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Gas Fusion

Gas-Fusion

At Hextek Corporation of Tucson, Arizona, we use Gas-Fusion to manufacture large lightweight substrates. The term Gas-Fusion refers to the process we use to manufacture our glass lightweight mirror blanks. Simply stated, the fabrication starts with several individual components that are fused together and subsequently pressurized to form the final structure. The glass components used to make a blank consist of tubing and plates. We use only Schott Borofloat 33® plates and Duran® tubes.

Material

The quality and consistency of this material is unmatched for borosilicate glass in these forms. A basic blank consists of an assembly of tubes (Duran) sandwiched between two face sheets (Borofloat 33). These components are loaded into a furnace and surrounded by tooling. The glass and tooling combination is heated to the point at which the glass starts to reach the plastic state. Concurrently, the tube ends create a seal by fusing to the faceplates (figure 1). With additional heating, pressurized gas is introduced into all the fused tubes simultaneously centered in holes on each tube through the back plate. The net effect is like expanding soap bubbles (figure 2). When the tubes continue to expand they bump into each other and form a vertical wall that becomes a rib (figure 3).


Gas Fusion Diagram


Process

The process lends itself to forming fillets between the rib and face plate eliminating the possibility of stress-risers at that interface. The pressurization has a secondary advantage by pushing on the upper plate preventing collapse of the entire blank. This is key to the success of process is the ability to heat the glass hot enough to accomplish complete fusion. We guarantee that every Hextek blank is 100% fused and that the fusion bonds will not come apart unless under extreme force.

Research

Historically, there have been issues with poorly made sandwich style mirror blanks that "delaminate." We have never had this problem because we use the proper combination of high temperature and pressure to accomplish the fusion. With more than 25 years in the field, we have used more than 600 mirrors in service there has never been any evidence of this problem. For this reason, NASA has selected our 1.6-meter substrates for use to test the James Webb Space Telescope mirror segments at cryogenic temperatures (32K) suspended inverted and supported from the back plate.