How to roll a square out of a circle yourself. Mechanical Engineering

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 strip stability when rolling on a smooth barrel as a function of h / b and ε

1) describe the technology for making blooms; sequence of operations; characteristic parameters.

2) draw sketches: blooms, models of ingots, side faces, section distortions, etc.

Control questions

1 What is included in the main task technological process rolling production?

2 What is the technological scheme for the production of rolled products?

3 What is a semi-product of rolling production?

4 Which ones do you know technological schemes production of semi-products and finished products?

5 What technological schemes for the production of rolled products can be organized using continuous casting processes?

6 What is roll calibration, roll gauge and smooth roll barrel?

7 What is maximum reduction and its influence during rolling?

8 What is the roll angle and its influence during rolling?

9 Under what conditions is strip edging carried out?

10 How are the broadening and elongation of the rolled strip determined?

11 What is strip stability and what indicator is it characterized by?

Laboratory work No. 2. Study of methods for calibrating rolls for rolling simple sections

2.1 Purpose of the work

Familiarize yourself with gauge systems for obtaining round and square profiles, mastering methods for calculating the main calibration parameters.

2.2 Basic theoretical information

Calibration is the procedure for rolling a successive series of transition sections of rolled profiles. Calibration calculations are carried out according to two schemes: along the rolling course (from the workpiece to the final profile) and against the rolling course (from the final profile to the workpiece). According to both schemes, to calculate and distribute deformation coefficients over gaps, it is necessary to know the dimensions of the original workpiece.

Rolling of section profiles begins in drawing passes, i.e., passes connected in pairs and intended for drawing metal. Various crimping and drawing gauges, for example, box, diamond-square, rhombus-diamond, oval-square, etc. (Figure 2.1).

Of all the crimp (pull) gauges, the most common is the box gauge scheme. The smooth barrel - box gauge pattern is often encountered.

a) – box; b) – rhombus – square; c) – rhombus – rhombus; d) – oval – square

Figure 2.1 – Schemes of exhaust gauges

When rolling medium- and low-grade steel, the diamond-square gauge pattern is widely used. The scheme of geometrically similar rhombus-diamond calibers, in which after each pass the roll is turned by 90°, is used quite rarely. Rolling according to this pattern is less stable than in the rhombus-square pattern. It is mainly used for rolling high-quality steels, when small reductions are carried out under plastic deformation conditions with an extension of up to 1.3.

The oval-square drawing pattern of gauges 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 rolling angles, which helps to obtain the same temperature over its cross section. The roll behaves steadily when rolling in oval and square gauges. The system is characterized by large hoods, but their distribution in each pair of calibers is always uneven. In an oval caliber, the hood is greater than in a square one. Large hoods make it possible to reduce the number of passes, i.e., increase the economic efficiency of the process.

Let's 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 various schemes depending on the diameter of the profile, the type of mill, and the metal being rolled. Common to all rolling schemes is the presence of a pre-finishing oval gauge. Before cutting the strip into the finishing gauge, it is turned by 90°.

Typically, the shape of the pre-finishing gauge is a regular oval with an axial length ratio of 1.4÷1.8. The shape of the finishing gauge depends on the diameter of the rolled wheel. When rolling a circle with a diameter of up to 30 mm, the generatrix of the finishing gauge represents a regular circle; when rolling a circle with a larger diameter, the horizontal size of the gauge is taken 1-2% larger than the vertical one, since their temperature shrinkage is not the same. The drawing coefficient in the finishing caliber is taken equal to 1.075÷1.20. Round profiles are rolled only in wires in one pass in the last – finishing gauge.

The so-called universal scheme for rolling a round strip using the square-step-rib-oval-circle system is widespread (Figure 2.2). When rolling according to this scheme, the dimensions of the strip emerging from the rib gauge can be adjusted within a wide range. Round profiles of several sizes can be rolled in the same rolls, changing only the finishing gauge. In addition, the use of a universal rolling scheme ensures good removal of scale from the strip.

1 – square; 2-step; 3 – rib; 4 – oval; 5 – circle

Figure 2.2 – Scheme of rolling round profiles

When rolling round profile relatively small sizes The square-oval-circle caliber scheme is often used. The side of the pre-finishing square, which significantly influences the production of a good round profile, is taken for small profiles to be equal to the diameter d , and for profiles of medium and large sizes 1.1 d.

When calculating the calibration of rolls in 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 passes, the rolling diameter is taken equal to the diameter of the rolls at the bottom of the pass. In rhombic and square - variable: maximum at the connector of the caliber and minimum at the top of the caliber. The circumferential speeds of different points of these calibers are not the same. The strip leaves the caliber with a certain average speed, which corresponds to the rolling diameter, approximately determined by the average reduced height of the caliber

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 coefficient is determined

, (10 )

where Fo ~ cross-sectional area of ​​the original workpiece;

Fn – cross-sectional area of ​​the rolled profile.

Then, taking into account the relation distribute the hood among the cages. Having determined the rolling diameter of the finishing stand rolls and taking the required rotation speed of the rolls of this stand, calculate the calibration constant:

font-size:14.0pt">where F 1 ... Fn – cross-sectional area of ​​strip in stands

1, ..., n ; v 1 ,...vn – rolling speed in these stands.

Rolling diameter of rolls when rolling in a box gauge

EN-US" style="font-size:14.0pt">2)

Where k- caliber height.

When rolling in square gauges

font-size:14.0pt"> (13 )

Where h - side of a square.

After this, the dimensions of the intermediate squares, and then the intermediate rectangles, are determined from the hoods. Knowing the calibration constant WITH, determine the rotation frequency of the rolls in each stand

n= C / FD1 (14 )

Square profiles are rolled with sides ranging from 5 to 250 mm. The profile can have sharp or rounded corners. Typically, a square profile with a side of up to 100 mm is obtained with unrounded corners, and with a side of over 100 mm - with rounded corners (the radius of rounding does not exceed 0.15 of the side of the square). The most common rolling system is square-diamond-square (Figure 2.3). According to this scheme, rolling in each subsequent caliber is carried out with a 90° bevel. After turning the piece coming out of the rhombic gauge, its large diagonal will be vertical, so the strip will tend to tip over.

Figure 2.3 – Scheme of rolling a square strip.

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 gauge

font-size:14.0pt">where a are the sides of the square profile in the hot state.

When rolling large square profiles, the temperature of the corners of the workpiece 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 = 1.41a, and width (horizontal diagonal) b = 1.42a. The margin for widening for squares with a side of up to 20 mm is taken to be 1.5 ÷ 2 mm, and for squares with a side of more than 20 mm 2 ÷ 4 mm. Exhaust hood in finishing square gauge is taken to be 1.1÷1.15.

When producing square profiles with sharp corners, the shape of the pre-finishing rhombic gauge is essential, especially when rolling squares with a side of up to 30 mm. The usual diamond shape does not provide squares with correctly shaped corners along the parting line of the rolls. To eliminate this drawback, pre-finishing rhombic gauges are used, the top of which has a right angle. The calculation of the sizing of a square profile begins with a finishing gauge, and then the dimensions of the intermediate drawing gauges are determined.

2.3 Methods for calculating calibration parameters of simple profiles

2.3.1 Rolling a round profile with a diameter d = 16 mm

In calculations, use the data in Figure 2.4 (section 2.4).

1 Determine the area of ​​the finishing profile

qкр1 = πd2 / 4, mm2 (16)

2 Select the drawing coefficient in the finishing caliber µcr and the overall drawing coefficient in the round and oval calibers µcr within the limits µcr = 1.08 ÷ 1.11, µcr ov = 1.27 ÷ 1.30.

3 Determine the area of ​​the pre-finishing oval

qov2 = qcr1· µcr, mm2 (17)

4 Approximately assume the widening of the oval strip in the round gauge ∆b1 ~ (1.0 ÷ 1.2).

5 Dimensions of the pre-finishing oval h2 = d - ∆b1, mm

b2 = 3q2/(2h2 +s2);

where the depth of cut in the rolls (Figure 2.4) is hр2 = 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 с3 – 0.82 r, mm (r = 2.5 mm), then according to Figure 2.4 we determine the depth of insertion of the 3rd caliber into the rolls hр3 = 9.35 mm, therefore, the gap in the 3rd caliber s3 = h3 – 2 · hр3, mm.

∆b2 = 0.4 √ (c3 – hov avg)Rks · (c3 – hov avg) / c3, mm/ (18)

where hov av = q2 / b2; Rks = 0.5 (D – hov avg); D – mill diameter (100÷150 mm).

Check the filling of the pre-finishing oval gauge. In case of overflow, a lower draft ratio should be adopted and the size of the pre-finishing square will 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 = CO2 / s32 (19)

We distribute this total draft between the oval and square calibers so that the draft 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 widening then:

H4 = 1.41 s3 – s3 – ∆b3, mm (22)

The amount of 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 expansion should be reduced using extrapolation.

B 4 = 3 q 4 / (2 h 4 – s 4), mm (23)

where s 4 = h 4 – 2 h time 4, mm; h vr 4 = 7.05 mm.

10 Determine the broadening in the 4th oval gauge (as in point 7)

font-weight:normal"> ∆b4 = 0.4 √ (C0 – h4 ov avg) Rks · (C0 – h4 ov avg) / C0, mm (24)

We check the filling of the 4th oval gauge. We summarize the results in Table 2.1, where it turns out that the 4th oval gauge is required for the 1st pass of a square workpiece with side C0, i.e. above we started the calculation from the last 4th pass (the final or required profile section) carried out in the 1st roll caliber.

2.3.2 Rolling a square profile with side c = 14 mm

In the calculations we also focus on the data in Figure 2.4 (section 2.4).

1 Determine the area of ​​the finishing (final) profile

Q1 = c12, mm2 (25)

2 Select the drawing coefficient in the finishing square caliber and the total drawing coefficient in the square and pre-finishing rhombic calibers, i.e. µkv = 1.08 ÷ 1.11; µsq · µр = 1.25 ÷ 1.27.

3 Determine the area of ​​the pre-finishing rhombus

Q2 = q1 µkv, mm2 (26)

4 Approximately take the broadening of the rhombic strip in a square gauge to be equal to ∆b1 = 1.0 ÷ 1.5

5 Determine the dimensions of the pre-finishing diamond

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 hр2 = 7.8 mm, therefore, the gap s2 = h2 – 2 hр2, mm.

6 Determine the area of ​​the pre-finishing square

h3 = qkv · µkv p, mm2 whence the side of the square c3 = √1.03 · q3

2.4 Required equipment, tools and materials

The work is carried out on a laboratory mill with calibrated rolls such as those shown in Figure 2.4. As blanks for both round and square rolled profiles, blanks with a square cross-section are used. In principle, this laboratory work is of a computational nature and ends with filling out tables 2.1 and 2.2.

Figure 2.4 – Calibration of rolls for round and square profiles

Table 2.1 – Calibration of round profile ø 16 mm

Pass number	Caliber number	Caliber shape	Caliber dimensions, mm	Strip dimensions, mm
hvr	b	s	h	b	with (d)
		Square blank
		Oval	7,05

The essence of the invention: the finishing gauge is symmetrical relative to the horizontal plane of the connector, and each part of the gauge is formed by three circular arcs of the same radius, while the central arc is limited by an angle of 26 - 32°, and the centers of the side arcs are shifted beyond the axis of symmetry of the streams by 0.007 - 0.08 radius arc. 1 ill.

The invention relates to metal forming and is intended for use primarily in ferrous metallurgy, as well as in mechanical engineering. The purpose of the invention is to simplify the adjustment of the caliber and increase the yield. The drawing schematically shows a finishing gauge for rolling round steel. The proposed finishing gauge for rolling round steel contains two streams 1 and 2, symmetrical with respect to the horizontal axis X and the vertical axis Y. Each of these streams has three sections 3,4 and 5, formed by arcs AB, BC, CD, A"B" , B"C" and C"D" of the same radius R. The central arcs BC and B"C" are limited by an angle of 26-32 o and outlined by a radius R from the intersection point of the X and Y axes of the caliber. The side arcs AB, A"B" and CD, C"D" are also outlined with a radius R, but from centers shifted beyond the vertical axis of symmetry Y of the caliber in the direction opposite to these arcs. Arcs AB and CD are drawn from centers O 2 and O 1, and arcs A "B" and C "D from centers O 3 and O 4. The amount of displacement of the centers beyond the vertical axis of symmetry Y is equal to half the tolerance range for the finished profile. The gauge is equipped releases (built with "camber") 6. They are built according to known methods, drawing from points A, D and A"D", tangents to the arcs A 1 AB, CDD 1 and A 1 A"B", C"D"D 1. The upper and lower grooves are installed with a gap of size S. During the operation of the rolling mill, before rolling in a new finishing pass, the gap size S is set such that the height of the pass corresponds to the minimum permissible value of the circle diameter size. After this, rolling is carried out. During the rolling process, as the grooves of the gauge wear out, they adjust it. In this case, the criterion is the “ovality" of the profile. Rolling is carried out in the gauge until it is worn out along the width corresponding to the maximum permissible size of the circle diameter along the width of the gauge (X axis). After this, they proceed to rolling in a new As a result of increased wear of the grooves in sections 4 and 5, the maximum diameter of the finished profile in the corresponding sections is obtained almost simultaneously with the corresponding dimensions along the X axis. At the same time, the size of the finished product vertically (along the Y axis) is easily adjusted by changing the size of the gap S. When When the dimensions of the central arcs 1 go beyond the limits specified in the claims, the positive effect of its use decreases, this can be seen from the table, which presents the results of rolling a 1600 mm circle. As shown by experimental rolling data, as a result of the use of the claimed finishing gauge for rolling round steel, the metal removal from the finishing gauge increased by 38%, the yield of second grades decreased by 60%. The claimed finishing gauge for rolling round steel is of undoubted interest for National economy, as it will reduce metal consumption: significantly increase labor productivity by at least 12% by reducing time for transshipment.

Claim

FINISHING GAUGE FOR ROLLING ROUND STEEL, formed by two streams symmetrical relative to the horizontal parting plane, bounded by circular arcs, characterized in that, in order to simplify the adjustment of the gauge and increase the yield, each of the streams is formed by three arcs of the same radius, while the centers of the side arcs are shifted beyond the vertical axis of symmetry of the streams by 0.007 0.08 of this radius, and the central arc is limited by an angle of 26 32 o.

DRAWINGS

,

MM4A - Early termination of a USSR patent or patent Russian Federation for the invention due to non-payment fixed time patent maintenance fees

Flat products (sheets, strips) are usually rolled in smooth cylindrical rolls. The specified rolled thickness is achieved by reducing the gap between the rolls. Rolling of long sections is carried out in calibrated rolls, i.e. rolls having annular grooves corresponding to the rolling configuration sequentially from the workpiece to the finished profile.

The annular cutout in one roll is called a groove, and the gap between two grooves in a pair of rolls located one above the other, taking into account the gap between them, is called a caliber (Fig. 8.1).

Typically, a square or rectangular blank is used as the starting material. The calibration task includes determining the shape, size and number of intermediate (transition) sections of the rolled product from the workpiece to the finished profile, as well as the order of arrangement of the gauges in the rolls. Roll calibration is a system of sequentially located calibers that ensure the production of rolled products of a given shape and size.

The boundary of the streams on both sides is called a socket or gauge gap. It is 0.5...1.0% of the roll diameter. The gap is provided to compensate for elastic deformations of the working cage elements that occur under the influence of rolling force (the so-called recoil, cage spring). At the same time, the interaxial distance increases from fractions of a millimeter on sheet mills to 5...10 mm on crimping mills. Therefore, when adjusting, the gap between the rolls is reduced by the amount of recoil.

The slope of the side faces of the caliber towards the vertical is called caliber release. The presence of a slope facilitates the centering of the rolled product in the pass, facilitates its straight exit from the rolls, creates space for the widening of the metal, and provides the possibility of restoring the pass during regrinding (Fig. 8.2). The amount of release is determined by the ratio of the horizontal projection of the side face of the caliber to the height of the stream and is expressed as a percentage. For box gauges the output is 10...25%, for rough shaped gauges - 5...10%, for finishing gauges - 1.0...1.5%.

IN- width of the gauge at the connector, b- width of the caliber in the depths of the stream, h to- caliber height, h r- height of the stream, S- gauge gap.

The distance between the axes of two adjacent rolls is called the average or initial diameter of the rolls - Dc, i.e. these are the imaginary diameters of the rolls, the circles of which are in contact along the generatrix. The concept of average diameter includes the gap between the rolls.

The center line of the rolls is a horizontal line dividing in half the distance between the axes of the two rolls, i.e. this is the line of contact of the imaginary circles of two rolls of equal diameter.

Neutral line of the caliber - for symmetrical calibers this is the horizontal axis of symmetry; for asymmetrical calibers, the neutral line is found analytically, for example, by finding the center of gravity. A horizontal line passing through it divides the area of ​​the caliber in half (Fig. 8.3). The neutral line of the gauge determines the position of the rolling line (axis).

The rolling (working) diameter of the rolls is the diameter of the rolls along the working surface of the caliber: . In calibers with a curved or broken surface, the rolling diameter is determined as the difference and, where is the average height, equal to the ratio, is the area of ​​the caliber (Fig. 8.4).

The ideal option seems to be when the neutral line of the caliber is located on the center line, i.e. they match. Then the sum of the moments of forces acting on the strip from the upper and lower rolls is the same. With this arrangement, the strip should exit the rolls strictly horizontally along the rolling axis. In the actual rolling process, the conditions on the contact surfaces of the metal with the upper and lower rolls are different and the front end of the strip can unexpectedly move up or down. To avoid such a situation, the strip is forced to bend more often down onto the wiring. The easiest way to do this is due to the difference in the rolling diameters of the rolls, which is called pressure and is expressed in millimeters - DD, mm. If , there is upper pressure, if - lower pressure.

In this case, the neutral line of the gauge shifts with the center line by the amount X(see Fig. 8.1) and , A . Subtracting the second equality from the first, we get . Where . Knowing and you can easily determine the initial and .

For example, mm and mm. Then mm and mm.

Typically, on section mills, an upper pressure of approximately 1% is used. On bloomings, a lower pressure of 10...15 mm is usually used.

In the rolls, the calibers are separated from each other by collars. To avoid stress concentration in the rolls and rolls, the edges of the gauges and collars are conjugated with radii. Deep in the stream , and at the connector .

8.2 Classification of calibers

Calibers are classified according to several criteria: by purpose, by shape, by location in the rolls.

According to their purpose, they are distinguished between crimping (extracting), roughing (preparatory), pre-finishing and finishing (finishing) gauges.

Crimping gauges are used to draw out rolled material by reducing its cross-sectional area, usually without changing its shape. These include box (rectangular and square), lancet, rhombic, oval and square (Fig. 8.5).

Roughing gauges are designed to draw out the rolled material while simultaneously forming a cross-section closer to the shape of the finished profile.

Pre-finishing gauges immediately precede finishing gauges and decisively determine the production of a finished profile of a given shape and size.

Finishing gauges give the final shape and dimensions to the profile in accordance with GOST requirements, taking into account thermal shrinkage.

Based on their shape, calibers are divided into simple and complex (shaped). Simple gauges include rectangular, square, oval, etc., shaped gauges include corner, beam, rail, etc.

By location in the windrows There are closed and open calibers. Open calibers include those in which the connectors are located within the caliber, and the caliber itself is formed by streams cut into both rolls (see Fig. 8.5).

Closed calibers include those in which the connectors are located outside the caliber, and the caliber itself is formed by an indentation in one roll and a protrusion in the other (Fig. 8.6).

Depending on the dimensions of the profile section, the diameter of the rolls, the type of mill, etc., drawing gauges are used in various combinations. Such combinations are called caliber systems.

8.3 Pull gauge systems

The system of box (rectangular) gauges is used mainly when rolling rectangular and square billets with a cross-sectional side of more than 150 mm on blooming, crimping and continuous mills, in roughing stands section mills(Fig. 8.7). The advantages of the system are:

-

the possibility of using the same gauge for rolling workpieces of different initial and final sections. By changing the position of the upper roll, the dimensions of the caliber change (Fig. 8.8);

Relatively small depth of the stream incision;

Good conditions for the removal of scale from the side faces;

Uniform deformation across the width of the workpiece.

The disadvantages of this gauge system include the impossibility of obtaining workpieces of the correct geometric shape due to the presence of slopes on the side faces of the gauges, relatively low drawing ratios (up to 1.3), and one-sided deformation of the roll.

The rhombus-square system (see Fig. 8.7-c) is used in billet and roughing stands of section mills as a transition from the box gauge system to produce workpieces with a square side of less than 150 mm. The advantage of the system is the ability to obtain squares of the correct geometric shape, significant one-time hoods (up to 1.6). The disadvantage of the system is the deep cuts into the rolls, the coincidence of the ribs of the rhombus and the square, which contributes to their rapid cooling.

The square-oval system (see Fig. 8.7-d) is preferable for obtaining a workpiece with a cross-sectional side of less than 75 mm. Used in roughing and finishing stands of section mills. Provides draws up to 1.8 per pass, small penetration of the oval caliber into the rolls, systematic updating of the rolling angles, which contributes to a more uniform temperature distribution, and stability of the rolls in the calibers.

In addition to the ones mentioned above, rhombus-rhombus, oval-circle, oval-oval, etc. systems are used.

8.4 Calibration schemes for simple profiles (square and round)

Rough roll gauges for rolling square profiles can be made in any system, but the last three gauges are preferably in the rhombus-square system. The angle at the vertex of the rhombus is taken to be up to 120 0. Sometimes, to better fulfill the corners of the square, the angle at the very top of the rhombus is reduced to a straight line.

When rolling squares with a side up to 25 mm, the finishing gauge is built in the form of a geometrically regular square, and with a side over 25 mm, the horizontal diagonal is taken to be 1...2% larger than the vertical one due to the temperature difference.

Roughing passes for rolling round profiles are also performed in any system, and the last three passes are made in the square-oval-circle system. The side of the pre-finishing square for small circles is taken equal to the diameter of the finishing circle, and for medium sizes - 1.1 times the diameter of the circle.

Finishing gauges for circles with a diameter of less than 25 m are made in the form of a geometrically regular circle, and for circles with a diameter of more than 25 mm, the horizontal axis is used 1...2% more than the vertical one. Sometimes, instead of an oval formed by one radius, a flat oval is used for greater stability of the roll in a round gauge.

Figure 8.9 shows the roll calibration diagrams of the 500 mill, which show the systems of drawing gauges in roughing stands discussed above, calibration of square, round and other profiles.

8.5 Features of calibration of flange profiles

,

Where a d- size of the finishing profile at the temperature of the end of rolling,

a x- standard profile size;

Yes- minus size tolerance a x;

To- coefficient of thermal expansion (shrinkage) equal to 1.012...1.015.

For large profiles, for which the tolerance obviously exceeds the thermal shrinkage value, the calibration calculation is carried out on a cold profile.

3. In order to achieve maximum productivity, roughing passes are calculated taking into account the maximum grip angles with subsequent clarification on the strength of the rolls, engine power, etc. In finishing and pre-finishing passes, the reduction mode is determined based on the need to achieve the highest possible profile accuracy and low wear of the rolls, i.e. .e. at low elongation ratios. Usually in fine calibers m= 1.05…1.15, in pre-finishing m = 1,15…1,25.

The total number of passes when rolling on reversing mills, in trio stands, and on linear type mills must be odd so that the last pass is in the forward direction.

Rolling on the designed casting and rolling module with a planetary cross-rolling mill is carried out in 13 stands, which, as shown in Fig. 7, are conventionally identified in the following groups: crimping (in the form of a planetary stand), roughing (6 stands), intermediate (4 stands) and 2 finishing groups (2 stands each).

In a planetary cross-roller crimping stand, rolling is carried out from a round cast billet into a round rolled billet with a high degree of deformation.

Subsequently, rolling of high-precision round high-strength alloy steel with a diameter of 18 mm is carried out as follows.

In the roughing group of stands, rolling from a round billet into an oval profile is carried out using one of the systems exhaust calibrations- oval - ribbed oval system, which is most suitable for the production of high-precision round profiles from high-strength alloy steels.

The necessary transition to a rhombic and square shape of the roll with subsequent longitudinal division is carried out in special gauges of the preparatory group of stands according to recommendations and methods.

And finally, in the finishing groups of rolling stands, each thread of divided rolled stock is produced according to the square-oval-circle system, which is widely used for converting a square section into a round one (for rolling small-section round steel.

The calibration of round steel with a diameter of 18 mm is calculated 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 used depending on the profile size, steel quality, type of mill and its range, as well as other rolling conditions. However, in all cases the pre-finishing gauge is either a conventional single-radius oval or a flat oval. But pre-finishing single-radius oval gauges with an axial ratio = 1.5 are more widely used, and for good stability in a round gauge, the oval profile must have a significant bluntness. The preparatory gauge is a separating gauge producing two diagonal rolls.

For all finishing rolling methods round gauge performed with a “camber” release to prevent overflow of the caliber and obtain the correct round profile. The construction of such a round gauge is shown in Fig. 14.

Fig. 14.

When designing a finishing round gauge, it is necessary to take into account the thermal expansion of the metal and tolerances for deviations in the dimensions of the finished profile.

The construction of a round gauge is carried out as follows. On the diameter circle, rays drawn from the center of the caliber at an angle to the horizontal axis determine the points at which the sides of the caliber begin to release and determine the width of the caliber.

To calculate the diameter of the profile in the hot state in the finishing stand of the mill (stand 13), the expression is used

=(1.0121.015)(+) (1)

where is the diameter of the profile in a cold state;

Minus tolerance

We will perform the calculation 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 gauge (according to Fig. 14) will be

Where is the release angle, which in practice for round steel diameters of 10-30 mm is taken to be 26.5

And then = = 20.22 mm.

The gap between the collars of caliber - S is chosen within the range (0.080.15) and then,

S = 0.111.81 = 2.0 mm.

The intersection points of the clearance lines S with the release line determine the width of the stream incision, which is defined as

Substituting the values ​​we get

20.22 - = 18.22mm. (3)

The rounding of the shoulders is carried out with a radius

= (0.08 - 0.10) and then

0.008518.1 = 1.5mm.

The profile will be round if width =. In this case, the degree of filling of the caliber will be

A correctly made round profile in the finishing gauge of the 13th stand will have a cross-sectional area

The finishing group of stands has both groups of stands with a nominal roll diameter of 250 mm, with the finishing (13th) - horizontal rolls, and the pre-finishing (12th) - vertical rolls.

So, the finishing (13th) stand has a round gauge, the pre-finishing (12th) stand has a single-radius oval gauge, and the preparatory gauge (11th) stand is a dividing double diagonal square.

The nominal diameter of the rolls of the 11th stand, already included in preparatory group stands are 330mm.

The rollers of the finishing and pre-finishing group of stands are made of bleached cast iron. The rolling speed of high-precision round sections made of high-strength alloy steels in the finishing stand of the mill is assumed to be about 8 . Rolling temperature 950°C.

To determine the drawing coefficient in a finishing caliber, you can use the formula, which has the form

1.12+0.0004 (6)

Where - corresponds to the diameter of the finishing gauge 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.

A simple single-radius oval gauge can be used as a pre-finishing gauge, the construction of which is shown in Fig. 15

Fig. 15.

To construct the gauge, the dimensions of the height of the oval gauge and the width are determined in accordance with the compression mode adopted when calculating the calibration. Practical calibrations use ovals with the aspect ratio

Pre-finishing oval area

257.3 1.127=290. (8)

The thickness of the pre-finishing oval = is determined as

18.1-2.3=15.8mm. (9)

Width of finishing oval

26.2mm. (10)

Compression in finishing gauge

26.2-18.1=8.1mm. (eleven)

Engagement angle in finishing gauge

Arccos(1-)=arccos(1-)=15°19" (12)

The permissible grip angle can be determined using a method taking into account the values ​​of the coefficients for the oval-circle rolling scheme according to the formula

where v is the rolling speed, ;

Coefficient taking into account the condition of the roll surface (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 during rolling;

K b; ; ;; ; ; - the values ​​of the coefficients determined for various rolling schemes (drawing calibers) are determined from the table; for the oval-circle system (=1.25; =27.74; =2.3; =0.44; =2.15; =19.8; =3.98).

Let us assume the degree of filling of the pre-finishing oval gauge = 0.9

And, then the maximum permissible value of the grip 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

If the degree of filling of the pre-finishing oval gauge = 0.9, we find the width of the pre-finishing oval gauge

29.1mm. (15)

The caliber shape factor is defined as

The radius of the outline of an oval-caliber stream

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 gauge using 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 oval caliber collars is accepted according to the limits (0.15-0.2)

S=0.16 =0.16 15.8=2.5mm. (18)

Radius of rounded corners in oval gauge = (0.1-0.4).

The blunting of an oval caliber 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

The elongation coefficient of the preparatory square in the oval gauge of the 12th stand can be determined according to the recommendations of the method. Thus, according to this method, it is recommended that the overall elongation coefficient when rolling a square in an oval and round gauge is determined from a graph depending on the diameter of the resulting round steel. For a given diameter of round steel equal to 18 mm, the overall elongation coefficient will be = 1.41. And since

The area of ​​the given square will be determined by formula (21) and will be

290 1.25=362 .

The construction of a standard diagonal square gauge is shown in Fig. 16

Rice. 16.

The apex angle should be 90° and =. The filling degree of the square gauge is recommended to be 0.9. It can be approximated

And then the side of the square caliber - c will be

19.2mm. (25)

The radius of curvature of the top of a square gauge is defined as

=(0.1h0.2) = 0.105 19.2 = 2mm (26)

The rounding of the riot is performed with a radius, which is defined as

= (0.10h0.15) = (0.10h0.15) = 0.11 19.2 = 3mm. (27)

The height of the profile emerging from the square caliber will be slightly less than the height of the caliber due to the rounding of the vertices with a radius, and then

0.83= 19.2-0.83 2=25.5mm (28)

As already noted, the gauge in the 11th stand is a double diagonal square gauge in which the separation is rolled. Construction and general form this caliber is shown in Fig. 17. In the same figure, the outline of the roll from the 10th stand entering this caliber is superimposed.

Fig. 17.

Longitudinal separation of a multi-strand roll with a controlled tear is carried out by creating tensile stresses in the jumper area under the action of axial forces from the side surfaces of the ridges of double-strand gauges embedded in the metal, as can be shown in Fig. 18.

Fig. 18.

At the moment of gripping, due to the crushing of the surface of the roll by the inner side faces of the caliber streams, a normal force N and a frictional force T arise. The resultant of these forces can be decomposed into transverse Q and vertical P components. Under the influence of the force P, the metal is compressed by the rollers, the force Q promotes the stretching of the jumper in the transverse direction and causes the appearance of a tensile resistance force of the jumper S and a resistance force to the plastic bending of the outer workpiece towards the connector of caliber G.

By measuring the thickness of the bridge of the specified roll - and the gap between the ridges of the rolls - t of the separating gauge (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 the conditions for separating the roll. The absence of a break in the neck at the point of separation of the profile neck 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 products by controlled tearing is recommended for use in finishing stands of rolling mills.

Studies of the longitudinal separation of double-thread rolled material by controlled tearing have shown that the thickness of the web of the rolled material inserted into the separating cage should be equal to 0.5 x 0.55 of the side of the square.

The study of the gap between the roll ridges affects the change in the curvature of the front ends of the divided square profiles when exiting the rolls. So, the straightness of the output was obtained with a gap = 16 mm equal to the thickness of the jumper, then we select

From the practice of calculating calibrations when rolling and separating square profiles, the compression ratio of the sides of a square profile is taken in the range of 1.10-1.15. And then, from the expression (by choosing) we determine the side of the square in 10 gauge

19.2 1.125=21.6 mm. (29)

The area of ​​the dividing double gauge 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 determined as

As stated above, the thickness of the jumper in the 10th stand can be determined as

To check for the capture of the rolled material entering the gauge of the 12th stand, it is necessary to calculate the absolute compression in this gauge and compare it with the permissible data.

When a square profile enters an oval gauge, the absolute compressions along the middle and edges of the profile will be different and are determined geometrically by the superposition of the square profile section on the oval gauge and will be in the middle of the gauge

Compression at the extreme points of a square in an oval caliber based on geometric transformations will be approximately?.

As you can see, these absolute reductions are less than the absolute reductions in the 13th gauge and, therefore, with the same nominal diameter of the rolls and the same material, checking for acceptable gripping conditions is not required.

Taking into account the above, the construction and general view of the preparatory gauge in the 10th stand (before rolling-separation) can be presented in Fig. 19.

Fig. 19.

Some caliber dimensions can be determined as follows: we take the length of the jumper based on existing calibrations during rolling-separation;

radius of curvature of the top of the square gauge in this stand

The value can be determined according to Fig. 17 using the formula

The height of the roll coming out of 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 gauge collars in the 10th stand is taken as mm.

The area of ​​the roll emerging from the gauge of the 10th stand can be determined according to Fig. 17 as

Substituting the values ​​of the indicated parameters we get

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 drawing coefficient in the gauge of the 11th stand is determined as

Theoretical width of the roll coming out of the 11th stand

Theoretical width of the roll emerging from the 10th stand (with a radius of curvature at the collar = 5)

To check the capture of the rolled material entering the gauge of the 11th stand, it is necessary to calculate the absolute compression at characteristic points of the gauge and compare it with the permissible data.

Thus, the magnitude of absolute compression in the area of ​​the jumper of a two-thread roll will be

and in the area where stream axes break, it will be

alloy steel rolled casting module

So, as you can see, here the region of the roll jumper needs to be checked for the capture condition.

The grip angle in the area of ​​the jumper when rolling in the 11th stand gauge can be determined as

where: D is the nominal diameter of the rolls in the 11th stand (D = 33 mm).

The permissible grip angle in this caliber can be determined using the method of M.S. Mutyeva and P.L. Klimenko, this requires a rolling speed in this stand, which will

5.67 m/s, (45)

and then the maximum permissible grip angle is determined by the formula (t = 980?)

Because the conditions for capture in the 11th separating caliber are met.

The gauge in the 9th stand of the intermediate group of stands is located in vertical rolls and can largely resemble a diagonal square gauge, but has its own characteristics. It is designed for rolling rhombic bars and in the area of ​​the connector has a more cramped shape than a regular diagonal gauge. Rolling in this caliber involves deformation processing of future lateral horizontal parts of double-strand rolled products, which will be subjected to rolling-separation. Taking into account the above, the construction and general appearance of this preparatory gauge in a 9-stand can be presented in Fig. 20.

Fig.20.

To determine a number of caliber parameters, we use some empirical dependencies obtained in similar calibrations during rolling-separation.

So, the side of the square, as for the 10th gauge, can be determined 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 beads 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 gauge will be

Based on practical data from rolling-separation calibrations, we assume that the radii of curvature at the tops of the gauges and at the shoulders are the same and equal to 5 mm, i.e. mm.

The gauge thickness of the 9th stand will be

Thickness of the roll coming out of the 9th stand gauge

Also, based on practical data, we accept the size of the gap along the caliber collars as 5 mm, i.e. mm.

The area of ​​the roll emerging from the 9th stand can be determined as

and then, substituting the values ​​of the indicated parameters, we get

The drawing coefficient in a 10-stand gauge is determined as

To check the grip of the rolled material entering the caliber of the 10th stand, it is necessary to calculate the absolute compression in this stand.

Since the shapes of the gauges of the 9th and 10th stands are very different in configuration, we will replace their area with the reduced one (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 absolute compression value will be

The given value of the grip angle in the caliber of the 10th stand will be

As you can see, 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 gauge is a rhombic gauge located in horizontal rolls. The construction and general appearance of this caliber is shown in Fig. 21.

Fig.21.

The dimensions of the rhombic gauge are determined in the process of calibration calculation, taking into account the specified value of the drawing coefficient in the caliber, the correct filling of the caliber, and also taking into account the obtaining of section dimensions that satisfy the rolling conditions in the next caliber.

In practice, rhombic calibers are used, characterized by size.

To prevent the formation of “straps” in the gaps of the gauge, it is recommended to take the filling degree of the gauges

We determine the maximum permissible grip angle in this caliber using the formula of M.S. Mutyev and P.L. Klimenko, if v = 3.9 m/s; t=990? and steel rolls according to the formula, at v=2-4m/s

and then the value of the maximum absolute compression will be

When rolling a rhombic billet in a square gauge (conventionally, we can consider rolling a rhombic billet in a 9-gauge). The side of a 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 coefficient in the 9th gauge; we can calculate the rolling area in the 8th gauge as

And then, the thickness of the roll coming out of the rhombic gauge of the 8th stand will be

The widening of the 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 widening, the width of the roll in the 9th gauge should be

and as you can see, such a roll from a rhombic gauge into a square one can be rolled without overfilling the gauge, 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

We take the gap at the caliber connector to be equal to 5 mm, i.e. .

Theoretical height of a rhombic gauge - can be determined by the formula

The bluntness of the rhombic stripe at the caliber connector is defined as

Theoretical width of a rhombic gauge - defined as

The vertex angle - in can be defined as

From (74)

in = 2 arctg1.98 = 126.4°

Side of a rhombus - defined as

In the roughing group of stands, consisting of 6 working duo stands with alternating horizontal and vertical rolls, the rolling of a round billet with a diameter of 80 mm, arriving from a crimping cross-roller planetary stand, is rolled along an oval-rib oval drawing pass system. This system has become widespread in the rolling of high-precision round steel from alloy and high-strength steels on continuous mills.

In the 7th stand of the roughing group, the gauge is a ribbed oval located in the vertical rolls. The construction and general appearance of this caliber are presented in Fig. 22.

Fig.22.

Based on practical data, the drawing coefficient in the rhombic caliber of the 8th rolling stand in the form of a rib oval can be recommended within the range of 1.2-1.4. And then, the area of ​​the roll coming out of the gauge in the form of a rib oval in the 7th stand will be

The total elongation factor in the roughing group of stands will be

where is the area of ​​the round bar coming out of the planetary crimping cage, .

Previously, based on practical foreign data, it was shown that taking into account the deformation of continuously cast billets with a diameter of 200 mm in a planetary stand, the optimal kinematic dependence of the roll coming out of this stand should have a circular cross-section with a diameter of 80 mm.

The average draft ratio in this caliber system will be

Usually, as practice shows, in a ribbed oval caliber the draft is within the limits, and in oval calibers the draft is usually higher. And then, taking the hood in oval rib calibers, it is recommended to calculate the hood in oval calibers using the formula

In the 2nd stand, the circle must be rolled in an oval caliber, which leads to a decrease in the drawing coefficient and then

At ratio, the roll becomes unstable when rolling in a ribbed oval gauge. Usually ovals with a ratio are used. In ribbed oval calibers, the ratio between the height and width of the caliber is

Let us determine the permissible grip angle in the rhombic gauge 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 compression at, will be

The thickness of the roll coming out of the 7th stand will be determined as

The width of the roll coming out of the 7th stand will be determined as

The radius of the oval is determined by the formula

The rounding of the collar is performed with a radius

We accept the size of the gap

The amount of blunting of the oval at is determined to be equal to the size of the gap, i.e. mm.

The general layout of the drawing passes of the roughing group of the mill stands is shown in Fig. 23.

Fig.23.

So, as you can see, in the 6th stand the gauge is oval and is located in horizontal rolls.

The area of ​​an oval of this caliber is determined as

The oval gauge is single-radius and schematically no different from the previously considered oval gauge in the chit group of stands (see Fig. 15).

Oval gauge height

where is the widening of the oval stripe in the rib oval caliber, it is recommended to determine by the formula

where D is the diameter of the rolls, equal to 420 mm

Width of roll coming out of oval gauge

As is known, the area of ​​an oval caliber is

Formula (93) can be represented as quadratic equation, the solution of which allows us to determine

after opening the brackets we get

And then, the absolute compression in the rib oval gauge of the 7th stand will be mm.

Let us determine the permissible grip angle in the rib oval of the 7th stand, if v = 2.8 m/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 permissible compression at.

As you can see, the capture conditions are met, and there will be broadening.

The final dimensions of the oval in the 6th stand gauge will be

The remaining dimensions of the oval gauge will be: the radius of the streams is defined as

The gap S along the caliber collars will be

Corner radius

As can be seen from Fig. 23, in the 5th stand the gauge is a rib oval and is located in vertical rolls.

Calibration of rolls in pairs of gauges of the 4th and 5th stands, 2nd and 3rd stands is carried out similarly to the given calculations for the calibration of gauges of 6th and 7th stands and, according to the general layout of the gauges (see Fig. 23), in the 2nd stand the gauge is made in the form single-radius oval and located in horizontal rolls. This caliber involves rolling a round profile with a diameter of 80 mm, coming from a 3-roll planetary crimping stand with an oblique arrangement of rolls.

The drawing coefficient in the oval gauge of the 2nd stand will be

Where is the cross-sectional area of ​​the round bar (80 mm in diameter) coming from the planetary crimping stand.

Absolute compression along the vertices in an oval gauge of a 2-stand will be

The average absolute reduction when rolling a circle in an oval gauge of the 2nd stand will be

When rolling a round billet in an oval gauge, the expansion 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.

Calibration of a crimping cross-roller planetary stand consists of installing inclined conical rolls, which, when rotating around their axis and planetary motion, should form a gap with the required inscribed circle (in the case under consideration, 80 mm in diameter) at the exit of the product from the rolls, and similarly with the required inscribed circle (diameter 200mm) at the entry of the workpiece into the rolls. The task of calibrating 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 diagram of the deformation zone, indicating the calibration parameters of inclined conical rolls necessary for rolling the workpiece in question, is presented in Fig. 24.

Determining the parameters indicated in the diagram is the task of calibrating the rolls of the crimping cross-shaft planetary stand.

Fig.24.

The dimensions presented in Fig. 22 characterize the following parameters:

Distance from the rolling axis at the crossing point;

The same, but total along the roll axis;

and are the radii of the workpiece and rolled product, respectively;

Angle of inclination of the generatrix of the deformation zone cone;

The angle of inclination of the forming surface of the roll;

Ш - angle of crossing of the roll with the rolling axis;

Accordingly, the radii of the roll at the pinch, the calibrating section and the maximum (at the entry of the workpiece);

A - tangential displacement of the roll (not shown in the figure).

Based on practical data obtained from the design conditions and operating experience of similar mills, it is recommended to select some elements and parameters for roll calibration within the following limits:

(i.e. the diameter of the roll at the pinch);

(i.e. maximum roll diameter);

W = 45-60° (i.e. we take the crossing angle w = 55°);

the angle between the line of centers of the workpiece shaft and the projection line of the roll is = 45°.

Draw coefficient in the 1st stand

The remaining two working rolls of the crimping stand have the same dimensions as those presented above for the roll being calculated.

In the calibration calculations, the parameters of rolling speed and temperature across the stands were used.

Thus, the exit velocities from the stands were calculated using 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 obtain:

The entry speed of the workpiece into the 1st (planetary) stand will be approximately 7.9 m/min.

The overall change in metal temperature during rolling can be determined by the formula

Where and is a decrease in the temperature of the metal due to heat transfer by radiation and convection to the environment;

Decrease in metal temperature due to heat transfer by thermal conductivity upon contact with rollers, wires, rollers of roller tables;

An increase in metal temperature due to the conversion of mechanical deformation energy into heat.

And then, based on the use of the method, the change in the rolling temperature during rolling in the caliber and moving to the next caliber will be

Where is the temperature of the roll before entering the considered caliber, ?;

P - perimeter of the cross section of the roll after passage, mm;

F is the cross-sectional area of ​​the roll after passing, ;

f - cooling time of the roll, s;

Increase in metal temperature in the caliber, ? and is determined by the formula

p - metal resistance to plastic deformation, MPA;

m is the elongation coefficient.

So, for example, the change in metal temperature during the movement of the workpiece from the heating furnace to the 1st stand of the mill according to formula (200) will be (if the heating temperature of the workpiece, f =, P = n 200 = 628 mm, F = 31416)

The increase in metal temperature in the 1st (planetary) stand due to intense deformation can be determined by formula (201) taking p = 100 MPa and and then

The final temperature of the metal after rolling in each stand, taking into account the change in rolling temperatures calculated using 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 workpiece with a diameter of 200 mm along the mill stands are given in Table 3.

Table 3. Basic calibrations for passes when rolling a 18mm circle from a 200mm workpiece.

Aisle no.	Type of caliber	Roll arrangement	Roll size	Compression, mm	Widening	Caliber area, F, mm	Coef. Hoods, m	Rolling temperature, t,?	Rolling speed v, m/s	Note
Thickness, h
Initial conditions:				Heating temperature
	3-roll	Oblique							Kosovalk. Planets. Cage.
	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 rolled material in caliber
	Single radius oval	Vertical									45° tilting
		Horizontal

Calculation diagrams of roll calibers for all mill stands when rolling a circle of 18 mm from a continuously cast billet 200 mm are shown in Fig. 25.

Calibration of profiles and rolls intended for rolling round and square steel

TO hot rolled round steel according to GOST 2590-71, they include profiles that have a circular cross-section with a diameter of 5 to 250 mm.

In general, the calibration scheme for round steel can be divided into two parts: the first is calibration for roughing and middle groups of stands and satisfies a number of profiles, being in this sense common to several final profiles of different sections (square, strip, hexagonal, etc.) , and the second is intended as a specific system for the last three to four stands and is characteristic only of this round steel profile. In roughing and middle groups of stands, gauge 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 gauge, the pre-finishing stand has an oval gauge, the gauge of the third stand from the end of rolling can be of different shapes, on which the calibration system depends.

General caliber diagrams of the last four passes when rolling round steel. From these diagrams it follows that oval gauges of two shapes are used as pre-finishing gauges: single-radius and with rounded rectangles - the so-called “flat” gauges. 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 rolling scheme, seven types of gauges used in the pre-oval stand can be noted. According to the second general scheme, only two types of gauges have found the greatest use: box square 1 and square 3, embedded in the roll barrel when positioned diagonally.

The systems and shape of the gauges used for roughing and middle groups of stands can be very diverse and depend on a number of factors, the main ones being 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 stripping of small-thickness undercuts of the rolled material by caliber collars; formation of 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 internal diameter, does not satisfy 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 most insignificant change in technological conditions (lowering the rolling temperature, producing pre-finishing caliber rolls, increasing the height of the oval, etc.), the streams become overfilled with metal. Obtaining a profile in accordance with the shape of the finishing gauge requires constant monitoring of the dimensions of the pre-finishing oval roll. In cases where the gauge is overfilled, 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 a camber (release) for a round steel profile, i.e., provide a slightly larger horizontal diameter compared to the vertical one. This is also necessary due to the fact that the oval-section rolled product entering the finishing gauge has a lower temperature at the ends of the major axis and the thermal shrinkage of the finished profile upon cooling in the direction of the horizontal diameter is somewhat greater than in the direction of the vertical diameter. Intensive wear of the finishing gauge of round steel vertically due to greater compression also contributes to the size exceeding the horizontal diameter by 1-1.5% over the vertical.

Round steel At domestic factories they tend to roll 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.