Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-09-02
2001-09-25
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S601000, C073S602000, C073S432100, C324S639000, C324S663000, C356S445000, C356S446000, C356S237600, C250S330000, C250S341800, C250S358100, C083S072000, C083S073000, C083S361000, C083S365000
Reexamination Certificate
active
06293152
ABSTRACT:
FIELD
The present invention relates to a method for determining warp potential, such as twist potential, in wood—including, without limitation, trees, logs, processed logs, lumber, and manufactured wood products.
BACKGROUND
Warp stability of lumber and wood products is an increasingly important consideration. Three types of warp, known as crook, bow, and cup, can be traced to differential length change within a board. FIG. 2 of Perstorper et al.,
Quality of timber products from Norway spruce,
WOOD SCI. TECH. 29 (1995), 339-352, incorporated by reference herein, illustrates different types of warp. Crook refers to in-plane, facewise curvature of wood relative to a longitudinal axis. Bow also refers to in-plane facewise curvature relative to a longitudinal axis. Crook and bow are closely related and differ primarily according to the planar surface used to define the warp. Crook refers to in-plane, facewise curvature of wood relative to a length axis. Twist, another type of warp, refers to a rotational instability about an axis of wood (usually the longitudinal axis). Twist appears to be associated with varying grain angle patterns (Brazier). Warp tendency apparently is influenced by a myriad of factors (see Table 1).
TABLE 1
Factor
Reference Authors
Compression wood
Ying, Kretschmann, Bendtsen
Drying stresses
Martensson and Svensson
Earlywood vs. late wood
Kifetew, Lindberg, Wiklund; Pentoney
grain angle
Balodis, Ormarsson
log sweep
Taylor and Wagner
Longitudinal shrinkage
Ormarsson; Simpson and Gerhardt; Ying,
Kretschmann, Bendtsen; McAlister and Clark
Microfibril angle
Barber and Meylan; Tang and Smith; Ying,
Kretschmann, Bendtsen; Walker
Moisture content
Simpson and Gerhardt
gradients
radial and tangential
Kifetew, Lindberg, Wiklund; Meylan
shrinkages
Specific gravity
Pentoney; Ying, Kretschmann, Bendtsen
stress and strain
Ormarsson; Sandland; Hsu and Tang; Fridley
and Tang; Simpson and Gerhardt, Irudayaraj
and Haghighi
Dimensional and warp stability have always been valued attributes. Furthermore, new products emerging from dimension lumber, such as premium-grade joists and studs, require superior dimensional and warp stability performance. The ability to quantify warp potential of wood products would enhance the capability of the forest products industry to service these important markets.
Moreover, inefficient processing of raw timber and lumber wastes tremendous forest resources. Lumber warp reduces product grade and product value. Additionally, warp-prone lumber and lumber products perform poorly in uses or environments unsuitable for warp-prone wood. Millions of dollars are wasted every year because no method exists for efficiently and accurately detecting warp-prone lumber.
If warp-prone wood could be nondestructively identified during or prior to processing and product placement, processing raw timber and lumber into wood products would become more efficient. Raw logs could be culled prior to manufacturing, and wood-products manufacturing processes could be altered to direct raw lumber to various end products according to quality and value. For example, warp-prone trees could be identified while standing in forests or after cutting, and processed into products where warp is an irrelevant consideration (e.g. paper products, chipping, etc.). Green warp-prone lumber could be identified at the mill, separated, and kiln-dried using special warp-reducing techniques (e.g. rapid-drying, high-heat drying, final steaming, restraint-drying, etc.). Lumber having low warp potential could be dried using simpler and more economical methods.
Natural resources are unnecessarily wasted by using certain types of wood in inappropriate applications. If warp tendency of raw logs could be predicted, then warp-prone logs could be processed differently. For example, warp-prone logs could be cut into lumber with cuts being coordinated to reduce warp. The orientation of boards taken from certain logs could be altered to reduce warp, or the thickness of the lumber could be varied, since thicker lumber generally warps less. Alternatively, warp-prone logs could be culled and processed for specific uses (e.g. chipped, lumber for pallets, etc.). Lumber cut from warp-prone logs also could be specially processed (e.g. special kiln drying techniques) or used in selected applications (e.g. relative constant moisture applications).
Additionally, warp-prone lumber could be identified for use in only certain applications. For example, exterior window and door casings experience fluctuating moisture and temperature conditions during use. Warp prone lumber, even if initially straight when dried, could warp in such changing environments. Consequently, if warp-prone lumber could be identified, its use in warp-inducing environments could be avoided. Extremely warp-prone wood may be suitable only for uses where warping is not a significant problem (e.g. for pallets, landscape applications, etc.). In such cases, warp-prone green lumber could be processed without expensive drying techniques.
Warp stability has been studied from both the experimental and theoretical viewpoints. For example, earlier studies explored the links between drying warp and certain lumber characteristics, such as knots, slope-of-grain, and juvenile-wood content [Beard, J., et al.,
The influence of growth characteristics on warp in two structural grades of southern pine lumber,
43 FOREST PROD. J. 6, 51 (June 1993); Balodis, V.,
Influence of Grain Angle on Twist in Seasoned Boards,
5 WOOD SCIENCE 44-50 (1972)]. While some relationships were discovered, no commercially viable processes for detecting warp apparently have been developed.
Others have attempted to mathematically model the mechanical phenomena that govern warp instability. A general approach considers elastic, shrinkage, creep, and mechanosorptive elements, including their anisotropic variability and temperature dependence. Such models are complicated. See, e.g., Ormarsson (1995).
Matthews et al's U.S. Pat. No. 4,606,645, which is incorporated herein by reference, describes measuring fiber angle in a fibrous solid material relative to three mutually orthogonal reference axes. The '645 patent is understood to teach the measuring and analysis of light reflected from a wood sample to determine the grain angle of the sample. These measurements are then understood to be used in evaluating the strength of the wood. This reference is not understood to relate to determining warp potential of wood.
Kliger et al. teaches a destructive method for analyzing a board. Longitudinal shrinkage was determined by cutting sticks from a piece of lumber, averaging the shrinkage of each stick to determine a single value for longitudinal shrinkage, and modeling crook. Kliger teaches only a fairly approximate method for modeling crook. Kliger's method also depends on destroying the wood piece to determine crook. Furthermore, the authors employed a model which specified only a single radius of curvature whereas warp in wood can occur about more than one radius of curvature.
A practical and accurate method for predicting crook and bow has, despite extensive efforts, not been developed. Additionally, the amount of information which must be known to predict warp has proved daunting.
SUMMARY
A method for determining twist potential of wood is described which addresses the problems identified above. One embodiment of the method comprises obtaining a grain angle of wood, such as trees or lumber, and then determining twist potential of the wood based on the grain angle. A preferred embodiment comprises indirectly and/or nondestructively determining a grain angle. The method can comprise obtaining grain angle information from a third party, and then determining twist potential, but more likely involves actually measuring at least one grain angle, and typically comprises measuring plural grain angles, to determine twist potential. Where the wood comprises lumber, grain angle determinations usually are made on at least one planar surface of the lumber. The method typically comprises de
Cramer Steven M.
Floyd Stan L.
Stanish Mark A.
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Miller Rose M.
Weyerhaeuser Company
Williams Hezron
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