The Steel Supply company carries many options when it comes to slide bearings, including: Fluorogold®, Teflon® (PTFE, or polytetrafluoroethylene), Carbon Filled PTFE, and Graphite.
Fluorogold® is one of the more unique products that The Steel Supply Company provides to steel fabricators. It is a PTFE based composite melded with glass fiber, which increases the structural properties of the material itself, including increased load capacity and enhanced friction coefficients.
There are certain factors to keep in mind, however, when designing a structural member that uses Fluorogold®. Below, we discuss two of the major factors that are most often overlooked in the design process for a slide bearing. By keeping these factors in mind during the design process, time and money can be saved when placing an order for a slide bearing.
The first factor we’ll discuss is the minimum PSI required for a Fluorogold® slide bearing to function, which is 70 PSI. It’s crucial that the slide bearing be placed under at least this minimum load pressure due to the self-lubricating properties of PTFE.
At a molecular level, PTFE is a long chain of carbon atoms with two fluorine atoms bonded to each carbon atom in the chain (a graphic depiction of this chemical structure is shown below). The bond between each atom in PTFE is incredibly strong and unreactive, and the electronegativity of the fluorine atoms makes it very difficult for any other molecule to bond with it (it’s very hard to stick to, which makes it incredibly slippery).
In practice, however, these long chains of carbon atoms that make up PTFE are not always straight. Any deviation from a straight line that the chain of atoms takes reduces the ability of PTFE to self-lubricate, which brings us back to the minimum operating PSI. At 70 PSI, the chain of carbon atoms described above are straightened enough to facilitate self-lubrication within the PTFE.
Often where this is overlooked is in the size of the slide bearing design. PSI is a measurement of the force applied per square inch on the slide bearing. While the force in the structure remains the same, the area to which it’s applied in the slide bearing can change. It’s common for engineers to specify slide bearings on the larger side, but by doing so, the PSI drops and becomes lower than the minimum PSI required for optimal self-lubrication.
The second factor that should be considered is the size of the top and bottom member of a slide bearing assembly. The top member should always be large enough so that, no matter how far the assembly slides, it is always covering the bottom member. The pictures below show how this should work in practice.
This is a crucial factor because it prevents any debris from settling into the slide bearing assembly and compromising the longevity of the Fluorogold® material. This is especially important when considering design for Fluorogold® slide bearing assemblies that will primarily operate in outdoor environments. A common example are the oil pipelines that have been built in parts of the country like North and South Dakota. Strong wind patterns that carry a large amount of dust can easily compromise a slide bearing assembly if the dust is allowed to settle on the bottom part of the assembly.
If you have any questions about Fluorogold® slide bearing assemblies, or need consultation on whether the current layout of your assembly will work with PTFE slide bearings, don't hesitate to reach out to one of The Steel Supply Company's representatives who can assist you.