glue is used. In the case oi NEMO, 12 spheri- 

 cal pentagons were made by first sawing 

 discs from a flat sheet of Plexiglas G (Rohm 

 & Haas), and then molding the flat disc to 

 the desired spherical shape. Each sphere was 

 then machined to a pentagonal shape. The 

 pentagons were then placed in an assembly 

 jig (six at a time) until two quasi-hemi- 

 spheres were formed which were then 

 bonded to each other (Fig. 5.8). In bonding 

 operations the pentagons were spaced 0.125 

 inch apart with plastic spacers and the joint 

 on each side was covered with an adhesive 

 backed aluminum foil (Scotch Brand No. 

 425). Swedlow's proprietary casting material 

 SS-6217 was used to bond the pentagons 

 together (18). Bubbles, visible in the bonding 

 cement, were removed by machining or drill- 

 ing and, after an annealing process, the 

 areas to be repaired were filled with SS-6217. 

 Two conical steel (cadmium plated 4130 

 steel) end plates are at the top and bottom of 

 the sphere; the former is the hatch and the 

 latter is for thru-hull penetrations. These 

 are held in place by retaining rings. 



Clamping: 



The present TRIESTE II has two hemi- 

 spheres, manufactured by Hahn and Clay, of 

 a high yield steel (HY-120); the weldability of 

 this material is unknown. Consequently, a 

 circumferential flange was machined along 

 the outer edge of each hemisphere; the two 

 sections were aligned by means of an align- 

 ment groove. Then a bolted "C" type clamp- 

 ing ring was fitted over both flanges around 

 the entire sphere to hold both halves to- 

 gether (Fig. 5.9). An 0-ring outboard of the 

 alignment groove serves as a low pressure 

 seal. The original Krupp sphere was of three 

 sections (two disk-like endcaps and a central 

 cylinder-like section). The three sections 

 were originally bonded together by epoxy 

 resin, but this glue failed, and the sphere 

 was subsequently held together by six metal 

 bands gripping two metal rings top and bot- 

 tom. 



Glass-lo-Metal: 



A special situation exists with joining 

 glass to metal as in DEEP VIEW. The soft- 

 ness of glass, its low Young's Modulus and 

 high Poisson's ratio, makes it difficult to 

 mate with metals which generally have the 



Fig. 5 8 The plastic hull of NEMO after bonding together of twelve spherical 

 pentagons. (NCEL) 



ACCESS HATCH 



SIGHTING PORT 



PLEXIGLASS WINDOW 



CLAMPING RING 



Rg. 5 9 Centerline section of TRIESTE ;/s pressure hull. Note tapered reinforce- 

 ment at viewport. 



254 



