QUASI-WELD-FREE AND NANOCRYSTALLINE APPROACHES TO LONG-LIFE BELLOWS SEALS IN CRYOCOOLERS & OTHER RECIPROCATING MACHINES

Two very different approaches to the sealing reliability probelm of reciprocating machines are to be investigated and compared. In one approach, bellows design improvements are the result of combining the excellent dead volume avoidance characteristics of welded bellows with the structural characteristics of formed bellows. Formed bellows avoid both the high strees concentration values and the large amount of uncertainty regarding these values by eliminating the need for circumferential welds. In the proposed design, circumferential welds are not used avoiding or minimizing fatigue problems which have caused failures whenever bellows-driven crycoolers have been tried. This combination of design improvements provides a Quasi-Weld-Free Bellows. The other approach being evaluated involves a material that shows promise of demonstrating greater resistance to the formation of fatigue cracks. This material is called nanocrystalline nickel or nickel alloy. A bellows can be made of this material by electro-forming processes.