Application of Ultra-fine Grinding Technology in Food Processing
Ultra-fine grinding technology is a new technology developed in the past 20 years. The so-called ultra-fine grinding refers to the use of mechanical or hydrodynamic methods to overcome the internal cohesive force of solids to grind them, thereby grinding the material particles of more than 3 mm to 10-25 microns. A material processing high-tech produced by the development of high-tech. Ultra-fine powder is the final product of ultra-fine grinding. It has special physical and chemical properties that ordinary particles do not have, such as good solubility, dispersibility, adsorption, and chemical reaction activity. Therefore, ultra-fine powders have been widely used in many fields such as food, chemicals, medicine, cosmetics, pesticides, dyes, coatings, electronics and aerospace.
- Technical Features
Fast speed and low temperature grinding: The ultra-fine grinding technology uses supersonic jet grinding, cold slurry grinding and other methods, which is completely different from the previous pure mechanical grinding methods. There will be no local overheating during the grinding process, and it can even be ground at a low temperature. The speed is fast and can be completed in an instant, so the biologically active ingredients of the powder are retained to the greatest extent, so as to facilitate the production of the required high-quality products .
Fine particle size and uniform distribution: Due to the use of supersonic airflow grinding, the distribution of forces acting on the raw materials is quite uniform. The setting of the classification system not only strictly restricts large particles, but also avoids over-grinding, and obtains ultra-fine powder with uniform particle size distribution. At the same time, the specific surface area of the powder is greatly increased, so that the adsorption and solubility are correspondingly increased. .
Save raw materials and improve utilization: After the object is ultra-finely ground, the ultra-fine powder with a near nanometer particle size can generally be directly used in the production of preparations, while the products of conventional grinding still need some intermediate links to meet the requirements of direct use and production , This is likely to cause waste of raw materials. Therefore, this technology is especially suitable for grinding precious and rare raw materials.
Reduce pollution: Ultra-fine grinding is carried out in a closed system, which not only avoids the pollution of the surrounding environment by micro-powder, but also prevents dust in the air from polluting the product. Therefore, by using this technology in food and medical health products, the microbial content and dust can be effectively controlled.
- Grinding method
Grinding medium grinding: Grinding medium grinding is the process of grinding material particles by means of the impact generated by the moving grinding medium (grinding medium) and the non-impact bending, squeezing and shearing forces. The grinding media pulverization process is mainly grinding and friction, namely extrusion and shearing. Its effect depends on the size, shape, ratio, movement mode, filling rate of the material, and the mechanical characteristics of the grinding of the material. There are three types of typical media grinding equipment: ball mill, stirring mill and vibration mill.
The ball mill is a traditional equipment used for ultra-fine grinding, and the product size can reach 20-40 microns. When the particle size of the product is required to be below 20 microns, the efficiency is low, the energy consumption is large, and the processing time is long. Stirring mill is developed on the basis of ball mill, mainly composed of grinding container, agitator, disperser, separator and feed pump. When working, under the action of centrifugal force generated by the high-speed rotation of the disperser, the grinding medium and the particle slurry produce impact shearing, friction and squeezing to grind the particles. The stirring mill can achieve ultra-micronization and homogenization of product particles, and the average particle size of the finished product can reach a few microns at least. Vibration mill is to grind particles by using the effects of impact shear, friction and extrusion produced by high-frequency vibration of the grinding medium. The average particle size of the finished product can reach 2-3 microns or less, and the pulverization efficiency is much higher than that of the ball mill. The processing capacity is more than 10 times that of a ball mill with the same capacity.
Airflow ultra-fine grinding: The jet mill can be used for ultrafine grinding. It uses compressed air or superheated steam, and the supersonic high turbulent airflow generated by the nozzle as the carrier of the particles, and the impact backlog occurs between the particles or between the particles and the fixed plate , Friction and shearing, etc., so as to achieve the purpose of grinding. There are six major types of airflow stainless steel grinders: disc type, circulating tube type, target type, collision type, rotary impact type, and fluidized bed type. Compared with ordinary mechanical ultra-fine stainless steel pulverizer, the airflow stainless steel pulverizer can grind the product very fine (the fineness of the powder can reach 2-40 microns), and the particle size distribution range is narrower, that is, the particle size is more uniform. Because the gas expands at the nozzle to reduce the temperature, there is no accompanying heat during the grinding process, so the grinding temperature rise is very low. This feature is particularly important for ultra-fine grinding of low-melting and heat-sensitive materials. However, the energy consumption of air jet grinding is large, and the energy utilization rate is only about 2%, which is several times higher than other grinding methods.
It is worth pointing out that it is generally believed that the particle size of the product is directly proportional to the feeding speed, that is, the larger the feeding speed, the larger the product particle size. This understanding is not comprehensive. This statement is reasonable when the feeding speed or the particle concentration in the stainless steel pulverizer reaches a certain value. Because the feeding speed increases, the particle concentration in the stainless steel pulverizer also increases, and particle crowding occurs. Even the particles flow like a plunger. Only the particles at the front of the “plunger” have the possibility of effective collision. The particles only collide and rub each other at a low speed, and generate heat. However, this does not mean that the smaller the particle concentration, the smaller the product size, or the higher the grinding efficiency. On the contrary, when the particle concentration is low to a certain level, there will be no chance of collision between the particles and the grinding efficiency will be reduced.