Process for making fluid-containing structure

Claim 1

A manufacturing process for molding very large seamless plastic containers having a size in the order of a mattress for supporting a human body, said process consisting essentially of the steps of: (a) loading a charge of plastisol into a mold having a large closed cavity with walls made of thin heat conductive sheet metal, said large closed cavity being terminated in at least one access hatch which is much smaller than the surface of the mold in which it is located; (b) maintaining a uniform initial temperature across the surface of said sheet metal mold so that said surface is free of localized hot and cold spots; (c) said process including rotating said mold manually during a brief period after the loading during step (a) and before the start of initial heat cycle period of step (b) in order to insure that the entire internal cavity surface is thoroughly wetted by said plastisol during said manual rotation; (d) continously, throughout the manufacturing process, rotating said mold simultaneously about a major and minor axis, the mold turning at two separate low speeds about said axes with the rate of turning about the major axis being about 3 r.p.m. and the speed ratio between the major and minor axes being in the range of 1:2.5 to 1:4.; (e) increasing the temperature of said mold from the initial temperature of step (b) to an intermediate temperature for an initial heat cycle period during which the plastisol reaches a slush point; (f) elevating the temperature of the mold above the intermediate temperature of step (d) to a high temperature for a final heat cycle period during which the plastic reaches a hardened and cured state; (g) cooling the mold uniformly from said high temperature of step (e) to approximately the initial temperature of step (b); and (h) collapsing and extracting the cured plastic container by drawing it in said collapsed condition through said hatch and from the mold.