WO2002081757A1

WO2002081757A1 - Cooling plate for a metallurgical furnace and method for manufacturing such a cooling plate

Info

Publication number: WO2002081757A1
Application number: PCT/EP2002/002650
Authority: WO
Inventors: Ly Giang Kien; Jiri Zlamal; Guy Thillen; Georges Rassel
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 2001-04-05
Filing date: 2002-03-11
Publication date: 2002-10-17
Anticipated expiration: 2003-10-05
Also published as: TW512174B; LU90755B1

Abstract

A cooling plate (10) for a metallurgical furnace, such as e.g. a blast furnace, comprises a cast cooling plate body (12) made of a ferrous metal and at least one cooling pipe (18) cast in the cooling plate body (12). The cooling pipe (18) is made of copper or of a copper alloy. A method for manufacturing such a cooling plate for a metallurgical furnace is also proposed.

Description

Cooling plate for a metallurgical furnace and method for manufacturing such a cooling plate

Field of the invention

The present invention generally relates to a cooling plate for a metallurgical furnace and to a method for manufacturing such a cooling plate.

Background of the invention

Cooling plates, also called "staves", have been used in blast furnaces for over a hundred years. They are arranged on the inside of the furnace armour and have internal coolant ducts, which are connected to the cooling system of the furnace. Their surface facing the interior of the furnace can be lined with a refractory material.

There are different methods for manufacturing such cooling plates.

According to a first method a mould for casting a cooling plate body is pro- vided with one or more sand cores for forming the internal coolant ducts. Liquid cast iron is then poured into the mould. This method has the disadvantage that the mould sand is difficult to remove from the cooling ducts and/or that the cooling duct in the cast iron is often not properly formed and that the cooling ducts are often not tight enough. In order to avoid the above disadvantages it has been suggested to arrange preformed steel pipes in the mould and to pour the liquid cast iron around the steel pipes. However, these cooling plates have not proved satisfactory. Indeed, due to carbon diffusion from the cast iron to the steel pipes, the latter become brittle and may crack. Contact between the cooling pipes and the cooling plate body may also be responsible for cracks in the cooling plate body, most probably because of a difference in the coefficient of thermal expansion of both materials.

In order to avoid such cracks in the steel cooling pipes and the cooling plate body, it has been suggested to provide the preformed steel pipes with a coating which prevents carbon diffusion and metallurgical bonding between the cast iron and the steel pipes. Moreover, as a result of casting, there is a small air gap between the steel pipes and the cooling plate body, whereby pipes and body can expand independently. However, these cooling plates have the disadvantage of a bad thermal transmission coefficient, because the small air gap has an insulating effect.

As an alternative to cast iron cooling plates, copper cooling plates have been developed. So far a number of production methods have been proposed for copper "staves".

Initially an attempt was made to produce copper cooling plates by casting in moulds, the internal coolant ducts being formed by a sand core in the casting mould. However, this method has not proved to be effective in practice, because the cast copper plates often have cavities and porosities, which have an extremely negative effect on the life of the plates, the mould sand is difficult to remove from the cooling ducts, and/or the cooling duct in the copper is not properly formed.

GB-A-1571789 suggests to replace the sand core by a pre-shaped metal pipe coil made from copper or high-grade steel when casting the cooling plates in moulds. The coil is integrally cast into the cooling plate body in the casting mould and forms a spiral coolant duct. ^■ This method has also not proved effective in practice, inter alia because cavities and porosities in the copper cannot be effectively prevented with this method.

A cooling plate made from a forged or rolled copper ingot is known from DE-A-2907511. The coolant ducts are blind holes introduced by mechanical drilling in the rolled copper ingot. With these cooling plates the above- mentioned disadvantages of casting are avoided. In particular, cavities and porosities in the plate are virtually precluded. Unfortunately the production costs of these cooling plates are relatively high, because the drilling of the cooling ducts is complicated, time-consuming and expensive.

WO-98/30345 teaches to cast a preform of the cooling plate with the help of a continuous casting mould, wherein rod-shaped inserts in the casting duct produce ducts running in the continuous casting direction, which form coolant ducts in the finished cooling plate.

While copper cooling plates generally have a far better thermal conductiv- ity than cast iron cooling plates, they however have a far lower wear resistance than the latter. Thus, furnace zones in which the cooling plates are exposed to severe mechanical stresses cannot be equipped with copper cooling plates. Furthermore, copper cooling plates are more expensive than cast iron cooling plates.

Object of the invention

The object of the present invention is to provide a cooling plate that can be easily manufactured and that nevertheless has a good wear resistance and a low heat transfer resistance. This object is achieved by a cooling plate as claimed in claim 1 or a method as claimed in claim 8 or 14.

Summary of the invention

According to the invention, a method for manufacturing a cooling plate is proposed. In a first method step, a mould for casting a cooling plate body is provided. Then, at least one cooling pipe is arranged in the mould. It shall be appreciated that this cooling pipe is made of copper or of a copper alloy. Next, a liquid ferrous metal is poured into the mould around the cooling pipe.

The present method, which proves easy to implement, allows to manufac- ture a cooling plate having a cast cooling plate body made of a ferrous metal and at least one cooling tube made of copper or of a copper alloy, which is cast in the cooling plate body. A first advantage of a copper or copper alloy cooling pipe is that it has a better thermal conductivity than conventional steel pipes, whereby a better heat transfer between the cooling plate body and a cooling fluid flowing through the cooling pipe is achieved. An even more important advantage is that the presence of a small air gap around the cooling pipe can be avoided. Indeed, copper and copper alloys are more ductile than steel. It follows that when the cooling pipe will be submitted to mechanical stress due to thermal expansion of the cast iron body, the cooling pipe will relatively easily deform, unlike steel pipes. Moreover, there should preferably be a close fitting between the copper tube and the cast around surrounding the latter, whereby the cooling efficiency of the cooling plate can be further increased.

As a result, the cooling plate of the invention has an improved cooling efficiency. Furthermore, cooling plates according to the invention have a good wear resistance and thus an increased lifetime, whereby maintenance costs of metallurgical furnaces can be reduced. The temperature of the cooling pipe is preferably controlled during manufacturing. This can be done by generating a flow of fluid through the cooling pipe. If the cooling pipe is to be heated, e.g. before the pouring of the liquid ferrous metal, a hot fluid is circulated through the pipe. Heating up the cooling pipe permits to avoid thermal shocks when pouring the liquid ferrous metal and also to avoid and/or remove a copper oxide layer on the surface of the cooling pipe.

If the cooling pipe is to be cooled, such as e.g. during the pouring of the liquid ferrous metal, a cool fluid is circulated through the cooling pipe.

Alternatively, an overheating of the cooling pipe may be avoided by storing a material having a high thermal capacity in the cooling pipe before pouring the liquid ferrous metal into the mould.

Preferably, the ferrous metal is chosen from the group consisting of cast iron, ductile cast iron, malleable iron and steel. More preferably, the ferrous metal is chosen from the group consisting of grey cast iron, grey cast iron with lamellar graphite, low alloy grey cast iron with lamellar graphite, middle alloy grey cast iron with lamellar graphite, high alloy grey cast iron with lamellar graphite, cast iron with a flake graphite, low alloy cast iron with a flake graphite, middle alloy cast iron with a flake graphite, high alloy cast iron with a flake graphite, cast iron with vermicular graphite, low alloy cast iron with vermicular graphite, middle alloy cast iron with vermicular graphite, high alloy cast iron with vermicular graphite, ductile iron, low alloy ductile iron, middle alloy ductile iron, high alloy ductile iron, austenitic ductile iron, austempered ductile iron, malleable cast iron, tempered cast iron, low alloy tempered cast iron, middle alloy tempered cast iron, high alloy tempered cast iron, white cast iron, low alloy white cast iron, middle alloy white cast iron, high alloy white cast iron, cast steel, low alloy cast steel, middle alloy cast steel and high alloy cast steel.

The cooling pipe may of course have a circular cross-section. The cooling pipe may however also have an oval cross-section or any other shape. Indeed, copper or copper alloy pipes can easily be given any shape, either during their production (e.g. by extrusion), or by mechanical deformation. The most pre- ferred material for the cooling pipe is copper alloy, in particular with low concentrations of Cr or Al.

It shall also be noted that, for increasing heat exchange between the cooling plate body and the cooling fluid flowing through the cooling pipe when the cooling plate is mounted in a metallurgical furnace, the cooling pipe may have a profiled outer surface. It may also be provided with cooling fins. As a matter of fact, for the same purpose of increasing heat exchange, the shape of the inner surface of the cooling pipe and that of the outer surface thereof may be chosen so as to provide an outer perimeter : inner cross-section ratio has high as possible. According to another aspect of the invention, another method for manufacturing a cooling plate for a metallurgical furnace is proposed. In a first stage, a first mould for casting a preformed cooling plate body is provided and at least one cooling pipe is arranged in the mould. It shall be appreciated that the cooling pipe is made of copper or of a copper alloy. Then a liquid ferrous metal is poured into the first mould around said at least one cooling pipe and allowed to solidify. Next, the preformed cooling plate body with the cast-in cooling pipe is removed from said mould. In a second stage, a second mould for casting a cooling plate body is provided and the preformed cooling plate body with the cast-in cooling pipe is arranged therein. Liquid ferrous metal is then poured into said mould around the preformed cooling plate body with the cast-in cooling pipe. Before pouring the liquid ferrous metal into the second mould, the cooling plate body with the cast-in cooling pipe is preferably heated in such a way that its outer surfaces reach a temperature about the melting temperature of the ferrous metal. Such a two-stage method allows a better control of the temperature of the copper or copper alloy cooling pipe during manufacturing, since the quantity of liquid ferrous metal is reduced in the first stage. Moreover, in the second stage the ferrous metal of the preformed body will absorb part of the heat. It shall however be noted that the temperature of the cooling pipe is preferably con- trolled when liquid ferrous metal is poured into the first mould, respectively the second mould.

Brief description of the drawings

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig.1 : is a front view of a preferred embodiment of a cooling plate in accor- dance with the invention;

Fig.2: is a rear view of the cooling plate of Fig.1 ;

Fig.3: is a section view along line A-A in Fig.2;

Figs.4 to 7: show sectional views of cooling pipes with different outer surface profiles; Fig.8: is a three-dimensional view of a portion of a cooling pipe provided with cooling fins;

Fig.9 and 10: show section views of possible inner shapes for a cooling pipe.

In the Figures, same reference numbers indicate similar or identical elements.

Detailed description of a preferred embodiment

Fig.1 to 3 illustrate different views of a preferred embodiment of a cooling plate 10 in accordance with the invention. The cooling plate 10 comprises a cooling plate body 12 made of a ferrous metal, preferably cast iron. As can be seen in the Figures, the cooling plate body 12 has the general form of a parallelepiped, whose front side and back side are respectively indicated 14 and 16.

It shall be appreciated that four cooling pipes 18 made of copper or of a copper alloy are cast in the cooling plate body 12. These cooling pipes 18 are represented by dashed lines in Fig.2. As can be understood from Fig.3, each cooling pipe 18 has a straight portion 20 essentially parallel to the front side of the cooling plate. The straight portion 20 terminates at both ends by a bent portion 22 protruding on the rear side 16 of the cooling plate body 12, for connecting each of the cooling pipes 18 to an cooling circuit of e.g. a blast furnace.

The present cooling plate 10 can be easily manufactured by casting. It shall be noted that, since the present cooling plate 10 comprises cooling pipes 18 made of copper or of a copper alloy, the latter are preferably cooled to prevent their melting. Indeed, the temperature of casting of molten cast iron generally ranges from 1 200 to 1 300°C, whereas the melting temperature of copper is of about 1 083°C.

Accordingly, the manufacture of the cooling plate 10 is preferably carried out as follows. A mould having the dimensions of the cooling plate body is provided and the cooling pipes are arranged in the mould. The cooling pipes are then connected to a temperature control circuit to control of the temperature of the cooling pipes by generating a flow of fluid therethrough. Next, molten cast iron is poured into the mould around the cooling pipes and allowed to solidify therein. The cooling pipes are then disconnected from the temperature control circuit and the obtained cooling plate removed from the mould. During the pouring of the liquid cast iron into the mould a cool fluid, such as e.g. water, oil or a gaseous fluid, is advantageously circulated through the cooling pipes, to avoid melting of the latter. The temperature control circuit may also be used to heat up the cooling pipes by generating a flow of hot fluid therethrough. Heating up the cooling pipes permits to avoid thermal shocks and to avoid and/or remove a copper oxide layer on the cooling pipes.

An alternative way of avoiding an overheating during casting is to store a material having a high thermal capacity in the cooling pipes before pouring the molten metal into the mould. Such a material may be e.g. corundum, quartz sand or the like.

The temperature of the cooling pipes is preferably controlled in such a way as to achieve a certain type of bonding between the cooling pipes made of copper or of a copper alloy and the cast iron cooling plate body. A first type of bonding may be called "mechanical bonding", wherein the cooling plate body and the cooling pipes are in close contact with each other, but their metals are not mixed with each other. The ductility of copper and copper alloys allows such a close contact between cooling pipes and cast iron, without risk of cracking.

Another type of bonding that can be achieved may be called "metallurgical bonding". In this case the metals of the cooling pipes and the cooling plate are welded to each other. This means that the outer surface of the cooling pipe has melted and that a thin layer of intermediate alloy made from the two metals has formed. Such a metallurgical bonding between the cooling plate body and the cooling pipes permits a better heat transfer from the cooling plate body to the cooling medium circulating through the cooling pipes when the cooling plate is mounted in a metallurgical furnace.

In the present embodiment, the cooling plate body advantageously has a series of regularly spaced parallel ribs 24 on its front side 14, so as to increase its heat exchange surface and thus improve the cooling efficiency of the cooling plate 10.

Cooling plates in accordance with the invention have proved to have a

"cooling effect" which is two to three times that of a conventional cast iron stave with steel pipes. This "cooling effect" is determined by measuring the hottest point on the hot side of the cooling plate 10, resp. the conventional stave, when exposed to a same heat source.

In another embodiment of the method of the invention, a cooling plate is manufactured in two stages. In a first stage, a first mould for casting a pre- formed cooling plate body is provided. The cooling pipes are arranged in the first mould and liquid ferrous metal is then poured in the first mould around the cooling pipes. The liquid ferrous metal is then is then allowed to solidify and the obtained preformed cooling plate body with cast-in cooling pipes removed from the first mould. As the quantity of cast iron in this first stage is less important than when cooling plates are cast in a single stage, it is easier to protect the cooling pipes against an overheating.

In a second stage, the preformed cooling plate body with cast-in cooling pipes is heated in such a way that its surfaces reach the melting temperature of the cast iron and is subsequently arranged into a second mould having the dimensions of the desired cooling plate. Liquid cast iron is then poured in the second mould around the preformed cooling plate body with cast-in cooling pipes and allowed to solidify therein. During the pouring of the liquid cast iron, the cooling pipes are preferably connected to a cooling circuit to generate a flow of cooling fluid through the cooling pipes.

It remains to be noted that, to increase heat exchange between the cool- ing plate body and the cooling fluid flowing through the cooling pipes 18, the latter may have a profiled outer surface, as illustrated in Figs.4 to 7. A cooling pipe may for example have one or several longitudinal ribs 26 on its outer surface, as shown in Figs.4 and 7. In Figs.5 and 6, there is one large longitudinal rib 28. The cooling pipe 18 may also e.g. be provided with radially extending cooling fins 30, as shown in Fig.8.

As a matter of fact, for the same purpose of increasing heat exchange, the shape of the inner surface of the cooling pipe and that of the outer surface thereof may be chosen so as to provide an outer perimeter : inner cross-section ratio has high as possible.

For increased inner surface, possible inner cross-sections for the cooling tubes are illustrated in Figs.9 and 10. It is clear that the cooling pipes illustrated in Figs. 4 to 8 may exhibit an inner cross-section such as in Figs. 9 and 10. In other words, the cooling pipes of the cooling plate 10 may have a complex inner shape and a profiled outer surface.

Claims

1. A cooling plate for a metallurgical furnace comprising: a cast cooling plate body made of a ferrous metal; and at least one cooling pipe cast in said cooling plate body; characterized in that said at least one cooling pipe is made of copper or of a copper alloy.

2. The cooling plate according to claim 1 , characterised in that said cooling pipe has a circular or oval cross-section.

3. The cooling plate according to any one of the preceding claims, characterised in that said at least one cooling pipe has a profiled outer surface.

4. The cooling plate according to any one of the preceding claims, characterised by cooling fins on the outer surface of said at least one cooling pipe.

5. The cooling plate according to any one of the preceding claims, characterised by a metallurgical bonding or a mechanical bonding between said at least one cooling pipe and said cooling plate body.

6. The cooling plate according to any one of the preceding claims, characterised in that said cooling plate body is made of a ferrous metal chosen from the group consisting of cast iron, ductile cast iron, malleable iron and steel.

7. The cooling plate according to the preceding claim, characterised in that said cooling plate body is made of a ferrous metal chosen from the group consisting of grey cast iron, grey cast iron with lamellar graphite, low alloy grey cast iron with lamellar graphite, middle alloy grey cast iron with lamellar graphite, high alloy grey cast iron with lamellar graphite, cast iron with a flake graphite, low alloy cast iron with a flake graphite, middle alloy cast iron with a flake graphite, high alloy cast iron with a flake graphite, cast iron with vermicular graphite, low alloy cast iron with vermicular graphite, middle alloy cast iron with vermicular graphite, high alloy cast iron with vermicular graphite, ductile iron, low alloy ductile iron, middle alloy ductile iron, high alloy ductile iron, austenitic ductile iron, austempered ductile iron, malleable cast iron, tempered cast iron, low alloy tempered cast iron, middle alloy tempered cast iron, high alloy tempered cast iron, white cast iron, low alloy white cast iron, middle alloy white cast iron, high alloy white cast iron, cast steel, low alloy cast steel, middle alloy cast steel and high alloy cast steel.

8. A method for manufacturing a cooling plate for a metallurgical furnace, comprising: providing a mould for casting a cooling plate body; arranging in said mould at least one cooling pipe; and pouring a liquid ferrous metal into said mould around said at least one cool- ing pipe; characterized in that said cooling pipe is made of copper or of a copper alloy.

9. The method according to claim 8, characterised in that the temperature of said at least one cooling pipe is controlled.

10. The method according to claim 9, characterised in that the temperature of said at least one cooling pipe is controlled by means of a fluid flowing therethrough.

11. The method according to claim 9, characterised in that a material having a high thermal capacity is stored in said at least one cooling pipe before said liquid ferrous metal is poured into said mould.

12. The method according to anyone of claims 8 to 11 , characterised in that said ferrous metal is chosen from the group consisting of cast iron, ductile cast iron, malleable iron and steel.

13. The method according to the preceding claim, characterised in that said ferrous metal is chosen from the group consisting of grey cast iron, grey cast iron with lamellar graphite, low alloy grey cast iron with lamellar graphite, middle alloy grey cast iron with lamellar graphite, high alloy grey cast iron with lamellar graphite, cast iron with a flake graphite, low alloy cast iron with a flake graphite, middle alloy cast iron with a flake graphite, high alloy cast iron with a flake graphite, cast iron with vermicular graphite, low alloy cast iron with vermicular graphite, middle alloy cast iron with vermicular graphite, high alloy cast iron with vermicular graphite, ductile iron, low alloy ductile iron, middle alloy ductile iron, high alloy ductile iron, austenitic ductile iron, austempered ductile iron, malleable cast iron, tempered cast iron, low alloy tempered cast iron, middle alloy tempered cast iron, high alloy tempered cast iron, white cast iron, low alloy white cast iron, middle alloy white cast iron, high alloy white cast iron, cast steel, low alloy cast steel, middle alloy cast steel and high alloy cast steel.

14. A method for manufacturing a cooling plate for a metallurgical furnace, comprising:

(a) providing a first mould for casting a preformed cooling plate body;

(b) arranging in said mould at least one cooling pipe made of copper or of a copper alloy; (c) pouring a liquid ferrous metal into said first mould around said at least one cooling pipe and allowing it to solidify;

(d) removing said preformed cooling plate body with said at least one cooling pipe cast therein from said first mould;

(e) providing a second mould for casting a cooling plate body; (f) arranging said preformed cooling plate body with said at least one cooling pipe cast therein in said second mould; and

(g) pouring liquid ferrous metal into said second mould around said preformed cooling plate body with said at least one cooling pipe cast therein.

15. The method according to claim 14, characterised in that before pouring said liquid ferrous metal into said second mould, said cooling plate body with at least one cooling pipe cast therein is heated in such a way that the outer surfaces thereof reach a temperature about the melting temperature of said ferrous metal.

16. The method according to claim 14 or 15, characterised in that the temperature of said at least one cooling pipe is controlled when said liquid ferrous metal is poured into said first mould, respectively said second mould.

17. The method according to anyone of claims 14 to 16, characterised in that said ferrous metal is chosen from the group consisting of cast iron, ductile cast iron, malleable iron and steel.

18. The method according to the preceding claim, characterised in that said ferrous metal is chosen from the group consisting of grey cast iron, grey cast iron with lamellar graphite, low alloy grey cast iron with lamellar graph- ite, middle alloy grey cast iron with lamellar graphite, high alloy grey cast iron with lamellar graphite, cast iron with a flake graphite, low alloy cast iron with a flake graphite, middle alloy cast iron with a flake graphite, high alloy cast iron with a flake graphite, cast iron with vermicular graphite, low alloy cast iron with vermicular graphite, middle alloy cast iron with vermicular graphite, high alloy cast iron with vermicular graphite, ductile iron, low alloy ductile iron, middle alloy ductile iron, high alloy ductile iron, austenitic ductile iron, austempered ductile iron, malleable cast iron, tempered cast iron, low alloy tempered cast iron, middle alloy tempered cast iron, high alloy tempered cast iron, white cast iron, low alloy white cast iron, middle alloy white cast iron, high alloy white cast iron, cast steel, low alloy cast steel, middle alloy cast steel and high alloy cast steel.