Linear bearings are rolling-element and fluid-film devices that reduce friction in motion systems where the motion acts along a straight — or sometimes curved — pathway. They are distinguished from radial bearings in which motion is rotary. Linear bearings are used in machine tool applications such as sliding doors, 3D printers, and automation settings where reducing friction and guiding linear motion is needed. They can be loosely grouped as ball and roller types that use the rolling motion of rolling elements and sliding types that rely on lubricant and low-friction surfaces. This article will discuss the distinct forms that linear bearings take and highlight some general applications.
SLIDE-TYPE BEARINGS
Sometimes called linear bushings, linear bearings are manufactured in sintered aluminum bronze, metal/polymer composites, carbon insert styles, polymer-lined sleeves, etc. and rely on a lubricating film to form between the bearing and the shaft while the two are in relative motion. Powdered-metal bronze bushings have been used for many years as die-post bushings. Their porous constructions, often with carbon plug inserts, are vacuum impregnated with oil that flows to and from the bearing under the frictional heat developed as the shaft moves and stops, providing a film of oil between the bearing and the shaft.
Polymer, self-lubricating linear bushings have captured some of the market that had been dominated by sintered metal bushings. The polymer itself — typically PTFE — provides slipperiness for the running shaft. These are popular in food packaging for their ability to run without lubricants and their ability to withstand washdown chemicals. They can run on unhardened shafts having high corrosion resistance. Because polymers are subject to cold flow at high loads and do not dissipate heat well, polymer is often bonded in thin sections to metal backers in the construction of these bearings.
Linear bushings can be crowned slightly to permit some angular adjustment of the bushing relative to the housing to adapt to shaft deflection. In more extreme cases, the bushing is supported in the housing by O-rings. Linear bushings are available as naked units or housed in pillow blocks and flanged units.
Bushings can be arranged as tandem installations in common housings to provide higher axial spread for the bearing surfaces. They are available as open and closed varieties, with the selection depending on how the shaft is supported. Shafts supported continuously over their lengths require open bushings that can clear the rod rails. Shafts supported on their ends can use closed bushings. Linear bushings are tolerant of dirt as a result of having no moving elements.
What Is a Rod End 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. To learn more about rod end bearings and how they work, keep reading. If you’re looking to purchase Rod Ends, Monroe has you covered.
Rod End Bearings Explained
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.
Rod end bearings are typically made using the following materials:
Steel
Stainless steel
High-carbon steel
Aluminum
Male vs Female Rod End Bearing: What’s the Difference?
A rod end bearing can be classified as either male or female depending on the way in which the threading is designed. Male rod end bearings are designed with external threading. In comparison, female rod end bearings are designed with internal threading. With interior threading, female rod end bearings can handle unique applications that aren’t possible with male rod ends bearings. Helicopters, for instance, often use female rod end bearings to adjust the direction of the blade. They allow pilots and aviation technicians to fine tune their blade adjustments.
You can see an example of both male and female rod end bearings in the photo above. The red rod end bearing is male because the threading is located on the exterior, whereas the black rod end bearing is female because the threading is concealed inside it.
