KR20040072726A - Cooling plate for a metallurgical furnace and method for manufacturing such a cooling plate - Google Patents

Abstract

A cooling plate (10) for a metallurgical furnace comprises a cast cooling plate body (12) made of a ferrous metal and at least one steel cooling pipe (20) cast in the cooling plate body (12). A metallic jacket (26) having a thickness in the millimetre range is provided on the outer surface of the steel cooling pipe (20) in the cooling plate body (12), the metallic jacket (26) being made from a metal selected from the group consisting of copper, copper alloys, nickel and nickel alloys.

Description

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

Cold plates, also called “staves,” have been used in blast furnaces for over 100 years. The cold plate is placed inside the furnace armor and has an internal coolant duct connected to the furnace's cooling system. The surface of the cold plate facing the interior of the furnace may be lined with refractory material.

There are several different ways of making such a cold plate.

According to a first method, one or more sand cores for forming coolant ducts are provided in a mold for casting a cooling plate body. Then the liquid cast iron is poured into the mold. This method is disadvantageous in that it is difficult to separate the mold sand from the cooling duct, and / or that the cooling tube is often not properly formed in cast iron, and that the cooling duct is often not rigid enough. Has

In order to avoid this drawback, a method has been proposed in which a preformed steel pipe is placed in a mold and the liquid cast iron is poured around the steel tube. However, this cold plate proved to be not very satisfactory. Indeed, carbon diffusion from cast iron into the steel tube may occur, causing the steel tube to brittle or crack. The contact of the body between the cooling tube and the cold plate may also cause the cold plate body to crack, most likely due to the difference in the coefficient of thermal expansion of both materials.

In order to avoid cracking of the steel cooling tube and the cold plate body, German Patent A-2128827 describes the coating of preformed steel tubes with metallic oxide to diffuse carbon and metallurgical bonds between cast iron and steel tubes. It is proposed to prevent the occurrence of bonding). In fact, German Patent A-2128827 seeks to provide an alternative to previous known cold plates in which steel tubes were coated with graphite or aluminum, or plated with copper or tin, such layers were carburising. Is not able to prevent). However, alternatives of applying metal oxide coatings to steel tubes are also not satisfactory. As a result of casting, the coating peels off and there is a small air gap between the steel tube and the cold plate body, which allows the tube and body to expand independently. Unfortunately, this cold plate has the disadvantage that the thermal transfusion coefficient is not good because its small air gap has an insulating effect.

U.S. Patent No. 4,150,818 discloses a casting cooling in which a steel cooling tube is coated with two layers, a combination of a metallic layer in contact with the steel tube and a stable metal oxide layer surrounding it. A metallurgy furnace comprising a plate body. The metal layer is made of a metal comprising individual or two or more selected from the group consisting of Ni, Co, Mn, and Ag. The thickness of the metal layer is 40-100 μm, the thickness of the metal oxide layer is 30-100 μm and the maximum of the total thickness of both layers is 200 μm. Although the metal layer prevents carburization into the steel tube, these cold plates are still unsatisfactory because of the metal oxide layer which has a detrimental effect with regard to the heat conductivity.

As an alternative to cast iron cold plates, copper cold plates have been developed. To date, several manufacturing methods have been proposed for copper “stays”.

Initially, attempts have been made to form internal coolant ducts by sand cores in molds to cast copper cold plates into molds. However, this method has proved to be inefficient in practice, which means that the cast copper plate often has cavities or porosities that have an extremely negative effect on the life of the plate, and that mold sand is removed from the cooling duct. This is because of the difficulty and / or the lack of adequate cooling ducts in copper.

British Patent A-1571789 proposed to replace sand cores with pre-shaped metal pipe coils made of copper or high-grade steel when casting cold plates in molds. . The coil is cast integrally with the cold plate body in the casting mold and forms a spiral coolant duct. This method has also proved ineffective in practice, among other things, because it did not effectively block cavities or porosity in copper.

Cold plates made from forged or rolled copper ingots are known from German patent A-2907511. The coolant ducts are blind holes that are mechanically drilled into the rolled copper ingot. With this cold plate the disadvantages of the casting method can be overcome. In particular, the cavities or small holes in the plates can be almost closed. Unfortunately, the production cost of such cooling plates is relatively high, because drilling the cooling ducts into the cooling plates is complicated, long and expensive.

WO 98/30345 discloses that rod-shaped inserts in the casting duct produce a duct in a continuous casting direction, forming a coolant duct in the finished cold plate. It teaches how to cast a preform of a cold plate with the help of a continuous casting mould.

Copper cold plates generally have much better thermal conductivity than cast iron cold plates, while they have much lower wear resistance than the latter. Therefore, it is not possible to install a copper cold plate in a furnace zone where the cold plate is exposed to severe mechanical stress. In addition, copper cold plates are more expensive than cast iron cold plates.

The present invention relates generally to cooling plates for metallurgical furnaces and to methods of making such cooling plates.

Purpose of the Invention

It is an object of the present invention to provide a cold plate that can be easily manufactured and has excellent wear resistance and low heat transfer resistance. This object is achieved by the cold plate as claimed in claim 1.

Summary of the Invention

The cooling plate for the metallurgical furnace according to the invention comprises a cooling plate body made of ferrous metal and one or more steel cooling pipes present inside the cooling plate body. A metallic jacket is provided on the outer surface of the steel cooling tube in the cold plate body. The metal jacket has a thickness in the millimeter range and is made of a metal selected from the group consisting of copper, copper alloys, nickel and nickel alloys.

In this cold plate, the steel tube is protected by a thick metal jacket which is believed to act as a physical barrier to carbon diffusion. In other words, since the metal jacket is thick, it is very unlikely that carbon from liquid ferrous metal, generally cast iron, will reach the steel cooling tube. This was chosen because the steel tube was coated with metal layers and metal oxide layers such as Ni, Co, Mn, or Ag with a total thickness of 200 μm and these metals could not form metal carbides, i.e., the metal layers were resistant to carbon diffusion. This is a significant difference from US Pat. No. 4,150,818, which acts as a chemical barrier.

In addition, the present cooling plate does not have a metal oxide layer used to prevent welding between the steel tube and the cast iron, thereby avoiding the air gap. In fact, the metal jacket acts as an intermediate layer, which prevents welding between the steel cooling tube and the cast iron body and can absorb strain and stress. Thus, the metal jacket is in tight contact with both the steel tube and the cast iron body. This is extremely advantageous with regard to heat transfer, since copper nickel and their alloys have high thermal conductivity. Since the metal jacket is in intimate contact between the different materials and has high thermal conductivity, intensive heat transfer from the cast iron body to the cooling tube is ensured.

Such a cold plate can be easily produced by casting. According to another aspect of the invention, a method of manufacturing a cold plate for a metallurgical furnace is provided. This includes the following steps:

Providing at least one steel cooling tube having a metal jacket on its surface having a thickness in the millimeter range made of a metal selected from the group consisting of copper, copper alloy, nickel and nickel alloy;

Providing a mold for casting the cold plate body;

Arranging said at least one cooling conduit with a metal jacket in a mold; And

Pouring liquid ferrous metal into a mold around said at least one cooling tube with a metal jacket.

This method proves relatively simple to implement because steel tubes are traditionally cast in the cold plate body. In handling, it is very convenient to use thick metal jackets, since metal jackets are more resistant and require less attention than metal layers of 100 or 200 μm which are susceptible to damage. Therefore, the use of a thick layer ensures a good coating on the steel tube and facilitates handling during the manufacturing process.

Thus, the present manufacturing method contemplates the manufacture of a cooling plate with improved thermal conductivity due to the metal jacket which enables intensive heat transfer from the cooling tube. In addition, cold plates with ferrous based plate bodies manufactured in this way have excellent wear resistance and increased lifespan, thereby reducing the cost of maintaining metallurgical furnaces.

Copper and copper alloys are particularly preferred as materials for metal jackets. Indeed, copper and copper alloys are very well compatible with the surrounding materials, namely steel and cast iron, and have high thermal conductivity. In addition, although copper has a lower melting point (1083 ° C) compared to the casting temperature of cast iron (typically 1200 to 1300 ° C), the use of a thick copper jacket prevents it from dissolving into liquid cast iron. . Indeed, because of its thick thickness, the copper jacket quickly absorbs heat without allowing the copper to be washed out (ie, melted and dispersed into the cast iron), allowing the liquid cast iron to solidify. Thus, the metal jacket can be made of a metal or alloy having a lower melting point compared to the surrounding material.

In addition, copper and copper alloys have a higher thermal expansion coefficient than steel and cast iron, which means that in operation the copper jacket will be fully compressed between the steel tube and the cast iron body. Thus, good contact between the different materials constituting the cold plate is ensured, which is advantageous for heat conduction.

In addition, in contrast to German Patent A-2128817, in which copper plated cooling tubes do not prevent carburizing into steel tubes, the present invention not only prevents carburizing of steel cooling tubes by using a thick copper jacket. It provides a concentrated heat transfering layer that can absorb mechanical stress between the steel tube and the cast iron body. In practice, these cold plates have proven to have a “cooling effect” that is significantly better (two to three times) than cast iron cold plates with steel tubes coated with conventional metal oxides.

The metal jacket should preferably have a thickness of at least 2 mm and at most 20 mm. More preferably, the thickness of the metal jacket should be in the range of 5 to 10 mm and most preferably on the order of 7 mm. The metal jacket is conveniently provided around the steel tube by casting because casting is a more economical way to form such thick metal layers.

The optimal thickness of the metal jacket can vary depending on the type of metal or alloy being the material and the casting conditions.

For example, in the case of a cast iron cold plate with a steel tube surrounded by a thick metal jacket made of copper, the copper jacket must be thick enough to absorb heat from the liquid cast iron so that it is not washed off. And, if the copper jacket is too thick, there will be a gap between the copper jacket and the cast iron body due to the shrinkage of the copper jacket. In addition, the result of casting may vary depending on casting conditions such as, for example, flow value, temperature, duration of liquid cast iron. Therefore, these parameters should preferably be taken into account when determining the optimum thickness of the metal jacket.

Looking more specifically at the cooling plate body, it can be made of various ferrous metals. However, the ferrous metal is preferably selected from the group consisting of cast iron, ductile cast iron, malleable iron and steel. Preventing carbon diffusion by metal jackets is particularly important when the cold plate body is made of cast iron with high carbon content.

Brief description of the drawings

Hereinafter, with reference to the accompanying drawings, the present invention will be described through an embodiment.

1: A sectional view of a preferred embodiment of a cold plate according to the invention.

Detailed Description of the Preferred Embodiments

1 shows in cross section a preferred embodiment of a cooling plate 10 according to the invention. The cooling plate 10 consists of a cooling plate body 12 made of ferrous metal, preferably cast iron. The cold plate body 12 has the general form of a parallel piped, the front side and the back side of which are indicated by (14) and (16), respectively. The front face 14 of the cold plate 10 is provided with a series of parallel ribs 18 at regular intervals which are advantageous for increasing its heat exchange surface and thus improving the cooling efficiency of the cold plate 10. .

Reference mark 20 indicates a steel cooling tube cast inside the cold plate body 12. Although not shown in the drawings, the cooling plate 10 includes a plurality of such cooling tubes 20. As can be seen, the cooling conduit 20 has a straight portion 22 which is essentially parallel to the front face 14 of the cooling plate 10. The straight portion 22 is terminated by curved portions 24 at both ends, and the curved portion 24 is connected to the cooling plate body 12 to connect the cooling tube 20 to a cooling circuit such as a furnace. Protruding into the rear (16) of the (protruding).

The cooling tube 20 in the cold plate body 12 has a metal jacket 26 surrounding its outer surface. In this embodiment the metal jacket 26 is advantageously made of copper or copper alloy and has a thickness in the range of 5 to 10 mm. During casting of the cast iron body, this thick copper jacket 26 acts as a physical barrier that prevents carbon from diffusing from the liquid cast iron into the steel cooling tube 20. The copper jacket 26 is in tight contact with both the steel cooling tube 20 and the cast iron body 12 because of its high thermal conductivity. The excellent thermal conductivity of the cast iron body 12 and the steel cooling conduit 20 and the intimate contact between the materials are intensive from the cast iron body 12 to the cooling fluid flowing inside the steel cooling conduit 20. Enable heat transfer. Also, due to the higher coefficient of thermal expansion of copper and copper alloys than steel and cast iron, there is a good contact between the cold plate body and the steel tube due to the dilatation of the copper jacket when the cooling plate is operated, i.e. under intensive heat. good contact is more guaranteed. Despite the fact that copper has a melting point (1083 ° C) lower than the temperature at which the cast iron is poured into the mold (typically 1200 to 1300 ° C), a thick layer of copper can absorb the heat of the liquid cast iron and solidify the liquid. Copper is washed away, ie, re-melt and not dispersed into the cast iron body.

The present cooling plate 10 can be easily manufactured by casting. Therefore, the production of the cooling plate 10 is preferably carried out as follows. A mold having dimensions of the cold plate body 12 is prepared, and a cooling tube 10 with a metal jacket 26 is arranged in the mold. Next, molten cast iron is poured into the mold around the cooling tube and allowed to solidify therein.

Metal jackets are preferably cast around steel tubes, because casting is a more economical way to form thick metal layers.

According to testing and simulation, the cold plate 10 according to the present invention has proved to be significantly better in the "cooling effect" than a traditional cast iron stave with steel tubes coated with metal oxides. The "cooling effect" is determined by measuring the hottest point of the hot side when the cold plate 10 and the traditional stave are each exposed to the same heat source. In particular, the front surface of a traditional cold plate is about 600 to 650 ° C., while the front surface of the cold plate 10 according to the invention is about 200 to 250 ° C.

A specimen cold plate was fabricated according to the method described above. The cooling tube used was an outer diameter of 75 mm and a wall thickness of 10 mm. The steel cooling tube was equipped with a 7 mm thick copper layer. A steel cooling tube with a thick copper layer of 7 mm was placed in the mold and the cast iron was poured into it at about 1250 ° C. After solidification a 200 mm cold plate was obtained, meaning that the copper jacket was surrounded by about 55 mm of cast iron.

The cold plate was cut transversely to observe the internal structure of the plate. After cutting, it was observed that a homogeneous thick copper jacket was formed around the cooling tube with no voids between the cast iron and the copper jacket. At the tube / jacket interface, there is always a tight connection due to the shrinkage of copper. Thus, both interfaces of the copper jacket were in tight contact, and the steel cooling tube could not be moved relatively to the cast iron body.

The cooling plate for the metallurgical furnace of the present invention has improved thermal conductivity compared to the existing cooling plate, and has excellent wear resistance, thus reducing maintenance costs.

Claims (11)

A molded cold plate body 12 made of ferrous metal; And In the cold plate 10 for a metallurgical furnace comprising at least one steel cooling tube 20 cast in the cold plate body 12, A metal jacket 26 having a thickness in the millimeter range on the outer surface of the steel cooling tube 20 in the cooling plate body 12 and made of a metal selected from the group consisting of copper, copper alloys, nickel, and nickel alloys. Metallurgical furnace cold plate 10 characterized in that there is. The cooling plate of claim 1 wherein the metal jacket has a thickness of at least 2 mm. Cooling plate according to claim 1 or 2, characterized in that the metal jacket (26) has a thickness of 20 mm or less. 4. The cooling plate according to claim 1, 2 or 3, characterized in that the metal jacket (26) has a thickness in the range between 5 mm and 10 mm, preferably about 7 mm. The cooling plate according to any one of claims 1 to 4, wherein the cooling plate body (12) is made of ferrous metal selected from the group consisting of cast iron, nodular cast iron, malleable iron and steel. Providing at least one steel cooling conduit 20; Providing a mold for casting the cold plate body 12; Arranging the at least one cooling conduit (20) in the mold; And In the method of manufacturing a cooling plate for a metallurgical furnace comprising the step of pouring a liquid ferrous metal into a mold around the at least one cooling tube (20), Wherein said at least one steel cooling conduit 20 has a metal jacket made of a metal selected from the group consisting of copper, copper alloys, nickel and nickel alloys having a thickness in the millimeter range on its outer surface. Method of manufacturing plate. 7. Method according to claim 6, characterized in that the metal jacket (26) has a thickness of at least 2 mm. 8. Method according to claim 6 or 7, characterized in that the metal jacket (26) has a thickness of 20 mm or less. 9. Method according to claim 6, 7, or 8, characterized in that the metal jacket (26) has a thickness in the range between 5 mm and 10 mm, preferably about 7 mm. 10. The method according to any one of claims 6 to 9, wherein the ferrous metal is selected from the group consisting of cast iron, spheroidal graphite iron, malleable iron and steel. Method according to one of the claims 6 to 10, characterized in that the metal jacket (26) is provided on the surface of the steel cooling tube (20) by casting.