A trommel is a piece of equipment used for several different purposes, including sorting ores in mining.
There are also trommels that are used in gravel pits to size different types of gravel, but this article deals with the trommel used in mining.
The trommels used in mining come in various sizes, depending on the size of the mining operation. There are commercial trommels, filled by a backhoe, and there are one-person, portable trommels that can be carried easily by a person up a mountain.
The basic purpose of the trommel is to separate ore from all of the other substances that are dug up in the process of mining. This piece of equipment is generally used in placer (or surface) mining, when looking for gold, tin, other metals or gemstones.
Trommels consist of four primary sections. The first is the feeder, or trough where the rough dirt, rock and ore is placed so it can slide into the trommel.
The trommel itself is a helix cylinder, based on the screw pump developed by Archimedes over 2000 years ago. The method is still very effective for the purpose.
There are spiral shaped riffles inside the rotating tube screen of the trommel. This design sends the light materials to flow out of the back of the tube (the tailings), while the heavier ores and stones flow to the high end of he tube.
The commercial sized machines use screens to separate the gravel out from the tailings and ore.
The next part is a sluice, where water is used to capture gold or other ore dust and settle it. Many models have a nugget trap to capture larger nuggets.
The last section catches the tailings as they leave the trommel.
The trommel is a simple but highly effective piece of mining equipment.