The purpose of an anti-vibration mount is to attenuate vibrations. The design of the vibration isolator is key to achieve the targeted stiffness and load capacity.
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The purpose of an anti-vibration mount is to attenuate vibrations. The design of the vibration isolator is key to achieve the targeted stiffness and load capacity.
This article aims to answer some of the recurrent questions about the design of anti-vibration mounts.
An anti-vibration mount is expected to last for many years, environmental conditions such as exposure to direct sunlight, oils or other deteriorating agents can cause the bond to weaken prematurely. In absence of these parameters certain maximum allowable bond stresses are used and should not be exceeded.
Compression 750 psi
Tension 150 psi
Shear 150 psi
A vibration isolator should have no region of high localized stress, particularly at the interfaces of the metal and rubber. Sharp changes in profile can cause high stress points, this might be caused by boltheads, boltholes, or indentations. Below are some examples:
For obvious reasons AMC MECANOCAUCHO prefers designs of anti-vibration mounts that incorporate a flat surface for bonding, as they provide lower regions of high localised stress.
At 60º C (140ºF) the rubber creep is from two to nine times greater than at 25ºC (80ºF) depending on the compound.
Anti-vibration mounts use rubber bonded to the metal to achieve an elasticity. However, depending on the type of loading the mounts receive they can exhibit different stiffness values.
TYPE OF LOADING LOAD-DEFLECTION (L/D) CHARACTERISTICS (A) Compression
(B) Shear
(C) Torsion
(D) Tension
(E) Buckling
The word compression is used to indicate a reduction in the dimension (thickness) of an elastomeric element in the line of the externally applied force. The stiffness characteristic of elastomers stressed in compression exhibit a nonlinearity (hardening) which becomes especially pronounced for strains above 30 percent. Compression loading is frequently employed to provide a low initial stiffness for vibration isolation and a relatively high final stiffness to limit the dynamic deflection under shock excitations. Because of the nonlinear hardening characteristics of compression loading, it is the least effective type of loading for energy storage and therefore is not recommended where the attenuation of force or acceleration transmission is the primary concern. (The energy stored by any spring is the area under the load-deflection curve.)
Shear loading, illustrated in the above figure, refers to the force applied to an elastomeric element so as to slide adjacent parts in opposite directions. An almost linear spring constant up to about 200 percent shear strain is characteristic of elastomer stress in shear. Because of this linear spring constant, shear loading is the preferred type of loading for vibration isolators because it provides a constant frequency response for both small and large dynamic shear strains in a simple springmass system. Shear loading is also useful for shock isolators where attenuating force or acceleration transmission is important, because of its more efficient energy storage capacity when compared to compression loading.
Tension loading refers to an increase in the dimension (thickness) of an elastomeric element in the line of the externally applied force. Elastomers stressed in tension exhibit a nonlinear (softening) spring constant. For a given deflection, tension loading stores energy more efficiently than either shear or compression loading. Because of this, tension loading has been occasionally used for shock isolation systems. However, in general, tension loading is not recommended because of the resulting loads on the elastomer-to-metal bond, which may cause premature failure of the material.
Buckling loading, occurs when the externally applied load causes an elastomeric element to wrap or bend perpendicular to the applied load. Buckling stiffness characteristics may be used to derive the benefits of both softening stiffness characteristics (for the initial part of the loaddeflection curve) and hardening characteristics (for the later part of the loaddeflection curve). The buckling mode thus provides high energy-storage capacity and is useful for shock isolators where force or acceleration transmission is important and where snubbing (i.e., motion limiting) is required under excessively high transient dynamic loads. This type of stiffness characteristic is exhibited by certain elastomeric cushioning foam materials and by specially designed elastomeric isolators. However, it is important to note that even simple compressive elements will buckle when the slenderness ratio (the unloaded length/width ratio) exceeds 1.6.
Combinations of the types of loading described above are commonly used, which result in combined load-deflection characteristics. Consider, for example a compression type isolator which is installed at an angle instead of in the usual vertical position. Under these conditions, it acts as a compression-shear type of isolator when loaded in the vertical downward direction. When loaded in the vertical upward direction, it acts as a shear-tension combination type of isolator.
The moulded shape of the rubber section of the vibration isolator has a great impact on the load deflection curve of the mount. Below are some examples of how the shape and design of the mount affects the stiffness of the anti-vibration mount.
Shape Force-travel characteristic curve Notes Symmetrical angled spring In top mount/wedge mount
Frequently used on rubber-metal mounts. Depending on the spring angle: degressive under compression to progressive with a steep angle. In the x direction, hard with a flat angle to soft with a steep angle. The spring rate in the y direction is always softest. Conical spring (section)
Frequently used on hydromounts. Behavior as for cup springs: linear to degressive, progressive at transition to cylindrical hollow spring. Radial spring rate variable, depending on core height and angle. Cylindrical hollow spring (section)
Frequently used as inner spring on hydromounts with intermediate ring. Degressive under tension, progressive under compression. Very soft and degressive in the radial direction. Rectangular spring
Frequently installed with bonding on one side as a stop or torque support buffer. Degressive under tension. Progressive under compression. Very soft and degressive in the transverse direction.
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Shape Force-travel characteristic curve Notes Cylindrical (section)
A standard article, bonded on both sides. Sometimes installed with one side used as a stop or torque support buffer. Degressive under tension, progressive under compression. Very soft and degressive in the transverse direction. Bushing (section)
Rubber between two tubes, standard catalog article. On engine mounts, mainly used as the small eye of pendulum mount. For good durability, the rubber must be radially preloaded (calibrated) The bush is considerably softer in the axial direction than in the radial direction. Loop (section)
Loops are special shapes used to close the working chambers of hydrobushings and box type mounts. They are also often used for setting the expansion spring rate.
Should you be interested in this topic do not hesitate to contact our applications engineers. They will be able to help and provide input. Contact form AMC-MECANOCAUCHO® Applications engineers.
Have you ever noticed how loud and shaky air compressors can be while they&#;re running?
Many people struggle with such excessive noise and vibration from their machines without realizing that the uses of rubber mounts can help.
These mounts are placed between the machine and its base to absorb vibrations and reduce noise, making the machine run more smoothly and quietly.
By understanding how to use rubber mounts, you can fix these common issues and improve the performance of your equipment.
With rubber mounts uses to reduce noise and absorb vibrations, no wonder that the applications of rubber mounts are varied in many appliances, from vehicles to electronic devices.
Have you ever found out these rubber mounts uses below in one of your equipment?
When you think about the uses of rubber mounts, one key application is to stabilize your car&#;s engine. You need rubber mounts because they absorb the vibrations from the engine, which reduces shaking and noise.
In that case, you need to place the rubber mounts between the engine and the car&#;s frame. By doing this, the rubber mounts can soak up the engine vibrations, while the metal part keeps everything in place.
This improves your car&#;s smoothness and quietness. It&#;s essential for you to regularly maintain the rubber mounts to ensure they function correctly.
In washing machines, you use rubber mounts to manage vibrations during the spin cycle. You should position the rubber mounts under the washing machine to absorb these vibrations and prevent movement and noise.
The rubber mounts use their properties to absorb the spinning drum&#;s vibrations, while the metal part keeps the machine steady.
So, if your washing machine is noisy or moving, you might need to replace the rubber mounts. These uses of rubber mounts are crucial for making your washing machine quieter and more stable.
Air conditioners benefit greatly from rubber mounts to control vibrations from the compressor. You need to install rubber mounts between the compressor and the air conditioner&#;s frame to absorb these vibrations.
The rubber mounts use their absorbing properties to reduce noise and keep the air conditioner steady.
So you need to check the rubber mounts if your air conditioner is noisy or shifting. Properly functioning rubber mounts uses will improve your air conditioner&#;s performance and lifespan.
In industrial settings, you can use rubber mounts to absorb strong vibrations from machines. You should place rubber mounts between the machine&#;s base and the support structure to manage these vibrations.
The rubber mounts use their absorbing capabilities to minimize noise and keep the machine stable.
Regularly checking and maintaining the rubber mounts is important for preventing operational problems. With these uses of rubber mounts, you can ensure that your industrial machines run smoothly and effectively.
For home appliances like refrigerators and dishwashers, the uses of rubber mounts to reduce vibrations and noise are important. Therefore, if you notice noise or movement in your appliances, you might need to pay attention to the rubber mounts.
In order to fix the noise and vibrations, you should locate the rubber mounts at the bottom of the appliances to absorb vibrations from their motors. Moreover, the rubber mounts use their properties to keep the appliances steady and quiet.
Understanding the uses of rubber mounts can help you maintain your appliances in good working order.
If your electronic devices do not perform well and have a short lifespan, you might need to replace their rubber mounts. In electronics appliances, rubber mounts uses are crucial to protect sensitive parts from vibrations.
Usually, the rubber mounts are put inside devices like computers and audio equipment to absorb vibrations that could cause damage. The rubber mounts use their ability to absorb these vibrations and protect the delicate components.
So, when your electronics are experiencing issues, checking the rubber mounts is a good idea. This one of the rubber mounts uses helps ensure the proper maintenance of your electronic devices.
Overall, the uses of rubber mounts are varied and essential for many types of machines and devices.
With their ability to help reduce vibrations and noise in many applications and machines, you can save your money on unnecessary fixes.
By understanding the different rubber mounts uses and keeping them in good condition, you can ensure that these devices operate smoothly and last longer.
So, have you checked the rubber mounts on your appliances?
If you do not have the spare yet, check out the rubber mounts catalog at Rubber Xperts!
We are a leading company in providing high-quality rubber products with years of experience and a wide range of client industries.
Need our assistance in choosing which types of rubber mounts you need for your equipment?
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