Application status and prospect of jet mill
Jet mill, also known as jet mill, refers to the equipment that uses the energy of high-speed airflow (300～500m/s) or superheated steam (300～400℃) to make particles collide, collide and rub each other to achieve ultrafine grinding. Compared with other types of shredders, it has the following advantages:
① Good product granularity. The average particle size (d50) of the material is generally below 5μm, and the particle size distribution is narrow. ②The product has high purity, especially suitable for the grinding of materials that are not allowed to be contaminated, such as medicines. ③It can crush low melting point and heat sensitive materials. ④The product has high particle activity. ⑤The production process is continuous and the production capacity is large.
Jet mills also have some shortcomings, such as: high equipment manufacturing costs, high energy consumption, and large processing costs; single machine processing capacity is poor, not suitable for large-scale production; product particle size is difficult to reach sub-micron level, when it is below 10μm The output has dropped drastically, and the processing cost has risen sharply.
Ultrafine powder technology is an emerging technology. According to the depth of powder processing technology and the changes in powder physical and chemical properties and application performance, the powder with a particle size of less than 10μm is usually called ultrafine powder.
The development of modern engineering technology requires many raw materials and products in powder form. For example, in the military, aerospace, aerospace, and electronic fields, the use of ultrafine powder can be used to make stealth materials; in the chemical industry, the ultrafine catalyst can increase the rate of petroleum cracking by 1 to 5 times; after the ultrafine grinding of drugs, the The surface energy is greatly increased, which improves the effectiveness of the medicine and is beneficial to the absorption of the human body.
Ultra-fine grinding equipment can be divided into different grinding methods: mechanical impact mill, vibration mill, jet mill, stirring mill, etc.
Application status of several ultra-fine jet milling equipment at present
(1) Collision jet mill
This kind of jet milling equipment is also often referred to as a counter-jet jet mill. It uses two high-speed airflows to entrain the particles to be crushed to collide with each other to achieve the grinding effect. It has a high energy utilization rate. It can effectively prevent the jet mill from being damaged due to high-speed impact and can solve the problem of being contaminated by grinding particles.
The advantages of this equipment are mainly reflected in: fast crushing speed, strong impact force, low energy consumption and so on.
(2) Flat jet mill
An early-developed jet mill is a device that uses the collision, shear and friction between particles and the inner wall of the crushing chamber to achieve grinding. Its main component is a disc crushing chamber, several (6-24) high-pressure working fluid nozzles, jet feeders, finished product traps, etc. arranged on the spray ring at a certain angle to the plane of the crushing chamber.
This model is simple in structure, easy to operate, and has a self-classification function, which is especially suitable for the crushing of brittle and soft materials. The outstanding shortcoming is that the grinding cavity is severely worn, which causes certain pollution to the product, and the limit particle size is relatively high.
(3) Fluidized bed jet mill
The working principle of this kind of pulverizing equipment is: adding materials to the pulverizing equipment, using two-dimensional setting of multiple nozzles to spray the impact energy, and the suspension and tumbling collision and friction generated after the expansion of the airflow to achieve the pulverizing effect. The upper airflow near the junction is graded by the grading device at the top under the influence of the negative pressure airflow, and the fine powder is discharged. The coarse powder will be affected by gravity and return to the crushing area to be crushed again.
The advantages of this equipment are mainly reflected in the good dispersion effect, the product size can be adjusted by the classifier, and the wear and energy consumption are relatively small, which is more suitable for large-scale industrial production.
(4) Impact ring jet mill
Replacing the fixed impact component with a rotatable impact ring can avoid the local wear caused by high-speed airflow or gas-solid flow in the previous two types of jet mills under the influence of continuous impact on a fixed position, prompting all positions on the overall ring surface Acting as the impacted surface in turn, the overall annular surface will be subjected to relatively close impact wear, which can promote the life of the impact ring to be extended as much as possible.
The main advantage of this equipment is that the direction of movement of the impact ring is opposite to the jet flow, so the relative speed can be increased, which helps to enhance the grinding effect.
(5) Circulating jet mill
JOM circulating jet mill is mainly composed of O-shaped circulating tube, high-pressure working fluid nozzle, venturi tube and feeding ejector. After the material enters the circulating pipe, the material is ground through friction and collision between the particles and the pipe wall.
Although this model is small in size and large in production capacity, it has serious wear on the pipe wall and is not suitable for grinding materials with high hardness and high purity. It usually requires the use of super hard and high wear-resistant materials (corundum, super hard alloy, etc.) ) As a lining.
The development trend of ultra-fine jet milling equipment in the future
At present, the research and development and manufacturing of ultra-fine jet milling equipment have been greatly developed, and have made important contributions to the powder industry, but there are few large-scale, specialized, high-purity, ultra-fine products that can be produced.
(1) Strengthen basic theoretical research and optimize process flow
Strengthen basic theoretical research to guide independent innovation and development of equipment, and on the basis of existing equipment, vigorously develop research on process optimization and optimize process flow. For mass-produced powders, special models can be developed in a targeted manner.
(2) Increase the output of a single machine and reduce the energy consumption per unit of product
With the increasing market demand for ultrafine powder products, especially the increase in large-scale users and the increasing requirements for product quality stability, the market demand for large-scale equipment continues to rise. Large-scale equipment can more effectively adapt to the development trend of gradual expansion of ultra-fine powder processing, and it also has many advantages such as low energy consumption per unit product, excellent product quality stability, and convenient management.