What Is a Trommel?

Mary McMahon
Mary McMahon

A trommel is a rotating drum with a screen that allows fine material to fall through while retaining larger materials. Trommels are useful in the processing of a wide variety of solids, particles, and mixtures. They come in an assortment of sizes to meet different manufacturing needs and can be used with accessory components to increase functionality, if necessary. Some industries that utilize trommels include the mining, gravel processing, and solid waste management fields.

Trommels are frequently used in gravel processing to sort gravel of different sizes.
Trommels are frequently used in gravel processing to sort gravel of different sizes.

To operate a trommel, a technician can start an engine that rotates the drum and then add material through an intake chute. It is possible to keep the device in continuous operation by adding more to the chute while the drum processes. As the drum turns, it aerates the materials inside. The smaller particulates fall towards the bottom and out the bottom of the screen, while larger materials work their way toward the opposite end, and eventually out the end and into an exit hopper.

Crushed rock is sometimes fed into a trommel to sift out the finer pieces.
Crushed rock is sometimes fed into a trommel to sift out the finer pieces.

It is possible to use conveyors with a trommel to move the fine and larger particulates. At a facility like a gravel processing plant, rock can move through a series of progressively coarser screens to yield different grades of rock. These can move from very small fill gravel to much larger chunks. Each grade contains rocks within a narrow set of parameters; smaller rocks fell out during earlier processing, while larger rocks were retained and moved along the conveyor.

Another tool some companies may opt to use with a trommel is a pulverizer. Pulverizers crush rock, stone, and other materials into smaller pieces. They can feed crushed materials into a trommel for sorting to generate a continuous supply of rock of a given size. These devices can connect to hoppers that directly load bags or trucks for transport, in settings where a facility processes materials for sale or shipment to other locations.

Mining, rock processing, and similar industries use these devices. They can also be useful in waste management, and on job sites, where workers can set up a portable device. Portability allows workers to sort through the materials they find on side, instead of having to ship them to a remote location. Small sizes typically have weaker motors and may not be able to process high volumes of material, but may be acceptable for basic applications like geotechnical exploration sites where geologists want to process material to determine if the site merits further investigation.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@allenJo - Speaking of buying stuff from the store, sometimes I buy topsoil from the local hardware soil. I am afraid that the quality of the soil that I get is not good.

Honestly, it’s only good for filler, that’s all. What do I mean by that? Instead of soil, I get mostly rocks, twigs, grass clippings and weeds.

There is very little soil in the mix. I am pretty sure that they used a trommel to create the topsoil but I don’t think that they did a very good job. I get better results creating my own topsoil by finding empty patches of lawn and digging that up, to be honest with you.


@SkyWhisperer - That’s okay if you just want to filter your rocks. But you can’t create smooth stones using your homemade device. For that you will need a pulverizer.

I don’t know if they sell those at home improvement stores. I tend to think that these machines are limited to industrial use. They require a lot of power and of course they can be very dangerous.

In that case, you’re pretty much out of luck, but I think you can just buy the smooth stones from a local supply store if you need them.


Trommels are used in creating gravel driveways too. Gravel driveways are made of gravel with varying grades of coarseness or smoothness. With a trommel you can change the grade of the stones so that it is more or less smooth, according to your liking.

You can get a simple trommel from a home improvement store, or build one yourself using different materials. Of course the important part of the trommel is the screen. You’ll have to adjust the size according to the size of the rocks. You can then rotate the cylinder manually and it will begin to filter out the rocks and you will have smooth gravel for your driveway.

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