JPH04161257A - Air jet grinding method using grinding medium - Google Patents

Abstract

PURPOSE:To finely ground a material to be ground in a reduced mill power unit by injecting air from an air jet nozzle to blow up the grinding media having a diameter larger than that of the material to be ground accumulated on the lower part of a grinding chamber and the supplied falling material to be ground to form a fluidized bed generating violent collision and abrasion. CONSTITUTION:A material M to be ground is supplied to a hermetically sealed vertical grinding chamber 1 from the feeder 2 provided to the grinding chamber 1. Air is injected from the air jet nozzles 4A, 4B provided under the feeder 2 and/or provided to the lowermost end of the grinding chamber 1 to blow up the grinding media 3 having a diameter relatively larger than that of the material M to be ground accumulated on the lower part of the chamber, and the supplied falling material M to be ground to form a fluidized bed A generating violent collision and abrasion. When the solid-gas mixed stream B separated from the fluidized bed A to rise reaches the classifying rotor 5 built in the top part of the grinding chamber 1, only a fine powder F is sucked to be discharged out of the grinding chamber 1 and a coarse powder R goes back in the chamber 1 to be again involved in the fluidized bed A to receive collision and abrasion. As a result, a fine ground product can be prepared in a reduced mill power unit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an air flow pulverization method in which a fluidized bed is formed by injecting a gas such as air or an inert gas to pulverize.

[Prior Art] The air-flow pulverization method is a method of obtaining fine powder by pulverizing food additives, organic pigments, and other organic and inorganic materials using an air-flow pulverizer.

Since the history of pneumatic crushers is not particularly new, numerous technological developments related to this have been proposed. In a general form, as illustrated in FIG. 3, a feeder 2a is connected to the side wall of a vertical crushing chamber 1a of a sealed cylindrical cane, and crushed material Ma is supplied into the chamber. Along with this, or instead of this, if a gas injection nozzle 4a is provided at the lower end of the grinding chamber and the gas is injected horizontally (or diagonally downward, or vertically upward), the crushed material Ma will flow as if in the lower part of the grinding chamber. Fluidized bed Aa like boiling liquid
The crushed materials Ma collide and rub against each other within this layer to become fine. The fine powder Fa crushed in this layer and the coarse powder Ra that has not reached the desired particle size are also mixed in and leave the fluidized bed and rise vertically in the room as a solid-gas mixed flow according to the air flow after injection. It reaches the classification rotor 5a built in the top of the crushing chamber 1a. Of this fluid, the fine powder Fa is suctioned and discharged from the discharge port 6a, but the coarse powder Ra has a large mass, so it is splashed by the centrifugal force of the classification rotor rotating at high speed, falls inside the grinding chamber, and returns to the lower fluidized bed Aa. It has a structure in which it merges into the interior and undergoes repeated crushing action.

[Problem to be solved by the invention] In the conventional air flow crushing method, for example, the collision speed required to crush 100 μm quartz particles by placing them on the jet air is such that all the kinetic energy is converted into crushing energy. Even if this assumption is made, it is theoretically calculated to be 66 m/s.

In order to strongly accelerate the particles in this way, a huge injection gas pressure is required, and the efficiency of replacing electrical energy with crushing energy to generate the injection gas is generally low, at a few percent or less. , mill power intensity (KWh
/l) must become large due to enormous energy loss.

On the other hand, the particle size of the product obtained requires the use of a large amount of injected gas, so even if it is recovered after passing through the classification rotor, the particle size of the product obtained is limited to an average diameter of several μm; Even though there was a strong demand for pulverization, it could not be met.

Therefore, in order to overcome this problem, the process must be set up so that the crushed material Ma to be fed to the feeder is at least 100 μm or less by pre-pulverizing it before being fed to the crusher, or alternatively, as shown in FIG. 1-317554), the arrangement and shape of the device were changed, such as by installing a center core 100 made of ceramic or the like in the center of the crushing chamber to further increase the chances of collision within the fluidized bed. Improvements are proposed.

Needless to say, the former cannot avoid being burdened with distractions and inefficiency, and the latter cannot necessarily be evaluated as being so strong that it directly leads to a significant activation of its effects.

Furthermore, a common problem with conventional methods is that when grinding adherent particles, an adhesion layer accumulates on the inside of the grinding chamber, filling the grinding chamber with particles, which prevents the smooth progress of the grinding process and sometimes impedes operation. It can even lead to.

In order to solve the above-mentioned problems, the present invention produces finer pulverized products from larger feed size granules with less mill power consumption, and even highly adhesive granules can interfere with this property. The purpose of the present invention is to provide an air flow crushing method that can be operated stably for a long period of time without being affected.

[Means for Solving the Problems] The air flow crushing method according to the present invention supplies crushed material into the crushing chamber from a feeder provided on the side wall of the sealed cylindrical vertical crushing chamber,
A gas is injected from a gas injection nozzle installed below the feeder and/or at the lowest end of the grinding chamber to blow up a grinding medium having a relatively larger diameter than the ground material accumulated at the bottom of the grinding chamber and the ground material that has been supplied and fallen. A fluidized bed that violently collides and scrapes is formed, and when the solid-gas mixed flow that leaves the fluidized bed and rises reaches the classification rotor installed at the top of the grinding chamber, it sucks in only the fine powder and discharges it outside the grinding chamber. All of the above-mentioned problems were solved by falling through the room, being caught up again in the fluidized bed, and subjected to collision and abrasion.

[Effects] It is generally preferable to use a material with a higher hardness than the pulverized material, such as ceramics, glass, or steel balls, as the pulverizing medium, but in addition to or in place of these materials, a self-driving medium made of the same material as the pulverized material may also be used. There may be cases where it is acceptable due to product purity requirements. However, as a common principle, it is essential that the diameter of the material be larger than that of the crushed material.

For example, the theoretical collision speed required to crush a 100 μm quartz particle by colliding a crushing medium with a mass of 1 g is Q, 1
m/s is sufficient, and this is equivalent to 1 in the case of self-pulverization by colliding 100 μm crushed particles (quartz particles) as described above.
/660 only.

The mass of a 100 μm quartz particle is approximately 1.4×10 −6 g, and the kinetic energy generated by collision with a grinding medium having a mass of 1 g is orders of magnitude larger. Even if crushed particles with a small mass are accelerated, their inertia is small, so they easily stall due to slight air resistance.However, the crushing media, which is accelerated by the jet air and forms a fluidized bed, has a dynamic force added to each. The large amount of energy maintains the crushing force at the time of collision for a long time, producing the effect of crushing the crushed material more finely and efficiently.

Conversely, there are no restrictions on the particle size of the crushed material fed to the feeder, and therefore the need for preliminary crushing can be waived.

In addition, even if the crushed particles tend to adhere to the inner wall of the grinding chamber, the fluidized crushing medium collides with the grinding medium and applies a strong impact force to knock them off, thereby greatly reducing concerns about the particles adhering to the inner walls.

[Example code] FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

The crushed material M is fed into a feeder 2 attached to the side wall of a vertical crushing chamber 1 with a sealed cylindrical shaft, enters the crushing chamber by a screw feeder 21 attached to the bottom of the feeder, and falls downward.

At the bottom of the grinding chamber, grinding media 3 made of a desired material such as ceramics and having a relatively larger diameter than the grinding material are accumulated, and together with the falling particles M, the gas injection nozzles 4A, 4B,
A fluidized bed A is formed by the gas injected from...

Therefore, there is a clear causal relationship between the amount of air injection and the cumulative amount of grinding media, and a fluidized bed with optimal activation must be set based on this relationship.

In Figure 1, multiple air jets are directed horizontally, but there are also cases where the circumference of the grinding chamber is divided equally and directed toward the center or tangential direction, diagonally downward or upward, or as shown in Figure 2. Another air injection nozzle 14 may be installed at the bottom end of the grinding chamber to forcefully blow air upward from the bottom. The fine powder F, which has been sufficiently subjected to collision and abrasion in the fluidized bed A, becomes part of the coarse particles R.
At the same time, it rides on the air flow and rises in the room as a solid-gas mixture flow B, and reaches the inside of the classification rotor 5 at the top.

The classification rotor rotates at high speed, and its axis is connected to the discharge vibro leading outside the crushing chamber, and the discharge pipe is further connected to a collector (not shown), which is under negative pressure, so that the fine powder F flows from around the axis of the classification rotor. It is sucked and collected into a collection machine, but
The coarse powder R is strongly subjected to the centrifugal force applied near the blades of the classification rotor, and falls naturally within the grinding chamber under the suction force, forming a return flow C that returns to the fluidized bed A again.

[Effects of the Invention] Since the air flow pulverization method using the pulverization medium according to the present invention undergoes the actions described above, the amount of pulverization per hour can be increased or the gas injection pressure can be reduced. Therefore, the mill power consumption (KWh/l) required for operation can be reduced.

In addition, since the crushing energy is large, the crushed material can be made finer, and on the other hand, if the gas injection pressure is kept low, the air volume is reduced, and if the rotation speed of the classification rotor is the same, the product can be made finer. On the other hand, even if relatively coarse powder is directly fed without requiring pre-pulverization, it is capable of pulverizing it into fine particles without any problem.

Furthermore, even with regard to particles that tend to be adhesive, it is possible to maintain smooth operation without being bothered by adhesion to the walls of the grinding chamber, which has great practical effects.

[Brief explanation of drawings]

FIGS. 1 and 2 are vertical sectional views showing different embodiments of the present invention, and FIG. 3 is a vertical sectional view illustrating the prior art. 1... Grinding chamber 2... Feeder 3... Grinding medium 4... Gas injection nozzle 5... Classification rotor 6...
...Exhaust vibrator 14...Air injection nozzle

Claims (1)

[Claims] (1) The crushed material is supplied into the grinding chamber from a feeder installed on the side wall of the sealed vertical grinding chamber, and gas is injected from the gas injection nozzle installed below the feeder and/or at the lowest end of the grinding chamber to the bottom of the grinding chamber. The relatively large-diameter grinding media and the fallen crushed particles are jetted up against the accumulated crushed particles to form a fluidized bed that violently collides and scrapes, and leaves the fluidized bed and the rising solid-gas mixed flow flows into the crushing chamber. When it reaches the classification rotor built into the top, only the fine powder is sucked in and discharged outside the grinding chamber, while the coarse powder moves backwards through the chamber and is drawn into the fluidized bed again where it is subjected to collision and abrasion. Air flow crushing method.