Vibration absorbers are shock reducing devices used to protect a wide range of machinery and equipment from damage caused by intermittent or consistent vibrations. Vibrations are an inevitable result of many mechanical procedures and items such as large industrial machines, air conditioning units, automobiles, washing machines and dryers, railway cars and vibratory finishing equipment.
The vibrations produced from the operation of certain kinds of processes and equipment can be a hazard to nearby objects. Therefore, items such as rubber pads, engine mounts, bushings and shock absorbers are used to reduce the transfer of energy between a machine and its components or outside environment by placing them between the floors and vibrating equipment to both reduce the noise of equipment-floor vibrations and to eliminate the risk of equipment damage. Vibration absorbers, or vibration isolators, also help to minimize the noise produced from engineering and mechanical operations. In addition, they provide vibration control and energy absorption for both small and large heavy-duty applications. For sensitive measuring equipment or control panels, even gentle vibrations could adversely affect the output of the machines. Hydraulic shock absorbers tend to provide the most powerful protection from jarring shocks and vibrations, leading to their common application in motor vehicles and precision equipment.
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. In addition, cars, trucks and other moving transportation vehicles use nearly every type of vibration absorption available to protect numerous parts within the engine and vehicle chassis from vibration and shock damage. 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.
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. 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.
Vibration absorption is a simple way to prevent equipment breakage and noisy operation. The components used to prevent excessive vibrations and noises from equipment processes are often simple and cheap. For a manufacturer, installing vibration absorbing parts is a decision that will quickly pay off. Replacing machinery parts or repairing damage caused by vibrations can be very costly. Damaged or ill working equipment could result not only in production slowing, or stopping altogether, but also in potential worker injury. Furthermore, excessive noise in a factory or manufacturing setting could contribute to an unsafe work environment, making the need for vibration absorption methods important to meet. Consumer households and commercial laundry businesses place rubber pads beneath washing machines and dryers which are specially designed to absorb the motion caused by spin cycles, reducing equipment noise and giving laundry equipment longer life. Household air conditioners typically have some form of vibration isolation preventing vibration between the air conditioner and its window housing. Rubber or foam vibration absorbers are used simultaneously for vibration isolation and for soundproofing in audio equipment applications such as speakers and sub-woofers. Common automotive and industrial applications for vibration isolating rubber bumpers and rubber pads include railway cabins, industrial machinery, radiators, electronic equipment, welding equipment and vibratory finishing equipment. The benefits are numerous and that is why vibration absorbers are used in such a variety of applications.
Vibrations are an inevitable byproduct of functioning machines, whether it is large or small. If the vibrations emanating from a machine are not contained, it can be damaging to the immediate surroundings as well as to the machine itself. Therefore, industrial machines, automobiles, washing machines, air conditioning units, railway cars, and other mechanized machineries are equipped with vibration absorbers.
Vibration absorbers are a range of components that absorb vibrations and isolate the machinery from the surroundings. Vibration absorbers, based on the technology used in making them, are classified as passive or active vibration absorbers.
Passive vibration absorbers involve specialized linkages and materials that absorb and reduce the mechanical vibrations, whereas active vibration absorbers consist of actuators that cancel out the vibration. Evidently, active vibration absorbers are more sophisticated than passive designs, as they involve a feedback mechanism in the form of an electronic circuit and sensors that read the vibration and based on the magnitude of vibration, produce cancelling vibration measures. Active absorbers are mainly used in complex buildings and structures to cancel the effect of wind as well as earthquakes.
The passive systems are more extensively used than active absorbers, as they are simple and can be installed and operated in conjunction with most the industrial equipment and machinery, such as motors, washing machines, HVAC systems, and pumps. However, some designs of passive vibration absorbers have application in civil structures, where they are used for base isolation. Other designs are found in laboratory equipment and high-end audio, which are sensitive to vibrations.
There are a number of passive vibration absorbers:
There are more designs, other than these systems, that have specialized application, including wire rope system, rubber base systems, and tuned dampers.
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.
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
Vibration is an undesirable result associated with mechanized equipment and machineries. The vibration emerging from machines can be damaging to equipment and the environment, therefore, an array of vibration absorbers are used for damping and isolating vibrations from machines. Whether it is industrial equipment, pumps, compressors, instruments, vehicles, aviation, or large structures, all are fitted with vibration absorbers, one or of other type.
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. 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.
Rubber mounts are most extensively used in a range of industries because it has some unique properties. Rubber reduces the transmission of vibration to a component and supporting structure, as rubber can act as a spring that has its own natural frequency. 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. In nutshell, rubber acts as a great damper, absorbs the vibration energy, and releases it efficiently. There are other properties that also make rubber a suitable material for vibration and shock isolation, including damping, ease of installation and handling.
The passive absorber or isolators made from rubber include pads, base isolators, and molded elastomers.
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.
- 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.