How to roll a square out of a circle. Fundamentals of roll sizing
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 round steel diameter from 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) - diameter round profile in a 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 compressions of the oval, the possibilities of size fluctuations in round gauge. 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 of medium and large sizes, the ovals, outlined by one radius, turn out to be too elongated along the major axis and, as a result, do not provide a reliable grip 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.
1. The profile of the hole, images, adjacent streams of rolls in the working position and the gaps between them, serves to give a given shape and size to the section of the roll. Usually k. is formed by two, less often - by three and four rolls. The shape can be simple - rectangular, round, square, rhombus, oval, strip, hexagonal, lancet and shaped - corner, I-beam, channel, etc. By design, i.e. the position of the parting line, which is divided into open. and closed, according to the location on the rolls - open, closed, semi-closed. and diagonal. By appointment - crimping, exhaust, roughing, pre-finishing and finishing k. Osn. el-you k. - gap m-du rolls, outlet k., connector, collars, rounded, neutral. line. Types of k. are shown in fig. 2. Replaceable technological tool, fix on the work roll. 3. Scaleless measure, a tool for controlling the size, shape and relative position of the parts of the product by comparing the size of the product with k. according to the occurrence or degree of fit of their surfaces:
beam gauge - k. (1.) for rolling rough and finishing I-beams. Use b. to. direct closed, open, tilt, and univers. Usually two-roll are used, less often - universal. four-roll b. k. Naib, distribution. direct closures b. to. Open. b. used as cutting and roughing when rolling large I-beams. Tilt, b. to. I-beam profiles are rolled with a decrease. slopes inside. edges of shelves and large flange heights. To the uni. b. k. wide-shelf I-beams of large sizes and I-beams with parall are rolled. shelves. When rolling lightweight I-beams, a horizon is used, position. diagonal. b. To.;
drawing caliber - k. (1.) of a simple form to reduce the cross section and hood (1.) of the roll with a given alternation of two or one caliber of the same type. In a number of cases, in to. give the roll dimensions, at which the formation of a given profile begins. When rolling simple profiles, they are usually draft gauges. In quality-ve in. used rectangular, square, rhombic, oval, hexagonal. and other calibers. Depending on the rolling conditions and requirements, the section of the rolled c. to. are located in the definition. last, naming. system drawing calibers;
diagonal caliber - closed to. (1.) with a diagonal. (different in height) located. connectors. D. to. usually cut into rolls with an inclination and are used for oblique calibration of I-beams, profiles and rails. Horizon, d. to. is used when rolling I-beams, profiles on continuous mills and Z-profiles. D. to. facilitates the exit of the roll from the rolls, but creates undesirable. side forces;
closed caliber - k. (1.), in which the parting line of the rolls is outside its contour. 3. k. are usually used for rolling shaped profiles; he, as a rule, has one vertex, an axis of symmetry;
Ribbed oval gauge
rhombic caliber - k. (1.) rhombic. config., embedded in the rolls along a small diagonal. Calculation, dimensions: C, \u003d 5K / 2sinp / 2, B - B - Sa, height taking into account rounding
Rhombic caliber
R, = R, -2K(1 + l/ek2) -1), a = R/R, = = tgp/2, / = (0.15-n0.20) R1, l, = (0.10 + 0.15) R " R \u003d 2 (R, 2 + R, 2) "2, in, \u003d 1.2 * 2.5 (Fig.). R. to. is used in the rhombus-rhombus and rhombus calibration system -square The angle at the top of the groove p varies from 90 to 130°, with an increase in the angle of increased drawing in the groove, averaging 1.2-1.3. -0.9;
Lancet square gauge
lancet square caliber - k. (1.) with the contour of a square with concave sides, cut into the rolls diagonally. Calculation, dimensions: Bk \u003d R, \u003d 1.41 C,; R = = (C,2 + 4D2)/8D; r \u003d (0.15 + 0.20) C,; B \u003d 5K - (2/3) 5. Area F \u003d C, (C, + (8/3) D), where D is the value of one-sided. convexity, C, - the side is inscribed, square (fig.). Max, side size c. c.c. C^ = C, + 2D. S. to. to. apply when necessary. transfer a large amount of metal to the finishing passes. At the same time, the output is preserved. roll temperature, because there are no sharp corners. S. to. to. - exhaust in the system of calibers oval-lancet square and sometimes pre-finishing for circles;
draft gauge - c. (1.), approx. section of the workpiece or roll to the configuration of the finished profile. Ch. to. shaped profiles in the course of rolling approach the finish k. The shape of the c. to. when rolling simple profiles is determined by the exhaust system of the k.
finishing gauge i-k. (1.) to give the roll a final profile, i.e. for the manufacture rental from the end transverse dimensions. sections. When constructing h. to. take into account thermal expansion. metal, uneven distribution of pred. temperatures in the roll, wear of calibers, profile correction, and other factors;
hex gauge - k. (1.) hex. contour, cut, into rolls along a large diagonal. Connector sh. to. is located on its sides. Dimensions w. k. exp. through vpi-
Hex gauge
dignity. circle diam. d: side C \u003d 0.577d, area -F \u003d 0.866d2, height R, \u003d 2 C (Fig.). Appl. it is clean in quality, caliber when rolling is six-tigran. steel and black. when rolling a hexagon. drill steel, when uniform and low reduction along the passes is required;
Square caliber
hexagonal caliber - k. (1.) hexagonal. contour, cut, into rolls along the minor axis; appl. in the exhaust system of calibers hexagon-square and as pre-clean. when rolling hexagonal profiles. Calculation, dimensions: 5D = 5K - I,; B \u003d 5K - S; ak = BJH, = 2.0+4.5; r \u003d r, \u003d (OD5 + 0.40) R,; Р = 2(Bf + 0.41R,) (Fig.). Predchistovoy sh. to. build as usual hexagonal, but for compensation. broadening of the metal and preventing. convexity of the side walls is clean. the hexagon bottom of the caliber is made with a convexity of 0.25-1.5 mm, depending on the size of the profile. Degree of filling sh. to. take 0.9;
l
box caliber
box caliber - k. (1.), images. trapez. cuts in rolls, for rolling pryamoug. and square, profiles. Estimated dimensions: 5d \u003d (0.95 + 1.00) V "; B \u003d Yad + (I, - S) tg (p; g \u003d (0.10h-0.15) I,; g, \u003d (0.8 + 1.0) / -, ok \u003d \u003d 4 / I , = 0.5 + 2.5; /> * 2(R, + B,) (Fig.) The depth of the cut, i.k., R, depends on the ratio of dimensions (R, / 00) of the profile specified in it. They are used, mainly, on blooming, swaging and continuous billet mills, swaging and blackening stands of section mills, and for the production of commercial blanks on rail and section mills.
square gauge - k. (1.)
square, contour, cut into rolls along dia
chased. Depending on the requirements, rental profile
performed with rounded or sharp tops
us. Calculation, dimensions: Hk \u003d Bf \u003d 21/2 C I, \u003d
\u003d 21/2 C. - 0.83 g, B \u003d B-s; r \u003d (0.1 + 0.2) ^;
/-,= (0.10^0.15)I,; P \u003d 2-21 / 2I, (Fig.). K. to. -
finishing when rolling square pro
lei and exhaust in rhombus-square systems,
oval-square and hexagon-square. In black
new calibers perform significant
rounding of the vertices with a radius of r. The height and width of the c. c. are, respectively, 1.40 and 1.43 of its sides.
When rolling squares with sharp corners, the k.k. has an angle at the top of the example, but 91-92 °, taking into account
volume of thermal shrinkage of the profile; L""" ° t -""" """ and
control caliber - to. (1.), for small high-rise compression and control of the sizes otd. el-tov peal; used when rolling a number of shaped and complex profiles, for example, I-beams, for wheel rims, door hinges, etc. K. to. perform closed and semi-closed. Closed to. to. provides more accurate dimensions of rolled elements, but more often they work with semi-closed to. to. In a closed to. to., the flange is crimped only in height, and in a semi-closed - in height and thickness in the open part of the caliber;
round caliber - k. (1.) with a circle contour on the main part of the perimeter; finishing when rolling round steel and exhaust in the oval-circle system. K. to. all types have a release or collapse. When constructing a finishing k. to., they usually take an outlet of 10-30 ° or 20-50 °, depending on the diameter. rolling circle. Estimated dimensions: Bf \u003d rf / cozy, B " \u003d Yak-. Stgy, g, \u003d (0.08 + 0, lO) d, P \u003d \u003d tk / (fig.). Since they tend to roll round steel with minus, tolerance D on dia., then for finishing k. to., taking into account thermal expansion, they take d \u003d 1.013, where rfxon "~ Diam. circle in a cold state;
multi-roll caliber - k. (1.) with a contour formed by three or more rolls, the axes of which lie in the same plane. In m.k., the metal is crimped in the vertical-transverse direction. with advantage all-round compression, which allows you to deform low-plastic materials. M. to. high dimensional accuracy of the profiles, therefore they are widely used in the finishing stands of small-section and wire mills for rolling steel and non-ferrous. metals. Four-roll open and closed calibers are often used for mountains. and hol. rolling of high-precision shaped profiles;
swaging caliber - k. (1.) to reduce the cross section of the roll and obtain blanks for section mills. In quality about. to. on blooming, swaging and billet mills use box calibers. Deformation in about. k. is not always accompanied by creatures, an exhaust, as, for example, in the first passes on blooming. However, to Fr. to. sometimes partially or completely include the calibers of exhaust systems of calibrations. Subsection, calibers for swaging and drawing depends on the purpose of the rolling mill, the system of calibers and a separate caliber;
oval caliber - k. (1.) of an oval or close to it contour, cut into rolls along a minor axis. O. to. is used as a pre-finishing when rolling round profiles and exhaust in the system oval - rib oval, etc. Depending on the purpose of the caliber and dimensions of the rolls, they use: 1. Single-radius about. to. (usual o.k.), app. as pre-finishing when rolling round steel. Their calculated dimensions (Fig.): R = R, + (1 + O/4; B = (R, - S) 1/2; r, = (0.10 + 0.40) ^; P = 2 [B* + + (4/3)R,2]1/2; when rolling large circles and in oval-circle and oval-oval systems; flat o.k., used in the same place as elliptical o.k. to-rykh B = OD, r = 0.5R, r = (0.2 + 0.4)R, O|t = 1.8 + 3.0, modified flat o.c., the contour of which is an image, a rectangle and lateral curvilinear triangles, taken as parabolic segments; trapezoidal (hexagonal) OK with straight outlines, used for good retention of the roll and alignment of the hoods
open caliber - k. (1.), parting line to-rogo within its contour; image, cuts in two or more rolls, cuts in one roll and a smooth barrel or smooth barrels. In simple o. to. connector image, approximately in the middle of the caliber and the side sections of the roll forming. shoulders of two rolls. In some shaped about. to. they form. stream walls in only one swath;
semi-closed caliber - shaped to. (1.) with the location of the connector on the side wall near the top of the stream; used as a control when rolling channels, strip bulbous, I-beam and other profiles. Compared to a closed control pass, it has a larger outlet and a shallow depth of cut in a closed stream, which weakens the roll less in diameter, allows you to compress the flanges of the rolls in thickness, increase the number of regrinds and the service life of the rolls;
pre-finishing caliber - k. (1.) for the penultimate. roll skips; to prepare the roll for forming. final profile. When rolling shaped
profiles in shape and / or size is very close to finishing, and when rolling simple profiles, it may differ. Rib gauges are often used as rolling gauges when rolling strip profiles and control gauges when rolling. flange profiles;
split caliber - 1. K. (1.) with a crest in the middle part, for the original. for-world. from blanks of flanged rolled elements; for example, when rolling I-beams from a rectangular. blanks are formed sections of flanges and walls, and when rolling rails - sections under the sole and head. Use open and closed rivers. to. Closed r. to. carry out on rolls of big dia. for the manufacture large flanges. Open symmetrical. R. C. with blunt crests are often used for rolling beam blanks from slabs. 2. K. for the longitudinal separation of double peals;
Rib Gauge
rib caliber - k. (1.), cut, into rolls of large size; used, in particular, when rolling strip steel to control the width of the roll. Predchistovoy r. to. also forms the edges of the rolled products. When rolling strips with straight edges, the convexity of the bottom of the pre-finishing river. k.D = = 0.5-5-1.0 mm, roll gap< 1/3 высоты полосы и выпуск 0,05+0,10 (рис.);
T
ribbed oval caliber - k. (1.) oval contour, cut, into rolls along the major axis. Calculation, dimensions: R \u003d 0.25 / ^ (1 + + 1 / a2), B \u003d B- 2L, r \u003d \u003d rt \u003d (0.10 + 0.15) 5, ak \u003d 4 / R, \u003d 0 .75 * 0.85, P \u003d 2 (I, 2 + (4/3) g, T2 (Fig.). Used as an exhaust in the oval - rib oval system;
Calibration of profiles and rolls intended for rolling round and square steel
TO hot rolled round steel according to GOST 2590-71, profiles are classified that have a cross-sectional shape of a circle with a diameter of 5 to 250 mm.
In the general case, the calibration scheme for round steel can be divided into two parts: the first is a calibration for rough and middle groups of stands and satisfies a number of profiles, being in this sense common for several final profiles of various sections (square, strip, hexagonal, etc.) , and the second is intended as a specific system for the last three or four stands and is characteristic only of this round steel profile. In draft and middle groups of stands, caliber systems can be used: rectangle - box square, hexagon - square, oval - square, oval - vertical oval.
For the last three to four profiling stands, the gauge system is also not constant. A certain pattern is observed only in the last two stands: the finishing stand has a round pass, the pre-finishing stand is oval, the pass of the third stand from the end of rolling can be of various shapes, on which the sizing system depends.
General schemes of calibers of the last four passes when rolling round steel. It follows from these schemes that oval calibers of two shapes are used as pre-finishing calibers: one-radius and with rounded rectangles - the so-called "flat" calibers. The first scheme is used when rolling round steel of most profile sizes, the second - mainly for round steel of large diameters and reinforcing steel.
According to the first general scheme of rolling, seven types of calibers used in the preshape stand can be noted. According to the second general scheme, only two types of calibers have found the greatest use: box square 1 and square 3, cut into the barrel of the roll when located diagonally.
The systems and form of calibers used for rough and middle groups of stands can be very diverse and depend on a number of factors, the main of which are the type of mill and the design of its main and auxiliary equipment.
Currently, there are a number of techniques for constructing a finishing gauge for round steel: outlining the gauge with two radii from different centers; chamfering at the roll connectors in order to prevent the stripe of small thickness undercuts of the roll with caliber collars; the formation of a release by the outline of the caliber along the connector, etc. Practice shows that a finishing gauge, outlined by one radius and having only one size - the inner diameter, does not meet the requirements for obtaining a geometrically correct high-quality profile, especially a large diameter profile. As a rule, in such a caliber, even with the slightest change in technological conditions (lowering the rolling temperature, the development of pre-finishing caliber rolls, increasing the height of the oval, etc.), the streams are overflowing with metal. Obtaining a profile in accordance with the shape of the finishing pass requires constant control of the dimensions of the pre-finishing oval bar. In cases of gauge overflow, it is not always possible to maintain the profile diameter, even within the plus tolerance.
In order to eliminate the noted shortcomings, it is recommended to design a finishing gauge with camber (release) for a round steel profile, i.e., to provide for a slightly larger horizontal diameter compared to the vertical one. This is also necessary due to the fact that the roll of oval section entering the finishing pass has a lower temperature in places at the ends of the major axis and the thermal shrinkage of the finished profile during cooling in the direction of the horizontal diameter is somewhat greater than in the direction of the vertical diameter. Intensive wear of the finishing caliber of round steel along the vertical due to greater reduction also contributes to the excess of the size by 1-1.5% of the horizontal diameter over the vertical one.
Round steel at domestic plants tend to be rolled to minus tolerances.
Determining the size of the horizontal diameter using the finishing gauge connector is recommended using analytically derived equations (N.V. Litovchenko), taking into account the dimensions of the profile diameters.
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 ratio 
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. Hood in fine square gauge 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 a square section are used. 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 |
||||||||||
hvp | b | s | h | b | with (d) |
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square billet |
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Oval | 7,05 | |||||||||||||
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 method for analyzing roll calibration systems for section mills is proposed. 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 rational calibration 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. To analyze the calibration systems, pairs of successive gauges were selected, which, on the one hand, allow us to consider all possible schemes of combinations of gauges, and on the other hand, provide research into the division limit of a complex system, such as the calibration of rolls of 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 range.
So, when rolling round steel with a diameter of 25-105 mm and hexagonal steel No. 28-48 on the medium-section mill "350" of the CherMK JSC "Severstal", the calibration systems used 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 shape |
|||||||
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
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