Abstract:
Apparatus for removing debris from a fluidized sand bed. One or more troughs extend radially from a vertical shaft. Associated with each trough is a perforated chute. The apparatus is placed into the fluidized bed of sand, and rotated. As the apparatus rotates, the perforated chute sifts, or separates, debris from the fluidized sand. That is, the fluidized sand flows through the perforations, but the debris does not. When the apparatus is removed from the fluidized bed, the debris tumbles down the chute, into the troughs, if it has not already done so, and is captured.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 10/669,902, filed Sep. 24, 2003 now U.S. Pat. No. 6,948,620, which is a divisional of U.S. application Ser. No. 09/902,376, filed Jul. 6, 2001, now U.S. Pat. No. 6,651,819, issued Nov. 25, 2003. 

   TECHNICAL FIELD 
   The Invention relates to removal of stray debris from fluidized sand beds. The beds are used in fabrication of molds used in metal casting. The debris, if not removed, can damage the patterns from which the molds are being made. 
   BACKGROUND OF THE INVENTION 
   In the metal casting art, metal is poured into a mold. The mold is generally constructed of a high melting-point ceramic material. In the process of making the mold, a wax replica, or pattern, of the actual item to be cast is first made. Object  3  in  FIG. 1  represents the pattern. The pattern  3  is dipped into a liquid ceramic slurry  6 , contained in tank  9 . Conceptually, the slurry  6  can be viewed as a thin liquid plaster. 
   Next, the pattern is removed from the slurry  6 , and, while still wet with a coating of the slurry, inserted into a fluidized bed  12  of sand, in tank  14 . The sand is fluidized by jets of compressed air (not shown) or other gas, which agitate the sand and cause the sand particles to become suspended in the tank  14 . 
   A problem arises at this point, because debris tends to get deposited into the fluidized bed. This debris is set into motion by the fluidized sand  12 , and the moving debris can collide with the pattern  3  and knock off parts of the pattern  3 , thereby creating even more debris. For example, as shown in  FIG. 2 , a section  15  of the pattern  3  is shown as being broken off, and now contained in the fluidized bed  12 . Prior to breakage, section  15  formed phantom part  16  of the pattern  3 . 
   In the prior art, the debris was typically removed by persons who, in essence, sifted the debris out of the sand, using sieves or screens. However, this process was unable to remove all debris. One reason is that the tanks  14  are deep and wide, compared with the size of the sieves and screens used. Also, the presence of the fluidized sand reduces visibility, so that the debris-removal operation involves a somewhat random sifting process of various areas of the tanks. 
   In addition, if larger sieves or screens were to be used to mitigate the problem just stated, the larger sieves and screens represented larger weights which the persons must manipulate and lift. In industry, requiring personnel to lift large weights is not favored, because of possible injury to the persons performing the lifting. 
   The Inventors have developed a system for more effectively cleaning the tank  14  which contains the fluidized bed of sand. 
   SUMMARY OF THE INVENTION 
   In one form of the invention, a helical screen is dipped into the fluidized bed, and then rotated. Fluidized sand flows through the screen, but debris does not, and is captured. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  illustrate a problem which occurs in the prior art, Item  3  is a wax prototype, item  6  is a ceramic slurry, and item  12  is a fluidized bed of sand. 
       FIGS. 3 ,  4 , and  5  illustrate a progressive assembly of one form of the invention, which is shown in  FIG. 5 . 
       FIG. 6  is a perspective view of one form of the invention. 
       FIG. 7  is a simplified cross-sectional view of  FIG. 6 , taken across section  47 , as seen by eye  50 . 
       FIGS. 8 ,  9 ,  10 , and  11  illustrate passage of the structure  40  of  FIGS. 6 and 7  through a sand cloud  70 . Sand cloud  70  represents the fluidized bed  12  in  FIG. 1 . 
       FIGS. 12 ,  13 , and  14  illustrate a sequence of events occurring in one form of the invention. 
       FIGS. 15 ,  16 , and  17  illustrate two different modes of operation of one form of the invention. 
       FIGS. 18 ,  19 ,  20 , and  21  illustrate a mechanism by which one form of the invention operates. 
       FIG. 22  illustrates a mode of operation which does not commonly occur under the invention. 
       FIG. 23  is a flow chart illustrating a sequence of processes undertaken by one form of the invention. 
       FIGS. 24 ,  25 ,  26 , and  27  illustrate additional forms of the invention. 
       FIG. 28  illustrates section  450  in  FIG. 5 , in cross-section. 
       FIG. 29  illustrates shaft  32  of  FIG. 5 , and a coordinate system superimposed thereon. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 5  illustrates one form of the invention, and the structure shown in  FIG. 5  will be explained by reference to  FIGS. 3 and 4 .  FIG. 3  illustrates a helical screen  30 , which is supported by a shaft  32 . 
     FIG. 4  illustrates walls, or dams,  34 , which are placed onto the helical screen  30 . The walls  34  extend radially from shaft  32 .  FIG. 5  illustrates a helical outer wall  36 , which is attached to the outer edge of the screen  30 , and the overall structure forms an auger  38 . The mechanisms by which the auger  38  operates will first be explained by an analogy to a two-dimensional inclined ramp, for simplicity. 
     FIG. 6  illustrates the ramp  40 , which is inclined, as indicated by angle  42  which ramp  40  makes with the horizontal, represented by plane  44 . A screen  46  forms the bottom, or deck, of the ramp  40 , and corresponds to screen  30  in  FIGS. 3-5 . 
   The screen  46  of  FIG. 6  is also shown in  FIG. 7 , which is a cross-sectional view taken at plane  47  in  FIG. 6 , as viewed by eye  51 . Upstanding barriers  53  serve to catch debris, in a manner to be later described, and correspond to walls  34  in  FIGS. 4 and 5 . 
   A simplified example of one mode of operation of the apparatus of  FIG. 6  will be given.  FIGS. 8-11  represent a sequence of events, wherein the ramp  40  of  FIG. 5  moves through a sand cloud  70  carrying debris items  73  and  74 . Sand cloud  70  represents a region of the fluidized bed  12  of  FIG. 1 . In  FIGS. 8-11 , the ramp  40  moves to the left or, equivalently, the sand cloud  70  moves to the right. 
   In  FIG. 8 , the ramp  40  approaches the sand cloud  70 . In  FIG. 9 , the ramp  40  enters the sand cloud  70 . In  FIG. 10 , the debris items  73  and  74  are captured by the combined action of the screen  46  and the barriers  53 . In  FIG. 11 , the ramp  40  has exited the sand cloud  70 , after extracting or filtering, the debris items  73  and  74  from the cloud  70 . 
   Therefore, as so far described, one form of the invention moves the ramp  40  of  FIG. 6  through a fluidized bed of sand, represented by sand cloud  70  in  FIGS. 8-11 , to thereby extract debris. 
   In another form of the invention, the auger  38  of  FIG. 5  is used for the extraction. As shown in  FIGS. 12-14 , the auger  38 , represented by cylinder  50 , is placed above the fluidized bed, as in  FIG. 12 . Auger  50  is then inserted into the fluidized bed  12 , as indicated in  FIG. 13 . The auger  50  is rotated while within the fluidized bed  12 , as indicated by arrow  55 . 
   The rotation causes the relative motion between the screen  46  in the auger of  FIG. 5  and the sand within the fluidized bed of  FIG. 13 . That is, the rotation in  FIG. 13  causes the auger  50  to experience a similar motion to that of the flat screen  46  shown in  FIGS. 8-11 . 
   In  FIG. 14 , the auger  50  is withdrawn from the fluidized bed  12 , carrying debris items  73  and  74 . 
   The auger  50  is carried by a gantry  71 , or robotic arm, shown in simplified form in  FIG. 12 . Such arms are known in the art. A motor  75  rotates the auger  50 . The gantry can be controlled by an operator (not shown) who controls the position of the gantry  71 , and thus the position of the auger  50 , by means of a joystick control  80 , or equivalent control. 
   Significantly, in one form of the invention, the auger  50  is not moved, nor is it rotated, by human muscle power. Instead, motor  75  performs the rotation, gantry  71  supports the weight of the auger  50 , and block  76  represents mechanisms which move the gantry  71  to various positions. 
   The Inventors point out that a small amount of human muscle power may be involved in operating the joystick  80  of  FIG. 12 . However, that muscle power provides no energy for lifting or moving the auger  50 . That muscle power only provides control inputs for other apparatus which move the auger  50 . 
   Alternately, the gantry  71  can be computer-controlled. For example, the gantry  71  can comprise an X-Y-Z table, known in the art, which can position the auger  50  at any selected position. A computer, or other controller,  90  runs one, or more, programs  95  which control the position of the gantry  71 . In this mode of operation, the operator merely launches the program, and the computer cycles the gantry  71  through an appropriate cleaning cycle, which would include the steps shown in  FIGS. 12-14 , and perhaps additional steps. 
     FIGS. 15-17  illustrate two types of additional steps, or cycles. In  FIG. 15 , the gantry (not shown) inserts the auger  50  into the fluidized bed  12 , and carries the auger  50  along the path  100  shown, and then withdraws the auger  50 . In the general case, the auger is carried, while rotating, through all regions of the fluidized bed, while the sand is kept fluidized. 
   It is contemplated that the auger  50  may cover the same parts of the tank more than once. For larger tanks, the auger  50  may take a raster-type patterns, or move along a tightening spiral into a center, and then spiral back out. Other paths are possible. 
   It is also contemplated that the debris-removal process may coincide with the deposition of the ceramic slurry described in connection with  FIG. 1 . For example,  FIG. 16  illustrates a mold-pattern  3  present within the fluidized bed  12 . The computer driving the gantry  71  is programmed to avoid the zone allotted to the pattern  3 , as indicated by the jog  105  in path  110 , which avoids the pattern  3 .  FIG. 17  illustrates a top view of the tank  14  which contains fluidized bed  12 , and shows a representative zone  105  which the auger  15  is prohibited from entering. 
   Therefore, as just described, two types of programs  95  in  FIG. 12 , or two modes, are available. In one type, it is presumed that the tank  14  is empty of patterns  3 , and that the auger  50  can be moved anywhere in the tank  14  at will. In the second mode, different regions of the tank are restricted, and allocated to patterns  3 . Region  115  in  FIG. 17  provides an example. The auger  50  is forbidden to enter those regions, when they are active. 
   A few specific details about the mechanism by which the auger  50  picks up debris will be discussed. This discussion applies directly to the ramp  40  of  FIG. 6 , and its principles also apply to the auger  38  of  FIG. 5 . 
     FIG. 18  illustrates four successive positions of the screen  46  of  FIG. 4 . Circles  155  represent the random paths of the sand particles in the fluidized bed  12  of  FIG. 1 . 
   As the screen  46  in  FIG. 18  moves in the direction of arrow  160 , it moves through the moving sand particles  155 . The paths of the sand particles will be somewhat disturbed by the presence of the ramp  40 , in the sense that the holes (not shown) in the screen  46  behave, to a certain extent, like very short corridors. The hole-corridors will slightly re-direct the paths of the sand particles. 
   However, that re-direction, in general, will be small. Further, after this small amount of re-direction, the sand particles will immediately collide with other sand particles, and become randomized again. 
   Therefore, the passage of the screen  46  through the fluidized sand is not seen as changing the random motion of the sand, although conservation-of-energy principles would indicate that the velocity of the sand particles may be slightly reduced because of the collisions with the ramp  40 . Nevertheless, it will be assumed that, as the ramp  40  moves through the moving sand particles  155 , the sand particles remain almost completely undisturbed by the ramp  40 . 
   The debris within the sand is also not disturbed, in a specific sense. For example, the screen  46 , even though inclined, does not behave as a ramp, or inclined plane, with respect to the debris. For example, as shown in  FIG. 15 , if the ramp  40  encounters a debris item  190  during the ramp&#39;s travel, the leftward motion of the screen  46  does not cause the particle  190  to move up the ramp, and occupy a final position indicated by block  195 . Restated, the situation of  FIG. 19  does not, in general, occur; debris item  9  does not climb the ramp and attain the final position of block  195 . 
   Instead, the debris particles behave as shown in  FIGS. 20 and 21 . Assume that four debris particles  200 ,  205 ,  210 , and  215  are suspended in the fluidized bed, not shown. As screen  46  moves to the left, it will collect the particles, and their final positions will resemble those indicated in  FIG. 21 . Significantly, the particles will not be positioned as indicated in  FIG. 22 . 
   Restated, either (2) the particles  200 ,  205 ,  210 , and  215  will remain at their same heights, with one height being indicated by arrow  216  in  FIG. 20 , or (2) they may fall to a lower height, and beheld there by one of the walls  53 . Particles  200  and  205  represent the latter case. But the particles will not, in general, climb the screen  46 , and be collected at a greater height, as  FIG. 22  would indicated. 
   The principle just described applies to particles of the size of ½ inch in diameter, and having a solid wax core. However, exceptions to the principle just stated can occur. For example, very small particles, especially if very light, can be buoyed up by the fluidized sand. For example, table tennis balls may climb the ramp. However, such particles will inflict only minor damage of the type described in the Background of the Invention, and may not need to be extracted from the fluidized bed. Further, such particles are considered unlikely to be found in the fluidized bed  12 . 
   Therefore, the debris which will be collected will, in general, not climb up the screen  46  as illustrated in  FIG. 22 . 
     FIG. 23  illustrates a flow chart of steps undertaken by one form of the invention, and some, or all, of these steps may be implemented by the programs  95  of  FIG. 12 . In block  300  in  FIG. 23 , the fluidized bed  12  of  FIG. 1  is brought into operation. In block  305 , the user selects a mode of operation. For example, the user may select the mode which drives the auger  50  along path  100  in  FIG. 15 . Alternately, the user may select the mode which utilizes path  110  in  FIG. 16 , and avoids zone  115  in  FIG. 17 . 
   In block  310  in  FIG. 23 , the mechanism  76  of  FIG. 12  moves the gantry  70 , so that the auger  50  is inserted into the tank  14 , as in  FIG. 15 . In block  315  in  FIG. 123 , motor  75  in  FIG. 12  rotates the auger  50 , and mechanism  76  cause combined rotation of the auger  50  and movement of auger  50  along an appropriate path, such as path  100  in  FIG. 15 , based on the mode selected in block  305 . In block  320  in  FIG. 23 , the auger  50  is removed from the tank  14 . 
   In one embodiment, the auger  50  in  FIG. 12  is separable from the motor  75 . That is, the auger  50  remains in a stowed position until needed, while gantry  70  is used for other purposes while the auger  50  is stowed. When the auger  50  is needed, the gantry removes it from stowage, and places the auger  50  into operation. 
   Various types of connections  350  in  FIG. 12  between the motor  75  and shaft  32  can be used. One connection is a simple rigid coupling. Another connection has some of the properties of a universal joint. For example, an actual universal joint can be used, of the type used on the driveshaft of an automobile. One of the properties of a universal joint is that torque is delivered to the shaft  32 , but the shaft  32  need not remain coaxial with the shaft, not shown, of the motor  75 . That is, shaft  32  can swing like a pendulum. 
   A connection resembling a universal joint is attained if shaft  32  bears a common eye-type hook, or loop, and motor  75  contains an ordinary lifting hook, which resembles the letter J. When the lifting hook, or J, engages the eye-hook, or loop, the lifting hook can lift the loops, and also apply torque to the loop. But the loop can still wobble about the lifting hook, thereby providing the universal-joint function, at least partially. In addition, the lifting hook is easily removable from the eye-hook, so that the gantry  70  can be used for other purposes. 
   The auger  38  in  FIG. 5  can be constructed in different ways. In  FIG. 5 , screen  30  is a woven-wire screen, having a mesh suitable for the size of the debris to be collected. Meshes of 1 to 10 wires per inch, which correspond to holes of 1×1 inch to 0.1×0.1 inch, respectively, are contemplated. Alternately, screen  30  can be replaced by sheet metal containing punched holes, or expanded sheet metal, or other equivalents. 
   In  FIG. 5 , walls  34  and  36  are solid material, such as sheet metal. They are imperforate, although they can be constructed of screen material, as in  FIG. 25 , described below. 
   In another embodiment, tubes or rods  375  are welded, or otherwise fastened, into the structure shown in  FIG. 24 .  FIG. 24  shows an open cage: no screens are present. Additional rods or tubes can be added for strength, as indicated by dashed items  380 . Then, screening  390  is installed, as in  FIG. 25 , to form walls  34  and  36 , and screen-deck  30 . 
     FIG. 28  illustrates a section  450  of  FIG. 5 , but in cross sectional view. Section  450  can be viewed as containing two parts: a trough or valley  455 , and a chute or barrier  460 . In the embodiment shown, the bottom  465  of the rough  455  is an extension of the chute  460 . Trough  455  has an open top. 
   In operation, debris and sand will flow in a generally horizontal direction into the chute  460 , as indicated by arrow  470 . Fluidized sand will flow through the holes in the chute  460 , but the large debris particles will not. The particles will cross over the open top of the trough  455  and collide with the chute  460 . When the section  450  is removed from the fluidized bed  12  in  FIG. 1 , the debris will tumble into the trough  455 , if it has not already done so. Sand will fall through the holes in both the chute  460  and the bottom  465  of the trough  455 . 
     FIGS. 26 and 27  illustrate other approaches. In  FIG. 26 , the chutes  460  are flat, and are co-planar with the axis  475  of shaft  32 . The troughs  455  lie one-above the other, in as tack. End caps  480  are shown removed to illustrate the troughs  455 . Dashed block  490  indicates that a mirror-image structure, containing troughs  455 , chutes  460 , and end caps  480 , can be fabricated 180 degrees opposite the structure shown, on the shaft  32 , or at other positions on shaft  32 . 
     FIG. 27  illustrates another embodiment. Chutes  460  are inclined, as is chute  460  in  FIG. 28 . However, the troughs  455  are stacked one-above-the-other, as in  FIG. 26 . Walls indicated by dashed lines  500  may be provided, to assist in capture of debris. Such walls can be provided for both chutes  460 . 
   In one form of the invention, the pitch of the helix, namely, dimension  400  in  FIG. 25 , is about 12 inches. Diameter, dimension  410 , is about 16 inches. Diameter of shaft  32 , dimension  415 , is about one inch. The holes in the screen are rectangular, at 0.187×0.187 inches. The holes could be circular, and of the same area as the rectangular holes just identified. 
   Tank  14  in  FIG. 1  was described as containing a fluidized bed  12  of sand particles. There is preferably no liquid in the tank. The sand acquires fluid-like properties by the action of moving gas. Fluidized beds are known in the art. 
     FIG. 29  illustrates shaft  32 , and a coordinate system superimposed thereon. Axis  501  represents the axial direction. Lines  505  are positioned at different axial positions. Thus, the different walls  34  in  FIG. 5  can be said to lie at different axial positions. The same statement applies to the troughs of  455  of  FIGS. 26 and 27 . 
   In  FIG. 29 , arrow  510  represents a radial direction, or a direction along a radius. Thus, troughs of  FIGS. 26 and 27  can be said to extend radially from the shaft  32 . 
   In  FIG. 29 , lines  515  and  520 , which are radial lines, represent different angular positions with respect to a reference point, such as point  516 . Thus, troughs  455  in  FIG. 27  occupy different angular positions. 
   Applying the preceding conventions, one sees that the walls  34  in  FIG. 5  (1) extend radially, (2) occupy different axial positions, and (3) occupy different angular positions. Further applying the preceding conventions, one sees that the troughs  455  in  FIG. 26  occupy different axial positions, but the same angular position. 
   Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.