Properties of damping materials and their uses

Mechanical engineers rely on damping materials wherever unwanted vibrations, oscillations, shocks or noises occur. If these vibrations remain uncontrolled, they can lead to precision losses, premature material wear, and even machine destruction. As a result, damping materials not only increase the service life and performance of machines, but also often protect them against damage. In addition to foams, felt and rubber, specialty plastics are also used for producing damping materials. This blog article provides an overview of the various damping materials and how to use them.

What is a vibration?

From a purely physical point of view, a vibration is a time-based periodic change in a physical parameter about its equilibrium state. Vibration can be described by the parameters amplitude, frequency and phase or phase angle. A vibration is a periodic mechanical vibration that can usually also be heard and felt. Mechanical oscillations or vibrations most commonly occur on rotating and oscillating components.

There are several forms of vibration:

• Harmonic: The time-based graph is described by a sine or cosine function, without damping or the like. External influences.
• Excited: A vibration excited by an external periodic force (increasing amplitude).  The exciter vibration is in the resonance range of the natural oscillation. The more the excitation frequency approaches the natural frequency, the stronger the resulting resonance.
• Damped: The amplitude of a damped vibration decreases over time due to energy losses, e. g. by friction or damping.

Natural oscillation and resonance

A so-called natural oscillation occurs when an external force acts on an elastically deformable body once. This natural oscillation is caused by the return force, which is proportional to the deflection and returns the body to its equilibrium state.

If force shocks with the same exciter frequency act on the body in addition to the natural oscillation, the natural oscillation and the exciter oscillation overlap to a higher amplitude, a so-called oscillation peak occurs. This can cause damage to the system. This is where vibration damping and vibration insulating materials step in.

You can also find out more about the different forms of vibration in our article on the intrinsic vibration behavior of springs.

Vibration absorption and isolating vibrations

Vibrations can be counteracted in a number of ways. Vibration absorption is the attempt to reduce the peak (amplitude) of a vibration by way of energy extraction.
Coupled hydraulic, pneumatic, and/or electric dampers or other mechanically dampening elements can also be used in addition to the property of a material used to achieve a damping effect by elastic deformation and internal friction.

Damping converts vibration energy into heat. The amplitude of the vibration is reduced, which reduces vibrations and makes them more controllable. The damping effect thus contributes significantly toward improving the service life and reliability of machines and machine components. However, since damping is usually achieved by converting kinetic energy to heat, the damping material can overheat if overloaded, the effects of which can range from a change in damping properties to the failure of the overloaded damper.

On the other hand, vibration isolation means ideally keeping the occurrence of vibration completely away from a system or, where applicable, transferring the resulting vibration to another system. This is usually done by installing elastic vibration isolators. Vibration isolation is effective when the natural frequency of the vibration isolated system is less than the lowest frequency component of the spurious vibration. Vibration isolators can be, for example: steel springs, rubber buffers, insulation plates made of cork, rubber, felt, sand, etc.]

There are several types of vibration isolation:

• Active vibration isolation: The environment of a machine is protected against vibration.
• Passive vibration isolation: The machine itself is protected against ambient vibrations.

Vibration cancellation is yet another principle, especially on large equipment/large machines. By attaching a mass-bearing additional oscillator, the energy of the excitation is removed and the vibration movement of the main system is cancelled out.

What are damping materials?

Damping materials are used to absorb or reduce vibration, noise (oscillations) in machines. For example, there are damping materials for the following types of damping:

• Oscillation vibration absorption / vibration damping: Movements of vibrating equipment and machinery are damped. The materials used for this purpose are elastic. They are placed between the source of the vibration and the object to be protected.
• Reduces unwanted mechanical vibrations, e.g. PU coating on surfaces.
• Sound insulation: Absorbs/insulates against sound waves to reduce noise. Sound proofing materials are often soft and porous. This can cause sound waves to refract in the material, become trapped, and be absorbed.
• Mechanical damping, e.g. shock absorption: Sudden impacts and loads, including acting forces, are absorbed and distributed. This protects sensitive components against damage. Shock-absorbing materials are elastic and can absorb a great deal of energy.

MISUMI offers a wide range of damping materials for a wide range of applications. The following overview provides assistance for selecting the appropriate MISUMI component:

In general, many plastics also have damping properties. Learn more about the properties of plastics in mechanical engineering in our article about plastics.

Which material is suited for vibration absorption?

Materials react differently to vibrations. Hardness is one characteristic that affects vibration. Hardness indicates how resistant a material is to the ingress of another material. The higher the hardness value, the more resistant the material is to deformation. The hardness is determined with different hardness test methods, e.g. hardness according to Rockwell or hardness according to Shore. Learn more about the different hardness tests in our article Hardness and Hardness Test Comparison.

Hardness also affects elasticity, which in turn affects the vibration frequency (the number of oscillations per unit of time). High-hardness materials have lower elasticity. The vibration frequency increases with increasing elasticity (spring constant) and decreasing mass of the body, see also the following overview of various damping materials:

• (1) Dampener sleeve
• (2) Damper plate
• (3) Vibration damping gels
• (4) Rubber coating version
• (5) Rubber-metal elements
• (6) RUBLOC
• (7) Vibration-absorbing plates
• * Load capacity (kg) for 4 units

The damping elements shown here are presented in detail below:

Rubber coatings

Surface-applied rubber coatings are an effective damping method against acoustic emissions. The elastic material converts the kinetic energy acting on the material into heat through deformation and internal friction, thereby reducing the vibration amplitude. The following figure shows a typical design of a dampening element, with a combination of vibration dampening gel and rubber coating.

The version with vibration dampening gel and rubber coating is designed for light loads and low vibrations. The gel absorbs low frequencies at a maximum working load of 25-35 kg and a minimum usable frequency of 13 Hz. The silicone base body with ethylene rubber coating is weather-resistant and suited for outdoor use. Silicone dampers also provide longer fatigue life than traditional rubber dampers.

Gel bushings or gel damper sleeves

Due to their high damping properties, gel bushings are specifically designed vibration damping elements that are used especially at high frequencies and low load capacities. The soft, gel-like material effectively absorbs vibrations. Gel bushings can be used as follows:

Vibration-absorbing gel

Vibration-absorbing gels, especially silicone-based gels, are ideal for vibration reduction in applications that have ultra-light to medium loads and low vibrations. They are characterized by high flexibility and adaptability. Compared to traditional rubber dampers, silicone gel dampers provide longer life and retain their damping properties even under long-term stress.

Vibration-absorbing gel plates

Vibration-absorbing gel plates are ideal for light loads and minimal vibrations that are difficult to dampen with conventional rubber. They are heat treated, do not exhibit undesired resonances and require uniform load distribution. These gel articles are only suited for vertical loads, as lateral displacements or torsional loads greatly reduce their efficiency and service life. They should also not be subjected to mechanical stresses.

Vibration-absorbing rubber brackets

Vibration-absorbing rubber brackets are suited for light to medium loads. Due to their durability and high load capacity, rubber brackets are often used in machine and vehicle applications, while providing high resistance to wear and external environmental influences.

RUBLOC

The RUBLOC® vibration damper is a trademark of Rubloc Imexin and is suited for light to medium loads with low to medium vibration. The special composition of dirt-repellent chloroprene rubber minimizes contamination of material surfaces that come into contact with the damper, while the remaining properties are similar to those of conventional chloroprene rubber. The diagonal propagation of the vibrations within the plates results in a high damping effect.

Sound proofing / sound insulation

Soundproofing or sound insulation refers to measures that prevent or reduce sound transmission. Sound insulation is designed to reduce sound. This is achieved either by reflecting or by absorbing the sound.

The texture of the surface greatly influences the ability to reflect or refract sound. Similar to the reflection of a beam of light in optics, smooth surfaces reflect sound directly back into the room, resulting in sound being cast back at nearly the same level. Rough or textured surfaces, on the other hand, refract the sound waves and diffuse them in different directions. Soundproofing solutions such as acoustic plates or foams take advantage of this principle. The wave energy of the sound is split into smaller amounts of energy by this diffusion and is attenuated accordingly by getting trapped in the material. There are also special acoustic foams and fiberboards that completely absorb sound wave energy. Sound insulation materials are suited for absorbing high frequencies but are less suited for low sound frequencies. Silicone gel mats, rubber buffers, etc. are better suited at low frequencies. While silicone gel mats have excellent and effective vibration absorption, rubber buffers are available for a wide range of applications due to their variety of designs, variants and materials.

The following shows the behavior of the various damping options:

Example - Use of plates for sound and shock absorption

MISUMI offers plates made of a wide variety of materials, e.g. polyurethane rubber (PU / PUR), low-return polyurethane rubber, antistatic polyurethane, nitrile butadiene rubber (NBR), polyurethane foam, felt, ceramic or polyethylene foam.

Foam plates and rubber sheets are particularly suited for damping in general and for sound proofing in particular. A wide range of applications can be addressed because they are available in a wide range of Shore hardnesses. Foam plates or rubber sheets can, for example, reduce the sound emissions of a system. They are also suited for damping material handling components in conveyor systems or as lateral guides to protect components and transported goods against damage during impact. In particular, hard rubber plates or low-impact rubber or foam plates reduce this impact energy.

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