We live in a world that values its plastic products. Plastic, and all of its variations, is one of the materials that makes modern life possible. Plastic packaging is actually good for the environment because it can be recycled and, when used for food storage, keeps food out of landfills where it takes up valuable real estate and contributes to global warming. One process to make various plastic products is rotational molding. With this method, small items like ping pong balls are possible. Medium size items like laundry trucks are possible. Even bigger things like tanks that can hold as much 20,000 gallons can be made with rotational molding techniques.
What is rotational molding?
That is a good question. This is an incredibly unique and specialized production process. It is also referrred to as “rotomolding” or custom roto molding. Plastic resin is heated, melted and fused in a closed mold. No pressure is involved in the process, which sets it apart from most plastic molding processes.
Rotational molding is a four step process:
- The plastic resin is loaded into the mold. At this point it is typically in a powder form.
- The mold is heated in an oven. As it is heated, the mold is rotated. As the plastic resin melts it begins to stick to the walls of the mold. So that the plastic resin powder does not accumulate in one area, the mold is rotated at varying speeds and the hollow portion is rotated through at least two axes. This helps make sure the walls of the mold are coated evenly. It is important to be careful with the amount of time the mold has in the oven. If it is in there too long, the plastic resin melt may degrade and the strength of the resulting product will be compromised. If it is in the over for too little time, the plastic resin melt may not go to completion. Often this causes large bubbles to form in the plastic. This has other negative effects on the finished product.
- A fan cools the mold. This takes a decent amount of time. The plastic resin has to be cool enough to be safe to handle. The part that was made through the rotational molding process shrinks away from the walls of the mold as it cools. This makes it easy to clean it. The cooling cannot happen too quickly. If you use water, for instance, to cool the mold, the parts will warp. If you are making laundry trucks, for instance, that would result in faulty parts and the possibility that the laundry trucks just will not function the way they should.
When it is cool enough to touch safely, the part is removed from the mold.
- The rotational molding can produce a very wide variety of products. There is a wide array of tooling methods that are used in this kind of process. Cast tooling is the most common kind of tooling used in rotomolding.
What can be made with custom roto molding?
- Storage bins and containers: Colored plastic bins and containers can be made this way. These are typically used to ship or store items. These bins and containers are often used for food storage and shipping. This is a good way to make sure the food is still edible and good when it arrives at its destination.
- Laundry trucks and carts: Laundry trucks and carts are used a lot in schools, hospitals, jails and prisons. The wheels and carts are produced to be as efficient as possible.
- Cones and barriers to be used on the road: The cones and barriers you see on the street are made via the rotational molding process.
- Toys: As has been mentioned, ping pong balls are made this way. So are decorative flamingos. In fact, a lot of the giant plastic toys and knick knacks found all over are made with rotational molding techniques.
- Water vessels: Some boats, kayaks and canoes are made this way. Many of the dock floats you see were produced via rotational molding.
Rotational molding is a versatile process for manufacturing a wide variety of products. The more you look around, the more items you will find that were produced this way.