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Spiral Classifier || Operation and Technique (1st)
Mar 31, 2018

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Spiral classifier is mainly used in the production process of metal beneficiation. According to the different sedimentation speed of mineral particles, the ore is classified by particle size. Spiral classifiers can be classified into three types: high weir, low weir, and submerged

Spiral classifier is composed of transmission, spiral (left or right) and sink, lifting device, lower base and feed inlet.

 

The water tank is installed at an angle, and the tilt angle is determined according to the equipment configuration in the process flow. The transmission drives the screw to rotate in the tank. The grinding-fine pulp enters the tank from the side feed inlet and a slurry settlement is formed at the bottom of the tank. Its surface area and volume are determined by the tank inclination angle and overflow weir height. The helix with low speed rotation can play a certain role in stirring. After the slurry is stirred, light and fine particles are suspended on it to form an overflow. Then overflow weir at the end face of the water tank and flowing into the next beneficiation process; the heavy particles sink at the bottom of the tank and form Sand is transported by the screw to the discharge outlet.

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The factors affecting the classifying effect are mainly divided into four aspects: equipment factors, ore property factors, operating condition factors and installation factors.

 

First, equipment aspects

1) Size of grading area

In terms of structural factors of equipment, the size of the classifying area in the tank is a decisive factor influencing the processing capacity and classifying granularity of classifier. Increasing the width of the tank, improving the height of the weir or reducing the inclination can increase the classifying area.

 

2) The level of overflow weir.

The level of the overflow weir of the spiral Classifier affects the sedimentation area size of the ore. During production, we can adjust the height of the overflow weir according to the requirements of grinding fineness. If need finer particles, insert wood to adjust the level of overflow of the classifier by welding with a certain height of angle iron at two sides of classifier. Sometimes the slime is accumulated for a long time and the height of the overflow weir can be naturally increased.

The height (H) of the overflow weir of the high-weir spiral classifier is 1/4-3/8 of the screw diameter D, and is mainly used for the classification of the ore with an overflow particle size of 0.83-0.15 mm. The submerged spiral classifier, H (height) is 3/4-1 of D (Diameter). It is mainly suitable for grading ore with an overflow particle size of 0.15-0.07mm. When the overflow fineness is high, H takes a small value and vice versa takes a large value.

 

3) Spiral speed.

The speed of rotation of the screw affects the degree of agitation of the liquid surface and the ability to transport sand back. The number of revolutions is related to the diameter of the screw.

The speed of the screw should be sufficient to deliver settled coarse particles. The faster speed of the screw shaft of the classifier, the stronger agitation effect on the pulp, and the more coarse particles entrained in the overflow product. In order to obtain rough overflows and handle materials that are faster than major sedimentation, the rotation speed of the spiral can be appropriately increased, but it cannot be too large, otherwise the classification effect will be damaged. For classifiers used in secondary grinding or grinding cycles, the screw speed is slowed down as much as possible. Lower speeds are generally used in spiral classifiers, especially for large spiral classifiers. In order to obtain a rough overflow flow, the speed of 2m diameter screw should not exceed 6r/min, and the speed of screw with 1m or more should be controlled at 2~8r/min. For example, a screw with 0.3m diameter, the spiral speed can be increased to obtain a coarse overflow, but it must not exceed 25 r/min. The appropriate speed should be determined by experiment. The speed of the common spiral classifier is selected as 1.5-10 r/min.

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