CRADLE TO GRAVE •
Factors operators need to consider in vibratory screening applications:
• Efficiency – The volume of the material stream determines the amount on the screen, which can influence how well it is separated.
• Material – The speed, volume and desired output of screening are dependent on the properties and angle of repose of the application.
• Angle of repose – The angle of repose is how the material spreads naturally across the surface. The loading method and type of vibratory motion assist in even distribution across the screen.
• Screen design – First, the screen must be able to withstand the additional weight. Then, whether dewatering or separating, the grid pattern, permeability, and type of vibratory motion need to promote the application’ s separation.
• Effective slope – The angle of applied vibration determines the speed at which the material moves down the screen. Gravity, amplitude, and frequency are factors in the screen’ s effectiveness.
• Vibratory amplitude and frequency – Increasing either the amplitude or the frequency will increase the volume of material moving through the system.
• Vibratory motion – There are two general vibratory motions, linear( back-and-forth or up-and-down), and elliptical( rotational).
Failure mechanisms in screen vibration Although the main topic is vibration, it isn’ t the only failure mechanism in the screening process. According to a comprehensive literature review, Causes Of Failures In Vibrating Screens: A Literature Review,“ The definition of failure mechanisms encompasses all factors that can cause or influence structural or component failures. In essence, it refers to any non-conformity that infiltrates the vibrating screen assembly, leading to future issues.” 2
When a screening rack goes out of service, it can significantly impact production. Simply adjusting the volume of material fed to the remaining units decreases efficiency, negatively affects the quality of separation and accelerates wear and tear, which raises the likelihood of additional breakdowns. This downtime increases labour costs, increases exposure to safety risk and elevates the cost of operation.
The study classified failure mechanisms into five distinct categories: 1. Design Deficiency – Inadequate engineered design either in the screen structure or the vibrator.
2. Manufacturing and Assembly Process Deficiency – Structural adjustments post-installation are common and can change the centre of gravity or increase the machine ' s weight, which reduces efficiency.
3. Operational Deficiency – Increasing volumes that exceed the recommended limits or the miscalibration of vibrators that put an undue strain on units are common operational deficiencies.
4. Inadequate Maintenance – Neglecting to monitor pads and springs on screening structures, not following lubrication procedures, and not addressing rust promptly are common and costly failure mechanisms.
5. Wear and Deterioration – These factors are unavoidable, but proper installation and maintenance of quality equipment can extend the system’ s lifespan.
Vibratory amplitude and frequency Amplitude refers to the magnitude or intensity of the vibration, indicating how far an object moves from its resting position. On the other hand, frequency indicates how many cycles of vibration occur per unit of time( measured in Hertz). Higher frequency can increase volume, but has the potential to increase screen wear and stress on the frame if force outputs are not considered.
The vibrator’ s force can be adjusted and must at least match the combined weight of the isolated rack and the load volume. When the machine is new, the vibrators are typically set to the force output that provides the best performance. Balance throughput volume with reliability. It’ s important to consider wear and maintenance when changing the vibrators ' force output.
Vibrator motion and placement In most horizontal screening applications, two vibrators on a rack work in tandem by counter-rotating to produce a linear motion. This motion generates a line of force that intersects with the machine ' s centre of gravity. The placement and angle of the vibrators influence how the motion occurs. With the correct slope and amplitude calculated, gravity will assist the material down the screen.
Linear side-to-side motion is effective for sectors such as mining and recycling, as it allows material to spread across the screen. Mounting vibrators on the sides of the rack causes larger materials to shift and roll to each side, enabling the heavier ends to face downward. In Construction and Demolition( C & D) Recycling, for example, this helps separate nails and other metal parts.
All images supplied by Martin Engineering
Screen vibrators are wear parts, so ergonomic access is important for workplace safety.
The steady increase in demand requires managers of older screen systems to increase production beyond the original specs.
www. africanmining. co. za African Mining Publication African Mining African Mining • April 2026 • 35