Abstract:
A method for production of a cooling plate ( 50, 80 ) with integrated coolant ducts ( 52, 84 ) for iron and steel making furnaces, in particular blast furnaces, is described. A preform of the cooling plate ( 50, 80 ) is continuously cast by a continuous casting mould ( 10 ), wherein rod-shaped inserts ( 28 ) in the casting duct ( 20 ) of the continuous casting mould ( 10 ) produce in this preform ducts ( 52, 84 ) running in the continuous casting direction, which form coolant ducts in the finished cooling plate.

Description:
The present invention relates to a method for production of a cooling plate for iron and steel making furnaces, as e.g. blast furnaces. 
     BACKGROUND OF THE INVENTION 
     Such cooling plates for blast furnaces are also called “staves”. They are arranged on the inside of the furnace armour and have internal coolant ducts, which are connected to the cooling system of the shaft furnace. Their surface facing the interior of the furnace is generally lined with a refractory material. 
     Most of these “staves” are still made from cast iron. As copper has a far better thermal conductivity than cast iron, however, it would be desirable to use copper “staves”. 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. 
     It is already known from GB-A-1571789 how 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. A high heat transmission resistance exists between the cooling plate body made from copper and the integrally cast pipe coil for various reasons, so that relatively poor cooling of the plate results. Furthermore, cavities and porosities in the copper can likewise not 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, however, because the drilling of the cooling ducts in particular is complicated, time-consuming and expensive. 
     Consequently a method with which high-quality copper cooling plates can be manufactured more cheaply is required. 
     According to the invention a preform of the cooling plate is continuously cast by means of a continuous casting mould, wherein inserts in the casting duct of the continuous casting mould produce ducts running in the continuous casting direction in the preform, which form coolant ducts in the finished cooling plate. A long cooling plate ready for use can then be manufactured relatively easily from the continuously cast preform without time-consuming drilling. It should be specially noted in this connection that cavities and porosities can be prevented far more effectively in continuous casting than in casting in moulds. Furthermore, the mechanical strength of a continuously cast cooling plate is far higher than that of one cast in a mould. The heat transmission is optimum, because the continuously cast ducts are formed directly in the cast body. As the cross-section of the continuously cast ducts need not be circular, new advantageous possibilities concerning the design and arrangement of the coolant ducts are opened up. It was also established that the special quality of the surface of a continuously cast cooling plate creates good preconditions for the adhesion of a refractory spraying compound. 
     During continuous casting prongs in the casting duct of the continuous casting mould can produce grooves running in the casting direction in a surface of the preform. These grooves increase the cooled surface of the finished cooling plate and form anchoring points for a refractory lining. However, such grooves can also be subsequently worked, e.g. cut, into a surface of the continuously cast preform. This procedure is necessary for example, if the grooves are to run at right angles to the continuous casting direction. 
     If particularly thin cooling plates are to be manufactured, the thickness of the continuously cast preform is advantageously reduced by rolling. The rolling makes the crystalline structure of the copper finer, which has a favourable effect on the mechanical and thermal properties of the finished cooling plate. Although the reduction by rolling increases the production costs of the cooling plate, it may thus be advantageous also to roll continuously cast preforms for thicker cooling plates. In this connection it should be emphasised that the ducts integrally cast into the preform surprisingly do not constitute an important obstacle to the subsequent rolling of the preform. This applies in particular, if the integrally cast ducts have an elongated, e.g. oval cross-section. 
     A plate is cut out of the continuously cast and if necessary rolled preform by two cuts at right angles to the casting direction, two end faces being formed at right angles to the casting direction, the distance between them corresponding essentially to the required length of the cooling plate. It should be noted that several cooling plates of the same or different length can advantageously be manufactured from one continuously cast preform. The production of particularly long cooling plates is likewise possible without additional cost. The plates cut from the preform have several parallel through ducts, which extend in the casting direction and terminate in the two ends. 
     The cross-section of the integrally cast ducts advantageously has an elongated shape with its smallest dimension at right angles to the cooling plate. In this way, cooling plates with a smaller plate thickness than those with drilled ducts can be manufactured, with the result that copper is saved. It should likewise be noted that ducts with elongated cross-sections can also be produced more easily in continuous casting. A further advantage is that in the case of ducts with elongated cross-sections larger exchange surfaces on the coolant side can be achieved in the cooling plate. Ducts with elongated (e.g. oval) cross-sections, as already described above, behave far more advantageously during rolling of the preform than ducts with circular cross-sections. 
     In the next production step connection holes terminating in the through ducts for feed and return pipes are advantageously drilled in the plate at right angles to the back, and the end terminations of the ducts are sealed. Connection pieces, which are led out of the furnace armour when a cooling plate is mounted on the latter, can subsequently be inserted in these connection holes. 
     Each continuosly cast duct can have its own feed and return connection Several continuously cast ducts can, however, also be connected to each other by transverse holes. These transverse holes are, for example, then arranged and sealed in such a way that a serpentine duct with a feed connection and return connection for each cooling plate results. 
     The cooling plate can advantageously be bent and centered in such a way that its curvature is adapted to the curvature of the blast furnace armour. This is the case in particular if cooling plates with a large width are used. This is likewise the case for cooling plates used in the blast furnace hearth. Such cooling plates for the hearth must in fact fit as closely as possible to the armour to absorb the pressures acting on the hearth lining. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For better illustration of the invention and its advantages different forms of construction are described in greater detail with reference to the enclosed drawings. 
     FIG. 1 shows a schematic longitudinal section through a continuous casting mould for the method according to the invention; 
     FIG. 2 a schematic cross-section along the section line  2 — 2  through the continuous casting mould according to FIG. 1; 
     FIG. 3 a plan view of the back of a finished cooling plate which has been manufactured by the method according to the invention; 
     FIG. 4 a longitudinal section along the section line  4 — 4  through the cooling plate in FIG. 3; 
     FIG. 5 a cross-section along the section line  5 — 5  through the cooling plate in FIG. 3; 
     FIG. 6 a perspective elevation of an arrangement of cooling plates in a shaft furnace; 
     FIG. 7 a plan view of the back of a cooling plate which is particularly suitable for the arrangement according to FIG.  6  and has been manufactured by the method according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show schematically the construction of a continuous casting mould  10  for the method according to the invention. This continuous casting mould  10  consists, for example, of four cooled mould plates  12 ,  14 ,  16  and  18 , which form a cooled casting duct  20  for a melt, e.g. a low-alloyed copper melt. The arrows  22  and  24  in FIG. 1 indicate feed and return connections for a coolant in the lateral mould plates  12  and  14 . The arrow  25  in FIG. 1 shows the casting direction. 
     In FIG. 1 it can be seen that three rod-shaped inserts  28  project into the casting duct  20 . The inserts are connected, for example, to a coolant collector  30 , which is arranged above the mould plates  12 - 18  above the casting duct  20 . Each of these rod-shaped inserts  28  advantageously consists of an outer tube  32  closed at the end and an inner tube  34  open at the end, which are arranged in such a way that they form an annular gap  36  for the coolant. The following coolant flow thus results for each of the three rod-shaped inserts  28 . In the collector  30  the coolant flows via a feed chamber  38  into the annular gap  36 . It cools the outer tube  32  over its full length and at the bottom end enters the inner tube  34  from the annular gap  36 . This inner tube  34  returns the coolant, to a return chamber  40  in the collector  30 . The rod-shaped inserts  28  can, however, also be designed as uncooled graphite rods. 
     In FIG. 2 it can be seen that the front mould plate  16  has several prongs  26 . The latter extend essentially over the full length of the mould plate  16  and project at right angles to the casting direction into the casting duct  20 . 
     According to the invention, a billet or ingot, which forms a preform of the cooling plate to be manufactured, is cast with the continuous castng mould  10  described above. The rod shaped inserts  28  produce ducts with a cross-section determined by the cross-section of the rod shaped inserts  28  in the continuous casting direction in the continuously cast preform. The prongs  26  in the mould plate  8  produce longitudinal grooves in the continuous casting direction in the continuously preform. 
     FIGS. 3 to  4  show a finished cooling plate  50  manufactured on the basis of a continuously cast preform. It should be noted, however, that the preform of the cooling plate  50  was cast with a continuous casting mould which had no prongs  26 , so that the original preform had essentially a rectangular cross-section without grooves. In FIG. 3 the three ducts  52 , which were produced according to the invention by the inserts in the continuous casting mould during continuous casting, are indicated by broken lines. As shown in FIG. 5, these inserts had an oval shape. They were arranged eccentrically in the rectangular cross-section of the preform in the continuous casting mould, as shown in FIGS. 4 and 5, i.e. they were nearer to the surface of the preform, which finally forms the back of the finished cooling plate  50 . 
     It has proved to be advantageous to cast the preform thicker than required for the finished cooling plate and subsequently to reduce the thickness of the preform by rolling to the thickness of the finished cooling plate. With this rolling of the preform the copper acquires a finer crystalline structure, which has a favourable effect on the mechanical and thermal properties of the finished cooling plate. It remains to state in this connection that an elongated cross-section of the cooling ducts from the outset is deformed far more advantageously during rolling than a circular cross-section. 
     A rectangular rough plate was subsequently cut out of the rolled preform by two cuts at right angles to the casting direction. The two end faces  54 ,  56  of the finished cooling plate were formed in this way. In this rough plate the ducts  52  consequently extended as through ducts between the two end faces  54 ,  56  and formed open terminations  58  therein. Grooves  58  were subsequently cut at right angles to the casting direction in the surface of this rough plate which was furthest away from the eccentric ducts  52 . To increase the mechanical strength of the plate still further, it could now be shot peened. 
     In the next production step connection holes  62  for feed and return pipes  64 ,  66  terminating in the ducts  52  were drilled at right angles to the plate surface in the back  68  of the plate. Before the end terminations  58  of the ducts  52  are finally closed by plugs  70 , the ducts could if necessary be finished mechanically. To complete the cooling plate  50  definitively only the feed and return connection pieces  64 ,  66  as well as the securing pins  72  and spacer connection pieces  74  had to be mounted on the plate. 
     In FIG. 5 it can be seen how the finished cooling plate  50  rests by means of the spacer connection pieces  74  on a furnace armour plate  76 . It should be noted that the cooling plate  50  in FIGS. 3-5 is intended for vertical installation in the furnace, i.e. the cooling ducts  52  run vertically and the transverse grooves  60  horizontally in the built-in cooling plates. Instead of the transverse grooves  60 , which run at right angles to the casting direction, the cooling plate  50  could also have longitudinal grooves, which run parallel with the casting direction. The latter would then advantageously be produced directly during continuous casting with a casting mould with prongs, as shown in FIG.  2 . 
     FIG. 6 shows an arrangement of cooling plates  80 , in which the grooves  82  were produced in this way directly during continuous casting. Inside the cooling plates  80  the cooling ducts  84  produced during continuous casting (see FIG. 7) therefore extend parallel with the grooves  82 . It should be noted that the cooling plates  80  are arranged horizontally in the furnace, i.e. the cooling ducts  84  and grooves  82  run horizontally in the built-in cooling plates  80 . The cooling plates  80  are bent and centered in such a way that their curvature is adapted to the curvature of the blast furnace armour (not shown). 
     FIG. 7 shows with broken lines an advantageous arrangement of the coolant ducts in one of the cooling plates  80 . Three continuously cast ducts  84   1 ,  84   2  and  84   3  as well as two short transverse holes  86  and  88  can be seen. The hole  86  connects the ducts  84   1  and  84   2  at one end of the plate  80  and is closed by a plug  90 . The hole  88  connects the ducts  84   2  and  84   3  at the other end of the plate  80  and is closed by a plug  92 . Like the ducts  52  in plate  50 , the ducts  84   1 ,  84   2  and  84   3  in the end faces  54 ,  56  of the plate  80  are likewise closed by plugs  70 . The reference number  94  indicates a feed connection, which terminates in the duct  84   1 , and the reference number  96  a return connection which terminates in the duct  84   3 . The coolant, which enters the plate  80  via feed connection  94 , must flow through the latter spirally before it can leave it again via the return connection  96 . In FIG. 6 it is shown schematically how the feed and return connections  94 ,  96  of the individual cooling plates  80  are connected to each other via pipe bridges  98 . The cooling plate  80  could, of course, have a feed and return connection for each cooling duct  84   1 ,  84   2  and  84   3  like the cooling plate  50 . 
     It should be noted that cooling plates mounted in the blast furnace above the blast tuyeres are advantageously provided with a refractory spraying compound on their side facing the interior of the furnace. To improve the adhesion of the refractory spraying compound to the cooling plates, the grooves  60 ,  82 , for example, can be designed as dovetail grooves. It is also advantageous to round the edges and corners of the grooves  60 ,  82  generously. This reduces the risk of crack formation in the refractory compound. 
     By contrast, cooling plates for the blast furnace hearth advantageously have a smooth front and back. They are thinner than the cooling plates shown with grooves and are advantageously made from a continuously cast preform, the thickness of which has been reduced by rolling. They are centered on the diameter of the armour in the hearth area, so that they rest with a close fit with their smooth back on the blast furnace armour. The hearth lining with shaped bricks made from carbon rests with a close fit against the likewise smooth front of the cooling plates. In this way it is ensured that relatively thin cooling plates can easily transmit the high pressures acting on the hearth lining to the blast furnace armour. 
     All cooling plates shown have three continuously cast ducts. Cooling plates with more or less than three continuously cast ducts can, of course, likewise be manufactured by the method according to the invention.