Most of us would have come across a light bulb. But have you ever wondered how the inert gases inside the light bulb stay without leaking out? It’s because of hermetic sealing. Apart from everyday things, industries need hermetic seals and connectors when they are looking for protection from moisture, dirt, or any other hazard. There are various types of hermetic seals classified based on the materials they fuse together, namely metal, ceramic, and glass. The article will help you understand the types of hermetic seals based on the materials they fuse together.
What Is Hermetic Sealing?
If a container or a mechanism is sealed with hermetic sealing technology, it means that any material—be it gas, solid, or liquid—cannot leak from the container because it is sealed airtight. They provide a vacuum so that the containers can channel or insulate electricity and prevent contaminants from entering the container. A hermetically sealed container can bear high pressure and temperatures.
Hermetic seals are created by a process called fusion welding where an electron beam or a high-energy laser is used to melt the material; the material that is melted is rapidly cooled to create the seal. This type of sealing is used in encasing electrical mechanisms or to trap gases as we saw in the light bulb example.
5 Types of Hermetic Seals
The 5 types of hermetic seals explained below have found their applications across various industries including military, aerospace, and pharmaceutical.
Glass-to-glass Hermetic Seals
Some applications require sealing glass components together. For example, when sealing components of a glass tube or sealing glass windows need an airtight seal, then glass-to-glass seals are the ideal choice. Seals with several layers of glass can be created.
Glass-to-metal Hermetic Seals
As the name suggests, glass-to-metal seals are used to join glass components to a metal surface. These seals, which are great electrical conductors, are ideal to protect electrical mechanisms from microbial growth and dust. Glass acts as an insulator between the metal packaging and components like connector pins. A common household example of a glass-to-metal seal is a common light bulb that contains gas. According to the material used, the following two types of glass-to-metal hermetic seals are used:
- Matched seals – This type of hermetic seal is made of materials that share the same characteristics of thermal expansion. Glass and oxide formed on the metal create a bond. However, these seals are weak and cannot endure high-pressure fluctuations between glass and metal.
- Compression or mismatched seals – This stronger alternative to matched seals has a stainless steel or steel packaging around the glass. Since the metal has a higher thermal expansion rate than glass, when cooled the steel housing contracts around the glass components forming a hermetic seal. They can withstand more high-pressure fluctuations and shock than matched seals.
These seals are run through a furnace to assemble the seal with a bond and then coated with a metallic pattern. This type of hermetic seal is more expensive than glass-to-metal seals as ceramic is more expensive than glass. However, ceramic is more resistant to shocks and high-stress environments. These seals last long, but they are more likely to chip than glass does. Though it can also be made in custom designs, they consume more time than creating a glass-to-metal seal. They are used in high voltage environments and their application extends across a number of fields such as aerospace, automotive, and medical.
Ceramic-to-glass Hermetic Seals
Ceramic withstands a higher temperature threshold than glass. These seals are used in applications that lay high amounts of stress on the seal.
Certain epoxy resins are used to seal brass, copper, and other materials and create vacuum seals. Hermetic epoxy seals have more design flexibility but they have a small window for variations in temperature, so they are limited to certain applications.
Hermetic sealing is used in a wide variety of industries. They are essential for the safe functioning of many healthcare and electronic products that we use. In your business, you might be using a system that uses hermetic feedthroughs and seals. However, a seal has to be perfect for a job that it is meant to do. If you do not know what type of system and material will be ideal for you, you might end up choosing the wrong type of seal. Even when you are planning to buy hermetic sealing solutions, it is necessary to have a basic understanding of the types of hermetic seals and their advantages and disadvantages. Hermetic seals can also be designed to fit specific projects or fit the unique specifications of a product. Choose a company that provides hermetic sealing solutions that are ideal for your application needs. Check if the company provides the type of seal that fits your budget and your application needs.