EP1153150A1 - Method for producing hard metal mixtures - Google Patents

Method for producing hard metal mixtures

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Publication number
EP1153150A1
EP1153150A1 EP00904876A EP00904876A EP1153150A1 EP 1153150 A1 EP1153150 A1 EP 1153150A1 EP 00904876 A EP00904876 A EP 00904876A EP 00904876 A EP00904876 A EP 00904876A EP 1153150 A1 EP1153150 A1 EP 1153150A1
Authority
EP
European Patent Office
Prior art keywords
mixing
mixture
powder
range
hard metal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP00904876A
Other languages
German (de)
French (fr)
Other versions
EP1153150B1 (en
Inventor
Benno Gries
Jörg Bredthauer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HC Starck GmbH
Original Assignee
HC Starck GmbH
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Filing date
Publication date
Application filed by HC Starck GmbH filed Critical HC Starck GmbH
Publication of EP1153150A1 publication Critical patent/EP1153150A1/en
Application granted granted Critical
Publication of EP1153150B1 publication Critical patent/EP1153150B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F29/00—Mixers with rotating receptacles
    • B01F29/40—Parts or components, e.g. receptacles, feeding or discharging means
    • B01F29/403—Disposition of the rotor axis
    • B01F29/4033—Disposition of the rotor axis inclined
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F29/00—Mixers with rotating receptacles
    • B01F29/60—Mixers with rotating receptacles rotating about a horizontal or inclined axis, e.g. drum mixers
    • B01F29/64—Mixers with rotating receptacles rotating about a horizontal or inclined axis, e.g. drum mixers with stirring devices moving in relation to the receptacle, e.g. rotating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F33/00—Other mixers; Mixing plants; Combinations of mixers
    • B01F33/86—Mixing heads comprising a driven stirrer
    • B01F33/862—Mixing heads comprising a driven stirrer the stirrer being provided with a surrounding stator
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
    • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
    • Y10T428/2991—Coated
    • Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]

Definitions

  • Hard metals are materials made from hard materials and binder metals. They are important as wear-resistant materials and are accessible for cutting and non-cutting shaping.
  • Hard materials are carbides or nitrides or carbonitrides of the refractory metals of IV., V. and VI. Subgroup of the Periodic Table of the Elements, with titanium carbide (TiC), titanium carbonitride (Ti (C, N)) and in particular tungsten carbide (WC) the largest
  • Cobalt is used in particular as binder metal.
  • mixed metal powders or alloy powders made of cobalt, nickel and iron and, if appropriate, other constituents are also used in minor amounts.
  • hard materials and binder metal each in powder form, are intimately mixed, pressed and then sintered, the binder metal by forming a melt during sintering to achieve very extensive compression and to build up a multi-phase structure with more favorable properties
  • the sintering result can be represented in the form of the residual porosity.
  • a certain residual porosity must be undershot.
  • Hard materials are usually used with average particle sizes of 3 to 20 ⁇ , preferably 3 to 10 ⁇ according to ASTM B 330. It should be very fine Hard material components should be avoided as these tend to recrystallize during the liquid phase sintem (Ostwal d-ripening).
  • the crystallites that have grown in this way have multidimensional point defects which are disadvantageous for certain performance properties of the hard metal, in particular for machining steel, in mining and in impact tools.
  • tungsten carbide can be plastically deformed to a certain extent if multi-dimensional point defects are cured at high temperatures above 1900 ° C. The carburization temperature at which the tungsten carbide was obtained is therefore essential for the performance properties of the hard metal.
  • the portion of the tungsten carbide phase dissolved in the hard metal at sintering temperature is qualitatively inferior to the undissolved portion in terms of these performance properties.
  • a further embrittlement can occur that WC-parts that have grown up by redissolving may have incorporated binder metals in the lattice.
  • the binder metal is regularly used with a smaller particle size, typically about 1 to 2 ⁇ according to ASTM B 330.
  • the binder metal is used in such an amount that it makes up approx. 3 to 25% by weight of the hard metal.
  • wet grinding in the attritor or in a ball mill using an organic grinding liquid and using grinding balls has established itself as the industrially used method for producing hard metal mixtures.
  • the use of a grinding fluid effectively suppresses the electrostatic repulsive forces.
  • the mixed grinding is a very complex process, which on the one hand requires a lot of space due to the required volume ratio of grinding media to ground material of about 6: 1 and on the other hand meals from 4 to 48 hours.
  • a certain amount of grinding abrasion and a certain size reduction can also be accepted with wet mixed grinding.
  • the object of the present invention is to provide a method for producing hard metal mixtures which avoids the disadvantages of the prior art, in particular is less technically complex and, moreover, owing to the homogeneity of the mixture and the avoidance of comminution of the hard material after the sintering of hard metals with excellent performance characteristics by minimizing the redissolved portion of the toilet phase.
  • the object is achieved in that the mixing in the vicinity of the mixture constituents by producing high shear rate of impact of the powder particles and in the distant region by circulating the mixture
  • mixing in the close range is understood to mean the mixing of a subset of the mixture, whereas the long range mixing is the mixing of the main quantity of the mixture batch, i.e. of the subsets among themselves.
  • the method according to the invention therefore consists in that, on the one hand, in the short-range mixing with high input of mixing energy (based on the amount of powder detected by the mixing element) to overcome the electrostatic repulsive forces of the powder particles with one another and, on the other hand, in the area mixing is mixed with low energy input to homogenize the powder mixture.
  • different mixing units are preferably used for short-range and long-range mixing.
  • the majority of the mix is in the area of long-range mixing by circulating the mix bed.
  • a rotary tube, a ploughshare mixer, a paddle mixer or a conical screw mixer are suitable, for example.
  • a subset of the mixture is in the area of short-range mixing, a mixing unit producing high mutual impact speeds.
  • Aggregates suitable for short-range mixing are, in particular, rapidly rotating mixing elements. According to the invention, preference is given to those with peripheral speeds of 8 to 25 m / s, particularly preferably 12 to 18 m / s.
  • the material to be mixed is preferably fluidized at least in the area of the short-range mixing in the gas atmosphere of the mixing container, the gas being strongly swirled by the mixing element and the powder particles colliding due to the shear rates prevailing in the vortices.
  • a suitable mixing element is, for example, a high-speed stirring element provided with wall-mounted stirring blades, a gap remaining between the container wall and the stirring blade, the width of which is at least 50 times the particle diameter.
  • the gap width is preferably 100 to 500 times the particle size.
  • Units suitable for short-range mixing are, for example, from US Pat. Nos. 3,348,779, 4,747,550, EP-A 200 003, EP-A 474 102, EP-A 645 179 and DE-U 29 515 434 known as the microwirl mill.
  • Such mills consist of a stator in the form of a cylindrical housing, in which a rotor is arranged axially, which has one or more circular disks arranged one above the other on a common drivable axis has, the circular disks on their circumference having a plurality of substantially radially and parallel to the rotor axis arranged grinding plates that protrude beyond the circular disks, leaving a gap between the stator and grinding plates, the "shear gap".
  • the gas-dispersed particles in the micro-vortex mill experience high acceleration forces due to the shear rate imposed on the gas between the rotor and stator, so that the particles collide with one another while overcoming the electrostatic repulsive forces .
  • a charge exchange or a dielectric charge transfer takes place, so that the repulsive forces of the particles among each other remain canceled after the impact.
  • the shear gap between the rotor and the stator should preferably have a clear width which is at least 50 times the mean diameter of the particle size with the larger mean diameter, i.e. the hard material particles.
  • a shear gap with an internal width which corresponds to 100 to 500 times the average diameter of the hard material particles.
  • the shear gap can typically have a clear width of 0.5 to 5 mm, preferably 1 to 3 mm.
  • the shear rate in the shear gap should preferably be at least 800 / s, particularly preferably 1000 to 20,000 / s.
  • the dwell time in the short-range mixing is selected so that the
  • the temperature of the powder mixture when passing through the close-range mixture does not rise above 300 ° C.
  • lower temperatures are preferred in order to reliably avoid oxidation of the powder particles.
  • a protective gas atmosphere for example argon
  • the dwell time for short-range mixing is in the range of seconds.
  • the total mixing time is preferably 30 to 90 minutes, particularly preferably more than 40 minutes, and more preferably less than 1 hour.
  • the powder mixture is recirculated between short-range and long-range mixing, i.e. Partial quantities of the powder mixture are taken as a continuous partial stream from the long-range mixing, fed to the short-range mixing and back into the
  • the circulation speed of the powder mixture is preferably selected by the short-range mixing such that during the total mixing time on average at least 5 passes, particularly preferably at least 10 passes each
  • Powder particle is ensured by the short-range mixing.
  • the two powder components or a raw mixture of the powder components can be fed continuously at one end of the circulation mixing unit and homogeneously mixed powder can be discharged continuously at the other end.
  • An alternative continuous implementation of the method consists in producing a raw mixture of the powder components in a first circulation mixing unit, continuously removing the raw mixture from the first circulation mixing unit, introducing it into the micro vortex mill, and then feeding it to a second circulation mixing unit, where it may be expedient to use Connection to the second circulation mixing unit is to carry out a further short-range mixing in a micro vortex mill and then a further long-range mixing in a circulation mixing unit.
  • the mix is fluidized both in the short-range and in the long-range mixing.
  • a suitable method for this has, for example, a floor and wall-accessible rotor with a shear gap to the container wall, the radial rotor blades being set against the vertical, so that the fluidized regrind is conveyed peripherally upwards in the container and is conveyed centrally downwards.
  • the angle of attack is preferably less than 25 °, particularly preferably 10 to 20 °.
  • This circulation of the mixed material for long-range mixing can be intensified by a coaxial rotor positioned in opposite directions with a diameter that is limited to only half the cross-section of the container. It has been found that excellent hard metal mixtures can still be achieved in such an aggregate if the container is filled up to 7% by volume with mixed material (weight of the mixed material divided by the density of the powder material).
  • Additives used in the carbide industry such as organic adhesion promoters, oxidation inhibitors, granule stabilizers and / or pressing aids, e.g. on paraffin or polyethylene glycol basis mixed with the hard material and binder powder and distributed homogeneously.
  • the pressing aids melt due to the heat generated during the mixing process, so that a uniform surface coverage is brought about. If the mixtures produced in this way do not yet have sufficient flowability or compressibility, a granulation step can be followed.
  • the hard metal mixtures according to the invention and their granules are for
  • FIG. 1 shows schematically a first embodiment of the invention
  • Fig. 2 shows schematically a second embodiment of the invention
  • Fig. 3 shows schematically a third embodiment of the invention
  • Fig. 4 shows the basic structure of a micro vortex mill as a sectional view
  • FIG. 5 shows a mixing device suitable according to the invention as a sectional view
  • FIG. 6 shows a further mixing device suitable according to the invention.
  • Example 7 shows the SEM image of the tungsten carbide powder used in Example 1
  • Example 11 shows the micrograph of a hard metal produced according to Example 2.
  • FIG. 1 schematically shows a long-range mixer A into which the two powders P1 and P2 are introduced continuously or discontinuously.
  • a partial stream of the powder mixture is continuously transferred from the low-range mixing unit A to the short-range mixing unit B and returned to the low-range mixing unit A.
  • the final mixing unit A finally becomes the finished one
  • Powder mixture PM taken continuously or discontinuously. 2 shows a basic arrangement which is particularly suitable for the continuous execution of the method according to the invention.
  • the powders P1 and P2 are introduced into a first mixing area mixing unit, in particular, for example, a rotary tube. They come out of the rotary tube into a first micro vortex mill Bl and are then transferred to a second form mixer A2. If necessary, a further short-range blending B2 and a long-range blending A3, not shown, can be connected.
  • FIG. 3 shows an arrangement which is particularly suitable for batch batch mixing.
  • the micro-vortex mill B as a short-range mixing element is arranged within the part-range mixing element A.
  • Fig. 4 shows the structure of a micro vortex mill 1.
  • This consists of a cylindrical housing 2, the inner wall of which forms the stator.
  • the inner wall of the cylindrical housing 2 can be covered with abrasion-resistant material.
  • An axis drivable for rotation is provided within the cylindrical housing 2, one or more, in particular 2 to 5, circular disks 4.1, 4.2 and 4.3 drivable with the axis are provided on the axis 3, each of which has a plurality of radial and parallel on its circumference have grinding plates 5.1, 5.2 and 5.3 arranged in relation to axis 3.
  • the outer edges of the grinding plates 5.1, 5.2 and 5.3 together with the inner wall of the cylindrical housing 2 form the shear gap 6.
  • the micro-vortex mill is arranged below the filling level within a mold mixing element, the micro-vortex mill also preferably has a conical cover 7 which is provided with openings 8 through which the free-flowing powder trickles well into the cylindrical housing 2.
  • An additional circular disk 9 provided with the axis 3 can be provided as a distributor plate.
  • FIG. 5 shows a device which can be used according to the invention, as is shown schematically in FIG. 3.
  • This consists of a mixing drum 10 which, via the axis 11, rotates at a low rotational speed, for example 1 to 2 revolutions. revolutions per minute, can be driven.
  • the drum is closed by the non-rotating cover cap 12.
  • the micro-vortex mill 1 is located inside the drum 10, as shown in FIG. 4.
  • Baffles 13 can also be arranged within the drum 10.
  • the filling level of the drum 10 is indicated by the dashed line 14.
  • the method according to the invention now consists in that the powder mixture continuously enters the micro-vortex mill 1 through the openings 8, where the short-range mixing takes place, and is returned to the mold area mixing through the cylinder which is open at the bottom.
  • FIG. 6 shows a device which can be used according to the invention, in which the material to be mixed is fluidized both in the short-range mixing and in the mixing area mixing.
  • the container 10 on a drivable axis 3, there is a floor and wall-accessible rotor with 4 rotor blades 5a, 5b, 5c and 5d, which form the shear gap 6 with respect to the container wall.
  • the mix is fluidized and, in addition to the rotation about the axis 3, is circulated as indicated by the arrow 22.
  • a partial amount of the fluidized mixed material reaches the shear gap 6, where the high shear rate of the fluid causes a strong acceleration of the particles.
  • example 1 The invention is illustrated by the following examples: example 1
  • Fig. 5 shows a SEM picture of the tungsten carbide powder before mixing.
  • Samples of the powder mixture are taken after 20, 30 and 40 minutes of mixing time. 8 shows an SEM image of the powder mixture obtained after a mixing time of 40 minutes.
  • the oxygen content before mixing is 0.068% by weight, after mixing 0.172% by weight.
  • the samples are processed into hard metal test specimens by pressing and subsequent sintering at 1380 ° C for 45 minutes.
  • a corresponding powder mixture is ground in a ball mill with hexane for 20 hours.
  • a hard metal test specimen is produced in the same way from the comparison powder mixture.
  • Grain size of 6 ⁇ m (FSSS, ASTM B 330) are mixed as in Example 1.
  • the Oxygen content before mixing is 0.058% by weight, after 40 minutes of mixing time 0.109% by weight.
  • a comparison mixture (example 2f) is also produced in a ball mill as in example 1.
  • 9 shows a SEM image of the starting tungsten carbide powder. 10 shows the powder mixture after a mixing time of 30 minutes.
  • Example 11 shows the micrograph of a hard metal according to Example 2d).
  • Example 13 kg of a cobalt metal powder with an average grain size of 1.55 ⁇ m, 117 kg of a less agglomerated tungsten carbide powder (FIG. 12) are mixed as in Example 1. 13 shows an SEM image of the powder mixture obtained.
  • the oxygen content before mixing is 0.065% by weight, after mixing 0.088% by weight.
  • the hard metal has a good structure and a good binder distribution.

Abstract

The invention relates to a method for producing a homogeneous mixture of hard material powders and binder metal powders without using grinding bodies, liquid grinding auxiliary agents and suspending media. According to the invention, the mixture components are mixed at close range while generating a high shearing collision velocity of the powder particles and are remotely mixed by rotating the mixing bed without resulting in a particle size reduction of the hard material powders.

Description

Verfahren zur Herstellung von HartmetallmischungenProcess for the production of hard metal mixtures
Hartmetalle sind Werkstoffe aus Hartstoffen und Bindermetallen. Sie haben Be- deutung als verschleißfeste Werkstoffe und sind der spanenden und spanlosen Formgebung zugänglich.Hard metals are materials made from hard materials and binder metals. They are important as wear-resistant materials and are accessible for cutting and non-cutting shaping.
Hartstoffe sind Carbide oder Nitride oder Carbonitride der Refraktärmetalle der IV., V. und VI. Nebengruppe des Periodensystems der Elemente, wobei Titancarbid (TiC), Titancarbonitrid (Ti(C,N)) und insbesondere Wolframcarbid (WC) die größteHard materials are carbides or nitrides or carbonitrides of the refractory metals of IV., V. and VI. Subgroup of the Periodic Table of the Elements, with titanium carbide (TiC), titanium carbonitride (Ti (C, N)) and in particular tungsten carbide (WC) the largest
Bedeutung erlangt haben.Have gained importance.
Als Bindermetalle wird insbesondere Kobalt eingesetzt. Allerdings werden jedoch auch Mischmetallpulver bzw. Legierungspulver aus Kobalt, Nickel und Eisen sowie gegebenenfalls weiteren Bestandteilen in untergeordneten Mengen eingesetzt.Cobalt is used in particular as binder metal. However, mixed metal powders or alloy powders made of cobalt, nickel and iron and, if appropriate, other constituents are also used in minor amounts.
Zur Herstellung von Hartmetallen werden Hartstoffe und Bindermetall, jeweils in Pulverform, innig vermischt, verpreßt und anschließend versintert, wobei das Bindermetall durch Bildung einer Schmelze während des Sinterns eine sehr weitgehende Verdichtung und den Aufbau eines mehrphasigen Gefüges mit günstigerFor the production of hard metals, hard materials and binder metal, each in powder form, are intimately mixed, pressed and then sintered, the binder metal by forming a melt during sintering to achieve very extensive compression and to build up a multi-phase structure with more favorable properties
Biegefestigkeit und Bruchzähigkeit ermöglichen soll. Die Wirkung des Bindermetalls ist dann optimal, wenn vollständige Benetzung der Hartstoffphase erzielt wird, wobei die von der Sintertemperatur abhängige Löslichkeit des Hartstoffs im Binder eine teilweise Umlösung und Neuanordnung des Hartstoffs bewirkt, so daß eine Gefügestruktur erzielt wird, die der Rißausbreitung einen großenBending strength and fracture toughness should enable. The effect of the binder metal is optimal when complete wetting of the hard material phase is achieved, the solubility of the hard material in the binder, which is dependent on the sintering temperature, causing a partial redissolving and rearrangement of the hard material, so that a structural structure is achieved which has a large effect on crack propagation
Widerstand entgegensetzt. Das Sinterergebnis läßt sich in Form der Restporosität darstellen. Zur Erzielung einer ausreichenden Bruchzähigkeit ist die Unterschreitung einer bestimmten Restporosität notwendige Voraussetzung.Opposed resistance. The sintering result can be represented in the form of the residual porosity. In order to achieve sufficient fracture toughness, a certain residual porosity must be undershot.
Hartstoffe werden üblicherweise mit mittleren Teilchengrößen von 3 bis 20 μ, vorzugsweise 3 bis 10 μ nach ASTM B 330 eingesetzt. Dabei sollen sehr feinteilige Hartstoffanteile vermieden werden, da diese während des Flüssigphasensintems zur Umkristallisation neigen (Ostwal d-Reifung). Die so gewachsenen Kristallite weisen mehrdimensionale Punktdefekte auf, die für bestimmte Leistungseigenschaften des Hartmetalls, insbesondere bei der Stahlzerspanung, im Bergbau und bei Schlagwerk- zeugen nachteilig sind. Beispielsweise läßt sich Wolframcarbid bis zu einem gewissen Grad plastisch deformieren, wenn mehrdimensionale Punktdefekte bei hohen Temperaturen oberhalb 1900°C ausgeheilt werden. Die Carburierungstemperatur, bei der das Wolframcarbid gewonnen wurde ist daher wesentlich für die Leistungseigenschaften des Hartmetalls. Der bei Sintertemperatur, typischerweise zwischen 1360 und 1450°C, umgelöste Anteil der Wolframcarbidphase im Hartmetall ist im Hinblick auf diese Leistungseigenschaften dem nicht-umgelösten Anteil qualitativ unterlegen. Eine weitere Versprödung kann dadurch eintreten, daß durch Umlösung aufgewachsene WC-Anteile Bindermetalle im Gitter inkorporiert haben können.Hard materials are usually used with average particle sizes of 3 to 20 μ, preferably 3 to 10 μ according to ASTM B 330. It should be very fine Hard material components should be avoided as these tend to recrystallize during the liquid phase sintem (Ostwal d-ripening). The crystallites that have grown in this way have multidimensional point defects which are disadvantageous for certain performance properties of the hard metal, in particular for machining steel, in mining and in impact tools. For example, tungsten carbide can be plastically deformed to a certain extent if multi-dimensional point defects are cured at high temperatures above 1900 ° C. The carburization temperature at which the tungsten carbide was obtained is therefore essential for the performance properties of the hard metal. The portion of the tungsten carbide phase dissolved in the hard metal at sintering temperature, typically between 1360 and 1450 ° C., is qualitatively inferior to the undissolved portion in terms of these performance properties. A further embrittlement can occur that WC-parts that have grown up by redissolving may have incorporated binder metals in the lattice.
Das Bindermetall wird regelmäßig mit kleinerer Teilchengröße eingesetzt, typischerweise etwa 1 bis 2 μ nach ASTM B 330.The binder metal is regularly used with a smaller particle size, typically about 1 to 2 μ according to ASTM B 330.
Das Bindermetall wird in einer solchen Menge eingesetzt, daß es ca. 3 bis 25 Gew.-% des Hartmetalls ausmacht.The binder metal is used in such an amount that it makes up approx. 3 to 25% by weight of the hard metal.
Vorteilhaft können bis zu 50 % gemahlene, recyklierte sinterfähige Hartmetallpulver mitverwendet werden.Up to 50% of recycled, recyclable sinterable hard metal powder can advantageously be used.
Neben der Auswahl des jeweils geeigneten Hartstoffes (Teilchengröße, Teilchen- größenverteilung, Kristallgefüge) und des Bindermetalls (Zusammensetzung, Menge,In addition to the selection of the most suitable hard material (particle size, particle size distribution, crystal structure) and the binder metal (composition, amount,
Anteil am Hartmetall) sowie der Sinterbedingungen spielt die Herstellung geeigneter Hartmetallmischungen, d.h. die Vermischung von Hartstoff und Binder vor der Ver- sinterung eine überragende Rolle mit Bezug auf die späteren Hartmetalleigenschaften. Wegen der elektrostatischen Abstoßungskräfte zwischen den feinen Pulverteilchen (dies bedingt immer niedrige Schüttdichten bei feineren Pulvern), der unterschiedlichen Teilchengröße und Dichte sowie der ungünstigen Mengenrelation beider Komponenten scheidet eine Trockenvermischung nach bisherigem Stand der Technik aus. Mit einer trockenen Vermahlung der beiden Komponenten würden zwar die elektrostatischen Abstoßungskräfte zwischen den Teilchen überwunden werden können, jedoch würde dies zu einer Teilchenverkleinerung insbesondere des Hartstoffs führen, bei der sehr viele Feinanteile erzeugt würden. Ferner ist der unvermeindliche Abrieb der Mahlwerkzeuge ein bisher ungelöstes Problem.Proportion of hard metal) and the sintering conditions, the production of suitable hard metal mixtures, ie the mixing of hard material and binder before sintering, plays an outstanding role with regard to the later hard metal properties. Due to the electrostatic repulsive forces between the fine powder particles (this always requires low bulk densities for finer powders), the different particle size and density, and the unfavorable quantitative relationship between the two components, dry mixing according to the prior art is ruled out. A dry grinding of the two components would overcome the electrostatic repulsive forces between the particles, but this would lead to a reduction in particle size, in particular of the hard material, in which a large number of fines would be generated. Furthermore, the inevitable abrasion of the grinding tools is a problem that has not yet been solved.
Demgemäß hat sich die Naßvermahlung im Attritor oder in einer Kugelmühle unter Verwendung einer organischen Mahlflüssigkeit und unter Einsatz von Mahlkugeln als das industriell angewandte Verfahren zur Herstellung von Hartmetallmischungen durchgesetzt. Durch den Einsatz einer Mahlflüssigkeit werden die elektrostatischen Abstoßungskräfte zusätzlich wirkungsvoll unterdrückt. Zwar gelingt es durch die nasse Mischmahlung im Attritor die Kornzerkleinerung des Hartstoffs in noch vertretbaren Grenzen zu halten, jedoch ist die Mischmahlung ein sehr aufwendiges Verfahren, das einerseits hohen Raumbedarf aufgrund des erforderlichen Volumenverhältnisses von Mahlkörpern zu Mahlgut von etwa 6:1 aufweist und andererseits Mahlzeiten von 4 bis 48 Stunden in Anspruch nimmt. Hinzu kommt das Erfordernis, im Anschluß an die Mischmahlung die Mahlkugeln von der Hartmetallmischung durch Sieben und die organische Mahlflüssigkeit durch Verdampfen abzutrennen. Ein gewisser Mahlabrieb und eine gewisse Kornzerkleinerung ist jedoch auch bei der nassen Mischmahlung in Kauf zu nehmen. Besonders betroffen sind solche WC- Pulver, die bei mindestens 1900°C carburiert wurden, enge Korngrößenverteilung ohne Feinanteil aufweisen und daher ohne Umlösevorgänge in höchstwertige Hartmetalle überführt werden sollen.Accordingly, wet grinding in the attritor or in a ball mill using an organic grinding liquid and using grinding balls has established itself as the industrially used method for producing hard metal mixtures. The use of a grinding fluid effectively suppresses the electrostatic repulsive forces. Although it is possible to keep the grain size reduction of the hard material within reasonable limits due to the wet mixed grinding in the attritor, the mixed grinding is a very complex process, which on the one hand requires a lot of space due to the required volume ratio of grinding media to ground material of about 6: 1 and on the other hand meals from 4 to 48 hours. In addition, there is the need to separate the grinding balls from the hard metal mixture by sieving and the organic grinding liquid by evaporation after the mixed grinding. A certain amount of grinding abrasion and a certain size reduction can also be accepted with wet mixed grinding. WC powders that have been carburized at at least 1900 ° C, have a narrow grain size distribution without fines and are therefore to be converted into high-quality hard metals without redissolving processes are particularly affected.
Nach einem sehr alten Vorschlag (GB-Patent 346 473) sollen die Probleme der Mischung von Hartstoffen und Bindermetall dadurch gelöst werden, daß die Hartstoffe mit dem Bindermetall elektrolytisch beschichtet werden. Dieses Verfahren hat sich jedoch nicht durchsetzen können. Nach neueren Vorschlägen (US-A 5 505 902 und US-A 5 529 804) wird das Bindermetall, insbesondere Kobalt chemisch auf die Hartstoffteilchen aufgebracht. Dabei werden organische Flüssigphasen eingesetzt, die nicht ohne Einfluß auf den Kohlenstoffhaushalt des Hartmetalls bleiben dürften.According to a very old proposal (GB patent 346 473), the problems of mixing hard materials and binder metal are to be solved by electrolytically coating the hard materials with the binder metal. This procedure has however, cannot prevail. According to more recent proposals (US-A 5 505 902 and US-A 5 529 804), the binder metal, in particular cobalt, is chemically applied to the hard material particles. Organic liquid phases are used, which should not have an impact on the carbon balance of the hard metal.
Aufgabe der vorliegenden Erfindung ist es, ein Verfahren zur Herstellung von Hartmetallmischungen anzugeben, das die Nachteile des Standes der Technik vermeidet, insbesondere technisch weniger aufwendig ist und darüber hinaus aufgrund der Homogenität der Mischung und der Vermeidung von Kornzerkleinerungen des Hart- Stoffs nach dem Versintern Hartmetalle mit hervorragenden Leistungseigenschaften durch Minimierung des umgelösten Anteils der WC-Phase ergibt.The object of the present invention is to provide a method for producing hard metal mixtures which avoids the disadvantages of the prior art, in particular is less technically complex and, moreover, owing to the homogeneity of the mixture and the avoidance of comminution of the hard material after the sintering of hard metals with excellent performance characteristics by minimizing the redissolved portion of the toilet phase.
Es wurde gefunden, daß die Aufgabe dadurch gelöst wird, daß die Vermischung im Nahbereich der Mischungsbestandteile durch Erzeugung hoher scherender Aufprall- geschwindigkeit der Pulverteilchen und im Fernbereich durch Umwälzung desIt has been found that the object is achieved in that the mixing in the vicinity of the mixture constituents by producing high shear rate of impact of the powder particles and in the distant region by circulating the
Mischgutes durchgeführt wird.Mixed goods is carried out.
Auf diese Weise gelingt die trockene Vermischung von Hartstoff- und Bindermetallpulvern ohne Einsatz von Mahlkörpern oder flüssigen Mahlhilfsmitteln oder flüs- sigen Suspendiermedien im wesentlichen ohne Kornzerkleinerung.In this way, dry mixing of hard material and binder metal powders is possible without the use of grinding media or liquid grinding aids or liquid suspending media, essentially without comminution of the grain.
Unter "Vermischung im Nahbereich" wird erfmdungsgemäß die Vermischung einer Teilmenge des Mischgutes in sich verstanden, wogegen die Fernbereichsvermischung die Vermischung der Hauptmenge des Mischungsbatches in sich, d.h. der Teilmengen untereinander, bezeichnet.According to the invention, "mixing in the close range" is understood to mean the mixing of a subset of the mixture, whereas the long range mixing is the mixing of the main quantity of the mixture batch, i.e. of the subsets among themselves.
Das erfindungsgemäße Verfahren besteht also darin, daß einerseits bei der Nahbereichsvermischung unter hohem Eintrag von Mischenergie (bezogen auf die von dem Mischorgan erfaßte Pulvermenge) zur Überwindung der elektrostatischen Ab- Stoßungskräfte der Pulverteilchen untereinander und andererseits bei der Fern- bereichsvermischung bei niedrigem Energieeintrag zur Homogenisierung der Pulvermischung vermischt wird.The method according to the invention therefore consists in that, on the one hand, in the short-range mixing with high input of mixing energy (based on the amount of powder detected by the mixing element) to overcome the electrostatic repulsive forces of the powder particles with one another and, on the other hand, in the area mixing is mixed with low energy input to homogenize the powder mixture.
Erfindungsgemäß bevorzugt werden für Nahbereichs- und Fernbereichsvermischung unterschiedliche Mischaggregate eingesetzt.According to the invention, different mixing units are preferably used for short-range and long-range mixing.
Die Hauptmenge des Mischgutes befindet sich im Bereich der Fernbereichsvermischung durch Umwälzung des Mischungsbettes. Geeignet sind beispielsweise ein Drehrohr, ein Pflugscharmischer, ein Schaufelmischer oder ein Kegelschnecken- mischer.The majority of the mix is in the area of long-range mixing by circulating the mix bed. A rotary tube, a ploughshare mixer, a paddle mixer or a conical screw mixer are suitable, for example.
Eine Teilmenge des Mischungsgutes befindet sich im Bereich der Nahbereichsvermischung, einem hohe gegenseitige Aufprallgeschwindigkeiten erzeugenden Mischaggregat. Für die Nahbereichsvermischung geeignete Aggregate sind insbesondere schnell rotierende Mischorgane. Erfindungsgemäß bevorzugt sind solche mit Umfangsgeschwindigkeiten von 8 bis 25 m/s, insbesondere bevorzugt 12 bis 18 m/s. Vorzugsweise ist das Mischgut zumindest im Bereich der Nahbereichsvermischung in der Gas-Atmosphäre des Mischbehälters fluidisiert, wobei das Gas durch das Mischorgan stark verwirbelt wird und die Pulverteilchen aufgrund der in den Wirbeln herrschenden Schergeschwindigkeiten aufeinanderprallen. Ein geeignetes Mischorgan ist beispielsweise ein mit wandgängigen Rührblättern versehenes schnell laufendes Rührorgan, wobei zwischen Behälterwand und Rührblatt ein Spalt verbleibt, dessen Breite mindestens das 50-fache des Teilchendurchmessers beträgt. Bevorzugt beträgt die Spaltbreite das 100 bis 500-fache der Teilchengröße.A subset of the mixture is in the area of short-range mixing, a mixing unit producing high mutual impact speeds. Aggregates suitable for short-range mixing are, in particular, rapidly rotating mixing elements. According to the invention, preference is given to those with peripheral speeds of 8 to 25 m / s, particularly preferably 12 to 18 m / s. The material to be mixed is preferably fluidized at least in the area of the short-range mixing in the gas atmosphere of the mixing container, the gas being strongly swirled by the mixing element and the powder particles colliding due to the shear rates prevailing in the vortices. A suitable mixing element is, for example, a high-speed stirring element provided with wall-mounted stirring blades, a gap remaining between the container wall and the stirring blade, the width of which is at least 50 times the particle diameter. The gap width is preferably 100 to 500 times the particle size.
Für die Nahbereichsvermischung ferner geeignete Aggregate sind beispielsweise aus den US-A 3 348 779, US-A 4 747 550, der EP-A 200 003, der EP-A 474 102, der EP-A 645 179 sowie der DE-U 29 515 434 unter der Bezeichnung Mikrowirbel- mühle bekannt. Derartige Mühlen bestehen aus einem Stator in Form eines zylin- drischen Gehäuses, in dem axial ein Rotor angeordnet ist, der eine oder mehrere auf einer gemeinsamen antreibbaren Achse übereinander angeordnete Kreisscheiben aufweist, wobei die Kreisscheiben auf ihrem Umfang eine Vielzahl von im wesentlichen radial und parallel zur Rotorachse angeordnete Mahlplatten aufweisen, die die Kreisscheiben überragen, wobei ein Spalt zwischen Stator und Mahlplatten verbleibt, der "Scherspalt". Wird der Rotor zu hoher Umdrehungsgeschwindigkeit angetrieben, typischerweise 1000 bis 5000 U/Min., erfahren die in der Mikrowirbel- mühle befindlichen gasdispergierten Teilchen aufgrund der dem Gas aufgeprägten Schergeschwindigkeit zwischen Rotor und Stator hohe Beschleunigungskräfte, so daß die Teilchen unter Überwindung der elektrostatischen Abstoßungskräfte aufeinanderprallen. Bei dem Aufprall der Teilchen findet ein Ladungsaustausch bzw. eine dielektrische Umladung statt, so daß die Abstoßungskräfte der Teilchen untereinander nach dem Aufprall aufgehoben bleiben.Units suitable for short-range mixing are, for example, from US Pat. Nos. 3,348,779, 4,747,550, EP-A 200 003, EP-A 474 102, EP-A 645 179 and DE-U 29 515 434 known as the microwirl mill. Such mills consist of a stator in the form of a cylindrical housing, in which a rotor is arranged axially, which has one or more circular disks arranged one above the other on a common drivable axis has, the circular disks on their circumference having a plurality of substantially radially and parallel to the rotor axis arranged grinding plates that protrude beyond the circular disks, leaving a gap between the stator and grinding plates, the "shear gap". If the rotor is driven at a high speed of rotation, typically 1000 to 5000 rpm, the gas-dispersed particles in the micro-vortex mill experience high acceleration forces due to the shear rate imposed on the gas between the rotor and stator, so that the particles collide with one another while overcoming the electrostatic repulsive forces . During the impact of the particles, a charge exchange or a dielectric charge transfer takes place, so that the repulsive forces of the particles among each other remain canceled after the impact.
Erfindungsgemäß bevorzugt soll der Scherspalt zwischen Rotor und Stator eine lichte Weite aufweisen, die mindestens dem 50-fachen mittleren Durchmesser der Teilchengröße mit dem größeren mittleren Durchmesser, d.h. der Hartstoffteilchen, entspricht. Bevorzugt ist ein Scherspalt mit einer lichten Weite, die dem 100- bis 500-fachen mittleren Durchmesser der Hartstoffteilchen entspricht. Typischerweise kann demgemäß der Scherspalt eine lichte Weite von 0,5 bis 5 mm, vorzugsweise 1 bis 3 mm aufweisen.According to the invention, the shear gap between the rotor and the stator should preferably have a clear width which is at least 50 times the mean diameter of the particle size with the larger mean diameter, i.e. the hard material particles. Preferred is a shear gap with an internal width which corresponds to 100 to 500 times the average diameter of the hard material particles. Accordingly, the shear gap can typically have a clear width of 0.5 to 5 mm, preferably 1 to 3 mm.
Vorzugsweise soll die Schergeschwindigkeit im Scherspalt, ausgedrückt als das Verhältnis von Umfangsgeschwindigkeit des Rotors und Spaltbreite mindestens 800/s, besonders bevorzugt 1000 bis 20.000/s betragen.The shear rate in the shear gap, expressed as the ratio of the peripheral speed of the rotor and the gap width, should preferably be at least 800 / s, particularly preferably 1000 to 20,000 / s.
Die Verweilzeit bei der Nahbereichsvermischung wird so gewählt, daß dieThe dwell time in the short-range mixing is selected so that the
Temperatur der Pulvermischung beim Durchgang durch die Nahbereichsvermischung nicht über 300°C ansteigt. Im Falle, daß in einer sauerstoffhaltigen Atmosphäre, insbesondere Luft, vermischt wird, sind niedrigere Temperaturen bevorzugt um eine Oxidation der Pulverteilchen sicher zu vermeiden. Im Falle, daß die Vermischung in Schutzgasatmosphäre, beispielsweise Argon, erfolgt, sind gegebenenfalls Tempera- turen bis 500° zulässig. Typischerweise liegt die Verweilzeit bei der Nahbereichsvermischung im Sekundenbereich.The temperature of the powder mixture when passing through the close-range mixture does not rise above 300 ° C. In the event that mixing takes place in an oxygen-containing atmosphere, in particular air, lower temperatures are preferred in order to reliably avoid oxidation of the powder particles. In the event that the mixing takes place in a protective gas atmosphere, for example argon, doors up to 500 ° permitted. Typically, the dwell time for short-range mixing is in the range of seconds.
Die Gesamt-Mischdauer beträgt vorzugsweise 30 bis 90 Minuten, insbesondere be- vorzugt mehr als 40 Minuten, und weiter bevorzugt weniger als 1 Stunde.The total mixing time is preferably 30 to 90 minutes, particularly preferably more than 40 minutes, and more preferably less than 1 hour.
Nach einer bevorzugten Ausführungsform der Erfindung wird die Pulvermischung zwischen Nahbereichs- und Fernbereichsvermischung rezirkuliert, d.h. Teilmengen der Pulvermischung werden als kontinuierlicher Teilstrom der Fernbereichsver- mischung entnommen, der Nahbereichsvermischung zugeführt und wieder in dieAccording to a preferred embodiment of the invention, the powder mixture is recirculated between short-range and long-range mixing, i.e. Partial quantities of the powder mixture are taken as a continuous partial stream from the long-range mixing, fed to the short-range mixing and back into the
Fernbereichsvermischung eingeleitet.Long-range merging initiated.
Vorzugsweise wird die Umlaufgeschwindigkeit der Pulvermischung durch die Nahbereichsvermischung so gewählt, daß während der Gesamtmischzeit im Mittel mindestens 5 Durchgänge, besonders bevorzugt mindestens 10 Durchgänge jedesThe circulation speed of the powder mixture is preferably selected by the short-range mixing such that during the total mixing time on average at least 5 passes, particularly preferably at least 10 passes each
Pulverteilchens durch die Nahbereichsvermischung gewährleistet ist.Powder particle is ensured by the short-range mixing.
Bei kontinuierlicher Durchführung des Verfahrens können die beiden Pulverkomponenten bzw. eine Rohmischung der Pulverkomponenten kontinuierlich an einem Ende des Umwälzmischaggregates eingespeist werden und an dem anderen Ende kontinuierlich homogen vermischtes Pulver ausgeschleust werden.If the process is carried out continuously, the two powder components or a raw mixture of the powder components can be fed continuously at one end of the circulation mixing unit and homogeneously mixed powder can be discharged continuously at the other end.
Eine alternative kontinuierliche Durchführung des Verfahrens besteht darin, in einem ersten Umwälzmischaggregat eine Rohmischung der Pulverkomponenten herzu- stellen, die Rohmischung kontinuierlich aus dem ersten Umwälzmischaggregat zu entnehmen, in die Mikrowirbelmühle einzuschleusen, und anschließend einem zweiten Umwälzmischaggregat zuzuführen, wobei es zweckmäßig sein kann, im Anschluß an das zweite Umwälzmischaggregat eine weitere Nahbereichsvermischung in einer Mikrowirbelmühle und anschließend eine weitere Fernbereichsvermischung in einem Umwälzmischaggregat durchzuführen. Nach einer weiter bevorzugten Ausführungsform der Erfindung wird das Mischgut sowohl in der Nahbereichs- als auch in der Fernbereichsvermischung fluidisiert. Ein geeignetes Verfahren hierzu weist beispielsweise einen boden- und wandgängigen Rotor mit Scherspalt zur Behälterwand auf, wobei die radialen Rotorblätter gegen die Senkrechte angestellt sind, so daß das fluidisierte Mahlgut in dem Behälter peripher nach oben gefördert wird und zentral nach unten gefördert wird. Vorzugsweise beträgt der Anstellwinkel weniger als 25°, insbesondere bevorzugt 10 bis 20°. Diese Zirkulation des Mischgutes zur Fernbereichsvermischung kann durch einen gegensinnig angestellten koaxialen Rotor mit einem nur auf den halben Behälter- querschnitt begrenzten Durchmesser intensiviert werden. Es wurde gefunden, daß in einem derartigen Aggregat noch hervorragende Hartmetallmischungen erzielt werden, wenn der Behälter bis zu 7 Vol-% mit Mischgut (Gewicht des Mischgutes dividiert durch die Dichte des Pulvermaterials) gefüllt wird.An alternative continuous implementation of the method consists in producing a raw mixture of the powder components in a first circulation mixing unit, continuously removing the raw mixture from the first circulation mixing unit, introducing it into the micro vortex mill, and then feeding it to a second circulation mixing unit, where it may be expedient to use Connection to the second circulation mixing unit is to carry out a further short-range mixing in a micro vortex mill and then a further long-range mixing in a circulation mixing unit. According to a further preferred embodiment of the invention, the mix is fluidized both in the short-range and in the long-range mixing. A suitable method for this has, for example, a floor and wall-accessible rotor with a shear gap to the container wall, the radial rotor blades being set against the vertical, so that the fluidized regrind is conveyed peripherally upwards in the container and is conveyed centrally downwards. The angle of attack is preferably less than 25 °, particularly preferably 10 to 20 °. This circulation of the mixed material for long-range mixing can be intensified by a coaxial rotor positioned in opposite directions with a diameter that is limited to only half the cross-section of the container. It has been found that excellent hard metal mixtures can still be achieved in such an aggregate if the container is filled up to 7% by volume with mixed material (weight of the mixed material divided by the density of the powder material).
Vorteilhaft können die für die Weiterverarbeitung der Pulvermischungen von derFor the further processing of the powder mixtures from the
Hartmetallindustrie eingesetzten Zusatzstoffe wie organische Haftvermittler, Oxidati onsverhinderer, Granulatstabilisatoren und/oder Preßhilfsmittel, z.B. auf Paraffinoder Polyethylenglykol-Basis gemeinsam mit dem Hartstoff- und Binderpulver vermischt und homogen verteilt werden. Die Preßhilfsmittel schmelzen aufgrund der während des Mischvorgangs erzeugten Wärme auf, so daß eine gleichmäßige Oberflächenbelegung bewirkt wird. Falls die so erzeugten Mischungen noch keine ausreichende Fließfähigkeit oder Preßfähigkeit aufweisen, kann ein Granulationsschritt nachgeschaltet werden.Additives used in the carbide industry, such as organic adhesion promoters, oxidation inhibitors, granule stabilizers and / or pressing aids, e.g. on paraffin or polyethylene glycol basis mixed with the hard material and binder powder and distributed homogeneously. The pressing aids melt due to the heat generated during the mixing process, so that a uniform surface coverage is brought about. If the mixtures produced in this way do not yet have sufficient flowability or compressibility, a granulation step can be followed.
Die erfindungsgemäßen Hartmetallmischungen und deren Granulate sind zurThe hard metal mixtures according to the invention and their granules are for
Herstellung von Hartmetallformkörpern durch Axialpressen, isostatisches Pressen, Extrusion oder Spritzgießen und Sintern geeignet.Manufacture of hard metal moldings by axial pressing, isostatic pressing, extrusion or injection molding and sintering.
Die Erfindung wird anhand der nachfolgenden Figuren näher erläutert:The invention is explained in more detail with reference to the following figures:
Fig. 1 zeigt schematisch eine erste Ausführungsform der Erfingung Fig. 2 zeigt schematisch eine zweite Ausführungsform der ErfindungFig. 1 shows schematically a first embodiment of the invention Fig. 2 shows schematically a second embodiment of the invention
Fig. 3 zeigt schematisch eine dritte Ausführungsform der ErfindungFig. 3 shows schematically a third embodiment of the invention
Fig. 4 zeigt den prinzipiellen Aufbau einer Mikrowirbelmühle als SchnittbildFig. 4 shows the basic structure of a micro vortex mill as a sectional view
Fig. 5 zeigt eine erfindungsgemäß geeignete Mischvorrichtung als Schnittbild5 shows a mixing device suitable according to the invention as a sectional view
Fig. 6. zeigt eine weitere erfindungsgemäß geeignete Mischvorrichtung.6 shows a further mixing device suitable according to the invention.
Fig. 7 zeigt die REM-Aufnahme des in Beispiel 1 eingesetzten Wolframcarbid- pulvers7 shows the SEM image of the tungsten carbide powder used in Example 1
Fig. 8 zeigt die REM-Aufnahme einer Wolframcarbid-/Kobalt-Pulvermischung8 shows the SEM image of a tungsten carbide / cobalt powder mixture
Fig. 9 zeigt die REM-Aufnahme des in Beispiel 2 eingesetzten Wolframcarbid9 shows the SEM image of the tungsten carbide used in Example 2
Fig. 10 zeigt die REM-Aufnahme einer Wolframcarbid-/Kobalt-Pulvermischung ge- maß Beispiel 210 shows the SEM image of a tungsten carbide / cobalt powder mixture according to Example 2
Fig. 11 zeigt das Schliffbild eines gemäß Beispiel 2 hergestellten Hartmetalls11 shows the micrograph of a hard metal produced according to Example 2
Fig. 12, 13 und 14 zeigen entsprechende Aufnahmen mit Bezug auf Beispiel 3.12, 13 and 14 show corresponding recordings with reference to Example 3.
Fig. 1 zeigt schematisch eine Fernbereichsmischeinrichtung A in die die beiden Pulver Pl und P2 kontinuierlich oder diskontinuierlich eingeleitet werden. Aus dem Fembereichsmischaggregat A wird ständig ein Teilstrom der Pulvermischung in das Nahbereichsmischaggregat B überführt und in das Fembereichsmischaggregat A zu- rückgeführt. Aus dem Fembereichsmischaggregat A wird schließlich die fertige1 schematically shows a long-range mixer A into which the two powders P1 and P2 are introduced continuously or discontinuously. A partial stream of the powder mixture is continuously transferred from the low-range mixing unit A to the short-range mixing unit B and returned to the low-range mixing unit A. The final mixing unit A finally becomes the finished one
Pulvermischung PM kontinuierlich oder diskontinuierlich entnommen. Fig. 2 zeigt eine insbesondere für die kontinuierliche Ausführung des erfindungsgemäßen Verfahrens geeignete prinzipielle Anordnung. Die Pulver Pl und P2 werden in ein erstes Fembereichsmischaggregat, insbesondere beispielsweise ein Drehrohr eingeführt. Sie gelangen aus dem Drehrohr in eine erste Mikrowirbelmühle Bl und werden anschließend in ein zweites Fembereichsmischaggregat A2 überführt. Gegebenenfalls kann eine weitere Nahbereichsvermischung B2 und eine nicht dargestellte Fernbereichsvermischung A3 angeschlossen werden.Powder mixture PM taken continuously or discontinuously. 2 shows a basic arrangement which is particularly suitable for the continuous execution of the method according to the invention. The powders P1 and P2 are introduced into a first mixing area mixing unit, in particular, for example, a rotary tube. They come out of the rotary tube into a first micro vortex mill Bl and are then transferred to a second form mixer A2. If necessary, a further short-range blending B2 and a long-range blending A3, not shown, can be connected.
Fig. 3 zeigt eine Anordnung, die insbesondere für die diskontinuierliche Batch-Ver- mischung geeignet ist. Die Mikrowirbelmühle B als Nahbereichsmischorgan ist innerhalb des Fembereichsmischorgans A angeordnet.FIG. 3 shows an arrangement which is particularly suitable for batch batch mixing. The micro-vortex mill B as a short-range mixing element is arranged within the part-range mixing element A.
Fig. 4 zeigt den Aufbau einer Mikrowirbelmühle 1. Diese besteht aus einem zylindrischen Gehäuse 2, dessen Innenwandung den Stator bildet. Die Innenwand des zylindrischen Gehäuses 2 kann mit abriebfestem Material belegt sein. Innerhalb des zylindrischen Gehäuses 2 ist eine zur Rotation antreibbare Achse vorgesehen, auf der Achse 3 sind eine oder mehrere, insbesondere 2 bis 5, mit der Achse antreibbare Kreisscheiben 4.1, 4.2 und 4.3 vorgesehen, die auf ihrem Umfang je eine Vielzahl von radial und parallel zur Achse 3 angeordnete Mahlplatten 5.1, 5.2 und 5.3 aufweisen. Die Außenkanten der Mahlplatten 5.1, 5.2 und 5.3 bilden gemeinsam mit der Innenwand des zylindrischen Gehäuses 2 den Scherspalt 6 aus. Wird die Mikrowirbelmühle innerhalb eines Fembereichsmischorgans unterhalb des Füllniveaus angeordnet, weist die Mikrowirbelmühle femer vorzugsweise eine konische Abdeckung 7 auf, die mit Öffnungen 8 versehen ist, durch die das rieselfähige Pulver gut in das zylindrische Gehäuse 2 einrieselt. Eine zusätzliche, mit der Achse 3 versehene Kreisscheibe 9 kann als Verteilerplatte vorgesehen sein.Fig. 4 shows the structure of a micro vortex mill 1. This consists of a cylindrical housing 2, the inner wall of which forms the stator. The inner wall of the cylindrical housing 2 can be covered with abrasion-resistant material. An axis drivable for rotation is provided within the cylindrical housing 2, one or more, in particular 2 to 5, circular disks 4.1, 4.2 and 4.3 drivable with the axis are provided on the axis 3, each of which has a plurality of radial and parallel on its circumference have grinding plates 5.1, 5.2 and 5.3 arranged in relation to axis 3. The outer edges of the grinding plates 5.1, 5.2 and 5.3 together with the inner wall of the cylindrical housing 2 form the shear gap 6. If the micro-vortex mill is arranged below the filling level within a mold mixing element, the micro-vortex mill also preferably has a conical cover 7 which is provided with openings 8 through which the free-flowing powder trickles well into the cylindrical housing 2. An additional circular disk 9 provided with the axis 3 can be provided as a distributor plate.
Fig. 5 zeigt eine erfindungsgemäß einsetzbare Vorrichtung, wie sie schematisch in Fig. 3 dargestellt ist. Diese besteht aus einer Mischtrommel 10, die über die Achse 11 zur Rotation mit geringer Rotationsgeschwindigkeit, beispielsweise 1 bis 2 Um- drehungen pro Minute, antreibbar ist. Die Trommel ist durch die nicht mitrotierende Abdeckkappe 12 verschlossen. Innerhalb der Trommel 10 befindet sich die Mikrowirbelmühle 1, wie in Fig. 4 dargestellt. Innerhalb der Trommel 10 können femer Leitbleche 13 angeordnet sein. Das Füllniveau der Trommel 10 ist durch die strichlierte Linie 14 angedeutet. Das erfindungsgemäße Verfahren besteht nun darin, daß die Pulvermischung kontinuierlich durch die Öffnungen 8 in die Mikrowirbelmühle 1 eintritt, wo die Nahbereichsvermischung stattfindet, und durch den unten offenen Zylinder in die Fembereichsvermischung zurückgeführt wird.FIG. 5 shows a device which can be used according to the invention, as is shown schematically in FIG. 3. This consists of a mixing drum 10 which, via the axis 11, rotates at a low rotational speed, for example 1 to 2 revolutions. revolutions per minute, can be driven. The drum is closed by the non-rotating cover cap 12. The micro-vortex mill 1 is located inside the drum 10, as shown in FIG. 4. Baffles 13 can also be arranged within the drum 10. The filling level of the drum 10 is indicated by the dashed line 14. The method according to the invention now consists in that the powder mixture continuously enters the micro-vortex mill 1 through the openings 8, where the short-range mixing takes place, and is returned to the mold area mixing through the cylinder which is open at the bottom.
Fig. 6 zeigt eine erfindungsgemäß einsetzbare Vorrichtung, in der das Mischgut sowohl bei der Nahbereichsvermischung als auch bei der Fembereichsvermischung fluidisiert ist. In dem Behälter 10 befindet sich auf einer antreibbaren Achse 3 ein boden- und wandgängiger Rotor mit 4 Rotorblättem 5a, 5b, 5c und 5d, die zur Behälterwand den Scherspalt 6 bilden. Die Rotorblätter sind um den Winkel α=23° gegen die zur Rotorachse senkrechte Ebene angestellt. Oberhalb des Rotors 5 ist ein gegensinnig angestellter Rotor 20 auf der Achse 3 vorgesehen, dessen Durchmesser etwa dem halben Behälterdurchmesser entspricht.6 shows a device which can be used according to the invention, in which the material to be mixed is fluidized both in the short-range mixing and in the mixing area mixing. In the container 10, on a drivable axis 3, there is a floor and wall-accessible rotor with 4 rotor blades 5a, 5b, 5c and 5d, which form the shear gap 6 with respect to the container wall. The rotor blades are set at an angle α = 23 ° to the plane perpendicular to the rotor axis. Above the rotor 5, an oppositely positioned rotor 20 is provided on the axis 3, the diameter of which corresponds to approximately half the container diameter.
Bei Rotation der Achse 3 in Richtung des Pfeiles 21 wird das Mischgut fluidisiert und zusätzlich zur Rotation um die Achse 3 wie durch Pfeil 22 umgewälzt. Eine Teilmenge des fluidisierten Mischgutes gelangt in den Scherspalt 6, wo die hohe Schergeschwindigkeit des Fluids eine starke Teilchenbeschleunigung bewirken.When the axis 3 rotates in the direction of the arrow 21, the mix is fluidized and, in addition to the rotation about the axis 3, is circulated as indicated by the arrow 22. A partial amount of the fluidized mixed material reaches the shear gap 6, where the high shear rate of the fluid causes a strong acceleration of the particles.
Die Erfindung wird anhand der nachfolgenden Beispiele näher erläutert: Beispiel 1The invention is illustrated by the following examples: example 1
Es werden 13,6 kg eines Kobaltpulvers mit einer mittleren Korngröße von 1,55 μm (FSSS, ASTM B 330) und 122,4 kg eines leicht agglomerisierten Wolframcarbid- pulvers einer mittleren Korngröße von 3 μm (FSSS, ASTM B 330) in ein prinzipiell in Fig. 5 dargestelltes Mischaggregat eingefüllt. Fig. 7 zeigt eine REM-Aufnahme des Wolframcarbindpulvers vor der Vermischung.13.6 kg of a cobalt powder with an average grain size of 1.55 μm (FSSS, ASTM B 330) and 122.4 kg of a slightly agglomerated tungsten carbide powder with an average grain size of 3 μm (FSSS, ASTM B 330) are combined filled in principle in Fig. 5 mixing unit. Fig. 7 shows a SEM picture of the tungsten carbide powder before mixing.
Nach 20, 30 und 40 Minuten Mischzeit werden jeweils Proben der Pulvermischung entnommen. Fig. 8 zeigt eine REM-Aufnahme der nach 40 Minuten Mischzeit erhaltenen Pulvermischung. Der Sauerstoffgehalt vor der Vermischung beträgt 0,068 Gew.-%, nach der Mischung 0,172 Gew.-%.Samples of the powder mixture are taken after 20, 30 and 40 minutes of mixing time. 8 shows an SEM image of the powder mixture obtained after a mixing time of 40 minutes. The oxygen content before mixing is 0.068% by weight, after mixing 0.172% by weight.
Die Proben werden durch Pressen und nachfolgendes Sintern bei 1380°C über 45 Minuten zu Hartmetall-Testkörpern verarbeitet.The samples are processed into hard metal test specimens by pressing and subsequent sintering at 1380 ° C for 45 minutes.
Zum Vergleich wird eine entsprechende Pulvermischung in einer Kugelmühle 20 Stunden mit Hexan gemahlen. Aus der Vergleichs-Pulvermischung wird in gleicher weise ein Hartmetall-Testkörper hergestellt.For comparison, a corresponding powder mixture is ground in a ball mill with hexane for 20 hours. A hard metal test specimen is produced in the same way from the comparison powder mixture.
An den Hartmetall-Tesfkörpern werden die Dichte in g/cm3, die magnetische Koerzitivkraft H^ in kA/m, die magnetische Sättigung in μTm3/kg (jeweils mit Foerster Koerzinat 1.096), die Härte nach Vickers bei 30 kg Last in kg/mm2 sowie die A-Porosität nach ISO 4505 gemessen. Die Ergebnisse sind in Tabelle 1 darge- stellt.The density in g / cm 3 , the magnetic coercive force H ^ in kA / m, the magnetic saturation in μTm 3 / kg (each with Foerster Koerzinat 1.096), the Vickers hardness at 30 kg load in kg are shown on the hard metal test specimens / mm 2 and the A porosity measured according to ISO 4505. The results are shown in Table 1.
Beispiel 2Example 2
11,9 kg eines Kobaltmetallpulvers mit einer mittleren Kömgröße von 1,5 μm und 122,4 kg eines leicht agglomerierten Wolframcarbidpulvers mit einer mittleren11.9 kg of a cobalt metal powder with an average grain size of 1.5 μm and 122.4 kg of a slightly agglomerated tungsten carbide powder with an average
Korngröße von 6 μm (FSSS, ASTM B 330) werden wie in Beispiel 1 vermischt. Der Sauerstoffgehalt vor der Vermischung beträgt 0,058 Gew.-%, nach 40 Minuten Mischzeit 0,109 Gew.-%.Grain size of 6 μm (FSSS, ASTM B 330) are mixed as in Example 1. The Oxygen content before mixing is 0.058% by weight, after 40 minutes of mixing time 0.109% by weight.
Ferner wird eine Vergleichsmischung (Beispiel 2f) in einer Kugelmühle wie in Beispiel 1 hergestellt.A comparison mixture (example 2f) is also produced in a ball mill as in example 1.
Fig. 9 zeigt eine REM-Aufnahme des Ausgangs- Wolframcarbidpulvers. Fig. 10 zeigt die Pulvermischung nach 30 Minuten Mischzeit.9 shows a SEM image of the starting tungsten carbide powder. 10 shows the powder mixture after a mixing time of 30 minutes.
Hartmetallproben werden wie in Beispiel 1 hergestellt. Die erhaltenen Testwerte sind in Tabelle 1 dargestellt.Hard metal samples are produced as in Example 1. The test values obtained are shown in Table 1.
Fig. 11 zeigt die Schliffaufnahme eines Hartmetalls nach Beispiel 2d).11 shows the micrograph of a hard metal according to Example 2d).
Beispiel 3Example 3
13 kg eines Kobaltmetallpulvers mit einer mittleren Korngröße von 1,55 μm, 117 kg eines weniger agglomerierten Wolframcarbidpulvers (Fig. 12) werden wie in Beispiel l- vermischt. Fig. 13 zeigt eine REM-Aufnahme der erhaltenen Pulvermischung. Der Sauerstoffgehalt vor der Vermischung beträgt 0,065 Gew.-%, nach der Vermischung 0,088 Gew.-%.13 kg of a cobalt metal powder with an average grain size of 1.55 μm, 117 kg of a less agglomerated tungsten carbide powder (FIG. 12) are mixed as in Example 1. 13 shows an SEM image of the powder mixture obtained. The oxygen content before mixing is 0.065% by weight, after mixing 0.088% by weight.
Fig. 14 zeigt ein Schliffbild des wie in Beispiel 1 hergestellten Hartmetalls. Die Hartmetall-Testergebnisse sind in Tabelle 1 dargestellt. Tabelle 114 shows a micrograph of the hard metal produced as in Example 1. The carbide test results are shown in Table 1. Table 1
Beispiel 4Example 4
2,6 kg Kobaltmetallpulver 1 μm FSSS nach ASTM B 330, 23,26 kg WC 0,6 μm FSSS (nach ASTM B 330), und 0,143 kg Cr3C2 1,6 μm nach ASTM B 330 sowie 375 g Paraffinwachs mit Schmelzpunkt 54°C werden in einem Mischer (gemäß Fig. 6) bei 1000 U/min. solange gemischt, bis eine Temperatur von 80°C erreicht ist. die so erhaltene Hartmetallmischung wird mit 1 ,5 to/cm2 zu Probekörpern gepreßt. Diese werden in einem Sinter-Ofen zunächst entwachst und dann bei 1380°C für 45 min. bei einem Druck von 25 bar gesintert. Das erhaltene Hartmetal hat eine Dichte von 14,45 g/cm3, eine Koerzitivkraft von 20,7 kA/m, eine magnetische Sättigung von 15.14 μT mVkg, eine Vickershärte von HV = 1603 kg/mm2 und eine Restporosität besser A02 B00 C00. Das Hartmetall weist ein gutes Gefüge und eine gute Binderverteilung auf.2.6 kg cobalt metal powder 1 μm FSSS according to ASTM B 330, 23.26 kg WC 0.6 μm FSSS (according to ASTM B 330), and 0.143 kg Cr 3 C 2 1.6 μm according to ASTM B 330 and 375 g paraffin wax Melting point 54 ° C in a mixer (according to FIG. 6) at 1000 U / min. mixed until a temperature of 80 ° C is reached. the hard metal mixture thus obtained is pressed at 1.5 to / cm 2 to test specimens. These are first waxed in a sintering oven and then at 1380 ° C for 45 min. sintered at a pressure of 25 bar. The hard metal obtained has a density of 14.45 g / cm 3 , a coercive force of 20.7 kA / m, a magnetic saturation of 15.14 μT mVkg, a Vickers hardness of HV = 1603 kg / mm 2 and a residual porosity better A02 B00 C00. The hard metal has a good structure and a good binder distribution.
Beispiel 5Example 5
2,57 kg Kobaltmetallpulver 1 μm FSSS nach ASTM B 330; 26 kg WC 6 μm FSSS nach ASTM B 330 werden wie in Beispiel 4 solange gemischt, bis eine Temperatur von 80°C erreicht war. Die so erhaltene Hartmetallmischung wird mit 1,5 t/cm2 zu Probekörpern gepreßt und anschließend bei 1400°C für 45 min. im Vakuum gesin- tert. Das erhaltene Hartmetall hat eine Dichte von 14,65 g/cm3, eine Koerzitivkraft von 5,5 kA/m, eine magnetische Sättigung von 17,1 1 μT Vkg, eine Vickershärte von HV30 = 1181 kg/mm3 und eine Restporosität von A00 B00 C00. Das Hartmetall weist ein gutes Gefüge und eine gute Binderverteilung auf. 2.57 kg cobalt metal powder 1 μm FSSS according to ASTM B 330; 26 kg of WC 6 μm FSSS according to ASTM B 330 are mixed as in Example 4 until a temperature of 80 ° C. has been reached. The hard metal mixture thus obtained is pressed at 1.5 t / cm 2 to test specimens and then at 1400 ° C for 45 min. sintered in a vacuum. The hard metal obtained has a density of 14.65 g / cm 3 , a coercive force of 5.5 kA / m, a magnetic saturation of 17.1 1 μT Vkg, a Vickers hardness of HV 30 = 1181 kg / mm 3 and a residual porosity from A00 B00 C00. The hard metal has a good structure and a good binder distribution.

Claims

Patentansprüche claims
1. Verfahren zur Herstellung einer homogenen Mischung eines aus Hartstoff- und Bindermetallpulvern bestehenden Mischgutes ohne Einsatz von Mahl- körpern und flüssigen Mahlhilfsmitteln und Suspendiermedien, dadurch gekennzeichnet, daß das Mischgut im Nahbereich unter Erzeugung hoher scherender Aufprallgeschwindigkeit der Pulverteilchen und im Fembereich durch Umwälzung des Mischgutes vermischt werden.1. A process for the production of a homogeneous mixture of a mixture of hard material and binder metal powders without the use of grinding media and liquid grinding aids and suspending media, characterized in that the mixture in the near area with high shear impact velocity of the powder particles and in the mold area by circulation of the mixture be mixed.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, daß das Mischgut in der2. The method according to claim 1, characterized in that the mixture in the
Nahbereichsvermischung fluidisiert ist und die hohe Aufprallgeschwindigkeit durch Verwirbelung des Fluids erzeugt wird.Short-range mixing is fluidized and the high impact speed is generated by swirling the fluid.
3. Verfahren nach Anspmch 1 oder 2, dadurch gekennzeichnet, daß die Nahbe- reichsvermischung in einem mit Rotor- und Statorelementen ausgerüsteten3. The method according to Anspmch 1 or 2, characterized in that the near-area mixing in one equipped with rotor and stator elements
Behälter mit Scherspalt zwischen den Elementen durchgeführt wird.Container with a shear gap between the elements is carried out.
4. Verfahren nach Anspmch 3, dadurch gekennzeichnet, daß der Scherspalt eine lichte Weite aufweist, die mindestens dem 50-fachen mittleren Durchmesser der Teilchensorte mit dem größeren mittleren Durchmesser entspricht.4. The method according to Anspmch 3, characterized in that the shear gap has a clear width which corresponds to at least 50 times the average diameter of the particle type with the larger average diameter.
5. Verfahren nach Ansprach 3 oder 4, dadurch gekennzeichnet, daß das Verhältnis aus Relativgeschwindigkeit von Rotor und Stator zu Scherspaltweite mindestens 800/s beträgt.5. The method according spoke 3 or 4, characterized in that the ratio of the relative speed of the rotor and stator to the shear gap width is at least 800 / s.
6. Verfahren nach einem der Ansprüche 3 bis 5, dadurch gekennzeichnet, daß der Rotor eine Umfangsgeschwindigkeit von 12 bis 20 m/s aufweist.6. The method according to any one of claims 3 to 5, characterized in that the rotor has a peripheral speed of 12 to 20 m / s.
7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß die Fembereichsvermischung in einem gerührten Behälter mit langsam drehenden Rührelementen erfolgt. 7. The method according to any one of claims 1 to 6, characterized in that the mixing area mixing takes place in a stirred container with slowly rotating stirring elements.
8. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Mischgut sowohl in der Nahbereichs- als auch in der Fembereichsvermischung fluidisiert ist.8. The method according to any one of claims 1 to 5, characterized in that the material to be mixed is fluidized both in the short-range and in the mixing area mixing.
9. Verfahren nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß die Gesamtmischzeit weniger als 1 h dauert.9. The method according to any one of claims 1 to 8, characterized in that the total mixing time lasts less than 1 h.
10. Verfahren nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, daß das Mischgut zusätzlich Preßhilfsmittel enthält.10. The method according to any one of claims 1 to 9, characterized in that the mixture additionally contains pressing aids.
11. Verfahren nach einem der Ansprüche 1 bis 10, dadurch gekennzeichnet, dass die Pulvermischung granuliert wird.11. The method according to any one of claims 1 to 10, characterized in that the powder mixture is granulated.
12. Hartmetallmischung hergestellt nach einem der Ansprüche 1 bis 11.12. Carbide mixture produced according to one of claims 1 to 11.
13. Gesinterter Hartmetallformkörper hergestellt aus einer Hartmetallmischung nach Anspruch 12. 13. Sintered hard metal molded body made of a hard metal mixture according to claim 12.
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