US 2710635 A
Description (OCR text may contain errors)
June 14, 1955 R. R. ALEXANDER 2,710,635
WOOD CHIPPER Filed Feb. 20, 1953 2 Sheets-Sheet 1 INVENTOR.
June 14, 1955 R. R. ALEXANDER 2,710,635
WOOD CHIPPER r Filed Feb. 20, 1953 2 Sheets-Sheet 2 M figa INV NTOR.
" 2 5 0 lax 2,710,635 Patented June 1 2, 1955 woou cnnrnu Ronald R. Alexander, Nashua, N. EL, assignor to Improved Machinery, Inc., Nashua, N. EL, a corporation of Maine Application February 2% 1953, Serial No. 337,992
4 Claims. (Cl. 144-462) This invention relates to wood chippers and more particularly to a novel chipper of the drum type adapted for cutting wood chips from pulpwood or other stock for use in, for example, paper manufacture.
Wood chippers of the drum type have a number of advantages over disk chippers, the primary ones being uniformity of knife velocity, and substantially smaller size and weight. The latter is particularly important in portable chippers, which are being used more and more due to the economies inherent in the handling and transporting of wood in chip rather than log or bolt form.
Heretofore, however, drum chippers have suffered from a number of defects, the most important of which was their inability to produce high quality chips of uniform fiber length such as are essential in the manufacture of paper pulp, and this was particularly true when operating drum chippers at high speed. Hence, such drum chippers have found little use in the pulp manufacturing industry, in spite of their known inherent advantages of constant knife speed, as well as light weight and small size.
I have found that the inability of heretofore known 5 chippers to produce suitable chips of uniform fiber length is due to a number of interrelated factors. For example, in conventional chippers, if the rotating knives are to take a uniform slice from the log to be chipped, the log must be held stationary while a knife is cutting, and it must be advanced for a uniform distance between each cut. That is, at each cut the log is drawn into the chipper by the knives and against the drum face, where it remains for the duration of the out, only moving as the knife leaves the piece. short distance from a position of rest and then stopped at each cut. The inertia of the log may be large, so that the amount of power available for stopping and starting it at each cut limits the knife striking frequency and the knife velocity to relatively low values if the essential uni- :5
form chips are to be produced. Surprisingly enough, though, I have found that, in a drum chipper, high knife velocities and striking frequencies produce substantially superior chips for pulp manufacturing purposes, since at high knife velocities of the order of 4000 F. P. M. (feet per minute) and higher, and striking frequencies of 40 per second and higher, the knives apparently cut more cleanly and tend to produce open grained ends to the chips, which are more absorptive and, hence, more easily broken down in chemical pulp manufacturing processes.
Accordingly, it has been an object of my invention to provide a self-feeding wood chipper of the drum type in which both high knife velocity and knife striking frequency may be attained to produce wood chips suitable for pulp manufacture. I have accomplished this result while at the same time producing chips of uniform fiber length, even from heavy large diameter logs, by advancing the log or other material to be chipped to the knives at a uniform rate rather than intermittently, thus entirely avoiding the stopping and starting of the log.
It is a particular feature of my invention that I provide on the drum between the knives a feed control means hav- Thus, the entire log must be advanced for a I ing a surface configuration which stabilizes the log and holds it firmly in position during its continuous steady advance, Whether with or without a power infeed conveyor, so that the succeeding knife cuts and resulting chip fiber lengths are uniform.
It is a further object of my invention to provide a transverse chip sizing means adapted to split the cut wood into chips, uniform in width, further improving cooking characteristics in the pulping process, since in this manner a uniform depth of side penetration of cooking liquors has proven of benefit. This method of transverse chip sizing does not necessitate employment of serrated edge cutting knives with their consequent problems of log instability and lowered production rate, and it has been shown that a chip so split instead of cut exposes the fiber bundles more efficiently for purposes of side penetration than a cut surface.
Still further objects and features of my invention will be apparent from the following description of a preferred embodiment thereof when read in connection with the drawings, in which:
Fig. 1 is a side elevational view, partly in cross section and broken away, of the drum type wood chipper of my invention;
Fig. 2 is an end elevational view, partly in cross-section, of the chipper of Fig. 1;
Fig. 3 is a mathematical illustration of the generation of an ideal surface for the feed control means;
Fig. 4 is a diagrammatic illustration of the wood chipper of Fig. 1 showing the generation of a practical surface for the feed control means; and
Figs. 5a and 5b are enlarged views showing the knife and chip sizing means of my invention in plan view and side cross-sectional view respectively.
Referring to Figs. 1, 2 and 5, the novel drum type wood chipper of my invention includes a base with up standing side portions 12 having mounted thereon m-ain bearings 14 adapted rotatably to support a main shaft 16 driven by any suitable power means (not shown) such as a diesel or electric motor. A curved base portion 18 is provided between said side portions 12. A generally cylindrical drum 2%, having chip collecting recesses 22' extending lengthwise of the periphery of said drum is mounted fixedly on said shaft 16 so that it may be rotated by said shaft about a central axis, end disks 24 preferably being provided on said drum, said drum and said end disks fitting relatively closely with said curved base portion 18.
One or more peripheral knives 25 (herein shown as four) are mounted on said drum 20 by suitable machine bolts 29 adapted to fit into suitably tapped holes in said drum, said knives extending generally lengthwise along the peripheral face of said drum and preferably parallel to the axis thereof, although knives having a helicoidal cutting edge may be used if desired. The knives 25 have their cutting edges 26 facing forwardly with respect to their direction of rotation and adjacent a leading face 27 of said knives, the trailing face 28 thereof being at a shorter radial distance from the axis of drum 20 than the cutting edge 26, so that the cutting edges of said knives describe a cylindrical path when shaft 16 with drum- 20 is rotated, the portion of the trailing face 23 adjacent the cuttting edge 26 being at a slight angle inwardly from a tangent to the cylindrical path of said cutting edges, such angle commonly being of the order of 5 degrees.
The leading face 27 of each of said knives 25 is disposed at shear angle of say 40 to the tangent of the cylinder of rotation of the knife cutting edge 26, and has mounted thereon a chip sizing member 30, said member being pressed firmly along the leading face 27 of said knife spaced inwardly from thecutting edge 26 thereof,
the bolts 29 serving to hold said members 30 and knives 25 together. The chip sizing members 39, as best shown in Figs. a and 5b, comprise members extending generally lengthwise of the knives 25, and spaced at a distance from the cutting edge of said knives. The fiat face of each of said members is mounted against a knife leading face 27. The working face of said chip sizing members has therein extending radially of drum 2!) a plurality of grooves 32 with lands 34 therebetween, the bottom of said grooves being at an obtuse angle, say between l00 and 150 degrees, to the leading face 27 of knives 25.
A fixed bed knife 40 is mounted along the forward edge of curved base portion 18 to cooperate with the cutting edges 26 of knives to sever the chips at the bottom of a log 16, said log being supported and guided by a bed plate 42 mounted forward of bed knife and between base side portions 12.
In order to advance a log 10 endwise into engagement with said knives 25, I have provided a chain conveyor supported by sprockets 52 on shaft 54 mounted in suitable bearings 55 on said base portions 12. The shaft 54 is driven by gearbox 56 through a sprocket 57 and chain 53 from a sprocket 59 on main drive shaft 16, the speed of said chain conveyor being in timed relation to the automatic advance of log 10 by knives 25 as hereinafter more fully explained.
Preferably and as shown, a log it] is presented to the drum 20 with its rotating knives 25 along a peripheral lower quadrantal portion only of the drum in which the knives 25 are effective to advance the log by reason of the forward component of the motion of said knives in said portion when the drum- 20 is rotated, for example, with a drum mounted to rotate about a horizontal axis and with a log 10 presented with its axis horizontal, a lower forward quadrant only of the drum is used for chipping purposes. If other than horizontal axes are used, the lower forward quadrant of the drum may be similarly defined by relation to the common plane of such axes. For uniformity of chipping it is further desirable that somewhat less than such quadrant be used as illustrated in Fig. 1, wherein the angle of the drum subtended by the log or other material to be chipped as a practical matter should be no greater than 80 degrees, preferably about 60 or less. plate 42 and bed knife 49 are raised somewhat above the horizontal tangent to the bottom of the cylindrical knife path, and a guard member 46 is mounted on upstanding base members 12 across the face of drum 2%, the lower surface of said guard member 46 being somewhat below the horizontal diameter of the cylindrical path of said knife means.
In order to provide for the essential uniform and continuous advance of the log so that the requisite high knife frequencies and velocities may be employed accord- :1
ing to my invention, I have provided between a knife cutting edge 26 and a next succeeding leading face 27 of said knife means a feed control means externally bounded by a curved surface which is spaced gradually and progressively inwardly of the cylindrical path defined by the cutting edges of knives 25. Thus such bounding surface extends from a cutting edge 26 at a gradually decreasing radial distance from the central axis of drum 20 to a next succeeding leading face 27 of a knife 25, the inward spacing of said surface at the leading face 27 determining the maximum depth of cut of each of said knives, it being understood that the depth of cut of each of said knives should be substantially equal. Such surface need not extend continuously except as is necessary to provide a firmendwise support for the log 10 or other material as it is advanced by the revolving motion of knives 25. In fact, as in the usual drum chipper, an opening into each of the chip collecting recesses 22 must be left immediately in advance of a knife 25 to provide for the collection of the severed chips until they are discharged To that end, the base lit) by centrifugal force when the particular chip recess 22 passes beyond the cut ed surface portion 2.3 of the base.
The ideal guiding surface may be best defined mathematically from Fig. 3 wherein a quadrant corresponding to that of a four knife chipper is shown. The radius about central axis 0 of the cylindrical path defined by the knife cutting edges is indicated by R, whereas the radius of the ideal spiral guiding surface at any point Q is defined by r, 0 being the angle of advance of said radius r from a leading face of a knife on the X axis of Fig. 3. Assuming N knives, and that each knife is to take a cut of depth equal to D, the distance S between knife radius R and guide surface radius r at any point may be expressed in polar coordinates as:
This formula is a general case by which the configuration of the feed control means of the novel chipper of my invention may be accurately found for any given case.
In practice, however, the generation of such ideal surface is both difficult and expensive, and I have found that with a chipper employing at least three and preferab'ty four knives, such an ideal spiral guiding surface may be approximated by a cylindrical surface the axis of which is parallel to but offset from the central axis of drum 20 and the radius of which is less than that of the path of knife cutting edges 26, as is best illustrated in Fig. 4. Such a surface may be defined by first determining a depth of cut P which will give a desired average length of fiber, which average length of fiber will be substantially equal to the value D of an ideal surface. Preferably, this is done by assuming an average center of a log, say of one-haif the radius R, at which point the fiber length of a chip may be assumed as equal to D and in such case the depth of cut P will be equal to D cos 0, a being 30. The are of knife periphery between the leading edge of one knife and the leading edge of a next succeeding knife is then divided into a number of equal increments of are by means of radii from the center of the drum. By measuring a cumulative distance inwardly from the periphery of the knife cutting edge along each succeeding radius a distance equal to F divided by the number of segments, a series of points P will be defined. The center a of an are which best approximates the curve through points P may then be determined by defining such are as one passing through any three points P, preferably the points at each end of the quadrant and a point P midway along the quadrant. The are so determined will have a radius C, less than that of the path of the knife leading edge, and center :1 thereof will be displaced from the axis of the drum generally in the direction toward said first knife trailing face 28. A cylindrical surface as above defined will provide chips in which the fiber lengths are substantially uniform within the narrow limits acceptable in pulp manufacturing processes.
Feed control members 60, with their outer surfaces formed either as an ideal spiral surface or as a practical cylindrical surface, are bolted to drum 20 between the knives 25 by suit'abie machine bolts 29 and 52. Bolts 29 serve to retain the leading edge of said members 60 adjacent the trailing face 28 of a knife 25, as well as to retain said knife 25 and its adjacent chip sizing member 30 as hereinbefore described. Bolts 62 retain the trailing edges of members 60 adjacent the leading side of chip collecting recesses 22, thus leaving said recesses open for a sufficient distance in advance of knives 25 to retain the chips cut during a cut across the face of log 10. Both leading and trailing bolts 29 and 62 are recessed below the surface of said feed control members 60, and the leading bolt 29 may be provided with plug 64 if desired.
As a specific example of a rotary chipper of my inventiou, assuming a 30" diameter knife path, four knives (as in Fig. 4), a drum rotational speed V of 1100 R. P. M., and a fiber length of A3" at each quarter revolution. Such dimensions will result in automatic log advance at about 230 ft./rnin. The knife striking frequency in such specific chipper will be about 73/sec., and the knife speed about 8600 lineal ft./ min. The fiber length of the chips produced by such machine in general varies no more than about &
The speed v of the conveyor 50 under such circumstances will be equal to that of log advance or about 230 ft./min., substantially as determined by the formula when D N V (feet per minute). Thus a 6" diameter conveyor drive sprocket 52 should be rotated at a speed of about 144 R. P. M.
With such a chipper in operation, when the log is advanced far enough by conveyor 50 to be engaged by the knives 25, they act to pull the end of the log against the feed control members 60 which cooperate with said knives to continuously and uniformly advance the log to be chipped endwise in the direction of its length by repeatedly chipping the wood along a curved surface in a direction transversely and forwardly of its length until it is entirely reduced to chips. bers 60 simultaneously stabilize the chipping action and limit the maximum extent and rate of infeed by surface contact with log 10 distributed over a major portion of the leading curved infeed end surface of said log. Since the knives cut while the log advances, by this method, a plurality of knives may be used efficiently, such that two or more knives may be cutting in the log at the same time, thus permitting the use of this stabilizing feature termed multi-knife action. The release of knife pull between strikes causes rebounding reflex action. How ever, it has been found that there is a minimum frequency of strike of about 40 strikes per second wherein the same stabilizing influence may be found with but one knife in the log of a time. For the purposes of clean cutting action of the knives, even on thin or light material, the chipping velocity of the knives should be at least 4000 feet per minute. Preferably such strike frequency should be 60 to 100 strikes per second and knife velocity 5,000 to 10,000 lineal feet per minute. I
In cooperation with the normal formation of chfp cards or sheets of a given thickness, the chip sizing members act on the cut card sheet to split it into relatively narrow and uniform widths, the change of direction produced by the angle between the bottom of the grooves 32 and knife leading face 27 serving to press tiiz: cards downwardly over the sharp lands, thus in effect splitting the cards longitudinally thereof.
The chips so formed are held in the chip recesses 22 until such recesses pass beyond the curved base portion 18, whereupon they will be discharged fromsaid recess'.";
by centrifugal force in the usual manner.
Though it is presently preferred that the wood feed be substantially horizontal with the resultant cutting being done in a lower forward drum quadrant, it will be understood that the wood feed may be other than horizontz. (i. e., inclined or even vertical) so long as the relative presentation made to the drum is such that the forward component of knife motion tends to advance the wood to be chipped and aid it's uniform presentation to the knives during chipping.
Thus it will be seen that there is provided a drum chipper which continuously and uniformly advances the material to be chipped to provide high quality chips of uniform fiber length.
1. A wood chipper of the generally cylindrical drum type rotatable about a central axis, including peripheral knife means mounted on said drum and extending gen- The feed control memerally lengthwise thereof, said knife means having an outer forwardly facing cutting edge and a trailing face extending rearwardly therefrom at an angle inwardly from a tangent to the path of said cutting edge, feed control means positioned on said drum between a trailing edge and a next succeeding leading face of said knife means, the external guiding surface of said feed control means being defined by a curved surface extending between said cutting edge of said knife means at a gradually decreasing radial distance from said central axis to said next succeeding leading face of said knife means and controlling the maximum depth of chipping cut, chip collecting means on said drum between said feed control means and said next succeeding leading face of said knife means, and guide means adapted to present pieces of wood to be chipped endwise to said knife means and in contact with said feed control means along a peripheral portion of said drum in which said knife means is effective to advance said material by reason of the forward component of the knife motion in said portion to the end that said material will be continuously and uniformly advanced by the cooperating knife and feed control means.
2. A wood chipper of the generally cylindrical drum type rotatable about a central axis, including a plurality of peripheral knives mounted on said drum and extending generally lengthwise thereof, said knives having outer forwardly-facing cutting edges, respectively, parallel to one another and having trailing faces extending rearwardly therefrom at an angle inwardly from a tangent to the path of said cutting edges, feed control means positioned on said drum between a trailing face and a next succeeding leading face of said knives, the external guiding surface of said feed control means being defined by a curved surface extending between said cutting edge of said knives at a gradually decreasing radial distance from said central axis to said next succeeding leading face of said knives and controlling the maximum depth of chipping cut, chip collecting recesses in said drum between said feed control means and said next succeeding leading face of said knives and extending radially inwardly of the external surface of said feed control means, and guide means adapted to present pieces of wood to be chipped endwise to said knives and in contact with said feed control means along a peripheral portion of said drum in Which said knives are effective to advance said material by reason of the forward component of the knife motion in said portion to the end that said material will be continuously and uniformly advanced by the cooperating knife and feed control means.
3. A wood chipper as claimed in claim 2 in which the curved surface externally bounding said feed control means is defined by a cylindrical surface of radius less than that of the radial distance from said central axis to the cutting edge of said knives and having its axis dis placed from the central axis.
4. A wood chipper as claimed in claim 1 in which said guide means includes a lower bed knife raised with respect to a horizontal tangent to the cylindrical path of said knives and an upper guard means lowered with respect to the horizontal diameter of said cylindrical path to present pieces of wood to be chipped to less than a quadrantal portion of said drum.
References Cited in the file of this patent UNITED STATES PATENTS 233,765 Innis Oct. 26, 1880 747,827 Wolfinger Dec. 22, 1903 829,927 Luther Aug. 28, 1906 1,473,545 Collier Nov. 6, 1923 1,543,919 Habighorst June 30, 1925 2,073,911 Tower Mar. 16. 1937 2,269,352 Bacon Jan. 6, 1942