Polyethylene Tanks
Polyethylene tanks, a type of poly tank, provide atmospheric, or non-pressure, storage of a multitude of substances. Since polyethylene has a broad range of chemical resistance of many materials, polyethylene tanks are utilized in numerous industries, particularly in agricultural, oil/gas, water, waste treatment, medical, scientific, food processing and pharmaceutical industries. Chemicals that polyethylene tanks have a particularly high resistance level to include acetatic acid, diethylene glycol, mercury, methanol, glycerin, acetone, iodine, motor oil, Vaseline, natural gas, transformer oil and caproic acid. However, polyethylene tanks are not well-suited for certain chemicals including chlorinated hydrocarbons such as solvents and gasoline. In addition, when contrasted to steel tanks, polyethylene tanks are advantageous due to a lack of susceptibly to corrosion, not requiring painting (since the colors can be molded into the tanks), and quick fabrication in just a matter of minutes. Additionally, certain polyethylene storage tanks, such as polyethylene water tanks and polyethylene fuel tanks, are UV-stabilized and food-grade.
Polyethylene tanks are typically made from virgin resins of high density polyethylene, abbreviated HDPE. While crosslinked high density polyethylene, abbreviated XLPE, can be used for polyethylene tanks, it is not a recommended material for many applications. Rotational molding is typically used to form polyethylene tanks. The process begins with a heated mold that causes the polyethylene within to melt; thus forming a puddle at the bottom of the mold cavity. Next, the mold is slowly rotated, usually around two perpendicular axes, resulting in the melted polyethylene flowing into the mold and sticking to its walls. The last part is the cooling phase in which the mold continues to rotate so that an even thickness is maintained throughout the part. Ideally, polyethylene tanks are constructed through the rotational molding process in a one piece, seamless construction. However, some polyethylene tanks are formed with a vertical seam, and, as a weak point in the tank, often causes splitting and water loss. Polyethylene tanks can be rotomolded in almost every possible configuration; rectangular, cone bottoms, drums, horizontal, cylindrical, open tops and flat bottoms. Polyethylene tanks are filled with a substance then sealed; the seal serves to keep the substance in or drain the substance out when necessary.