EP1900422A1 - Dispersing machine and its use in manufacturing powder mixtures - Google Patents

Abstract

The dispersing machine for the production and homogenization of tungsten carbide- or cermet powder mixture, comprises rotor- and stator elements, which are formed such that a gap volume is present between them in operating position. A shear force is bringable in the gap volume through relative contrary movement of the rotor- and stator mantle surfaces. The rotor (12) and stator (14) consist of a sintered tungsten carbide. The tungsten carbide parts of the machine are formed from separated manufactured support and present in a tungsten carbide-steel-bonding material. The dispersing machine for the production and homogenization of tungsten carbide- or cermet powder mixture, comprises rotor- and stator elements, which are formed such that a gap volume is present between them in operating position. A shear force is bringable in the gap volume through relative contrary movement of the rotor- and stator mantle surfaces. The rotor (12) and stator (14) consist of a sintered tungsten carbide. The tungsten carbide parts of the machine are formed from separated manufactured support and present in a tungsten carbide-steel-bonding material. The machine part surfaces are powder-coated with tungsten carbide. The mantle surfaces pointing to an operating volume (16) of rotor and/or stator are provided with grooves or channels. A rotor head (12A) provided with a suspension-guiding surface structuring or guidance mechanism is detachably fastened outside of the operating volume to the rotor. The operating volume in suspension flow direction is formed between the rotor and the stator and narrows itself in constant monotonously manner. The smallest distance between the rotor and the stator at the operating volume is 0.1 mm. A conical annular gap is formed as gap volume between the rotor and the stator. The height or length of the operating volume in the direction of flow, is 1-3 times equal to the smallest diameter of the rotor. The length-diameter-ratio is >= 3 than the quotient from effective rotor length and smallest effective rotor diameter. A return line from the discharge is present to the inlet of the rotor-stator-unit or into a preliminarily container for the recirculation of the homogenized suspension. An agitator for slurring of suspensions is present in the preliminarily container.

Description

The invention relates to a dispersing machine and its use for the production of powder suspensions, in particular metallic powder suspensions, especially suspensions of hard metal powder mixtures or cermet mixtures. The dispersing machine works with dispersing liquid (also referred to as milling liquid) into which the feed powder materials are dispersed. In subsequent process steps, the liquid can be removed in a known manner, so that finally a homogeneous powder mixture is obtained.

In particular, the invention relates to rotor and stator components in rotor-stator grinding units for use in the production of homogeneous suspensions of metallic powder components and liquid grinding aids, as required for example in the powder metallurgy as a process step.

Powder metallurgy involves producing metallic powders and making parts from these powders by molding and sintering. For a number of materials, this process has become firmly established for the production of metallic components and fittings. The advantages of this technique are found when the components are made of expensive materials or refractory metals or alloys. In a special way, the powder metallurgical production is required when melt metallurgical processes are not successful, such. B. in the hard metals and cermet alloys.

To prepare the powder mixtures, the powdery starting materials are homogenized in grinding and homogenizing using liquid grinding aids, further processed in drying and granulation to free-flowing powders, formed by pressing and cutting process to geometric bodies and sintered after reaching the highest possible final contour and thus in Consolidated their properties.

Suitable grinding aids are water, low-boiling hydrocarbons (ethanol, acetone, heptane) u. a. The selection depends on the drying process and the pressing aids used.

Of particular importance in the production process of hard metals is the homogenization of the powdered feedstocks, because only when the hard material particles are sufficiently and uniformly surrounded by the binder metal phase and wetted by this, the cohesion in the structure and the purposive property of the cemented carbide can be achieved.

As a prerequisite for a good wettability is achieved in the homogenization achieved reiblegierte and cold-welded compound of Co-shares on the surfaces of the WC crystallites. It is the result of high energy input during milling and its implementation in work to overcome adhesion and binding forces. Today, attritors are widely used for this process step, which have proved to be much more effective in comparison with ball and vibratory mills.
In all of these grinding units, the operating principle is the same in that a relative movement of the freely movable grinding body is superimposed on a movement of the material to be ground. In this case, the material to be ground also gets between the grinding media, whereby it is exposed to a high pressure at the same time, as a result of which its comminution takes place. As a further result of the movement of grinding media and millbase, the powders are homogeneously distributed. In order to achieve reproducible results, a long grinding time is essential.

Depending on the grain size of the feedstock, the duration of the grinding treatment is designed; Fine powders must be ground for a long and coarse shorter. In addition, however, dependencies of the grinding time or intensity of the grinding process and of the Mahlkörperform also apply. Comparable are the meal intensities of 1 hour in the attritor with about 4 hours in the vibrating mill and about 12 hours in the ball mill with the same grinding media considered. According to Schedler, "Carbide for the practitioner"; VDI-Verlag 1988, the grinding intensity also increases with the size of the aggregate, so that in general a shorter grinding time is required.

On the other hand, the grinding and homogenization process (fragmentation of the powder agglomerates) is all the more intense when small volume media is used (many media contact points); Large-volume grinding media are used for gentle mixture production (fewer media contact points).
The homogeneity of a mixture, a compact and the sintered molding also has an effect on subsequent process steps and on the properties. Homogeneous bodies disappear uniformly without warping and the strength properties are not subject to fluctuations.

However, efforts have repeatedly been made to realize a comminution and homogenization of the hard metal components by combining the mechanisms impact, impact, pressure and shear or dominance of individual ones. The main driving force of such proposals were primarily the high energy consumption and the long grinding time, which are required in the Mahlkörper-Mahleinrichtungen, and the high investment costs and usually led to a larger Mahlraumvolumen.

Furthermore, rotor-stator grinding units are known, inter alia under the name corundum mills, colloid mills or cone mills. The grinding tools consist of corundum, steel materials or by means of thermal spraying armored steel.

For hard metal-containing metallic powders, as they are also hard metal and cermet powder mixtures, such grinding elements are generally unsuitable. The cause is the inevitable wear on the grinding elements during the dicing process; the hard powder mixtures are highly abrasive. Of even greater disadvantage, however, is the oxidic character of the corundum tools, which is harmful to quality, especially in hard metal mixtures.
An embodiment of the grinding elements in steel or stainless steel leads only to the extent that the contaminated, resulting from the component wear material has metallic character. However, since the hard material particles to be processed in the hard metal and cermet powder mixtures have a significantly higher hardness (> 1800 HV) and wear resistance compared to steel components (approximately 350 HV), the grinding elements have only short service lives.

There are also known by thermal or high-speed sprayed carbide coatings of the components known. These can reduce wear until they are worn out. Thereafter, the problems presented to the steel material occur again.

These grinding tools are equipped with a relatively small shear surface. As a result, a large number of material passages by pumping the suspension is required. In the case of highly abrasive materials, frequent replacement of the geometrically complicated components is required.

The object of the invention is to design a dispersing machine so that the indicated, existing in the prior art disadvantages are avoided and the mill can be used for the production of hard material-containing metallic homogeneous powder mixtures.

The object is solved with the features of claim 1 and the use according to claim 12, wherein advantageous embodiments and further developments of the invention are mentioned in the dependent claims.

In rotor-stator grinding units conditions have been found which meet the requirements for fragmentation and homogenization to a high degree. These grinding units work without freely moving grinding media. A trained as a rotationally symmetric conical body high-speed rotor rotates with very narrow gap in a correspondingly larger angle, for example, conical trained stator, so that a large amount of shear work is done between the two components of the grinding tool. In addition, sudden changes of pressure and relaxation, negative pressure, friction, forced operation, impact and impact are also effective. The size of the work done depends on the speed of the rotor or its peripheral speed. Furthermore, the shear gap also influences the work performance. By suitable, diverse surface designs of the opposite, the shear gap forming lateral surfaces of the rotor and stator, the shear force can be varied in addition within wide limits.

The grinding gap itself is preferably conical, so that its width can be adjusted continuously by moving the rotor plane. In this way succeeds an excellent adaptation to the requirements of the ground material, which are predetermined primarily by powder grain size and composition. These measures realize individually or together more gentle or aggressive zerteilungen.

By using grinding fluid and the addition of plasticizers, a sprayable, press-aid-containing suspension is produced in one process step.

In general, the dispersing machine according to the invention for the production and homogenization of powder suspensions has rotor and stator elements which form grinding tools with a gap between them in the working position. The gap volume between rotor and stator represents a working volume, in which by relatively opposite movement of the opposing rotor and stator lateral surfaces or tool part surfaces shear forces can be introduced, which act directly on the powder agglomerates and particles and these in the dispersing or Dispersing grinding liquid to homogeneous suspensions. In this case, both rotor and stator or parts of the rotor and stator, which comprise the lateral surfaces of these machine parts, consist of a shaped, sintered hard metal.

In the prior art, it is already common to coat tool parts for wear inhibition with hard metals. For this purpose, powder coating techniques are used which provide a hard metal overlay of a non-optimally dense hard metal. For the intended application of the preparation and homogenization of powder suspensions, wherein Hartmetallpulversuspensionen are included, such coatings are not abrasion resistant enough. However, the problem can be solved by either the entire tool part - here rotor and stator in total - or a support or a near-surface part of the tool part (for example, a conical sleeve as a support for a conical, ie frusto-conical rotor or a hollow truncated cone shaped stator) separately formed sintered solid carbide full member and connected to a substrate to the tool part.

Preferably, the cemented carbide parts of the dispersing machine are made in a composite with steel, e.g. Shrunk or sintered.

The thickness of a separately prepared, sintered, shrunk or otherwise bonded overlay should be at least 3 mm, preferably at least 10 mm, and thus many times thicker than a conventional powder coating. In this way, the tool parts can be reground several times.

The advantages of this design consist in the significantly lower wear than in corundum or steel materials, so that significantly longer service life can be achieved. Contamination of harmful oxidic or foreign metallic materials does not occur.

Furthermore, all components of the dispersing machine, through which the suspension flows, may be internally provided with a cemented carbide coating. The advantages of this design are the significantly lower wear, so that considerably longer service life can be achieved.

In a further possible embodiment of the invention, the lateral surfaces of the rotor and / or stator facing the working volume may be at least partially surface-structured and preferably provided with grooves or channels for this purpose. In this way, inlet contours or structures for feeding the ground material into the annular gap can be realized. The structuring can be placed as module components on the rotor inlet side and connected to the drive shaft.

Particularly advantageously, a rotor head provided with a suspension-conducting surface structuring or with guide devices can be detachably fastened to the rotor outside the working volume. In this way, the rotor itself is better represented as a geometrically simple body, while manufacturing technically more complicated guide devices are located on the rotor head. This facilitates the flexibility and handling of the dispersing machine (it can be used for various processing tasks different suspension-conducting heads are provided) and the regrinding of the rotor component.

Preferably, the working volume formed between the rotor and stator narrows steadily monotonically in the direction of suspension flow. For example, in a double-cone design, this can be achieved by slightly varying the cone pitches of the rotor and stator. The smallest distance between rotor and stator is located at the working space end and should be less than 3 mm, preferably less than 0.1 mm.

In a preferred embodiment, a cylindrical or preferably conical annular gap is formed between the rotor and the stator as the gap volume. The conical annular gap is designed in a particularly preferred embodiment so that a Statorhohltgelstumpf and a truncated cone face with different inclinations of the lateral surface. The gap becomes narrower in the flow direction of the suspension. It is particularly advantageous that adjust the gap width by moving the rotor in the longitudinal direction and can be adapted to the processing task.

The height or length of the working volume through which the suspension flows is preferably about 1 to 6 times, more preferably 1 to 3 times the smallest diameter of the rotor.
In particular, the length-diameter ratio as the quotient of the effective rotor length and the smallest effective rotor diameter is preferably equal to 1, more preferably equal to 3.

The elongated design of the refining elements in the rotor-stator unit enables a particularly effective deagglomeration of the powder suspensions by the significant increase in the effective shear surface and thus at the same time the drastic increase in the residence time of the powder agglomerates in the shear area. This improves the homogeneity and distribution per run, so that the required suspension quality is achieved with lower durc hgangszahlen and thus in less time. Responsible for this is the effective grinding and homogenization, in which the grinding elements are directly opposite and form the shear area. This range is determined by the ratio of the length of the shear area to the rotor run-out diameter. This ratio should be greater than or equal to 1, preferably greater than or equal to 3. The inlet diameter of the rotor is the rotor thickness directly at the transition of the Zuführungsleitflächen to the compact rotor. Simultaneously with the metallic components, it is preferable to add pressing aids and optionally wetting agents. At the relatively low temperatures, the pressing aid is applied mechanically to the cemented carbide or cermet powders; by the wetting agent too fast separation of the suspension components is prevented.

In a further development of the invention, the mill unit on the inlet side has a supply container for the supply of the components to be homogenized, preferably already in the form of a suspension. In addition, means for slurrying the suspension may be present in the feed tank, for example at least one agitator or other mixing device.
For the recirculation of the homogenized suspension may advantageously be present at least one return line from the outlet to the inlet of the rotor-stator unit or in the supply tank.

Working volumes in the sizes of 1 to 12 cm ^{3 are} realized in this dispersing machine. At rated outputs of 1.8 to approx. 10 kW, this results in power densities of approx. 800 kW / dm ³ . This value is still better than the agitator ball mill by a factor of about 8000. The power density is defined here as the quotient of nominal power and working volume in kW / dm ³ . In comparison, the power densities of ball mills are approx. 0.03 kW / dm ³ , of vibrating mills approx. 0.06 kW / dm ³ and of Attritor approx. 0.1 kW / dm ³ .

The special novel properties of the mill enable its use for the production of metallic powder mixtures, even those which cause high wear and / or are highly agglomerated. The dispersing machine for hard metal powder mixtures or cermet powder mixtures is particularly suitable.

Fig. 1:

Schnittansicht einer konischen Rotor-Stator-Einheit;

Fig. 2:

Explosionsansicht des Beispiels aus Figur 1;

Fig. 3:

Schnittansicht des Einlaufmodulbauteils für den Rotorkopf;

Fig. 4:

perspektivische Ansicht des Rotorkopfs aus Fig. 3;

In the following the invention will be explained in more detail with reference to figures and illustrated by way of example. Show it:

Fig. 1:

Section view of a conical rotor-stator unit;

Fig. 2:

Exploded view of the example of Figure 1;

3:

Section view of the inlet module component for the rotor head;

4:

perspective view of the rotor head of Fig. 3;

Figure 1 shows a sectional view of a generally designated 10 conical rotor-stator unit, the core portion of a cone mill. In this conical embodiment, the rotor 12 is designed as a truncated cone, the stator 14 is formed like a hollow cone and the Zuführungsleitflächen 20 for the initiation of the suspension are part of a formed as a modular component rotor head 12A. The rotor head 12A is placed on the rotor inlet side and connected to the drive shaft together with the rotor. The working volume 16, which was also referred to above as the gap volume, shear gap, annular gap, rotational volume or cone gap volume, is formed in a cuff-shaped manner between the rotor and the stator. Rotor and module component are fastened by means of the bore 18 on the drive shaft (not shown). The stator 14 is provided with a flange, other installation options in the mill housing, not shown here, are of course possible and familiar to the expert. The flow direction goes from the Zuführungsleitflächen 20 for thickening of the rotor. The effective shear range extends from the beginning of rotor A to the last common point of contact between rotor and stator B. At B, the grinding gap is decisive. It should be <3 mm, preferably <0.1 mm. The working volume is traversed by the powder suspension to be treated and homogenized in the longitudinal direction, ie in the direction of the drive shaft 18. The size of the gap volume can be adjustable at the mill, which is particularly advantageous in particular in the conical design of the rotor when the gap width is adjusted by the rotor is inserted to different degrees in the stator. Depending on the insertion depth so remains a narrower or a wider gap between the surfaces.

Figure 2 shows the same embodiment in exploded view. Identical parts are marked with the same reference numbers.

FIG. 3 shows the modular component which forms the rotor head in a sectional view. In principle, it consists of a circular plate in the diameter of the rotor head. On two sides of the circumference are projecting surfaces, the Zuführungsleitflächen attached. In the center of the plate is the hole for receiving on the drive shaft.

In Fig. 4 is a slightly perspective view of the rotor head, which is shown in Figure 3 in plan view, the task of the guide surfaces even better visible. They direct the suspension to the shear gap.

Summary :

The dispersing machine (homogenizing mill) is used to produce and homogenize powder suspensions in grinding or dispersing liquids and has essentially a counterparts rotor and stator element pair that is shaped so that in working position therebetween is a free conical gap caused by rotation forms a corresponding volume, the working volume in which shear forces are introduced by rapid rotor rotations, wherein the flowed through by the suspension length of the working volume in the flow direction corresponds to 1 to 5 times the inlet or head diameter of the rotor. The components rotor and stator are of simple geometric shape, therefore easy regrindable and consist of hard metal or a carbide-steel composite, while the machine components are flowed through inside provided with a hard metal coating. The dispersing machine works completely without free-moving grinding media. Due to the elongated shape and the coating, the dispersing machine is particularly suitable for the effective production of homogeneous suspensions in the hard metal and cermet production.

Claims (15)

Dispersing machine for the production and homogenization of powder suspensions with rotor and stator elements, which are designed so that there is a gap volume in working position between them, in which shear forces can be introduced by relatively opposing movement of the opposing rotor and stator lateral surfaces, characterized in that both the rotor and the stator or parts of the rotor and stator which comprise the lateral surfaces of these machine parts consist of a sintered hard metal. Dispergiermaschine according to claim 1, characterized in that the hard metal parts of the dispersing machine are formed from a separately prepared support. Dispersing machine according to claim 1 or 2, characterized in that the hard metal parts of the dispersing machine are present in a hard metal-steel composite material. Dispergiermaschine according to any one of claims 1 to 3, characterized in that of the suspension to be homogenized suspension around machine part surfaces are powder coated with hard metal. Dispergiermaschine according to any one of claims 1 to 4, characterized in that the working volume facing lateral surfaces of the rotor and / or stator are at least partially surface-structured and preferably provided for this purpose with grooves or channels. Dispergiermaschine according to any one of claims 1 to 5, characterized in that provided with a suspensionsleitenden surface structuring or guiding devices rotor head outside the working volume is releasably secured to the rotor. Dispersing machine according to one of claims 1 to 6, characterized in that the working volume formed between the rotor and the stator narrows steadily monotonically in the direction of suspension flow. Dispersing machine according to one of claims 1 to 7, characterized in that the smallest distance between the rotor and stator at the working volume is less than 3 mm, preferably less than 0.1 mm. Dispersing machine according to one of claims 1 to 8, characterized in that between the rotor and stator as a gap volume, a cylindrical or preferably conical annular gap is formed. Dispersing machine according to claim 9, characterized in that the height or length of the working volume flowing through the suspension in the direction of flow is about 1 to 6 times, preferably 1 to 5 times, more preferably 1 to 3 times equal to the smallest diameter of the rotor. Dispergiermaschine according to claim 10, characterized in that the length-diameter ratio as a quotient of effective rotor length and the smallest effective rotor diameter equal to 1, preferably equal to 3. Dispergiermaschine according to any one of claims 1 to 11, characterized in that at least one return line from the outlet to the inlet of the rotor-stator unit or in the feed tank for the recirculation of the homogenized suspension is present. Dispersing machine according to one of claims 1 to 11, characterized in that it has a feed tank within the same machine unit on the inlet side. Dispergiermaschine according to claim 13, characterized in that means for slurrying the suspension in the supply tank are present, preferably at least one agitator. Use of the dispersing machine according to one of claims 1 to 14 for the production of metallic powder mixtures, preferably hard metal powder mixtures, or cermet powder mixtures.

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