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Gravity rollers have been used in cereal milling operations for decades, and are one of the simplest designs found among milling machines. However, just because they operate using simple principles doesn’t mean they aren’t sophisticated and efficient devices. Like most other milling machines, they function by exerting huge amounts of pressure and force on the grain, breaking it into smaller pieces or turning it into powder. They are used in a number of industries, and are often complementary devices alongside ball mills or hammermills. They are most often seen in agriculture though, where they are effective at reducing the size of cereal grains. Gravity rollers are rotating drums, usually made from stainless steel, that are operated in pairs. Occasionally, a single drum is used against a flat surface. They are designed to rotate in opposite directions and in extremely close proximity to each other. The space between the drums is nearly imperceptible. As cereal grains are fed into the device, they are caught by the drums. Because the drums rotate in opposite directions, they pull the grains down. As the grains pass through, they are crushed where the drums are closest together. In most applications, the grains are turned into flour, which is then channeled to other machines for purification or enrichment.
In agricultural settings, gravity rollers are designed to be food safe. The Food and Drug Administration sets standards for all surfaces that come in contact with the grains, including the drums. While these machines are normally used to make flour, they can be calibrated to create larger products that are uniformly sized. This may be done when the different grain components, like the endosperm and bran, will be used in separate products. Most of the time, the cereal is tempered before it is run through the milling machine. When grains are tempered, moisture is added to them that soften up the starchy endosperm. The outer coating of the grain, called the bran, actually grows tougher when it is exposed to moisture. This makes it easier to shatter once it is fed through the gravity rollers.
In most milling operations, the grains are fed through a series of drums that grind the material into finer and finer sizes. The initial set of gravity rollers are known as break rollers, and are used to shatter the kernel to get to the softer bits inside. The product is then run through several sets of reduction drums. Along the way, separators and aspirators channel pieces of various sizes away from the reduction drums for further processing.
These devices aren’t just used in the agricultural industry. They are effective whenever a stream of raw material needs to be reduced in size for additional processing. Another industry that makes regular use of break and reduction drums is the mining and ore processing industry. Large chunks of ore mined from the ground must be ground down so that they can be recovered from the surrounding rock. One of the best ways to do this is with break and reduction drums, which can shatter large volumes of ore quickly while being cost-effective.
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