This was accomplished in the following manner: First, the spherical 

 pentagons were made smaller (distance across tips decreased from 8.660 inches 

 to 8.553 inches and true chord length from 5.352 inches to 5.286 inches) so that 

 0.125-inch-wide joints could be incorporated between the individual pentagons 

 in the assembled hull. Second, an assembly jig was utilized that, although ini- 

 tially developed for providing precise alignment and clamping of all pentagons 

 during solvent-bonding of joints (Figure 43), could be also used for accurate 

 alignment and support of six pentagons during bonding operations employing 

 cast-in-place adhesive. Third, after removal of all spacers between pentagons, 

 the joint spaces were taped over on the interior and exterior surfaces of the 

 hull with Rohm & Haas 670 cellophane fiber tape to contain the adhesive 

 during casting. Fourth, the adhesive was mixed in the proportions recom- 

 mended by the supplier, degassed under vacuum for approximately 15 minutes, 

 and poured into the joint spaces by means of a gravity-fed funnel. The recom- 

 mended procedure for mixing of PS-18 adhesive with a 60-minute pot life at 

 room temperature was to dissolve one 2.4-gram capsule of catalyst (50-50 mix 

 of granular benzoyl peroxide and camphor) in 113 grams of resin (methyl meth- 

 acrylate monomer and methyl methacrylate polymer resin) followed by addition 

 of 3 cc of promoter to the two already mixed components. Since the spacers 

 were removed prior to taping over the interior surface of the joints between the 

 six pentagons, the adhesive could be placed into all the joints of a hemisphere 

 in one pour. Thus the adhesive was mixed in one batch and placed into the 

 joint spaces in a single continuous pour. Fifth, upon setting of the adhesive 

 which occurred in approximately an hour, the tapes were stripped from the 

 joints and the six pentagons bonded into a hemisphere were removed from 

 the jig. A similar procedure was repeated with the other six pentagons. Upon 

 completion of the second hemisphere, both hemispheres were placed upon 

 each other separated by spacers which, prior to placement of the tape on the 

 exterior of the joint, were removed. The joint between the hemisphere was 

 subsequently filled with adhesive. Sixth, the model was placed into an oven 

 for annealing at 175°F for 24 hours. The residual stresses remaining in the 

 capsule after annealing were of approximately the same magnitude and uni- 

 formity (Figure 44) as those resulting from solvent-bonding of model capsules 

 (approximately 1,300-psi shear stress in the joints). 



The successful casting of joints in the model capsules and subsequent 

 testing that showed no significant difference in structural response to hydro- 

 static pressure from models bonded with solvent cement proved conclusively 

 that casting of PS-18 adhesive into 0.125-inch-wide joints (Figure 45) was 

 acceptable from both fabrication and operational viewpoints and thus should 

 be applied to bonding of large-scale acrylic plastic capsules. 



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