US Patent 7942176 Drum shell formation

In the method of forming a drum shell that consists of plywood, the steps that includes forming the shell under pressure and heat into cylindrical configuration, providing inner and outer cooling platens adapted to respectively engage the interior and exterior surfaces of the heated shell, trapping the heated shell between the platens, at elevated pressure, allowing the shell to cool by heat transfer from shell side wall or walls into pressure exerting side walls, and while trapped between such platens, at elevated pressure, and removing the cooled shell from between the cooling platens.