CA2129865A1 - Scraper for wood chip cracking apparatus - Google Patents

Abstract

ABSTRACT

A wood chip cracking apparatus employs oppositely rotating rolls which have surfaces of matrices of pyramid-shaped projections. The pyramids are aligned circumferentially so that the gaps between circumferential rows of pyramids form continuous V-shaped groves which encircle the rolls. To clean the surface of the rolls and prevent the build-up of wood chips or other material 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 replaceable, segmented blade constructed of one-quarter inch stainless steel with high wear-resistance properties. The edge of the blade has triangular teethwhich fit between the rows of pyramids on the surface of the rolls. The teeth ofthe blade are spaced one to two millimeters from the sides of the pyramids which form the surface of the rolls. The teeth prevent the build-up of material between pyramid-shaped projections.

Description

212 9 8 ~ ~ HB100263603 `: :
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"

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.

212 9 ~ HB100263603 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.

- 212 ~ 3 ~ a HB100263603 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.
;' ' 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 212 ~ ~ ~ a HB100263603 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 :: .
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 212~86~

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.

212 ~ ~ 5 ~
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.

212~

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 _~ HB100263603 2 ~

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 g ~ ~

-~ 212 ~ HB100263603 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.
- 10- -;

~ 212 ~ HB100263603 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.

~ ~'

Claims (12)

1. An apparatus for destructuring wood chips comprising:
first and second rolls disposed for rotational operation about horizontal rotational axes which are substantially parallel to each other, wherein the first and second rolls are spaced from each other a pre-selected distance for applying compressive force to wood chips passing therebetween, and wherein at least one of said rolls has an aggressively contoured roll surface formed by a matrix of outwardly extending projections;
at least one of said first and second rolls being connected to means for rotating said at least one roll along a longitudinal axis; and at least one scraper mounted in spaced, parallel relation to the horizontal axis of said at least one roll, wherein the scraper has projecting portions which extend radially inwardly toward said at least one roll and interdigitate with the outwardly extending projections of the roll contoured surface, such that rotation of said roll with respect to the scraper effects a cleaning action of the roll surface.

2. The apparatus of Claim 1 in which both of said first and second rolls are similarly aggressively contoured, and wherein at least one scraper is mounted in spaced parallel relation to each of said first and second rolls, the scrapers interdigitating with the aggressively contoured surfaces, so effecting cleaning action of the roll surfaces.

3. The apparatus of Claim 2 in which said aggressively contoured surfaces of said first and second rolls consist of a matrix of pyramid-shaped projections on the roll surfaces, and wherein the scraper projecting portions define triangular teeth, the triangular teeth conforming to said pyramids and interdigitating therewith.

4. The apparatus of Claim 1 further comprising:
a third roll disposed for rotational operation substantially parallel and spaced from said second roll a pre-selected distance less than the pre-selected distance between the first and second rolls, said second and third rolls receiving chips from said first and second rolls, thus providing progressive destructuring of wood chips, and wherein the third roll has an aggressively contoured surface;
at least one scraper mounted in spaced parallel relation to said third roll, the scraper interdigitating with the aggressively contoured surface of said third roll, so effecting a cleaning action of the surface of the third roll.

5. The apparatus of Claim 1 wherein the scraper is made of a high wear-resistant material.

6. In an apparatus for destructuring wood chips having first and second rolls disposed for rotational operation substantially parallel to each other, and spaced from each other over a pre-selected distance for applying compressive force to wood chips passing therebetween, wherein at least one of said rolls has an aggressively contoured roll surface including a matrix of outwardly extending discrete projections, said projections being of a height substantially equivalent to the desired chip thickness; and means for supplying a flow of wood chips to said first and second rolls and for distributing the wood chips along the axial extent of said first and second rolls, at least one of said first and second rolls being connected to means for rotating said at least one roll along its longitudinal axis, wherein the improvement comprises:
at least one scraper mounted in spaced parallel relation to at least one of said first and second rolls, wherein the scraper has a plurality of projections which extend toward a roll surface and interdigitate with the aggressively contoured surface, so effecting a cleaning action of the roll surface.

7. The apparatus of Claim 6 in which both of said first and second rolls are similarly aggressively contoured, and wherein at least one scraper is mounted in spaced parallel relation to each of said first and second rolls, the scrapers interdigitating with the aggressively contoured surfaces, so effecting cleaning action of the roll surfaces.

8. The apparatus of Claim 7 in which the aggressively contoured surfaces of said first and second rolls consist of a matrix of pyramid-shaped projections on the roll surfaces, and wherein the scrapers have portions defining triangular teeth, the triangular teeth conforming to said pyramids and interdigitating therewith.

9. The apparatus of Claim 6 wherein the scraper is made of a high wear-resistant material.

10. An apparatus for destructuring wood chips comprising:
a frame;
a first roll rotatably mounted to the frame about an axis of rotation;
a second roll rotatably mounted to the frame about an axis of rotation substantially parallel to the first roll, wherein the first and second rolls are spaced from each other a pre-selected distance for applying compressive force to wood chips passing therebetween, and wherein at least the first roll has a contoured roll surface formed by a matrix of outwardly extending projections; and at least one scraper mounted to the frame in spaced, parallel relation to the horizontal axis of the first roll, wherein the scraper has projecting portions which extend radially inwardly toward the first roll and interdigitate with the outwardly extending projections of the roll contoured surface, such that rotation of the first roll with respect to the scraper disengages wood chips from the roll surface.

11. The apparatus of Claim 10 wherein a scraper is mounted to the frame in interdigitating relationship to each of the first roll and the second roll.

12. The apparatus of Claim 10 further comprising:
a third roll rotatably mounted to the frame about an axis of rotation substantially parallel to the first roll, wherein the third roll is spaced from the second roll a pre-selected distance which is less than the pre-selected distance between the first roll and the second roll, and wherein the third roll has a surface having a plurality of projections which extend radially outwardly, and wherein the second roll and the third roll receive chips from the first roll and the second roll to further destructure the wood chips; and at least one scraper mounted to the frame in spaced parallel relation to the third roll, wherein the scraper has radially inwardly extending projections which interdigitate with the outwardly extending projections of the third roll, such that rotation of the third roll with respect to the scraper disengages wood chips from the third roll.