Vibration Acoustics

AREAS OF APPLICATION

Our products are used in sectors such as:

  • Generation of electrical energy.
  • Air compressors and Blowers.
  • Pumps and Pumping equipment.
  • Industrial vehicles.
  • Machine Tools.
  • Marine propulsion and auxiliary equipment.
  • Agricultural and construction equipment machinery.
  • Acoustic isolation of premises.
  • HVAC Industry
  • Chiller Installation
  • FCU / AHUs Installation
  • Transformer Installation

1.-NOISE AND VIBRATION PROBLEMS IN PREMISES

Sound that is unpleasant to the human ear is known as noise, and ecologically speaking is a form of pollution that is becoming increasingly more widespread due to town and city development.

It could be defined as a vibratory phenomenon propagated in an elastic medium (ceilings, walls, floors and the air itself) causing perturbations in it. To isolate any premises or venue properly, the first step is to identify the composition and the values of the noise (spectrum of frequencies, noise level etc.).

Once we know the magnitude of the noise or the vibrations to be insulated, we must built an unconnected off-the-floor frame which gives us the insulating and dampening values we need.

2.- BOX-IN-BOX Concept

The “box in box” concept consists of acoustically isolating a room by placing flexible elements between the structure of the building and the elements that can be seen and are in direct contact with people.

We offer a wide range of mounts for noise and vibration isolation of floors, ceilings and walls. There are Solutions available with rubber technology, Sylomer®, springs or a combination of them.

3.- ANTI VIBRATION SOLUTIONS

A. RUBBER

Natural frequency between 10-15Hz. Effective in medium and high frequencies. Small static deflections. High dampening.

B. SYLOMER

Natural frequency between 7-12Hz. Effective in medium and high frequencies. Very small static deflections.

C. SPRING

Natural frequency between 2-7Hz. Effective in low and medium frequencies. Large static deflections. Same static and dynamic behavior. Low dampening, excellent isolation.

4. THE IMPORTANCE OF THE DYNAMIC FREQUENCY OF THE ANTIVIBRATION MOUNTS

Real data are required to carry out a study and calculation of a premises. The static stiffnesses that are provided by static load-deflection graphs are not valid for the calculation of a realistic insulation.

Experience Shows that the static calculations are very different from reality.

At the moment, AMC has a dynamic testing machine that can generate the most common types of vibration on premises, giving real frequency values, insulation, loss angle and critical dampening rate

5. INSTALLATION, 50% OF THE SOLUTION. OUR ADVICE: INSTALLATION OF PERIMETER SEAL.

The correct installation of these mounts is a critical factor to obtain optimal results of acoustical isolation. To achieve this, it is important To make a proper perimeter sealing, in order to avoid acoustic bridges that could lead to the transmission of noise through the walls.

1. Calculations

Calculates anti-vibration solutions by taking into account data such as weight, mount positions, type of machine, C. of G., frequency of excitation, etc.

2. Design

After studying each client’s specific needs for the application and the Isolation performance required, MASS TECHNOLOGIES can design new products where conditions permit.

3. Test and Dynamic Characterization

Continuous development of new products demonstrates its support in R&D. Our laboratory is equipped with the most advanced dynamic testing equipment.

4. Vibration Measurement

We provides its clients with many years of experience and know how in measuring vibrations and noise in the field so as to reduce machine-produced emissions of noise and vibrations.

THEORY OF VIBRATION ISOLATION

MASS SPRING SYSTEM

A mass spring system may be represented by a mass “M”, excited by a force ”F” and supported on an elastic stiffness

element “K” with a dampening factor “C”. The frequency of the mass spring system is equal to:

The effectiveness of the suspension may be measured by transmissibility, i.e. by the force which is transmitted by the machine to the ground or floor. It is defined as the ratio between the force transmitted to the ground, FOT, and the

original force produced by the vibration FO. Another practical term is often used to describe the efficacy of an anti-vibration mount, namely the degree of insulation, which is:

Transmissibility Equation: E=(1-T)x100%

Examining this curve allows us to reach basic conclusions for an effective isolation.

If the frequency of excitation is  times less the natural frequency, transmissibility is greater than one, then the force

transmitted is greater than the excitation force, there is magnification of the vibrations. When we work in this area, the existing damping in the system is important. The greater the latter, the smaller the magnification of the vibrations will be.

If the frequency of excitation is   times greater than the natural frequency, transmissibility is less than one, or in other words the force transmitted is less than the force originated in the system, then we are in the damping area. To achieve the greatest isolation, the lowest possible natural frequencies should be sought. There are two ways of doing this:

  • By increasing the system mass.
  • By reducing the stiffness of the anti-vibration mount.

 

To increase the efficacy of the isolation in the damping area, it is advisable to have low damping, although weak damping

generates greater displacement when passing through the resonance, it is advisable to use a damping coefficient t so  that passage through the resonance does not give rise to inadmissible displacement for the machine.

 

STATIC AND DYNAMIC STIFFNESS: All elastomers suffer dynamic stiffening but metallic springs have a very low dynamic stiffening due to the low internal friction of the metals. Therefore we can consider that the springs have identical static and dynamic stiffness.

DAMPING: The metallic springs have very low damping. As we have mentioned previously, the metal spring coils, do not show any internal friction and therefore there is no energy dissipation through this phenomenon. Dynamic laboratory tests have shown in practice that the damping for this kind of mounts is almost null and this is the reason why these mounts have been combined with viscous dampers for applications where more damping is demanded. For example genset suspensions.

CREEPING AND LONG-TERM BEHAVIOUR: The spring mounts do not have the creeping and continuous increase of deflection all elastomers have, but spring coils have also certain relaxation that depend on the applied load and the temperature. The higher the load and temperature  are, the higher is the relaxation. Temperatures above 80ºC and high loads, may cause a small loss of height in the spring. This set is always lower than the usual values of elastomers.

 

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