Low Noise Level Chipper

Abstract

The cutting rotor of a low noise level chipper is closely confined within a housing and yet is provided with a series of air escape passages through the body of the rotor so that air which is otherwise trapped within the close confines of the housing and acted upon by the rotor to produce piercing noise is instead released through the rotor itself during rotation thereof whereby to preclude the emission of such noise. A number of generally rectangular blocks are spaced apart along the axle shaft of the rotor to define such air escape passages and are provided with elongated knives at their aligned corners that cooperate with a common shear bar to disintegrate the materials fed to the chipper during operation thereof.

Description

This invention relates to high speed wood chippers such as commonly used by tree trimming or removing crews to disintegrate branches, brush, and small logs fed into the chipper in order to clear the work site of the tree parts. Upon disintegration of the material, the chips are projected through a discharge chute into a large container such as the enclosed bed of a truck, whereupon the collected chips can be simply hauled away.

Typical chippers operate at extremely high rotative speeds such as 3,000 rpm or better in order to handle the mass of material fed thereinto without choking or overloading the power unit associated with the chipper. While such high speeds are desirable from a purely functional standpoint, they have heretofore been and are increasingly becoming undesirable from an environmental standpoint because such high speeds are conducive to the creation of a continuous, sharp, piercing noise from the spinning rotor of the chipper. With the increasing emphasis on eliminating environmental noise pollution in addition to water and air control, a growing number of local, state and federal governmental entities are developing standards which would severely limit the allowable noise emissions of machines such as wood chippers. The problem can be brought into even clearer focus when it is considered that tree trimming and removing operations are largely confined to residential locations which are likely to be rather densely populated and are most often carried out during the summer months when residents are participating in outdoor activities of various nature and their homes are open to the sights and sounds of the neighborhood.

While a definite amount of noise is produced during the relatively short interval that material is being fed through the chipper, a great amount of noise is produced over a prolonged period simply by rotation of the rotor itself between the periodic feedings of material into the chipper. It is believed that one reason for such noise from the rotating rotor itself is the construction of the rotor, its relationship to the housing with in which it is disposed, and the subsequent effect by these factors upon air that is drawn into the chipper during operation. Heretofore, chippers have commonly been provided with rotors that have massive, solid cylinders provided with knives spaced circumferentially about their periphery. The cylinders rotated within very close confines within their respective housings so that air drawn into the vicinity of the rotor by virtue of its spinning action had no place to go except through the restricted space between the cylinder and the cutter bar operating in conjunction with the knives of the cylinder. Consequently, the air would become trapped within the immediate vicinity of the rotor and would be subjected to repeated impacting and compacting blows from the whirling knives. While it is considered that part of the noise was emitted as a result of purely impact action, it is also theorized that a portion was derived from the instantaneous, high pressure compaction and expansion of the air as it passed from one side of the cutter bar to the opposite side thereof into the discharge chute. With the advancement of each knife toward the cutter bar, a pocket of air would be trapped between the blade and the cutter bar, hence compressing the pocket under high pressure until the knife passed the cutter bar, whereupon pressure would be instantaneously released, causing a retort not appreciably dissimilar to that of a balloon popping or a cork being removed from a pressurized vessel. By the time the rotor reached operational speeds of approximately 3,000 rpm, the individual retorts were blended together in a continuous piercing noise that shattered the calm of an otherwise quiet neighborhood.

Accordingly, it is an important object of the present invention to provide a chipper wherein the noise level produced by the spinning rotor is held to a minimum without sacrificing the ability to handle large masses of wood materials at relatively high operating speeds if such high speeds are desired.

As a correlary to the foregoing, it is another important object of this invention to provide a chipper wherein the rotor thereof, while operating in a relatively confined space enclosed except for an inlet and outlet on opposite sides of the rotor, is constructed in a manner to provide a series of air escape passages through the body thereof so that during operation, air which would otherwise be trapped within the confined operating space of the rotor is instead allowed to pass through such passages and to the discharge outlet, thereby preventing the production of piercing noise.

An additional important object of this invention is the provision of a special, low-noise rotor as aforesaid wherein the low noise characteristics thereof can be obtained without complicated or unduly expensive construction techniques.

FIG. 1 is a fragmentary, largely schematic vertical cross-sectional view through a chipper embodying the principles of the present invention;

FIG. 2 is a fragmentary, vertical cross-sectional view of the chipper taken substantially along Line 2--2 of FIG. 1, parts of the housing being broken away to reveal details of construction; and

FIG. 3 is an enlarged, fragmentary detail view of the special rotor of the chipper illustrating the manner in which the knives thereof are secured to the mounting plate members of the rotor.

The chipper 10 has an outer housing 12 that is supported by a number of vertical and horizontal frame pieces such as 14 and 16, and the housing 12 has a material receiving inlet 18 at one end thereof and a material discharging outlet 20 at the opposite end thereof. Inlet 18 is located at the innermost open end of an entrance hopper 22 forming a part of the housing 12, and the inlet 18 has its upper termination defined by the lowermost extremity 22aof hopper 22 while its lower termination is defined by a cutter bar 24 projecting into the normal path of travel of material from inlet 18 to outlet 20. A feed platform 26 underlies hopper 22, leading to inlet 18 for cooperating with hopper 22 to direct materials into inlet 18 during operation of the chipper 10. The outlet 20 has its upper termination defined by an upper, horizontal frame piece 16 and its lower termination defined by a generally L-shaped apron 28 behind the cutter bar 24. Although not shown, it is to be understood that a discharge chute or spout is commonly coupled with the outlet 18 for receiving chipped material therefrom and directing the same into a suitable receiving container.

Disposed within the housing 12 across the path of travel of material moving between inlet 18 and outlet 20 is a special rotor 30 constructed in accordance with the principles of the present invention. Rotor 30 has an axle shaft 32 extending transversely to the path of travel of material through housing 12 and journaled by a pair of suitable bearings 34 at opposite ends thereof (only one bearing 34 being illustrated). Three generally rectangular, massive black members 36 are secured to shaft 32 such as by welding and are spaced axially along the latter to define a series of air escape passages 38 between the members 36 and between the endmost members 36 and their proximal portions of housing 12. The passages 38 thus extend transversely to the axis of rotation of rotor 30 to openly communicate the inlet 18 and outlet 20 with one another through the body of rotor 30 on opposite vertical sides of shaft 32.

The plate members 36 are concentrically arranged on shaft 32 and are each disposed with their corner sections 40 in alignment with those of an adjacent member 36, each corner 40 being prolongated to facilitate the proper mounting and installation of a series of elongated knives 42 about the periphery of rotor 30 on the outermost faces 44 of members 36. As illustrated, four knives 42 are utilized, one at each corner 40 of the plate members 36, and each knife 42 spans all three of the members 36, terminating at its opposite ends in close proximity to the proximal portions of housing 12. As illustrated best in FIG. 3, each knife 42 is secured to the members 36 by virtue of screws 46, and each knife 42 is provided with a cutting edge 48 that passes in close proximity to cutter bar 24 during actuation of rotor 30 for cooperation with cutter bar 24 in chopping or disintegrating materials fed to rotor 30.

As illustrated best in FIG. 1, the knives 42 move not only in close proximity to the shear bar 24 during actuation of rotor 30, but also in close proximity to extremity 22a of hopper 22, thereby severely restricting the available space for air flow between rotor 30 and cutter bar 24, and between rotor 30 and extremity 22a. Moreover, in view of the fact that extremity 22a is spaced but a short distance above platform 26 when compared to the overall size of rotor 30, the inlet 18 is significantly reduced in size relative to rotor 30 so that incoming air is directed solely to the major portion of rotor 30 instead of toward the outer periphery thereof for bypass around the same to outlet 20. Further, the housing 12 is substantially imperforate between inlet 18 and outlet 20 so that air flowing into housing 12 through inlet 18 cannot avoid the rotor 30 such as by lateral escape means, but instead must move directly to the rotor 30. While such an arrangement has heretofore been provided in other chippers and is necessary in order to properly control the introduction of wood materials to rotor 30 and the subsequent discharge of the chips from housing 12, such confined control over the air flow has contributed to the emission of piercing noise in previous chippers, but not in chipper 10 of the present invention as will hereinafter become abundantly clear.

It is contemplated that the chipper 10 may be mounted on the bed of a trailer (not shown) to render the same mobile and may either be powered by the power take-off from a tractor to which the trailer is hitched or, it may be provided with its own prime mover mounted directly on the trailer in which case the towing vehicle may simply be a truck or the like not provided with a power take-off. In either event, a large pulley 50 may be provided on one external end of shaft 32 for supplying driving power to the latter through a belt connection to the source of power.

Operation

When rotative power is supplied to the shaft 32 through pulley 50, the rotor 13 is driven in a counterclockwise direction viewing FIG. 1 at speeds ranging from 700 rpm to 3,000 rpm. Wood material such as brush, branches and small logs may be fed to rotor 30 through hopper 22, whereupon the whirling knives 42 almost instantaneously grab the fed material and disintegrate the same, projecting the chips thereof rearwardly of housing 12 through outlet 20 and an appropriate chute (not shown) for collection at a remote point. This manner of operation is quite similar to the basic aspects of operation of prior chippers in that the same basic chipping function is performed at relatively high speeds. Moreover, the operation of the rotor 30 in close proximity to extremity 22a of hopper 22 and to the cutter bar 24 is similar to that of prior chippers in that such an arrangement limits the flow of incoming air to a path of travel that is directly to rotor 30 instead of peripherially around the latter for bypass to the outlet 20. But while this restricted air travel led to excessive noise emission in prior chippers, such an arrangement does not in fact produce piercing noise in the present chipper because of the air escape passages that are provided between block members 36.

Thus, while in the past, the incoming air might be impacted by the whirling knives 42 and instantaneously compacted between the cutter bar 24 and an approaching knife 42 for subsequent instantaneous expansion on the opposite side of cutter bar 24, air entering inlet 18 can now simply pass through the passages 38 to outlet 20 without ever being subjected to the compacting action of the knives 42. Once the incoming air stream is contacted by a knife 42 moving downwardly past extremity 22a, the air is immediately swept into and through passages 38 ahead of the knife 42 so that it is not squeezed between knife 42 and cutter bar 24.

Consequently, the impact action of the knives 42 against the incoming air is drastically reduced inasmuch as no backup surface functioning as an anvil is presented such as in the chippers having solid cylinders as part of their rotors. Moreover, the instantaneous compaction and expansion of the incoming air heretofore existing is no longer caused because once such compaction attempts to begin, the air immediately takes the path of least resistance through the passages 38 to outlet 20. Therefore the staccato-like, repetitious retorts caused by the violently expanding air in prior chippers operating at low speeds and the strident, piercing noise when such retorts merged together at high speeds are completely avoided with the special rotor 30.

Noteworthy is the fact that many conventional chippers heretofore available operated at decibel levels of approximately 120 to 125, which levels are extremely irritating to the human ear. Many environmentalists and noise pollution control authorities consider 85 decibels as an acceptable level for noise emissions, and the chipper 10 provided with the special rotor 30 of the present invention has been operated at levels of 75 decibels or lower while at full operating speeds, thus placing the chipper 10 well within the normally accepted noise control range.

Claims

Having thus described the invention, what is claimed as new and desired to be secured by Leters Patent's.

1. In a low noise level, high speed, wood and brush chipper:

a housing having an inlet and an outlet;

a cutting rotor rotatable within said housing between said inlet and outlet thereof across the normal path of travel of material moving through the housing,

said housing being substantially imperforate between said inlet and outlet and being provided with means limiting incoming air to flow to said rotor without appreciable bypass of the latter about the periphery thereof to the outlet; and

a cutter bar mounted in the housing directly below the axis of rotation of said rotor for cooperating with the latter to disintegrate wood materials presented thereto into chips,

said rotor including a shaft, a series of massive, solid blocks spaced along said shaft for rotation therewith, a plurality of elongated knives supported on said blocks with their chopping edges in parallel relationship to said shaft and the cutter bar, and fastener means securing the blades on the blocks,

said blocks each having a pair of opposed, radial sides and a continuous, broad, flat, peripheral face extending between said sides,

said blades lying against said faces of the blocks and said fastener means extending into said faces to retain the blades in place,

said blocks defining transverse air escape passages therebetween for continuously releasing air to said outlet during rotation of the rotor.

2. A low noise level chipper as claimed in claim 1, wherein said inlet is of reduced size relative to said rotor, having one terminus thereof disposed in spaced opposition to said cutter bar and in close proximity to the periphery of the rotor, and air limiting means including said one terminus.

3. A low noise level chipper as claimed in claim 1, wherein said blocks are each generally rectangular, there being a knife at each corner thereof.