Of all the materials used by water barrel manufacturers, plastics such as high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene are the most common; however, metals such as stainless steel may also be used in instances in which the water has not been and will not be treated with chlorine as it is highly corrosive to most metals. The most popular plastic choice, polyethylenes do have a downside as they are somewhat permeable to hydrocarbon vapors and should be kept away from stored gasoline, kerosene and similar substances.
HDPE, however, offers a distinct benefit in that it is a FDA-approved material. Proper water storage is incredibly important for many industries including: sports and recreation, for applications such as hiking, climbing and other cardio-related activities; beverage, for water bottling applications, especially if water is collected from natural sources; agricultural and gardening, for use in irrigation applications; and wastewater, for use in storage of potentially hazardous tainted water.
As water barrels are most often plastic, then they are generally going to be formed through an injection blow molding process (metal would be formed through rotational molding or similar processes). The injection blow molding process is a combination of injection molding and blow molding. To begin injection blow molding, a parison is formed when a thermoplastic preform is heated to a molten state and then injected around a hollow mandrel, referred to as a blow stem. Once semi-cured, the newly formed parison is soft and formable.
Still around the stem, the parison is then placed into the blow molding chamber. Next, the steel blow stem is extended, forcing elongation of the plastic to the desired barrel size, typically 55 gallon, and also enhancing the tensile strength of the barrel. Then, the hollow blow stem is used to inject compressed air into the parison, causing the near-molten plastic to inflate like a balloon.
The inflation results in compression against the walls of the mold cavity, forcing the barrel to take shape. After cooling and hardening, the mold ejects the newly formed water barrel is ejected. Immediately, the water barrel exhibits a seamless design and does not require further trimming. As injection blow molding machines use multiple mandrels, they may be used to form a maximum of 12 water barrels at once.