Abstract:
A first quantity of all the molding sand necessary to produce a mold is fed in the mold space, the first quantity being one of at least two parts divided from the total molding sand. The mold space is evacuated and then air is introduced into the mold space at the air-pressure rising rate of 30--to 500 kg/cm 2  /sec. Another quantity of the molding sand is fed into the mold space, the mold space is evacuated and then air is introduced into the mold space at the air-pressure rising rate of 30--to 500 kg/cm 2  /sec. The apparatus includes a sand passage through which each quantity of sand is fed into the mold space, and a gate for closing the sand passage thereby closing the mold space to allow the mold space to be evacuated and then subjected to a pressure increase.

Description:
FIELD OF THE INVENTION 
     This invention relates to an apparatus and a method for producing a mold (including a core) by means of air pressure, in particular, for producing a mold in a mold space in a pattern box. 
     DESCRIPTION OF THE PRIOR ART 
     Conventionally, a method to introduce molding sand via a valve at one time into a mold space in an evacuated pattern box is well known (for example, see Japanese Patent (B) 63-21582). However, in this method, since air and molding sand enter the mold space at the same time, the air reaches many parts of the mold space before the molding sand. Thus the air tends to prevent the molding sand from entering these parts. 
     Further, the molding sand that flows into the mold space tends to go straight due to its inertia. Accordingly, any parts of the mold space that extend in different directions from the flow of the molding sand are not filled with it. Especially, narrow or upwardly-extending parts tend not to be filled. To eliminate this phenomenon, vent plugs are provided in such parts to create a vacuum in them. However, to determine the best positions for vent plugs is very difficult, and a pattern box provided with vent plugs has a high cost and takes a lot of work. 
     This invention is conceived to resolve these disadvantages. Its purpose is to provide a molding method and an apparatus that can fill the narrow or upwardly-extending parts of a mold space, and that can fill a complicated mold space. 
     SUMMARY OF THE INVENTION 
     This invention is based on a discovery that if molding sand is charged part by part (aliquots) into a mold space of a pattern box, and each part is subject to air pressure, the pattern box is sufficiently filled with the molding sand. The air may be pressurized air, or ambient air that flows into a mold space wherein there is a vacuum. 
     In one of the methods of the present invention, a predetermined amount of molding sand that fills the mold space of a pattern box is divided into two parts. A first part of the molding sand is charged into the mold space. Then an air flow at a set speed is introduced into the mold space. Then the second part of the molding sand is charged into the mold space, and an air flow at a set speed is again introduced into the mold space. 
     The present invention also provides a molding apparatus to carry out this method. 
     Other structures, advantages, and features of the present invention will be apparent from the description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a first embodiment of the molding apparatus of the present invention. 
     FIG. 2 is a cross-sectional view of a second embodiment of the molding apparatus of the present invention. 
     FIGS. 3(a)-3(h) show the method of the invention carried out by the apparatus of FIG. 2. 
     FIG. 4 is a cross-sectional front view of a third embodiment of the molding apparatus of the present invention. 
     FIG. 5 is a cross-sectional side view of the apparatus of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments will now be explained in detail by reference to the accompanying drawings. FIG. 1 shows a first embodiment of a molding apparatus of the present invention. An upper hopper 1 has a belt feeder 3 that acts as means to meter and feed molding sand 2. By setting the operating time of the belt feeder 3 a first feeding amount and a second feeding amount of the molding sand are preset. 
     A port 4, which receives the molding sand 2, is disposed under an end of the belt feeder 3. This port 4 communicates with a feeding pipe 6. The pipe 6 is connected to a pattern box 8 so that the pipe communicates with the mold space 7 of the pattern box 8. The port 4 has a gate 5, which closes the pipe 6. The pattern box 8 is placed on a table 9, which moves vertically. 
     An air-suction pipe 10 is connected to the feeding pipe 6. A vacuum pump 12 is connected to the air-suction pipe 10 through an air-suction valve 11. An air-supply pipe 13 is also connected to the feeding pipe 6. The air-supply pipe 13 is connected to a compressed-air-supply tank 15 via an air-introducing valve 14. 
     In operation, by setting the operating time of the belt feeder 3, all the molding sand 2 that is necessary to produce a mold is divided into at least two parts, to preset the first and second feeding amounts of the molding sand. For a small mold, the molding sand may be divided into two to three parts, and for a large one, it may be divided into three to ten parts. Further, for a complicated mold, the number of the divided parts of the molding sand is increased in comparison with the number for a simple one. 
     Then the gate 5 is opened, and the fist amount of the molding sand metered by the belt feeder 3 drops through the port 4 into the mold space 7. The air-introducing valve 14 is closed when the molding sand is fed. The gate 5 is then closed. Under these conditions the assembly of the pipe 6 and pattern box 8 is sealingly closed. Then, the air-suction valve 11 is opened, and a vacuum in the mold space 7 is created by the vacuum pump 12. When the air pressure of the mold space 7 reaches a vacuum between 2 to 100 torr, the air-suction valve 11 is closed. Then the air-introducing valve 14 is opened so that a first compressed-air flow is introduced from the tank 15 at a pressure-rising rate of 30 to 600 kg/cm 2  /sec. Preferably, two or three compressed air flows are introduced into the mold space 7. Thus the molding sand in the mold space is subjected to the air flow or flows. Then the gate 5 is again opened. 
     The second amount of the molding sand is fed into the mold space by the belt feeder 3, and the gate 5 is closed. Then the air in the pattern box 8 is removed by the pump 12, and in the same way a compressed-air flow or flows are introduced into the mold space 7. These steps are repeated until the final amount of the divided molding sand is fed into the mold space. Thus the space is filled with molding sand, and the mold or core is produced. After this, the table 9 is lowered, and the mold is taken out. 
     As a modified embodiment, the compressed-air tank 15 may be eliminated, and ambient air flows may be introduced into the mold space instead of compressed-air flows. 
     In the first embodiment, self-curing molding sand is used. However, instead of it gas-cured molding sand may be used. If so, a gas generator 16 is connected to tie pattern box 8 so that curing gas communicates with the mold space. The curing gas is introduced into the mold space through a plate 17 after the final air flow is introduced into the mold space. 
     Although in the first embodiment a vacuum is created in the mold space 7 before the second amount of the molding sand is fed, this vacuum may not be necessary, and some air flows may be introduced into the mold space after the air-introducing valve 14 is opened. 
     In this invention the pressure-rising rate of air flows is preferably 30 to 600 kg/cm 2  /sec, and a rate of 100 to 400 kg/cm 2  /sec is more preferable. If the rate is more than 400 kg/cm 2  /sec, the air-introducing valve must be large, and thus it is not economical. 
     The range of the vacuum of the mold space is preferably between 2 to 100 torr, and within this range the highest vacuum is more preferable. 
     When the compressed-air flows are introduced into the mold space, the pressure of the compressed air is preferably 2 to 9 kg/cm 2 , and a range of 4 to 9 kg/cm 2  is more preferable. Within his range the highest vacuum is best if air of such pressure is available. 
     FIG. 2 shows a second embodiment of the molding apparatus of the present invention. The apparatus has a column 21. A roller conveyor 22 is mounted on a horizontally-extending part of the column 21. A pattern box 28, which has a plurality of molding-sand-feeding mouths, is transferred by the conveyor 22. A cover 29 is mounted on an arm 28E, which is in turn slidably mounted on a vertical guide bar 25 secured to the vertically-extending put of the column 21. The arm 28E is vertically moved along the guide bar by an actuator 23 so that the cover 29 is pressed against a filling frame M attached to the top of the pattern box 28. The cover 29 has an intermediate floor 29A, which has a central opening 29D. A cylinder 30 is mounted on the arm 28E. The cylinder 30 has an air-introducing valve 14. This valve covers the central opening to close a space 29C defined by the cover 29, filling frame M, and pattern box 28. An air passage 29B, which communicates with ambient air, is formed in the cover such that the space 29C communicates with ambient air when the valve 14 is opened. Pattern box 28 defines a molding space including upright space 28A, horizontal space 28C, and vertical space 28D between upright space 28A and horizontal space 28C. 
     The operation of the molding apparatus is now explained. In this operation gas-cured molding sand 2 is introduced into the pattern box 28 and cured. A minimum number of vent holes and vent plugs are provided in the pattern box. 
     As in FIG. 3(a), the filling frame M is placed on the halves of the pattern box, and as in FIG. 3(b) a part of the molding sand is fed into the filling frame. The molding sand fed into the box is leveled, and then as in FIG. 3(c) the space is closed by the cover. 
     Then the valve 11 is opened to create a vacuum in the closed space of 2 to 100 torr. The valve 11 is then closed, while the valve 14 is opened so that the ambient air flow enters the passage 29B, opening 29D, and space 29C at the air-pressure rising rate of 50 to 600 kg/cm 2  /sec (preferably, at the rate of 200 to 400 kg/cm 2  /sec). Accordingly, an amount of molding sand is introduced into the mold space in the pattern box 28 as in FIG. 3(d). These steps are repeated at least twice, and the results are shown in FIGS. 3(e)-(h). 
     After this, the pattern box and filling frame are moved to a gas-curing station (not shown), and the molding sand in them is gas-cured there. 
     FIGS. 4 and 5 show a third embodiment of the molding apparatus of the present invention. The apparatus includes a frame F on which are mounted, from top to bottom, a sand-container 38, mixer assembly 34, molding-sand feeder means 31, pressure-reducing means 32, ambient-air-introducing means 33, and pattern-box-transfer means 35. 
     The mixer assembly 34, which is disposed under the sand-container 38, includes upper and lower mixers 34a, 34a and a binder-supplying device (not shown). The vane 34b of each mixer rotates, mixes, and advances the sand. 
     A sand-feeding hopper 31a is disposed under the output end of the lower mixer 34a. The hopper 31a and a sand-introducing gate 31b disposed under the hopper constitute a sand-feeding means 31. When the gate 3lb is opened, a predetermined amount of mixed molding sand is fed into a mold space 39 in a pattern box 42. 
     The pressure-reducing means 32, which includes a hollow container V has a port V1 which, is disposed under the sand-feeding means 31. At one end the hollow container V communicates with the opening of the pattern box 42. At the other end it communicates with a vacuum pump 12 through an air-suction valve 11 and a filter 32c. A vacuum is created in the mold space 39 to a range between 2 to 100 torr. 
     Further, air-introducing means 33 is integrally mounted on the hollow container V. This means has an air-introducing valve 33a through which ambient air is introduced into the mold space 39 (see FIG. 4). 
     The pattern box 42 is horizontally transferred by a conveyor 35, and is raised to a predetermined level by a cylinder 36. The hollow container is lowered and sealingly its port V1 is pressed against the opening of the pattern box 42 by an actuator 40 mounted on the frame F. 
     In operation, the molding sand fed onto mixers is supplied with a binder from a binder-supply device (not shown). As in the first embodiment, since the time to operate and stop the mixers is preset an amount of mixed molding sand to be discharged is preset. 
     Creating a vacuum in the mold space 39 and introducing into it ambient-air flows are done as in the first embodiment.