CN117258956A - Jet mill - Google Patents

Abstract

The invention relates to the technical field of material crushing equipment, and provides an airflow crusher, which comprises: crushing the cavity; the classifying wheel is arranged at the inner upper part of the crushing cavity; the motor is arranged on the outer side wall of the crushing cavity and is in transmission connection with the classifying wheel; wherein, the middle part in the crushing cavity is fixedly provided with a vertical isolation pipe so as to divide the area into an inner crushing area, an outer crushing area and a return channel; the pulverizing zone can be introduced with supersonic air flow to pulverize the material entering into the pulverizing zone into coarse powder and fine powder, the coarse powder enters into the bottom of the pulverizing zone via the return channel downwards at the classifying wheel to participate in pulverizing again, and the fine powder is discharged out of the pulverizing cavity via the classifying wheel. The isolation pipe is arranged in the crushing cavity, the middle part of the crushing cavity is divided into an inner crushing area, an outer crushing area and a return channel, so that material crushing and coarse powder descending return of large particles are performed in two areas which are independently separated, the air flow interference between the two areas is reduced, more single stable air flow can be formed in the local areas, and adverse factors such as turbulence and turbulence in the crushing process are favorably controlled.

Description

Jet mill

Technical Field

The invention relates to the technical field of material crushing equipment, in particular to an air flow crusher.

Background

The jet mill refers to equipment for crushing materials under the action of high-speed air flow, wherein the materials pass through the impact among particles, the impact shearing action of the air flow on the materials and the impact, friction and shearing action of the air flow on the materials and other parts. Since 1882, goslin has proposed a patent for pulverizing by using pneumatic kinetic energy, and various types of pneumatic pulverizer have appeared on the market. Currently, jet mills which are widely used in industry mainly include opposed jet mills, circulating jet mills, flat jet mills, and fluidized bed jet mills. Among them, flat type and fluidized bed type jet mills are widely used.

Compared with mechanical pulverizer, the jet mill has high pulverizing strength, high energy utilization rate (the jet mill can reach 2% -10%, and the common pulverizer is only 0.6%), simple equipment structure, capability of performing aseptic operation, convenient cleaning, fine granularity of the pulverized product, which can reach several micrometers or even submicron, and capability of keeping particles regular and smooth surface. In addition, the jet mill can realize the combined operation of crushing and drying, crushing and mixing, crushing and chemical reaction and the like in the mill.

Compared with other pulverizer, the jet mill has the advantages of narrow particle size distribution, high pulverizing efficiency, low energy consumption, less product pollution, less abrasion of accessories, and the like, but the equipment cost is higher. Because the material needs to be treated into fluidization and then is crashed by the airflow beam, the airflow crasher generally needs to have enough fineness for crashed material, and the requirement for the material with high density is more obvious.

Although the air flow pulverizer has obvious advantages, the air flow pulverizer has the defects that for example, auxiliary equipment is more, the cost is high, the material pouring phenomenon can occur when a pulverizing system is blocked, a large amount of dust is sprayed out, and the operation environment is deteriorated; the crushed materials have limitations, such as materials containing more oil, water and fiber are not easy to crush.

At present, the traditional jet mill mainly utilizes compressed air to be sprayed into a crushing area through 3-7 reverse nozzles, and crushed materials form fluidization under the action of pressure difference. The accelerated materials in the crushing area collide and rub each other at the intersection of the nozzles to realize crushing, the crushed fine materials are brought to the superfine classification wheel for classification by the ascending air flow, the fine materials meeting the product requirements are collected by the cyclone separator, and the coarse materials are settled and returned to the crushing area to be continuously crushed.

However, the above process has several drawbacks:

1. the fine material rising and the coarse material falling are carried out in the same area of the crushing area, and the flow fields of the fine material rising and the coarse material falling are different and are easy to form superposition interference to cause unstable air flow;

2. the material is repeatedly rubbed and crushed in the crushing area, so that the material is easy to excessively crush, the granularity of the material is unqualified, and the like, thereby not only wasting energy, but also failing to meet the related technical requirements;

3. the air flow of the crushing area is only used for collision and friction of materials, the energy conversion is single, and the utilization rate is low;

4. the airflow speed sprayed by the reverse nozzle is limited, the kinetic energy obtained by the material is not ideal, and the crushing of some superhard materials cannot be met.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides an air flow pulverizer, which aims to solve the problems that in the prior art, the material is unstable in pulverizing air flow, the material is excessively pulverized to waste energy, the air flow energy utilization rate is low, and the air flow speed is limited to not meet the requirement of pulverizing some superhard materials.

In order to achieve the above purpose, the present invention provides the following technical solutions:

a jet mill comprising:

crushing the cavity;

the classifying wheel is arranged at the inner upper part of the crushing cavity; a kind of electronic device with high-pressure air-conditioning system

The motor is arranged on the outer side wall of the crushing cavity and is in transmission connection with the classifying wheel;

wherein, the middle part in the crushing cavity is fixedly provided with a vertical isolation pipe so as to divide the area into an inner crushing area, an outer crushing area and a return channel; the comminution zone may be introduced with a supersonic gas flow to comminute the material entering the interior thereof into coarse powder and fine powder, the coarse powder entering the bottom of the comminution zone via the return channel downwardly at the classifying wheel to participate in comminution again, the fine powder exiting the comminution chamber via the classifying wheel.

In one embodiment disclosed in the application, the crushing cavity is provided with an air inlet pipe and an elephant trunk which penetrate through the outer side wall of the crushing cavity in a sealing mode, the inner end of the air inlet pipe is communicated with the crushing area, and the outer end of the air inlet pipe is communicated with an external air compressor through a pipeline;

the chute is positioned above the air inlet pipe, the inner end of the chute is connected with the isolation pipe in a penetrating way in an inclined downward way, and the outer end of the chute is vertically connected with a material hopper;

the inner lower part of the crushing cavity is provided with a discharge hole for outputting coarse powder which cannot be crushed;

the classifying wheel is provided with a discharge pipe connected with the downstream cyclone separator and used for outputting qualified fine powder.

In one embodiment disclosed in the application, a bulk cone is arranged at the top of the crushing zone;

the bulk cargo cone is fixedly connected to the middle part of the top end of the isolation pipe through a supporting rib.

In one embodiment disclosed in the application, an alloy ring groove with shearing teeth is arranged on the inner side wall of the isolation pipe of the bottom material movement area of the crushing area.

In one embodiment disclosed herein, the shearing teeth are uniformly distributed about the circumference of the axis of the isolation tube.

In one embodiment disclosed in the application, a Laval nozzle is arranged at the inner end of the air inlet pipe;

compressed gas from an air compressor enters the air inlet pipe and then is accelerated to be the supersonic air flow through the Laval nozzle.

In one embodiment disclosed in the application, the internal runner of the laval nozzle is formed by connecting a plurality of different annular curved surfaces;

the internal flow passage is divided into four sections in turn along the direction of the air flow: a stabilizing section, a tapering section, a compressing throat section and an expanding section;

the annular curved surface buses corresponding to the tapered section, the compression throat section and the expansion section are all involute.

In one embodiment disclosed in the application, the shearing teeth and the bulk cone are made of hard alloy;

the Laval nozzle is made of tungsten-cobalt alloy in a powder metallurgy mode.

In one embodiment disclosed herein, the air inlet pipe comprises an outer pipe with a flange and a ceramic lining conduit inlaid inside the outer pipe;

the Laval nozzle is internally arranged at one end of the ceramic lining conduit far away from the flange and is pressed by a lock nut;

and the middle part of the lock nut is provided with a hole, and the lock nut is in threaded connection with the outer tube.

In one embodiment disclosed in the application, the air inlet pipe is uniformly distributed with four air inlet pipes around the circumference of the axis of the isolation pipe;

correspondingly, the number of the Laval nozzles is four.

Compared with the prior art, the invention has the beneficial effects that:

1. the isolation tube that sets up will smash the inside and outside crushing district and return channel of cavity internal middle part for the coarse powder decline of material crushing and macroparticle returns and is gone on in two regions of independent separation, has reduced each other the air current interference and arouse the unstability of air current, can form more single stable air current in local region, is favorable to controlling adverse factors such as turbulent flow, turbulent flow that appear in crushing in-process, conveniently optimizes the amount of wind and the power of calculating entire system.

2. The bulk cone arranged at the top of the crushing area and applied to the front end of the classifying wheel forcedly disperses and shunts the mixed powder and the airflow, so that the agglomeration of large particles and fine particles can be reduced, the classification efficiency is improved, the excessive crushing of materials is reduced, the improvement of the granularity quality and the saving of the overall energy loss after the crushing of the materials are facilitated, the local abrasion of the classifying wheel can be reduced, and the service life of the classifying wheel is prolonged.

3. The material to be crushed is crushed by the supersonic airflow and is mechanically and physically crushed through the shearing teeth arranged at the bottom of the crushing zone, so that the energy of the airflow can be more efficiently converted into the material crushing, the crushing effect of unit energy is enhanced, and the energy utilization rate is improved.

4. Through the improved Laval nozzle arranged at the inner end of the air inlet pipe, the compressed air can be accelerated to supersonic air flow when passing through the inner flow channel of the special profile of the air inlet pipe, further, the larger air flow speed is provided for crushing the whole material, and the material is endowed with larger kinetic energy, and the air inlet pipe is particularly helpful for crushing some superhard materials.

5. The wear resistance can be enhanced through the ceramic lining conduit inlaid in the outer tube, and meanwhile, the outer tube made of metal is isolated, so that metal impurities brought by scouring of compressed gas on the metal surface can be reduced, and the pure quality of crushed materials is effectively ensured; the internal and detachable installation form of the laval nozzle is adopted, so that the installation and replacement of the laval nozzle are required to be carried out in a crushing area, the length of the laval nozzle is shortened, and the laval nozzle can be independently replaced under the condition that the later-stage laval nozzle is worn, and the structural form and the installation alignment angle of the laval nozzle are not changed.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of the structure of the present invention;

FIG. 2 is a schematic view of the structure of the pulverizing zone and return channel;

FIG. 3 is a schematic view of the cross-sectional structure of A-A of FIG. 2;

fig. 4 is a schematic structural view of an intake pipe;

fig. 5 is a schematic structural view of a laval nozzle.

Detailed Description

Hereinafter, only certain exemplary embodiments are briefly described. As will be recognized by those of skill in the pertinent art, the described embodiments may be modified in various different ways without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. In order to simplify the present disclosure, components and arrangements of specific examples are described below. They are, of course, merely examples and are not intended to limit the invention.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Referring to fig. 1 to 5, the present invention provides a jet mill comprising:

a pulverizing chamber 100;

a classification wheel 200 installed at the inner upper portion of the pulverizing chamber 100; a kind of electronic device with high-pressure air-conditioning system

The motor 300 is arranged on the outer side wall of the crushing cavity 100 and is in transmission connection with the classifying wheel 200;

wherein, the vertical isolation tube 110 is fixedly arranged at the middle part in the crushing cavity 100 to divide the region into an inner crushing region, an outer crushing region and a return channel; the pulverizing zone may be introduced with a supersonic gas flow to pulverize the material entering the interior thereof into coarse powder and fine powder, the coarse powder entering the bottom of the pulverizing zone via a return channel downward at the classifying wheel 200 to participate in the pulverization again, and the fine powder exiting the pulverizing chamber 100 via the classifying wheel 200.

Specifically, the crushing cavity 100 is provided with an air inlet pipe 120 and a chute 130 which pass through the outer side wall of the crushing cavity in a sealing way, the inner end of the air inlet pipe 120 is communicated with the crushing area, and the outer end of the air inlet pipe is communicated with an external air compressor (not shown in the figure) through a pipeline; the chute 130 is positioned above the air inlet pipe 120, the inner end of the chute is connected with the isolation pipe 110 in a penetrating way in an inclined downward way, and the outer end of the chute is connected with the material hopper 140 in a vertical upward way; the crushing cavity 100 is provided at the inner lower portion thereof with a discharge port 150 for outputting coarse powder which cannot be crushed; the classifying wheel 200 is provided with a discharge pipe 210 connected to a downstream cyclone (not shown) for outputting acceptable fine powder.

In operation, the material to be crushed enters the crushing zone from the hopper 140 through the chute 130, compressed gas generated by the air compressor is accelerated by the air inlet pipe 120 to obtain supersonic airflow to enter the crushing zone so as to endow the material with extremely large kinetic energy, the material is crushed into mixed powder of coarse powder and fine powder by collision and high-speed catch-up movement under the drive of the supersonic airflow and friction shearing with the inner wall of the isolation pipe 110, the mixed powder moves upwards to reach the classifying wheel 200 under the suction effect of the induced draft fan (positioned at the downstream of the cyclone separator and not shown in the figure) connected in series at the tail end of the jet mill, the ascending mixed powder is discharged out of the crushing cavity 100 through blade gaps between the classifying wheels 200 under the drive of the motor 300, and coarse powder of larger particles falls down under the action of centrifugal force generated after colliding with the high-speed rotating blades and enters the crushing zone again through the return channel so as to be crushed until all the materials which can be crushed are qualified and cannot be crushed through screening of the classifying wheel 200, and the coarse powder (dropping into the large particles) is discharged into the crushing cavity 100 through the discharging port 150. That is, the provided isolation tube 110 divides the inner middle part of the crushing cavity 100 into the inner crushing area, the outer crushing area and the return channel, so that the material crushing and the coarse powder descending and returning of large particles are performed in two areas which are separated independently, the instability of air flow caused by the air flow interference between the materials is reduced, more single stable air flow can be formed in the local area, the control of adverse factors such as turbulence and turbulence in the crushing process is facilitated, and the air quantity and power of the whole system are conveniently optimized and calculated.

The top of smashing district is equipped with bulk cargo awl 160, and bulk cargo awl 160 is fixed connection in isolation tube 110 top middle part by supporting rib 161. The bulk cone 160 has two main functions: firstly, the ascending mixed powder airflow is forcedly dispersed to form oblique flow so as to further disperse the large and small particles in the mixed powder, and partial small particles are prevented from being adsorbed and adhered on the large particles or a plurality of small particles are clustered together, so that the difficulty brought by the adsorption and agglomeration to material classification is reduced; by the forced dispersion of the bulk cone 160, the defects of the adsorption and agglomeration can be reduced, so that the excessive crushing of materials is reduced, and the classification efficiency is improved. Secondly, local erosion of the classifier wheel 200 directly by the rising air flow and local wear of the classifier wheel 200 are avoided, so that the dispersed air flow is distributed through the classifier wheel 200 in a more uniform manner. The addition of the bulk cone 160 allows for a more uniform classification, more spread out the size particles, and increased particle size sorting effect. That is, the bulk cone 160 disposed at the top of the crushing area and applied to the front end of the classifying wheel 200 forcibly disperses and shunts the mixed powder and the air flow, so that the agglomeration of large particles and fine particles can be reduced, the classifying efficiency is improved, the excessive crushing of the materials is reduced, the improvement of the granularity quality and the saving of the overall energy loss after the crushing of the materials are facilitated, the local abrasion of the classifying wheel 200 can be reduced, and the service life of the classifying wheel is prolonged.

An alloy ring groove 111 with shearing teeth 112 is arranged on the inner side wall of the isolation tube 110 in the bottom material movement area of the crushing area. Under the drive of supersonic airflow, the material to be crushed is flushed on the shearing teeth 112 of the alloy ring groove 111, and the shearing teeth 112 mechanically and physically cut and collide with the material; the shearing teeth 112 greatly enhance the shearing force of the alloy ring groove 111 on the material, and are beneficial to crushing the material. That is, the material to be crushed is crushed by the supersonic airflow and is mechanically and physically crushed through the shearing teeth 112 arranged at the bottom of the crushing zone, so that the energy of the airflow can be more efficiently converted into the material crushing, the crushing effect of unit energy is enhanced, and the energy utilization rate is improved.

In this embodiment, the shearing teeth 112 are uniformly distributed about the circumference of the axis of the spacer tube 110.

To enhance wear resistance to extend its useful life, both the shearing teeth 112 and the bulk cone 160 are made of cemented carbide.

The inner end of the air inlet pipe 120 is provided with a modified Laval nozzle 180, and compressed air from an air compressor enters the air inlet pipe 120 and is accelerated to the supersonic air flow through the Laval nozzle 180.

Referring to fig. 5, the internal flow path of the laval nozzle 180 is formed by connecting a plurality of different special annular curved surfaces, and is divided into four sections in sequence along the air flow direction: the stabilizing section 181, the gradually-reduced section 182, the compressed throat section 183 and the expanded section 184, wherein annular curved surface generatrix (namely profile curve) corresponding to the gradually-reduced section 182, the compressed throat section 183 and the expanded section 184 are all involute, and each section has important significance. The main difference between the laval nozzle 180 and the traditional laval nozzle is that the profile curve corresponding to the internal flow passage is formed by combining a plurality of sections of involute, and the profile curve is not formed by traditional arc lines or straight lines, so that the processing and manufacturing are difficult to complete in a traditional mechanical processing mode, and therefore, a special die is required to be designed, and tungsten-cobalt alloy is adopted to be manufactured in a powder metallurgy mode.

The specific formation process of the supersonic airflow is as follows:

after the compressed gas with the pressure of 0.3-1.6 MPa is generated by the air compressor and enters the air inlet pipe 120, the compressed gas reaches the tapered section 182 in a laminar flow manner through the stabilizing section 181 of the Laval nozzle 180, so that the compressed gas is compressed sharply, reaches the maximum value in the compression throat section 183 and exceeds the critical pressure, is subjected to explosion emission in the expansion section 184, is continuously propelled in an acceleration manner, and finally is accelerated to the supersonic speed of Mach 3.5-5, the supersonic speed air flow drives the material particles entering the crushing area to move at a high speed, and the redundant pressure is further expanded in the crushing area, so that a high turbulence state is formed. That is, by the improved Laval nozzle 180 mounted at the inner end of the inlet pipe 120, the compressed gas can be accelerated to supersonic flow through the inner flow channel of its special profile, further providing greater flow velocity for the comminution of the whole material, giving the material greater kinetic energy, and particularly providing great assistance for comminuting some superhard material.

Referring to fig. 4, the air inlet pipe 120 includes an outer pipe 121 with a flange and a ceramic lining conduit 122 inlaid inside the outer pipe 121; the Laval nozzle 180 is internally arranged at one end of the ceramic lining conduit 122 far away from the flange and is pressed by a lock nut 123; the lock nut 123 has a hole in the middle and is screwed to the outer tube 121. The compressed air passes through the ceramic lining conduit 122 and the laval nozzle 180 inside the air inlet pipe 120 in sequence and enters the crushing area. That is, the ceramic lining conduit 122 inlaid in the outer tube 121 can enhance the wear resistance, and isolate the outer tube 121 made of metal, so that the metal impurities brought by the scouring of the compressed gas to the metal surface can be reduced, and the pure quality of the crushed materials can be effectively ensured; the internal and detachable installation form of the laval nozzle 180 is adopted, so that the installation and replacement of the laval nozzle 180 need to be carried out in a crushing area, the length of the laval nozzle 180 is shortened, and the laval nozzle 180 can be independently replaced without changing the structural form and the installation alignment angle under the condition that the later-stage laval nozzle 180 is worn.

In the present embodiment, the air inlet pipes 120 are uniformly distributed around the circumference of the axis of the isolation pipe 110 (see fig. 3 for details); correspondingly, there are four laval nozzles 180. The four laval nozzles 180 are arranged with their air jets centered with respect to each other, thereby forming a spray plane.

Referring to fig. 1, an observation window 170 and a pressure gauge 190 are further disposed on an outer sidewall of the crushing cavity 100 corresponding to the isolation tube 110, the observation window 170 is disposed opposite to the hopper 140, and is used for checking a descending condition of coarse powder (material) in the return channel, and the pressure gauge 190 is located above the observation window 170 and is used for monitoring an internal pressure of the crushing cavity 100.

The above embodiments are only preferred embodiments of the present invention, and are not limiting to the technical solutions of the present invention, and any technical solution that can be implemented on the basis of the above embodiments without inventive effort should be considered as falling within the scope of protection of the patent claims of the present invention.

Claims (10)

1. A jet mill, comprising:

crushing the cavity;

the classifying wheel is arranged at the inner upper part of the crushing cavity; a kind of electronic device with high-pressure air-conditioning system

The motor is arranged on the outer side wall of the crushing cavity and is in transmission connection with the classifying wheel;

wherein, the middle part in the crushing cavity is fixedly provided with a vertical isolation pipe so as to divide the area into an inner crushing area, an outer crushing area and a return channel; the comminution zone may be introduced with a supersonic gas flow to comminute the material entering the interior thereof into coarse powder and fine powder, the coarse powder entering the bottom of the comminution zone via the return channel downwardly at the classifying wheel to participate in comminution again, the fine powder exiting the comminution chamber via the classifying wheel.

2. The jet mill according to claim 1, wherein:

the crushing cavity is provided with an air inlet pipe and a chute which penetrate through the outer side wall of the crushing cavity in a sealing way, the inner end of the air inlet pipe is communicated with the crushing area, and the outer end of the air inlet pipe is communicated with an external air compressor through a pipeline;

the chute is positioned above the air inlet pipe, the inner end of the chute is connected with the isolation pipe in a penetrating way in an inclined downward way, and the outer end of the chute is vertically connected with a material hopper;

the inner lower part of the crushing cavity is provided with a discharge hole for outputting coarse powder which cannot be crushed;

the classifying wheel is provided with a discharge pipe connected with the downstream cyclone separator and used for outputting qualified fine powder.

3. The jet mill according to claim 2, wherein:

the top of the crushing zone is provided with a bulk cone;

the bulk cargo cone is fixedly connected to the middle part of the top end of the isolation pipe through a supporting rib.

4. A jet mill according to claim 3, wherein alloy ring grooves with shearing teeth are mounted on the inner side wall of the isolation tube in the bottom material movement area of the crushing zone.

5. The jet mill of claim 4 wherein the shearing teeth are uniformly distributed about the circumference of the axis of the isolation tube.

6. The jet mill according to claim 4 or 5, characterized in that:

a Laval nozzle is arranged at the inner end of the air inlet pipe;

compressed gas from an air compressor enters the air inlet pipe and then is accelerated to be the supersonic air flow through the Laval nozzle.

7. The jet mill as claimed in claim 6, wherein:

the internal flow passage of the Laval nozzle is formed by connecting a plurality of different annular curved surfaces;

the internal flow passage is divided into four sections in turn along the direction of the air flow: a stabilizing section, a tapering section, a compressing throat section and an expanding section;

the annular curved surface buses corresponding to the tapered section, the compression throat section and the expansion section are all involute.

8. The jet mill as claimed in claim 7, wherein:

the shearing teeth and the bulk cone are made of hard alloy;

the Laval nozzle is made of tungsten-cobalt alloy in a powder metallurgy mode.

9. The jet mill according to claim 7 or 8, wherein:

the air inlet pipe comprises an outer pipe with a flange and a ceramic lining conduit inlaid in the outer pipe;

the Laval nozzle is internally arranged at one end of the ceramic lining conduit far away from the flange and is pressed by a lock nut;

and the middle part of the lock nut is provided with a hole, and the lock nut is in threaded connection with the outer tube.

10. The jet mill as claimed in claim 9, wherein:

the air inlet pipe is uniformly distributed with four air inlets around the circumference of the axis of the isolation pipe;

correspondingly, the number of the Laval nozzles is four.