DE102015224974A1 - Method and apparatus for producing sinterable material-containing microspheres - Google Patents

Abstract

The invention relates to a method for producing a sinterable substance-containing microspheres (40), in particular ceramic microspheres or metallic microspheres. The method comprises providing (50) a suspension (2) containing a sinterable powder, generating (51) suspension drops (20) of the suspension (2), a predetermined amount of the suspension (2) being used to produce a suspension drop (20). into a nozzle chamber (32) of a nozzle (3) is guided and in the nozzle chamber (32) for ejecting the suspension drop (20) from a nozzle opening (30) of the nozzle (3) a short - term overpressure is generated and the subjecting (52) Suspension drop (20) a hardening process for forming the sinterable material containing microspheres (4) from the suspension drops (20).

Description

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for producing sinterable material-containing microspheres, in particular ceramic microspheres or metallic microspheres, in particular for producing sinterable material-containing grinding balls having a diameter of at most 100 μm. More particularly, the present invention relates to a method and apparatus for producing sinterable-containing microspheres by means of an inkjet injector assembly.

BACKGROUND OF THE INVENTION

Ceramic grinding balls are usually produced in a dripping process with the aid of needle injectors or in a so-called cutting harp method. In both processes, a suspension containing a ceramic powder is dripped and the resulting droplets of the suspension are cured by ion exchange in a Lacktat bath.

With the dripping method described, however, no grinding balls with diameters in the micrometer range, in particular with diameters of at most 100 μm, can be produced.

Alternatively, pressing methods are available for the production of ceramic grinding balls of different sizes.

The object of the present invention is to provide a method and a device with which a microsphere containing sinterable material, in particular ceramic or metallic microspheres, having a homogeneous spherical size distribution, homogeneous sintered density and high sphericity can be produced in a simple and effective manner.

SUMMARY OF THE INVENTION

This object is achieved by the method for producing sinterable substance-containing microspheres according to claim 1 and the device for producing sinterable substance-containing microspheres according to claim 10.

The present invention relates to a method for producing a sinterable substance-containing microspheres (also referred to below as "microspheres"), for example microspheres of a sinterable material, in particular ceramic microspheres or metallic microspheres, for example micro-milling spheres. The method comprises providing a suspension containing a sinterable powder (hereinafter also referred to as "suspension"), producing suspension drops of the suspension and subjecting the suspension drops to a hardening process for forming the microspheres from the suspension drops. According to the method, a predetermined amount of the suspension is fed into a nozzle chamber of a nozzle for generating a suspension drop and generates a short-term overpressure in the nozzle chamber for ejecting the suspension drop from a nozzle opening of the nozzle.

Since a nozzle with a nozzle chamber, in which a short-term overpressure is generated for ejecting a suspension drop from the nozzle opening, for example an inkjet injector, can be used to produce very small suspension droplets whose droplet size depends on a size of the can be varied by suitable choice of structural and functional properties of the nozzle to be prepared microspheres. As a result, the production of microspheres with a very small spherical size is made possible with simultaneously low scattering width of the spherical size distribution, high sphericity and, moreover, due to the surface tension of the suspension, almost ideal surface structures. The microspheres produced by the process according to the invention may have a diameter which is less than 1 mm, in particular less than 100 μm, in particular less than 50 μm. In addition, the microspheres may have a sphericity which is at least 0.8, in particular at least 0.9.

The microspheres produced by the process according to the invention can be used, for example, as micro-milling spheres. Typically, micro-milling balls, in particular ceramic micro-milling balls and / or metallic micro-balls, are used in the comminution and / or dispersion of particulate substances, for example in the pharmaceutical industry, the chemical industry, the paint and / or paint industry and metal and / or ceramic processing ,

The suspension containing the sinterable powder may contain, in addition to the sinterable powder, a solvent, an organic and / or inorganic binder system and / or one or more rheological additives. The solvent may be water or contain water. The organic binder system may be, for example, a lactate system. The rheological additives may contain, for example, a dispersing aid, a defoamer and / or a stabilizer.

The sinterable powder contained in the suspension may contain a sinterable substance ( Material), for example a sinterable substance or a sinterable mixture of two or more pure substances, which is preferably processable into a powder having a particle size of less than 1 μm. For example, the sinterable material may comprise a ceramic material, a metallic material and / or a glass material or consist of one or more of these materials. The ceramic material may comprise zirconia, alumina, silicon carbide, silicon nitride, tungsten carbide, and / or other ceramic material or may consist of one or more of these materials. Zirconium oxide and aluminum oxide are characterized by their high hardness and high resistance and are ideally suited for use as a base material for grinding balls. The metallic material may comprise a cemented carbide, for example tungsten carbide-cobalt, or a pure metal, or may consist of one or more of these substances.

The sinterable powder may comprise powder particles having a particle size smaller than 1 μm, in particular smaller than 500 nm. Due to the small size of the powder particles of the sinterable powder, the sinterable powder can be uniformly distributed in the suspension, resulting in a homogeneous density of the microspheres to be produced. In addition, due to the small size of the powder particles blockages of the nozzle with the sinterable powder can be avoided to a large extent. The particle size of the sinterable powder may, for example, have a monomodal, bimodal or multimodal distribution.

The suspension containing the sinterable powder may comprise a proportion of sinterable powder in the range of 30% to 70%, in particular of about 50%.

The suspension drops produced can each have a drop volume in the range from 5 pl to 5000 pl, in particular in the range from 10 pl to 1000 pl. The drop volume of the suspension drops may be greater than a volume of the final microspheres, as chemical reactions occurring during curing and subsequent processing steps may cause a reduction in volume.

The short-term overpressure in the nozzle chamber for generating the suspension drops can be generated, for example, by applying a voltage pulse to means arranged in the region of the nozzle chamber for generating an overpressure. For example, the short-term overpressure can be generated by applying a voltage pulse to a piezo element, to a heating element and / or to an ultrasound transmitter.

The voltage pulse can be adapted to the nozzle chamber, in particular its shape and / or size, and to the means for generating the overpressure, in particular on the nature, size and / or positioning on or in the nozzle chamber, that suspension drops with a predetermined Drop volume can be generated.

The short-term overpressure can prevail during a time interval between the activation of the means for generating the overpressure until the ejection of the suspension drop. This time interval can be at most 0.5 ms, in particular at most 0.1 ms.

For hardening, the suspension drops are fed to a hardening process. This can be done for example by an ion exchange and / or another hardening process. The ion exchange can be carried out, for example, by introducing the suspension drops into a curing bath, for example a lactate bath.

After curing by means of a curing bath, the microspheres can be removed from the curing bath. To remove the microspheres, the curing bath can be screened or filtered with the microspheres. Alternatively, a sieve can be provided in the curing bath, which can be removed from the curing bath together with the microspheres.

Subsequently, the microspheres can be subjected to further processing steps.

For example, the microspheres formed can be dried. For this purpose, the microspheres for a predetermined period of time, for example a few hours, in a drying device, such as a drying oven, introduced and dried therein at a temperature in the range of 30 ° C to 60 ° C.

Subsequently or alternatively, the microspheres formed can be sintered. For this purpose, the microspheres may be introduced into a sintering device, for example a sintering furnace, for a given period of time, for example a few hours, at a temperature a few degrees (° C) below a melting temperature of the sinterable powder, and optionally at an external pressure be sintered at elevated pressure. Optionally, drying and sintering may be in the same oven.

Alternatively or additionally, the microspheres can be classified. The microspheres can be classified according to their size, their density and / or their sphericity. The drying and / or Sintering and classifying can be done in any order.

The present invention further relates to an apparatus for producing sinterable material-containing microspheres, for example microspheres of a sinterable material, in particular ceramic microspheres or metallic microspheres. The device for producing microspheres comprises a feed line for providing a suspension containing a sinterable powder, a nozzle arrangement for producing suspension drops of the suspension and a curing device for subjecting the suspension drops to a hardening process and for forming the microspheres from the ejected suspension drops. The nozzle assembly comprises a nozzle having a nozzle chamber for receiving a predetermined amount of the suspension via the supply line, a nozzle opening communicating with the nozzle chamber and means for generating a short-term overpressure in the nozzle chamber.

The device according to the invention makes it possible to produce microspheres with a very small sphere size while at the same time having a low scattering range of the spherical size distribution, high sphericity and, moreover, due to the surface tension of the suspension, almost ideal surface structures.

The device is designed in particular for producing microspheres by means of the above-described method for producing microspheres.

The suspension containing the sinterable powder may contain, in addition to the sinterable powder, a solvent, an organic and / or inorganic binder system and / or rheological additives. The sinterable powder and the suspension containing the sinterable powder may be as described above with respect to the process for producing microspheres.

The supply line for providing the suspension may be a pipe or a hose. The supply line can be connected to a receiving opening with a storage and / or mixing container for storing and / or preparing the suspension containing the sinterable powder. With an outlet opening, the supply line can be connected to the nozzle arrangement, in particular to the nozzle chamber of the nozzle, in order to introduce the suspension from the supply and / or mixing container via the supply line into the nozzle arrangement, in particular into the nozzle chamber.

The nozzle may preferably be designed such that a volume of the suspension drops to be produced deviates by at most 5%, in particular at most 2%, from a predetermined volume. This can be achieved if the nozzle is manufactured with a predetermined accuracy and the means for generating a short-term overpressure in the nozzle chamber are exactly controllable.

The nozzle chamber may be a cavity having, for example, the shape of an ellipsoid or a cuboid or another shape. The cavity can receive an amount of suspension which corresponds to a multiple of a suspension drop to be generated. The cavity can absorb a maximum of 10000 pl of the suspension.

The nozzle orifice communicating with the nozzle chamber may have a diameter in the range of 10 μm to 200 μm. For example, the nozzle opening may be formed as an opening in a housing forming the nozzle chamber or in a nozzle chamber wall forming the nozzle chamber.

The nozzle may have one or more nozzle openings. The nozzle orifices of the nozzle can be arranged so that partial droplets, which simultaneously emerge from the nozzle orifices, combine to form a drop of suspension. A microsphere can then be produced from the suspension drop combined from the partial drops. The nozzle openings may have the same or different diameters, which are preferably between 10 .mu.m and 100 .mu.m.

The means for generating the short-term overpressure in the nozzle chamber may be arranged, for example, on or in the housing forming the nozzle chamber or in the nozzle chamber. The means for generating the short-term overpressure may be designed to produce a short-term overpressure which is suitable for generating suspension drops, each with a drop volume in the range from 5 pl to 5000 pl, in particular in the range from 10 pl to 1000 pl, by means of the nozzle opening is. The short-term overpressure may be a single pressure pulse through which a complete drop of suspension is expelled from the nozzle. Alternatively, the short-term overpressure may comprise one or more successive pressure pulses, a partial drop being ejected from the nozzle by each pressure pulse. The successive pressure pulses are preferably timed such that the ejected partial drops combine to form a suspension drop from which a microsphere can then be produced.

For example, the means for generating the short-term overpressure may comprise a piezoelectric element which in the region of the nozzle chamber on the housing which forms the nozzle chamber is arranged that sets a reduction in the volume of the nozzle chamber upon activation of the piezoelectric element. Alternatively or additionally, the means for generating the short-term overpressure may also comprise a heating element, which is arranged for example in the nozzle chamber. However, other means for generating the short-term overpressure or combinations of different means for generating the short-term overpressure may also be used.

The nozzle of the nozzle arrangement can be, for example, an inkjet injector. For example, the nozzle may be a piezoinjector with a piezo element as means for generating the short-term overpressure, a thermal injector with a heating element as means for generating the short-term overpressure, an ultrasonic injector with an ultrasound generator as means for generating the short-term overpressure or another inkjet injector ,

The nozzle assembly may comprise a plurality of identical nozzles arranged in a row or a matrix. The nozzles can be arranged at a predetermined distance from each other. The distance is preferably so great that the suspension drops produced simultaneously do not collide during the curing process in the curing device, especially during their fall into a curing bath and optionally during their sinking in the curing bath. Alternatively, the distance between two or more adjacent nozzles may also be chosen such that drops emerging from the two or more adjacent nozzles combine to form a suspension drop from which the microsphere can then be produced.

If the curing device is designed as a curing bath, the nozzle arrangement can be arranged at a predetermined distance from the curing bath, in particular above the curing bath. For example, a distance may be in the range of 20 cm to 50 cm. This makes it possible that the suspension drops have a high sphericity when immersed in the curing bath.

The curing bath, which may comprise a lactate bath as described above with respect to the process of the invention, may have a depth of between 50 cm and 100 cm. This allows the suspension drops to harden sufficiently during the sinking operation to avoid changes in shape during the impact on a bath floor.

The nozzle arrangement may be designed to be movable in one plane in one or more directions. For example, if the curing device is designed as a curing, the nozzle assembly may be disposed above the curing, the nozzles are aligned with its nozzle opening in the direction of Aushärtebads and displaceable in a horizontal plane above the Aushärtebad. For example, the nozzle assembly may comprise a plurality of nozzles arranged in a row and may be displaced back and forth in one direction above the curing apparatus. This allows a rapid production of microspheres, while avoiding that suspension drops that have not yet cured sufficiently collide in the curing device.

The device for producing microspheres can, as already mentioned above, comprise a storage and / or mixing container for storing and / or preparing the suspension containing the sinterable powder. The storage and / or mixing container may be a storage container in which the suspension is stored, or a mixing container in which the ingredients of the suspension are mixed. The storage container may include an agitator to prevent the contents of the suspension from separating. The mixing vessel may comprise a funnel and / or a scale to introduce the contents of the suspension in the required amount into the mixing vessel, and / or an agitator to mix the ingredients of the suspension.

The device for producing microspheres may further comprise a drying device for drying the microspheres formed, for example a drying oven, a sintering device for sintering the microspheres formed, for example a sintering oven, and / or a classification unit for classifying the microspheres formed. In addition, the apparatus for producing microspheres may comprise means for removing the microspheres from the curing device, for example the curing bath, from the drying unit, the sintering unit and / or the classification unit.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. Show it:

1 a schematic representation of an apparatus according to the invention for producing ceramic microspheres;

2 a flow diagram of a method for producing ceramic microspheres;

3A B shows a first exemplary embodiment of a nozzle of the device according to the invention for producing ceramic microspheres, and

4A B shows a second embodiment of a nozzle of the device according to the invention for producing ceramic microspheres.

DESCRIPTION OF EMBODIMENTS

1 shows a schematic representation of a device according to the invention 1 for producing ceramic microspheres. The device 1 includes a storage container 10 , a supply line 11 , a nozzle arrangement 12 with three nozzles 3 and a collection container 13 that with a curing bath 130 is filled.

The storage tank 10 is formed to a suspension containing alumina 2 save. To homogeneity of the suspension 2 to ensure includes the storage container 10 a stirrer 100 with which the suspension 2 is mixed continuously. The storage tank 10 covers in its soil 101 an opening 102 for discharging the suspension 2 in the supply line 11 ,

The supply line 11 is with a receiving opening 110 in the area of the opening 102 with the storage tank 10 connected. The supply line 11 includes three outlet openings 111 , each with one of the nozzles 3 the nozzle assembly 12 connected is. The outlet openings 111 are located below the receiving opening 110 ,

The nozzles 3 the nozzle assembly 12 are designed as inkjet injectors and are discussed below with reference to 3A to 4B described in detail.

The nozzles 3 the nozzle assembly 12 are on a carrier 120 arranged in a row, with a nozzle opening 30 every nozzle 3 down or into one of the storage container 10 directed away from the direction.

The collection container 13 is directly below the nozzle assembly 12 arranged so that from the nozzles 3 generated suspension drops 20 in the curing bath 130 fall and there to ceramic microspheres 4 Harden.

2 shows a flowchart of a method 5 for producing ceramic microspheres with the aid of the device described 1 ,

at 50 becomes an alumina-containing suspension 2 provided. This is the storage container 10 the device 1 with the suspension 2 filled. This allows the suspension 2 to the nozzles 3 the nozzle assembly 12 reach.

at 51 become suspension drops 20 the suspension 2 generated. This is a predetermined amount of the suspension 2 in a nozzle chamber 32 every nozzle 3 guided and in the nozzle chamber 32 to eject the suspension drop 20 from the nozzle opening 30 the nozzle 3 generates a short-term overpressure. The overpressure is generated by activating a means for generating an overpressure. As with respect to 3A to 4B will be described below, the means for generating the overpressure, a piezoelectric element 33 or a heating element 34 be.

at 52 become the suspension drops 20 in the curing bath 130 in the collection container 13 brought in. The generated suspension drops 20 in the curing bath 130 collected.

3A and 3B show a first embodiment of a nozzle structure of the nozzles 3 the nozzle assembly 12 in the form of a piezo injector 3a ,

The piezo injector 3a includes a nozzle opening 30 , a line section 31 , a nozzle chamber 32 and a piezo element 33 , The pipe section 31 is via an inlet opening with the nozzle chamber 32 connected to the suspension 2 in the nozzle chamber 32 involved. The piezo element 33 is the side of the nozzle chamber 32 arranged on a nozzle chamber wall. The nozzle opening 30 stands with the nozzle chamber 32 in connection and is arranged opposite the inlet opening.

In 3A is the piezo injector 3a shown in a state in which the piezoelectric element 33 is not activated. The nozzle chamber 32 is up to an outlet end of the nozzle opening 30 filled with suspension. Will the piezo element 33 activated, the piezo element changes 33 , as in 3B shown its shape so that the volume of the nozzle chamber 32 decreases and overpressure in the nozzle chamber 32 arises. This is the suspension 2 in the nozzle opening 30 from the nozzle opening 30 pressed, leaving a drop of suspension 20 from the nozzle opening 30 replaces.

4A and 4B show a second embodiment of a nozzle structure of the nozzles 3 the nozzle assembly 12 in the form of a thermal inkjet injector 3b ,

The thermal inkjet injector 3b includes a nozzle opening 30 , a line section 31 , a nozzle chamber 32 and a heating element 34 , The pipe section 31 is via an inlet opening with the nozzle chamber 32 connected to the suspension in the nozzle chamber 32 involved. The heating element 34 is in the center of the nozzle chamber 32 arranged. The nozzle opening 30 stands with the nozzle chamber 32 in connection and is arranged opposite the inlet opening.

In 4A is the thermal inkjet injector 3b shown in a state in which the heating element 34 is not activated. The nozzle chamber is up to an outlet end of the nozzle opening 30 with suspension 2 filled. Will the heating element 34 activated, it forms, as in 4B shown to the heating element 34 around a steam bubble 21 from vaporized suspension so that an overpressure in the nozzle chamber 32 arises. Through this, the suspension in the nozzle opening 30 from the nozzle opening 30 pressed, leaving a drop of suspension 20 from the nozzle opening 30 replaces.

Claims (15)

Method for producing sinterable material-containing microspheres ( 40 ), comprising: providing ( 50 ) of a suspension containing a sinterable powder ( 2 ); Produce ( 51 ) of suspension drops ( 20 ) the suspension containing the sinterable powder ( 2 ), wherein to produce a suspension drop ( 20 ) a predetermined amount of the suspension containing the sinterable powder ( 2 ) in a nozzle chamber ( 32 ) of a nozzle ( 3 ) and in the nozzle chamber ( 32 ) for discharging the suspension drop ( 20 ) from a nozzle opening ( 30 ) of the nozzle ( 3 ) a short-term overpressure is generated; and undergoing ( 52 ) of the suspension drops ( 20 ) a hardening process for forming the sinterable substance-containing microspheres ( 4 ) from the suspension drops ( 20 ). Process according to claim 1, wherein the suspension containing the sinterable powder ( 2 ) further contains a solvent and / or a binder system. A method according to claim 1 or 2, wherein the sinterable powder has a particle size smaller than 1 μm, especially smaller than 100 nm. Method according to one of claims 1 to 3, wherein the sinterable powder comprises or consists of a ceramic powder and / or a metallic powder. Method according to one of claims 1 to 4, wherein the suspension ( 2 ) comprises a proportion of sinterable powder in the range of 20% to 70%. Method according to one of claims 1 to 5, wherein the generated suspension drops ( 20 ) each have a drop volume in the range of 5 pl to 5000 pl. Method according to one of claims 1 to 6, wherein the short-term overpressure in the nozzle chamber ( 32 ) by applying a voltage pulse in the region of the nozzle chamber ( 32 ) means for generating an overpressure is generated, in particular by applying a voltage pulse to a piezoelectric element ( 33 ), a heating element ( 34 ) and / or an ultrasonic transmitter. A method according to any one of claims 1 to 7, further comprising: drying the formed microspheres containing a sinterable material ( 4 ); Sintering the formed microspheres containing a sinterable substance ( 4 ); and / or classifying the formed microspheres containing a sinterable substance ( 4 ). Contraption ( 1 ) for producing sinterable material-containing microspheres ( 4 ), in particular by means of a method ( 5 ) for producing sinterable material-containing microspheres ( 4 ) according to one of claims 1 to 8, comprising: a supply line ( 11 ) for providing a suspension containing a sinterable powder ( 2 ); a nozzle arrangement ( 12 ) for producing suspension drops ( 20 ) the suspension containing the sinterable powder ( 2 ), which has a nozzle ( 3 ) with a nozzle chamber ( 32 ) for receiving a predetermined amount of the suspension containing the sinterable powder ( 2 ) via the supply line ( 11 ), one with the nozzle chamber ( 32 ) in communicating nozzle opening ( 30 ) and means for generating a short-term overpressure in the nozzle chamber ( 32 ); and a curing device ( 130 ) for subjecting the suspension drops to a curing process and for forming the microspheres containing a sinterable substance ( 4 ) from the ejected suspension drops ( 20 ). Apparatus according to claim 9, wherein the nozzle opening ( 30 ) has a diameter in the range of 10 microns to 200 microns. Apparatus according to claim 9 or 10, wherein the means for generating the short-term overpressure in the nozzle chamber ( 32 ) are adapted to generate a short-term overpressure, which is used to generate suspension drops ( 20 ), each with a drop volume in the range of 5 pl to 5000 pl, in particular in the range of 10 pl to 1000 pl, by means of the nozzle opening ( 30 ) suitable is. Device according to one of claims 9 to 11, wherein the nozzle ( 3 ) is an inkjet injector, in particular a piezo injector ( 3a ) with a piezo element ( 33 ) as a means for generating the short-term overpressure, a thermal injector ( 3b ) With a heating element ( 34 ) as means for generating the temporary overpressure, an ultrasonic injector with an ultrasonic generator as means for generating the short-term overpressure or another inkjet injector. Device according to one of claims 9 to 12, wherein the nozzle arrangement ( 12 ) several identical nozzles ( 3 ) arranged in a row or a matrix. Device according to one of claims 9 to 13, wherein the nozzle arrangement ( 12 ) at a predetermined distance to the curing device ( 12 ) and / or is movable in a plane in one or more directions. Device according to one of claims 9 to 14, further comprising a storage and / or mixing container ( 10 ) for storing and / or preparing the suspension containing the sinterable powder ( 2 ), wherein the storage and / or mixing container ( 10 ) via the supply line with the nozzle arrangement ( 12 ) connected is; a drying device for drying the formed, a sinterable substance-containing microspheres ( 4 ); a sintering device for sintering the formed, a sinterable substance-containing microspheres ( 4 ); and / or a classification unit for classifying the formed sinterable substance-containing microspheres ( 4 ).

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