Engagement Rings Under 400 – Metal O-rings will be the metallic variants of typically used elastomeric O-rings. They are generally utilised in stationary sealing applications that are incompatible with all the chemical and physical characteristics of elastomeric O-rings. These O-rings have high tolerance to radiation as well as high vacuum, and are usually used for flanged programs. Ideally, metal O-rings are placed in both closed and open grooves and axial pressure is applied between two parallel surfaces. Furthermore, grooves that maintain the O-rings are made to be perpendicular to the direction of the fluid stream. When placed between surfaces and compressed to a predetermined elevation, deforms and creates contact between the jointing and sealing faces. Inherently, O-rings’ metallic elasticity displays a affordable deflection and creates maximum sealing contacts during operation to ensure the sealing action. In addition to elastic deflection of the metal, structural assembles of the O-rings also play a significant part in creating the sealing force. Even though most metals can be used for fabricating metal O-rings, the option of metals must be such that the linear expansion co-efficient of the O-ring metal fluctuates slightly from the linear expansion co-efficient of the metal(s) of jointing surfaces. Metal O-rings are vulnerable to rusting unlike elastomeric O-rings, and as such, are coated with a suitable substance to prevent rusting. This material is softer than the base metal and serves an additional purpose of negating the impact of surface abnormalities. The coating materials that are ordinarily utilized are soft metals, such as silver, and non-metals such as PTFE.
Metal O-rings are largely categorized according to their fundamental structural characteristic, they are categorized as follows:
Solid Metal O-Rings
Solid metal rings are wires of round profile attached like a ring. These kinds of O-rings require special grooves for their efficient functionality. This requirement of special grooves restricts the usage of strong metal O-rings to specific programs, such as engine cylinder heads. Solid metal rings are usually manufactured in copper and suitable for use in nuclear reactors, for checking radiation leaks. These O-rings can handle pressures of around 4MPa and temperatures hitting 500°C and are suitable for moderate pressure and medium sized vacuum applications.
Hollow Metal O-Rings
Hollow metal O-rings are structurally more sophisticated in comparison with good metal O-rings and formed by curved tubes bent to the shape of a ring. These O-rings are sub-classified based on the characteristics of the hollow segment of the ring.
- Plain Hollow O-Rings
- Self Energized Hollow O-Rings
- Stress Filled Hollow O-Rings
These are hollow metal O-rings with nitrogen at atmospheric pressure or vacuum within them. Plain hollow O-rings are used in low stress or low vacuum applications. Although plain hollow O-rings display similarity in temperature and pressure handling capabilities with good metal O-rings, they offer considerably better spring-back and sealing capacities. Normally, plain hollow metal O-rings are produced from Inconel 750 and garnished with silver.
Self-energized hollow O-rings have vents or holes on their surfaces to use the system pressure or atmospheric pressure for sealing action. Based on the orientation of such grooves, the O-rings are categorized into internally vented O-rings and externally vented O-rings. Internally vented O-rings made from mild steel and garnished with PTFE can withstand pressures of around 3500 kg/sq cm and temperatures of 600°C. Externally vented O-rings are used in applications where the outside pressure is higher than the pressure within the seal.
Stress Filled Hollow Rings:
Stress filled hollow O-rings are altered plain hollow rings using pressurized inert gasses in them. These O-rings can be utilised in tongue and groove flanges and will handle temperatures from cryogenic temperatures up to 850°C. Stress filled O-rings are used in vacuum cleaning applications.
- Metal O-rings can’t be utilized in highly dynamic sealing applications
- These O-rings are rendered useless when they are used once because they can’t retain their shape after only use
- Wide tolerances of the groove can’t be adapted by the metal O-rings, especially in larger sizes
- Careful fitting ought to be done in order to prevent their deformation before their seal is tightened.