Wood Technology: Day Two part one

Topics covered in this section listed below:

Terminology Wood science

Hardwoods and Softwoods

Seasoning and Drying

Warps and Defects

Board Footage

Grading

Urban Lumber

Parts of a tree:

The Outer bark is the tree's protection from the outside world. It keeps the moisture out during rain, prevents the loss of moisture when the air is dry, insulates against cold and heat, and wards off insects. the inner bark or "Phloem" is the pipeline through which the food is passed to the rest of the tree. It lives only for a short time then dies and turns to cork, to become part of the outer protective bark. The Cambium Cell layer is the growing part of the truck. It annually produces new bark and wood in response to hormones that pass down through the phieom with the food from the leaves. Sapwood is the tree's pipeline for the water moving up to the leaves.

Sapwood is the new wood as newer rings of sapwood are laid down its inner Cell lose their vitality and turn to heartwood. Heartwood is the essential supporting pillar of the tree. Although dead it will not decay or lose strength while the outer layers are intact.

Courtesy of St. Regis Paper Company

Wood Science: tree cells

Wood cells; the structural elements of wood tissue are of various sizes and shapes and are quite firmly cemented together. Dry wood cells may be empty or partly filled with deposits, such s gums and resins or with tyloses. The Majority of wood cells are considerably elongated and pointed at the ends, these cells are customarily call fibers or tracheids. The length for wood fibers is a highly variable within a tree and among species. Hardwood fibers average about 1 mm (w/25 in.) in length, softwood fibers range from 3 to 8 mm (1/8 to 1/3 in.) in length.

In addition to fibers, hardwoods have cells of relatively large diameter known as vessels or pores. These cells form the main conduits in the movement of sap. Softwoods do not contain vessels for conducting sap longitudinally in the tree; this function is performed by the trachieds.

Both hardwoods and softwoods have cells (usually grouped into structures or tissues) that are oriented horizontally in the direction from pith toward bark. these groups of cells conduct sap radially across the grain and are called rays or wood rays. The rays are most easily seen on edge grained or quartersawn surfaces and they vary greatly in size in different species. in oaks and sycamores the rays are conspicuous and add to the decorative features of the Wood. Rays also represent the planes of weakness along which seasoning checks readily develop. Another type of wood cells known as longitudinal or axial parenchyma cells, function mainly in the storage of food.

Day One con't next blog posting