Linear Rotary Bearings

Linear Rotary Bearings

The shaft of a linear rotary bearing runs through the hole called the bore, and typically ranges from 6 to 20 millimeters wide in diameter. Cylindrical in shape, linear rotary bearings are usually not more than a few centimeters long. The exterior of the bearing is smooth and, depending on the material, polished. Inside the housing of the linear rotary bearing are spherical elements called ball bearings that are held loosely inside the bearing and ride in tracks called races or raceways. As a shaft enters the linear rotary bearing, the ball bearings spin freely, allowing the shaft to rotate smoothly and without resistance as it slides in and out. Linear rotary bearings are used widely by the manufacturing, medical, agricultural and construction industries as important components in drills, printing equipment, die cutters, engines, industrial robots, automobile assembly lines, dental tools and more.

Linear rotary bearings are similar to bushings with one exception. Bushings are common linear bearings that slide on a shaft without the assistance of spherical elements, relying on lubrication to overcome the high surface contact area. Adding ball bearings reduces the coefficient of friction by 100 times and increases the life of the bearing as well as introducing rotary movement. The interior space is utilized to accommodate the maximum number of balls because the more ball bearings there are, the less the unit load for each ball, the longer life the bearing will have and the smoother the shaft will slide and rotate. The balls are generally arranged in oval raceways because oval raceways have infinite ball flow; that is, the ball bearings spin on their axis as well as circulating around the oval track, half of which is exposed. Pillow block linear bearings are mounted bearings that often incorporate rotary movement as well as linear using the same process described here. In other linear rotary bearings, the balls do not travel in a raceway but are instead held in separate spaces, rotating individually. Ball bearings must be perfectly spherical in order to prevent wear and minimize friction, and the diameters of the bore and shaft must be carefully considered. If the bearing is intended for mostly linear motion, a greater clearance between the bearing and the shaft is recommended to decrease incidental rotation. For applications requiring both linear and rotary motion with high precision, the bearing and shaft can be matched in diameter leaving the minimum amount of effective clearance.