PE and Rotational Molding
Most rotational molding is done using PE. PE is made in pellets. Because rotational molding is done at a low temperature the pellets are ground into a dust form so the material melts easier. The PE dust is measured and poured inside the mold. As the mold rotates it is heated the powder bounces around the inside until the mold is hot enough for the plastic to sticks to the sides. When the material cools you have a part that matches the inside of the mold.
Great Things about Rotational Molding
- You can use the same mold for different wall thickness.
- Molds are cheap for their size.
- Most parts can be welded.
- Materials except for XPE can be recycled.
- Lots of Rotational Molded parts are made with recycles material. Both per and post-consumer materials.
- You can pick almost any color in low quantity.
- Parts can be made with FDA materials.
- You can make a tank cross-linked on the outside and LLDPE on the inside. Giving you a strong tank that is FDA approved.
Polyethylene fabrication on a part that comes out of the mold 90% done is much easier. If you are rotational molding a tank you may only need to cut the top off and add a drain fitting.
Finally rotational molding is slow you only get about one part per hour. So if you need more than 40 parts a week you may need more than one mold. Most rotational molders are big with 3 or 4 arms for mold. Each arm can hold 1 to 16 molds per arm. All the molds run at the same time so all the parts have to have the same wall thickness or the thinner parts will burn.
Bell Plastics does low volume rotational molding. If you need a million parts we are not the right company.
Rotational Molder Tanks
Bell Plastics has many molds for rotational tanks. We make custom tanks for people that can’t use a stock tank. Need a tank with a 3/4 wall or a special color. Rotational molded tanks have no seams. The lines you see on the outside of the tanks are parting line or mold lines. The lines are on the outside of the tank but the inside will be smooth.
Rotational molded gas tanks are getting more and more common. In some ways it is one of the best uses of plastics. Most gas tanks are cross linked polyethylene on the outside with nylon on the inside. After the cross linked PE is molded and before it is allowed to cool the mold is opened and nylon powder is added. The mold is closed and put back into the oven and the cycle is repeated.
As a result you get a strong tank that won’t deform under low temperature and it will hold gas.
Down side is you can’t recycle finished tank.
It is very hard to rotational mold less then .100 inch or 2.54 MM thick.