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Lignum Vitae LLC: Growing Environmentally Safe Water-Lubricated Bearings From Trees
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t may come as a surprise to learn that some of the best industrial bearings in the world are made not of space-age synthetic materials but of the wood of a tropical tree. Lignum vitae is a hard wood with a distinctive resin that makes excellent waterlubricated bearings. With increasing concerns about the pollution that can be caused by leaks in oil-lubricated bearings, waterlubricated bearings are becoming more popular. Bob Shortridge is the president of Lignum Vitae North America, LLC, which creates water-lubricated bearings for hydro and military applications around the world. In this interview, Mr. Shortridge tells us why he brought lignum vitae wood back into the marketplace, how he started his company, and about his business today. Hydro Leader: Please tell us about your background and how you came to be in your position.
I realized that lignum vitae was more than just wood and saw enormous potential in the modern hydroelectric marketplace. After being used extensively in hydro and marine applications for more than a century, it had been largely replaced by modern plastics and engineered composites. These materials, though, come with a number of expensive challenges for today’s hydro plants. Lignum vitae is self and water lubricated and offers decades of uninterrupted performance and improved environmental compliance while reducing ongoing maintenance costs, costly downtime, and fines. I started to promote lignum vitae as the environmentally friendly bearing and got the attention of hydro plants, many of which had been originally equipped with lignum vitae bearings, and some of which were looking for only their third bearing change since 1931. There is literally no other bearing available today that can offer 40–45 years of uninterrupted service before needing to change. Hydro Leader: How does a lignum vitae bearing compare to a metal or oil-lubricated bearing?
Lignum vitae logs stored in Lignum Vitae North America’s warehouse.
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Hydro Leader: Where does lignum vitae come from, and how rare is it? Bob Shortridge: Initially, I was able to find lignum vitae at exotic wood yards around the United States and Europe. From these sources, I was able to launch the business with about 38 tons of material. It is indigenous to what the U.S. Department of Agriculture calls plant hardiness zone 13, which spans from Miami to Costa Rica. Overharvesting during World War II led the Convention on International Trade in Endangered Species (CITES) to set clear guidelines for the sustainable harvest of lignum hydroleadermagazine.com
PHOTOS COURTESY OF LIGNUM VITAE NORTH AMERICA.
Bob Shortridge: My background is in construction. For 35 years, I built highly engineered, heavy timber homes, buildings, and ski resorts anywhere heavy wind, snow, and seismic conditions called for structures that could withstand extreme conditions. My passion for engineering the indestructible led me to a lignum vitae auction at the Newport News shipyard. I bought 2½ tons of the wood and started researching its history and uses. I was surprised to learn that lignum vitae wood was used to fashion the first successful stern tube bearing for shipping when sailing vessels gave way to screw vessels. It was patented in hydro in 1882.
Bob Shortridge: It is difficult to do a direct comparison, because factors such as the machine’s balance and alignment and how the material is used have a big effect. The simplest explanation is that lignum vitae works using what is known as a mixed mode of lubrication. That means that it is both self lubricating and water lubricated. We’ve refurbished about 400–500 hydro plants since 2005 and have found that lignum vitae was used in two different ways: as long strips or tubes and as end-grained blocks. The end-grained blocks were the most effective because they took advantage of the material’s natural hardness and lubricity of its distinctive resin. The material can ride directly under the shaft under a pure load, or it can work hydrodynamically, becoming a wear-free component. When it's working hydrodynamically, there's a thin boundary of water between the shaft and the bearing. That’s why some of these bearings don’t wear for 40–45 years.
