Sealing rings and oil seals are elements available in various standard and special materials for the sealing lip (elastomer component), metal insert and spring. The material used for the sealing lip is normally indicated. The description of elastomer materials follows the nomenclature used in DIN ISO 1629 and ASTM D 1418. The raw material used for the elastomer element is synthetic rubber produced by the chemical industry. Elastomers differ from each other in the basic polymer from which they are made.
The finished material to obtain the elastomer that will make up the oil seal is obtained by combining the raw material, rubber, with numerous ingredients such as fillers, pigments, plasticizers, processing aids, anti-aging agents, vulcanizing agents, vulcanization accelerators, retardants, etc. . This process makes it possible to obtain the specific characteristics required for the material. you
Sealing rings of both standard materials are commercially available useful for a wide range of applications, as well as special materials for applications where very high characteristics are required. The sealing ring reaches its final shape through a vulcanization process during which the metal insert is firmly joined to the rubber. After a chemical-physical transformation, the rubber goes from a predominantly plastic state to an elastic state, acquiring its characteristics. The seal is obtained through a subsequent cutting operation or during the molding phase. The spring is inserted at the end of the process.
Let's look specifically at the various standard and specialty materials available for the sealing lip:
Nitrile rubber (NBR)
NBR oil seals are manufactured using a copolymer elastomer of butadiene and acrylonitrile and are used in most conventional fluid sealing applications. The percentage of acrylonitrile determines the classification between low, medium and high nitrile. The higher the percentage, the greater the resistance to oils and hydrocarbons derived from petroleum. At the same time, however, flexibility at low temperatures decreases. For this reason, the standard NBR compound used is the best compromise between resistance to oils and hydrocarbons, flexibility and mechanical resistance.
Operating temperature: -30°C to 100°C (120°C according to nitrile classification)
Black color
Benefits:
- good resistance to mineral oils and greases
- good resistance to water and radiator fluid
- good tear and abrasion resistance
- good flexibility
Limitations:
- low resistance to ozone, atmospheric agents and direct sunlight
- not resistant to glycol-based fluids
- poor resistance to polar fluids (ketones, ethers, esters), chlorinated hydrocarbons, aromatic solvents.
Fluorinated Rubber (FPM)
Better known as Viton® (it is a Du Pont brand), its main indication is resistance to high temperatures. Viton oil seals are usually brown in color.
Operating temperature: -30°C to 200°C
brown color
Benefits:
- excellent resistance to mineral oils and greases, including most additives and hydrocarbons
- resistant to most chemicals, with the exception of ketones, ethers and esters
- Excellent resistance to aging, ozone and atmospheric agents
Limitations :
- hardening at low temperatures
- lower abrasion resistance than NBR compound
Silicone Rubber (SIL)
Also known as MVQ or VMQ, its main advantage is its relative stability as the temperature varies. Silicone oil seals and O-rings are available upon request.
Operating temperature: from -60°C to 200°C
Red
Benefits:
- stability to temperature variations
- good resistance to mineral oils and greases
- Excellent resistance to aging, ozone and atmospheric agents
- good chemical resistance to alkalis
Limitations:
- Not recommended for use with hydrocarbons containing benzene or paraffin and light mineral oils
- does not resist water, acids and non-mineral brake fluids
- low tensile strength and abrasion resistance
Ethylene Propylene Rubber (EPDM)
Characterized by high resistance to abrasion, aging and atmospheric agents, this compound finds specific uses where a discrete operating temperature range is required.
Operating temperature: -50°C to 150°C
Black color
Benefits:
- resistant to non-mineral oils, car brake fluid
- resistant to polar fluids, aging, water
Limitations
- low resistance to mineral oils and greases
Polyurethane
This elastomer is characterized by exceptional abrasion resistance, better than all other rubbers, strength and tear resistance, while maintaining excellent flexibility at low temperatures.
Operating temperature: -40°C to 100°C
Benefits:
- high mechanical resistance
- good flexibility
- excellent abrasion resistance
- good resistance to petroleum and derivatives, atmospheric agents and ozone
Limitations:
- low resistance to aqueous, acidic or alkaline solutions, hot water, glycol, steam, ketones
- degrades quickly as temperatures increase
