Mechanical engineering and mechanics. Design of gauges Construction of finishing gauge for round steel

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 - D c, 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:

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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.

Rough rolling gauges round profiles are also performed in any system, and the last three calibers are performed 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

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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.

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 using 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

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

Oval-circle system

Figure 1.8. Diagram of metal rolling in a gauge system

"oval-circle".

The system is a special case of the “oval-rib-oval” system and, if necessary, allows you to create “universality” of calibration, ensuring the production of round profiles of standard diameters from intermediate working stands (during the rolling of metal in the mill), which reduces downtime of the mill for transshipment . However, the “universality” of roll calibration systems somewhat complicates the implementation of the metal compression mode on the mill, which to some extent can be attributed to the disadvantages of the system. The low stability of a single-radius oval in a round gauge prevents the rolling of metal while maintaining high values ​​of the partial “draw” of the metal, and the value of the average “draw” of the metal in the “oval-circle” system is (). It is not rational to use the gauge system as an exhaust system, although it is indispensable as a finishing system, which is successfully implemented at the 350 OEMK mill.

Some elements of calibers of simple form are common to all types of calibers.

The gap between the rolls (roll collars), . Under the influence of forces from the rolled metal, the distance between the rolls increases due to the selection of gaps in the stand parts and the elastic deformation of the stand. At the same time, the height of the caliber will increase. Therefore, the drawing of the gauge should show its shape and dimensions at the time of rolling the strip, that is, together with the gap (Figure 5.1).

The gap allows you to change the height of the gauge during rolling, thereby changing the profile of the rolled metal. With a large gap, the contact zone between the metal and the rolls is small, the contour of the pass is not closed, and therefore the performance of the dimensions and shape of the rolled product deteriorates. For this reason, clearances in finishing gauges should be kept to a minimum.

The gap size is taken as a fraction of the nominal diameter of the rolls (Table 1.2.) or the height of the pass (strip height).

Table 1.2. Minimum gaps between roll collars

Group of stands of small-section (medium-section) and wire line of mill 350	No. of cages	, mm
Rough group
I intermediate
II intermediate
Finishing
Finishing block

Figure 1.9. Scheme of construction and typical elements of a caliber: a – a geometric figure forming a caliber and the contours of the surfaces of a pair of smooth rolls (here the contours are two solid thin lines); b – roll streams with curves; c – position and dimensions of the rolled strip; d – final caliber diagram.

Caliber width represents a horizontal characteristic dimension relative to the roll axis (hereinafter horizontal and vertical will be implied relative to the roll axis) geometric figure forming a caliber (Figure 1.9.).

Caliber height- characteristic vertical size of the geometric figure forming the caliber (Figure 1.9.).

Gauge insertion width- this is the width of the geometric figure forming the caliber at the level of intersection with the line of the roll collar (Figure 1.9.).

Gauge plunge depth- this is the distance from the roll collar to the bottom point of the gauge (Figure 1.9.).

Radiuses of curvature along the bottom of the caliber and along the shoulders usually expressed in fractions of the caliber height. Curves make a smooth transition in places where there is a sharp change in the caliber contour or at the collar-caliber boundary (Figure 1.9.). Roundings are necessary to reduce stress concentrations in the roll elements.

Collar width between grooves (end flange) – the horizontal size of the uncut part of the roll barrel between adjacent grooves (between the last gauge and the edge of the working surface of the roll).

The width of the collar between the calibers:

End flange width:

, (1.4)

where is the length of the roll barrel (Appendix 1)

Number of streams on the roll barrel;

In expression (1.4) two quantities vary: . The resulting value must satisfy condition (1.5). Thus, in addition to finding the dimensions of the piles, the number of streams on the barrel is selected.

Caliber release. To ensure free exit of the strip from the rolls without pinching, the width of the stream should increase from the bottom to the center of the groove. Therefore, the side walls of the caliber are made inclined relative to the contour of the geometric figure forming the caliber. The tangent of the angle of inclination is called the caliber release. Sometimes caliber output is expressed as a percentage.

Strip height - vertical characteristic size of the strip emerging from the rolls.

The width of the line - horizontal characteristic size of the strip emerging from the rolls.

Dulling the stripe at the gauge connector (Figure 1.9) shows the vertical size of the part of the rolled strip free from contact with the rolls.

The width and bluntness of the strip are additional geometrically clear parameters that describe an important characteristic of rolling in calibers - degree of filling of the caliber with metal. The degree of filling is determined by the formula.

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 round gauge, the pre-finishing stand is oval, the gauge of the third stand from the end of rolling can be of various 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.

Domestic factories tend to roll round steel 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.