Hydraulic Seal Materials

• Elastomers: rubber-elastically deformable polymers and thermoplastic elastomer-thermoplastics which can be deformed elastically within a defined temperature range.
• Plastomers: plastically deformable polymers.

The most important factor property of a material for sealing is its elasticity . It enables the material to have the capability of changing shape without disrupting the cohesion of its molecules. Elasticity gives seals their two most important properties:

• to adapt to the changing profile of the sealed surfaces
• to react automatically to pressure changes by altering the contact pressure.

The following are important properties to be considered when selecting a seal material:

mechanical
• tensile strength and hardness
• resistance to abrasion
• sliding and friction properties
• flexibility and resilience
• compression set and elongation

thermal
• temperature resistance
• caloric conductability
• thermal expansion
• joule effect
• softening

physical and chemical
• compatibility with media
• swelling
• aging

Because of other considerations the optimum effect of each of these properties can rarely be used in combination. For example wear can only be kept to a minimum if the surface being sealed has an oil film and this is dependent on the seal profile and material and system pressure. It always has to be considered that the properties do not compliment each other and often an improvement of on causes a deterioration of the others. Therefore it is important to select the properties to satisfy the operating conditions.