CA2036571C - Machine and method for separating out fines, pins and over-thick wood chips - Google Patents

Abstract

Abstract of the Disclosure Fines, pins, and over-thick wood chips are separated from wood chip material by using a series of three roller screens having chip agitating and conveying protuberances.
The screens are arranged and adapted such that over-thick chips are separated by the first screen, fines are separated by the second screen, and pins are separated by the third screen.

Description

Description MACHINE AND METHOD FOR æ~PARATI~G OUT
FINES, PINS, AND OVER-THICK WOOD CHIPS

Technical Field The present invention relates to the sorting of wood chip material into over-thick chips, f ines, pins, and acceptable chips.
Bac~qround of the Invention In the processing of wood chips preparatory to introduction to a digester, it is preferred to reprocess chips which are thicker than a predetermined thickness (commonly about 8 m~) and to discard those chip particles which have fibers shorter than a preset minimum length or which are in the form of flakes thinner than a preset thickness, because these are relatively poor digésting materials. For purposes of the present description, the chips to be reprocessed will be called "over-thickn, and the chip particles with overly short fibers and flakes will be called ~fines.~
"PinsN are an additional category of particles in wood chip material which it is preferred to take into consideration in many pulping operations, since they do not result in as high a quality of pulp as do normally acceptable chips and can cause plugging in the digester.
Pins may be classified as a toothpick-like material which will pass through a 77 mm round hole on a Statsvets-type separator, but not through a 3 mm round hole. When pins are classified in this manner, fines are considered to be sawdust-li~e material that, when wet, will pass through a 3 mm round hole on a Statsvets-type classifier.
The advantage of initially separating a relatively large percentage of the pins is that they may be accurately blended in a predetermined amount with the otherwise acceptable chips if they are to be used in the pulping operation or can be discarded in whole or in part with the fines. In operations in which the pins are not ~eparated as a class, the smaller pins become part of the fines, and the remaining pins become part of the acceptable chips.
The screening of wood chip material is not only difficult because of the presence of fines and pins, but it is also complicated by the fact that the chips normally vary in length from about 20 to 30 mm, and in width from about 15 to 20 mm. Thus, the thickness of the chips is usually considered smaller than the other dimensions.
The traditional screening apparatus for pulp chips has been (a) sloped, vibratory holed screens given an oscillating or circular motion, commonly in the range of 2 to 3 inches, at a relatively high speed, to shift the properly sized chips through the holes in the screen, and (b) disk screens such as that shown, for example, in U.S.
Patent No. 4,301,930, which comprises a bed of parallel, corotating shaft~ carrying interdigitated disks having clearances de~ined by the max$mum chip thic~nes~ to be tolerated.
Di~k screens have been considered by many in the cellulose industry a~ superior to vibratory screens, but, as indicated in U.S. Patent No. 4,660,726, a disk screen has a relatively low screening capacity per square meter o~ ~creening sur~ace, and, a~ indicated in U.S. Patent No.
4,538,734, it is very di~icult to attain and maintain uniform slot widths between the disks of a disk screen, particularly when the ~lot widths are required to ~e so narrow. As a consequence, there have been e~orts to provide improved techniques for mounting and replacing the disks of disk screens and attempts to develop a suitable alternative to disk scr¢ens. Such attempts have included oscillating bar screens, such as shown in U.S. Patent No.
4,660,~26, and synchronously driven, intermeshing screw spirals, such as disclosed in U.S. Patent No. 4,430,210.

3 ~ ,,, ._ ~.....

Summary of the Invention Although roll screens, or grizzlies, have long been used for sizing or separating various products, they have not been considered suitable for separating over-thick chips, pins, or fines from wood chip material, norhave they been considered suitable for removing chips classified as normally "over-length. n In the past, it was not recognized that roll screens could be used successfully for sorting functions with respect to wood chips if the surfaces of the rollers were such as to adequately agitate the chips and assist the conveying action of the roller~.
In carrying out the invention, there is utilized a plurality of side-by-side, transversely spaced rollers which collectively provide a bed for receiving the wood chips to be sorted and have their surfaces provided with chip-agitating protuberances. These protuberances may be knurls and/or ridges when separating out over-thick chips, and are preferably knurls when separating out fines and pins. The roller~ are rotated in the same direction so that the protuberances ~unction to tumble and push the chips along the bed. When the protuberances on the rollers are knurl~, they are preferably pyramidal (full pyramid~ or frustums of pyramids), and when the protuberance~ are r$d~ed, the ridges are preferably tapered and helical for the length of the rollers (the width of the bed). When pyr~midal protuberance~ are used, they preferably are formed by two helical sets of routed v-grooves of opposite hand, and, when the protuberances are ridges~ they preferably are formed by a single helical set of routed v-grooves.
When separating out the over-thick chips, the gaps between rollers are sized to receive only the chips of proper thickness (~acceptable chipsN). As the rollers rotate, the acceptable chips, together with the fines and pins, occupying the spaces between ~he rollers above the sizing gaps pass downward through the gaps, preferably onto a second roller bed. The over-thick chips in the spaces between the rollers are nudged ahead by the oncoming chips and continue to be conveyed along the first roller bed by the rollers for discharge from the forward end of the bed, for reprocessing.
The second roller bed is used to separate out the fines, and it is preferred to use rollers with pyramidal knurls for this purpose. The spaces between the knurls are sized to receive primarily the fines having ~oo short a fiber length, and the rollers are preferably spaced apart at their maximum diameters by a gap sufficient to pass the fines having the form of flakes which are too thin. As the rollers rotate, the fines occupying the spaces between the knurls and between the rollers pass downward from the roller bed and discharge into a hopper or onto a discharge conveyor. The tumbling of the chip~ by the knurls causes the fines to settle between the knurls and between the rollers, for discharge.
At the same time, the tumbling chips are conveyed by the rotating roller action along the second bed and have a larger gap between rollQrs for passage therebetween of the pins, for collecti~n. Th~ remainl`ng chips (~acceptable chip~n) discharge from the third be~. In the preferred practice, only the material passing between the rollers in about the first hal~ of the length of the first bed is fed onto the second roller bed, because this material normally contain~ all of the coll~ctible fines, and in excess 80%
of the pins. The chips pa~sing through the remaining rollers in the first bed are then classified as "acceptable chips, n and are combined with the chips discharging from the third roller bed.
A typica} roller can have, for example, a diameter of 3.5 inches, a protuberance depth of 0.1 inch, a protuberance width and spacing of 0.25 inch, and a helix 3S angle of 27 degrees. Typical rollers for removal of fines and pins are preferably of smaller diameter, such as, for example, 2.187 inches. The rollers on the fines-separating bed may have their knurl depths about one-half that on the rollers of the previous bed, and the knurl depth on the rollers of the pins-separating bed may be the same as ~or the rollers ~or sorting out over-thick chips.

Brief Des~ri~tion Qf the Drawinas Figure 1 is a top perspective of a machine embodying a roller bed in accordance with the present invention.
Figure 2 is a side elevational view of the machine as viewed from the left in Figure 1, and without a side cover plate.
Figure 3 is a detail view of a first embodiment of rollers, taken as indicated in Figure 4.
Figure 4 is a fragmentary perspective view showing end portions of two of the knurled rollers of the first embodiment having pyramidal knurls.
Figure 5 i5 a ~ragmentary top plan view of one of the knurled rollers of the fir~t roller embodiment.
Figure 6 i8 a fragmentary view to an enlarged scale showing an example of suitable dimensions for the pyramidal knurl~ of the fir~t roller embodiment.
Figure~ 7 and 8 are views taken in a manner similar to Figures 3 and 4, showing a second embodiment of rollers with protuberances in ridge form.
Figure 9 i~ a f ragmentary plan view showing an arrangement of the second embodiment of rollers.
Figure 10 i8 a fragmentary plan view showing an alternative arrangement combining use of the first and second embodiment of rollers.
Figure 11 shows the action of the rollers with respect to an over-length chip when viewed from one end of the rollers.
Figure 12 is a view taken in a manner similar to P~gure 3, illustrating a third roller embodiment having pyramidal knurls, each in the form of a frustum of a pyramid (frusto-pyramidal) rather than being a full pyramid.
Figure 13 i8 a iragmentary view to an enlarged scale showing an example of suitable dimensions for the ~nurls on the third roller.
Figure 14 i~ a ~ide view illustrating a system for separating out over-thick chips, fines, and pins using three roller beds in accordance with the present invention.
Detailed Description of thç Inyçn~iQn ~ eferring to the drawing~, a bed 20 is formed by a plurality of ~ide-by-side, knurled rollers 22 which have parallel rotary axes. These rollers are ~ournal-mounted between up~tanding side plates 23, 2~ provided a~ part of a framework 25. The rollers 22 are necked at each end, and the necks 22a, 22b extend through bearings mounted in the side plate~ 23, 24. Neck 22b of each roller i8 extended relative to neck 22a to receive a single sprocket 26 in the ca~e of the two rearmost rollers and to receive inner and outer sprocket 27, 28 in the case o~ the other rollsrs .
It will be noted that alternate of the rollers 22 i~ reversed endwise so that there are two sets of ~prockets, one ~et being outboard of side plate 23 and the neck~ 22a of the second set, and the second ~et being outboard of side plate 24 and the necks 22a of the first set. At the forward end of the ~id~ plate~ 23, 24, there i~ mounted a cross-sha~t 30, in turn having end sprockets 32, 33 and an intermediate sprocket 34. The end sprockets are connected by chain~ 36 to the most ~orward outer sproc~et 28 on the respective side of the machine.
Alternating inner and outer chains 38, 39 then alternately connect the inner and outer sprockets to drive alternate of the rollers 22 at one side of the machine and to drive the other rollers at the other side of the machine from the sha~t 30. The latter is in turn powered by a chain 40 ~f, ~
from a drive sprocket 41 on the output shaft 42a of a variable-speed drive unit 42 mounted at the front of the framework 25. The described drive arrangement permits rollers with a relatively small diameter, and which are close together, to be used and driven in a simple manner in the same direction of rotation, from a single motor.
In the roller bed 20 embodiment of the present invention, the rollers 22 are preferably provided with knurls 44, each of which has a generally pyramidal shape.
These knurls may be formed by routing two sets of v-grooves 45, 46 of opposite hand in crisscrossing spiral paths along the length of the rollers, starting from opposite ends. As indicated in Fig. 6, by way of example, each of the v-grooves in each set may have a MOUTH WIDTH
of 0.25 inch (6.3 mm) and a depth of 0.10 inch (2.5 mm), and the lead anqle on the spiral cuts may be 27 degrees.
Referring to Fig~ 3, one of the v-grooves 45 results in the generally triangular, opposed faces 44a, 44b, and one o~ the v-groove~ 46 re~ults $n the generally triangular, oppo~ed face~, 44c, 44d. Each o~ the knurls 44 i9 hence formed by two ad~oining v-grooves 45 and two ad~olning v-grooves 46, Referring to Fig. 12, the pairs of adjoining v-grooves 45, 46 may be separated such that the four faces 44a-d are trapezoid~ 44a'-d', rather than triang~es, thereby providing frusto-pyramidal knurls 44' separated by v-groovea 45~, 46'. As indicated in Fig. 13, the frusto-pyramidal knurls 44' may be given, for example, half the height of the full pyramidal knurl8 44.
It is preferred to chxomium plate the rollers 44 to increase the wear life. In thi~ regard, the rollers can be removed and replated from time to time.
As an alternative to having all of the rollers 22 knurled as above described for separating out over-thick chips, so~e or all of the rollers may be formed with respective spiraling tapered ridges 47, 48, as shown in Fig. 7 and ~. These ridges ~7 may be formed, for example, by routing only one set of v-grooves 45, 46, rather than two sets on each roller. Rollers 22a may have the spirals o~ their v-grooves 45 in one direction, and rollers 22b may have the 8p~ ral8 0~ their v-grooves 46 of the opposite hand. When used on a bed for separating out over-thick chip~, the rollers 22a preferably alternate with respect to the rollers 22b. Ridged rollers 22a, 22b can be used for the entire bed, as shown in Fig. 10, or can be alternated with the knurled rollers 22, as indicated in lo Fig. 8, or in some other suitable pattern. In each instance, the protuberances (knurls or ridges) on the rollers are spaced apart between rollers by a gap (see Fiq. 11) determining the maximum chip thickness desired, which commonly will be 8 mm. This gap has been exaggerated in the drawings for clarity.
Chips being processed to remove over-thick chips are fed into the rear portion of the bed 20 from an overhead hopper or chute (not shown), and are confined by the sidewalls and a ~loped rear wall 46. Depending upon which rollers are used, the chips are tumbled by the knurls 44 on the rotating rollars 22 and by the tapered ~piraling ridge~ 47, 4A on the rotating rollers 22a, 22b, and are gradually simultaneously conveyed by the rollers toward the forward end of the bed 20 to discharge therefrom into a hopper or onto a discharge conveyer.
When the ridge~ rollers 22a, 22b are used, as the chips tumble and movo forward, the ridge~ 47, 48 tend to move the chips in a zigzagging travel path because the spirals o~ the ridges 47, 48 are o~ oppogite hand.
The tumbling chip~ tend to tilt downward in the forward direction as they move between rollers. If the chip~ are not over-thick, they pass between the rollers.
Over-thick chips negting above the gap between two rollers are nudged by advancing ch~ps therebehind sufficiently to cause the upwardly advancing portion of the roller at the ~ront of the gap to move the over-thick chips ahead.
Thu~, the space above the gap between rollers (the nip) f ~

does not become clogged with over-thick chips.
Ultimately, the over-thick chip6 discharge from the front o~ the bed 20 while the chips within the desired thickness range pas~ downward through the gaps between the rollers ~or further separating, to remove the fines and pins therein.
In accordance with the present invention, it is preferred to next remove fines from the chip material after removing the over-thick chips. As shown in Fig. 14, thi3 can be done efficiently by feeding acceptable chips wlth fines and pins onto a second bed 120 formed with rollers 122, liXe rollers 22 but preferably of small diameter (2.187 inches, for example), and w~th the protuberances of adjoining rollers spaced closer together, 0.06 inch (1.5 mm), for example. On the second roller bed, it i8 preferred to use rollers of the type having either full pyramidal knurls 44 or frusto-pyramidal knurls 44'. When removing fines, it is preferred to have roller periphery speeds in the range of 50 to 150 feet per minute.
Normally, by the time the chips have travelled about halfway along the length o~ the first bed 20, ~ub~tantially all of the ~ines and at least 80~ of the pin~ have passed downward through the bed, together with acceptable chips. As indicated in Fig. 14, these acceptable chip~ and the fine~ and pins therein axe guided by a diverter and ~unnel onto the infeed end o~ roller bed 120 as they drop from the 2irst bed 20. The second bed 120 screens out the ~ines, which then drop into a hopper 124, for example, while the acceptable chips continue for the ~ull length of the bed 120 to discharge onto a third roller bed 220, preferably o~ the type having rollers with pyramidal protuberances. The third roller bed 220 may be below the level of the second bed 120 or continue at the same level. The knurls on adjacent rollers on the third bed 220 may be spaced apart by a roller gap of about 3 mm, for example.

~ 2 ~ r As the acceptable chips and pins are conveyed by the rollers along the third roller bed 220, most of the pins pass downward through the bed for collection in a hopper, for example, for later blending with the acceptable chips in a predetermined ratio or for burning with the fines if there is a surplus of pins. The acceptable chips discharge rrom the end of the bed 220 and are combined with the acceptable chips, which pass through the second half of the first roller bed 20 In a typical installation, the first roller bed 20 may have an arrangement of rollers 22a, 22b with ridge-type protuberances such as in Fig. 9, the second bed 120 may have rollers with frusto-pyramidal protuberances 44', and the third roller bed 220 may have rollers with full pyramidal protuberances 44. The dimensions of the ridges 47, 48 in the instance of the first roller bed 20 and the dimen~ions of the pyramidal protuberances 44 in the inotance of the third roller bed 220 may be a ~ndicated in Fig. 6. The dimen~ions of the ~rusto-pyramidal protuberances 44' in the instanaQ o~ the second roller bed may be as indicated $n Fig. 13. With such an arrangement of protuberance types as respects the three roller beds, and with roller gaps as previou~ly indicated, the fines removal efficiency is in excess of 80% through a range of roll speeds from about 60 to lS0 feet/minute when the loading rate o~ chip material fed to the first roller bed is appropriately ad~uqted inversely to the roller speed. It will be appreciated that the gap between rollers may be varied depending upon the dimen~ional de~inition of ~ines and pins ~elected.
Regardles~ of protuberance profile or roller-to-roller gap, performance of the roller beds can be adjusted to optimize performance through a wide range of chip loading rates. Generally, the fines removal efficiency decreases and the pin separation efficiency increases for a given roll speed as the chip loading rate is increased.
For example, at a roll peripheral speed of 100 feet/minute, the fines removal efficiency declines from about 95% to about 80% when the chip loading rate is increased from a low loading rate to a high loading rate.
Decrea~ing the depth o~ the valley between the protuberances in the fines removal roller bed 120 from 0.1 inch to 0.05 inch,, for example, decreases the fines removal efficiency by about 20~, but increases the pins separation efficiency (decreases pins 106s) to an extent which may ~ustify the increase of fines in the acceptable chips category. On the other hand, in other installations, this decrease in fines remo~al efficiency may not be acceptable, in which ca~e the roller beds 120 and 220 for fines removal and pins separation, respectively, may be the same except that the roller-to-roller gap will be greater in the roller bçd 220.
For most pulp operations, it is not only desiredto re;ect chips having thicknesses in excess of about 8 mm, it is also preferred to reject chips having a lengths in exce~s of about 1 3/4 inches (~over-length~ chips). In such a case, the rollers 22 are given an outward diameter of about 3 1/2 inches, namely, about twice the over-length limit. Referring ~o Fig. 11, when a chip is moving from the fixst quadrant of a roller toward the fourth quadrant Or the next roller, with its length extending generally in the direction of travel, the leading end o~ the chip normally engagea the fourth quadrant of the leading of the two roller~ before the chip can as~u~e a sufficiently vertical position to drop through the nip between the rollers. This engagement of the leading end of the chip with the leading roller and the continued engagement of the chip with the first quadrant of the trailing rol}er causes the chip to tilt upward at it leading end, as indicated in Fig. 11. The angle of tilt with the horizontal normally must exceed 45 degrees in order for the chip to shift to a substantially vertical position so that it can drop between the rollers. Otherwise, the forward propulsion effect of the fourth quadrant position . .

12 ~ ~ rs ~ ~

of the leading roller is so great that the chip is conveyed forward therebeyond. Ultimately, most of the over-length chipQ discharge with the over-thick chips at the forward end of the roller bed 20.
Although it i~ preferred to use rollers with pyramidal knurls, other tapered shapes can be used.
Similarly, the tapered ridges 47, 48 can be varied in slope and lead angle.
From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the inVQntiOIl i5 not limited except as by the appended claims.

Claims (16)

1. A method of separating fines, pins, and over-thick chips from wood chip material to obtain acceptable wood chips, said method comprising:
feeding the chip material at an infeed end of a first roller screen having agitating and conveying rollers spaced apart to pass chips of acceptable thickness between such rollers and to discharge over-thick chips at a discharge end, said first roller screen having a leading length segment commencing at said infeed end along which most of the fines and pins pass therethrough together with acceptable chips;
delivering the pins, fines, and acceptable chips passing through said leading length segment of said first roller screen onto an infeed end of a second roller screen having agitating and conveying rollers adapted to pass the fines between such rollers and to discharge the pins and said acceptable chips at a discharge end;
delivering the pins and acceptable chips discharging from said second roller screen onto an infeed end of a third roller screen having chip agitating and conveying rollers adapted to pass the pins between such rollers and to discharge the acceptable chips at a discharge end;
collecting the pins; and combining the acceptable chips passing through the remainder of the length of said first roller screen following said leading length segment with the acceptable chips discharging from the discharge end of said third roller screen.

2. A method according to claim 1 in which said leading end segment of the first roller screen extends about halfway along the length of the first roller screen.

3. A method according to claim 1 in which the material passing through said leading length segment feeds by gravity onto said second roller screen.

4. A method according to claim 1 in which the rollers in said second and third roller screens each have a pattern of crisscrossing tapered grooves forming pyramidal chip agitating and conveying protuberances.

5. A method according to claim 1 in which the rollers of said first, second, and third roller screens have chip-agitating protuberances, the protuberances on the rollers of the first roller screen being spaced from the protuberances on the adjacent rollers by a gap larger than the gaps between the protuberances on adjacent rollers of the second roller screen and third roller screen, and the gap between the protuberances on adjacent rollers on the third roller screen being greater than the gap between the protuberances on adjacent rollers of the second roller screen.

6. Apparatus for sorting wood chip material, comprising:
a first roller screen having chip-agitating and conveying rollers spaced apart such as to pass chips of acceptable thickness between such rollers and to discharge over-thick chips at a discharge end;
a second roller screen arranged to receive pins, fines, and acceptable chips from said first roller screen and having chip-agitating and conveying rollers spaced apart such as to pass fines between such rollers and to discharge pins and acceptable chips at a discharge end;
a third roller screen arranged to receive pins and acceptable chips from the discharge end of said second roller screen and having chip-agitating and conveying rollers spaced apart such as to pass pins between such rollers and to discharge acceptable chips at a discharge end; and the rollers of said second roller screen having chip-agitating and conveying protuberances of generally pyramidal shape formed by crisscrossing tapered grooves.

7. Apparatus according to claim 6 in which the rollers of said first and third roller screens have chip-agitating and conveying protuberances formed by tapered spiral grooves.

8. Apparatus according to claim 6 in which each of said rollers of the first roller screen has chip-agitating and conveying protuberances of generally pyramidal shape formed by crisscrossing tapered grooves.

9. Apparatus according to claim 8 in which said grooves in the rollers of said first roller screen are shallower than said grooves in the rollers of said second roller screens.

10. Apparatus according to claim 6 in which the rollers in each of said roller screens are separated by gaps, the gaps in the first roller screen being wider than the gaps in the second and third roller screens, and the gaps in the second roller screen being narrower than the gaps in the first and third roller screens.

11. Apparatus according to claim 7 in which the spiral grooves on the rollers of the second roller screen are shallower than the spiral grooves on the rollers of the third roller screen.

12. Apparatus for sorting fines and pins from wood chip material after removal of over-thick chips, said apparatus comprising:
a fines-separating roller screen and a pins-separating roller screen arranged in series and each having its rollers formed with generally pyramidal chip-agitating and conveying protuberances formed by crisscrossing spiral grooves, the rollers in said fines separating roller screen being separated by a gap which is less than the gap separating the rollers in said pins-separating roller screen.

13. Apparatus according to claim 12 in which the spiral grooves in the rollers of said fines-separating roller screen are shallower than the spiral grooves in the rollers of said pins-separating roller screen.

14. Apparatus according to claim 13 in which said generally pyramidal protuberances on the rollers of said fines-separating roller screen are frusto-pyramidal in shape.

15. A roller screen comprising:
a roller bed defined by parallel, side-by-side rollers separated from one another by a gap, each of said rollers having a uniform pattern of tapered, crisscrossing spiral grooves forming frusto-pyramidal protuberances; and means for rotating said rollers in the same direction of rotation.

16. A roller screen comprising:
a roller bed defined by parallel, side-by-side rollers separated by a gap from one another, each of said rollers having a center rotary axis and a uniform pattern of like-tapered protuberances which are radially equidistant from said rotary axis and have a frustum shape arranged with the base of the frustum at the minimum outside diameter of the roller and the other end of the frustum at the maximum outside diameter of the roller, said gap being located between said maximum outside diameters of adjacent rollers; and a means for rotating said rollers in the same direction of rotation.