METHOD OF CASTING

Abstract: A method of casting an article in a thermosetting material utilising a mould (M1) having a casting cavity (1a &cir& _) corresponding to the configuration of the item to be cast, and a reservoir cavity (6, 7) communicating with the casting cavity (1a &cir& _), the method comprising introducing molten thermosetting material into the casting cavity (1a &cir& _) and the reservoir cavity (6, 7), permitting cast material in the casting cavity (1a &cir& _) to initially cool and at least partially solidify whilst applying heat from an extrinsic source (8, 9, 9A &cir& _) to the material in the reservoir cavity (6, 7).

Description: Title: Method of casting Description of Invention This invention relates to a method of casting a thermosetting material and more particularly, but not exclusively, to a method of casting metal. In a conventional metal casting method, molten metal is introduced into a casting cavity of a mould via one of more feedways, the feedway and any ancillary reservoir, called a header, providing a reservoir of molten metal to make up for shrinkage of the metal in the casting cavity as the metal in the casting cavity initially cools and at least partially solidifies. To ensure that the metal in the feedway or any header does not cool too quickly such that it solidifies before the casting cavity has filled, or at least before the metal in the casting cavity has initially cooled and at least partially solidified, it is common practice for the feedway and/or header to have a volume of a significant size in relation to the volume of the casting cavity. For example, the total of the feedway and any header may be substantially the same as the volume of the casting cavity. By careful mould design and perhaps using chills to hasten the cooling of the metal in the casting cavity in certain areas, and other techniques, the rate of cooling of the molten metal in the feedway and any header can be controlled to an extent. Exothermic inserts are used in some applications to maintain the temperature of the metal in the mould outside of the casting cavity, but these are expensive and can only provide local heating to areas of the mould. With all such known techniques of casting metal, heat is wasted in melting metal prior to introduction into the mould, which metal then solidifies in the feedway/header and is subsequently scrapped. Also removal of the feedway/header from the eventual casting, can involve expensive machining processes particularly where the volume of the feedway/header is large. According to the invention I provide a method of casting an article in thermosetting material utilising a mould having a casting cavity corresponding to the configuration of the item to be cast, and a reservoir cavity communicating with the casting cavity, the method comprising introducing molten thermosetting material into the casting cavity and into the reservoir cavity, permitting the cast material in the casting cavity initially to cool and at least partially solidify whilst applying heat from an extrinsic source to the material in the reservoir cavity. Thus the size of the feedway and any header can be reduced to a minimum because a large volume is not required to prevent premature cooling of the material in the feedway or any header. Thus the amount of casting material for the feedway and any header is minimised and hence the amount of material required to be melted for use in the casting method is reduced compared with a conventional casting method. Thus the method in accordance with the invention increases efficiency of casting in energy terms. Furthermore, the casting material can be heated to a lower temperature overall before introduction into the mould because the feedway and any header does not require heat from the molten material in the casting cavity in order to remain molten. The invention will now be described with reference to the accompanying drawings in which : FIGURE 1 is an illustrative sectional view through a mould for use in a conventional casting method. FIGURE 2 is an illustrative sectional view through a mould for use in a casting method in accordance with the invention. FIGURE 3 is an illustrative sectional view through a mould similar to figure 2, but showing a modification. Referring to figure 1, a mould M is provided for casting metal, the mould M being a sand mould and including a casting cavity 1 which is of a configuration corresponding to an item to be cast. Molten metal is introduced into the mould M at an opening 5 and flows along a feedway 4 through an ingate G into the casting cavity 1. The mould M includes a pair of ancillary reservoirs 2,3, which are also known as "headers". As the metal in the casting cavity 1 solidifies, shrinkage is made up by drawing additional molten metal into the casting cavity 1 from the headers 2,3, and the feedway 4 which are each reservoir cavities. Molten metal flows into the casting cavity 1 in a generally upwardly or downwardly direction as the ingate G from the feedway 4 and an ingate Gl from the header 2 open generally vertically. The header 3 is provided at the end of the feedway 4. Conventionally, the volumes of the headers 2,3, and feedway 4 have to be large to ensure that molten metal therein does not cool too quickly and solidify in the headers 2,3, and feedway 4 before the metal in the casting cavity 1 initially cools and at least partially solidifies, such that molten metal would not be available from the headers 2,3, and feedway 4 to make up for shrinkage. Referring now to figure 2, a mould Ml is provided in which a feedway 7 having a smaller volume than the feedway 4 of a conventional mould M, is provided, and a single header 6 is provided which again has a volume significantly less than the volume of either of the headers 2,3, of the figure 1 mould M. Otherwise the mould Ml has a casting cavity la, like the mould M in figure 1, and molten metal is introduced into the casting cavity la. by pouring into an opening 5a. from where it flows along feedway 7 via ingate Ga into the casting cavity la. In accordance with the invention, as the molten metal in the casting cavity la, initially cools and at least partially solidifies, the molten metal in the feedway 7 and in the header 6 is subjected to heat by a heating means extrinsic to the molten metal heing cast. Jtβ Heating is achieved in this example, by passing an electrical current through the metal in the mould Ml whereby the metal in the feedway 7 and the header 6 experiences resistive heating. In this example, a first electrode is indicated at 9A and is located in the mould Ml such that when the molten metal is cast, the electrode 9A is in electrical contact with the metal in the feedway 7 adjacent to the opening 5a. A - second electrode 9 is located in the mould Ml such that when the molten metal is cast, the electrode 9 is in electrical contact with the metal in the header 6, the current path thus being from the feedway 7, through the metal in the casting cavity la, and to the header 6. Because the volumes of the feedway 7 and the header 6 are so small compared with the volume of the casting cavity la, the metal in the casting cavity la ^ does not experience any significant resistive heating effect. The electrical current of course needs to be of a sufficient magnitude that the relatively small volume of metal contained within at least the feedway 7 and preferably also the header 6, resists the flow of current thus to cause a resistive heating effect. The electrodes 9,9A, are conveniently made of carbon and are connected by suitable cables 8, to a controller 10 which is in turn connected to an electrical power source 11. The controller 10 is preferably operable to adjust the magnitude " of the current and hence the power of the electrical heating in the mould Ml and preferably includes a timer so that the heating of the metal in the feedway 7 and header 6 can be completely cut off after a predetermined time. Preferably the controller 10 reduces the current flowing during the initial cooling and at least partial solidification of the metal in the casting cavity la. from a maximum immediately after the metal is cast, for example linearly or logarithmically or according to any other cooling characteristic, depending on the nature, size and type of the item to be cast, and the configuration of the mould Ml. Figure 3 shows a modification to the mould Ml shown in figure 2, but similar parts are labelled by the same reference numerals. In the figure 3 arrangement, the opening 5a into which molten metal is poured, is spaced significantly above the top of the casting cavity la, namely by a distance H so as to increase the pressure of the molten metal within the casting cavity la, during casting. Various modifications may be made without departing from the scope of the invention. The configuration of the casting cavity la, shown in the drawings, is of course purely illustrative, and in practice may be of a complex shape corresponding to the configuration of the item to be cast. The casting cavity la_ may be formed by using a removable pattern of the item to be cast, or utilising a pattern which is built into the mould and lost during the casting process. The mould Ml need not be a sand mould but could comprise any other moulding material suitable for the thermosetting material to be cast therein. In the example described, heating of the metal in the feedway 7 and header 6 is achieved by means of a resistive heating effect utilising carbon electrodes 9,9A- The positions of the electrode 9,9A, could be changed as appropriate. It is envisaged that the first electrode 9A could comprise a carbon rod inserted into the opening 5a, into which the molten metal has been poured. Any other alternative means for heating the metal in the feedway 7 and/or the header 6 whilst the metal in the casting cavity la, initially cools and at least partially solidifies, may be provided. For example, heating may be achieved by resistive heating, or induction heating by means of one or more strategically positioned coils. Although in the arrangement shown in figures 2 and 3, a single header 6 only is provided, in another arrangement, no header at all need be provided, or more than one header may be provided as desired. In the arrangement described with reference to figure 2, the current flow path extends through the metal in the casting cavity la. In another arrangement, the electrodes 9,9A may be located such that the current flow path does not include the metal in the casting cavity la. Although the invention has been described with specific reference to a method of casting metal, the invention has application to the casting of any other thermosetting material, either in a disposable mould such as a sand mould, or in a permanent mould such as in die casting or injection moulding of thermosetting plastics materials. The features disclosed in the foregoing description, the following claims or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A method of casting an article in a thermosetting material utilising a mould having a casting cavity corresponding to the configuration of the article to be cast, and a reservoir cavity communicating with the casting cavity, the method comprising introducing molten thermosetting material into the casting cavity and the reservoir, permitting cast material in the casting cavity initially to cool and at least partially solidify whilst applying heat from an extrinsic source to the material in the reservoir cavity. 2. A method according to claim 1 wherein the reservoir cavity comprises one of a header and a feedway for the introduction of the molten material from the exterior of the mould, from which reservoir cavity molten material is drawn during initial cooling and at least partial solidification of the cast material in the casting cavity, to make up for shrinkage. 3. A method according to claim 2 wherein the reservoir cavity communicates with the casting cavity at an ingate which opens from the casting cavity to the reservoir cavity generally vertically such that the casting material flows from the reservoir cavity into the casting cavity generally upwardly or downwardly. 4. A method according to any one of claims 1 to 3 wherein the thermosetting material is metal. 5. A method according to claim 4 wherein heat is applied to the metal in the reservoir cavity by passing an electrical current through the metal in the reservoir cavity of a magnitude sufficient to cause heating due to the resistance of the metal in the reservoir cavity. 6. A method according to claim 5 which includes locating in the mould a first electrode which, when the molten metal is cast, is in electrical contact with the metal in the reservoir cavity, and locating in the mould a second electrode which when the molten metal is cast, is in electrical contact with the cast metal at a position spaced from the first electrode, so as to provide a path for electric current from the first, electrode to the second electrode via the metal in the reservoir cavity. 7. A method according to claim 6 wherein the mould has two reservoir cavities, one being a header which communicates directly with the casting cavity, and the other comprising a feedway which also communicates directly with the casting cavity, and to the exterior of the mould, and into which molten metal is introduced, the method including locating the first electrode such that when the molten metal is cast the first electrode is in electrical contact with the metal in the feedway and locating the second electrode so that when the metal is cast, the second electrode is in electrical contact with the metal in the header, such that the current flow path includes the metal in the casting cavity. 8. A method according to any one of claims 1 to 7 wherein the molten metal is introduced into the casting cavity and the reservoir cavity under gravity. 9. A method according to claim 8 when the mould is made substantially of sand. 10. A method according to any one of the preceding claims wherein the mould is made substantially of an insulating material. 11. A method according to any one of the preceding claims wherein the amount of heating effect of the heating means is reduced as the material in the casting cavity initially cools and at least partially solidifies. 12. A method according to any one of claims 1 to 11 wherein the heating effect of the heating means is removed altogether once the cast material in the casting cavity has at least partially solidified.

Inventors: BURDETT SAVILE, BURDETT, SAVILE
Applicants: BURDETT SAVILE, BURDETT, SAVILE
Application year: 1993
Main classification: B22D27
IPC codes: B22C9, B22D7, B22D17, B22D27, B29C45, B29K101