The traditional approach to granulator noise control is based on using palliative high-cost acoustic enclosures to reduce the spread of noise without tackling the noise generation at source. This approach is not only expensive, but it also has a substantial impact on access and therefore productivity and maintenance. Typical granulators generate noise levels close to, or above, 100dB(A). As such, they pose a very serious risk to hearing as it is not possible to guarantee adequate protection using PPE.
There is an alternative engineering approach that cuts the noise at source with the following benefits:-
- very low-cost compared with acoustic enclosure
- no effect on access, so no effect on productivity
- no effect on maintenance activities
- rapid deployment with minimum downtime
Granulator noise sources
Granulator noise is usually generated by 3 mechanisms:-
- Airborne sound from the blades or hammers, both aerodynamic (when run without material) and mechanical (impacts)
- Vibration from the granulator blades or hammers radiated as sound by the structure
- Web vibration radiated as noise on web-fed granulators
- Fan or blower noise from dust control and extract systems
Noise control modifications
The airborne sound path can be controlled internally, whilst high performance, rugged structural retrofit damping and impact control cut the vibration radiated noise. Blower noise is usually reduced using aerodynamic noise control technology that cannot clog and will last the lifetime of the fan without cleaning or maintenance.
Granulator noise control case study
The hearing risk posed by the 100dB(A) noise level from this plastic granulator was reduced at source by 98% (18dB) by designing a web damper coupled with internal modifications to the infeed path. Neither modification had any effect on operation or access. The cost of the granulator noise control modifications was c £5k compared with the previously proposed acoustic enclosure cost of c £30k.
