Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/12—Apparatus having only parallel elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/42—Drive mechanisms, regulating or controlling devices, or balancing devices, specially adapted for screens
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/46—Constructional details of screens in general; Cleaning or heating of screens
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B13/00—Grading or sorting solid materials by dry methods, not otherwise provided for; Sorting articles otherwise than by indirectly controlled devices
  • B07B13/14—Details or accessories
  • B07B13/16—Feed or discharge arrangements
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
  • D21B1/00—Fibrous raw materials or their mechanical treatment
  • D21B1/02—Pretreatment of the raw materials by chemical or physical means
  • D21B1/023—Cleaning wood chips or other raw materials

Definitions

• the present invention relates to improvements in method and apparatus for screening particulate material such as wood chips.
• the invention pertains to a screening deck defining a screening area, wherein the deck is formed of a series of parallel bars with spaces therebetween, with the bars uniquely shaped, and, in one form, further engaging the particulate material in a direction opposite its movement, to increase its retention time and orient the material in the direction of the slots between the bars.
• the chipping mechanism produces various types of chips which vary considerably in size and shape.
• the chips supplied For the digesting process in the production of wood pulp, it is desirable that the chips supplied have a uniform thickness in order to achieve optimum yield and quality, that is, to obtain a pulp which contains a low percentage of undigested or overtreated fibers. Under preferred conditions of digesting, the pulping liquid penetrates into chips uniformly. If chips are provided which have too great a thickness, the digester will produce chips with an untreated core of undigested fibers. If chips are provided which are too thin, the digester will produce chips that are overcooked and of low quality. To insure proper digestion of the chips in the production of pulp, the supply should not contain any chips having an excessive thickness which will give rise to lack of adequate penetration during the digestion process.
• Apparatus has been provided heretofore for screening chips, and customarily these screening devices are of the disk screen type which have a plurality of generally- circular disks mounted on parallel, rotating shafts.
• the disks are mounted coaxially on each shaft and spaced for each other, and the disks interleave with the disks of adjacent shafts to form screening gaps between the disks of one shaft and the disks of adjacent shafts.
• One drawback associated with such disk screening apparatus is the fact that the effective or open screen area in a given screen dimension is necessarily limited, and the number of shafts provided with the disks will, therefore, be large in an industrial installation requiring substantial production capacity. Also, by reason of precision requirements of the gaps between the disks, the manufacturing costs are relatively high.
• the disk screening apparatus heretofore used is also highly sensitive to sand, stones and scrap, and therefore subject to wear. To reduce such wear, it has been common to plate the disk with hard chromium, further increasing cost.
• a further object of the invention is to provide a bed type screening apparatus having a large screening area and requiring less operating power than devices heretofore available.
• a further object of the invention is to provide an improved screening apparatus which is subject to less clogging and better transportation of the chips over a screening bed having features which orient the chips and provide more consistency in the screening operation, while limiting pinching, wedging or other chip quality degrading effects.
• a screening deck or bed which extends substantially horizontally, providing a large screening area. While the inventive features are susceptible of uses in other industries, for the purposes of description herein, the structure and operation will be described in connection with the screening of wood chips for which the features of the present invention are particularly well adapted.
• Chips are distributed across a receiving end of the screening deck which is formed by a series of parallel bars.
• both sets of bars are oscillated for effecting screening and moving the chips in a forward direction.
• the bars having a uniquely shaped upper edge with a central planar portion and laterally tapering sides sloping away from the planar top whereby the screening function is
• an arrangement is made wherein the advancing chips are engaged by a plurality of teeth moving in a direction opposite the progressive movement of the chips, thereby increasing the retention time of the material and orienting the material in a longitudinal direction.
• Figure 1 is a side elevational view shown somewhat in diagrammatic form of a screening device constructed in accordance with the principles of the present invention
• Figure 2 is a fragmentary plan view of driving mechanism for oscillating bars of the screening device
• Figure 3 is another side elevational view shown somewhat in schematic form, similar to Figure 1 but illustrating the arrangement of drive mechanism;
• FIGS 4 and 5 are schematic elevational illustrations taken along the screening bed showing different positions of the screening bars during screening operation.
• Figure 6 is a top plan view showing the screening bed.
• the mechanism includes a horizontal upwardly facing screening bed 10 having a receiving end 11 where the wood chips are received and a discharge end 12 where the reject material is discharged.
• the wood chips to be screened are received at the receiving end 11 and move along the bed from left to right as shown in Figure 1, with the chips of acceptable width passing between screening bars and the chips which are too large and other reject material which is too large continuing to move along the bed to be discharged at the discharge end 12 of the screening apparatus.
• the screen is for separating oversize from acceptable material.
• the screen can be used to remove undersized material.
• the material falling through the screen would be rejects and that discharged at discharge end 12 would be the acceptable material.
• Further use herein of the terms reject and accepts or variations thereof are for differentiation in description and are not meant as limitations on the use of the present invention.
• the screening bed is formed by a plurality of parallel bars 13 and 14 such as illustrated in Figure 6, with the bars having uniformly wide spaces therebetween.
• the spaces are of predetermined width such that chips which are too large and which would be too thick to be satisfactorily penetrated by the liquor in a digester are not accepted but will stay on top of the screening bed to move off to the discharge end 12.
• alternate screening bars are joined in sets, forming two grids which are oscillated by being moved both up and down and forward and back in a manner to advance the chips.
• the grids of bars each are mounted on movable frames which are carried on rotors having the movable frame eccentrically connected tnereto.
• the movable frames are connected to similar eccentric supports mounted on rotors.
• Figures 1, 2, and 3 best illustrate the mounting of the grid of bars 14, wherein a frame 15 is carried on rotors 18 and 19 on the inlet end, eccentrically connected to the rotors at supports 20 and 21 respectively. At the discharge end of the screening bed, the frame 15 is connected to eccentric supports 22 and 23 on rotors 30 and 31.
• the frame of bars 13 is similarly connected by eccentrically mounted supports on rotors at both the inlet and outlet ends.
• the bars will oscillate alternately up and down and alternately forward and back.
• a main prime mover driver 25 For driving the movable bars in oscillation, a main prime mover driver 25 is provided. This drives a chain 40 driving a sprocket 32.
• the sprocket contains additional sprockets driving chains or belts 26 and 27 which are connected to drive the rotors 19 and 31. These rotors carry sprockets which, through chains or belts 28 and 29, drive the upper rotors 18 and 30.
• the cycle will be presumed to start from a position wherein the grids are at substantially equal height as illustrated in Figure 4, wherein the tops of all bars define a substantially horizontal plan. From this position, one grid moves upwardly and the other grid moves downwardly.
• Figure 5 depicts the grids with the bars 14 being at the upper most position in the operating cycle, and the bars 13 being at the lower most position in the operating cycle.
• the combined movement of the bars up and down and forward and rearward conveys the oversize chips from the inlet end to the discharge end, and also aids in turning the chips so that the thickness dimension is presented to the space between bars for proper screening.
• a feature of the present invention is the unique shape of the upper surface of the bars. This shape aids in material agitation and in material orientation, and promotes unclogging of the openings while inhibiting initial clogging of the openings between the bars.
• the bars have an upper planar surface 13a, 14a which is flat and parallel to the horizontal bed.
• the horizontal portion 13a, 14a are tapered portions which provide planar surfaces 13b, 14b and 13c, 14c facing generally upwardly but sloping away from the top surface. These surfaces have been found to tend to prevent clogging of the gaps between the bars and to aid in material agitation.
• top surfaces 13a, 14a are about one-eighth inch
• side surfaces 13b, 14b and 13d, 14c are disposed at a forty-five degree angle from the top surface, and extend approximately one-quarter inch.
• distributing auger 34 is mounted for rotation and is driven by a chain 33.
• Such augers are conventional devices for distributing material along their length and will not be described in greater detail herein.
• a further feature of the present invention is the provision of independent means engaging the wood chips in a direction counter to their flow, to increase retention time on the bed and to orient the chips in a longitudinal direction.
• the fingers are carried on a rotor 35 which is driven by a drive chain 36 in rotation in a clockwise direction as shown in Figure 1 .
• the fingers 37 pass through the chips against the direction of movement of the chips along the grids. This increases the retention time of the chips on the screen and tends to orient the material in the longitudinal direction, improving the screening operation and improving the efficiency and uniformity by properly aligning the chips for screening.
• shafts with fingers are used. In some instances, one may be adequate and in others more than two may be desirable.
• Shafts with evening fingers positioned downstream from the inlet may be provided with fingers spaced more closely than shafts closer to the inlet end. The more closely spaced fingers will properly orient more chips, and, since the volume of chips on the screen downstream from the inlet is reduced from the volume at the inlet end, the closely spaced fingers will not overly retard chip advancement.
• wood chips are distributed laterally along the receiving or head end 11 of the screening deck 10.
• the wood chips move along the screening bed longitudinally toward the discharge end 12, and those which are sufficiently thin will pass through the spaces between the bars.
• the bars supported on the movable grids will oscillate up and down in the manner shown in Figures 4 and 5.
• fingers 37 carried on. rotor 35 are moved against the direction of chip movement. Acceptable chips of the maximum tolerable width and narrower will pass through the spaces between the bars, and other unacceptable chips will continue on down the screening deck toward the discharge end 12.
• each bar should be only slightly less than the bar height dimension. Thus, if bars two inches high are used, the distance from the upper most elevation of bar movement to the lower most elevation should be only slightly less than two inches. Some vertical overlap should be maintained so that proper proper screen opening size is maintained between adjacent bars, and so that chip wedging does not occur. However, the overlap region should be minimal when the grids are at the extreme positions shown in Figure 5. This opens up the screen below each screen opening, again minimizing chip wedging and allowing "caught" chips to pass through without clogging the screen.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Combined Means For Separation Of Solids (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=24525039

Family Applications (1)

Country Status (6)

Cited By (4)

Citations (3)

• 1991
  • 1991-12-11 NZ NZ240941A patent/NZ240941A/en unknown
  • 1991-12-13 WO PCT/US1991/009353 patent/WO1992011408A1/en active Application Filing
  • 1991-12-13 AU AU91560/91A patent/AU9156091A/en not_active Abandoned
  • 1991-12-18 PT PT99846A patent/PT99846B/pt not_active IP Right Cessation
  • 1991-12-18 ZA ZA919929A patent/ZA919929B/xx unknown
  • 1991-12-18 MX MX9102661A patent/MX9102661A/es unknown

Patent Citations (3)

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