DE202014101739U1 - Abrasive grain with knots and extensions - Google Patents

Abstract

Abrasive grain (10) with at least one node (11) and at least four extensions (12-12 '' ') extending from the node (11), characterized in that for each plane running through the node (11) at least one first extension (12-12 "") runs on a first side of the plane and at least one second extension (12-12 "") runs on a second side of the plane which is opposite the first side.

Description

The present invention relates to defined shape abrasive grains, abrasive grain aggregates, abrasive grain production methods, casting tools, abrasive grain abrasive articles, methods of making abrasive articles, and methods of abrading a surface with an abrasive article.

Abrasive grains, in particular ceramic abrasive grains, of defined shape and size have been known for some time.

The US 5,201,916 discloses, among other things, flat abrasive grains having, for example, a triangular, rectangular or circular shape. These abrasive grains are prepared from a dispersion containing α-alumina convertible particles and a volatile component liquid. The dispersion is poured into a mold having a flat base and depressions whose shapes are complementary to the desired shapes of the abrasive grains. Subsequently, a part of the volatile component is removed, so that a precursor of the desired shape is formed. The precursor is then removed from the mold, calcined and finally sintered to form the finished abrasive grain.

The abrasive grains produced by this method have two opposing bases that are substantially the same geometric shape. The abrasive grains are given a longer life because of the abrasive grains during grinding constantly break off small pieces, so that new cutting surfaces arise. The abrasive grains thereby sharpen themselves. Of abrasive grains with a base in the form of a triangle, in particular an equilateral triangle, it is assumed that in electrostatic scattering about one to two thirds orient so that a tip points away from the documents, while more Orient the abrasive grains so that the tip faces the surface.

In an in EP 615 816 initially described elongated, rod-shaped precursors are produced by extrusion, which are then divided into individual abrasive grains. The rod-shaped abrasive grains may thus have, for example, a cylindrical or prismatic shape.

In the WO 2009/085841 describes another production process in which the precursor is dried in the mold under conditions that lead to the breaking of the precursor. The fragments have at least partially surfaces and edges which are complementary to the corresponding surfaces and edges of the mold and therefore have the angle defined by the mold. These surfaces and edges provide increased cutting ability. The other surfaces and edges created by breaking are irregular.

The WO 2010/077495 discloses abrasive grains containing a continuous or non-penetrating opening or having a cup-like shape. Also, production processes for such abrasive grains are described there. Other abrasive grains with undefined openings are in the WO 2010/077518 disclosed. The WO 2010/077491 also deals with abrasive grains with a shell-like shape.

From the WO 2010/077519 abrasive grains are known having two opposite major surfaces and extending therebetween, inclined to the major surfaces side surfaces. The various side surfaces of an abrasive grain may be inclined at different angles relative to the major surfaces.

The document WO 2011/068724 also shows abrasive grains having a base side and a tip and inclined side surfaces extending therebetween. Similar abrasive grain shapes are also available in the WO 2011/109188 described.

The document WO 2010/077509 deals with abrasive grains that have a surface with a multitude of furrows. These grooves are created by means of complementary ridges on the bottom of the mold.

The WO 2011/068714 shows pyramidal abrasive grains with a parallelogram, in particular rhombic, a dragon-shaped and a superelliptic base.

The WO 2011/139562 discloses abrasive grains in the form of tetrahedra and modifications thereof. For example, the side surfaces may be concave or convex, the corners of the tetrahedron may be truncated, or the edges may be curved.

In the WO 2012/018903 described abrasive grains contain two or more plate-shaped portions which are arranged at an angle to each other.

At the in WO 2012/061016 described method, an abrasive structure is first prepared, which contains abrasive grain precursors, the fragile webs together are connected. After sintering, the abrasive grains are separated from each other by breaking the webs.

Alternatively, abrasive grains of defined shape can also be produced by a screen printing process. This describes, for example, the WO 96/12776 , In this case, a dimensionally stable dispersion is passed through openings with a defined shape on a conveyor belt and then cured. The openings may for example be contained in a movable endless belt.

An advancement of the Siebdruckverfahrens is in the WO 2011/087649 disclosed. In this method, the dispersion is forced through the openings of the endless belt by means of a differential pressure. With a suitable choice of the viscosity of the dispersion abrasive grains can be produced with this method, the cross-section of which tapers from a first main side to a second opposite main side.

In the WO 2012/061033 For example, methods for producing abrasive grains of defined shape by means of laser radiation are described. In addition, other special forms of abrasive grains are disclosed. For example, the abrasive grains may include a major element and at least three rod-shaped elements extending therefrom. In particular, the abrasive grain may have the shape of a cross, a capital letter "T", a star or a Greek lower case "λ".

It is generally assumed that abrasive grains having a defined shape have improved properties in several respects: If the abrasive grains already have a defined shape and size at the beginning of their production, then a subsequent sorting step is not necessary, with which the abrasive grains would otherwise have to be divided into different size fractions. In addition, the shapes and sizes remain almost unchanged even between different production batches, which makes the grinding properties very reproducible. Furthermore, the abrasive grains may, for example, provide increased overall removal, have a longer life, produce increased surface finish of the machined surface, or provide a more reproducible sanding result.

Nevertheless, the abrasive grains known from the prior art have a number of disadvantages. For example, are from the WO 2012/061033 Abrasive grains are known which have elongated extensions. Such abrasive grains are made of a flat material, correspondingly all these extensions lie in a common plane. When such abrasive grains are placed on a substrate by mechanical scattering, most of these abrasive grains come to rest on one of the flat sides, and only a small portion of the extensions face away from the substrate and are available for the abrasive process. After a short period of use, usually as soon as projecting corners of the abrasive grain are broken off, the cross-section of an abrasive grain which acts on the surface to be machined, very large; that is, the abrasive grain is with its entire surface engaged in or on a surface to be machined. Thus, the grinding performance of such an abrasive grain is significantly reduced. During the duration of a grinding process, the grinding performance varies greatly. An orientation must therefore be achieved by an electrostatic scattering, which, however, is far more complex than a mechanical scattering.

It is therefore an object of the present invention to at least partially overcome the disadvantages of the prior art. In particular, therefore, an abrasive grain is to be provided which, contrary to the state of the art, ensures that a majority of the abrasive grains are likely to come to rest on an abrasive base, especially during mechanical scattering, that a surface to be treated has a longer service life and during this Service life can be processed with uniform as possible grinding action.

This object is achieved by an abrasive grain having at least one node and at least four extensions extending from the node. According to the invention, for any arbitrary plane passing through the node, at least one first extension shall extend on a first side of the plane and at least one second extension shall run on a second side of the plane opposite the first side. This means that at least one such extension extends on both sides of each plane. However, such an extension does not have to be at right angles to such a plane.

An abrasive grain having such a shape allows for a desired orientation of the abrasive grain, particularly an orientation that allows at least one extension of the abrasive grain to protrude from an abrasive pad. In particular, such an alignment can also be achieved with mechanical scattering. Namely, if an abrasive grain coincides with the mechanical scattering on a flat abrasive pad, according to the invention extends in any case at least one extension away from the plane of the pad and is thus available for the grinding process.

It is particularly advantageous if an axis of at least one extension in one Angle extends from the pad, which is at least 30 °, preferably at least 60 °, more preferably at least 75 ° and particularly preferably 90 °. This can be achieved by extending an axis of the extension at said angle to a support plane of the abrasive grain. Here, a support plane is an imaginary plane of the abrasive grain having the following property: When the abrasive grain is placed on a horizontal support plane such that the support plane coincides with the support plane, the abrasive grain is stable against tipping over. This is the case when the perpendicular projection of the center of gravity of the abrasive grain on the support points lies within the convex hull of the points where the abrasive grain rests on the support plane. So if the abrasive grain with the support plane on a flat abrasive pad, so agrees the angle between the extension and support plane with the angle between extension and abrasive pad match.

Thus, for example, with a uniform distribution of exactly four extensions, an abrasive grain in the form of a tetrapods, as described below in the 1 and 2 is shown. Such an abrasive grain has a high degree of symmetry and stands on three of the extensions on a base, while the axis of a fourth extension has a direction away from the base direction. However, the invention is not limited to four extensions; The abrasive grain may also contain more than four extensions, for example six or eight extensions. The extensions may in particular be aligned in the corners of an imaginary cube, octahedron, dodecahedron or icosahedron; Such abrasive grains also have a high degree of symmetry.

A further advantage of the inventive shape of the abrasive grain is that the small cross-section of such an extension, which is small in relation to the overall size of the abrasive grain, enables a better abrasive behavior. In addition, an advantageous pressure angle can be ensured in the material to be processed by a suitable choice of the outer contour of the extension, as will be explained in detail below.

To increase these advantages even further, the extensions can be composed of geometric basic shapes. In this case, in particular polygons (such as triangles or quadrilaterals, for example trapezoids or even star-shaped polygons), circles and ovals are regarded as geometrical basic forms. This is especially useful to allow similar grinding behavior in all orientations of the abrasive grain or to provide abrasive grains with directional properties.

An extension can also be similar to a screw twisted in itself. Such an abrasive grain has a right angle to the axis of an extension, therefore in any possible grinding direction, a different grinding behavior. However, an aggregate of abrasive grains applied to a substrate by mechanical scattering has a homogeneous behavior in all grinding directions, since experience has shown that the orientation of mechanically scattered abrasive grains is evenly distributed about an axis perpendicular to the substrate. Another advantage of such twisted extensions is better anchoring in the binder. The twisted contour allows in particular a kind of toothing with the binder.

The cross-sectional area of an extension may also taper along an axis of an extension extending from the node. This gives the abrasive grain a better internal stability and a higher resistance to external forces, in particular by the forces that are opposed by the surface to be machined.

An extension can also be tapered substantially at an end facing away from the node and, in particular, form a corner or point which further increases the abrasive properties. It is alternatively also conceivable that the extension ends in an end face. This end face may be flat and perpendicular to the direction of an axis of the extension. The end face can also have break edges due to its manufacture, which in particular can act as cutting edges and can improve the abrasive behavior. Has proven particularly advantageous an end surface which is substantially concave. By a concave end surface creates an advantageous pressure angle to the surface to be machined. Alternatively, however, a convex end surface is conceivable.

Advantageously, an axis of at least one projection with the cutting edge, which is formed by a plane through this axis with the outer contour of the abrasive grain, encloses an angle which is between + 45 ° and -45 °, preferably between + 40 ° and -40 °, more preferably between + 30 ° and -30 °, more preferably between + 25 ° and -25 °, more preferably between + 20 ° and -20 °, and most preferably between + 10 ° and -10 °. The angle is referred to as positive when the projection tapers at its end facing away from the node; he is considered negative when thickening there.

The shape and size of the abrasive grain can be determined using a microscope, for example. The abrasive grain according to the invention can have a size in the entire size range which is also customary for conventional abrasive grains. Usually lead abrasive grains with larger Sizes for a higher material removal from a machined surface than smaller abrasive grains. For example, the abrasive grain may have a size in the range of 100 microns to 2000 microns. This size can be determined experimentally with the help of a microscope. It is understood as the diameter of an enveloping circle of the microscopic image of the abrasive grain, ie the smallest diameter of a circle enclosing the image.

• – Hohlräume oder Bläschen aufgrund eingeschlossener Luft und/oder anderer Gase in einer Dispersion, aus der die Schleifkörner hergestellt werden;
• – fehlende Ecken und/oder Kanten, welche durch ein nicht komplettes Ausfüllen einer Giessform und/oder während eines Entfernens eines Vorprodukts des Schleifkorns aus einer Giessform entstehen;
• – eingefallene Seitenflächen und/oder Kanten, die durch ein Schrumpfen während des Entfernens eines Teiles der flüchtigen Komponenten der Dispersion entstehen; insbesondere eingefallene Flächen, die aus der oberen freien, nicht in Kontakt mit der Giessform stehenden Fläche der Dispersion entstehen;
• – Abplatzungen, welche durch einen Trocken- und/oder einen Sinterprozess hervorgerufen werden;
• – abgebrochene Ecken und/oder Kanten, welche durch einen Transport und/oder während einer Weiterverarbeitung der Schleifkörner als Schüttgut entstehen.

The shape of the abrasive grain described above is an idealization. However, the invention also includes abrasive grains which deviate from this idealized form within the manufacturing tolerances. Possible deviations from the idealized form may have one or more of the following causes:

• - cavities or bubbles due to trapped air and / or other gases in a dispersion from which the abrasive grains are made;
• - Missing corners and / or edges, which result from an incomplete filling of a mold and / or during removal of a precursor of the abrasive grain from a mold;
• - sunken side surfaces and / or edges caused by shrinkage during the removal of part of the volatile components of the dispersion; in particular sunken surfaces arising from the upper free surface of the dispersion not in contact with the mold;
• - flaking, which are caused by a dry and / or a sintering process;
• - Broken corners and / or edges, which arise as a result of transport and / or during further processing of the abrasive grains as bulk material.

The deviations from the idealization need not necessarily lead to adverse properties of the abrasive grain. For example, broken corners and / or edges can also cause additional cutting edges to be created compared to the idealization, which can even positively influence the grinding effect.

In particular, the invention also encompasses abrasive grains whose shape only substantially coincides with the idealized shape. For example, contours of cuts by the abrasive grain are also considered to be substantially rectilinear if they are at least partially or even completely curved and have a radius of curvature that is at least twice, preferably at least five times, more preferably at least ten times the diameter of the abrasive grain. The location where two surfaces of the outer contour meet is referred to essentially as an edge, and a point of the outer contour of a section is considered substantially as a corner when the radius of curvature there is at most 10%, preferably at most 5%, particularly preferably at most 2 % of the diameter of the abrasive grain. Furthermore, end surfaces are also understood to be essentially flat if they are curved and have radii of curvature which amount to at least twice, preferably at least five times, particularly preferably at least ten times the diameter of the abrasive grain.

Preferably, however, the abrasive grain has an idealized shape as described above.

The abrasive grain may, for example, contain or consist of a ceramic material, in particular a polycrystalline ceramic material. Preferably, the abrasive grain contains alumina, more preferably α-Al ₂ O ₃ .

Alternatively or additionally, the abrasive grain may also contain at least one further metal oxide, such as sodium oxide, magnesium oxide, iron oxide, silicon oxide, calcium oxide, zirconium oxide, yttrium oxide, zinc oxide, cobalt oxide, nickel oxide, hafnium oxide, chromium oxide, praseodymium oxide, samarium oxide, ytterbium oxide, neodymium oxide, lanthanum oxide, Gadolinia, ceria, dysprosia, erbia, lutetia, titania, manganese oxide, or any combinations thereof.

Many of these metal oxides are derived from impurities in the starting raw materials, such as alumina. However, with sufficiently low levels of abrasive grain, such contaminants do not have a negative impact on the production and application of the abrasive grain. Some of these impurities may even have a positive effect on the abrasive grain.

For example, levels of zirconia or yttria can come from grinding balls that can be used in a grinding step in the production of the abrasive grains. Proportions of iron oxide can come from a milling vessel used in such a milling step.

Also alternatively or additionally, the abrasive grain may contain other hard materials, such as silicon carbide.

Furthermore, the abrasive grain may contain at least one decomposition product of a disperser described in more detail below, at the production of abrasive grains was used. Further, the abrasive grain may contain at least one nucleating agent or its decomposition product used in the production of the abrasive grains. The nucleating agent may, for example, be the magnesium oxide already mentioned above.

In addition, the abrasive grain and at least one of the other in the EP 615 816 A1 described substances.

The ingredients mentioned can be determined by means of chemical analysis methods known per se.

The abrasive grain may contain or consist of a microstructure with one or more different phases. In this case, a first phase may consist of aluminum oxide, particularly preferably of α-Al ₂ O ₃ . A second phase can consist of one or more of the abovementioned further metal oxides and / or further hard materials.

The proportion of aluminum oxide, in particular of α-Al ₂ O ₃ , in the abrasive grain, for example, at least 25 wt .-%, preferably at least 50 wt .-%, more preferably at least 70 wt .-%, particularly preferably at least 95 wt .-% be.

The abrasive grain may have a coating which covers only a part of the surface, in particular only one or more edges and / or only one of a plurality of areal areas of the surface. The coating may be, for example, a ferromagnetic or a paramagnetic coating. Such a partial coating of the surface with a ferromagnetic or a paramagnetic material makes it possible to align the abrasive grain in a predetermined direction in a magnetic field applied during the scattering. Alternatively, it may be a coating of a material having increased thermal conductivity, or a coating which allows increased adhesion of the abrasive grain to the abrasive backing.

Another aspect of the invention relates to a set of abrasive grains. An aggregate of abrasive grains is understood here and below to mean an associated collection of abrasive grains. For example, it may be a collection of abrasive grains contained in a container and stored and / or transported, for example, in a bag.

Such an accumulation of abrasive grains can be used to make an abrasive article. As a whole of abrasive grains, the entirety of all abrasive grains present in an abrasive article is also considered.

The totality of abrasive grains preferably contains at least 20% by weight, preferably at least 50% by weight, particularly preferably at least 90% by weight, of abrasive grains according to the invention, as described above. The remaining abrasive grains contained in the entirety may also have a defined shape, which, however, deviates from the inventive shape, or they may not have a defined shape, since it is, for example, broken abrasive grains. These other abrasive grains, which are included in their entirety, are also referred to as "supporting grains".

It is conceivable and within the scope of the invention that the abrasive grains according to the invention contained in the entirety are formed differently from one another. For example, the entirety of abrasive grains may include a first portion of abrasive grains of a first embodiment of the present invention and a second portion of abrasive grains of a second embodiment of the present invention which is different from the first embodiment of the present invention. In particular, the abrasive grains of the first embodiment according to the invention can differ in their size and / or in their shape from the abrasive grains of the second embodiment according to the invention.

The entirety of abrasive grains can consist exclusively of identical abrasive grains according to the invention; in particular, the whole then has a punctiform size distribution.

The totality of abrasive grains may have substantially a size distribution corresponding to a standard size used in the abrasive industry, such as the American National Standards Institute (ANSI), the Federation of European Producers of Abrasives (FEPA) standards, or the Japanese Industrial Standard (JIS) standards. , For example, the totality of the abrasive grains may be substantially P12, P16, P20, P24, P30, P36, P40, P50, P60, P80, P100, P120, P150, P180, P220, P240, P280, P320, P360, P400. P500, P600, P800, P1000, P1200, P1500, P2000, P2500, P3000 or P5000 according to the FEPA standard. In this case, a size distribution "essentially" means that at least 90% by weight, preferably at least 95% by weight, more preferably at least 99% by weight and particularly preferably all abrasive grains of the totality of abrasive grains fulfill this standard.

As has already been described above, it is also conceivable that the entirety contains at least two different proportions of abrasive grains according to the invention and / or at least one fraction of non-inventive abrasive grains. Everyone these proportions may in themselves have a size distribution which corresponds in each case to one of the abovementioned size standards customary in the abrasives industry.

• a) Herstellung oder Bereitstellung einer Dispersion, enthaltend α-Aluminiumoxid-Partikel und/oder Partikel, welche in α-Aluminiumoxid umwandelbar sind, sowie mindestens ein flüchtiges Dispersionsmittel, bevorzugt Wasser;
• b) Einfüllen der Dispersion in mindestens eine Vertiefung einer Giessform;
• c) optional Abrakeln einer Oberseite der Giessform, um zumindest einen Teil der Dispersion zu entfernen, der über die Oberseite der Giessform übersteht;
• d) Entfernen eines Teiles der flüchtigen Komponenten der Dispersion, so dass mindestens ein Schleifkorn-Vorprodukt entsteht;
• e) Entfernen des Schleifkorn-Vorprodukts aus der Giessform;
• f) optional Kalzinieren des Schleifkorn-Vorprodukts;
• g) Sintern des Schleifkorn-Vorprodukts, um mindestens ein Schleifkorn zu erhalten.

An abrasive grain according to the invention or an entirety of abrasive grains according to the invention can be obtained, for example, with the following US 5,201,916 be prepared known methods:

• a) preparation or provision of a dispersion containing α-alumina particles and / or particles which are convertible into α-alumina, and at least one volatile dispersing agent, preferably water;
• b) filling the dispersion into at least one well of a casting mold;
• c) optionally, doctoring a top of the mold to remove at least a portion of the dispersion that overhangs the top of the mold;
• d) removing a portion of the volatile components of the dispersion to form at least one abrasive grain precursor;
• e) removing the abrasive grain precursor from the mold;
• f) optionally calcining the abrasive grain precursor;
• g) sintering the abrasive grain precursor to obtain at least one abrasive grain.

Before and / or during the preparation of the dispersion in step a), the raw materials, in particular α-alumina particles and / or particles which are convertible into α-alumina, can be ground. This can be done for example by means of a ball mill, in particular by means of a planetary ball mill.

The dispersion may contain at least one dispersant. Such a dispersant facilitates the formation of the dispersion and increases its stability, for example, by forming layers around the individual grains which prevent agglomeration. The dispersant may be, for example, a polymer. As a rule, the dispersant decomposes at the latest during sintering in step g).

For producing the abrasive grain according to the invention as described above, a casting tool can be used, wherein the casting tool comprises at least one casting mold having at least one depression with a respective surface, the surface being complementary to the shape of at least part of the surface of the abrasive grain.

Preferably, a plurality of depressions in the mold, so that a plurality of abrasive grains can be cast with a casting.

In a further development of the US 5,201,916 known method, the above-mentioned mold is advantageously only a part of a multi-part casting tool, which additionally comprises at least one mold element, in particular a further mold or a punch element, with which in addition to the surface formed in the first mold at least a portion of the remaining surface of the abrasive grain is malleable.

For example, stamping elements can be provided which are guided into the filled depressions of the first mold, whereby also abrasive grains with undercuts can be formed.

Preferably, the stamp elements do not completely close the recesses of the mold, so that the volatile component of the dispersion can escape.

More complex forms of abrasive grain bodies are moldable in composite molds, similar to injection molding. For this purpose, at least one casting mold has at least one filling opening through which the dispersion can pass into the depressions.

The casting mold and / or the stamping element may for example contain or consist of silicone. The depressions may have an open top surface through which the dispersion can be filled.

The intermediate product formed in step d) should preferably be mechanically stable enough to be further processed as bulk material in the subsequent steps. The optional calcination in step f) is particularly advantageous or even necessary if the dispersion contains several different raw materials and a phase transformation is required.

Yet another aspect of the invention relates to an abrasive article containing a set of abrasive grains as described above. In particular, therefore, at least 20% by weight, preferably at least 50% by weight, particularly preferably at least 90% by weight, of all the abrasive grains of the abrasive article can be formed as abrasive grains according to the invention, as described above. The remaining abrasive grains may also have a defined shape, which, however, deviates from the inventive shape, or they may not have a defined shape.

The abrasive article may be, for example, a coated abrasive article, a nonwoven abrasive article, a bonded abrasive article, or an abrasive brush.

A coated abrasive article contains a particularly flexible backing such as paper, vulcanized fiber, a film, a textile material, a foam, or multi-layered combinations thereof. The abrasive grains may be attached to the backing by means of a make coat. The base binder and the abrasive grains may be covered with a size coat. Optionally, a second capping agent may also be present above said capping binder (English: "supersize coat").

As base binder, capping agent and second capping agent, it is possible to use all binders known per se, for example of synthetic resin, such as a phenolic resin, an epoxide, a urea resin, a melamine resin or an unsaturated polyester resin. The coat binder and / or the second coat binder may also contain other conventional active ingredients and / or fillers.

The abrasive article may be in various shapes, for example as a grinding wheel or abrasive belt.

The invention also includes a method for producing an abrasive article according to the invention as described above. The method includes a step in which a set of abrasive grains is fixed to and / or in a substrate, in particular by means of a binder. The substrate may be, for example, a particularly flexible base of a coated abrasive article, a nonwoven material of a nonwoven abrasive, a matrix of bonded abrasive or bristles of a brush. In the case of a coated abrasive article, the application of the base binder and / or the abrasive grains and / or the coat binder and / or the second coat binder can be carried out by a method known per se. For example, the abrasive grains may be applied electrostatically or mechanically (i.e., gravimetrically). Due to the inventive shape of the abrasive grains, a large proportion of the abrasive grains is oriented so that the above-described advantage also applies to mechanical scattering: At any orientation on a flat abrasive pad at least one extension extends away from this pad and thus to one working surface down. This means that a more complex electrostatic scattering can be dispensed with.

Further, the invention is also directed to a method of abrading a surface with an abrasive article as described above. The surface may in particular be a painted surface. In the case of a painted surface, abrasive grains having sizes of 500 μm or less are particularly suitable.

In the following the invention with the aid of several embodiments and drawings will be explained in more detail. Showing:

1 a three-dimensional view of a first embodiment of an inventive abrasive grain;

2 : a side view of the abrasive grain 1

3 : A top view of the abrasive grain from the 1 and 2 ;

4A to 4G : possible cross sections of the section AA 1 ;

5A to 5H : possible contours in the area of the extension of the section BB 1 ;

6 : Detail of the pressure angle;

7 to 12 : further embodiments.

The 1 shows a first preferred embodiment of an abrasive grain 10 with a knot 11 , From this node 11 out four extensions extend in the directions of the vertices of an imaginary tetrahedron 12 - 12 ''' , The extensions 12 - 12 ''' So each have an angular distance of about 109.5 ° from each other. Every level of the node 11 has at least one extension on its two opposite sides 12 - 12 ''' on. This constellation is exemplary in 2 to see, with a plane that is symbolized by the cut BB. An abrasive grain 10 which has at least four such extensions 12 - 12 ''' has the advantage that at least one of these Fortsetze 12 - 12 ''' pointing away from a support plane. A support plane is a horizontal plane parallel to section AA, for example, on which the abrasive grain 10 can rest. By way of example, the abrasive grain lies on three points 120 ' - 120 ''' each of an extension 12 ' - 12 ''' on. Thus, the in 2 above shown extension perpendicular to the support plane away. This is beneficial when the abrasive grain 10 is applied to a substrate, which then forms the support plane. Of course, in alternative embodiments it is also possible for the extensions to be in the corners of any other regular or irregular one geometric body extend, as long as the inventive properties are met.

It will be obvious to those skilled in the art that the invention is not limited to four extensions 12 - 12 ''' is limited, but that, for example, five or six or more extensions are conceivable. In particular, an abrasive grain could 10 be constructed so that the continuations 12 - 12 ''' at a level in the node 11 , which is parallel to a support plane, are mirrored, whereby the mirrored part could also be twisted to the original part. This is for example in 8th shown. Another embodiment in 7 shows by way of example an abrasive grain with eight projections pointing in the direction of the corners of an enclosing imaginary cube. The advantage of these abrasive grains is the fact that always more than one extension pointing away from a support plane and correspondingly more extensions of a grain can be used for grinding. The extensions are shown by way of example in the figures as quadrangular or round, of course, other geometries are conceivable.

Each of the extensions 12 - 12 ''' can have different geometries. The cross section to an axial direction in the direction of the axis X is in 2 shown as section AA. The 4A to 4G show examples of possible cross sections. Cross sections of such extensions 12 - 12 ''' may be composed of basic geometric shapes. Basic geometric shapes are polygons (such as triangles or squares, such as trapezoids or star-shaped polygons), circles, and ovals. A circular surface according to 4A may be deformed after the manufacturing process, such. In 4B shown. An exemplary outer contour 13 after making the abrasive grain is in 4C shown. As in 4D is shown by way of example, various manufacturing tolerances may occur on a triangular cross-sectional area, some of which may have further advantageous properties. The outer contour 13 for example, a flat section 131 , a concave section 131 '' and a convex section 131 '' contain. Also corresponding edges 15 between surfaces do not have to be pointed, but may be rounded; in 4D is such an edge 15 ' shown.

In general, the cross sections about the axial extent of the extension 12 - 12 ''' also different outer contours 13 to have. Also a twisted outer contour 13 is possible, so that a kind of screw may arise, shown by way of example in the embodiment in FIG 11 , The extensions off 9 have a triangular cross-section and are tapered, unlike the embodiment 12 , with blunt ending processes. Another embodiment with a quadrangular cross section of the extensions is shown in FIG 10 shown.

Considering the course of the cross section over the axial extent of the extension 10 ie from the node 11 up to an exemplary end face 14 in the direction of the axis X, also different configurations are possible. This is shown in the 5A to 5H , which is a cross section through an extension 12 - 12 ''' demonstrate. So can the thickness of the extension 12 - 12 ''' be constant ( 5A ) or lose weight ( 5C ). By way of example, the outer contour 132 of such a cross-section also concave (outer contour 132 ' in 5B ) or convex (outer contour 132 '' 5D ) or a mixture between such forms. In particular, the concave outer contour 132 ' is of advantageous effect, since in a preferred position of the abrasive grain 10 to a support plane an advantageous pressure angle δ between an axis X of an extension 12 and a tangent T to its contour 13 to a surface to be machined O, which is preferably substantially parallel to the support plane, is formed. Preferably, this angle is between + 45 ° and -45 °, more preferably between + 40 ° and -40 °, more preferably between + 30 ° and -30 °, even more preferably between + 25 ° and -25 °, more preferably between + 20 ° and -20 ° and more preferably between + 10 ° and -10 °. In the in 6 shown example in which the extension 12 Tapered at its end remote from the node, the angle δ is positive. In the cross section according to 5B he is negative, because there is the extension 12 Thickened at the end facing away from the node. In particular, it is possible that such an outer contour has at least one step ( 5H ). An extension 12 - 12 ''' of such an abrasive grain 10 can, starting from the node 11 , preferably in an end face 14 ends, exemplified in the 1 - 3 . 7 . 8th . 10 and 12 , But it is also possible that such an extension 12 - 12 ''' pointed ( 5G ), shown by way of example in the embodiment 9 , Such an endface 14 can be even or convex (end surface 14 ' in 5E ) or concave (end surface 14 '' 5G ). Particularly preferred is such an area 14 substantially perpendicular to the direction of an axis X of such an extension 12 - 12 ''' , In particular, such surfaces 14 also be formed by removing the abrasive grain precursor from a mold and having breaklines.

The abrasive grains according to the invention can be prepared, for example, by a process described below: First, a dispersion of 200 g of α-Al ₂ O ₃ , 0.4 g of MgO, 90 g of water as dispersant and 0.5 g of dispersant is prepared. The MgO acts as a nucleating agent. As a dispersant, for example, the product Dolapix CE64, available from Zschimmer & Schwarz, 56108 Lahnstein, Germany. The dispersion thus obtained is ground for 30 minutes at 200 revolutions per minute in a planetary ball mill, for example a planetary ball mill PM400, available from Retsch GmbH, 42781 Haan, Germany. Subsequently, the milled dispersion is filled into a silicone mold which contains recesses complementary to at least a portion of the shape of the desired abrasive grains. For some embodiments of the abrasive grain, an additional molding element as described above may be used, for example a further casting mold, with which at least a part of the remaining surface of the abrasive grain can be formed in addition to the surface formed in the casting mold. Then the volatile component, ie the water, is removed from the dispersion. This creates an abrasive grain precursor which is removed from the mold. In a final step, the precursor is sintered as bulk material at 1550 ° C for 5 minutes. The disperser is burned out during sintering.

An abrasive article according to the invention can be prepared, for example, as follows: On a pad of vulcanized fiber having a thickness of 0.8 mm, a phenolic resin dispersion is applied as a base binder precursor in an amount of 120 g / m ² . Subsequently, 600 g / m ^{2 of} the inventive abrasive grains are applied by means of electrostatic scattering. The base binder precursor is then cured to a base binder. Over the base binder and the abrasive grains is applied a phenolic resin dispersion in an amount of 800 g / m ² as a coat binder precursor, which is also cured.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5201916 [0003, 0054, 0059]
• EP 615816 [0005]
• WO 2009/085841 [0006]
• WO 2010/077495 [0007]
• WO 2010/077518 [0007]
• WO 2010/077491 [0007]
• WO 2010/077519 [0008]
• WO 2011/068724 [0009]
• WO 2011/109188 [0009]
• WO 2010/077509 [0010]
• WO 2011/068714 [0011]
• WO 2011/139562 [0012]
• WO 2012/018903 [0013]
• WO 2012/061016 [0014]
• WO 96/12776 [0015]
• WO 2011/087649 [0016]
• WO 2012/061033 [0017, 0019]
• EP 615816 A1 [0042]

Claims (12)

Abrasive grain ( 10 ) with at least one node ( 11 ) and at least four from the node ( 11 ) extending extensions ( 12 - 12 ''' ), characterized in that for each by the node ( 11 ) extending level at least a first extension ( 12 - 12 ''' ) runs on a first side of the plane and at least one second extension ( 12 - 12 ''' ) runs on a second side of the plane opposite the first side. Abrasive grain ( 10 ) according to claim 1, characterized in that at least one extension ( 12 - 12 ''' ) to an axial direction has a cross section which is composed of basic geometric shapes. Abrasive grain ( 10 ) according to one of the upper claims, characterized in that the cross-sectional area of at least one extension ( 12 - 12 ''' ) from the node ( 11 ) tapers off. Abrasive grain ( 10 ) according to one of the upper claims, characterized in that at least one extension ( 12 - 12 ''' ) at one of the nodes ( 11 ) facing away from the end pointed. Abrasive grain ( 10 ) according to one of the upper claims, characterized in that at least one extension ( 12 - 12 ''' ) on an end face ( 14 - 14 ''' ), which in particular substantially at right angles to the direction of an axis (X) of the extension ( 12 - 12 ''' ). Abrasive grain ( 10 ) according to one of the upper claims, characterized in that an axis (X) of at least one extension ( 12 - 12 ''' ) extends at an angle to a support plane which is at least 30 °, preferably at least 60 °, more preferably at least 75 °, and most preferably 90 °. Abrasive grain ( 10 ) according to one of the preceding claims, characterized in that the axis (X) with the cutting edge formed by a plane through this axis (X) with the outer contour encloses an angle between + 45 ° and -45 °, preferably between + 40 ° and -40 °, more preferably between + 30 ° and -30 °, more preferably between + 25 ° and -25 °, even more preferably between + 20 ° and -20 ° and particularly preferably between + 10 ° and -10 °. Abrasive grain ( 10 ) according to one of the preceding claims, characterized in that at least one of the extensions ( 12 - 12 ''' ) is twisted in itself. Abrasive grain ( 10 ) according to one of the preceding claims, characterized in that it contains or consists of a ceramic material, in particular a polycrystalline ceramic material, preferably alumina, particularly preferably α-Al ₂ O ₃ . Totality of abrasive grains ( 10 ), characterized in that it comprises at least 20% by weight, preferably at least 50% by weight, particularly preferably at least 90% by weight of abrasive grains ( 10 ) according to any one of the preceding claims. Casting tool for producing at least one abrasive grain ( 10 ) according to one of claims 1 to 9, wherein the casting tool comprises at least one casting mold which has at least one depression, preferably a plurality of depressions, with a respective surface, the surface being complementary to the shape of at least part of the surface of the abrasive grain ( 10 ). Abrasive article containing a total of abrasive grains ( 10 ) according to claim 10.

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