, dry and wet strength agents, pigments, dyes, dewatering and retention agents as well as defoamers. Diatomaceous earth, silica gel, perlite, zeolites and activated carbon, for example, have proven suitable filter aids for the suspension.

[0040] In order to maintain the liquid level 12 in the fluid tank 10, the suspension can be continuously replenished into the fluid tank 10 by means of a supply device (not shown in detail). In any case, however, the liquid level 12 of the suspension covers the separating device 14 along its upper side at a predeterminable distance during the precoating process.

[0041] When the vacuum pump of the vacuum device 26 is started, a pressure gradient builds up on the outer wall 16 of the separation device 14, with the result that the fibers from the suspension are successively deposited by precoating, forming a porous filter wall 34. The layered construction of the filter wall 34 in question thus takes place with a gradually increasing wall thickness of a filter medium 35 by precoating the fibers from the suspension, wherein the liquid or aqueous portions of the suspension, after the fibers have deposited on the outside of the outer wall 16 of the separation device 14, pass through their perforation via the lower connection 30 into the collecting container 28 and from there further in the direction of the vacuum pump via the further connection 32 and the line 33. The precoating or separation process can continue until a filter cake is separated, with a filter wall 34 of predeterminable wall thickness.In this way, a seamless filter cake or filter body 36 with a wall thickness that can be predetermined almost anywhere can be obtained in a simple manner. The liquid suspension is attracted by the pressure difference, i.e. the pressure gradient generated by the vacuum device 26, which leads to more and more fiber material, particularly in the form of cellulose fibers, accumulating uniformly around the outer wall 16 of the separation device 14 until the desired wall thickness for the filter wall 34 is achieved. A limitation of the achievable wall thickness is inevitably caused by gravity, in that the fiber material flows downwards at the separation device 14 as viewed in the direction of Figure 1, or by the finite differential pressure that arises because the perforation in the outer wall 16 of the separation device 14 becomes completely blocked with fiber material over time.

[0042] Once a filter body 36 according to the embodiment shown in Figure 1 has been obtained using the manufacturing method shown, the filter body 36 is removed from the separation device 14, the filter body 36 in question being shown as an example in Figure 2. In this procedure, the separation device 14 remains in the fluid tank 10 and is available for a renewed precoating process with fiber material for the purpose of producing a new filter body 36. Within the scope of an embodiment not shown in detail, it would be possible to divide the separation device 14 into individual pressure zones which build up different pressure gradients separately from one another in order to thus produce a wide variety of geometries for a filter body 36.It would thus be conceivable to build up a stronger pressure gradient in the base-side area of ​​the separation device 14, so that more fiber material is deposited on the base side and in this way a conical geometry that decreases noticeably towards the top is created on the outside of the filter body 36.

[0043] To complete and produce a filter element 38 as a whole, a support tube body 40, which is formed from longitudinal and transverse bars 42 and 44, respectively, can be introduced into the inside of the filter body 36, which is closed at the top end, as shown in Figures 5, 6, and 7. The longitudinal bars 42 form, as shown in Figure 6, a three-bladed flow guide body 46, which is radially enclosed at its free ends by the ring-like transverse bars 44. Between the transverse bars 44, a continuous perforation (not shown in detail) is introduced into the outer wall 48 of the relevant support tube body 40, which allows the fluid to be guided downwards on the inside of the support tube body 40 towards a lower end cap 50 when flowing through the filter element 38 from the outside to the inside.The annular end cap 50 has a central opening 52, which is bordered at the edge by a sealing ring 54 for sealing the filter element 38 to device parts (not shown in detail) of an associated filter housing. For this purpose, the end cap 50 has, as viewed in the direction of Figure 6, two diametrically opposite projecting wings 56, which allow the filter element 38 to be connected in the manner of a bayonet lock to connecting parts of the device housing of a filter device as a whole.

[0044] As Figures 2 and 5 to 7 further show, the filter body 36 has, on its side opposite the end cap 50, a dome-shaped wall part in the form of a half-shell 58, wherein the hemispherical shape merges integrally into the rest of the filter wall 34 with the same wall thickness.

[0045] The support tube body 40 is largely similar to the separation device 14 according to Figure 1, except for the upper dome-shaped wall part 20 of the separation device 14, and in this respect it is also possible, as shown in Figure 1, to remove the filter body 36 obtained by precoating together with the separation device 14 from the tank, so that the filter element 38 according to Figure 5 is then already obtained except for the end cap 50. With this solution, a corresponding separation device 14 would then have to be inserted into the tank 10 for a new separation or precoating process.

[0046] The filter body 36 according to the illustration in Fig. 2 can also represent a type of intermediate product for obtaining a further type of filter element 38 according to the illustration in Fig. 8. For this purpose, according to the illustration in Fig. 3, the upper, dome-shaped wall part 20 is separated by means of a fictitiously indicated separating cut 60, and according to the illustration in Fig. 4, the hollow cylindrical wall part 18 of the filter body 36 remains, with two opposite central openings 52. According to the illustration in Fig. 8, a correspondingly adapted support tube body 40 with 3-wing geometry can then be used, and the end of the filter body 36 is provided with two annular end caps 50, each with a sealing ring 54, in order to complete the filter element 38 as a whole.

[0047] As shown in particular in Fig. 10, at least one of the end caps 50 can again be provided with opposing wings 56 of a bayonet lock for the purpose of connecting the filter element to the connection points of a filter housing (not shown). Furthermore, in an embodiment of a filter element 38 (not shown in detail), it is possible to design one of the two end caps 50, in particular the lower end cap 50, as closed, and in this way the lower central opening 52 in the filter body 36 is closed, so that when flow through the filter element 38 from the outside to the inside and against the supporting effect of the support tube body 40, the filtrate flow is discharged exclusively via the upper annular end cap 50.

[0048] The embodiment of a filter element according to Figs. 11 to 13 largely corresponds to the embodiment shown in Figs. 8 to 10; however, the relevant filter body 36 made of fiber material is surrounded by an additional filter medium 62 which, contrary to the illustrations, can also be pleated instead of a hollow cylindrical structure. The relevant filter medium 62 can then primarily serve to separate particle contamination from a fluid stream, whereas the inner filter body 36 serves as a filter medium for cleaning off so-called varnish, which is not necessarily considered to be contaminated with particles. Furthermore, the inner filter body 36 can, as already explained, serve to dewater a fluid stream, since cellulose material in particular has the property of being able to absorb water.In this respect, oil-water separation can also be achieved, provided that the corresponding fluid flow is directed from the outside to the inside through the two-stage filter element 38. However, any remaining particulate contamination can then also be removed by the downstream filter body 36 in addition to the filter medium 62. In this respect, the filter body 36 made of fiber material also removes particulate contamination from a fluid flow.

Claims

Patent claims 1 . A method for producing a filter from fibers for a filter element (38) comprising at least the following method steps: - construction of a filter wall (34) with gradually increasing wall thickness of a filter medium (35) by washing the fibres from a suspension, - Termination of the precoating at the earliest after receipt of a hollow filter body (36) closed at one end consisting of the filter medium (35) of a predetermined wall thickness, - separating the closed end (20) of the filter body (36), and - receiving the filter body (36) between two end caps (50).

2. Method according to claim 1, characterized in that the filter body (36) is dried in a time sequence before or after the closed end (20) of the filter body (36) is separated.

3. Method according to claim 1 or 2, characterized in that the hollow filter body (36) is formed from a hollow cylinder which has two mutually opposite central openings (52), of which at least one (52) is kept at least partially free by an assignable end cap (50) and that the respective end cap (50) is provided with an annular receptacle for receiving the filter body (36) at the end.

4. Method according to one of the preceding claims, characterized in that the suspension is stored in a tank (10) in which a separating device (14) is accommodated below a liquid level (12) in the tank (10), at which a pressure gradient is built up by means of a vacuum device (26) in such a way that the fibers are deposited by precoating, building up the filter wall (34).

5. Method according to one of the preceding claims, characterized in that the separating device (14) remains in the tank (10) and the filter body (36) obtained in each case is removed from the tank (10) by means of the separating device (14), or in that the separating device (14) is designed in the manner of a support tube body (40) and is removed from the tank (10) together with the filter body (36).

6. Method according to one of the preceding claims, characterized in that the closed end (20) of the filter body (36) is formed from a dome, in particular in the form of a shell, preferably in the form of a hollow hemisphere.

7. Method according to one of the preceding claims, characterized in that the wall thickness of the filter body (36) is formed differently by a differently acting pressure gradient at the separation device (14) and / or that differently designed filter bodies (36) are produced by correspondingly adapted different geometries of the separation device (14).

8. Method according to one of the preceding claims, characterized in that at least one end cap (50) is provided with a sealing device (54) which is arranged in the direction of the adjacent central opening (52) of the filter body (36).

9. Method according to one of the preceding claims, characterized in that the filter body (36) constructed from fiber material is surrounded by a further filter medium (62), preferably in pleated form.

10. A process according to any one of the preceding claims, characterized in that the suspension comprises cellulose fibers in a sufficient amount of water and is preferably provided with further components, such as fillers, additives, and filter aids.

11. A filter element with a filter body produced by a process according to any one of the preceding claims 1 to 10.

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