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You are here: Home / FAQs / Plain bearings (sleeve bearings) and the shafts they ride

Plain bearings (sleeve bearings) and the shafts they ride

August 9, 2017 By Lisa Eitel

As mentioned earlier — in the FAQ Plain bearings: What are they? — plain bearings are made of many graphite, bronze, and plastics that include PTFE, nylon, and polyacetal. Material improvements have made plastic plain bearings (or sleeve bearings) increasingly common, even in demanding motion applications.

Shaft material and wear of plain bearings

The shafts on which plain bearings ride have significant impact on plain-bearing performance and life. One common option is cold-rolled carbon steel. This shaft material makes for a suitable mating surface for plain bearings made of polymers. Ceramic shaft surfaces induce more wear, though are sometimes chosen for their ability to withstand harsh environmental conditions. Though aluminum shafts are lightweight and easy to machine, they also induce accelerated plain-bearing wear. Aluminum shaft that’s anodized slightly improves the assembly performance.

sleeve bearing surface roughness
Shaft surfaces for mating with plain bearings shouldn’t be too smooth or rough.

In fact, shaft surfaces for mating with plain bearings shouldn’t be too smooth or rough. Overly sooth surfaces will cause stick-slip adhesion variations — in turn causing higher friction resistance to bearing movement. More of a disparity between dynamic and static friction will make for faster bearing wear and jerkier motion.

In contrast, overly rough shaft surfaces quickly abrade plain bearings. In fact, the rates of wear induced by shaft-bearing interfaces can vary a hundredfold. Some manufacturers recommend shaft-surface finishes to 64 root mean square (rms) for precision applications needing low friction; a smoother shaft with roughness of 20 rms or so is more suitable where long plain-bearing life is a design objective.

Recall that the rms expression of surface roughness is derived from measurements of a surface’s microscopic peaks and valleys. Ra is an alternative measure some in industry use to quantify roughness — in this case, as an average roughness of a surface’s peaks and valleys. So the two measures express the same quality, only in different formats.  Note that large and outlying peaks or flaws on a shaft surface will affect the RMS value more than its equivalent Ra value.

Uncontrolled static discharges can negatively affect electronic components, hinder production processes, or even heighten fire risk. Now, self-lubricating iglide F2 EDS bearings from igus deliver electrostatic discharge (ESD) properties for such applications. Its low surface resistance (103 and 109 Ω depending on component geometry) reduces charging voltage level and helps deplete charges.

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Filed Under: Bearing Basics, FAQs, Featured

Reader Interactions

Comments

  1. Ryan Murphy says

    August 2, 2019 at 8:22 pm

    Hi Lisa,

    I was wondering where the plot of “Effects on Plain Bearings of Shaft Surface Roughness” was sourced from? It could be very useful to a project I am working on, but I want to ensure the validity of it.

    Thank you,

    Ryan

    • Lisa Eitel says

      August 2, 2019 at 10:20 pm

      Hi Ryan! Thank you for your interest. This is fairly common knowledge in the motion industry. However, specific values (and verifiable data) are available through the plain-bearing manufacturers igus as well as PBC Linear. You may want to poke around their online design resources and product data PDFs and other data sheets for more information. Best wishes for your project.

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