Building a finishing gauge for round steel. Development of rational schemes of calibers of rolls of section mills
Vinogradov Aleks, head of a chair, candidate of technical science, associate professor
Marina Anatolyevna Timofeeva, candidate of technical science, associate professor
Cherepovets State University, Russia
Championship participant: the National Research Analytics Championship - "Russia";
A new technique for the analysis of roll calibration systems has been proposed section mills. As criteria, it is proposed to use the coefficients of non-uniformity and efficiency, which determine the degree of development of the structure during the rolling of profiles. On the example of calibration systems for the production of a round profile with a diameter of 28 mm, possible deformation schemes are analyzed, as well as the advantages and weak spots each of them.
Keywords: gauge systems, section rolling, efficiency criterion.
A new technique for the systems analysis ofsection mill roll’s calibrations was proposed. The following criteria for analysis were proposed to use: the coefficients of uniformity and coefficient of efficiency, they determine the maturity structure at the profile rolling. Example of calibration systems for the production of round profile 28 mm was analyzed for possible scheme of deformation, as well as strengths and weaknesses of each scheme.
keywords: system calibration, rolling of sections, the efficiency criterion.
Formulation of the problem. Building a rational calibration of the rolls of a section rolling mill is a difficult task. And its complexity is determined by the priority of one or another expected result. It is known that some calibrations are “sharpened” for the fastest possible shaping, others for a better study of the structure. Calibrations exist that provide more accurate cross-sectional dimensions or enable energy-efficient deformation modes.
Calibration systems known from literary sources have many varieties, subcircuits, and sometimes, solving one problem, significantly worsen the conditions of another. Therefore, the development of a methodology for analyzing a calibration system based on reasonable criteria is an urgent scientific task.
The methodology of the work. For the analysis of calibration systems, pairs of successive calibers were selected, which, on the one hand, allow us to consider all possible combinations of calibers, and, on the other hand, provide research into the division limit of a complex system, such as the calibration of rolls of a continuous section mill.
The non-uniformity coefficients are chosen as the system efficiency criteria K inf and efficiency To ede, which determine the degree of elaboration of the metal structure:
(1)
(2)
Where ? i= b i/ a i- component of the forming matrix;
a i, b i are the lengths of the radius vectors in i-th point of the cross section of the workpiece and the outgoing strip, respectively;
n- the number of radius vectors.
Coefficients of non-uniformity and efficiency of forming, which determine the degree of development of the metal structure, largely depend on the shape of alternating calibers, the ratio of the lengths of the axes of unequal calibers. The wrong choice of the ratio of the axes leads to the appearance of cracks and breaks in the strip during the rolling of profiles, especially from hard-to-deform steels.
There are two main stages in the process of rolling any section profile: rolling of a square continuously cast billet in the roughing and intermediate stands of the mill in order to obtain a roll of the required shape and dimensions for the finishing group of stands and rolling in the finishing stands. When constructing a rational calibration of the rolls of a rolling mill, it is necessary to strive to use the same calibers in the roughing and intermediate stands when obtaining rolled products of a wide profile assortment.
Yes, while rolling round steel with a diameter of 25-105 mm and hexagonal steel No. 28-48 on the medium-section mill "350" CherMK JSC "Severstal" used calibration systems differ only in the finishing and some intermediate stands.
Let's try, based on the criteria for the efficiency of forming, to analyze the development of the structure for various calibration systems. As an example, consider the rolling of round steel with a diameter of 28 mm.
When modeling, the following conditions were taken as boundary conditions: ensuring the capture of the strip by rolls, i.e. ? i ≤ [?] i , ensuring the stability of the roll in the caliber and ensuring the required width of the roll.
Work results. The results of mathematical modeling for possible combinations of calibers are presented in the form of graphical dependencies in Figures 1-4.
Coefficient K inf(Fig. 1) characterizes the non-uniformity of metal deformation along the cross section of the profile. Greater value coefficient indicates a greater non-uniformity of such deformation when obtaining the same profile and, as a result, better workability of the metal structure. For the compared calibration schemes, non-equiaxed gauges known from the literature (for example, oval, rhombic), with different ratios of the axes, were used.
Rice. 1. Coefficient of integral non-uniformity of forming K inf:
1- oval-circle; 2 - flat oval-circle; 3 - oval-square; 4 - oval-rib oval;
5 - rib oval-oval; 6 - rhombus square.
When rolling a round profile in a finishing pair of calibers, it is possible to use the oval-circle and flat oval-circle systems. As shown in figure 1 (lines 1,2) the value of the maximum value of the coefficient K inf 1.4-1.5 times more when used as a pre-finishing flat oval caliber.
Thus, from the point of view of a better study of the structure, the flat oval-circle system is the most preferable. In doing so, it must be taken into account that this system in the production of small-sized round steel, it requires a high accuracy of setting the mill to eliminate defects in the round profile “mustache” or “lampas”, as well as “flat edges” arising from overfilling or underfilling of calibers.
In the production of round and hexagonal steel, intermediate and pre-finishing stands often use ribbed oval gauge systems, such as oval-ribbed oval and ribbed oval-oval. In these systems, as studies have shown, the value of the coefficient of uneven shape change K inf largely depends not only on the ratio of the axes of a single-radius oval gauge (Fig. 1, lines 4 and 5), but also on the ratio of the axes of the ribbed oval. As the simulation results showed, best conditions deformation is provided by the “rib oval” caliber, the shape of which is close to a circle, i.e. the ratio of the axes of the rib oval in the intermediate and pre-finishing stands is 0.94-0.96. With such a ratio of the axes of the rib oval, the area of high-altitude deformation becomes commensurate with the area of transverse deformation, which leads to an increase in the value of the coefficient K inf. By changing the ratio of the axes of the rib oval from 0.75 to 0.95, the shape change coefficient changes from 0.038 to 0.138. In the task of rolling an oval shape with an axis ratio of 1.5 to 2.65 into an oval rib pass, the ratio of the axes of which is 0.95, the coefficient K inf changed from 0.06 to 0.31. Thus, the intensity of growth of deformation unevenness in the rib oval-oval system is greater than in the oval-rib oval system.
In the intermediate stands of a section mill, in the production of a round profile, it is possible to use the oval-square gauge system, in which, as shown by modeling, the ratio of the axes of the oval roll can be 1.5 times greater than in the oval-circle system at the same elongation ratios. This leads to more than a doubling of the coefficient K inf(lines 1, 3 Fig. 1), which provides a better study of the metal structure.
In the rhombus-square gauge system, which can also be used in intermediate stands, the coefficient of integral shape change unevenness is approximately 3 times less than in the oval-square system, since the ratio of the axes of the rhombic gauge can be 1.2-1.8, and the oval gauge 2-2.7. Such a ratio of the axes of the rhombic caliber is due to the restriction on the capture condition. Therefore, in the production of round steel, it is more expedient to use an oval-square caliber system as an exhaust one.
Analysis of data on the coefficient of efficiency of deformation in the elements of the caliber To ede(Fig. 2), which makes it possible to assess how rational this system of calibers is in terms of elongation, shows that the maximum coefficients occur in the oval-square system (Fig. 2, curve - 3), the value of which, on average, is 2 times higher than the values of the coefficients To ede for other systems.
When comparing the oval-circle and flat oval-circle systems (Fig. 2, lines 1 and 2), it can be seen that the deformation is more effective in the oval-circle system, where the value of the coefficient To ede with the same ratios of the axes of oval calibers, 1.5-1.8 times more.
Rice. 2. Form change coefficient K ede: 1- oval-circle; 2 - flat oval-circle;
3 - oval-square; 4 - oval-rib oval; 5 - rib oval-oval; 6 - rhombus square.
When using a ribbed oval pass, the coefficient of deformation efficiency in the elements of the pass is greater when rolling in the oval-ribbed oval system than in the latter ribbed oval-oval system (Fig. 2, lines 4 and 5). So, changing the ratio of the axes of the rib oval from 0.75 to 0.95 in the rib oval-oval system, the coefficient of shape change K ede varies from 0.06 to 0.11. In the task of rolling an oval shape with an axis ratio of 1.5 to 2.65 into an oval rib pass, the ratio of the axes of which is 0.95, the coefficient K ede changed from 0.017 to 0.154.
Thus, the intensity of growth of the deformation efficiency in the oval-ribbed oval system is greater than in the ribbed oval-oval system.
Taking into account the noted regularities in the distribution of the coefficients of shape change in various systems of calibers, four variants of calibration schemes for intermediate, pre-finishing and finishing stands of the 350 medium-section mill when rolling round steel with a diameter of 28 mm are proposed (see Table 1). The proposed options differ in the systems of calibers in the intermediate and pre-finishing stands. In all variants, the maximum possible coefficients of forming efficiency were obtained K inf And To ede on the stands of the mill "350" when the boundary conditions are met.
The distribution of efficiency coefficients by mill stands is shown in fig. 3, 4. To compare the proposed options, the average values of the coefficients of shape change were calculated K inf, To ede and drawing ratio for six stands of mill No. 7-12. The calculation results are presented in Table 2.
From Table. 2 shows that the maximum average value of the coefficient K inf takes place in variant 4 when using the oval-rib oval gauge system in intermediate stands, the maximum average value of the coefficient To ede and elongation ratio in variant 2, when using the oval-square and oval-circle systems.
Thus, rolling using the calibration scheme of option 4 will provide the maximum workability of the metal structure compared to other options, and hence the minimum grain size of the metal structure of the finished profile.
The third option is characterized by the minimum average values K inf And To ede, which ensures minimal energy consumption and can be recommended for the assortment subjected to subsequent heat treatment, leveling the difference in the resulting structures.
Fig.3. The distribution of the coefficient of shape change K inf during rolling of a round profile with a diameter of 28 mm on the mill "350".
Rice. Fig. 4. Distribution of the coefficient of form change K ede during rolling of a round profile with a diameter of 28 mm on the mill "350"
Table 1 - Options for sizing rolls of a medium-section mill "350" in the production of a round profile with a diameter of 28 mm.
caliber form |
|||||||
1 option | box (1,2) | flat oval (2.25) | |||||
Option 2 | box (1.6) | ||||||
3 option | box (1.5) | rib oval (0.96) | |||||
4 option | box (1,2) | rib oval (0.96) | rib oval (0.96) | ||||
Note: () - the ratio of the axes of the unequal caliber
Table 2 - Average values of deformation indices and coefficients of form change during rolling of a round profile according to various calibration schemes
option parameter * | ||||
TO inf c p | ||||
TO ede Wed |
* - ?cp 7-12 - average hood for stands No. 7-12; ? ? - total extract for stands No. 7-12
Option 2 is a compromise and can be used to obtain profiles with low requirements for the structure, but allows to reduce energy costs for rolling profiles.
Conclusion. Thus, the analysis and modeling of the calibration of the rolls of the section mill "350" by varying such parameters as the ratio of the sides of non-equiaxed calibers (oval, rib oval) and the elongation coefficients in the pre-finishing and finishing stands showed the possibility of developing rational calibration schemes according to the criteria "better workability of the structure" or "maximum energy efficiency".
Literature:
1. A.I. Vinogradov, S.O. Korol On the issue of creating calibration rolls that increase the efficiency of production of profiles from hard-to-deform materials / Bulletin of Cherepovetsky state university. - 2010.- №3(26).- p.116-120
2. B.M. Ilyukovich, N.E. Nekhaev, S.E. Merkuriev Rolling and calibration. Reference book in 6 volumes, volume 1, Dnepropetrovsk, Dnepro-VAL.-2002
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Dear Alexey Ivanovich and Marina Anatolyevna! Let's talk right away. In order to give a competent commentary on this report, one should be at least an expert in the field of rolling production. And since we are not such, we are forced to comment on the report from the position of just metallurgists. In our opinion, in connection with the constantly growing requirements for improving the efficiency of section rolling mills, the choice of a rational system (scheme) for sizing rolls is an important problem for manufacturers. The simpler and more accessible its solution, in this case, through the use of mathematical modeling, the greater its attractiveness for factory workers. The authors chose one of the most important parameters of efficiency - the degree of elaboration of the metal structure, characterized by two coefficients: unevenness and efficiency (the indexes of the coefficients are incomprehensible - "inf." and "ede"). Of course, it was possible to choose several parameters at once as an optimality criterion, for example, related to minimizing costs: the minimum energy consumption for deformation, the minimum number of passes and tilts, the minimum wear of calibers, etc. But, obviously, this would complicate the solution of the problem, although and would optimize it more. Without knowing anything about other available methods for calculating roll calibration systems for section rolling mills, it is difficult to assess the degree of its novelty and advantages. However, it is important that the methodology developed by the authors made it possible to determine rational calibration schemes for a particular mill of a particular enterprise. In the development of the work and to confirm the effectiveness of the schemes determined as a result of modeling and the performed calculation, it is possible to recommend the authors to carry out real rolling with metal sampling to determine the microstructure (grain size, etc.), successively at various stages of metal advancement in the rolling process (after ferrous, intermediate and finishing group of stands). In addition, in our opinion, in order to improve the quality of manufactured metal products and improve rolling conditions, it is advisable to contact steelworkers in this direction, since the latter have a large arsenal of tools that ensure the optimization of the structure and level of physical and mechanical properties of cast CW. Obviously, it is important, together with them, to select the optimal profile (for example, a square with rounded corners, etc.) in terms of shortening cycles and “facilitating” subsequent rolling operations. But this is so - the reflections that your report led us to. It was nice to be in the section not alone. Good luck on your way to improving technological parameters and rolling modes. Titova T.M., Titova E.S.
This is not the first attempt to use the coefficient of efficiency and unevenness in the calibration of rolls of rolling mills. But in the long case there is a deep system analysis in combination with a mathematical justification. One can only welcome the efforts of the author in our time, when interest in technical science is waning. A. Vykhodets
Goal of the work: familiarization with the principles of sizing rolls for rolling square and round profiles.
Theoretical information
I. General issues of roll sizing.
Long products are obtained as a result of several: consecutive passes, the number of which depends on the ratio of the sizes and shapes of the initial and final section, while in each pass the section changes With a gradual approach to the finished profile.
Rolling of section metal is carried out in calibrated rolls: i.e. in rolls with special cutouts corresponding to the required configuration of rolled stock in a lath pass. Annular cut in one roll / fig. 4".L/ is called stream I, and the gap between two streams located one above the other working together, taking into account the gap between them, is called gauge 2.
Rolling in calibers, as a rule, is an example of a pronounced non-uniform deformation of the metal and V most cases by constrained broadening.
When calibrating rolling rolls, the amount of reduction by passes has to be taken simultaneously with the determination of the successive shapes and sizes of the calibers /Fig. 42.2/, providing high-quality rolled products and accurate profile dimensions.
Gauges used in rolling are divided into the following main groups depending on their purpose.
Crimp or draw gauges - designed to reduce the cross-sectional area of the billet mm mm. Drawing calibers are square with a diagonal arrangement, rhombic, oval. A certain combination of these calibers forms caliber systems, for example, rhombus-square, oval-circle, etc. /Fig.42.3/.
Rough go preparatory calibers", in which, along with a further reduction in the section of the rolled product, the profile is processed with a gradual approximation of its dimensions and shapes to the final section.
Finishing or finishing gauges , to complete the profile. The dimensions of these calibers are 1,2...1,5% more finished profile; the allowance is given for the shrinkage of the metal when it is cooled.
2. Caliber elements
Gap between rolls. The height of the caliber is the sum of the depth of the virez in the upper h t and lower h2, rolls and magnitudes S between rolls
During rolling, the pressure of the metal tends to push the rolls apart, while the gap 5 increases, which is called the recoil, or spring, of the rolls. Since the gauge drawing is displayed 
compresses its shape and dimensions at the time of the strip passage, then the gap between the rolls when installed in the stand is reduced less than the gap indicated in the drawing by the amount of return of the rolls. At the same time, it is necessary to take into account the fact that during operation the distance between the rolls change in steel grade, wear of rolls, etc. / have to be changed in order to adjust the mill. This setting can be carried out if there is a gap between the rolls, which is accepted for shrinking mills I...I.5%, for other mills 0.5..1 %
on the roll diameter.
Issue caliber. The side walls of the box caliber / fig. 42.3 "have some slope To roll axes. This inclination of the walls of the caliber is called release. During rolling, the release of the pass provides a convenient and correct insertion of the strip into the pass and the free exit of the strip from the pass. If the walls of the caliber are perpendicular to the axis of the rolls, a strong pinching of the strip would be observed, and there would be a danger of binding the rolls, since broadening almost always accompanies the rolling process. Typically, the release of the caliber is squeezed in percent /~ 100 %/ or in degrees µ and is accepted for box gauges 10..20%
Top and bottom pressure It is very important during rolling to ensure a straight exit of the strip from the rolls. For this purpose, wires are used, since during rolling there are reasons that caused the strip to bend towards the upper and lower rolls, this requires the installation of wires on the lower and upper rolls. But this setting
can be avoided if the strip is given a certain direction in advance, which is achieved by using rolls with different diameters. The difference between the diameters of the forks is conventionally called "pressure", Will the diameter of the upper roll is larger, they speak of "upper pressure" / fig. 42.4/,
if the diameter of the lower roll is assumed to be large, then in this case there is "neither 
lower pressure". The pressure value is expressed as a difference in diameters in millimeters. For long sections, they tend to have an upper pressure of more than I %
from the average diameter of the rolls.
The dimensions and tolerances of the caliber are somewhat different from the dimensions and tolerances of the rolled profile, which is explained by the different coefficients of thermal expansion of metals and alloys when heated. For example, sizes finishing gauges for hot rolling steel profiles should be 1.010-1.015 times the size of the finished profiles.
The dimensions of the calibers increase during rolling, which is due to their development. Upon reaching dimensions equal to the nominal plus tolerance, the caliber becomes unsuitable for further work and is replaced with a new one. Therefore, the greater the tolerance on the dimensions of the profile, the longer the service life of the calibers, and, consequently, the productivity of the mills. Meanwhile, the increased tolerance leads to an excessive consumption of metal for each meter of the length of the products. It is necessary to strive to obtain profiles with dimensions that deviate from the nominal in a smaller direction.
In practice, calibers are built not with positive ones, but with average tolerances or even with some minus. The improvement of rolling mill equipment, the improvement of production technology and the introduction of automatic equipment for setting rolls will contribute to the production of rolled products with increased accuracy.
GOST 2590-71 provides for the production of round steel with a diameter of 5 to 250 mm.
The rolling of this profile, depending on the steel grade and dimensions, is carried out in different ways (Fig. 116).
Methods 1 and 2 differ in the options for obtaining a pre-finishing square (the square is precisely fixed diagonally and it is possible to adjust the height). Method 2 is universal, as it allows you to get a number of adjacent sizes of round steel (Fig. 117). Method 3 is that the prefinishing oval can be replaced by a decagon. This method is used for rolling large circles. Method 4 is similar to method 2 and differs from it only in the shape of the rib gauge. The absence of sidewalls in this caliber contributes to better descaling. Because this way allows wide adjustment of the dimensions of the strip coming out of the rib gauge, it is also called universal gauge. Methods 5 and 6 differ from the rest in higher hoods and greater stability of the ovals in the wiring. However, such calibers require precise adjustment of the mill, since even with a small excess of metal, they overflow and form burrs. Methods 7-10 are based on the use of an oval-circle sizing system.
A comparison of possible methods for producing round steel shows that methods 1-3 make it possible in most cases to roll the entire range of round steel. Rolling of quality steel should be carried out according to methods 7-10. Method 9, as it were, is intermediate between the oval-circle and oval-oval systems, it is most convenient in terms of regulating and adjusting the camp, as well as preventing sunsets.
In all considered methods of rolling round steel, the shape of the finishing and pre-finishing passes remains almost unchanged, which contributes to the establishment of general patterns of metal behavior in these passes for all cases of rolling.
The construction of a finishing gauge for round steel is carried out as follows.
Determine the estimated diameter of the caliber (for a hot profile when rolling to minus) d g \u003d (1.011 ÷ 1.015) d x - part of the tolerance +0.01 d x, where 0.01d x, - magnification diameter for the above reasons; d x \u003d (d 1 + d 2 / 2) - the diameter of the round profile in the cold state. In practice, when calculating the second and third members of the right side of the equality can be considered approximately the same, then
d g \u003d (1.011 ÷ 1.015) (d 1 + d 2) / 2,
where d 1, d 2 are the maximum and minimum allowable diameter values according to GOST 2590-71 (Table 11).
Depending on the size of the rolled circle, the following angles of inclination of the tangent α are chosen:
We accept the value of the gap t (according to rolling data), mm:
Based on the data obtained, a caliber is drawn.
Example. Build a finishing gauge for rolling round steel with a diameter of 25 mm.
- Let's determine the calculated diameter of the caliber (for a hot profile) according to the equation above.
We find from the table: d 1 \u003d 25.4 mm, d 2 \u003d 14.5 mm; whence d g \u003d 1.013 (25.4 + 24.5) / 2 \u003d 25.4 mm. - We choose α=26°35′.
- We accept the gap between the rolls t=3 mm.
- Based on the data obtained, we draw a caliber.
Pre-finishing gauges for a circle are designed taking into account the accuracy required for the finished profile. The more the shape of the oval approaches the shape of a circle, the more accurately the finished round profile is obtained. Theoretically, the most suitable profile shape to obtain the correct circle is an ellipse. However, such a profile is rather difficult to hold at the entrance to the finishing round gauge, so it is used relatively rarely.
The flat ovals hold the wires well and, in addition, provide large swages. But the thinner the oval, the lower the accuracy of the resulting round profile. This is due to the degree of broadening that occurs during compression. The broadening is proportional to the compression: where there are small reductions, there is also a small broadening. Thus, at small reductions of the oval, the possibilities of size fluctuations in a round gauge are very small. However, the opposite phenomenon is true only for the case when a large oval and a large hood are used. The oval for small sizes of round steel is close in shape to the shape of a circle, which makes it possible to use an oval of single curvature. The profile of this oval is outlined with only one radius.
For round profiles medium and large ovals, outlined by one radius, are too elongated along the major axis and, as a result, do not provide a reliable capture of the strip by the rolls. The use of sharp ovals, in addition to not providing an accurate circle, adversely affects the stability of the round gauge, especially in the output stand of the mill. The need for frequent replacement of rolls sharply reduces the productivity of the mill, and the rapid development of calibers leads to the appearance of second grades, and sometimes marriage.
The study of the causes and mechanism of the development of calibers produced by N.V. Litovchenko showed that the sharp edges of the oval, which cool faster than the rest of the strip, have significant resistance to deformation. These edges, entering the caliber of the finishing stand rolls, act on the bottom of the caliber as an abrasive. Rigid edges at the tops of the oval form hollows at the bottom of the gauge, which lead to the formation of protrusions on the strip along its entire length. Therefore, for round profiles with a diameter of 50-80 mm and more, a more accurate profile execution is achieved by using two- and three-radius ovals. They have approximately the same thickness as an oval outlined by one radius, but due to the use of additional small radii of curvature, the width of the oval decreases.
Such ovals are flat enough to hold them in wires and provide a secure grip, and a more rounded contour of the oval, approaching the shape of an ellipse in its shape, creates favorable conditions for uniform deformation across the width of the strip in a round gauge.
Rolling on the projected casting and rolling module with a planetary cross-roller mill is carried out in 13 stands, which are conditionally, as shown in Fig. 7, allocated in following groups: crimping (in the form of a planetary stand), roughing (in the amount of 6 stands), intermediate (of 4 stands) and 2 finishing groups (2 stands each).
In the reduction planetary cross roll stand, rolling is performed from a round cast billet into a round rolled product with a large degree of deformation.
Further rolling of high-precision round high-strength alloy steel with a diameter of 18mm is carried out as follows.
In the roughing group of stands, rolling from a round billet into an oval profile is carried out according to one of the systems drawing calibers ok - system oval - ribbed oval, which is most suitable for the production of round profiles of high precision from high-strength alloy steels.
The necessary transition to the rhombic and square shape of the roll with subsequent longitudinal separation is carried out in special calibers of the preparatory group of stands according to the recommendations and methods.
And, finally, in the finishing groups of rolling stands, each thread of the separated roll is produced according to the square-oval-circle system, which is widely used for converting a square section into a round one (for rolling low-grade round steel.
Calculation of the calibration of round steel with a diameter of 18 mm is performed against the rolling stroke.
Calculation of calibers of the finishing group of mill stands. For rolling round steel, several calibration schemes are used, which are applied depending on the size of the profile, the quality of the steel, the type of mill and its assortment, as well as other rolling conditions. However, in all cases, the pre-finishing gauge is either a regular one-radius oval or a flat oval. But pre-finishing one-radius oval calibers with axes ratio = 1.5 are more widely used, and for good stability in a round caliber, the oval profile must have a significant bluntness. The preparatory gauge is a separating gauge that produces two diagonal rolls.
With all rolling methods, the finishing round pass is performed with a “camber” - release to prevent overfilling of the pass and obtain the correct round profile. The construction of such a round gauge is shown in Fig. 14.
Fig.14.
When designing a finished round gauge, it is necessary to take into account the thermal expansion of the metal and the tolerances for deviations in the dimensions of the finished profile.
The construction of a round caliber is as follows. On the circumference of the diameter, rays drawn from the center of the gauge at an angle to the horizontal axis will determine the start points for the release of the sides of the gauge and determine the width of the gauge.
To calculate the diameter of the profile in the hot state in the finishing stand of the mill (stand 13th), the expression is used
=(1.0121.015)(+) (1)
where is the diameter of the profile in the cold state;
Minus tolerance
The calculation will be made when rolling 30KhGSA alloy steel into a high-precision round profile. And, then, according to GOST 2590-88, the tolerances will be: + 0.1mm and -0.3mm, and the profile diameter in the hot state will be
1.013 (18-) = 18.1 mm.
The width of the finishing pass (according to Fig. 14) will be
Where is the outlet angle, which in practice for round steel diameters of 10-30 mm is 26.5
And then = = 20.22 mm.
The gap between the collars of caliber - S is chosen within (0.080.15) and then,
S = 0.111.81 = 2.0 mm.
The points of intersection of the gap lines S with the outlet line determine the width of the stream entry, which is defined as
Substituting the values we get
20.22 - = 18.22mm. (3)
The rounding of the collars is performed with a radius
= (0.08 - 0.10) and then
0.008518.1 = 1.5mm.
The profile will be round if the width =. In this case, the degree of filling of the caliber - will be
A correctly made round profile in the finishing pass of the 13th stand will have a cross-sectional area
The finishing group of stands has both groups of stands with a nominal diameter of rolls of 250 mm, while the finishing (13th) - horizontal rolls, and the pre-finishing (12th) - vertical rolls.
So, the finishing (13th) stand has a round caliber, the pre-finishing (12th) stand has a single-radius oval caliber, and the preparatory caliber (11th) stand is a dividing double diagonal square.
The nominal diameter of the rolls of the 11th stand, already included in preparatory group stands is 330mm.
The rolls of the finishing and pre-finishing group of stands are made of chilled cast iron. The rolling speed in the finishing stand of the mill for high-precision round sections made of high-strength alloy steels is taken to be about 8 . Rolling temperature 950°C.
To determine the elongation ratio in a finishing pass, you can use the formula , which has the form
1.12+0.0004 (6)
Where - corresponds to the diameter of the finishing caliber in the hot state, i.e. =
1.12=0.0004 1.81 = 1.127
The broadening in the finishing circle is determined by the formula, which has the form
?= (7)
Where D is the nominal diameter of the rolls, mm.
1.81=2.3mm.
As a pre-finishing gauge, a simple one-radius oval gauge can be used, the construction of which is shown in fig. 15
Fig.15.
To construct the caliber, the dimensions of the height of the oval caliber and width are used, determined in accordance with the reduction mode adopted in the calculation of the sizing. Practical calibrations use ovals with a size ratio
Prefinishing oval area
257.3 1.127=290. (8)
The thickness of the pre-finishing oval =, is defined as
18.1-2.3=15.8mm. (9)
Prefinishing oval width
26.2mm. (10)
Compression in finishing pass
26.2-18.1=8.1mm. (eleven)
Grip angle in finishing pass
Arccos(1-)=arccos(1-)=15°19" (12)
The permissible gripping angle can be determined by the method, taking into account the values of the coefficients for the oval-circle rolling scheme according to the formula
where v - rolling speed, ;
Coefficient taking into account the state of the surface of the rolls (for cast-iron rolls = 10);
M - coefficient taking into account the grade of rolled steel (for alloy steel M=1.4);
t is the temperature of the rolled strip, ?;
The degree of filling of the previous caliber in the course of rolling;
K b; ; ;; ; ; - the values of the coefficients determined for various rolling schemes (drawing passes) are determined according to the table; for the oval-circle system (=1.25; =27.74; =2.3; =0.44; =2.15; =19.8; =3.98).
We take the degree of filling of the pre-finishing oval caliber = 0.9
And, then the maximum allowable value of the capture angle in the finishing gauge will be
Because the<, условия захвата в чистовом калибре обеспечивается.
The ratio of the axes of the oval profile specified in the finishing gauge is
With the degree of filling of the pre-finishing oval caliber = 0.9, we find the width of the pre-finishing oval caliber
29.1mm. (15)
Gauge shape factor is defined as
The radius of the outline of the stream oval caliber
17.4mm. (16)
Let us determine the permissible ratio of the axes of an oval strip according to the condition of its stability in a round caliber according to the method according to the formula
Where: ; ; ; ; ; - values of the coefficients determined for the oval-circle rolling scheme, determined from the table (
Since, the profile stability conditions are met.
The gap S along the shoulders of the oval caliber is accepted according to within (0.15-0.2)
S=0.16=0.16 15.8=2.5mm. (18)
Radii of rounded corners in oval gauge = (0.1-0.4).
The blunting of an oval gauge in practice is most often
0.2 15.8=3.2mm (20)
The cross-sectional area of one of the preparatory squares in the double dividing gauge of the 11th stand can be determined as for a conventional diagonal square gauge.
And then, its area will be equal to
The stretch ratio of the preparatory square in the oval caliber of the 12th stand can be determined according to the recommendations of the methodology. So, according to this method, it is recommended to determine the total elongation ratio when rolling a square in an oval and round caliber from a graph depending on the diameter of the resulting round steel. With a given diameter of round steel equal to 18 mm, the total drawing ratio will be = 1.41. And since
The area of the given square is determined by the formula (21) and will be
290 1.25=362 .
The construction of a standard diagonal square caliber is shown in Fig. 16
Rice. 16.
The apex angle must be 90° and =. The filling degree of the square gauge is recommended 0.9. Approximately can be taken
And then the side of the square of caliber - c will be
19.2mm. (25)
The corner radius of the square gauge is defined as
=(0.1h0.2) = 0.105 19.2 = 2mm (26)
The rounding of the rebellion is performed with a radius, which is defined as
= (0.10x0.15) = (0.10x0.15) = 0.11 19.2 = 3mm. (27)
The height of the profile emerging from the square gauge will be slightly less than the height of the gauge due to the rounding of the tops with a radius, and then
0.83= 19.2-0.83 2=25.5mm (28)
As already noted, the caliber in the 11th stand is a double diagonal square caliber in which the separation is rolled. Construction and general form this caliber is shown in Fig. 17. In the same figure, the contour of the outline of the roll from the 10th stand entering this caliber is superimposed.
Fig.17.
Longitudinal separation of the multifilament roll by controlled rupture is carried out by creating tensile stresses in the jumper zone under the action of axial forces from the side surfaces of the ridges of two-strand calibers embedded in the metal, as can be shown in Fig.18.
Fig.18.
At the moment of capture, due to the crushing of the rolled surface by the inner side faces of the grooves of the caliber, a normal force N and a friction force T arise. The resultant of these forces can be decomposed into transverse Q and vertical P components. Under the action of the force P, the metal is compressed by the rolls, the force Q contributes to the extension of the bridge in the transverse direction and causes the appearance of a force of resistance to tension of the bridge S and a force of resistance to plastic bending of the extreme workpiece towards the connector of the gauge G.
By measuring the thickness of the jumper of the specified roll - and the gap between the crests of the rolls - t of the separating caliber (see Fig. 17), it is possible to change the radius of curvature of the front ends of the divided profiles at the exit from the rolls and to the conditions for separating the roll. The absence of a jumper neck at the point of separation of the profiles makes it possible to obtain a high-quality surface of the finished profile with a minimum number of subsequent passes with compression of the separation points. In this regard, the method of longitudinal separation of rolled stock by controlled rupture is recommended for use in the finishing stands of rolling mills.
Studies of the longitudinal separation of a two-strand roll by a controlled break have shown that the thickness of the web of the roll given into the separating stand should be equal to 0.5x0.55 of the side of the square.
The study of the gap between the crests of the rolls affects the change in the curvature of the front ends of the divided square profiles when leaving the rolls. So, the straightness of the output was obtained with a gap of \u003d 16 mm equal to the thickness of the jumper, then we select
From the practice of calculating calibrations during rolling-separation of square profiles, the compression ratio of the sides of a square profile is taken within 1.10-1.15. And then, from the expression (choosing) we determine the side of the square in the 10th gauge
19.2 1.125=21.6 mm. (29)
The area of the dividing double caliber of the 11th stand is actually equal to twice the area of the calculated diagonal square.
And then (30)
The distance between the axes of the streams in the caliber of the 11th stand - , is determined as
The length of the jumper between the streams in this caliber is defined as
As mentioned above, the thickness of the lintel in the 10th stand can be determined as
In order to check for capture of the rolled product entering the caliber of the 12th stand, it is necessary to calculate the absolute reduction in this caliber and compare it with the allowable data.
When a square profile enters an oval gauge, the absolute reductions in the middle and edges of the profile will be different and are determined geometrically by superimposing the section of the square profile on the oval gauge and will be in the middle of the gauge
Compressions at the extreme points of a square in an oval caliber, based on geometric transformations, will approximately be ?.
As can be seen, these absolute reductions are less than the absolute reductions in the 13-gauge and, therefore, with the same nominal diameter of the rolls and the same material, a check for permissible grip conditions is not required.
In view of the foregoing, the construction and general view of the preparatory pass in the 10th stand (before rolling-separation) can be shown in Fig.19.
Fig.19.
Some dimensions of the caliber can be determined as follows: we take the length of the jumper based on the existing calibrations during rolling-separation;
corner radius of the square gauge in this stand
The value can be determined according to Fig. 17 by the formula
The height of the roll, leaving the caliber of the 10th stand
The distance between the axes of the streams in the caliber of the 10th stand - , is determined as
The size of the gap along the collars of the caliber in the 10th stand is taken mm.
The area of the roll coming out of the caliber of the 10th stand can be determined according to Fig. 17, as
Substituting the values of the indicated parameters, we obtain
The area of the undivided roll in the caliber of the 11th stand is equal to twice the area of the diagonal square roll, i.e.
And then, the elongation ratio in the caliber of the 11th stand is defined as
Theoretical roll width coming out of the 11th stand
Theoretical width of the roll coming out of the 10th stand (with a curvature radius at the collar = 5)
In order to check for capture of the rolled product entering the caliber of the 11th stand, it is necessary to calculate the absolute reduction at the characteristic points of the caliber and compare it with the allowable data.
So, the value of absolute compression in the region of the jumper of a two-strand roll will be
and in the region of the break of the axes of the streams will be
alloy steel rolled casting module
So, as you can see, here it requires a check for the condition of capture of the region of the roll bar.
The angle of capture in the region of the bridge during rolling in the caliber of the 11th stand can be determined as
where: D is the nominal diameter of the rolls in the 11th stand (D = 33mm).
The permissible angle of capture in this caliber can be determined by the method of M.S. Mutiev and P.L. Klimenko, this requires a rolling speed in this stand, which will be
5.67 m/s, (45)
and then the maximum allowable angle of capture is determined by the formula (t = 980?)
Since, the capture conditions in the 11th separating gauge are met.
The gauge in the 9th stand of the intermediate group of stands is located in vertical rolls and may to a large extent resemble a diagonal square gauge, but has its own characteristics. It is intended for rolling rhombic rolls and has a more constrained shape in the parting area than a conventional diagonal caliber. Rolling in this caliber provides for the deformation study of the future side horizontal parts of the two-strand rolled products, which will be subjected to rolling-separation. In view of the foregoing, the construction and general view of this preparatory caliber in the 9-stand can be presented in Fig.20.
Fig.20.
To determine a number of gauge parameters, we use some empirical dependences obtained in similar gauges during rolling-separation.
So, the side of the square, as for the 10 gauge, can be defined as
The value representing the middle part of the caliber is recommended to be taken as 40% of the diagonal part of the caliber.
Based on practical data, we take the slope of the shoulders in the middle part of the caliber within 25%, this allows us to obtain the maximum width of the roll.
The width of the diagonal square part of the caliber will be
Based on the practical data of calibrations for rolling-separation, we accept the radii of curvature at the tops of the calibers and at the collars to be the same and equal to 5 mm, i.e. mm.
The thickness of the caliber of the 9th stand will be
The thickness of the roll coming out of the caliber of the 9th stand
Also, on the basis of practical data, the size of the gap along the shoulders of the caliber is taken to be 5 mm, i.e. mm.
The area of the roll coming out of the 9th stand can be defined as
and then, substituting the values of the indicated parameters, we obtain
The elongation ratio in the caliber 10-stand is defined as
In order to check for the capture of the roll entering the caliber of the 10th stand of the roll, it is necessary to calculate the absolute reduction in this stand.
Since the shapes of the calibers of the 9th and 10th stands differ greatly in configuration, we will replace their area with the reduced (rectangular shape), where the width of the strip will be equal to the width of the roll, and the thickness of the reduced strip can be determined
The given value of the absolute reduction will be
The given value of the capture angle in the caliber of the 10th stand will be
As can be seen, the given capture angle is significantly less than the previously calculated maximum values for similar conditions and, therefore, the capture condition must be met.
The most appropriate form of 8-stand pass is a rhombic pass located in horizontal rolls. The construction and general view of this caliber is shown in Fig.21.
Fig.21.
The dimensions and rhombic caliber are determined in the process of calculating the sizing, taking into account the given value of the elongation coefficient in the caliber, the correct filling of the caliber, and also taking into account the receipt of cross-sectional dimensions that satisfy the rolling conditions in the next caliber.
In practice, rhombic calibers are used, characterized by a value.
To prevent the formation of "lamps" in the gaps of the caliber, it is recommended to take the degree of filling of the calibers
We determine the maximum allowable angle of capture in this caliber according to the formula of M.S. Mutiev and P.L. Klimenko, if v=3.9m/s; t=990? and steel rolls according to the formula , at v=2-4m/s
and then the value of the maximum absolute reduction will be
When rolling a rhombic billet in square gauge(conditionally, one can consider rolling a rhombic roll in the 9th gauge). The side of the reduced square can be defined as
The possible width of the roll coming out of the rhombic caliber of the 8th stand will be
We accept the drawing ratio in the 9th gauge, you can calculate the area of the roll in the 8th gauge as
And then, the thickness of the roll coming out of the rhombic caliber of the 8th stand will be
The broadening of a rhombic strip in a square gauge if the side of the square (diagonal) gauge is >30mm is determined by the following formula.
and then, substituting the values, we get
Taking into account the broadening, the width of the roll in the 9th gauge should be
and as you can see, such a roll from a rhombic caliber in a square one can be rolled without overfilling the caliber, because and as you can see.
The remaining dimensions of the rhombic caliber are determined from the following empirical recommendations
The ratio of the diagonals in the caliber is calculated
The size of the gap at the caliber connector is taken equal to 5 mm, i.e. .
Theoretical height of a rhombic caliber - can be determined by the formula
Blunting - a rhombic strip at the gauge connector is defined as
Theoretical width of a rhombic gauge - defined as
The vertex angle - in can be defined as
From (74)
at = 2 arctan1.98 = 126.4°
Side of a rhombus - defined as
In the roughing group of stands, consisting of 6 duo working stands with alternating horizontal and vertical rolls, the rolling of a round billet with a diameter of 80 mm, coming from a swaging planetary stand, is rolled through an oval-ribbed oval drawing pass system. This system has become widespread in the rolling of round steel of increased accuracy from alloyed and high-strength steels on continuous mills.
In the 7th stand of the roughing group, the gauge is a rib oval located in vertical rolls. The construction and general view of this caliber are shown in Fig.22.
Fig.22.
The drawing ratio in the rhombic caliber of the 8th stand of rolled out in the form of a rib oval, based on practical data, can be recommended in the range of 1.2-1.4. And then, the rolled area emerging from the caliber in the form of a rib oval in the 7th stand will be
The total elongation ratio in the draft group of stands will be
where is the area of the round roll coming out of the planetary crimping stand, .
Previously, on the basis of practical foreign data, it was shown that, taking into account the deformation in the planetary stand of continuously cast billets with a diameter of 200 mm, the roll coming out of this stand should have a circular section with a diameter of 80 mm.
The average elongation ratio in this caliber system will be
Usually, as practice shows, in a ribbed oval caliber, the hood is within the limits, and in oval calibers, the hood is usually higher. And then, taking the hood in ribbed oval calibers, it is recommended to calculate the hood in oval calibers according to the formula
In the 2nd stand, the circle must be rolled in an oval caliber, which leads to a decrease in the elongation ratio and then
At the ratio, the roll becomes unstable when rolling in a ribbed oval caliber. Usually use ovals with a ratio. In ribbed oval gauges, the ratio between the height and width of the gauge is
Let us determine the permissible angle of capture in the rhombic caliber of the 8-stand, if v = 3.4 m/s; t=995? and cast-iron rolls, according to the formula in the range v = 2-4m/s.
And then, the value of the maximum absolute reduction at, will be
The thickness of the roll coming out of the 7th stand will be and is determined as
The width of the roll coming out of the 7th stand will be and is determined as
The radius of the oval is determined by the formula
The rounding of the shoulder is performed with a radius
We take the size of the gap
The value of the blunting of the oval at is determined equal to the value of the gap i.e. mm.
The general layout of the drawing calibers of the roughing group of mill stands is shown in Fig.23.
Fig.23.
So, as you can see, in the 6th stand, the caliber is oval and is located in horizontal rolls.
The area of an oval of this gauge is defined as
The oval caliber is made single-radius and schematically does not differ in any way from the previously considered oval caliber in the chit group of stands (see Fig. 15).
Oval gauge height
where is the broadening of the oval strip in the ribbed oval gauge, it is recommended to determine by the formula
where D is the diameter of the rolls, equal to 420mm
Peel width coming out of the oval gauge
As you know, the area of an oval caliber is
Formula (93) can be represented as quadratic equation, whose solution allows us to determine
after opening the brackets we get
And then, the absolute compression in the ribbed oval gauge of the 7th stand will be mm.
Let us determine the permissible angle of capture in the rib oval of the 7th stand, if v = 2.8m/s; t=1000? and steel rolls and then, according to the formula in the range of 2-4 m / s, the permissible grip angle will be
And then, the value of the maximum allowable compression at.
As you can see, the capture conditions are met, and the broadening will be.
The final dimensions of the oval in the caliber of the 6th stand will be
The remaining dimensions of the oval gauge will be: the radius of the streams is defined as
The gap S along the collars of the caliber will be
Corner radius
As can be seen from Fig. 23, in the 5th stand, the gauge represents a ribbed oval and is located in vertical rolls.
Calibration of rolls in pairs of calibers of the 4th and 5th stands, 2nd and 3rd stands is carried out similarly to the above calculations for the calibration of calibers of 6th and 7th stands and, according to the general layout of the calibers (see Fig. 23), in the 2nd stand the caliber is performed in the form one-radius oval and is located in horizontal rolls. In this caliber, it is supposed to roll a round profile with a diameter of 80 mm, coming from a planetary 3-roll crimping stand with an oblique arrangement of rolls.
The drawing ratio in the oval caliber of the 2nd stand will be
Where is the cross-sectional area of a round roll (diameter 80 mm) coming from a planetary crimp stand.
The absolute reduction along the vertices in the oval caliber 2-stand will be
The average absolute reduction when rolling a circle in an oval caliber of the 2nd stand will be
When rolling a round billet in an oval caliber, the broadening can be determined using the approximate formula
The possible width of the roll in the oval caliber of the 2nd stand will be
which, as you can see, is somewhat smaller and, therefore, there will be no overflow of the caliber.
The calibration of the crimping oblique planetary stand consists in the installation of inclined conical rolls, which, when rotating around its axis and planetary movement, should form a gap with the necessary inscribed circle (in this case, 80 mm in diameter) at the exit of the roll from the rolls, and similarly with the necessary inscribed circle (diameter 200mm) at the entry of the billet into the rolls. The task of sizing rolls includes determining the length of the deformation zone, which is determined by the conical part of the roll, the angle of inclination of the rolls, and the diameter of the rolls.
The general scheme of the deformation zone, indicating the calibration parameters of inclined conical rolls necessary for the rolling of the billet under consideration, is shown in Fig. 24.
Determining the parameters indicated in the diagram is the task of calibrating the rolls of the reduction planetary roll stand.
Fig.24.
The dimensions shown in Fig. 22 characterize the following parameters:
Distance from the rolling axis at the crossing point;
The same, but total along the axis of the roll;
and - respectively, the radii of the workpiece and rolled products;
The angle of inclination of the generatrix of the cone of the deformation zone;
The angle of inclination of the forming surface of the roll;
W - the angle of crossing the roll with the rolling axis;
Accordingly, the roll radii at the pinch, sizing section and maximum (at the billet inlet);
A - tangential displacement of the roll (not shown in the figure).
Based on practical data obtained from the design conditions and experience of such mills, it is recommended to select some elements and parameters of roll calibration within the following limits:
(i.e. roll diameter at the nip);
(i.e. maximum roll diameter);
W \u003d 45-60 ° (i.e. we take the crossing angle w \u003d 55 °);
the angle between the line of centers of the billet shaft and the projection line of the roll u = 45°.
Elongation ratio in the 1st stand
The remaining two working rolls of the reduction stand have the same dimensions as those presented above for the calculated roll.
In the calibration calculations, the parameters of the roll speed and temperature by stands were used.
Thus, the exit speeds from the stands were calculated by the formula
And then, taking the speed of the finished roll (in the form of a circle with a diameter of 18 mm) from the last stand of the mill 8 m / s, we get:
The billet entry speed into the 1st (planetary) stand will be approximately 7.9 m/min.
The total temperature change of the metal during rolling can be determined by the formula
Where and - lowering the temperature of the metal due to the release of heat by radiation and convection to the environment;
Decrease in metal temperature due to heat transfer by thermal conductivity in contact with rolls, wires, roller tables;
An increase in the temperature of the metal due to the transition of the mechanical energy of deformation into heat.
And then, based on the use of the method, the change in the temperature of the roll during the rolling in the caliber and moving to the next caliber will be
Where is the roll temperature before entering the considered caliber, ?;
P - the perimeter of the cross-section of the roll after the passage, mm;
F - cross-sectional area of the roll after the passage, ;
f - cooling time of the roll, s;
The temperature increase of the metal in the caliber, ? and is determined by the formula
p is the resistance of the metal to plastic deformation, MPa;
m is the elongation factor.
So, for example, the change in the temperature of the metal during the movement of the workpiece from the heating furnace to the 1st stand of the mill according to the formula (200) will be (if the heating temperature of the workpiece, f=, P=p 200=628mm, F=31416)
The increase in metal temperature in the 1st (planetary) stand due to severe deformation can be determined by formula (201) assuming p=100MPA and then
Finally, the temperature of the metal after rolling in each stand, taking into account the change in the temperatures of the roll, calculated by formulas (107) and (108) and the practical corrections made, will be: and
The main dimensions of the roll and calibration parameters when rolling a circle with a diameter of 18 mm from a billet with a diameter of 200 mm along the mill stands are shown in Table 3.
Table 3. Basic calibrations for passes when rolling a circle? 18mm from a billet? 200mm.
|
passage number |
Type of caliber |
Roll arrangement |
Peel size |
Compression, mm |
Broadening, |
Gauge area, F, mm |
Coef. Hoods, m |
Tem-ra roll, t,? |
Rolling speed v, m/s |
Note |
|
|
Thickness, h |
|||||||||||
|
Initial conditions: |
Heating temperature |
||||||||||
|
3 roll |
Inclined |
Kosovalk. Planets. Crate. |
|||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
vertical |
||||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
vertical |
||||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
vertical |
||||||||||
|
Horizontal |
|||||||||||
|
Diagon. square type |
vertical |
||||||||||
|
double diagonal. square type |
Horizontal |
||||||||||
|
Double diagonal square |
Horizontal |
Separation of the roll in the caliber |
|||||||||
|
Single radius oval |
vertical |
45° tilt |
|||||||||
|
Horizontal |
Calculation schemes of roll calibers for all stands of the mill when rolling a circle? 18mm from a continuously cast billet? 200mm are shown in fig. 25.
1,06
1,05
1,04
1,03
1,02
1,01
0 1.0 1.2 1.3 1.4 1.5 1.6 1.7 1.8 h / b
Figure 1.5 - Graph of the stability of the strip during rolling on a smooth barrel depending on h / b and ε
1) describe the manufacturing technology of blooms; sequence of operations; characteristic parameters.
2) draw sketches: blooms, models of ingots, side faces, distortions of sections, etc.
Control questions
1 What is included in the main task technological process rolling production?
2 What is a technological scheme for the production of rolled products?
3 What is a semi-product of rolling production?
4 What do you know technological schemes production of semi-finished products and finished products?
5 What technological schemes for the production of rolled products can be organized using the processes of continuously cast billets?
6 What is roll gauge, roll gauge and smooth barrel?
7 What is the maximum reduction and its effect on rolling?
8 What is the roll angle and its effect on rolling?
9 Under what conditions is the strip turning carried out?
10 How are the broadening and stretching of the rolled strip found?
11 What is strip stability and what indicator is it characterized by?
Laboratory work No. 2. Studying the methods of sizing rolls for rolling simple section profiles
2.1 Purpose of work
Familiarize yourself with the systems of gauges for obtaining a round and square profile, mastering the methods for calculating the main calibration parameters.
2.2 Basic theoretical information
Calibration is the order of rolling a successive series of transitional sections of rolled profiles. Calibration calculations are carried out according to two schemes: in the course of rolling (from the billet to the final profile) and against the rolling stroke (from the final profile to the billet). For both schemes, in order to calculate and distribute the deformation coefficients over gaps, it is necessary to know the dimensions of the original workpiece.
The rolling of section profiles begins in drawing calibers, i.e., calibers connected in pairs, designed for metal drawing. Different schemes of crimping and drawing calibers are used, for example, box, rhombus-square, rhombus-rhombus, oval-square, etc. (Figure 2.1).
Of all crimp (pull) calibers, the most common is the box caliber scheme. Often there is a scheme of a smooth barrel - a box caliber.
 |
a) - box; b) - rhombus - square; c) - rhombus - rhombus; d) - oval - square
Figure 2.1 - Schemes of drawing calibers
When rolling medium - and low-grade steel, the rhombus-square gauge scheme is widely used. The scheme of geometrically similar rhombus-rhombus gauges, in which after each pass the roll is turned over by 90 °, is used quite rarely. Rolling according to this scheme is less stable than in the rhombus–square scheme. It is mainly used for rolling high-quality steels, when small reductions are made under the conditions of plastic deformation with a drawing up to 1.3.
The oval-square drawing scheme is one of the most common and used on medium-, small-section and wire mills. Its advantage over other schemes is the systematic updating of the roll angles, which helps to obtain the same temperature over its cross section. The roll behaves stably when rolling in oval and square calibers. The system is characterized by large extracts, but their distribution in each pair of calibers is always uneven. In the oval caliber, the hood is larger than in the square one. Large hoods make it possible to reduce the number of passes, i.e. increase the economic efficiency of the process.
Consider the calibration of rolls for some simple and shaped profiles of mass production, for example, round profiles with a diameter of 5 to 250 mm and more are obtained by rolling.
Rolling of round profiles is carried out according to different schemes depending on the diameter of the profile, type of mill, rolled metal. Common to all rolling schemes is the presence of a pre-finishing oval pass. Before the task of the strip in the finishing gauge, it is turned over by 90 °.
Usually the shape of the pre-finishing gauge is a regular oval with a ratio of the lengths of the axes 1.4 ÷ 1.8. The shape of the finishing pass depends on the diameter of the rolled circle. When rolling a circle with a diameter of up to 30 mm, the generatrix of the finishing pass is a regular circle; when rolling a circle of a larger diameter, the horizontal size of the pass is taken 1-2% more than the vertical one, since their temperature shrinkage is not the same. The drawing ratio in the finishing pass is assumed to be 1.075÷1.20. Round profiles are rolled only in postings in one pass in the last - finishing caliber.
The so-called universal scheme for rolling a round strip along the square-step-rib-oval-circle system is widespread (Figure 2.2). When rolling according to this scheme, it is possible to control the dimensions of the strip emerging from the rib pass over a wide range. In the same rolls it is possible to roll round profiles of several sizes, changing only the finishing pass. In addition, the use of a universal rolling scheme provides good descaling from the strip.
1 - square; 2- step; 3 - rib; 4 - oval; 5 - circle
Figure 2.2 - Scheme of rolling profiles of circular cross section
When rolling a round profile, relatively small sizes Often a square-oval-circle caliber scheme is used. The side of the pre-finishing square, which significantly affects the production of a good round profile, is taken for profiles of small sizes equal to the diameter d , and for profiles of medium and large sizes 1.1 d.
When calculating the roll sizing of continuous mills, it is especially important to determine the rolling diameters. This allows the rolling process to be carried out without the formation of a loop or excessive strip tension between the stands.
In rectangular calibers, the rolling diameter is taken equal to the diameter of the rolls along the bottom of the caliber. In rhombic and square - variable: the maximum at the gauge connector and the minimum at the top of the gauge. The circumferential speeds of various points of these calibers are not the same. The strip exits the groove with a certain average speed, which corresponds to the rolling diameter, which is approximately determined by the average reduced height of the groove
font-size:14.0pt">In this case, the rolling diameter
font-size:14.0pt">Where D - the distance between the axes of the rolls during rolling.
The simplest calibration calculation is for mills with individual roll drives. In this case, the overall elongation ratio is determined
,
(10
)
where Fo ~ cross-sectional area of the original workpiece;
fn is the cross-sectional area of the rolled profile.
Then, taking into account the relation 
distribute the hood over the stands. Having determined the rolling diameter of the finishing stand rolls and assuming the required rotational speed of the rolls of this stand, the calibration constant is calculated:
font-size:14.0pt">where F 1 ... Fn - cross-sectional area of the strip in stands
1, ..., n; v 1 ,...vn are the rolling speeds in these stands.
The rolling diameter of the rolls when rolling in a box caliber
EN-US" style="font-size:14.0pt">2)
Where k- caliber height.
When rolling in square calibers
font-size:14.0pt"> (13 )
Where h - side of a square.
After that, the dimensions of the intermediate squares, and then the intermediate rectangles, are determined from the hoods. Knowing the calibration constant WITH, determine the frequency of rotation of the rolls in each stand
n= C / FD1 (14 )
Square profiles are rolled with sides from 5 to 250 mm. The profile may have sharp or rounded corners. Usually a square profile with a side of up to 100 mm is obtained with non-rounded corners, and with a side of more than 100 mm - with rounded corners (the radius of curvature does not exceed 0.15 of the side of the square). The most common rolling system is square-rhombus-square (Figure 2.3). According to this scheme, rolling in each subsequent caliber is carried out with 90° canting. After tilting the roll, which has left the rhombic caliber, its large diagonal will be vertical, so the strip will tend to tip over.
Figure 2.3 - Scheme of rolling a strip of square section.
When constructing a finishing square gauge, its dimensions are determined taking into account the minus tolerance and shrinkage during cooling. If we designate the side of the finishing profile in the cold state as a1, and the minus tolerance is ∆a and take the coefficient of thermal expansion equal to 1.012 ÷ 1.015, then the side of the finishing square caliber
font-size:14.0pt">where a are the hot sides of the square profile.
When rolling large square profiles, the temperature of the workpiece corners is always lower than the temperature of the edges, so the corners of the square are not straight. To eliminate this, the angles at the top of the square gauge are made larger than 90° (usually 90°30"). At this angle, the height (vertical diagonal) of the finishing gauge h \u003d 1.41a, and the width (horizontal diagonal) b = 1.42a. The margin for broadening for squares with a side of up to 20 mm is assumed to be 1.5 ÷ 2 mm, and for squares with a side of more than 20 mm 2 ÷ 4 mm. The extract in the finishing square caliber is taken equal to 1.1÷1.15.
In the production of a square profile with sharp corners, the shape of the pre-finishing rhombic pass is essential, especially when rolling squares with a side of up to 30 mm. The usual form of diamonds does not provide squares with corners of the correct form along the parting line of the rolls. To eliminate this drawback, pre-finishing rhombic calibers are used, the top of which has a right angle. The calculation of the square profile calibration starts with the finishing gauge, and then the dimensions of the intermediate drawing gauges are determined.
2.3 Methods for calculating the calibration parameters of simple profiles
2.3.1 Rolling a round profile with a diameter d = 16 mm
In calculations, be guided by the data in Figure 2.4 (Section 2.4).
1 Determine the area of the finishing profile
qcr1 = πd2 / 4, mm2 (16)
2 Select the elongation ratio in the finishing pass µcr and the total elongation ratio in the round and oval calibers µcr s within µcr = 1.08 ÷ 1.11, µcr ov = 1.27 ÷ 1.30.
3 Determine the area of the pre-finishing oval
qw2 = qcr1 µcr, mm2 (17)
4 Approximately take the broadening of the oval strip in the round gauge ∆b1 ~ (1.0 ÷ 1.2).
5 Pre-finishing oval dimensions h2 = d - ∆b1, mm
b2 = 3q2/(2h2 +s2);
where the depth of cut in the rolls (Figure 2.4) is hvr2 = 6.2 mm. Therefore, the gap between the rolls should be equal to s2 = h2 - 2 6.2, mm.
6 Determine the area of the pre-finishing square (3rd gauge)
q3 = qcr µcr ov, mm2 hence the side of the square c3 = √1.03 q3 , mm,
and the height of the caliber h3 = 1.41 s3 - 0.82 r, mm (r = 2.5 mm), then according to Figure 2.4 we determine the depth of the cut of the 3rd caliber into the rolls hvr3 = 9.35 mm, therefore, the gap is 3 - eat caliber s3 = h3 – 2 hvr3, mm.
∆b2 = 0.4 √ (с3 – hov avg)Rks (с3 – hоv avg) / s3 , mm/ (18)
where how cf = q2 / b2 ; Rks \u003d 0.5 (D - hov cf); D – mill diameter (100÷150 mm).
Check the filling of the prefinishing oval pass. In case of overflow, a smaller draw ratio should be adopted and the size of the pre-finishing square should be reduced.
8 Check the total draft between the workpiece with side C0 and square c3 and distribute it between the oval and square gauges:
µ = µ4 ov µ3 kv = С02 / s32 (19)
We distribute this total hood between the oval and square calibers in such a way that the hood in the oval caliber is greater than in the square one:
µ4 = 1 + 1.5 (µ3 - 1); µ3 = (0.5 + √0.25 + 6µ) / 3 (20)
9 Determine the area of the oval
q4 = q3 µ3 , mm2 (21)
The height of the oval h4 is determined in such a way that when rolling it in a square gauge there is room for broadening then:
H4 = 1.41 s3 - s3 - ∆b3, mm (22)
The value of the broadening ∆b3 can be determined from the graphs given in the textbook, "Calibration of rolling rolls", 1971.
The diameter of the laboratory mill is small, so the broadening should be reduced using extrapolation.
B 4 \u003d 3 q 4 / (2 h 4 - s 4 ), mm (23)
where s 4 \u003d h 4 - 2 h vr 4, mm; h BP 4 = 7.05 mm.
10 We determine the broadening in the 4th oval caliber (as in pp7)
font-weight:normal"> ∆b4 = 0.4 √ (С0 – h4 sr)Rks (С0 – h4 sr) / С0 , mm (24)
We check the filling of the 4th oval caliber. The results are summarized in Table 2.1, where it turns out that the 4th oval caliber is necessary for the 1st pass of a square billet with side C0, i.e. above, we started the calculation from the last 4th pass (final or required profile section) carried out in the 1st caliber of the rolls.
2.3.2 Rolling a square profile with side c = 14 mm
In calculations, we also focus on the data of Figure 2.4 (Section 2.4).
1 Determine the area of the finishing (final) profile
Q1 \u003d s12, mm2 (25)
2 Select the elongation ratio in the finishing square pass and the total elongation ratio in the square and pre-finishing rhombic passes, i.e. µkv = 1.08 ÷ 1.11; µkv µr = 1.25 ÷ 1.27.
3 Determine the area of the prefinishing rhombus
Q2 = q1 µkv, mm2 (26)
4 Approximately take the broadening of the rhombic strip in a square gauge equal to ∆b1 = 1.0 ÷ 1.5
5 Determine the dimensions of the prefinishing rhombus
H2 = 1.41s – ∆b1 , mm b2 = 2 q2 / h2 , mm. (27)
The depth of cut in the rolls for this caliber according to Figure 2.1 hvr2 = 7.8 mm, therefore, the clearance s2 = h2 - 2 hvr2, mm.
6 Determine the area of the pre-finishing square
h3 = qkv µkv r, mm2 whence the side of the square c3 = √1.03 q3
2.4 Necessary equipment, tools and materials
The work is carried out on a laboratory mill with roll calibration as, for example, shown in Figure 2.4. As blanks, both for round and square rolled profiles, blanks with square section. In principle, this laboratory work is of a calculated nature and ends with filling in tables 2.1 and 2.2.
Figure 2.4 - Calibration of rolls for a round and square profile
Table 2.1 - Calibration of the round profile ø 16 mm
pass number | caliber number |
Caliber form | Caliber dimensions, mm | Strip dimensions, mm |
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hvp | b | s | h | b | with (d) |
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square billet |
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Oval | 7,05 | |||||||||||||
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