Wednesday, 26 February 2020
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Reducing vibrations and structure-borne noise

Lifts and air conditioning systems produce noise and vibrations during operation. What counts is good insulation, especially when such systems are set up next to offices, bedrooms or living quarters.

(Photo: © Sahlberg)

Double elastic bearings with KSD elements is the ideal solution. Lifts and air conditioning or ventilation systems are now standard in modern residential blocks, office complexes, hotels and cinemas. However, this machinery emits vibrations, oscillations and structure-borne sound into its surroundings. People frequently find the associated noises annoying – especially if the systems impinge on offices, living areas, bedrooms, cinemas and concert halls. Well-designed machine bearing systems are an effective measure to produce greater peace.

The solution chosen is often elastic bearings with spring damper elements. These are usually inadequate against structure-borne noise and the equipment requires double elastic bearings. However, compared to conventional damping components, this can usually only be realised by means of an additional intermediate concrete foundation, which is expensive.

Using KSD elements is far less complicated. Here the transmission of structure-borne noise into the surrounding structures is cut by up to an additional 20 dB compared to single elastic bearings. No intermediate concrete foundation is required. This reduces the structural height and weight and permits faster construction progress.

KSD elements can be deployed almost anywhere

KSD elements consist of two layers of a mixed cell polyurethane elastomer. The layers are separated by a heavy intermediate mass. A hot galvanised steel plate on the upper surface of the elements ensures even distribution of the pressure on the elastomer layer. There are seven types for different load demands; a maximum static load of 20,000 N (Newton) per element is possible.

HandwerkIn addition, KSD elements are resistant to oils, grease and moisture and effortlessly withstand temperatures between -20° C and +70° C. As a result, they are suitable for deployment outdoors.

Due to their good structure-borne insulation, they are above all suitable for insulating air conditioning and ventilation systems, whose surroundings are critical in terms of noise and vibration. The higher costs compared to single elastic bearings should already be taken into consideration in the planning phase.

Rope spring buffers are recommended

Normally, KSD elements are used in lifts beneath the car frame and pulley carriers. Rope spring buffers are recommended for the elastic suspension of the car and counterweight. Rope spring buffers are likewise oil and grease-resistant and made out of high quality chloroprene rubber. This material retains the ability to reduce the oscillations between rope and car for years and compensate different rope lengths.

Even great temperature fluctuations are no problem. Due to its stacking capacity, high static deflections, optimal oscillation behaviour and insulation of low frequency oscillations are possible. Furthermore, rope spring buffers provide outstanding structure-borne insulation and – despite their low structural height – provide good noise insulation with low post-oscillation.

Assembly simplified

Another advantage is that the spring travel can be precisely determined. The almost linear characteristic curve permits applications in a wide load area with relatively constant spring ratios. The burdened pressure surfaces of the rope spring buffers are fitted with vulcanised fabric as a result of which they can absorb far greater forces than cellular material of the same size.

Due to their special shape and configuration, the external diameter does not expand under load. Moreover, the geometric shape, which centres itself during installation, simplifies the assembly. As a result, old lifts can also be retrofitted without much effort with rope spring buffers.

Christopher Paul
The author is an application technician for oscillation technology at Sahlberg.

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