Method of molding a manhole frame for spherical tanks

摘要

A access-hole frame for the construction of a spherical tank made of nonmetal moldable material, the frame having a cylindrical neck, an outwardly extending flange at the top side of the neck, and a collar configured as a segmented sphere to be integrated with the spherical wall of the tank. Bolt holes are drilled around the flange for bolts that hold an access-hole cover to the access-hole frame. A three-piece die provided for making the access-hole frame includes a bottom die piece and two top pieces that are bolted together to form an integral top die piece that fits over the bottom die piece. The access-hole frame is formed in accordance with a manufacturing process by placing the three-piece die in stages upon a rotatable table and spraying the nonmetal moldable material onto the rotating bottom and top die pieces.