Patent Publication Number: US-2002000448-A1

Title: Abrasive particle metering device

Description:
[0001] This application claims the benefit of U.S. Provisional Application No. 60/208,635 filed Jun. 1, 2000. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention pertains to metering devices and more particularly to metering devices dispensing abrasive material in carefully regulated amounts and rates. The carefully metered abrasive material is delivered to the intake of a high-velocity cutting machine wherein it is accelerated to high velocities to precisely cut an object by erosion.  
       [0004] 2. Description of Prior Art  
       [0005] The predominant prior method to deliver a regulated amount of abrasive material for use in a high-velocity erosive cutting device involves a vibratory track in which abrasive material slides down a sloped track under the influence of gravity. The vibration helps to distribute the abrasive material and overcome the frictional force resisting the flow of the abrasive material. The distributed abrasive material streams off the end of the track and is presented to the intake of the high-velocity cutting device.  
       [0006] The rate of vibratory oscillation is generally controlled by electrically driven mechanical oscillators. Those oscillators are sensitive to the voltage fluctuations that commonly occur in industrial applications. Variations in oscillatory rates cause significant variations in the amount of abrasive material dispensed. At present, the cost of the abrasive material is the single highest consumable cost incurred in the cutting operation. Thus, excess vibration can cause excess abrasive material to be dispensed, unnecessarily increasing operational costs. Too little vibration, caused by undervoltage fluctuations, may present too little abrasive material to the cutting device intake, adversely affecting the quality of the cut. Thus, there exists a need to better regulate the amount of abrasive material dispensed in this type of operation.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention uses an innovative design to produce an abrasive particle metering device having a supply of fluid abrasive material; a feed tube through which the abrasive material flows; a metering wheel located very near to the feed tube, onto which the feed tube dispenses the abrasive material, and off of which a metered amount of abrasive material is ejected; a funnel to redirect and transport the metered amount of abrasive material; and a motor to drive the metering wheel. The abrasive material is supplied from a storage hopper or some external source. The amount of abrasive material ejected from the metering wheel depends on the rotational rate of the metering wheel. The motor controls the rotational rate of the metering wheel. The flow tube can have a contoured tip to conform to the perimeter of the metering wheel, and the flow tube can be raised or lowered relative to the metering wheel to accommodate various abrasive materials. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0008]FIG. 1 is a section view of an abrasive particle metering device constructed in accordance with this invention.  
     [0009]FIG. 2 is a section view of the abrasive particle metering device of FIG. 1, taken along the line  2 - 2  of FIG. 1.  
     [0010]FIG. 3 is an elevation view of the metering wheel and drive shaft of the abrasive particle metering device of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0011]FIG. 1 shows an abrasive particle metering device  10  constructed in accordance with the present invention. The metering device  10  comprises a storage compartment  12  adapted to hold a quantity of abrasive material  14 , a feed tube  16 , a metering wheel  18 , a motor assembly  20 , and a funnel  22 .  
     [0012] The storage compartment  12  serves to stage a quantity of abrasive material  14 . The abrasive material  14  can be an abrasive cutting powder or an abrasive slurry, and may or may not be heated. The abrasive material  14  is sufficiently fluid to flow under the influence of gravity alone or can be assisted by an external source of pressure. If gravity is the main impetus for flow of the abrasive material  14 , better results are obtained if the storage compartment  12  is vertically oriented. The abrasive material  14  may be comprised of particles with sizes ranging from 40-mesh to 140-mesh, for example, although the invention is not limited to such particle sizes.  
     [0013] The storage compartment  12  can be pre-filled with abrasive material  14  or can serve as a conduit should one wish to supply abrasive material  14  from an external source (not shown). The storage compartment  12  has a top  24 , a bottom  26 , and a side wall  28 . The side wall  28  may be a completely impervious wall, or it may incorporate a pervious inner wall (not shown) that creates a flow space between the pervious inner wall and the impervious outer wall. The top  24  of the storage compartment  12  is fitted with a connector  30  to permit the abrasive material  14  to be easily transferred into the storage compartment  12 . The connector  30  may be, for example, a standard barb-type fitting designed for easy connection and disconnection. The connector  30  is fastened to the top  24  of the storage compartment  12  by conventional means such as a bulkhead fitting  32 . The bulkhead fitting  32  has a threaded lower end  34  to which a pipe nipple  36  attaches. The pipe nipple  36  extends a short distance into the interior of the storage compartment  12 . The abrasive material  14  enters the storage compartment  12  upon discharge from the pipe nipple  36 .  
     [0014] The abrasive material  14  exits the storage compartment  12  by flowing either through and down the flow space (not shown) of the side wall  28  or through an opening  38  in the bottom  26  of the storage compartment  12 . In either case, the abrasive material  14  exits the storage compartment  12  through the feed tube  16 .  
     [0015] The feed tube  16  is a cylindrical tube that allows for the transfer and delivery of the abrasive material  14  from the storage compartment  12  to the metering wheel  18 . The feed tube  16  discharges the abrasive material  14  down onto the metering wheel  18 . The feed tube  16  is adjustably mounted to the bottom  26  of the storage compartment  12  by a clamp  40 . The clamp  40  can raise or lower the feed tube  16  in response to manual or automated commands. The feed tube  16  has a top end  42  and a bottom end  44 , with a conduit  46  through the tube. The top end  42  passes through and seals against the walls bounding the opening  38  in the bottom  26  of the storage compartment  12 . The top end  42  extends a short distance into the storage compartment  12  to allow the feed tube  16  to be adjusted to any desired height within a maximum and minimum range of heights. The top end  42  of the feed tube has an upper tip  48 . The upper tip  48  defines the exit from the bottom  26  of the storage compartment  12 .  
     [0016] As shown in FIG. 2, the bottom end  44  of the feed tube  16  has a lower tip  50 . The lower tip  50  defines a contour  52  conforming to the curvature of the metering wheel  18 . The conforming curvature of the contour  52  keeps the gap between the lower tip  50  and the metering wheel  18  equal over the perimeter of the lower tip  50 . Thus, as the feed tube  16  is manually or automatically adjusted to a desired distance from the metering wheel  18 , the contour  52  maintains the desired gap. In this way, metering device  10  can accommodate various particle sizes of the abrasive material  14 .  
     [0017] The metering wheel  18  can comprise a wheel, a screw auger, a conveyer belt, or some other rotational element. For ease of discussion, each of those rotational elements shall be inclusively referred to as the metering wheel  18 . The metering wheel  18  serves to dispense the abrasive material  14  in a manner that is linearly dependent on the rotational rate of the metering wheel  18 . Thus, a constant amount of abrasive material is dispensed if the rotational rate of the metering wheel is held constant.  
     [0018]FIG. 3 shows the metering wheel  18  as a cylindrical wheel. The metering wheel  18  has an outer surface  54 . The abrasive material  14  is dispensed onto the outer surface  54 . The outer surface  54  may be smooth or rough. A rough surface tends to improve the cohesion of the abrasive material  14  to the metering wheel  18 . The metering wheel  18  is attached to a drive shaft  56  lying along the cylinder axis of the metering wheel  18 . The drive shaft  56  is rotatably mounted to a housing  58  so that the drive shaft  56  is perpendicular to the cylinder axis of the feed tube  16 . The housing  58  can be an open trough or may completely enclose the metering wheel  18 . The housing  58  may be attached to a fixed structure or it may be mounted to a movable carriage.  
     [0019] As shown in FIG. 1, the metering wheel  18  is driven by a motor assembly  20 . The motor assembly  20  comprises a motor  60 , a coupling  62 , and perhaps a gearbox. The motor  60  may be, for example, electric, pneumatic, or hydraulic. Examples of electric motors that may be used include ac motors, servo motors, pulse width modulated motors, and stepper motors. The output of each of those motors can be regulated by controlling one or more inputs to the motor. Controlling the input to the motor is the means by which the rotational rate of the metering wheel  18  is controlled. The input to the motor may be controlled manually, by digital computer, or by an analog circuit. The motor  60  may or may not be connected to a gearbox. Depending on motor characteristics such as power and motor shaft rotational rates, the motor  60  can be geared to produce a desired range of power and rotational rate outputs. The motor shaft, or gearbox output shaft if one is present, connects to the coupling  62 . The coupling  62  connects to the drive shaft  56  to drive the metering wheel  18 . The motor assembly  20  mounts to the housing  58  so that the coupling  62  aligns with the drive shaft  56 .  
     [0020]FIG. 1 shows that the funnel  22  also mounts to the housing  58 . The funnel  22  has a wide end  64  and a tapered end  66 . The wide end  64  mounts to the housing  58  opposite the feed tube  16 . The funnel  22  serves to direct the metered abrasive material  14  to an exit at the tapered end  66 . The tapered end  66  connects to a pipe  68 . The pipe  68  conveys the metered abrasive material  14  as it appears at the tapered end  68  to a conventional high-pressure jet spray device (not shown). The abrasive material  14  is then entrained by conventional means into the carrier fluid of the jet spray device and discharged at high speed.  
     [0021] The present invention offers many advantages over the prior art. The amount of abrasive material  14  metered out can be manually or automatically regulated to control cutting parameters such as draft angle, washout, speed of cut, and sharpness of comers. Metering device  10  improves cut quality because the metered amount of abrasive material dispensed is highly controllable and the resolution of feed rate adjustment is fine. Expensive waste from excess abrasive material being consumed is eliminated. The rotational inertia of the rotational element helps maintain accurate metering that is less sensitive to voltage fluctuations than conventional methods.  
     [0022] While the invention has been particularly shown and described with reference to a preferred and alternative embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.