Vibration screening equipment is an important equipment necessary for departments such as mining, mineral processing, coal preparation, building materials, and chemical engineering. Its performance directly affects production capacity and technical and economic indicators. For a vibrating screen, the same fault may be caused by different reasons, and the solutions may also be different. Therefore, it is necessary to master some common fault diagnosis and solution methods for vibrating screens in production practice.

Exciter failure

The vibration exciter is the source of vibration generated by the screen body, and the amplitude can be adjusted through counterweight. When the exciter works, the centrifugal force generated by the eccentric mass rotation is used as the excitation force. When the dual axis exciter rotates synchronously, the screen box undergoes reciprocating linear vibration, and the material is screened through the pores on the screen surface, ultimately completing the screening work of the finished ore. There are generally several situations where the exciter malfunctions:

1. Start under heavy load

Due to sudden shutdown caused by production or other equipment failures, the sieve box is filled with mineral materials. If the exciter is restarted under heavy load, it is highly likely to cause damage to the universal coupling and other components of the exciter. Therefore, it is important to avoid restarting the vibrating screen under heavy loads.

2. Damaged damping system

If the damping spring fails or there is too much material accumulation under the screen, it can cause the damping system to be uncoordinated and cause damage to the exciter. Regular inspection of vibration damping springs should be carried out, and springs that have failed or deformed should be replaced in a timely manner. When replacing, all vibration damping springs should be replaced as much as possible, and the stiffness of each group of springs before and after replacement should be consistent.

3. Installation quality issues during maintenance

Improper adjustment of the clearance between the exciter during maintenance and installation can lead to errors in the axial and radial joints between the exciter, the motor, and the universal coupling, as well as the relative position of the eccentric block of the exciter. This can cause excessive vibration of the exciter and generate high temperatures, seriously affecting the normal operation of the vibrating screen. When installing the two motors, it is recommended to choose motors of the same model with the same damping and shutdown time as much as possible to ensure synchronous operation of the two motors; Before installing the exciter, it is necessary to ensure that the two motors run in opposite directions; The motor and the exciter must be in the same vertical plane, especially during the maintenance of the exciter. For a pair of exciters used simultaneously, the quality of the eccentric wheels used should be consistent.

When repairing and disassembling the exciter, the following points should be noted:

The disassembly and assembly of the vibration exciter should be carried out in a clean area; All components must be cleaned and deburred before assembly; Do not directly strike the inner and outer rings of the bearing; Before assembly, all assembly surfaces should be coated with lubricating oil, such as lithium grease; Carefully inspect the sealing ring, and if there is aging or damage, replace it in a timely manner; Install an appropriate amount of lubricating oil that meets the regulations, such as lithium grease; When assembling the Y-shaped sealing ring, pay attention to the end face facing inward; All bolts shall be tightened according to regulations, and tightened every one or two days in the initial installation stage, three or more consecutive times, and inspected every two days thereafter.

The vibrating screen has a crack fault

During the operation of the vibrating screen, the screen frame trembles and causes bending fatigue, which can easily cause local deformation or cracking of the screen frame, side plates, etc. There are several main reasons for the vibration cracking failure of the vibrating screen during use:

1. The damping spring fails

After long-term use, the spring undergoes permanent deformation due to rubber aging or long-term stress, causing the spring to fail, resulting in different heights of the four sets of vibration damping spring seats on the vibrating screen body, resulting in inconsistent amplitudes in various parts of the vibrating screen, leading to cracking of the connecting parts of the vibrating screen or welding seams of the connecting parts. The vibration damping spring should be regularly inspected, and the spring material is generally 60Si2MnA, and the heat treatment hardness should reach HRC45-50.

2. There is a deviation in the mass of the eccentric wheel of the vibration exciter

The function of the vibration exciter and the upper eccentric wheel is to cause vibration on the vibrating screen. The magnitude of its mass directly affects the vibration amplitude of the vibrating screen. The eccentric wheel has a deviation in mass, and the vibration force generated during operation is dispersed, reflected in the vibrating screen body. The amplitude of each part is inconsistent, causing the connecting part of the vibrating screen to vibrate or the welding joint of the connecting part to crack.

3. The eccentric wheel weight perpendicular does not coincide with the natural weight perpendicular,

When installing the vibration exciter, after connecting the exciter with a universal coupling, due to the torque of the transmission shaft, the corresponding eccentric wheel's weight perpendicular line may not coincide with its natural weight perpendicular line, resulting in asynchronous rotation of the eccentric wheel and inconsistent amplitude of each part of the vibration screen. The vibration of the connection part of the vibration screen or the cracking of the welding joint of the connection part may occur.

4. Improper counterweight of the eccentric wheel of the vibration exciter

Improper balancing of eccentric wheels can also cause imbalance in the amplitude of the vibrating screen; If the counterweight is added too much, it will cause the amplitude to exceed the allowable value, which will cause the connection part of the vibrating screen to crack or the welding joint of the connecting part to crack.

5. Thin sieve plate

The breakage of the sieve frame may also result in thin sieve plates. The best way to solve this problem is to appropriately thicken the side plates, or add additional plates locally to the side plates near the exciter to enhance the rigidity of the entire sieve body, so that the sieve frame is less prone to vibration and breakage. When repairing welding, the weld seam should be along the longitudinal direction of the screen frame, and transverse welds are absolutely not allowed, otherwise the pipe beam is more likely to break from the transverse weld seam.

Broken screen frame or broken pipe beam

According to the principles of fracture mechanics, the shaking of the screen frame causes bending fatigue, which makes it prone to fracture. If the screen frame is broken, there may be a thin screen plate. The best way to solve this problem is to appropriately thicken the side plate, or add additional plates locally to the side plate near the exciter to enhance the rigidity of the entire screen body, so that the screen frame is less prone to vibration and breakage. In addition, there may also be an overall structure that is unreasonable.

There are generally the following situations for pipe beam fracture:

The most common reason is that the wall of the pipe beam is too thin. The solution is to replace the pipe beam with the same model of thick wall pipe or use a larger model of pipe beam, but it is also not advisable to use too large or too thick pipe beams.

2. There must be longitudinal and transverse pressure strips at the connection points of each sieve plate of the dehydration and media removal sieve mesh to prevent water from leaking out from the gaps of the sieve mesh, thereby causing the fracture of the flushing pipe beam.

3. The wider the sieve, the easier it is for the pipe beam to break. Based on on-site usage experience and reference to German manufacturing technology, it is best to use double channels when the sieve width exceeds 3m, that is, the sieve has three side plates, which can effectively avoid beam breakage.

4. If the fracture of the pipe beam is not severe, in order to not affect production, repair welding can be carried out on the pipe beam for continued use. During repair welding, the weld seam should be along the longitudinal direction of the pipe beam, and transverse welds are absolutely not allowed, otherwise the pipe beam is more likely to fracture from the transverse weld seam.

Bearing overheating

In general, the normal temperature of bearings should be maintained at 35-60 ℃. If the bearing temperature is too high during use, the following reasons may exist:

1. The radial clearance of the bearing is too small

Due to the large load and high frequency carried by the bearings on the vibrating screen, and the constantly changing load, the bearings must adopt large clearance. If a bearing with regular clearance is used, the outer ring of the bearing must be ground again to create a large clearance.

2. The bearing gland is pressed too tightly

There must be a certain gap between the gland and the outer ring of the bearing to ensure normal heat dissipation and certain axial movement of the bearing. This gap can be adjusted through the sealing gasket between the end cover and the bearing seat.

3. Poor bearing lubrication

Lack of oil or contamination of the bearing oil can cause overheating of the bearing. At this time, it is necessary to inject oil, clean, replace oil and seal the bearing, check the oil quality and injection situation, and there may also be bearing wear or bearing quality issues.

Abnormal sound or high noise

1. Screen box or side plate vibration cracking

The screen frame and side plates should be regularly checked for vibration cracks. For vibration cracks, the parts should be welded or replaced in a timely manner.

2. Bearing damage

Bearings should be regularly lubricated with oil and damaged bearings should be replaced in a timely manner.

3. The sound generated by the side plate, rear end plate, and other plate structures of the screen box

Due to the fact that the side panels and rear panels of the screen box are all made of thin plates that are welded, connected or riveted together, these large areas of thin plates will emit strong noise under the excitation force. The magnitude of the radiation noise on the plate surface is proportional to the square of the vibration speed of the plate surface. Therefore, the purpose of noise reduction can be achieved by applying constrained damping materials to the plate surface.

4. The screen is not tightly pressed or some bolts are loose

Due to prolonged vibration, the screen or bolts may naturally loosen, and it is necessary to regularly inspect and tighten the bolts in various parts.

5. The spring is damaged

Due to changes in the stiffness of springs that have been used for a long time, with varying lengths and collisions with the base and screen box, the springs should be replaced in a timely manner or replaced with rubber springs.

6. The sound generated by the vibration of the exciter bearing itself

Add a soft soundproof cover on the outside of the exciter.

7. Collision between material and chute

Due to the fact that the chutes of the vibrating screen are all welded with steel plates, the collision and friction of materials inside the chutes can also generate large noise. Therefore, laying rubber lining plates or making boxes on the inner walls of the feeding and discharging chutes can reduce the noise of the chutes.

1. The motor or electrical components are damaged

Firstly, check the motor. If the motor is damaged, replace it; Secondly, check the electrical components in the control circuit. If the electrical components are damaged, they need to be replaced.

2. Insufficient voltage

Test the power supply voltage and change the power supply.

3. Vibrator failure

Check the viscosity of the lubricating grease inside the vibrator, add appropriate lubricating grease, and then check if the vibrator is faulty. Check and replace the vibrator.

4. Excessive accumulation of materials

There is too much remaining material or accumulated material in the sieve surface and undersize hopper of the vibrating screen, which increases the starting load of the vibrating screen. It is necessary to thoroughly clean the remaining material or accumulated material in the sieve surface and undersize hopper in a timely manner.

Sieve machine sway phenomenon

If there is a lateral sway phenomenon in the screening machine, the most likely reason is that there is a height difference or a significant difference in stiffness between the springs. In this case, it is necessary to measure the height and stiffness of the springs and replace them if necessary. Therefore, in production, it is necessary to strengthen the maintenance of the vibration damping and buffering springs of the vibrating screen, regularly clean the dust and materials around the springs, maintain good buffering effect, and adjust the top wires of the four buffering and damping blocks between the vibrating screen body and the shell to minimize the lateral oscillation of the screen machine as much as possible

3. The fixing bolts of the vibration exciter are loose or there is no anti loosening spring washer added, which causes the vibration source center to vibrate and causes the bearing to heat up and be damaged.

Solution: After using the exciter for the first time and running for 2 and 50 hours, recheck the fastening bolts and tighten them immediately if any looseness is found.

Improper selection of lubricating oil, excessive or insufficient filling, can cause bearing heating.

Solution: Under normal circumstances, it is advisable to fill 2/3 of the lubrication chamber with lubricating oil. Excessive oil can easily cause heat, and exhaust must be done using exhaust bolts. Generally, when there is no oil leakage, the vibration exciter should be filled with lubricating oil once every 80-100 hours, with a maximum of 1kg added at a time, and the waste oil should be discharged in a timely manner.

The exciter is the power source of the vibrating screen, and improving the design and processing quality, correct use and careful maintenance are the prerequisites to ensure the good operation of the exciter bearing.