Pulpwood Chipper

Abstract

Wood chipper has rotating chipper disc and fan wheel spaced from disc. Housings surround disc and fan wheel with passageway from disc to fan wheel housing for chips. Blades on fan wheel engage chips to impel them out of top discharge opening. Total arrangement provides low angles of impact to minimize chip damage.

Description

BACKGROUND OF THE INVENTION

In the making of paper pulp from wood, and particularly in utilizing a chemical pulping process, it is desirable that the wood chips be uniform in size both in width and length as well as in thickness, and that the chips have a minimum content of slivers or pins and sawdustlike particles that will pass, for example, a 3/8-inch screen.

To obtain wood chips of the desired size it is conventional practice to pass logs or wood scraps through a chipper which comprises a massive rotating disc having radially extending knives arranged to cut off the ends of the wood or logs fed into the chipper so that chips of predetermined length are formed. The disc on which the knives are mounted is provided with passageways so that the severed chips may pass to the rear of the disc. For practical reasons chippers are constructed so that the knives impact upon the log or wood as the knives are rotating substantially downwardly. The chips will have high velocity imparted to them by reason of the impact of the knife upon the wood being cut and their trajectory will be in a generally downward direction. Chippers are in two general classes with respect to their discharge, namely bottom discharge and top discharge, the terms being descriptive of the location at which chips are taken from the chipper housing. In the top discharge chipper it is necessary to change the direction of the chips from their general downward direction and cause them to be moved upwardly and through the outlet at the top of the housing. Such change of direction is generally done by placing blades upon the back and periphery of the cutter disc for engaging and propelling the chips. The geometry of prior chippers has been such that the blades have been engaged the chips at a relatively high differential velocity with substantial damage to the chips and production of large amounts of slivers and pins and sawdustlike particles. In addition to their infringement upon the blades, the prior chippers have presented surfaces against which the chips can impact at a high velocity and at a high incidence angle resulting in further breakage of the chips.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a configuration for a top discharge chipper which will minimize damage to chips.

The chipper of the invention comprises a rotary cutter disc with the usual substantially radial knives for cutting chips from a log or wood pieces fed to the disc. Mounted rearwardly of the cutter disc is a fan wheel having impeller blades on the periphery for engaging and propelling chips. The cutter disc and fan wheel are surrounded by suitable housing means enclosing and providing protection of each, the housing portion about said fan wheel having a chip discharge opening in the top. The housing means is arranged to provide a tunnel for conveying chips from the chipper to the area adjacent the periphery of the fan wheel with impact surfaces so arranged that chips impacting against the surfaces hit at a low angle to minimize damage to the chips. Chips not impacting against such impact surfaces have a path that carries them into the path of travel of the blades on the fan wheel, the speed of which is so related to the component speed of the chips that minimum damage to chips occurs by reason of contact between the blades and the chips. The blades on the fan wheel and the housing are so arranged that chips will be propelled by the blades out of the discharge opening.

For a more detailed description of the invention reference is made to the accompanying drawings.

DRAWINGS

FIG. 1 is a perspective view of a chipper constructed in accordance with the invention;

FIG. 2 is a horizontal section taken substantially along line 2--2 of FIG. 1;

FIG. 3 is an enlarged fragmentary elevation of a chipper taken substantially along line 3--3 of FIG. 4;

FIG. 4 is an enlarged sectional view taken substantially along line 4--4 of FIG. 3; and,

FIG. 5 is a fragmentary sectional view taken substantially along line 5--5 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The illustrated chipper comprises a chipper disc 12 mounted on a horizontal shaft 14 driven from a suitable motor (not shown). The shaft 14 is shown as supported in a trunnion 16 mounted on a suitable supporting base 18 and is otherwise suitably supported. The illustrated chipper is of the horizontal infeed type and is illustrated as having an infeed spout 20 extending through an opening 22 in the base 18. As will be apparent, the invention is equally applicable to chippers having a vertically inclined feed spout.

The cutter disc 12 is enclosed within a protective coaxial housing 24, the front wall of which 26 is provided with an opening 28 communicating with the spout 20. One wall of the opening 28 defines a vertical anvil 30 and the bottom edge defines a horizontal anvil 32 against which log or boards are pressed as they are engaged by the knives on the cutter disc.

The chipper disc 12 may be of any conventional construction and is provided with a plurality of removably mounted knives 36 which project from the front face thereof, the disc having openings or slots 38 adjacent to each of the knives through which severed chips may pass from the front to the back of the disc 12. The knives 36 of the illustrated chipper are offset from but parallel to radii of the disc 12, but, as will be apparent, the invention is equally applicable to chippers using the more conventional arrangement wherein the knife edges extend along radii of the disc. The position of the knives 36 with respect to the spout opening 28 at various times has been indicated by dotted lines in FIG. 3 and the points of intersection of the knives with the periphery of opening 28 have been indicated in FIG. 3 by the letters a to i inclusive.

Mounted on the shaft 14 rearwardly of the disc 12 with respect to the position of the spout 20 is a wheel which may be, for example, a flywheel 40 which is surrounded by a housing 42. The housing is provided with a tangential outlet 44 at the top thereof and the flywheel 40 is provided with a plurality of impeller blades 46 for engaging chips and propelling them out of the outlet 44 at a high velocity. The blades 46 extend outwardly from the periphery of the flywheel 40 but also have a portion 48 extending inwardly along the front face 49 of the flywheel 40. The periphery 51 of the housing 42 is coaxial with the flywheel 40 and the blades 46 are sized so as to provide relatively close clearance between the housing and the edges of the blades to prevent accumulation of chips between them. Extending between and communicating with the disc housing 24 and the flywheel housing 42 is a tunnel 50 which provides a passageway for the travel of chips from the cutter disc 12 into the housing 42. The tunnel 50 has a curved bottom surface 52 concentric with the shaft 14 and is of a radius preferably just slightly greater than that of the disc 12. In a chipper having a disc of 150 cm. radius, the curved surface of the tunnel may have a radius of about 155 cm.

In a chipper of the type illustrated, the cutter disc is rotated at a relatively high velocity, for example, at a speed of from 200 to 720 revolutions per minute and the disc may have a diameter from about 50 to 177 inches. A chip which is severed from a log or other piece of wood has a velocity imparted to which is roughly 20 percent greater than the tangential velocity of the knife 36 at the point of impact. Thus, in a chipper rotating at 300 r.p.m. having a cutter disc diameter of 300 cm. and a spout opening of relative dimensions such as is shown in FIG. 3, a chip cut from a piece of wood contacted by a knife at the point g in the edge of the spout would have a velocity of about 156 ft. per second. A chip cut by the knife at the point e would have a velocity considerably less and of the order of 70 ft. per second. (All further velocities mentioned herein will assume a disc of above diameter and speed.) While chips at such lower velocity can impact directly upon a surface with lesser damage than chips of a high velocity, chips of the higher velocity suffer substantial damage when impacting in a direction substantially normal to a surface or at a large angle, that is, one greater than about 45.degree. .

The severed chips are given a predictable trajectory which is dependent upon the angle of impact with the knife and the velocity of the knives. In a chipper such as illustrated, the trajectory would be downward and to the left as viewed in FIG. 3. Referring to FIG. 4, the approximate area of impact of the chips on the tunnel surface 52 has been plotted and shaded with cross hatching. The points of impact of chips severed at various points a to i, inclusive, indicated on the periphery of the spout opening 28 have been indicated in FIG. 4 by the identical letter and the suffix 1. That is, a chip severed at the point a would impinge upon the tunnel surface 52 at the point a.sub.1. The theoretical area 54 of impact of chips on projection of the surface 52 beyond the meeting edge 56 of the tunnel 50 and the fan housing 42 is also indicated in FIG. 4. The area 54 has been dotted and is bounded by a line bearing indications of the theoretical points of impact of chips projecting from the points a-f inclusive.

The further from the center of the disc to the point of severance the smaller will be the impact angle of a chip. For example, the angle of impact of a chip severed at the point a with the shipper geometry illustrated is about 30.degree. as measured by the angle between the path of the chip and a plane tangent to the tunnel surface 52 at the point of impact a.sub.1 of such chip. At such a low angle of impact no substantial damage to the chips will occur even though they have a velocity of about 149 ft. per second. Chips severed at points of lesser distance from the center of the cutter disc 12 will impact at higher angles but their velocity will be lower so that chip damage is inconsequential. A chip severed at point e, for example, would impact at an angle of about 65.degree. but would have a velocity of only about 72 ft. per second. It is desired that the tunnel surface 52 be so related to the trajectory of the chips that chips having a velocity greater than about 100 ft. per second impact at an angle no greater than about 45.degree. . With chips of lower velocity, higher angles of impact may be permitted. In some instances it may be desirable that the tunnel surface be frustoconical to lessen the angle of impact. Obviously chip damage and fines production will depend not only upon the chipper geometry but also upon the condition and species of the wood being processed.

Those chips which fail to impact against the surface 52 will pass into the housing 42 and will have a substantial component of motion in the direction of rotation of the flywheel 40 but which component will be less than the speed of the vanes 46 which have a tangential velocity of about 125 ft. per second. As may be seen from FIG. 5, the chips directed to the area 54 will pass outwardly of the periphery of the flywheel 40 and into the path of the vanes 46. The differential velocity between the vanes 46 and the chips and the angle of impact will be such that no substantial damage to the chips will occur.

Chips which rebound from the tunnel surface 52 will have a rebound angle only about half of the angle of impact and will lose little speed and thus will be directed towards the outer periphery of the flywheel 40 but in its direction of rotation so as to be engaged by the portion of the vanes 46 which extend up alongside of the flywheel. Again, the angle of impact and the velocity difference is such that no substantial damage to the chips will occur.

The chips engaged by the blades 46 will be accelerated and discharged through the outlet 44 which may be connected to any suitable conveying system. The velocity of the chips as they discharge from the outlet 44 will be such that they can be transported a substantial distance. In some instances it may be desirable to place fan blades on the back side of the flywheel 40 in order to increase the volume of air discharging through the outlet thus to increase the air to chip ratio.

Having illustrated and described a certain preferred embodiment of the invention, it should be apparent that the invention permits of modification in arrangement and detail.

Claims

I claim:

1. A wood chipper comprising a rotary cutter disc having a plurality of substantially radial knives along one face of said disc for cutting chips from lengths of wood fed toward said face, and passageways therethrough for permitting the severed chips to pass through the disc,

a wheel mounted on the side of said disc opposite said one face in spaced relation to and coaxially with said cutter disc, and adapted to be driven in the same direction of rotation as said disc, said wheel having a plurality of chip impelling blades projecting from the periphery thereof,

housing means surrounding said cutter disc and wheel and providing a passageway for travel of said chips from said disc to the vicinity of the periphery of said wheel whereby said impeller blades will engage said chips and propel them around the inner periphery of said housing,

and a tangential outlet in said housing means for discharging chips therefrom.

2. In a wood chipper comprising a rotary cutter disc having a plurality of substantially radial knives along one face of said disc for cutting chips from lengths of wood fed toward said face, from which knives the chips are propelled at high velocities along a predetermined path extending angularly away from the axis of rotation of said disc, said disc having passageways therethrough for permitting the severed chips to pass through the disc,

a shaft supporting said cutter disc,

a wheel mounted on said shaft on the side of said disc opposite said one face in spaced relation to said cutter disc, said wheel having a plurality of blades projecting from the periphery thereof,

a cutter disc housing surrounding said cutter disc,

a wheel housing surrounding said wheel,

a tunnel means extending between and communicating with said housings and providing a passageway for travel of said chips along said path from said chipper disc to the interior of said wheel housing and having chip receiving surfaces for receiving chips at an angle no greater than 45.degree.,

the radius of said wheel and the spacing between said cutter disc and said wheel being such that said chip path does not intercept said wheel but does intercept the path of travel of said blades whereby said blades will engage said chips to propel them about the interior periphery of said wheel housing,

and a tangential outlet in said wheel housing for discharging chips therefrom.

3. In a wood chipper comprising a rotary cutter disc having a plurality of substantially radial knives along one face of said disc for cutting chips from lengths of wood fed toward said face, from which knives the chips are propelled at high velocities along a predetermined path, and passageways therethrough for permitting the severed chips to pass through the disc,

a shaft supporting said cutter disc,

a wheel mounted on said shaft on the side of said disc opposite said one face in spaced relation to said cutter disc, said wheel having a plurality of blades projecting from the periphery thereof, and traveling in the general direction of the movement of chips in said path,

housing means surrounding said cutter disc and wheel and providing a passageway for travel of said chips along said path and having chip receiving surfaces for receiving chips at an angle no greater than 40.degree.,

the radius of said wheel and the spacing between said cutter disc and said wheel being such that said wheel is spaced from said chip path, at least a portion of said chip path extending into the path of travel of said blades,

and a tangential outlet in said housing for discharging chips therefrom.

4. In a wood chipper comprising a rotary cutter disc having a plurality of substantially radial knives along one face of said disc for cutting chips from lengths of wood fed toward said face, from which knives the chips are propelled at high velocities along a predetermined path, and passageways therethrough for permitting the severed chips to pass through the disc,

a shaft supporting said cutter disc,

a wheel mounted on said shaft on the side of said disc opposite said one face in spaced relation to said cutter disc, said wheel having a plurality of blades projecting from the periphery thereof, and traveling in the general direction of the movement of chips in said path,

housing means surrounding said cutter disc and flywheel and providing a passage for travel of said chips along said path,

the radius of said wheel and the spacing between said cutter disc and said wheel being such that said wheel is spaced from said chip path, at least a portion of said chip path extending into the path of travel of said blades,

and a tangential outlet in said housing for discharging chips therefrom.

5. In a wood chipper comprising a rotary cutter disc having a plurality of substantially radial knives along one face of said disc for cutting chips from lengths of wood fed toward said face, from which knives the chips are propelled at high velocities along a predetermined path, and passageways therethrough for permitting the severed chips to pass through the disc,

a shaft supporting said cutter disc,

a wheel mounted concentrically to said cutter disc on the side of said disc opposite said one face in spaced relation to said cutter disc, said wheel having a plurality of blades projecting from the periphery thereof, and traveling in the general direction of the movement of chips in said path,

housing means surrounding said cutter disc and wheel and providing a passageway for travel of said chips along said path,

the radius of said wheel and the spacing between said cutter disc and said wheel being such that at least a portion of said chip path extends into the path of travel of said blades,

and a tangential outlet in said housing for discharging chips therefrom.