Note: Descriptions are shown in the official language in which they were submitted.
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MEASURING AND SORTlNG WOOD MEMBERS
BASED ON SPECIFIC GRAVITY
BACKGROUND OF THE INVENTION
This invention relates generally to sorting wood members, such as, trees
or logs within a collection of such m~mh~rs based on measuring each l~wll~l~el'sspecific gravity and allocating each llwll-l>el to a sort caLego-y based on the specific
gravity.
It has long been known that wood raw materials (trees, bucked logs,
10 lumber, chips) having variable specific gravities or d~n~iti~s can be allocated to
di~e-~--L end uses based, at least in part, on the density. For example, in m~nllf~ctllring
lumber when higher ~L-ellgLll is sought, the sawmill will seek to cut denser logs (higher
specific gravity) since denser wood will yield ~L..~Ilge- 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 frommeasuring 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 .~cenLly published entitled "l~t~hing Wood
Fiber Characteristics to Pulp and Paper Processes and Products," M.F. Williams,
TAPPI Journal 1995, which discloses activities in New 7e~1~n-1 where allocation of
raw materials based on density was appa ~--Lly undertaken to improve pulp and paper
m~mlf~ctllring~ The New 7e~l~ntl 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 7.e~1~ncl 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
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within the tree, and the age of the tree. While others have sorted groups of trees
and/or parts of trees based on their eAI,e~;led (or pl~d;cLed) average specific gravity, it
has not been s~-ggested that each m~ll,er within a collection should have its specific
gravity detected and sorted acco--lillg to its individual mea~urt;lllenl.
Accoldillg to accepted co,lvelllion, the forest products industry defines
"specific gravity" or "wood specific gravity" as the ratio of the mass of dry wood to its
green wood vo1ume (~,A~lt;ssed as the mass of water ~ p1AAed by that volume).
Because of the amount of absoll,ed water in green wood, wood specific gravity isroughly half that of its actual specific gravity, whose srientific 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, inr.llltlin~ the mass of extractives like lignin).An example of the way the specific gravity variability is presellLly
utilized in a pulp and paper mAmlfActllring complex follows. In the souLll~;lll United
States, there are pulp and paper cc,lllpl~ -~ where products are mAnllfAAr,tllred that
favor a source of chips having a relatively higher or lower specific gravity. For
lllplc, at the Weyerhaeuser Conlpany Columbus, Miss;s~ )i complex fluff pulp is
mAmlfAr,tllred ~Itili7ing a kraft production process which favors chips having arelat*ely higher specific gravity (applu~ y 0.46+) along with fine paper grades
which prefer lower specific gravity chips (applu~illla~cly 0.43-). The present raw
material ~ egy 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 mAmlfActllring 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 ~ ) 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.
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Since individual logs are not l-lea~ul t;d to detect their particular specific
gravities before allocation in a pulp m~mlf~ctllring setting, the .lifrerence in average
specific gravity of any two or more sorts will be less than it could be if individual logs
or log s~,...~ were measured and allocated accordi~ to their particular specificgravities. The result flowing from measuring each log's specific gravity will be that
only those with the l~lali~,ely 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
pelllli~ g the average specific gravity of each sort to be ~ sted upwardly or
do~llw~dly if the end use (products) will benefit. Similarly, for those end products
p~er~;llil~g 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 ~xpl~in~d above, there are signific~nt bent;fiLs in providing sort
c~legolies based on Illc&suled specific gravity. Higher qll~nfities 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 m~mlf~chlring and end
product pl U~J~;I ties.
Thus, from the folegc,illg, one object ofthe invention is to measure and
allocate to a specific gravity sort calego,y subst~nti~lly 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 speçific~tion to follow.
SIJMMARY OF THE ~VENTION
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.
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The,e~lel lt;4ui~ lt;llls of the end uses will serve to dele"",ne d~m~ntl for the
".~."1~ in each ofthe sort c~e~o.;~s
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sçh~m~tic lep,.;s~ ion illustrating the collection of
individual wood n,e",l~e, :~ and transport to a central measu, illg and sorting site.
Figure 2 is a s~ ;c r~,~ ion of a pulp mill wood yard where
the present invention is illu~L,aled and used to form chip piles with each having a
prede~ d average wood specific gravity.
Figure 3 illu~,a~es a device for providing a ",ea:jule of a log's specific
gravity.
DETAILED DESCRIPTION OF 1~ PREFERRED EMBODIMENT
Turning first to Figure 1 what is shown is a pulp and paper
m~nllf~ctllring facility typical of one p,t:se"~ly existing in North America and the
geographical t~liLoly surrounding it from which will come the trees harvested toprovide the wood raw material. While many pulp mills are ~ltili~in5~ recycled wood
fiber as a portion of their raw m~t~ri~l re~lui.~."~;"L, most all rely primarily on
surrounding co"""e,cial li",l~e,lands. From the timberlands, whether owned and
m~n~ged 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 ~ p 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 Li"~be,lallds (either from fee OWII11~h~l) or contracted timber), logs from
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logging co~ ;lu-:, with their source ~)f timber, or w-ood chips from outside suppliers.
Ul~ -aLel~/ this raw material arrives at the mill site for procçceing Typically the full
Iength trees will need to be cut into suitable lengths for subsequent h~n-11ing and
procPscing Very typically when the site is for pulp and paper procPcsing the trees and
5 long logs will be cut into 4 and 8 foot se~ x These are then del~a-ked and sent to
chippillg stations where wood chips are produced. The wood chips then become theraw material for pulp ~ p~stçrs 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 mea~u.el..e..l and
10 allocation process will be described that practices the present invention. As will be
readily al~pa t; .L, there are modifications that can be made, such as specific gravity or
mea~u.c;lllenl~ marking and sorting in the woods, while still pr~ctilin~ the invention.
Another ~parenl modific~tion would be measuring and sorting logs at a sawmill
facility. Another would be measurement of individual chips and allocating individual
15 chips accol-li--g to specific gravity. Each of these possible impl~mPnt~tions may have
favorable application at di~t;.e-ll sites, and co..lbinalions ofthese can be used together
to provide even additional benGrlLs. For example, one could sort log se~mPntc in the
woods and send them to ~li~r~--L sites, and subsequPntly sort the chips produced from
either or both pop~ tionc
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 d~L~;--- i--ed by the products
sPlected for prod~ction, 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 procPccin~, in a process step
referred to as "xl~chin5~," each individual member will have its specific gravity
determined at a specific gravity measuring station. The.eafler deb~rkin~ and chipping
take place.
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While a range of mea~ult;.lltlll for specific gravities for individual log
seP~ can vary from about 0.30 (lower specific gravity) to about 0.65 (higher
specific gravity) a predelel~ ed sort calegoly would have all individual ~ lllbel:" for
..pl~; with a specific gravity above 0.45 being ~ ified into the high calegc"y and
5 below 0.45 going to the low calego,y. As depicted in Figure 2, process streams can be
created where all ",e",be,~ with the higher specific gravity will be processed into chips
and the higher specific gravity chip pile will thusly be genel~ed. Similarly, the lower
specific gravity chip pile will be gel e~ d. As previously pointed out, since each
individual member within the population of available members is measured the average
10 specific gravity of the higher density chip pile will increase and conversely the average
specific gravity of the lower density pile will decrease. For CA~Ili lc, 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 thosesPlecte~l products favoring relatively higher or lower wood den.~itips The difference in
15 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 pn~ m~tic nail or pin gun is illustrated at 10 and can be operated
at low pres~ule. It can rapidly imbed a reusable or disposable pin (e.g. nails) into the
wood and the depth of penetration (or conversely height l~ il-g above the surface)
20 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
res llting height will be autom~tic~lly sensed and the log marked or otherwise sorted
into the presPlected specific gravity category as described above. Other specific
gravity detecting means could be l~fili7e~l~ some of which could employ
25 ele~;~lo...~gnetic radiation as non-contact ~etecting means. Such means are plesenlly
commercially available.
