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Questions fréquentes


Are the springs metates appropriate for vibration insulation?

The metal springs are not sensitive to large temperature differences and are resistant to most organic substances.
For vibration isolation of machines, preferably using metal springs made ​​of steel. In the steel springs there is no difference between static and dynamic rigidity. When using metal springs, arebe obtained vertical natural frequencies of 1.5 to 8 Hz.

Steel springs are capable of storing large strain energies with significant amplitudes of flexion. Its elastic characteristics do not vary with time.
The compression coil spring metal spring is generally used for vibration isolation of machines due to its characteristics of large linear deformation (deformation under load curve) and the wide range of stiffness levels available.


Are the elastomers the solution of isolation and vibration damping?

For the elastic deformation and small Young's modulus, the elastomers are suitable materials for springs. Compared with metal springs have a higher damping.
Characteristics such as stiffness and damping depend on the selection of basic material and components of the mixture of materials and the shape of the dock. They are also affected by environmental conditions such as temperature. The long-term aging is largely dependent on the composition of the material.
In the elastomeric springs are usually different static stiffness and dynamic stiffness, with a higher dynamic than static. Should only be calculated natural frequencies of the system isolated from the dynamic stiffness.

When we use elastomeric springs, can be obtained vertical natural frequencies of 6 Hz to 20 Hz.
In general, the curve of deflection under load of the spring is not linear, but in practice can be linearized to the service load.
For large compression loads and distributed, are commonly used elastomeric spring-shaped plates or screens. Normally, for these applications, the vertical natural frequencies are greater than 12 Hz


How wil the process of calculating and determining in a solution for vibration isolation?

The increased complexity of the calculation of the insulation system is to determine the percentage of required insulation. This value depends on the acoustic quality objective to be achieved and a number of factors including:

  • Position of the nearest protected area.
  • Terms of the support structure of the building.
  • Features of the machine or machines to be installed (power, mass, center of gravity, rotation frequency, distribution, etc).
  • Unions through conduits to vary its response to vibration.

Since this analysis should be performed on each project and depends on the acoustic quality objectives and conditions of each installation, which in this example will be based on performance objectives and specific vibration isolation, for example 90% and 95%.

We assume that it is the isolation of a single machine, and we resolve six cases:

  • Case A1: centrifugal fan of 500 rpm, and 90% required insulation.
  • Case A2: centrifugal fan of 500 rpm, and 95% required insulation.
  • Case B1: Axial fan of 750 rpm, and 90% required insulation.
  • Case B2: Axial fan of 750 rpm, and 95% required insulation.
  • Case C1: 1500 rpm pump and isolation required 90%.
  • Case C2: 1500 rpm pump and isolation required 95%.

To correctly select a vibration support is necessary to provide the deflection and calculate the weight acting on it.

To do this we using the following formulation (inverse of the transfer) which determines the percentage of isolation as a function of the excitation frequency and natural frequency of the system:

△ (%) = 100 [1 - 1 / (((ft / d) ^ 2) - 1)]

If △ (%) = 90 or 95% and given that: ft (rpm) = ft/60 (Hz)

and solving the equation (1) fn and operating in each case we obtain:

             A1 - 90% A2 - 95% B1 - 90% B2 - 95 % C1 - 90% C2 - 95%
fn (Hz)     2,5            1,8          3,76           2,72          7,53        5,4

For A2 the required natural frequency is so low (below 2 Hz) that requires the application of compressed air isolators natural frequency between 1 and 2 Hz.

In all other cases and from the formula that relates the deflection fn we obtain the deflection in millimeters required for each case:

d = (15.76 / d) ^ 2

                      Case 1    Case 2    Case 3    Case 4   Case 5   Case 6
d (mm)              39    -------------     17.5         33.5        4.4         8.5

From here we will go to catalog and on the minimum deflection function obtained and the different considerations auto_install obtain the proper insulating.


Isolation system design based on the acoustic requirements. Laws and regulations.

Everyone knows the national and regional laws governing limits of transmission of both airborne noise and vibration, so we will not insist on them. Just do the following considerations.

  • The air noise allowed at night to stay protected are very audible and thus annoying.
  • The values ​​for the assessment of maximum transmitted vibration are clearly permissive. In fact, several studies on the transfer of machinery generated relatively far from the protected areas or relatively close to railway buildings have shown that despite the enforcement, there are very significant differences between the value of the transmission spectra generated when by machinery or if passing train and when it is not. This difference can cause serious inconvenience to be perceived subjectively. Finally, we must not forget that vibration levels are below standard, according to the response of the structure of the building, create air noise bothersome, even at times may exceed permitted levels of airborne noise.

All this means rethinking the appropriateness of continuing to work with legal values ​​are too lax and perhaps obsolete.

"We intend therefore comply with the rules and get by or on the contrary we want to provide our facilities for serious sound quality objectives to eliminate the discomfort caused by our equipment and facilities and also for our own benefit and improve their operational stability and significantly reduce maintenance costs and breakage?

The answer to this question lies in the hands of all, manufacturers and installers of machinery, equipment suppliers and insulation materials and even as agents directly involved.

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