FI57545B - FOERFARANDE FOER OMVANDLING AV SMAELT METALL TILL METALLPRODUKTER - Google Patents

Description

r ^ -a-Tl ΓβΙ rt1vAdvertisement rncAc [BJ <11) UTLÄGGNI NGSSKRIFT 3 r 0 4 5 w (si) K ».ik.3 / in * .ci.3 B 22 D 25/00

FINLAND I - FI N LAN D (21) Pnunttlhukumut - Pwtntunueicning 618 / TU

(22) HukumltpWvl - AmMcnlngsdif 01.03.7 ^ (23) Alkupllvl — GlMghuttdug 01.03-7 ^ (41) Tullut | ulklMlul - Bllvlt offuntllg O6.O9.7t IWtti. j * reki.teHh.IHtu. Nihtivikdpunon. date of month

Patent- och regiuterut / reluen '' Amakuit uttagd och utUkrtfun publtcurad 30.05.80 (32) (33) (31) utuolkuu · —Begird prlorlut 05.03.73 USA (US) 337931 (71) Olsson International, Inc., One Oliver Plaza , Pittsburgh, Pennsylvania 15222, USA (72) Erik Allan Olsson, Zurich, Switzerland-Switzerland (CH) (7 * 0 Oy Roister Ab (5 ^ +) Method for converting molten metal into metal products - Förfarande för. Omvandling av smält meteli This invention relates in particular to, but not exclusively to, the manufacture of articles of ferrous metals and ferro-alloys.

When liquid or molten metal is poured into a mold, solidification begins in the solidified layer, which forms almost immediately where the metal contacts the mold, and continues inward toward the center of the metal mass in the mold. The rate of solidification depends on the following three factors: 1) the coefficient of heat transfer through the walls of the mold; 2) excess heat in the molten metal exceeding the melting temperature, which must be removed in order to reach the solidification temperature of the metal; and 3) the coefficient of heat transfer to the walls of the mold through the already solidified metal layers in the mold.

In order to determine the solidification rate of molten metal, a simplified formula is often used in casting technology, which is good enough for the process 1/2 described here. This formula is: s = k (T) '.

In this equation, s is the thickness of the metal shell solidified from the molten metal in millimeters; T is the time in minutes that has elapsed since solidification began, and k is the coefficient associated with the metal to be cooled. For steel

Ι / S

the coefficient k varies from 22 to 33 mm / minute 'and can be calculated on the basis of data obtained from various practical tests. The exponent 1/2, of course, denotes the square root. This formula does not show overheating, i.e. in molten metal, the effect of heat exceeding the melting temperature, but need not be considered in this application.

This equation shows that the growth rate of the bark, i. solidification from the outside to the inside, decreases rapidly after the shell has begun to form and the shell thickness has begun to increase. At the beginning of cooling or solidification, for example, the formation of a 3 mm thick shell takes only about 0.028 minutes. if k is 30. After 4 minutes, the shell thickness is 60 mm, and then an increase in shell thickness by 5 mm requires about 4 »7 minutes.

The solidification rate has a significant effect on the structure and composition of the metal. The metal layer, which hardens rapidly right next to the mold wall, has small, randomly oriented crystals that form the so-called "Cold zone". The thickness of this zone varies depending on the composition of the steel or other metal from about 5 to about 10 or possibly twelve mm. Socalled the "compacted steel" forms a "cold zone" with a thickness of about 10 mm. In the cold zone, the chemical composition corresponds exactly to that of the molten metal and also has much better mechanical properties than the metal that subsequently hardens, or at least this is the case for most steels. As the cooling rate slows inward, large crystals - dendrites - develop from the cold zone, resulting in a structure that is brittle at the rolling temperature and in which internal cracks can easily form unless only minor cross-sectional reductions are made in the initial rolling steps. Near the center of the light, the crystalline structure usually changes again and has rather large, randomly oriented dendritic crystals.

In addition to the fact that the dendritic crystal size increases and the orientation of light changes in light, the composition of the metal also varies. As discussed above, the composition of the metal in the cold zone most closely resembles the composition of the molten metal, while the components discarded in the first crystallization are increasingly concentrated toward the center. The last solidifying agent thus contains the most of these ingredients, which have become continuously discarded in the crystallization process. This separation tendency increases with a longer solidification time, so that the separation is worse in the larger lights than in the smaller ones. Moreover, in castings cast in molds, the chemical composition of the metal is seldom uniform in the polar section areas of the light, which are examined at intervals along the entire length of the light. Continuous casting can substantially eliminate variation in this chemical composition in different regions along the length of the light, but from the outside toward the center, variation in chemical composition and 3,57545 structure cannot be avoided, especially in high light.

In order to overcome the effect of this variation and to develop the required mechanical properties, it may be necessary to reduce the cross-sectional area of the light by rolling or forcing. The original structure of the light, containing large crystals, must be broken by rolling or forcing to reduce the size of the light in a ratio of about 1: 5 to 1:30, depending on the size of the light and the composition of the metal. Heat treatment to achieve harmonization of the composition by diffusion may also be necessary or desirable.

The conversion of molten metal into finished or even semi-finished, rolled products with a relatively high tonnage per year requires large investments in foundries, rolling mills and reheating furnaces and incurs high labor costs as well as high fuel costs due to many jobs. Although continuous casting has significantly reduced costs not only by reducing labor costs and increasing output, continuous casting can economically produce lights with a smaller cross-sectional area, eliminating large ingot rolling or casting to semi-finished size and lengths. Investment and labor costs are still high per tonne of finished product.

It is an object of the present invention to provide an improved method for converting molten metal into metal products.

According to the present invention, there is provided a method of converting molten metal into metal products characterized in that metal layers having a thickness such that, as a result of rapid solidification, have a fine-grained structure and uniform grain size similar to a fine-grained surface area after solidification, joining and compressing in a non-oxidizing atmosphere to fuse the contact surfaces facing each other to form a uniform semi-finished product having a structure and composition substantially resembling the structure and composition of the individual layers, the compression pressure being adapted to the high temperature plasticity the semi-finished product is subjected to a treatment known per se, such as hot-rolling, forging, pressing or extrusion; to produce a pre-rolled, forged, extruded or extruded product.

The invention further provides an apparatus for carrying out the method, which apparatus is characterized by one or more cooling means used to cool molten metal applied to a part of their cooling surface, one or more molten metal containers and tanks closely connected to the cooling surfaces of the cooling members, for metal layers solidified or solidified on the cooling surface and thereby removed from the molten metal, and means for stacking and compressing the solidified layer or layers to fuse opposite layer surfaces together to form a uniform product.

11 57545

The molten metal can solidify in contact with the cold surface into a thin sheet and combine with one or more similarly formed strips or sheets at high temperature and pressure in a non-oxidizing environment where they fuse together to form one thicker strip or sheet with a thickness less than the sum of the thicknesses of different strips or plates, but with the good mechanical properties and chemical uniformity of the individual plates. Such an integrated strip or sheet can then be rolled with relatively light and few rolls into a finished product, e.g. a metal sheet of any selected thickness number. This eliminates the need to cast thick light, cool it to a solid state and reduce it in heavy rolling mills and many stages to the final thickness. Other methods can be used to obtain the desired combined thickness by layering, e.g., bending the sheet over itself or rolling it tightly either longitudinally or transversely over itself, or twisting it tightly either longitudinally or transversely over itself, or by twisting together several flat-sided layers into a rod-like shape.

In order that the invention may be better understood and other features thereof will become apparent, the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a form of device according to the invention; Fig. 2 shows a schematic perspective view of another form of device for implementing the method according to the invention; Figures 3 ~ β show schematic cross-sectional views of the manufacture of a thickened body by bending a flat plate over itself, Figure 3 shows a thin, flat plate, Figures U and 5 show different successive bending steps, and Figure 6 shows how the layers are finally on top of each other; and Fig. 7 is a perspective view of a portion of another apparatus implementing the method of the invention and showing how a portion of a continuously produced thin light can be cut to a predetermined length and tightly twisted into a fusible semi-finished unit having a circular cross-section and fusible or weldable peripheral rolls.

Figure 1 shows a refractory lined vessel 2, the casting bucket 3 has an adjusted discharge opening H from which molten metal is discharged into vessel 2 so that molten metal 8 is at a constant depth in vessel 2. Several hollow, water-cooled rollers 5 extend over vessel 2 and three rolls are shown.

Each roll is positioned so that its shaft and bearings, indicated by circles 6 and 7, are above the surface of the molten metal 8 in the vessel 2. The lower part of the circumference of each roll 5 extends below the surface of the molten metal.

Some suitable tool (not shown) drives the rollers at the same speed. The vessel 2 has a hood 9 »so that a non-oxidizing space formed by an inert gas or vacuum can be maintained on the vessel. As each roll rotates, a metal layer 10 having a thickness of 5 to about 10 mm and 12 mm or even more is continuously formed on the surface of each roll, and the composition of this layer generally corresponds to the metal in the cold zone, as described above.

Thus, the thickness of the layer formed on each roll depends on the length of the arcuate of the roll embedded in the molten metal, the thickness of the metal forming the rolls, the rotational speed of the roll, and the condition of the molten metal in terms of excess heat and metal quality.

As the roller on the left in the device of Fig. 1 rotates, a solidified metal layer 10 is formed on it, which is lifted from the molten metal of the vessel. The scraper 11 removes this layer, which can now be considered as light, from the top of the roll and forms a support for the still brittle light as it moves towards the upper end of the roll, which is shown in the middle in the device of Fig. 1. The light passes over a similar layer 12 exiting the roller in the center of the apparatus, with the colder and stronger lower surface of the first formed light over the hotter, newly formed top surface of layer 12 and the press roll 15 applying a light, uniform pressure which causes the two layers to merge or weld together into one thicker track. This thicker path passes over the intermediate scraper and support 14 and then over the solidified layer 15 at the top of the roll to the right of the device of Figure 1, and the colder lower surface of the now connected first two layers now contacts the newly formed surface of layer 15. Again, the fusion takes place under the uniform pressure exerted by the pressure roller 18. The pressure rollers 13 and 16 may be belt-operated or may rotate by contact with the upper end of the light alone. The light 17, which now comprises three separately formed layers brought together after leaving the molten metal mass from which they come, passes over the scraper 16 and out through a guide 19 at the discharge end of the device, which guide is an extension of the hood 9. The guide through which the light passes prevents air from flowing into the space under the hood or the exit of inert or non-oxidizing gas. The hood has a line 20 through which air can be removed from the hood or through which inert gas is supplied. Each pressure roller 13,16 is provided with pressure control means 13 ', 16 ·.

Each water-cooled roll 3 can be provided with a means 21 which places a release layer on the surface of the roll and which is in the form of a second roll located next to the descending surface of the roll 3. The new molten metal entering the vessel 2 rises through openings 22 in the dummy base 23 6 57545 under the rollers, where the refractory baffles 24 keep the slag or surface contaminants away from where the various rollers enter the molten metal.

Once the light has come out of the guide 19 », it is desirable to pass it through the reducing rolling device 29 at a sufficient distance from the casting device to allow the metal to cool to the normal rolling temperature. From this roll it can be cooled to a semi-finished product or it can be rolled immediately to a steady state. Figure 1 shows a roller 29 right next to the outlet of the guide 19. Although the roller stand may be located in this way, it is clear that it can be located considerably far from the outlet of the guide 19.

Although three rollers are shown in the figures, more can be used.

It is also to be understood that many narrow strips may be formed side by side by one or more rollers and may subsequently be fused together to form bars. Furthermore, it is to be understood that although the device just described includes rollers, as these are a simple example of a device with a continuously moving, cooled surface that is a roller surface, chilled, endless belts or continuously cooled mold elements may also be used to some extent, which are arranged in the same way as the track parts. However, in all of these different forms of the device, the lights are formed separately from the molten liquid in the vessel and then brought together and solidified above the surface of the vessel molten liquid, or after the lights have otherwise passed out of contact with the molten metal mass from which they are formed.

Although the thickness of the cold zone is defined as 9-12 mm for different steels, layers less than 9 am thick can be formed and solidified if necessary, or layers thicker than 12 mm. If the maximum of 12 mm is exceeded, some advantages may be lost in terms of product quality, but since it is not practical to continuously cast strips less than 100 mm thick, an improved product can be ensured and the cost of starting with much thicker light can be eliminated, e.g. in conventional casting with a strip made by continuous casting, and later rolled into a finished product. In other words, forming a uniform structure from layers whose thickness may exceed the thickness of the cold zone may be more economical and the product may be better than in conventional practice where a thick body is initially cast and processed into a thin product.

Figure 2 shows an apparatus for carrying out a method for converting molten metal into a rod body. It has one hollow, water-cooled roller 50 designed to rotate in a refractory lined vessel 31 # with molten metal at a constant depth fed by a feed means not shown, but which may be similar to, for example, the casting 3 of the device shown in Figure 1 7 57545. The lower part of the circumference of the roller 30 is embedded in molten metal. As in Figure 1, any suitable drive mechanism (not shown) drives this roller 30. For clarity, Figure 2 does not show a hood that normally maintains a controlled, inert state or vacuum over molten metal.

Successive protrusions and grooves are formed in the surface of the roll 30, so that as the metal solidifies, a light 32 is formed on the roll with successively opposite planar surfaces 33 »connected to each other at the protrusions and grooves of the cast. That is, instead of forming layers or individual lights completely separate from each other as in the device shown in Fig. 1, a light is formed comprising a plurality of partially separate layers connected in a multiplied manner at protrusions and grooves. As the light exits the water-cooled roll, it travels toward a pressing device having two vertical spindles 34 and in which a plurality of planar faces 33 of partially separate layers are forced and pressed against each other and fused together to form a rod 35 which can be further reduced to a finished product. , which will be modified later. A scraper, not shown, but which may be similar to that shown in Figure 1, may be used to support the light when ee is removed from roller 30. The release agent may also be applied to rollers in the same manner as water-cooled rollers in the apparatus shown in Figure 1.

During operation of the device shown in Figure 1 and the device shown in Figure 2, light is continuously generated.

Figures 3-6 show another procedure in which the combined folds or parts of a single light are brought together and similar to that of Figure 2. In this conversion hand, a flat light is formed by a water-cooled roller or other cooled, moving part, and the light is later removed from the roller or moving part. Figure 3 shows such a flat light 40. As shown in Figure 4, the center portion 41 of the light is kept flat, while side edges 42 that are as wide as the center portion are turned up on each side of the light. The second side part is bent inside over the middle part according to Fig. 5 and then according to Fig. 6 the second side part is folded inside on top of the first one and it is pressed flat! to melt the contact surfaces together. This process can be performed at continuous lengths or by continuously cutting the light made into pieces of a predetermined length. Once the composite casting 43 thus formed has cooled to the normal rolling temperature, it can be rolled in a reducing rolling mill according to Fig. 1.

8 57545

In Fig. 7 a flat light similar to Fig. 3 is cut either transversely or longitudinally to the desired size and then twisted tightly together, as in step 30, and the resulting round body is passed between grooved rollers 31 applying sufficient pressure while the metal is still hot to fuse the coils into one closed or tubular into a piece which, after cooling, can still be rolled or machined.

The dimensions, temperatures and pressures associated with the methods described in this specification can be varied and thus cannot be accurately determined. The expert is assumed to be able to determine the parameters for a given process after a reasonable experiment. In some cases, it may be necessary to use additional heat during pressing, folding, or twisting to cause the fusion of separate lights or layers or corrugations or twisted areas of the same light. The combined product shown as an example in the accompanying drawings shows lines at which the contact surfaces converge, but in practice this layer, the structure, may not be visible.

It should be noted, however, that when a metal solidifies from a liquid to a solid state, some metals acquire plastic properties only a few degrees below the solidification temperature, while for others the temperature range may be J.00 ° C or higher, perhaps up to 200 ° C, for solid state and good plastic properties. between the development of properties. The welding or fusion or fusion of the light layers can take place in or near the solid phase, i. when it is apparently rigid although due to poor plasticity some fluid metal may still be between the dendritic boundaries. In other words, welding, fusion, or integration usually occurs above a temperature at which the plasticity of the metal is sufficient for normal rolling. As a general rule, the pressure exerted by the compression rollers first compressing the layers should result in a reduction in the pdc of the combined body formed by the two or more layers in the range of 0.2 to 2. Low carbon steel containing about 0.10 C rapidly develops good plastic properties at a lower solid state temperature and can in many cases be subjected to pressure to reduce cross-section when the metal is pressed into a uniform piece, whereas a lot of impurities such as S, P, Cu, Sn etc., the plasticity of the steel is poor even at temperatures below 130 ° of solidity and cannot withstand a reduction of more than 0.3 n. The pressure to cause melting should therefore be such that the reduction in thickness is only large enough to achieve good bonding, i. about + 2 i »depending on the tolerance of the metal. If the pressure exceeds these critical limits, then the sealed product has weak areas or internal defects. Once the normal rolling edge temperature is reached, the combined light can be reduced by up to $ 20 or more for a thickness of 9,57545 in just one rolling.

It is not difficult to understand that if, for example, three of each block of flats each have a cuff zone thickness, e.g. 10 mm, is combined into one JO mm piece and reduced by 20 to a semi-finished product to be converted into sheet metal with a thickness of e.g. 20, a much smaller workload is required than to obtain Vals of several centimeters thick light to the same thickness number, and no high heat treatment is required in this process because the metal is wholly or largely metal having a cold zone thickness, crystal structure and composition, as described above.

Although the present invention specifically encompasses a method and apparatus in which a single roll layer is deposited on a surface of a layer formed at a distance from and parallel to the first roll, the invention can be applied to any method in which two counter-rotating rollers sink into molten metal and each roll the formed solidified but hot separate metal layers are press welded together in the gap between the rollers. As shown herein, additional shell layers can be compression welded to the combined two-layer plate light thus formed if a greater thickness is required.

Claims (13)

10 57545 A process for converting molten metal into metal products, characterized in that metal layers having a thickness such that, as a result of rapid solidification, obtain a fine-grained structure and a uniform uniform composition throughout the area of the fine-crystalline surface zone of the ingot or continuous cast after solidification, joining and compressing in a non-oxidizing atmosphere to fuse the contact surfaces facing each other to form a uniform product which is a semi-finished product whose structure and composition resemble essentially the structure and composition of the individual layers, the compression pressure being adapted to the known processing such as hot rolling, forging, pressing or extrusion of pre-rolled, forged, extruded n or to obtain an extruded product. Method according to Claim 1, characterized in that the compression is carried out at a temperature above the normal rolling temperature of the metal at a pressure which causes a reduction in the total thickness of the layers of at most 2%. Method according to Claim 1, characterized in that the layers have a thickness of at most 12 mm and in that the layers are made of the same molten metal. A method according to claim 1, characterized in that a plurality of simultaneously cast layers are joined and pressed together to fuse them from the contact surfaces. A method according to claim 1, characterized in that one layer is joined together by bending its parts on top of each other, after which they are pressed together to fuse the contact surfaces facing each other. A method according to claim 1, characterized in that one layer is joined together by forming pleats thereon, after which the pleats are pressed together to fuse the contact surfaces facing each other. A method according to claim 1, characterized in that the moving cooling surface is partially cast or covered with molten metal and that the layer solidified on the cooling surface is removed, which layer, after being removed from the cooling surface, is folded or joined to one or more similarly formed layers, and pressed together to achieve fusion at the contact surfaces. ”57545 Apparatus for carrying out a method for producing metal products in the form of semi-finished products for subsequent hot rolling or forging according to any one of claims 1 to 7, characterized by one or more cooling means (5) used to cool molten metal (8) applied to part of their cooling surface. tightly connected vessels or tanks (2) containing molten metal and having a molten metal inlet, scrapers (11, 1U, 1Ö) for metal layers (10, 12, 15) solidified or solidified on the cooling surface and thereby removed from the molten metal, and members (13); , 16) to assemble and compress the solidified layer or layers to fuse the facing surface surfaces together to form a uniform product. Device according to Claim 8, characterized in that the cooling surface is the jacket surface of a rotating cylindrical body (5) with cooling channels. Device according to Claim 8, characterized in that the cooling element is an endless strip. Device according to Claim 8, characterized in that the cooling element is formed as an endless strip of articulated cooling plates. Device according to Claim 8, characterized in that the compression members are formed by rollers or rollers (13, 16). Device according to Claim 8, characterized in that the vessel (2) or container containing molten metal is common to two or more cooling elements (5) · 57545