US3736967A

US3736967A - Feeder for wood flaking or chipping machine

Info

Publication number: US3736967A
Application number: US00172070A
Authority: US
Inventors: W Wood; J Fechner
Original assignee: Potlatch Forests Inc
Current assignee: Potlatch Forests Inc
Priority date: 1971-08-16
Filing date: 1971-08-16
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05

Abstract

A device for producing wood particles, such as chips, wafers, flakes or strands, by moving solid wood material toward a moving cutter head. Movement of the material is accomplished along a feed conveyor in the form of an endless conveying apparatus having transverse pushing bars. The conveyor is powered by a pneumatic power source, such as a rotary pneumatic motor directly geared to the conveyor elements. The resilient nature of the pneumatic power source assures quick recovery of the wood material as it is urged toward the moving cutter head, thereby producing particules of more uniform thickness.

Description

llnited States atn 1 Wood et al.

[ ,FEMBQ 5, 1973 [54] FEEDER FOR WOOD FLAKKNG OR CHIPPING MACHINE Inventors: Warren A. Wood, Oswego, Oreg.; John T. Fechner, Lewiston, Idaho 3] Assignee: Potlatch Forests, Inc., San Francisco, Calif.

22 Filed: Aug. 16,1971

21 Appl.No.: 172,070

[52] US. Cl. "144/172, 144/242 R, 144/245 A, 91/275 [51] Int. Cl ..B27c1/12 [58] Field of Search ..9l/218, 275; 418/181, 270; 144/172, 242 D, 242 R, 245

[56] References Cited UNITED STATES PATENTS 2,969,095 1/1961 Brookhyser et al ..144/172 X 3,435,861 4/1969 Shields .l44/242 R 1,321,932 ll/l9l9 McQueen ..4l8/l8l X 2,529,777 11/1950 Mclnnis ..9l/275 X 3,080,042 3/1963 Sherman ..l44/242 R Primary ExaminerAndrew R. Juhasz Assistant Examiner-W. D. Bray Attorney- Greek Wells, Richard J. St. John and David P. Roberts [57] ABSTRACT A device for producing wood particles, such as chips, wafers, flakes or strands, by moving solid wood material toward a moving cutter head. Movement of the material is accomplished along a feed conveyor in the form of an endless conveying apparatus having transverse pushing bars. The conveyor is powered by a pneumatic power source, such as a rotary pneumatic motor directly geared to the conveyor elements. The resilient nature of the pneumatic power source assures quick recovery of the wood material as it is urged toward the moving cutter head, thereby producing particules of more uniform thickness.

3 Claims, 4 Drawing Figures PATENTEDJUN 5l975 3 736,967

SHEET 1 [IF 2 FIG 1 FIG 2 PATENTED 5l975 $736,967

SHEET 2 [1F 2 FIG 4 FEEDER FOR WOOD FLAKING OR CHIPPING MACHINE BACKGROUND OF THE INVENTION In the production of particleboard, solid wood is chipped or reduced to particles of differing denomination by urging the wood materials into contact with moving knives or other cutting surfaces designed to produce particles of a desired configuration and thickness. The cutting head is typically in the form of a cylindrical drum or circular disc. Other variations are in use for specific particle production.

In most installations, the wood material is pushed toward the cutter head in a batch-type feed assembly, which opens to receive a charge of wood materials and then pushes the charge toward the cutter head. These often are operated by cylinders.

Other prior devices have used chains opposed to one another to squeeze the wood materials between the chains and push them toward the cutter head. However, the pressure required to effectively squeeze solid wood often damages wood fibers and the resulting feed is not uniform for wood material of differing density, moisture content, etc.

According to the present disclosure, transverse lugs can be used on the working flight of a conveyor to feed the wood material by pushing it along a path tangential to the cutting knives on a cylindrical drum. The use of positive pushing power is permitted, without risking damage to the wood fibers, because of the elastic nature of the particular feed that is disclosed herein.

SUMMARY OF THE INVENTION The disclosed invention comprises the combination of a moving cutter head, together with a feed conveyor having a working flight including transverse pusher elements for abutting raw wood materials and moving them into engagement with a cutter head. A pneumatic power source, in the form of a pneumatic motor having a rotary output shaft, is directly connected to the feed conveyor for imparting a yieldable force urging the pusher elements of the working flight toward the cutter head. The quick response of the air motor and the resilient nature of the resulting forces assures greater uniformity in particular thickness in the particles produced by the cutter head.

It is a first object of this invention to provide a feed Q assembly for particle manufacturing machines which assures quick response of solid materials against a moving cutter head structure.

Another object of the invention is to provide maximum recovery of solid wood material against a cutter head after removal of each particle, without risking physical damage to the fibers of the remaining wood material.

Another object of this invention is to provide such an assembly in which the elements used are readily available and economically competitive with alternative structures not capable of meeting the same operating standards.

These and further objects will be evident from the following disclosure, taken together with the accompanying drawings, which illustrate a preferred form of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of the apparatus, showing the relationship of the cutter head and feed conveyor;

FIG. 2 is a top view of the apparatus shown in FIG.

FIG. 3 is an end view taken from the right in FIG. 1; and

FIG. 4 is a sectional view taken substantially along line 4-4 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT This disclosure is concerned with a feeder for production of wood particles, such as particles used in the manufacture of various types of particleboard. As a matter of definition, a wood particle can cover a wide range of types. The commercial standard CS236-66 of the U. S. Department of Commerce recognizes the possible range of shape of wood particles used in the production of particleboard by specifying the wood requirement as follows: The wood particles shall be flakes, chips, shavings, slivers, and similar forms that are produced from any natural wood by cutting, hammermilling, grinding and similar processes.

The present development is concerned with the production of particles such as chips, wafers, flakes or strands, cut in discrete form from solid wood materials. It is particularly concerned with particles which are desirably of uniform thickness. To produce uniform thickness of particles cut from raw wood material, it is essential that the raw wood material be advanced an identical distance each time that particles are cut from its surface as presented to the cutting head. This is the principal purpose of the present disclosure.

As used herein, the word chips shall refer to small pieces of wood chopped off a block or other source of solid wood material by arr-like cuts. A flake" is a small wood particle of pre-determined dimensions normally produced as a primary function of specialized equipment with the cutting action across the grain so as to produce a particle of uniform thickness, essentially flat, and having the fiber direction essentially in the plane of the flakes. A flake generally resembles a small piece of veneer. A strand" is a relatively long shaving of relatively small thickness and width, consisting of long flat bundles of wood fibers having parallel surfaces. A wafer would generally be recognized as being a very thick flake. The present disclosure is concerned with machinery designed to produce wood particles having relatively uniform thickness, as opposed to many other types of wood particles of random or indefinite dimensron.

The general features of the apparatus are illustrated in FIGS. 1-4. These drawings illustrate the basic components of the apparatus, with auxiliary devices, such as a hopper or feed conveyor, and secondary flailing and discharge conveyor assemblies not being illustrated.

The apparatus is mounted on a rigid framework It), illustrated in skeletal form, with protective guard plates and shields removed. The upper portion of framework 10 includes side plates 11 which mount a transverse shaft 12 on which is mounted a cutting head 13 in the form of a cylindrical drum centered about the axis of shaft 12. The cutter head 13 is formed by securing a plurality of parallel discs in abutment with one another, each disc having a number of staggered knives 14 projecting beyond the cylindrical periphery of cutter head 13 and designed to individually form substantially rectangular flakes upon passage of each knife across a source of solid raw wood material. The precise details of the cutter head and knife structure are not necessary to this disclosure.

The shaft 12 and cutter head 13 are rotated by a primary motor 15 fixed to framework 141). The drive chain is generally shown at 16. The cutter head 13 is preferably rotated at a constant speed, pre-selected with reference to the feed rate at which solid material enters the machine.

The cutter head 13 slices the wood material across the lower portion of the cylindrical disc, the wood mateiral being vertically supported by an anvil structure 17 mounted to framework 10. Adequate clearance is provided between the protruding knives l4 and anvil 17 to permit discharge of the cut particles to the right under cutter head 13, as viewed in FIG. 4.

Solid raw wood material, preferably in the form of blocks, is fed to the locations between cutter head 13 and anvil 17 by a feed conveyor shown generally at 18. Conveyor 18 includes a rigid supporting frame 20 fixed to framework 10 and an endless conveyor in the form of a chain 21 positioned in a vertical plane and having an upper working flight directed toward cutter head 13. Chain 21 has a plurality of equally spaced transverse pusher lugs 22 fixed to it, each being designed to engage and push behind a single block of wood material as the material is urged toward the cutter head 13.

The disclosed feed apparatus provides a continuous and positive pushing force to the blocks of wood material (shown at 23 in FIG. 4) as these blocks of material abut the cylindrical periphery of cutter head 13. To assure maximum responsiveness in relocating each block of material as the wood particles are sliced therefrom by knives 14, the conveyor 18 is positively powered by a pneumatically-driven power source, such as a rotary pneumatic motor 25. As illustrated, the motor 25 drives a mechanical gear box 26 connected to the drive sprocket for chain 21 by means of a drive chain 27. This arrangement provides a positive connection between the pneumatic motor 25 and lugs 22, assuring maximum responsiveness throughout the feed arrangement. The air motor 25, which can be stalled when necessary in order to push blocks of wood material at its end adjacent to the rotating cutter head l3, operates as a pneumatic cushion at relatively low pressures. The compressive nature of air permits momentary variations in the pressure and accommodates the momentary changes in the speed of the wood material during and immediately following the cutting of each particle.

The general concept of this disclosure is to assure maximum responsiveness in returning the incoming surface of each wood block to a position abutting the cylindrical face of cutter head K3 prior to engagement by the succeeding moving knife 14. Assuming that the wood material is maintained against the cylindrical periphery of cutter head 13, each particle sliced by a knife 14 will have uniform thickness, dependent upon the setting of the individual knives with respect to the cutter head. We have found that substantially greater uniformity can be achieved by the presently-disclosed use of a pneumatic motor than by conventional magazine or batch-type feed arrangements. At the same time, this arrangement permits continuous operation of the feed conveyor 18 and allows it to receive incoming blocks of raw wood material from a hopper (not shown) or other source of material with a minimum of human supervision.

in order to permit the use of mechanical pushing lugs 22, the force exerted on the wood blocks must be maintained at a level below that force at which the compression of each block against the cutter head would exceed the compressive strength of the wood fibers. It also is necessary to insure that the progressing movement of each block toward the cutter head be very rapid in order to achieve a high degree of accuracy in cutting the wood particles to the desired size and shape. Both of these desirable results can be successfully accomplished by the above combination of a continuous conveyor positively powered by a pneumatic power source.

To show how this feeding device is designed to achieve the result of very rapid movement while not creating excessive forces which might damage the wood fiber, the following mathematical comparison has been developed between comparable mechanical units powered by both pneumatic and hydraulic pressure.

The first area of concern relates to the necessary forces. Mathematically, the force (F) is directly related to mass (M) and acceleration (a) according to the following formula:

If the applied force at lugs 22 is arbitrarily chosen at 100 lbs., the resulting acceleration of the blocks of wood material can be derived for both pneumatic and hydraulic power sources. The weight of one cubic foot of air at 100 psi is 0.585 pounds, whereas one cubic foot of a typical hydraulic. fluid weighs 50 pounds and is essentially incompressible over the normal operating pressure range. Using the above formula, the comparable acceleration between the pneumatic and hydraulic systems differs by a factor of 50/.585 or 85. Therefore, for a given force (100 pounds) air at 100 psi (.585 pounds/ cubic feet) responds times faster than hydraulic fluid at the same pressure psi (50 pounds/- cubic feet).

To analyze the pressure range at which comparable response time would be achieved in moving blocks of wood material toward cutter head 13 by both pneumatic and hydraulic pressure, reference is made to a simple hydraulics formula describing flow in pipes:

Q= 1096.5 X CXA X MP where Q is the flow rate, C is the coefficient of flow for a fluid, A is the pipe area, P is the pressure in inches of water and p is the fluid density. For similar flow conditions, the coefficient of flow (C) will be a constant for a given fluid.

To arrive at an indication of velocity, one begins with the basic formula:

Q Velocity (V) X Area (A) Combining these two formulas, velocity can be computed as follows:

V= 1096.5 c J PM,

To arrive at an indication of velocity for air at 100 psig (.585 pounds/cubic feet), the formula must be solved as follows:

v= 1096.5 c s am/.585 V 80,800 c Following a similar derivation for hydraulic fluid at 100 psig (50 pounds/cubic feet):

Relating the comparable velocity of air and hydraulic fluid, it will be seen that the velocity of air in the above equations is 9.3 times greater than the comparable velocity of hydraulic fluid. Thus, at the same pressure, air flows 9.3 times faster than hydraulic fluid. It therefore follows that to achieve equal velocity, the hydraulic fluid must be at approximately 1,000 psig, and even at that pressure, air will respond 85 times faster than the hydraulic fluid. It is seen from this study that to achieve substantially equal response time with hydraulic fluid requires much higher operating pressures. In applications relating to production of wood particles, such high pressure is not a practical solution. The high pressure necessary would be applied to the wood material through lugs 22 and would exceed the normal compressive strength of the wood fibers as they are pushed perpendicular to the grain of the wood. The general range of compressive strength of such wood fibers perpendicular to the grain is 300 to 500 psi. In some species, even lower compressive strength values are encountered.

As can be seen, the faster response acheived by use of pneumatic pressure is particularly important in the acheivement of fast response of the wood material in maintaining the surface being cut against the moving cylindrical face of the cutter head 13. The disclosed conveyor permits substantial gear reduction between the air motor 25 and chain 21, so that relatively small movement of lugs 22 is reflected as substantial movement of the air motor 25 and rapid response time becomes increasingly important. The expansion ability of the pneumatic media allows the present apparatus to take advantage of the low mass at high acceleration rate of compressed air, as compared to hydraulic fluid.

The substantial advantages in responsiveness achieved by use of pneumatic pressure to move lugs 22 is not seriously affected by momentary reduction in the air pressure due to linear displacement of lugs 22 as the wood blocks are moved toward the cutter head 13 in incremental steps. The exemplary air system described above can effectively compensate for drops in air pressure from 100 pounds to 98 pounds or even pounds and still remain considerably greater in effectiveness than a comparable hydraulic system.

While described specifically hereinas applied a feed toward a cylindrical drum cutter head, the present feed could be utilized in moving solid wood materials toward other moving devices, such as a disc. Therefore, the specific details illustrated and described herein are not intended to limit the scope of the invention, which is set out in the following claims.

Having thus described our invention, we claim: 1. In an apparatus for production of wood particles such as chips, wafers, flakes or strands, the combination of:

a cutter head having a plurality of knives and intermediate recessed guide surface areas moving about a predetermined path;

an endless feed conveyor having a working flight directed along a path which intersects the path of the knives, said feed conveyor having transverse pusher elements thereon facing toward the direction of movement of the conveyor along its working flight for abutting raw wood blocks and pushing each block into engagement with the knives and intermediate guide surface areas;

and a rotary pneumatic motor drivingly connected to said feed conveyor for imparting to said working flight a yieldable force urging said transverse pusher elements towards the cutter head, the resulting pressure exerted on the raw wood blocks by said force being less than that at which the wood fibers thereof are physically damaged by crushing.

2. An apparatus as set out in claim 1 wherein the pneumatic motor includes an output shaft geared directly to the endless conveyor.

3. An apparatus as set out in claim 1 wherein the cutter head is a cylindrical drum having projecting knives protruding beyond the cylindrical periphery thereof, whereby wood material is accelerated along the feed conveyor toward the cylindrical periphery of the drum as the knives remove wood particles therefrom.

Claims

1. In an apparatus for production of wood particles such as chips, wafers, flakes or strands, the combination of: a cutter head having a plurality of knives and intermediate recessed guide surface areas moving about a predetermined path; an endless feed conveyor having a working flight directed along a path which intersects the path of the knives, said feed conveyor having transverse pusher elements thereon facing toward the direction of movement of the conveyor along its working flight for abutting raw wood blocks and pushing each block into engagement with the knives and intermediate guide surface areas; and a rotary pneumatic motor drivingly connected to said feed conveyor for imparting to said working flight a yieldable force urging said transverse pusher elements towards the cutter head, the resulting pressure exerted on the raw wood blocks by said force being less than that at which the wood fibers thereof are physically damaged by crushing.

2. An apparatus as set out in claim 1 wherein the working flight comprises a portion of an endless conveyor for moving the pusher elements in a longitudinal path along said working flight toward said cutter head; said pneumatic power source comprising a rotary pneumatic motor having an output shaft positively driving said endless conveyor.

3. An apparatus as set out in claim 1 wherein the pneumatic motor includes an output shaft geared directly to the endless conveyor.

4. An apparatus as set out in claim 1 wherein the cutter head is a cylindrical drum having projecting knives protruding beyond the cylindrical periphery thereof, whereby wood material is accelerated along the feed conveyor toward the cylindrical periphery of the drum as the knives remove wood particles therefrom.