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Several crushing techniques for large particles

Several crushing techniques for large particles

  • June 18,2020.

Several crushing techniques for large particles


Foreword

In the preparation of ultrafine powders at present, the physical crushing method has lower cost, larger output, and higher efficiency than the chemical synthesis method. It is no exaggeration to say that the physical crushing method "pulverize" large particles of material into ultrafine powder  in a simpler and rougher way. Therefore, the main method to prepare ultrafine powder is physical crushing.


=== Brief introduction of ultrafine powders ===


Ultra fine powders technology is a new technology developed in the mid 1970s. Due to super fine particle size and narrow particle size distribution,  ultra fine powders has large specific surface area, high surface activity, fast chemical reaction rate, fast dissolution rate, high strength of sintered body and unique electrical, magnetic, optical and other properties, therefore, it is widely used in material, chemical industry, biopharmaceuticals, optical, electromagnetic, thermal energy, and other fields.



=== Preparation method of ultra-fine powders ===


There are many ways to prepare ultrafine powder, but there are mainly two ways from the principle of preparation: one is chemical synthesis, the other is physical crushing.


Chemical synthesis method is, through chemical reaction or phase conversion, the ions, atoms and molecules are formed through crystal nucleus and the crystals grow up to prepare powder. Due to the complex production process, high cost and low output, chemical synthesis method is not widely used in the preparation of ultrafine powder.


The physical crushing method is to crush material through the action of mechanical force. Compared with chemical synthesis, physical crushing method has the advantages of low cost, large output and simple and rough method. Therefore, the main method to prepare ultrafine powder is physical crushing.


From the perspective of equipment, different crushing methods can be explained more clearly, and the selection of equipment under different requirements can also play a certain reference role. Now we are introducing some of the most commonly used physical crushing equipment as below.


1 - Jet Mill

The Jet Mill takes the supersonic and high turbulent flow produced by the compressed air or superheated steam through the nozzle as the carrier of the particles. Impact extrusion, friction and shear action occur between the particles or between the particles and the fixed plate, so as to achieve the purpose of crushing.


Advantages: Compared with the ordinary mechanical impact ultramicro crusher, the Jet Mill can crush the product very finely, the particle size distribution range is narrower, which means the particle size is more uniform. Because the gas expands at the nozzle and can cool down, and there is no associated heat in the crushing process, so the crushing temperature rise is very low. This characteristic is particularly important for ultrafine grinding of low melting point and heat sensitive materials.


Disadvantages: the existence of internal blind areas will cause the phenomenon of unable to smash. It has certain requirement for upper limit of feed particle size, and it is difficult to crush the material with high density, fiber and flake.

PQW Fluidised Bed Opposed Jet Mill

PQW Fluidised Bed Opposed Jet Mill (Photo is from PUHLER)



2 - Planetary Bead Mill

Under the help of a special device, the planetary bead mill uses motor to drive the transmission shaft to rotate,  the fixed gear drives the transmission gear shaft to rotate, so that the bead grinding chamber produces both revolution and rotation to drive the grinding media in the grinding chamber to produce strong impact, friction and other effects, so that the materials between the grinding media is being crushed and superfined. The planetary bead mill can grind and mix products with different particle sizes and different materials in two ways: dry and wet. Minimum particle size of grinding products can be 0.1μm, widely used in building materials, geology, ceramics, minerals, metallurgy, electronics, chemical industry, light industry, medicine, beauty, environmental protection and other industries.

Planetary Bead Mill

(Planetary Bead Mill,Photo is from MITR)



3 - Agitation Mill, Sand Mill/Bead Mill

Agitation Mill and Sand Mill are similar in working principle, and are developed on the basis of ball mill. Compared with the ordinary ball mill, high speed, high medium filling rate and small medium sizes are used to obtain the extremely high power density, greatly shortens the grinding time of fine materials, it is the highest energy utilization superfine mill, very promising devices. Agitation Mill greatly improves the efficiency when processing materials less than 20μm, the final product's average particle size can be up to a few microns. High power mill can be used for products with maximum particle size below micron, it has been successfully used in pigment, ceramics, paper making, coatings and chemical products.

Working principle of Sand Mill/Bead Mill

Working principle of Sand Mill/Bead Mill(Photo is from internet)



4 - Vibration Mill

Vibration mill uses spring to support the body of the mill, the main shaft with eccentric block makes it vibrate. The material is crushed by the vibration of medium and material during operation. It is characterized by high medium filling rate and high action times per unit time (the impact times are 4 ~ 5 times of the ball mill), therefore, its efficiency is 10 ~ 20 times higher than ordinary ball mill and energy consumption is several times lower. By adjusting vibration amplitude, vibration frequency and medium type, the average particle size of vibration mill products can reach 2 to 3μm or less, and submicron products can be easily obtained for brittle materials.


In recent years, through practice, vibration mill gains more and more attention, the reason is that the particle size of some material products can reach sub-micron level, and has a strong mechanical and chemical effect, and simple structure, low energy consumption, high grinding efficiency, easy for industrial scale production.。

Working principle of Vibration Mill

Working principle of Vibration Mill(Photo is from internet)



5 - Press Roller Mill, Ring Roller Mill

Press Roller Mill and Ring Roller Mill use the material layer extrusion crushing technology to achieve the ultra-fine crushing, that is, materials under high pressure to produce stress concentration and cause cracks and expansion, and then produce many micro cracks, forming surface cracks and finally achieve the material crushing. This avoids the broken energy waste generated by the mechanical crushing, and reduce energy consumption greatly. But at the same time, the amount of wear and tear of the grinding rollers and grinding rings is very large, which is not suitable for some minerals which have the requirement of iron content after crushing. And also not suitable for ultrafine crushing of materials with high viscosity.

Working principle of Press Roller Mill

Working principle of Press Roller Mill(Photo is form internet)



6 - Colloid Mill

The working principle of colloid mill is to make relative movement between a pair of conical rotating teeth and fixed teeth. The material is crushed, emulsified, homogenized and dispersed by shear force, friction force, centrifugal force and high-frequency vibration when passing through the gap between fixed and rotating teeth. In order to reduce the large amount of heat generated by friction, it is generally equipped with a cooling system.

Working principle of Colloid Mill

Working principle of Colloid Mill(Photo is from internet)

Colloid mill is a new type of wet ultrafine particle processing equipment, suitable for all kinds of emulsification, dispersion, crushing, and grinding. Widely used in food (such as jam, fruit juice, protein, dairy products, beverages, etc.), pharmaceuticals (such as pulping, nutrient solution, proprietary Chinese medicine, paste agent, etc.), daily chemical industry (such as toothpaste, cosmetics, detergents, etc.), chemical industry (such as pigment, coating, lubricant, catalyst,  etc.), emulsified asphalt, coal flotation agent, ceramic glaze, explosives and other industries.



7 - High-speed Mechanical Impact Mill

Mechanical impact mill has high crushing efficiency, large crushing ratio, simple structure, stable operation, suitable for crushing medium and hard materials. The mill not only has two crushing effect of impact and friction, but also has airflow crushing effect. Due to the high speed operation of the ultra-fine product impact mill, there are problems of wear and heat, therefore, appropriate measures should be taken for the heat-sensitive material crushing.

Working principle of High-speed Mechanical Impact Mill

Working principle of High-speed Mechanical Impact Mill(Photo is from internet)


By cnpowder.com.cn

Author: Shanchuan

© Copyright: 2020 PUHLER (Guangdong)Smart Nano Technology Co.,Ltd. All Rights Reserved.

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