Vibration absorbers serve to prevent the inherent vibrations of operating machinery from damaging the components of the systems. Vibration absorbers include a huge selection of components used to protect other components in a machine from the inevitable vibrations, shock, and impact of operating machinery. This encompasses everything including rubber pads and foams, air springs and spring dampeners, and sophisticated wire rope systems and negative-stiffness isolators.
Elastomeric rubber bumpers, or rubber mounts, are mounted between two pieces of machinery to prevent vibrations from transferring through metal-to-metal contact. Consistent contact between two rigid parts results in expedited deterioration and therefore higher maintenance, repair and replacement costs. In order for a mechanical system to be its most cost effective, it has to be operating at its highest output which can often be affected by the amount of vibration caused. Through vibration damping methods, machines can run at higher speeds, and as improved linear deceleration can be achieved, higher processing rates will result in higher outputs for the manufacturer.
Without a shock absorber in place, normal operation would tear many machines apart in a matter of hours or even minutes. Two moving components of stainless steel moving against one another may break down immediately, while lasting for months safely with a simple piece of rubber with an appropriate natural frequency between them.
As essentially every heavy machine creates vibration in operation, vibration reduction technology can be found in nearly any industry involving machinery. Cars, manufacturing systems, washing machines, dishwashers, trains, air conditioners, all of these use some form of vibration control. Any machine with rubber feet for floor vibration control or rubber washers is using vibration absorbers.
Shock mounts and vibration mounts are commonly used to absorb jolts and bumps from the traveling surfaces and to prevent damages and discomfort to those in the vehicles. Molded rubber engine mounts are particularly crucial because the engine is a large source of vibration, and the metal-to-metal vibrations between the engine and the car body would quickly damage the engine. Rubber mounts are also used in industrial areas to prevent contact between vibrating machinery and other surfaces.
The concept of a vibration absorber is so simple and so integrated with the history of machinery that it's difficult to identify a 'first absorber'. There are a few potential candidates which may have been used for energy absorption to prevent rudimentary machines from shaking and vibrating too much, such as leather, cork, bladders of air, or heavy paper.
Alongside the gradual refinement of industry throughout the past few centuries, modern vibration absorbers naturally followed.
How It Works
While there are countless forms of vibration absorbers out there, the vast majority work on the simple principle of being more flexible and compressible than the materials they support. This can be achieved any number of ways, from springs and hydraulics to simple rubber pads, but all work on this principle of allowing safe compression, vibration, or flex in a system mostly composed of rigid pieces.
Rubber is a commonly used material in the vibration absorption process as it holds many elastic properties which enable it to absorb large amounts of kinetic energy with minimal rebounding energy. Rubber is made from long and coiled chains that give rubber the ability to recover from extreme deformation, and when rubber is vulcanized and fillers are added, it gets a multitude of characteristics, including, resilience, resistance to temperature, longevity, and ability to easily bond with metals. However, the most important properties of rubber, which make it the most sought after material, are non-linear stiffness and high shear modulus. Unlike coiled springs made from steel that shows stiffness only linearly, rubber can damp motion or vibrations from many directions because of its natural elastic ability. It also provides excellent slip resistance and so rubber bumpers, pads and mounts can also be used to further secure equipment and machines and to prevent their movement as a result of vibrations. Natural and synthetic rubber materials such as butyl, EPDM, fluoroelastomer, nitrile, neoprene and silicone are used in applications specifically requiring various characteristics of heat resistance, chemical resistance and hysteresis.
Other vibration absorbers rely on different qualities to create a smoother operation. Hydraulic shock systems for example are composed of a cylinder and piston rod with a hydraulic fluid of sorts. These are commonly used in vehicles to prevent jolts and bumps from the road disturbing the interior of the vehicle. The shock impact the piston rod which is forced into the hydraulic fluid. The fluid absorbs the kinetic energy and transfers it into heat energy which is then dissipated. In this way, a minimal amount of energy from the initial jolt reaches the vehicle itself. Pneumatic air shocks work in a similar way using air instead of hydraulic fluid, but converting the kinetic energy into heat.
- Passive vibration absorbers
- Active vibration absorbers
- Air springs 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 for use in a variety of vibration isolation applications.
- Brushings are placed between moving parts to absorb vibration.
- Cam followers are driven by circular motion. The cam follower traces the surface of the cam transmitting its motion to the required mechanism.
- Dashpots are absorption devices that use fluid to enact resistance. Once downward force is no longer being applied, the plunger-like device remains in position. Dashpots are used normally in small devices, such as instrumentation and precision manufacturing machinery.
- Helical isolators achieve attenuation of both shock and vibration and are made entirely of non-corrosive materials. Helical isolators are most commonly used for vibration and shock absorption in such industrial and commercial machinery as compressors, hammers, printing machines and other applications in which shock isolation is important to the effective and efficient running of the apparatus.
- Engine mounts are vibration isolators placed between an engine and the structure that supports the engine, in order to reduce the effects of vibration, noise and shock encountered during engine operation.
- Machinery mounts protect machines from vibrations emanating from within the equipment itself, as well as from other pieces of equipment. Machinery mounts are used on compressors, screw machines, pumps and generators.
- Rubber mounts are rubber components that isolate the vibration from moving parts.
- Rubber pads are vibration dampeners often placed between industrial equipment and the surface upon which the equipment rests. Rubber pads may have a ribbed pattern to prevent slippage.
- Shock absorbers use various methods to dampen vibrations caused by sudden motion and mechanical shocks.
- Shock mounts isolate and absorb the kinetic energy created by oscillatory mechanical components in order to reduce the noise pollution and physical wear otherwise caused by continuous vibration.
- Vibration mounts are rubber mounts used to protect a variety of industrial items, including engines, machinery and equipment components. Vibration mounts effectively reduce or eliminate oscillation.
- Vibration isolators are used to protect equipment by keeping the vibration of a component from spreading to the entire machine or work environment.
- Wire rope isolators consist of a metal cable configured in sets of strands. Wire rope isolators are used in applications in which exposure to chemicals, oils and high or low temperatures is common.
Benefits and Advantages
In all applications, the primary advantage of a vibration absorption component lies in its ability to minimize the wear and tear on other components. Unchecked shaking, vibration, and shock without any form of absorption will quickly tear any apart any system, no matter how ruggedly it may be constructed.
Even ignoring the massive cost advantage in using relatively inexpensive vibration absorption solutions to minimize wear and tear on vibrating components, you also have the massive gap in safety between a system in which shock absorption fails slowly and noticeably and a system in which major components fail catastrophically.
It's not an exaggeration to say 100% of modern industry and machinery depends on vibration absorbers to be safe, affordable, or viable at all.
How to Use Vibration Absorbers
It's difficult to put together a single guide to using vibration absorbers, given the wide variety of designs.
Maximizing the use of any vibration absorber comes down to the initial design. If you understand your application and design effectively, you'll have zero problems with installation or operation. If your design fails to account for all factors, you'll notice problems sooner or later.
For this reason, it's critical that you have your engineers carefully assess the needs for vibration isolation. A mistake in the design stage will cost you significant amounts of time and resources later.
Design and Customization
When designing and customizing your vibration absorption system, you'll need to make a few key decisions. Some of these will be rather straightforward, but others will require the insight of an engineer, unless you're operating based on a pre-existing standard.
A vibration absorber system can be a simple rubber mount or a complex system that can give six-degrees of freedom. However, a complex system is used only in a few applications and mostly supporting joints are used at a large scale.
The most common vibration absorbing system consists of supporting joints that link equipment or machinery to the surroundings, which reduces the unwanted transmission of vibrations. A well-designed vibration absorber consists of rubber envelope. The envelope has a spring that is fitted internally.
When rubber mounts are exposed to the load of the machine, the rubber goes under deformation and the spring is stretched. Generally, the rubber twists in the direction of the cross section of the spring. This action is what absorbs the vibration emerging from a machine and equipment. This mechanism, involving combined rubber and spring deformation, effectively isolates the vibration. If the vibration is not contained at this stage, it can cascade into catastrophic failure of the machine. Therefore, in all systems, the joints and mounts are critical for vibration insulation by averting the resonance effects, which can even collapse bridges.
Design of Rubber Mounts
The degree of rubber deformation is what that characterizes how much vibration can be absorbed without the mount being permanently damaged. Therefore, the degree of deformation a system can go into is kept in mind while designing the device and the spring. The other factor that is kept in mind is the shock loading. It is common for vibration absorbers to be exposed to shock loads, however, they are more damaging and detrimental to the device than the general periodic vibrations. Moreover, the vibration absorbers or isolators are designed to endure challenging environment, including corrosive and outdoor environments.
Vibration absorbers or isolators generally need flanges and sleeves to be fastened securely. The installation is important for engineers, as a minuscule gap or loose fastening of equipment and the supporting foundation can lead to malfunctioning of vibration absorbers. When they are fastened securely, they end transmitting vibration in the surroundings and their life too is cut short significantly, as the gap between can amplify the vibration.
Fabrication of Rubber Isolators
There are number of ways to manufacture rubber absorbers. However, the idea is to bond the spring and the rubber intimately. The connection should endure different conditions and environments, including more than ambient temperature. With different fabricating techniques, such as extrusion and molding with the help of a press, the rubber and the spring is permanently connected. However, the crucial step is the curing or vulcanization. It is this step where crude rubber material is reinforced. In the vulcanization step, additives, like, sulfur change the natural polymer structure, as bridges are made between polymer chains. Mainly, five types of additives are used, including, sulfur, peroxides, urethane cross linkers, metallic oxides, and acetoxysilane. Each of the additives gives unique property to the rubber. The additive is decided by the manufacturer based on the application.
Active or Passive
Majorly, vibration absorbers are of two types, passive and active. Passive vibration absorbers, as the name suggests, does not have any active parts and consists of rubber mounts, pads or mechanized springs that work as energy absorption equipment. The passive absorber or isolators made from rubber include pads, base isolators, and molded elastomers. The most common are rubber pads or elastomers as well as cork and dense foam. They are utilized to isolate vibration from machineries, household equipment, and vehicles. They are specifically used when medium to high frequency vibration and noise need to be isolated from heavy machineries. The typical natural frequency range is 3 to 40 Hertz, and based on requirement different pads are used. The rubber is also used in making bonded or molded mounts; they are used in instruments, aviation and machineries when vibration is in range of 10 to 20 Hz. Rubber is also used in base isolators, which are used in large structures and buildings. They are used to isolate low seismic frequencies.
Active vibration absorbers have electronic sensors and force cancellation measures that include electric power and control systems. Passive vibration absorbers perform two functions, first they isolate the payload from vibrations that originate in the support and second, they isolate the support from vibrations that originate in the payload. With the use of passive absorbers, machines, like washers, generators, and pumps, are isolated from the floor as they cause vibration in the floor and building. Rubber products, such as, engine mounts, shock mounts, and vibration mounts are used for isolating each equipment and instrument from the floor.
First and foremost, you'll need to determine whether your application demands active vibration absorption technology or simpler, less expensive passive absorption. In some fields, this is determined for you by industry standards or other overriding concerns, but in other applications you'll need to make the decision yourself.
What sorts of surfaces will be in contact with your vibration absorber? In some cases, this will be a non-factor, while in others, it will be perhaps the most critical component of your design. Make sure you aren't putting together a perfect absorption solution that wears down instantly due to abrasive surfaces—or damages the metal connector you're trying to protect in the first place.
Do you need your absorbers to last a long time without being replaced, or are you looking to build a system in which regular replacements are more cost and/or time efficient? This can govern any number of factors, including material, active vs passive, width of absorbing pads, and more.
A sterile environment with moderate temperatures and no caustic chemicals will naturally create different demands from the materials and design than a hot, high-pressure caustic environment.
How much weight will be on the vibration absorbers during operation?
Will the vibration absorbers be exposed to other forms of force, i.e. rotation, tearing forces, etc.? Will this change the resonant frequency?
A vibration absorption solution which only needs to keep your system from tearing itself apart, with no other requirements, will naturally look quite different from a solution in place on an identical system where even the slightest floor vibration could prove problematic.
Safety and Compliance
Because vibration absorbers encompass such a wide range of products with a massive number of specific applications across an endless supply of industries, it's difficult to offer a one-size-fits-all answer to safety and compliance. Nonetheless, there are a few universal principles of safety you'll want to keep in mind:
- Check vibration absorbers regularly
- Replace failing vibration absorbers immediately
- Do not rely upon a damaged or failing vibration absorber, ever
- Exercise extreme caution when dealing with any active vibration absorber under load
Beyond these, make sure you look into the specific safety and regulatory compliance considerations of your specific application, industry, and type of vibration absorber. Heavy duty shock absorbers, for example, can be quite dangerous in and of themselves, such as when adjusting compression, while a simple passive rubber absorber would be hard-pressed to injure anyone—unless you installed it wrong, or in the wrong role, and equipment failed as a result.
Outside of safety and compliance, immediate design requirements, and the other factors we've discussed, there are a few other considerations you may or may not want to keep in mind as you shop for vibration absorbers and choose a manufacturer or supplier. These aren't the only other factors, but they're a good start on keeping your eye on the big picture:
- Upkeep. How much will it cost to maintain your system with a particular type of absorber? How easy is it to replace absorbers in your system? Will trained personnel be available to maintain, replace, or otherwise manage the vibration absorbers?
- Scalability. If your operation grows in size, will your current plans hold up? Alternatively, will your system scale up to a larger size or more intense operation with your current plan for vibration absorption? If not, is that an acceptable limit?
- Flexibility. Do you need to be able to adjust your vibration absorber solutions down the line to improve system efficiency, or do you already have a firm design in mind that won't need to be changed? If the former, you need a strategy that allows for adjustments later, to a greater or lesser degree.
Four Steps for Buying Vibration Absorbers
Vibration absorbers are of many types, since they are used for isolating vibration from a number of mechanized equipment, and sometimes, even in large engineering structures. Evidently, there cannot be a single design that can fulfill all requirements. Therefore, if you are looking to buy vibration absorbers, you should go through a number of guidelines that can help you to select an appropriate absorber.
The first step includes characterizing the items that need to be isolated. You need to know the size, weight and moving parts of the equipment. The size will help you to decide what type of isolation would be appropriate, for example, a small machine may need only a single mount, whereas a heavy machine may need a combination of absorbers, mounts and pads. Similarly, weight helps you to decide the correct mount, since different isolators are made for different weight categories. Moving parts of equipment plays a major role in generating vibrations, therefore, moving parts must be designated in terms of speed, mass, and distance it travels. This is the primary information you will need before going to a supplier.
The second step involves understanding the environment where the equipment is installed or working. Industrial absorbers are different from laboratory absorbers; therefore, knowing the environment is important. There are a number of things that you have to observe in an environment, including, whether the facility is covered, corrosive, and encounters high temperature. Absorbers or isolators made for indoors cannot work optimally when exposed to UV rays; therefore, if the application involves outdoors, specific isolators are required. Similarly, rubber products like rubber bumpers, rubber pads, and rubber mounts are not very resistant to chemicals, and if they are installed in corrosive environment, they are made from different compounds that make then chemically resistant.
The third step involves knowing the nature of the vibration. A buyer needs to know the frequency, amplitude, and direction of the vibration emerging from the equipment. To know the frequency of vibration, an accelerometer can be used and a professional can be hired to do so. The amplitude of the frequency will help to conclude whether you need isolation or not. Similarly, the direction helps you to decide the locations where vibration absorbers are needed. However, this usually is needed when equipment and facility is new, in old settings, these things can be deduced from the parts that need to be replaced.
The final steps involve the cost and maintenance. Other than the cost of vibration system, a number of things need to be considered. Some systems need compressed air or soundproofing to work optimally, therefore, factor in the cost of air compression or noise cancellation in the final number. Other factors are shipping, installation, and site survey. Maintenance is other cost-inducing factor that governs the operation cost; a good quality isolation system that effectively reduces lower vibration frequencies and magnitudes costs more, and can work for longer time. However, it is not only the quality that decides the maintenance cost, you need to be careful of the compatibility of isolation system in terms of factors discussed above, including location of installation and environment.
It can be difficult to assess manufacturers for vibration absorbers, as it's rare that you've had much interaction with such companies until the moment you need them. Fortunately, there are a few rules of thumb you can use to identify the good manufacturers and avoid the bad ones. Some of these points are universal to any supplier or manufacturer, so feel free to apply them the next time you're looking at any potential business partner:
You should, first and foremost, always know what you're paying for and what you're getting from a manufacturer. You shouldn't be surprised by extra charges at the time of delivery, nor should you open up a shipment to discover things you assumed would be there weren't included in your purchase.
A good manufacturer should be professional. This can be somewhat difficult to assess at first contact, but you should watch out for certain telltale signs of problems to come; inconsistent response to calls, rude or apathetic support staff, broken websites or orders systems, and unreliable scheduling all point to an unprofessional operation. Work with a company that takes its business seriously.
You shouldn't need to speak to a dozen different manufacturers to fill your needs for vibration absorbers in most cases. You instead want a manufacturer with the versatility to provide your various necessities without a huge headache. The fewer companies you need to deal with, after all, the less your overhead will be.
When you want to change, a good manufacturer can keep up with what you want to do next. You shouldn't be chained so tightly that you can improve your operations when you identify a better type of vibration absorber, or a better design. A manufacturer that slows down your rate of improvement and refinement isn't one you want to get involved with.
Guarantees and Warranties
While it's the nature of vibration absorbers to wear down and fail over time, there should still be an expectation that they won't fail immediately. A good manufacturer will back its products with certain promises, concretely defined in your contract. A bad manufacturer will offer weaker promises, or obfuscate enough that they can slip out of replacements or other compensation should their products fail early.
The final point of a great manufacturer lay in the quality of the support staff. You'll be interacting with sales teams, receptionists, and help desks more often than anyone else at a company, in most cases; make sure there's a good degree of quality here. If you need to call with a problem or to check up on an order, it shouldn't be an ordeal.
The Right Manufacturer
While it's crucial that you select a generally superior manufacturer for your needs, it's just as important that you choose a manufacturer that suits your business and its goals. In other words, you don't just need a 'good' manufacturer, you need to pick the right manufacturer. Here are a few tips to help you further narrow down your options.
Communicating with your manufacturer shouldn't be a challenge or unpleasant. If you have trouble keeping in touch with a manufacturer due to scheduling conflicts, different preferred methods of communication, or any other reason, that can quickly become a significant challenge to your professional relationship.
It's not enough that a manufacturer have expertise in vibration absorbers, they need to have experience relevant to your specific application and industry. This only becomes more important as you get into more specialized equipment, or projects with more stringent specifications, compliance requirements, and fine tolerances. Not only will familiarity with your specific needs help ensure you obtain the right products, it will make every aspect of your relationship with a manufacturer more efficient and effective.
A mismatch in scale between a company and its supplier or manufacturer can quickly turn into a major headache. If the supplier is too small, then keeping up with the necessary volume is of course going to be a challenge, especially if your company grows further. If the supplier is conversely used to much larger volumes of vibration absorbers, it won't prioritize your company's needs in many cases. You want to consider not only the matching of your business in scale today, but tomorrow—you don't want to outgrow a manufacturer if you don't have to.
When your logistics work well together with a manufacturer, it tends to make every other aspect of your relationship easier to manage and more efficient. If you're relying on a highly automated, modern system of logistical software, it's going to be a pain to deal with a manufacturer who only takes orders handwritten or over the phone. The inverse, of course, will be true as well; sometimes, a cutting-edge logistical solution that makes life easier for your manufacturer only serves to obfuscate and create problems on your end.
Vibration Absorbers Terms
– Amplitude is the maximum value of a repetitively oscillating quantity (i.e. acceleration, displacement).
– The reduction of oscillatory motion in a vibratory object through the loss of energy in the form of heat during vibratory cycles. Vibration dampers increase the amount of vibratory energy lost during an object’s oscillatory motion, which decreases the vibration of the object.
– An indication of a vibration isolator’s ability to provide vibration control. Deflection refers to the amount that an elastomer, such as a rubber mount, moves due to a force, such as vibration or shock.
– The movement of an object from its initial placement. Vibration is a common cause of displacement.
– A material, such as rubber, that is capable of returning to its initial length after being stretched at room temperature to at least twice its original length.
Energy absorption is the process of reducing the strength and magnitude of vibratory motions. Specialized materials and devices accomplish this by converting kinetic energy into heat which is then diffused.
– The vibration of an object due to an applied force.
– A measurement representing the level of vibration to which an object can be subjected before sustaining damage.
– The occurrence of vibratory movement during an object’s displacement without the application of an external force.
– The repetition of vibratory motion during a specified period of time.
– Also referred to as "cycles per second," it is a measurement of vibratory motion or frequency that occurs per second.
– The integral of force over a time interval.
– The rate of change of acceleration with time.
– The number of cycles that an object freely vibrates during a given unit of time.
– Motion that repeats itself at measurable intervals of time.
– An increase in the vibratory motion of an object that occurs when an object’s natural frequency and the frequency of the force applied to an object are equivalent to one another. This frequency point is termed the resonant frequency.
– A force to which an object is subjected that disturbs the object’s stability, causing an imbalance of equilibrium. Shock is often isolated in conjunction with vibration to stabilize an object’s equilibrium.
– Steady state vibration exists in a system, if the velocity is a continuous periodic quantity.
– The amount of vibration generated by an object that is transmitted to the object’s support structure.
Vibration control involves isolating, dampening and canceling secondary oscillatory movements in industrial settings using a number of different devices and materials which absorb the kinetic energy of a vibration before it reaches adjacent surfaces.
Vibration damping within an industrial setting is a method of controlling and reducing vibrations made by machinery when design strategies have reached their limits.