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33 Chapter 3: Using Timber

and heated. The resulting pulp is washed and bleached and pressed into mats. Further processing of those mats of pulp eventually creates paper. Once the pulp is made, it is passed into a machine to make the paper. The pulp is sprayed into a thin layer on a moving wire screen. The screen is huge: it can be nearly 20 feet (6 meters) wide and moves at speeds of 60 miles (96.5 kilometers) per hour. The water in the pulp drips off while it is on the moving screen, leaving behind a matted sheet of damp cellulose fibers. This is then passed over rollers, which press it and dry it. Logs destined for lumber are sent to the sawmill. Several different saws are at work at a sawmill. A head rig saw is one of the saws. This one makes a rough cut of a log. This helps ready the log for the different types of lumber it can become. The center- most part of a log is oldest and may have more knots than other parts. This wood is typically processed into heavy planks. The wood surrounding the center is younger and less knotty. It may become the lumber found in a home improvement store.

A tree becomes lumber at a sawmill.