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IES 2000 Vibration Control Systems

IES engineers design simple and cost effective vibration control systems. Industrial equipment creates vibration and can transfer it to an enclosure or facility. Isolator springs pads and mats can solve the problem. 

It is known that the rotational movement of an unbalanced mass is generating vibrations transmitted to the surrounding construction elements mainly through the bearing points of the load. The disturbing frequency is equal to the rotation frequency of the motor or engine of the vibrating equipment.

The method of reducing the amount of energy and displacement transmitted to the surface below the equipment is to install an elastic element between the equipment and the bearing surface. This elastic element is characterized by its constant k<N/m> and rated load <kg> or <lbs>. Given these data, each elastic element has a natural vibration frequency. The target in design is to select such an elastic element that its natural vibration frequency is several times lower than the disturbing frequency. This selection will provide a theoretical efficiency given by the following equation:

This is the common vibration isolation selection for equipment designed to be installed on ground or on a perfectly rigid surface. The equation (1) is based on the assumption that the deflection in the vibration isolator is extremely large as compared to the floor deflection, and that the moving mass of isolated equipment is extremely small as compared to the floor mass.

When the vibrating equipment is installed on a floor at an upper story location the floor has a mass and a spring rate of its own. To account for the floor deflection the selected vibration isolator should have a deflection at least 6.5 times higher than the deflection of the floor. For example if the equipment is located on a 20 ft bay the floor deflection might be as much as 1/360 x 240"=0.66". Then the vibration isolator should have a minimum static deflection of 4.25". It is obvious that using a vibration isolator that has a static deflection of 1" will be very good at ground level but will do nothing for the floor isolation at an upper level installation.

The need for higher deflection materials has caused reclassification of products: Pad materials, such as neoprene, cork, combinations of cork and neoprene, fiberglass, sisal fibers, felt, lead or any other material, provide limited deflection. These deflections are normally 10-20% of the pads thickness. Therefore, pads are good for high frequency noise breaks, and since their deflections are almost small in comparison to upper floor deflections, their use should generally be confined to basement areas, non-critical jobs or situations where job costs must be kept to an absolute minimum regardless of performance.

Neoprene mountings fall into the 0.2" to 0.5" deflection range. They do provide sufficient static deflection to offer protection under small high-speed equipment such as close coupled pumps up to 3 HP, vent sets, small heating ventilating units, etc., where the unbalanced forces are so small that in all probability only a noise break and minor vibration relief need be provided.

Steel spring mountings are by far the most widely used commodity on critical jobs today. Steel springs are practical through 5" of static deflection and even more on specific occasions. Springs provide an easily variable design medium, and steel spring installations are as permanent as the machine itself when selections are made within proper stress values. Most modern isolators are simply steel springs that have been designed with large enough diameters to provide stability without the need for a supplementary, often detrimental, housing. They are generally manufactured with adjustment bolt and a pad made of neoprene or some other material in series with the spring to attenuate the high frequencies.

Environmental noise testing can be done for many types of noise and vibration. Solution designs vary from enclosures, noise barriers or silencer design for the device and vibration isolation.