Title of Invention

A MOULD FOR CASTING A LIQUID METAL AND CAST MOULDING AN OBJECT WITH THE MOULD

Abstract The inventive mould for casting a liquid metal comprises a shaped surface (24) corresponding to a castable product surface and contacting the liquid metal. Said mould also comprises a heat removing part (10) made of a material whose thermal conductivity is greater than 150 W/mK. The invention can be used for producing cast-iron pipes.
Full Text

Mould for casting a liquid metal and associated method
The present invention relates to a mould for casting a liquid metal, of the type comprising a shaped surface which corresponds to the surface of the product to be produced by casting and which is to come into contact with the liquid metal.
The invention is applicable in particular to installations for producing pipes by casting.
Moulds for producing cast iron pipes by casting are known. Those moulds have the general shape of a hollow cylinder about an axis of rotation and comprise an extremity corresponding to the plain end of the pipe and an extremity corresponding to the socket end of the pipe. The internal surface of the mould forms the external surface of the pipe produced.
During the production of pipes, the mould is driven in rotation about its axis, and a liquid metal is cast on the internal surface of the mould. The metal is cast successively from the socket-end extremity to the plain-end extremity.
The known moulds are produced from a low-chromium alloy steel in order to withstand the temperature of the liquid steel.
Owing to the high temperature of the liquid metal and the variation in the temperature of the mould during the successive casting of several pipes, cracks appear on the internal surface of the mould. During casting, liquid metal enters those cracks. The metal located in the cracks

prevents the removal of the pipe from the mould and leads to scores on the external surface thereof.
When the cracks exceed a predetermined size, the mould has to be repaired by machining the internal surface or by filling the cracks by welding. However, those operations modify the internal surface in such a manner that the pipes produced after repair may no longer comply with the required tolerances.
The service life of the known moulds is therefore limited.
The known steel moulds have another disadvantage. During the casting of the first pipes, the steel mould becomes plastically deformed to a considerable degree. Consequently, the mould is produced with dimensions which take that initial deformation into account. In order to bring the mould to its desired dimensions, several pipes, for example six, are cast. Those pipes do not comply with the required tolerances and have to be discarded. The necessity to produce those "lost" pipes leads to a reduction in the output of the casting installation.
An object of the present invention is to propose a mould for casting liquid metal which has a long service life while at the same time permitting the casting of articles having low tolerances.
To that end, the invention relates to a mould of the above-mentioned type, characterized in that it comprises a heat-removing portion produced from a material having a thermal conductivity higher than 150 W/mK.

According to particular embodiments, the invention comprises one or more of the following features:
- the material has a thermal conductivity higher than 300
- W/mK;
- the material has a thermal conductivity higher than 325
- W/mK;
- the heat-removing portion is composed of an alloy based on
- copper, in particular comprising more than 50% by weight of
- copper;
- the alloy based on copper comprises chromium, in
- particular from 0.25%-to 2% by weight;
- the alloy comprises zirconium, in particular from 0.05% to
- 0.25% by weight;
- the heat-removing portion forms at least part of an
- external surface of the mould;
- the heat-removing portion forms at least part of the
- shaped surface;
- the heat-removing portion extends continuously between the
- shaped surface and the external surface;
- the mould comprises a covering forming at least part of
- the shaped surface and extending from the shaped surface to
- the heat-removing portion;
- the covering and the heat-removing portion have thermal
- expansion coefficients such that the thermal expansion of
- the covering is greater than the thermal expansion of the
- heat-removing portion under the effect of the cast metal;
- the covering is composed of a material having a hardness
- greater than the hardness of the heat-removing portion,
- especially of chromium or nickel or of an alloy based on
- chromium and/or nickel;
- the shaped surface is rotationally symmetrical about an
- axis; and
- the mould is a mould of a pipe.

The invention relates also to a method for producing an object by casting, of the type comprising the step of casting the liquid metal in a mould, characterized in that the mould is a mould such as defined above.
The method according to the invention may comprise the following features:
- the metal is a cast iron, especially grey cast iron or
- spheroidal graphite cast iron; and
- the method is also characterized by a step of annealing
- the object produced by casting.
The invention will be better understood on reading the following description which is given purely by way of example and with reference to the appended drawings in
which:
- Figure 1 is a diagrammatic view of an installation for
- producing pipes according to the invention;
- Figure 2 is a detail of the installation of Figure 1,
- showing the mould on a larger scale;
- Figure 3 is a view in partial section of the mould
- according to the invention taken on the line II-II of Figure
- 2; and
- Figure 4 shows a variant of the mould of Figure 3.
Figure 1 shows an installation for producing cast iron pipes according to the invention which is indicated by the general reference 2.
The installation 2 comprises a receptacle 4, a pouring device 6, a casting duct 8, a rotary mould 10, a cooling

device 12 and a device 14 for removing a finished pipe. The installation 2 is used to produce pipes 16.
The receptacle 4 is a crucible composed of refractory material and containing liquid metal, for example cast iron.
The pouring device 6 is a tilting device having a volume corresponding to the amount of liquid metal necessary for a pipe 16. The tilting device can be inclined between a position for receiving liquid metal from the receptacle and a position for pouring the liquid metal into the casting duct 8.
The casting duct 8 is a channel which leads from the pouring device 6 to the mould 10. It comprises an inlet 20 located in the vicinity of the device 6 and an outlet 22 extending into the mould 10. The duct 8 is inclined relative to the horizontal in such a manner that the outlet 22 is located lower down than the inlet 20, thus enabling the liquid cast iron to flow by gravity.
The rotary mould 10, also called a "shell", has a rotationally symmetrical shape, in the present example a generally cylindrical shape, having an axis X-X inclined relative to the horizontal in such a manner that it is parallel with the duct 8. In the following, the terms "axially" and "radially" will be used with reference to that axis X-X. The mould 10 has an internal shaped surface 24 which is the negative surface of the .pipe 16, as well as a cylindrical external surface 26 (see Figure 2). The surface 26 does not come into contact with the liquid metal during casting. As indicated in Figure 3, the internal surface 24 is provided with cavities 27 for entraining the liquid metal. The mould 10 comprises a plain-end extremity 28,

facing the inlet 20, and a socket-end extremity 30 facing away from the inlet 20. The plain-end extremity 28 forms the plain end of the pipe 16 while the socket-end extremity 30 forms the socket end of the pipe 16.
The mould 10 can be driven in rotation about the axis X-X by a drive device (not shown) . Furthermore, the mould 10 can be driven in translation along the axis X-X between a position for the commencement of casting, in which the outlet 22 is opposite the socket-end extremity 30, and a position for the end of casting, in which the outlet 22 is opposite the plain-end extremity 28.
The cooling device 12 is a sprinkling rose which is suitable for spraying cooling liquid, for example water, onto the external surface 26 of the mould 10. By way of variation, the device 12 may be constituted by a system for the circulation of water in the known manner.
The removing device 14 is suitable for removing the cast pipe 16 axially from the mould 10.
The devices 6, 12 and 14, the receptacle 4 and the casting duct 8 are known per se and are not described in more detail.
The mould 10 according to the invention is composed entirely of CuCrZr which is an alloy based on copper. The alloy comprises more than 50% by weight of copper, preferably more than 60% by weight of copper, and in particular more than 75% by weight of copper.
In the present case, it is composed of an alloy of copper, chromium and zirconium, especially in accordance with the

standard DIN 17666. A particularly suitable alloy comprises 1% by weight of chromium and 0.15% by weight of zirconium, the remainder being copper and unavoidable impurities. This alloy has an average thermal conductivity at 220°C of 340 W/mK.
The alloy may comprise from 0.25% to 2% by weight of chromium, and preferably from 0.5% to 1.5% by weight.
The alloy may comprise from 0.05% to 0.25% by weight of zirconium, and preferably from 0.10% to 0.20% by weight.
According to the invention, at least some of the material of the mould 10 has a thermal conductivity higher than 150 W/mK, especially higher than 300 W/mK and in particular higher than 325 W/mK.
The production of a pipe 16 by means of the installation 2 according to the invention is effected as follows.
Liquid cast iron, corresponding to the amount of cast iron necessary for the pipe 16, is introduced into the pouring device 6 by the crucible 4.
The mould 10 is then driven in rotation about the axis X-X and it is brought into its position for the commencement of casting.
Subsequently, the liquid cast iron is poured from the device 6 into the duct 8, flows along the latter and is poured into the mould 10 at the socket-end extremity 30.
The mould 10 is brought successively towards its position for the end of casting.

The liquid cast iron located in the mould is pressed against the surface 24 by centrifugation, solidifies and forms the pipe 16.
Owing to the high thermal conductivity of the material of the mould 10, the temperature gradient between the internal surface 24 and the external surface 26 is small. In other words, the heat introduced by the liquid cast iron is removed rapidly from the surface 24 towards the Surface 26. Consequently, little thermal stress is produced in the mould 10, which reduces or prevents the appearance of cracks. The mould 10 therefore has a long service life.
For example, for the mould 10 of CuCrZr having a wall
thickness of 20 mm and a cast steel at 1400 C, the internal surface 24 reaches a temperature of 150°C, while the external surface 26 reaches a temperature of 100°C. The temperature gradient is therefore 50°. Under analogous conditions, prior art moulds of steel lead to a temperature gradient of approximately 580°C.
Surprisingly, the heat is removed from the internal surface 24 sufficiently rapidly to prevent the latter from reaching the melting temperature (approximately 1083°C) of the material of the mould. It should be noted that, in general, the thermal conductivity of the material of the mould is selected to be sufficiently high to prevent the mould from melting at the surface 24.
The cast iron solidifies rapidly in the mould, at a solidification rate of from 1.20 mm/s to 0.80 mm/s. Owing to the rapid solidification, the carbon contained in the cast iron precipitates in the form of Fe3C (iron carbide) in a

region in contact with the surface 24, while, in a region at a distance from the surface 24, the carbon is substantially in the form of graphite. The rapid solidification therefore leads to a large gradient from iron carbide - graphite in the pipe 16. During the annealing operation, which converts the iron carbide into graphite, the external surface of the pipe 16 is heated more rapidly than the internal surface thereof. Consequently, for a required rate of conversion of iron carbide into graphite, the pipe 16 can be annealed at a low temperature or for a short time. The mould 10 according to the invention is therefore particularly suitable for casting objects of grey cast iron or spheroidal graphite cast iron.
In addition, after the removal of a pipe 16, the mould 10 reaches its initial temperature rapidly.
Therefore, the pipes can be produced at a rapid rate.
The mould 10 according to the invention also leads to only slight local deformation of the external surface of the pipe owing to the rapid solidification. The pipe therefore has a better appearance.
During the casting of the first pipes, the plastic deformation of the mould 10 according to the invention is slight. Even the first pipes produced thus comply with the required dimensions and can be used. Thus, the installation has a large output.
Figure 4 shows a variant of the mould of Figure 3. In the following, only the differences with respect to the mould of Figure 3 will be described, identical elements bearing the same references.

The mould 10 is a composite mould- It comprises an external heat-removing layer 40 which forms the external surface 26, and an internal protective layer 42 which forms the shaped internal surface 24.
The layer 40 is produced from the same material as the mould 10 described above.
The layer 42 is composed of a material which has a hardness greater than the hardness of the layer 40. It is composed, for example, of chromium or nickel, or of an alloy based on those metals. The layer 42 protects the layer 40 from scores generated during the removal of the pipe 16.
Moreover, the thermal expansion coefficients of the materials of the layers 40 and 42 are selected in such a manner that the thermal expansion of the internal layer 42, caused by the heating brought about by the cast iron, is greater than the expansion of the external layer 40. Thus, during the casting operation, the internal layer 42 is pressed against the external layer 40 and does not become detached therefrom.
In general, at least one portion of the mould, which portion is used to remove the heat of the cast iron from the shaped surface, is composed of a material having a high thermal conductivity, such as the alloy based on copper.
In a variant, the alloy of the mould 10 or of the heat-removing portion is based on copper comprising small amounts of tellurium or small amounts of silver and phosphorus.

In a variant which is not shown, the mould 10 comprises an internal heat-removing layer having high thermal conductivity which forms at least part of the internal surface 24, and an external layer composed of a different material, such as chromium or nickel or chromium and nickel in order to increase the hardness, or chromium and zinc in order to prevent the formation of scale.
Although the mould according to the invention is particularly suitable for casting pipes composed of cast iron, it can be used to cast other objects composed of other metals.
CLAIMS
1. Mould for casting a liquid metal, of the type
2. comprising a shaped surface (24) which corresponds to the
3. surface of the product (16) to be produced by casting and
4. which is to come into contact with the liquid metal,
5. characterized in that it comprises a heat-removing portion
6. (10, 40) produced from a material having a thermal
7. conductivity higher than 150 W/mK.
8. Mould according to claim 1, characterized in that the
9. material has a thermal conductivity higher than 300 W/mK.
10. Mould according to claim 2, characterized in that the
11. material has a thermal conductivity higher than 325 W/mK.
12. Mould according to any one of the preceding claims,
13. characterized in that the heat-removing portion is composed
14. of an alloy based on copper, in particular comprising more
15. than 50% by weight of copper.
16. Mould according to claim 4, characterized in that the
17. alloy based on copper comprises chromium, in particular from
18. 0.25% to 2% by weight.
19. Mould according to either claim 4 or claim 5,
20. characterized in that the alloy comprises zirconium, in
21. particular from 0.05% to 0.25% by weight.
22. Mould according to any one of the preceding claims,
23. characterized in that the heat-removing portion forms at
24. least part of an external surface (26) of the mould.

25. Mould according to any one of the preceding claims,
26. characterized in that the heat-removing portion forms at
27. least part of the shaped surface (24).
28. Mould according to claims 7 and 8 taken together,
29. characterized in that the heat-removing portion extends
30. continuously between the shaped surface (24) and the
31. external surface (26).
32. Mould according to any one of claims 1 to 9,
33. characterized in that it comprises a covering (42) forming
at least part of the shaped surface (24) and extending from the shaped surface {24) to the heat-removing portion.
11. Mould according to claim 10, characterized in that the
12. covering (42) and the heat-removing portion (40) have
13. thermal expansion coefficients such that the thermal
14. expansion of the covering (42) is greater than the thermal
15. expansion of the heat-removing portion (40) under the effect
16. of the cast metal.
17. Mould according to claim 10 or 11, characterized in
18. that the covering (42) is composed of a material having a
19. hardness greater than the hardness of the heat-removing
20. portion {40), especially of chromium or nickel or of an
21. alloy based on chromium and/or nickel.
22. Mould according to any one of the preceding claims,
23. characterized in that the shaped surface (24) is
24. rotationally symmetrical about an axis (X-X).
25. Mould according to claim 13, characterized in that it
26. is a mould of a pipe.

27. Method for producing an object by casting, of the type
28. comprising the step of casting the liquid metal in a mould,
29. characterized in that the mould is a mould (10) according to
30. any one of the preceding claims.
31. Method according to claim 15, characterized in that the
32. metal is a cast iron, especially grey cast iron or
33. spheroidal graphite cast iron.
34. Method according to claim 15 or 16, characterized also
35. by a step of annealing the object produced by casting.
Dated this 28 day of September 2006


Documents:

3607-CHENP-2006 CORRESPONDENCE OTHERS.pdf

3607-CHENP-2006 CORRESPONDENCE PO.pdf

3607-CHENP-2006 FORM-2.pdf

3607-CHENP-2006 FORM-3.pdf

3607-CHENP-2006 PETITION.pdf

3607-CHENP-2006 POWER OF ATTORNEY.pdf

3607-CHENP-2006 CORRESPONDENCE OTHERS 05-08-2009.pdf

3607-chenp-2006 description (complete) 05-08-2009.pdf

3607-CHENP-2006 OTHER DOCUMNET 05-08-2009.tif

3607-chenp-2006-abstract.pdf

3607-chenp-2006-claims.pdf

3607-chenp-2006-correspondnece-others.pdf

3607-chenp-2006-description(complete).pdf

3607-chenp-2006-drawings.pdf

3607-chenp-2006-form 1.pdf

3607-chenp-2006-form 18.pdf

3607-chenp-2006-form 5.pdf

3607-chenp-2006-pct.pdf


Patent Number 240047
Indian Patent Application Number 3607/CHENP/2006
PG Journal Number 18/2010
Publication Date 30-Apr-2010
Grant Date 26-Apr-2010
Date of Filing 28-Sep-2006
Name of Patentee SAINT-GOBAIN PAM
Applicant Address 91 AVENUE DE LA LIBERATION, 54000 NANCY,
Inventors:
# Inventor's Name Inventor's Address
1 GIRARDIN,DENIS 16 RUE DE BLENOD, 54700 MAIDIERES
PCT International Classification Number B22C 3/00
PCT International Application Number PCT/FR05/00777
PCT International Filing date 2005-03-30
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 0403444 2004-04-01 France