CA2047384C - Method and apparatus for hot top casting of reactive metals - Google Patents
Method and apparatus for hot top casting of reactive metalsInfo
- Publication number
- CA2047384C CA2047384C CA 2047384 CA2047384A CA2047384C CA 2047384 C CA2047384 C CA 2047384C CA 2047384 CA2047384 CA 2047384 CA 2047384 A CA2047384 A CA 2047384A CA 2047384 C CA2047384 C CA 2047384C
- Authority
- CA
- Canada
- Prior art keywords
- hot top
- mould
- gas
- magnesium
- casting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/0401—Moulds provided with a feed head
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
- B22D21/002—Castings of light metals
- B22D21/007—Castings of light metals with low melting point, e.g. Al 659 degrees C, Mg 650 degrees C
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
- Treatment Of Steel In Its Molten State (AREA)
- Manufacture Of Alloys Or Alloy Compounds (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
- Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
Method and apparatus for use in hot top continuous casting of reactive metals, especially magnesium and magnesium containing alloys. To prevent oxidation a protective gas is supplied to the porous refractory hot top material (1) and eventual joints. It is arranged a closed chamber (7) between hot top (1) and a jacket (8) for supply of gas. It is preferred to use sulphur hexafluoride eventually in mixture with other gases.
Description
2~473~3~
The invention concerns a method and an apparatus for hot-top casting of reactive metals such as magnesium and magnesium alloys.
The wish for a more rational casting of magnesium has resulted in a change to direct chill casting with use of hot top. This is a process commonly used for aluminium casting. Direct chill casting is performed by supplying liquid metal into the one end of an openended water-cooled mould. The metal is solidified at the walls of the mould and the solidified product is continously withdrawn downwardly out of the other part of the mould, where the "ingot" is further chilled by direct water cooling. A hot top mould in principle consists of a watercooled mould and an insulating ceramic hot top which acts as a metal reservoir of uniform temperature. With the ceramic hot top it is possible to make a channel system between several moulds, in such a way that several ingots can be cast at same time.
To obtain a best possible product it is important to have a good heat balance in the mould. The solidification is determined of mould design, casting speed, amount of cooling water, metal temperature, metal level in the mould and amount of lubricating agent which shall lubricate between the mould wall and ingot.
Incorrect casting parametres can lead to casting defects and a 20~
defective cast surface of the ingot. Casting defects also arises where there are poor joints between hot top and mould, and by unfavourable mould design.
By hot top casting of magnesium light, porous refractory mater-ials are used with extremely low thermal conductivity as a part of the mould system. This method is especially useful for casting of ingots from 100 mm diametre or more. It is important that the product has a uniform, smooth surface without surface defects and oxide to be suitable for extrusion. A smooth surface is important for the extrusion rate. For billets/ T-shaped ingots which shall be used in aluminium alloys it is of importance that the surface is oxidefree to prevent contamination of the metal. It is also important that there are no cracks/ cavities in the surface where humidity can penetrate. Humidity in the metal will give an explosive evaporation when it is supplied to the molten aluminium and will represent a severe security risk.
Test of this method with magnesium however gave a product with black oxide coating and casting defects. This is a common problem which can arise at conventional casting of reactive metals such as magnesium and magnesium alloys. The reason for this can be the use of incorrect casting parametres. Too high speed or too little water-cooling can lead to reaction between water vapour and magnesium because of unsufficient primary chilling. Too much water, too high metal level or too slow casting speed can lead to that already solidified metal will melt caused by insufficient heat transport in the air gap which is formed between mould and metal when the metal shrinks during solidification. The most common reason for oxide at the surface is that the molten metal is oxidized and the oxide pulled down to the mould along the surface of the ingot.
To prevent this, a commonly used method in the magnesium industry is to protect the surface with a gas, such as SF6. When oxygen 20~73~3~
reacts with molten magnesium there is formed a porous oxide where oxygen can pass through, this makes further oxidation possible.
The function of SF6 can possibly be explained by that the SF6 molecule being absorbed to the cxide surface and therby prevent-air access for further oxidation. The gas gives protection with up to 1 % mixture in air.
Covering the melt with SF6 to prevent oxidation gave in this case no better result. Casting oil is usually used to lubricate the mould. It was P~A~; ned whether the oil used possibly could have contained any water which could cause the miscolouring, but without result. It was found that one of the causes of the surface defects was that the black oxide coatinq was stuck in the oil and that this disturbed the solidification process. Neither varying the casting parametres nor the work to find alternative air tight materials with better dimentionally tolerances gave any improvements to the final product. Tighter materials in addition leads to higher thermal conductivity and it can be difficult to control the heat balance in the mould.
At last the cause of the problem was found to be that air was sucked in through the porous hot top material and through the joint between hot top and mould. Magnesium is a powerful reduc-tion agent. When the metal is oxidized the oxygen in the air is consumed and causes a depression (vacuum) which has effect on the porous ceramic materials with the result that air is sucked in through the pores and all joints ( selfgeherating vacuum ). This leads to that the oxidation continues and the ingot being casted will have a black surface.
The object of this invention is thus to prevent oxidation of magnesium before and during solidification by direct chill casting with the use of porous hot top materials.
This and other objects of the invention is obtained by the method :' 2~7t~
and apparatus as described below, and the invention is further defined and described in the enclosed patent claims.
One possible solution to the problem would be to coat the mater-ial with a gas tight insulating material towards the metal for thereby prevent gaspassage. In practice this appeared to be difficult as it was not easy to find a suitable material which both could resist magnesium, having high insulation capacity and being tight.
Another solution would be to tighten the insulating blocks at the backside and remove remainder air in the pores of the insulation.
It was surprisingly found that the selfgenerating vacuum could be utilized to solve the problem. By introducing an inert / reducing gas atmosphere behind the hot top material the gas will act as an oxidation preventive for magnesium and prevent further oxidation.
The best result was obtained by using SF6 of high concentration.
After the pores are saturated, the gas consumption could be reduced. The system must be tightened to prevent penetration of air through slits etc. It was obtained a product with smooth surface without miscolouring.
The invention should be futher described with reference to the enclosed drawings, figure 1-2, where Figure 1 shows the mould system before start.
Figure 2 shows the system in operation.
The best solution to the oxidation problem was found to be that the hot top material and eventual joints were saturated with a protective gas. This can in practise be performed by introducing a protective gas such as SF6 of high concentration into the closed chamber between the hot top and hot top jacket. When the 7;~
enclosed air in the hot top is consumed, the protective gas will be sucked into the hot top and joints instead of or together with air and prevent futher oxidation. The quality of the metal surface will be improved even if the joints are not quite tight.
A demand to tight joints would complicate the maintenance of the hot top and mould.
The protective gas should be of high concentration. In the experiments it was used sulphur hexafluoride. This gas can also be used in mixtures with carbondioxide and inert gases. Other protective gases containing fluorides, chlorides or borides of high concentration, could also be used.
In figure 1 it is shown how a hot top mould with covering of protective gas can be constructed. In figure 2 is the same system shown during casting. An insulating hot top 1 of a porous refrac-tory material is placed above a watercooled mould 2. By startup there is used a start block 3 of steel or aluminium. The water is directed into the cooling channel 4, cools the mould wall 5 and flows out of the mould and directly out to the solidified shell 6 of the ingot (fig. 2). The metal is supplied to the mould through a channel system in the hot top or through a transfer conduit to the mould. In the chamber 7 between the hot top 1 and hot top jacket it is arranged a perforated conduit 9 around the hot top which distributes the protective gas evenly in the chamber. The gas will be sucked in through the porous refractory materials and eventual joints and thereby protect the molten metal in the solidification area against oxidation. It is arranged a lid 10 at the top to prevent air access. The gas flow is controlled by a flowmeter. Another perforated gas conduit protects the molten metal surface against oxidation.
The following example will further illustrate the invention.
~:~4~3~34 ExamPle A pure magnesium round ingot ~billet) with diametre 535 mm was cast in a hot top mould as shown in the figures. The casting speed was 60 mm/min and the amount of cooling water 30 m3/hour.
The billet got a black oxidized surface. A volume stream of 2 m3/min SF6 was supplied behind the hot top material, and the oxide coating disappeared. When the refractory material was saturated with SF6 and the chamber behind the mould filled, the gas amount could be reduced to below 0,5 dm3/min.
., .
:
The invention concerns a method and an apparatus for hot-top casting of reactive metals such as magnesium and magnesium alloys.
The wish for a more rational casting of magnesium has resulted in a change to direct chill casting with use of hot top. This is a process commonly used for aluminium casting. Direct chill casting is performed by supplying liquid metal into the one end of an openended water-cooled mould. The metal is solidified at the walls of the mould and the solidified product is continously withdrawn downwardly out of the other part of the mould, where the "ingot" is further chilled by direct water cooling. A hot top mould in principle consists of a watercooled mould and an insulating ceramic hot top which acts as a metal reservoir of uniform temperature. With the ceramic hot top it is possible to make a channel system between several moulds, in such a way that several ingots can be cast at same time.
To obtain a best possible product it is important to have a good heat balance in the mould. The solidification is determined of mould design, casting speed, amount of cooling water, metal temperature, metal level in the mould and amount of lubricating agent which shall lubricate between the mould wall and ingot.
Incorrect casting parametres can lead to casting defects and a 20~
defective cast surface of the ingot. Casting defects also arises where there are poor joints between hot top and mould, and by unfavourable mould design.
By hot top casting of magnesium light, porous refractory mater-ials are used with extremely low thermal conductivity as a part of the mould system. This method is especially useful for casting of ingots from 100 mm diametre or more. It is important that the product has a uniform, smooth surface without surface defects and oxide to be suitable for extrusion. A smooth surface is important for the extrusion rate. For billets/ T-shaped ingots which shall be used in aluminium alloys it is of importance that the surface is oxidefree to prevent contamination of the metal. It is also important that there are no cracks/ cavities in the surface where humidity can penetrate. Humidity in the metal will give an explosive evaporation when it is supplied to the molten aluminium and will represent a severe security risk.
Test of this method with magnesium however gave a product with black oxide coating and casting defects. This is a common problem which can arise at conventional casting of reactive metals such as magnesium and magnesium alloys. The reason for this can be the use of incorrect casting parametres. Too high speed or too little water-cooling can lead to reaction between water vapour and magnesium because of unsufficient primary chilling. Too much water, too high metal level or too slow casting speed can lead to that already solidified metal will melt caused by insufficient heat transport in the air gap which is formed between mould and metal when the metal shrinks during solidification. The most common reason for oxide at the surface is that the molten metal is oxidized and the oxide pulled down to the mould along the surface of the ingot.
To prevent this, a commonly used method in the magnesium industry is to protect the surface with a gas, such as SF6. When oxygen 20~73~3~
reacts with molten magnesium there is formed a porous oxide where oxygen can pass through, this makes further oxidation possible.
The function of SF6 can possibly be explained by that the SF6 molecule being absorbed to the cxide surface and therby prevent-air access for further oxidation. The gas gives protection with up to 1 % mixture in air.
Covering the melt with SF6 to prevent oxidation gave in this case no better result. Casting oil is usually used to lubricate the mould. It was P~A~; ned whether the oil used possibly could have contained any water which could cause the miscolouring, but without result. It was found that one of the causes of the surface defects was that the black oxide coatinq was stuck in the oil and that this disturbed the solidification process. Neither varying the casting parametres nor the work to find alternative air tight materials with better dimentionally tolerances gave any improvements to the final product. Tighter materials in addition leads to higher thermal conductivity and it can be difficult to control the heat balance in the mould.
At last the cause of the problem was found to be that air was sucked in through the porous hot top material and through the joint between hot top and mould. Magnesium is a powerful reduc-tion agent. When the metal is oxidized the oxygen in the air is consumed and causes a depression (vacuum) which has effect on the porous ceramic materials with the result that air is sucked in through the pores and all joints ( selfgeherating vacuum ). This leads to that the oxidation continues and the ingot being casted will have a black surface.
The object of this invention is thus to prevent oxidation of magnesium before and during solidification by direct chill casting with the use of porous hot top materials.
This and other objects of the invention is obtained by the method :' 2~7t~
and apparatus as described below, and the invention is further defined and described in the enclosed patent claims.
One possible solution to the problem would be to coat the mater-ial with a gas tight insulating material towards the metal for thereby prevent gaspassage. In practice this appeared to be difficult as it was not easy to find a suitable material which both could resist magnesium, having high insulation capacity and being tight.
Another solution would be to tighten the insulating blocks at the backside and remove remainder air in the pores of the insulation.
It was surprisingly found that the selfgenerating vacuum could be utilized to solve the problem. By introducing an inert / reducing gas atmosphere behind the hot top material the gas will act as an oxidation preventive for magnesium and prevent further oxidation.
The best result was obtained by using SF6 of high concentration.
After the pores are saturated, the gas consumption could be reduced. The system must be tightened to prevent penetration of air through slits etc. It was obtained a product with smooth surface without miscolouring.
The invention should be futher described with reference to the enclosed drawings, figure 1-2, where Figure 1 shows the mould system before start.
Figure 2 shows the system in operation.
The best solution to the oxidation problem was found to be that the hot top material and eventual joints were saturated with a protective gas. This can in practise be performed by introducing a protective gas such as SF6 of high concentration into the closed chamber between the hot top and hot top jacket. When the 7;~
enclosed air in the hot top is consumed, the protective gas will be sucked into the hot top and joints instead of or together with air and prevent futher oxidation. The quality of the metal surface will be improved even if the joints are not quite tight.
A demand to tight joints would complicate the maintenance of the hot top and mould.
The protective gas should be of high concentration. In the experiments it was used sulphur hexafluoride. This gas can also be used in mixtures with carbondioxide and inert gases. Other protective gases containing fluorides, chlorides or borides of high concentration, could also be used.
In figure 1 it is shown how a hot top mould with covering of protective gas can be constructed. In figure 2 is the same system shown during casting. An insulating hot top 1 of a porous refrac-tory material is placed above a watercooled mould 2. By startup there is used a start block 3 of steel or aluminium. The water is directed into the cooling channel 4, cools the mould wall 5 and flows out of the mould and directly out to the solidified shell 6 of the ingot (fig. 2). The metal is supplied to the mould through a channel system in the hot top or through a transfer conduit to the mould. In the chamber 7 between the hot top 1 and hot top jacket it is arranged a perforated conduit 9 around the hot top which distributes the protective gas evenly in the chamber. The gas will be sucked in through the porous refractory materials and eventual joints and thereby protect the molten metal in the solidification area against oxidation. It is arranged a lid 10 at the top to prevent air access. The gas flow is controlled by a flowmeter. Another perforated gas conduit protects the molten metal surface against oxidation.
The following example will further illustrate the invention.
~:~4~3~34 ExamPle A pure magnesium round ingot ~billet) with diametre 535 mm was cast in a hot top mould as shown in the figures. The casting speed was 60 mm/min and the amount of cooling water 30 m3/hour.
The billet got a black oxidized surface. A volume stream of 2 m3/min SF6 was supplied behind the hot top material, and the oxide coating disappeared. When the refractory material was saturated with SF6 and the chamber behind the mould filled, the gas amount could be reduced to below 0,5 dm3/min.
., .
:
Claims (6)
1. Method for hot top direct chill casting of reactive materials, especially magnesium and magnesium alloys, c h a r a c t e r i z e d i n that a protective gas is supplied to the hot top material (1) and eventual joints.
2. Method according to claim 1, c h a r a c t e r i z e d i n that a protective gas is supplied to a closed chamber (7) behind the hot top material (1).
3. Method according to claim 2, c h a r a c t e r i s e d i n that the gas is spread through a perforated conduit (9).
4. Method according to claim 1, c h a r a c t e r i s e d i n that SF6 is used as protective gas eventually in mixture with other gases, or suitable gases containing fluorides, chlorides or borides.
5. Apparatus for hot top direct chill casting of reactive metals, especially magnesium or magnesium alloys, with a hot top of insulating refractory material (1) arranged on a water cooled mould (2), c h a r a c t e r i z e d i n that it is arranged a closed chamber (7) between the hot top (1) and a jacket (8) for supply of protective gas.
6. Apparatus according to claim 5, c h a r a c t e r i z e d i n that an annular perforated conduit (9) is arranged for distribution of the gas.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO904127 | 1990-09-21 | ||
| NO904127A NO171303C (en) | 1990-09-21 | 1990-09-21 | PROCEDURE AND DEVICE FOR HOT-TOP CASTING OF REACTIVE METALS |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2047384A1 CA2047384A1 (en) | 1992-03-22 |
| CA2047384C true CA2047384C (en) | 1997-09-09 |
Family
ID=19893505
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2047384 Expired - Fee Related CA2047384C (en) | 1990-09-21 | 1991-07-18 | Method and apparatus for hot top casting of reactive metals |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2047384C (en) |
| FR (1) | FR2667002B1 (en) |
| NO (1) | NO171303C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2703609B3 (en) * | 1993-03-30 | 1995-02-10 | Lorraine Laminage | Continuous casting process in charge of metals and ingot mold for its implementation. |
| FR2800654B1 (en) | 1999-11-05 | 2001-12-14 | Lorraine Laminage | LINGOTIERE WITH WIDE SECTION FOR VERTICAL CONTINUOUS CASTING IN METAL LOAD |
| NO20023101L (en) * | 2002-06-26 | 2003-12-29 | Norsk Hydro As | Device for st degree equipment |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2517834A1 (en) * | 1975-04-22 | 1976-11-04 | Linde Ag | Continuous casting plant using double gas curtain - to protect molten metal flowing from ladle into mould. |
| GR61761B (en) * | 1975-11-12 | 1979-01-09 | Linde Ag | Casting plant |
| CH663165A5 (en) * | 1983-08-24 | 1987-11-30 | Lauener Eng Ag | CASTING MACHINE FOR CONTINUOUSLY casting METAL AND METHOD FOR THE OPERATION THEREOF. |
| JPS61119359A (en) * | 1984-11-15 | 1986-06-06 | Showa Alum Ind Kk | Continuous casting method of magnesium or ally thereof |
| FR2599650B2 (en) * | 1985-07-30 | 1988-08-26 | Pechiney Aluminium | METAL LOADING DEVICE |
-
1990
- 1990-09-21 NO NO904127A patent/NO171303C/en unknown
-
1991
- 1991-07-18 CA CA 2047384 patent/CA2047384C/en not_active Expired - Fee Related
- 1991-09-20 FR FR9111617A patent/FR2667002B1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| FR2667002B1 (en) | 1994-09-23 |
| FR2667002A1 (en) | 1992-03-27 |
| NO171303C (en) | 1993-02-24 |
| NO904127L (en) | 1992-03-23 |
| NO171303B (en) | 1992-11-16 |
| NO904127D0 (en) | 1990-09-21 |
| CA2047384A1 (en) | 1992-03-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |