Ball milling-the method of producing manganese metal powder

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The technological production process of manganese metal powder

Ball mill is the oldest grinding miller that is widely used in the preparation of chemical materials, ceramic raw materials, coating and other superfine powders. Ball mill has big crushing ratio, simple structure and strong mechanical reliability. Its wearing parts are easy to check and replace. Besides, it has mature technology and can be standardized and operated under different conditions, for example, it can be used in the crushing and drying together with crushing and mixing at the same time. It can be both used in the dry ground and wet grinding. However, it has low crushing efficiency and high energy consumption of specific yield. It cannot be operated continuously. Moreover, its grinding medium is easy to wear and will cause wide noise when operated.

In the manganese powder production process with ball milling, the grinding medium and material will be divorced from the cylinder wall and fall along the parabolic path by the action of gravity before being promoted to a certain height under the role of centrifugal force and friction force, after this process, they will be again promoted to a certain height and fall along the parabolic path. With the repetition of the above process, the materials between the grinding medium will be crushed by its impact effect; meanwhile, the particles will be attrited by grinding, friction, shear and other impact with the rolling and sliding of grinding medium.

The operation process

a. Coarse crushing

The flake metal manganese is easy to heap up and has poor mobility. In the ball mill process, it is easy to grind along the manganese side and has low crushing efficiency; especially for those manganese flakes with long time electro-deposition and large thickness, this phenomenon is extremely outstanding. Therefore, it requires coarse crushing for the manganese flakes before being sent to the ball mill. Coarse crushing is being conducted in the roll crushing mill. As there will be frequent spark in the process of asahi process drawing crushing the manganese flakes, inert gas is needed so as to protect us from being hurt. Dust collecting facilities should be also set as there will be a little dust in the coarse crushing process.

b. Ball milling

Ball mill is main equipment in the preparation of manganese powder with ball-milling method. As the high hardness of metal manganese and the strict requirements of manganese powder products on the iron content, corundum is suitable for the production of ball mill lining and ball mill material.

The working parameter of ball mill, such as the ball capacity, charge amount and mill speed are selected according to the conventional ball mill. When adding the grinding balls, coarse broken material and sieve materials into the ball mill, the air in it should be pumped out after the completion of charging so as to avoid the blast caused by high concentrations of metal manganese dust. After this process, filling with the nitrogen, sealing, turning the ball mill and starting timing.

As the superfine manganese metal powder is easy to oxidize, the amount of -0.05mm manganese powder should be controlled less than 20 percents and not more than 25 percents at most. So the milling time should be not too long. After about 3 hours of milling, the discharging and screening process can be started.

Fire will be easily occurred in the discharging operation process, in which the dust concentration is high, the powder temperature will rise due to the ball mill temperature, there will be spark caused by the collision between ball and ball, ball and mill cylinder together with ball and picking device and in turn cause the blast. Therefore, the discharging should be conducted under the protection of inert gas and use the dumping device with special design.

In the production of manganese powder with ball-milling method, its advantages are reflected in no overflow dust and the controllability of blast; its disadvantages are reflected in the batch operation and low production efficiency.

c. Screening

Screening is crucial in producing qualified fine powder product. In the grinding process, the particle size of materials will be dropped off with the extension of time; meanwhile, as the specific area and specific surface energy of the material are increasing, the trend of mutual reunion in the subparticle will also be built up. In order to improve reduction efficiency and reduce energy consumption, except for improving the mill and adding grinding aid in the crushing process, timely screening qualified fine grained product and avoid the “overgrinding” of qualified fine grained material play important roles. Therefore, high efficient grading equipment should be set in the super fine crushing technology. High frequency vibrating screen is suitable equipment for the screening of metal manganese powder, in which portion dust will be occurred, so the dust prevention and dust extraction are needed.

d. Packaging

As the electrolytic metal manganese powder is active and as new manganese powder is easy to oxidize in the air, packaging is important in ensuring the quality of manganese powder. Usually there are two-layer of packaging, in which the inlayer is plastic film bag or aluminum foil bag with vacuum supply, while the external packing is metal bucket. The packing specification varies from 50,100,250,500kg and so on.