Generally batteries are manufactured with different type of seals between jar to cover and terminals to cover. These types of seals include epoxy sealing, heat sealing, and Glass to Metal (GTM) sealing. Types of seals and the materials used depend on battery chemistry, operating temperature range and environmental conditions under which batteries. Often life of the battery is also a factor in choosing the seal type. The most commonly used seals are epoxy and heat sealing. These types of seals are not reliable under extreme operating conditions. Epoxy and heat seals can break under thermal cycling, higher temperatures, and aging. GTM provides oxide free reliable sealing for the batteries at high operating temperatures and pressures. Batteries with GTM provide longer life due to enhanced hermetic sealing and better thermal stability, and also due to excellent electrolyte resistance.
Many different glass-to-metal seals were proven to be more reliable hermetic seals even under extreme operating conditions. Some of the metals used were mild steel, stainless steel and titanium. Aluminum is a better choice for batteries used in some applications due to its inherent corrosion resistance and light weight. However, with the existing processes and materials it is hard to manufacture GTM with Aluminum. The melting point of Aluminum is around 660 C while that of glass is much higher. At Electrodes and More we successfully found a process, and materials to do GTM with Aluminum.
GTM involves bonding of glass and metal to create hermetic seal. There are different ways to produce GTM, essentially involves melting the glass and bonding it to the metal parts through high-temperature sintering process. Often the sintering atmosphere is controlled depending on the materials involved. Oxides are used sometimes to get better bonding between metal and the glass. Thermal expansion co-efficient (TEC) of the metal and the glass have to be matched. The above processes where the TEC of the metal and the glass are matched are called Matched Seal. The processes, where metal with different TEC than the Glass, is called compression process.
There are two important criteria for a GTM with good hermetic seal.
The molten glass must be capable of wetting the metal to for a tight bond and
The thermal expansion of the glass and metal must be closely matched.
When one material goes through a hole in the other, such as a metal wire through a glass bulb, and the inner material's coefficient of thermal expansion is higher than that of the outer, it will shrink more as it cools, cracking the seal. If the inner material's coefficient of expansion is slightly less, the seal will tighten as it cools, which is often beneficial.
Advantages of GTM Seals:
Good joint strengths
Good high temperature capability
Capable of producing many joints simultaneously
Simple, flexible process
Some of the challenges are
unable to cope with large CTE mismatches
precise control of glass composition requires
Having Aluminum cans and lids with GTM can improve the specific energy for your battery; capacitor and or can reduce your product weight significantly.
If you are interested in GTMs for your products with Aluminum or other metals feel free to contact us with your requirements. We have some standard configurations available in stock. You can buy some samples of those to test the concept and can move forward with the final design. We can make both cylindrical and rectangular cans and lids to fit your need.