In Mineral Processing, the SPIRAL Classifier on the other hand is rotated through the ore. It doesnt lift out of the slurry but is revolved through it. The direction of rotation causes the slurry to be pulled up the inclined bed of the classifier in much the same manner as the rakes do. As it is revolved in the slurry the spiral is constantly moving the coarse backwards the fine material will flow over the top and be travelling fast enough to be able to work its way downwards to escape. The Variables of these two types of classifiers are The ANGLE of the inclined bed, this is normally a fixed angle the operator will not be able to adjust it.
The SPEED of the rakes or spirals, the DENSITY of the slurry, the TONNAGE throughput and finally the SETTLING RATE of the ore itself.To be effective all of these variables must be balanced. If the incline is too steep the flow of slurry will be too fast for the rakes or spirals to separate the ore. If the angle is too flat the settling rate will be too high and the classifier will over load. The discharge rate will be lower than the feed rate, in this case. The load on the rakes will continue to build until the weight is greater than the rake or spiral mechanism is able to move. This will cause the classifier to stop and is known as being SANDED UP. If the speed of the rakes or spirals are too fast, too much will be pulled, out the top. This will increase the feed to the mill and result in an overload in either the mill or classifier as the circuit tries to process the increased CIRCULATING LOAD.
The DENSITY of the slurry is very important, too high the settling will be hampered by too many solids. Each particle will support each other preventing the heavier material from quickly reaching the bottom of the slurry. This will not allow a separation to take place quickly. The speed at which the slurry will be travelling will be slow and that will hamper effective classification. Another variable is the TONNAGE. All equipment has a limit on the throughput that anyone is able to process, classifiers are no different. This and the other factors will have to be adjusted to compensate for the last variable, the ore itself. Every ore type has a different rate of settling. To be effective each of the previous variables will have to be adjusted to conform to each ones settling characteristics.
The design of these classifiers (rake, spiral, screw) have inherent problems, First, they are very susceptible to wear, caused by the scrubbing action of the ore, that plus all of the mechanical moving parts create many worn areas to contend with. The other problem that these classifiers have is that they are easily overloaded. An overloaded classifier can quickly deteriorate into a sanded-up classifier. Once that happens the results are lost operating time, spillage and a period of poor Mineral Processing and Separation performance.
Another mechanical classifier is the spiral classifier. The spiral classifier such as the Akins classifier consists of a semi-cylindrical trough (a trough that is semicircular in cross-section) inclined to the horizontal. The trough is provided with a slow-rotating spiral conveyor and a liquid overflow at the lower end. The spiral conveyor moves the solids which settle to the bottom upward toward the top of the trough.
The slurry is fed continuously near the middle of the trough. The slurry feed rate is so adjusted that fines do not have time to settle and are carried out with the overflow .liquid. Heavy particles have time to settle, they settle to the bottom of the trough and the spiral conveyor moves the settled solids upward along the floor of the trough toward the top of the trough/the sand product discharge chute.
In the mineral processing area, the trommel screens(aka. Rotary drum screens) and vibrating screens are both widely used screening & classification equipment. But whats the difference between the trommel screens and vibrating screens, and how to choose the most suitable screens for your mineral processing application? Or even how should we choose the right screening equipment for specific mining conditions?
Thorough we all may know that they are both are widely used screening equipment, but the different working methods and principles also mean the difference in output, as well as the types of materials suitable for screening processing.
Vibrating screens are screened using the exciting force generated by a vibrating motor and belong to vibrating screens. Commonly used mine vibrating screens include circular vibrating screens and linear screens.
The trommel screen is another screening form. During the screening process, the equipment will not vibrate, but generally, the motor and reducer drive the drum to rotate through the bearing. The material in the drum passes through the screen from high to low due to the rotation of the drum. And it is successfully screened out, so the trommel screen belongs to a type of rolling screening.
trommel screen: It is a cylinder. The outer surface of the cylinder uses one or more layers, or several sections of screens to increase the screening specifications. The volume of the trommel screen is generally large, mainly including motors, reducers, drum devices, screens, and machines. It is composed of a frame, a sealing cover, and an inlet and an outlet. A steel ring must be added to the drum device to prevent the trommel screen from deforming.
The roller device is installed on the frame obliquely. The motor is connected with the roller device through a coupling through a reducer, and drives the roller device to rotate around its axis. When the material enters the drum device, due to the tilt and rotation of the drum device, the material on the screen surface is turned and rolled. The qualified materials (products under the screen) are discharged through the outlet at the bottom of the rear end of the drum, and the unqualified materials (on the screen) The product is discharged through the discharge port at the end of the drum.
Using the vibration motor as the vibration source, the material is thrown up on the screen while moving forward in a straight line. The material enters the inlet of the screening machine evenly from the feeder, and produces several kinds of screens through the multi-layer screen. The upper and lower objects are discharged from their respective outlets.
The screen surface is fixed on the screen box, and the screen box is suspended or supported by springs. The bearing of the main shaft is installed on the screen box and is driven by the pulley to rotate at high speed. The eccentric counterweight plate is installed on the main shaft and generates centrifugal inertia force with the rotation of the main shaft, so that the screen box forms an approximate circular orbit vibration.
The trommel screen can be divided into single-layer, double-layer and three-layer vibrating screens according to the number of layers of the screen. This vibrating screen is also similar, according to the number of screen surface layers can be divided into single-layer, double-layer, three-layer and four-layer vibrating screen.
The vibrating screen is a screening equipment with a vibrating motor as the vibration source, so the screening accuracy is high. The trommel is a high-output screening equipment, and the screening accuracy is not as high as the vibrating screen.
For the trommel screen, the material is turned over and rolled in the drum, so that the material stuck in the sieve hole can be ejected to prevent the sieve hole from being blocked. For the circular vibrating screen, the material moves in a parabolic circular trajectory on the screen surface, so that the material is dispersed as much as possible to improve the materials bounce force, and the material stuck in the screen hole can also jump out, reducing the hole blocking phenomenon.
Vibrating screen and trommel screen have their own working methods and screening principles. Some raw materials can be screened through them. However, for different sites and different material requirements, suitable screening machines should be selected to achieve better screening results.
Spiral Chute is a type of gravity separation equipment, which is applicable to separate metallic minerals whose granularity is between 4-0.02, such as iron as well as other nonferrous metals, rare metals and nonmetallic minerals with adequate gravity difference.
Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.