Claims
- 1. A high-yield technique for converting logs of small diameter into large rectangular panels, said technique comprising the steps of:
- A. longitudinally cutting each log into raw pieces, all of whose broad faces lie in a plane parallel to a tangent to the curvature of the log, the cuts being spaced to produce a pair of opposing side pieces having like thicknesses and at least one center piece;
- B. faceting the uncut surfaces of the side pieces to provide stock pieces having a trapezoidal cross section;
- C. faceting the uncut surfaces of the center piece to produce a stock piece having a rectangular cross section;
- D. fitting together said stock pieces in a complementary manner to form a stack of layers each of which has a substantially uniform thickness, thereby creating a dry block;
- E. wet-coating the stock pieces in the dry block with a curable adhesive and reassembling the wet pieces to form a wet block;
- F. subjecting the wet block to compression for a period sufficient to cure the adhesive and to interlaminate the stock pieces thereof to produce an integrated block; and
- G. dividing the integrated block into panels.
- 2. A technique as set forth in claim 1, wherein some of the layers are composed of stock pieces having a rectangular cross-section and others by stock pieces having a trapezoidal cross section.
- 3. A technique as set forth in claim 2, wherein the layers of trapezoidal stock pieces are provided with end pieces constituted by stock piece halves to present vertical block edges.
- 4. A technique as set forth in claim 1, wherein the stock pieces are derived from tapered logs and therefore have a wedge-like formation; the comlementary pieces being reversely-oriented to effectively cancel out the taper.
- 5. A technique as set forth in claim 1, wherein said logs are of balsa wood.
- 6. A technique as set forth in claim 5, wherein said raw pieces are kiln-dried before being faceted into stock pieces.
- 7. A technique as set forth in claim 6, wherein said raw pieces are dried to a moisture content of about 12 percent.
- 8. A technique as set forth in claim 1, wherein said curable adhesive is a water-resistant synthetic adhesive.
- 9. A technique as set forth in claim 8, wherein said adhesive is urea formaldehyde.
- 10. A technique as set forth in claim 1, wherein said integrated block is divided in a direction producing end grain balsa panels.
- 11. A technique as set forth in claim 1, wherein said integrated block is divided in a direction producing flat grain balsa panels.
RELATED APPLICATION
This application is a continuation-in-part of my copending application Ser. No. 050,699, filed June 21, 1979, which relates back to an application Ser. No. 860,617, filed Dec. 14, 1977, entitled "Technique for Converting Balsa Logs into Panels," now U.S. Pat. No. 4,122,878.
This invention relates generally to the conversion of round logs into lumber products by cutting the logs into pieces which are then joined together, and more particularly to a technique in which each log is cut and faceted to form a pair of side pieces having a trapezoidal cross section and at least one center piece having a rectangular cross section.
A technique in accordance with the invention, though applicable to various species of wood, is of particular value in connection with balsa wood derived from a tropical American tree (Ochroma pyramidale). Balsa wood has outstanding properties unique in the lumber field; for on the average, it weighs less than 9 pounds per cubic foot, this being 40% less than the lightest North American species. Its cell structure affords a combination of high rigidity and compressive and tensile strength superior to any composite or synthetic material of equal or higher density. While a technique in accordance with the invention will be described herein only in regard to balsa wood, it is to be understood that it is also applicable to other wood species.
The cost of balsa wood products has heretofore been keyed to the low yield obtainable when employing conventional techniques to convert balsa logs into usable products. The traditional conversion technique results in a low yield in that the amount of balsa convertible into usable lumber is usually less than half the total volume of wood in the log, the balance being wasted.
The economics of converting balsa logs into commercially-available lumber products must take into account a number of factors, such as growth time, kiln drying costs and the relationship of yield to tree diameter. The traditional conversion technique derives balsa lumber products from logs having a diameter of 12 inches or greater and inevitably results in products which are expensive. It not only requires about eight years before the trees can be harvested to produce logs of this size, but kiln costs are high and the yield is low, in that a large percentage of the wood is wasted in the conversion process.
A marked improvement in the economics of converting balsa logs into usable products is gained by the technique disclosed in my prior U.S. Pat. No. 4,122,878, entitled "Technique for Converting Balsa Logs into Panels," the entire disclosure of which is incorporated herein by reference. In this patented technique, logs are radially cut into sectors having the same apex angle, each sector then being longitudinally sliced at its apex and arc to form a truncated piece having a trapezoidal cross-section, only a relatively small percentage of the wood being wasted. The pieces are thereafter fitted together in a complementary manner and interlaminated to form an integrated stock block which is dividable into panels.
The technique disclosed in my prior patent makes it possible to commercially exploit a broad range of balsa log diameters, running from small diameter logs cut from trees which take only 9 to 10 months to grow, to large diameter logs cut from more mature trees that take at least 5 to 8 years to grow. In this way, better use can be made of the available acreage. And because the logs are cut radially, the resultant area of the exposed surfaces is greater than that obtained with conventionally cut logs, thereby markedly reducing kiln drying time and its attendant costs. But even more important is the fact that the yield is exceptionally high; for, as compared to a traditional conversion which requires 60 logs of 12-inch diameter and 16 feet length to produce 1,000 board feet of balse product, the technique disclosed in my prior patent yields the same amount of product from merely 20 such logs.
The technique disclosed in my prior patent attains its greatest efficiency both with respect to yield and labor costs when used in conjunction with logs whose diameter exceeds 10 inches. In terms of labor costs, the efficiency factor drops off for logs of smaller diameter; for then the trapezoidal pieces are relatively small and require, per 1,000 board feet of finished integrated blocks, much more handling than pieces derived from logs of larger diameter.
For example, assuming an integrated block whose dimensions are two feet by four feet by six feet, if the pieces from which the block is formed are sector-cut pieces taken from logs having diameters in the range of 6 to 8 inches, the number of pieces necessary to complete this block is far greater than the number required when the pieces are sector-cut from logs having diameters of 10 to 12 inches. Whether the log is of small or large diameter, eight sectors are cut therefrom, but the total volume of eight sectors taken from a small diameter log is much below that of sectors from a large diameter log. Since each piece has to be separately handled and individually wet-coated when assembling the pieces into a block, much more handling is involved all along the production line when using smaller pieces.
On the other hand, as noted in my prior patent, since young balsa trees of small diameter (10 inches or less) are more readily available than older trees of larger diameter, there are distinct economic advantages in converting trees of small diameter into usable lumber. In planting balsa trees, if one harvests trees while their diameters are small, this makes possible a rapid turnover in the order of 4 to 6 years, whereas for trees which are not harvested until they are 11 to 12 inches in diameter, the growth period is 6 to 8 years. However, with the technique disclosed in my prior patent, the increased handling requirements entailed when using small diameter trees and the resultant increase in production costs tend to offset the economic advantages gained by exploiting such trees.
In view of the foregoing, the main object of this invention is to provide a high yield technique for efficiently converting balsa logs of relatively small diameter into large rectangular panels.
A significant feature of the present invention, as compared to the technique disclosed in my prior patent in which logs 10 inches in diameter or smaller are sector-cut into eight pieces, is that in the present technique only three or four pieces are cut from the log, thereby substantially reducing the handling requirements in forming an integrated block from these pieces. And because fewer pieces are required to create the block, the quantity of adhesive necessary for interlaminating the pieces is reduced.
Also an object of the invention is to provide a technique in which derived from logs are stock pieces having a trapezoidal cross section as well as stock pieces having a rectangular cross section, all of which pieces may be used to create an integrated block. Alternatively, the stock pieces having a rectangular cross section can be used as traditional lumber, particularly since, as contrasted to pieces which are sector cut from a log and have a width equal to the radius thereof, these stock pieces have a width almost equal to the diameter of the log.
Briefly stated, in a technique in accordance with the invention each log of small diameter (10 inches or less) is cut longitudinally into raw pieces whose broad faces all lie in a plane parallel to a tangent to the curvature of the log. These cuts are spaced to produce opposing side pieces having like thicknesses and at least one center piece.
After the raw pieces are kiln dried, the uncut surfaces of the side pieces are faceted to provide stock pieces having a trapezoidal cross section, whereas the uncut surfaces of the center pieces are faceted to provide a stock piece having a rectangular cross section. Thus the only waste lies in the thin chordal slabs removed from the pieces.
The stock pieces are then fitted together in a complementary manner to create uniform layers thereof which are stacked to define a dry block. The pieces in the dry block are then wet-coated with a curable adhesive and reassembled to form a wet block which is subjected to compression until the adhesive is cured and the stock pieces interlaminated to form an integrated block. Finally, the integrated block is divided into panels of the desired thickness and grain direction.
US Referenced Citations (5)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 1453014 |
Dec 1968 |
DEX |
Continuation in Parts (1)
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Number |
Date |
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| Parent |
50699 |
Jun 1979 |
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Patent Grant
4262717
