Abnormal vibration, amplitude deviation and temperature rise on a vibrating screen rarely occur in isolation. Diagonal vibration, torsional vibration, insufficient amplitude and excessive vibration look similar, but their root causes differ. Troubleshooting should move through the excitation system, the support system, the drive system and the installation condition layer by layer, rather than replacing parts in response to a single symptom.
Diagonal vibration abnormality: two diagonal corners vibrate normally while the other two have almost no amplitude
An amplitude difference along the diagonal means the actual forces and motion at the four support points are no longer symmetrical.
Check the excitation system first. The two vibration motors on a linear vibrating screen have no mechanical coupling and rely on self-synchronization to establish a stable phase relationship. Self-synchronization requires several conditions: the moment of inertia difference between the two motors must not exceed 5% of the smaller value, the exciting force deviation must not exceed 10%, and the center distance between the two motors must be at least 0.8 times the screen box width. Outside these conditions, phase locking cannot be established and the exciting force at the four corners is uneven. The phase angle of the main and auxiliary eccentric blocks on both side plates of the same shaft must also match. If they do not, the exciting force output on the two sides of one shaft differs, and the screen body swings diagonally.
Then check the supports. If the four spring supports are not on the same horizontal plane, or the springs differ in stiffness or free height, the reaction forces at the support points differ. During installation, the spring height difference should be kept within 5 mm. Springs outside this tolerance should be replaced as a set, not mixed with new and old springs. If the screen frame itself is a parallelogram rather than a proper rectangle, stiffness along the diagonal directions differs, and the same spring compression produces different amplitudes.
For handling, stop the machine and disconnect power. Set the eccentric block angle and counterweight on both sides to the same value, and confirm that the phase marks on the main and auxiliary eccentric blocks are aligned. Measure the free height of the four springs and their compression after installation. Replace or shim any spring with a height difference above 5 mm. If the screen frame diagonal dimensions do not match, reinforce the screen body or correct the frame. Running at reduced frequency and observing whether the diagonal amplitude difference decreases with frequency helps determine whether the problem is insufficient stiffness or uneven exciting force.
Torsional vibration: common on linear vibrating screens
Torsional vibration appears as the screen box swinging about its longitudinal axis. Material drifts, swirls or piles up on one side of the screen surface. The main cause is that the exciting forces on the two sides are not in the same plane, or the drive phases are misaligned.
Check the universal drive shaft first. After disassembly and maintenance, the cross joint yokes at both ends must be aligned on the same phase plane. A common misalignment is 90° or 45°. When the yokes are not aligned, the shaft itself generates torsional vibration, energy is consumed inside the shaft system, and the effective exciting force transmitted to the screen surface drops. Check against the manufacturer's alignment marks and check cross bearing clearance. If clearance exceeds the limit, replace the drive shaft assembly. Also check the phase angle of the main and auxiliary eccentric blocks on both vibrators of the same shaft one by one. A phase mismatch also produces torsional vibration.
Next check the spring supports. The tightening error of the four spring supports must not exceed 5 mm, and the spring stiffness on both sides should be as close as possible. If the installation foundation is not level or the screen surface is tilted laterally, material naturally piles up on the low side, which can be mistaken for torsional vibration. Retighten anchor bolts and spring seat bolts one by one, and calibrate foundation flatness to the equipment requirement.
Insufficient amplitude
Insufficient amplitude requires distinguishing among insufficient exciting force, excessive load and vibration absorbed by the supports.
Check the power supply first. A vibrating screen is designed for 380 V three-phase power. Irregular wiring or low voltage reduces motor output power and directly lowers amplitude. Check supply voltage and wiring. If voltage fluctuation is large, install a voltage stabilizer.
On the excitation side, the eccentric block angle is the key. The exciting force of a vibration motor is inversely related to the eccentric block angle: the smaller the angle, the greater the exciting force and the larger the amplitude. The quantitative relationship is F = 2 × m × e × ω² × cos(θ/2), where θ is the angle between the eccentric blocks at the two ends. To adjust, cut off power, loosen the fastening bolts of the adjustable eccentric block, rotate the adjustable blocks at both ends to the same mark on the scale, keep both ends of the same motor consistent and the two motors consistent with each other, then tighten with a torque wrench. Adjusting only one side or setting different angles on the two sides introduces new polarization.
On the load side, a feed rate above rated capacity leaves a thick material layer on the screen and the material and steel balls suppress amplitude. Control the feed rate, keep the material layer even, and avoid local accumulation in the hopper and on the screen surface.
On the support side, the spring net deflection may be unsuitable. If net deflection is too small, the spring transmits insufficient exciting force. If net deflection is too large, the body may leave the springs in the resonance range. For steel helical springs, static compression is generally kept at 20% to 30% of free height. Actual installation pre-compression can follow 20% to 30% of free height, or be selected as δ = (6 to 20)A, with the larger value for large screens, where A is the working amplitude. If net deflection is outside the reasonable range, recalculate the spring parameters and replace the springs as a set.
Excessive vibration
Excessive vibration is usually not caused by too much exciting force but by failed isolation or insufficient constraint.
If spring hardness is too high, isolation is poor, the machine jumps during operation, and the dynamic load on the foundation and anchor bolts rises. Replace the damping springs with a hardness that matches the equipment weight and excitation frequency. Do not increase stiffness arbitrarily.
If the installation floor is uneven or anchor bolts are loose, the screen body swings additionally in the horizontal plane and vibration intensity rises. Level the foundation and retighten anchor bolts at regular intervals.
Check motor rotation direction and power matching. The two vibration motors must rotate in opposite directions. Otherwise the exciting forces combine in the wrong direction and the screen body vibrates abnormally. Mixing motors of different power also breaks the symmetry of the exciting forces on the two sides.
Spring supports, eccentric block fasteners and drive shaft connection flanges carry alternating loads for long periods. Hansheng Automation can machine spring support seats, eccentric block locking components, universal shaft connection flanges and screen box fasteners from customer drawings, with material and surface treatment agreed on the drawing. Single units or small batches are supported.
Bearing overheating and screen mesh blockage
For bearing overheating, check lubrication and clearance first. During test running and normal operation, vibrating screen bearings are generally kept in the 35 to 60°C range. After 4 hours of continuous no-load operation, bearing temperature must not exceed 75°C and temperature rise must not exceed 45°C. If either limit is exceeded, stop the machine and check whether the grease has deteriorated, whether the fill amount is correct, whether bearing clearance has increased from wear, and whether there is abnormal friction inside the vibrator. Replenish grease at the specified interval. If grease has deteriorated or contains dust, remove it completely and refill.
Screen mesh blockage is mostly related to material moisture and screen tension. Material with high mud content or high moisture tends to adhere at the screen openings. In dry screening, feed moisture should be kept below 5%. If necessary, switch to wet screening or add water spray. Insufficient screen tension leaves local slack areas where material stalls and blocks the openings. Clean the screen surface regularly, check tension bolts, and replace or retighten screens that are worn or loose.
Our precision parts machining capability is not limited to vibrating screen excitation and support components. In addition to tobacco packaging machine parts and filling machine parts, we machine non-standard parts to drawings for printing machines, food machines and other equipment, and we accept small-batch orders for yacht precision parts and RC car precision parts. Hansheng Automation works within precision parts machining. Material, tolerance and surface treatment are agreed on the drawing, and parts are machined and delivered accordingly.
