MEASURING AND SORTING WOOD MEMBERS BASED ON SPECIFIC GRAVITY

Abstract: A measuring and sorting system is based on detecting the specific gravity of each member of a population of wood members, such as logs or trees and allocating the measured member to a sort category with an assigned specific gravity range. The sorted members are thereafter utilized as raw material for a downstream use depending upon desired specific gravity needs.

Description: MEASURING AND SORTING WOOD MEMBERS BASED ON SPECIFIC GRAVITY BACKGROUND OF THE INVENΗON This invention relates generally to sorting wood members, such as, trees or logs within a collection of such members based on measuring each member's specific gravity and allocating each member to a sort category based on the specific gravity. It has long been known that wood raw materials (trees, bucked logs, lumber, chips) having variable specific gravities or densities can be allocated to different end uses based, at least in part, on the density. For example, in manufacturing lumber when higher strength is sought, the sawmill will seek to cut denser logs (higher specific gravity) since denser wood will yield stronger lumber. In using wood chips to produce pulp and paper products it is known that certain product grades will accommodate less dense wood while other grades require denser wood. It has been suggested in a published paper entitled "Control Over the Quality of Loblolly Pine Chips," Veal et al., TAPPI Journal 1987, that there are benefits obtainable from measuring the specific gravities of individual tree stems and allocating the stems based on differences in measured specific gravities; see in particular pages 53 and 54. Another paper has been recently published entitled "Matching Wood Fiber Characteristics to Pulp and Paper Processes and Products," M.F. Williams, TAPPI Journal 1995, which discloses activities in New Zealand where allocation of raw materials based on density was apparently undertaken to improve pulp and paper manufacturing. The New Zealand activity, however, does not teach or suggest measuring the specific gravity of each member within a collection and then sorting into smaller groups having a defined specific gravity range. The New Zealand paper recognizes the expected differences in average specific gravities of groups of trees based on a particular growing region. The present invention involves the recognition that there is tree-to-tree variation in specific gravity in a collection of trees coming from the same growing region, as well as from a plurality of growing regions, the location of wood from within the tree, and the age of the tree. While others have sorted groups of trees and/or parts of trees based on their expected (or predicted) average specific gravity, it has not been suggested that each member within a collection should have its specific gravity detected and sorted according to its individual measurement. According to accepted convention, the forest products industry defines "specific gravity" or "wood specific gravity" as the ratio of the mass of dry wood to its green wood volume (expressed as the mass of water displaced by that volume). Because of the amount of absorbed water in green wood, wood specific gravity is roughly half that of its actual specific gravity, whose scientific definition is the ratio of its density (mass divided by volume at the same state) to the density of water. In this description the term "specific gravity" will mean "unextracted wood specific gravity" (i.e., wood specific gravity, including the mass of extractives like lignin). AJI example of the way the specific gravity variability is presently utilized in a pulp and paper manufacturing complex follows. In the southern United States, there are pulp and paper complexes where products are manufactured that favor a source of chips having a relatively higher or lower specific gravity. For example, at the Weyerhaeuser Company Columbus, Mississippi complex fluff pulp is manufactured utilizing a kraft production process which favors chips having a relatively higher specific gravity (approximately 0.46+) along with fine paper grades which prefer lower specific gravity chips (approximately 0.43-). The present raw material strategy calls for two sorts. The younger trees that are harvested (in a 15-19 year age range) are collected in one location and are processed into the relatively lower specific gravity chips which are used in manufacturing the fine paper grades. Older trees (20+) are harvested to create the raw material source for chips going to the production of the fluff pulp grades, where the average specific gravity will be about 0.46. In another typical methodology taking into account additional sources of raw material with known specific gravity characteristics, an allocation of tree tops, cores (from peeling veneer), and the younger harvested trees (usually thinnings) will go to the lower specific gravity sort while the outer, basal, older age trees, and sawmill residual chips will go to the higher specific gravity sort. Since individual logs are not measured to detect their particular specific gravities before allocation in a pulp manufacturing setting, the difference in average specific gravity of any two or more sorts will be less than it could be if individual logs or log segments were measured and allocated according to their particular specific gravities. The result flowing from measuring each log's specific gravity will be that only those with the relatively higher specific gravities will be allocated to the end use desiring the higher specific gravity, regardless of the age or source of the log, thereby permitting the average specific gravity of each sort to be adjusted upwardly or downwardly if the end use (products) will benefit. Similarly, for those end products preferring a raw material with a relatively lower specific gravity a raw material source can be produced that has a lower average specific gravity thereby bringing more precision into the sorting and allocation process. As explained above, there are significant benefits in providing sort categories based on measured specific gravity. Higher quantities of relatively higher and lower specific gravity wood sources are obtainable where the more precise raw material sorts can be utilized to advantages in both product manufacturing and end product properties. Thus, from the foregoing, one object of the invention is to measure and allocate to a specific gravity sort category substantially all members of a population of available logs or trees. Another object is to provide specific gravity sort categories with more absolute differences between sorts. Still, a further object is to increase and/or decrease the average specific gravity of members within the predetermined sort categories. These and other objects will be better understood by referring to the drawings and the specification to follow. SUMMARY OF THE INVENΗON Briefly stated the invention is practiced in one form by measuring the specific gravities of a collection of individual wood members, such as logs, where each member is then allocated to a sort category based on its measured specific gravity. Thereafter requirements of the end uses will serve to determine demand for the members in each of the sort categories. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation illustrating the collection of individual wood members and transport to a central measuring and sorting site. Figure 2 is a schematic representation of a pulp mill wood yard where the present invention is illustrated and used to form chip piles with each having a predetermined average wood specific gravity. Figure 3 illustrates a device for providing a measure of a log's specific gravity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning first to Figure 1 what is shown is a pulp and paper manufacturing facility typical of one presently existing in North America and the geographical territory surrounding it from which will come the trees harvested to provide the wood raw material. While many pulp mills are utilizing recycled wood fiber as a portion of their raw material requirement, most all rely primarily on surrounding commercial timberlands. From the ti berlands, whether owned and managed by the pulp mill owner, or owned by others will come the trees that are transported to the pulp mill. As previously mentioned, it is known that standing trees of the same species have variable specific gravities. Specific gravity will vary depending upon age, geographical location and simply genetic and microsite variation within a stand of trees of the same age. Depending upon the needs of the mill or other entity wishing to harvest and utilize the timber, harvesting plans are developed that can take into account the variable specific gravities within the stands of trees with the potential to be harvested. Of course, age, size, species and other factors will be considered. As a pulp mill continuously acquires raw material, it can acquire whole trees from timberlands (either from fee ownership or contracted timber), logs from logging contractors with their source of timber, or wood chips from outside suppliers. Ultimately this raw material arrives at the mill site for processing. Typically the full length trees will need to be cut into suitable lengths for subsequent handling and processing. Very typically when the site is for pulp and paper processing the trees and long logs will be cut into 4 and 8 foot segments. These are then debarked and sent to chipping stations where wood chips are produced. The wood chips then become the raw material for pulp digesters where they are "cooked" in order to delignify them and generate the wood pulp fibers. Turning now to Figures 2 and 3 a specific gravity measurement and allocation process will be described that practices the present invention. As will be readily apparent, there are modifications that can be made, such as specific gravity or measurement, marking and sorting in the woods, while still practicing the invention. Another apparent modification would be measuring and sorting logs at a sawmill facility. Another would be measurement of individual chips and allocating individual chips according to specific gravity. Each of these possible implementations may have favorable application at different sites, and combinations of these can be used together to provide even additional benefits. For example, one could sort log segments in the woods and send them to different sites, and subsequently sort the chips produced from either or both populations. Trees and logs from all sources are delivered to a log yard where they can be stored and/or sorted according to known typical categories such as size and species. When the pulp mill calls for chips with properties determined by the products selected for production, normally they are conveyed from a chip pile having a collection of chips with the desired properties, such as species, specific gravity, etc. The present invention interposes a specific gravity measurement and allocation step for each member of the log population to be converted into chips. After all long trees and logs are converted into the standard length for further processing, in a process step referred to as "slashing," each individual member will have its specific gravity determined at a specific gravity measuring station. Thereafter debarking and chipping take place. While a range of measurement for specific gravities for individual log segments can vary from about 0.30 (lower specific gravity) to about 0.65 (higher specific gravity) a predetermined sort category would have all individual members, for example, with a specific gravity above 0.45 being classified into the high category and below 0.45 going to the low category. As depicted in Figure 2, process streams can be created where all members with the higher specific gravity will be processed into chips and the higher specific gravity chip pile will thusly be generated. Similarly, the lower specific gravity chip pile will be generated. As previously pointed out, since each individual member within the population of available members is measured the average specific gravity of the higher density chip pile will increase and conversely the average specific gravity of the lower density pile will decrease. For example, the average specific gravity in the low density pile can be decreased to 0.42 and raised in the higher density pile to 0.49 thereby providing sources of chips more beneficial to those selected products favoring relatively higher or lower wood densities. The difference in specific gravity of piles sorted by age and site only is limited to about 0.03. In Figure 3, one example of a suitable device for measuring specific gravity is shown. A pneumatic nail or pin gun is illustrated at 10 and can be operated at low pressure. It can rapidly imbed a reusable or disposable pin (e.g. nails) into the wood and the depth of penetration (or conversely height remaining above the surface) is correlated to specific gravity. In a commercially usable embodiment a single pin or probe would be used repeatedly, rather than being used once and disposed, and the resulting height will be automatically sensed and the log marked or otherwise sorted into the preselected specific gravity category as described above. Other specific gravity detecting means could be utilized, some of which could employ electromagnetic radiation as non-contact detecting means. Such means are presently commercially available.

Claims: CLAIMS 1. A method for sorting and allocating from a population of wood members having variable specific gravity according to each member's specific gravity, comprising: preselecting a plurality of specific gravity ranges as sort categories based on the available actual specific gravities in logs and trees within the supply area of at least one using facility and on the desired specific gravities for predetermined raw materials used for manufacturing forest products, detecting the specific gravity of each member of a population of members where the members have variable specific gravities, and allocating each member to a sort category containing members having their individual specific gravity fall within the preselected range assigned to the sort. 2. A method as in claim 1 in which two sorts are established, one for members with relatively low wood specific gravity and the other for members with relatively higher wood specific gravity. 3. A method as in claim 1 in which the detecting step is carried out by measuring the members resistance to a mechanically applied force. 4. A method as in claim 1 in which the detecting step is carried out by non-contact measuring means. 5. A method as in claim 1 further establishing a collection of sorted members within a sort category according to a downstream demand for members having the average specific gravity within the sort category.

Inventors: MARRS GEVAN R, MARRS, GEVAN, R.
Applicants: WEYERHAEUSER CO, WEYERHAEUSER COMPANY
Application year: 1996
Main classification: B07C5
IPC codes: B07C5