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Types
A washing trommel, also referred to as a washing drum, is a cylindrical elongated tube used to clean and separate undesired substances from desired substances. Screen type washing trommels are commonly used in mining. Archimedes, or reverse helix, type washing trommels are commonly used in gold prospecting and to wash machine parts.
History
Archimedes' screw was invented over 2,000 years ago by the Ancient Greek scientist Archimedes. It was originally used as a hand pump to pull water from the Nile delta for irrigation purposes and to pump water out of ships. The Archimedes, or reverse helix, washing trommels were designed based on this ancient invention.
Features
The screen type washing trommels that are used for commercial mining are large machines used to wash fine particulates off the iron ore, coal or gravel as they pass through the machine. The washing trommel is fitted with large metal screens that handle the final separation of the desired product from the undesired product.
The reverse helix or Archimedes washing trommel is fitted with a reverse screw on the inside of the tube. It is rather like a giant screw turned inside out with the threads or ridges running up the inside of the cylinder. This type of washing trommel is commonly used in gold mining and for washing machine parts. The threads are spaced for the pieces of gold or machine parts to fit within them.
Function
Screen type trommels are angled down slightly so that the material being washed and separated travels through at a downward slope. The material being mined is washed with water as it travels through the cylinder. Special lifters installed within the cylinder assist in the washing process by lifting and mixing the material as it passes through. The undesired matter that remains after washing is separated from the ore, coal or gravel at the end of the trommel by screens that are specially designed and sized to allow the material being mined to drop through into a hopper.
The Archimedes trommel is commonly set at an upwards angle. As it spins, the threads carry the metal parts or gold pieces up the cylinder. The parts are sprayed with cleaning fluid as they travel through the trommel to wash off grease and dirt. Gold is separated from gravel, dirt and any other undesired materials when it is sprayed with water as it passes through the trommel. The dirt, gravel and dirty water or cleaning solution are expelled from the back of the spinning drum during the cleaning and separating process.
Other Uses
Trommel washers are also utilized in environmental restoration processes. They play an integral part in removing contaminants from sand, soil and gravel.