Patent ID: 8371496

Claim:
A method for closing an interior tube of a multi-walled glass body to form a first chamber, while the interior tube is surrounded by an exterior tube, at least at the closure, the method comprising the steps of: inserting, in the interior tube in the vicinity of the closure, at least one energy-absorbing glass element, in solid or in powder form, the glass element and containing metal or metal oxide particles that absorb radiative energy more readily than the glass in the multi-walled glass body; fusion-melting the energy-absorbing glass element to the interior tube at the closure, using radiative energy generated by at least one energy radiator with heat generated in the metal or metal oxide particles softening the glass in the glass element and in the adjoining interior tube, resulting in a soft melting zone being displaced relative to the exterior tube; and sensing the displacement with a sensor, which signals a control unit to control the fusion-melting step.