Note: Descriptions are shown in the official language in which they were submitted.
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PATENT APPLICATION ::
IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
., TITLE ~ ~ -
SCRAPER FOR WOOD CHIP CRACKING APPARATUS
FIELD OF THE INVENTION
The present invention relates to an apparatus for treating wood chips to
enhance liquor penetration in subsequent pulping operations. More particularly,
the present invention relates to a destructuring apparatus in which chips are
passed between closely spaced rolls having surfaces that are aggressively
10 contoured for causing chips to be cracked by compressive forces exerted on the
chips by the rolls.
BACKGROUND OF THE INVENTION
In the production of paper from wood fibers, the wood fibers mu~t be
freed from the raw wood. In one widely used method, this is accomplished by
15 cooking the wood fibers in a solution until the matbtial holding the fibers
together, lignin, is dissolved. In order to achieve rapid and uniform digestion by
the cooking liquor, the wood, after it has been debarked, is passed through a ~ ~;
chipper which reduces the raw wood to chips on the order of one inch to four
inches long. The chipper tends to produce a large percentage of over-thick chips20 which, after separation by a screen, must normally be reprocessed through a
chip slicer to reduce them to the desired thickness. This reprocessing through aslicer has the undesirable effect of creating excessive sawdust and splinters. -
The production of sawdust and splinters reduces the overall yield of high-quality ;~
fibers from a given amount of raw wood. Because the cost of the raw wood is-~
25 a major contributor to the cost of paper produced, reslicing the oversized chips
incurs a considerable cost.
A long studied but only recently commercialized alternative to reslicing
over-thick wood chips is a process known as "delaminating" or "destructuring"
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the chips. The chips are fed through opposed rolls which compress the chips as
they pass through the nip of the rolls. The compression and re-expansion of the
chip is intended to fracture the chip or at least disrupt the integrity of the chip to
! increase the chip porosity and allow the cooking liquor to penetrate the chip
5 more rapidly, thus effectively reducing the chip's thickness. ~uch delamination
or destructuring devices used smooth or only mildly roughened surfaces, and
throughput was low. The belief was that more aggressive surfaces, while
perhaps increasing throughput, would result in unacceptable fiber damage.
U.S. patent No. 4,953,795 to Bielagus discloses an apparatus employing
aggressively contoured roll surfaces consisting of a matrix of pyramid projections
on the roll surfaces. The teaching of Bielagus results in rolls which destructure
the wood chips by cracking them preferentially in the direction of the grain.
The use, as disclosed in Bielagus, of aggressively contoured roll surfaces
15 having a matrix of outwardly extending discrete projections has proven critical to
the practical utilization of the chip destructuring process for the preparation of
wood chips. However, the aggressively contoured roll surfaces can become
clogged when handling wet, sticky or slimy and pitl~y wood chips. ~
What is needed is an apparatus for cracking wood chips which can handle ~.
20 wet, sticky and pithy chips without clogging.
SUMMARY OF THE INVENTION
The wood chip cracking apparatus of this invention employs oppositely
rotating rolls having highly aggressive surfaces. The aggressive surfaces in a
preferred design will have matrices of pyramid-shaped projections, machined,
25 cast, or otherwise formed into their surfaces. The pyramidal projections are
aligned circumferentially so that the gaps between circumferential rows of
pyramidal projections form continuous V-shaped grooves which encircle the rolls
and extend longitudinally of the rolls.
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To clean the surface of the rolls and prevent the build-up of wood chips
therebetween, a scraper is employed. .The scraper consists of a backing plate
mounted rigidly with respect to the frame on which the rolls are mounted and a
5 replaceable, segmented blade constructed of one-quarter inch stainless steel
with high wear-resistant properties. The edge of the blade has triangular teeth
which interdigitate with the rows of pyramidal projections on the surface of therolls. The teeth of the blade are spaced one to two millimeters from the sides of
the pyramidal projections which form the highly aggressive surface of the rolls.10 The scrapers will preferentially be located beneath the rolls where the scraped
material will readily fall away. However, in a retro-fit of an existing design, they
may be mounted wherever practical around the circumference of the opposed
rolls.
It is an object of the present invention to provide a wood chip cracking
15 apparatus which can process wet, sticky, and pithy wood chips.
It is another object of the present invention to provide an improved wood
chip cracking apparatus which employs continuous cleaning of the aggressive
contoured surface of the rolls employed in the wood chip cracking apparatus.
Further objects, features, and advantages of the invention will be apparent ~ -~
20 from the following detailed description when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view, partly cut away, of a wood chip cracking
apparatus.
FIG. 2 is a cross-sectional view of the wood cracking apparatus of FIG. 1
taken along section line 2-2 showing the scraper apparatus of this invention.
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FIG. 3 is a cross-sectional view of the wood cracking apparatus of FIG. 2
taken along section line 3-3 wherein the scraper apparatus of this invention is
shown.
FIG. 4 is an enlarged cross-sectional view of the apparatus of FIG. 2 taken
5 along section line 4-4.
FIG. 5 is a front elevational view of the blade of the scraper shown in FIG.
2.
FIG. 6 is an enlarged fragmentary view of the blade of FIG. 5.
FIG. 7 is a fragmentary isometric view of a portion of the roll surfaces of
10 the chip cracking apparatus of FIG. 1.
FIG. 8 is a fragmentary cross-sectional view of the scraper blade and roll
surface showing the teeth of the blade interdigitating with the aggressive
features of the roll.
FIG. 9 is a schematic view of a wood chip cracking apparatus installation
15 employing the scraper of this invention.
FIG. 10 is a schematic view of another wood chip cracking apparatus
installation employing the scraper of this invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to FIGS. 1-10 wherein like numbers refer to
20 similar parts, a chip conditioning apparatus 20 is shown in FIGS. 1, 2 and 3.The chip conditioner 20 employs a scraping assembly 22 as shown in FIGS. 2, 3
and 4 to improve the performance of the chip conditioner 20.
The chip conditioner 20 has a first roll 24 and a second roll 26 which are
moùnted for rotation by bearings 28 to the frame 30. The rolls 24, 26 have
25 aggressively contoured surfaces 32, 34 and counter-rotate in spaced parallel
relation to form a nip 36. As best shown in FIG. 7, the aggressively contoured
surface of the roll is preferably composed of pyramids 38 which are arranged in
circumferential rows 40 to form the aggressive surfaces 32, 34, of the rolls 24,26. In a preferred embodiment, the peaks of the pyramids 38 are spaced
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one-half inch apart, and the depth from the peak to the base of the individual
pyramids is approximately a quarter inch. In operation, the peaks of the
pyramids 38 may be placed in a peak-to-peak orientation or in a peak-to-valley
~r orientation. In use, the pyramids 38 cause the chips to be fractured along the
5 direction of fiber orientation, regardless of the orientation at which the chip
enters the space between the rolls.
In the embodiment shown in FIG. 7, the roll surface comprises a matrix of :
pyramid-shaped projections 38 which are formed into the roll surfaces 32, 34
producing circumferential V-shaped vaileys 41. Axial V-shaped valleys 42 are
10 formed in the rolls 24, 26 at right angles to the circumferential valleys 41
between the pyramids 38. The intersecting valleys 41, 42 form the four-sided
pyramids 38 which extend radially outwardly from the roll surfaces 32, 34.
The shape and operation of the aggressively contoured surfaces 32, 34
are more fully explained in U.S. patent 4,953,795 to Bielagus, issued September ~ :~
15 4, 1990, which is incorporated herein by reference.
The chip conditioner 20 has electric motors 43 which drive speed
reducers 45 through matched V-belts 44. The speed reducers 45 are connected
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to the central drive shafts 46 of the rolls 24, 26.
The roll 26, together with its bearings 28 and speed reducer 44, is
20 horizontally adjustable by means of hydraulic actuators 48. These control thewidth of the nip 36 by moving the roll 26 in spaced, parallel relation to the
opposed roll 24. Chips 56 to be processed are fed through a chip infeed 50
mounted over the nip 36 formed between the rolls 24, 26. The infeed 50 is
located above the nip 36 and is supplied with chips 56 by a means for supplying
25 chips 56 such as a vibrating conveyor 52 shown in FIGS. 9 and 10.
Any means for supplying chips 56, such as an auger, a hopper,
conventional c!onveyor or chute, etc., may be used. A chip supply which
supplies an even flow of chips 56 is to be preferred. Wood chips 56, while
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normally free flowing can frequently become sticky so that they will adhere to
the surfaces 32, 34 of the rolls 24, 26. For example, softwood trees such as
pines and firs produce resinous materials which can be exuded onto the surface
of the wood chips 56, causing them to stick to the rolls. Further, when the
5 chips 56 are wet, or when the chips 56 become sticky or slimy through the
growth of bacteria, molds, slime molds and the like, the chips 56 may become
prone to adhering to the surfaces 32, 34 of the rolls 24, 26.
This tendency to adhere is more clearly understood when it is realized that
the chips 56 will normally be compressed by up to a factor of 5 when passing
10 through the rolls 24, 26. This compression brings the chips 56 into intimate
contact with the roll surfaces 32, 34, and intimate contact is normally
associated with the process of adhesion. If the chips 56 do not fall freely fromthe rolls as indicated by the arrow 54 in FIG. 2, the chips 56 may remain on thesurfaces 32, 34 of the rolls 24, 26 and reenter the nip.
This recycling of chips 56 has two major disadvantages. First, the chips
56 which are recycled are overly stressed with the result that fibers produced
from them may be of lower quality. Second, the recirculating chips 56 can
overload the chip conditioner 20 with the result that the material flow rate must
be decreaséd or the newly incoming chips 56 will not be properly conditioned.
To overcome these problems, a scraper assembly 22, shown in FIGS. 2
and 3, is constructed as part of the chip conditioner 20. The chip scraper
assembly 22 consists of a lateral support beam 58 to which is welded or
otherwise affixed a backing bar 60, tG which are bolted one or more blade
segments 62 by bolts 63. As shown in FIG. 10, each blade segment 62 has
25 triangular teeth 64 which in profile match the circumferential grooves 41 formed
between the pyramids 38 which form the highly aggressive surfaces 32, 34 of
the rolls 24, 26.
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A scraper assembly lateral support beam 58, in a preferred embodiment,
is mounted to the frame 30 above the each roll 24, 26. As shown in FIGS. 2
and 3, the scraper assembly 22 positions the blade segments 62 with the teeth
n 64 radially disposed downwardly into the grooves 41 of the rolls 24, 26. Thus,
5 if wood chips 56 become jammed between the aggressive pyramids 38 in the
circumferential valleys 41 of the rolls 24, 26, they will be freed by the teeth 64.
The profile of the teeth 64 matches the profile of the circumferential
valleys or grooves 41 so that the teeth 64 may be closely spaced to within fortyto eighty thousandths of an inch (1-2 mm) of the roll surfaces 32, 34. The
10 blade segments 62, shown in FIG. 5, have bolt holes 68 through which bolts 63pass to attach the blade segments 62 to the backing bar 60. The backing bar 60
supports the blade segments and stiffens them against vibration and flexure. :j
The blade segments 62 are formed of relatively thin-gauge, one-quarter inch
stainless steel made of Nitronic 30 stainless steel. Nitronic 30 stainless steel is
15 a material of high wear resistance designed to resist metal-on-metal rubbing.
In some cases, it may be desirable to use a somewhat thicker segment of
perhaps a half-inch thickness. When thicker segments are used, the teeth will :
preferably have tapered cutting edges through the thickness of the blade
segment 62. The blade segments 62 may conveniently be made in two foot
20 sections so that a single blade segment 62 can be used in machines of different
capacity. The machine shown in FIGS. 1, 2 and 3 has rolls four feet long, uses
two blade segments 62 and can process in the range of one-hundred-and-ten
cubic meters of wood chips per hour. The use of blade segments 62 allows the
scraper assembly 22 to be readily adapted to chip conditioners of various
25 i~ngth5
FIG. 9 shows an alternative embodiment binary chip conditioner 120. The
binary chip conditioner 120 employs a first roll 124 and a second roll 126,
which form a first nip 136. The rolls 124, 126 are mounted on bearings 128.
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The rolls 124, 126 counter-rotate, so progressing the chips 56 through the nip
136.
i A third roll 127 forms a second nip 137 where the rolls 126, 127 are
opposed. The second nip 137 has a smaller gap than the first nip 136. In this
5 way, the chips 56 are progressively destructured. Progressive destructuring has
the twin advantages of more completely fracturing the chips 56 while at the
same time avoiding excessive compression of the chips 56 which can lead to
decreased fiber quality.
The two-step destructuring process accomplished by the chip conditioner
10 120 functions in the following way. When the chips 56 are fed from the
vibrating conveyer 52 to the first nip 136, the width of the first nip is set toavoid excessive compression of the thickest chips 56. As the thickest chips 56
transit the nip 136, they are destructured or fractured along the grain by the
highly aggressive surface 132, 134 of the rolls 124, 126. Thus fractured, the
chips 56 pass on to a transfer table 139 which supports the chips 56 between
the first roll 124 and the third roll 127. The rotationai movement of the secondroll 126 above the transfer table 139 produces a sweeping effect, which moves
the chips 56 across the table 135 into the second nip 137. On reaching the
second nip 139, the chips 56 are further compressed on surfaces 133,134 so
20 all the overly thick chips 56 are destructured. Excessive compression is
prevented because the cracks in the largest chips 56 cause them to be more
yieldable in the second nip, thus avoiding excessive compression.
The chip conditioning device 120 has hydraulic actuators 148 for
adjusting the spacing between the nips 136 and 137. The chip conditioning
25 device 120 advantageously accomplishes the work of two chip conditioners 20
while also saving considerably in parts and equipment. The chip conditioner 120
requires only three rolls and one frame 130, as opposed to four rolls and two
frames required by the chip conditioner 20. Thus, if progressive destructuring is
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desired, the chip conditioner 120 will be more cost effective than two separate -
chip conditioners 20.
On a newly designed machine, the scraper assembly 122, shown
schematically in FIG. 9 may be placed in the optimal positions with respect to
5 the rolls 124, 126, 127. For rolls 124 and 127, where the bottom of the roll is
readily accessible, the scrapers 122 will preferably be positioned below the roll
so that materials scraped from between the rows 40 of pyramids 38 which form
the aggressive surface of the rolls may readily fall freely from the rolls. On roll
126 where the bottom of the roll is not readily accessible, the scraper 122 will10 be positioned so that material will be scraped on to the downstream facing side.
FIG. 10 show~ a tertiary chip conditioner 220 which has a first roll 224, a
second roll 226, a third roll 227, and a forth roll 229. The tertiary chip
conditioner 220 functions similarly to the binary chip conditioner 120, but adds15 an in-line fourth roll 129 which forms a third nip 238. Thus, the tertiary chip
conditioner 220 has a first nip 236, a second nip 237, and a third nip 238. The
first nip 236 is more widely spaced than the second nip 237, which is turn is
more widely spaced than the third nip 238. Hydrau1ic actuators 248 and 249
are provided to control the spacings of the three nips 236, 237, 238.
20 Movement of the hydraulic actuator 248 controls the spacing of the first nip
236 and the second nip 237. The hydraulic actuator 249 controls the spacing
of the third nip 238.
The theory of operation of the tertiary chip conditioner is similar to the
theory of the binary chip conditioner 120, only the destructuring is accomplished
25 progressively at the three nips. The chips 56 which are fed into the first nip
pass across to a chip table 239, where they are swept into the second nip 237,
where they progress over the top of the roll 227 and then enter the third nip
238. The function of a tertiary chip conditioner could be accomplished by three
successive runs through three single nip chip conditioners 20. However, by
30 combining the functions as illustrated in FIG. 10, more than a one-third reduction
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in required rolls and equipment is achieved by using four rolls to form three nips
236, 237, 238~
!`Scraper bars 222 are positioned on the first three rolls 224, 226 and 227
of the tertiary chip conditioner 220 in a way simiiar to the positioning of the chip
5 scrapers 122 on the binary conditioner 120. Where the bottom of the roll is
readily accessible, the scrapers 222 will preferably be positioned below the roll
so that materials scraped from between the rows 40 of pyramids 38 may readily
fall freely from the rolls. The scrapers 222 are thus positioned beneath the rolls
224, 227, and 229. On the roll 226 where the bottom of the roll is not readily
10 accessible, the scraper 222 will be positioned so that material will be scraped on
to the downstream facing side.
It should be understood that although the highly aggressive surface is
shown as formed by a matrix of pyramids, other shapes can be used, including
but not limited to the following: cones, frustrums of cones, parabolas,
15 hyperboles, tetrahedrons, and the like. Each such aggressive surface-forming
shape would reguire a particular blade profile with teeth that match the
circumferential path formed by the geometric or arbitrary shapes forming the
highly aggressive surface of the rolls.
It should also be understood that wherein the blade of the scraper is
20 shown to be rigidly mounted to the frame, it could be hingedly mounted or
elastically mounted.
It should also be understood that wherein the material for the blade is
suggested to be high-wear- resistant stainless steel, other materials could be
used, including high-carbon steel, tungsten carbide, mounted ceramic inserts,
25 plastic, composites and the like.
It should further be understood that wherein the blades of the scraper are
shown extending along a radial line with respect to the rolls, they could be used ~`~
in any position from tangent to perpendicular to the surface of the rolls.
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It should also be understood that wherein the teeth are shown integrally
formed with the blade, the teeth may be discrete elements. Further, the teeth
can be formed of yet smaller discrete elements.
It should also be understood that wherein in FIGS. 1-3 the scraper
5 assembly 22 is shown as retrofitted to an existing machine design, the machine could be redesigned to place the scrapers beneath the rolls.
It should also be understood that the invention is not confined to the
particular construction and arrangement of parts herein illustrated and described,
but embraces such modified forms thereof as come within the scope of the
10 following claims.
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