Comparison of vibration isolators with silicone to anti-vibration products made of natural rubber compounds

August 19, 2014

Comparison of vibration isolators with silicone to anti-vibration products made of natural rubber compounds

Vibro-SiL Silicone Vibration Control Products is our newest addition in the existing range of vibration isolators under the brand VIBRO. The constantly increased demand for a raw material that will offer increased capabilities in regards to extreme temperature, without reducing the vibration efficiency motivated us to create the new anti-vibration product category Vibro SiL.. All the products included in this category are primarily made of silicone gel compounds specially selected in order to meet all specific demands.

These products offer reliable solutions to vibration control projects in food refrigeration rooms, bakery ovens, in food industry, in military and avionic applications.

General characteristics and properties of silicone Rubber compounds are collected below from several bibliographic sources such as, ,

The most important characteristic in regards to vibration control and vibration isolation is damping. The damping characteristics of silicone and rubber are compared. That offers engineers another parameter in selecting the most appropriate vibration isolators for each project.

Heat & Cold resistance

Silicone rubber can sustain high and low temperatures significantly better than organic rubbers that are primarily used as a raw material for anti-vibration products. Silicone rubber can be used indefinitely at 150oC with almost no change in its vibration isolation capabilities. It withstands use even at 200 oC for 10.000 hours and in some cases it can even sustain heat of 350 oC for short periods. Therefore silicone rubbers are thus suitable as a material for rubber components used in high temperature environments. That is particularly useful for projects that require -antivibration products in high temperature countries like the Gulf and Middle East.

On the other hand, silicone rubber also has excellent resistance to cold temperatures. The embrittlement point of typical organic rubber is between -20 oC and -30 oC, compared to -60 oC to -70 oC for silicone rubbers. Even at temperatures at which organic rubber turn brittle, silicone rubber remains elastic. That is a very critical parameter for vibration isolation products as deflection is possibly the most significant factor to achieve high vibration isolation. Some products withstand extremely low temperatures of even – 200 oC. That makes anti-vibration products with this capabilities very popular in Northern Europe, Canada, Russia and other countries requiring vibration isolation products that can sustain low temperature.

Generally speaking, silicone rubber hardness when heated in air with decreasing elongation as it deteriorates; but in sealed conditions it softens as it deteriorates, and its operating life at high temperature is shorter in sealed conditions than in air.

This softening results from the degradation of the silioxane polymer. Adjusting the silicone rubber formula, using a different curing agent, and/or post curing can help prevent softening in hot, sealed conditions. Such properties are also available.

Flame retardancy

If silicone rubber is brought close to a flame, it will not ignite easily; but once ignited it will continue burning. It is possible to impart flame retardancy and/or self extinguishing properties by adding a small amount of flame retardant. Some silicone rubber products have received UL94 V-0 certification according to the UL94 (USA) standards for flammability classification. When they do burn almost no black smoke or noxious gas is produced during combustion because these products contain none of the organic halogen compounds typically found in organic polymer rubbers. They are used in consumer electronics and business equipment; in closed spaces such as aircraft, subways and building interiors. These silicone rubbers contribute to making all these environments safer.

Compression Set

When using rubber materials for gaskets that will be under compression in heat conditions, the ability of these materials to recover from compression deformation is a crucial consideration. The compression set of silicone rubber is consistent over a wide temperature range from -60 oC to + 250 oC. Although the compression set of typical organic rubber is relatively low around room temperature, it increases significantly as temperatures rise. Silicone rubbers generally require post curing. Post curing and selection of a proper curing agent are particularly recommended when using silicone rubber to make molded items for which low compression set is desired.

Vibration Absorption

The loss modulus (tan δ)* of silicone rubber is generally low, making it ill-suited for use as a vibration insulator. Products with enhanced vibration absorption performance, however, absorb vibration consistently over a wide temperature range, from -50oC to +200 oC

Additional technical details in regards to silicone vibration control efficiency and other  is presented below.

G-Properties of Silicone rubber
Silicone rubber is characterised by an excellent retention of many desirable properties over a wide range of temperatures. From indefinitely at -50°C to up to five years at 200°C. At moderate temperatures silicone rubbers offer unlimited lifetime.

Mechanical properties
a-Tensile and fatigue properties
As one might expect those properties will vary with the particular stock, how it has been processed and postcured. It is worth mentioning that some vulcanisates, particularly high strength stocks, will demonstrate a great change in modulus as they are subjected to repeated stress cycling. This is the “Mullins effect”. It is due to the rupture of filler-polymer physical (hydrogen) bonds during flexing. These weak bonds re-form when the specimen is at rest for some time. As stated before, silicone rubber is known for the retention of its properties. Its tensile strength is not particularly high but, compared to other rubbers, it is not very much affected by temperature.

b-Hardness and compression set
The practical hardness range of silicone rubber is 25 to 75 Shore A. Softer as well as harder grades can be obtained with a considerable sacrifice in other properties. This is done by reducing the molecular weight or increasing the filler content. The specific gravity of silicone rubbers ranges from 1.1 to 1.6. The FMVQ gums have the highest density.
As shown in the graph, below, the resistance to compression set of silicone rubber is excellent over its entire service temperature range. Low compression set is an essential property in seals, “O” rings and gaskets.
The torsional modulus attains a value of 700 kg/cm² at the temperatures shown in front of each rubber nomenclature.

c-Release and vibration damping
The most critical characteristic is vibration dampening which is the use of silicone for our range of anti-vibration products. The release characteristics of silicone rubber are superior to any other rubber. They are used as coatings on release papers or machinery parts. Furthermore, silicone rubber is ideal as vibration damping material. It exhibits little change in transmissibility or resonant frequency overh the temperature range (-54°C to 149°C). Its dynamic absorption characteristics do not change with ageing. It is an ideal material for noise and vibration control.

Electrical properties
Silicone rubber is the best flexible electrical insulator available. Furthermore it retains dielectric strength and power factor over a wide range of temperatures.

The above properties combined with the high thermal conductivity of silicone rubber, its extreme resistance to ozone and a corona resistance make it an exceptional electrical insulating material but primiraly and excelent sollution for vibration isolation, especially in projects that due to extreme temperature silicone anti-vibration products are required.

Thermal properties
a-Thermal expansion
The thermal expansion of silicone rubber is very high. It is twice that of rubbers and twenty times that of steel. As a result silicone mouldings shrink upon cooling. The addition of silica fillers reduces considerably the expansion.
b-Thermal conductivity
The k value of silicone rubber is two to three times higher than that of organic rubbers. It contributes to faster cure times. It also improves the heat dissipation in applications where heat is generated by friction, flexing and conduction.

Gas permeability
Silicone rubber is highly permeable to gases. It is twenty times more permeable to CO2 than natural rubber and two hundred times compared to polyethylene. This property can be used advantageously in applications where gas separation is required.

As silicone in non-toxic, bio-compatible and sterilizable, it’s a natural material choice when elastomers are required for medical applications.

For more technical information regarding anti-vibration products made of silicon gel compoundsvibration consultancy services and our technical proposal for your project do not hesitate to contact us at [email protected]

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About Antonios Argoudelis
Linkedin Profile Antonios is our Mechanical Vibration in HVAC systems specialist. During his studies as an Industrial Engineer and his MSc in Noise and Vibration control he had the opportunity to set the foundations for enriching the VIBRO vibration isolation product range with more advanced systems.
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