If you check out most linear bearing manufacturer’s websites, you will see an assortment of different shaft material options. Take the drylin product offerings for example: Hard-anodized aluminum, case-hardened steel, multiple stainless materials, carbon fiber… where do you even start when you begin working on a new project? In this post, I will go over each shaft material in detail, and with blog-like brevity. Although you may hear me mention linear plain bearings throughout, I will make sure to point out how recirculating ball bearings may be used on these shaft materials just in case you are using recirculating ball bearings for your project.
Hard-Anodized Aluminum (6061-T6)
Centerless-ground, hard-anodized aluminum has been the default shafting material used with linear plain bearings for decades. Many of its features go hand-in-hand with the main benefits of plain bearings—it is lightweight, non-magnetic, easy to machine, and corrosion resistant in many environments. This also offers a serious cost benefit when compared to stainless steel, especially within applications that involve salt-spraying, or those that may need to resist wash-down. Please note that most aluminum shafting is stocked in six to twelve foot lengths, which are then cut down to shorter lengths based upon your orders. This means that the saw-cut ends will no longer be anodized, consequently introducing raw aluminum into the picture.
There are exceptions when the parts can be ground, cut-to-length, and even machined prior to anodize, but this is usually for higher volume applications and isn’t cost-effective for every project. That being said, the parts still need some way to be held onto the anodize racks, and if there isn’t a small hole or feature to hold it, there will still be an area without anodize—which may not be ideal for underwater or sensitive laboratory applications. We have also had some customers that strip and re-anodize parts to meet their requirements; however, this is problematic for the outer diameter tolerance of the shaft itself. Once you strip a shaft of its hard coat, you can no longer build it back up to its original dimension. Therefore, the shaft may be undersized, introducing more clearance into the bearing system itself. It should be noted that igus® does not recommend applications exceeding 365F (180C), in which case, steel shafting is recommended.
If you are using plain bearings, choose materials that work best for aluminum. If you are using igus® bearings, the default material is usually either the J200 or J. Keep in mind that ball bearings cannot run on aluminum and will damage the shaft due to the high surface pressure in the ball bearings. To learn more about drylin® liners click here.
300 Series Stainless: 304 and 316
The 300 series family is your best bet for corrosion-resistance since it is better than hard-anodized aluminum, the chrome-plated, or the 400-series stainless steels that many linear suppliers offer. 316 stainless steel, in particular, is the absolute best possible solution for highly corrosive applications, and is generally used in many of the marine-industry applications we see at igus®—drone sailboats, guide shafting for jets in large-scale water features, and many seating and furniture applications that are designed within yachts and motor boats. If you are looking for resistance to chlorides and chlorinates, 316 would absolutely be your best solution.
As a lower cost alternative for applications that are not exposed to salines or chlorides, 304 is about 20-30% less than its 316 sister material. We see 304 being used frequently in packaging, food processing, and lab applications. It is important to keep in mind that the 300-series cannot be hardened, and therefore is not suitable for recirculating ball bearings—only plain bearings. Suggested drylin liner materials would be T500(X) for high temperatures and corrosion-resistance, A160 for FDA compliance, and E7 for more general applications.
400-series Stainless Steel
This family, especially the 420C or 440C set, is necessary for recirculating ball bearings because the surface hardness of the shafting is 50RC+ on the Rockwell hardness scale, which is required for resisting the high point-to-point pressures of ball bearings. This hardness actually makes these materials popular for cutlery, knives, and surgical instruments. However, be careful about designing any snap-ring grooves or tapped holes into that hardened area since many a machine shop will no-quote trying to mill or drill into that hardened surface, or they will charge you for special tooling. Another downside of the 400-series—it does not offer the same corrosion-resistance as the 300-series, making it prone to corrosion in salt water and moderate-to-highly acidic situations. Although, you could save a few dollars using the 400-series over the 300-series if your application is not prone to corrosion. A final benefit of the 400-series vs. 300-series stainless products is that they are less deflective for unsupported, higher load applications.
Outside of the benefits for ball bearings, these shafts are great for drylin sliding materials T500(X), applications that require high temperatures and chemical-resistance, the A160 material for FDA compliance, and the E7 material for more general applications.
Chrome-Plated Carbon Steel
Chrome-plated 1060 or 1055 shafting is not as commonly used in North America as it is in Europe, but is available as a moderately corrosion-resistant material for chemical wash-downs while at a lower price than even the 400-series stainless. The reason why some customers may choose a chrome-plated shaft is because it has a highly polished and shiny surface, whereas stainless steel products can sometimes have a more matte, or even dull, finish. Since chrome-plated carbon steel is hardened to RC60 and above, it can be used for ball bearings as well. If you are using drylin components, liners T500 (X) are the best liner options for lifetime and friction on this material.
Hardened Carbon Steel (1060/1055)
The workhorse of the linear bearing industry, especially for ball bearings, this shafting is hardened to RC60 and above and is a mainstay for linear ball bearings; however, it is not always as advantageous when it comes to self-lubricating plain bearings, where aluminum shafting or stainless steel shafting dominates. Since linear plain bearings do not require oil, the steel will effectively corrode over time if not under perfect conditions, which makes ball bearings a better match because they do require maintenance and scheduled oiling. With that being said, hardened carbon steel is a more rigid material than aluminum, although most engineers and manufacturers within the plain bearing industry would still direct customers to a stainless product if aluminum was not rigid enough for certain unsupported applications. If you are using drylin components, E7 is a great liner material for dry running with hardened carbon steel.
Carbon fiber is a very uncommon linear shaft material, yet it is available—at least from igus®. Most applications that use carbon fiber shafting either involve a non-magnetic material (often in medical imaging machinery), or something that requires ultra-low weight and strength. A shaft with a diameter of 20mm weighs only 0.17kg, so when compared to a 20mm steel shaft, which weighs 2.46kg, there is a huge weight difference.
Another thing to consider is that the price for carbon fiber is very high in contrast to the other materials above—about five times the cost of aluminum and one and a half times the cost of 316 stainless steel. If you are searching for a lightweight shaft that will not be as expensive, another possible solution could be a hollow aluminum shaft (AWMR), which is nearly twice as heavy (regarding the above example, it would be .32kg) yet still much lighter than steel. As far as I know, linear ball bearings cannot run on this material, although plastic plain bearings can. Our iglide® J standard JUM liners work well on this material, as do our press-fit L250 bearings.
There are a lot of materials available for your linear project, and I hope that all of this information hasn’t been too overwhelming; however, I hope that this has helped narrow your choices down. Linear plain bearings perform differently on different shaft materials, so having a proper knowledge of which shaft material will work best with a particular linear bearing is essential in ensuring the most efficient operation possible for your application.
If you are still curious about linear bearings, and the possibility of using linear plain bearings, I highly recommend watching this video on how to use the drylin linear bearing configurator , which compares the different materials for lifetime and friction-force requirements.