The present invention relates to improvements in a drum chipper providing for air cooling, which is advantageous for chipping, pulverizing or granulating heat sensitive materials such as plastic.
Drum chippers are commonly used in the wood processing industry to reduce the size of logs by removing chips or flakes for the purpose of shaping the log for subsequent finish processing into lumber. However, drum chippers are also often employed for processing waste wood materials to produce the chips themselves, which are used in the manufacture of engineered board products, such as oriented strand board, pulp and paper. For this latter purpose, it is commercially important to produce chips having defined quality characteristics.
The cutting head of the drum chipper has an elongate, cylindrical shape, and has a plurality of correspondingly elongate knives mounted on the cylindrical surface. The cutting head spins about its cylindrical axis. Compared to disc chippers where the knives are disposed on the periphery of the disc, the elongate knives of the drum chipper provide for cutting a relatively large surface area.
The cutting head, particularly the knives, become heated as a result of chipping work, and some of this heat is transferred to the material being worked. For chipping wood, this heating is not generally sufficient to significantly change the chipping dynamics. However, a hot cutting head can transfer enough heat to a material that is heat sensitive, such as plastic, to degrade chipping performance. This can be readily appreciated by thinking about the extreme case where the cutting head transfers enough heat to the material being chipped to melt or bum it. Thus, for chipping some materials, such as plastic, it is important to provide for cooling the cutting head.
Such cooling is typically provided by the use of open spaces between the knives and the cutting head. As the cutting head spins, air is able to flow around the knife through the spaces and, by convection, carry away much of the heat generated at the knives.
The knives are unsupported by the cutting edge over their spans, so that they are as a result of this configuration much more susceptible to deformation in response to chipping forces. Accordingly, it is important that the knives be able to function as structural members as well as cutting members. To resist bending over the length of their spans, the knives must have sufficient bulk.
The required bulk of the knives raises the material cost of the knives. And since the knives are more costly, they are more costly to dispose of, which makes it more important to repair the knives and less economically practical to replace the knives when their cutting edges wear. Removing and replacing a knife is more difficult when it is heavy, and repairing the knife requires additional labor as well as the acquisition, repair, maintenance and storage of costly equipment.
Accordingly, there is a need for a drum chipper and method providing for air cooling that eliminates these and other disadvantages of the prior art.
A drum chipper and method providing for air cooling. A basic apparatus comprises a drum member, a knife, and a carrier for mounting the knife to the drum member. The carrier comprises an upper clamping member and a lower clamping member for clamping the knife therebetween. The carrier is adapted to mount to the drum member at axially spaced apart mounting positions thereon.
In a preferred method, the basic apparatus is used to chip plastic material.
In a preferred apparatus, the carrier is spaced above and unsupported by the drum member over a span defined between the mounting positions to provide for airflow between the drum member and the carrier.
It is to be understood that this summary is provided as a means of generally determining what follows in the drawings and detailed description and is not intended to limit the scope of the invention. Objects, features and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings.
Reference will now be made in detail to specific preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
One of the knife carriers 14, namely the carrier 14a, is shown exploded from the drum member. The carrier 14a is shown in more detail in
A knife carrier 14 is shown assembled in
Returning to
It is an outstanding advantage of the knife carrier that it completely eliminates the requirement for the knife itself to provide the structural rigidity necessary to span the open spaces. The knife may therefore be optimized for the single purpose of cutting, and can be formed of a minimal amount of material for this purpose. Thence it becomes economically feasible, due to the decreased material costs of the knife, to simply dispose of the knife once the cutting edge wears.
The carrier, on the other hand, has a wear rate that is much less than that of the knife. Therefore, making the carrier as bulky and sturdy as is required to perform the function of supporting the knife does not impose nearly the same penalties that providing this function in the knife itself imposes.
In providing for a physically smaller knife, the carrier provides for decreased shipping, storage, and handling costs associated with the knife in addition to decreased material and manufacturing costs for the knife. Moreover, the knife can be made narrow enough that it need not be turned on its side and wedged into pockets in the rings as shown in
With reference to
The knife is symmetric about a plane of reflective symmetry “POS.”
The deflector ridges define a channel 42 having a channel surface 42a. The channel 42 is effectively a recess in the front side of the knife, which may be provided by other features, such as a keyway. A back surface 44 of the knife 20 is received by the upper clamping member 16.
The recess provided, in the preferred embodiment, by the deflector ridges 38 and the associated channel 42 define an interlocking feature adapted for interlocking with a toe portion 43 of the lower clamping member 18 (
Turning to
The knife carrier 14a as mounted to the drum member 12 is circumferentially, or azimuthally, adjacent two carriers, namely 14c, on the one side of the carrier 14a, and 14d, on the other side of the carrier 14a. The carrier 14a is not parallel to either of the adjacent carriers 14c and 14d, but the carriers 14c and 14d on either side of the carrier 14a are parallel to each other. Moreover, none of the carriers are parallel to the axis L. The angle that the elongate axes EA of the knives 20 make with axis L is referred to as a “slicing angle.”
Providing a non-zero slicing angle progressively phases-in different points of the cutting edges of the same knife so that they come into contact with the material being cut at different times. This concentrates the cutting force at the phased-in points and reduces as well as smooths out the power requirements. Alternating the slicing angle of azimuthally adjacent carriers varies the timing between cuts made at the same axial position of the cutting head, which further smooths out the power requirements. Preferably, the slicing angle measured with respect to the axis L not only varies between azimuthally adjacent knife carriers, but alternates direction such as is shown in
It is to be understood that, while a specific drum chipper and method providing for air cooling has been shown and described as preferred, other configurations and methods could be utilized, in addition to those already mentioned, without departing from the principles of the invention.
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.