Method for producing an abrasive particle, and abrasive particle

Abstract

The invention relates to a method for producing an alumina based abrasive particle (1), comprising at least the following steps: forming a sol as a solution or dispersion of alumina particles, gelling the sol by adding gelling agents, forming shaped bodies from the gel using an additive procedure, drying and firing the shaped bodies while retaining the previously achieved geometry of the abrasive particles. Hereby, it is provided that an optically binding binder is added to the sol and/or the gel, the gel is applied additively layer by layer and the binder is set using electromagnetic radiation so as to form the shaped bodies. The produced abrasive particle may be formed, in particular, by six intersecting or overlapping triangular volume regions.

Claims

1. An alumina based abrasive particle, comprising six essentially plane-parallel volume bodies, each volume body always comprising two triangular walls essentially parallel to each other and a ridge face and the triangular walls always comprising two cathetuses of equal length and joining at a central region of the abrasive particle and a longer hypothenuse.

2. The abrasive particle according to claim 1, wherein it is formed exclusively from the volume bodies and intermediate regions connecting the volume bodies or representing overlaps of the volume bodies.

3. The abrasive particle according to claim 1, wherein it comprises essentially a flattened tetrahedal outer shape having essentially four lateral regions each having a triangular shape, the six ridge faces being formed between the lateral regions, and recesses being formed in the lateral regions.

4. The abrasive particle according to claim 1, wherein always three ridge faces join in a top face and the abrasive particle comprises four triangular, equal-sided top faces.

5. The abrasive particle according to claim 4, wherein the volume bodies are provided as plane-parallel pads or ridges with a consistent wall thickness.

6. The abrasive particle according to claim 5, wherein a wall thickness ratio is defined as the ratio of the wall thickness to the hypothenuse length and lies in the range between 0.05 and 0.5.

7. The abrasive particle according to claim 1, wherein it is formed from polycrystalline α alumina material.

8. A grinding article, comprising: a substrate having an upper face on the upper face of the substrate a multiplicity of abrasive grains according to claim 1, and a binder material applied to the upper face of the substrate and surrounding a lower region of the abrasive particles.

Description

(1) The invention is subsequently illustrated on the example of a few embodiments by means of the accompanying drawings. These show in:

(2) FIG. 1-4 schematic representations of the geometric shapes of an abrasive particle according to an embodiment of the invention, in various perspective views;

(3) FIG. 5 an elevation of an abrasive particle corresponding to FIG. 1-4 with widening ridges;

(4) FIG. 6, 7 transparent images of an abrasive particle according to an embodiment of the invention, in various perspective views;

(5) FIG. 8 a perspective view of an abrasive particle according to an embodiment of the invention;

(6) FIG. 9 an elevation of the abrasive particle according to FIG. 8;

(7) FIG. 10-12 further perspective views of the abrasive particle from FIGS. 8, 9;

(8) FIG. 13 a grinding article comprising a multiplicity von abrasive grains;

(9) FIG. 14 an enlarged detail from FIG. 13 with the integration of an abrasive particle on the grinding article;

(10) FIG. 15 a flow chart of a method for producing the abrasive particles according to an embodiment of the invention.

(11) An abrasive particle 1 on the basis of α alumina (aluminium oxide, Al203) is shown in more detail in the embodiment of FIGS. 6, 7 as well as the embodiment of FIGS. 8 through 12 and formed by six identical ridges 7 (volume bodies) that approach each other towards a central region or, as shown in an idealized manner in FIG. 1, towards a centre point M. The ridges 7 area each plan-parallel with two parallel triangular ridge walls 6 and a ridge face 3 connecting the ridge walls 6. Thus, the ridge face 3 always lies perpendicular with respect to the two ridge walls 6. Three ridge faces 3 each join in a top face 4 which thereby forms a equal sided triangle having a side length corresponding to the wall thickness d of the ridges 7 (see, in particular, the indications of the geometric distances or lengths respectively in FIG. 10). The ridge walls 6 each form an equal sided triangle with two cathetuses 15 of the cathetus length k extending inwards from a top face 4 and a hypothenuse 16 of the hypothenuse length h connecting two top faces 4, where h>k.

(12) For illustration purposes in FIG. 11 the six ridges are designated as first ridge 7a, second ridge 7b, third ridge 7c, fourth ridge 7d, fifth ridge 7e, and sixth ridge 7f. The six ridges 7a through 7f join towards the middle in transition areas extending outwards towards the top faces 4, or, one could say, these transition areas represent overlaps of the ridges 7 extending inwards.

(13) Thus, the ridge faces 3 are—as can be seen, in particular, in the embodiment of FIGS. 8 through 12—rectangular towards the edges h and d.

(14) Thus, the abrasive particle 1 deviates from the ideal outer shape of a tetrahedron with a centre point M as shown in FIG. 1; however, it exhibits a tripartite symmetry, i.e. four tripartite axes. Compared to the tetrahedron shape the lateral faces 2 recessed inwards towards the centre point M whereby the lateral faces 2 are limited each by three hypotenuses 16 and the recesses 5 are each defined by three cathetuses 15 or three ridge walls 6 respectively.

(15) Thus, each ridge 7 is formed having one outer ridge face 3 between two recesses 5.

(16) Thus, the points of contact of all cathetuses 15 of the ridges 7 join at about the centre of gravity M of the abrasive particle 1.

(17) In deviation from this embodiment, for example, versions with ridge walls 6 are possible that do not run exactly parallel so that no ridges are created with a consistent thickness but rather, for example, becoming somewhat thicker from their ridge faces 3 towards the middle or, respectively, run non-planar or planar but not parallel.

(18) Thus, the abrasive particles 1 form a symmetrical body which automatically stands always on one lateral face 2, i.e. three hypotenuses 16. This is shown in more detail, for example, in FIG. 14: the abrasive particle 1 lies on one upper face 9 of a substrate 10 formed e.g. by a fabric. Further, on the upper face 9 of the substrate 10 a binder material 12 is applied as casting compound covering the lower region of the abrasive particles 1 leaving open an upper region. The binder material 12 cures thereby allowing the creation of a grinding article 14 according to FIG. 13 where a multiplicity of abrasive grains 1 is fixed on a substrate, e.g. a fabric 10, and in which binder material 12 is fixed and secured. Hereby it can be seen, for example, from FIG. 13 in the edge regions, that the lower region of the abrasive particle 1 is surrounded by the binder material 12 in a form-fit manner because the Binder 12 always enters the recesses 5 of the abrasive particles 1 thereby surrounding the ridge walls 6, in particular, in the lower, widened region of the abrasive particles 1.

(19) Further, the tripartite shape of the abrasive particle 1 exhibits a strong resistance against tilting against loads in any direction because—as can be seen, in particular, from the views of FIGS. 9 and 11—every tilt moment is countered by one or two ridges 7.

(20) A wall thickness ratio w is defined as the ratio of the wall thickness d to the hypothenuse length h, i.e.
w=d/h

(21) The wall thickness ratio w determines the stability, i.e. in particular the resistance against tilting, and a total height G of the abrasive particle 1. The embodiment of FIGS. 6, 7 shows ridges 7 with a small wall thickness ratio w; the preferred embodiment of FIGS. 8 through 12 shows ridges 7 with a larger wall thickness ratio w, preferably lying in the range between 0.05 and 0.5.

(22) The arrangement of the abrasive particles 1 on the substrate 10 according to FIG. 13 may be regular or irregular.

(23) The creation of the abrasive particles 1 happens in accordance with the flow chart of FIG. 15 by means of a sol gel process with additive application, also referred to as “3D printing:”

(24) Following commencement in St0, a sol is generated in step St1 in that, for example, nano particles of alumina are treated in an aqueous dispersion, for example, as boehmite, e.g. with additives (step St1). Subsequently, in step St2 a gel is created from this sol in that gelled substances, for example nitric acid, are added. Further, in step St3, an optical binder is added which cures upon receiving electromagnetic radiation of a specific frequency, e.g. in the UV range. In addition (e.g. in step St1 or St2) α alumina seeds, i.e. α alumina mono-crystals may be added for later crystallite generation, as it is known as such in sol gel processes.

(25) In step St4, the gel so generated is successively applied layer by layer onto a base whereby, after a layer has been applied, subsequently, according to step St5, the gel material is cured at the desired spots of the material by means of a laser having the relevant frequency and being suitably focussed, and at other spots remains as non-cured mass or is being removed. The steps St4 through St5 can be repeated successively until the shaped bodies have been completed. The remaining gel mass may be removed subsequently, in step St6, or even upon completion of each step St5 of optical curing.

(26) Thus, a 3D print or an additive application or ablation from the gel phase is achieved by means of laser curing whereby on a substrate a multiplicity of abrasive grains 1 are created from gel with optically cured binder. The abrasive particles 1 may be placed closely together on the substrate, i.e., in particular, more densely than on the manufactured grinding article of FIG. 14, whereby the abrasive particles 1 upon production are formed e.g. alternatingly on a lateral face 2 and on a top face 4, i.e. interleaved, but spaced apart, so as to create a high number of abrasive grains 1 on a substrate.

(27) Subsequently, the green bodies so generated, which already exhibit the desired shape of the abrasive particles 1, are subjected to thermal treatment. Already, the Laser treatment has led to heating, which may already have fulfilled the step of drying; otherwise, for example, the following steps are carried out subsequently: if required, further drying in step St7 calcining at about 800° Celsius in step St8 whereby the Binder is oxidized, firing at about 1400° Celsius in step St9.

(28) The alumina based abrasive particles 1 so generated are subsequently further processed, for example, to produce the grinding articles 14 according to FIG. 13.

LIST OF REFERENCE NUMERALS (PART OF THE DESCRIPTION)

(29) 1 abrasive particle 2 lateral face 3 ridge face 4 triangular top face 5 recess 6 wall, preferably ridge wall 7 volume body, preferably ridge 7a first ridge 7b second ridge 7c third ridge 7d fourth ridge 7e fifth ridge 7f sixth ridge 9 upper face 10 substrate, e.g. fabric 12 binder material 15 cathetus 16 hypotenuse M centre point k cathetus length h hypotenuse length d wall thickness (arm length of the top face 4) St0 start St1 step of forming a sol St2 step of forming a gel St3 step of adding an optical binder St4 step of successive and layer by layer application onto a base St5 step of binding/curing the gel material using a laser St6 step of removing remaining gel mass St7 step of drying, may be carried out in St5 already St8, St9 thermal treatment of the green bodies St8 step of calcining at about 800° Celsius with oxidization of the binder St9 step of firing at about 1400° Celsius