Abstract:
Provided is a shot-blasting apparatus which is capable of efficiently perform dust collection and ventilation of an inside of a projection chamber, even using a dust collector having a small-size and low-cost suction device. The shot-blasting apparatus comprises: a cabinet ( 10 ); a plurality of process chambers ( 13   a,    13   b ) provided inside the cabinet in such a manner that each of the process chambers is capable of housing a workpiece therein and selectively movable between a carry-in-and-out position and a projection position; an air inlet port ( 19 ) for introducing external air into each of the process chambers therethrough; and an air outlet port provided at a position opposed to the air inlet port across the process chamber set at the projection position, and linearly communicated with an internal space of the process chamber set at the projection position, wherein, according to suction from the air outlet port, air is caused to flow from the air inlet port into the process chamber set at the projection position, and led to the air outlet port while passing through the process chamber set at the projection position.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a shot-blasting apparatus, and more specifically to a shot-blasting apparatus configured to project shots onto a workpiece. 
       BACKGROUND ART 
       [0002]    There has been known a shot-blasting apparatus configured to project shots onto a workpiece disposed in a projection chamber to process a workpiece (see the following Patent Document 1). In the shot-blasting apparatus, due to collision of shots against the workpiece in the projection chamber, a large amount of powder dust is inevitably generated in the projection chamber. Therefore, such powder dust generated in the projection chamber is collected by a dust collector to thereby keep a working environment around the apparatus clean. 
         [0003]    As an example of the shot-blasting apparatus, a type shown in  FIGS. 1 and 2  is commonly known. This type of shot-blasting apparatus comprises a cabinet  1 , and a rotary hanger  2  installed inside the cabinet  1 . The rotary hanger  2  is equipped with a hanger hook for suspendingly supporting a workpieces. 
         [0004]    The rotary hanger  2  is a member which has a drum shape (cylindrical shape) and comprises two process chambers  3   a ,  3   b  arranged at radially opposed positions, wherein the hanger hook is configured to suspend a workpiece in each of the process chambers. The rotary hanger  2  is configured to be rotatable intermittently about a longitudinal axis extending in a vertical direction, as indicated by the arrowed lines R 1 . 
         [0005]    According to this rotation, each of the process chambers  3   a ,  3   b  is selectively moved between a carry-in-and-out position on the side of a front end of the apparatus and a projection position on the side of a back end of the apparatus. Each of the process chambers serves as a carry-in-and-out chamber  3   a  for carrying in and out the workpiece at the carry-in-and-out position and as a projection chamber  3   b  for projecting shots to the workpiece at the projection position. 
         [0006]    In this type of shot-blasting apparatus, after placing a new workpiece on the hanger hook in the carry-in-and-out chamber  3   a , the rotary hanger  2  is rotated 180 degrees to allow the carry-in-and-out chamber  3   a  having the workpiece disposed therein to be located on the side of the back end of the apparatus so as to serve as the projection chamber  3   b . Then, a projector is activated to project shots onto the workpiece suspended in the projection chamber  3   b.    
         [0007]    In this type of shot-blasting apparatus, a cabinet suction port  4  is provided in a back-end region of the cabinet  1  at a position on the side of one lateral edge of a top wall of the cabinet  1 , to introduce external air into the cabinet  1  through the cabinet suction port  4 . Further, a separator suction port  6  is provided in a separator  5  disposed at a widthwise center of the back-end region of the cabinet  1 , to suck external air therethrough. The external air introduced from the cabinet suction port  4  and the separator suction port  6  flows into a dust collector (not shown) via ducts  7 ,  8 . 
         [0008]    The above conventional shot-blasting apparatus is thus configured to remove powder dust from air in the projection chamber  3   b  by the dust collector having a suction device. 
       CITATION LIST 
     Patent Document 
       [0009]    Patent Document 1: JP 2005-329482A 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0010]    As mentioned above, in the above shot-blasting apparatus, both of the cabinet suction port  4  as an external air supply port to the cabinet, and the separator suction port  6 , are provided in the back-end region of the cabinet. Thus, external air introduced from the cabinet suction port  4  located in the back-end region of the cabinet, into the cabinet, and external air sucked from the separator suction port  6  located in the back-end region of the cabinet, are caused to flow through the back-end region of the cabinet (i.e., through a region located backward of the projection chamber), and led outside the cabinet (shot-blasting apparatus) via the ducts  7 ,  8 , without passing through the projection chamber, as indicated by the arrowed lines in  FIG. 1 . 
         [0011]    Thus, a flow path of external air introduced into the cabinet is not formed to pass through the projection chamber  3  as a powder dust source, thereby leading to a problem of failing to effectively remove powder dust in the projection chamber  3   b.    
         [0012]    Moreover, the two suction ports are provided at different positions, so that the suction device for sucking air into the dust collector requires a large suction force, thereby leading to a problem that the suction device for sucking air into the dust collector sizes up, and an operation cost and a device cost become higher. 
         [0013]    The present invention has been made in view of the above problems, and an object thereof is to provide a shot-blasting apparatus capable of efficiently perform dust collection and ventilation of an inside of a projection chamber, even using a dust collector having a small-size and low-cost suction device. 
       Solution to Technical Problem 
       [0014]    The present invention provides a shot-blasting apparatus which comprises: a cabinet; a plurality of process chambers provided inside the cabinet in such a manner that each of the process chambers is capable of housing a workpiece therein and selectively movable between a carry-in-and-out position on the side of a front end of the apparatus and a projection position on the side of a back end of the apparatus; an air inlet port for introducing external air into each of the process chambers therethrough; and an air outlet port provided at a position opposed to the air inlet port across the process chamber set at the projection position, and linearly communicated with an internal space of the process chamber set at the projection position, wherein, according to suction from the air outlet port, air is caused to flow from the air inlet port into the process chamber set at the projection position, and led to the air outlet port while passing through the process chamber set at the projection position. 
         [0015]    In the shot-blasting apparatus having this feature, external air inflowing from the air inlet port flows into the air outlet port while reliably passing through the projection chamber, so that it becomes possible to enhance ventilation efficiency of an inside of the projection chamber. 
         [0016]    In one preferred embodiment of the present invention, the air outlet port is provided at a position opposed to the air inlet port across a central region of the process chamber set at the projection position. 
         [0017]    In the shot-blasting apparatus having this feature, external air inflowing from the air inlet port flows into the air outlet port while reliably passing through the projection chamber, so that it becomes possible to further enhance the ventilation efficiency of the inside of the projection chamber. 
         [0018]    In another preferred embodiment of the present invention, the shot-blasting apparatus comprises an approximately cylindrical-shaped rotary hanger having a top plate, a bottom plate, and a partition plate connecting the top plate and the bottom plate together to form the process chambers, wherein the rotary hanger is rotatably disposed within the cabinet, and wherein the chambers are spaced apart from each other in a circumferential direction of the rotary hanger. 
         [0019]    More preferably, in the above preferred embodiment, the process chambers are provided at intervals of a given angle. 
         [0020]    More preferably, the shot-blasting apparatus according to the above preferred embodiment comprises an external air introduction chamber provided adjacent to each of the process chambers, wherein the external air introduction chamber is partitioned with respect to the process chambers by the partition plate, and has an external air introduction port communicated with the air inlet port and the air outlet port. 
         [0021]    More preferably, in the above preferred embodiment, the air inlet port is provided in the partition wall. 
         [0022]    More preferably, in the above preferred embodiment, the external air introduction chamber is divided into two small chambers by a division plate disposed to extend in a vertical direction and provided with a vent hole. 
         [0023]    More preferably, in the above preferred embodiment, the air inlet port is covered by a hood attached to the partition plate from the side of the external air introduction chamber. 
         [0024]    The shot-blasting apparatus according to yet another preferred embodiment of the present invention further comprises a dust collector communicated with the air outlet port. 
         [0025]    In still another preferred embodiment of the present invention, the air outlet port is formed in a bucket elevator disposed in a back-end region of the cabinet. 
         [0026]    In the shot-blasting apparatus having this feature, it becomes possible to reduce the number of ducts required for air releasing to downsize the entire apparatus. 
       Effect of Invention 
       [0027]    The present invention can provide a shot-blasting apparatus capable of efficiently perform dust collection and ventilation of an inside of a projection chamber, even using a dust collector having a small-size and low-cost suction device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a horizontal sectional view showing a conventional shot-blasting apparatus. 
           [0029]      FIG. 2  is a sectional view taken along the line A-A in  FIG. 1 . 
           [0030]      FIG. 3  is a horizontal sectional view showing a shot-blasting apparatus according to one embodiment of the present invention. 
           [0031]      FIG. 4  is a horizontal sectional view of a main part of the shot-blasting apparatus in  FIG. 3 . 
           [0032]      FIG. 5  is a sectional view taken along the line B-B in  FIG. 4 . 
           [0033]      FIG. 6  is a front view of the shot-blasting apparatus in  FIG. 3 . 
           [0034]      FIG. 7  is a right side view of the shot-blasting apparatus in  FIG. 3 . 
           [0035]      FIG. 8  is a left side view of the shot-blasting apparatus in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    With reference to the drawings, a shot-blasting apparatus according to a preferred embodiment of the present invention will now be described. 
         [0037]      FIG. 3  is a horizontal sectional view showing the shot-blasting apparatus according to this embodiment. The shot-blasting apparatus according to this embodiment is a type configured to project shots onto a workpiece disposed in a projection chamber, to thereby process the workpiece. 
         [0038]    The shot-blasting apparatus comprises a cabinet  10 , and a rotary hanger  11  disposed within the cabinet  10 . The rotary hanger  11  is a drum-shaped (cylindrical-shaped) rotary hanger disposed such that a longitudinal axis thereof is oriented in a vertical direction. The rotary hanger  11  is configured to be rotated about the longitudinal axis by a rotational drive mechanism. 
         [0039]    The rotary hanger  11  comprises a top plate and a bottom plate attached, respectively, at an upper end and a lower end thereof. The rotary hanger  11  has a columnar internal space, which is circumferentially divided into four sub-spaces by three partition plates  12   a ,  12   b ,  16  each extending in a radial direction and in the vertical (axial) direction. 
         [0040]    More specifically, the columnar internal space of the rotary hanger  11  is divided into: first and second process chambers  13   a ,  13   b  opposed to each other in the radial direction and each having an approximately trapezoidal-shaped cross section; and first and second external air introduction chambers  17 ,  18  each formed at a position circumferentially interposed between the first and second process chambers  13   a ,  13   b  and adjacent to the respective first and second process chambers  13   a ,  13   b , and having a sector-shaped cross-section. Each of the first and second process chambers  13   a ,  13   b  and the first and second external air introduction chambers  17 ,  18  extends in the vertical direction over the overall height dimension of the rotary hanger  11 . 
         [0041]    Each of the first and second process chambers  13   a ,  13   b  has the same cross-sectional shape, and each of the first and second external air introduction chambers  17 ,  18  also has the same cross-sectional shape. Thus, the first and second process chambers  13   a ,  13   b  are arranged at intervals of a given angle, specifically, at positions opposed in the radial direction. 
         [0042]    Each of the first and second process chambers  13   a ,  13   b  has a shape in which a surface thereof on a radially outward side of the rotary hanger  11  has no wall, i.e., a shape opened radially outwardly. On the other hand, in each of the first and second external air introduction chambers  17 ,  18 , a surface thereof on the radially outward side of the rotary hanger  11  is closed. Thus, each of the first and second external air introduction chambers  17 ,  18  is formed as a closed space, except an aftermentioned suction port  19 , an aftermentioned air inlet port  22  and the like. 
         [0043]    As mentioned above, the rotary hanger  11  is configured to be rotated about the longitudinal axis by the rotational drive mechanism. Thus, according to rotation of the rotary hanger  11 , each of the first and second process chambers  13   a ,  13   b  can be selectively set at a position (carry-in-and-out position) on the side of a front end of the apparatus (a lower side in  FIG. 4 ), i.e., at a position where the first process chamber  13   a  is located in  FIG. 4 , and at a position (projection position) on the side of a back end of the apparatus (an upper side in  FIG. 4 ), i.e., at a position where the second process chamber  13   b  is located in  FIG. 4 . 
         [0044]    In the shot-blasting apparatus according to this embodiment, the cabinet  10  is formed with a carry-in-and-out port  14  communicated with the process chamber  13   a ,  13   b  set at the position on the front-end side of the cabinet  10 , to allow an operation for carrying a workpiece in and out of the process chamber  13   a  ( 13   b ) set at the carry-in-and-out position to be performed through the carry-in-and-out port  14 . 
         [0045]    The rotary hanger  11  also has a hanger hook (not shown) attached to the top plate thereof to suspendingly support a jig couplable to a workpiece. The hanger hook is disposed in the first and second process chambers  13   a ,  13   b  to allow a workpiece to be suspended within each of the first and second process chambers  13   a ,  13   b . This hanger hook is configured to be rotatable about its own vertical axis, as with the aforementioned conventional hanger hook. Based on the above structure, a workpiece can be attached to the jig suspended from the hanger hook in the process chamber  13   a , through the carry-in-and-out port  14  on the front-end side of the cabinet  10 . 
         [0046]    As shown in  FIG. 3 , a projection unit  23  is disposed behind the cabinet  10 . In the shot-blasting apparatus according to this embodiment, the projection unit  23  is composed of two heretofore-known centrifugal projection units arranged one-above-the-other. The projection unit  23  is operable to project shots onto a workpiece disposed in the process chamber  13   b  (or  13   a ) set at the projection position, to perform shot-blasting. 
         [0047]    The shot-blasting apparatus according to this embodiment further comprises a bucket elevator  25  forming a part of a circulation unit for shots. The circulation unit is designed to collect and circulatingly reuse shots projected from the projection unit  23 . 
         [0048]    As shown in  FIGS. 6 to 8 , the circulation unit of the shot-blasting apparatus according to this embodiment comprises a screw conveyer  26  disposed beneath the process chamber  13   b  located at the projection position. The screw conveyer  26  is operable to convey shots falling downwardly from the process chamber  13   b  set at the projection position, rightwardly in  FIG. 6 , according to rotation of a built-in screw about its axis. The screw conveyer  26  is configured such that a downstream end thereof is connected to a lower portion of the bucket elevator  25  to feed the conveyed shots into the bucket elevator. 
         [0049]    The bucket elevator  25  comprises a quadrangular prism-shaped casing, and an endless rubber belt configured to be driven by a motor  27  disposed within the casing. A large number of buckets are attached to the endless rubber belt. In the bucket elevator  25 , the buckets are operable to sequentially scoop up the used shots conveyed by the screw conveyer  26 , and conveyed the scooped shots to a top of the apparatus, i.e., a top of the cabinet  10 , as with a heretofore-known bucket elevator. The shots conveyed to the top by the bucket elevator  25  are stored in a shot tank via a chute, whereafter the shots are sent to a shot introduction pipe  29  via an openable-closable gate  30 , and re-projected from the projection unit  23 . 
         [0050]    The shot-blasting apparatus further comprises a dust collector  31 , and a heretofore-known foreign-substance separation unit having a separator, each provided in an upper-end region thereof. The separator is configured to separate and collect foreign substances mixed with shots, such as fine powder, by using a blower  32 . 
         [0051]    In the shot-blasting apparatus according to this embodiment, the bucket elevator  25  has a suction port (air outlet port) provided at a lower end thereof, and a suction passage for the blower  32  provided thereinside, wherein the blower  32  is operable, upon being activated, to suck air around the lower end of the bucket elevator  25  and send the sucked air to the dust collector  31  so as to collect powder dust generated in the projection chamber and others due to projection of shots. 
         [0052]    As mentioned above, each of the first and second external air introduction chambers  17 ,  18  having a cross-sectionally sector shape is formed at a position circumferentially interposed between the first and second process chambers  13   a ,  13   b . The first external air introduction chamber  17  is divided into primary and secondary small chambers  17   a ,  17   b  by a division plate  35 , and the second external air introduction chamber  18  is divided into primary and secondary small chambers  18   a ,  18   b  by a division plate  36 , wherein each of the division plates  35 ,  36  is disposed to extend in the radial direction and in the vertical direction. 
         [0053]    Each of the division plates  35 ,  36  has a lower portion formed with a vent hole  20  to establish each fluid communication between the first small chambers  17   a ,  17   b  and between the second small chambers  18   a ,  18   b , through the vent hole  20  in a corresponding one of the division plates  35 ,  36 . 
         [0054]    Each of two portions of the top plate of the rotary hanger  11  covering the respective primary small chambers  17   a ,  18   a  is formed with a suction port (external air introduction port)  19  communicated with external air. Thus, each of the primary small chambers  17   a ,  18   a  is communicated with a space outside the apparatus via a corresponding one of the suction ports  19 . 
         [0055]    Each part of the partition plates  12   b ,  12   a  located between adjacent ones of the secondary small chambers  17   b ,  18   b  whose top plate has no suction port, and the process chambers  13   b ,  13   a , is formed with two air inlet ports  22  arranged one-above-the-other and each having a vertical directionally elongate rectangular shape and providing fluid communication between adjacent ones of the secondary small chambers  17   b ,  18   b  and the process chambers  13   b ,  13   a.    
         [0056]    Each of the first and second process chambers  13   a ,  13   b  can be communicated with a corresponding one of the secondary small chambers  18   b ,  17   b  via the air inlet ports  22  in a corresponding one of the partition plates  12   a ,  12   b . That is, external air flowing into the primary small chamber  17   a  ( 18   a ) via the suction port  19  formed in the portion of the top plate corresponding to the primary small chamber  17   a  ( 18   a ) flows into the secondary small chamber  17   b ,  18   b  via the vent hole  20  of the division plate  35  ( 36 ), and further flows into the process chamber  13   b  ( 13   a ) via the air inlet ports  22  of the partition plate  12   b  ( 12   a ). 
         [0057]    Each of the air inlet ports  22  is covered by a hood  21  from the side of the secondary small chamber  17   b  ( 18   b ). The hood  21  comprises a right triangular-shaped side plates arranged side-by-side in parallel relation to each other, and a rectangular-shaped bottom plate connecting the two side plates together. The rectangular-shaped bottom plate has a width approximately equal to a width of the air inlet port  22 , and a length greater than a vertical directional length of the air inlet port  22 . 
         [0058]    Further, one of adjacent sides of the right triangle-shaped side plate extending in the vertical direction has a length approximately equal to the vertical directional length of the air inlet port  22 . 
         [0059]    The hood  21  is formed in a cross-sectionally angular C shape by joining opposite lateral edges of the bottom plate to respective oblique sides of the two side plates arranged in parallel. 
         [0060]    No component is disposed in a space between shorter adjacent sides of the two side plates. Thus, an opening opened upwardly is formed between the shorter adjacent sides of the two side plates. The secondary small chamber  17   b  ( 18   b ) is communicated with the process chamber  13   b  ( 13   a ) through the opening  22   a.    
         [0061]    On the other hand, as shown in  FIG. 5 , the bottom plate of the hood  21  is disposed on the side of the secondary small chamber  17   b  ( 18   b ) with respect to the air inlet port  22 , in such a manner as to extend upwardly from a lower edge thereof connected to a lower edge of the air inlet port  22 , while being gradually spaced away from the partition plate  12   b  ( 12   a ). Therefore, the bottom plate of the hood  21  is disposed in such a manner as to be horizontally spaced apart from the air inlet port  22  toward the secondary small chamber  17   b  ( 18   b ). 
         [0062]    This hood  21  inhibits shots flying from the processing chamber  13   b  ( 13   a ) toward the secondary small chamber  17   b  ( 18   b ) via the air inlet port  22  from intruding in the secondary small chamber  17   b  ( 18   b ). 
         [0063]    In addition, the secondary small chamber  17   b  ( 18   b ) and the primary small chamber  17   a  ( 18   a ) are partitioned therebetween by the division plate  35  ( 36 ), so that the division plate  35  ( 36 ) further inhibits a part of shots intruding in the secondary small chamber  17   b  ( 18   b ) through the opening  22   a  of the hood  21  from intruding in the primary small chamber  17   a  ( 18   b ). 
         [0064]    The shot-blasting apparatus according to this embodiment is configured such that, when one  13   b  ( 13   a ) of the first and second process chambers is set at the projection position, the air inlet ports  22  for introducing external air into the process chamber  13   b  ( 13   a ) are disposed at positions opposed to the air outlet port formed in the lower end of the bucket elevator  25 , across a central region of the process chamber  13   b  ( 13   a ). 
         [0065]    The hood  21  has the opening opened upwardly, so that, although the air inlet port  22  is covered by the hood  21  in a lateral or circumferential direction, the process chamber  13   b  ( 13   a ) and the secondary small chamber  17   b  ( 18   b ) are communicated with each other through the opening. 
         [0066]    The number of the air inlet ports  22  is not limited to two. For example, it may be four. 
         [0067]    Further, the shape of the side plate of the hood  21  is not limited to a right triangular shape, but may be any other suitable shape such as another triangular shape or a rectangular shape. 
         [0068]    Next, an operation of the shot-blasting apparatus constructed as above will be described. 
         [0069]    First of all, shots are input from a shot input port (not shown), and then motors for the dust collector  31 , the screw conveyer  26 , the bucket elevator  25 , the projection unit  23  and others are activated according to a manual operation of an operator control panel  34 , to circulate the shots around the entire apparatus. For example, the shot is a SUS 304 based shot. 
         [0070]    Subsequently, an operator carries a workpiece in the process chamber  13   a  ( 13   b ) set at the carry-in-and-out position, through the carry-in-and-out port  14  on the front-end side of the cabinet  10 . Specifically, the workpiece is attached to the jig suspended from the hanger hook. In the example, the workpiece is an aluminum die-cast component. 
         [0071]    Subsequently, the rotary hanger  11  is rotated 180 degrees to move the process chamber  13   a  ( 13   b ) having the workpiece disposed therein, from the carry-in-and-out position to the projection position on the back-end side of the apparatus. Then, the hanger hook is rotated about its own axis at a rotation speed of 10 to 15 rpm. Further, the openable-closable gate  30  is opened to feed shots stored in the shot tank  28  via the shot introduction pipe  29 , so that the shots will be projected onto the workpiece. 
         [0072]    When the process chamber  13   b  is set at the projection position as shown in  FIG. 4 , ambient air is sucked from the suction port (air outlet port) at the lower end of the bucket elevator  25 , by a suction force of the blower  32 . Thus, external air is sucked from the suction port  19  formed in a portion of the top plate corresponding to the small chamber  17   a  of the first external air introduction chamber  17 , into the small chamber  17   a . Then, as shown in  FIG. 5 , the external air sucked in the small chamber  17   a  flows into the adjacent small chamber  17   b  through the vent hole  20  formed in the lower portion of the division plate  35 , and flows into the second process chamber  13   b  obliquely downwardly through the air inlet ports  22  for air circulation. 
         [0073]    On the other hand, the second external air introduction chamber  18  is isolated from the suction force of the blower by a part of the partition plate  12   a  having no opening, so that no external air is sucked from the suction port  19 . 
         [0074]    As shown in  FIG. 4 , the external air flowing into the process chamber  13   b  obliquely downwardly through the air inlet ports  22  flows through the central region of the process chamber  13   b  where duct is most likely to be generated. Subsequently, the external air is sucked into the opening formed at the lower end of the bucket elevator  25  on the back-end side of the cabinet  10 , and sucked into the dust collector  31  via the bucket elevator  25 . As above, a flow path existing inside the bucket elevator  25  is located at a diagonal position of the cabinet  10  with respect to the suction port  19 , and utilized as a suction flow path leading to the dust collector. Air from which powder dust is removed by the dust collector  31  is released into the atmosphere. 
         [0075]    In this way, each of the air inlet ports  22  and an inlet of the suction flow path leading to the dust collector are disposed at positions opposed to each other across the central region of the process chamber  13   b  set at the projection position, so that it becomes possible to allow an air flow path along which external air supplied from the air inlet ports  22  flows to pass through a center of the process chamber  13   b  set at the projection position, thereby obtaining far excellent ventilation efficiency as compared to conventional techniques. 
         [0076]    As mentioned above, the shot-blasting apparatus according to this embodiment is configured such that a flow path of air sucked from the suction port  19  formed in a top portion of the rotary hanger  11  passes through the central region of the process chamber  13   b  set at the projection position, so that it becomes possible to enhance the ventilation efficiency of the inside of the process chamber to perform efficient dust collection. 
         [0077]    In addition, the number of external air suction ports per projection chamber is substantially one, so that it becomes possible to efficiently perform ventilation, using a relatively low-power type as the blower  32 , thereby facilitating downsizing of the apparatus. 
         [0078]    Furthermore, the inside of the bucket elevator  25  is utilized as a suction flow path, so that it becomes possible to reduce the number of ducts, thereby facilitating downsizing of the entire apparatus. 
         [0079]    It should be understood that the present invention is not limited to the above embodiment, but various changes and modifications may be made therein within the technical scope thereof as set forth in appended claims.