The classifier which form closed-circuit work with grinding mill in the factory need the machine which can lift grit, so this kind of classifier called mechanical classifier, actually the classifying process conduct still depending on the different sedimentation rate of the particle. Mechanical classifier sometimes wash the ore which contain the clay or desliming and dewatering for the ore except pre-classification and classification check as the auxiliary equipment of grinding. According to different lifting way for the grit, mechanical classifier can divided into spiral classifier, rake classifier and bowl classifier etc. The spiral classifier is simple structure, easy operation, big inclination of classify tank, so that it can be connected with the grinding mill by gravity flow easily, that is why it is widespread in application. Other kinds of classifiers in our country are still in use, but has stopped manufacturing.

The shape of spiral classifier is a rectangular tank, the tank inclination is 12°to 18.5°, and the bottom of tank seems a semicircle. In the tank equipped with 1 or 2 long axis, and along the axis, continuously installed with spiral blade. The drive mechanism drives the spiral axis start rotation. Slurry is fed from the side of tank, it become settlement classified layer at the bottom. Coarse particles sink to the bottom and then spiral blade transport it to the discharge at the top, at same time it will be dewatered during this transportation, unsettled fine particles carried by slurry flow and discharges from the overflow weir. Classifying process is basically same with the desliming cone, on the classifier tank there is a lifting mechanism which can adjust the distance of blade and bottom , and the axis can be lifted up when close down to avoid that settled sand bury the blade.

According to liquid level the spiral classifier can be divided into high weir type and submersion (or sinking ) type, The overflow weir of high weir classifier is higher than the center of the spiral axis at lower end, but lower than the upper edge of the spiral blade. The length of liquid level is short, so its surface can directly gets the stirring effect by the spiral blade, therefore it suitable for coarse particle classification, usually the classified particle size is over 0.15mm. The spiral blade of submersion classifier at lower end completely submerged under the liquid level, the classifying area is big and smooth, suitable for fine particle classification, which is less 0.15mm, and with higher overflow productivity. In addition, there is a low weir spiral classifier, its liquid level lower than the spiral bearing at the lower end, the liquid level is very small, but the stirring effect is strong, mainly used for washing gravel ore containing mud.

The inclination with horizon of FLG300 500,700,1000 classifier are 14 ° - 18 ° 25 ", FLG1200, 2FLG1200, FLG1500, 2FLG1500, FLG1200 2FLG1200 are 12 ° - 16 °. The motor drives the spiral axis to rotating through the reducer, the slurry from ball mill enter into the spiral classifier from one side at front-end, at the front-end of spiral classifier forms a deep slurry pool, inside the spiral blade keep rotating let the slurry gets enough agitating, that causes the fine particles flow on the top of water, and cross the overflow weir and go into the discharge chute, but the coarse particles sink to the bottom of tank, and lifted up by rotary spiral blade go to the end of spiral classifier, from discharge chute return to the ball mill for re-grinding.

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