Patent Grant
7207513
Many different types of material are comminuted, i.e., the size of the material's particulates are reduced, for a variety of different reasons. For example, coal excavated from a mine is frequently comminuted to make the particulate size smaller and more uniform to facilitate the coal's transportion and/or to provide consistent combustion in a furnance. Food stuffs, such as wheat, are frequently comminuted to produce flour. And rock containing a desirable ore is frequently comminuted to provide easier access to the ore and the metal included in the ore.
A common way of comminuting material is to collide a particle of the material with an impact surface. The collision generates a force on and inside the particle that causes the particle to fracture into two or more smaller pieces. The amount of force generated in the collision is directly proportional to the impact speed of the particle—the speed of the particle relative to the impact surface at the moment of collision—and increases as the impact speed increases. As the amount of force generated on and inside the particle increases, the size of the pieces that result from the collision of the particle with the impact surface decreases.
There are many different comminuting devices that collide a particle of material with an impact surface. For example, Hammer mills comminute particles of material with a rotating set of hammers having impact surfaces. In operation, the material is dropped into the mill and fed by gravity to the hammers. The hammers smash the particles of the material into smaller pieces and also throw some of the particles and pieces against a side of the mill. In a hammer mill the impact speed of the particles largely depends on the rotational speed of the hammers.
Another type of comminuting device is a pin mill. The pin mill comminutes particles of material with multiple rings of pins spinning in opposite directions. In operation, the material is dropped into the center of the mill and moves outward through the paths of the pins in each ring. As the particles of material move, the pins knock the particles. In a pin mill, the impact speed of the particles largely depends on the speed of the pins moving along the paths.
Another type of comminuting device is a jet mill. Jet mills comminute particles by accelerating the particles with a jet of air and directing the accelerated particles against an impact surface, which may or may not be stationary, or against an opposing jet of particles. In operation, a jet of air is generated and the particle is then fed into the jet to accelerate it. Once accelerated to a desired speed, the particle is directed toward and collides with the impact surface or another particle of an opposing jet. In a jet mill, when the impact surface is stationary, the impact speed of a particle largely depends on the speed of the particle, and when the impact surface moves, or an opposing jet of particles is used, the impact speed of a particle largely depends on the combined speed of the particle and the impact surface or particle of the opposing jet.
Unfortunately, each of these comminuting devices has some problems. Each of these devices is not very efficient for comminuting many types of material, i.e., a comparison of the amount of energy these devices consume to comminute a material with the value of the material at a given particulate size. Each comminuting device consumes a substantial amount of energy to comminute a material to a desired particulate size. Because hammer and pin mills typically generate a maximum impact speed of about 350 ft/sec compared to an impact speed of about 550 ft/sec or more, which is typically desired for efficient comminution, as indicated in tests, a significant reduction in a material's particulate size typically requires the material to be run through these mills more than once. Thus, the amount of energy consumed during the comminuting process includes the amount of energy required to operate these mills during multiple runs. Furthermore, to generate a higher impact speed (greater than about 550 ft/sec), the hammers and pins would have to rotate/move faster than their conventional structures will allow without sustaining substantial wear or catastrophic failure. Although jet mills can generate higher impact speeds than hammer and pin mills, the amount of energy jet mills consume can also be significant because they generate a jet of air to accelerate a particle, which typically requires a substantial amount of energy.
The present invention provides a comminuting device that can generate an impact speed exceeding 200 ft/s while consuming less energy than conventional comminuting devices, and thus, is more efficient than conventional comminuting devices. For example, the comminuting device may generate an impact speed of about 1,500 ft/s. The comminuting device comprises a throwing wheel that generates centrifugal and tangential forces in particles of material to accelerate the particles toward a desired impact speed, an impact rotor that includes an impact surface to fragment the particles when the particles collide with the impact surface, and a motor operable to power the impact rotor and the throwing wheel. To increase the impact speed of the particle, the impact surface is moved toward the particle as the particle exits the throwing wheel. Thus, the comminuting device can generate impact speeds that exceed the impact speeds generated by conventional comminuting devices and consequently fracture a particle into smaller pieces after one run. Furthermore, because the throwing wheel uses centrifugal force to accelerate the particle toward the impact speed, the comminuting device consumes less energy during the acceleration of the particle than a conventional jet mill. Consequently, the comminuting device can generate greater impact speeds with less energy than conventional comminuting devices.
In one aspect of the invention, the throwing wheel comprises a center through which a wheel axis passes, a periphery, a hub located at the center to receive particles of material, and a channel extending from the hub toward the periphery to direct the particles of material from the wheel hub toward the periphery. When the throwing wheel rotates about the wheel axis, the wheel exerts a tangential force on a particle received in the hub, and the particle accelerates toward the periphery by centrifugal force. At the periphery, the particle exits the throwing wheel on a trajectory. The particle's trajectory may be modified by changing the direction that the channel extends from the hub toward the periphery. For example, the channel may extend from the hub in a straight or substantially straight direction and intersect the periphery at about 90°. Or the channel may extend from the hub in a straight or substantially straight direction and intersect the periphery at an angle other than 90°. Or the channel may extend from the hub in a curved direction. By modifying the particle's trajectory, one may increase or decrease, as desired, the impact speed of the particle.
In another aspect of the invention, the impact rotor comprises a body including a rotor axis about which the impact rotor rotates when a motor powers the impact rotor, and a peripheral region located a radial distance away from the rotor axis. The impact rotor also comprises a plurality of impact teeth, each extending from the peripheral region and each including an impact surface to fragment particles of material when the particles collide with the impact surface. Each impact surface is angularly positioned relative to the rotor axis and a radius perpendicularly extending from the rotor axis toward the impact surface to increase the force generated in a particle at the moment of collision. For example, to maximize the particle's impact speed, the impact surface is angularly positioned to be perpendicular with the particle's trajectory at the moment of collision. The impact teeth may be removable from the impact rotor to allow one to remove and replace a worn or otherwise undesirable impact surface. Furthermore each impact surface may be removable from their respective impact tooth.
In yet another aspect of the invention, the comminuting device may include two or more impact rotors each sized to revolve their respective impact surface on a circular path about a common rotor axis with the two or more circular paths being concentric with each other. To sustain a high impact speed for a particle that collides with the outer impact surface, the impact rotors may rotate in directions opposite their adjacent impact rotor.
The following discussion is presented to enable one skilled in the art to make and use the invention. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
By rotating the throwing wheel 22 and the impact rotor 24 in opposite directions, the impact speed of the particles become a combination of the particles' speed and the impact surface's speed. If, at the moment of collision, the trajectory of the particle is aligned but opposite the trajectory of the impact surface 26, then the particle's impact speed will be the sum of the particle's speed and the impact surface's speed. Thus, the comminuting device 20 may generate impact speeds exceeding those generated by conventional comminuting devices. This increase in impact speed combined with an orientation of the impact surface 26 that aligns the direction of the impact surface 26 with the trajectory of the particles increases the force generated on and in the particles at the moment of collision. Consequently, particles of the material may be fragmented into smaller pieces after one run through the comminuting device 20, which allows the comminuting device 20 to comminute material more efficiently.
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In one embodiment, the throwing wheel 22 and the impact rotor 24 are mounted in the comminuting device 20 such that the wheel axis 34 and the rotor axis 30 are aligned or substantially aligned. The throwing wheel 22 may be mounted to the motor 32 using any desired fastening technique such as bolts and nuts, and the impact rotor 24 may be mounted to the motor 28 likewise. The motors 32 and 28 may be any desired motor, for example an electric motor designed to power their respective throwing wheel 22 and impact rotor 24 at a desired rotational speed for a given material flow rate through the comminuting device 20.
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Other embodiments of the comminuting device are contemplated. For example, the comminuting device may include two or more impact rotors 52 as shown in
When a particle leaves the throwing wheel 22 through an exit 46, the trajectory of the particle includes a directional component that is tangent to the periphery 54 and another directional component that is radial to the hub 42. The magnitude of each of these directional components depends on the velocity and acceleration of the particle as the particle leaves the wheel 22. By modifying the direction of each channel 44 as they extend toward the periphery 54, and the angle that each channel 44 intersects the periphery 54, one can modify the two directional components of the particle's trajectory.
In one embodiment, the throwing wheel 22 includes 20 channels 44 (only three shown for clarity) that extend from the hub 42 toward the periphery 54 in a straight or substantially straight direction and intersect the periphery 54 at about 90°. Each channel 44 may have any desired cross-section, such as a rectangular cross-section as shown in
Other embodiments of the throwing wheel 22 are contemplated. For example, in
The impact rotor 24 includes a body 76 that may be any desired shape, and each impact surface 26 may be located, as desired, and angularly positioned, as desired, relative to the rotor axis 30 and a respective radius 78 (only one shown for clarity) that extends perpendicularly from the rotor axis 30. For example, to maximize the particle's impact speed, each impact surface 26 should be perpendicular with the particle's trajectory at the moment of collision. The angular position relative to the rotor axis 30 is identified as α, and the angular position relative to the radius 78 is identified as θ (the line 82 is parallel with the rotor axis 30). In one embodiment, the body 76 may be a circular disk having a peripheral region 80 defined between the radii 9.12 inches and 11.0 inches away from the rotor axis 30. Each impact surface 26 may be located at the peripheral region 80 and may be angularly positioned such that α is about 0°, and θ is about 56°. In other embodiments, however, the angular position of each impact surface 26 may be defined within a range of α and a range of θ. For example, α and θ may range between 0° and 90°.
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Other embodiments are contemplated. For example, the impact rotor 24 may not include impact plates 86, and instead, each impact tooth 84 may include an impact surface 26 that may or may not be hardened depending on the material to be comminuted. In addition, each impact tooth may extend from the peripheral region 80 of the body 76 in other directions as shown and discussed in
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Other embodiments are contemplated. For example, each impact surface 90 may be angularly positioned such that a is greater than 0° but canted opposite to the direction shown in
The comminuting device 112 includes an impact rotor 114 that is cylindrical and has impact surfaces 116 to collide with and fracture particles of material, and two particle accelerators 118 to accelerate the particles of material and direct them toward the impact rotor 114. The comminuting device 112 comminutes particles of material by first accelerating the particles with one of the accelerators 118 to an approximate speed of 200–300 ft/sec. Then, the particles are directed toward the impact rotor 114 that rotates to move the impact surfaces 116 at a speed 650 ft/sec or greater toward the particles leaving the accelerators 118. Thus, the comminuting device 112 can generate impact speeds of approximately 850 ft/sec or greater.
In one embodiment, the particle accelerator 118 includes a throwing wheel 120 (shown in
Because the speed of a particle exiting the accelerator 118 largely depends on the throwing wheel's outer diameter 122 and rotational speed, the accelerator 118 may be designed to accelerate particles to any desired exit speed. The exit speed may be substantially determined by multiplying the rotational speed of the throwing wheel 120 times the distance of the particle from the axis 126 (half of the outer diameter 122). Thus, the exit speed may be increased by increasing the throwing wheel's outer diameter 122 and/or rotational speed, and may be decreased by decreasing the throwing wheel's outer diameter 122 and/or rotational speed.
In operation, the accelerator 118 receives particles of material through the hopper 130, which directs the particles toward the inlet 132. Once in the inlet 132, the particles move away from the axis 126 and are picked up and accelerated by a blade 124 of the rotating throwing wheel 120. As the particles' speed increases, centrifugal force moves the particles toward the outer diameter 122 and through progressive regions of the blade 124 whose respective speed increases. Thus, as the particles continue to move toward the outer diameter 122, the blade 124 continues to accelerate the particles toward an impact speed. Then, the outlet 120 receives and directs the particles toward the impact rotor 114.
The impact rotor 114 includes impact surfaces 116 to collide with and fracture the particles of material that have been accelerated by the particle accelerator 118. To increase the impact speed of the particles, a motor 134 (shown in
This application is a Continuation-In-Part of the commonly owned U.S. patent application Ser. No. 10/042,052, filed 18 Oct. 2001, titled “APPARATUS AND METHODS FOR COMMINUTING MATERIALS”, now abandoned, which is hereby incorporated by reference in its entirety. This application also claims priority from commonly owned U.S. Provisional Patent Application No. 60/480,907, filed 23 Jun. 2003, titled “DEVICE FOR COMMINUTING MATERIALS”, presently pending, which is hereby incorporated by reference in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20040113002 A1 | Jun 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60480907 | Jun 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10042052 | Oct 2001 | US |
| Child | 10644654 | US |
