Rotomoulding and Martini Shakers


Imagine the following situation. Suppose you have in front of you a large, burning candle and an empty martini shaker. Suppose that there is enough melted wax in the burning candle that it would fill about an eighth of the volume of the martini shaker. Imagine now that you’ve poured the melted wax into the bottom of the martini shaker. If you were to swirl the melted wax around a little, you’d notice that some of the wax would stick to the sides of the shaker and quickly harden. Now imagine that you’ve put the cap on, and imagine that you’re shaking the shaker up and down.

I’ve used this example to try and explain the concept of rotomoulding in the simplest form, but the metaphor breaks down a bit at this point. You can imagine that the inside of the martini shaker is now covered nearly uniformly with a thin layer of wax. If there was some way that the martini shaker could magically be made to disappear, what would be left would be a wax replica of the martini shaker (though it would be very slightly smaller than the original). Unfortunately, there’s no way to extract the wax replica without ruining it.

In rotomoulding, this isn’t a problem. First of all, rotomoulding isn’t used to make molded products out of wax. Polyethylene, PVC and other plastics are the materials that are formed in rotomoulding processes. Rotomoulding can be used to produce plastic tanks, lawn furniture, novelty products, kayaks and a wide variety of other products. What all of these products have in common is that, immediately following their emergence from the rotomoulding process (before they’re subject to hole drilling or any finishing process), they are hollow. In this way, rotomoulding differs from other plastic forming processes like extrusion and injection molding, both of which produce plastic products with solid cross-sections.