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 Most cities in India have high noise norms. The fallout of high noise levels is development of symptoms like high blood pressure and heart ailments. People in a city like Mumbai, claim experts, are often exposed to noise levels in the region of 80-85 decibels, almost twice as loud as the safe levels WHO has recommended for cities. Looking at the damaging effects of higher noise levels, it is only logical for noise norms to get stricter, especially vehicular noise pollution. The noise generated by an engine is not from a single source. It is in fact an addition of various noises generated by different engine components. Roughly divided into airborne noise generated by valves, tyres, transmission, etc, the other is structure borne noise. If the airborne noise is generated by components deep inside the engine, and is transmitted by the surrounding air to the outside of the engine, structural noise is generated at the surface of the engine. Typical examples of structural noise include the oil-pan (sump), engine structure and the body.
Given the nature of its origin, it is difficult to treat structure borne noise. However, treated successfully, there's little else that is as rewarding. The effect is substantial reduction in overall noise. Consider Antiphon AB of Sweden. Represented in India by Amiabo Trading, Pune, the company has over the years developed a wide range of noise control materials and products, often in close cooperation with its clients. Addressing structure borne noise, at the core of Antiphon's technology is a laminate sheet. The laminate sheet consists of two metal sheets of half the thickness joined together by a noise damping polymer. At first, the laminate sheet looks like any normal piece of sheet metal. Tapping at part of it however reveals the difference. The sheet transmits hardly any noise. There is no ringing sound either. Referred to as Antiphon MPM, the laminate sheet actually replaces the structural sheet metal that would otherwise be used, often without any increase in the thickness and weight of the materials. The structure borne sound damping material can often eliminate the need for special screening or sound absorption, which would otherwise take up a considerable amount of space and increase the weight of a product. Formable and weldable sandwich consisting of two metal facing sheets enclosing a visco elastic inner layer as mentioned earlier in the article, The two metal facing sheets in Antiphon, are in most applications of cold rolled steel, but in principle any type of metal or alloy can be used. Also drill-able, an interesting aspect of the laminate sheet is that the visco elastic inner layer is optimised for different temperature ranges between -5°C and +125°C. In this way it is possible to achieve maximum vibration damping of structure borne sound when the sandwich material is used in various applications such as engine parts, vehicle bodies, white goods or office machines.
We are talking mainly about automobiles here, and engines and transmissions to be precise. So white goods and office machines left aside, the Antiphon laminate sheet is being increasingly employed by automakers for diverse applications like oil sumps, transmission covers, etc. Automakers, according to S Sridhar of Amiabo Trading, are switching over to stamped parts of laminate sheet steel, which reduces the overall noise generated by the engine. Adds Sridhar, “The switch-over from using normal sheet steel to laminate sheet steel is not as simple. There is learning curve for the stamper as the stretch and deformation characteristics of the laminate steels are different from those of normal sheet steel.”
Antiphon AB, through its associate in India, is providing a comprehensive service to developers of parts and components in terms of assessing the noise characteristics. The company is also providing a comprehensive service to stampers, and with assistance to physically turn out the parts. The guidance provided by Antiphon, according to S Sridhar, includes material selection (optimum grade of steel for that particular part), selection of the correct grade of laminate, correct shape of the blank to be used and suggestion on modifications to the basic dies used for optimum results. Sridhar, drawing attention towards an oil pan report by Greaves, says that clients of Antiphon in India include Tata Motors, ASAL, Mahindra & Mahindra and SKH Metals. He concludes that his company is in discussions with Metalman-Cellini and Greaves Cotton.
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