were formed by the welding of orange pee! 

 sections to form a hemisphere; not all hemi- 

 spheres are formed in this manner. ALVIN's 

 spherical pressure hull is composed of two 

 hemispheres, both of which were originally 

 flat, steel discs subsequently placed on a 

 spinning table while a hydraulically-powered 

 roller applied pressure over a form to shape 

 the disc into the desired hemisphere (Fig. 

 5.6). This same procedure, hot spinning, was 

 used to form the hulls of DEEP QUEST, the 

 DSRV's, GUPPY, and several other U.S. sub- 

 mersibles. 

 Following another complete inspection of 



the welds of BEN FRANKLIN, over 2,000 

 measurements were made to check hull 

 straightness and circularity. Radius toler- 

 ance is ±5 mm of the theoretical radius at 

 any point; straightness tolerance is ±2.5 mm 

 from a straight line between any two adja- 

 cent stiffeners. Both sections were sand- 

 blasted and painted with two coats of zinc- 

 based epoxy and one coat of paint. 



The two sections, flanges welded in each 

 and machined to 1.25-inch thickness, were 

 bolted together with 60 bolts. A shoulder 

 projects from the aft section into the forward 

 section to transfer shear loads at the joint. 



Fig 5 6 Hoi spinning ALVINs pressure hull Roller al lell ol picture applies pressure while the steel sphere is spun and maintained at a high temperature (WHOI) 



252 



