DE202014101741U1 - Partially coated abrasive grain - Google Patents

Abstract

Abrasive grain (10; 10 ') with a core (11; 11') and at least one coating (12; 12 '), characterized in that the coating (12; 12') only covers part of the surface of the core (11; 11 ') covers, in particular only one or more edges and / or only one of several flat areas (14; 14') of the surface.

Description

The present invention relates to coated abrasive grains having a core and a coating covering that core. Further, the invention relates to wholly abrasive grains, methods of making abrasive grains, abrasive article abrasive articles, methods of making abrasive articles, and methods of abrading a surface with an abrasive article.

Coated abrasive grains are known per se. For example, abrasive grains made of diamond are coated with nickel, cobalt or composite metals. Diamond has a higher thermal conductivity than other known abrasive grain materials. This can be detrimental to the bonding of the abrasive grains in a binder and in particular lead to premature grain breakage. A coating with the materials mentioned reduces the heat conduction, so that the disadvantages listed are avoided. In addition, such a coating can increase the adhesion between abrasive grain and binder.

In the EP 1 995 020 abrasive grains are disclosed which carry a magnetic coating. The abrasive grains can be aligned by means of an external magnetic field. As is known to those skilled in the art, the abrasive properties of an abrasive article are critically dependent on the orientation of the abrasive grains. If, for example, elongate abrasive grains are aligned with their longitudinal axis perpendicular to a substrate, this leads to an increased abrasive effect.

In general, however, a magnetic coating does not result in the abrasive grains being able to be reliably aligned in a desired manner in an external magnetic field. This is because the magnetic moment induced by an external magnetic field of ordinary magnitude is usually too small for many abrasive grain shapes to produce the force required for alignment. In principle, to increase this magnetic moment, the thickness of the coating could be increased. However, this would on the one hand increase the cost of the coating material and on the other hand lead to reduced grinding properties.

It is therefore an object of the present invention to provide a coated abrasive grain in which the disadvantages described above do not occur or at least be reduced. In some embodiments, the abrasive grain should align with as high a probability as possible in a desired, predefined orientation, particularly with the aid of an external magnetic field. In other embodiments, the friction heat occurring during grinding should be able to be removed as controlled as possible.

These and other objects are achieved by an abrasive grain having a core and a coating. Under the core is understood here and below, the main component of the abrasive grain, so the "actual abrasive grain" with which a grinding effect can be achieved. This core may consist of the materials described in more detail below, in particular a ceramic material, such as alumina.

According to the invention, the coating covers only part of the surface of the core. In particular, it can only cover one or more edges or only one of several flat areas of the surface. Compared with the abrasive grains known from the prior art, the core of the abrasive grains according to the invention is therefore not completely covered with the coating.

With only a partial coating of the surface can be achieved that the coating unevenly covered the core of the abrasive grain. In this way, in particular a possibly present symmetry of the abrasive grain can be canceled. Uneven coverage is particularly present when the core can be thoughtfully divided into two parts by an imaginary plane, the surface of a first part being partially or completely covered by the coating and the surface of a second part being not coated.

The only partial coating can lead to a plurality of advantages, which are explained below for several embodiments.

In one possible variant, the coating is ferromagnetic. For example, it may contain or consist of iron, cobalt or nickel or any combination thereof. Alternatively, or in addition, the coating may be paramagnetic and, for example, contain or consist of at least one rare earth element, such as praseodymium, neodymium, samarium, terbium or any combination thereof. In particular, the coating may be a sintered ceramic containing at least one element of the rare earths. Alternatively, the coating may also be a composite containing small magnets embedded in a plastic matrix. A partial coating with a ferromagnetic material causes a relatively high magnetic moment can be generated in an external magnetic field, which facilitates alignment. In addition, it can be determined by the choice of the coated part of the surface, how the abrasive grain aligns relative to an external magnetic field.

In other embodiments, the coating ( 12 ) has a thermal conductivity of at least 1.2 W · m ^-1 · K ^-1 , preferably at least 28 W · m ^-1 · K ^-1 , particularly preferably at least 80 W · m ^-1 · K ^-1 .

If such abrasive grains are heated to a base before being sprinkled, the inhomogeneous thermal conductivity on the surface of the abrasive grain results in an inhomogeneous temperature distribution on the surface. The abrasive grain is then preferably held to the base binder when it reaches the base binder with a portion of the higher temperature surface. The locally elevated temperature leads namely to a firmer bond. Other abrasive grains that come onto the base binder with part of the lower temperature surface will adhere less strongly or not to the base binder. Overall, this leads to an orientation of the abrasive grains. In this orientation, the heat generated when working a surface can be particularly well derived: this heat is namely produced at the end remote from the base of the abrasive grain and is then preferably removed in the direction of the base.

Suitable materials with such thermal conductivities are, for example, a variety of metals, such as iron, silver, copper or aluminum, and ceramics, such as silicon carbide. Alternatively or additionally, a particular ceramic sintered material may be used which contains at least one element of the rare earths; With a suitable choice of this element, the coating can be paramagnetic at the same time and therefore also have the advantages described above.

In yet a further variant, the material of the coating may be chosen such that it has a greater adhesion than the material of the core. In particular, the material of the coating may have a greater adhesion to a base binder to which the abrasive grain can be applied.

Even a partial coating with such a material may contribute to an orientation of the abrasive grains on a base binder. The abrasive grains which fall on the base binder when sprinkled with a coated part of the surface are in fact more likely to be held by the latter.

To increase the adhesion, in particular for mechanical anchoring between the abrasive grain and a binder, the coating may be porous, for example. In particular, it may have a porosity of at least 20%, preferably at least 50%, particularly preferably at least 80%. The porosity is the ratio of the void volume contained in the coating and the total volume of the coating. In particular, the porosity of the coating may be greater than the porosity of the core of the abrasive grain.

Alternatively, a greater adhesion can also be achieved in that the coating contains or consists of a chemical adhesion promoter. The chemical adhesion promoter may be, for example, a suitable polymer.

It is conceivable and within the scope of the invention that the core of the abrasive grain is covered by several different coatings - for example a first coating which is ferromagnetic, and a second coating which has a thermal conductivity as mentioned above. At least one of these multiple coatings covers only part of the surface of the core, while the further coatings can cover the entire surface. However, the abrasive grain preferably contains only a single coating.

The thickness of the coating can be in the range from 5 μm to 80 μm, preferably from 10 μm to 40 μm, particularly preferably from 20 μm to 30 μm. It is not absolutely necessary for the coating to have a homogeneous thickness in the areas in which it is present.

The abrasive grain according to the invention and the core of the abrasive grain according to the invention may have a defined shape and a defined size, in particular one of the shapes described in the following documents.

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 process have two opposite ones Base surfaces, which have 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, which are interconnected via frangible webs. 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.

Alternatively to the geometries described above, however, the abrasive grain and its core may also have an undefined shape. For example, the cores of the abrasive grains may also be broken or grown and therefore have a corresponding shape.

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. Typically, larger sized abrasive grains result in greater 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 can be understood, for example, as the diameter of an enveloping circle of the microscopic image of the abrasive grain, ie as the smallest diameter of a circle enclosing the image.

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

Alternatively or additionally, the core of 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, Lanthana, 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 core of the abrasive grain may contain other hard materials, such as silicon carbide.

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

In addition, the core of 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 core of 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 α-Al ₂ O ₃ , in the core of 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. -%.

As an alternative to the materials described above, it is also conceivable and within the scope of the invention that the core of the abrasive grain consists of a non-ceramic material, such as diamond or cubic boron nitride.

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 remainder of the abrasive grains included in the assembly may also have a coating which, however, completely covers the surface of the core, or they may not have any coating at all.

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 may differ in the type of coating.

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. Each of these proportions may have a size distribution per se, each of which corresponds to one of the abovementioned size standards customary in the abrasives industry.

An abrasive grain according to the invention or an entirety of abrasive grains according to the invention can be produced, for example, by a process according to the invention. This method includes a step of applying to at least one abrasive grain core or at least one abrasive grain core precursor a coating that covers only a portion of the surface of the abrasive grain core or abrasive grain precursor. In particular, the coating may cover only one or more edges or only one of a plurality of areal areas of the surface.

In some possible embodiments, the coating may be applied to the abrasive grain core or abrasive grain core precursor, particularly by spraying, brushing and / or printing. This allows a particularly strong connection between the core and the coating.

• a) Herstellung oder Bereitstellung mindestens eines Schleifkorn-Kern-Vorprodukts;
• b) Sintern des Schleifkorn-Kern-Vorprodukts, um mindestens einen Schleifkorn-Kern (10) zu erhalten.

The method may include the following steps:

• a) producing or providing at least one abrasive grain core precursor;
• b) sintering the abrasive grain-core precursor to at least one abrasive grain core ( 10 ) to obtain.

The coating can be applied before step b) or after step b). If the coating is applied before step b), it may be baked during sintering in step b).

• i) 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;
• ii) Einfüllen der Dispersion in mindestens eine Vertiefung einer Giessform;
• iii) optional Abrakeln einer Oberseite der Giessform, um zumindest einen Teil der Dispersion zu entfernen, der über die Oberseite der Giessform übersteht;
• iv) Entfernen eines Teiles der flüchtigen Komponenten der Dispersion, so dass mindestens ein Schleifkorn-Kern-Vorprodukt entsteht;
• v) Entfernen des Schleifkorn-Kern-Vorprodukts aus der Giessform;
• vi) optional Kalzinieren des Schleifkorn-Kern-Vorprodukts.

The step a) can be based on that from the US 5,201,916 Known methods include the following substeps:

• i) production or provision of a dispersion comprising α-alumina particles and / or particles which are convertible to α-alumina, and at least one volatile dispersing agent, preferably water;
• ii) filling the dispersion into at least one well of a casting mold;
• iii) optionally doctoring a top of the mold to remove at least a portion of the dispersion which overhangs the top of the mold;
• iv) removing a portion of the volatile components of the dispersion to form at least one abrasive grain-core precursor;
• v) removing the abrasive grain core precursor from the mold;
• vi) optionally calcining the abrasive grain core precursor.

The coating can be applied between the steps iv) and v), for example by spraying, brushing and / or printing. After application, in particular before partial step v), the coating can optionally be dried. Alternatively, the coating between the partial steps v) and vi) can be applied, for example by spraying, brushing and / or printing. Also in this variant, the coating can be optionally dried after application.

Before and / or during the preparation of the dispersion in partial step i), the raw materials, in particular α-aluminum oxide particles and / or particles which can be converted into α-aluminum oxide, are 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 b).

The mold can contain or consist of silicone, for example. The depressions may have an open top surface through which the dispersion can be filled. The depression should preferably be matched to the abrasive grain to be produced and arranged in the casting mold so that the part of the abrasive grain to be coated can originate from the upper free surface of the filled dispersion. The recesses of the mold each have a surface whose shape is complementary to the shape of at least part of the surface of the desired abrasive grain.

In an alternative method, prior to sub-step ii), first the material of the coating is filled into the depressions of the casting mold and then the casting mold is tilted, so that its upper side slopes to a horizontal and the material of the coating accumulates on at least one side wall of the depression , In this tilted orientation of the mold, the material of the coating is at least partially solidified, for example by drying and / or sintering. Subsequently, the casting mold is oriented again so that its top is horizontal. The material of the coating then remains only on some of the side walls. If the dispersion is subsequently introduced in sub-step ii), only a part of its surface comes into contact with the material of the coating.

The intermediate product formed in partial step iv) should preferably be mechanically stable enough to be further processed as bulk material in the subsequent steps. The optional calcination in substep vi) 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 coating which, however, covers the entire surface of the core. The remaining abrasive grains can also have no coating.

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 a basic binder, coat binder and second coat binder all known binders can be used, for example, of synthetic resin, such as a phenolic resin, a Epoxy, 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). In the case of partial coating with a ferromagnetic material, the abrasive grains may be exposed to an external magnetic field during application. As a result, an orientation of the abrasive grains can be brought about.

Furthermore, the invention is also directed to methods of grinding 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 an embodiment and a drawings will be explained in more detail. It shows

1 a first embodiment of an inventive abrasive grain with a partial coating of a ferromagnetic material;

2 a first casting mold for producing an abrasive grain according to 1 ;

3 a second casting mold for producing an abrasive grain according to 1 ;

4a and b: two views of a second embodiment of an inventive abrasive grain with a partial coating of a ferromagnetic material.

1 shows a possible embodiment of an abrasive grain 10 , The core 11 of the abrasive grain 10 has the shape of a straight prism with two opposite base surfaces 15 in the form of equilateral triangles, of which only one is recognizable here. The lateral surface of the prism contains three rectangular partial surfaces 14 . 14 ' . 14 '' of which only the part surfaces 14 and 14 ' are visible. Of these partial surfaces is only a first partial area 14 with a coating 12 from an example ferromagnetic material covered, such as a ferrous material; the two other faces 14 ' . 14 '' as well as both base areas 15 are not covered. Alternatively, of course, instead of the ferromagnetic coating, a thermally conductive or an adhesion-increasing coating could also be present, as detailed above.

This uneven coverage with the coating 12 manifests itself in particular in the fact that an imaginary plane E is the core 11 of the abrasive grain 10 mentally into a first part 11-1 and a second part 11-2 splits, with the surface of the first part 11-1 partly from the coating 12 covered, the surface of the second part 11-2 but does not wear any coating. Due to the only partially existing coating 12 becomes a symmetry of the nucleus 11 canceled.

If such an abrasive grain 10 in the presence of an external inhomogeneous magnetic field is scattered on a substrate coated with a base binder, this leads to an orientation of the abrasive grain 10 as explained in detail above.

The 4a and 4b show a perspective view and a side view of another inventive abrasive grain 10 ' with a core 11 ' , This core 11 ' is thoughtfully composed of a prism-shaped base body 20 ' and a tower body 21 ' , The base surface of the base body 20 ' corresponds to the sectional view of a double-T anchor, which is known as the logo of Robert Bosch GmbH. The tower body 21 ' is saddle roof shaped and known as a logo of the company sia Abrasives Industries AG. The bottom 14 ' of the base body 20 ' is from a coating 12 ' covered, for example, from a paramagnetic material; the other parts of the surface of the core 11 ' however, they are not coated.

The abrasive grain cores 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 dispersing agent, 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 ground dispersion is filled into a mold of silicone containing wells in the shape of the desired abrasive grains. Then the volatile component, ie the water, is removed from the dispersion.

In one possible variant, the coating is then applied to a portion of the resulting abrasive grain-core precursor, for example by spraying. For the production of in 1 shown abrasive grain 10 For example, a casting mold 30 be used part of in the 2 is shown. For simplicity, here is only a single recess 31 shown, although the mold 30 Of course, a large number of identical such depressions are preferred 31 having. The depression 31 is formed such that from the top, not in contact with the mold 30 standing surface of the dispersion, the partial surface 14 of the abrasive grain 10 out 1 can be formed. On this surface, the coating can be sprayed.

After application, the coating can optionally be dried. Thereafter, the abrasive grain-core precursor 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.

In another variant of the method, the in 3 illustrated mold 30 ' be used. The surface of a depression 31 ' this mold 30 ' contains a floor area 34 ' in the shape of an equilateral triangle, which is one of the base surfaces 15 of the abrasive grain 10 out 1 equivalent. In addition, the surface of the depression contains 31 ' three side walls 35 ' that the sub-areas 14 . 14 ' . 14 '' of the abrasive grain 10 correspond. In a first step, the material of the coating is in the wells 31 ' filled and then the mold 31 ' so tilted that their top 32 ' is inclined to a horizontal and the material of the coating on one of the side walls 35 ' accumulates. In this tilted orientation of the mold 31 ' the material of the coating is at least partially solidified, for example by drying or sintering. Subsequently, the casting mold 31 ' again oriented so that their top 32 runs horizontally. The material of the coating then remains only on one of the side walls 35 ' , And the dispersion can be filled.

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

• EP 1995020 [0003]
• US 5201916 [0021, 0061]
• EP 615816 [0023]
• WO 2009/085841 [0024]
• WO 2010/077495 [0025]
• WO 2010/077518 [0025]
• WO 2010/077491 [0025]
• WO 2010/077519 [0026]
• WO 2011/068724 [0027]
• WO 2011/109188 [0027]
• WO 2010/077509 [0028]
• WO 2011/068714 [0029]
• WO 2011/139562 [0030]
• WO 2012/018903 [0031]
• WO 2012/061016 [0032]
• WO 96/12776 [0033]
• WO 2011/087649 [0034]
• WO 2012/061033 [0035]
• EP 615 816 A1 [0045]

Claims (10)

Abrasive grain ( 10 ; 10 ' ) with a core ( 11 ; 11 ' ) and at least one coating ( 12 ; 12 ' ), characterized in that the coating ( 12 ; 12 ' ) only a part of the surface of the core ( 11 ; 11 ' ), in particular only one or more edges and / or only one of a plurality of areal areas ( 14 ; 14 ' ) of the surface. Abrasive grain ( 10 ; 10 ' ) according to claim 1, characterized in that the coating ( 12 ; 12 ' ) is ferromagnetic and in particular contains or consists of iron, cobalt or nickel or any combination thereof and / or the coating ( 12 ; 12 ' ) is paramagnetic and in particular contains or consists of at least one element of the rare earths, such as praseodymium, neodymium, samarium, terbium or any combination thereof. Abrasive grain ( 10 ; 10 ' ) according to one of the preceding claims, characterized in that the coating ( 12 ; 12 ' ) has a thermal conductivity of at least 1.2 W · m ^-1 · K ^-1 , preferably at least 28 W · m ^-1 · K ^-1 , particularly preferably at least 80 W · m ^-1 · K ^-1 . Abrasive grain ( 10 ; 10 ' ) according to claim 3, characterized in that the material of the coating ( 12 ; 12 ' ) contains or consists of at least one metal, such as iron, silver, copper or aluminum, and / or at least one ceramic, such as silicon carbide. Abrasive grain ( 10 ; 10 ' ) according to one of the preceding claims, characterized in that the material of the coating ( 12 ; 12 ' ) has a greater adhesion than the material of the core ( 11 ; 11 ' ), in particular a greater adhesion to a base binder. Abrasive grain ( 10 ; 10 ' ) according to claim 5, characterized in that the coating ( 12 ; 12 ' ) is porous and in particular has a porosity which is greater than the porosity of the core ( 11 ; 11 ' ). Abrasive grain ( 10 ; 10 ' ) according to one of the preceding claims, characterized in that the thickness of the coating ( 12 ; 12 ' ) in the range of 5 microns to 80 microns, preferably from 10 microns to 40 microns, more preferably from 20 microns to 30 microns. Abrasive grain ( 10 ; 10 ' ) according to one of the preceding claims, characterized in that the core ( 11 ; 11 ' ) of the abrasive grain ( 10 ; 10 ' ) contains or consists of a ceramic material, in particular a polycrystalline ceramic material, preferably aluminum oxide, more preferably α-Al ₂ O ₃ . Totality of abrasive grains ( 10 ; 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. Abrasive article containing a total of abrasive grains ( 10 ; 10 ' ) according to claim 9.

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