US2143497A - Method of and apparatus for cleaning wood chips and the like - Google Patents

Description

Jan. 10,1939. s R HMBERG 2,143,497

METHOD OF AND APPARATUS FOR CLEANING WOOD CHIPS AND THE LIKE Filed Nov. 19, 19:54 2 Sheets-Sheet;

Jail. 10, 1939.

S. RAHMBERG METHOD OF AND APPARATUS FOR CLEANING WOOD CHIPS AND THE LIKE Filed Nov. 19, 1954 2 Sheets-Sheet 2 Patented Jan. 10, 1939 METHOD OF AND APPARATUS FOR CLEAN- OFFICE ING WOOD CHIPS AND THE Sven Bahmberg, Wallvik, Sweden; Axel Bostrom Martin and istrators of the deceased Application November 19 8Claims.

customarily prepared for treatment in digesters for the making of similar materials.

I Thepresence of sawdust in digesters is highly objectionable, as is also the presence of specks of dirt, bark,- or other impurities in pulp which is to be made into high grade papers. Hence, chips should be thoroughly cleaned before entering the digester. It is customaryjin preparing wood for digesters, to out the wood by 'means of a chipper intochips which average about inch square. After the wood has been run through the chipp p r pulp, and for other per, the chips are often run through a crusher so as to break up over-size chips or splinters. According to common practice, the chips are run into a cylindrical screen drum or shaking screens either directly from the chipper or from the crusher. The ordinary type of screen drum is rotated on an inclined axis, the upper portion of it being provided with holes about inch in diameter for the escape of sawdust and other undesirablematter; It is found that holes of this size permit the escape of small chip fragments and splinters which are valuable as material for pulp, but which are lost with the sawdust. Furthermore, the ordinary screens now in use fail to eflect a complete separation of dirt and sawdust from the chips, especially if the chips are moist or have adhering thereto bits of 1 bark and the like which are rich in rosin. Par- 1 ticular trouble is often experienced with the thin black bark surrounding the knotsin the wood, this bark breaking up into fine pieces in the chipper and tending to adhere to the chips. Such fragments cause specks in the paper ultimately made from the pulp, which are objectionable particularly in the better grades of paper. 1 v

According to the present invention, the chips are subject to a treatment which not only eflectively cleans the chips but also results in a saving of substantially all of the small chips and splinters which are customarily lost through the chip screens'now in common use. According to the invention, the chips are tumbled in a rotating screen drum havingopenings about $5; inch in diameter.

such as air, steam, or an equivalent, are projected from near the axis-of the screen-toward the inner surface thereof.- These fluid jets, which are preferably of high velocity, impinge on the tumbling chips and dislodge therefrom all impurities, including dirt, sawdust, bits of bark,

A numberof fineblast jets of fluid,

Bahmberg executors and adminestate of, said Sven Rahmberg,

1934, Serial No. 753,691 Sweden December 11, 1933 and the like. Suitable means is employed to promote and accelerate the flow of cleaning fluid through the meshes or holes of the screen so that all the loose particles of sawdust or foreign matter are at once expelledfrom the interior of the screen drum. If desired, apparatus may be provided for separating the chips of proper size not only from sawdust and dirt but also from large splinters of wood which may come from the chipper.

For a more complete understanding of the invention, reference may be had to the following description of an embodiment thereof and to the drawings, of which- Figure 1 is a longitudinal sectional view of apparatus embodying the invention.

Figure 2 is a section on the 1ine 2-2 of Figure 1.

Figure 3 is a diagrammatic plan view of an installation of apparatus embodying the invention.

Figure 4 is a longitudinal sectional view of a screen drum for separating large splinters from the chips in conjunction with the cleansing thereof.

Figure 5 is a section on ure 4. a

The invention may be embodied in a hollow screen drum Ill. The screen may be of woven wire or of perforated sheet metal, the openings in either event being preferably about y inchin diameter and as closely spaced as is practicable. As shown, the screen drum may be in the form of an approximate cylinder, preferably increasing somewhat in diameter from the supply end to the discharge end; The screen drum i0 is mounted for rotation on a suitable shaft II, this shaft being journaled in bearings l2 and I 3 carried by 'a frame ii. The portion of the shaft II, which extends through the bearing l2 and through the entire length of the screen drum in, is preferably hollow, the hollow portion terminating in a reduced portion l8 which is journaled in the bearing l3. Projecting from the hollow shaft II at a suitably large number of points are blast nozzles 20. These nozzles may for the the line 5-5 of Figblast nozzles adjacent to the ends of the screen drum I 0 are preferably inclined toward the 'middle of the screen as at 2| and 22. All of these blast nozzles communicate with the hollow interior of the shaft ll, so that fluid supplied to the shaft ll under pressure is projected through the various nozzles toward the inner surface of the screen. The screen may have cylindrical extensions and 25 of sheet metal at its ends. On the interior surface of the,screen Hi there may be any convenient number of helical fins or ribs 21 which extend to impart axial movement to the chips which are tumbling within the rotating screen drum. The cylindrical extension 25, which, as indicated in Figure 1, is at the supply end of the screen, may beprovided with similar fins 28. Chips to be cleaned may be introduced into the extension 25 of the screen drum as by a chute which leads through a stationaryend plate 3|. At the opposite or dis-, charge end of the screen drum is an end plate 32 having a discharge opening 33 therein. This opening may be of any convenient size, shape and location, such, for example, as illustrated in Figure 2.

The screen is located within a casing which may be made approximately air-tight. This casing may be of suitable size and construction as desired. As shown in Figure l, the casing is approximately barrel-shaped, having a pair of frusto- conical portions 35 and 36 which are connected by a circumferential channel member 31. The circumferential channel in the member 31 communicates with an outlet or suction vent through which the cleaning fluid which enters the screen through the nozzles 20, 2| and 22 may be sucked from the interior of the casing. In the structure illustrated in Figure 1, the imperforate extensions 25 and 25 of the rotating screen drum project from the ends of the casing portions 35 and 38 and hence act as portions of the casing, together with the end plates 3| and 32. Suf'flcient clearances are preferably left between the stationary heads 3|, 32 and the moving parts 25, 26, and also between the stationary channel member 31 and the adjacent moving portions of the drum to ensure free rotation of the drum. The casing is thus nearly air-tight except for the supply chute 30, the discharge opening 83, the nozzles 20, 2| and 22, and the suction vent 40 so that a strong suction can bemaintained through the meshes or holes of the screen ill. As indicated in Figure 3, the screen drum ill may be rotated by means of a suitable power-transmission device such as a gear wheel which is mounted on the reduced end portion l6 of the shaft ii and which meshes with a pinion 5| mounted on the shaft of a motor 52. Air or other cleaning fluid may be supplied to the hollow shaft H by means of a connecting pipe leading from a suitable air pump 56 driven by a motor 51. The suction vent 40 may be suitably connected to a pump Bil which may be driven by a motor 6|. Any other desired driving means may be employed for rotating the screen and for operating either or both of the pumps.

In operating the mechanism, the screen drum may be rotated at any suitable speed, depending on its diameter, the speed of rotation of a 23-foot screen drum being preferably from 10 to 15 R. P. M. Wood chips to through the chute 30 directly from the chipper, or from a conveyor, or from any other suitable source. The chips enter the end compartment adjacent to the smaller, end of the screen drum and are moved along axially by the helical flns 28 as the screen drum is revolved. These flns also assist'in tumbling the chips thoroughly within the screen as they progress from the supp y end thereof to the discharge end. During their progress through the screen drum, tumbling chips are subiected to blasts-of cleaning fluid, such'as cleaning operation.

be cleaned are supplied air, which is pumped into the hollow shaft II and is discharged through the nozzles 20, 2| and 22, preferably at high pressure. These nozzles are preferably of comparatively small diameter so that, although the cleaning fluid is projected at high velocity into the interior of the screen, the total volume of fluid thus entering the screen is not excessive. The flow of cleaning fluid outwardly through the perforations of the screen is expedited by suction maintained on the vent 40 as by a suction pump 50. As indicated on the drawings, the cross sectional area of the vent 40 is large in comparison with that of the individual nozzles 2|! so that the air or other fluid discharged at high velocity but in relatively small volume through the nozzles 25 is readily carried off by the vent 40. This pump is preferably of such capacity as to be capable .of maintaining the pressure in the space between the screen i0 and the casing members 35 and 36 somewhat below atmospheric pressure, if desired, so that there may be a slight inflow of air through the chip supply and discharge openings in the casing. The skin friction of the rotating screen causes a rotary flow of the air within the casing in the direction of rotation of the screen. itself, this air also tending to flow toward the channel 31 and thence out through the vent 40, carrying with it the sawdust and dirt particles which have been dislodged from the chips by the blasts of air or other cleaning fluid from the nozzles. The inclination of the nozzles 2| and 22 toward the middle of the screen tends to drive the dirt-laden air within the screen drum toward the middle of the screen to pass through the screen opposite the channel 31 and 3 the suction vent 40, and also tends to prevent flow of air toward the chip supply and discharge openings in the ends of the casing. The chips, after progressing from the supply end of the screen to the discharge end, fall through the discharge opening 33 and are caught by a receptacle or conveyor (not shown).

In the chipping process as ordinarily practiced, the pulp-wood logs are fed to the chipper at an angle so that the knives of the chipper strike obliquely across the quently happens that a log which is nearly all cut will turn so that the chipper blades cut it lengthwise, this resulting in large slivers which are undesirable for the digester. According to the present invention, such large slivers can be separated from the chips simultaneously with the To this end, I may provide apparatus such as is illustrated in Figures 4 and 5. This embodiment of the invention may include a revoluble drum 10, similar to the drum 35, with an-extension 1| at the supply end rotating against an end plate 12 and having oblique ribs 13 to feed the chips received through the chute 30. A suction channel 11 surrounds the grain of the wood. It fremid-periphery of the drum 10 where the halves m of the drum are separated, this channel leading to suction outlet 18 which preferably leads to a suitable pump as illustrated in Figure 3. If desired, suitable flexible strips 19 may be carried by the channel 11 to bear against the adjacent portions of the rotating drum 10 so as'to close the clearance between these parts.

Within the drum 10 and rotatable therewith, are a pair of coaxial screens and 8|, the outer screen 8|! having relatively small openings therein, the inner screen 8| having larger openings. For example, the screen 80 may have openings varying from V5 inch at the supply end to about inch at the opposite end thereof. The inner screen may have openings varying from about inch at the supply end to 1 or 2 inches at the a other end. These aperture sizes and those here inaft-er given are by way of example only and not by way of limitation. The screens 80 and ill preferably diverge somewhat in diameter toward the discharge end. Beyond the discharge end of the drum H1 is an imperforate extension 83 which may be substantially a continuation of the screen member fill. The extension t3 revolves with the drum 1t and terminates in an open discharge 7"1. The inner screen 3! extends through the interior of the extension 33 and projects a substantial distance beyond the discharge end thereof, this portion of the screen 85 having large perforations or meshes of the order of 1 or 2 inches. To promote axial movement by the chips in the drum, helical ribs 35 may be mounted on the inner surface of the screen dd and drum extension dt as indicated.

Chipped wood is received by this apparatus direct from the chipper and is at once subjected to the cleaning action of high-velocity jets of fluid such as air, steam or an equivalent. lihe particles of sawdust and dirt dislodged by the jets are immediately sucked through the meshes of the screen and are discharged through the outlet 18. The chips and slivers of proper size pass through the meshes or perforations of the screen iii as they travel toward the discharge end. The oversize fragments remain within the screen 8! until discharged through its open end beyond a partition wall conventionally indicated at 81. The cleaned chips of proper size are discharged from the end of theextension 83 on the rear side of the near side of the partition wall it? and are then ready for delivery to a digest-er.

It is evident that various modifications and changes may be made in the embodiment of the invention herein shown and described without departing from the spirit or scope thereof as defined in the following claims.

Iclaim:

1. A method of cleaning wood chips and the like, which comprises tumbling the chips in a rotating hollow screen drum, projecting fluid jets radially from near the axis of the drum toward the inner surface thereof, and projecting fluid jets from near the axis at points adjacent to the ends of the screen obliquely toward the middle of the drum.

2. A method of cleaning wood chips andthe like, which comprisestumbling the chips in a rotating hollow screen drum, projecting fluid jets from near the axis of the screen drum toward the inner surface thereof, including jets adjacent to the ends of the screen and inclined toward the middle thereof, and maintaining a lower than atmospheric pressure at the outer surface of the screen.

3. Amethod of cleaning wood chips and the like, which comprises continuously feeding chips into one end of a hollow screen drum, continu ously rotating the drum, permitting chips to escape from the opposite end of the drum, and

projecting fluid jets from near the axis of the drum toward the inner surface thereof, including jets adjacent to the ends of the screen inclined,

nozzles being adjacent to the ends of the screen and being inclined toward the middle thereof.

5. Apparatus for cleaning wood chips or the like, comprising an elongated approximately cylindrical screen rotatable on a horizontal axis, said screen having openings therethrough of sufficient size for the passage of standard chips, means for introducing chipped wood into one end of said screen, an outer screen coaxially surrounding a portion of the first said screen and.

extending for a portion of the length thereof from the supply end, said outer screen having relatively small openings, means for projecting jets of fluid radially from near the axis of said outer screen, and means for maintaining suction at the outer surface of said outer screen.

6. A method of cleaning wood chips, which comprises tumbling the chips in a rotating screen drum, subjecting the tumbling chips to a series of jets of gaseous fiuld at sufiiciently high velocity to dislodge from the chips particles of matter adherent thereto, and maintaining a lower than atmospheric pressure surrounding the sides of the drum, whereby discharge of said gaseous fluid through the ends of the drum is avoided.

7. Apparatus for cleaning wood chips, comprising a rotatable screen drum having openings in the sides thereof approximately ,4; inch in diameter, a casing enclosing said drum and having apertures'for the admission of chips into one end of the drum and the discharge of chips from the other end of the drum, means within the drum for projecting a series of fluid jets toward the inner surface of the screen, and means for maintaining in said casing a lower than atmospheric pressure, whereby discharge of fluid from said jets through said apertures is avoided.

, 8. Apparatus for cleaning wood chips or the like, which comprises a barrel-shaped casing having end-openings for supply and discharge of chips and a suction vent midway between the ends, a frusto-conical hollow screen drum tapering in diameter from the discharge and of the drum to the supply end and rotatable on its aids, helical fins secured to the inner face of the screen to rotate therewith whereby to assist the chips in their advance toward the discharge end-opening, and means for projecting jets of fluid radially from near said axis toward the inner surface of the screen.

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