Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Reexamination Certificate
2000-03-29
2002-02-12
Gravini, Stephen (Department: 3749)
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
C034S417000, C034S493000, C034S497000, C034S212000
Reexamination Certificate
active
06345450
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for treating green wood and for accelerating the curing or drying of green wood prior to fabrication of the wood into various wood products, objects, structures, or related items.
BACKGROUND OF THE INVENTION
All woods have a fibro-vascular tissue composed of cellulose and its components belonging to the subdivision called spermatophytes (IV) in the plant kingdom (with the single exception of tree ferns). The spermatophytes can be further subdivided into two classifications; gymnosperms or “softwoods” and the angiosperms or “hardwoods”. It must be emphasized that the terms softwood and hardwood have no bearing on the density or degree of hardness of such woods but refers to their classification. Some woods that are classified as softwoods, such as yellow pine, are physically harder than some woods that are classified as hardwoods such as aspen or basswood. Further, agniosperms can be again divided into very distinct classes; the monocotyledons or the palms, bamboos, canes and grasses and the dicotyledons (the majority of angiosperms that provides us with useful woods).
Since a living tree contains very large amounts of water, lumbermen often refer at various stages from the initial cutting of a tree up through the sawing and drying of lumber to the moisture content (“MC”) of the wood. The moisture content of the wood, usually expressed in a percentage, is a ratio of the amount of water in a piece of wood that is compared to the weight of such wood when all of the moisture has been removed. One of the methods that is employed (the “moisture content on the over-dry basis”) to determine the MC of wood at any stage during the lumber production process is to weigh a given sample of wood and record such weight (the “wet weight”). The sample is then placed into an oven and heated at temperatures not to exceed 217 F until all of the moisture has been removed (the “oven dry weight”) and that weight is recorded. It can be determined that the oven-dry weight has been reached when, after weighing at various intervals, the sample stops losing weight. The oven-dry weight is then subtracted from the wet weight and the resultant is then divided by the oven-dry weight. That resultant figure is then multiplied by 100 to determine the percentage of MC. The formula is represented as follows:
%
MC
=
(
wet
weight
-
oven
-
dry
weight
)
oven
dry
weight
of
wood
×
100
The type of units employed for the above calculation, i.e. ounces, grams, pounds, kilograms, etc., is not important as long as all weights are recorded in the same type of units since the calculations are based upon a ratio of such weights. Other methods of determining MC have been developed as well as electronic machines that compute the MC based upon known electrical and other reactions. Regardless of the method employed to determine such MC, a working knowledge of moisture content and how it affects wood is important to the present process.
When a tree such as red or white oak, fir, maple, spruce, ash or any one of the many species of trees that yield wood that is useful in the production of wood products is initially cut down, it has a MC of anywhere from about 60% to 100% (this moisture content has been found to be even higher, as much as about 200% for some species). This is called the “green moisture content” (“GMC”). Opposed to popular belief, the green moisture content does not vary greatly with the season that a log is cut. This moisture or water has to be removed or dried from the wood in order to make the wood stable and thus usable in any phases of the lumber industry that require either air dried and/or kiln dried lumber. The drying or curing of green wood thus comprises the controlled removal of water from the wood to a level where the wood becomes sufficiently stable for fabrication into various products. The “curing” process or “curing” as used herein refers to moisture removal by the controlled act of air drying, kiln drying, or a combination of both.
After a tree is felled and is sawn into lumber of various sizes and types, it is stacked in a particular manner in preparation for the drying and/or pre-drying process. During this curing process, many problems may occur that can either damage, destroy or degrade the quality of the wood and render it less desirable and in some cases, not usable at all. The sawn lumber can develop cracks in the ends (“end checks”), cracks in the internal portions of the lumber (“honeycomb” or “honeycombing”), cracks in the surface (“surface checking”), as well as many types of warps and bends (“cup”, “bow”, “crook”, etc.). Such problems are all related to the presence of moisture in the wood itself and the movement of, and subsequent removal of, such moisture from the time a tree is felled until the completion of the curing process. The significance of the removal of moisture during the curing process[s] becomes more understandable through a thorough understanding of the actual structure of wood itself.
The layers in a typical tree are: a) the outer bark; b) the inner bark; c) the cambium layer; d) the sapwood and e) the heartwood. The outer bark is a rough textured layer composed of dry, dead tissue that provides the tree with its first line of defense against external injury and insect infestation. The outer bark is separated form the next layer called the inner bark by a thin layer called the bark cambium. The inner bark is a soft, moist layer that contains living cells that play a role in the transfer of food to the growing parts of the tree. The cambium layer is a very small microscopic layer that is just inside the inner bark. The main function of the cambium layer is to produce both bark and wood cells.
The sapwood is composed of light colored wood and is made up of both living and dead tissues. The heartwood is the central section of the tree that is laden with resins and tannins and is basically inactive. Heartwood is formed by the transformation of sapwood as the tree ages. Both the sapwood and the heartwood are composed of many layers or “rings”. These are called annual rings and each one represents the amount of growth a tree undergoes for a given year of its life. The heartwood is less permeable than that of sapwood and subsequently needs more drying time and is subject to more drying defects than sapwood. The infiltration of resins, gums and other materials in the heartwood make it more resistant to moisture flow and also make such heartwood darker in color.
The internal structure of wood is basically oriented around the flow of moisture since a tree distributes the nutrients it requires for growth in a liquid medium or sap. A basic element of such internal structure is the wood cell. There are two basic distribution processes that sap movement can occur in a tree. Such processes are called diffusion and condition. In a wood cell, diffusion occurs when sap passes through the cell walls by the action of the protoplasm which covers cells that are rather new or young. Conduction occurs when the cells age somewhat and lose their protoplasm and develop pits or spot through which, sap passes easily. As some cells age, they might also break down at the ends and form tracheal vessels, sometimes referred to as the “through passageways”, which utilize conduction as a transfer medium. The basic unit of a tree or the wood cell is characterized by different elements that utilized either one or both of such distribution methods. Each wood cell has a cell wall structure composed of several different layers and a central cavity. The cell wall is composed of lignin, cellulose and hemi-celluloses. These wood cells which are tube-like in shape have different functions dependent upon their particular anatomical construction. The tracheal vessels are longitudinal tubes composed of dead material. They are relatively long and large in diameter and play a role in the upward conduction of sap. The tra
Browning & Bushman P.C.
Gravini Stephen
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