JPS649904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for forming a hollow body corresponding to the dimensions of a product ingot by welding at least one side plate made of cladding material with another thinner side plate to form a tubular hollow body. This hollow body is inserted into a larger outer mold, and a fine-grained refractory insulation material is filled between the bottom of the outer mold and the lower end of the hollow body and between the side of the outer mold and the side of the hollow body, and then the hollow body is It relates to a method for producing clad ingots, in particular clad slabs, in which core material is cast.

This West German patent no.
According to the method known from No. 736,672, the desired overall fusion is not achieved during casting. If the incoming steel (core material) is not extremely heated during casting into this known hollow body, the relatively thick side plates of cladding material act like chill mold walls. The cast core material, like an ingot in a mold, separates from the side plates during cooling and shrinkage, creating gaps. This gap is further enlarged by the fact that the side plate itself is heated on one side by the molten steel, thereby curving outward and warping into a pillow shape.

While the hollow body in which the core material has been cast is cooled in the mold and reheated in the preheating furnace, the shrinkage and expansion tendencies of the core material being cooled (regular steel) and the cladding material being heated (mostly special steel) overlap. intersect.
This further promotes gap formation. The gap opens towards the ends, allowing normal outside air to enter between the cladding and the core. As a result, the surface of the gap is oxidized, and this oxidation is further accelerated by the temperature increase. Bonding during subsequent rolling is no longer possible due to the oxide film formed.

The close bond produced by casting between the cladding material and the core material is difficult to achieve due to the considerably larger heat capacity compared to the core material of the side panels, and is only possible if the core material is significantly overheated. Additionally, melting is less near the edges of the clad surface than in the center due to differences in heat extraction. The corewood is contaminated by the melting of the cladding material. Impurity of the core material with Cr, NiC or Mn can result in defective products even with a small amount of melting. Moreover, the cladding material then becomes thinner and uneven.

In order to ensure a sufficiently thick layer of clad material after subsequent rolling of the clad ingot, the material thickness of the side plates is usually between 3 and 3 of the total thickness of the clad ingot.
15%, and according to the method known from DE 736 672, this thickness ratio is above the abovementioned upper limit.
However, with such size ratios, sufficient heating and fusion due to the heat content of the normally molten core of the side plates, which initially have a normal temperature, is very difficult to achieve.

A number of other studies and proposals have been made to cast molten steel between two clad plates. The aim was always to create a tight connection through the welding of the side panels made of cladding material already after casting. When working with highly superheated steels, i.e. high casting temperatures, it is practically difficult to match this temperature and the material thickness of the hollow body to each other to ensure working within a narrow range between melt initiation, fusion and cooling. It became clear that. According to German Patent No. 736,672, the side surfaces of the hollow body, which do not have cladding plates, are made of thin plates and are therefore fused together. Furthermore, significant overheating of the heartwood increases energy costs.

Furthermore, from German Patent No. 2333359 of the applicant, a method for producing clad ingots is known, according to which the clad plate is arranged close to the wall of the mold, leaving gaps on its narrow sides. It will be done. This narrow side is closely connected to the core by shrinkage (rather than fusion) during subsequent core casting, so that a peripheral seal is obtained in case a gap is formed between the clad plate and the core.

However, this known method is only suitable for relatively thick clad plates. This is because the degree of the desired seal, i.e. the shrinkage seal between the narrow side of the cladding plate and the core, improves with increasing surface area of the narrow side depending on the surface area of this narrow side. However, since the cladding material is clearly more expensive than the core material and the proportion of cladding material should therefore be kept as small as possible, this known process, which requires a thick cladding material, has been used relatively rarely. Furthermore, energy costs will increase.

The object of the invention is to avoid the disadvantages of the known method and to avoid the formation of open gaps communicating with the atmosphere between the cladding material and the core material, thereby achieving a good bond between both materials during the rolling process, and to It is an object of the present invention to improve the above-mentioned method so that it is possible to save on the cost.

This object is achieved by closing the lower part of the hollow body with a bottom plate welded to its lower end and covering the upper end region of the hollow body with a cover plate before the hollow body is inserted into the outer mold.

By means of these two plates, bottom plate and cover plate, it is achieved that the gap formed between the cladding material and the core material is not open to the external atmosphere. As a result, its inner surface is not oxidized and the subsequent bonding of the two materials during rolling is not disturbed. According to the method of the invention, although the side plate bulges outward in a pillow-like manner during casting, the periphery is connected to the side plate, the bottom plate and the cover plate, so that no open gaps occur.

In contrast to the pure rolling cladding process, no special shaping of the surface of the side plate facing the core is required, and in particular this surface does not have to be completely flat. During core casting, all irregularities of the side plate are filled with core material, and during subsequent shrinkage a replica of this side plate surface is formed. The side panels and the core therefore already match each other in shape due to the joining that takes place during subsequent rolling.

However, with the method of the invention it is particularly advantageous that the solidified clad ingot can be rolled in one heat, especially at the highest possible rolling temperature, while saving energy. In this case, the clad hot ingot can be rolled into a product without intermediate heating, using the heat that is still present. Overall, this represents a significant energy saving, since reheating of the ingot to rolling temperature is avoided.

Because of the insulation provided by the refractory insulation material, the core material solidifies relatively slowly, significantly more slowly than during conventional mold casting. The heat dissipation can then be controlled over a wide range by means of the insulation. The ingot can be brought gradually closer to the desired rolling temperature, or it can be held in a high enough range for rolling for several hours. Reheating is thus also avoided if the rolling mill is a large bottleneck, if there is a breakdown of the rolling mill or if the transport route to the rolling mill is long. There is therefore sufficient time and temperature margin to remove the clad ingot for rolling.

The bottom plate is, in principle, welded to the lower end of the hollow body closely around the periphery, but the cover plate must be welded to the upper end of the hollow body similarly tightly around the periphery, in which case it must be provided with injection holes, or the bottom plate must be welded to the bottom edge of the hollow body. After the core of the hollow body is cast, it is placed on the surface of the molten core. The cover board, like all other boards, must have a wall thickness as thin as possible, and one that will not dissolve in any way, so that the close contact between the cover board (and other boards) and the heartwood is A perfect bond is already achieved during the casting process.
The relatively thin plates follow the shrinking movement of the core ingot with very little resistance, so that no cracks occur.

A base plate and a cover plate that are curved convexly to the outside are advantageous. This provides a margin of material at the locations that normally exhibit constrictions during rolling of clad ingots.
This increases the overall usable proportion of the clad ingot.

It is particularly advantageous to place a hood over the hollow body or the cover plate when the cover plate with the injection holes is welded on before casting, and to fill it up to above the cover plate during casting. The portion of the core material above the cover plate fills the shrink pipe formed below the injection hole. For this to be possible, the hood area must be better insulated to the sides and above than the bottom area.

If the cover plate is placed over the surface of the molten core only after the hollow body has been filled with the core material, the core is kept particularly closed to the outside air by the cover plate, although the shrink pipe that is formed is not completely filled.

The wall thickness of the side plate made of cladding material is about 5 to 15% of the thickness of the ingot. As a result, a cladding coating of sufficient thickness is obtained even when rolled into sheet metal.

The wall thicknesses of the side, bottom and cover plates are chosen to withstand the high heat of the ingot, and the coating on their inner surfaces and other measures ensure that the plates do not slag or oxidize during casting.

After casting the core material, to suppress upward heat release,
After casting, a layer of refractory insulation material is also placed on the top.
The thickness of this layer and the thicknesses of the side and bottom layers are selected depending on the respective parameters of the casting process. In particular, the thermal conductivity and heat capacity of the insulation material are considered together with the heat content of the surrounding shell and core. The aim here is to adjust the heat extraction in such a way as to ensure that the usual rolling temperatures of 1450 DEG to 1100 DEG C. are achieved.

Flowable sand may be used as a refractory insulation material. This is because sand is usually available cheaply. In addition, commonly used fluid refractory granular materials such as slag sand, sandstone, clay, etc. are used. It is only important that the melting point and sintering temperature be above 1500°C. If necessary, a light lateral pressure can be exerted on the side panels and the side panels via the heat-insulating material so that no gaps occur during cooling between the heat-insulating material and the outer surface of the hollow body.

To prevent the outer wall of the hollow body from oxidizing, mix a little powdered coal into the insulation material, or cover the top of the insulation material with carbon-containing insulation powder.

In principle, the entire gap between the outer mold and the hollow body is filled with fine-grained refractory insulation material, but in order to save time and effort, the gap between the hollow body and the outer mold can be formed in layers, e.g. Provides a permanent insulation layer,
It is advantageous to use fine-grained refractory insulation material only in the layer that is in direct contact with the hollow body.

According to the method of the invention, the casting temperature can be kept very low because there is no risk of premature solidification due to sufficient insulation. If sufficient thinning of the core material is achieved by slow cooling, and at the same time the core material is slightly superheated, it can also be alloyed within the hollow body due to the low cooling rate. The low cooling effect and slow solidification of the ingot allows the core material to be adjusted to very high purity. This is because the core material remains liquid for a very long time, the heat flow circulates through the core material for a long time, and the intervening particles are better floated and separated.

It is advantageous to add a light material, such as charcoal, to the hollow body before casting. This material rises with the heartwood scene and suppresses upward heat radiation. Furthermore, this material makes the atmosphere inside the hollow body reducing and reduces oxides or slag particles. However, this assumes that these materials do not influence the composition of the core material.

The thickness of the side plate made of cladding material is limited by the heat content of the molten core material to be cast, when the side plate is rolled using casting heat and the rolling heat of the side plate is obtained from the heat content of the core material. Depending on the size of the ingot, which usually ranges between 10 and 40 tons, side plate thicknesses of 5 to 15% are advantageous. If the thickness of the side plate is large, West German patent no.
The shrinkage method according to No. 2333359 may be advantageous in some cases.

The inner surface of the hollow body must be metallically shiny, and the cladding surface and possibly also the inner surface must be protected with a coating that only burns when wetted with steel. The reservoir prevents crust formation during top pouring.

The hollow body serving as a mold shown in FIG. 1 or FIG.
and a cover plate 25. Two side plates 22, 23 and a bottom plate 24 as shown in FIG.
is manufactured in one piece by bending the strip into a U shape. The side plates 20, 21 are inserted into the U-shaped body thus formed and welded from the inner and outer surfaces, as shown in broken lines in FIG. Weld seams 26 and 27 are shown in FIG. A cover plate 25 is welded from the outside and has injection holes 28.
The cover plate 25 therefore has approximately the same dimensions as the bottom plate 24.

Before casting, a hood 29 is placed over the welded cover plate 25. The hood fills the injection hole 28 during the casting process, and due to the insulating wall of the hood, the portion of the core material above the cover plate 25 is kept in a molten state for a sufficiently long time, thereby filling the injection hole 2.
The shrink pipe formed below 8 is filled.

Instead of the hollow body with the cover plate 25 welded before casting according to FIG. 2, different embodiments of the cover plate 25 are shown in FIGS. 3 and 4. As is clear from this figure, the cover plate of this embodiment has a bottom plate 24.
It has smaller dimensions and fits into the hollow body with sufficient clearance as shown in FIG. This cover plate has a hook 30, which is attached to the cover plate 2.
5 is held several centimeters below the upper edge of the hollow body.

The cover plate 25 of FIGS. 3 and 4 is placed above the level of the molten core. In this case, the cover plate 25 and the side plate 2
0, 21 or the side plates 22, 23, a certain amount of molten core material spills upwards, eliminating the need to weld the cover plate 25 before casting as in the embodiment of FIGS. 1 and 2. A reliable seal is guaranteed.

The hollow body shown in Fig. 1 is surrounded by a hollow body and an outer mold 31.
It is surrounded by two layers of refractory insulation material filling the gap between. There are two layers 32, 33 of insulating material as shown in FIG. The outer layer 32 is manufactured as a permanent lining of lightweight refractory--asbestos board. The inner layer 33 is made of sand. This inner layer 33
is removed after each casting process and then filled again after insertion of a new hollow body.

After removing the cast hollow body, the inner layer 33 slides down to the bottom of the outer mold 31. Similarly, a portion of the lightweight refractory board collapsed. This preferably flowable material must be removed from the outer mold 31 again. It is therefore advantageous to form the bottom of the outer mold 31 in the form of a hopper, like a container for granular material, so that by opening the lower flap, the fluid part of the refractory insulation material can slide off the lower end of the hopper. This greatly simplifies the circulation of the refractory insulation material.

As shown, the wall thickness of the plates 22-25 is significantly smaller than the wall thickness of the two side plates 20', 21. side plate 20,
The wall thickness of 21 is approximately 10% of the total width of the hollow body. The thickness of the plates 22 to 25 is approximately 2% of the dimension of the larger side of the cross section of the hollow body. Depending on the physical properties of the material used, the thickness of the refractory insulation material is chosen to be large enough that cooling of the cast material is slow enough and homogenization of this material is achieved sufficiently well. The total thickness of the refractory insulation material is advantageously greater than 50 cm.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an ingot mold, Figure 2 is an exploded perspective view of the hollow body in Figure 1 with an injection hole in the cover plate, and Figure 3 is a perspective view of the hollow body without an injection hole in the cover plate. , and FIG. 4 is a longitudinal sectional view of the hollow body of FIG. 3 after casting. 20, 21... Side plate, 22, 23... Side plate, 24
...bottom plate, 25...cover plate, 29...hood, 30...
Hook, 31...outer mold, 32, 33...insulating material.

Claims (1)

[Claims] 1. (a) A hollow body corresponding to the dimensions of a product ingot by combining at least one side plate of cladding material with another thinner side plate to form a tubular hollow body. (b) insert this hollow body into a larger outer mold, and fill the space between the bottom of the outer mold and the lower end of the hollow body and between the side of the outer mold and the side of the hollow body with fine-grained refractory insulation material; (c) a method of producing a clad ingot in which the core material is subsequently cast into the hollow body, the lower part being closed by a bottom plate welded to the lower end of the hollow body before the hollow body is inserted into the outer mold; A method for producing a clad ingot, characterized by covering the area with a cover plate. 2. The method according to claim 1, wherein an injection hole is provided in the cover plate and the cover plate is tightly welded to the upper edge of the hollow body before core material is cast. 3. The method according to claim 1, wherein the cover plate is placed on the surface of the molten core material after the core material is cast into the hollow body. 4. The method according to claim 2 or 3, wherein a hood is installed on top of the hollow body or on a cover plate provided with injection holes, and during casting, the hood is cast until it exceeds the cover plate. 5 3 to 15 of the thickness of the ingot as cladding material
5. The method according to claim 1, wherein the material has a wall thickness of 3% to 10%. 6 The wall thickness of the side plate is 0.2 of the long side of the ingot cross section.
~2% and selected to withstand the high heat of the ingot.
The method described in any one of the preceding paragraphs. 7. The method according to any one of claims 1 to 6, wherein the upper part of the hollow body is also covered with a refractory heat-insulating material after casting. 8. At least the metallically shiny inner surface of the hollow body is coated with a high melting point coating, and this coating decomposes and burns only when it gets wet with molten steel. Claim 1
7. The method according to any one of paragraphs 7 to 7. 9 Fluid sand, slag sand, as insulation material
The patent claims that the ingot is made of clay, clay or other commonly used refractory granular material, the melting point and sintering temperature of which is above 1800 K, and the thickness of this insulating layer is 5 to 50% of the long side of the cross section of the ingot. The method according to any one of paragraphs 1 to 8. 10 The heat dissipation from the side plate is promoted at the initial stage of casting by moisture in the heat insulating material there and by water injection later, and the temperature is maintained only by the dry heat insulating material within the rolling temperature range. A method according to any one of ranges 1 to 9. 11. Claims 1 to 10 in which up to 1% by weight of pulverized coal is mixed into a flowable insulation material, or the top layer of the insulation material is covered with a carbon-containing insulation powder.
The method described in any one of the preceding paragraphs. 12 A part of the gap between the mold and the hollow body is lined with a lightweight refractory material such as an asbestos board as a permanent heat insulating layer, and only the gap between the hollow body and this permanent lining is filled with a fluid heat insulating material. The method according to any one of paragraphs 1 to 11. 13. The method according to any one of claims 1 to 12, wherein the casting temperature is maintained at the lowest temperature at which the product can flow out of the pan. 14. Process according to one of claims 1 to 13, in which up to 5% of the alloy metal is alloyed into the hollow body depending on the heat of the core material (steel). 15 Charcoal or a similar buoyant material is charged into the hollow body before casting, and this material suppresses upward radiation as the steel rises, creating a reducing atmosphere within the hollow body;
Reduces oxides and slag and at the same time core material (steel)
Claim 1 which hardly changes the composition of
15. The method according to any one of paragraphs 1 to 14. 16 Consisting of a hollow body having at least one side plate made of cladding material and other thinner side plates, a bottom plate and a cover plate, and a large outer mold into which this hollow body is inserted, between the bottom of the outer mold and the lower end of the hollow body and In an apparatus for manufacturing clad ingots, in which a layer of fine-grained refractory and insulating material is arranged between the sides of the outer mold and the sides of the hollow body, the hollow body is in the form of a rectangular parallelepiped, and the side plates, side plates and bottom plate are Apparatus for producing clad ingots, characterized in that they are joined by at least one welded seam. 17 The cover plate 25 has the injection hole 28, and the peripheral edge of the cover plate is connected to the side plate 20 or 21 and the side plate 2.
Claim 16 welded with 2 and 23
Apparatus described in section. 18. The device according to claim 16, wherein the two opposing side plates 22, 23 and the bottom plate 24 are manufactured by bending a single band plate into a U shape.