What Is a Metal Seal?
A metal seal is a gasket that’s made out of a metallic alloy. It’s capable of demonstrating airtight performance under more severe conditions than O-rings, etc., which are generally made of resin or rubber.
Metal seals maintain and demonstrate airtight performance in high-temperature, cryogenic, high-pressure, and ultra-high-vacuum environments that exceed the capability of ring seals and gaskets made of resin and rubber materials.
There are many types of metal seals in terms of cross-sectional shape, structure, and material. When using metal seals, careful selection is required, taking into consideration the sealing structure, environmental conditions, required specifications, and the fluids with which they come into contact.
Uses of Metal Seals
Metal seals are used under conditions that polymer-based O-rings and gaskets cannot withstand.
Although polymer-based seals can withstand temperatures of up to 320°C, metal seals can withstand temperatures up to nearly 1,800°C. Metal seals are also used under severe conditions such as cryogenic environments of -270°C or lower, ultra-high-pressure environments exceeding 600 MPa, and ultra-high-vacuum environments of 1 x 10^10 Pa or lower.
They are used in ultra-high-vacuum facilities, ultra-high-pressure facilities such as supercritical facilities, and storage facilities for low-molecular gases such as helium and hydrogen.
Principle of Metal Seals
There are several types of metal seals depending on the cross-sectional shape.
- C-shape: Metal C-ring
- O-shape: Metal O-ring
- Flat: Metal gasket
Other types include the flare type used for flared tubes, resilient seals with a complex cross-sectional structure for higher sealing performance, and the boss type, which is used for creating a seal between a screw and a matching female mating side.
Metal C-rings and perforated metal O-rings work by allowing fluid pressure to penetrate the inside of the O-ring, thus increasing adhesion. They are also referred to as self-sealing types.
In addition, there are composite types with coil springs or C-shaped inserts embedded, and hybrid types with different material films coated on the outer layer.
Metal seals have superior performance compared to polymer seals. However, if metal elements leak, they cannot be reused. High precision is required to achieve flatness and negate the roughness of the mating seal surface. The chemical and special gas resistance characteristics of an alloy seal are limited. Additionally, uniform torque tightening control is required when the seal area is large. There are also many operational precautions and restrictions to observe when utilizing metal seals.