WO2021069600A2

WO2021069600A2 - Method for producing a coated filter element, application device for coating a filter body, and coated filter element

Info

Publication number: WO2021069600A2
Application number: PCT/EP2020/078293
Authority: WO
Inventors: Walter Herding; Urs Herding; Christoph WEIH; Stefan Hajek
Original assignee: Herding Gmbh Filtertechnik
Priority date: 2019-10-10
Filing date: 2020-10-08
Publication date: 2021-04-15
Also published as: DE102019127302A1; WO2021069600A3

Abstract

The invention relates to a method for producing a coated filter element (2), comprising the following steps: providing a filter body (4); and thermal spraying of a plastic material (30) onto the filter body (4) by means of an application device (32) such that the thermally sprayed plastic material (30) forms a porous and fluid-permeable surface filtration layer (28) on the filter body (4). The invention also relates to a correspondingly produced filter element.

Description

Method for producing a coated filter element, application device for coating a filter body, and coated filter element The invention relates to a method for producing a coated filter element, an application device for coating a filter body, and a coated filter element.

In the method according to the invention for producing a coated filter element, a filter body is provided and a porous and fluid-permeable surface filtration layer is formed on the filter body by means of thermal spraying of a plastic material. The filter body can in particular be a sintered filter body, for example made of sintered plastic material such as polyethylene, polypropylene, polyamide, polyimide, polysulfone, polysulfide, in particular polyphenylene sulfide, or polymethacrylate, in particular polymethyl methacrylate.

The plastic material can be in powder form and in particular comprise pure plastic powder or mixtures of plastic with other materials such as metals and / or ceramics, for example Cu, Ag, Ti0 ₂ . If plastic powder is referred to in the following in a simplified manner, it is to be understood that this term refers to all of these possibilities mentioned.

Sintered filter elements with filter bodies made of plastic, in particular made of sintered polyethylene particles, which have a surface filtration layer are known from the prior art. The surface filtration layer consists of a composition of plastic particles that contains a non-stick component such as polytetrafluoroethylene (PTFE). To form the surface filtration layer, the composition or a precursor of the composition is dissolved, emulsified or dispersed in a liquid phase and the resulting solution, emulsion or suspension is sprayed onto the filter body. The surface film then forms with evaporation of the liquid phase. tration layer, if necessary after corresponding crosslinking or curing processes have taken place.

One object of the invention is to provide an improved method for forming a porous and fluid-permeable surface filtration layer on a filter body.

The method already mentioned at the beginning for producing a coated filter element according to a first aspect of the present invention comprises the steps: providing a filter body and thermal spraying of a plastic material onto the filter body by an application device, such that the thermally sprayed plastic material is a forms porous and fluid-permeable surface filtration layer. The surface filtration layer proposed according to the invention is formed on the surface of a porous filter body, in particular a porous filter body made of plastic particles sintered together, in particular one of the plastic materials mentioned at the beginning, by a novel application process that does not require the production of a sprayable solution, emulsion or suspension and with which in principle no curing or crosslinking reactions are required. For this purpose, the method proposed here makes use of techniques for the formation of the surface filtration layer, such as are used in thermal spraying, in particular of metal powders, ceramic powders or other materials with a high melting point. In the case of thermal spraying of metals, ceramics or plastics, the aim is normally to form a coating that is as uniform and homogeneous as possible with the smoothest possible surface on the substrate.

In thermal spraying, a material that is initially powdery is converted into a molten state, usually with the help of a flame. The melted particles of the material to be applied are then sprayed onto a substrate to be coated with high kinetic energy. Due to their molten state and the high impact energy, the particles can diverge somewhat after they have been applied to the substrate. In this way, the individual particles come into contact with each other after application and combine to form a homogeneous and smooth one Surface layer (hereinafter also referred to as coating). The diverging particles can also come into particularly intimate contact with the substrate surface, in particular with irregularities in the material structure on the surface and thus anchor themselves firmly to the substrate surface. The spreading of the particles is promoted by the transfer of thermal energy to the material to be sprayed on. In principle, this can be achieved by efficient transfer of thermal energy to the individual particles in the spray jet. Another measure that promotes the formation of a high-quality surface layer is to heat the substrate to a sufficiently high temperature in a respective area to be coated or to keep it at such a sufficiently high temperature. The latter measure is particularly interesting for coating materials that have a low to medium melting range because it allows the material powder to be melted indirectly via a protective gas layer. In this way, direct contact of the material powder with a flame used for melting can be avoided. Because the material powder does not have to be exposed to the highly oxidative conditions prevailing in a flame, the occurrence of undesired oxidation reactions during or as a consequence of melting can be effectively suppressed with an indirect transfer of thermal energy from the flame to the material powder. For the flame spraying of plastic powders, which generally have a comparatively low melting range, the indirect transfer of thermal energy (usually by radiant heat) from a flame to the plastic powder to be melted via a protective jacket made of inert gas has proven to be a useful means of Choice developed. In the case of other coating materials that, like many metals or even ceramics, have a very high melting point or melting range, this indirect procedure is not easily possible because the substrate to be coated is not sufficiently heat-resistant to be heated to a temperature at which the sprayed-on particles remain fluid enough to run into one another sufficiently after hitting the substrate surface. In such cases, the necessary flowability of the particles to be sprayed on must be ensured by sufficient melting of the individual particles before they strike the substrate surface. For this purpose, the metal powder or ceramic powder to be applied is often fed directly into the flame. For the reasons mentioned above, when thermally spraying plastic powders with a low to medium melting range to form a high-quality coating, efforts have been made to avoid direct contact between the plastic powder to be sprayed on and a flame used to introduce the thermal energy required to melt the plastic.

The present invention describes a solution with which molten plastic material can be applied as a surface filtration layer to a filter body with a porous structure by means of a thermal spraying process. The surface filtration layer formed in this way penetrates into the pores of the filter body present on the surface and thus reduces the cross section of these pores. However, it has been found that the process conditions can be set so that there is no complete blocking of the pores of the filter body and the forming coating of sprayed-on plastic material remains porous enough that the coated filter body continues to be permeable to the fluid phase of a Raw fluids loaded with solids to be filtered out remain, but solid particles to be filtered out remain caught on the porous coating and cannot penetrate into the pore structure of the filter body. For this reason, a filter body provided with a coating formed in this way is suitable for filtering solid particles from fluids by means of surface filtration. The coating formed according to the invention by means of thermal spraying of a plastic material should accordingly be referred to as a surface filtration layer. Examples of conventionally known flame spraying experiences are wire flame spraying, atmospheric plasma spraying, powder flame spraying, and plastic flame spraying.It has been shown that all of these flame spraying methods can in principle also be used to form a porous coating according to the invention if the modifications described here are observed . In the flame spraying process, a powdery coating material made of metal, ceramic or plastic is melted by means of a flame and the melted particles of the coating material thus formed are then applied to a substrate to be coated by a conveying fluid. Conventional flame spraying processes are used to form coatings for corrosion protection and to increase the chemical resistance of workpieces. The coatings conventionally produced by means of flame spraying are not permeable to fluids. Conventionally known designs of plastic flame spraying, in which the plastic powder to be applied to the substrate is not introduced directly into a flame in order to melt the plastic powder, but rather the plastic powder is guided past the flame and thus indirectly melted, have proven to be unsuitable for Production of coverings or coatings that are suitable as surface filtration layers.

Surprisingly, it has been found that coverings or coatings suitable for surface filtration can be produced from plastic materials such as polyethylene, polyamide, polyvinylidene fluoride, polyetheretherketone, polytetrafluoroethylene or mixtures of these materials if one ensures that an efficient transfer of thermal energy from the flame to the Particles of the plastic material take place so that they are melted before they hit the filter body to be coated and are sufficiently flowable.

If this energy transfer takes place very efficiently, the spray jet formed by melted plastic particles and a conveying fluid can be guided comparatively quickly over the surface of the filter body to be coated. In this process, only relatively moderate heating of the areas of the filter body that have just been coated results. Obviously, these process conditions lead to the formation of a coating or a coating made of the plastic material on the surface of the filter body, which on the one hand adheres well to the filter body and effectively reduces the size of the pores of the filter body opening onto the surface, but nevertheless a Retains sufficient residual porosity so that the pressure drop across the filter element remains within an acceptable range. In addition, it was found that a coating according to the invention, despite its porosity, has an only slightly fissured and thus comparatively smooth surface, so that solid particles deposited on this upper side fall off when pressure pulses are applied to the filter element. Therefore, such a filter element coated according to the invention is suitable for recurring cleaning by a countercurrent pulse method.

Another advantage arises from the fact that the thermally sprayed surface filtration layer according to the invention does not require a binder and therefore additional lent has an increased chemical stability compared to the previously used surface filtration layers.

In order to improve the transfer of thermal energy to the particles 5 of the plastic powder to be melted, the plastic material can even be passed directly through a flame and so the particles of the plastic powder can be melted directly through the flame. As an experimental finding, it has been found that sufficiently pure porous layers or coatings can be produced on porous filter bodies in this way, even though the plastic material was exposed to the highly oxidative environment in a flame.

An essential aspect of the indirect charging of the plastic powder, which is conventionally practiced for plastic powder during flame spraying, via an inert gas layer or protective gas layer (e.g. air, nitrogen, noble gas) formed between the flame and the plastic powder, is that the strongly oxidative conditions in a flame promote chemical reactions and thus change The chemical nature of the plastic material to be sprayed on as a coating can be expected when the plastic powder to be melted is passed through the flame. Supplying plastic powder in such a way that the plastic powder is isolated from the flame by an inert insulating gas / protective gas, on the other hand, suppresses undesired chemical reactions of the plastic powder in the oxidative environment of the flame. In this way it can be ensured that the plastic material maintains a desired chemical composition over the entire injection molding process and thus ultimately controls the quality of the coating. The conventionally practiced indirect transfer of energy from the flame to the plastic powder has another positive effect: Because the indirect transfer of thermal energy from the flame to the plastic material mainly takes place through thermal radiation at temperatures of around 3000 ° C, the plastic powder must be compared be slowly passed the flame so that a sufficient

Melting of the plastic powder takes place. This results in a comparatively slow conveying speed for the plastic powder in the spray jet, with the result that the spray jet applies fewer plastic particles per unit of time to the substrate to be coated. The spray jet must therefore be guided more slowly over the substrate to be coated, so that more thermal energy per unit area is applied to the substrate during the spraying process is transmitted. As a result, the substrate heats up, the more so the slower the spray jet is guided over the substrate surface. The comparatively strong heating of the substrate then facilitates the formation of a relatively homogeneous coating with a smooth surface on the substrate because the plastic particles solidify more slowly after they have been applied to the substrate.

As a result of the direct introduction into the flame as suggested here, particles of the plastic material are melted quickly. This makes it possible, at a higher conveying speed of molten plastic particles in the spray jet, to spray a larger amount of plastic material onto the filter body per unit of time. With the same amount of molten plastic material, a shorter time is required in the method according to the invention to apply the plastic material to the filter body. For this reason, with the method according to the invention, the heat input per area on the filter body is smaller than with conventional plastic flame spraying. In the end, it turned out that this effect makes it possible to spray porous coatings onto porous filter bodies so that the coating can serve as a surface filtration layer. The plastic material can be fed axially or radially to the flame. In the case of axial feeding, the plastic material is guided along a direction in which the flame extends. This enables the plastic material to be heated evenly by the flame. Radial feeding of the plastic material means the lateral introduction of the plastic material into a flame. The radial feed allows a lighter constructive solution than the axial feed. The plastic material can be fed into the flame as pure plastic powder if the flowability is sufficient. Alternatively, the plastic material can be supplied to the flame in a colloidal configuration (as a solution, emulsion or suspension) with the aid of a carrier fluid present in liquid or gaseous form. In particular, the particulate plastic material can be fed to the flame in the form of a suspension, with particles of the plastic material being transported in a carrier liquid. This method of proceeding, which is useful, for example, with plastic materials that contain poly tetrafluoroethylene (PTFE) or consist entirely of PTFE, should be understood by the term “feeding plastic powder”. The main component of the filter body can be a sintered material, in particular a sintered plastic material such as, for example, the plastics or mixtures specified above. Sintering describes a type of formation of a sintered structure from individual particles into a solid body under the action of heat. The starting material for the formation of a solid body with a sintered structure is normally in powder form, ie composed of individual starting material particles. During sintering, the powdery starting material combines and the starting material particles form a coherent solid structure, the sintered structure. The formation of the sintered structure, in particular its structure, can be controlled by the sintering temperature and the sintering time. During sintering, the initially powdery material solidifies primarily through diffusion, i.e. migration of atoms of individual starting material particles in contact with one another via a contact point into a respective adjacent starting material particle, and recrystallization, ie new crystal formations at work-hardened points of the sintered structure. To form filter bodies by means of sintering processes, the exertion of pressure during the sintering process is avoided. As a rule, the procedure is such that the powdery starting material is not pressed, but is poured into a sintering mold that is vibrated while the powder is being poured in so that the powder particles take up a reasonably tight packing. A porous filter can thus be created during sintering, which enables a fluid - in particular gas or liquid - to flow through.

The plastic material thermally sprayed on to form a porous surface filtration layer can preferably comprise polyethylene (PE), polyamide (PA), polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) particles or a mixture of these materials. In particular, good results have been achieved when a plastic material has been sprayed on which contains PA, PE, PVDF, PEEK or a mixture of these materials as the main component with an admixture of polytetrafluoroethylene (PTFE) particles in order to achieve non-stick properties. The thermally sprayed-on plastic material can contain other admixtures, for example metals, in particular silver, to form an antibacterial layer, or ceramics such as Ti0 ₂ / VO to form a catalytic layer. Experiments on the part of the applicant have shown that these materials can be used to produce high-quality porous coatings in particular when the art powder - be it as a free-flowing powder or with the help of an auxiliary material, such as an emulsion or suspension - is fed directly into the flame and is melted in the flame without the interposition of a protective or insulating (gas) jacket.

The melted plastic powder can be transported to the filter body by a conveying fluid, in particular a conveying gas or a conveying liquid. The delivery liquid can be a suspension or in any case form a suspension together with the plastic material to be sprayed on. The conveying fluid forms a carrier fluid for the particles of the plastic powder and ensures that the melted plastic material is applied quickly and precisely to the filter body. The particles of the plastic powder can already be carried by the conveying fluid to the flame in the solid state and then transported to the surface of the filter body in the still solid or already molten state. The conveying fluid and the particles of the plastic powder form a spray jet directed from the application device to the surface of the filter body. As a rule, the flame of the application device will also be directed onto the surface of the filter body, so that the spray jet and the flame are directed essentially parallel to one another.

The molten plastic material is usually sprayed onto the filter body in particulate form. A desired permeability or porosity of the surface filtration layer can be influenced by setting the particle speed at which the plastic particles move in the spray jet. The particle speed of the plastic material depends in particular on the conveying speed of the conveying fluid, the conveying speed being understood as the speed at which the conveying fluid flows from the application device to the surface of the filter body. The higher the particle speed or the conveying speed is set, the lower the resulting porosity or permeability of the surface filtration layer will be. This may be related to the fact that during thermal spraying, increasing flow of sprayed-on plastic particles onto or on the surface of the filter body and / or increasing compaction of the sprayed-on layer by subsequent plastic particles lead to a decreasing porosity or permeability of the sprayed-on layer. Both the merging and the compaction process lead to the The number of pores in the coating is reduced because more and more pores are closed. At the same time, the diameter of the pores that still exist becomes smaller and smaller with increasing flow into one another and / or compaction. The conveying speed or particle speed of the plastic material in the spray jet can be adjusted, for example, by means of a nozzle in the application device and the pressure conditions upstream and downstream of the nozzle.

The porosity is defined as the ratio between the void volume and the total volume of a substance. The higher the value of the porosity, the higher the permeability of the surface filtration coatings described here.

The resulting porosity of the surface filtration layer is also dependent on the temperature to which the filter body is heated during thermal spraying. The warmer the filter body, the slower the sprayed-on plastic material solidifies and therefore remains flowable longer after it hits the filter surface. The porosity and thus also the permeability of the sprayed-on layer or of the sprayed-on coating decreases with increasing temperature of the filter body. It is assumed that the fundamental thing is to be found in the fact that sprayed-on particles from the plastic material flow into the pores of the filter body on the one hand and combine with other sprayed-on particles from the plastic material on the other. Both processes are favored if the sprayed-on particles are kept in a flowable state for as long as possible.

The particle speed in the spray jet can be greater than 10 m / s, in particular greater than 60 m / s, or greater than 90 m / s. For common thermal spraying processes such as flame spraying or atmospheric plasma spraying, particle speeds can be between 10 and 450 m / s, in particular between 60 and 200 m / s, or between 90 and 200 m / s. In the case of high-speed spray processes such as HVOF (= High Velocity Oxygen Fuel), the particle speed can also be selected to be higher, namely between 450 m / s and 800 m / s, or between 450 m / s and 650 m / s. In one embodiment, the by the conveying fluid and molten

Spray jet formed by plastic powder particles with an additional fluid be hit in order to form a spray cone impinging on the filter body of the spray jet in the desired manner. The spray cone can in particular be shaped in such a way that it covers a specific impingement surface on the filter body. By applying the additional fluid to the spray jet, the impingement surface formed by the spray jet on the filter body can be enlarged or widened. The greater the expansion of the spray jet, the larger the area coated on the filter body at a given point in time. This relationship is particularly important with regard to setting the transfer of thermal energy through the flame of the application device to the filter body, because the larger the impact area, the faster the spray jet can be moved over the filter body and the less the heating of the Filter body. Furthermore, with the aid of this widening, the spray jet can better reach contours or structures on the surface of the filter body, as a result of which the surface filtration layer is formed evenly on the filter body.

The additional fluid can be introduced into the spray jet by means of an attachment attached to the application device. The attachment can in particular have a flow profile surrounding the spray jet (also referred to as a shroud). This flow profile or shroud can, for example, be designed to surround the spray jet formed from conveying fluid and plastic particles in a ring shape. The additional fluid can in particular be introduced into the spray jet at an angle or in the most possible axial direction. The introduction can take place in a ring, i.e. as evenly as possible around the spray jet, or only at individual points around the spray jet. In the case of an annular introduction, several outlet holes can be evenly distributed over the attachment in the circumferential direction. The exit holes can also be selected in such a way that two exit holes are paired in opposite areas of the attachment. By suitably supplying the additional fluid, the spray cone can in particular assume a wider, oval shape.

The spray jet can be guided over the surface of the filter body to be coated at a speed between 0.05 m / s and 5 m / s. At these relatively high speeds, the spray jet and / or the flame only lingers for a very short time at a predetermined point on the filter body. This measure helps to keep the temperature of the filter body above the entire injection process only slightly increased. The resulting low heat input per area of the filter body by the spray jet and / or the flame causes the plastic material to solidify quickly after being applied to the filter body and therefore only remain flowable for a correspondingly shorter period of time.

The distance between the nozzle tip of the application device and the surface to be coated can in particular be set between 0.05 m and 0.5 m. This measure also contributes to the fact that the temperature of the filter body increases only slightly over the entire spraying process.

The spray jet can have a mass flow of 5 g / min to 250 g / min (0.08 g / s to 4.2 g / s), the mass flow relating to the mass of plastic material conveyed in the spray jet per unit of time. If metallic additives are added, the mass flow can be even higher, for example up to 8.4 g / s. This mass flow allows the heat transfer required to melt the plastic material to take place directly in the flame and the spray jet to move quickly over the surface of the filter body. In addition to the already described possibility of reducing the input of thermal energy onto the filter body and thus producing the porosity desired for a surface filtration layer, a surface filtration layer can also be quickly produced on the filter body in this way.

The conveying fluid used to transport the plastic material to be applied as a coating can be a gas, a liquid or even a suspension.

The plastic material in the application device can be conveyed to the flame with a fluidized bed conveyor, a plate conveyor, a disk conveyor, or a suspension conveyor. All of these configurations make it possible to convey a large amount of powdery or granular plastic material to the flame, where the plastic material is then acted upon by the conveying fluid. If desired, the plastic material can be transported upstream of the flame with the aid of a conveying fluid. Depending on the plastic material (eg PTFE), it can be advantageous to use a suspension conveyor to transport the plastic material to the flame. The suspen- Sion conveyor can, for example, convey the particles of the plastic material in a suspension, in particular in an aqueous or alcoholic suspension. In one embodiment, the surface filtration layer can have a smaller pore size than the filter body. This favors cleaning of the coated filter element because solid-like foreign substances are usually larger than the pores of the surface filtration layer and therefore stick to the surface of the surface filtration layer.

The pore size describes the size of the free spaces that are formed in the filter body or in the surface filtration layer. The smaller the pore size, the better even the smallest solid particles are filtered out of a fluid. The term "pore size" relates in particular to an average size of the pores for a given pore size distribution. For example, the characteristic pore diameter at dio = 5 pm, d ₅ o = 15 to 25 pm, and d ₉₅ = 50 pm at dg ₅ . This means that 10% of the pores are not larger than 5 μm, in particular that 50% of the pores are not larger than 15 to 25 μm, and in particular that 95% of the pores are not larger than 50 μm.

According to a further aspect, the invention also relates to an application device for forming a surface filtration layer from a plastic material on a filter body by means of a thermal spray-on method. The application device comprises a nozzle, a burner for generating a flame designed to melt the plastic material, a plastic delivery channel with a plastic delivery channel outlet for providing the plastic material in the flame, and at least one delivery fluid channel with a delivery fluid channel outlet for providing a delivery fluid such that the delivery fluid with the plastic material melted in the flame forms a spray jet directed through the nozzle onto the filter body.

The application device can have a housing in which the plastic delivery channel and / or the delivery fluid channel are arranged. If necessary, the nozzle and / or the burner for generating the flame can also be arranged in the housing. The application device can have at least one fuel channel with a fuel channel outlet which is designed to provide a fuel for forming the flame. If necessary, the fuel channel can also be arranged in the housing.

The nozzle is designed so that when the powdery plastic material is supplied via the plastic feed channel outlet and the fuel via the fuel channel outlet, a mixture of plastic material and fuel forms upstream of the nozzle, which is accelerated through the nozzle in the direction of the surface of the filter body. The plastic feed channel outlet and the feed fluid channel outlet can in particular be arranged in the nozzle.

The plastic feed channel outlet, the burner and the feed fluid channel outlet can be formed coaxially in the nozzle in a certain embodiment. This enables a compact design of the nozzle. Furthermore, such an arrangement allows uniform heating of the plastic material in the flame, even with a large mass flow of the plastic particles conveyed in the pointed jet. The application device can furthermore have an attachment, the attachment having an additional fluid channel with at least one additional fluid channel outlet. The attachment can be designed in such a way that it acts on the spray jet with an additional fluid in order to set, in particular to enlarge, a spray cone formed by the spray jet. By adjusting the spray jet, the molten plastic material can be applied to the filter body in a particularly targeted manner. A particularly uniform surface filtration layer can thus be produced on the filter body.

The attachment can preferably be arranged on the nozzle. The attachment can in particular be arranged at a nozzle outlet of the nozzle. Alternatively, the attachment can also be formed integrally with the nozzle, so that the nozzle as a whole forms the attachment.

According to a further aspect, the invention also comprises a system for producing a filter element. The plant includes a device for sintering a nes filler body, as well as at least one application device according to the invention as described above.

The further refinements and advantages set out above in relation to the method and the application device also apply to the system according to the invention. To avoid repetition, reference is made to the points mentioned, which expressly also belong to the disclosure of the system for manufacturing a filter element. According to a further aspect, the invention also comprises a filter element which has a filter body and a porous and fluid-permeable surface filtration layer which is applied to the filter body. According to the invention, the surface filtration layer is a thermally sprayed plastic material layer.

The main component of the filter body can be a sintered material, in particular a sintered plastic material, such as the plastics or mixtures specified above, for example polyethylene, polypropylene, polyamide, polyimide, polysulfone, polysulfide, in particular polyphenylene sulfide, or polymethacrylate, in particular polymethyl methacrylate.

The further refinements and advantages explained above in relation to the method and the application device also apply to the filter element according to the invention. To avoid repetition, reference is made to the passages mentioned, which expressly also belong to the disclosure of the filter element.

The invention and special embodiments of the invention are explained in more detail below using exemplary embodiments.

FIG. 1 shows a side view of a filter element 2 according to the invention.

FIG. 2 shows a cross section through part of the filter element from FIG. 1. FIG. 3 shows a spray device according to the invention and part of a filter body and an impact surface of a spray jet. FIG. 4 shows the spray-on device from FIG. 3 with an attachment and an impact surface modified by the attachment. FIG. 5 shows a top view of the attachment from FIG.

FIG. 6 shows a schematic view of an embodiment of a spraying device. FIG. 1 shows a side view of a filter element 2 according to the invention with a filter body 4, a filter base 8 and a filter head 10.

The head 10 of the filter element 2 is attached to a partition 12 of a filter housing (not shown), in which the partition 12 separates a raw fluid side 18 from a clean fluid side 20, "hanging" (in the case of a horizontally arranged partition) or "sideways". or "protruding away" (with an upright partition), the so-called clean fluid-side installation of the filter element 2 is shown. Here, a side surface of the head 10, the two side walls 14 of the filter body 4 protrudes and is directed towards the foot 8 , attached to a clean fluid side 20 of the partition 12, and the filter element 2 protrudes through an opening in the partition 12 into a raw fluid side 18. In this way, the filter element 2 can be replaced from the "clean" clean fluid side 20. Alternatively, The so-called raw fluid-side installation of the filter element 2 is possible, with the head 10 with its side surface a n attached to the raw fluid side 18 of the partition wall 12. The installation and removal takes place here via the raw fluid side 18.

As mentioned, the filter element 2 can also be attached laterally instead of hanging. In this lateral installation position of the filter element 2, either installation of the filter element 2 on the clean fluid side or on the raw fluid side can be provided. The partition wall 12 is part of a filter device (not shown further) and separates the raw fluid side 18 of the filter device from a clean fluid side 20.

During operation of the filter device, the medium to be filtered is sucked into the filter device through an opening (not shown) or pressed into the filter device by excess pressure and flows from the raw fluid side 18 through the two porous side walls 14 into a hollow interior of the filter element 2 and is from There it is sucked through a flow opening (not shown) in the feeder head 10 onto the Reinfiuidseite 20. From there it is released to the outside of the filter device through an opening, also not shown. The solid particles to be separated from the medium to be filtered are retained by a finely porous surface filtration layer 28 on the surface of the filter element 2 and some of them adhere. This layer of adhering solid particles is blown off at regular intervals by cleaning, for example by a blast of compressed air that is opposite to the direction of flow, and then falls to the ground on the raw fluid side 18 of the filter device.

The filter element 2 has a lamellar structure. The two side walls 14 form numerous ribs that run parallel to one another and each run in the longitudinal direction between the filter head 10 and the filter base 8. First wall sections of the respective side wall 14 run essentially at the same distance from one another at right angles to the longitudinal direction and second wall sections run from an inner end region of a first wall section to an outer end region of a next first wall section. The filter element 2 thus has an essentially fir-tree-like shape in cross section. The provided at right angles to the longitudinal axis first Wandab sections ensure a particularly high stiffness of the first side walls at right angles to the longitudinal direction, which can effectively rule out buckling or bulging of the relatively large Seitenwän de 14, especially when the filter element 2 is attached to the side. The second wall sections, together with the first wall sections, form a relatively acute angle, preferably in the range of approximately 30 °, which further increases the rigidity.

In the preferred installation position with lateral fastening, the second wall sections run from the inside to the outside below, so that particles are not so easily deposited on them when the filter is in operation. During cleaning, too, the flow component is essentially at right angles to the second wall sections, as a result of which the particles are blown away from the longitudinal direction outward during cleaning. Figure 2 shows a cross section of the side wall 14 of the filter body 4. The filter body 4 is through sintered filter body particles 22, in this case plastic part chen, ie particles made of a plastic. In particular, the plastic particles are polyethylene particles or else particles of another of the above-mentioned plastics or plastic compositions. The filter body particles 22 represent a main component of the filter body 4. In order that the filter body particles 22 establish a connection to one another, the filter body 4 was heated to a sintering temperature for a suitable period of time. The filter body particles 22 have sintered necks 24 formed at contact points between adjacent filter body particles 22, ie at points where adjacent plastic particles touched or almost touched one another. The plastic particles have grown together at the sintered necks 24, so that a porous flow-through sin tergefüge has formed, which forms a coherent, porous flow-through filter body 4.

During the sintering process, the filter body particles 22 are melted just enough that they connect to one another at their points of contact. The pore size can be controlled by the particle size and by the process parameters in the manufacture of the filter body 4. In addition, a finer porous coating, which forms the surface filtration layer 28, is applied to the raw fluid side of the filter element 2, which can also be referred to as the inflow side.

The surface filtration layer 28 has been applied to the filter body 4 on one side 26, that is the right side in FIG. 2, which forms the inflow side during operation, using the thermal spraying method according to the invention, as explained above and described in more detail below. The surface filtration layer 28 is made from a plastic material 30. The plastic material 30 typically has anti-adhesive properties and / or anti-bacterial properties, for example by adding appropriate materials such as PTFE particles to develop anti-adhesive properties or silver particles or titanium oxide particles to produce antibacterial properties. The

Plastic material 30 is applied in that it is fed into an application device 32, in particular in a powdery or granular form, and in the application device 32 preferably passes directly through a flame 42 and is melted in the flame 42. The molten plastic material 30 is then conveyed by a conveying fluid 34 as a colloid from the flame 42 to the surface of the filter body 4 to be coated and onto the filter body. injected by 4. The conditions when spraying the plastic material 30 are such that the sprayed-on plastic material 30 cools down relatively quickly on the filter body 4 and largely loses its flowability or even solidifies. In particular, the plastic material 30 sprayed onto the filter body 4 should have lost its flowability before it can form a continuous, fluid-impermeable coating that would no longer be porous by flowing into one another with other particles or drops of the plastic material 30 sprayed onto the filter body 4. In the case of thermal spraying according to the present invention, the filter body 4 is coated with a porous and fluid-permeable surface filtration layer 28 without the need to use solvent, adhesive or any other binder. The rapid cooling of the Kunststoffma material 30 is promoted by the fact that the filter body 4 is only heated to a small extent by the flame 42 during the coating. According to the invention, it has been found that it is advantageous for the production of the porous surface filtration layer 28 by means of a thermal coating process if the plastic material 30 is heated so that it melts faster than with indirect heating, as is normally practiced and considered indispensable in plastic flame spraying becomes. Figure 3 shows part of a schematically illustrated application device 32 according to the invention for thermal spraying of a plastic material 30 on a filter body 4. The application device 32 is designed to melt plastic material 30, which is usually supplied in powder form, with a conveying fluid channel outlet through a conveying fluid channel 36 38 supplied conveying fluid 34 (usually a conveying gas, for example compressed air or nitrogen, a liquid such as water or alcohol, or a suspension formed by particles carried in a liquid) so that a spray jet 56 is formed in which individual particles or Droplets of the plastic material 30 are carried in the conveying fluid 34. The spray jet 56 forms a colloidal system and is sprayed onto the filter body 4. After the plastic material 30 has cooled and solidified, the surface filtration layer 28 is formed on the filter body 4 from the plastic particles or droplets sprayed on in this way. The plastic material 30 preferably has a powder form when it is fed into the application device 32. Alternatively, the plastic material can also be designed as a plastic strand. In the spray jet 56, the plastic material 30 is in a colloidal configuration with individual particles or droplets the plastic material 30 in a more or less molten aggregate state, which are carried by the conveying fluid 34. Depending on the flowability, powdered plastic material 30 can also be present in a colloidal configuration upstream of the application device 32, that is to say it can be passed to the flame with the aid of a carrier fluid (gas or liquid).

The application device 32 has a burner 40 to which fuel and oxygen are supplied and which generates a flame 42. The fuel is fed to the burner 40 through a fuel channel 44 via a fuel channel outlet 46. Furthermore, the application device 32 has a plastic conveying channel 48 with a plastic conveying channel outlet 50 through which the plastic material 30 is conveyed into the flame 42. The plastic feed channel outlet 50 and the feed fluid channel outlet 38 are arranged coaxially in a nozzle 52. In further refinements, the fuel channel outlet 46 and an oxygen supply channel 54 can also be arranged coaxially in the nozzle 52. However, a coaxial arrangement of the corresponding outputs is not absolutely necessary. It is sufficient if the plastic material 30 is conveyed through the application device 32 in such a way that the plastic material 30 is passed directly through the flame 42 generated by the burner 40 and thus melts directly in the flame 42. This means in particular that there is no protective or insulating layer made of air or an inert gas between the flame 42 and the plastic material 30, as would be usual in plastic flame spraying. In the configuration shown in FIG. 3, the flame 42 is formed in the same direction as the spray jet 56, namely towards the surface of the filter body 4 to be coated. The individual particles of plastic material 30 in the spray jet 56 therefore melt during the time in which they are carried by the conveying fluid 34 from the nozzle 52 to the surface of the filter body 4.

The plastic material 30 can be transported to the flame 42 in the application device 32 by a fluidized bed conveyor, a plate conveyor, a disk conveyor, or a suspension conveyor. The melted plastic material 30 and the delivery fluid 34 together form a spray jet 56 which is directed from the application device 32 to the surface of the filter body 4 and in which the plastic material 30 is in the form of particles to the filter body 4 is transported. The particles of the plastic material 30 formed after passing through the nozzle 52 are intended to largely melt in the flame 42, that is to say to be in largely liquid form, when they strike the surface of the filter body 4.

The plastic material 30 is sprayed onto the filter body 4, in particular in the form of particles. The desired permeability of the surface filtration layer is dependent on the particle speed at which the plastic material 30 is sprayed on by the conveying fluid 34. The higher the particle velocity, the lower the permeability of the surface filtration layer 28 can be. This means that the porosity of the surface filtration layer 28 decreases as the particle velocity increases.

So that better cleaning of the surface filtration layer 28 can take place and the filter body 4 is not clogged by solid particles, the surface filtration layer 28 preferably has a smaller mean pore size than the filter body 4.

The spray jet 56 formed by the conveying fluid 34 and the molten plastic material 30 forms a spray cone which forms a circular impingement surface 58 on the surface of the filter body 4 to be coated. The shape of the impingement surface 58 is particularly dependent on a conveying speed and a conveying direction of the plastic material 28 and the conveying fluid 34. In FIG. 3, the impingement surface 58 is shown schematically below the filter body 4 in order to illustrate the shape of the impinging surface 58.

The conveying fluid 34 can in particular be a conveying gas, for example air or an inert gas such as nitrogen or a noble gas, or a liquid (water or alcohol) which forms a suspension with the plastic particles. The conveying fluid 34 forms a carrier phase in which the particles of plastic material 30 formed when passing through the nozzle 52 are transported as a colloid in the spray jet 56 to the filter body 4. The flame 42 generated by the burner 40 is also directed in the direction of the spray jet 56, so that the particles of plastic material 30 melt in the flame 42 during transport in the spray jet 56 and are finally sprayed onto the surface of the filter body 4 in a liquid state become. The introduction of the plastic material 30 into the flame 42 can take place both axially and radially. In the axial introduction shown in FIG. 3, the plastic material 30 is always conveyed essentially in the direction of the spray jet 56 both upstream and downstream of the nozzle 52. As can be seen in Fig. 3, the conveyance of the plastic material 30 takes place in a radially inne Ren area of the nozzle 52 around the axis and the conveying fluid 34, like the fuel 54, is directed inwards from radially outer areas of the nozzle 52, in order to suitably atomize the plastic material 30 or to generate the flame 42.

FIG. 4 shows a schematic representation of the application device 32 with an attachment 60 which is arranged on the nozzle 52, in particular on a downstream aterial outlet of the nozzle 52. The attachment 60 can also be formed integrally with the nozzle 52. The attachment 60 has an additional fluid channel 64 (see FIG. 5) in which an additional fluid 62 is guided. The additional fluid 62, generally air or an inert gas such as nitrogen or a noble gas, is introduced into the spray jet 56 via one or more additional fluid channel outlets 66. The introduction can take place both essentially axially, ie in the direction of the spray jet 56 or at an angle close to zero degrees to the spray jet 56, and also essentially radially, ie orthogonally to the spray jet 56 or at an angle close to 90 degrees lying angle to the spray jet 56 take place. This introduction of the additional fluid 62 has the effect that the spray cone of the spray jet 56 changes and, as a result, the impingement surface 59 is oval instead of circular. The enlargement of the impingement surface 59 allows a larger area on the filter body 4 to be coated with plastic material 30. This enables the coated filter element 2 to be produced more quickly. Furthermore, the material of the filter body 4 is heated to a lesser extent by the flame 42 during the coating process, because the application device 32 can be guided more quickly over the filter body 4 in order to completely cover the filter body 4 coat.

In Figure 5, the attachment 60 is shown in plan view. The additional fluid channel outlets 66 are formed in a line which is guided around the circumference of the spray jet 56 in a ring-like manner. In the example shown, the two additional fluid channel outlets 66 are arranged opposite one another in pairs. The essay 60 offers a quick and inexpensive solution for changing or widening the spray jet 56, or better the shape of the spray jet 56.

The additional fluid 62 can in particular be introduced into the spray jet 56 at an angle or in a ring shape via the attachment 60.

FIG. 6 shows the application device 32 in an exemplary embodiment. The application device 32 has a housing 70 in which the plastic conveyor channel 48 is arranged. The nozzle 52 has a modular structure. This means that the plastic delivery channel outlet 50, the fuel delivery channel outlet 46, the delivery fluid channel outlet 38 and an oxygen delivery channel outlet 55 are formed by several axially interlocking components 72, 74, 76 and 78. The respective supply of plastic material 30, conveying fluid 34, fuel and oxygen to the application device 32 takes place via respective inlets 80, 82, 84 and 86, in this case the inlets 82, 84, 86 for conveying fluid, fuel and oxygen on an underside of the housing 70 and the input 80 for the plastic material 30 are arranged on a rear side of the housing 70 which is concealed here. The inputs are connected to the corresponding channels. The housing 70 of the application device 32 can also have a different arrangement or a different structure. It is also within the scope of the invention to implement the guidance of the plastic material 30, the delivery fluid 34, the fuel and the oxygen differently.

The surface filtration layer 28 not only has anti-stick properties, but also antibacterial properties. The properties of the surface filtration layer 28 can be adjusted more finely by changing process parameters. Process parameters are understood to be the type of fuel, the air supply, the delivery rate of plastic material 30, of delivery fluid 34, a type of injection, the process speed, and the additive admixtures to the plastic material 30.

The method for producing a coated filter element 2 essentially has the following steps: First, the filter body 4 is provided in a coating system which has an application device 32. The plastic material 30 is melted in the flame 42 of the applicator 32. The plastic material 30 is sprayed in the molten state by the conveying fluid 34 in the spray jet 56 onto the filter body 4. When solidifying, the plastic material 30 forms the surface filtration layer 28 on the Filter body 4 off. Because the method according to the invention involves relatively little heat input to the filter body 4, the plastic material 30 sprayed onto the filter body 4 solidifies quickly and therefore cannot completely flow together with adjacent sprayed-on particles or droplets of plastic material 30. The sprayed-on plastic material 30 can flow to a certain extent into existing pores of the filter body 4 for the same reason, but not completely clog them. In this way, pores or spaces are created in the surface filtration layer produced by the plastic material 30, so that the surface filtration layer 28 is porous and fluid-permeable.

One way to make the spray device 32 particularly easy is to convert a spray gun for wire flame spraying. In particular, only one gas head unit of the spray gun is used. Instead of a wire guide, a tube can be inserted into the spray gun as a plastic feed channel 48 through which plastic material 30, e.g., in powder form, is fed to the burner 40. The plastic material 30 can then be axially promoted in the flame 42 ge. A radial indexing, or an indexing located between the axial and the radial, by injectors is also conceivable. The plastic material 30 is melted in the flame 42 and sprayed onto the filter body 4 by the conveying fluid 34 or conveying gas or atomizing gas. The plastic material 30 can also be applied by atmospheric plasma spraying or powder flame spraying, because with these methods too the plastic material 30 is sprayed on with particle speeds of greater than 10 m / s. As a result, a porous and fluid-permeable surface filtration layer 28 can also be formed.

An example of a thermally sprayed surface filtration layer according to the invention in a filter element has a filter body made of sintered polyethylene particles, which was provided with a surface coating made of polyamide by means of flame spraying. The filter body is commercially available under the name Herding sintered lamellar filter HSL 450/8. After sintering and before flame spraying, the filter body had a pore size between 50 and 70 μm. The polyamide coating was applied to the filter body with a modified flame spray gun according to FIGS. 3 and 6, the flame spray gun (burner head of type 16E) via a plate conveyor type Twin 10-C for the coating material (delivery rate 30g / min, 2 bar). A distance from the nozzle to the surface of the filter body to be coated of 0.17 m and a spray angle of 90 ° were selected. Before spraying, the polyamide particles used had a particle size of less than or equal to 45 μm for 50% of the polyamide particles. The process conditions for flame spraying were set to the following relative proportions: C ₂ H ₂ 45 scale divisions, 0 ₂ 50 scale divisions, Air 41 scale divisions at 4.5 bar each. The gun was passed over the surface to be coated at a coating speed of 1 m / s. The result was a filter element with a surface filtration layer made of polyamide. The polyamide coating had a thickness of 250 μm, the pore size of the polyamide coating being less than 20 μm.

The coated filter body was exposed to a b value of 1.6 m ³ / (m ² × min) (V = 85.4 m ³ / h) in air that was not loaded with foreign substances. A pressure loss between 30 and 40 mm water column was measured.

The coating remained positively and non-positively connected to the filter body with any type of load, especially when it was subjected to compressed air pulses (up to 35 mbar) for the simulated cleaning of the filter body. No delamination of the surface filtration layer was found.

Claims

Expectations

1. A method for producing a coated filter element (2), with the following steps: providing a filter body (4); and

Thermal spraying of a plastic material (30) onto the filter body (4) by an application device (32) such that the thermally sprayed plastic material (30) forms a porous and fluid-permeable surface filtration layer (28) on the filter body (4).

2. The method according to claim 1, wherein the plastic material (30) is melted directly in a flame (42).

3. The method according to claim 1 or 2, wherein the main component of the filter body (4) is a sintered material, in particular a sintered plastic material.

4. The method according to any one of the preceding claims, wherein the thermally sprayed plastic material (30) comprises polyethylene (PE), polyamide (PA), polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK) or a mixture of these materials, in particular together with Polytetrafluoroethylene (PTFE).

5. The method according to any one of claims 2 to 4, wherein the molten plastic material (30) with a conveying fluid (34), in particular a conveying gas or a conveying liquid, through a nozzle (52) of the application device (32) in particle form to the filter body (4 ) is transported.

6. The method according to claim 5, wherein a particle speed at which the molten plastic material (30) is applied to the filter body (4) is set to be greater, the lower a desired porosity of the surface filtration layer.

7. The method according to claim 6, wherein the particle speed is greater than 10 m / s, in particular greater than 30 m / s, in particular greater than 60 m / s, in particular which is greater than 90 m / s, or between 10 and 450 m / s, in particular between 60 and 450 m / s, or in particular between 90 and 200 m / s.

8. The method according to any one of claims 5 to 7, wherein a spray jet (56) formed by the conveying fluid (34) and the particulate plastic material (30) is acted upon with an additional fluid (62) in order to to shape impinging spray cone, in particular in such a way that the spray cone covers a desired impingement surface (58) on the filter body (4).

9. The method according to claim 8, wherein the additional fluid (62) is introduced into the spray jet (56) by means of an attachment (60) attached to the application device (32).

10. The method according to claim 8 or 9, wherein the spray jet (56) is guided at a speed between 0.05 m / s and 5 m / s over the surface to be coated of the filter body (4).

11. The method according to any one of claims 8 to 10, wherein the spray jet (56) has a plastics material mass flow of 0.08 g / s to 4.2 g / s.

12. The method according to any one of the preceding claims, wherein the plastic mate rial (30) in the application device (32) with a fluidized bed conveyor, a plate conveyor, a disk conveyor, or a suspension conveyor to the flame (42) is conveyed.

13. The method according to any one of the preceding claims, wherein the surface filtration layer (32) has a smaller pore size than the filter body (4).

14. Application device (32) for forming a surface filtration layer (28) from a plastic material (30) on a filter body (4) by means of a thermal spray-on process, comprising: a nozzle (52) a burner (40) for generating a for melting the plastic material ( 30) formed flame (42); a plastic feed channel (48) with a plastic feed channel outlet (50) for providing the plastic material (30) in the flame (42); at least one conveying fluid channel (36) with a conveying fluid channel outlet (38) for providing a conveying fluid (34) such that the conveying fluid with the plastic material (30) melted in the flame (42) passes through the nozzle (52) onto the filter body (4 ) directed spray jet (56) forms.

15. Application device (32) according to claim 14, wherein the plastic feed channel outlet (50) and the feed fluid channel outlet (38) are arranged in the nozzle (52).

16. Application device (32) according to claim 15, wherein the plastic feed channel outlet (50), the burner (40) and the feed fluid channel outlet (38) are formed coaxially in the nozzle (52).

17. Application device (32) according to one of claims 14 to 16, furthermore having an attachment (60), wherein the attachment (60) has an additional fluid channel (64) with at least one additional fluid channel outlet (66); the attachment (60) being designed to apply an additive fluid (62) to the spray jet (56) in order to set, in particular to enlarge, a spray cone formed by the spray jet (56);

18. Application device (32) according to claim 17, wherein the attachment (60) is arranged on the nozzle (52).

19. Plant for producing a filter element (2) comprising a device for sintering a filter body (4); and an application device (32) according to any one of claims 14 to 18.

20. A filter element (2) comprising: a filter body (4), and a porous and fluid-permeable surface filtration layer (28) which is applied to the filter body (4); wherein the surface filtration layer (28) is a thermally sprayed plastic material layer.

21. Filter element (2) according to claim 20, wherein the thermally sprayed plastic material (30) comprises PE, PA, PVDF, PEEK, or a mixture of these materials, in particular together with PTFE.

22. Filter element (2) according to one of claims 20 or 21, wherein the filter body (4) has a sintered material, in particular a sintered plastic material, as the main component.