GB1594270A

GB1594270A - Casting method employing a vacuumshaped mould

Info

Publication number: GB1594270A
Application number: GB53122/77A
Authority: GB
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1977-07-13
Filing date: 1977-12-21
Publication date: 1981-07-30
Also published as: AT357282B; BE862744A; FI63531C; NL7800104A; SE7800546L; TR20369A; FI63531B; DK32678A; DE2802103A1; JPS6110215B2; IT1090298B; ATA42578A; JPS5419422A; FI780081A; FR2397246A1; NO774391L; FR2397246B1; CH627671A5

Abstract

In the casting method by means of a mould produced with the application of a vacuum, a blind riser (10) with a vent opening (12) is formed and a conical body (13) is arranged in the upper region of the blind riser (10), which body is intended to extend to below the level reached by the molten metal in the blind riser (10) after it has been poured in. Due to the contact between the molten metal and the conical body (13), heat is stored in the heat-resistant material (4) of the mould in the area around the blind riser (10), delaying the solidification of the molten metal in the blind riser (10). This favours the flow of additional molten metal from the blind riser into the casting inside the mould and, as a result, shrinkage losses are compensated. <IMAGE>

Description

(54) CASTING METHOD EMPLOYING A VACUUM-SHAPED MOULD (71) We, MITSUBISHI JUKOGYO KA BUSHIKI KAISHA, a Japanese body corporate, of 5-1, Marunouchi 2-chome, Chiyoda-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a casting method for a vacuum-sealed casting process employing a vacuum-shaped mould.

To construct a vacuum-shaped mould, air tight shielding material (for example, a plastics film) is coated on the surface of a pattern or profile and on the surface of the sprue or gate, feeder, and blind feeder if provided. After the coated pattern has been located in a predetermined position within upper and lower flasks or moulding boxes, which latter are connected to an evacuating mechanism, moulding material in the form of a granular refractory material (for instance, moulding sand) not containing a binder is introduced into the flasks.Subsequently the upper and lower surfaces of the flasks containing said moulding sand are tightly enclosed with an air-tight shielding material and the interstices of the moulding sand in the flasks are subjected to a vacuum (sub-atmospheric) pressure, by the evacuating means, which may comprise for example, a vacuum pump connected to evacuating openings in the flasks. Said moulding sand is thereby aggregated and compacted by the difference between the atmospheric pressure surrounding the pattern and said vacuum pressure. Thereby a mould-cavity surface is formed which follows the configuration of the pattern, by said shielding material film sucked onto the adjacent surface of said moulding sand.Now, if the pattern is removed from the flasks and the interstices of the moulding sand are maintained under vacuum pressure, then there is obtained a vacuum-shaped mould having the same shape as the pattern and with a sprue, riser, etc. Therefore, by the method of pouring molten metal into the formed cavity of said mould, whilst continuing to apply a vacuum to the vacuum-shaped mould, a casting of the pattern is obtained.

In known forms of such casting method a feeder for feeding molten metal to said casting during cooling to allow for shrinkage is normally provided and will now be discussed with reference to Figure 1. In this figure, 1, 1' are upper and lower separable flasks each having an evacuating mechanism.

Evacuation ports 2, 2' are provided for the flasks 1, 1' respectively, and these evacuation ports are adapted to be connected to evacuating means (not shown) such as, for example, a vacuum pump. Filters 3, 3' are disposed in the evacuation paths of the respective flasks as shown in Figure 1. The flasks are shown filled with the said granular refractory material 4 (for example, moulding sand) not containing a binder, the surfaces of which material 4 have been lined, by sucking action as described above, with an air-tight shielding material material 5 (such as, for example, a plastics film) previously coated on the surface of the pattern. The lined cavity thus left after removal of the pattern is denoted 6 which is open to a sprue 7, and feeders 8 and 9. The feeder 9 is especially deep and is provided generally in the case where a casting having a complex configuration is to be cast.

In addition to the so-called feeding effect during cooling, the feeders 8 and 9 of the prior art prevent deformation of the cavity 6 by admitting atmospheric pressure through to the cavity even if the air-tight film 5 (which is sucked onto, and thereby lines, the surface of the cavity 6 by the aforementioned vacuum pressure) is melted by the heat of the molten metal when it is poured through the sprue 7.

However, the aforementioned vacuumshaped mould of the prior art has the following shortcomings: (i) Since molten metal of far greater volume than that fed to the casting during cooling is necessary because of the espe cially deep feeder the casting yield is greatly reduced.

(ii) Since the stretch limit of air-tight plastics film is often exceeded if the surface of the pattern is lined with only a single sheet, it is necessary for a sub-pattern for the feeder 9 to be separately lined with an air-tight plastics film and to connect this latter film in an air-tight manner to the film lining the main pattern, so that a large amount of extra work and manpower is required. resulting in increased cost.

(iii) Depending upon the location of the deep feeder 9, it may interfere with an auxiliary evacuation pipe 21 or other obstruction of the flask 1 so that it may become necessary to change the structure of the flask 1.

An object of the present invention is to provide a casting method for a vacuum sealed casting process employing a vacuumshaped mould having a feeder which can eliminate or substantially reduce the short comings of the above-described prior art method.

According to one aspect of the invention a casting method employing a vacuum-shaped mould constructed by coating a pattern with plastics film or other air-tight shielding material, depositing moulding material on the film, and forming the surface of the mould cavities by sucking said shielding material onto the moulding material with the aid of evacuation means arranged to apply suction to said shielding material via said moulding material, said moulding material being moulding sand or other granular refractory material in any case not containing a binder, the mould having a blind feeder, and pouring being effected whilst said evacuation means is applying suction to said moulding material, is characterised in that the blind feeder has a vent hole and is provided in its upper portion with a conical atmospheric pressure core, member which is in alignment with said vent hole, a shrinkage cavity is formed within said blind feeder by transfer of air through said conical member from said moulding material and/or from the atmosphere.

According to another aspect of this invention, the vacuum shaped mould is characterised in that the blind feeder has a vent hole and at its upper portion a conical atmospheric pressure core member in alignment with the vent hole whereby a shrinkage cavity is formed within said blind feeder by transfer of air through said conical member from said moulding material and/or from the atmosphere.

In order that the invention may be readily understood and further features made apparent one preferred embodiment of a casting method in accordance therewith, and modifications thereof, will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a prior art method of forming vacuum-shaped moulds, Figures 2 and 3 are schematic sectional views showing further prior art methods of forming vacuum shaped moulds, and Figures 4, 5 and 6 are schematic sectional views showing various forms of mould for the preferred embodiment of casting method.

Referring now to Figure 2, in one further prior art method, granular refractory material 4 (for example, moulding sand) not containing a binder, is contained in the moulding flasks, and air-tight shielding material 5 such as. for example a plastics film, is provided, in the general manner described above, as sucked-on linings for the surfaces of the refractory material. (After vacuumcompacting the sand around the coated pattern, the pattern is removed to leave a cavity 6). The various constructions, functions and mutual structural relationship of the flasks and their components are substantially the same as those of the prior art discussed hereinbefore with reference to Figure 1 (identical components are given the same reference numerals).

The blind feeder 10 is formed contiguously to the cavity 6, and at an appropriate position in the upper portion of the blind feeder 10 (preferably the highest point) a conical member 11 is provided which projects downwardly. Said conical member is constructed as as to fulfil the same function and obtain the same advantages as the well-known atmospheric pressure core, generally referred to as a "Williams" core.

The blind feeder 10 has a vent hole 12 communicating with atmosphere, the hole 12 and conical member 11 bieng disposed as shown in the Figure. These members are located within a flask which has an evacuating mechanism as described and illustrated with reference to Figure 1.

When molten metal is poured into the cavity 6 of the above-described vacuumshaped mould through a sprue (not shown in Figure 2), the cavity blind feeder 10 and the vent hole 12 are filled with said molten metal.

However, when the casting in the cavity begins to cool, and thus shrink, the molten metal in the blind feeder 10 is fed to the casting. In this case, the tip end of the conical member 11, which is at the top of the blind feeder 10, is so sharp that the moulding material, (e.g. the moulding sand) is thermally saturated by the heat of the molten metal. Consequently when the casting begins to solidify, the metal around said conical member 11 remains molten, and since an inner pressure within the moulding sand (of the order of 400 mmHg below atmospheric pressure) is exerted, pressurized feeding of the molten metal to the casting tends to take place.However, this pressurized feeding tends not to be sufficient to attain a particularly sound casting, due to the fact that the vent hole 12 is of relatively small crosssection and consequently, molten metal in the vent hole will tend to solidify before feeding commences.

In a modification of the prior art method of Figure 2, as illustrated in Figure 3, an atmospheric pressure core (Williams core) 13 is disposed at an appropriate position at the highest point of the blind feeder 10, and after the vent hole 12 (cavity) has been separately shaped during the mould manufacture and lined with an air-tight shielding film, this film and the air-tight shielding film lining the blind feeder 10 are joined by means of a tape 14. When the atmospheric pressure core 13 is employed, as is the case with the embodiment shown in Figure 3, there is an advantage that there is little fear of causing deformation of that portion. This is because the atmospheric pressure core 13 is relatively difficult to deform since it is made of a sand containing a binder (e.g. oil sand, or CO2 sand).Nevertheless the tendency for the molten metal in the vent hole 12 to solidify before feeding takes place still exists.

It will be appreciated that with the mould arranged as in Figures 2 and 3, and also with the mould arrangement in accordance with the invention described hereinafter with reference to Figures 4 to 6, as molten metal is poured into the cavity portion 6, the air-tight shielding film 5 lining the inner surfaces will be melted by the heat of the said molten metal, so that the pressure difference across the film between the vacuum within the moulding sand 4 and the cavity 6 would be expected to equalise, the hence deformation of the cavity 6 would normally be expected to occur. However, whilst atmospheric pressure continues to be exerted upon the cavity 6 through the vent hole 12, and the blind feeder 10, the above-mentioned pressure difference can be maintained and the possibility that deformation of the cavity 6 may arise is substantially eliminated.

Accordingly, it is advantageous to attempt to ensure that molten metal does not enter the vent hole.

Referring now to Figure 4, in accordance with the invention, in order to avoid the tendency for molten metal to solidify in the vent hole 12, the atmospheric pressure core 13 is located in the blind feeder 10 at the bottom end of and aligned with the vent hole 12 via an auxiliary pipe 16. The vent hole is defined by a pipe 15 which is joined to the auxiliary pipe 16 by means of a tape 17, and it will be appreciated that the molten metal will not enter the pipe 15, thereby enhancing the pressurised feeding effect compared with the prior art methods of Figures 1, 2 and 3 to provide an improved casting yield.Furthermore, in this embodiment, since there is no possibility that the molten metal will overflow through the vent hole onto the surface of the flask (which would result in the melting of the air-tight shielding film lining the outer surface of the flask), there is the advantage that the vacuum pressure within the moulding sand does not vary.

In a variation of the embodiment illustrated in Figure 5, the volume of the blind feeder is small (consequently the atmospheric pressure core 13 is also small). The location of the core 13 is similar to that in Figure 4 but an auxiliary pipe 16 is not used.

In this variation, after the atmospheric pressure core 13 has been located at the top of the blind feeder of the pattern, it is coated with an air-tight shielding film at the same time as the pattern surface is so coated. The pipe 15 for introducing the atmospheric air is located after removal by cutting away of the air-tight shielding film at the top of the atmospheric pressure core 13, and then they are joined by means of a tape 18.

In still another variation of the embodiment illustrated in Figure 6, an atmospheric pressure core 13 similar to that of Figure 5, is provided with a boss 19 for receiving the bottom end of the pipe 15: this has an advantage that, upon introducing moulding sand into the flask, one does not rely solely upon the tape 18 to resist deformation.

It will be appreciated that by use of a casting method in accordance with the present invention, the molten metal feeding effect from the blind feeder becomes greatly effective. Thus, sufficient molten metal feeding can be expected with a blind feeder of small volume, without the possibility of molten metal overflowing through the vent hole. This has the practical advantage that not only is the yield of the raw material enhanced, but also there is little chance of producing a casting with defects.

WHAT WE CLAIM IS:- 1. Casting method for a vacuum sealed casting process employing a vacuum-shaped mould constructed by coating a pattern with plastics film or other air-tight shielding material, depositing moulding material on the film, and forming the surface of the mould cavities by sucking said shielding material onto the moulding material with the aid of evacuation means arranged to apply suction to said shielding material via said moulding material, said moulding material being moulding sand or other granular refractory material in any case not containing a binder, the mould having a blind feeder, and pouring being effected whilst said evacuation means is applying suction to said moulding material, characterised in that the blind feeder has a vent hole and is provided in its upper portion with a conical atmospheric pressure core member which is in alignment with said vent hole, whereby a shrinkage cavity is formed within said blind feeder by transfer of air through said conical member from said moulding material and/or from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the vent hole will tend to solidify before feeding commences. In a modification of the prior art method of Figure 2, as illustrated in Figure 3, an atmospheric pressure core (Williams core) 13 is disposed at an appropriate position at the highest point of the blind feeder 10, and after the vent hole 12 (cavity) has been separately shaped during the mould manufacture and lined with an air-tight shielding film, this film and the air-tight shielding film lining the blind feeder 10 are joined by means of a tape 14. When the atmospheric pressure core 13 is employed, as is the case with the embodiment shown in Figure 3, there is an advantage that there is little fear of causing deformation of that portion. This is because the atmospheric pressure core 13 is relatively difficult to deform since it is made of a sand containing a binder (e.g. oil sand, or CO2 sand).Nevertheless the tendency for the molten metal in the vent hole 12 to solidify before feeding takes place still exists. It will be appreciated that with the mould arranged as in Figures 2 and 3, and also with the mould arrangement in accordance with the invention described hereinafter with reference to Figures 4 to 6, as molten metal is poured into the cavity portion 6, the air-tight shielding film 5 lining the inner surfaces will be melted by the heat of the said molten metal, so that the pressure difference across the film between the vacuum within the moulding sand 4 and the cavity 6 would be expected to equalise, the hence deformation of the cavity 6 would normally be expected to occur. However, whilst atmospheric pressure continues to be exerted upon the cavity 6 through the vent hole 12, and the blind feeder 10, the above-mentioned pressure difference can be maintained and the possibility that deformation of the cavity 6 may arise is substantially eliminated. Accordingly, it is advantageous to attempt to ensure that molten metal does not enter the vent hole. Referring now to Figure 4, in accordance with the invention, in order to avoid the tendency for molten metal to solidify in the vent hole 12, the atmospheric pressure core 13 is located in the blind feeder 10 at the bottom end of and aligned with the vent hole 12 via an auxiliary pipe 16. The vent hole is defined by a pipe 15 which is joined to the auxiliary pipe 16 by means of a tape 17, and it will be appreciated that the molten metal will not enter the pipe 15, thereby enhancing the pressurised feeding effect compared with the prior art methods of Figures 1, 2 and 3 to provide an improved casting yield.Furthermore, in this embodiment, since there is no possibility that the molten metal will overflow through the vent hole onto the surface of the flask (which would result in the melting of the air-tight shielding film lining the outer surface of the flask), there is the advantage that the vacuum pressure within the moulding sand does not vary. In a variation of the embodiment illustrated in Figure 5, the volume of the blind feeder is small (consequently the atmospheric pressure core 13 is also small). The location of the core 13 is similar to that in Figure 4 but an auxiliary pipe 16 is not used. In this variation, after the atmospheric pressure core 13 has been located at the top of the blind feeder of the pattern, it is coated with an air-tight shielding film at the same time as the pattern surface is so coated. The pipe 15 for introducing the atmospheric air is located after removal by cutting away of the air-tight shielding film at the top of the atmospheric pressure core 13, and then they are joined by means of a tape 18. In still another variation of the embodiment illustrated in Figure 6, an atmospheric pressure core 13 similar to that of Figure 5, is provided with a boss 19 for receiving the bottom end of the pipe 15: this has an advantage that, upon introducing moulding sand into the flask, one does not rely solely upon the tape 18 to resist deformation. It will be appreciated that by use of a casting method in accordance with the present invention, the molten metal feeding effect from the blind feeder becomes greatly effective. Thus, sufficient molten metal feeding can be expected with a blind feeder of small volume, without the possibility of molten metal overflowing through the vent hole. This has the practical advantage that not only is the yield of the raw material enhanced, but also there is little chance of producing a casting with defects. WHAT WE CLAIM IS:-

1. Casting method for a vacuum sealed casting process employing a vacuum-shaped mould constructed by coating a pattern with plastics film or other air-tight shielding material, depositing moulding material on the film, and forming the surface of the mould cavities by sucking said shielding material onto the moulding material with the aid of evacuation means arranged to apply suction to said shielding material via said moulding material, said moulding material being moulding sand or other granular refractory material in any case not containing a binder, the mould having a blind feeder, and pouring being effected whilst said evacuation means is applying suction to said moulding material, characterised in that the blind feeder has a vent hole and is provided in its upper portion with a conical atmospheric pressure core member which is in alignment with said vent hole, whereby a shrinkage cavity is formed within said blind feeder by transfer of air through said conical member from said moulding material and/or from

the atmosphere.

2. A vacuum-shaped mould constructed by coating a pattern with plastics film or other air-tight shielding material. depositing moulding material on the film. and forming the surface of the mould cavities by sucking said shielding material onto the moulding material with the aid of evacuation means arranged to apply suction to said shielding material via said moulding material. said moulding material being moulding sand or other granular refractory material in any case not containing a binder. the mould having a blind feeder. characterized in that the blind feeder has a vent hole and at its upper portion a conical atmospheric pressure core member in alignment with the vent hole whereby a shrinkage cavity is formed within said blind feeder by transfer of air through said conical member from said moulding material and/or from the atmosphere.

3. A mould according to Claim 2, wherein the conical core member is provided with a boss and an auxiliary pipe extends through the mould and is located on the boss, said auxiliary pipe defining said vent hole.

4. A casting method for a vacuum sealed casting process employing a vacuum shaped mould substantially as hereinbefore described with reference to figures 4, 5 and 6 of the accompanying drawings.

5. A mould for a vacuum sealed casting process constructed, arranged and adapted for use substantially as hereinbefore described with reference to Figures 4, 5, or 6 of the accompanying drawings.