Insulating layer and method for installing rolls of metals and alloys on an insulating layer in a bell-type furnace

Abstract

The invention relates to the field of non-ferrous and ferrous metallurgy, in particular to the production of rolled products in the form of strips of metals, alloys and steels, and improves the heat treatment process in bell-type furnaces. An insulating layer is provided for use in the heat treatment of rolled metals and alloys in bell-type furnaces, that consists of ceramic particles. Further, a method for heat treatment of rolled metals and alloys in bell-type furnaces is provided, wherein the end of the roll installed in the furnace is placed on an insulating layer. The technical effect comprises reduction of metal losses in the form of trimmings from ends of the roll due to a significant reduction in the severity of deformation of the metal strip in the edge region and a decrease in the depth of its occurrence, as well as the absence of additional coating defects formed due to disruption of gas exchange processes in the interturn gaps, and higher durability of the insulating layer.

Description

[0001] INSULATING LAYER AND METHOD FOR INSTALLING ROLLS OF METALS AND ALLOYS ON AN INSULATING LAYER IN A BELL-TYPE FURNACE

[0002] SPECIFICATION

[0003] Field of the Invention

[0004] The invention relates to the field of non-ferrous and ferrous metallurgy, in particular to the production of rolled products in the form of strips of metals, alloys and steels, and improves the process of heat treatment in bell-type furnaces.

[0005] Background Art

[0006] As is known (RU 2190026 C2), during the heat treatment of metal rolls in bell-type furnaces, the rolls cool most intensively from the ends and from the side of the outer geneatrix, while cooling occurs at a slower rate in the middle, along the height and diameter of the roll.

[0007] When carrying out heat treatment in bell-type furnaces, an accompanying process that forms edge deformation of different depths is the settling of the roll under the influence of its own weight in the seating area. In most cases, metal rolls annealed in bell-type furnaces weigh no more than 10 tons. The geometric parameters of the rolls make it possible to provide a sufficiently large theoretical contact surface area to distribute the mechanical load from the weight of the roll at high temperatures without the negative effect of settling of the end surface. However, the actual area of the contact surface of the layered body in this case cannot be accurately determined, since there is always some unevenness in the winding of the strip from the end of the landing, allowed by technological standards. Under real process conditions, the load from the weight of the roll is distributed randomly and unevenly into separate zones of protruding turns, which at high temperatures can lose stability under the influence of a vertical load and deform according to a simple bending pattern. In this case, even a slight deviation of the stack of rolls processed in a belltype furnace from the absolute vertical can significantly intensify the process of edge deformation at any depth.

[0008] With an increase in the depth of defects in the form of edge deformation in the plane of the sheet, the amount of trim and metal consumption when cutting the roll according to customer orders increases significantly (in most cases, end trimming involves 3.0% to 8.0% based on the initial weight of the metal roll).

[0009] Missed and uncut edge deformation of different depths may also be revealed by the consumer, which entails claims and associated goodwill risks for the manufacturers. The development of technological methods that help minimize defects of this type is an urgent and economically feasible task for all industries that involve rolled sheet annealing in belltype furnaces.

[0010] The most effective way to solve the problem is to eliminate the main cause of edge deformation, namely ensuring the free movement of the roll turns along the surface of the support disk during the annealing process and reducing the friction coefficient.

[0011] There are known methods for minimizing this type of defect during heat treatment of metal rolls in bell-type furnaces, where the following means are used to minimize the defect:

[0012] - adjustment of the heat treatment and cooling mode in bell-type furnaces (RU 2125104 Cl, RU 2190026 C2; RU 2165466C1, RU 2158315C1, RU 2138749 Cl, RU 2132884 Cl);

[0013] - creating an anti-friction layer between the end surfaces of the roll and the annular disk of the support by providing at least four semicircles with detachment lines of each pair of semicircles being offset one with respect to another, placing at least three semicircles on the upper end of the roll with the ends of semicircels being arranged in overlapped relation, while the semicircles are manufactured from grain-oriented electrical steel (RU2184157C2);

[0014] - blow of the under-muffle space of the bell-type furnace (RU 2182933 C2);

[0015] - changing the gas regime during processing in the bell-type furnaces (RU2190025 C2);

[0016] - using an antifriction layer comprising ground talc, magnesia, calcined sand, alternating with a layer of semicircles made of transformer steel (RU2178005 Cl).

[0017] All of the above methods either require an additional technological operation with high energy costs and the use of expensive equipment (US 20140106130 Al), or do not allow achieving a significant reduction in the proportion of edge deformation of different depths and the associated loss of usable metal due to a slight decrease in the friction coefficient, and in cases of using bulk materials (ground talc, magnesia) due to disruption of the moisture removal process and accumulation of moisture in the edge regions in contact with these materials, additional coating defects that worsen the marketable appearance of the steel.

[0018] Patent RU2178005C1 is chosen as the closed prior art, according to which an additional distributed load is created by applying a layer of bulk material to the elements covering the upper ends of the rolls, in particular, a layer of bulk material selected from annealed sand or magnesia is applied.

[0019] The disadvantage of the above-mentioned invention is the presence of a layer of ground bulk material selected from annealed sand or magnesia, which fills the space between the turns from the end of the roll resting on these materials. The presence of even a small amount of these materials is undesirable during further technological operations, in particular during the production of transformer steel clogging of the surface may take place and the materials enter the layer of the applied electrical insulating coating, whereby the electrical resistance coefficient will decrease.

[0020] Summary of Invention

[0021] The problem to be solved and the technical result to be achieved by the present are as follows:

[0022] - reduction of metal losses in the form of trimmings from roll ends due to a significant reduction in the severity of deformation of the metal strip in the edge region and a decrease in the depth of its occurrence, as well as the absence of additional coating defects formed due to disruption of gas exchange processes in the interturn gaps;

[0023] - increasing the durability of the insulating layer.

[0024] To solve the problem and to achieve the technical result, an insulating layer is provided for use in the heat treatment of rolled metal and alloys in bell-type furnaces, characterized in that the insulating layer consists of ceramic particles.

[0025] During heat treatment of rolled metal products made of metals and alloys in bell-type furnaces, the end of the roll installed in the furnace is placed on the specified insulating layer consisting of ceramic particles. Creating an insulating layer consisting of ceramic particles between the ends of the roll installed in the furnace and the support disk of the furnace makes it possible to reduce losses of usable metal due to deformation of the strip in the lower edge region during high-temperature annealing in bell-type furnaces.

[0026] Ceramic particles can be manufactured by any known method; the following description provides an example of one of the possible manufacturing methods.

[0027] Preferably, the ceramic particles are ceramic particles comprising at least 40% Z1O2, or ceramic particles comprising at least 25% AI2O3, or a mixture of these ceramic particles.

[0028] Preferably, the ceramic particles are ceramic particles comprising at least 50% Z1O2, or ceramic particles comprising at least 40% AI2O3, or a mixture of these ceramic particles.

[0029] More preferably, the ceramic particles are ceramic particles comprising at least 65% Z1O2, or ceramic particles comprising at least 50% AI2O3, or a mixture of these ceramic particles.

[0030] In an even more preferred embodiment, the ceramic particles are ceramic particles comprising at least 80% Z1O2, or ceramic particles comprising at least 75% AI2O3, or a mixture of these ceramic particles.

[0031] In an even more preferred embodiment, the ceramic particles are ceramic particles comprising at least 85% Z1O2, or ceramic particles comprising at least 90% AI2O3, or a mixture of these ceramic particles. Most preferably, the ceramic particles are ceramic particles comprising at least 95% Z1O2, or ceramic particles comprising at least 99% AI2O3, or a mixture of these ceramic particles.

[0032] Use of the above ceramic particles provides unhindered movement of the rolls along the surface of the support disk of the bell-type furnace during the annealing process and reduction of metal losses.

[0033] Preferably, the above ceramic particles comprise additives selected from CeCh, Y2O3, SiCh, HfO2, MgO, CaO, TiO2, K2O, Na2<D, Fe2<D3, or mixtures thereof.

[0034] These additives, depending on their amount added to the ceramic material, allow providing a high strength, hardness, and wear resistance; high specific gravity (respectively small volume), high heat resistance; corrosion resistance, and heat resistance of ceramic particles. Furthermore, the ceramic particles may comprise other additives and fillers known in the art to improve properties and / or save expensive materials.

[0035] Preferably, the insulating layer has a thickness of 0.5-10.0 mm, preferably 2.0-8.0 mm, more preferably 4.0-7.0 mm.

[0036] If the thickness of the layer is less than 0.5 mm, the positive effect of using an insulating coating will be insignificant; creating an insulating layer with a thickness of more than 10.0 mm is not economically feasible, since it will not provide additional benefits, but will be more expensive.

[0037] Preferably, a size of the ceramic particle is 0.5-5.0 mm, preferably 1.0-4.0 mm, more preferably 1.5-2.5 mm, more preferably 2.0-2.5 mm.

[0038] The use of ceramic particles ranging in size from 0.5 to 5.0 mm can further increase the durability of the insulating layer. The use of ceramic particles smaller than 0.5 mm can lead to their clogging into the roll ends and rapid consumption of the material of the insulating layer, and the use of ceramic particles larger than 5 mm can lead to rapid deformation of the ceramic particles and the need for more frequent replacement of the insulating layer.

[0039] Preferably, the difference between the maximum size of the ceramic particles and the minimum size of the ceramic particles is less than 0.2 mm, preferably less than 0.1 mm.

[0040] The use of ceramic particles of substantially the same size, that is, particles with a small difference between the maximum and minimum sizes, can further improve the relative movement of particles in the insulating layer and reduce the deformation of the strip in the lower edge region during high-temperature annealing in bell-type furnaces.

[0041] The technical effect of improving the quality of the coating in the edge region of the roll ends is achieved due to the inertness of the layer of ceramic material, which does not release an oxidizing agent during the heat treatment process. Meanwhile, the formation of an insulating layer from individual rather large (compared to the technical solution of RU2178005C1) aggregates with a size in the range of 0.5-5.0 mm does not prevent from diffusion of gases from the interturn gaps during heat treatment in bell-type furnaces, which further improves the quality of coating in the edge region of the roll ends.

[0042] Preferably, the ceramic particles have a substantially spherical shape, ball shape, or have a shape of an elongated grain.

[0043] This shape makes it possible to further reduce the deformation of the strip in the lower edge region during high-temperature annealing in bell-type furnaces.

[0044] Preferably, the ceramic particles have a polished surface.

[0045] The use of polished (smooth) particles makes it possible to further improve the relative movement of particles in the insulating layer and reduce the deformation of the strip in the lower edge region during high-temperature annealing in bell-type furnaces.

[0046] Moreover, to solve the problem and achieve the technical result, a method of heat treatment of rolled metal and alloys in bell-type furnaces is proposed, wherein the end of the roll installed in the furnace is placed on the above-mentioned insulating layer.

[0047] In a preferred embodiment, the insulating layer is placed on support surfaces equipped with stops configured to limit the spillage of ceramic particles from the support surface.

[0048] This allows reducing the loss of the insulating layer by scattering / spillage from the supporting surface. Here, spillage means the loss of particles, a mixture of particles, as a result of falling from the supporting surface.

[0049] The proposed method for heat treatment of rolled products made of metals and alloys in bell-type furnaces is applicable for metals, alloys and steels with a thickness of 0.05 to 1 mm and comprises the formation of stacks of rolls, installation of a heating bell, heating to the heat treatment temperature, holding, turning off the heating elements and removing the bell.

[0050] A new aspect of the method is adding a ceramic insulating layer based on zirconium oxide (at least 40% Z1O2) or aluminum oxide (at least 25% AI2O3) with a thickness of 0.5 to 10 mm and size of ceramic particles base on zirconium oxide or aluminum oxide 0.5 to 5 mm is added between the rolls of metals, alloys and steels and the support disks. To attain uniform thickness of the layer and to prevent spillage of the material, support surfaces equipped with stops are used, in particular, disks with welded borders 70 to 100 mm high and 2 to 5 mm thick, while the material of the borders is similar to the material of the disk.

[0051] Due to mechanical strength of ceramic material based on zirconium oxide (ZrCh) or aluminum oxide (AI2O3) and absence of any chemical reactions with these materials during the annealing process, this ceramic insulating layer is used repeatedly, the number of anneals is not limited. Losses of ceramic insulating material based on zirconium oxide or aluminum oxide are minimal, in contrast to other materials used as an antifriction layer: ground talc, magnesia (prior art), calcined sand, which are clogged into the intertum space from the end of the roll supported by these materials (presence of even a small amount of these materials is undesirable during further technological operations; in particular; during the production of transformer steel, clogging of the surface may take place and the materials can enter the layer of the applied electrical insulating coating, whereby the electrical resistance coefficient will decrease).

[0052] The analysis of scientific, technical and patent literature shows that the distinctive features of the claimed method do not coincide with those of known technical solutions. Therefore, a conclusion is made that the claimed technical solution meets the criterion of inventive step.

[0053] Detailed Description of the Embodiments

[0054] Below is a description of the experiments conducted by the inventors of the present invention. The conditions and results of the experiments are examples used to demonstrate feasibility and results of the present invention, which is not limited by the given examples.

[0055] A study of the present invention on grain-oriented electrical steel is given as an example, based on the fact that heat treatment is carried out at elevated temperatures of 1150-1220°C with high temperature gradients throughout the cross section of the roll, and also based on the fact that transformer steel is the most marginal product, which has the highest requirements for the absence of geometry defects requiring additional trimming and, as a result, significant losses during production.

[0056] Example

[0057] 1. Preparation of ceramic particles

[0058] Table 1 represents the pilot formulations in accordance with the experimental plan.

[0059] The main component (AhO3 or ZrOi) was supplemented with additives selected from CeOi, Y2O3, SiO2, as well as additives selected from HfCL, MgO, CaO, TiCL, K2O, Na2<3, Fe2O3, as modifying additives. The above-mentioned modifying additives, depending on the amount introduced into the composition of the ceramic material, allowed providing a high strength, hardness, and wear resistance; high specific gravity (respectively small volume), high heat resistance; corrosion resistance, and heat resistance of ceramic particles. Furthermore, the ceramic particles may comprise other additives and fillers known in the art to improve properties and / or save expensive materials. The starting components in the ratios indicated in Table 1 were loaded into a vibrating mill for grinding and mixing.

[0060] Next, the mixture was dried.

[0061] The prepared mixture was pressed to make samples ranging in size from 0.5 to 5.0 mm, having a spherical shape, ball shape and elongated grain shape. Since it is actually difficult to provide a perfect spherical shape, the shape of the resulting ceramic particles is described as follows: essentially spherical (may be not perfectly spherical, but close in shape to a sphere), ballshaped (may be not a perfect ball, but close thereto), an elongated grain (shape similar to that of a grain whose length in one direction is greater than the length in the other direction). This description more accurately matches the shape of the ceramic particles.

[0062] The samples were sintered in a vacuum furnace.

[0063] 2. Preparation of rolled metal

[0064] The chemical composition of melted steel comprised, wt.%: C 0.018-0.035, Mn 0.1-0.4, Si 3.00-3.50, Al 0.01-0.035, N 0.08-0.015, Cu 0.4-0.6, balance iron, and inevitable impurities. The resulting slabs were heated, followed by hot rolling, to obtain a hot-rolled strip with a thickness of 2.5 mm. The strips were etched and then rolled to a thickness of 0.70 mm in a cold rolling mill.

[0065] After rolling, the strips were heated in an induction furnace before decarburization. The strip speed was varied to provide different heating and cooling conditions. Then each strip was subjected to decarburization annealing in a humid nitrogen-hydrogen atmosphere at a constant temperature of 840°C. Further processing included a second cold rolling to a thickness of 0.27 mm and the application of a magnesium coating.

[0066] 3. High-temperature annealing of rolled metal (heat treatment of steel in rolls) in belltype furnaces

[0067] High-temperature annealing (heat treatment of steel in rolls) was carried out in bell-type furnaces heated to 1150-1220°C at a rate of 10-20°C per hour in a hydrogen atmosphere.

[0068] In this case, the end of the roll installed in the furnace was placed on an insulating layer consisting of ceramic particles.

[0069] After heat treatment in the roll, the remaining magnesia was removed from the strips and an electrical insulating coating was applied, followed by straightening annealing, certification to identify defects, and final processing on longitudinal cutting units with trimming the roll ends to the extent depending on the degree of edge deformation of different depth.

[0070] Table 1 represents the examples, features, and results of using the ceramic insulating layer in the proposed method. Table 1. Influence of the features of the ceramic insulating layer on the proportion of metal to be trimmed due to edge deformation defects of different depth; original roll weight percentage to be trimmed at the ends due to edge deformation defects*

[0071] * The result is the percentage (%) of the initial weight of the roll to be trimmed from the ends due to edge deformation defects, which was determined by weighing the roll before and after trimming the edge deformation on slitting units, using the following formula:

[0072] Result, % = (M-M1) / MTOO%, where

[0073] M is the weight (ton) of the metal roll before trimming;

[0074] Ml is the weight (ton) of the metal roll after trimming.

[0075] The result is rounded to the nearest 0.1%.

[0076] As follows from the data in Table 1, use of the claimed technical solution allows minimizing the proportion of edge deformation defects of different depths and the amount of metal to be trimmed compared to the prior art from the level of 4.8-5.2% to 0.2-0.4%.

[0077] The best results, according to Table 1, were observed when using a Z1O2 -based ceramic layer compared to an AhCh-bascd ceramic layer. Meanwhile, the results obtained with an AI2O3 ceramic layer are also superior to the results of the prior art. An important factor when choosing a preference for the material of the insulating layer is its cost. Thus, when comparing the results obtained when using the insulating layer according to the invention, it should be taken into account that the best results were obtained with more expensive ZrCT-bascd ceramic material. The economic feasibility of use when choosing a material should be determined in each specific case, depending on the degree of marginality of the metal processed in bell-type furnaces. When using a mixture of ceramic particles comprising Z1O2 and ceramic particles comprising AI2O3, it is possible to select the optimal ratio that will provide a sufficiently low percentage of the initial weight of the roll to be trimmed from the ends due to edge deformation defects, with a corresponding reduction in the cost of materials.

[0078] Furthermore, as a result of tests, it was found that the proposed insulating layer comprising ceramic particles allows prolonging the service life of the insulating layer. A conventional insulating layer of finely ground materials (prior art) should be replenished after each annealing due to the losses of these materials getting into the intertum gaps of the roll. The proposed insulating layer comprising ceramic particles retains its properties over a significant number (at least 10) of annealing cycles, which leads to lower material consumption.

Claims

CLAIMS1. An insulating layer for use in a heat treatment of rolled metals and alloys in bell-type furnaces, characterized in that the insulating layer consists of ceramic particles, wherein the ceramic particles are ceramic particles comprising at least 40 wt.% Z1O2, or a mixture of ceramic particles comprising at least 40 wt.% Z1O2 and ceramic particles comprising at least 25 wt.% AI2O3.

2. The insulating layer according to claim 1, characterized in that the ceramic particles are ceramic particles comprising at least 50 wt.% Z1O2, or a mixture of ceramic particles comprising at least 50 wt.% ZrOi and ceramic particles comprising at least 40 wt.% AI2O3, preferably the ceramic particles are ceramic particles comprising at least 65 wt.% Z1O2, or a mixture of ceramic particles comprising at least 65 wt.% Z1O2 and ceramic particles comprising at least 50 wt.% AI2O3, more preferably, the ceramic particles are ceramic particles comprising at least 80 wt.% ZrO2, or a mixture of ceramic particles comprising at least 80 wt.% Z1O2 and ceramic particles comprising at least 75 wt.% AI2O3, more preferably, the ceramic particles are ceramic particles comprising at least 85 wt.% ZrO2, or a mixture of ceramic particles comprising at least 85 wt.% Z1O2 and ceramic particles comprising at least 90 wt.% AI2O3, more preferably, the ceramic particles are ceramic particles comprising at least 95 wt.% ZrO2, or a mixture of ceramic particles comprising at least 95 wt.% Z1O2 and ceramic particles comprising at least 99 wt.% AI2O3.

3. The insulating layer according to claim 2, characterized in that the ceramic particles comprise additives selected from CeC , Y2O3, SiCh, HfCh, MgO, CaO, TiCh, K2O, Na2<D, Fe2<D3 or mixtures thereof.

4. The insulating layer according to claim 1, characterized in that the insulating layer has a thickness of 0.5-10.0 mm, preferably 2.0-8.0 mm, more preferably 4.0-7.0 mm.

5. The insulating layer according to claim 1, characterized in that a size of the ceramic particles is 0.5-5.0 mm, preferably 1.0-4.0 mm, more preferably 1.5-2.5 mm, more preferably 2.0- 2.5 mm.

6. The insulating layer according to claim 1, characterized in that a difference between a maximum size of the ceramic particles and a minimum size of the ceramic particles is less than 0.2 mm, preferably less than 0.1 mm.

7. The insulating layer according to claim 1, characterized in that the ceramic particles have a polished surface.

8. The insulating layer according to claim 1, characterized in that the ceramic particles have a substantially spherical shape, a ball shape or have a shape of an elongated grain.

9. A method of installing rolls of rolled metals and alloys in a bell-type furnace, wherein an end of the roll to be installed in the furnace is placed on the insulating layer according to any one of claims 1-8.

10. The method according to claim 9, characterized in that the insulating layer is placed on supporting surfaces equipped with stops configured to limit spillage of the ceramic particles from the supporting surface.

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