Linear bearings generally use a pad, bushing, or roller system to carry a load on a rail that need not be a straight line. The rail can be most any length, although that dimension is limited by the actuator.
The durability of the bearing is determined by the load and required speed. Furthermore, rails can generally be any profile – simple flat surfaces, round polished rods, or complex profiles with polished ground surfaces on which balls or cylindrical rollers can ride. Hard (Rockwell 60) and ground bearing surfaces work best.
Further classifications might be by size. For instance, miniature linear bearings might work well moving a biologic slide sample just a few millimeters beneath a microscope lens while industrial-bearings on injection molding machines carry tooling of several tons.
Bushings provide possibly the simplest linear bearing. These thin-walled cylinders can be injection molded of proprietary polymers infused with a lubricant. An oil-infused bronze design, also cylindrical, rides on a polished round rod. This linear-bearing classification is often referred to as slides.
Purpose-built linear bearings are available for frequently encountered tasks, such as pull-out equipment drawers or storable work surfaces. These usually light-duty devices let polymer wheels or ball bearings ride on stamped or rolled steel rails. Telescoping arrangements allow designing pull-out equipment drawers into cantilevered positions while supporting up to 50 lb or more for maintenance.
Except for linear bearings, many linear materials are also required such as Linear Guide, Linear Stage, Linear Shaft, Miniature Linear Rail, Linear Block, etc. Also, some other bearings are worth mentioning like rod end bearing and needle roller bearing.
A rod end bearing is a common type of mechanical joint used on the ends of control rods. The steering columns in most cars, trucks and other vehicles, for example, feature tie rods with a rod end bearing. Of course, tie rods are designed to connect a vehicle's steering rack to its steering knuckle. As a result, tie rods must be able to rotate according to the direction in which the wheel is turned. Rod end bearings allow tie rods to perform this rotation in a precise and controlled manner.
Also known as a heim joint in the United States or a rose joint in the United Kingdom, a rod end bearing is a mechanical joint that features a rounded ball-like swiveling tip. They were invented in Germany during the 1930s to 40s for use in aircraft control systems. This promoted a company called H.G. Heim Company to patent and produce its own rod end bearings in North America, which is why the mechanical joint now has the moniker "heim joint."
H.G. Heim Company has since closed its doors for business, but rod end bearings are still produced and used throughout the world. Automotive tie rods are just way in which rod end bearings are used. They are used in countless other applications in which an articulating joint is needed, including aircraft control systems, steering links, track rollers and more.