Method for producing a heat sink in the form of a stave for a melting furnace

Abstract

The invention relates to a method for producing a heat sink (1) in the form of a stave for a melting furnace, wherein at least one groove (5) for forming a cooling channel is machined into the rear face (2) of a plate body (3) and is subsequently closed on the rear face by at least one cover plate (4), said cover plate (4) being welded to the plate body (3) in order to form the heat sink (1). The cover plate (4) is connected to the rear face (2) by means of a friction stir welding (FSW) process, said FSW process forming a lap joint seam (8) which runs at a distance to the at least one groove (5).

Description

[0001] Method for manufacturing a cooling element in the form of a stave for a melting furnace

[0002] The invention relates to a method for manufacturing a cooling element in the form of a stave for a melting furnace according to the features of claim 1.

[0003] Cooling elements are used, for example, in shaft furnaces behind a refractory lining. The refractory lining is located on cooling elements, known as staves, which have grooves on their front face facing the furnace interior for receiving refractory material. The staves are made of copper or a low-alloy copper alloy with internal water cooling. Typical weights for such cooling elements are in the range of 1,500 to 2,000 kg. Cooling channels in the staves can be produced by deep drilling. It is also known to mill cooling channels into the base of a cooling element and close them with a cover or a cap plate (DE 198 06 788 C2, DE 10120614 A1, DE 40 35 893 C1). The connection is made by welding, for example, by inserting a cover into a cooling groove and welding it in place with a butt weld. This requires precisely manufactured covers.A cover plate can be installed using an explosive welding process. This is a complex process. Alternatively, a cover plate can be welded along its edges and connected through additional openings in the cover plate to create fillet welds (perforated welds). These openings must be created before welding.

[0004] The invention is based on the objective of demonstrating a cost-effective and flexible method for manufacturing such a cooling element in the form of a stave.

[0005] This problem is solved by a method comprising the features of claim 1. The dependent claims relate to advantageous embodiments of the invention.

[0006] The method according to the invention relates to a cooling element in the form of a stave with a two-part structure, comprising a plate body having grooves for forming cooling channels. The grooves are arranged in a rear wall of the plate body. The grooves, open at the rear, are then covered by a cover plate that is welded to the plate body. In its installed position, the front of the cooling element faces the interior of a furnace. It may have mounting grooves for a refractory material. The cooling element is a stave for a melting furnace.

[0007] According to the invention, the cover plate is joined to the back surface by friction stir welding (FSW). The FSW process creates a lap joint weld that runs at a distance from the at least one groove. This distance from the groove means that the lap joint weld is not located in the area of ​​the groove contour. The lap joint weld is a linear weld that is produced starting from the back surface of the cover plate by immersing the FSW tool into the cover plate and penetrating to the back surface of the plate body. The root of the lap joint weld is located in the plate body. Corresponding to the shape of the rotating pin of the FSW tool, the lap joint weld has steep flanks and a flattened root surface, similar to a steep-flank weld.

[0008] Friction stir welding (FSW), in which a rotating tool is guided along the weld path, generates frictional heat that plasticizes the material and mixes it in the joining zone. This results in high weld strength with minimal weld distortion. The FSW process offers significant advantages in the production of heat sinks, as it allows for cost-effective fluid-tight connections between the base plate and the cover plate. In particular, the grooves can have a curved profile without the need for matching curved covers to close them. Welding in a cover also requires longer weld seams and therefore more time. A single cover plate, preferably the same size as the back of the base plate, is suitable for covering and sealing all the grooves simultaneously.Of course, multi-part cover plates can also be used.

[0009] In the welding process, individual weld points are first applied using the FSW method to fix the cover plate, and then the desired lap joint is created. The weld points are positioned so that they are located within the lap joint.

[0010] Cooling elements for melting furnaces, especially staves, are made primarily of copper or copper alloys. These are also very large components. The total weld thickness of the overlap butt weld exceeds 5 mm, particularly in the range of 8 mm to 20 mm, preferably up to 16 mm. With such large total weld thicknesses, considerable forces act on the friction stirring tool, necessitating robust machine tools and the precise interaction of coordinated parameters such as speed, feed rate, and tool material, as well as a tailored tool geometry.

[0011] The overlap weld produced according to the inventive method is clearly identifiable as such externally. It is characterized by the characteristic path created on the workpiece surface by a shoulder of the FSW tool. The shoulder displaces material that protrudes beyond the welded-on cover plate. The excess material is milled off after welding. What remains is the typical characteristic path of the FSW tool and the entry point of the rotating pin. An FSW weld is also clearly identifiable in the micrograph. A fine-grained microstructure forms, exhibiting the silhouette of the stirring pin of the FSW tool.In this way, a lap joint produced by the FSW process can be distinguished from other lap joints, for example, those produced by conventional MIG welding or electron beam welding.

[0012] The FSW process is particularly well-suited for producing fluid-tight connections in heat sinks with large masses because the large mass allows for good heat dissipation during welding. The components are less prone to warping. A large mass is defined as a heat sink weighing 1,000 kg or more, particularly between 1,500 and 2,000 kg. Typical dimensions of a heat sink according to the invention in the form of a stave are, for example, 2,000 mm in length and 900 mm in width with a thickness of 140 mm. Due to manufacturing processes, heat sinks according to the invention can be thinner and therefore lighter than heat sinks in which the cooling channels are created by deep drilling. The thickness can be reduced to less than 120 mm, particularly to a thickness of 90 to 110 mm, and especially to a thickness of 100 mm. If the boundary conditions permit, thicknesses of less than 100 mm are also targeted for staves.

[0013] The rear side of the heat sink faces the furnace wall in its installed position. The heat sink is fixed to the furnace wall via its rear side. Coolant is supplied and discharged via coolant connections attached to the heat sink. These connections are preferably located on the rear side of the heat sink and extend from there through the furnace wall. The coolant flows through the heat sink via at least one cooling channel or via several cooling channels located within the heat sink plate at a distance from the hot front surface and the furnace-wall-facing rear surface. The cooling channels are initially machined into the rear surface as grooves, particularly by milling. The wall thickness up to the front surface is not constant due to the retaining grooves for the refractory material located there. The cooling channels preferably, but at least predominantly, run at a 90° angle to the retaining grooves on the front surface.

[0014] Milling the cooling channels has the advantage that the finished cooling channel can have any desired shape. According to the invention, it has a curved shape in particular. Regardless of the shape of the at least one cooling channel, a continuous, overlapping butt weld is formed at a distance from an edge of the cover plate. This continuous, closed line weld forms a fluid-tight barrier at the edge for the entire cooling element. Since the weld root is always located within the cooling element due to the geometry of the agitator pin, and the weld is thus fully welded, a fluid-tight connection is always ensured.

[0015] To minimize the number of coolant connections on the rear of the heat sink, a groove preferably has only a single coolant inlet and a single coolant outlet. For this purpose, the groove can be U-shaped or have a meandering curve to cover as large an area of ​​the heat sink as possible for effective cooling. In the context of the invention, a curved shape means that the cooling channel does not run in a straight line but has a single or multiple bend. The distance of the cooling channel from the front is preferably constant along its length, i.e., the depth of the groove remains constant. However, the distance of the cooling channel from the front can also be varied along its length as required, i.e., the depth of the groove is not constant. In this way, the cooling channels according to the invention can be adapted to local thermal requirements during manufacturing.This is an advantage over deep-drilled cooling channels. Furthermore, the cross-sectional area can be varied by partially widening or narrowing the groove. This allows the local flow velocity to be altered. The groove preferably has a rectangular cross-section. Undercut grooves can also be produced. The cross-sectional shape (undercut or not undercut) can vary along its length. The inventive method enables individual adjustments to the cooling channels without requiring any modifications to the cover plate. Only the course of the overlapping butt joints may need to be adjusted, which only requires reprogramming.

[0016] A single cooling channel with a uniform cross-section and a meandering path is particularly advantageous in manufacturing. In this case, webs are located between individual longitudinal sections. These webs are the areas that remain between the grooves or the single, multiply curved groove. The webs can be used for connection to the cover plate. According to the invention, an overlap butt weld produced by FSW is formed as an additional support weld on at least one web. If several webs are present, several FSW-produced overlap butt welds can be manufactured as support welds. Preferably, additional overlap butt welds are located on each web. The overlap butt welds serve not only as support welds but also as a fluid-tight barrier between adjacent webs. This does not mean that all overlap butt welds must be connected to each other.According to the invention, it is also possible to produce several overlap butt welds on the webs, each produced individually by FSW. The term "individualized" means that the overlap butt welds are not connected to each other. The remaining gaps between the overlap butt welds theoretically allow bypass flow of a coolant; however, the cover plate preferably lies flat and so tightly against the back side that any gap, if present, does not allow any significant bypass flow. The cover plate also has a thickness of at least 10 mm, preferably 15 mm. The thickness of the plate body is several times greater than the thickness of the cover plate. The materials are rigid. Preferably, the gaps are also small and no larger than 1 to 3 times the weld width of the overlap butt welds.

[0017] The overlapping butt welds serve to support and hold the heat sink. The inventive method allows for the production of cover plates and plate bodies from different materials, for example, using a plate body made of a copper alloy and welding it to a cover plate made of a steel or aluminum alloy. The cover plate made of a steel or aluminum alloy serves to fix pipe fittings in the area of ​​the coolant inlet and coolant outlet. Between the coolant inlet and the coolant outlet, i.e., in the area of ​​the greatest temperature gradient, mixing of the coolant flows is undesirable. A lap butt weld is preferably produced between the coolant inlet and the coolant outlet. In this area, the lap butt weld primarily serves for sealing and / or flow guidance.

[0018] The material of the heat sink is preferably a copper alloy, in particular oxygen-free copper or a low-alloy copper alloy. It can be a copper-chromium-zirconium alloy. This alloy is not weldable using the conventional MIG welding process, but it is weldable using the FSW process. This material has significantly higher heat resistance, which is a major advantage in material selection, especially for a heat sink. A bimetallic design of the heat sink allows for good cooling and heat distribution on the side facing the furnace interior, while the rear component, i.e., the cover plate, can be made of steel, copper, or aluminum to ensure particularly high resistance to thermal distortion of the heat sink. The cover plate can also be made of a copper alloy.

[0019] The at least one groove preferably has a constant depth, i.e., a constant distance to the hot side. To adjust the cooling capacity locally or regionally, the at least one groove, or at least one of several grooves, can be designed such that the groove depth varies along its length. The groove depth is measured from the back side. As the depth increases, the distance to the hot side decreases, and the cooling capacity increases in that area. For this purpose, the groove can be deeper over a certain length than in other lengths. The groove can have lengths of varying depths, with the depth remaining constant in each length. Transition sections are possible to avoid abrupt changes in depth. The depth can also change continuously, e.g., increasing or decreasing continuously in the direction of flow. In particular, the change in depth is linear.The inventive method allows the production of relatively thin heat sinks as staves. Compared to deep-drilled heat sinks, material usage is reduced by approximately 30%.

[0020] The invention is explained below with reference to an exemplary embodiment shown purely schematically in the drawings. The drawings show:

[0021] Figure 1 shows a rear view of a heat sink;

[0022] Figure 2 shows a cover plate for the heat sink of Figure 1;

[0023] Figure 3 shows a section along the line 13-13 of Figure 1 and

[0024] Figure 4 is a detail of Figure 3.

[0025] Figure 1 shows a heat sink 1 in a rear view of its rear side 2. Figure 3 shows the heat sink 1 in cross-section. The heat sink 1 has a plate body 3 and a cover plate 4 welded to its rear side 2 to cover milled grooves 5 in the rear side 2. Figure 1 shows that there is a single groove 5, indicated by a dashed line, which has a meandering shape with several parallel sections that can be traversed in opposite directions. The groove leads to a central coolant inlet 6 and an adjacent central coolant outlet 7 approximately in the middle of the rear cover plate 4, as shown in Figure 2. The groove 5, together with the cover plate 4, functionally forms a cooling channel within the heat sink 1. The groove 5 is sealed by a continuous, continuous lap weld 6, produced by friction stir welding.For this purpose, the cover plate 4 is placed on the back 2 of the plate body 3. The cover plate 4 has the same dimensions as the plate body 3. The lap joint 8 runs at a distance from an edge 9 and also from the groove 5. It is therefore not a butt joint or fillet weld. The weld geometry is shown in the enlarged view of Figure 4. In this embodiment, the cover plate 4 has a thickness A of, for example, 15 mm, while the essentially trapezoidal lap joint 6 has a thickness B of 16 mm. Consequently, there is an overlap of approximately 1 mm at the flattened weld root. The profile of the stirring pin is clearly visible in the hatching of Figure 4. To produce the lap joint 8, a frustoconical stirring pin of the FSW tool is immersed in the cover plate 4 and guided along the weld path parallel to the cover plate 4.It is lowered into the material of the cover plate 4 until it completely penetrates it and its tip enters the back 2 of the plate body 3. The two materials, melted by friction—a copper alloy of the plate body 3 and a steel of the cover plate 4—are mixed and then solidify. The continuous overlapping seam 8 serves both to connect the plate body 3 to the cover plate 4 and to provide a fluid-tight seal for the groove 5. The groove 5 has a depth T.

[0026] Figure 1 shows that further overlap butt welds 10, 11, 12 are formed on webs 13, 14, 15 between individual longitudinal sections of the groove 5. These further overlap butt welds 10, 11, 12 are also produced by the FSW process. They are isolated, i.e., not connected to each other. This is not necessary. They fulfill two functions: the connection of the two plate-shaped bodies and the prevention of coolant flow between adjacent longitudinal sections of the groove 5. They thus also have a sealing function. In particular, the overlap butt weld designated by reference numeral 12 between the coolant inlet 6 and the coolant outlet fulfills this sealing function in the area of ​​a web 15 that is arranged between the coolant inlet 6 and the coolant outlet 7.

[0027] In this embodiment, the cover plate is made of a steel material, while the plate body 3 is made of a copper material. This is a bimetallic arrangement. Reference symbol:

[0028] 1 - Heat sink

[0029] 2 - Back of 1

[0030] 3 - Plate body

[0031] 4 - Cover plate

[0032] 5 - Nut in 3

[0033] 6 - Coolant inlet

[0034] 7 - Coolant outlet

[0035] 8 - circumferential overlap butt seam

[0036] 9 - Edge of 3

[0037] 10 - further overlap butt seam

[0038] 11 - further overlap butt seam

[0039] 12 - further overlap butt seam

[0040] 13 - Bridge of 3

[0041] 14 - Bridge of 3

[0042] 15 - Bridge of 3

[0043] A - Thickness of 4

[0044] B - Thickness of 6

[0045] T - Depth of 5

Claims

Patent claims 1. A method for manufacturing a cooling element (1) in the form of a staves for a melting furnace, wherein a front face of the cooling element (1) in the installed position faces the interior of the furnace and has grooves for receiving refractory material, wherein the cooling element (1) comprises a plate body (3) and at least one cover plate (4), wherein at least one groove (5) for forming a cooling channel is machined into a rear side (2) of the plate body (3) and is subsequently closed at the rear by the at least one cover plate (4), which is welded to the plate body (5) to form the cooling element (1), characterized in that the cover plate (4) is joined to the rear side (2) by friction stir welding, wherein a lap joint (8, 10, 11, 12) is formed by friction stir welding, in that a friction stir welding tool is inserted from the rear side of the cover plate (4) and extends into the rear side of the plate body (5). penetrates,such that a weld root of the overlap butt weld (8, 10, 11, 12) is located in the plate body (5), wherein the overlap butt weld (8, 10, 11, 12) runs at a distance from the at least one groove (5).

2. Method according to claim 1, characterized in that a continuously closed overlap butt joint (8) is produced by friction stir welding at a distance from an edge (9) of the cover plate (4), which completely surrounds the at least one groove (5).

3. Method of claim 1 or 2, characterized in that a groove (5) with a U-shaped or meandering curved profile is produced between a coolant inlet (6) and a coolant outlet (7), such that webs (13, 14, 15) are formed in the rear side (2) between longitudinal sections of the groove (5), wherein an overlap butt weld (10, 11, 12) produced by FSW is formed as a support weld on at least one web (13, 14, 15).

4. Method according to claim 3, characterized in that several isolated overlap butt welds (10, 11, 12) produced by FSW are produced on the webs (13, 14, 15).

5. Method according to claim 3 or 4, characterized in that the coolant inlet (6) and the coolant outlet (7) are produced adjacent to each other in the cover plate (4), wherein an overlap butt weld (12) produced by friction stir welding is arranged between the coolant inlet (6) and the coolant outlet (7).

6. Method according to one of claims 1 to 5, characterized in that a plate body (3) made of a copper material is welded to a cover plate (4) made of a copper, steel or aluminium material by means of friction stir welding.

7. Method according to any one of claims 1 to 6, characterized in that a plate body (3) is provided made of a copper alloy, wherein the copper alloy is a copper-chromium-zirconium alloy.

8. Method according to one of claims 1 to 7, characterized in that the at least one groove (5) is produced with a depth (T) that varies in its longitudinal direction.

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