Rotational molding is a highly versatile manufacturing option that allows for unlimited design possibilities with the added benefit of low production costs and is especially suitable for hollow parts and parts with low residual stress (no stress corrosion). The rotational molding process starts with a good quality mold that is placed in a molding machine that has a loading, heating, and cooling area. Several molds may be placed on the machine at the same time. Pre-measured plastic resin is loaded into each mold which is then closed. Then the molds are moved into the oven where they are slowly rotated on both the vertical and horizontal axis while being heated to the melding temperature of the plastic. The melting resin sticks to the hot mold and coats every surface evenly. The mold continues to rotate during the cooling cycle so the parts retain an even wall thickness. Once the parts are cooled, they are released from the mold. The rotational speed, heating and cooling times are all controlled throughout the process. Rotational molding offers design advantages over other molding processes. With proper design, parts that are assembled from several pieces can be molded as one part, eliminating expensive fabrication costs. The process also has a number of inherent design strengths, such as consistent wall thickness and strong outside corners that are virtually stress free. If additional strength is required, reinforcing ribs can be designed into the part. When cost is a factor, rotational molding has the advantage over other types of processes as well. In comparison to injection and blow molding, rotational molding can easily produce large and small parts in a cost effective manner. Tooling is less expensive because there's no internal core to manufacture. Since there is no internal core, minor changes can be easily made to an existing mold. Roto-moulding is mainly used for smaller production volumes, like Pipelife's Septic Tank.