DE102019112791B3 - GRINDING DEVICE FOR ROUNDING PARTICLES - Google Patents

Abstract

Grinding device (1) for rounding particles,
with a vortex chamber (4) for treating particles under their suspension in a fluid stream which is generated by fluid jets which are blown into the vortex chamber (4) at different points by means of a blowing device,
wherein the blowing device comprises a number of first blowing openings (9) which drive a fluid flow circulating in a first main flow direction about the central axis (L) of the swirl chamber (4),
characterized in that
the blowing device comprises a number of second blowing openings (10) which drive a fluid flow, which flows in a second main flow direction about the central axis (L) of the swirl chamber (4) and is opposite to the first main flow direction.

Description

The invention relates to a grinding device for rounding particles. The grinding device comprises a swirl chamber for the treatment of the particles suspended in a fluid flow and is moreover in accordance with the preamble of claim 1. The invention also relates to a corresponding method and optionally the associated use.

TECHNICAL BACKGROUND

Particles whose average grain size is in a certain range and which have as few sharp edges as possible are required for a wide variety of technical applications.

A prominent application is the production of so-called permanent or permanent magnets.

A permanent magnet or permanent magnet consists of a magnetizable material, for example iron, cobalt or nickel. In many cases, rare earth metals are alloyed, especially neodymium, samarium, praseodymium, dysprosium, terbium or gadolinium. Rare earth magnets are characterized by the fact that they have a high magnetic remanence flux density and thus a high magnetic energy density.

Such permanent magnets are made from crystalline powder. The magnetic powder is pressed into a mold in the presence of a strong magnetic field. Under the influence of the magnetic field, the crystals align with their preferred magnetization axis in the direction along the magnetic field.

The compacts are then sintered. During sintering, the pulverized constituents of the powder are connected to one another or compacted by heating, but none or at least not all of the starting materials are melted. The compacts are heated - often under increased pressure - in such a way that the temperatures remain below the melting temperature of the main components, so that the shape (shape) of the workpiece is preserved.

It is known for the production of a starting material, as is required for the production of permanent magnets and in particular for the production of Nd-Fe-B (neodymium-iron-boron) magnets, to ground alloys comprising rare earth metal to form an intermediate product. All or part of the regrind can also be recycled material from old magnets.

Conventional size reduction techniques are generally suitable for the production of powdery intermediate products.

It is problematic, however, that fine particles of this type, which have rare earth magnetic powders using conventional methods, for example in fluidized bed jet mills or similar grinding plants, have sharp corners and edges. These sharp corners and edges are highly undesirable for a variety of reasons.

For example, magnets that were manufactured using such a sharp-edged powder show poorer magnetic values or lower magnetic energy densities than can be expected from calculations that require largely round-ground powder particles, i.e. particles that essentially have no sharp corners and edges.

In the DE 10 2010 048 777 A1 A method and a device for surface treatment of an object are shown, wherein at least one jet of a blasting medium is generated, and the object is kept in a floating state by the at least one jet, and the surface of the object is treated by the at least one jet.

In the DE 601 12 642 T2 A blasting device is shown which is suitable for carrying out a surface treatment of sintered products such as permanent magnets based on rare earth metals and ceramics.

THE TASK UNDER THE INVENTION

The invention has for its object to provide a device for producing smoothed particles of a certain size, d. H. for the production of particles with at least a reduced number of corners and edges.

THE INVENTION SOLUTION

In terms of the device, the solution according to the invention is achieved by a grinding device for rounding particles in accordance with the first main claim.

The grinding device according to the invention has at least one swirl chamber for the treatment of particles which are suspended in a fluid stream. A “being suspended” is understood to mean that the particles are at least predominantly carried by the fluid flow for the period of their processing.

Said fluid flow, which moves in the swirl chamber, is generated by fluid jets which are blown into the swirl chamber at different points by means of a blowing device. A fluid jet is understood to mean a locally flowing, bundled fluid. A fluid jet is not only bundled in this sense, but in any case if it has an absolute or average diameter of less than or equal to 10 mm directly at its outlet mouth.

The diameter of the fluid jet depends on the nozzle diameter and the nozzle shape (cylindrical or conical), but can also be significantly larger in individual cases.

The blowing device has a number of first blowing openings for blowing fluid jets into the swirl chamber, coming from the outside. These blowing openings tend to drive a fluid flow that tends to circulate in a first main flow direction around the central axis of the swirl chamber.

According to the invention, the blowing device additionally comprises a number of second blowing openings. These also serve to blow fluid jets into the swirl chamber, coming from outside. These second blowing openings tend to drive a fluid flow that tends to circulate in a second main flow direction about the central axis of the swirl chamber and is opposite to the first main flow direction.

To clarify, it is preferred that a turbulent, circular flow is created in the vortex chamber by the said blowing in of the fluid jets, not only, but especially when a rapidly rotating classifier wheel is also involved in the formation of the flow in the vortex chamber. The term “main flow direction” therefore describes (roughly) the resulting direction in which the local fluid flow or the vertically oriented layer that makes it up, generally with a finite thickness, moves, without prejudice to any local turbulence that may be superimposed.

In terms of the method, the solution according to the invention is achieved with the features of the corresponding independent method claim.

OPTIONAL POSSIBILITIES FOR DEVELOPING THE INVENTION

The blowing device is preferably designed as a guide ring, preferably separately exchangeable, with built-in blowing openings. This guide ring then forms a guide wall of the swirl chamber, i. H. a flow control device. This influences the movement of the fluid flow in the circumferential direction. As a rule, this is done in that the guide ring forces the fluid flow on its circular motion in the swirl chamber.

If the guide ring can be replaced separately, possible, usually abrasive wear on the guide ring can be easily compensated for by installing a new guide ring.

The separate interchangeability can be particularly interesting, however, where a multifunctional device is to be realized: as long as a guide ring with one of the unidirectional blow opening arrangements known from the prior art is installed, the device can be operated as a jet mill with aggressive blowing.

As soon as a guide ring according to the invention with oppositely oriented groups of blowing openings is installed, the device can be operated as a grinding device while blowing in at a lower speed. The particles are then - at least essentially - not broken up any further. Instead, only their edges are broken or rubbed off.

Ideally, the central longitudinal axes of the first blowing openings in the inflow direction lie in a first common plane which is arranged normal to the imaginary axis around which the fluid flow circles. Then the central longitudinal axes of the second blowing openings in the inflow direction lie in a second common plane which is offset with respect to said first common plane and which is arranged normal to the imaginary axis about which the fluid flow circles. The offset is preferably 3 mm to 40 mm, more preferably 5 mm to 25 mm.

Ideally, the fluid jets from two directly adjacent, oppositely blowing blowing openings brush essentially tangentially. Accordingly, the blowing openings are positioned and / or equipped with jet-shaping nozzles.

In this way, a zone of strong shear is created between two adjacent fluid jets, which tends to force the particles in question to self-rotate. Such a self-rotation is particularly advantageous for the grinding of particles that come into contact with one another.

The blowing openings are not necessarily but ideally formed by steel-forming nozzles. As a result, the blown-in fluid jets can each be shaped such that they fan out later than without nozzle shaping. As a result, they retain the ability to drive the desired circular flow in the vortex chamber longer at least within the shift for which they are responsible.

In some special cases, the jet-forming nozzles can have a nozzle body which is raised in relation to the inner circumferential surface of the guide ring. In this way, the nozzle body protrudes into the circular flow of the suspension - mostly more than insignificantly, namely usually by at least 5 mm in the radially inward direction.

This creates a particularly characteristic swirl. The additional turbulence created in this way is too mild to cause the particles to be broken up again. However, it is energy-rich enough to significantly intensify the movement of the particles, which leads to the desired grinding against one another.

The nozzles preferably have a nozzle body which is cylindrical or preferably conical in the outlet region. As just described, appropriately designed nozzles discharge a conically expanding fluid jet into the interior of the swirl chamber and thus produce a particularly effective grinding effect.

Ideally, the nozzle bodies are installed in bores in the guide ring.

Protection is also claimed for the use adapted to the invention (special operating mode and equipment) of a jet mill known per se as a grinding device for particles.

Finally, the claim to protection for a guide ring or “nozzle ring” equipped with an arrangement according to the invention of blowing openings or nozzles as a spare part or retrofit part is also reserved by way of a divisional application.

Further functions, advantages and further development possibilities result from the following description of an embodiment with reference to the figures.

Figure list

• The 1 shows the entire grinding device in a section perpendicular to the central longitudinal axis L .
• The 2nd shows the grinding device according to 1 in one to the central longitudinal axis L parallel cut.
• The 3rd shows a section of the 1 , but seen from behind.
• The 4th shows an enlarged section 3rd .
• The 4a shows another excerpt from that of 3rd displayed area, but with the selection of a slightly different cutting plane.
• The 4b shows a detail section that shows how immediately adjacent nozzles, as they are from 4th are shown, lie relative to each other.
• The 4c shows schematically the swirl chamber of the grinding device and its additional outlet.
• The 5 shows the same as that 4th , perspective obliquely from behind, cut.
• The 6 shows the same as that 4th , seen in perspective from behind, uncut.
• The 7 shows a RE M image of particles before grinding.
• The 8th shows a RE M image of particles after grinding according to the invention.
• The same shows the same 9 and 10th in relation to the satellite-like loading of abrasion particles.

PREFERRED EMBODIMENT

The best overall overview of the exemplary embodiment according to the invention is given by 1 and 2nd .

These two figures each show a meaningful axial section or longitudinal section through a grinding device according to the invention 1 .

The grinder 1 comprises a housing part or a housing 2nd . The housing 2nd forms a cavity inside. The cavity takes a guide ring 3rd on, which is sometimes called the “nozzle ring”, at least when it is optionally available with nozzles 12 is equipped. The cavity is shown to be the 2nd preferably with a front cover 2a locked. This front cover 2a is ideally designed so that it provides easy and quick access to the cavity when needed.

The guide ring 3rd divides the cavity into a swirl chamber 4th and the vortex chamber 4th surrounding ring channel 5 .

The ring channel 5 is via the fluid inlet 5a externally supplied with fluid from a pump or pressure source, not shown here. The ring channel 5 is used to continuously introduce fluid during the grinding process.

This fluid becomes the swirl chamber 4th fed in different places in the form of fluid jets. For the sake of better visibility it is Cutting surface on the guide ring 3rd in 1 and the other figures are not shown hatched, but exceptionally delicately dotted. At 4th is the cut area in the area of the local eruption, which makes the area actually behind the plane of the drawing visible, rather than with hatching with a coarse dotted line.

The vortex chamber 4th is with a particle inlet 6 Mistake. The latter is preferably designed as a vertical chute. Such an optional design allows the swirl chamber 4th with batch operation, gravity-assisted loading with the particles to be ground. The loading is then preferably carried out in such a way that at the start of a new grinding cycle approximately 25% to 50%, better approximately 30% to 40% of the volume of the swirl chamber 4th is filled with the particles to be ground.

In the case of batch operation, as is optionally practiced by this exemplary embodiment, the rounded particles can optionally be discharged via the classifier wheel, preferably by lowering the classifier wheel speed, which is accompanied by a reduction or removal of the blocking action of the classifier wheel. In this case, the grinder has 1 a speed control or speed control for the classifier wheel, which is designed so that it performs a speed reduction during the discharge process or unloading process.

Alternatively, the grinder can have one or more additional product exits 5b have, over which the rounded particles can be withdrawn, usually regardless of or without reducing the classifier speed. The 4c illustrates schematically how such an additional product outlet is designed and arranged.

The additional product outlet is expedient 5b with a flap or a valve 5c locked. The product can then be suctioned off. The ring channel 5 is passed through a pipe coming from the vortex chamber and penetrating it, which leads all the way to the outside, so that the vortex chamber 4th and the ring channel 5 do not come into direct connection with each other due to the additional product outlet.

In terms of process technology, there is also the possibility of an at least temporary overpressure in the grinding device 1 to work.

This then pushes the product out of the rounded particles after opening the flap or valve out of the swirl chamber.

The grinding device according to the invention 1 can also be equipped for continuous operation instead. In this case, the product leaves the machine continuously through the classifier wheel, which is operated at a suitable speed.

This approach can be used, for example, in the so-called “separation of satellites”, for example in connection with additive manufacturing. Satellite is understood to mean small particles or abrasion adhering to the actual useful particles, which has to be separated off. It is sufficient here to only briefly use the product, for example (mostly grinding in the sense of the invention). As soon as the satellites are separated, the particle size of the respective useful particle changes. Then the product of the useful particles can pass through the classifier at a constant classifier speed.

The secondary outlet via the classifier wheel can be seen from the exemplary embodiment shown here 7 .

The classifier wheel is designed in a known manner. It consists of a rotating drum. Typically, this in turn consists of two flank-forming tires which are connected to one another by means of spaced-apart bars or blades which are generally parallel to the axis of rotation.

About this classifier wheel 7 the very fine and inevitably occurring abrasion that occurs during grinding is usually separated and dissipated.

At the same time, a fluid stream corresponding to the currently newly blown-in fluid stream - at least essentially - becomes a classifier fluid stream via the interior of the classifier wheel 7 and deducted from there over the end face facing away from the swirl chamber. The classifier fluid flow that flows away entrains the abrasion, which is too small and low in mass to be kept away from the classifying wheel located in the center by the centrifugal forces. The actual particles, which are to be ground for a predetermined time, are too large. They circle so strongly in the vortex chamber that they are kept away from the classifier wheel in the center by the centrifugal forces acting on them. Otherwise they are rejected by the classifier wheel - back to the vortex chamber. This means that the actual particles cannot be removed from the swirl chamber via the classifier wheel. The operating speed of the classifier wheel is set accordingly, depending on the size of the particles to be processed or the desired classification quality.

The processing, ie the grinding, of the particles for the purpose of rounding their outer contour or outer surface takes place in that through the blowing openings 9 and 10th Fluid jets into the swirl chamber 4th be blown in. These tear the in the vortex chamber 4th located particles and drift in the vortex chamber 4th one mainly around the longitudinal axis L circulating fluid flow.

The grinding device typically includes a controller. This limits the jet speed of the fluid jets blown in through the blow openings.

The limitation is such that the particles are not so violent that they collide and / or impact the housing 2nd brought that they break up into comparable large pieces and are thus crushed again and again, that is, ground. The jet speed is preferably limited to values in the range between 150 m / sec and 300 m / sec, depending on the material currently being sanded.

An essential part of the grinding device according to the invention is its specially designed blowing device.

How to do it most accurately using the 3rd and 4 and 4a to c (but can also partly be understood from the other figures), the blowing device comprises a number of first blowing openings 9 . From every first blow opening 9 into the vortex chamber 4th escaping fluid flow and its jet expansion are shown schematically by a fluid flow cone 8th illustrated. These fluid streams drive a fluid stream circulating in a first main flow direction about the central axis of the swirl chamber. In addition, the blowing device has a number of second blowing openings 10th . Such a blow opening 10th illustrates the outbreak 11 who only in the 4th is shown. The eruption shows a section of the plane that is actually behind the drawing plane, in which the center lines of the oppositely oriented blowing openings 10th lie or the opposing nozzles forming them 12 . That from every second blow opening 10th into the vortex chamber 4th escaping fluid flow and its jet expansion are also caused by a fluid flow cone - albeit recognizable in the opposite direction 8th illustrated. These fluid streams drive a fluid stream which circulates in a second main flow direction about the central axis of the swirl chamber and which is opposite to the first main flow direction. This can be understood quite intuitively using the 4a and 4b .

In this way, two fluid flows tending to circulate in opposite main flow directions are generated. A flow area with a pronounced shear is established between these two fluid flows, cf. also again 4b . The particles that are entrained in this area appear to be forced by the shear to produce a pronounced rolling action that overlaps their turbulent translational movement. At the same time, this tangential flow past one another leads to micro vortices and corresponding turbulence, which increases the contact intensity and mixing.

Although in the present case the grinding machine according to the invention works with a kinetic energy that is significantly lower than the kinetic energy used in a jet mill, an unexpectedly strong grinding effect arises when the particles rub against one another in the manner mentioned .

However, the particles are not broken up.

As far as breakage occurs, mostly only fragments are broken off, the average diameter of which in many cases is at least a power of ten smaller than the average diameter of the remaining particle. As soon as a particle no longer has any sharp edges, there is essentially no further breaking off.

The conditions are favorable when the first blowing openings 9 blow all in the same direction and the second blow openings 10th blow all in the same direction.

Ideally, the relevant first blow openings are 9 at an angle A from about 15 ° to 45 ° and ideally from 25 ° to 35 ° relative to the tangent, which is on the inner circumferential surface of the guide ring in the region of the mouth of the relevant blow opening 9 in the guide ring 3rd is created, cf. 4th .

The same applies analogously to the second blowing openings 10th . These are at opposite angles B from approximately 15 ° to 45 ° and ideally from 25 ° to 35 ° relative to the tangent arranged on the inner surface of the guide ring 3rd in the area of the mouth of the relevant blow opening 10th in the guide ring 3rd is created, cf. also 4th .

Another dimensioning rule to be used preferably results from 4a that are essentially the 4th corresponds. Immediately adjacent blow openings on the shortest route 9 , 10th form with the perpendicular to their central longitudinal axes LL a blow opening pair angle C. between 45 ° and 90 °, better between 45 ° and 60 °.

During initial work with the solution according to the invention, it has been found that the number of pairs consists of opposing blowing openings 9 and 10th ideally at 4th to 12 and just better 4th to 8th should be.

The whole thing is particularly effective when the blow openings are in the same direction 9 and the opposite blow openings 10th with their center lines LL (the latter seen in the respective flow direction) do not lie in the same plane, but in different planes that are offset V mentioned amount are offset from each other - seen in the direction along the imaginary axis L around which the fluid flow in the swirl chamber 4th circles. The corresponding is, for example, in 4b presented very clearly.

Easy to recognize from the figures and especially the 4th is that the blow holes 9 and 10th preferably through nozzles 12 are formed, the nozzle body of which is a separate component in the guide ring 3rd is fixed, preferably screwed. The guide ring is used for this purpose 3rd a number of holes penetrating it obliquely in the radially inward direction. A nozzle body is fixed or screwed into each of these bores.

It is also worth mentioning that the grinding device according to the invention need not be a stand-alone device. Rather, it is possible to equip one of the known jet mills, such as the Conjet type from the applicant's house, in such a way that it can be used for purposes other than the grinding machine according to the invention.

For this purpose, a guide ring equipped with the appropriate spraying is used 3rd inserted into the existing machine and then ensured that the existing machine only works with a significantly reduced jet speed, as is absolutely necessary for the invention.

The high effectiveness of the grinding device according to the invention show the 7 and 8th .

The 7 shows using a conventional jet mill ground particles from a permanent magnetic material (rare earths) in 5,000 times SEM magnification. The inadequate rounding of the particles, which extends all the way to sharp edges, is clearly visible.

In contrast, the 8th the same material after grinding, preferably for several minutes, in a grinding device according to the invention. The fillet quality is significantly better.

The 9 shows particles that were ground using another method not according to the invention. The large particle in the center of the picture shows just how heavily it is contaminated by satellites with fine, dust-like abrasion particles that interfere in many applications. The 10th shows particles that were ground round on the grinding device according to the invention. Your contamination with satellite-like abrasion particles is practically zero.

Reference symbol list

1

Grinding device

2nd

casing

2a

cover

3rd

Guide ring or nozzle ring, if equipped with nozzles

4th

Vortex chamber

5

Ring channel

5a

Fluid inlet

5b

Fluid outlet or additional fluid outlet

5c

Valve

6

Particle inlet

7

Classifier wheel

8th

schematically indicated fluid flow cone of the injected fluid with “jet expansion”

9

first blow opening

10th

second blow opening

11

Outbreak for a more detailed illustration of an oppositely oriented nozzle 12 with a second blow opening 10th

12

jet

L

Central longitudinal axis or longitudinal axis or axis

A

angle

B

angle

C.

Blow pair angle

V

Offset

LL

Center line of a blow opening

Claims (11)

Grinding device (1) for rounding particles, with a swirl chamber (4) for treating particles under their suspension in a fluid stream which is generated by fluid jets which are blown into the swirl chamber (4) at different points by means of a blowing device, the Blowing device comprises a number of first blowing openings (9) which drive a fluid flow circulating in a first main flow direction about the central axis (L) of the swirl chamber (4), characterized in that the blowing device comprises a number of second blowing openings (10) which drive a fluid flow, which flows in a second main flow direction about the central axis (L) of the swirl chamber (4) and is opposite to the first main flow direction. Grinding device (1) after Claim 1 , characterized in that the blowing device is designed as a preferably separately exchangeable guide ring (3) with built-in blowing openings (9, 10), which forms a guide wall of the swirl chamber (4), which influences the movement of the fluid flow in the circumferential direction. Grinding device (1) according to one of the preceding claims, characterized in that the first blowing openings (9) lie in a first common plane which is arranged normal to the imaginary axis (L) about which the fluid flow circles, and the second blowing openings ( 10) lie in a second common plane that is offset from the first common plane with offset (V) and that is normal to the imaginary axis (L) around which the fluid flow circles. Grinding device (1) after Claim 3 , characterized in that the fluid jets of two immediately adjacent, oppositely blowing blowing openings (9, 10) graze substantially tangentially. Grinding device (1) according to one of the preceding claims, characterized in that the blowing openings (9, 10) are each formed by steel-forming nozzles (12). Grinding device (1) after Claim 5 , characterized in that the jet-shaping nozzles (12) have a nozzle body which is raised and projects into the circular flow of the suspension. Grinding device (1) after Claim 6 , characterized in that the nozzles (12) have a nozzle body which is cylindrical or preferably conical in the outlet region. Grinding device (1) according to one of the preceding claims in connection with Claim 2 , characterized in that the nozzles or nozzle bodies are installed in bores of the guide ring (3). Grinding device (1) according to one of the preceding claims, characterized in that a classifying wheel (7) is arranged in the center of the swirl chamber (4), via which the abrasion occurring in the course of grinding the particles in the swirl chamber (4) can be removed or the rounded material can be discharged by reducing the speed. Method for grinding particles suspended in a fluid stream in a swirl chamber (4), wherein fluid jets are blown into the swirl chamber (4) at different points by means of a blowing device, characterized in that the fluid jets are blown in groups in such a way that they are blown into one drive the first main flow direction around the central axis (L) of the swirl chamber (4) fluid flow and that they drive a fluid flow circulating in a second main flow direction around the central axis (L) of the swirl chamber (4), which is opposite to the first main flow direction. Use of a jet mill for grinding particles without crushing them further, using a jet speed which is reduced compared to the grinding operation and a blowing device with the extent of one of the Claims 1 to 9 given characteristics.

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