World Grain - November 2012 - 102

FEEDOPERATIONS

metal to support shafts that do not continuously turn such as a shaft turned by a hand wheel or intermittent power source. As the speed increases, the bearing support may be lined with a sleeve

ity but also a high friction resistance to the turning shaft or journal. In order to reduce the friction between the shaft and the bearing surface, metal or other types of bushings are often in-

Roller bearings are used in applications like conveyer belt rollers, where they must hold heavy radial loads.

is transmitted from the inner race to the ball and from the ball to the outer race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly. But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform or squish, ruining the bearing. ROLLER BEARINGS Roller bearings are used in applications like conveyer belt rollers, where they must hold heavy radial loads. In these bearings, the roller is a cylinder, so the contact between the inner and outer race is not a point but a line. This spreads the load out over a larger area, allowing the bearing to handle much greater loads than a ball bearing. However, this type of bearing is not designed to handle much thrust loading. TAPERED ROLLER BEARINGS Tapered roller bearings can support both large radial and large thrust loads. The rolls are mounted at an angle within the races so that their contact line can handle both radial and thrust loads simultaneously. This may be a single circle of

of different metals for intermittent or slow speed light loadings. As speeds or radial load increases, a ball or roller bearing is used to carry the radial load and minimize friction between the shaft and its mounting PLAIN BEARINGS A plain bearing, also known as a friction bearing, is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore the journal (i.e., the part of the shaft in contact with the bearing) slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. Plain bearings, in general, are the least expensive type of bearing. They are compact and lightweight. They have a high load-carrying capac-

serted into the bearing housing to support the shaft. These bushings are usually made of a different type of material than the shaft. Some of the most common materials are babbitt, bronze, cast iron, graphite, plastic, nylon, Teﬂon and even oil impregnated arguto wood bearings used in many screw conveyor interior ﬂighting bearing hangers. BALL BEARINGS Ball bearings are probably the most common type of bearing. These bearings can handle both radial and small thrust loads and are usually found in applications where the load is relatively small, but the shaft is turning at higher speeds. The balls are enclosed in a cartridge formed by an inner and an outer enclosure called a race. The load

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World Grain - November 2012

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