Method of forming threaded polar openings for composite pressure vessels

A method of filament winding a pair of pressure vessels, each of said vessels having a large opening that is internally threaded with threads that are integral therewith, said method comprising:

• (a) providing first and second thread formers as part of a mandrel used in making said vessels, said thread formers spaced by a spacer having a common center axis with said thread formers and other portions of said mandrel and respectively configured to provide said threads for each of said openings;
• (b) winding filament about said mandrel in a helical layer having filament disposed, relative to lines parallel with said center axis, at an angle having an absolute value between about 5.degree. and 35.degree., said winding being over said thread formers, spacer and other portions of said mandrel;
• (c) winding filament over said helical layer in a hoop layer having filament disposed, relative to lines parallel to said center axis, at an angle having an absolute value between about 82.degree. and 89.degree., said hoop layer terminating at locations axially proximate those ends of said thread formers that are remote from said spacer;
• (d) winding filament over said helical layer on said spacer at an angle, relative to lines parallel with said center axis, that has an absolute value between about 82.degree. and 89.degree.;
• (e) cutting said helical layer circumferentially about said spacer midway between said thread formers;
• (f) pulling said helical layer into each of said thread formers with a first tow of filament wound at the pitch of said threads;
• (g) removing said filament carried on said spacer;
• (h) laying a first filamentary cloth around said thread former carrying said thread first tow therein and a second filamentary cloth around said second thread former carrying said first tow therein;
• (i) pulling said first and second filamentary cloths into said thread formers with a second tow wound at the pitch of said threads;
• (j) continuing fabrication of said pressure vessels by winding a second helical layer as in (b), winding a second hoop layer as in (c), winding filament on said spacer over said second layer as in (d), cutting said second helical layer as in (e), pulling said second helical layer into said thread formers with a third tow as in (f), removing filament from said spacer as (g), laying third and fourth filamentary cloths as in (h), and pulling said first and second filamentary cloths into said thread formers with a third tow as in (i);
• (k) building up said pressure vessel after still another helical layer and filamentary cloths are pulled by a fourth tow into said thread formers, said building up comprising winding hoop and helical layers about said mandrel over said thread formers;
• (l) curing thermosettable resin carried by said cloths, hoop and helical layers and tows to provide said pressure vessel.