Classification and working principle of jet mill
Jet mill, as one of the ultrafine grinding equipment, is also one of the important equipment in the grinding industry. After the compressed air of the fluidized bed pulverizer is frozen, filtered and dried, it forms a supersonic airflow through the nozzles and is injected into the pulverizing chamber to fluidize the material. The accelerated material merges at the intersection of the jet airflows of several nozzles, resulting in violent The collision, friction and shearing of the particles can achieve ultra-fine grinding of the particles.
The ground material is transported to the impeller classification area by the rising airflow. Under the action of the centrifugal force of the classification wheel and the suction force of the fan, the coarse and fine powder are separated. The airflow enters the cyclone separator, the fine dust is collected by the bag filter, and the purified gas is discharged by the induced draft fan. The flat jet mill has a wide range of applications due to its simple structure and easy manufacturing.
Structure: It is mainly composed of crushing chamber, nozzle opening, discharge opening, air flow outlet, compressed air inlet, classification zone, etc.
Working principle: The compressed air or superheated steam is transformed into high-speed air flow through the nozzle. When the material is sent into the crushing chamber through the feeder, it is sheared by the high-speed air flow. The strong impact and intense friction make the material grind into ultra-fine products. It is widely used in ultrafine grinding of non-metallic minerals and chemical raw materials. The particle limit of the product depends on the solids content in the confluent gas stream. Under the opposite ratio of unit energy consumption, the products produced by jet mill are more refined, particle size distribution is more uniform, activity is also greater, and the dispersion performance is better than the price. Due to the Joule-Thomson cooling effect caused by the adiabatic expansion of the compressed gas during the grinding process, some low-melting or heat-sensitive materials can be used in the grinding process.
The classification of jet mills currently has the following five types in the industry. They can be divided into horizontal disc (flat) jet mills, circulating tube jet mills, target jet mills, counter jet jet mills and fluidized bed jet mills.
The principle of airflow grinding: dry oil-free compressed airflow or too many nozzles, high-speed jet drives the material to move at a high speed, causing the material to collide, rub and compress. The crushed material reaches the classification area with the airflow, and the material that meets the fineness requirements is finally collected by the collector . If the material does not meet the required particle size, return to the crushing chamber, continue grinding until the required fineness is reached, and stop setting. Due to the high velocity gradient near the nozzle, most of the grinding occurs near the nozzle. In the crushing chamber, the collision frequency of particles and particles is much higher than the collision frequency of particles and the device wall. In other words, the main grinding effect of jet mill is the collision or friction between particles.