Vibration Damping: What Is It and What Rubber Is Best for It?

Posted By:  Sperry & Rice

Sometimes in products, or in industrial applications, vibration is an issue that requires a solution. In our business, we create solutions called vibration damping, and we do it with extruded rubber components.

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In fact, when vibration is an issue, the right rubber formulation can make all the difference. But first, let’s get back to basics. What is vibration?

Vibration is a mechanical occurrence where shaking or oscillations occur due to imbalances in a rotating part (like a motor) or uneven friction. If vibration isn’t controlled, it can cause damage to the entire assembly or unit, specific parts, or even worse, fail and cause damage far beyond a part failure. To prevent any of these bad things from happening, you need vibration damping materials and components.

Vibration damping uses materials, often rubber, to absorb vibrations caused by machinery or moving parts. It 

can take the form of rubber vibration mounts, pads, washers, isolators, or gaskets, and can be made with a variety of rubber compounds, but are commonly made of natural rubber, EPDM, neoprene, and butyl rubber.

We’ll cover these materials one by one, but first, a few qualities that vibration dampeners require: adhesion to substrates, durometer, and resistance to other substances (ie, chemicals, oils, heat). Which material you choose for your vibration damping needs will depend on your application, and it’s important to know how different rubber compounds perform under different conditions.

Substrate Adhesion

No material can deaden vibrations if it doesn’t adhere to your parts or components. If a rubber doesn’t adhere well to your substrates, it will fall off and render the damping useless. 

Durometer

Making sure the rubber used in your damping components isn’t too hard or too soft is crucial. Too hard and you may lose damping ability; too soft and your part may tear and fall off. It’s important to test different formulations to determine the exact right durometer for your project.

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Resistance

Considering the environment in which your rubber components will be used is extremely important. Vibration dampeners need to survive and lead a productive life, so understanding what elements the rubber will be exposed to is crucial. Temperature, oils, chemicals, weather, etc., can wear down parts and cause failure so it’s vital to understand rubbers’ interactions with its environment.

There are a few different vibration damping rubber materials used in most applications:

Natural Rubber

Natural rubber is a good vibration damping material that features high tensile strength, but its main drawback is that it doesn’t hold up well outdoors or in conditions that feature oils, due to its poor oil resistance.

EPDM

EPDM is a synthetic rubber that features high resistance to heat and weather and features excelled substrate adhesion and durometer. It can also be formulated in numerous different compounds for many different applications.

Neoprene

Neoprene excels in two specific areas for vibration damping: its superior adhesion to substrates, and its resistance to oil. Neoprene is a bit more expensive than other rubbers but its ability to stick to substrates (especially metal) and its ability to perform in oily conditions makes it a great damping option.

Butyl Rubber

Butyl rubber is a synthetic rubber that features low gas and moisture permeability and is extremely resistant to heat, abrasion, and tearing, which makes it an excellent option for damping vibrations.

As you can see, vibration damping parts and components can be made with a variety of rubbers, but it is crucial to find the best performing and most cost-effective option for your project. But that can be difficult unless you are a rubber expert. Fortunately, Sperry & Rice has a trained team of engineers experienced in all rubber formulations to help you determine which is right for your next project.

Sperry & Rice offers innovative engineering, advanced manufacturing processes, and comprehensive quality controls to produce precision extruded synthetic rubber components for the HVAC, automotive, transportation, and appliance industries. Our reputation lies in making sure that the rubber we provide makes the finished products of our clients reliable, and of the highest quality. 

I need some explanation of the terms damping and isolation. Is it correct to define damping as reducing the response at the resonant frequency. while isolation is defined as reducing response due to shifting of the frequency away from the resonant frequency.

I am a little confused, because what we normally call vibration dampers (rubber, wire etc.) does not really reduce the response at the frequency, but rather shifts the frequency into the isolation area. So, is "vibration damper" the correct term to use for such a device?

Thanks for any clearifications.

Is it correct to define damping as reducing the response at the resonant frequency.

I think that is roughly correct. Damping corresponds to energy absorption which reduces the magnitude of a resonant peak.

Isolation is typically an attempt to prevent vibration from transmitting through some path which may be accomplished by adjusting resonant frequency of the mounting. For example often large fans are mounted on a spongy spring isolation mount which has resonant frequency far below fan speed. This tends to reduce transmission of fan vibration to the base.

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Eng-tips forums: The best place on the web for engineering discussions. izax1 : 1. Damping normally has an effect over a much wider range of frequencies than just the resonant frequency, although it will have a greater effect there.
2. In addition to isolators, whose primary functional intent is to isolate something from vibration rather than to alter frequency, there is a device called a vibration absorber, whose function is to intentionally alter the frequency response of a structure such that it has minimal response at some problem excitation frequency. Such a device does not necessarily involve damping, but there is a variant known as a damped vibration absorber which does introduce additional damping. Some people refer to damped absorbers as dampers, which may or may not apply, either intentionally or accidentally, to some of the devices you refer to. "When we say dampers (for rubber mounts etc.), we are mostly talking about isolators."

About the only time I want any damping around is when a resonance is being excited.

If the mounted resonant frequencies are low, like 1/3 the forcing frequency, yes. Then isolation can occur, and any "damping" provided by the rubber (which would tend to increase the fan vibration passed to the floor) is of little consequence.
If the fan must start and stop or run at wicked low speed, having some damping to reduce the vibration as the fan passes thru the mounted natural frequencies.

Hydraulic engine mounts work that way. At high engine speeds damping would just get in the way. Its good They provide damping to limit amplitude at low engine speeds or maybe when the mounted powertrain gets "bump tested" jumping over railroad crossings.
Firstly, damping removes vibrational energy from a system by converting it into heat energy whereas isolation attempts to prevent energy from reaching the isolated component by temporarily storing it and releasing it again once the impulse has past.

Isolation is a reduction in the ability of a system to react to an excitation. This is achieved by the use of a flexible decoupling element between the equipment and mounting surface. It allows the inertia of the isolated component to oppose and thereby reduce the vibratory motion transmitted to the support. Damping removes energy from a system by converting kinetic energy into heat energy (in the case of conventional shock absorbers, for example)
Every isolator has a peak resonant frequency below which transmissibility is almost unity and above which attenuation occurs. However, should the natural frequency of an isolated system coincide with the forcing frequency then resonance will occur i.e. amplification of vibrations. In this case, damping is required to reduce the amplitude of the resonant response by removing energy from the system. The ideal isolator would have as little damping as possible in its isolation region and as much as possible at the systems natural frequency to reduce amplification at resonance – this is clearly not possible with standard damping systems.
If there is no resonance present in the important operating frequencies of a system then damping can actually make things worse as it leads to a loss of isolation efficiency. The damper will act somewhat like a strut and vibrations are then transmitted to the isolated element. For example rubber is not an ideal isolator as it not only has isolation properties but also some damping properties inherent to the material. This can increase the transmission of non-resonant vibrations.

Rob45

You may be right, but I have come across supplier who at least communicate that they don't differ between the two. May be that is because they think the customer will not understand the difference.

The main problem though, is on the engineer's side, when they get the impression that rubber mounts (or any other device normally termed "damper") reduces the respons at the natural frequency, when they, in reality, shifts the frequency (to a lower value) That can generate wrong solutions to a design.
It is interesting to read this long list of posts and realize that most of the responders don't understand how isolators work. Some have hinted about the effects, but nobody really answered the initial question.

First, an isolator works by shifting the natural frequency of the supported mass. To be effective, the isolators must lower the spring-mass resonant frequency well below primary forcing frequencies. How far below the resonance is located determines the isolation effectiveness or efficiency. Note that there is NO mention of damping in this spring-mass system.

However, on start/stop, the spring-mass system will run through a fundamental resonance. In order to limit motion at the resonance, most isolators employ damping. Large amounts of damping will hurt the effectiveness of the isolation system, so a tradeoff is required.

Isolators constructed out of rubber or other natural energy dissipating materials have inherrent damping. It is not necessary to have the damping in order to isolate, but most manufacturers make their mounts from damping materials to cover all possible applications.

In answer to the original question, the correct terminology would probably be damped vibration isolators, since you can purchase isolators that have very little damping (such as spring towers).