All metals exhibit certain properties unique to themselves. Metals used in seals and gaskets must meet certain application criteria in order to function as designed. This article will go in-depth of common concerns of metallic properties and how they react under compression or pressure.
Metals exhibit both plastic and elastic deformation when under stress. Elastic deformation is a term used to describe a material that is able to return to its original shape after stress is applied. This is commonly related to stretching a rubber band and how it would return to its original shape after released. Metals can undergo elastic deformation as well, but compared to rubber its elastic qualities is considerably less. Elastic deformation provides recovery for sealing parts, this is commonly referred to as spring back.
Spring back is the difference between the working height and the free height after stress has been released. Free height is the sectional height of an uncompressed part. This is the original shape of the part before installation. Working height is measured after the part is installed.
Plastic deformation is when the stress applied to a material exceeds its elastic limit. At this point the material can no longer return to its original shape and is permanently deformed. If stress is increased further from this state eventually the material will break, resulting in overall part failure.
Metallic gaskets are either going to be used for applications where there will be extreme temperature or high levels of pressure. These are common areas where metallic gaskets excel compared to rubber and other elastomers. Engineers should select a metal seal with a working pressure sufficient enough to accommodate the pressure exposure of their system.
Another consideration to account for when installing a metallic gasket is the surface that it will be in contact with. The roughness of the mating surface will directly affect the leak rate of the gasket. Discontinuities, scratches or pits should be blended or smoothed out to limit chances of possible leakage. Surfaces with smoother finish can also cause impaired sealing.
There needs to be an optimum surface roughness for the gasket to seal properly. This depends on the application and the material used for the gasket. Engineers need to provide information on what the surface roughness should be for the gasket to function optimally.