Spiral chute is a relatively new type of gravity separation equipment, in recent years for sorting disseminated weakly magnetic iron ore and achieved good results. Its main features are: simple structure, low cost; high space utilization, small floor space; no moving parts, no power, low energy consumption; convenient operation and maintenance; high operating rate and productivity; (0.02 to 0.3 mm). Therefore, it has been widely used in weak magnetic iron ore dressing plants.
A Construction spiral chute mainly consists of six parts: the ore separator, the ore tank, the spiral trough, the intercepting trough, the mining bucket and the trough bracket. The specifications are ф1200, ф6900, ф600, ф400, etc. The structure of the 4th glass fiber spiral chute of ф王200×720mm5 for industrial production is shown in Fig. 1.

a Separator The ore separator is a slurry distribution device for the spiral chute, located at the uppermost part of the spiral groove. The miner has two types: self-rotating and fixed. The former is to use the reaction force to discharge the slurry flow to the mine pipe, to promote the rotation of the ore cylinder, and to evenly distribute the slurry into the four-flow channel; the latter is a fixed network pipe distributor, with the positive pressure of the slurry in the cylinder, from the periphery The four discharge pipes evenly distribute the slurry to the feed tank. The fixed type miner has a simple structure, no running parts, and the remaining tubes of one tube can work as usual, so the slurry designing device is adopted for the shaping design.
b The ore supply tank is located between the ore separator and the spiral tank. Its function is to buffer and stabilize the slurry from the ore tank, and then uniformly and slowly feed the ore plate into the spiral groove along the tongue. Inside. The width of the ore tank should be appropriate, otherwise it will affect the sorting effect. The sizing design uses a feed channel with a width of 200 mm, which is about 2/5 of the width of the spiral groove. [next]
c Spiral groove The spiral groove is the main part of the spiral chute, and the mineral sorting process is completed in the spiral groove. The cross-sectional contour of the spiral groove is a cubic parabola. The equation is x=ay ^{2 and the} coordinate graph is shown in Fig. 2(a); the cross-sectional contour is shown in Fig. 2(b).

The spiral groove is not a unitary structure, but a plurality of spiral pieces are connected to each other by bolts. The spiral piece is made of glass fiber reinforced plastic, which is called glass fiber reinforced plastic. FRP has the characteristics of light weight, high strength, corrosion resistance and easy forming. The Ñ„1200mm chute has a spiral thickness of 5mm and each piece weighs 12kg, which is about 1/5 of the weight of the same size steel spiral. Typically in order to improve performance and life of spiral grooves in its inner surface coated with a wear-resistant polyurethane or epoxy resin emery doped with gold, while some flight processing, the use of a surface layer containing diabase A wear layer along the rock powder.
d Interception tank The interception tank is connected to the discharge end of the lower part of the spiral groove. The ore slurry sorted by the spiral groove forms a different grade of ore at the ore discharge end, and is intercepted into products of different grades when passing through the interception tank. As the operating conditions of the spiral chute change, the mineral zoning will also change, so the cutting trough is required to flexibly adjust the cutting width. There are three main types of intercepting tanks designed to meet this requirement: valve block type, scraper type and swash plate type. The valve block type is a triangular valve block as the intercepting width adjusting member, which is flexible and reliable in use and convenient to operate, and is adopted for the stereotype design.
e Mining hopper The mining hopper is a concentric annular cylinder that can be used to collect the different grade flows intercepted by the four intercepting tanks and deliver them to the next operation. The slope of the tank bottom of the mining hopper should be greater than 25% to ensure the smooth discharge of the pulp of different grades, concentrations and densities.
f Slot bracket The chute bracket refers to the pillar around the spiral groove and the upper cross frame. The pillar is made of channel steel to ensure sufficient strength. The upper cross-shaped frame serves both to support the splitter and to position the four grooved supports. [next]
B. Spiral chute sorting principle and sorting process Spiral chute is the reverse selection of gravity, inertial centrifugal force, water flow force and groove friction force of light and heavy ore particles in the downward flow along the spiral slope. . The movement of the slurry flow on the spiral groove surface is relatively complicated, and in general it produces motion in both directions. One is a longitudinal flow that is turned around the vertical axis of the spiral groove and faces downward along the groove, called the main flow; the other is a lateral flow that rotates around a certain equilibrium layer of the ore flow itself, called a lateral circulation or a secondary flow. The longitudinal flow rate of the upper stream is large, and the flow rate of the lower layer is small; the upper layer of the lateral circulation flows toward the outer edge of the groove, and the lower layer faces the inner edge of the groove. The distribution of the liquid flow in the spiral groove is shown in Fig. 3.

The ore-bearing particles fed to the spiral groove surface, under the combined action of the longitudinal flow and the lateral circulation, due to the difference in density, grain size, shape, etc., the difference in the longitudinal and lateral movement speeds along the spiral groove is generated, and the sedimentation to the bottom of the groove The early, late, and fast, slow, and different, resulting in the stratification of the ore particles by density and particle size. The stratification is the first stage of the sorting process, which is basically completed after the first lap of the spiral groove. After stratification, the light ore particles are in the upper layer, and the longitudinal main flow direction and the super-outer edge of the direction are transverse circulation, and gradually flow along the extended spiral to the outer edge of the groove; while the heavy ore particles in the lower layer are affected by the vertical mainstream. Small, moving in the direction of gravity and direction toward the inner edge of the inner rim, gradually moving along the converging spiral to the inner edge. This causes the stratified ore particles to be zoned again. The zoning is the second stage of the sorting process, which usually takes 3 to 5 laps to complete. After the above two stages, the cutting tank and the mining hopper discharge the sorting products of different grades out of the chute, and the sorting process ends.
The ф1200mm spiral chute was used to select iron ore with 27% of original ore grade and 63% of grain size of 63μm. The distribution of different grades of ore particles along the spiral groove is shown in Fig. 4. The results show that the grade of the inner side of the spiral groove is the highest, the grade of the ore grain is the lowest at the groove width of the inner edge of 300-400 mm, and the outer edge of the groove is due to the accumulation of a certain amount of fine-grained high-grade ore particles, so that the average grade is slightly There is a rebound. The particle size distribution along the spiral groove section is: under normal ore conditions, more than 70% of the ore particles are concentrated in the middle of the spiral groove; about 20% of the ore is located at the inner edge of the groove; less than 10% of the fine ore Close to the outer edge.

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C Factors affecting the sorting of spiral chutes
There are many factors affecting the sorting process of the spiral chute. For example, the nature of the ore selected, the process parameters of the operation process, and the structural parameters and performance of the spiral chute itself have different effects on the sorting effect.
a Effect of chute structure parameters Spiral groove diameter The processing capacity of the spiral chute is roughly proportional to the square of the outer diameter of the spiral groove. The volume and flow rate of the large-diameter chute are larger than those of the small-diameter chute, so the processing capacity per unit time is high. In addition, the difference in the diameter of the spiral groove is different for the recovery of each grade of mineral. Comparison experiments with three kinds of spiral chutes with different outer diameters and other similar parameters are used to align Dashan ore. When the ore size is -74μm is 60%, the ore grade is 28~29%, and the ore concentration is 30%. For the +100μm particle size, the recovery rates of ф1200mm and ф600ram spiral chutes are about the same, the recovery rate of ф400mm is slightly lower; for the 40~100μm particle size, the recovery rates of ф1200mm and ф600mm chutes are basically the same, while the recovery rate of ф400mm is slightly Higher; for the -40μm particle size, the ф600mm and ф400mm chutes are comparable, while the ф1200mm chute is significantly reduced. The general rule is that the smaller the diameter of the spiral chute, the smaller the lower limit of the recovery particle size.
Longitudinal inclination The longitudinal inclination varies along the groove section of the tank, with a large inner edge and a small outer edge. The larger the longitudinal inclination, the faster the slurry flow rate and the greater the centrifugal force of the material. A small inclination angle should be used when selecting fine-grained materials. A large inclination angle should be used when selecting coarse-grained materials. In order to make the slurry go smoothly and obtain better sorting indicators, it is required to select a suitable longitudinal inclination. The magnitude of the longitudinal inclination is usually expressed by the ratio of P to the outer diameter D, that is, the aspect ratio. The separation test of iron ore with different grain sizes shows that when the selected materials are fine, the smaller P/D value is better, but when P/D<0.3, the slurry cannot flow smoothly on the groove surface. There is deposition on the inside of the tank. When selecting fine-grained materials, P/D should be selected as 0.4 or so; when selecting ordinary fine-grained materials, P/D should be 0.6, and the pitch of Ñ„1200mm spiral chute used in industry is P=720mm, P/D= 0.6.
Transverse Inclination The intersection of the tangent to the curve of the spiral groove and the axis of the water is called the lateral inclination. The lateral inclination has a great influence on the distribution of the ore flow on the groove surface. The horizontal inclination angle is large, and the water flow depth is also large. When selecting fine ore, a small lateral inclination angle should be adopted. The lateral inclination of each section on the section curve is varied, with a large outer edge and a small inner edge. In order to facilitate the representation of the magnitude of the lateral inclination, it is usually expressed by the lateral lower inclination angle γ. The lateral lower oblique angle is the angle between the line connecting the inner edge and the outer edge of the spiral groove section and the horizontal axis. The industrial ф1200mm spiral chute is designed to adopt a lateral downward inclination angle of γ=9°.
The number of turns of the spiral groove determines the length of the separation distance. This should be determined according to the nature of the selected materials and the requirements of the operation index. When the target mineral and the gangue mineral are difficult to separate in the selected materials, Use more laps. Most of the industrial use is 4 to 6 laps. Usually, it can meet the selection requirements, and the number of turns should not be too much. Because the number of turns is large, the height of the entire spiral chute will increase, occupying a large space, which brings difficulties to equipment configuration and slurry transportation. The industrial Ñ„1200mm spiral chute is designed with 5 turns.
Inner surface of the chute The inner surface of the chute is required to be flat and uniform, and has certain wear resistance to avoid the occurrence of pulling grooves, deformation and damage. Therefore, the inner surface of the FRP spiral chute is usually coated with polyurethane wear-resistant rubber and epoxy resin plus diamond or diabase powder. Roughness has little effect on the selection criteria. [next]
b Influence of process parameters Feeding volume The size of the ore volume directly affects the thickness and velocity of the ore flow. When selecting coarse materials, the ore volume should be large. When selecting fine materials, the ore volume should be small. When the rough selection, the ore volume should be large, and the volume of the ore should be small when it is selected. The practice of selecting hematite shows that as the ore volume increases, the tailings grade increases, the concentrate grade increases slightly, and the metal recovery rate decreases. Under normal ore concentration, the industrial Ñ„1200mm spiral chute has a feeding volume of 180-220L/min.
If the ore concentration is too large, the concentration of the ore will increase, the looseness of the ore layer will be poor, the sedimentation of the particles will be hindered, the stratification effect and the moving speed of the ore along the trough surface will be affected, and the concentrate grade and recovery rate will decrease. However, the concentration of the ore is too small, which not only reduces the processing capacity of the chute, but also makes the mineral layer thinner. It does not have the conditions of stratification and zoning according to density, and the slurry flow rate is increased, and the re-election is less than stratified. The sedimentation is discharged, resulting in an increase in the tailings grade and a decrease in the recovery rate. However, the spiral chute is not sensitive to the change in the concentration, and the effect on the sorting index is not significant in a wide concentration range.
The suitable ore concentration is also related to the nature of the selected materials. For example, when selecting the Gongchanglingling ore, the suitable ore concentration for rough selection is 38~46%; the suitable ore concentration for selected operations is 50~60. %. When selecting Nanfen magnetic separation tailings with a low mineral content (8-10% iron content), the suitable ore concentration is 25-35%. Generally speaking, in the case of not affecting the selection index, it is advisable to use a higher concentration of the ore supply as much as possible, which can improve the processing capacity of the chute and reduce the load of the concentration operation.
c Effect of ore properties The effective sorting size of the ore-sorting spiral chute is 74-20 μm. The suitable processing grades of different diameter chutes are also different. When selecting iron ore, the lower limit of particle size of ф400mm and ф600mm spiral chutes is 20μm. The lower limit of the particle size of the ф1200mm spiral chute is 30/μm. For better sorting results, the spiral chute, like all other re-election equipment , requires a narrower particle size range for the selected material. Therefore, it is very important to de-sludge and classify materials before they are selected.
Particle shape When the selected mineral particles are round, polygonal, flaky or irregular, the motion state in the ore flow is very different. The ore-like ore-like ore-shaped ore-shaped ore-shaped ore-shaped ore-shaped ore-shaped ore-shaped ore-like ore-shaped ore-shaped ore-shaped ore-like ore
Mineral Density The greater the difference in density between the target mineral and the gangue mineral in the ore selected, the more favorable it is to the selection. Evaluating the difficult program for the ore sorting can be judged by the following formula:

Where δ - the density of the target mineral;
δ - the density of gangue minerals.
When M>1, the material can be sorted; when M=0.75~1, the sorting effect is poor; if M<0.75, it can't be sorted.

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