Most rubber O-rings are made from synthetic rubber polymers which have been manufactured to cure or solidify. The curing process, whether induced by heat, irradiation or chemical reaction produces rubber O-rings that cannot be reheated or re-shaped. There are probably thousands of individual types of rubber O-rings and the number available is continually expanding. The type selected depends on:
· Composition
· Application
· Physical and chemical properties
· The degree of lubrication required
· Its durometric properties, i.e. how hard the o ring is.
Why Lubricant is Important
Lubrication is necessary to keep wear and tear on the surfaces that move over each other to an absolute minimum and thus contribute to extending the life of the ring and the materials in which it is enclosed. The lubricant is normally interspaced between the surfaces. A helpful analogy would be to compare its function to that of the synovial fluids found in the hinge joints of the knee or elbow. The study of the dynamics involved in the movement of fluids, lubricants and the wear and tear they produce is an engineering discipline in its own right called tribology.
Durability
The hardness of a material is defined at its simplest as the degree of resistance to permanent indentation from an impact on the materials. A durometer measures the hardness of polymers, rubbers and elastomers, (a polymer that demonstrates varying degrees of elasticity and viscosity).
Nitrile Rubber O-rings:
One of the most common chemicals used in the manufacture of rubber O-rings. It has low production costs and is chemically stable and is mechanically strong. Chemically, all nitriles contain a cyanide group (CN) chemically bonded to an alkyl group. In organic chemistry an alkyl group is any saturated hydrocarbon (where the maximum number of hydrogen atoms is chemically bonded to a number of carbon atoms), where a hydrogen atom has been replaced by a different atom or compound. As a family of molecules, nitriles contain a cyanide (CN) group. The simplest is known as ethanenitrile (CH3CN). There is a triple chemical bond between the carbon and nitrogen atoms in the CN group, which helps explain the stability of nitrile rubbers. A variety of monomer subunits (the building blocks from which any polymer is made) can be used to synthesise nitrile rubbers. Overall, the more nitrile that is contained in the rubber, the more resistant it is, however, the trade-off is reduced flexibility. These rubbers are not resistant to chlorinated hydrocarbons or fuels and oils that are highly aromatic (containing many six carbon benzene rings). They are resistant to standard grade oils and fuels, lubricants, fluids, silicone based oils and many other substances up to about 85⁰C.
Silicone Rubber:
An elastomer that is stable over a wide temperature range, (-55⁰C to 300⁰C) is chemically stable and resistant to corrosive gases as well as being physically very strong. Silicone is itself a polymer containing atoms of carbon, hydrogen and oxygen and is not to be confused with the non-metal chemical element silicon. The use of silicone is not limited to rubber o rings; it is employed in footwear, baking, food storage, clothing, electronics and as a sealant in many home DIY materials. The only substances they are not generally resistant to most fuels, oils, aromatic compounds as well as strong acids or caustic alkalis. The addition of fluorine atoms in precise quantities to manufacture compounds called fluoro-silicone elastomers creates a polymer that is much more resistant to oils and fuels.
There are many other examples of rubber o rings on the market. The crucial point is to ensure that the correct type of ring is applied to a particular process or activity.
http://www.birminghamseals.co.uk/
· Composition
· Application
· Physical and chemical properties
· The degree of lubrication required
· Its durometric properties, i.e. how hard the o ring is.
Why Lubricant is Important
Lubrication is necessary to keep wear and tear on the surfaces that move over each other to an absolute minimum and thus contribute to extending the life of the ring and the materials in which it is enclosed. The lubricant is normally interspaced between the surfaces. A helpful analogy would be to compare its function to that of the synovial fluids found in the hinge joints of the knee or elbow. The study of the dynamics involved in the movement of fluids, lubricants and the wear and tear they produce is an engineering discipline in its own right called tribology.
Durability
The hardness of a material is defined at its simplest as the degree of resistance to permanent indentation from an impact on the materials. A durometer measures the hardness of polymers, rubbers and elastomers, (a polymer that demonstrates varying degrees of elasticity and viscosity).
Nitrile Rubber O-rings:
One of the most common chemicals used in the manufacture of rubber O-rings. It has low production costs and is chemically stable and is mechanically strong. Chemically, all nitriles contain a cyanide group (CN) chemically bonded to an alkyl group. In organic chemistry an alkyl group is any saturated hydrocarbon (where the maximum number of hydrogen atoms is chemically bonded to a number of carbon atoms), where a hydrogen atom has been replaced by a different atom or compound. As a family of molecules, nitriles contain a cyanide (CN) group. The simplest is known as ethanenitrile (CH3CN). There is a triple chemical bond between the carbon and nitrogen atoms in the CN group, which helps explain the stability of nitrile rubbers. A variety of monomer subunits (the building blocks from which any polymer is made) can be used to synthesise nitrile rubbers. Overall, the more nitrile that is contained in the rubber, the more resistant it is, however, the trade-off is reduced flexibility. These rubbers are not resistant to chlorinated hydrocarbons or fuels and oils that are highly aromatic (containing many six carbon benzene rings). They are resistant to standard grade oils and fuels, lubricants, fluids, silicone based oils and many other substances up to about 85⁰C.
Silicone Rubber:
An elastomer that is stable over a wide temperature range, (-55⁰C to 300⁰C) is chemically stable and resistant to corrosive gases as well as being physically very strong. Silicone is itself a polymer containing atoms of carbon, hydrogen and oxygen and is not to be confused with the non-metal chemical element silicon. The use of silicone is not limited to rubber o rings; it is employed in footwear, baking, food storage, clothing, electronics and as a sealant in many home DIY materials. The only substances they are not generally resistant to most fuels, oils, aromatic compounds as well as strong acids or caustic alkalis. The addition of fluorine atoms in precise quantities to manufacture compounds called fluoro-silicone elastomers creates a polymer that is much more resistant to oils and fuels.
There are many other examples of rubber o rings on the market. The crucial point is to ensure that the correct type of ring is applied to a particular process or activity.
http://www.birminghamseals.co.uk/