RU2232665C1 - Method for continuous casting of metallic rectangular cross-section billets and apparatus for performing the same - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method comprises steps of feeding metal into working cavity of mold; cooling billet by means of water-cooled walls of mold realized at changing intensity of heat removal along width of each wall of mold due to lowered cooling intensity (from its maximum value in central part of walls until minimum value near wall edges) according to predetermined relationship. Apparatus includes mold with grooves in its walls for circulation of cooling water. Grooves of each wall have different pitch. Relation of total width of grooves to length of zone of arranging said grooves is variable along width of wall and it changes from maximum value in central part of wall until minimum value along wall edges according to predetermined relationship.

EFFECT: enhanced quality of continuously cast billet, uniform cooling of mold.

2 cl, 4 dwg

Description

The invention relates to the field of metallurgy, in particular to continuous casting.

A known method of continuous casting of steel billets of rectangular cross section, which consists in the formation and crystallization of steel in the working cavity of the mold formed by its walls, by cooling them with a calculated intensity. The intensity of the internal cooling system is calculated based on the heat sink Q necessary for crystallization along the length of the mold l at a given casting speed ν and the thickness of the crust δ. If we consider the average temperature of the solidified metal t, then the specific heat given off by the elementary mass of the melt during solidification:

where c _p , c _m - specific heat, respectively, of the melt and hardened metal;

ΔН is the heat of solidification, kJ / kg.

At a given casting speed (δ), the specific consumption of the hardened metal through a mold of length l and sides of walls B and b is:

The total heat flux discharged in the mold:

The cooling water of the internal system of the mold with a specific heat with _oh [kJ / kg · K], heating at Δt _ox , can divert this heat flux with a flow rate of:

[м³/ч].

[m ³ / h].

In accordance with the geometric dimensions of the working cavity (B, b), this flow rate is evenly distributed over the walls. Structurally, this is realized by a uniform step across the width of each wall and the dimensions of the cooling channels (2).

A disadvantage of the known method is that according to experimental data, with cooling uniform in the width of the mold wall, the thickness of the ingot crust is uneven within 25 ... 40%, increasing from the minimum value in the center to the maximum in the corners of the mold.

The resulting thickness variation of the solidified crust of the ingot and, as a result, the resulting transverse temperature gradients in the crust of the billet are the cause of the formation of longitudinal cracks that arise both along the surface and along the crystallization front.

The desired technical result of the claimed method for continuous casting of billets and a device for its implementation is to eliminate the above disadvantages by ensuring uniform cooling of the mold and obtaining a uniform billet crust thickness.

This is achieved by the fact that in the known method of continuous casting of metal billets of rectangular cross section, including supplying metal to the working cavity of the mold, cooling the billet with water-cooled walls of the mold with the calculated intensity and density of the heat sink according to the invention, cooling the billet in the mold is carried out with a change in the density of the heat sink along the width of each water-cooled walls by lowering the cooling intensity from the maximum value in the central part of the walls to mini minimum value to their edges according to the following relationship:

where P is the flow rate of water for cooling the mold wall, m ³ / h,

m _min = (0.6 ... 0.85) m is the value of the minimum wall cooling intensity with smaller values for large wall widths and with large values for smaller widths, m ³ / h,

M - the current value of the intensity of the cooling wall within: m _min ≤ M ≤ m, m ³ / h

To implement the continuous casting method, a device is proposed that contains a mold, in the walls of which grooves are made for cooling water circulation, grooves are made in each wall with different steps, the ratio of the total width of the grooves in sections to the lengths of these sections is variable in width from the maximum value along the central section of the wall to the minimum value along the edges of the wall according to the following relationship:

where H is the ratio of the total width of the grooves along the entire wall to its width,

b _min = (0.6 ... 0.85) · b is the ratio of the total width of the grooves of the section along the edges of the wall to its width with smaller values for large H and large values for smaller H;

R is the current value of the ratio of the total width of the grooves in the section to the length of this section in the range: b _min ≤ R ≤ b.

For the practical implementation of the proposed method, the cooling width of the wall is divided into sections, each of which has its own cooling intensity. The minimum value of the heat sink density is provided at the edges of the wall, the maximum - in the middle part.

As follows from the proposed relationship of the cooling intensity along the wall width (Δb = bb _min ):

where α is the angle corresponding to half the width of the wall (figure 2).

в (1), получим:Substituting Values

in (1), we obtain:

We square both sides, we get the equation:

whose solution:

Considering that the technological expression of the Δb value can be considered the value Δm = mm _min and the wall width b are the values of M and H, the resulting expression (4) can be presented in two versions:

which justifies the dependencies proposed by the invention.

The proposed method can be implemented in various ways, since it is possible to vary the cooling along the width of the face of the ingot due to the corresponding differentiation of the speed of movement of the cooler, changes in the calculated passage sections of the channels, and the sizes of the heat transferring faces of the walls of the molds.

The essence of the invention is explained below by the accompanying drawings.

Figure 1 - General view of the mold.

Figure 2 - section aa, figure 1.

Figure 3 is a section bB, figure 2.

Figure 4 is a sectional view of Figure 2, sectional view of the mold wall.

The proposed mold contains heat transfer working walls: wide 1 and narrow 2 of a material with a high coefficient of thermal conductivity, such as copper or bronze. Relative to the middle, each of the walls is divided into sections: B ₁ , B ₂ , B ₃ , B ₄ , B ₅ , B ₆ for a wide wall and b ₁ , b ₂ for a narrow one.

At each site, a different heat sink intensity is provided.

The heat flux diverted through a heat transfer wall of thickness δ is proportional to the heat sink area:

The heat sink intensity depends on what the total area F is the area irrigated by the cooler. Based on the unit height of the mold, it is permissible to operate only with the transverse dimensions of the heat sink wall. In this case, the change in the heat sink intensity, expressed as the ratio of the total width of the cooling grooves, measured along the wall in any adjacent sections (b _i , b _{i + 1} ), to their lengths is shown in figure 2 in the form of a diagram, i.e. the shaded area under curve 3 is along a wide face (width B) and under curve 4 is along a narrow face (width b).

As experimentally established, the greatest uniformity of the thickness of the crystallizing crust is achieved for large values of the intensity (P) of cooling the wall (water flow) and the ratio (H) of the total width of the grooves along the entire wall to its width - at lower ratios m and m _min , also b and b _min and vice versa.

At each site, a certain constant flow of water is carried out, proportional to the total width of the grooves. The change in water flow along the width of the wall, as shown in figure 2, is characterized by curves 3, 4, passing through the middle of each of the sections. However, this character extends to any other adequate points, for example, a curve can be built at the extreme points in the sections.

Each of the walls 1, 2 is pulled together with studs 5 and nuts 6 with the corresponding steel wall 7, 8, 9, 10 using the perimeter of the seal 11. Together, the walls are pulled together by bolts 12 using springs 13 and nuts 14. Regulation of the narrow walls is carried out using threaded rods 15, fixed relative to the housing by nuts 16.

Figure 2 conditionally made cuts in the area with collector grooves 17 in the steel walls for supplying and discharging water through openings 18.

The proposed method and the mold for its implementation will allow to obtain a workpiece with a uniformly thick crust, which will improve the quality of the workpiece.

Sources of information

1. A.S. No. 952422, cl. B 22 D 11/055, 1982

2. A.S. No. 1329897, cl. B 22 D 11/055, 1987 - prototype.

Claims (2)

1. The method of continuous casting of metal billets of rectangular cross section, including the supply of liquid metal into the working cavity of the mold, cooling the billet with water-cooled walls of the mold with the calculated intensity and density of the heat sink, characterized in that the cooling of the workpiece in the mold is carried out with a change in the density of the heat sink along the width of each water-cooled wall for due to a decrease in the intensity of its cooling from a maximum value in the central part of the walls to a minimum value I said to them on the edges of the following relationship:

where R is the flow rate of water for cooling the mold wall, m ³ / h; m is the value of the maximum intensity of the cooling wall, m ³ / h; m _min = (0.6 ... 0.85) m is the value of the minimum wall cooling intensity with smaller values for large wall widths and with large values for smaller widths, m ³ / h; M - the current value of the intensity of the cooling wall within: m _min ≤ M≤ m, m ³ / h 2. A device for continuous casting of metal billets of rectangular cross section, containing a mold, in the walls of which grooves are made for circulation of cooling water, characterized in that the grooves in each wall are made in sections with different steps, the ratio of the total width of the grooves in sections to the lengths of these sections varies along the width of the wall and varies from the maximum value along the central section to the minimum value along the edges of the wall according to the following relationship:

where H is the ratio of the total width of the grooves along the entire wall to its width; b is the ratio of the total width of the grooves of the Central section to its width; b _min = (0.6 ... 0.85) · b is the ratio of the total width of the grooves of the section along the edges of the wall to its width, with lower values for large values of H and large values for smaller values of H; R is the current value of the ratio of the total width of the grooves in the section to the width of this section within b _min ≤ R≤ b.

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