4 Types of Vibration Anomalies of Vibrating Screen

The vibrating screen is one of the equipment we often use in daily production. It can effectively screen and filter materials. However, sometimes we may encounter abnormal vibrations, such as polarization, torsional vibration, small amplitude, and violent vibration of the vibrating screen. This will not only affect production efficiency but also cause damage to the equipment. So, why do these 4 types of problems occur in vibrating screens? And how to solve them?

Four Types of Vibration Anomalies of Vibrating Screen

1. Polarization of Vibrating Screen

Causes of Vibrating Screen Polarization

The main reasons for the polarization of the vibrating screen include the following:

1）Spring support problem

• If the four support points of the spring are not on the same horizontal line, or the spring is unevenly stressed, the difference is large, which will cause polarization of the vibrating screen. The height of the spring needs to be adjusted to ensure that the spring height is consistent when it is stationary.
• The springs are not stressed at the same time, and the difference is large. It needs to be adjusted to detect whether the height of the spring is consistent when it is stationary.
• There may be problems with the four spring fulcrums of the vibrating screen. The free length of the springs is the same, but the compression modulus is inconsistent. Check whether the fixed points are stable, balanced, and consistent.

2）Vibrating screen exciter problem

The problem of the exciter is also a common cause of polarization. Check whether the exciter is working properly.

3）Motor counterweight problem

If the angle of the counterweight on the vibrating screen motor changes, or the angle of the eccentric block of the vibration motor is inconsistent, this will also cause polarization. Check whether multiple vibration motors have individual motors that are off-axis or faulty.

4）Vibration motor problem

• The center of the vibration screen motor is far away from the center of the coupling at the end of the vibrator when the machine is stopped.
• The angles of the eccentric blocks of the vibration motor are inconsistent. Check whether individual motors are off-axis or faulty among multiple vibration motors. ‌

5) Screen body stiffness problem

If the screen body stiffness is insufficient, including whether the screen plate is fixed, ‌ this will also cause polarization. The rigidity of the screen body should be checked to ensure it is not loose, including whether the screen plate is fixed. ‌

6) The overall stiffness of the vibration screen machine is insufficient

If the compression of the spring is the same, it is mostly because the overall stiffness of the vibration screen is insufficient. You can observe whether the situation improves by reducing the frequency. This kind of fault is more difficult to handle.

Solutions to the polarization of the vibrating screen

• Check whether the angles of the eccentric blocks of the two vibrating motors are adjusted to be consistent, tighten them, and strictly prohibit the eccentric blocks from shifting after the bolts are loosened.
• Select support springs with consistent stiffness, moderate flexibility, and sufficient load-bearing capacity to ensure the overall smooth operation of the vibrating screen.
• The feeding process should be continuous and uniform to avoid unilateral feeding or excessive feeding, which will cause difficulties in discharging the vibrating screen.
• The installation position and matching angle of the vibration motor are very important. Generally, the installation angle between the vibration motor and the vibrating screen is 30-45 degrees, which will enable the double amplitude of the vibrating screen to achieve the best use effect.

The above methods can effectively solve the polarization problem of the vibrating screen, ensure the normal operation of the equipment, and extend its service life.

2. Torsional Vibration of Vibrating Screen

The “torsional vibration” phenomenon often occurs in linear vibrating screens, because to ensure sufficient efficiency and vibrating force, it is usually equipped with two motors for driving. When the exciting forces generated by the two motors offset each other in the direction parallel to the motor axis and overlap into a combined force in the direction perpendicular to the motor axis, the material on the vibrating screen moves normally in a linear manner, which is the normal working trajectory of the vibrating screen. However, if the directions of the above two vibrating forces are deflected, offset, or the spring damping parameters and different components of the vibrating screen fail, it will cause the screen box to produce a “torsional vibration phenomenon”, accompanied by problems such as material deviation, resonance, and stagnation. When the equipment has a “torsional vibration” phenomenon, it will not only affect the screening effect, but also damage the equipment structure, resulting in uneven distribution of vibration force, cracking of the equipment screen box, and greatly shortening the service life of the vibrating screen.

Causes of “torsional vibration”

• The direction of the exciting force generated by the vibrator of the vibrating screen is deflected or offset; 
• The spring damping system and different components of the linear vibrating screen fail;
• The linear vibrating screen is not placed on a horizontal surface, and the screen surface cannot remain horizontal.

How to solve torsional vibration?

1) Design and manufacturing

• Check whether the screen frame is a standard rectangle, not a parallelogram.
• Check whether the spring support of the screen machine is on the same horizontal plane during the design and manufacturing process and whether the selected spring stiffness is the same.
• Whether the self-synchronization between the two vibrators is normal.
• The phase angles of the main and auxiliary eccentric blocks of the vibrating screen on the two side plates on the same axis are adjusted to be consistent because it is related to whether the generated exciting force is consistent.

2) Installation

• Whether the spring support of the screen machine can be installed on the same horizontal plane, whether the current compression amount is the same, and whether the error cannot exceed 5mm.
• When the universal joint is installed, whether the phase angles on both sides are the same, and other reasons need to be further judged according to the specific screen machine and the application conditions.

3. The small amplitude of the vibrating screen

The reasons for the small amplitude of the vibrating screen may include vibrator failure, insufficient power supply voltage, too few eccentric blocks or too small angles, large feed amount leading to excessive material accumulation, unreasonable spring design, and equipment failure.

Reasons for the small amplitude of the vibrating screen

• Insufficient power supply voltage
  If the line is not connected according to the regulations, the voltage is insufficient, which will cause the vibration screen amplitude to be too small.
• Too few eccentric blocks
  You can try to increase the number of eccentric blocks to increase the amplitude.
• The angle of the eccentric block is too small
  If it is equipped with a vibration motor, the angle of the eccentric blocks at both ends of the motor shaft will also affect the amplitude. The smaller the angle, the greater the exciting force and the amplitude. On the contrary, the amplitude becomes smaller, so the amplitude can be adjusted by changing the angle.
• Large feed volume and large accumulation of materials
  If the stone delivered to the screen surface at one time exceeds its bearing range, the remaining material or accumulation in the screen surface and the under-screen funnel will be too much, resulting in an increase in the equipment load and affecting the amplitude.
• Unreasonable spring design
  When designing the spring, the net variable of the spring should be less than the height of the device, otherwise, the amplitude of the vibration screen will be too small; but if the net variable of the spring is too large, it may cause the body to detach from the spring.
• Causes of equipment failure
  For example: Damage to the motor or electrical components, vibrator failure, etc.

Small Amplitude Solutions

Solutions to the above problems include but are not limited to, inspecting and repairing the vibrator, ensuring the correct voltage supply, adjusting the number and angle of eccentric blocks, controlling the feed rate, properly designing springs, and promptly repairing or replacing damaged equipment parts.

4. Violent vibration of the vibrating screen

Reasons & Solutions

‌The reasons and solutions for excessive vibration of the vibrating screen mainly include the following aspects:

• Excessive excitation force: If the power and model of the vibration motor do not match, or if the excitation force of the motor is adjusted beyond the rated range to increase the screening output or accuracy, the vibrating screen may vibrate too much. The solution is to adjust the excitation force within the bearing range of the motor or consult the manufacturer to recommend a reasonable model.
• Excessive hardness of the vibration damping spring: The vibration damping spring is used to connect the screen base and the screen frame. If the spring hardness is too large, the buffering effect may not be achieved, resulting in vibration during equipment operation. The solution is to choose a better spring or adjust the spring hardness.
• Improper installation: If the installation ground is uneven or improperly installed, it may cause excessive vibration. When installing the vibrating screen, pay attention to the flatness of the ground and correct installation.
• Loose anchor bolts: Under long-term vibration, the anchor bolts may loosen, causing the vibrating screen to vibrate too much. The solution is to check and tighten the anchor bolts.
• Motor steering problem: If the motor steering is inconsistent or the power is different, it may cause the vibrating screen to jump violently. The solution is to readjust the motor direction or eccentric block to ensure that the motor direction is consistent.
• Bearing problem: The accuracy, lubrication, and matching problems of the bearing may also affect the vibration of the vibrating screen. For example, the bearing surface waviness, poor lubrication, or the matching problems between the outer ring and the support hole may cause the vibrating screen to vibrate too much. The solution is to improve the bearing surface processing accuracy, improve the lubrication conditions, and adjust the matching between the outer ring and the support hole.

Vibrating screen polarization, torsional vibration, small amplitude, and severe vibration are the most frequently consulted problems during the use of a vibrating screen. This article summarizes the causes and solutions of these four types of vibration failures, which can help improve the production efficiency of the vibrating screen and extend the service life of the equipment.