Tuesday, April 15, 2014

Old is new again: wood as an industrial material.

Old is new again.

It seems positively archaic to use wood in mechanical applications, but it’s the newest thing.

And in many applications, wood turns out to be not only good, but in certain applications the right wood can be significantly better than the metal or plastic alternatives.

A preferred industrial timber is lignum vitae, the exceedingly hard wood that started being used as propeller shaft bearings in steamships in the middle 1800s.

(Image: The blue flowers of lignum vitae at Ala Moana Beach Park. Image courtesy of Forest and Kim Starr.)

More than 150 years later, machinists are turning back to it, for good reasons. One of them: besides being harder than some metals, it is resistant to rot, and it thrives in underwater applications.

That last feature means it can be used, for example, in ship steam engines and in underwater hydroelectric facilities, where lignum vitae bearings can be water-lubricated—reducing the risk that petroleum lubricants will damage the aquatic environment.

The online magazine Hydroworld.com describes a 100-year-old hydroelectric plant that went from lignum vitae to composite bearings, and then opted to go back to the wooden bearings for their long life.

Lignum vitae is an American tree that seldom grows to more than a foot thick, although there are records of larger ones. Trees are harvested when they are a few hundred years old. It is used for the heads of carving mallets and butcherblocks, since it’s so heavy and less likely to mar or dent metal. British cops carried lignum vitae truncheons, and heavy croquet balls have been turned from the wood.

Its fibers are dense and interlocked, making it far less likely to split than other woods.

Several similar woods are sometimes sold as lignum vitae, the real thing being Guiacum officinale or Guaiacum sanctum. There are other lignum vitae—it means wood of life—sold in landscaping, which are close relatives but not the same species.

In Honolulu, Foster Botanic Garden has an example of Guaiacum sanctum. Ala Moana Beach Park has Guaiacum offinale. And they are grown in landscaping for their pale leaves, pretty blue flowers and slow-growth habit.

A couple of species of South American trees in the Bulnesia genus, called Verawood or Argentine lignum vitae, sometimes replace the real thing in commerce. Species of eucalyptus and acacia sometimes get the title as well.

Persimmon, a member of the ebony family, is also a very hard wood that performs well in underwater applications.

Few metal bearing materials can match the history of lignum vitae. There are hydroelectric plants across the world that have been turning on lignum vitae bearings for a century and longer. They operate in fresh as well as salt water.

A company called Lignum Vitae Bearings sings the praises of the wooden material as “the only environmentally responsible renewable industrial bearing known to man.” 

© Jan TenBruggencate 2014

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