As detailed by ScienceDirect in their article, “Glass to Metal Seal,” glass-to-metal seals play a crucial role in the reliability and performance of various components, particularly in environments where thermal stress and mechanical durability are paramount. These seals are designed to insulate the casing of a device from its wire conductor, ensuring airtight connections that withstand significant temperature fluctuations.
The process involves placing low-expansion borosilicate glass beads between a casing and a conductor, both typically made from Kovar, a controlled expansion alloy. When heated to 1000°C in a vacuum furnace, the glass melts and bonds with the oxide-free metal surfaces. Upon cooling, the similar thermal expansion coefficients of Kovar and borosilicate glass ensure that the thermal stresses within the seal remain minimal. This is particularly important given the brittle nature of glass, which is prone to cracking under tensile stress.
Glass-to-metal seals are critical components in devices like receivers, where they connect materials with different thermal expansion properties. The seal’s performance is vital for maintaining airtightness, especially in conjunction with components like bellows, which may undergo significant mechanical stress during operation. Over the receiver’s lifetime, the bellow might be compressed and expanded up to 10,000 times, necessitating a seal that can endure such rigorous conditions without compromising integrity.
To ensure the durability and reliability of these seals, various testing methods have been developed. Chiarappa introduced a test bench for accelerated aging, focusing on the glass-to-metal seal, glass tube, and bellow assembly. This test bench subjects the seal to temperature variations from 20 to 250°C and axial forces that simulate real-world stresses, while monitoring the helium leak rate to assess the seal’s effectiveness.
Similarly, Pernpeintner presented a test bench for testing entire receivers, simulating both mechanical and thermal stresses on the bellow. These testing methodologies are crucial for validating the long-term performance of glass-to-metal seals in high-stress environments.
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Article with all rights reserved, courtesy of sciencedirect.com