Techno Linear Motion Catalog19Technical Information5) Load Bearing MechanismsLoad bearing mechanisms are the structural backbone of any linear/rotary motion system, and are a criticalconsideration. This section will introduce most of the more common types of load bearing mechanismsfound in linear motion machinery. In general, bearings allow smooth, low friction motion between twosurfaces loaded against each other. The motion can be either rotary (such as in a turning shaft) or linear(such as a machine part moving back and forth). Some applications require that a bearing accommodateboth types of motion simultaneously, which is referred to as a combination bearing. In both cases thereshould be a strong attempt to provide enough lubrication to keep the bearing surfaces separated by a filmof oil. The absence of physical contact provides most bearings with long service lives.Bearings are evaluated on the basis of how much load they carry, at what speeds they can carry the load,and how long they will serve under those conditions. Friction, start-up torque, shock- and impact-resistance,operating environment, rigidity, size, cost, complexity, and lubricating procedures are also important designconsiderations.The following diagram reveals the basic bearing families more widely found in linear motion systems. Thedistinction between families is made by the type of motion and type of loading being considered. Bearingsaccommodate rotational and/or translational motion. Translational bearings, or linear bearings, are loadedperpendicular (radial) to the direction of motion. Rotational bearings can be loaded either perpendicular tothe axis of rotation (radial) or parallel to the axis of rotation (thrust).Most bearings can be classified into one of two general types. The distinction between bearing types ismade by the nature of the bearing mechanism. The two types each have a number of different possibleconfigurations, and some of the more common configurations will now be discussed. Since many bearingsare either specialized or of proprietary design, this discussion is by no means intended to be all exhaustive,but rather to serve as an introduction.Plain Bearings, or Journal Bearings, are the most basic type ofbearing. They have no moving parts, they support loads through slidingcontact, and are usually the least costly to install. Some plain bearingsare self-lubricating and maintenance-free while others are not. In fact,some plain bearings are classified as to the lubricating method required.Typically, plain bearings will operate right up to the point of failure withlittle or no warning signs. Since the motion involved is usually low level,the results of failure are typically noncatastrophic, and replacement orrepair is fairly simple. There are several ways to size plain bearings foran application, as outlined at the end of this section.ThrustTRANSLATION(OR LINEAR)JOURNALOR RADIALBEARINGBearingsurfaceTHRUSTBEARINGRadialLoadROTATIONMotionMotionLoadLoadPLAIN BEARINGBearingJournal