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Noise can be a source of major cost - both direct and indirect - to industry. Hearing damage claims, insurance, and subsequent noise control measures can all prove extremely costly. However, the latter is an area where large cost savings can be achieved, both on existing and new plant, subject to purchasing specifications. According to Peter Wilson, a Partner at the Industrial Noise & Vibration Centre in Slough, one common mistake which can prevent these savings being realised is to automatically resort to enclosures; an expensive option, but rarely the most effective. Wilson, a mechanical engineer with over twenty years experience in noise and vibration, is a staunch advocate of the view that noise control is an engineering problem that should be solved by engineering means, in particular through noise control at source. He says: "Effective noise control must be based on an accurate diagnosis and not on assumptions. All the options must be considered, not just the conventional high cost palliatives of enclosures and silencers." His belief is borne out with evidence from a growing number of case studies illustrating how noise problems have been successfully solved at source through the specification of sound deadened steel (SDS). One example is the dramatic reduction of high noise levels at a magistrates court in Barrow, achieved through the use of Sontech sound deadened steel. Tests carried out by specialist noise consultants, Hepworth Acoustics, revealed the source of the noise to be rain falling on 0.9mm aluminium flashing around the roof lights. They advised that a reduction of 5 dB(A) would be significant and that a 10dB(A) reduction, which would halve the perceived loudness, would be "very good". A wide range of sound damping products were considered, but rejected as being insufficiently waterproof or robust enough for the coastal location. The solution was to retrofit 1mm Sontech to the flashings, which resulted in an excellent 13 dB(A) reduction in noise levels. In another case, motor components group, Unipart, was concerned about potential noise levels from a new materials handling system being installed at its Demand Chain Management Division warehousing and distribution headquarters in Cowley. The company was keen that noise levels should fall well within health and safety legislative regulations and a target level of 80 dB(A) was set. This covered noise arising from the drives, mechanisms and pneumatics used in the distribution area., as well as that generated by the impact of full and empty tote boxes used during the handling process. A number of mechanical solutions, using conventional techniques, including ceiling baffles and cladding to ceilings and walls were considered, but discarded as it became clear that they could not achieve the desired result. The system designer, Logan Fenamac (UK) Ltd, then called in consultants from the Industrial Noise and Vibration Centre to advise on a suitable alternative. Detailed proposals were devised, using various materials, which enabled them to take the solution closer to the source of the problem. However, documented test reports showed that, on retrofit modifications to the parts of the system where the impact of the totes was creating a high level of noise, Sontech sound deadened steel proved most effective. A 1/2" closed-cell foam faced with Sontech achieved a 9 dB(A) reduction on the system's chutes and an 8 dB(A) reduction on the return conveyor shelf. 4 and 5 dB(A) reductions were achieved respectively on the side guards and end stops. Commenting on the use of Sontech, Logan's Operations Director, Michael Jeffrey, said: "To cover the sorter hall with ceiling baffles would have cost over £100,000. Sontech offered us a much better solution at a very small fraction of this figure. During tests we were amazed at the result. When the inside of a work station was clad with the sound dampened material, noise from the tote handling operation was reduced significantly." Developed by Corus Service Centres, Sontech is produced by bonding two metal skins together with a visco elastic polymer core 60 microns thick. Its composition makes it particularly effective in applications where noise is generated by impact and panel resonance. Noise producing energy is absorbed by the two metal skins moving relative to each other and generating shear strain, which is in turn dissipated as negligible heat. The higher the strain which is transferred to the polymer, the higher the energy dissipation. Tests carried out on the material to compare its properties with un-damped steel have shown fewer and lower broad-based resonance peaks for the sound deadened steel, indicating a higher level of damping over a wider range of frequencies. The degree of noise reduction achieved will depend on the shape of component, method of support, and end use, although a reduction of up to a 30 dB(A) reduction is possible. Sound deadened steel has traditionally been used in the automotive industry, but Corus Service Centre's unique, highly flexible production facilities have made the product available for use in a broad spectrum of industries and noise sensitive applications. It has the capability to produce Sontech in a huge range of sizes, grades of steel or different combinations of metals e.g. Plastisols, Aluminium/Zintec or a Zintec/stainless steel composite. In addition, most workshop operations used for ordinary steel and aluminium can also be carried out using Sontech, including guillotining, blanking, piercing, drilling, painting and mechanical joining. To avoid distortion during bending and folding, the bending sequence should be from the inside out, allowing the skins to slip relative to each other. In addition, Sontech can also be resistance welded. However, the visco-elastic core acts as an insulator so, in order to weld one sheet of Sontech to another, or to other components, a shunt path will first need to be set up to allow local heating of the resin. This softens the resin and allows it to be compressed. For further information contact: Clive Way or James Billingham | |
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