How to adjust the vibration force of the vibrating screen
The vibration force of a vibrating screen is a critical factor that directly impacts screening efficiency, material flow rate, and overall equipment performance. Whether you’re dealing with fine powders or coarse aggregates, proper adjustment of vibration force ensures optimal separation and prevents excessive wear or mechanical failure. Understanding how to fine-tune the vibration settings can help you adapt to different materials, improve productivity, and extend the lifespan of your machine. In this guide, we’ll walk you through the basic principles and step-by-step methods for adjusting the vibration force of your vibrating screen effectively and safely.
Vibrating screen vibration force adjustment
Adjusting the vibration force (often referred to as excitation force or G-force) of a vibrating screen is crucial for optimizing screening efficiency, preventing damage to the screen, and adapting to different material types or feed rates. The exact method depends heavily on the specific design of the screen’s vibrator mechanism, but here are the common ways it’s done:
1. Adjusting Eccentric Weights (Most Common Method):
Mechanism: Most vibrating screens use rotating shafts with eccentric counterweights. The rotation of these unbalanced weights generates the vibration. The amount of force generated depends on the mass of the weights and their distance from the center of rotation (eccentricity).
How to Adjust:
Adding/Removing Weight Plates: Many systems have counterweights composed of several stacked plates or blocks. By adding or removing these plates (usually in symmetrical pairs on both sides of the shaft or on corresponding shafts), you change the total rotating unbalanced mass, thus increasing or decreasing the vibration force.
Changing Weight Position (Angle/Radius): Some designs feature adjustable counterweights that can be rotated relative to the shaft or to each other.
Single Adjustable Weight: A single block might be designed to slide radially outwards (increasing force) or inwards (decreasing force) and then be locked in place.
Multiple Adjustable Weights: Often, there are two or more weight segments per side. By changing the angle between these segments, you change the effective eccentricity (the distance of the combined center of mass from the shaft center). Moving them closer together (aligned) maximizes the force; moving them further apart (opposed) minimizes or cancels out the force.
Location: These weights are typically located at the ends of the vibrator shaft(s), often enclosed within protective guards.
Procedure:
Safety First: ALWAYS lock out and tag out the power supply to the screen before removing guards or making adjustments.
Remove the protective guards covering the eccentric weights.
Loosen the bolts securing the weights.
Add/remove plates or adjust the angular position of the weights according to the manufacturer’s instructions. Crucially, adjustments must be identical on both sides of the screen (or on corresponding shafts) to maintain balanced vibration and prevent damage.
Ensure weights are securely tightened to the specified torque.
Reinstall the guards.
Test run the screen and observe performance.
2. Adjusting Speed (RPM):
Mechanism: Vibration force is proportional to the square of the rotational speed (RPM). Therefore, changing the speed significantly impacts the force.
How to Adjust:
Variable Frequency Drive (VFD / VSD): If the screen motor is controlled by a VFD, adjusting the frequency output directly changes the motor speed and thus the vibration force. This is the easiest and most flexible method if available.
Changing Pulleys (Sheaves): For belt-driven systems without a VFD, you can change the size ratio of the motor pulley and the vibrator shaft pulley. A smaller motor pulley or a larger vibrator pulley will decrease speed (and force); a larger motor pulley or a smaller vibrator pulley will increase speed (and force). This requires calculating the correct pulley sizes and potentially changing the belt length. This is a less common adjustment method used more for initial setup or major process changes.
Considerations: Changing speed also affects the vibration frequency, which can influence screening efficiency differently than just changing the force (amplitude/stroke). There’s usually an optimal speed range for a given screen design and application.
3. Adjusting Stroke Angle (Angle of Throw):
Mechanism: Primarily relevant for linear-motion screens driven by two counter-rotating shafts (geared exciters). The relative timing (phasing) of the weights on the two shafts determines the direction of the linear stroke.
How to Adjust: By changing the relative angular position of the gears connecting the two exciter shafts, the angle of throw can be adjusted. This doesn’t directly change the total force generated but alters its direction, affecting how material travels across the deck (e.g., faster conveying vs. more lifting action).
Note: This is distinct from adjusting the magnitude of the force by changing the weights themselves.
Important Considerations Before Adjusting:
Consult the Manufacturer’s Manual: This is the MOST IMPORTANT step. Every screen is different. The manual will provide specific instructions, diagrams, torque specifications, and safety procedures for your model.
Safety: Lockout/Tagout (LOTO) procedures are mandatory before working on the equipment. Rotating parts can cause severe injury.
Symmetry: Ensure any adjustments to weights are made identically on both sides of the screen to prevent uneven forces, rocking motion, and potential structural damage.
Incremental Changes: Make small adjustments and observe the effect on screening performance and machine vibration before making further changes.
Monitor Performance: Check for desired material flow, separation efficiency, screen blinding/pegging, and listen for unusual noises or excessive structural vibration after adjustment.
Check Fasteners: After adjustment and a short test run, re-check that all bolts securing the weights are tight.
When Might You Need to Adjust Vibration Force?
Changes in material characteristics (density, particle size, moisture content).
Changes in feed rate.
Poor screening efficiency (e.g., excessive carryover of fines, poor stratification).
Blinding or pegging of the screen media.
Excessive structural vibration or noise.
Insufficient material conveying speed.
By understanding these methods and following the manufacturer’s guidelines carefully, you can effectively adjust the vibration force to optimize your vibrating screen’s performance.
