Plain Linear Bearings | FAQs

There are multiple advantages that the Simplicity linear bearing with a FrelonGold liner has over linear ball bearings, but there are two that stand out the most. First, they are self-lubricating or do not require additional grease and oil to be added to operate properly. Linear ball bearings require grease to be used. Secondly, the Simplicity plain bearings handle contamination extremely well by creating a natural seal on the shaft and pushing the dirt, dust, chips, and other contaminants to the end of the stroke. Linear ball bearings must have added seals that often allow particulate to slip past and into the raceways where it will catch in between the balls and stop them from rotating which leads to failure.

There are two main reasons you might want to consider a linear ball bearing over a plain bearing. First would be that they have a low coefficient of friction meaning the balls will roll more freely than the surface of a plain bearing will slide. This will result in the ball bearing being better suited to higher speed applications. Second would be in places where a preload is required. In other words, the balls can be slightly “squeezed” by the casing around the bearing and the “play” between the bearing and shaft is removed. These bearings might be used where more precision may be needed.

The short answer is no. The term “plain bearing” applies to any bearing that does not have rolling elements, but instead is made up of a solid surface that slides along the shaft or raceway. The bearing surface could be plastic, bronze, or other polymer-based materials. PBC Linear Frelon and FrelonGold were specifically developed through intensive tribological testing for linear motion applications. Also, note that these materials from PBC Linear are not inserts, but rather the material is bonded permanently into place with a structural adhesive similar to how airplane wings are bonded together creating a one-piece bearing.

The easiest way is to purchase them already mounted in standard pillow blocks where they are fixed in place with retaining rings and/or a pin. If standard pillow blocks are not an option, you could create your own housing and retain the bearing at the ends with retaining rings or bore the housing to specification and then press fit the bearing. Instructions for bearing installation can be found in the RST catalog here: Catalog

In general, stainless steel jacketed bearings will hold up the best in harsh chemicals, and many polymer-based materials can be chemically inert. It is always best to check with a specific manufacturer on chemical compatibility. PBC Linear bearings Chemical Reaction Chart can be found here: Chart

The smaller grooves toward the ends of a linear bearing are designed for retaining rings that can hold the bearing in a housing. The larger inner grooves on Simplicity linear bearings are for O-rings that will help cushion slight movements when used in a self-aligning pillow block.

Both plain bearings and linear ball bearings will work in cantilevered load applications, but keep in mind there are consequences for each. With a plain bearing, the load must stay within the 2:1 ratio or the bearings will bind causing stick-slip or possibly locking up the motion. Linear ball bearings may continue to operate beyond the 2:1 ratio, but keep in mind that the balls will be causing increased point pressure on the shaft resulting in galling and severely shortened life. You can learn more about the 2:1 ratio here: Video

No, PBC Linear is committed to manufacturing in the USA and has a 50-acre campus with over 250,000 square feet of production space where approximately 100 machines keep their spindles turning to produce millions of bearings each year.

You cannot use a linear ball bearing in a pivoting or rotating motion due to the arrangement of the balls in the raceways. However, because a plain bearing like Simplicity has a solid gliding surface for the bearing, it can move in any or multiple directions at the same time.

There is no known formula for accurately and reliably predicting the life of a plain bearing because there are too many dependent variables.

• Many of the factors are dependent upon the coefficient of friction, which can change and is difficult to exactly determine. Page 15 of the Round Shaft Technology catalog describes some of the application parameters and factors affecting wear life.
• A “life calculator” provides estimates, but infinite variables result in too many possibilities. In addition, the failure mode depends upon the user’s definition – is life defined as complete wear out of the liner, or increased running clearance due to wear that results in too much play?
• Testing under the specific application conditions is the best method to determine life. An online resource comparing PBC Linear to a competitor under specific conditions can be easily viewed here: White Paper
• PBC Linear has a wear rate vs. life expectancy example for linear plain bearings detailed on our online Catalog.