Spiral classifier is a common classification equipment in beneficiation area, mainly has high weir type single spiral and double spiral, submerged single spiral and double spiral classifier. High weir spiral classifier is suitable for the coarse grain grading, the grading overflow particle size is generally greater than 0.15mm, Submerged spiral classifier is suitable for fine particle grading, the grading overflow particle size is less than 0.15mm in general. Spiral classifier is widely used in ball mill in the concentrator and deserves to shunt mineral sand into a closed cycle process, or use to graded sand and fine mud in the gravity concentrator, and metal beneficiation process for the pulp particle size classification, and washing of desliming, dehydration and other operations.
The advantages of the spiral classifier are simple construction, stable and reliable work, easy operation, and easy to operate with a mill with a diameter less than 3.2m.
2. Classification and working principle of spiral classifier
The main part of the spiral classifier is a semicircular flume, consisting of a spiral device composed of shafts and blades, supporting the upper and lower bearing parts of the screw shaft, the transmission and lifting mechanism of the spiral shaft (Fig. 1 and Figure 2). Its specifications are represented by the diameter of the spiral.
Figure 1. working principle of spiral classifier
Figure 2. High weir double spiral classifier
1. transmission; 2.water tank; 3. left and right spiral shaft; 4 inlet; 5. lower support; 6. lifting mechanism
According to the number of spiral axes, the spiral classifier can be divided into single helix and double helix classifier. According to the height of overflow weir, it can be divided into three kinds: high weir type, low weir type and submerged type.
The position of the overflow weir with high weir spiral classification is higher than that of the bearing center at the lower end of the spiral shaft, but it is lower than the upper edge of the spillway end spiral. It has a certain settlement area, which is suitable for the classification of coarse grain, and the granularity more than 100 mesh can be obtained.
The overflow weir of the low weir spiral classifier is lower than the center of the overflow end bearing, so the area of the settlement area is small and the overflow production capacity is low. It is usually not used for classification operations, but is used to flush mineral sand for desliming.
The entire spiral of the overflow screw of the submerged spiral classifier is immersed in the liquid surface of the settlement area. The settlement area has large area and depth, which is suitable for fine grain classification, and can get less than 100 mesh overflow particle size.
working principle of spiral classifier: The grinded pulp into the tank from the feed port is located in the settlement area of central water tank installation is inclined bottom slurry classification sedimentation zone, the rotational speed of spiral, stirring the slurry, the light fine particles suspended above, flow to the overflow side weir overflow, into the next process processing, heavy particles settling to the bottom of the groove, a screw conveyor to the discharge port as the return sand discharge. Usually, the spiral classifier is closed with the mill, and the coarse sand is returned to the mill and regrinder.
3. structure of spiral classifier
The structure of the high weir type double spiral classifier is shown in Fig. 2, the water tank 2 is welded by steel plate and section steel, and there is a feed inlet on the side wall of the trough body. The bottom part of the tank body has a sand returning port at the bottom. The bottom of the tank has a water release valve at the bottom of the body. The valve closes in normal work and opens the pulp in special cases, such as failure. A vertical hollow shaft is mounted on the shaft, and the supporting plate rack is matched with the spiral guide angle on the clamping shaft, and the left and right spiral blades are fixed on the supporting plate. The spiral mechanism mostly adopts double head pitch screw, and the wear-resisting lining plate is arranged on the edge of the blade (usually made of medium manganese nodular cast iron). Screw rotation, hand stirring slurry make light of fine particles float, while the coarse particles sink to the bottom of the upper end of the carriage. Hollow shaft is usually made of seamless steel pipe or welded with long steel sheet after forming. The upper and lower ends of the hollow shaft are welded with a shaft neck, the upper end is supported in a rotatable cross axle, and the lower end is supported in the lower support. The bearing of the cross axle is shown in Figure 3, and the axle heads on both sides of the support are supported on the transmission frame, which can make the spiral axis rotate and can also be used as a lifting movement.
Figure 3. Cross bearing support
1. shaft 2.; bearing; 3. bushings; 4. thrust bearings; 5. gland; 6. end cap
The bearing support of the lower end is immersed in the pulp for a long time, so a good sealing device is required. The 3 kinds of commonly used seal: mechanical seal, seal pressure of rolling bearing bearing bearing bearing and resin pressure seal rubber bushing. The sealing performance of these structural types is not ideal. Later, the bearing of the mechanical seal rolling bearing was improved. The maze type and high pressure dry oil joint seal type were adopted (Figure 4), which improved the sealing performance and prolonged the service life of the bearing to a year or so.
Figure 4. High pressure dry oil multiplate seal
1. multi-layer seal; 2. support seat; 3. rolling bearing; 4. shaft
The spiral shaft is driven by a motor, a reducer, a cylindrical gear and a conical gear, and the transmission device is mounted on the upper end of the equipment. As for parking will be buried in sand spiral blade caused difficult to start, which is provided with a spiral shaft lifting mechanism, by a motor through a speed reducer and a pair of bevel gear drives the screw rod to lift shaft. In addition, if the rough sand layer is too thick to rotate when the coarse sand layer is rotated, it can also be slightly raised to prevent the damage of the blade and other parts.
4.Main specification of spiral classifier
4.1. water tank slope
The slope is usually between 12°-18°30 ', and when the size is fine, a small value is taken, and a large value is obtained.
4.2. Overflow weir height
When the granularity is fine, the height of the overflow weir should be small, and on the contrary, the large value should be taken.
4.3. length of spiral shaft
The length is determined according to the height of the overflow weir h, the dip angle of the trough a, and the length l of the return sand dehydration zone (Figure 5).
Figure 5. length of spiral shaft
4.4. spiral diameter
The spiral diameter D is determined by the number of spiral (single or double) and overflow flow.
4.5. lead of spiral。
The lead of spiral is related to the necessary factors such as the amount of return sand, the diameter of spiral and the speed of the spiral. The practical experience shows that the spiral diameter should be 0.5-0.6 times of the spiral diameter.
4.6. Rotary speed of spiral shaft
Its speed should not only return to the sand in time, but also do not produce a strong stirring effect, in order to ensure the required overflow size. The rotation speed of the spiral shaft is usually 3-12r/min, and the large spiral classifier takes its small value and vice versa. When the granularity of the overflow is coarse, the rotating speed of the spiral shaft is higher, and on the contrary, it should be lower.
Figure 6. 2FC2000 submerged type spiral classifier
5.Specification of spiral classifier
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Spiral classifier is of mechanical classification equipment designed by the principle of the different solid grainsize and specific density owning the different sedimentation rates in the liquid, consequently the fine particles floating in the water overflow, coarse particles sinking on the bottom of the channel are spiraled to the upper to discharge. It can classifiedly filter the pulp from grinding mill, and then the coarse materials are fed into the mill inlet by spiral pieces, the fine materials are discharged from the overflow pipe.