Reactive Dynamic Mass Balancing; Plant Noise and Machine Vibration
Plant Noise Surveys; Environmental Noise Measurement & Control
Acoustic Doors; Compliant Mountings

Dove Thermal Engineering has innovated a compact and low-cost reactive mass balancing system that eliminates machine vibration and reduces plant noise from centrifuging dryers (where both mass and distribution of the load varies with run time). In contrast to the intricacies of conventional electro-mechanical systems that partially limit machine vibration, the only moving part in its detection stage is the core of a LVDT (Linear Variable Differential Transformer). This gauges micron-scale displacements between shaft and foundation ring and signals to a Mitsubishi modular PLC. A set of three equi-spaced radial water pockets let into the rear of the load drum distribute a fixed mass of water between them by means of solenoid-operated valves, continuously resolving dynamic balance and zeroing machine vibration within the system. Engineers of a certain age will appreciate the entire set-up being built as a working Meccano model before translation onto full-size, 6-foot drum, machines. This employed a dry ballasting arrangement, which we later developed for use in other types of rotating equipment where mutually variable masses and their distribution give rise to machine vibration.

In schemes to reduce transmissions of environmental and plant noise, passive arrangements for absorption of machine vibration may offer a first line of defence, either at source or at the building limits. Whilst no substitute for good machine design, maintenance and operation, compliant mountings are an effective low-cost means of attenuation in many instances.

Various classes of plant must be rigidly connected to massive embedded or floating foundations to counteract cyclically shifting forces. For example, to overcome problems of boundary plant noise emission from heavy, low speed rotating equipment at the Leicester works of Eversmart Express, we designed a set of architectural acoustic doors with compliantly-mounted internal leaves tuned to absorb plant noise at prevailing frequencies and harmonics. The company had been issued with a Prohibition Order limiting hours of operation to uneconomic levels, whilst near-continual street access was required. The replacement doors had a leaf area approaching 10 sq.m, and gave SRI values of 27, 40, 55 and 73 dB at 63, 125, 250 and 500 Hz respectively. The Order was lifted upon their installation, enabling 12-hour working to be resumed.

It was one of many projects within the UK dyeing industry dealing with plant noise and machine vibration, effluent control, fabric processing, steam raising and other manufacturing services requirements. Beyond this, we have undertaken environmental noise surveys to BS4142 in support of planning applications, public inquiries and factory development programmes.