Rotomolded Tanks

Rotomolding Process of Tanks

In the process of rotomolding a tank, a heated hollow is filled with a charge or shot weight of material. Additionally, it is often slowly rotated across the two parallel heat axes, allowing the softened material to disseminate and adhere to the mold walls. The mold rotates continuously during the heating phase to prevent drooping or distortion and during the cooling phase to maintain the thickness throughout the portion.

The mold is mounted in the oven, which has natural gas burners heating it, and bolted at the dividing line. At 4 to 12 rpm, it is hydraulically rotated. Polyethylene is added layer by thin layer as the plastic melts. When the plastic has fully formed and hardened, it adopts the shape of the mold, which is then taken out of the oven. Once the tank has cooled, the mold is removed to reveal the finished item. In a rotomolding setup, expert manual labor is required. For instance, special workers are required to open and close the molds during the rotomolding process. The die's opening and closing require strenuous manual labor.

Materials Used to Make Rotomolded Tanks

Rotationally-molded tanks can be created using a variety of thermoplastic substances, such as polyethylene, polypropylene, Halar, and polyvinylidene fluoride, all of which are high-purity plastics. Depending on the application of the product, additive materials are frequently added to the plastic resin to improve attributes including strength, moisture, chemical, and temperature resistance, color, and flame retardancy.

Plastic tanks are among the largest goods made using rotational molding. As a result, producers use the biggest rotomolders to make them. They need a lot of room, a place where intense heat can be generated, and a place to cool things off. If necessary, the rotational molding machine will need room to turn around two separate axes in each of these locations.

The polymer resin is usually in fine-powder form when making the tanks so it is easier to get into all the nooks and crannies of the tank-shaped mold. Even distribution of the plastic can be a difficulty because the process is conducted at low speeds and low pressure. However, sophisticated designs like two-compartment tanks are feasible if the plastic granules are fine enough. Rotomolded tanks can store anything from a few gallons to several thousand gallons and are made to be either horizontal or vertical in configuration.

Advantages of Rotomolding

• Low operating pressures enable the creation of rotomold tooling from inexpensive metals like aluminum.
• Wall thickness is constant thanks to the mold's continuous rotation during the heating and cooling cycles.
• Complex double-walled open containers can be made using the double-wall construction method without further processing.
• High durability: pieces are molded as a single, solid piece, avoiding the necessity for weakening connection methods like welding and joint fabrication.
• High stability: Since the molding material is not subjected to external pressure, it is more stable and there is less chance that the finished item will have flaws.
• Strength: Rotomolding produces thicker corners, lowering the likelihood that they may fail at certain stress-concentration places.
• Aesthetics: Surface finishes like fine-detail textures, logos, emblems, and letters are easily accommodated by the soft metal utilized for the rotomold tooling.

Disadvantages of Rotomolding

• High cycle times: rotomolding can take up to three hours to complete one part at eight rotations per minute.
• Limited material choices: Poly-based resins are the only materials that can be utilized for rotomolding since they can easily be transformed from granules to a fine powder and have great thermal stability.
• High cost of raw materials: The cost of adding the necessary additives, the expense of grinding the material into a powder, and the high criteria for thermal stability all contribute to high material costs.
• Low repeatability: Due to a lack of repeatability, the rotomold tooling's soft metal must be repaired or replaced after 3,000 cycles and may result in quality problems.
• High labor costs: rotomolding requires more labor intensity than equivalent production because mechanization and automation have not yet been implemented.