Also known as pellet presses, pellet mills are machine presses that are used to create pellets from some type of powdered material. Machinery of this type is common in preparing feeds for livestock, as well as creating a wide range of household products. There are several different common configurations of the pellet mill, varying in size, design, and mode of operation.
One pellet mill category is known as the large-scale mill or press. Mills of this type are often used to create livestock feeds or produce wood pellets for use in stoves. Within this class, ring die and flat die mills are employed to create the desired size of pellets. A flat die mill makes use of a die that receives the powder near the top of the device, where it is pressed firmly with a roller. As the roller progresses over the powder, it is compressed and forced through slots in the body of the die. Cutters are used to clip the compressed powder into pellets as it emerges from the slots.
The ring die pellet mill is equipped with radial slots along the surface of the die. The powder is fed into the device and spreaders smooth the powder into a more or less even coat. Two or more rollers compress the substance, pushing the powder through the radial slots. As with the flat die mill, cutters cut the pellets as they emerge from the slots.
With small-scale mills, the screw-type pellet mill is the most common type. The powder is placed into a shaped pocket, then compressed by means of the use of a screw press. A screw-type press may be operated manually, or managed with the use of hydraulic attachments that help to control the pressure applied to the powder.
With all pellet mill designs, heat may be used as part of the compression process, allowing the pellets to develop with the desired texture. Often, some method of cooling the pellets immediately after cutting is employed, making it easier for the pellets to retain the proper shape. Depending on the type of product produced, the recently milled pellets may undergo a spray or quick bath that helps to seal the surface of the product, allowing it to retain shape, texture, and freshness for a significant amount of time.
Along with food items for livestock and wood pellets for consumption in pellet stoves or heaters, a pellet mill may be used to produce products such as rat poison or fertilizer products for gardens and lawns. This means that workers often wear some type of protective clothing during the production and handling of the pellets. In addition, the packaging is normally designed to not only protect the product from deterioration, but also to advise the buyer of how to use the product safely.
By Malcolm Tatum