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Rotational movement of an unbalanced mass generates vibration 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:

E=100*[1-1/((fd/fn)2-1)] (1)

Where:

E-percentage of vibration isolated

fd-Disturbing frequency of the isolated machine

fn-Natural frequency of the isolated machine fn<Hz>=15.8/(d st)0.5 where d st is the static deflection of the elastic element in <mm>

For a 1" static deflection we will have a 3.14 Hz natural frequency that will isolate 98% of the vibratory force of a piece of equipment running at 1800 rpm located at the ground level.

This is the common vibration isolation selection for equipment designed to be installed on the 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". 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.

Complete solution designs for machines, motors, and drives vary and usually include enclosures, noise barriers or silencer design for the device and vibration isolation. For some applications other isolators are common

Air springs use a contained column of air inside an elastomeric bellows or sleeve to buffer cyclic motion, provide vibration isolation, or serve as a pneumatic actuator. They can be used as a primary suspension spring or a secondary component inside a coil spring for automotive and heavy transportation applications. Other applications include vibration isolation on rotating machinery, use as linear actuators in place of pneumatic or hydraulic cylinders, and load lifters.

Air springs can be thought of as heavy-duty balloons that provide a smoother riding suspension when compared to metallic or plastic springs, when used for actuation and isolation tasks within industrial equipment and within vehicle suspensions. They incorporate a carefully designed rubber and fabric bellows that contains a column of compressed air. The rubber bellows itself does not provide force or support load - the column of air does this when the air spring is inflated according to the load required of it. Load capacity can vary from 40-40,000kg.

As actuators air springs provide linear motion. They offer a favorable stroke to compressed height ratio when compared to air cylinders and can accept a wide variety of actuation media such as air, water, nitrogen or anti-freeze.

As isolators, air springs are effective in reducing the harmful effects of vibration. They can simultaneously isolate vibration and regulate load height, as well as allow constant vibration isolation under varying loads.

Air springs provide a number of distinct advantages when used in place of air cylinders or other types of springs. Most notably, their cost is generally much lower than that of a pneumatic cylinder with comparable capabilities. Additionally, they are more compact, with a minimum height generally less than the available stroke. And with their flexible bellows design, lacking seals or guides, they can be installed more easily with side load flexibility.

In terms of performance, air springs offer another wide range of advantages. They do not require lubrication, which leads to greater system cleanliness, and less overall maintenance to continuing performing at a high level. Since they do not need to be lubricated, air springs are designed without seals, which cause them to induce less friction, and are better able to handle constant force, especially in high-speed applications. Since there are no seals sliding against exposed surfaces, an air spring can often survive abrasive and corrosive environments that require special consideration when a conventional cylinder is used. However, careful consideration should be used to keep air springs away from petroleum-based fluids and chemicals that attack rubber.

Gas springs provide controlled motion and speed for elements, such as lids and doors, that open and close. They typically rely on the fluid dampening of a gas such as nitrogen in the cylinder.

Linear dampers is an inclusive term that can be applied to many forms of dashpots and shock absorbers; typically used for devices designed primarily for reciprocating motion attenuation rather than absorption of large shock loads.

Shock absorbers typically contain both a fluid or mechanical dampening system and a return mechanism to the unengaged position. They vary from small device application to large industrial and civil engineering uses.

Dashpots are typically distinct in that while they use controlled fluid-flow to dampen and decelerate motion, they do not necessarily incorporate an integral return mechanism such as a spring. Dashpots are often relatively small, precise devices used for applications such as instrumentation and precision manufacturing.

Shock absorbers are devices designed to provide absorption of shock and smooth deceleration in linear motion applications. They may be mechanical (e.g. elastomeric or coil spring) or rely on a fluid (gas, air, hydraulic) which absorbs shock by allowing controlled flow from outer to inner chamber of a cylinder during piston actuation. The piston rod is typically returned to the unloaded position with a spring.

Linear Dampers is an inclusive term that can be applied to many forms of dashpots and shock absorbers; typically used for devices designed primarily for reciprocating motion attenuation rather than absorption of large shock loads.

Shock Absorbers typically contain both a fluid or mechanical dampening system and a return mechanism to the unengaged position. They vary from small device application to large industrial and civil engineering uses.

Dashpots are typically distinct in that while they use controlled fluid flow to dampen and decelerate motion, they do not necessarily incorporate an integral return mechanism such as a spring. Dashpots are often relatively small, precise devices used for applications such as instrumentation and precision manufacturing.