DK147967B - PROCEDURE FOR THE PREPARATION AND REPRODUCTION OF CONTINUOUS CASTED STRINGES AND APPARATUS FOR USE IN EXERCISING THE PROCEDURE - Google Patents

Description

1A7967 i

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for the manufacture and further processing of molded strings in which a circular heat sink is moved through a metal melt which, in a non-oxidizing atmosphere, solidifies to a thin layer which is continuously removed from the heat sink by the heat sink and the layer is released from the heat sink. and at least two such layers, directly after solidification, are flattened face to face and compressed for pressure welding to facing contact faces.

A method of this kind is known from the specification of United States Patent No. 3542116. In this known method, two circulating heat sinks are used which move through their respective metal melts and the two metal layers formed on the circulating heat sinks are welded together immediately after their formation. After the two layers are welded together to form a composite band, they are folded into tubular form and passed through a container with a further melt to deposit another metal along the outside of the composite metal tube.

It is the object of the present invention to provide a method of the aforementioned kind in which finished, hot-worked articles of metal having a fine crystalline structure and using less mechanical work can be produced than has hitherto been possible.

In order to illustrate the idea of the present invention, it is to be noted that when liquid or molten metal is poured into a mold, the solidification starts from a solidified layer which forms almost immediately where the metal touches the mold wall and the solidification propagates inward toward the center of the metal mass. in the mold. The rate at which solidification proceeds depends on the following three factors: _ (1) The heat transfer coefficient through the mold walls, (2) The excess heat in the molten metal out of the melt heat to be extracted to reach the metal solidification temperature, and (3) The heat transfer coefficient through the already solidified metal layers in the mold and to the mold walls.

To determine the solidification rate of a molten metal, a simplified formula is often used in the casting technology and is sufficient for the process described herein and reads as follows:

s = k. / T

In this equation, the s shell thickness is in millimeters of the metal solidified from the molten metal, T is the elapsed time in minutes from the start of the solidification, and k is a factor associated with the metal to be cooled. The factor k for steel ranges from 22 to 33 mm / min. and can be calculated from various data derived from practical tests. The influence of superheating, i.e. s. The heat present in the molten metal, in addition to the heat required to melt the metal, is not disclosed in this formula, but need not be included for understanding the present invention.

The equation indicates that the velocity at which the shell grows, i.e. the solidification from the outside to the interior decreases rapidly from the beginning of the shell formation and with the increase of the shell thickness. At the beginning of the cooling or solidification, e.g. the formation of a shell with a thickness of 5 mm only takes about 0.028 min if k is 30. After 4 min. the shell will be 60 mm thick and it will then take approximately 4.7 minutes before the shell thickness is increased by another 5 mm.

The rate of solidification has considerable effect on the structure and composition of the metal. The metal layer, which solidifies rapidly immediately at the mold wall, has small randomly oriented crystals which form a so-called "quench zone". The thickness of this "quench zone", depending on the composition of the steel or other metal, will vary between approx. 5 mm and approx. 10 mm or possibly 12 mm. Soiled steel forms a "quench zone of about 10 mm in thickness. In the" quench zone, "the chemical composition will closely match the composition of the molten steel or metal, and its mechanical properties are also better than the metal which solidifies later, or in any This applies to most steels as the cooling rate decreases inward from the "quench zone", large crystals, dendrites, are formed which result in a structure that is brittle at rolling temperature and can easily produce internal fractures unless small cross-sectional reductions occur at the Towards the middle of the cast, the crystalline structure will usually shift again with several randomly oriented dendrite crystals which are rather large.

In addition to the increased size and position of the dendrite crystals in the cast, the composition of the metal also varies. In the "quench zone", as stated above, the composition of the metal is more or less similar to the composition of the molten metal, whereas components which have been rejected from the crystals formed first are increasingly concentrated towards the center. Accordingly, the last solidified material contains the highest concentration of these elements which has been continuously rejected during crystallization. This tendency for excretion increases along with increased solidification time, so that large pieces of castings exhibit more severe discharge than smaller pieces. Likewise, the chemical composition of the metal in castings cast in molds will rarely prove to be uniform in cross-section through the casting, which is examined at intervals along the entire length of the casting. Continuous casting can substantially eliminate this variation in chemical composition at different longitudinal areas of the cast, but the difference in chemical composition and structure from the outside to the middle is not avoided, especially with large castings.

To overcome the effect of such variation and to develop the necessary mechanical properties, it may be necessary to reduce the cross-sectional dimension of the castings by rolling or 7 forging. The original large crystal cast structure must be broken down by rolling or forging by reducing the cast size to a ratio of maybe 1: 5 to 1:30 depending on the cast size and the metal composition. Heat treatment in order to obtain a composition equalization by diffusion may also be necessary or desirable.

The conversion of molten metal to a reasonable tonnage per Years of finished or even semi-finished rolled products require large investments in casting plants, rolling mills and heat treatment ovens as well as large labor costs and with many operations also high fuel costs. As the continuous casting has significantly lowered costs by reducing labor costs and increasing yields, castings with smaller cross-sectional areas can be produced economically, avoiding rolling of large cast blocks or pieces down to bar size and yet large pr. tons of finished product.

It is the object of the present invention to provide a process of the kind mentioned in the first, by means of which it is possible to make forged, pressed or extruded products of fine crystalline structure, without the necessity of carrying out the essential elements mentioned above. mechanical machining in the form of repeated rolls with significant reductions for the degradation of large crystals, and without the need to use heat treatments to provide the otherwise necessary equalization of the metal structure, and this is achieved according to the invention by moving the cooling surface with such velocity that the melt solidifies fine crystalline throughout the cross-section of the layer and with uniform composition, that the welding of the same metal layers is adapted to the plasticity of this metal at temperatures above the metal working temperature, and so that the thickness reduction is at most 2%, and in this way fr manufactured semi-finished products are hot-rolled, forged, pressed or extruded to obtain a finished heat-machining dimension. Hereby it is achieved that immediately in connection with the casting, namely according to the number of layers used, even very thick castings having the desired fine-crystalline structure can be built up, and without the need to make it otherwise to obtain a uniform fine-crystalline structure requires substantial thickness reduction so as to avoid such and the associated costs, since the welding of the fine-crystalline layers requires only a relatively modest thickness reduction. It should be noted that the aforementioned U.S. patent does not disclose that the present invention is based on the recognition of the advantage of building a body of fine-grained structure, the U.S. patent only mentioning the formation of two layers, which are welded immediately after formation using pressure to produce a composite material.

From the foregoing explanation, it will be understood that the present invention is directed solely to making castings of one and the same metal.

According to the prior art according to the aforementioned US patent specification, two rotating heat sinks are used to make each layer which is welded together. Such a method can also be used in accordance with the present invention, but the process is carried out in a simpler manner if according to the present invention, as the layers used for welding, layers of one and the same molded strip which are folded or used are used. is rolled in the transverse direction for the layering of the layers flat to flat.

The present invention also relates to a suitable apparatus for use in the practice of manufacturing and further processing molded strings, which apparatus has one or more rotatably mounted cooling surface rollers and container means in which the cooling surface rollers extend partially and serve on the cooling surface rollers depositing at least two metal layers, which apparatus further has means for releasing said at least two metal layers from the cooling surface rollers, and means for laying the layers face to face directly after solidifying and welding the layers for pressure welding in the facing contact faces, which apparatus further has means for maintaining a non-oxidizing atmosphere in the apparatus. According to the present invention, the apparatus is characterized in that the cooling means roll container nails are constituted by one of these common containers and that the cooling surface rollers are arranged to drive them at such a circumferential speed that the layers solidify fine crystalline through the cross-section of the layers and that the members the pressure welding of the layers is controlled in such a way that the pressure welding means, during the pressure welding, of the layers of the same metal, exert a pressure adapted to the metal at that temperature above the heat working temperature of the metal, so that the reduction in thickness at the pressure welding is at most 2%, and that the apparatus has means for hot rolling, forging, pressing or extruding the semi-finished product thus produced to obtain finished heat-working dimension

A particularly simple embodiment of the apparatus according to the present invention has only one cooling surface roll and according to the present invention is characterized in that it has, in an axial section, a wavy surface to form a wavy band and that the means for pressure welding the formed by the waveguides layers consist of a roller set for compressing the band across the waves. This apparatus is simplified in comparison to the prior art apparatus according to the aforementioned United States patent, in that only a single cooling surface roll is required.

The invention will now be described in more detail with reference to the drawing, in which fig. 1 shows a longitudinal section through an embodiment of an apparatus for carrying out the method according to the invention; FIG. Fig. 2 is a perspective schematic view of another embodiment of the apparatus for carrying out the method according to the invention; 3 shows a thin, flat plate before folding it into a thicker plate; FIG. 4 and 5 show subsequent phases of the folding; 6 is a view of how the layers eventually overlay each other, and FIG. 7 is a perspective view of another embodiment of an apparatus for carrying out the method according to the invention, showing how a section of a continuously formed thin molding can be cut to a predetermined length and rolled tightly to merge into a semi-finished, simple one. body of circular cross-section and melted or welded in rollers with peripheral grooves.

In FIG. 1 denotes 2 a container of refractory lining. 3 denotes a regulated spout casting 4 for insertion of metal into the container 2 in such a way that a constant depth of molten metal 8 is maintained in the container 2. There are a number of hollow, water-cooled rollers 5 extending across container 2 (only three such rolls are shown in the drawing). Each roller is arranged such that its shaft and bearings indicated by circles 6 and 7, respectively, are approximately level with the molten metal 8 in the container 2. The lower part of the periphery of each roller 5 dips into and is located below it. molten metal surface.

The rollers are driven at the same speed by any suitable means (not shown). There is a cap 9 above the container 2 which allows to maintain a non-oxidizing atmosphere of an inert gas or vacuum over the container. As each roll rotates, a layer of metal 10 with a thickness of up to between 5 mm and about 5 mm is formed on each roll surface. 10 or 12 mm or even more, and the composition of this layer mainly corresponds to a metal in the quench zone previously described. The thickness of the layer formed on each roll depends on the length of the arcuate surface of the roll which is submerged in the molten metal, the thickness of the metal from which the rollers are formed, the speed of rotation of the roll and the state of the molten metal with regard to the degree of superheat and the the nature and quality of the metal.

When left in the apparatus of FIG. 1, a solidified layer 10 of metal is formed thereon and supported by the molten metal in the container. A scraper 11 removes this layer, which can now be considered a molding, from the top of the roll and supports the still brittle molding as it moves forward toward the top of the roll indicated in the apparatus. The molding now runs on a corresponding layer 12 which is about to leave the roll in the center of the apparatus, the colder and firmer underside of the originally formed molding now lies over the warmer newly formed upper side of layer 12, while a pressure roll 13 exerts a slight, uniform pressure to provide fusion or welding of the two layers to a single thicker web. This thicker web moves over an interposed scraper and support 14 and then extends over a solidified layer 15 at the top of the roll shown to the right in the apparatus, whereby the colder underside of the now combined first two layers will contact the freshly formed surface of the layer 15. Here, too, there is a fusion under uniform pressure which is applied by a pressure roller 16. The pressure rollers 13 and 16 can be force-driven or can be rotated by virtue of the contact with the upper surface of the molding. The molding 17, which now comprises three separately formed layers which are brought together after leaving the molten metal mass from which they arise, runs over a scraper 18 and out through a guide 19 at the outlet end of the apparatus, which is an extension. of the cap 9. The guide with the passing molding serves to limit the amount of air which seeks to enter the space under the cap or the amount of inert or non-oxidizing gas which seeks to penetrate. There is a duct 20 on the cap through which air can be removed from the cap or through which inert air can be supplied. Each pressure roller 13 and 16 has pressure adjusting means 13 'and 16', respectively, which are indicated schematically.

147967 8

Each water-cooled roller may have a member 21 by which a coating of a release agent may be applied over the surface of the roller, which application means is formed as yet another roller disposed close to the descending surface of the roller 5. New molten metal penetrating into the roller the container, rises through openings 22 in a false bottom 23 below the rollers, where refractory plates 24 serve to keep slag or other surface impurities away from the place where the various rollers move into the molten metal.

When the molding emerges from the guide 19 and at a sufficient distance from the molding machine for the metal to cool to a normal rolling temperature, the molding can be sent, and will preferably be passed through a thickness-reducing rolling apparatus 25. From this roller, it can be cooled to a semi-finished one. product or rolled directly to finished state. The roller 25 is shown in FIG. 1 shown as adjacent immediately to the outlet of the guide 19. Although the rolling mill can be placed in such a position, it is clear that the roller 25 can be placed at a considerable distance from the outlet of the guide 19.

Although three rolls are used in the illustrated embodiment, more than three rolls may also be provided. Likewise, it is clear that many narrow webs can be formed separately and side by side on one or more rollers, and subsequently fused to provide rods or beams. Furthermore, it will be understood that while the apparatus specifically described herein has rollers since they provide an easily understandable illustration of an apparatus providing a continuously moving chilled surface such as the surface of a roll, but to some extent depending upon the the product, using cooled, endless bands or a continuous sequence of chilled mold elements arranged in a manner similar to the placement of elements in a crawler foot belt. However, in all these different embodiments, the castings are formed separately from molten metal in a container and then brought together and joined above the level of the molten metal in the container, or after the castings are otherwise brought out of contact with the molten metal mass from which they originate.

Although it is stated that the thickness of the quench zone may vary between 5 and 12 mm for various metals, layers of less than 5 mm may be conveniently formed and joined together, and it may also be convenient to exceed 12 mm. If this maximum of 12 mm is exceeded, some of the advantage in terms of product quality can be lost, but since it is not practically continuous to cast strips of less than 100 mm thickness, an improved product can be ensured thereby avoiding the cost of start with a much thicker molding such as a continuous cast web made by traditional casting and then roll it down to finished product. In other words, building a unit structure from layers that exceed a quenching zone thick look can be more economical and can provide a better product than the traditional practice of first casting a heavy section, which is then machined down to thin product.

FIG. 2 shows an apparatus for practicing a method of converting a molten metal into a log. A single hollow water-cooled roller 30 is arranged to rotate in a refractory cladding container 31, maintaining a constant depth of molten metal by means of a non-shown supply source, such as may be similar to the casting spoon 3 of the apparatus of FIG. First

The lower part of the periphery of the roller 30 is immersed in the molten metal. As in FIG. 1. this roller 30 is also driven by any suitable drive mechanism (not shown). For the sake of clarity, an enclosing cap, which would usually be provided to maintain a regulated inactive atmosphere or vacuum over the molten metal, is not shown in FIG. 2nd

The surface of the roller 30 is formed with a series of ridges and grooves, so that as metal solidifies on the roller, a molding member 32 is formed with a series of facing flat surfaces 33 which are interconnected at the backs and bottoms of the molding. In other words, instead of forming layers or individual moldings, they are completely separated from each other, as in the apparatus of FIG. 1, there is formed a molding comprising several partially spaced layers which are interconnected at the backs and bottoms of the molding. After leaving the water-cooled roller, the molding moves toward a compression mechanism formed by two vertical rollers 34, wherein the different planar surfaces 33 of the partially spaced layers are pressed against each other and fused together to form a beam shape 35 which may optionally be further reduced to a finished product or optionally constitute the raw material for subsequent conversion into a finished product. Also, a scraper (not shown) similar to the scrapers of FIG. 1, which supports the molding when scraped off the roll 30. One can also apply to the rollers 30 an abrasive in the same way as the release agent is applied to the water-cooled rollers in the apparatus of FIG. First

During operation of the apparatus of FIG. 1 and the apparatus of FIG. 2, the mold is formed continuously.

In FIG. 3-6, another method is shown in which interconnected folds or parts of a single molding are brought together, which is similar to that of FIG. 2. In this modified embodiment, a flat molding is formed on a water-cooled roll or other cooled moving element, and the molding is then scraped from the roll or moving element.

In FIG. 3, such a flat casting member 40 is shown. As shown in FIG. 4, the center portion 41 is held flat by the molding, while side edges 42 of the same width as the middle portion are forced up on each side of the molding. One side portion is folded over the middle portion, as shown in FIG. 5, and then the second side portion, as shown in FIG. 6, over the first one and pressed evenly to create fusion of the interconnected surfaces. This method can be applied to continuous pieces or by cutting the continuously formed molding to predetermined lengths. When the thus-formed composite blank 43 is cooled to a normal rolling temperature, it can be rolled through a reducing rolling mill, as shown in FIG. First

In FIG. 7 becomes a flat molding as shown in FIG. 3, either cut transversely or longitudinally to the desired dimension and then rolled tightly within itself as indicated at 50, and the resulting round body is passed through grooved rollers 51 to apply sufficient pressure while the metal is still hot to fuses the coils into a solid or tubular cross-sectional shape, which upon cooling can be further rolled or machined.

The dimensions, temperatures and pressures of the processes described herein can be varied in many ways and therefore a clear specification cannot be given. However, it is clear that a person skilled in the art will, through sensible experiments, be able to put figures on the various parameters. In some cases, additional heat may be required while the compression, folding or rolling takes place to effect fusion of the individual castings or layers or folds or rolled areas of one and the same casting member. For all purposes of clarity, the composite product is indicated by lines where the contact surfaces are present, but in reality such a laminated appearance will not occur.

However, it can be stated that as the metal goes from liquid to solid state, some metals will develop plastic properties at a few degrees below the solidus temperature, while for other metals there is a range of 100 ° C or perhaps more than 200 ° C between the solidus temperature and the emergence of good plastic properties. The welding or melting of the moldings may take place at or around the solidus line, i.e. where they appear as a solid, although everything indicates that p.g.a. poor plasticity is still some liquid metal in the dendrite boundaries.

In other words, welding, fusing or closing will usually occur above a temperature where the metal has sufficient plasticity for normal rolling. As a general rule, the pressure applied by the pressure rollers which first compress the layers should cause a thickness reduction of the aggregate of the two or more layers lying in the range of 0.2% to 2%. Carbon steel with a low content of approx. 0.10% rapidly develops good plastic properties below the solidus line and can be subjected to pressure during the compression of the metal into a unitary body, thus providing a 20% reduction of the cross-sectional area, whereas steel with high impurities, e.g.

S, P, Cu, Sn, etc. will have poor plasticity as far as 150 ° below the solidus line and cannot withstand a reduction of more than 0.3%.

Therefore, the pressure which will cause the fusion must be mainly such that the thickness reduction is never greater than necessary to produce a good adhesion, which is of the order of 2%. If the pressure exceeds such critical limits, the compressed product will have various weaknesses or internal defects. When the normal rolling temperature is reached, the combined molding can be reduced by as much as 20% or more in thickness by a single rolling passage.

It is e.g. it is not difficult to understand that if three layers of quench zone thickness of maybe 10 mm are joined to a single workpiece of 30 mm thickness and reduced 20% to a semi-finished product, much less work is needed to transform it into e.g. metal plate with a thickness of 0.25 or 0.5 mm other than rolling a casting block of several centimeters thickness down to the same thickness, and the extensive heat working is not necessary in this process because the metal is complete or substantially metal with quench zone thickness and crystal structure, as stated above and with quench zone composition.

Although a method and apparatus in which a layer formed on a roll is specifically laminated to the surface of a layer formed on a second roll which is spaced from the first and rotates in the same direction, the invention may be also used for any method in which two facing rollers rotate in opposite directions and each are submerged in the molten metal bath and the separate layers of solidified but hot metal formed on each roll are pressurized together in the gap between the two rolls. The thus-formed, two-layer plate blank can then be welded together with other metal webs, as described herein, where a greater thickness is desired.

Claims (3)

147967 Patent Claims. A method of manufacturing and further processing molded strings in which a circular heat sink is passed through a metal melt which, in a non-oxidizing atmosphere, solidifies to a thin layer which is continuously removed from the heat sink by the heat sink and the layer is loosened. from the heat sink, and at least two such layers directly after solidification are applied face to face and compressed for pressure welding into opposite contact faces, characterized in that the cooling surface is moved at such a rate that the melt solidifies fine crystalline throughout the cross-section of the layer and with uniform composition that the pressure welding of the layers of the same metal is adapted to the plasticity of this metal at temperatures above the metal working temperature and so that the thickness reduction is not more than 2% and that the semi-finished product thus manufactured is hot-rolled, forged, pressed or extruded to obtain of finished hot working dime board. Method according to claim 1, characterized in that layers of one and the same molded strip which are folded or rolled in the transverse direction are used as the layers used for the pressure welding. Apparatus for use in the method of claim 1 for manufacturing and further processing molded strings, said apparatus having one or more rotatably provided heat sink rollers (5; 30) and container means (2; 31), wherein said heat sink rollers ( 5; 30) partially projecting and serving to deposit at least two metal layers (10,12, 15; 32) on the cooling rollers (5; 30), the apparatus further having means (11,14,18) for resolving the said at least two metal layers (10,12,15; 32) from the heat sink rollers (5; 30) and means (13,16,34) for joining the layers (10,12,15; 32) face to face directly after solidification and compression the layers (10, 12, 15; 32) for pressure welding in the facing contact surfaces, the apparatus further having means (9, 19, 20) for maintaining a non-oxidizing atmosphere in the apparatus, characterized in that the container means (2; 31) for the heat sink rollers (5; 30) is constituted by one of these common containers (2) and that heat sink rollers nes (5; 30) drive means are adapted to drive these with one