Alumina ceramic 3.6 in flotation spheres for 11 km ROV/AUV systems

Spherical flotation units of 99.9% Al₂O₃ ceramic have been successfully produced by Deepsea Power & Light for application to 11 km ROV/AUV systems. The 3.6-inch (91.45 mm) OD seamless hollow spheres with 034 weight/displacement ratio have routinely withstood proof testing to 30,000 psi (207 MPa), 1000 hour sustained pressurization to 25,000 psi, and 10,000 pressure cycles to 20,000 psi (138 MPa). Each of the spheres provides 0.6 lb (272 gr) of lift. When encased in a 0.2-inch thick buoyant elastomeric boot, they withstood impact on concrete from a 6 ft elevation. Together with syntactic foam, they will provide most of the required lift for the WHOI HROV system with 36,000 ft (11 km) depth capability. An extensive QA procedure has been developed for each sphere, which requires not only adherence to tight dimensional and thickness specifications but also acoustic emission criteria during pressure testing. Deepsea Power & Light is also in the process of developing a roto-molding process for casting of alumina ceramic spheres with larger diameter for the whole range of ocean depths from 10,000 ft (3000 m) to 36,000 ft (11,000 m). Spheres with 5-inch (127 mm) and 8-inch (203.2 mm) outside diameter have already been successfully cast. The casting of even larger spheres will proceed upon acquisition of a larger furnace.