RU2001712C1 - Supporting roller of secondary cooling zone of slab machine for continuous casting of slabs - Google Patents

Abstract

The invention relates to metallurgy, in particular to continuous casting machines for producing rectangular cross-section blanks. SUBSTANCE: device for supporting a workpiece of a secondary cooling zone of a slab of a continuous slab continuous casting machine includes a monolithic body with a working layer and a central (axial) channel for supplying a cooler. In this case, the channel for supplying a cooler is made in three stages, the diameters of the steps are related by the ratio: D D D. where 0, D, O are the internal diameters of the channel of the first, second and third stages, respectively, while the sizes of the steps satisfy the condition: I 038 V. R R / V, where I. - the length of the middle stage, mm; B - roller barrel length, mm; R is the radius of the first stage, mm; R is the radius of the second stage, mm The implementation of the invention will eliminate the elastic deflection of the support roller and / or create compression of the two-phase billet in the zone of the end of the liquid well and reduce the buckling of the hard crust of the two-phase ingot, which significantly improves the quality of the continuous billet. 1 ill.

Description

The invention relates to metallurgy, in particular to continuous casting machines for producing rectangular cross-section blanks.

A support roller for a continuous casting machine (CCM) is known, including a monolithic casing with a central cylindrical water-cooled channel. The design of the roller provides for uniform temperature distribution along the length of the barrel of the roller in the contact area of the roller with the cast billet and the concentration of the reaction forces of the roller supports at its ends, which leads to the deflection of the roller in the area of its contact with the forming two-phase billet under the action of the ferrostatic column of liquid metal and deterioration quality cast billets.

Also known is a roller of a continuous casting machine adopted for the prototype, which, in order to improve the quality of the workpiece by crimping, is shaped (trapezoidal profile) with a bulge in the center of the wide facet of the ingot. The disadvantage of this roller is the uneven effect on the ingot with the trapezoidal profile of the roller due to its deflection and removal of portions of the central part of the surface of its barrel from the axis of the ingot. Moreover, this drawback entails the redistribution of contact pressures along the contact line of the roller and the ingot and the occurrence of increased contact stresses in the areas of the formed workpiece adjacent to the vertices of the trapezoid of the roller. This increases the risk of hot cracks in the forming preform and increases the level of loads on the supporting elements (rollers) and their bearing bearings.

The present invention is aimed at solving the problem of improving the quality of cast billets by reducing the buckling of the billet and making it squeezed in the center of a wide face due to thermal deformation of the roller due to redistribution of temperature fields in it.

For this, in a device containing a monolithic casing with a working layer and a central (axial) channel for supplying a cooler, the channel is made three-stage, and the diameters of the steps are related by the ratio:

Di

where Di. Da Oz inner diameters of the channel of the first, second and third stages, respectively;

while the sizes of the steps satisfy the condition:

Pep 0 ,, R2 -,

where PCP is the length of the middle stage, mm; B - roller barrel length, mm; RI is the radius of the first stage, mm; Rg is the radius of the second stage, mm It is known that in the process of continuous

metal casting a two-phase billet under the action of a ferrostatic column of liquid metal experiences a deflection of the hard crust, which affects the quality of the ingot. The purpose of the supporting elements is to minimize the specified deflection. However, due to the need to comply with the principle of the location of the support rollers in the secondary cooling zone with a minimum

by an acceptable step, the rollers in contact with the two-phase billet experience some elastic deflection, which depends on the center of the roller in the stream (i.e., on the value of the ferrostatic pressure) and

is in the range of 2.0-3.0 mm. Deflection of the rollers, as well as buckling of the workpiece, degrades the quality of the forming ingot, because entails the appearance of cracks in the crystallizing layers of the metal at the solidification front and contributes to the occurrence of segregation processes in the metal. Attempts to install additional supporting elements to the already existing ones in the secondary cooling zone were not successful.

as this complicates the equipment and makes it difficult to access the main equipment during preventive scheduled repairs.

In contrast to the known devices, in the claimed supporting roller of the secondary cooling zone of the continuous casting machine, the channel for supplying cooler in the roller casing is made in three stages, moreover, DI Oz D2, where Di, D2, Oz are the diameters of the first, second and

third steps respectively. The cross section of the cooler supply channel causes a redistribution of the heat flux in the roller body. Its central part, corresponding to the width of the second stage,

gives less heat to the cooler than the edge sections. Higher heating of the layers of the central part of the roller corresponding to the second stage will lead to a change in the profile of the supporting

roller and creating a bulge in its central part. The indicated convexity, the profile of the barrels of the supporting rollers can be compensated for by the phenomenon of elastic deflection of the axes of the rollers and even the creation of compression of the workpiece over a wide face. The convexity height of the roll barrel profile thus created depends on the ratio of the diameters of the steps of the cooling channel. The creation of the maximum convexity of the roller barrel is most expedient for roller barrels supporting the workpiece in the zone of the end of the liquid well, where the thickness of the liquid phase is minimal and it is possible to compress the workpiece in order to close the opposing crystallization fronts and seal the axial layers of the forming ingot.

The length of the second stage is limited by conditions, the choice of which is determined by the following considerations. The compression of a two-phase preform is most advantageously carried out across the width of the liquid well without deforming the edge portions of the preform with a fully crystallized structure. Therefore, areas of a fully crystallized structure must be excluded from the reduction process.

It is known from the practice of metallurgical plants that in the process of continuous casting of billets of rectangular cross-section (slabs), the width of the cast billets with respect to the length of the barrels-supporting rollers is within B3 0.75 ... 0, where 63 is the width of the cast billets ; In - the length of the barrels of the supporting rollers.

In this case, the minimum boundary 0 is determined from the conditions of maintaining the stiffness of the guiding apparatus (no deflections of the rollers), and the maximum 0, takes into account the possibility of the workpiece being displaced relative to the casting axis during the beginning and end of casting. - These values determine the portion of the working length of the roller, which is in contact with the hot workpiece; -AT. In the course of experiments on the introduction of radioactive isotopes, conducted with the participation of the inventors in the CCC of the Azovstal casting slabs of various sections, it was found that the minimum width of the liquid well in the zone of the end of its crystallization with respect to the width of the preform (and, accordingly, with respect to the length the working section of the roller) is 0.50 ... 0 .. When choosing the length of the middle step when creating the roller, it is necessary to bear in mind the possibility of casting blanks from the whole assortment used in practice on the UNRS. Taking into account the indicated circumstance, the minimum area of adjustment of the position of the axis of the supporting roller, corresponding to the width of the liquid phase of the formed workpiece, must be limited by the condition

Shortly 0 ,, - 0., which ensures the inadmissibility of crimping the fully crystallized workpiece and guarantees no overloads

5 support rollers and their bearings. If the specified ratio is not fulfilled, for example, at Corr. 0, a situation may arise when casting ingots of minimum width, when, due to the adjustment of the axis of the roller, the completely crystallized region of the ingot is subjected to reduction. This can lead to overload and failure of the rollers and their bearing supports. In the case of Worr.

5 0, the thermal profile of the roller will not correspond to the distribution of loads from the ferrostatic pressure of the liquid phase, which reduces the efficiency of the claimed device.

0 The choice of the condition for the ratio of the diameters of the stages of the cooling channel is determined by the following considerations. Reducing the diameter of the cooling channel when the cooler moves from the first stage to

5, the second is associated with a decrease in the cross-sectional area, and accordingly, a decrease in the throughput of the cooling channel. In laboratory experiments on models of rollers with a stepped channel (when using water as a cooler and at flow rates typical of operating continuous caster), it was found that, provided the fluid is incompressible, coolants (water), and this condition corresponds to the practice of industrial casting, halving the cross-sectional area of the flow of cooler (x RI / 2 l x xR22) leads to water hammer,

0 at which the resistance to movement of the coolant flow sharply increases. Therefore, effective cooling of the roller using a stepped cooling channel is possible only under the condition R2 RI /

5 / v2 During the design and creation of the roller, it is possible to carry out its transitional part from the first to the second stage - conical in shape, or with a second order forming in the form of a curve, which additionally reduces the hydraulic resistance to fluid movement. At the same time, in the transitional part of the channel and in the cylindrical part of the second stage, a transition occurs from the laminar fluid flow to

5 turbulent, which not only does not impede the movement of the flow, but also improves the conditions of heat exchange with the roller due to the turbulization of the coolant flow. Failure to meet the condition R2 R1 / 2 can lead to a significant decrease in the rate of movement of the coolant flow along the channel of the roller, which violates the conditions of its cooling and can lead to overheating of its working surface, which is unacceptable.

The drawing shows the construction of a roller having a three-stage cooling channel,

The support of the forging and the roller of the secondary cooling zone of the slab continuous casting machine consists of a monolithic casing 1 with a working layer 2. The channel 3 for supplying cooler in the roller casing has three stages 4, 5, b. The transition part 7 from the first (from the supply side of the cooler) stage 4 to the second stage 5 is made in the form of a cone (7). The interface between the cylindrical part of the first stage 4 and the transition part 7 has a radius of curvature gc, providing optimal conditions for the movement of the coolant flow.

During the casting period, the coolant flow enters channel 3 and, moving sequentially along the non-slip stage 4,5, 6, it draws a certain amount of heat from the roller body 1 received from the forming ingot through the working layer 2. Moreover, the parts of the roller body corresponding to the stage m 4 and 6 of cooling, have a lower temperature in comparison with the central ones, which determines the value of their thermal expansion. The central part of the roller with a minimum diameter of the cooling channel, due to its thermal expansion, determines the deviation from the cylindrical shape inherent to the roller in the cold state. Moreover, the additional convexity of the roller, depending on the ratio of the diameters of the steps of the cooling channel, compensates for the elastic deflection of the roller or compresses the workpiece with rollers in the zone of the end of the liquid well.

Thus, the installation of rollers with a stepped cooling channel in the secondary cooling zone of the continuous casting machine makes it possible to ensure a higher quality of the workpiece in comparison with existing technologies.

Claims (1)

The claims SUPPORTING ROLLER OF THE SECONDARY COOLING ZONE OF THE SLAB SLOW MACHINE OF CONTINUOUS PREPARATION, comprising a monolithic body with a working layer and a central (axial) channel for supplying a cooler, characterized in that the channel for supplying a cooler in the roller case is made up of three steps, with a diameter of three steps the device can serve as a caster roller No. 4 of the KCC of the Azovstal steel mill with a diameter of 380 mm, designed to crimp the forming preform in the area of the end of the liquid well in the horizontal portion of the curved installation. The total length of the roller is 2600 mm. The barrel barrel length is 2050 mm. The length of the second stage of the cooling channel is 780 mm with a section of the cast billet 250 1650 mm. The length of the cylindrical part of the first and third stages of the cooling channel is 880 and 890 mm, respectively. The transition part between the first and second steps is made conical under the condition a --- 30 °. The mating between the cylindrical surface of the first stage and the surface of the cone is made with a radius of mating of the surface of 220 mm. The inner diameter of the first and second steps, respectively, 110 and 87 mm. The use of a roller with the specified parameters allows at speed castings of 0.75 m / min for a workpiece with a cross-sectional size of mm to obtain a compression of 1.88 mm from each roller in the cassette, which corresponds to a compression ratio of 1.5% over the height of the cross-section of the workpiece. Marked compression of the workpiece when installing rollers of the specified design in the zone of the end of the liquid well provides an improvement in the quality of the axial zone by eliminating the axial crack defect and reducing axial defect looseness. Thus, the claimed combination of distinctive features of the supporting roller of the secondary cooling zone of the slab continuous casting machine provides the task of improving the quality of continuously cast billets. (56) Institute of ferrous metallurgy. Dnepropetrovsk, 1986, 1-8, Manuscript deposited at the Chermetinformation Institute, 06/10/86 N 3429-FM. are related by Di Oz D2, where Di. D2, Oz - internal diameters of the channel, respectively, of the first, second and third stages. at the same time, the sizes of the steps satisfy the conditions 1av 0.38 V, R2 Ri / V2. where 1Ср is the length of the middle stage, mm; B - roller barrel length, mm; RI is the radius of the first stage, mm; RZ radius of the second stage, mm. .t t