JPH1085583A - Method for producing fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To granulate or pulverize in a high yield by forming a molten body of a powdery substance in the form of a liquid film flow of a specified thickness and carrying out the collision of the liquid film flow with a gas film flow of sufficient amount for shearing the liquid film flow at the specified gas flow velocity in a manner of crossing both film flows each other. SOLUTION: A molten body 9 or slurry of a powdery substance in a vessel 8 is passed through a stopper 10 and fed from a hot molten material injection opening or a jet outlet 7 onto a central section of a rotating desk surface 3 to form a liquid film flow. If necessary, the rotating desk 1 is heated in a non- contact manner by a high-frequency induction heating coil 4, and also a hot molten material injection nozzle or a jet nozzle 6 is heated similarly by a high- frequency induction coil 5. On the other hand, inactive gas fed from a gas feed source is jetted in the state of annular film encircling the rotating desk 1 from an annular nozzle 2 set close to the periphery of the rotating desk 1. The collision of the liquid film flow with the gas film flow is generated by the crossing of both film flows all over the circumference of the rotating desk 1 by the above constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pigment for paint, a metal fine powder suitable for injection molding, or an inorganic or organic fine powder.

[0002]

2. Description of the Related Art Paint pigments and materials used for injection molding are fine powders having a particle size of about 10 to 20 .mu.m. If the intended powdery substance is a metal, the molten
Although pulverization to 20 μm is possible with a conventional gas atomizer, it is only a small part of the product and is inefficient and impractical. With a water jet atomizer pressurized to several hundred atmospheres, fine powder having an average particle size of 10 μm or less is possible, but the quality is deteriorated due to oxidation.

On the other hand, many of inorganic and organic substances are at most about 1 μm even in an agglomerated state, and it is necessary to granulate the substance to 10 to 20 μm in order to make the substance into a pigment for paint or a fine powder suitable for injection molding. Conventional methods for this purpose include a rolling granulation method and a spray-dryer method. Among them, the spray-dryer method, which is suitable for fine powder granulation, has a limit of up to several tens of μm, and the yield is poor.
The spray dryer method is further divided into two typical treatment methods, one of which is a method in which a liquid or slurry is dropped on a rotating disk and scattered by centrifugal force, and the other is a method in which a liquid or slurry flowing down from a nozzle is sprayed. Is a method in which gas is blown to the air to be scattered.

[0004]

In the pulverization using centrifugal force, factors such as the diameter of a rotating disk, the number of rotations, the surface tension of a molten metal or a slurry-dispersing medium, viscosity, and wettability to the surface of a rotating body are related. . In particular, the diameter of the rotating desk and the number of rotations are primary factors. Of course, a larger centrifugal force is advantageous for miniaturization, but it is a high-speed rotation of 40,000 to 50,000 rpm, and the diameter is more than 10 cm. The adoption of such a rotating desk is not practical because it is limited by the strength of the material against the centrifugal force and the magnitude of the load on the motor. On the other hand, after the gas is sprayed, the gas diffuses rapidly and three-dimensionally, so the shearing force in the thickness direction is not sufficient for the molten metal or slurry flowing down in a columnar shape, and especially the molten metal with high viscosity and surface tension Is in a situation where pulverization to the particle size intended by the present invention is insufficient. At present, each of the above methods is tens of μ
m is the limit.

SUMMARY OF THE INVENTION The present invention solves the problems of the conventional art with respect to the production of paint pigments, metal fine powders and inorganic or organic fine powders suitable for injection molding, and a method for producing fine particles having a particle size intended by the present invention. Device is provided. Here, the pulverization referred to in the present invention means pulverization to a particle size suitable for the purpose of use.Therefore, certain inorganic substances and organic substances become granulated, and molten metals and the like become granulated. Is pulverized.

[0006]

According to the present invention, the object is achieved as follows. That is,

(1) A melt of a desired powdery substance is coated with a film thickness of 1
And a gas film flow of an amount sufficient to shear the liquid film flow with a gas velocity of 10 μm or less.
Collapsing the two membrane streams so that they cross each other at 0 m / sec or more;

(2) At this time, the melt of the target powdery substance is composed of a molten metal, and the liquid film flow is a droplet film flow composed of a collection of droplets having a particle size of 200 μm or less. Injecting the gas into a film so as to intersect the film flow, preferably at an angle close to 90 ° to 90 °;

(3) The target powdery substance is 1 μm.
In the case of an ultrafine powder of m or 1 μm or less, the substance is suspended in an appropriate dispersion medium to form a slurry, and the slurry is a liquid film stream having a film thickness of 1000 μm or less or a droplet composed of droplets. A gas film flow having a gas flow rate of 100 m / sec or more, preferably 1000 m or more, which is sufficient to shear the liquid film flow or the droplet film flow with respect to the liquid film flow or the droplet film flow.
no 90 ° both film flow comrades in m / sec or faster to be collision so as to intersect at an angle close to 90 ^o,

(4) As an apparatus therefor, a container for storing a melt or slurry of a target powder material, a nozzle attached to the container, and discharge of the melt or slurry discharged from the nozzle. The use of an apparatus for producing fine powder, comprising a rotating desk arranged to receive a flow at its center and an annular nozzle for gas injection arranged surrounding the rotating desk.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The differential of gas momentum change due to collision with respect to time is the force of gas exerted on a liquid film or droplet, and the vertical component force on the liquid film or droplet surface is the shearing force of the gas by the gas. At the same gas flow rate, 90
When injected at an angle of °, maximum shear is obtained. However, the gas distant from the nozzle is rapidly and three-dimensionally diffused depending on the structure of the nozzle and also in the gas itself, so that it changes temporally and locally even while the gas is in contact with the liquid film or droplet, It is considered that the actual shearing force effective for pulverization depends on such a difference in change in locally acting gas momentum, that is, a difference in collision force. However, since the force is estimated to be attenuated in half proportion to the cube of the distance from the gas nozzle, the film thickness and the nozzle position must be selected according to the physical properties of the melt or the slurry dispersion medium.

In this case, if the flow rate and the flow rate of the gas become excessive, the fine droplets are repelled by the collision, and the scattered droplets are injected into the gas injection nozzle or the melt or slurry pouring port or the discharge port. Deposits may cause trouble. This situation depends on the conditions of gas injection and the angle of injection with respect to the film flow.
Adjustment may be made by appropriately deviating from 90 °, and a separate nozzle may be prepared to blow gas to forcibly change the course. As the gas, an inert gas is used. In general, the injection of a pressure of about 7 to 8 kgf / cm ² is sufficient even in the pulverization of the molten metal, but it is adjusted by the physical properties of the target melt and slurry.
In this case, the higher the gas pressure, the finer the powder.

In order to discharge the melt or slurry from the peripheral edge in the form of a film or a droplet film, and to control the thickness up to the thickness, among many factors related to the size, number of revolutions, material, etc. of the rotating desk, In particular, the angle at which the melt or slurry rises at a certain angle near the periphery of the desk and leaves the periphery in the tangential direction of the desk under the influence of gravity is ± 5 ° around 15 °. It is important to adjust the range so that it is above horizontal. However, in some cases, by making the tangential direction of the desk lower than the horizontal, the intersection angle with the gas can be made close to 90 ^° , and the distance between the liquid film or the droplet flow and the gas nozzle can be reduced. Thereby, pulverization can be further advanced.

The cross-sectional structure of the rotating desk may be either uneven or irregular, and the shape is not limited. However, assuming that the above conditions are satisfied, the peripheral end is inclined as shown by 3 in FIGS. 1 and 2. A dish-shaped rotating desk with a "spit" is recommended. The control of the thickness of the film flow is related to the material and particle size of the powder to be produced and is determined by the desired particle size of any material. A slurry using water or an organic solvent-based dispersion medium can be a liquid film having a thickness of 1000 μm or more. However, in the case of a molten metal salt or a molten metal having a viscosity or surface tension that differs by one digit or more, a 200 μm or It is desirable that the droplet film flow be pre-ground on a rotating desk to a degree less than that. The film thickness is controlled by controlling the supply amount of the melt or slurry and controlling the number of revolutions of the rotating desk, and this control simultaneously determines the speed of the melt or slurry of the raw material leaving the periphery of the rotating desk. This causes a difference between the liquid film and the droplet film.

FIG. 1 shows an apparatus suitable for carrying out the present invention. In FIG. 1, a melt or slurry 9 in a container 8 is supplied from a pouring port or a discharge port 7 to a central portion of the rotating desk surface 3 via a stopper 10. Means for heating the rotating desk 1 in a non-contact manner by the high-frequency induction heating coil 4 to prevent solidification of the molten metal on the desk is also employed. Similarly, the pouring nozzle 6 can be heated by the high-frequency induction heating coil 5 so that the pouring port can be extended to just above the rotating desk while preventing clogging due to coagulation, and scattering caused by dripping can be suppressed.

The rotating desk 1 is rotated around a rotation axis by a suitable rotating means (not shown), and powder to be supplied to the center of a thin plate-shaped rotating surface 3 having a "collar" is provided. Is discharged from the periphery of the desk by the centrifugal force of the rotation of the desk. The desk can be heated by high-frequency induction heating 4 as needed. There is an air chamber surrounding the desk for high-pressure gas, and gas sent from a gas supply source (not shown) to the air chamber is jetted from a nozzle 2 placed close to the rotating desk. The jets should intersect the film flow of liquid or droplets from the desk, preferably at an angle of 90 ° or closer. Since the nozzle is an annular nozzle, and the gas is injected in a ring-like film state surrounding the rotating disk, collision between the film flows due to the intersection of the two film flows is performed over the entire circumference of the rotating disk.

The above-mentioned conditions necessary for carrying out the present invention are determined from the following test results using the apparatus shown in FIG.

Test Example 1 An alloy having a composition of Sn-37% Pb was melted in an alumina container 8 by high-frequency induction heating, and the temperature was 300 ° C.
1 and flowed down from the pouring nozzle 6 to the center of a 50 mmφ rotating desk made of titanium having a surface shape indicated by 3 in FIG. With respect to particles discharged from the desk into the space without gas injection from the annular nozzle, the ratio of each particle size was tested using the pouring amount and the disk rotation speed as parameters. The metal particles emitted from the edge of the desk at a desk rotation speed of 30,000 rpm
When the pouring amount is 1-2 kg / min (referred to as condition A), 100 μ
m or less accounted for 86%. More pouring volume than above and 30,
At a desk rotation speed of 000 rpm or less (referred to as condition B), the ratio of -100 μm decreases, and at a pouring rate of 3 kg / min and a desk rotation speed of 20,000 rpm, the ratio of -100 μm is 37%.
Met.

Next, the nozzle was placed at a position 2 mm below the droplet film flow, nitrogen was injected, and the test was performed while changing the injection speed. The discharge condition of the droplet film flow that occupies most of 200 μm or less, ie, pouring rate 2 kg / min, desk rotation speed 30,000 rpm
Under (condition A), the film flow was tested at a gas flow rate of 400 to 2000 m / sec under an upward angle of about 17 ° with respect to the horizontal and a gas amount of 2 Nm ³ / min. The results are shown in Table 1. Good results have been obtained with gas velocities between 800 and 2000 m / sec. In particular, when the gas flow rate exceeded 1000 m / sec, scattering of fine powders started, and at 2000 m / sec, further pulverization progressed. As a result, the yield of -45 µm particles was 78%. From the above results, the gas flow rate is 800 to 2000 m / sec
And it was found that it was preferably at least 1000 m / sec. At 1000 m / sec, the yield of -45 µm particles was 62%, and the average particle size at that portion was 12 µm.

On the other hand, when there are many droplets exceeding 100 μm, that is, at a pouring rate of 3 kg / min and a disk rotation speed of 20,000 rpm
(Condition B), even at a gas flow velocity of 1000 m / sec, -4
The yield of 5 μm particles was poor. Thus, the effect of the gas flow rate was examined while maintaining the droplets discharged from the peripheral end of the rotating desk at 100 μm or less and the gas velocity mainly at 1000 m / sec. The results are shown in Table 2. Table 2 also shows a comparative example without gas injection, but hardly produced -45 μm particles. As can be seen from Table 2, even under the condition B, as the gas flow rate increases, the pulverization can be manufactured with a higher yield.

FIG. 4 summarizes the relationship between the diameter of the formed droplets and the particle size of the produced powder in a series of these tests for a gas velocity of 1000 m / sec.

[0022]

[Table 2]

Next, the installation position of the tip of the nozzle was examined.
The nozzle tip was set at a position separated from the film flow by 1, 5, 10, 20 or 50 mm below, and nitrogen was jetted toward the droplet film flow above. The results are shown in Table 3 including the results at the 2 mm position. When the droplet diameter was 100 μm or less, the gas flow rate was 1000 m / sec, and the other conditions were all tested under the above conditions, the yield of -45 μm particles was about 60% in the range of 1 to 10 mm. It is necessary to strictly manage some fluctuations, and in the case of 10 mm, the average particle diameter tends to increase slightly. Although it is possible to reach the 50 mm position, the adoption of the 20 and 50 mm positions is limited only when it is necessary.

In this test, the indication of the pressure control valve of the nitrogen cylinder was 7 to 8 kgf / cm ² , and the gas flow rate was 2000 m / se.
c, even when the gas flow rate is ³ Nm ³ / min, and the gas flow rate is 4 N / min, the indication of the pressure regulating valve is 10 kgf / cm ^2.
It was only.

[0025]

[Table 3]

(Test Example 2) About 1
μm copper oxide was made into a 70 wt% slurry with water, 1 wt% of an acrylic resin was added as a dispersant and a granulating agent, and the mixture was uniformly mixed with a par mill. Fig. 1 shows the cross section of this slurry.
Flowed down to the center of a 50 mmφ SUS rotating desk, which was the same as 3 above. The rotational speed of the desk was changed while the amount of slurry supplied was in the range of 1 to 5 kg / min, and the state of the liquid film discharged from the peripheral edge of the desk was photographed at high speed from the side by removing the annular jet nozzle. Table 4 shows the results.

[0027]

[Table 4]

As can be seen from Table 4, the desk rotation number 4000
~ 7000rpm range and slurry supply 2-3kg / m
Under the condition of in, the slurry becomes a liquid film and the film thickness is 1000
μm or less. The film thickness exceeded 1000 μm when the rotation speed was lower than the above range or the slurry supply amount was higher than the above range. Further, when the number of rotations of the desk was higher than the above range and the slurry supply amount was lower than the above range, the slurry discharge from the peripheral end of the desk changed from the liquid film flow to the droplet film flow.

Next, the tip of the gas injection nozzle is placed at a familiar position 10 mm and 5 mm below the slurry liquid film flow or the droplet film flow, and the film flow discharged upward from the horizontal by 15 ° from the peripheral edge of the desk. Nitrogen at a flow rate of 50 to 2000 m / sec
Injected in the range. Table 5 shows the yield and the average particle size of particles of 45 μm or less discharged into a hopper maintained at 200 ° C. under the conditions of a liquid film flow and a droplet film flow having a film thickness of 1000 μm.

[0030]

[Table 5]

As shown in Table 5, the nozzle position is 10 m
At both locations of m and 5 mm, -45 μm particles were recovered at a gas flow rate of 100 m / sec or more, and the yield increased as the gas flow rate increased. -45 at gas flow velocity 1000m / sec
The yield of μm particles was 60% or more. Liquid film thickness is 10
Above 00 μm, pulverization did not proceed, and the yield of −45 μm was reduced to about 40%. The above situation is for nozzle position 10
mm and 5mm are the same, but the gas flow rate is 1000m /
Beyond sec, the effect of finer particles was better at the nozzle position of 5 mm. From these results, in the case of a slurry, a liquid film flow having a thickness of 1000 μm or less or a droplet film flow composed of a collection of droplets is used, and the gas flow velocity is in the range of 100 or more m / sec, preferably 1000 m / sec or more. .

As described above, in the present invention, the inert gas is jetted in a film form from the annular nozzle 2 surrounding the turntable 1 so as to intersect with the film flow discharged from the peripheral end of the turntable. Can be realized by a film flow ejected from a slit provided in a side wall of the container and a gas flow crossing the film flow. In addition, it can be determined by adjusting the diameter of a large number of fine holes arranged like slits instead of slits. Furthermore, a conical film flow can be jetted from a conical discharge port, and this can also be realized by an annular gas nozzle disposed around the discharge port. In any case, the position of the tip of the gas nozzle is important. The distance from the tip to the liquid film flow is preferably 50 mm or less, and if it is larger than this, the particle size distribution of the fine powder tends to become coarse. Various gases can be used as the gas to be used, in addition to nitrogen gas and air.

[0033]

Example 1 An alloy having a composition of Sn-37% Pb was melted by high-frequency induction heating in an alumina container 8 using the apparatus shown in FIG. 1 and maintained at 330 ° C., which was about 150 ° C. higher than the melting point of 183 ° C. The pouring nozzle 6 has an inner diameter of 3 mm, an outer diameter of 8 mm, and a length of 10
cm SUS pipe is covered with a heat insulating material, and a high-frequency induction heating coil 5 is wound thereon. The annular gas nozzle 2 is installed around the rotating desk 1 and has a speed of 1000 m /
At a flow rate of sec, nitrogen was injected substantially perpendicular to the droplet film flow at a position 2 mm above the nozzle tip. Gas flow rate is 2Nm ³ / m
in. The desk is made of Ti having a diameter of 50 mm and coated with a plasma sprayed film of zirconia. A thin dish-shaped structure having a "brim" around the same shape as 3 in FIG. 1 was preheated to about 300 ° C. by the high-frequency induction heating coil 4. . The pouring port 7 was placed at a distance of 10 mm from the desk to prevent the molten metal from scattering from the desk when flowing down. The pouring nozzle 6 is heated to 300 ° C. by high-frequency induction heating, and the molten metal is placed at the bottom of the alumina container 2.
Pouring was performed at a rate of 2 kg / min from a hole of mmφ through a stopper-10. The desk 1 was set at 30,000 rpm and emitted upward from the periphery of the desk at about 15 ° above the horizontal direction in the form of a film having a thickness of about 1000 μm and composed of droplets of about 100 μm or less, which was further pulverized by gas injection. .

The alloy powder produced under the above conditions had a particle yield of −45 μm of 62% and an average particle diameter of 12 μm.

Example 2 Each of the metals shown in Table 6 was melted in an alumina container by high-frequency induction heating and kept at 100 ° C. higher than the melting point of each metal. The pouring nozzle 6 has an inner diameter of 3 mm,
A carbon pipe having an outer diameter of 8 mm and a length of 10 cm was covered with a heat insulating material, and a coil for high-frequency induction heating was wound thereon and heated to a temperature 100 ° C. higher than the melting point of the corresponding metal. The conditions were the same as in Example 1 except that the pouring speed was set to 1 kg / min, and the position of the tip of the gas injection nozzle was set to be below 5 mm away from the droplet film flow. Table 6 shows the results.

[0036]

[Table 6]

(Example 3) Agglomerated to have an average particle size of about 1 μm
Was added to water to make a 70% by weight slurry, and 1% by weight of an acrylic resin was added as a dispersing agent and a granulating agent, followed by uniform mixing with a par mill (not shown). 1 mmφ from the bottom of a SUS container made of Teflon-coated slurry
Burning propane at 3 kg / min
The solution was dropped on a rotating desk kept in an atmosphere of ° C. The cross section of the desk is made of SUS of 50 mmφ of the same type as in Example 1, and the rotation speed is
At 6,000 rpm, about 12 ° to the horizontal direction, air is discharged upward from the annular nozzle surrounding the desk at approximately 12 ° with respect to the horizontal direction.
Fired at an angle. At a gas flow rate of 3 Nm ³ / min and a gas flow rate of 1000 m / sec, the yield of -45 μm particles is 64.
%, And the average particle size in that portion was 14 μm.

[0038]

The present invention comprises two processes, a first stage for forming a liquid film or a droplet film spreading in a film form, and a second stage for impinging an inert gas at a high speed on the film flow. Fine powder having a particle size range that cannot be obtained by the method can be produced in high yield. The energy consumed in the first stage of creating the membrane flow is small, for example, the centrifugal force is also small, so that the limitation on the size and material of the rotating desk can be greatly reduced and the load on the motor can be reduced. In addition, the first step greatly enhances the efficiency of the second step, so that even at a low gas injection pressure of 10 kgf / cm ² or less, the particle size of the fine powder can be reduced and the product yield can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus suitable for performing the method of the present invention.

FIG. 2 is a schematic sectional view showing a rotating disk and an annular nozzle portion in the apparatus of FIG. 1;

FIG. 3 is a schematic plan view of FIG.

FIG. 4 shows the relationship between the droplet diameter of a liquid film formed according to the method of the present invention and the average particle diameter of the obtained powder (gas velocity: 1000 m / s)
It is a figure which shows the case (gas injection by ec).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 rotating desk 2 annular gas injection nozzle 3 open V-shaped rotating desk surface 4 high-frequency induction coil for heating rotary desk 5 high-frequency induction coil for pouring nozzle heating 6 nozzle for introducing melt or slurry 7 melt or slurry Discharge port 8 Melt or slurry container 9 Melt or slurry 10 Stopper

[Table 1]

Claims (4)

[Claims] 1. A melt of a target powdery substance having a thickness of 100
A liquid film flow of 0 μm or less, and a gas film flow of an amount sufficient to shear the liquid film flow with respect to the liquid film flow is applied at a gas velocity of 100 m / s.
A method for producing fine powder consisting of colliding two membrane flows under ec or more. 2. The fine powder according to claim 1, wherein the melt of the target powder material is a molten metal, and the liquid film flow is a droplet film flow composed of a collection of droplets having a particle size of 200 μm or less. Method of manufacturing. 3. A slurry obtained by suspending a target powdery substance in a dispersion medium is formed into a liquid film flow having a thickness of 1000 μm or less or a liquid film flow composed of a collection of liquid droplets. Producing a granulated fine powder comprising impinging a sufficient amount of gas film flow such that the film flow is sheared at a gas velocity of 100 m / sec or more so that both film flows intersect. Law. 4. A container for storing a melt or slurry of a target powder substance, a nozzle attached to the container, and the melt or slurry discharged from the nozzle.
And an annular nozzle for gas injection arranged so as to receive the discharge flow at the center thereof and an annular nozzle for gas injection arranged so as to surround the rotary desk.