WO2010068113A1

WO2010068113A1 - A method of casting metals in a mould

Info

Publication number: WO2010068113A1
Application number: PCT/NO2009/000425
Authority: WO
Inventors: Stein Berg Oshaug; Geir Berg Oshaug; Arnfinn Dyrkorn; John Campbell; Bjarne Anders Heggset
Original assignee: OSHAUG METALL AS
Current assignee: OSHAUG METALL AS
Priority date: 2008-12-11
Filing date: 2009-12-10
Publication date: 2010-06-17
Anticipated expiration: 2011-06-11

Abstract

A method of casting metals by filling a mould (6; 26) from a furnace (1; 21) by tilting of the furnace, by which the mould is tilted in a manner coordinated with the tilting of the furnace, whereby a flow of metal in a channel (4) or coupling between the furnace and the mould is kept at a substantially constant level below an oxide film, and whereby a critical flow velocity, above which the flowing metal may tear off parts of the oxide film, is not exceeded at any point or at any time during the entire casting process.

Description

A method of casting metals in a mould.

The present invention relates to a method of casting metals by filling a mould from a furnace by tilting of the furnace.

It is well known that some metals and metal alloys form a tenacious and strong film of oxide on the surface when they melt. Examples of such metals and alloys are aluminium bronze and nickel aluminium bronze. During the casting of such metals parts of this oxide may be transferred into the mould together with the metal or alloy, and strong turbulence may cause that the oxide is entrained in the cast parts and brings about serious defects by making the parts inhomogeneous and thereby lowering the strength of the parts. By casting of for instance propellers for ships, which may partly be subjected to extreme stresses, it is of great importance that the propeller material is homogeneous and free of defects.

Prior art.

As an attempt to avoid such detrimental oxide inclusions, filters have been used in order to remove oxide from the channel through which the metal flows from the melting receptacle (furnace) and into the mould. However, due to a rather high flow velocity downstream of such filters, additional oxide may be torn loose from the surface oxide film and be mixed into the cast metal.

Several casting techniques have been developed in order to avoid high flow velocities for the casting metal, i.e. to avoid exceeding of what will be referred to as the "critical flow velocity" for the metal, which is the velocity above which the flowing metall may entrain the oxide film, which will be incorporated into the flowing metal.

Most of the known techniques are based on some kind of tilting of the mould, but the methods involve pouring of the metal from the melting furnace and into some kind of intermediate transfer ladle, and this intermediate pouring step unfortunately causes detrimental inclusions of oxide in the metal. DE 606988 describes an example of such a technique.

Some known methods are based on the fact that the oxide is lighter than the metal, whereby the oxide inclusions will rise to the surface of the metall and can be skimmed off. However, of course, not all oxides can be successfully removed in this way. In addition, more oxide will be created during the next pouring action.

US 6929053 describes a device for and a method of casting metals. A mould is equipped with a fill system comprising a horizontal tube having a horizontal axis of rotation and a mechanism for rotating the tube about the axis. The tube is fixedly connected to the mould and is in communication with the mould through filler tubes which, during approximately 90° rotation of the horizontal tube and the mould, receive metal from the horizontal tube and fill the mould from the bottom.

The present invention.

An aim of the present invention is to permit transfer of a flowing metal from a melting furnace to a mould in a substantially horizontal transfer, with no vertical fall at any point and without exceeding the critical flow velocity for the creation of defects.

The casting may be carried out in such a manner that tilting of the mould is coordinated with the tilting of the furnace, whereby the flowing metall in a launder (a channel or channel coupling) between the furnace and the mould is kept at a substantially constant level, and that the critical flow velocity is not exceeded at any point or at any time during the entire casting process. In an automated process monitoring of the level in the launder can in principle provide a feed-back signal to regulate the tilting velocity of the furnace in such a manner that the level of metal in the launder mainly is kept substantially constant and below the oxide film.

This technique avoids that any oxide being torn loose from the surface film and mixed into the flowing metal. The coordination is mainly determined by the volume of the mould relatively to the tilting angle and the angular velocity of the mould. A constant level in the launder and a flow velocity lower than the critical velocity will ensure that the oxide film is not mixed into the flowing metal.

Too rapid tilting of the furnace will cause the level of the flowing metal to rise in the launder, increasing the velocity of the flow . Conversely, too slow tilting of the mould may also result in the level of the flowing metal rising in the launder. The furnace and the mould require to be tilted in such a manner that the surface of the metal in the furnace, launder and mould is substantially level. Thus, it is important that the tilting of both the furnace and the mould are strictly coordinated. In the examples to be described in this description the connection between the furnace and mould is a passive member, being merely attached by sealable pivot connections between the furnace and mould, so that any residual motion is dictated by the controlled motions of the furnace and mould.

As indicated, the connection may comprise an articulated coupling, comprising coupling parts, between the furnace and the mould. This solution is more compact, but entails the use of more sophisticated materials in the articulated coupling when the temperature of the metal is high and the amount of metal to be transferred is large.

Casting by use of a launder (a channel) between the furnace and the mould can be carried out as follows:

A furnace and a mould are fastened to frames. One end of a channel is coupled to the furnace containing a sufficient amount of liquid metal. The mould, having an inlet, is coupled to the opposite end of the channel. The mould and the frame are placed in a starting position. The furnace is tilted until the metal flows through the outlet of the furnace, into the channel and into the mould inlet. The tilting continues until the desired level of liquid metal in the channel is reached. The mould and the frame are gradually tilted in the opposite direction, while tilting of the furnace continues in such a manner that the metal flow in the channel is maintained at the desired level. When the mould has been tilted back to its starting position filling is complete. At that point the furnace has completed its task (and may or may not be empty) and is tilted back to its starting position.

Casting by use of an articulated coupling between the furnace and the mould can be carried out as follows:

A furnace and a mould are fastened to frames, and the mould, having an inlet, is placed in a starting position. The furnace is tilted until coupling parts on the furnace and the mould, respectively, form a sealed, articulated coupling therebetween. The furnace is tilted upwards until the metal flows from the furnace, through the coupling parts and into the mould inlet. The tilting of the furnace continues upwards until the desired level of liquid metal in the coupling is reached. The mould and the frame are gradually tilted in the opposite direction (downwards), while upward tilting of the furnace continues in such a manner that the metal flow in the coupling is maintained at the desired level. When the calculated tilting angle for the mould has been reached (i.e. the mould has been filled), the furnace is tilted back to the position corresponding to the starting position for the mould. When the mould has been tilted back to the starting position, the furnace is also tilted back to its starting position.

By having the tilting axis of the mould situated 20 - 30 mm higher than the tilting axis of the furnace, the channel will have a sufficient slope in the direction towards the furnace for permitting excess metal to flow back to the furnace for later use. This also facilitates cleaning of the channel and the coupling parts.

During the entire filling of the mould the level of the flowing metal can be monitored by use of a sensor, and the sensor may be coupled to the electric equipment, for adjusting the rate of tilting of the furnace in order to achieve a constant level. In this way the flow should avoid the oxide film being introduced in the flowing metal.

The features of the process include:

The method provides a controlled flow velocity, which, acting through large cross sections of channels, can provide for rapid filling of large volumes. The flow velocities can be kept low at all times during the transfer from the furnace to the mould, and the flow will be approximately laminar, whereby mixing of the oxide film into the metal will be prevented.

No pouring action takes place in the manner of a plunging jet, so that turbulent mixing of oxide into the metal is avoided.

By not exceeding the critical flow velocity the oxide film formed on the surface will not be disturbed and will act to protect the liquid against further exposure to air and oxidation.

Oxide film formed in the mould during filling will mainly be situated in the interface between the cast metal and the inner wall of the mould.

The invention will in the following be explained more detailed, with reference to the accompanying drawings. Explanation of the drawings.

Figs. 1 and 2 show in a side view and a top view, respectively, a furnace and a mould, respectively, mounted on frames, for casting of metal by use of a channel between the furnace and the mould.

Fig. 3 shows a sequence, in a vertical section, illustrating an embodiment of the method according to the invention using the furnace, the channel and the mould shown in the Figs. 1 and 2.

Fig. 4 shows in a side view and a top view, respectively, a furnace and a mould, respectively, mounted on frames, for casting of metal by use of an articulated connection in the form of a detachable hinged coupling between the furnace and the mould.

Fig. 5 shows details of the articulated connection in Fig. 4.

Fig. 6 shows a sequence, in a vertical section, illustrating an embodiment of the method according to the invention using the furnace, the articulated connection and the mould shown in Fig. 4.

Description of the method and equipment for carrying out the method.

The equipment shown in the Figs. 1 - 3, for casting by use of a channel between the furnace and the mould, comprises the following:

A tiltable furnace 1 is provided, having a tilting axis, and can be tilted approximately 95°. The tilting axis is situated at the outlet 2 of the furnace. An articulated coupling 3 is provided between the furnace 1 and a channel 4, and a corresponding articulated coupling 8 is provided between the channel 4 and the mould 6. Fiber seals may be provided between parts of the coupling 3. The seals are consumable parts, and can easily be replaced. The channel 4 comprises an outer shell made of steel and an inner lining of refractory material. Both ends of the channel 4 are adapted to an articulated coupling.

The furnace 1 and the mould 6 are tiltably mounted on jigs 11 and 5, respectively. The maximum tilting angle of the mould is approximately between 100 and 105°. A mould inlet 7 at the end of the channel 4 is situated at the top of the mould 6. A spring unit 10 is provided for exerting an axial force on the couplings 3 and 8 in order to prevent leakage during transfer of liquid metal.

Cylinders 12 and 13 are provided between the jigs 11, 5 and the furnace 1 and the mould 6 to tilt both the furnace and the mould.

Electrical and hydraulic equipment is provided for the operation of the casting process.

The sequence of the casting process is shown in Fig. 3. The casting may be carried out in such a manner that tilting of the furnace 1 and tilting of the mould 6 are coordinated, whereby the flowing metall in the channel 4 between the furnace 1 and the mould 6 is kept at a substantially constant level, and that the critical flow velocity is not exceeded at any point or at any time during the entire casting process. In an automated process, by use of the electrical and hydraulic equipment, controlling of the level in the channel will regulate the tilting velocity of the furnace 1 in such a manner that the level of metal in the channel 4 is kept substantially constant.

A sensor 14 may be provided for checking the level of metal in the channel 4. The sensor 14 may be coupled to the electrical equipment for adjusting the tilting of the furnace 1.

Fig. 3 shows the following:

Stage 1 : Furnace and mould in the starting position.

Stage 2: Mould tilted upwardly. Stage 3: Furnace tilted until the metal starts flowing in the channel.

Stage 4. The level of flowing metal is adjusted.

Stage 5: The mould is tilted downwardly, tilting of the furnace continues.

Stage 6: The mould is tilted further downwardly, tilting of the furnace continues.

Stage 7: The mould is tilted further downwardly, tilting of the furnace continues until the mould has been filled.

Stage 8: The furnace and the mould are tilted back to their starting position.

The equipment for casting without the use of a channel, by use of an articulated coupling between the furnace and the mould, is shown in the Figs. 4 - 6, comprises the following: A tiitable furnace 21 is provided, having two tilting axes 22 and 25. The furnace 21 is tilted about the axis 22, by use of a cylinder 29, in such a manner that the furnace outlet 23 and the inlet 24 of the mould are coupled together. The furnace 21 is tilted about a second axis 25, by use of a cylinder 30, for transfer of the liquid metal to the mould 26. The furnace outlet 23 and the mould inlet 24 form an articulated connection, through which the liquid metal can flow. The mould 26 is mounted on a jig 28 and can be tilted about an axis 27, by use of a cylinder 31.

Details of the articulated coupling appear from Fig. 5, showing, in a vertical section and a top view, respectively, the furnace outlet 23 and the mould inlet 24.

The casting process appears from the sequence shown in Fig. 6. The casting may be carried out in such a manner that tilting of the furnace 21 and tilting of the mould 26 are coordinated, whereby the flowing metall in the articulated coupling between the furnace 21 and the mould 26 is kept at a substantially constant level, and that the critical flow velocity is not exceeded at any point or at any time during the entire casting process. In an automated process, by use of the electrical and hydraulic equipment, controlling of the level in the articulated coupling will regulate the tilting velocity of the furnace 1 in such a manner that the level of metal in the articulated coupling mainly is kept constant.

A sensor 14 may be provided for checking the level of metal in the articulated coupling. The sensor 14 may be coupled to the electrical equipment for adjusting the tilting of the furnace 21.

Fig. 6 shows the following:

Stage 1 : Furnace and mould in the starting position.

Stage 2: Mould tilted to its uppermost position. Stage 3: Furnace tilted and coupled to the mould.

Stage 4. Metal starts flowing through the articulated coupling.

Stage 5: Tilting of the furnace continues, the mould is tilted slightly downwardly.

Stage 6: Tilting of the furnace continues, the mould is tilted further downwardly.

Stage 7: Tilting of the furnace continues, the mould is tilted further downwardly. Stage 8: Tilting of the furnace continues, the mould is tilted further downwardly. Stage 9: The furnace is tilted back, metal in the articulated coupling flows back into the furnace, the mould is tilted further downwardly.

Stage 10: Tilting of the furnace and the mould stops, the mould has been filled and is in its starting position. Stage 11 : The furnace is tilted back to its starting position.

Claims

Claims.

1. A method of casting metals by filling a mould (6; 26) from a furnace (1 ; 21) by tilting of the furnace, c h a r a c t e r i z e d i n tilting of the mould in a manner coordinated with the tilting of the furnace, whereby a flow of metall in a channel (4) or coupling between the furnace and the mould is kept at a substantially constant level below an oxide film, and that a critical flow velocity, above which the flowing metal may tear off parts of the oxide film, is not exceeded at any point or at any time during the entire casting process.

2. A method according to claim 1 , in which the level of the flowing metal is monitored and the tilting of the furnace (1 ; 21) and the mould (6; 26) is adjusted in order to avoid an excessive level.

3. A method according to claim 1 or 2, in which the metal flows in a channel (4) from the furnace (1 ; 21) to the mould (6; 26).

4. A method according to any of the claims 1 - 3, in which the metal flows through an articulated coupling from the furnace (1 ; 21) to the mould (6; 26).