Lignum Vitae

 

lignum vitaeLignum Vitae is one of the oddest of the oddities in Michigan and certainly one of the rarest of the rarities. Lignum vitae is a type of wood. It is harvested from trees that grow in the Caribbean and the northern coast of South America. It has been an important export crop to Europe for hundreds of years and it has been essential to Sault Ste. Marie since the early 1900s. Without this unusual wood, the Cloverland Hydroelectric Plant with 74 high speed turbines handling a water flow of 28,000 feet per second, might not have been built. The plant was used to produce electricity for Union Carbide. In 1963 Edison Sault acquired the plant and, today, it serves over 40,000 urban and rural customers. Lignum Vitae was an essential component in the construction of the plant and the production of electricity.

Lignum Vitae is extremely dense, so dense in fact, that it will not float. A cube that is 12 inches square weighs between 25 and 30 pounds. Besides density, lignum vitae has other characteristics that made it ideal for use as bearings for those high speed turbines. The natural oils in the wood have lubricating properties that create a film between the wood and the metal shaft about 2 to 3 thousandths of an inch thick. Turns out that is just about perfect for spinning turbine shafts. Another effect of this film of oil is that you can stop the turbine and leave it in rest for extended periods of time without danger of corrosion. Such a rest stop isn’t possible with metal bearings. Each turbine requires a main bearing and 3 steadying bearings 120 degrees apart. In the old days, logs of lignum vitae were kept at the electric plant, submerged in water. When a bearing wore out and had to be replaced, a log was brought up and a coin cut from the end. The log was then submerged again. The coin would be taken into the shop for machining.

At this writing some bearings made of lignum vitae are still used at the plant. The oldest has been in service for more than 60 years. The trees that produce this rare wood are now farmed. It remains in demand because some places have water that has high acidity unlike the pure waters of Lake Superior. Acidic waters cause rapid corrosion which plays havoc with metal bearings. You can check out the turbines and Lignum Vitae one day each year during the Engineers Day Festival in Sault Ste. Marie. On that day only the interior the Cloverland Hydroelectric Plant is open to visitors.