What Is Resonance in Vibratory Screening?

Resonance in vibratory screening is a destructive operating condition that occurs when the screener's motor speed matches the system's natural frequency, causing uncontrolled vibration amplitudes that can damage the machine, its mounting structure, and surrounding equipment. Every vibratory screener has a natural frequency determined by its mass and spring stiffness, and operating at or near this frequency causes energy to accumulate rather than dissipate, producing violent shaking far beyond the designed stroke.

All vibratory separators — whether manufactured by ScreenerKing, Sweco, Kason, Midwestern Industries, or others — must pass through their resonant frequency zone during startup and shutdown as the motor accelerates to or decelerates from operating speed. Proper machine design ensures this pass-through happens quickly, limiting exposure to the resonance zone to fractions of a second. Problems arise when equipment is operated at or near resonance for extended periods, which can occur with improperly programmed variable frequency drives (VFDs), worn springs, or incorrect motor speed settings.

Resonance vs. Normal Operating Vibration

Why This Matters

Resonance is the most damaging condition a vibratory screener can experience. Understanding and avoiding it is essential for equipment longevity and operator safety:

• Equipment damage — Resonance can crack welds, break springs, destroy bearings, tear screen cloth, and damage the vibrating motor in seconds. A single extended resonance event can require thousands of dollars in repairs.
• Structural damage — The amplified forces transmit through the support structure to the building floor, mezzanine, or platform. Without proper vibration isolation, resonance loads can damage structural steel and concrete.
• Safety hazard — Uncontrolled machine movement at resonance creates a serious risk to nearby personnel. Product can be thrown from the screener, and fasteners can loosen or break.
• VFD risk — Variable frequency drives allow operators to adjust motor speed, but slow acceleration/deceleration ramp rates can hold the screener in the resonance zone. VFDs must be programmed to ramp through the critical speed zone rapidly.

Related Glossary Terms

• Natural Frequency — The system's inherent vibration frequency that defines the resonance point
• Critical Speed — The RPM at which the motor speed matches natural frequency
• Vibration Isolation — Springs and mounts that contain vibration and define natural frequency
• G-Force — The controlled force multiple that becomes uncontrolled at resonance
• Spring — The isolation component whose stiffness determines natural frequency
• Amplitude / Stroke — The vibration displacement that spikes at resonance

Resonance FAQs

What is resonance in vibratory screening?

Resonance occurs when the vibratory screener's operating frequency matches its natural frequency, causing vibration amplitude to increase dramatically and uncontrollably. This condition produces excessive noise, structural stress, and potential equipment damage. All vibratory screeners pass through resonance briefly during startup and shutdown, which is why speed ramping and proper spring isolation are critical design features.

How do you prevent resonance in a vibratory screener?

Resonance is prevented by designing the screener to operate well above its natural frequency (typically at 3 to 5 times the natural frequency), using properly rated isolation springs, ensuring rapid pass-through of the resonant frequency zone during startup and shutdown, and maintaining correct motor speed. Variable frequency drives (VFDs) must be programmed with fast ramp rates to avoid dwelling at critical speed.