Reform and transformation of high frequency vibrating screen Henan Hongxing

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Transformation and transformation of high frequency vibrating screen

High frequency vibrating screen, alias High frequency screen It is mainly used for wet screening or solid-liquid classification of materials less than 0.5mm. It is mainly used in coal mine processing. As an important equipment for slime screening, its main operation mode is high frequency, high vibration intensity and small amplitude. Its advantages include stable performance, high efficiency, large processing capacity and low moisture content of products. Although the high-frequency vibrating screen has been widely used in various industries, its design is not perfect. Customers often reflect the phenomenon of reciprocating movement of materials when starting. The manufacturer of Hongxing high-frequency vibrating screen will transform it.

 High frequency vibrating screen

1. Failure phenomenon and cause analysis

When the high-frequency vibrating screen starts to move back and forth, a straight line along the vibration direction angle is drawn on the side plate of the screen box, and the motion track of the straight line becomes a similar rotating track. According to this, the vibration direction of the screen is no longer changed, and the vibration direction of the screen is also determined. In addition, the vibration screen bearing block also accompanied with heating phenomenon.

High frequency vibrating screen adopts double motor drive, self synchronous linear vibration, no gear forced transmission. The vibrating screen is excited by a double unbalanced vibrator with synchronous opposite rotation. Two groups of the same eccentric blocks in the vibrator operate synchronously and reversely. In each instantaneous position, the components of centrifugal force generated by two groups of eccentric blocks are always superimposed on each other along the vibration direction, while the component forces of normal centrifugal force are always offset each other, thus forming a single direction excitation force, which makes the screen box vibrate in a reciprocating straight line. The reason for the above problems is that the centrifugal force generated by the two groups of eccentric blocks is not correctly superimposed and offset, that is, the two groups of eccentric blocks are not self synchronous movement, resulting in random vibration of the vibrating screen. Therefore, in order to solve the above problems, it is necessary to find out the reasons why the two groups of eccentric blocks are not self synchronized.

When the fault occurs, the temperature of the bearing rises obviously, so it can be preliminarily judged that the bearing is moving relative to the bearing seat. When the exciter was disassembled, it was found that there were obvious traces of relative movement of the bearing on the inner wall of the bearing housing. The bearing used in high frequency vibrating screen is common clearance. The bearing is installed in the bearing pedestal. Considering the thermal expansion factor, the outer cylindrical surface of the bearing is matched with the inner hole of the bearing seat, and the inner hole of the bearing and the shaft are in transition fit. When too much grease is added into the exciter, the oil resistance increases. When the oil resistance is greater than the friction force between the bearing and the bearing seat, the bearing will move relative to each other, which will cause the two sets of exciters not to run synchronously. Therefore, the clearance fit between bearing and bearing seat is one of the reasons for the above problems.

The bearing seat of the vibration exciter of the vibrating screen is installed in the hole on the side plate of the screen box, and is fixed with high-strength bolts of steel structure. Field measurement shows that the inner hole of the bearing housing is deformed, the deformation is as high as 0.1 mm. Due to the deformation of the bearing seat, the clearance between the inner ring and outer ring of the bearing decreases, which increases the resistance between the cylindrical roller and the inner and outer rings of the bearing. When the resistance is greater than the friction between the bearing outer ring and the bearing seat, the bearing will move relative to each other. Therefore, the deformation of bearing housing during assembly is also the cause of the above problems.

2. Transformation measures

According to the above analysis, in order to solve the problem of reciprocating motion of high-frequency vibrating screen materials, it is necessary to reasonably select the tolerance fit between the bearing seat and the bearing, and take measures to prevent the bearing seat from deformation.

(1) Selection of fitting tolerance between bearing pedestal and bearing

In China, clearance fit is always used in the matching of vibration screen exciter bearing and bearing seat. The bearing is of common clearance. The purpose of this design is to prevent the bearing from locking due to the temperature rise and expansion. At present, it is necessary to consider not only the expansion of bearing due to temperature rise, but also the relative motion between the bearing and the housing. Therefore, the fit of bearing seat and bearing outer ring is changed into transition fit. Because the load of the bearing of high frequency vibrating screen is large and the load is always changing, the bearing must have enough original radial clearance to ensure that the bearing still has residual radial clearance when it works, and the oil film formed can ensure the bearing can work normally. Considering the expansion caused by temperature rise, the clearance will be reduced to some extent. Therefore, the bearing with larger clearance should be selected to increase the bearing clearance.

(2) Measures to prevent deformation of bearing pedestal

In order to prevent the bearing block from deformation during assembly, according to the characteristics of high frequency vibration screen exciter, measures are taken to increase the rigidity of bearing block and improve the installation accuracy of bearing seat.

The original wall thickness of bearing block is 30mm, but now the wall thickness of bearing pedestal is changed to 40mm, which can effectively prevent the deformation of bearing block due to poor rigidity. The bearing seat is installed in the hole on the side plate of the screen box and fixed by 12 steel structures with high-strength torsional shear bolts. The hole between the bearing seat and the side plate of the screen box is a clearance fit. The surface roughness of the inner hole of the side plate and the cylindrical surface of the bearing seat is Ra12.5, and the surface of the side plate combined with the end face of the bearing seat is the rough surface of the steel plate. Because of this fixing method, the bearing seat is not positioned on the side plate. Therefore, reaming hole bolts will be used. The fit between bearing seat and side plate hole is changed to small transition fit, and the surface roughness of inner hole of side plate and outer cylindrical surface of bearing housing is changed to ra6.3. In addition, the surface of the side plate combined with the end face of the bearing seat is rough, and the surface of the steel plate is not smooth, which easily leads to the deformation of the bearing seat during installation. Therefore, the surface of the side plate needs to be processed, and the roughness is Ra12.5.

(3) Other measures

In order to ensure that the vibrating screen moves in a straight line, that is, to ensure the self synchronous movement of four groups of exciters, the two groups of vibration exciters on both sides of the screen box on the same horizontal line must be effectively connected together, and the coaxiality error should be within 0.5mm. The welding intermediate shaft is used to connect the two groups of exciters of the original high frequency vibrating screen. Due to welding deformation, the coaxiality error of flange holes at both ends is large. Therefore, the welded intermediate shaft is replaced by universal transmission shaft.

3. Transformation

After the improvement of high frequency vibrating screen in a coal preparation plant, the deformation of bearing pedestal is only 0.02mm. The vibrating screen runs stably, and the backward movement of materials disappears. The temperature rise of bearing pedestal is about 20 ℃, and the vibration direction angle of each part is about 43 ° (the design direction angle is 45 ℃). All indexes conform to the coal industry standard and achieve the expected goal of technical transformation.

The resistance between the cylindrical roller and the inner ring of the high frequency vibrating screen bearing is greater than the friction resistance between the outer ring and the bearing seat, which is the main reason for the relative movement of the bearing. In the design of self synchronous vibrating screen, the bearing seat and bearing must be selected with reasonable coordination, and measures shall be taken to ensure that the bearing seat will not deform during assembly. When the bearing is not locked due to temperature rise, the relative movement of bearing relative to bearing seat shall not occur.

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