Image Credit: PFC| Schott 

Hermetic seals provide a vacuum or leak-tight seal, insulate or channel electricity, and prevent the ingress of contaminants. Containers that use hermetic sealing are able to withstand high temperatures and hold pressures up to 150,000 pounds per square inch (psi). The seal is created through a process called fusion welding. Fusion welding uses a high-energy laser or an electron beam to increase the temperature of a material to molten and in a liquid state. The molten material rapidly cools to create a seal.

Types of Hermetic Seals

Common types of hermetic seals include:

• Metal-to-metal hermetic seals are created by firing two or more metal components with the addition of gold, silver, nickel or copper filler materials.
• Ceramic-to-metal hermetic seals are run through a high-temperature furnace to create a final assembly with a permanent hermetic bond. The hermetic seal is then coated with a metallic pattern. The ceramic material is made from ceramic and glass powers of a particular particle size as well as a binding agent and solvent used to creat a homogeneous slurry.

Sealing process. Image Credit: Schott

• Glass-to-metal hermetic seals have two types:

  • Matched glass-to-metal hermetic seals are made of metal alloys and components that share similar thermal expansion characteristics.

  • Mismatched or compression glass to metal hermetic seals feature a steel or stainless steel metal housing that has a higher thermal expansion rate than the glass component. Upon cooling, the metal housing contracts around the glass, creating a hermetic seal that is reinforced both chemically and mechanically.

Sealing process. Image Credit: Schott

Materials

They are made of ceramic, glass, or metal materials and joined in a specific configuration by furnace brazing.

Applications

Hermetic seals are used in a variety of applications and industries. Ceramic-to-metal hermetic seals are used in automotive, aerospace, and medical applications. Products that create a component hermetic seal are also used in the nuclear power industry. Hermetic glass seals are used in many food processing applications to prevent contamination and ensure the delivery of safe, usable products. Glass-to-metal seals are suitable for high-pressure environments and protect electronic components from dirt, dust, and microbial growth. These hermetic seals are also excellent electrical conductors. The glass not only provides the seal, but functions as an insulator between the metal housing and other metal components such as connector pins.

Resources

Hermetic Sealing