What is the Vibrating Screen and How Does it Work?
What is the vibrating screen?
Vibrating screen is necessary screening equipment in the sand aggregate production line, which plays an important role in improving the output and quality of the sand aggregate production line. The vibrating screen has simple structure, stable operation, high screening efficiency and large processing capacity. The screen is the main working part and also the main vulnerable part to complete the screening process.
Vibrating screen is widely used in mining metallurgy, coal, building materials, chemical industry, cement, glass, grain, medicine and other industries due to its simple structure, small floor area, convenient installation, easy maintenance, low noise, reliable performance and other advantages.
What are the components of the vibrating screen and how does it Work?
Circular vibrating screen is composed of screen box, vibration exciter, support device and other components.
Screen Box: The screen box is the core structure, comprising the screen frame, screening surface, and tensioning devices. The screen surface is where the material separation takes place.
Vibration Exciter: This is the heart of the vibrating mechanism. It typically consists of two side-mounted vibration motors connected by a universal coupling. The eccentric rotation of these motors generates the vibration force.
Support System: The screen box is suspended on a sturdy support system, usually made up of a series of shock-absorbing springs. This allows the screen to vibrate freely while maintaining stability.
The screen box has an inertial vibrating screen with approximate circular motion track, which is also called a single axis vibrating screen. The vibration force generated by the vibration source of the circular vibrating screen is an inertial force with positive change in direction around a fixed axis. Its essence is the centrifugal force generated by the eccentric mass rotating around a fixed axis.
The working principle of the circular vibrating screen is that after the starting of the vibrating screen, the vibrating screen exciter drives the vibrating screen box to make a directional jump movement together. During this process, the materials smaller than the screen surface aperture fall to the lower layer through the screen hole, becoming the undersize materials while the materials larger than the screen surface aperture are discharged from the discharge port after continuous jump movement, and finally the screening process is completed.
What's the difference between linear and circular vibrating screen?
Whether it is crushing production line or sand production line, vibrating screen is basically required. The main purpose of screening is to separate materials with different properties, so that the particle size of materials can meet the requirements of finished products. At present, there are mainly two kinds of vibrating screens commonly used on the market: linear vibrating screen and circular vibrating screen.
They mainly have the following differences:
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1, different working principles
In terms of working principle, the operations of the linear vibrating screen and the circular vibrating screen are both realized by the motion of the screen driven by the vibrating motor. However, the linear vibrating screen is completed by the synchronous reverse motion of the two motors so that the motion of the materials produces an approximate linear trajectory. After the motion of the circular vibrating screen generated by the motor, the movement of the materials presents an approximate circular trajectory to achieve screening.
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2, different vibration exciters
Linear vibrating screen is also called biaxial vibrating screen, because linear vibrating screen is generated by a double motor vibration force, so that the material is thrown up on the screen, while moving forward in a straight line; And the circular vibrating screen is also called a single axis vibrating screen, because it has only one shaft, which is adopt the eccentric block as the vibration force.
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3. Different efficiency
The materials of the linear vibrating screen move in a straight line on the screen surface. If the moisture content or viscosity of the materials is large or the feeding is uneven, the screen holes will be blocked by the materials; the circular vibrating screen uses eccentric blocks as the exciting force (its exciting force is relatively strong), and then moves in a circular manner. Therefore, the materials are relatively dispersed and have a large bouncing force. Even if they are stuck in the screen hole, they can jump out, greatly reducing the screen hole plugging rate, and the efficiency will be relatively higher.
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4. Different application fields
Linear vibrating screen is mainly used to screen fine materials with light specific gravity and low hardness, and is widely used in light industry, metallurgy, coal and other industries; circular vibrating screen is mainly used to screen coarse materials with large proportion and high hardness. It is more suitable for screening sand and gravel in quarries, and also can be used in coal preparation, mineral processing, power, chemical industry and some other industries.
Linear vibrating screen is more suitable for small mining or screening of fine materials, generally used to screen materials of about 2mm; circular vibrating screen is suitable for large-scaled mining and is generally used to handle materials of about 5mm.
Customers should choose the appropriate equipment according to their own actual situation, so as to make the best use of the vibrating screen.
As a professional manufacturer with over 30 years’ experience, we have many customers in China and abroad. And vibrating screen is the necessary auxiliary equipment in production line. We mainly produce circular vibrating screen. So, in the following part, we mainly introduce circular vibrating screen.
What is the function of vibrating screen in sand and gravel aggregate production line?
1, pre-screening of raw materials
Sometimes screening is also required before crushing. For example, the range of particle size of raw materials is large. Large pieces of materials need to be coarsely crushed by jaw crusher, while small pieces of materials can be directly screened before entering the subsequent equipment to avoid over crushing. The screening at this time is called pre-screening.
For sand and gravel processing plants, pre-screening can avoid invalid crushing of materials, thus improving the production capacity of crushing equipment and reducing power consumption.
2, check screening
After primary crushing and secondary crushing, materials need to be further screened and graded. If the particle size reaches the requirements, they will continue to enter the next stage of crushing or sand making. If the particle size does not meet the standard, they will continue to be crushed until they reach the particle size standard for the next treatment process.
The purpose of check screening is to screen out the unqualified large materials from the products of crushing equipment, so that the products do not exceed the required upper limit of particle size.
3, finished product screening
The aggregate processed by one production line has more than one kind of finished products with different particle sizes, and different users have different requirements for the particle size of sand and gravel aggregate. Finished product screening is to screen products into a variety of particle sizes and supply them to various users.
Parameter selection of vibrating screen
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(1)Throwing index
In general, according to the use of the screen, the throwing index of the circular vibrating screen is generally taken as KV=3~5, and the throwing index of the linear vibrating screen should be taken as KV=2.5~4. For materials that are difficult to screen, take the large value, and for materials that are easy to screen, take the small value. The larger value shall be taken when the screen opening size is small, and the smaller value shall be taken when the screen opening size is large.
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(2) Vibration intensity
The selection of vibration intensity K is mainly limited by material strength and component stiffness. At present, the K value of the mechanical level is generally within the range of 3~8, while the vibrating screen is often within 3~6.
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(3) Inclination of screen surface
Generally, the circular vibrating screen is 15 °~25 °, the smaller value is taken when the amplitude is large, and the larger value is taken when the amplitude is small.
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(4) Amplitude of screen box
The amplitude A of the screen box is an important parameter for the design of the vibrating screen, and its value must be appropriate to ensure that the material is fully layered, reduce clogging, and facilitate screen penetration. Generally, A is taken as 3~6mm, and when the screen hole is large, the amplitude should take larger value; and when the screen hole is small, the amplitude should take smaller value.
Frequent problems of vibrating screen
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Why is the screening quality poor?
The main reasons for poor screening quality of vibrating screen are:
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1. Screen hole is blocked
When the mud content and water content in the feeding raw material are high, the material will stick to the screen hole and block the screen hole. At this time, first clean the screen hole, and then properly adjust the water spraying amount and screen surface inclination.
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2. The screen hole is seriously worn
When the screen mesh is used for a long time, it will cause serious abrasion of the screen mesh, which will seriously affect the screening effect. At this time, the worn screen mesh should be repaired. When the wear is serious, the screen mesh should be replaced.
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3. Uneven feeding of vibrating screen
When the feed chute of the screen is too narrow, the materials cannot be evenly distributed along the entire screen surface, which makes the screen surface cannot be effectively used, and will affect the screening effect. At this time, the width of the feed chute should be adjusted to make the feeding of the vibrating screen uniform.
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4. The material on the screen is too thick
The material on the screen is too thick, which may be caused by the increase of feeding amount, blockage of screen hole, and small inclination of screen surface, etc. At this time, it should be adjusted according to the specific situation.
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Why is the amplitude small?
Here are the main reasons that cause the amplitude of the vibrating screen too small:
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1. The voltage of power supply voltage is insufficient
If the circuit is not connected as required, the voltage is insufficient, which will cause the vibration amplitude of the vibrating screen to be smaller.
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2. Too few eccentric blocks
Try increasing the number of eccentric blocks to increase the amplitude.
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3. The included angle of eccentric block is too small
If the motor adopts vibration motor, the included angle of the eccentric blocks at both ends of the motor shaft will also affect the amplitude. If the included angle decreases, the excitation force will increase, and the amplitude will increase. Otherwise, the amplitude will decrease. Therefore, the amplitude can be adjusted by changing the included angle.
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4. Large feeding amount and large material accumulation
If the material transported to the screen surface at one time exceeds its bearing range, there will be too much material accumulated in the screen surface and screen hopper, which will increase the equipment load and affect the amplitude.
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5, The spring design is not reasonable
When designing, the net variable of the spring should be less than the height of the device, otherwise, the amplitude of the shale shaker will be smaller; however, if the net variable of the spring is too large, it may cause the body to disengage from the spring.
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6. Equipment failure
For example, the motor or electrical components are damaged, and the vibrator failure etc.
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How to adjust the amplitude?
When the vibrating screen efficiency cannot meet the requirements during operation, we can adjust the amplitude:
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If the vibration source is the exciter, the weight of the eccentric block can be increased (decreased) (the secondary eccentricity can be increased or decreased);
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If the vibration source is a vibrating motor, the amplitude adjustment depends on the included angle of the eccentric blocks at both ends of the motor shaft to change the magnitude of the exciting force. If the included angle is small, the exciting force will become larger and the amplitude will become larger; On the contrary, the included angle increases, the exciting force decreases, and the amplitude decreases.
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For the shaft eccentric vibrator, the counterweight on the flywheel and pulley can be increased or decreased to increase or decrease the amplitude of the vibrating screen.
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In addition, note that the adjustment amount of the vibration source (vibration exciter or vibration motor) on the vibrating screen must be the same; otherwise the equipment will be damaged.
