RU2308349C2 - Method for manufacturing molds of machines for continuous casting of billets - Google Patents

Abstract

FIELD: ferrous metallurgy, namely continuous casting of metals.

SUBSTANCE: method comprises steps of forming inner lining and parts of mold body having grooves on their surfaces. Grooves are formed by inclination angle relative to said surfaces and then body parts and lining are mutually compressed. At plastic deforming, material of lining partially fills inclined grooves whose inclination angles are in range 45 -70°. Protrusions arranged over grooves are also formed in lining in parts of body.

EFFECT: lowered consumption of copper, increased useful life period of molds, enhanced conditions for cooling ingots.

4 cl, 8 dwg, 1 ex

Description

The invention relates to ferrous and non-ferrous metallurgy and can be used in metallurgical plants and in foundries of engineering plants for the manufacture of molds for continuous casting of steel and non-ferrous metals.

In industry, for continuous casting of metals, composite precast molds are used, including an outer steel casing and an inner copper lining; sometimes from its alloys: bronze, brass (see US patent No. 4299267, NKI 164-502, MKI B22D 27/02).

Copper cladding is performed in the form of a closed pipe, sleeve or in the form of individual plates. At the same time, holes for supplying cooling water are made in the copper cladding or in the outer casing.

The fastening of the copper cladding to the steel casing with the help of studs is possible only with the thickness of the specified cladding over 30-40 mm. The use of such a cladding made of copper or its alloys leads to the appearance of significant thermal stresses in it, which helps to accelerate the wear of the cladding, its permanent deformations and significantly reduces the durability of the molds.

The closest analogue of this method is the method according to US patent No. 4949773 MKI5, B22D 11/04; NKI 164-91, adopted as a prototype. The method involves applying grooves on the inner surfaces of the parts of the steel body, then filling these grooves with wax. After connecting the copper cladding with the body parts with studs or welding, the wax is removed from the grooves by heating the mold in a special furnace.

In order to reduce the thickness of the copper cladding and thereby reduce thermal stresses in it, improve heat transfer from the ingot to the coolant (water), various mechanical devices, bolts, wedges, welding the cladding with the body with electrodes or explosion in special chambers are used. But a welded bimetallic structure, the basis of which is the connection of steel and copper, during heating and cooling during casting leads to significant thermal stresses and the development of cracks in the welds.

The connection of the copper cladding to the steel case by gluing or joint rolling of steel and copper sheets does not provide a reliable connection, and the appearance of gaps and cracks on the contact surfaces is dangerous due to the possibility of water leakage.

This method is aimed at solving the technical problem - to provide the possibility of reliable connection of the copper cladding with the details of the steel case while providing the possibility of reducing the thickness of the specified cladding, which will make it possible to reduce copper consumption and increase the durability of the molds of continuous metal casting machines.

This technical problem is solved due to the fact that the grooves on the surfaces of the steel parts of the mold body are inclined to the surfaces of the body parts in opposite directions, while the connection of the body parts with their inner lining is carried out by compressing them with plastic deformation of the lining and partially filling it with the material of these grooves in body parts. In addition, inclined grooves are performed with angles of inclination to their surface equal to 45-70 °.

On the surfaces of the parts of the inner lining, protrusions are made and placed above the corresponding grooves in the details of the housing, the width of the protrusion being 0.85-0.95 of the width of the corresponding groove; the grooves on the surfaces of the body parts are symmetrically relative to the normal passing through the center of the part, while the angles of inclination of the corresponding grooves are equal and oriented in opposite directions.

It is these distinctive features of the method that provide the solution to the technical problem and there is a direct causal relationship between the distinguishing features and the solution to the problem.

For parts of the inner lining of the mold thermal stresses during elastic deformation are equal to:

where E is the modulus of elasticity of the wall material;

α is its coefficient of linear thermal elongation;

Δt is the temperature difference across the wall thickness equal to:

where q is the specific heat flux in the stationary mode;

δ is the wall thickness;

λ is the coefficient of thermal conductivity of its material.

As a result, we obtain the value of thermal stresses equal to:

Having taken, for example, for copper, E = 1.5 · 10 ⁵ MPa; α = 10 ⁻⁵ g ^-1 ; q = 3 · 10 ⁶ W / m ² (the value of the specific heat flux at the meniscus, where it is maximum); δ = 2.5 · 10 ^-2 m; λ = 300 W / m · g (for copper), we obtain by the formula (3):

These are significant stresses, which, taking into account the stress concentration near corner points, for example, when using molds with corrugated (wavy) surfaces, can lead to the appearance of plastic deformations. Further, during cyclic loads from casting to casting, accumulation of residual deformations and distortion of the mold shape are possible.

In recent years, due to the widespread use of “under-level” steel casting technology with meniscus protection by slag or exothermic mixtures, crystallizers fail not due to wear of their walls, but due to permanent deformations, warping, and profile distortion (more often in meniscus, where the heat maximum flow). Sometimes thermal fatigue cracks occur. The decrease in the thickness of the copper cladding layer in this example from 2.5 · 10 ^-2 m to 1.2 · 10 ^-2 m reduces thermal stresses and strains by 2.08 times, i.e. up to 90 MPa, but this is also high voltage.

It is known that reducing the thickness of the copper lining reduces thermal stresses in it and improves cooling of the ingot. In the monograph by F.N. Tavadze, M.Ya. Brovman, Sh.D. Ramishvili and V.Kh. Rimen “The main directions of development of the continuous casting process” (Moscow: “Nauka”, 1982. - 217 pp.) It says: “ To achieve a high heat transfer rate, the walls of the mold must be thin and water-cooled. However, with an excessive decrease in the wall thickness, their rigidity decreases, as a result of which the effective life of the mold is reduced ”(see page 79 of this monograph).

Known methods for the manufacture of molds allow casting steel slabs to use copper plates with a thickness of at least 20-40 mm (depending on the size of the mold). In this case, the temperature differences along the wall thickness according to the formula (2) are equal to:

and thermal stresses σ = 150-300 MPa.

For high-grade ingots of small sections it is possible to use shell molds with a copper wall thickness of 6-15 mm.

The proposed method allows to reduce the thickness of the copper cladding to 1.5-2.5 mm while ensuring its tight connection with the surface of the steel casing and high structural rigidity. The joint compression of the body parts and the cladding with the metal of the cladding filling part of the area of the inclined grooves on the surface of the body ensures their tight connection and high rigidity and reliability, which can not be provided by studs, welding by electrodes or pressure, or gluing of these parts.

A feature of the method is that the specific design and location of the grooves allows you to firmly, reliably connect the copper and steel parts of the mold, to ensure high rigidity of the copper lining. The combination of parts by compression with plastic deformation of copper and partial filling of the grooves in it with a steel part reduces the consumption of copper and the cost of manufacturing molds.

The connection of the cladding with the steel casing, achieved by the implementation of the proposed method, is strong and reliable even with a very small thickness of the cladding. The method does not lead to the appearance of large residual stresses and warping, which is always possible when connecting parts by welding.

A device for implementing the method is illustrated by drawings (see figures 1-8); while figure 1, 2 shows a diagram of two operations during the implementation of the method, figure 3 is a diagram of the implementation of the method with the protrusion on the inner surface of the cladding in its area located above the groove in the steel part of the body. Figure 4 shows the location of the cladding section with a protrusion on its surface located above the surface of the steel casing, and Fig. 5 shows a diagram of filling the groove with the material of the cladding section after its plastic deformation. FIG. 6 shows the surface of a part of a steel mold body for casting slabs, and FIGS. 7 and 8 are cross-sections along planes A-A and B-B shown in FIG. 6.

The following notation is accepted here. The cladding part 1 made of copper or its alloys should be connected to the part of the steel casing 2, and this part can be made integral or composite and located in the outer bearing casing 3. On the surface of the part 2 inclined grooves 4 and 5 are made, here seal 6 and grooves 7, 8 are located.

The compression operation with plastic deformation of the cladding part is performed using the press plate 9. A protrusion 10 can be performed on the part of the copper cladding (on either of the two surfaces of the specified cladding part). An inclined groove 11 is made in the end part of the mold, and the groove 12 is for supplying cooling water to the mold.

Here is the operational description of the method. The first operation consists in the manufacture of cladding parts 1 from copper (or its alloys) and parts of the housing 2, for example, from rolled metal. After connection, these parts must be installed in the housing 3, forming one of the four walls of the rectangular mold. Parts 2 can also be made by forging or welding. Detail 2 in this example consists of two halves subjected to machining.

The second operation consists in the fact that inclined grooves 4 and 5 are made by milling (or planing) on the surface C of the part 2. After processing, the two halves of the part 2 are connected, with a rubber sealant in the plane of the connector. Symmetrically relative to the plane O ₁ -O ₂ (figure 1), grooves 4 and 5 are grooves 7, 8. They are also inclined, the angles of inclination of the grooves 4 and 8, 5 and 7 are equal in absolute value (modulo) and opposite in direction . It is this arrangement of grooves that ensures a firm connection of parts 1 and 2 when tensioning part 1 (creating tensile stresses in it is useful; when this part is heated during operation of the mold, tensile stresses in it are reduced).

The third operation consists in the fact that the part 1 is laid on the part 2 along the plane C and connected by joint compression with plastic deformation of the cladding part 1 and its partial filling of the grooves 4, 5 and 7, 8 in the part 2. Compression is carried out by the press plate 9. However, it is possible to carry out this plastic deformation also by joint rolling, or to compress individual sections along plane C in order to reduce the amount of force in each individual stage of deformation. The symmetry of the arrangement of the slots relative to the plane O ₁ -O ₂ provides a positive effect.

The grooves on the surface of the steel part 2 are performed symmetrically with respect to the center of the part, i.e. plane O ₁ -O ₂ (figure 1, 2) with the opposite direction of the angles, i.e. the angles of inclination of the grooves 4 and 8, as well as 5 and 7, are equal and opposite in sign, which ensures a firm connection of the parts 1 and 2. The angles between the side surfaces of the grooves and the contact surface of the copper and steel parts 1 and 2 are the angles α (Fig. 3, 4), which are taken equal to 45-70 °, so that the angle between the walls of the grooves and the normal to the contact surface of the parts 1, 2 (normal to the plane O ₁ -O ₂ (figure 4)) is β = 20-45 ° .

The use of grooves known in the art, as well as the joining of parts by compression, does not make it possible to reduce the thickness of the copper cladding and the high strength (and density) of the joint, which is ensured only when using these distinguishing features.

If we take an angle α less than the lower limit, i.e. less than 45 °, the flow of metal into inclined grooves will not occur over the entire cross section, since such a process will require more power than the flow along the contact surface of steel and copper parts (parts 1 and 2), and the flow process that requires less power (see, for example, Johnson V., Kudo X. Mechanics of metal extrusion. - M .: Metallurgy, 1965. - 176 p .; Kolmogorov V.L. Mechanics of metal forming. - M: Metallurgy, 1980. - 688 p.).

If we take an angle α of more than the upper limit equal to 70 °, then the angle of inclination of the groove surfaces to the normal to the contact surface of the copper and steel parts will be low, which will not ensure tight adhesion of these parts, especially in conditions of alternating heating and cooling; under such conditions, the mold wall is located during its operation on continuous metal casting machines, when it is heated during casting (up to 250-300 ° C in the area of the meniscus of liquid steel) and cooled between melt times.

Therefore, a decrease in the performance of the crystallizer occurs both when the upper limit of the angles α is exceeded, and when they are less than the lower limit, which proves the optimality of the specified range of angles.

An embodiment of the method is the execution on the surface of the cladding part 1 of the protrusions, i.e. local bulges located above the corresponding grooves in the details of the steel casing 2. These protrusions 10 can also be located on the surface of the part 1, opposite the contact surface with the part 2, i.e. on surface E (see FIG. 3), or on a surface adjacent to surface C of part 1 (see FIG. 4). The width of the protrusion ring b ₁ (Fig. 4) in this case is performed slightly less than the width of the groove at surface C, which, after plastic deformation is realized, ensures good filling of the groove (see Fig. 5). Figure 5 shows the width of the groove at surface C, equal to b ₂ , and take

b ₁ = (0.85-0.95) b ₂ .

If the width of the protrusion is less than 0.85 · b ₂ , then a gap may occur between the walls of the groove and the cladding metal that fills part of the groove after plastic deformation of the cladding part. Since it is provided that water is supplied into the groove to cool the walls of the mold, the presence of such gaps is unacceptable - it can cause water to leak into the mold. But you can not take the width of the protrusion b ₁ greater than 0.95 · b ₂ , as this can lead to a mismatch of the position of the protrusions and some grooves. Then, after plastic deformation, a part of the metal of the protrusions will not fall into the groove in the part 2, but will remain in the form of a fold between the parts 1 and 2, which will reduce the adhesion strength of these parts and may violate the tightness.

The above confirms the optimality of the proposed interval of the relationship between the values of b ₁ and b ₂ . The lateral surfaces of the grooves 4, 5, 7, 8, as well as 11 near the end surfaces are made not parallel, but inclined at angles of 5-10 °; therefore, the grooves are made tapering by increasing their depth. This provides a more tight connection of the cladding parts when they are jointly compressed with the body parts.

The protrusions 10 can be formed by machining during manufacture, but there will be a larger amount of waste with chips. It is better to manufacture parts 1 with protrusions on their surface forged or rolled. Some copper alloys may require processing after heating to 700-900 ° C. Joint compression of parts 1 and 2 can also be carried out after heating, depending on the choice of material.

In this mold, the grooves in the details of the case serve to solve not one, but two tasks: firstly, they are channels for supplying water, and secondly, these channels provide a tight and reliable connection of the inner lining, usually made of copper or copper alloys, and steel casing.

All the grooves after plastic deformation of the cladding parts 1 are only partially filled with the cladding material, as shown in FIG. 5 (as well as in FIGS. 7 and 8). The remaining unfilled part of the grooves forms channels through which water is circulated, which is necessary for cooling the mold. At the same time, water flowing at a speed of at least 2.5-3.0 m / s contacts not only with the steel body, but also directly with the facing surfaces in the grooves, which provides intensive cooling of both the mold and the ingot formed in it.

The connection of the details of the cladding and the body will be optimal if the grooves are made symmetrically relative to the normal to the contact surface passing through the center of the wall or surface area, i.e. relative to the plane O ₁ -O ₂ shown in figures 1, 2.

Of course, adhesion will also be achieved at different groove angles, unless they are the same in direction. But with a symmetrical arrangement, when the inclination angles of the corresponding grooves in each pair are equal in magnitude and oriented in opposite directions (from the plane O ₁ -O ₂ ), uniform stretching of the thin part of the cladding 1 is ensured, which creates its tight pressing against the part 2. If the grooves run obliquely directed plane to the O ₁ -O _2, then after plastic deformation of the lining 1 can be compression stress, which does not contribute to the tight contact parts 1 and 2. This may cause delamination of the part 1 with its small tol loss of stability.

The inclined arrangement of the grooves with their opposite directions on opposite sides of the symmetry plane of the part 2 ensures tightness and tightness of the connection. However, you can, in addition, apply conventional well-known seals, such as rubber cords, along the contour of a copper plate.

This method opens up the possibility of using not only copper, but also other materials (brass, bronze, and even steel or aluminum alloys) for facing the molds. Steels have a thermal conductivity coefficient that is approximately 10 times smaller than copper, and to ensure uniform heat fluxes, the steel sheet should be approximately 10 times thinner than the copper sheet. Instead of copper sheets with a thickness of 10-20 mm, it is necessary to use steel sheets of 1-2 mm, which is impossible with the known methods. This method allows the use of sheets even up to 0.5 mm thick with protrusions on their surface.

The fourth operation is final and it consists in machining the surface E, which is the working surface of the mold. It is subjected, for example, to polishing to ensure the required dimensional accuracy and surface cleanliness. In some cases, it will be possible to exclude this operation, to use the knurling of surface E with a roller.

After connecting the copper cladding 1 with the steel supporting part 2, it is possible to additionally coat the surface E of the copper using, for example, aluminizing, chromium plating or any other known coating process.

С учетом этого определим скорость воды в пазах

Такая скорость движения воды допустима (она не должна быть менее 2,5-3,0 м/с) и обеспечит эффективное охлаждение кристаллизатора.We give a specific example of the implementation of the method. We apply the method for the mold of the continuous casting machine of steel ingots with a section of 170 × 170 mm. Each mold wall has a width of 200 mm, while in the steel plate 2 a rectangular groove is made with dimensions of a section 18 × 25 mm — along the plane of symmetry and four inclined grooves 4, 5 and 7, 8 with dimensions of a cross section of 20 mm — groove width (bottom) and 25 mm - groove depth. The angle of inclination of the side walls of the grooves 5 and 7 to the plane C is 60 and 65 ° (the narrowing of the groove down is 5 °), and the grooves 4 and 8 are 45 and 50 °. The grooves 4 and 8, 5 and 7 are performed symmetrically with respect to the plane of symmetry O ₁ -O ₂ with opposite directions of the slope angles. On the copper billet 1, protrusions are made with a width equal to the width of the grooves in the part 2, i.e. 20 mm, a height of 7 mm, after which a blank 1 is applied with a thickness of 5 mm (excluding protrusions) and subjected to both parts of the joint compression deformation. In this process, the copper of part 1 partially fills the grooves in part 2 to a depth of 7 mm during plastic deformation, providing a tight connection of parts 1 and 2. The cross-sectional area in each of the grooves of the water channel will be 20 × (25-7) = 20 × 18 mm . The cross-sectional area of the groove is 2 × 1.8 = 3.6 cm ² or 3.6 · 10 ^-4 m ² . In total, there are five grooves in the wall with a total cross-sectional area of F = 3.6 · 5 · 10 ^-4 = 1.80 · 10 ^-3 m ² . The water consumption per meter of the perimeter of the cross section of the casting must (according to experimental data) be taken equal to 90-100 m ³ / hour. Taking the flow rate equal: Q = 100 (4 · 0.17) = 68 m ³ / h, we obtain the flow rate for each of the four walls: Q ₁ = 0.25 · Q = 17 m ³ / h. With a margin of 1.3, we take the flow rate equal to Q ₂ = 22.1 m ³ / hour or

With this in mind, we determine the speed of water in the grooves

Such a water velocity is permissible (it should not be less than 2.5-3.0 m / s) and will provide effective cooling of the mold.

Compression of part 1 together with part 2 is carried out to a thickness of copper part 1 equal to h = 2.5 mm The average specific pressure is equal to:

where b is the width of the plate, equal to b = 50 mm;

σ _t - yield strength of copper.

We believe that one fourth accounts for one full-width wall. Given the above, the specific pressure is equal to:

and at σ = 300 MPa, p = 1800 MPa.

With a total width of 200 mm and a length of the deformable section equal to 200 mm, the force will be:

P = p · 0.2 · 0.2 = 0.04 · 1800 = 72 MN

and for successive compression of a plate 0.8 m long in four stages (0.2 m sections), a press of P = 80 MN is required.

A smaller press can also be used by deforming in sections of shorter length. Part 2 can be performed not a composite of two parts, as shown in figures 1 and 2, but an integral of forgings or rolled products.

Composite part 2 is more difficult to manufacture, but allows for easier disassembly of the wall, for example, after the wear of the copper cladding 1 to separate it from the steel part 2. The smaller thickness of the copper part 1 (2-3 mm) will significantly reduce temperature drops and increase resistance and durability, will provide uniform cooling of the ingot. At the same time, in the grooves in which water flows, the thickness of the copper is higher, which ensures the reliability of the product.

The application of the method provides a reduction in copper consumption by 3-8 times and an increase in the durability of the molds, as well as intensive cooling of the ingots.

Claims (4)

1. A method of manufacturing molds of continuous metal casting machines, including making grooves on the surfaces of the steel parts of the housing and connecting the housing parts to the inner lining of copper or its alloys, characterized in that the grooves are inclined to the surfaces of the housing parts in opposite directions, the connection of the parts the case with the inner lining is carried out by compressing them with plastic deformation of the cladding and partial filling of the specified grooves in the details of the case with the cladding material. 2. The method according to claim 1, characterized in that the grooves are performed with tilt angles equal to 45-70 °. 3. The method according to claim 1, characterized in that on the surface of the inner lining perform protrusions and place them above the corresponding grooves in the details of the housing, while the width of the protrusion is 0.85-0.95 of the width of the corresponding groove. 4. The method according to claim 1, characterized in that the grooves on the surfaces of the parts of the body are symmetrically relative to the normal passing through the center of the part, while the angles of inclination of the corresponding grooves are equal and oriented in opposite directions.

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