Glass-to-Metal

Glass-to-Metal Sealing Meets Challenges of the Most Demanding Applications


Single & Dual-Lead Seals

There are two types of glass seals available at Specialty Seal Group: Compression Seals and Matched Seals. In the design of Compression Seals the expansion coefficients of the steel, glass and ID members are placed in decreasing expansion fashion. This process will maintain the glass under compressive stresses over a wide temperature range. Glass, like ceramic, has little strength when subjected to tension. However, under compression, glass is strong.

If a higher cycle range is needed, you should consider Kovar* Matched Seals. Specialty Seal Group uses a fundamental glass sealing process to manufacture glass seals in which the Kovar metal thermal expansion coefficient matches the glass thermal expansion coefficient. The outcome is a highly effective hermetic seal.

Glass Specifications

In both Compression and Kovar Seals, the glass is selected to minimize stresses that cause cracks. However, Kovar Seals typically require Corning Glass 7052 or its equivalent, with milky white, gray, and black being the popular color options.

The most common glass for Compression Seals is Corning Glass 9013 or its equivalent.

Conductor Material (Terminal, Lead)

Nickel-iron 52% is standard conductor material is because of its low thermal expansion in Compression Seals. The specific resistivity of the material is 260OHM-Cir-MIL per foot. Copper cored alloys are selected when higher current capacities are needed. The copper core is ½ of the outside diameter and its resistivity is 71 OHM-CIR-MIL per foot.

Kovar Seals typically use Kovar for the conductor.

External Body (Eyelet, Flange)

Compression Seals' body components can be machined formed stamped, or coined. The materials normally low-carbon steel, leaded steel, stainless steel, or Monel. The external body of a Compression Seal must be thick enough in cross section to maintain compression around the glass and sustain the tensile stresses without yielding. Also, because of high forces around the glass, a tangential stress is set up in this ring. So the ring must be thick enough to sustain tensile stresses. If it is not sufficiently heavy, the glass will crack. General guidelines for ring thickness are:

  • 030” minimum wall thickness for small seals up to ¼" dia.
  • 060” minimum wall thickness for seals ¼” to 1" dia.

Kovar Matched Seals do not require heavy external body cross-section thickness. Therefore, Kovar Seals should always be designed with lighter stamped outer bodies.

Specialty Kovar Glass-to-Metal Seals


Designs
  • Designed and manufactured to buyer’s specifications
  • Custom designed from customer’s descriptions to solve unique sealing problems
Functions
  • Stress-Free Glass-To-Metals Seals
  • Maintained Integrity to wide range of environments
  • Phase stability with Low Thermal Expansion over wide temperature ranges
Optional Finishes
  • Tin: Hot Solder
  • Nickel: Sulfamate, Watts, Electronics
  • Gold: Electroless, Electrolytic
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Multi-Header Terminals


Designs
  • Strain Relief Eyelet to absorb stresses
  • Multiple Pin Styles for any application
  • Custom Designs
Functions
  • For hermetically sealing Multiple Conductors into Relays, Transformer, Switches etc.
  • Eliminate extra circuit functions through Multi-Port Termination
  • Permits Conductors if High Conductivity
Optional Finishes
  • Standard Finish, Pre-Tinned
  • Other finishes available on order
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Single-Lead Terminals (Low Voltage)


Application
  • For hermetically sealing transforms, vacuum chambers, and other equipment subject to low pressures.
Materials
  • Insulator - Corning Glass #7052 or equivalent
  • Conductor - with glass-matching thermal expansion rate
Lead Types
  • Solid Lead for lower current ratings made of a matched expansion alloy
  • Tubular Lead for higher current ratings permit passage of copper, silver, or other lead metals through hermetically sealed unit wall
Body Styles
  • Standard Body for low voltage
  • Standard Body for high voltage
  • Optional finishes available
Voltage
  • Low range, all styles
  • Flashover Voltage range 1500 to 4000
  • Current Rates range 1.7 to 25.0
Operating Temperatures
  • -65 deg. C to 250 deg. C

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