ACM mill noise is measured in dB(A) (A-weighted decibel), taken at 1 meter from the mill housing under normal steady running. The noise comes from three main sources: high-speed hammer/rotor mechanical impact, particle collision inside the grinding chamber, and induced draft fan airflow turbulence.
Typical Noise Range (JACAN ACM reference)
- Small / pilot ACM: 78–83 dB(A)
- Medium industrial ACM (diatomaceous earth, mineral fillers): 82–88 dB(A)
- Large mining-grade ACM: 85–90 dB(A)
With optional acoustic enclosure and vibration isolation pads, noise can drop down to 72–78 dB(A).
OSHA 8-hour occupational exposure threshold: 85 dB(A). Systems above 85 dB(A) require hearing protection for operators.
Key operational variables affecting ACM noise
- Rotor tip speed & hammer count
Higher tip speed and more hammers raise impact frequency → louder noise. When you increase hammer count to generate more fines, the overall sound level rises. Fewer hammers and moderate tip speed reduce mechanical noise, which aligns with diatomite gentle deagglomeration operation. - Material characteristics
Hard, dense, abrasive minerals create louder particle impact noise inside the chamber. Soft porous materials such as diatomaceous earth produce lower noise compared with crystalline silica or ruthenium powder. - Airflow setting
Higher fan airflow (max airflow setting for coarse grades) increases aerodynamic whoosh and turbulence noise. Reduced airflow for fine grades lowers fan noise but rotor impact noise remains the dominant source. - Mechanical health status
Worn hammers, loose fasteners, rotor imbalance or damaged bearings produce sharp, irregular abnormal noise, often jumping above 90 dB(A). Regular inspection is required.
Noise source breakdown
- Rotor & hammer impact + particle collision: main broadband mechanical noise
- Induced draft fan: continuous airflow turbulence and fan blade noise
- Vibration transmission: noise transferred to frame, foundation and ductwork
Noise control specifications for mineral processing lines
- Vibration isolation mounts under mill base to cut structure-borne noise
- Optional full acoustic enclosure with sound-absorbing panels (common for mining and filler plants)
- Fan silencer installed on exhaust air duct
- Proper rotor dynamic balancing after hammer replacement
- Flexible soft connections between mill and ductwork to block vibration transfer
A standard ACM mill normally runs at 78–90 dB(A) at 1 m. Noise increases with higher rotor tip speed, more hammers, harder feed materials and maximum airflow. Acoustic enclosures can reduce noise to ~72–78 dB(A). Hammer count adjustment for fines production directly changes mechanical impact noise. Operators must implement hearing protection when steady noise exceeds 85 dB(A).
