Calcium carbonate ultrafine powder grinding and classifying technology

The processing of ground calcium carbonate is simply the process of using crushing and grinding equipment to process calcium carbonate minerals into various powders that can meet the requirements of industrial applications. Because different industrial applications have different requirements on the particle size, shape, whiteness and particle size distribution of ground calcium carbonate powder, the processing technology of ground calcium carbonate should also comprehensively consider the process route and equipment selection according to the product positioning. Generally speaking, the design of grinding equipment is based on different principles: impact, extrusion, friction, shear and combination of various forces, etc. Different designs will have different grinding effects and product fineness.

The common processing equipment of ground calcium carbonate produced by large-scale dry process includes Raymond mill, Vertical mill, Ring roller mill and Ball mill. Due to the different crushing principle and discharging method of the equipment, the processed powder has great differences in grain type, particle size distribution and unit energy consumption, so the positioning of the product also has obvious differences.

The ball mill can cooperate with the air classifier to form a closed-circuit circulation system, after the grading of the coarse powder can be returned to the ball mill for re-grinding, and the Raymond mill, vertical mill, vibration mill due to the capacity of the mill is very limited, return difficult, unable to form a closed-circuit circulation system, to return to the treatment of problems.

The ball mill is also a low speed operating equipment, impact and friction energy consumption to minimize.  Therefore, it is not only an ideal choice for grinding high hardness, abrasive mineral raw materials, but also the most economical choice for grinding white filler minerals such as low hardness calcium carbonate.

It can be seen from the particle size distribution map that the particle size distribution of the grinding products of the ball mill is the widest. Through the air classifier, the products with different fineness requirements can be separated. At the same time, the output of the ball mill is large, with scale effect, so it has a strong market adaptability and competitiveness.

The technology of Ball mill & Air classifier

The production line adopts the international popular continuous production process: ball mill and air classifier system. The technological process mainly includes crushing (generally using two-stage crushing), grinding, classifying, packaging, magnetic separation, transportation, lifting, etc. After the ball mill can be parallel or series multiple classifier at the same time to produce more than one size of the product.

Working principle: The raw material is fed into the hollow cylinder through the hollow shaft neck for grinding. The cylinder is equipped with grinding media of various diameters (steel ball, steel bar or gravel, etc.). When the cylinder rotates around the horizontal axis at a certain speed, the medium and raw materials in the cylinder under the action of centrifugal force and friction force, as the cylinder reaches a certain height, when its own gravity is greater than the centrifugal force, it will escape from the cylinder body wall and drop or roll down, smashing the ore due to the impact force. At the same time, the sliding motion of the grinding medium also produces grinding effect on the raw material during the rotation of the mill. The ground material is discharged through a hollow journal.

Features: Wide range adjustment, good grain shape (low abrasion value), stable quality, large scale (the maximum size of a single line is 1250 mesh, about 100,000 tons).

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The technology of Raymond Mill

Raymond mill is the earliest and most widely used grinding equipment in China, with low fineness, suitable for the production of 400 mesh of coarse ordinary powder. A small amount of 500 ~ 1250 mesh products can be obtained through secondary classification. Suitable for large scale production of coarse powder and small scale production of fine powder.

Working principle: Raymond mill rollers works under the action of centrifugal force tightly on the ring rolling, the shovel knife scooping up material to the grinding roller and grinding ring in the middle, the material under the action of ground pressure, broken into powder, and then under the action of fan blow into powder material up through analysis of machine, to fulfill the requirements of fineness of materials through the analysis of machine, can’t meet the requirements of the return to continue to grinding, grinding chamber through the analysis of the material into the cyclone separation of machine to collect. Use industrial press cloth to separate the air exhaust into powder.

Features: Low oil absorption value, low processing cost, low investment. Big Equipment noise, dust pollution is serious.

The technology of Table Roller Mill & Air Classifier

Vertical mill is a typical material layer extrusion crushing equipment, the most fine can reach 1250 mesh, through the second, third classification of the most fine can reach to 3000 mesh, generally suitable for mohs hardness of less than 7 materials.

Working principle: The motor through reducer driven in mill, material from the feed opening fell into a grinding disc, move to the edge of mill under the action of centrifugal force and grinding roller of roller compaction, shredded material from mill edge overflow, at the same time from the nozzle ring (ring) wind speed up stream to efficient separator, which is one with vertical mill meal after separator is returned to the mill wheel, grinding again; The fine powder is ground with the air flow and collected in the dust collecting device of the system, which is the product. Coarse granular materials not taken up by the hot gas flow and accidental entry of metal parts sink from the wind ring, after scraping out by the scraper, through the external circulation of the bucket machine feeding into the grinding again grinding.

Features: Low oil absorption value, low processing cost, large scale, but equipment noise big, high maintenance cost, large investment, domestic technology is not up to standard.

The technology of Ring Roller Mill

As the roller is small and many, the fit clearance with the grinding ring is also small, the most fine grinding can be up to 2500 mesh. Low energy consumption and low fine powder content. Generally suitable for mohs hardness below 5, narrow particle size (low oil absorption value), moderate fineness of materials. But for hard materials, if they are light color (white), the degree of dialogue has a great influence.

Working principle: It adopts the principle of impact, extrusion and grinding to crush the material. There is a large active gap between the grinding ring and pin shaft installed on the grinding ring bracket. When the grinding ring bracket rotates with the spindle, the grinding ring is swung to the grinding ring by centrifugal force, and the inner wall of the grinding ring is pressed and rotates around the pin axis. When the material passes through the gap between the grinding ring and the grinding ring, it is impacted, squeezed and ground by the grinding ring. Under the action of gravity, the crushed material falls into the swing plate and is then thrown into the air flow into the grading chamber for classification. The qualified fine powder is collected through the grading wheel into the rear passage collection system, and the coarse material is thrown into the shunt ring for internal avoidance, and then falls back into the crushing chamber for crushing. The grinding ring is single layer or upper and lower double layer distribution. When the double-layer grinding ring crusher works, the material is crushed again when passing through the gap between the second grinding ring and the grinding ring.

Features: Low oil absorption value, low processing cost, low investment, but large equipment wear, high maintenance rate, poor product stability, small scale.

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