Acoustic Cleaning - History and Design

History and Design

An acoustic cleaner consists of a sound source similar to an air horn found on trucks and trains, attached to the material-handling equipment, which directs a loud sound into the interior. It is powered by compressed air rather than electricity so there is no danger of sparking which could set off an explosion. It consists of two parts:

• The acoustic driver. In the driver, compressed air escaping past a diaphragm causes it to vibrate, generating the sound. It is usually made from solid machined stainless steel. The diaphragm, the only moving part, is usually manufactured from special aerospace grade titanium to ensure performance and longevity.
• The bell, a flaring horn, usually made from spun 316 grade stainless steel. The bell serves as a sound resonator, and its flaring shape couples the sound efficiently to the air, increasing the volume of sound radiated.

The overall length of acoustic cleaner horns range from 430 mm to over 3 metres long. The device can operate from a pressure range of 4.8 to 6.2 bars or 70 to 90 psi. The resultant sound pressure level will be around 200dB.

There are generally 4 ways to control the operation of an acoustic cleaner.

• The most common is by a simple timer.
• SCADA (Supervisory Control and Data Acquisition).
• PLC (programmable logic controller).
• Manually by Ball valve.

An acoustic cleaner will typically sound for 10 seconds and then wait for a further 500 seconds before sounding again. This ratio for on/off is approximately proportional to the working life of the diaphragm. Provided the operating environment is between – 40 and 100 °C a diaphragm should last between 3 and 5 years. The wave generator and the bell have a much longer life span and will often outlast the environment in which they operate.

The older bells which were made from cast iron were susceptible to rusting in certain environments. The new bells made from 316 spun steel have no problem with rust and are ideal for sterile environments such as found in the food industry or in pharmaceutical plants.

Acoustic cleaning began in the early 1970s with experiments using ship horns or air raid sirens. The first acoustic cleaners were made from cast iron. From 1990 onwards the technology became commercially viable and began to be used in dry processing, storage, transport, power generation and manufacturing industries. The latest technology uses 316 spun stainless steel to ensure optimum performance.