Glass To Metal Sealing Basics
Please contact us to confirm your exact sealing requirements if you are unsure which type of seal is best for your application. We can supply sealing products for any of the most common housing materials listed below or for virtually any known material combination for the manufacture and supply of Glass to metal seals. Some of the most common are listed below.
• Stainless steel – 300 series, non magnetic, corrosion resistance
• Mild steel – cold rolled steel
• Kovar – Nickel cobalt ferrous alloy
• Hastelloy / Inconel – non magnetic, corrosion resistance, good tensile strength
• Titanium – Non magnetic, light weight, good tensile strength
Compression seals are our most common glass to metal seals we supply sealing materials for. They are the best choice when high mechanical strength is required and being ideally suited for applications in which the seal may encounter high stresses or pressures during it use. A compression glass to metal seal is always designed so that the housing’s (header) co-efficient of thermal expansion is higher than that of the glass. In the solidification heat cycle of the glass; after the melting has occurred, the shell contracts around the glass, the glass therefore enters into compression. This sealing technology is used in a wide variety of applications and designs, generally constructed using steel, stainless steel or Inconel housings and nickel iron pins. Some critical, specialist applications that utilise compression glass to metal seals can be found in harsh and demanding environments; pressure sensors or transducers, military, automotive and aerospace applications.
For other material combinations please contact us.
Compression (Matched) Seals – Typically a Chemical bond
Typical seal materials – (Header (Stainless Alloys, S.A.E 1010 Cold Rolled Steel) > (Glass (S05/S02 9013/9010) = Pin (Alloy 52, No4 Alloy, Chomel)
Matched compression seals typically have pins and glass with roughly the same CTE values. This allows the compressive forces in the glass to be exerted by the header (outer body/shell) which has a considerably higher CTE. The electrical feedthrough pins are structurally supported in the glass primarily by the chemical bonding at the glass to pin interface. The most common design for a matched compression seal is a multiple feedthrough seal with individual seals isolated by individual glass beads to each pin. This method of isolating feedthroughs individually has certain benefits. Firstly electrical resistance is maintained while reducing the change of failure in the glass caused by cracking between multiple pins either by mechanical stressing/bending of the pins or thermal heating of the pins due to electrical/thermal loading. Each feedthrough/glass subdivision serves as a distinct compression seal in the larger assembly. The drawback being, failure of one of the feedthrough subassemblies renders the entire header defective. The second common model contains multiple matched pins supported in the bulk glass. The primary disadvantage to this design is the potential for large areas unreinforced across the diameter and relying upon the stress limit of the bulk glass to resist differential bulging pressure. Matched compression seals offer reasonable mechanical strength compared to weaker matched seals or stronger Compression Ultra (Fortified) designs.
Matched seals (Non Compression) – Chemical Oxide Bond
Typical seal materials – Header (Kovar) > Glass (B02/B017 (7056/7052) = Pin (Kovar)
Matched seals are achieved when the shell and glass are selected to have a similar coefficient of thermal expansion, over the required operating temperature. Matched seals are generally strain free glass to metal seals at ambient temperature. The strength of a Matched Seal is achieved with a chemical bond forming between the glass and an oxide created on the metal housings.
Match seals can be designed to suit a variety of metals, ceramics and other glasses. Typically with the shell housing and pin contact being Kovar, for other material combinations please contact us.
Ultra Compression Seals (Fortified) – Chemical & Mechanical Bond.
Typical seal materials – Header (Stainless Alloys, Inconel Alloys) > (Glass Ceramic MGC1, MGC2) = Pin (Alloy 52, Hastelloy C-276)
The Ultra compression (Fortified) seals harness the CTE modifying capabilities of our (MGC) Mansol Glass Ceramics. This means the MGC material’s CTE is between that of the header and feedthrough(s). The glass bonds chemically and mechanically constrains the pins by compression, yet is still able to be strengthened by the contracting header. The MGC Glass-ceramics’ CTE is controlled by the sealing profile to produce a precise crystallisation which is possible due to the unique MGC formulation. The MGC Glass-ceramic nucleation agents are unique to Mansol and make sure the resulting seals are mechanically superior and feature strong chemical bonding at the glass to metal interfaces. For seals requiring robust performance and the ability to withstand large differential pressures between the outer and inner faces, Ultra compression seals are superior. Usually Ultra compression seals consist of coaxial or feedthroughs in one glass bead. This is usually done as a design aid to stop cracking between numerous pins.