How does the vibrating screen work?
Vibrating screens have been widely used in mining, metallurgy, coal, water conservancy, transportation, and chemical industries to complete various processes, such as screening, grading, washing, de-intermediation and dehydration of materials . As an intermediate link between mining and smelting, mineral processing efficiency not only directly affects mineral processing productivity, but also has a profound impact on the rational use of national resources.
The vibrating screen works by using the double-rotation vibration generated by the vibrator. The upper rotating weight of the vibrator makes the screen surface vibrate in plane, while the lower rotating weight makes the screen surface vibrate the cone surface. Its combined effect The effect is that the screen surface produces double-rotating vibration. Its vibration trajectory is a complicated spatial curve. The curve is projected as a circle on the horizontal plane, and projected as an ellipse on the vertical plane. The amplitude can be changed by adjusting the excitation force of the upper and lower rotating weights. Adjusting the spatial phase angle of the upper and lower weights can change the curve shape of the screen surface movement trajectory and change the movement trajectory of the material on the screen surface.
Vibrating screen equipment can be divided into: mining vibrating screen, light fine vibrating screen, and experimental vibrating screen according to its weight.
Mine vibrating screens can be divided into: heavy-duty screens, self-centering vibrating screens, elliptical vibrating screens, dewatering screens, circular vibrating screens, banana screens, linear vibrating screens, etc.;
Light fine vibrating screen can be divided into: rotary vibrating screen, linear screen, straight row screen, ultrasonic vibrating screen, filter screen, etc.;
Experimental vibrating screen: flapping screen, top-strike vibrating screen, standard inspection screen, electric vibrating screen, etc.
According to the material running track of the vibrating screen, it can be divided into:
According to the linear motion trajectory: linear vibrating screen (the material moves forward on the screen surface in a straight line);
According to the circular motion trajectory: circular vibrating screen (materials move circularly on the screen surface);
According to the reciprocating motion trajectory: fine screening machine (materials reciprocate forward on the drying surface).
In recent years, although vibrating screening machinery has achieved unprecedented development, the theoretical framework of vibrating screens has been stable and becoming mature. Various types of vibrating screens have been introduced one after another, but vibrating screens with high screening efficiency and large output have always been vibrating. The new direction of sieve research and development.
The coal or ore mined in the mining field, or the crushed material, before the material is used or further processed, it needs to be divided into several grades of similar particle size or be dehydrated, de-intermediated, de-slimed, and sometimes a combination of several items. Yes. When performing the above work, there is always the problem of grading materials through the holes of the screen surface, and the grading of materials through the holes of the screen surface is called sieving. Through the research on the screening process of materials, it is found that the screening of materials can be divided into two stages:
1. Fine-grained materials smaller than the mesh size reach the screen surface through the material layer composed of coarse-grained materials;
2. The fine particle material passes through the sieve holes on the sieve surface to complete the sieve.
When the vibrating screen is working, the two motors synchronously and reversely rotate to make the exciter produce a reverse excitation force, forcing the screen body to drive the screen to move longitudinally, so that the material on it is periodically thrown forward for a range due to the excitation force. So as to complete the material screening operation. It is suitable for screening sand and gravel materials in quarries, and can also be used for product classification in coal preparation, mineral processing, building materials, electric power and chemical industries.
The working part of the vibrating screen is fixed, and the material is screened by sliding along the working surface. Fixed grid sieve is one of the most widely used in concentrators, generally used for pre-screening before coarse crushing or medium crushing. It has a simple structure and is convenient to manufacture. It does not consume power and can directly unload the ore onto the screen surface. The main disadvantages are low productivity and low screening efficiency, generally only 50-60%. The working surface of the vibrating screen is composed of horizontally arranged rolling shafts. There are plates on the shafts, and fine-grained materials pass through the gaps between the rollers or plates.
In order to smoothly complete the screening process of the material, the condition of relative movement between the material and the screen surface must be satisfied. Therefore, the screen box of the vibrating screen should have suitable movement characteristics, on the one hand, it can make the material on the screen surface become loose.
On the other hand, it can make the coarse particles blocked on the sieve holes escape, and keep the fine-grained materials smoothly through the sieve. In the actual production process, the actual screening process is: “After a large number of broken materials with different particle sizes and mixed coarse and fine particles enter the screen surface, only a part of the material contacts the screen surface. In this part of the material contacting the screen surface, It is not entirely a fine particle material smaller than the mesh size,
Most of the remaining fine particles smaller than the mesh size are distributed throughout the entire material layer.
Through the movement of the screen box, the material layer on the screen surface is loosened, so that the gap that exists between the large particles is further expanded, and the small particles take the opportunity to pass through the gap and transfer to the lower layer; at the same time, due to the small particles between the materials The gap is small, and large particles cannot pass through. Therefore, the position of large particles increases continuously during the movement. As a result, the original messy material particle group separates, that is, it is layered according to the particle size, forming an arrangement rule with small particles on the bottom and coarse particles on the top.
The fine particle material that reaches the screen surface, because its size is smaller than the sieve hole size, can smoothly penetrate the screen, and finally realize the separation of coarse and fine particle materials and complete the screening process.” However, sufficient separation is impossible. In time-sharing, there is generally a part of the fine particles remaining in the coarse particles on the sieve and cannot penetrate the sieve. Research shows that although the size of the fine particles is smaller than the sieve hole, the difficulty of their penetration is not the same. Compared with sieve holes, the smaller the particle size, the easier it is to penetrate the sieve, and vice versa, the more difficult it is.