EP0956173B1 - Metal powder granulates, method for their production and use of the same - Google Patents

Abstract

PCT No. PCT/EP96/04983 Sec. 371 Date May 27, 1998 Sec. 102(e) Date May 27, 1998 PCT Filed Nov. 14, 1996 PCT Pub. No. WO97/19777 PCT Pub. Date Jun. 5, 1997The invention concerns metal powder granulates comprising one or a plurality of the metals Co, Cu, Ni, W and Mo. The invention further concerns a method for the production of these granulates and the use thereof. The production method is characterized in that a metal compound comprising one or a plurality of the groups comprising oxides, hydroxides, carbonates, hydrogenocarbonates, oxalates, acetates, formiates with binder and optionally in addition between 40 and 80% solvent, relative to the solids content, is granulated as the starting component, and the granulates are thermally reduced in a hydrogen-containing gaseous atmosphere to form the metal powder granulates, the binder and the solvent, if used, being removed completely.

Description

The present invention relates to metal powder granules composed of one or more the metals Co, Cu, Ni, W and Mo, a process for its production as well as its use.

Granules of the metals Co, Cu, Ni, W and Mo have a variety of uses as sintered materials. For example, copper metal granules suitable for making copper sliding contacts for motors, tungsten granules find possible uses for the production of W / Cu drinking contacts, Ni and Mo granules can be used for corresponding semi-finished product applications. Cobalt metal powder granules are used as binder components in Composite sintered bodies e.g. Hard metals and diamond tools.

DE-A 43 43 594 discloses that free-flowing metal powder granules by atomizing and sieving suitable grain areas can. However, these granules are for the manufacture of diamond tools not suitable.

EP-A-399 375 describes the production of a free-flowing tungsten carbide-cobalt metal powder granulate. The fine components are the starting components Powder agglomerated together with a binder and a solvent. In a further process step, the binder is then removed thermally and the agglomerate, in order to obtain the desired flowability, at 2500 ° C. in Aftertreated plasma. Fine cobalt metal powders can be made using this process but do not granulate, because at temperatures above the melting point processing problems similar to those of processing atomized powders occur.

DE-A 44 31 723 shows that pastes are obtained from oxide compounds when water-dilutable, non-ionic rheological additives be added. These additives can be removed thermally and on in this way solid layers can be produced on substrates. This method aims however that the substrates with fine-particle, completely agglomerate-free Particles are coated.

EP-A 0 659 508 describes the production of metal powder granules general formula RFeB or RCo, where R is for rare earth metals or compounds, B stands for boron and Fe for iron. After that, first an alloy of the components and these by grinding to the desired fineness brought. Then binders and solvents are added and the Slurry dried in a spray dryer. Disadvantage of this method - especially for the production of diamond tools - is that initially the Metals are alloyed and by melting fine cobalt metal powder their characteristic properties, as described in DE-A 43 43 594, lose. It is therefore the most suitable for the production of cobalt metal powder granules State of the art, e.g. from the brochures on the granulating machine G 10 from Dr. Fritsch KG, Fellbach in Germany, or the solid processor of PK-Niro in Soeborg / Denmark shows the fine cobalt metal powder to mix with binders and organic solvents and in to produce suitable granulating devices suitable granules. The solvents are carefully removed by evaporation after granulation, but the binders remain in the granules and influence the properties strong.

The granules obtained in this way have a rounded grain shape. The surface is relatively dense with no large pores or gas outlet openings. The bulk density determined according to ASTM B 329 is relatively high at 2.0-2.4 g / cm ³ (Table 2). 1 shows the scanning electronic (SEM) image of a commercially available granulate from Eurotungstene, Grenoble France, in FIG. 2 that of a commercially available granulate from Hoboken Overpelt, Belgium. The rounded grain shape and the high bulk densities lead to the desired, improved flow properties of the cobalt, but in practice they pose considerable processing problems.

For example, relatively high press forces have to be applied during cold pressing in order to obtain green compacts with sufficient strength and edge stability. This is due to the fact that with a spherical or rounded particle shape the formation of positive locking, which is important for the strength of the green compacts Connections, i.e. to put it simply, the hooking of the individual particles is difficult. At the same time, a tight closed Structure an increase in deformation resistance. Both factors lead to the increase in the necessary pressing forces during cold pressing. This can be done in the In practice, however, there is increasing wear on the cold dies, i.e. a lesser Durability of the cold press molds result, which in turn leads to increased production costs leads.

The compression behavior can be described quantitatively by measuring the compression factor F _comp . The following applies to F _comp : F comp = (ρ p - ρ O ) / ρ p with (ρ ₀ ), the bulk density in g / cm ^{3 of} the cobalt metal powder granulate in the original state and (ρ _p ) the density in g / cm ³ after pressing.

The most serious disadvantage, however, is that the Binder used granules remain in the granules (see Table 1).

In the following, binder is understood to mean a film-forming substance which, if appropriate, is dissolved in a solvent and is added to the starting components in a suitable granulation process in such a way that the powder surface is wetted, or if appropriate after removal of the solvent, by forming a surface film on the primary grains these are held together. This produces granules of sufficient mechanical strength. As an alternative, substances can also be used as binders, which ensure the mechanical strength of the granulate particles through capillary forces. Typical levels of carbon from the binder in commercial cobalt metal powder granules EUROTUNGSTENE Grenoble / France HOBOKEN Overpelt / Belgium HOBOKEN Overpelt / Belgium product Co ultrafine granulated Co extrafine soft granules Co extrafine hard granules Carbon content 1.5% 0.98% 0.96%

Are these cobalt metal powder granules, for example with the Most commonly used hot press technology manufactured, so must to the organic To remove the binder completely, the heating-up time can be extended. This can be a Reduce production by up to 25%. However, the heating times not prolonged, carbon nests are observed in the hot-pressed segments through cracking processes of the binders. This often leads to one significant deterioration in tool quality.

Another disadvantage is the use of organic solvents, which after the granulation are carefully removed by evaporation. First of all, that is Removal of the solvents by the thermal treatment is expensive. In addition the use of organic solvents has significant disadvantages with regard to environmental compatibility, plant safety and the energy balance. The Working with organic solvents often requires considerable equipment Expenditure on suction and disposal facilities, as well as on filters to prevent the emission of organic solvents during granulation. On another disadvantage is that the systems must be explosion-proof, which in turn increases investment costs.

The disadvantages when working with organic solvents can theoretically can be avoided by dissolving the binder in water. The In this case, however, fine cobalt metal powders are partially oxidized and thereby unusable.

It is an object of this invention to provide a metal powder granulate make, which does not have the disadvantages of the powder described.

It has been possible to provide a binder-free metal powder granulate which consists of one or more of the metals Co, Cu, Ni, W and Mo, with a maximum of 10% by weight <50 μm according to ASTM B214 and the total carbon content less than 0. 1 wt .-%, particularly preferably less than 400 ppm. This binder-free metal powder granulate is the subject of this invention. Furthermore, the surface and grain shape of the product according to the invention has been significantly optimized. 3 shows the SEM image of the metal powder granules according to the invention using the example of a cobalt metal powder granules according to the invention. It has a cracked, jagged structure that facilitates the formation of positive connections. Furthermore, it can be seen from the SEM picture that the granulate according to the invention is very porous. This significantly reduces the resistance to deformation during cold pressing. The porous structure is reflected in the bulk weight. The cobalt metal powder granulate preferably has a low bulk density between 0.5 to 1.5 g / cm ³ , determined according to ASTM B 329. In a particularly preferred embodiment, it has a compression _factor F _comp of at least 60% and at most 80%. This high compression factor leads to excellent compressibility. For example, cold pressed sintered bodies can be produced at a pressure of 667 kg / cm ² , which have excellent mechanical edge stability.

Table 2 below shows the bulk density of the product according to the invention in its original state (ρ ₀ ), the density after pressing (ρ _p ) and the compression _factor F _comp in comparison to commercially available granules. Typical bulk density in original condition (ρ ₀ ), after pressing with 667 kg / cm ² (ρ _p ) and the compression factor of the cobalt metal powder granulate according to the invention in comparison to commercially available products Manufacturer HCST Goslar / Germany EUROTUNGSTENE Grenoble / France HOBOKEN Overpelt / Belgium HOBOKEN Overpelt / Belgium product cobalt metal powder granules according to the invention Cobalt metal powder granulate ultrafine Cobalt metal powder granules extrafein soft granulated Cobalt metal powder granules extrafine hard granulated Bulk density (ρ ₀ ) (g / cm ³ ) 1.03 2.13 2.4 2.4 Compression density (ρ _p ) (g / cm ³ ) 3.45 4.31 4.69 4.79 Compression _factor F _comp (%) 70.1 50.6 48.8 49.8 Assessment of the molded body stable, without edge break reduced edge stability significantly reduced edge stability low edge stability

The green compacts were produced in a uniaxial, hydraulic press with a load of 2.5 t and a square ram area of 2.25 cm ² and a weight of 6 g

This invention further relates to a method for producing the metal powder granules according to the invention. It is a process for the production of binder-free metal powder granules from one or several of the metals Co, Cu, Ni, W and Mo, being the starting component a metal compound from one or more of the groups of metal oxides, hydroxides, carbonates, bicarbonates, oxalates, acetates and formates with Binder and optionally additionally with 40% - 80% solvent is granulated to the solids content and the granules thermally by addition in a hydrogen-containing gas atmosphere to the metal powder granules is reduced, the binder and optionally the solvent is removed without residue. Will one or more of the metal compounds mentioned no oxidation occurs during the granulation process the fine cobalt metal powder when working in aqueous solutions. The method according to the invention thus opens up a possibility of solvents to use, which consist of organic compounds and / or water can, being particularly preferred, but not limited to, water as Solvent is used. The added binders are either without solvent or dissolved in the solvent or suspended or used emulsified. The binders and solvents can be inorganic or be organic compounds consisting of one or more of the elements carbon, Hydrogen, oxygen, nitrogen and sulfur built up and free of Halogens and, with the exception of traces that are unavoidable due to manufacture, free of metals are.

The selected binders and solvents can also be added Temperatures of less than 650 ° C are removed thermally without residue. As a binder one or more of the following compounds are particularly suitable: Paraffin oils, paraffin waxes, polyvinyl acetates, polyvinyl alcohols, polyacrylamides, Methyl cellulose, glycerin, polyetylene glycols, linseed oils, polyvinyl pyridine.

The use of polyvinyl alcohol as a binder is particularly preferred and water as a solvent. The granulation of the starting component is achieved according to the invention in that the granulations as plates, build-up, Spray dryer, fluidized bed, press granulation or granulation in high speed Mixers is carried out.

The method according to the invention is particularly preferably carried out continuously or discontinuously in a ring mixer granulator.

These granules are particularly preferably subsequently in a hydrogen containing gas atmosphere at temperatures from 400 ° C to 1100 ° C, especially from 400 - 650 ° C, reduced to metal powder granules. Here it can Binder and, if necessary, the solvent are removed without residue. Another embodiment variant of the method according to the invention consists in that the granulate after the granulation step first at temperatures of 50 ° C is dried to 400 ° C and then at temperatures from 400 ° C to 1100 ° C in a hydrogen-containing gas atmosphere to the metal powder granulate is reduced.

The metal powder granules according to the invention are ideal for Manufacture of sintered and composite sintered bodies. Subject of this invention is thus also the use of the metal powder granules according to the invention as Binder component in sintered bodies or composite sintered bodies made of hard powder and / or diamond powder and binders.

In the following the invention will be explained by way of example without any Restriction can be seen.

Example 1:

In an intensive mixer RV 02 from Eirich, 5 kg of cobalt oxide with 25 % By weight of a 10% aqueous methyl cellulose solution and 8 minutes granulated at 1500 rpm. The resulting granulate was under at 600 ° C. Reduced hydrogen. After sieving over 1 mm, a Cobalt metal powder granules with the values listed in Table 3.

Example 2:

100 kg of cobalt oxide with 70% by weight of a 3% polyvinyl alcohol solution mixed. The rod-shaped formed Exdrudate was turned directly into cobalt metal powder granules in a rotary tube at 700 ° C implemented and then sieved over 1 mm. It came into being Cobalt metal powder granules with the values listed in Table 3.

Example 3:

In a 5-1 laboratory mixer from Lödige, 2 kg of cobalt carbonate with 70 % of a 1% aqueous polyethylene glycol mixture granulated at 160 rpm. The starting product granulate was at 600 ° C in a push-through furnace Reduced hydrogen. A cobalt metal powder granulate with the in Table 3 values.

Example 4:

60 kg were placed in an RMG 10 ring mixer granulator from Ruberg Cobalt oxide with 54 wt .-% of a 10% polyvinyl alcohol solution at maximum Number of revolutions of the granulator and the granulate formed in the process 550 ° C in a quiescent bed under hydrogen to cobalt metal powder granules reduced. After sieving, a cobalt metal powder granulate was formed with the values listed in Table 3.

The compression factor F _comp was determined with the aid of a uniaxial, hydraulic press with a load of 2.5 t with a press ram area of 2.25 m ² and a weight of 6 g. Properties of the granules containing cobalt described in the examples example Total carbon content (ppm) Bulk density (g / cm3) Sieve analysis according to ASTM B 214 (%) + 1000 µm - 1000 µm + 50 µm - 50 µm 1 200 1.4 3.4 90.5 6.1 2 360 1.2 6.9 91.0 2.1 3rd 310 0.8 4.5 89.9 5.6 4th 80 1.0 0.2 96.1 3.7

Claims (13)

1. Granulated metal powder consisting of one or more of the metals Co, Cu, Ni, W and Mo, characterised in that it contains at maximum 10 wt.% of the fraction -50 µm in accordance with ASTM B 214 and the total carbon content is less than 0.1 wt.%.
2. Granulated metal powder according to claim 1, characterised in that the total carbon content is particularly preferably less than 400 ppm.
3. Granulated metal powder according to either of claims 1 or 2, characterised in that the granules have a porous, cracked, fissured structure.
4. Granulated cobalt metal powder according to one or more of claims 1 to 3, characterised in that it has a bulk density in accordance with ASTM B 329 within the range of 0.5 to 1.5 g/cm³, particularly preferably 1.0 to 1.2 g/cm³.
5. Granulated cobalt metal powder according to one or more of claims 1 to 4, characterised in that it has a compression factor F_comp of at least 60% and at maximum 80%.
6. Process for producing granulated metal powder according to one or more of claims 1 to 5, characterised in that, as parent component, a metal compound from among the oxides, hydroxides, carbonates, hydrogen carbonates, oxalates, acetates, formates, with binder and optionally in addition with 40% to 80% solvent, based on the solids content, is granulated and the granular material is reduced to the granulated metal powder thermally in a hydrogen-containing gaseous atmosphere, the binder and optionally the solvent being removed without leaving any residue.
7. Process according to claim 6, characterised in that organic or inorganic compounds which are synthesised from one or more of the elements carbon, hydrogen, oxygen, nitrogen and sulfur and are free from halogens and metals are used as binder and optionally solvent.
8. Process according to one or both of claims 6 and 7, characterised in that the binders and optionally solvent can be removed thermally at temperatures of less than 650°C without leaving any residue.
9. Process according to one of claims 6 to 8, characterised in that the granulation is carried out in the form of pelletising granulation, spray-drying granulation, fluid-bed granulation, disk granulation, pressure granulation or granulation in high-speed mixers.
10. Process according to claim 9, characterised in that the granulation in high-speed mixers is carried out in the form of a ring-mixed granulation.
11. Process according to one or more of claims 6 to 10, characterised in that the granules are reduced to the granulated metal powder in a hydrogen-containing gaseous atmosphere at temperatures of 400°C to 1100°C, particularly preferably of 400°C to 650°C.
12. Process according to one or more of claims 6 to 11, characterised in that the granular material is first dried thermally at temperatures of 50°C to 400°C and the granular material is then reduced to the granulated metal powder in a hydrogen-containing gaseous atmosphere at temperatures of 400°C to 1100°C.
13. Use of the granulated metal powders according to one or more of claims 1 to 5 as binder components in sintered compacts or in laminated sintered compacts produced from powdered hard material and/or from diamond powder and binders.

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