Patent Publication Number: US-6662855-B1

Title: Molding device and molding method or sand mold

Description:
FIELD OF THE INVENTION 
     This invention relates to an apparatus and a method for producing a sand mold, in particular, to an apparatus and a method for producing a sand mold wherein both introducing molding sand into a mold space and compacting the introduced molding sand are performed at one station. 
     DESCRIPTION OF THE PRIOR ART 
     In a conventional method of producing a sand mold by a mold-producing installation wherein both molding and teeming are performed while a sand mold is being held in a flask, it is known that introducing molding sand into a flask and compacting the introduced molding sand are performed in two different stations, which are spaced apart from each other (for example, JP 3-35842, A). Since both introducing molding sand into a flask and compacting molding sand introduced into another flask are simultaneously performed at that installation, sand molds are produced at a high rate. However, the installation requires both a molding-sand introducing station and a molding-sand compacting station, and further, requires more time and energy to transfer flasks between the two stations. Further, a molding machine must be provided with transfer equipment. For these reasons, a problem is caused in that the molding machine is complicated and expensive. 
     In another conventional method of producing a sand mold, wherein both the introduction and compaction of molding sand is performed in a single station, a ram must be horizontally moved above a mold space to compact the molding sand that has been introduced into the mold space. This also requires installing transfer equipment. Thus the same problem is caused, in that the molding machine is complicated and expensive. 
     The purpose of the present invention is to resolve those problems and to provide an apparatus and a method for producing sand molds wherein the cycle of producing them is shortened, and energy consumption is reduced. 
     SUMMARY OF THE INVENTION 
     In one aspect of the apparatus of the present invention for producing a sand mold, a plurality of nozzles are mounted on a lower portion of a sand hopper that contains molding sand, and a plurality of squeeze feet, the pressure of which is controlled, are mounted on the lower portion of the sand hopper at locations adjacent to a side of each nozzle. The sand hopper is supported by supporting means in such a manner that it can move vertically. A pattern plate having a pattern, a flask, a filling frame, and the sand hopper having the squeeze feet that are disposed above the filling frame all define a mold space. The molding sand in the sand hopper is introduced into the mold space by discharging it from the nozzles of the sand hopper, and the molding sand in the mold space is compacted by the squeeze feet when the sand hopper is lowered to the mold space. In the molding machine so arranged, both introducing molding sand into the mold space and compacting the molding sand in the mold space are performed at one station (a molding-sand introducing and compacting station). Thus the purpose of the invention is achieved. 
     In an example of the aspect, the supporting means hold the flask so that it moves vertically. 
     In an example of the aspect, either the supporting means or the sand hopper holds the filling frame so that it moves vertically relative to the sand hopper. 
     In both examples the molding space is readily defined, and the filling frame can be positioned at the level of a pass line (a transfer passage for flasks) that passes through the molding-sand introducing and compacting station of the molding machine. 
    
    
     Other aspects and advantages of the present invention will be understood when some preferred embodiments, which will be described below by reference to the accompanying drawings, are reviewed. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a schematic side view of a molding machine of an embodiment of the present invention, also showing a pass line along which flasks are transferred, and which relates to the molding machine. 
     FIG. 1 b  is a schematic front view of the molding machine of FIG. 1 a.    
     FIG. 2 is a front view of a molding machine of the first embodiment of the present invention. 
     FIG. 3 is a bottom view of a sand hopper of the molding machine of FIG.  2 . 
     FIG. 4 is a schematic sectional view of the squeeze feet of the molding machine of FIG.  2 . 
     FIG. 5 is an explanatory drawing showing a sand hopper of the molding machine together with an aeration device. 
     FIG. 6 shows the molding machine of FIG. 2 where a mold space has just been defined. 
     FIG. 7 shows the mold space of FIG. 6 into which molding sand has been introduced. 
     FIG. 8 shows the molding sand in the mold space of FIG. 7 that has just been compacted. 
     FIG. 9 shows a sand mold held in a flask that is moved from the state shown in FIG. 8, i.e., being separated from a pattern plate, and that is located on the pass line. 
     FIG. 10 is a front view of the molding machine of the second embodiment of the present invention. 
     FIG. 11 shows the molding machine of FIG. 10 where a mold space has just been defined. 
     FIG. 12 shows the mold space of FIG. 11 into which molding sand has been introduced. 
     FIG. 13 shows the state of the molding sand in the mold space of FIG. 12 being primarily compacted. 
     FIG. 14 shows the sand mold being further, or secondarily, compacted from the state as in FIG.  13 . 
     FIG. 15 shows the molding machine shown in FIG. 14 wherein a sand mold held in a flask has been separated from a pattern plate and located on the pass line. 
     FIG. 16 shows the molding machine of FIG. 15 wherein a new, empty flask has been transferred into the molding-sand introducing and compacting station of the molding machine, and a new pattern plate has been disposed at the station by a transfer device. 
     FIG. 17 is a front view of the molding machine of the third embodiment of the present invention. 
     FIG. 18 is a sectional view showing some nozzles and squeeze feet of a sand hopper of the molding machine of FIG.  17 . 
     FIG. 19 is a cross-sectional bottom view along line XV—XV showing an array of the nozzles and the squeeze feet. 
     FIG. 20 shows the molding machine of FIG. 17 wherein a mold space has just been defined. 
     FIG. 21 shows the mold space of FIG. 20 into which molding sand has been introduced. 
     FIG. 22 is an explanatory drawing to show the introduction of compressed air into the molding sand in the mold space of FIG. 21 to pre-compact the molding sand. 
     FIG. 23 shows the molding sand being further compacted from the state shown in FIG. 22 by the molding-sand introducing and compacting device of the molding machine. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The outline of the molding machine of the present invention is explained relative to FIG. 1; the first embodiment of the molding machine is explained relative to FIGS. 2-9; the second embodiment of it is explained relative to FIGS. 10-16, and the third embodiment is explained relative to FIGS. 17-23. In the specification and these drawings the same reference numbers are used for the same or similar elements. 
     In FIG. 1 a  a pass line  2  (a transfer passage for flask  4 ) is disposed so that it passes through a molding machine  8  (for producing a sand mold) of the present invention. Empty flasks  4  are transferred along the pass line  2  from the left, and each flask  4  is located at a molding-sand introducing and compacting station  10  of the molding machine  8 . A sand mold  6  is produced in the flask  4  by a molding-sand introducing and compacting device  12  at the station  10 , and the sand mold  6  held in the flask  4  is transferred to a teeming station (not shown) that is located on the pass line  2 . 
     As shown in FIG. 1 b , a pattern plate is carried by a carrier  14  and is transferred from the outside of the molding-sand introducing and compacting station  10  to the station  10  by a transfer device  16 . 
     A first embodiment of the molding machine is explained in detail relative to FIGS. 2-9. First, as in FIG. 2, a base  20  is fixedly mounted on a floor, and a plurality of upwardly facing cylinders  22  are mounted on the base  20 . Although the number of the cylinders  22  may normally be two or four, two cylinders  22 ,  22  are used in the example shown in the drawing. A rigid mounting frame  26  is secured to the distal ends of the piston rods  24 ,  24  of the cylinders  22 ,  22 . A sand hopper  28  is fixedly mounted on the central portion of the mounting frame  26 . The cylinders  22 ,  22  and the mounting frame  26  act as supporting means for vertically carrying the sand hopper  28 . A chute  30  having a slant wall for guiding sand is disposed on the top of the sand hopper  28 , and a slide gate  32  is disposed under the chute  30  such that sand is introduced by a known device from above into the sand hopper  28  through the chute  30  and an opening  34  when the gate  32  is opened. FIG. 2 shows the sand hopper  28  being almost filled with molding sand S 1 . A pipe  36  for introducing compressed air into the sand hopper is connected to the upper part of the sand hopper  28  through its wall. The pipe  36  is connected to a valve  38  that is in turn connected to a source of compressed air (not shown). 
     As shown in FIGS. 2 and 3, the lower portion  40  of the sand hopper  28  diverges, and the diverging portions are tapered and have two nozzles  42 ,  42  at their lower ends. A cover member  44  fits on the nozzles  42 ,  42 , and a plurality of (twelve in the example shown in the drawings) squeeze feet  46  are mounted on the cover member  44  at locations adjacent to one side of the nozzles  42 . 
     FIG. 4 is a schematic sectional view of the squeeze feet  46 . As is shown in this drawing, the leftmost squeeze foot  46  is in its upper position, and the two right squeeze feet  46  are in their lower positions. When air is introduced into a first air passage  48  of any one of the squeeze feet  46 , while air is being discharged from its second air passage  50 , that the squeeze foot  46  is raised to its upper position as the leftmost squeeze foot. In contrast, when air is introduced into the second air passage  50 , while air is being discharged from the first air passage  48 , the squeeze foot  46  is lowered to its lower position. Any one of the squeeze feet  46  may be located in an intermediate position between the upper and lower positions. If the pressure of the air in a squeeze foot is appropriately controlled, the position of the squeeze foot, in particular when a force is applied to it, can be controlled. Each squeeze foot acts as a ram, the pressure of which is controlled. The squeeze foot is a kind of an air (pneumatic) cylinder, and thus alternatively a ram that is mounted on an ordinarily used pneumatic cylinder may be used. Further, alternatively a hydraulic or electrical cylinder may be used if its pressure is controlled. Thus the squeeze foot includes the use of such cylinders in this invention. 
     FIG. 2 is now referred to again. The squeeze feet  46  all are at their upper positions in this drawing. When they are in the upper positions, their lower ends and the lower ends of the nozzles  42  are in the same horizontal plane. A filling frame  52  is disposed adjacent to the circumference of the external wall of the lower portion  40  of the sand hopper  28 . A pair of cylinders  56 ,  56  that are attached to the external wall of the lower portion  40  of the sand hopper  38  carry the filling frame  52  such that it moves vertically relative to the supporting means  22 ,  26  and the sand hopper  28 . A plurality of vent holes  54  are formed in the filing frame  52 . These vent holes  54  are provided for controlling discharging air caused by aeration (this will be explained in detail below). The molding sand S 1  in the diverging portions of the lower portion of the sand hopper  28  (portions upstream of and adjacent to the nozzles  42 ,  42 ) is fluidized by an aeration device  58 . 
     As is shown in FIG. 5, plates  62  formed with many holes are disposed inside the walls of the diverging portions so that air chambers  60  are formed there. Compressed air is supplied by a compressed air supplying and blowing device  64  through the chambers  60  to the molding sand S 1  in the sand hopper to fluidize it. 
     FIG. 2 is again referred to. A pair of upright members  66  are suspended from the mounting frame  26 , and a roller device or conveyor  68  is disposed on the lower ends of the upright members  66 . The conveyor  68  acts to transfer the flasks  4  along the pass line  4  shown in FIG. 1 a . The flask  4  shown in FIG. 2 is located on the pass line  2 . 
     A pattern plate carrier  14   a  is disposed under the hopper  28  and the flask  4  (i.e., it is disposed at the molding-sand introducing and compacting station  10  in FIG.  1 ). The carrier  14   a  is connected via the transfer device  16  to another pattern plate carrier  14   b  located outside the molding-sand introducing and compacting station  10 . The transfer device  16  in the embodiment is a revolving mechanism that changes the locations of the pattern plate carriers  14   a ,  14   b  by rotating them. Alternatively, as a transfer device a reciprocating linear movement device that has a single pattern carrier plate and that linearly moves it between two places, one being at the molding-sand introducing and compacting station  10 , the other being outside the station, may be used. A gap  70  of about 5mm is located between the bottom of the pattern carrier plate  14   a  and the base  20 , and a plurality of springs, for example, plate springs (not shown), are disposed in the gap  70 . The pattern plate carrier  14   a  is supported by the springs. The pattern plate carriers  14   a ,  14   b  may respectively carry different pattern plates (for example, a pattern plate  72   a  for a cope and a pattern plate  72   b  for a drag). A pattern  74   a  is fixed to the pattern plate  72   a  located on the carrier plate  14   a . A plurality of vent holes (not shown) are formed in the pattern plate  72   a  and the pattern plate carrier  14   a.    
     A plurality of cylinders  76  are embedded in the pattern plate carrier  14   a  (and  14   b ), and a leveling frame  80  that encloses a circumferential edge of the pattern plate  72   a  ( 72   b ) is attached to the piston rods  78  of the cylinders  76 . The top of the leveling frame  80  in FIG. 2 is in its upper position and protrudes from the top surface of the circumferential edge of the pattern plate  74   a  ( 74   b ) at that position. The lower position of the top of the leveling frame  80  is at the same level as the top surface of the circumferential edge of the pattern plate  74   a  ( 74   b ) (see FIG.  8 ). 
     The operation of the molding machine arranged as explained above will be explained below. 
     From the state shown in FIG. 2 the supporting cylinders  22 ,  22  and the cylinders  56 ,  56  of the filling frame are actuated to lower the flask  4 , the sand hopper  28 , and the filling frame  52  so that the flask  4  is placed on the leveling frame  80  and so that the filling frame  52  is placed on the flask  4 . At that time the pattern plate carrier  14   a  is pushed toward the base  20  against the resilient force of the springs. The squeeze feet  46  are then lowered to their lower positions so that they protrude into the filling frame  52 . This state is shown in FIG.  6 . Under that state a mold space (a space into which molding sand is introduced) is defined by the pattern plate  72   a  having the pattern  74   a , the flask  4 , the filling frame  52 , and the sand hopper  28  that includes the squeeze feet  46  (the molding-sand introducing and compacting device  12  in FIG.  1 ). The pattern  74   a  protrudes upward at the center of the lower part of the mold space, and correspondingly the squeeze feet  46  protrude downward at the center of the upper part of the mold space. 
     The aeration device  58  of FIG. 2 is then operated to fluidize the molding sand S 1  held in the lower portion  40  of the sand hopper  28  at the locations upstream of and adjacent to the nozzles  42 ,  42 , and the valve  38  is opened to introduce compressed air into the sand hopper  28  through the pipe  36 , so that the molding sand is discharged from the nozzles and introduced into the mold space, as shown in FIG.  7 . Since the aeration device  58  is used to fluidize the molding sand S 1  in the lower portion  40  of the sand hopper  28 , the pressure of the compressed air that is introduced into the sand hopper through the pipe  36  can be low (for example, 0.05-0.18 MPa, preferably 0.05-0.10 MPa). As is performed in this embodiment, introducing molding sand into a mold space by supplying a compressed airflow under a low pressure to the surface of the molding sand S 1 , and by simultaneously fluidizing the molding sand S 1  of the lower portion  40  of the sand hopper (this introduction of the molding sand is herein called “aeration introduction”), enables, in comparison with the blowing introduction of molding sand, the molding sand to be gently introduced, and in particular, to be introduced into a mold space having a complicated pattern (in particular, having a long pocket). The aeration introduction also reduces the amount of air to be used. By reason of these advantages, preferably the aeration introduction is used. However, alternatively, the molding sand S 1  can be introduced by the conventional blowing introduction, according to the case. When the blowing introduction is used, the pressure of the air to be introduced from the compressed-air introducing pipe  36  is 0.2-0.5 MPa (it is unnecessary to fluidize the molding sand S 1  in the lower portion  40  of the sand hopper by aeration). Further, alternatively it is possible to introduce the molding sand into the mold space by just aerating the molding sand S 1  in the lower portion  40  of the sand hopper. Discharging the air that is introduced into the sand hopper  28  to introduce the molding sand into the mold space is performed by controlling the vent holes  54  formed in the filling frame  52  and the vent holes (not shown) formed in the pattern plate  72   a.    
     From the state shown in FIG. 7 the cylinders  56 ,  56  of the filling frame are caused to be free to move, and the supporting cylinders  22 ,  22  are actuated under a pressure that is higher than the controlling pressure of the squeeze feet  46  to lower the sand hopper  38  and the squeeze feet  46 . Further, the cylinders  76  for the leveling frame are set so that their actuating fluid is free to be discharged from them, and the sand hopper  28  and the squeeze feet  46  are further lowered until the squeeze feet  46  reach their upper positions. Thus the molding sand S 2  in the mold space is compacted (as in FIG.  8 ). Since the leveling frame  80  is kept at its position during the squeezing operation up to the intermediate point in the squeezing operation and then released from that position, the sand mold is well compacted. 
     Removing the sand mold  6  with the flask (FIG. 9) is now explained. From the state shown in FIG. 8 the cylinders  56 ,  56  of the filling frame are retracted, and the cylinders  76  are actuated to raise the leveling frame  80  and push it against the flask  4 . The piston rods  24 ,  24  of the supporting cylinders  22 ,  22  are then extended to raise the sand hopper  28 . Thus, as shown in FIG. 9, the filling frame  52  is raised relative to the sand hopper  28 ; the flask  4  holding the produced sand mold  6  therein is raised to the level of the pass line  2 , shown in FIG. 1 a , by the roller device (conveyor)  68  mounted on the lower ends of the upright members  66 ; and the sand hopper  28  is raised to a position above the flask  4 . The sand mold  6  having the flask  4  is then transferred along the pass line  3  to the teeming station. The sand mold  6  having the flask is raised a small distance from its stationary state when it is removed from the pattern plate. Since this raising is performed when the piston rods  24 ,  24  of the supporting cylinders  22 ,  22  are maximally retracted, accurate removing is achieved. 
     In relation to FIGS. 10-16, the second embodiment is now explained. A flask  4  (FIG. 10) is on the pass line  2  of FIG. 1 a  and is located at the molding-sand introducing and compacting station  10 . In the second embodiment, a base  20 , pattern plate carriers  14   a ,  14   b , cylinders  76  embedded in the pattern plate carriers  14   a ,  14   b , leveling frames  80  attached to the piston rods  78  of the cylinders  76 , a gap  70  disposed between the base  20  and each pattern plate carrier, springs disposed in the gap, a transfer device  16 , a slide gate  32 , a sand-introducing opening  32 , a compressed-air introducing pipe  36  of a sand hopper  28 , a filling frame  52 , vent holes  54  of the filling frame, cylinders  56 ,  56  of the filling frame attached to the sand hopper  28 , a flask  4 , a conveyor  68  that carries the flask, and a pair of upright members  66 ,  66  for supporting the conveyor are the same as those in the first embodiment. Thus the same reference numbers are used for these elements, and they will not be further described. 
     In FIG. 10, four upwardly facing cylinders  22  are mounted on the base  20 , and a rigid mounting frame  26  is secured to the distal ends of the piston rods  24  of the cylinders  22 . A sand hopper  28  is secured to a substantially central part of the mounting frame  26 . The lower portion of the sand hopper  28  is divided into a plurality of (four in the example shown in the drawing) sand passages, and four nozzles  42  are formed at their distal ends. A plurality of squeeze feet  46  are arranged in a grid array adjacent to a side or sides of the nozzles  42 . The structure of each squeeze foot  46  is the same as that of the squeeze foot shown in FIG. 4 relative to the first embodiment. When the squeeze foot  46  is in its upper position, its bottom is at the level of the bottom of each nozzle  42 . In FIG. 10 the central squeeze foot  46  is in its lower position, and the right and left squeeze feet  46  are in a position between the upper position and the lower position. As in the first embodiment, air chambers  60  for aeration are provided inside the peripheral walls of the four divided portions of the lower portion of the sand hopper  28 . Compressed air is supplied to the chambers  60  by using a device like the compressed-air supplying and blowing device shown in FIG.  5 . Thus the compressed air jet is supplied from the chambers  60  to the molding sand S 1  adjacent to and upstream of the nozzles  42  to fluidize it there. 
     The operation of the molding machine of FIG. 10 is now explained. From the state shown in FIG. 10 the piston rods  24  of the supporting cylinders  22  are retracted to lower the sand hopper  28  and the flask  4 , while the cylinders  56 ,  56  of the filling frame  52  are being actuated to lower the filling frame  52  relative to the sand hopper  28 , as shown in FIG.  11 . In FIG. 11 the leveling frame, the pattern plate, the flask, the filling frame, and the sand hopper that includes the squeeze feet define a mold space. The squeeze feet  46  protrude into the mold space. As is used in the first embodiment, by using the aeration introduction where the aeration device is operated to fluidize the molding sand in the lower portion of the sand hopper  28 , while compressed air of a low pressure is being introduced through the air introducing pipe  36 , the molding sand S 1  in the sand hopper  28  is introduced into the mold space. FIG. 12 shows the molding sand S 2  introduced into the mold space. As in FIG. 13, the cylinders  56  of the filling frame are retracted, while the piston rods  24  of the supporting cylinders  22  are being further retracted to compact the molding sand S 2  in the mold space (the primary squeeze). In this primary squeeze the squeeze feet  46  are retracted to their upper position, and the height of the molding sand S 2  substantially equals the total height of the leveling frame  80  and the flask  4 . Further, the slide gate  32  is opened to the right, and the opening  32  is exposed. Further, in the primary squeeze the operation of retracting the supporting cylinders  22  is continued until the pressure of the primary squeeze, which is measured by a sensor (not shown), reaches its nominal pressure, or until the encode position of the piston rods of the cylinders  22  reaches the nominal value of the primary squeeze. 
     The cylinders  76  of the leveling frame  80  are then set so that the actuating oil in them is free to be discharged therefrom, while the supporting cylinders  22  are being retracted under a pressure higher than that of the primary squeeze to lower the squeeze feet  46 , the filling frame  52 , and the flask  4  to further compact the molding sand S 2  (the secondary compaction). Thus the leveling frame  80  is lowered to its lower position, which is at the level of the upper surface of the circumferential edge of the pattern plate  72   a , as shown in FIG.  14 . If the pressure of the secondary squeeze does not reach the nominal pressure even when the leveling frame  80  reaches its lower position, a further squeeze is performed by retracting the cylinders  56 ,  56  of the filling frame and by further retracting the supporting cylinders  22 . 
     When the pressure of the secondary squeeze reaches the nominal pressure of the secondary squeeze, a timer (not shown) starts, and squeezing under the nominal pressure of the secondary squeeze is maintained for a predetermined period of time. Due to the squeezing being maintained for a predetermined period of time, the air contained in the molding sand S 2  in the flask (a sand mold) can be squeezed out. If the leveling frame  80  does not reach its lower position at that time, the cylinders  56 ,  56  of the filling frame are extended to lower the filling frame  52  until the leveling frame  80  reaches its lower position. By doing so, the bottom of the flask  4  is at the same level as the bottom of the sand mold. 
     As in FIG. 15, the cylinders  76  are then actuated to raise the leveling frame  80 , and the piston rods  24  of the supporting cylinders  22  are extended. Thus the sand hopper  28 , the filling frame  52 , the squeeze feet  46 , and the pair of upright members  66  are together raised to their original positions, and the flask  4  holding the sand mold  6  is picked up by the conveyor  68  attached to the pair of the upright members  66  and is located on the pass line. Molding sand S 1  is introduced into the sand hopper  28 . 
     As in FIG. 16, a new, empty flask is transferred along the pass line to the molding-sand introducing and compacting station, and the transfer device  16  is rotated to change the pattern plates  72   a ,  72   b  so that the pattern plate  72   b  is positioned at the station. Further, the outside squeeze feet  46  are lowered to their lower position so that the central squeeze feet  46  are concave relative to the outside ones. This concave shape corresponds to the opposite, concave pattern plate  72   b.    
     The same molding process is repeated. 
     By means of FIGS. 17-23 the third embodiment of the molding machine will be explained. The flask  4  shown in FIG. 17 is located at the molding-sand introducing and compacting station of the molding machine and located on the pass line  2  of FIG. 1 a . The molding machine in FIG. 17 has four downwardly facing supporting cylinders  22  that are fixed to a predetermined place (for example, a ceiling frame). A rigid mounting frame  26  is secured at its four corners to the distal ends of the piston rods  24  of the supporting cylinders  22 . A pair of upright members  66  are suspended from the sides of the mounting frame  24  (the sides where the supporting cylinders  22  are located in FIG.  17 ). A roller device (conveyor)  68  that transfers the flask  4  along the pass line is mounted on the lower ends of the upright members  66 . 
     A sand hopper  28  is secured to the central portion of the mounting frame  26 . The sand hopper  28  is supported by the supporting means (the supporting cylinders  22  and the mounting frame  26 ) so that it moves vertically. Molding sand S 1  has been introduced into the sand hopper  28  through a chute  30  and an opening  34 , which is exposed when a slide gate  32  is opened. The lower end of the sand hopper  28  is divided into several portions (nine portions in the example shown in the drawing), each of which is shaped as a funnel, and these portions penetrate the mounting frame  26  and form nozzles  42  at their distal ends. When a valve  38 , which is connected to a source of compressed air (not shown), is opened to introduce compressed air into the hopper through the pipe  36 , the molding sand S 1  is discharged downwardly from openings  43  formed in the distal ends of the nozzles  42 . 
     In FIGS. 17-19 an array of squeeze feet  46  (sixteen squeeze feet in the example shown in the drawings) are disposed adjacent to the sides of the nozzles. These squeeze feet are mounted on the mounting frame  26  and have the same structure and do the same work as those used in the first embodiment. A pair of downwardly facing cylinders  82 ,  82  are mounted on the mounting frame  26  at the sides of the sand hopper  28 , and a bottom cover  84  is secured to the distal ends of the piston rods of the cylinders. The cover  84  is arranged to close the openings  43  of the nozzles  42  when the piston rods of the cylinders  82 ,  82  are fully extended. 
     In FIG. 17 another pair of downwardly facing cylinders  56 ,  56  for a filling frame are mounted on the mounting frame  26  inside the supporting cylinders  22 , and a filling frame  52  is secured to the distal ends of the piston rods of the cylinders  56 ,  56 . A groove is formed in the bottom of the mounting frame  26 , and the upper end of the filling frame  52  enters the groove when the filing frame is in its upper position (i.e., when the piston rods of the cylinders  56 ,  56  of the filling frame are fully retracted). A plurality of air supply pipes  86  that penetrate the walls of the mounting frame  26  are disposed, and each air supply pipe  86  is connected to a source of compressed air (not shown) through a valve  88 . As in the first embodiment, a pattern plate  72   a  having a pattern  74   a  is disposed under the sand hopper  28  and the flask  4 . 
     The operation of the molding machine arranged as explained above is now explained. From the state shown in FIG. 17, the piston rods  24  of the supporting cylinders  22  are extended to lower the mounting frame  26  (and therefore the sand hopper  28 , the upright members  66 , and the flask  4 ), while the cylinders  56  are being actuated to lower the filling frame  52 . Further, four central squeeze feet  46  (as in FIG. 19) are extended to their lower positions. Thus, as in FIG. 20, the flask  4  is placed on the pattern plate  72   a ; the filling frame  52  is placed on the flask  4 ; and the sand hopper  28  that includes the squeeze feet  46  is located just above the filing frame  52 . The pattern plate  72   a , the flask  4 , the filling frame  52 , and the sand hopper  28  that includes the squeeze feet  46  define a mold space. The air supply pipes  86  in FIG. 20 are in fluid communication with the mold space. 
     From the state shown in FIG. 20 the valve  38  is opened to introduce compressed air into the sand hopper  38 , as shown by arrows in FIG.  21 . Thus the molding sand S 1  in the sand hopper  28  is introduced into the mold space by the blowing introduction. The air introduced during this blowing introduction is discharged from the vent holes (not shown) formed in the pattern plate  72  and from the air supply pipes  86 . As is clear from FIG. 21, the molding sand S 2  introduced into the mold space is concave at the top central part and is also concave at the bottom central part (because the part is occupied by the pattern). From this state, as shown in FIG. 22, the cylinders  82 ,  82  are actuated to lower the bottom cover  84  to close the openings  43  of the nozzles, and the compressed air is introduced into the mold space through the air supply pipes  86  as shown by the arrows to pre-compact the molding sand S 2 . 
     The cylinders  56 ,  56  of the filling frame are then retracted, while the piston rods  24  of the cylinders  22  are being extended under a pressure higher than the control pressure of the squeeze feet  46  to further lower the sand hopper  28  until the squeeze feet  46  reach their upper locations, to further compact the molding sand S 2  in the mold space. Thus, as shown in FIG. 23, the upper surface of the molding sand S 2  is leveled by the bottoms of the squeeze feet  46 , and the molding sand is uniformly compacted regardless of the different thicknesses (heights) it may have in the flask  4  and the filling frame  52 . 
     From the state shown in FIG. 23 the piston rods  24  of the supporting cylinders  22  are retracted to raise the sand hopper  28 . Thus the flask  4 , holding a produced sand mold, is brought up to the level of the pass line  2  by the conveyor  68 . 
     The sand mold held in the flask is transferred along the pass line away from the molding-sand introducing and compacting station of the molding machine, and a new flask  4  is transferred into the station. Further, molding sand S 1  is introduced in the sand hopper  28  through its upper opening  34 , and the slide gate  32  is then closed. The cylinders  82  are then actuated to raise the bottom cover  84 , so that the molding machine is restored to its original state (the state shown in FIG.  17 ). 
     Although some embodiments of the present invention have been explained above, these are exemplary only, and do not limit the present invention. The invention is to be defined by the claims.