Abstract: A rotational molding method for forming two separate molded parts each including an undercut portion includes providing a mold formed from two mold parts connected at a mold junction, introducing a particulate plastics material and rotating the mold about two axes while applying heat to the mold so as to cause the plastics material to melt within the hollow interior and adhere to the inside surface. An annular heat conduction member extends from an outer edge outside the mold through the junction between the two mold parts to an inner edge inside the hollow interior and carries two undercut mold portions for molding respective undercut portions of the two separate molded parts. A band of a heat insulating material such as Teflon is located around the junction between the parts on the inside of the heat conducting member which prevents the adherence of the plastics material at the band so that the mold molds the separate molded parts each separately from the other.

Abstract: The invention is a tank-baffle system including a baffle member mounted in a tank and connected to the tank with a male-female interlocking arrangement thus avoiding the use of welding, adhesive or bolts. The invention is especially suitable for use in polyethylene tanks.