ES2938351B2 - Electroconductive ceramic material filter - Google Patents

Description

DESCRIPTION

Electroconductive ceramic material filter

FIELD OF THE INVENTION

The elements obtained with this patent may have application in sectors related to the aerospace industry, the military industry, the chemical industry, the electrical and electronic industry and the nuclear industry. Likewise, its application is also possible in other industrial sectors such as those related to the metal-mechanical and automotive sectors.

STATE OF THE PRIOR ART

In recent years there has been a growing interest in the development of materials for applications that require high wear resistance, high hardness, high mechanical resistance at high temperatures, as well as good chemical stability and good behavior against aggressive environments, characteristics that are provided by ceramic materials. Likewise, the use of these materials has been increasing in recent years and, in many cases, they have replaced metallic materials in applications where the combination of low density and high fusion temperatures is necessary.

Ceramic materials can be classified into non-conductive ceramic materials, natural conductive ceramic materials and doped conductive ceramic materials (Puertas, I.; Luis, C.J., Revista de Metalurgia, Vol. 38 (5), 2002, pp. 358-372). In the first case, there are ceramic materials such as alumina (AbO<3>), zirconia (ZrO<2>), silicon carbide (SiC) and silicon nitride (Si<3>N<4>). . In the second case, ceramic materials such as boron carbide (B<4>C), titanium diboride (TiB<2>) and zirconium diboride (ZrB<2>) stand out. The third and last case is the most varied since it would be composed of non-conductive ceramic bases from the first case (Al<2>O<3>, ZrO<2>and Si<3>N<4>, among others) together with electroconductive ceramic phases of the second case or others such as, for example, titanium nitride (TiN) or titanium carbide (TiC). Due to the excellent mechanical properties (even at high temperature) and resistance to corrosion and wear that ceramic materials present, they have a high number of applications in various sectors of industrial interest such as the aeronautical and aerospace sector, the automotive sector and the electrical and electronic industry sector, among others (Puertas, I.; Luis, C.J., Revista de Metalurgia, Vol. 38 (5), 2002, pp. 358-372); (Luis, C.J.; Puertas, I., Journal of Materials Processing Technology, Vol. 189 (1-3), 2007, pp. 301-309); (Pachaury, Y.; Tandon, P., Vol.

25, 2017, pp. 369-390). Among the applications that can be found in the bibliography related to ceramic materials that can be processed by electroerosion, it is worth highlighting the work of (Sciti, D.; Zoli, L.; Silvestroni, L.; Cecere, A., Di Martino, G.D. ; Savino, R., Materials & Design, Vol. 109, 2016, pp. 709-717), who design and manufacture a nozzle for rocket engines whose central component is a 50% ZrB<2>ceramic composite material. and carbon fiber that is machined by electro-erosion. On the other hand, in (Clijsters, S. ; Liu, K.; Reynaerts, D.; Lauwers, B., Journal of Materials Processing Technology, Vol. 210 (4), 2010, pp. 631-641) they apply a strategy EDM machining for the manufacture of a silicon-infiltrated silicon carbide (SiSiC) test piece with different types of geometric characteristics. Likewise, (Liu, K.; Reynaerts, D.; Lauwers, B., CIRP Annals, Vol. 58 (1), 2009, pp. 217-220) manufacture the micro -gas turbine impeller. The material used in its manufacture is a ceramic composite material of silicon nitride (Si<3>N<4>) and titanium nitride (TiN). Another example of application consists of the one carried out by (Lauwers, B.; Kruth, J.-P.; Brans, K., CIRP Annals, Vol. 56 (1), 2007, pp. 225-228) where through A machining strategy that combines EDM milling (roughing) and plunge EDM (finishing) produces a boron carbide (B<4>C) powder spray nozzle.

Regarding the patents that have to do with the present invention, it is worth mentioning that there are several in which equipment and methods are claimed for machining holes, slots, cavities and various shapes. (Kato, K.; Kurosaka, Y; Dohi, Y., Sep. 2003, US6627838 (B2)) propose a machine for machining small holes by EDM with the use of tubular electrodes of 1 mm in diameter and smaller that are found in rotation. (Maradia, U.; Kliuev, M., May 2019, US2019/0151972 (A1)) claim a method to carry out EDM machining of shapes, such as slots or blind or through cavities, by drilling holes in different process conditions. (Malshe, A.P; Virwani, K.R.; Rajurkar, K.P., Oct. 2008, US2008/0257867 (A1)) propose equipment for EDM machining of conductive parts at a nanometric scale. To do this, they use electrodes with a series of tips with radii according to their ends in the nanometric order, mainly for the machining of holes.

As has been seen, the aforementioned inventions claim devices or methods for carrying out EDM machining of shapes (slots, holes and cavities, for example) on conductive or semiconductor parts. However, in this patent what is claimed are components for specific filtering applications in especially aggressive operating conditions and that are manufactured by sinking EDM processes from bodies of conductive ceramic materials, mainly hot-pressed boron carbide. (B<4>C), silicon-infiltrated silicon carbide (SiSiC) and titanium diboride (TiB<2>).

BRIEF DESCRIPTION OF THE INVENTION

With regard to the present invention, it should be noted that it is specifically oriented to the development of components for filtering applications, which have through holes and/or through slots, through the use of bodies of conductive ceramic materials and electroerosion processes. Among the above components, we can mention silicon carbide ceramic filters infiltrated with silicon with cylindrical geometry, which may or may not be hollow, which serve to filter corrosive liquids and impurities and which make it possible to work in continuous operating temperature conditions. up to 1350 °C. This takes advantage, on the one hand, of the inherent mechanical properties of said ceramic material: SiSiC (such as hardness and mechanical resistance at high temperatures, as well as resistance to wear and corrosion in particularly aggressive environments) and, on the other hand, On the other hand, the versatility of EDM processes for the manufacture of said components with complex geometries that, due to their mechanical properties, would not be feasible to develop using conventional manufacturing processes. The aforementioned components could not be machined using traditional turning and/or drilling techniques, because their high hardness value would give rise to very high wear values for the cutting tools used, and these could even break. Added to this would also be the resulting poor surface finish and low dimensional precision of said components thus manufactured.

The object of the present invention (obtaining components with bodies of conductive ceramic materials that have through holes and/or through slots, which can be used for filtering applications) is achieved through a manufacturing process of the aforementioned conductive ceramic materials that It includes the following two steps:

- Manufacture of electrodes made of conductive material (for example: copper, graphite, graphite infiltrated with copper, copper-tungsten, etc.). These electrodes will be manufactured with an inverse geometry to that desired by the EDM process, which may be varied dimensionally to take into account the separation distance (electrode-piece) during the process.

- Electroerosion by penetration of a body of conductive ceramic material (for example: boron carbide (B4C), silicon carbide infiltrated with silicon (SiSiC) and titanium diboride (TiB2), among other conductive ceramic materials) to obtain components filters that have through holes and/or through slots.

In this way, the present invention refers, as already indicated above, to a filter made of electroconductive ceramic material.

The electroconductive ceramic material filter object of the present invention has through holes and/or through slots, developed by penetration electroerosion.

According to a possible embodiment of the electroconductive ceramic material filter, the ceramic material is hot-pressed boron carbide (B4C), whose operating temperature range is between 200 °C and 800 °C.

According to another possible embodiment of the electroconductive ceramic material filter, the ceramic material is silicon-infiltrated silicon carbide (SiSiC), whose operating temperature range is between 200 °C and 1350 °C.

According to another possible embodiment of the electroconductive ceramic material filter, the ceramic material is titanium diboride (TiB2), whose operating temperature range is between 200 °C and 2000 °C.

The ceramic material body of the filter may have a cylindrical geometry and through holes with a circular cross section.

Alternatively, the ceramic material body of the filter may have a cylindrical geometry and through holes with a polygonal cross section.

Alternatively, the ceramic material body of the filter may have a geometry with a polygonal cross section and through holes with a circular cross section.

Alternatively, the ceramic body of the filter may have a geometry with a polygonal cross section and through holes with a polygonal cross section.

DESCRIPTION OF THE DRAWINGS

Figure 1 shows a possible configuration of the filter elements, according to the present invention, in which the through holes, machined by electro-erosion on a body of a conductive ceramic material, have a square cross section.

Figure 2 shows a possible configuration of the filter elements, according to the present invention, in which the through holes, machined by electro-erosion on a body of a conductive ceramic material, have a rhomboidal cross section.

Figure 3 shows a possible configuration of the filter elements, according to the present invention, in which the through holes, machined by electro-erosion on a body of a conductive ceramic material, have a circular cross section.

Figure 4 shows a possible configuration of the filter elements, according to the present invention, in which the through holes, machined by electro-erosion on a body made of a conductive ceramic material, have a circular cross section and different diameters.

Figure 5 shows a possible configuration of the filter elements, according to the present invention, in which the through slots, machined by electro-erosion on a body of a conductive ceramic material, have a rectangular cross section.

Figure 6 shows a possible configuration of the filter elements, according to the present invention, in which the through slots, machined by electro-erosion on a body of a conductive ceramic material, are arranged on the surface of a hollow cylinder. These slots are located at different heights on the surface of the cylinder, so that in the 0° and 180° orientation they are at the same height and in the 90° and 270° orientation they are also at the same height, but presenting a offset in relation to the previous ones, the number of slots being variable. That is, the slots that face each other are arranged at the same height and are of equal dimensions.

Figure 7 shows a possible configuration of the filter elements, according to the present invention, in which the through slots, machined by electroerosion on a body of a conductive ceramic material, are arranged on the surface of a hexagon whose interior is hollow and cylindrical in shape. In the drawing, the through slots are arranged at the same height on the opposite faces of the hexagon and at different heights on the non-facing faces.

DETAILED DESCRIPTION OF THE INVENTION

The purpose of the present invention is to obtain components for filtering applications by using bodies of conductive ceramic materials (1) such as, for example, silicon-infiltrated silicon carbide, boron carbide and titanium diboride, which have holes. through (2) and/or through slots (3), machined from electro-erosion processes. As mentioned, these components will be manufactured from a conductive ceramic material, which will make it possible to have the advantages that these materials present related to: hardness, resistance to abrasion, behavior against acids and bases and mechanical resistance to high temperatures, among others. These components include: slotted filters, filters with holes that have a radially symmetrical distribution, as well as any other conductive ceramic element that has through holes (2) and/or through slots (3), in order to be used for filtering applications. The machining process using electroerosion allows the obtaining of said ceramic components with great precision and a good surface finish that, on the contrary, would not be possible to obtain with conventional machining processes or would be very expensive.

As already mentioned, ceramic materials have excellent mechanical properties, especially hardness and mechanical resistance to compression, which are maintained at high temperatures, as well as good resistance to corrosion. It should be noted that one of the most interesting aspects of these conductive ceramic materials is their maximum continuous use temperature which, in the case of boron carbide, is 600 °C to 800 °C, in the case of titanium diboride, varies from 1000 °C to 2000 °C and, in the case of silicon carbide, reaches 1350 °C (Luis, C.J.; Puertas, I., Journal of Materials Processing Technology, Vol. 189 (1-3), 2007, pp. 301-309); (Torres, A.; Luis, C.J.; Puertas, I., Journal of Alloys and Compounds, Vol. 690, 2017, pp. 337-347). Likewise, boron carbide and titanium diboride have a thermal conductivity that, in general, is on the order of that of steels but which, in the case of silicon carbide, is clearly higher than these.

Among the components that can be obtained with the present invention include: slotted filters, filters with holes that have a radially symmetrical distribution, as well as any other body of ceramic material (1) that has through holes (2) and/or slots. pass-throughs (3) for use in filtering applications, using conductive ceramic materials. More specifically and as an example, mention may be made of silicon-infiltrated silicon carbide ceramic filters with cylindrical geometry and with cylindrical through holes (2), for use in filtering impurities in foundry processes.

The object of the present invention is achieved through a manufacturing process for conductive ceramic materials that includes the following two steps:

- Manufacture of electrodes made of conductive material (for example: copper, graphite, graphite infiltrated with copper, copper-tungsten, etc.). These electrodes will be manufactured with an inverse geometry to that desired by the EDM process, which may be varied dimensionally to take into account the separation distance (electrode-piece) during the process.

- Electroerosion by penetration of a body of conductive ceramic material (1) (for example: boron carbide (B4C), silicon carbide infiltrated with silicon (SiSiC) and titanium diboride (TiB2), among other conductive ceramic materials) for the obtaining filtering components that have through holes (2) and/or through slots (3).

In general, over recent years, ceramic materials have always been used in demanding applications, but in a relatively reduced way, due to the problems involved in the development of pieces with complex shapes using the aforementioned materials, mainly associated with the low machinability of these materials, through the use of conventional machining methods such as milling, turning or drilling, and the high wear of the cutting tools used, among other drawbacks.

Therefore, sinking EDM is a non-conventional manufacturing process that presents a series of competitive advantages over other processes that could be used to manufacture said ceramic components. Among these advantages, we can mention: its machinability does not depend on the hardness of the material, the ability to machine parts with complex geometries, the non-existence of mechanical stress on the part, a relatively high machining speed, the good surface finish that is achieved. achieved in the pieces, as well as their surface integrity, among others. On the contrary, the most important disadvantage that it presents is that ceramic materials must have sufficient electrical conductivity, where it has been estimated that their electrical resistivity should not exceed the range of 100 Wcm to 300 Wcm (Clijsters, S.; Liu , K.; Reynaerts, D.; Lauwers, B., Journal of Materials Processing Technology, Vol. 210, 2010, pp.

Therefore, with the present invention, it is possible to obtain ceramic components for use in systems and/or processes that require filtering elements. Said components will have different geometries when EDM with the aforementioned electrodes, which will be characterized by all of them having through holes (2) and/or through slots (3). With this, it will be possible to use it in equipment and/or processes that require aggressive operating conditions that would make the use of conventional components unviable. Among these particularly aggressive operating conditions, it is worth highlighting those that take place at high temperatures (from 600 °C to 2000 °C) and in which, in addition, it is necessary to use components that have to withstand high values of wear due to friction. and/or by contact, as well as oxidation-corrosion phenomena. To do this, it is necessary to use materials such as the ceramic materials mentioned above, given the chemical stability and good mechanical properties they present, even at high temperatures.

In a preferred embodiment of the invention, the developed components comprise bodies of the following ceramic materials, for example: boron carbide, titanium diboride, zirconium diboride, silicon-infiltrated silicon carbide, as well as any other type of conductive ceramic material. . Regarding the electrodes, conductive materials may be used, such as: copper, graphite, graphite infiltrated with copper and copper-tungsten, among others. From this, components will be developed that have through holes and/or through slots, equally spaced or not, to serve in filtering applications.

The manufacturing of the aforementioned components by penetration EDM will be carried out in a dielectric medium, preferably oil-based, to which elements such as graphite, graphene, alumina and other types of materials may be added to facilitate the EDM process. In a preferred embodiment of the process, a special mineral oil-based dielectric medium for EDM will be used without using additives in order to EDM the conductive ceramic materials.

In the manufacture of filters from cylindrical bodies or with any other type of geometry of revolution, rotation can be applied to the piece, so that the surface of the conductive ceramic material is progressively EDMed until the through holes are generated and/or or through slots.

EXAMPLES OF EMBODIMENT OF THE INVENTION

Example 1: Filter with a silicon-infiltrated silicon carbide (SiSiC) ceramic body with cylindrical geometry with cylindrical holes for foundry applications using sand molding of metallic materials. Said component has dimensions of 50 mm in diameter and a thickness of 5 mm, the holes being 3 mm in diameter and these also being equally spaced at a distance of 3 mm along the entire useful surface of the filter. The filter is placed just at the entrance of the sand mold, above the sprue, and serves to prevent impurities larger than the diameter of the filter holes from entering the mold distribution system. Said filter would be suitable to work in continuous operating temperature conditions of up to 1350 °C.

Example 2: Filter with a square geometry silicon-infiltrated silicon carbide (SiSiC) ceramic body with through holes of also square cross-section for foundry applications by sand molding of metallic materials. Said component has dimensions of 40 mm x 40 mm and a thickness of 4 mm, the square holes being 2.5 mm x 2.5 mm and these also being equally spaced at a distance of 2.5 mm along the entire length. the useful surface of the filter, which would give rise to rows of 7 holes each. The filter is placed just at the entrance of the sand mold, above the sprue, and serves to prevent impurities larger than the size of the filter holes from entering the mold distribution system. As in the case of the previous example, said filter would be suitable for working in continuous operating temperature conditions of up to 1350 °C.

Example 3: Screening element that uses a body of hot-pressed boron carbide (B4C) conductive ceramic material for the separation of materials that are very hard and/or corrosive and/or that are at a certain continuous operating temperature (up to about 700 °C). Specifically, the material used in this application is manufactured in the form of a disc with a diameter of 200 mm and a thickness of 10 mm. All the holes in the screening element have a square section, with dimensions of 5 mm x 5 mm and are spaced at a distance of 2 mm.

Example 4: Filter with a ceramic body type of silicon carbide bushing infiltrated with silicon (SiSiC) with a hollow cylindrical geometry with an external diameter of 75 mm and an internal diameter of 70 mm. Said filter has through holes with a square cross section of 2 mm x 2 mm. These holes are uniformly distributed angularly every 8°, along the entire cylindrical side surface, giving rise to a total of 45 square holes. Furthermore, these 45-hole distributions are repeated along the entire height of the filter with a separation distance between them of 2 mm. Its function is the filtering of highly corrosive liquids and/or at a continuous operating temperature of up to 1350 °C.

Example 5: Filter with a ceramic body type titanium diboride (TiB?) bushing with a hollow cylindrical geometry with an external diameter of 60 mm, an internal diameter of 54 mm and a length of 100 mm. Said filter has through slots arranged vertically, along the entire length of the cap, with a width of 2 mm and with a separation distance between them also of 2 mm. These slots are uniformly distributed angularly every 8°, along the entire cylindrical side surface, giving rise to a total of 45 through slots. Its function is the filtering of highly corrosive liquids and/or at a continuous operating temperature of up to 2000 °C.

Claims (8)

1. - Filter made of electroconductive ceramic material (1) characterized in that it has through holes (2) and/or through grooves (3) developed by penetration electroerosion. 2. - Electroconductive ceramic material filter (1) according to claim 1, characterized in that the ceramic material is hot-pressed boron carbide (B<4>C), whose operating temperature range is between 200 °C and 800°C. 3. - Electroconductive ceramic material filter (1) according to claim 1, characterized in that the ceramic material is silicon carbide infiltrated with silicon (SiSiC), whose operating temperature range is between 200 °C and 1350 °C. 4. - Electroconductive ceramic material filter (1) according to claim 1, characterized in that the ceramic material is titanium diboride (EB<2>), whose operating temperature range is between 200 °C and 2000 °C. 5. - Electroconductive ceramic material filter (1) according to claims 2 to 4, characterized in that the ceramic material body (1) has a cylindrical geometry and through holes (2) with a circular cross section. 6. - Electroconductive ceramic material filter (1) according to claims 2 to 4, characterized in that the ceramic material body (1) has a cylindrical geometry and through holes (2) with a polygonal cross section. 7. - Electroconductive ceramic material filter (1) according to claims 2 to 4, characterized in that the ceramic material body (1) has a geometry characterized by having a polygonal cross section and through holes (2) with a circular cross section. 8. - Electroconductive ceramic material filter (1) according to claims 2 to 4, characterized in that the ceramic material body (1) has a geometry characterized by having a polygonal cross section and through holes (2) with a polygonal cross section.