Abstract: A method of forming an element to have a preselected element density, for floating at least partially on a surface of an at least partially liquid hydrocarbon mixture having a known liquid density. The method includes determining the preselected element density based on the known liquid density. A mold cavity is provided that is formed to define an exterior surface of the element with an exterior surface area formed to provide the element having the preselected element density. A polymer resin and a foaming agent are mixed together in preselected proportions to provide a material mixture, which is heated to at least partially liquefy the material mixture. The at least partially liquefied material mixture is injected into the mold cavity over three respective predetermined time periods at three respective velocities, under three respective pressures.

Abstract: A method of forming an element to float at least partially on a surface of an at least partially liquid hydrocarbon mixture. The method includes mixing a polymer resin and a foaming agent together in preselected proportions to provide a material mixture, and heating the material mixture, to at least partially liquefy it. The material mixture is injected into a mold cavity configured to define the element's exterior surface in a series of at least three steps, commencing with an initial step. In each step, the material mixture is injected over a predetermined time period at a predetermined velocity and under a predetermined pressure. Each predetermined velocity in the steps following the initial step is less than the predetermined velocity in an immediately preceding step thereof. Each predetermined pressure in the steps following the initial step is less than the predetermined pressure in the immediately preceding step thereof.