Lignum Vitae North America introduces a game changing new product, End Grain Water Lubricated Bearings, and how to get maximum life from them.
Since 2005 LVNA has provided water lubricated solutions for over 300 hydro-electric installations worldwide. These solutions were developed at our headquarters in Powhatan Virginia in response to challenges presented by our customers. Previous solutions for wicket bushings, mechanical seals, segmented seals, thrust bearings, shell bearings, and main guide bearings have all been born from this new facility.
In 2020 several customers requested a bearing configuration that could extend the bearing life for non-adjusting machines to address vibration issues and unplanned outages plaguing the plant for years. All the machines studied had lignum vitae installed originally then converted to composites over time. This change required a clearance of 1mil. per inch of shaft for the composite, vs. zero for lignum vitae, effectively adding 30mil additional clearance to a 30” shaft that brought the typical wear down from decades to a “new normal” of months. This new clearance introduced an imbalance in many units that led to a “hammering effect” causing inordinate adjustments and replacements. This challenge was met by our R&D group that immediately began extensive study into the problem and offer solutions.
Many of the machines in question are around 100 years old adding to the challenge of gaining back longevity that they previously experienced with LV. Rough housings with 100 years of rust added yet another layer to the challenge. Lignum vitae is the hardest wood commercially available with a hardness like aluminum and as slippery as Teflon. Lignum vitae holds the distinction as the only known tree with no silica present, instead it has a self-lubricating resin in every cell making it a perfect bearing material and true anomaly of nature.
LVNA had engaged Falex testing laboratory in 2015 to determine various structural parameters such as modulus of elasticity, coefficient of friction, sliding speeds and wear rates. LVNA was also in possession of extensive testing of lignum vitae performed over 100 years ago by the Society of Naval architects and engineers “SNAME” in 1915 and second test done in 1965 for the U.S. Navy that exhibited the EXACT same structural data that Falex documented in 2015. This information guided LVNA to recommend using “End grain” blocks stacked in rows with little to no space and milled as close to zero as possible to help facilitate hydrodynamic action as speeds allow.
When end grain was selected the next step was to determine how to join the ends of blocks for rigidity and stiffness. After some research it was determined end grain blocks may have never been joined in the manner proposed that led to next steps. 1900 era original installation techniques suggested labor intensive methods deemed unnecessary by LVNA that led to end grain joining tests. Multiple joining techniques were undertaken to represent the underwater environment they operate in. Swell tests, tension and compressive loads were applied until they exceeded all criteria without any metallic fasteners or complicated installation. Ultimately a permanent proprietary solution was found that exceeded all the customers’ needs making “end grain staves” available in several widths, thickness, and lengths.
The new staves can be easily installed in square, dovetailed slots, or smooth bores to be bolted, driven into existing dovetail slots, or laid parallel with no need for expensive installation tools. End grain will not shrink away from the shaft and has the unique ability to be milled as close to zero clearance as possible and hold the clearance in a submerged state or when de-watered for months.
Further study by Dr. Chris Ettles of Bearing Sciences demonstrated how lignum vitae can be held at very close clearance due to a phenomena unique to lignum vitae known as a “mixed mode of lubrication” by taking the initial “hard start” directly to the lignum vitae then turns hydrodynamic as speeds allow effectively reducing wear to zero. It was discovered when the lignum vitae contacts the shaft and is warmed a small amount of resin inherent to the wood creates a glazed surface creating an effective hydrodynamic surface that allows a wedge of water between the resin glaze produced and shaft itself. This glazed surface is unique to lignum vitae and is readily available in every cell of the material, is not water soluble and cannot be washed away.
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Material training on-line or in person and samples are available on request.
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