FILTER ELEMENT FOR FLOW STABILIZATION AND / OR PURIFICATION OF THE MELT OBTAINED DURING CASTING AND METHOD FOR PRODUCING A FILTER ELEMENT - Patent application

Abstract

A filter element for flow stabilization and / or purification of a melt used in casting, through which the melt is guided, is designed as a three-dimensional ribbed structure with openings as channels through which the liquid melt is guided. The ribs of the ribbed structure are formed by particles made of a material that can be used as a mold material in casting techniques and a binder that can bind the particles together. The ribs are also provided on their surface with a coating of a polymer resin.

Description

[Technical field]

[0001] The present invention relates to a filter element for flow stabilization and / or purification of the melt obtained during casting, and to a method for producing a filter element. [Background technology]

[0002] In the field of molten metal filtration, various approaches exist to increase the filtration efficiency of filters used for this purpose. In most cases, the filter material is modified or replaced by other substances. Thus, for example, US Pat. No. 5,399,433 describes increasing the filtration efficiency of "common molten metal filter shapes" with an active surface coating. The term "common molten metal filter shapes" refers to open-cell foam ceramic shapes, honeycomb shapes, spaghetti filter shapes, perforated filter shapes and woven fiber filters, none of which have a defined filter and flow structure to laminarize the melt in the best possible way. US Pat. No. 5,499,433 and US Pat. No. 5,499,433 describe the use of carbon-bonded materials for melt filtration of iron and aluminum. The filters are defined as "foam structure". US Pat. No. 5,499,433 relates to the removal of gases from the melt with a filter, US Pat. No. 5,499,433 relates to the use of filters for continuous molten metal filtration and US Pat. No. 5,499,433 relates to the removal of inclusions of different chemical composition with a ceramic molten metal hybrid filter, which also describe filters with a foam structure or a filter structure that is not clearly defined.

[0003] Patent document 7 describes a method for the production of metal filters made of molybdenum or tungsten. Molybdenum or tungsten powders of different particle sizes are sintered, the sintered bridges provide the strength of the filter, and the non-sintered areas represent the pores for molten metal filtration. In this type of filter production, there is no clearly defined filter or flow structure. In the technical solution described in patent document 8, a filter element is described that is composed of a three-dimensional geometric cage and is intended to perform the task of metal refining. The filter element is produced by printing a thermoplastic resin and coating and firing the printed framework with a ceramic slip or by printing a ceramic slip. These filter elements can have a defined filter structure, but they only perform the task of melt refining and not of laminarization. Furthermore, the filter elements are not recyclable or can only be recycled to a very limited extent, since they consist of sintered ceramics that do not pyrolyze after use. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE 102011109681 [Patent Document 2] DE 102011109682 [Patent Document 3] DE 102020000969 A1 [Patent Document 4] DE 102011109684 [Patent Document 5] DE 102016106708 A1 [Patent Document 6] DE 102018201577 [Patent Document 7] International Publication No. 2017 / 008092 [Patent Document 8] European Patent No. 3325428 Summary of the Invention [Problem to be solved by the invention]

[0005] The invention is based on the problem that it is possible to produce defined filter and flow structures which, by flow stabilization and / or effective retention of impurities which may be contained in the molten metal, make it possible to convert a turbulent flow into a largely laminar flow of the liquid melt and which also allow a simple and environmentally friendly disposal of used filter elements. [Means for solving the problem]

[0006] According to the invention, this problem is solved by a filter element having the features of claim 1. Claim 6 relates to a manufacturing method. Advantageous embodiments and developments of the invention can be achieved by the features specified in the dependent claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The filter element of the present invention has a three-dimensional rib structure with openings as flow paths to direct molten liquid. The molten liquid can flow through the openings formed in the rib structure between the ribs, and the ribs can be fabricated such that the flow is stratified by flow stabilization and impurities such as oxides are retained by the filter element.

[0008] The rib structure is formed from particles made of a material that can be used as a mold material in casting techniques and a binder, the particles being integrally bound with the binder, and the surfaces of the ribs being coated with a polymer resin.

[0009] Preferably, particles based on SiO2, based on Al2O3, based on aluminosilicates, formed of cerium-stabilized ZrO2 or chromite can be used, the term "predominantly" being defined to mean a proportion of at least 80% by volume, particularly preferably at least 90% by volume, more preferably at least 95% by volume.

[0010] Quartz sand or chromite, a mineral composed primarily of chromium and iron oxide, also known as mullite, can be used.

[0011] The particles can be integrally bound with a furan resin binder, a phenolic resin binder, or an inorganic binder as a binder. The furan resin binder can be a furfuryl alcohol-based binder. The phenolic resin binder can be a heat-curing type (e.g., an acid-curing phenolic resol binder) or a cold-curing type. The inorganic binder can be an aqueous alkali silicate-based binder.

[0012] Depending on the binder used, curing can be achieved by heat treatment at a sufficiently high temperature, by exposure to suitable electromagnetic radiation, or by the addition of binder-specific curing components.

[0013] The coating covering the surface of the rib is made of a polymeric resin such as epoxy resin. The coating is hermetically sealed and has a layer thickness of at least 50 μm.

[0014] The ratio of the binder that binds the particles together is in the range of 1 volume % to 5 volume % relative to the amount of the particles that are bound together, and preferably, the ratio is about 2 volume %.

[0015] The ribs of the rib structure are made of granular materials with an average particle size d in the range of 63μm to 1000μm. 50 The particle is formed of particles having the following structure:

[0016] The openings forming the flow channels are provided with open pockets to accommodate impurities contained in the melt at predetermined locations and dimensions, which, with properly controlled manufacturing, can be achieved by additive manufacturing steps, which are described in more detail below.

[0017] In the manufacturing process, the ribs with the particles are formed layer by layer by locally defined integral bonding of the particles made of a material that can in principle be used as a molding material in casting techniques with a binder. At the start of the curing process or after the binder has cured, the surface of the ribs is covered with a polymer resin. The curing can start with the formation of a single layer of the rib structure and continue until complete curing is achieved. If complete curing has not yet been achieved, the next layer can be structurally formed. In these cases, preferably, a curing component can be applied together with the binder or the curing can be achieved using irradiation with suitable electromagnetic radiation. However, as an alternative, a heat treatment can also be performed at a temperature sufficient to cure the binder. The heat treatment can be performed on an element body that already has the three-dimensional basic rib structure of the filter element.

[0018] In powder bed based additive manufacturing, loose particles, or particles that already contain a portion of a binder or are coated with a binder, are applied as a layer to a structural substrate, exposing the particles of the top layer to the binder in a locally defined manner, thereby bonding the particles in a locally defined manner within the plane of the respective layer. The binder is applied in a metered, two-dimensionally controlled manner along the surface of each layer formed by the loose particles.

[0019] After the particles have been integrally bound to the binder to form a predetermined geometric rib structure for the plane of the respective layer, the structural base is lowered by a layer thickness and a new layer of free particles is applied in which the particles are again integrally bound to the binder to form the predetermined geometric rib structure for this plane.

[0020] The process steps of layer application, locally defined integral bonding of particles and binder, and lowering of the structure base are repeated until the desired three-dimensional rib structure of the filter element is formed.

[0021] After that, the loose particles that are not bonded together are first removed, and then a coating is applied to the surface of the ribs using a polymer resin. The coating can be formed by dipping, submerging or spraying.

[0022] As an alternative to powder bed-based production, uncoated filter elements can be produced by pure printing. In this case, a paste / suspension formed of particles and a binder, possibly a hardening component, is applied layer by layer through at least one nozzle until a three-dimensional rib structure with ribs and openings is formed as channels, and then a coating is applied to the surface of the ribs using a polymer resin. Depending on the respective binder, hardening takes place only after a layer or coating of the paste / suspension has been formed or after the complete rib structure has been formed. The paste / suspension is applied by metering either in the form of individual droplets or in the form of filaments. In this case, at least one nozzle is appropriately positioned by a two-dimensional movement of its outlet opening, and the mass flow rate of the applied suspension is controlled in a locally defined manner according to the shape and dimensions of the rib structure.

[0023] For example, a commercially available 20 ppi ceramic foam filter (50 mm × 50 mm × 20 mm) can be scanned using micro-computed tomography to obtain a faithful CAD model of the ceramic foam filter. This CAD model is then additively manufactured in three dimensions using sand and binder. In this method, quartz sand (SiO2:>99.1 vol%, average particle size d) mixed with an activator (p-toluenesulfonic acid) is used. 50 A furan resin (binder content: 2% by volume) is applied layer by layer to the structural substrate, and then the binder is printed and cured to form a furan resin (binder content: 2% by volume). To increase the mechanical and thermal strength, the filter shape in the form of the printed three-dimensional rib structure is then impregnated with a polymer resin on the surface of the ribs.

[0024] The filter elements thus obtained were tested for their thermal shock behavior and for the dynamic and thermal loads that occur during aluminum casting using the test method for determining the thermal shock resistance of molten aluminum. The filter elements withstood the loads and did not break. Furthermore, the thermal decomposition of the filter elements was already visible as bright spots on the filter elements. This means that after use the filter elements decompose down to their basic components and it is also possible to recover the residual molten material.

[0025] In the preliminary tests described here, a ceramic foam filter structure was chosen as a template to control additive manufacturing since it acts as a worst case for the mechanical and thermal forces generated due to the low rib thickness of 0.5 mm.

[0026] Casting tests with aluminum melts have shown that, despite the low rib thickness, additively manufactured filter elements, consisting essentially of bonded particles of molding material, can withstand the expected loads and also achieve purification of the melt. Furthermore, further tests have shown that the filter elements according to the invention can be pyrolyzed after use and thus completely separated from the solidified aluminum and impurities deposited on the filter element during use. The invention can be used to provide filter elements with defined retention and / or flow structures. Applications have shown that even very filigree three-dimensional rib structures can be implemented and that these structures, after impregnation of the rib surface with a polymer resin, can withstand the loads that occur at least in the case of aluminum casting.

[0027] According to the invention, a flow-optimized filter geometry can be provided by additive manufacturing with advantageous filter element materials. Thus, filter elements with improved flow conditions can be constructed and manufactured. The design flexibility and reproducible manufacturing process avoid the disadvantages of ceramic foam filters. When processing the filter element material, the loose flowable particles are wetted or mixed with the binder in layers. In this way, sufficient strength can be achieved by material bonding. After use and after passing through the liquid melt, the filter element at least partially disintegrates due to the thermal decomposition of the binder. The material bonds between the particles are at least largely dissolved and the used particles can be introduced again in loose form into the material cycle of the foundry. No material is generated to be disposed of in landfills.

[0028] The present invention offers the possibility of an optimized configuration or layout of the overall geometry of the filter element, including in particular the dimensions of the ribs, the openings with the alignment of the channels formed by the openings, so that the liquid melt can flow in such a way that a laminar flow is achieved after passing through the filter element, with the greatest possible retention capacity for impurities. This allows the development and practical application of filter elements with well-defined channels and branching pockets. The reproducible design-free processing of filter materials is a new method that has not yet been established on the market.

[0029] Upon investigation, it was discovered that no such filter element construction is currently in use or under development. The development of such an additively manufactured filter element would be characterized by a high degree of innovation.

[0030] The invention also has ecological and economic advantages as a result of using the new filter structure. Compared to ceramic foam filters, the additive manufacturing of flow-optimized filter structures requires significantly less energy, since the sintering step of the ceramic slip is no longer necessary. This makes production much more environmentally friendly and foundries can reduce their CO2 emissions by using the filter elements according to the invention. Additively manufactured filter elements can decompose due to the thermal effect of the melt after casting and return particulate matter to the material cycle, thus saving on landfill and transport costs. Furthermore, additively manufactured filter elements can be produced considerably cheaper than ceramic foam filters, both in large- and small-scale production. A further important advantage of the development is that the filter structures can be specially configured for the respective field of application.

[0031] The starting materials used are low cost and the production of the filter elements requires relatively little energy.

Claims

1. A filter element for stabilizing the flow and / or purifying the molten material obtained during casting, The filter element has a three-dimensional rib structure with openings that serve as flow channels through which the molten liquid passes. The ribs of the rib structure are formed from particles made from a material usable as a molding material in casting technology and a binder that integrally binds the particles together, and the ribs have a polymer resin coating on their surface. Filter element.

2. The aforementioned particles are SiO ２ It mainly consists of Al ２ O ３ It mainly consists of aluminosilicate, and cerium-stabilized ZrO ２ or formed of chromite, and / or The particles are integrally bound with a furan resin binder, a phenol resin-based binder, or an inorganic binder, and / or The aforementioned coating is made of polymer resin. The filter element according to claim 1, characterized in that

3. The proportion of the binder to which the particles are integrally bound is maintained in the range of 1% to 5% by volume relative to the amount of integrally bound particles. A filter element according to claim 1 or 2, characterized in that...

4. The ribs are formed of particles having an average particle size d50 in the range of 63 μm to 1000 μm. A filter element according to claim 1 or 2, characterized in that...

5. An opening pocket is formed in the opening that forms the flow path, which receives impurities contained in the molten liquid at a predetermined position and size. A filter element according to claim 1 or 2, characterized in that...

6. A method for manufacturing a filter element according to claim 1 or 2, wherein rib particles made from a material usable as a molding material in casting technology are formed in layers by locally and integrally bonding with particles having a binder, and the surface of the ribs is coated with a polymer resin at the start of curing of the binder or after curing. A method characterized by the following features.

7. The free particles, or particles already containing or coated with a binder, are applied as layers to a structural substrate, and the particles of each uppermost layer are exposed to the binder in a locally defined manner, thereby bonding the particles to each other in a locally defined manner within the plane of each layer. After forming a predetermined geometric rib structure on the plane of each layer by integrally bonding the particles with the binder, the structural base is lowered by the thickness of the layer, a new layer of free particles is applied, and the particles are again materially bonded with the binder to form a predetermined geometric rib structure within this plane. It is characterized by the following: The steps of coating the layer, locally defining the integral bonding of the particles and the binder, and lowering the structural base are repeated until the predetermined three-dimensional rib structure of the filter element is formed, after which, first, any loose particles that are not integrally bonded are removed. Next, the polymer resin coating, which hardens under normal conditions and / or by heat treatment and / or irradiation with electromagnetic radiation and / or addition of a catalyst, is applied to the surface of the rib. The method according to claim 6.

8. The paste formed from the particles and the binder is applied layer by layer through at least one nozzle until the three-dimensional rib structure having the ribs and openings is formed as a flow channel, and thereafter the polymer resin coating is applied to the surface of the ribs. The method according to claim 6, characterized in that