Molding Method

Abstract

This application relates to a molding method including steps of embedding a form made of an instantaneously combustible material in a filler material in a flask covering the top of the flask, inducing negative or sub-atmospheric pressure in the filler material thereby compacting same, and pouring a molten metal into the form, whereupon the form material is gassified and the resultant gases are positively removed from the mold system.

Description

This invention relates to a molding method.

In one molding method known in the art as a full mold method which permits simplification of a molding operation, an instantaneously combustible form made of a bubble producing synthetic resinous material is embedded in a filler material in a flask, and a molten metal is poured into the form to produce a casting.

Some disadvantages are associated with this molding method. Gases produced when the form is burned by the heat of the molten metal or the shrinkage of the form caused by the heat of the molten metal may destroy the shaping surfaces of the form and render them irregular. As a result, the filler material may get entangled in the molten metal, causing fusion and penetration to occur in surfaces of the casting produced.

Moreover, gases produced when the form is burned by the heat of the molten metal may stay in the mold and their pressure may cause the molten metal to flow in reverse current to the gate. This makes it impossible to perform pouring satisfactorily, thereby preventing a product of good quality from being produced.

This invention has as one of its objects the provision of a molding method which obviates the aforementioned disadvantages of the prior art.

Another object of the invention is to provide a molding method in which an instantaneously combustible form is embedded in a filler material to form the filler material into a shape which is in conformity with the shaping surface of the form and a molten metal is poured into the form after a negative or sub-atmospheric pressure is induced in the filler material to maintain the shape of the filler material. Part or the whole of the gases produced when the form is burned by the heat of the molten metal is drawn into the filler material to reduce the influence of gases on the product. The filler material is rendered compact and maintained in the desired shape by the negative pressure. Thus, the filler material need not contain a binder therein, thereby facilitating removal of the filler material from the product after being taken out of the mold and making it unnecessary to effect adjustments of the composition of the filler material. This molding method enables increases in operational efficiency, with the filler material being used again and again.

Another object of the invention is to provide a molding method in which an instantaneously combustible form is covered with a shield member before being embedded in a filler material to form the filler material into a shape which is in conformity with the shaping surface of the form, and a molten metal is poured into the form after a negative or sub-atmospheric pressure is induced in the filler material to render the filler material compact and have the shape of the filler material maintained. The presence of the shield member between the filler material and the molten metal precludes disintegration of the filler material, entanglement of the filler material in the molten metal to cause fusion and penetration to occur on the surfaces of the casting produced. This molding method enables a casting of a predetermined shape and high quality to be produced positively.

Another object of the invention is to provide a molding method in which a gas vent is provided on an instantaneously combustible form embedded in a filler material to form the filler material into a shape which is in conformity with the shaping surface of the form, and a molten metal is poured into the form. By this arrangement, gases produced when the instantaneously combustible form is burned by the heat of the molten metal can be readily vented to atmosphere as soon as they are produced without remaining in the mold and the molten metal can be poured into the form without any trouble, so that a casting of a predetermined shape and high quality can be produced positively.

Other and additional objects as well as features and advantages of the invention will become evident from the description set forth hereinafter when considered in conjunction with the accompanying drawings, in which:

FIG. 1, FIG. 2 and FIG. 3 are vertical sectional views of the mold used in the different embodiments of the molding method according to this invention;

FIG. 4 is a flask used in another embodiment of the molding method according to this invention; and

FIG. 5 and FIG. 6 are vertical sectional views showing molding steps of the molding method according to this invention.

A first embodiment of the invention will be described with reference to FIG. 1 in which 1 designates a flask having an open top and provided with an evacuation pipe system 2 formed therein with a multitude of openings 3 and having a filter 4 made as of wire netting wound thereon. The evacuation pipe system 2 is formed at one end thereof with an evacuation port 5.

6 is a form made of an instantaneously combustible synthetic resinous material, such for example as foamed polystyrene, and having a shape similar to the shape of a casting to be produced. As shown, the form 6 comprises a main body 7 of a polygonal annular shape defining an opening 8 and having a plurality of openings 9 in the body, a runner 10 and a gate 11, the runner 10 and gate 11 being also made of an instantaneously combustible synthetic resinous material and formed integrally with the main body 7.

In operation, the form 6 is placed in the flask 1 and a filler material 12 which may be molding sand or other heat resisting particle material fills the flask so that the filler material 12 may fill the openings 8 and 9. The flask 1 and the form 6 are vibrated as a unit by means of a vibrator (not shown) to solidly pack the filler material.

Then, the open top of the flask 1 is covered with a lid 13 which may be of a synthetic resin film, and the interior of the flask 1 is evacuated by a vacuum pump (not shown) or any other suction means which is connected to the evacuation port 5 of the evacuation pipe system 2 so as to induce a negative or sub-atmospheric pressure in the flask. A molten metal is poured through the gate 11 and the runner 10 into the main body 7 of the form 6. The form 6 is burned by the heat of the molten metal, and a casting similar in shape to the main body 7 of the form 6 can be produced.

The interior of the flask is maintained at a sub-atmospheric pressure while the molding operation is being performed, so that the integrity of the filler material 12 is maintained without undergoing disintegration.

The openings 8 and 9 in the form 6 may be formed by using separate cores.

A second embodiment of the invention will be described with reference to FIG. 2 in which 21 is a flask having an open top and having an evacuation chamber 22 formed therein by partitioning a central portion of the flask 21 from the evacuation chamber 22 by a porous partition 23. A filter 25 which may be made of wire netting is mounted on the inner side of the porous partition 23 such that the filter closes small openings 24 in the porous partition 23. Evacuation ports 26 which are maintained in communication with the evacuation chamber 22 are provided in the flask 21 and connected to a vacuum pump (not shown) or other suction means.

27 designates a form made of an instantaneously combustible material. The form 27 is made of a foamed synthetic resinous material or other material which is readily burned by the heat of a molten metal when the latter is poured and formed into a shape which is similar to the shape of a product to be produced by casting.

A runner 28 made of an instantaneously combustible material is formed integrally with the pattern 27 at one side thereof, and a gate 29 made of an instantaneously combustible material is formed integrally with the runner 28 at its upper portion. The gate 29 diverges upwardly.

A shield member 30 covers outer surfaces of the form 27, runner 28 and gate 29. The shield member 30 may be provided by applying a synthetic resin liquid to the outer surfaces of the form, runner 28 and gate 29 to provide a coat, by bringing a synthetic resin film into intimate contact with the outer surfaces of the form, runner 28 and gate 29, or by forming a layer of plaster or clay on the outer surfaces of the form, runner 28 and gate 29.

A filler material 31 which may be molding sand or other heat resisting particle material containing no binder therein is filled in the central portion of the flask 21 partitioned from the evacuation chamber 22 by the porous partition 23 to a suitable depth, and the form 27 integrally formed with the runner 28 and gate 29 is place on the filler material 31 in the central portion of the flask 21.

Then, the filler material 31 is again filled in the central portion of the flask 21 to embed the form 27, runner 28 and gate 29 in the filler material 31. Thereafter, a lid 32 which may be of a synthetic resin film is placed on the open top of the flask 21.

If the suction means connected to the evacuation ports 26 provided in the flask 21 is actuated, then the interior of the central portion of the flask 21 is evacuated through the evacuation chamber 22. Thus, a negative or subatmospheric pressure is induced in the central portion of the flask 21 and relative movements of the particles of the filler material are precluded and the filler material 31 is rendered compact and formed in the shape of the shaping surfaces of the form 27, runner 28 and gate 29 along the outer surfaces thereof.

If a molten metal is poured into the gate 29 while the filler material 31 in the flask 21 is maintained at a sub-atmospheric pressure, then the molten metal flows into the form 27 while burning the gate 29 and runner 28 by its heat, and the form 27 itself is burned by its heat too. At this time, the shield member 30 is attracted to the filler material because the filler material is maintained at a sub-atmospheric pressure, although the inner surface of the shield member may be carbonized by the heat of the molten metal. In this way, the shield member 30 provides cover to the surface of the filler material and helps such surface to be rendered compact and maintained in the same shape as the surface of the form 27, thereby preventing disintegration of the filler material, production of inclusions and occurrence of fusion.

A third embodiment of the invention will be described with reference to FIG. 3. A form 27 shown therein is similar to that shown in FIG. 2 except for the fact that the former is formed integrally at the other side thereof with a gas vent 33, and a gas passage 34 extending through the gas vent 33 into the interior of the form 27. A shield member 30 covers outer surfaces of the form 27 as well as the runner 28, gate 29 and gas vent 33.

The form 27 as well as the runner 28, gate 29 and gas vent 33 is embedded in a filler material 31 filled in a flask 21 in the same manner as described with reference to the second embodiment. A lid 32 is placed on the upper surface of the flask 21 with an upper end of the gas vent 33 extending outwardly through the lid.

The interior of the flask 21 is evacuated to induce a sub-atmospheric pressure therein so as to render compact and form the filler material in the shape of the form 27, runner 28, gate 29 and gas vent 33 along outer surfaces thereof.

If a molten metal is poured in the gate 29, then the molten metal flows into the form 27 while burning the gate 29 and runner 28 by its heat, and the form 27 itself is burned by its heat too. At this time, gases produced by the burning form 27 are vented to atmosphere through the gas passage 34 in the gas vent 33 without staying in the form.

In the embodiment shown and described above, the gas vent 33 has been described as being formed integrally with the form 27. It should be understood, however, that the gas vent need not be made of a combustible material, and that the gas vent may be made of a material different from the material used for making the form and formed independently of the form to be placed on top of the form.

Other embodiments will be described with reference to FIG. 4, FIG. 5 and FIG. 6.

In FIG. 4 and FIG. 5, 41 designates a rectangular flask having open top and bottom and formed in its walls with a plurality of openings 42 for permitting air to pass therethrough. A filter 43 made as of wire netting is provided on the inner side of each wall of the flask 41 to close the openings 42.

A ventilatory frame 45 having a communication passage 44 maintained in communication with the openings 42 is provided around the outer surfaces of the walls of the flask 41, and support projections 46 and 47 project outwardly from the middle of the opposite end walls of the ventilatory frame 45, one 47 of said support projections 46 and 47 being formed therein with a communication port 48 connected to the communication passage 44.

In FIG. 5, 49 is one of a pattern members made of wood and in two pieces which is formed on one surface thereof with a shaping surface 50 which is formed at one end thereof with ribs 51 for forming weirs and a rib 52 for forming a runner contiguous with the ribs 51. An air passage 53 is formed in the pattern member 49, and a plurality of air ducts 54 are formed in the pattern member 49 to maintain communication between the air passage 53 and the shaping surface 50. A communication opening 55 is formed in the pattern member 49 to connect one end of the air passage 53 to atmosphere.

In performing a molding operation, a shield member 56 which is 20 to 50 microns in thickness and formed of a synthetic resin film is brought into intimate contact with the shaping surface 50 of the pattern member 49 by heating or using a solvent while air on the shaping surface 50 side is withdrawn from the communication opening 55 through the air passage 53 and air ducts 54, so that the shield member 56 is formed into a shape similar to the shape of the shaping surface 50 and ribs 51, 52.

A runner forming member 57 for the gate made of an instantaneously combustible synthetic resinous material is mounted on the rib 52, and a gas vent forming member 58 also made of an instantaneously combustible synthetic resinous material is provided at the other end of the shaping surface.

A flask 41 is brought into engagement with the shaping surface 50 of the pattern member 49 through the shield member 56 being disposed therebetween, and a filler material 59, such for example as molding sand or other heat resisting particle material, is filled in the flask 41 from above. Then, the flask 41 and pattern member 49 are caused to vibrate as a unit by a vibrator (not shown) so as to compactly pack the filler material.

The upper surface of the flask 41 is covered with a lid 60 which may be formed of a synthetic resin film. The interior of the flask 41 is evacuated by suction means connected to the communication port 48 in the support projection 47 through the communication passage 44 formed in the ventilatory frame 45 and the plurality of openings 42 provided in the flask 41, so that a negative or sub-atmospheric pressure is induced in the flask 41 to draw the shield member 56 and lid 60 to the filler material 59 and preclude relative movements of the particles of the filler material. Thus, a shield is formed by the shield member 56 between the shaping surface of the pattern member 49 and the filler material 59.

The interior of the flask 41 may be evacuated through a plurality of evacuation lines each formed therein with a multitude of openings and having a filter wound therearound and arranged in side by side relationship in the flask.

After a sub-atmospheric pressure is induced in the flask 41, the suction means is disconnected, and the pattern member 49 is separated from the flask 41 while air under pressure is supplied from the communication opening 55 formed in the pattern member 49 through the air passage 53 and air ducts 54 to the shield member 56 disposed in engagement with the shaping surface 50 of the pattern member 49. As a result, the shield member 56 formed in a shape similar to the shaping surface 50 of the pattern member 49 remains on the flask side.

An operation similar to the aforementioned operation is performed with reference to another flask 41. The two flasks 41 are brought into engagement with each other with a core 61 being interposed therebetween, so as to form a cavity 62 of the shape of the casting to be produced between the shield members 56, 56 and the core 61.

In pouring a molten metal, the molten metal is directly poured in a gate 63 formed by the runner forming member 57 made of an instantaneously combustible synthetic resinous material to burn part of the shield members, so that the molten metal begins to fill the cavity 62 through a runner 64 and weirs 65 formed in the shield members. The runner forming member 57 is burned by the heat of the molten metal, but an opening similar in shape to the member 57 is formed in the filler material 59 because a negative pressure is present in the interior of the flasks 41, 41.

As the molten metal successively fills the cavity 62, gases in the cavity 62 are forced to move to the uppermost portion of the cavity, so that the gas vent forming member 58 is burned by the heat of the gases. However, an opening similar in shape to the gas vent forming member 58 if formed in the filler material in the same manner as described with reference to the gate 63, thereby permitting the gases in the cavity 62 to be vented out of the cavity into the flasks.

The instantaneously combustible synthetic resinous material used for forming the runner forming member 57 for the gate and the gas vent forming member 58 may be selected from bubble producing synthetic resins, such for example as polystyrene and polyethylene.

By pouring the molten metal through the runner formed of an instantaneously combustible synthetic resinous material, the need to provide a runner in the filler material when molding is effected is eliminated. Molding is facilitated by using the runner forming member made of an instantaneously combustible synthetic resinous material for forming a runner in the filler material according to this invention.

Claims

What is claimed is:

1. A molding method, comprising: embedding both a form made of an instantaneously combustible material, and a gas vent for venting gases formed from combustion of said material, in a mass of heat resistant particulate material contained in a flask; covering the open top of the flask with a plastic film as a lid; inducing a negative or sub-atmospheric pressure in said mass thereby compacting said mass while maintaining the shape of said form; and pouring a molten metal into the form while still inducing said negative or sub-atmospheric pressure the molten metal gassifying said combustible material; and removing resultant gases through said vent.

2. A molding method as set forth in claim 1 further comprising the step of covering said form made of an instantaneously combustible material with a shield member.

3. A molding method as set forth in claim 2 further comprising the step of providing a runner forming member made of an instantaneously combustible material in said shield member.

4. A molding method as set forth in claim 1 wherein said gas vent is formed of an instantaneously combustible material.