The working principle of VTTJ is extremely simple. Two parts (at least one with tube shape) are screwed one into the other with a mechanical interference that creates a metallic seal. One part presents a cylindrical slot, the other presents a conical ring, whose diameter is slightly larger than the one of the cylindrical slot. When the two parts are screwed together, a plastic deformation occurs in the mechanical interference region. The plastic deformation generates an absolutely hermetic seal, as demonstrated by several tests carried out on various geometries of the junction. To avoid unscrewing of the two parts, and to make the junction compatible with high thermal and/or structural loads, one can proceed with a finishing phase using galvanic electrodeposition of copper.
The new VTTJ technique permits to manufacture metallic junctions having a perfect seal (compatible with the requirements of high vacuum environments) that is reliable in time also in presence of high temperatures and high structural loads. The process is carried out completely in cold conditions, hence in any phase the materials are prevented from possible damages due to overheating. On the other hand, using any other existing technique able to give a vacuum compatible seal (like friction welding, electron beam welding, brazing etc.) there is always a certain overheating in the junction area, with possible cracks or other types of degradation of the materials (annealing, recrystallization, inclusions etc.).
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