1. The profile of the hole, images, adjacent grooves of the rolling rolls in the working position and the gaps between them, serves to give the specified shape and size to the section of the roll. Usually the roll is formed by two, less often by three or four rolls. The shape of the boxes can be simple - rectangular, round, square, diamond-shaped, oval, strip, hexagonal, lancet and shaped - corner, I-beam, channel, etc. By design, i.e. position of the parting line, they are divided into open. and closed, according to location on the rolls - open, closed, semi-closed. and diagonal. By appointment - crimping, drawing, roughing, pre-finishing and finishing. Main. el-you k. - gap between the rollers, outlet k., connector, collars, rounding, neutral. line. Types of circuits are shown in Fig. 2. Replaceable technological tool, fastened on the work roll. 3. Scale-free measuring tool for controlling sizes, shapes and relative position parts of the product by comparing the size of the product with the fit or degree of fit of their surfaces:
beam gauge - k. (1.) for rolling rough and finishing I-sections. Use b. to. straight closed, open, inclined, and universal. Usually two-rollers are used, less often - universal ones. four-roll b. K. Naib, dist. straight closed b. j. Open b. They are used as split and rough steels when rolling large I-beams. In tilt, b. to. roll I-profiles with reduction. internal slopes shelf edges and high flange heights. To the university b. Wide-flange I-beams are rolled large sizes and I-beams with para-rall. shelves. When rolling lightweight I-beams, use a horizon positioned diagon. b. To.;
drawing gauge - a (1.) simple form for reducing the cross-section and drawing (1.) of the roll with a given alternation of two or one gauge of the same type. In some cases c. they give the roll dimensions, at which the formation of a given profile begins. When rolling simple profiles, they are usually rough gauges. As a rectangular, square, rhombic, oval, hexagonal are used. and other calibers. Depending on the rolling conditions and requirements, the cross section of the roll. to. are located in a certain position. last name exhaust gauge system;
diagonal gauge - closed k. (1.) with diagonal. (different in height) location of the bed. connectors. D.K. usually cut into rolls at an angle and are used for oblique calibration of I-beams, profiles and rails. Horizon, d.k. is used when rolling I-beams, profiles on continuous mills and Z profiles. D.K. facilitates the exit of the rolled product from the rolls, but creates undesirable material. lateral forces;
closed pass - a roll (1.), in which the parting line of the rolls is outside its contour. 3. K. is usually used for rolling shaped profiles; it, as a rule, has one rotation, an axis of symmetry;
Rib oval gauge
rhombic gauge - k. (1.) rhombic. config., cut into the rolls along a small diagonal. Calculation, dimensions: C, = 5K/2sinp/2, B - B - Sa, height taking into account roundings
Diamond caliber
I, = I, -2K(1 + l/ek2) -1), a = I/I, = = tgp/2, / = (0.15-nO,20)I1, l, = (0.10 +0.15)R„ P = 2(R,2 + R,2)"2, in, = 1.2*2.5 (Fig.). R.K. is used in the rhombus-rhombus and rhombus calibration system - square. The angle at the top of the caliber p varies from 90 to 130°, with an increase in the angle of updraft in the caliber, on average, 1.2-1.3. Recommended degree of filling of the caliber 0.8 -0.9;
Lancet square caliber
lancet square gauge - k. (1.) with the outline of a square with concave sides, cut into the rolls diagonally. Calculation, dimensions: Vk = R, = 1.41 C; R = = (C,2 + 4D2)/8D; g = (0.15+0.20)С; B = 5K-- (2/3)5. Area F = C, (C, + (8/3) D), where D is the size of one side. convexity, C, is the inscribed side of a square (Fig.). Max, side size c. k.k. C^ = = C, + 2D. S. k. k. is used when necessary. transfer a large amount of metal to the finishing passes. At the same time, the values are preserved. rolling temperature, because there are no sharp corners. S. k. k. - exhaust in the oval-arrow square caliber system and sometimes pre-finishing for circles;
rough gauge - k. (1.), approx. cross-section of the workpiece or roll to the configuration of the finished profile. The black parts of shaped profiles during rolling approach the shape of the finished steel. The shape of the black parts when rolling simple profiles is determined by the exhaust system of the metal;
finishing gauge i-k. (1.) to give the rolled product a final profile, i.e. for manufacturing rolled from the end transverse dimensions sections. When designing h.c. take into account thermal expansion. metal, uneven distribution rolling temperatures, wear of calibers, additional profile adjustment and other factors;
hex gauge - k. (1.) hex. contour, cutting, into the rolls along a large diagonal. Connector w. k. located on its sides. Dimensions w. k. expression through vpi-
Hex gauge
rank circle dia. d: side C = 0.577d, area -F = 0.866d2, height H, = 2 C (fig.). Appl. The quality is clean, the caliber when rolling is hexagonal. steel and black when rolling hexagons. drill steel, when uniform and low compression along the passes is required;
Sss carbon caliber
hexagonal gauge - k. (1.) hexagonal. contour, plunge, into the 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 = 5K - S; ak = BJH, = 2.0+4.5; g = g, = (OD5+0.40)R; P = 2(Bf + 0.41R) (Fig.). Predchistova highway they are built like a regular hexagonal one, but for compensation. expansion of the metal and preventing the convexity of the side walls is clean. hexagon bottom of the caliber is made with a convexity of 0.25-1.5 mm, depending on the size of the profile. Filling degree w. k. take 0.9;
l
Box gauge
box gauge - k. (1.), image. trapeze cutting into rolls, for rectangular rolling. and square, profiles. Design dimensions: 5d = (0.95+1.00) В„; B = Poison + (I, -- S)tg(p; g = (0.10h-0.15)I,; g, = (0.8+1.0)/-, ok = = 4/I , = 0.5+2.5; />* 2(R, + B) (Fig.).The depth of cut-in of the cell I, depends on the ratio of dimensions (R,/R0) of the profile specified in it. They are mainly used on blooming, crimping and continuous billet mills, crimping and ferrous stands of section mills and for producing commercial billets on rail and beam and large-section mills.
square gauge - k. (1.)
square, contour, cut into the rolls along the dia
drove. Depending on the requirements, rental profile
performed with a rounded or sharp tips
us. Calculation, dimensions: Hk= Bf= 21/2 C I, =
= 21/2 C. - 0.83g, B =B-s;r= (0.1+0.2)^;
/-,= (0.10^0.15)I,; P = 2-21/2R, (Fig.). K.K. -
finishing when rolling square pros
lei and exhaust in rhombus-square systems,
oval-square and hexagon-square. In black
new calibers perform significant
the rounding of the vertices with a radius r. The height and width of the coque are, respectively, 1.40 and 1.43 of its sides.
When rolling squares with sharp corners, the square has an angle at the apex of the example, but 91-92° taking into account
volume of thermal shrinkage of the profile; L"" "°t -""" " "" and
control gauge - k. (1.), for small high-altitude compression and control of the dimensions of the part. el-tov roll; used when rolling a number of shaped and complex profiles, for example, I-beams, for wheel rims, door hinges, etc. K. are made closed and semi-closed. A closed k.k. provides more accurate dimensions of the rolled elements, but more often they work with semi-closed k.k.
round gauge - k. (1.) with a circle outline on the main part of the perimeter; finishing when rolling round steel and drawing in the oval-circle system. K.K. of all types have release or collapse. When constructing a finishing k.k., they usually take an outlet of 10-30° or 20-50°, depending on the diameter. rolled circle. Design dimensions: Bf = rf/cosy, B" = Yak-.Stgy, g, = (0.08+0, lO)d, P = = tk/(fig.). Because they tend to roll round steel with minus, tolerance D on dia., then for finishing k.k. taking into account thermal expansion, take d = 1.013, where rfxon "~ Diam. circle in a cold state;
multi-roll gauge - a roll (1.) with a contour formed by three or more rolls, the axes of which lie in the same plane. In the m.c., the metal is compressed in the vertical-transverse direction. with advantage all-round compression, which allows the deformation of low-plasticity materials. M. k. provide. high dimensional accuracy of profiles, therefore they are widely used in finishing stands of small-section and wire mills for rolling steel and non-ferrous materials. metals Four-roll open and closed gauges are often used at mountains. and cold rolling of high-precision shaped profiles;
crimp gauge - k. (1.) for reducing the cross-section of the rolled product and obtaining blanks for section mills. As o. because on blooming, crimping and blanking mills, box gauges are used. Deformation in o. K. is not always accompanied by creatures, hood, as, for example, in the first passes on blooming. However, to Fr. c. sometimes calibers are partially or completely attributed exhaust systems calibrations The subsection of gauges for crimping and drawing depends on the purpose of the rolling mill, the gauge system and the individual gauge;
oval gauge - (1.) an oval or close to it contour, cut into the rolls along the minor axis. O.K. is used as a pre-finishing material when rolling round profiles and as a drawing material in the oval - rib oval system, etc. Depending on the purpose of the caliber and the size of the rolls, the following are used: 1. Single-radius o. k. (ordinary o.k.), appl. as a pre-finishing agent 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; a^ = Bk/H, = 1.5 + 4.5. Elliptic and two- or three-radius o.c., used as pre-finishing when rolling large circles and in oval-circle and oval-oval systems; flat o.c., used in the same place as elliptical o.c. and as pre-finishing when rolling periodic reinforcing profiles, in of which 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 curved triangles, taken as parabolic segments; trapezoidal (hexagonal) o.k. with straight outlines, used for good retention of the roll and alignment of hoods
open gauge - k. (1.), the parting line of which is within its contour; image, cuts in two or more rolls, cut 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 shaped roll. the shoulders of two rolls. In some shaped o. because they are formed. the walls of the stream in only one roll;
semi-closed gauge - shaped connector (1.) with a connector located on the side wall near the top of the stream; used as a control when rolling channels, strip-bulb, I-beam and other profiles. Compared to the closed control gauge, it has a larger outlet and a small plunge depth of the closed groove, which weakens the roll less in diameter, allows the flanges of the rolls to be compressed in thickness, increases the number of regrinds and the service life of the rolls;
pre-finishing gauge - k. (1.) for penultimate. skipping the roll; to prepare the roll for forming. final profile. When rolling shaped
profiles are very close in shape and/or size to the finished one, but when rolling simple profiles it may differ. As p.c., rib gauges are often used when rolling strip profiles and control gauges when rolling flange profiles;
split gauge - 1. K. (1.) with a ridge in the middle part, for initial. for-world. from blanks of flanged rolled elements; for example, when rolling I-beams from rectangles. The workpiece forms sections of flanges and walls, and when rolling rails, sections for the sole and head are formed. Use open and closed rivers. k. Closed rivers They are performed on rollers of large diameter. for manufacturing large flanges. Open symmetrical R. K. with blunt ridges are often used for rolling beam blanks from slabs. 2. K. for longitudinal separation of double rolls;
Rib gauge
rib gauge - k. (1.), cut-in, into large-sized rolls; used, in particular, when rolling steel strips to regulate the width of the roll. Predchistovaya R. It also forms rolled edges. 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
rib oval gauge - k. (1.) oval contour, cut into the rolls along the major axis. Calculation, dimensions: R = 0.25/^(1 + + 1/a2), V = V- 2L, r = = rt = (0.10+0.15)5, ak = 4/R, = 0 .75*0.85, P = 2(R,2 + (4/3)r,T2 (Fig.). Used as an exhaust oval in the system - rib oval;
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Ministry of Education of the Republic of Belarus
Educational Institution Gomel State Technical University named after P.O. Sukhoi
Department: “Metallurgy and Foundry”
Explanatory note
For the course project
course: “Theory and technology of rolling and drawing”
on the topic: “Development of calibration of rolling rolls for a round profile with a diameter of 5 mm”
Completed by a student of group D-41
Rudova E.V.
Checked by Ph.D. assistant professor
Bobarikin Yu.L.
Gomel 2012
1. Introduction
2. Selection of finishing gauges and calculation of rolled cross-sectional areas
3. Selection of drawing gauges and calculation of roll sections
4. Determination of caliber sizes
5. Calculation of rolling speed
6. Calculation temperature regime rolling
7. Determination of friction coefficient
8. Calculation of rolling force
9. Calculation of rolling torque and power
caliber section profile rolling rolls
1 . Introduction
The basis of section rolling production technologies is plastic deformation of the metal in various types rolling mill roll calibers.
Sections are rolled from the workpiece in several passes in the calibers of rolling rolls, which give the rolled metal the required shape. To produce rolling metal assortments of simple and shaped profiles (round, square, hexagonal, strip, corner, channel, T-shaped, etc.), it is necessary to calculate the calibration of the rolling rolls.
Roll calibration is called the determination of the shapes of the sizes and the number of gauges measured on the rolls to obtain the finished profile.
Roll caliber- this is a gap formed by cuts in the rolls or a stream in a vertical plane passing through the axes of the rolls.
Calibration should ensure rolling from the workpiece of the required profile of the required shape and size within the accepted tolerances, as well as good quality rolled products, maximum rolling productivity, minimal wear and energy consumption spent on the operation of the rolling mill.
Rolling of the profile is first carried out in drawing passes, intended only to reduce the cross-sectional area of the rolled workpiece. When the cross-sectional area of the workpiece is reduced, the latter is extended in length without bringing the cross-sectional shape of the strip closer to the required one, which is why these gauges are called exhaust. After passing through the drawing passes, the workpiece is rolled in finishing passes. Finishing gauges are divided into pre-finishing and finishing gauges. In pre-finishing gauges (there may be several or one), with a further reduction in area, the cross-section configuration approaches the given shape of the finished profile, and its individual elements are formed. In the finishing gauge (there is always one), the required profile shapes and sizes are finally formed; it is placed on the last rolling pass.
2. Selection of finishing gauges and calculation of cross-sectional areaseniya peal
Selection of quantitiesmaterials and forms of finishing gauges
The number and shape of finishing gauges, i.e. finishing and pre-finishing gauges, depends on the shape of the finished or final profile and on the adopted calibration system for finishing gauges.
For a round profile, the finishing gauges are a pre-finishing oval gauge and a finishing round gauge. After the pre-finishing oval gauge, the oval profile roll is bent by 90° and enters the finishing round gauge, where the round profile is finally formed (Fig. 2.1). In this case, the shape of the pre-finishing oval gauge depends on the size of the finishing profile. The figure shows a pre-finishing oval gauge for medium and small finishing profile sizes.
Rice. 2.1 Scheme of round profile finishing gauges
Roll turning can be carried out using special turning guides between the rolling stands for continuous mills or turning devices, between rolling passes for foundry mills. In addition, on continuous mills, the 90° turning condition can be achieved by alternating roll stands with horizontal and vertical roll axes.
For rolling round profiles in the group of finishing gauges, we use finishing round and pre-finishing oval gauges.
Determining the dimensions of the final profile while hotIresearch institute
To increase the service life of calibers, calculations are made to obtain a profile with minus tolerances in its dimensions. In order to take into account the reduction in the dimensions of a profile rolled in a hot state during cooling, it is necessary to multiply the size of the profile dimensions in a cold state by the coefficient 1,01-1,015 .
Taking a minus tolerance for a round final profile, we find the size of the circle in the cold state:
Hot finishing wheel size:
Determination of elongation coefficients in finishing gauges.
For a finishing round gauge, the elongation coefficient where k is the number of finishing gauges, as well as for a pre-finishing oval gauge, will be determined according to the graph in Fig. 2.2.
Fig. 2.2 Dependence of the drawing coefficients in the finishing wheel, as well as in the pre-finishing oval, on the corresponding diameter of the wheel .
Note: if a round profile with a diameter of less than 12 mm inclusive is rolled, then the drawing coefficients in the finishing and pre-finishing gauges are determined according to practical recommendations for a specific profile. Taking into account the design features of the rolling mill 150 BMZ, we take the average draws equal to 1.25.
Determination of cross-sectional areas of profiles in finishing potsbrah.
The areas of profiles in finishing gauges will be determined by the dependencies:
where is the cross-sectional area of rolled products in the finishing gauge, determined by
according to hot dimensions of the final profile; - cross-sectional area of the roll in the last pre-finishing gauge; - cross-sectional area of the roll in the penultimate pre-finishing gauge. Let us determine the cross-sectional area of the strip in a finishing round gauge:
The cross-sectional area of the strip in the pre-finishing oval gauge is equal to:
The cross-sectional area in the last rough pass and, accordingly, in the last rolling pass of the drawing group of pass passes, is determined by the formula:
3. Selection of exhaust gauges andcalculation of cross-sectional areas of rolls
Selecting a draft system
As a rule, drawing calibers are formed according to certain systems, which are determined by the alternating uniform shape of the calibers.
Each drawing caliber system is characterized by its own pair of calibers, which determines the name drawing caliber system.
Pair of draw gauges- these are two successive gauges in which the workpiece moves from an equiaxed state in the first gauge to a non-equiaxed state, and in the second again to an equiaxed state, but with a decrease in cross-sectional area.
The following drawing gauge systems are used: rectangular gauge system, rectangle - smooth barrel system, oval - square system, rhombus - square system, rhombus - rhombus system, system square-square, universal system, combined system, oval-circle system, oval-rib oval system.
On small- and medium-sized modern continuous rolling mills, the following systems are more often used: diamond-square, oval-square, oval-circle and oval-rib oval.
These calibration systems ensure good quality of rolled products and stable position of the rolled products in the calibers.
When rolling in drawing rolls, the roll is always turned over or rotated around its longitudinal axis at a certain angle (usually 45° or 90 °) when the roll passes between stands from the first gauge of a pair of gauges to another gauge.
The turning can be replaced by alternating horizontal and vertical rolling stands, which provides the effect of turning without turning the workpiece.
Roll turning or alternation of horizontal and vertical rolling stands or rolls is necessary to transform the non-equiaxial state of the workpiece after passing the first pass of a pair of drawing passes into an equiaxed state in the second pass of the pair.
One of the most promising calibration systems is the oval - rib oval system, which ensures stable rolling conditions and good quality of rolled products.
In this system, in oval gauges, the workpiece goes into a non-equiaxial oval state with a large difference in the sizes of the oval axes, and in ribbed oval gauges - into an equiaxial oval state with a small difference in the sizes of the axes after deformation of the previous non-equiaxial oval along the major axis. Thus, the workpiece sequentially passes through the types of gauges: oval - ribbed oval - oval - ribbed oval, etc. until the required reduction in the cross-section of the workpiece is obtained.
Determination of average draft inarach drawing gauges and numbersrolling passes.
To determine the number of rolling passes n First, we determine the estimated number of pairs of exhaust gauges:
where is the cross-sectional area of the workpiece in the hot state;
The cross-sectional area of the workpiece in the last drawing pass.
Having determined the exact number of pairs of exhaust calibers, then it is necessary to establish a refined value of the average draft for a pair of exhaust calibers
The number of rolling passes in drawing passes is:
The number of rolling passes for the entire rolling technology is equal to:
Where To- number of finishing gauges.
Here it is necessary to check whether the total number of rolling passes will not exceed the number of rolling stands of the mill according to the inequality:
Where With- number of rolling stands of the mill.
The cross-sectional area of the workpiece in the hot state, taking into account a wide tolerance on the cross-sectional size, will be determined by the nominal cross-sectional size:
For the oval system - rib oval. Let's accept.
The estimated number of pairs of exhaust gauges is:
We will accept the exact number of pairs of exhaust gauges.
The adjusted average draw value for a pair of draw calibers is:
The number of rolling passes in drawing passes according to (3.3) is equal to:
The number of rolling passes is:
Let's check condition (3.4): .
The results of the distribution of rolling passes and types of gauges among the mill stands are recorded in Table 3.1.
Definition of hoods for pairs of hoods.
The draw of each pair of calibers is determined by the dependence:
where is the change in value
When making changes to the values of hoods for each pair of calibers, it is necessary to take into account the equality of 0 of the algebraic sum of all changes, i.e. the following condition must be met:
Let us determine the draws for each pair of calibers, taking into account their redistribution so that the initial pairs of calibers would have larger draw values, and the last ones - smaller ones.
Let us make changes for each pair of calibers according to expression (3.5), remembering that the algebraic sum of these changes must be equal to 0:
Determination of drafts by rolling passes in the drawing systemandcalibers
Let us determine the hoods for the rib ovals with the known formula:
We determine the hoods for ovals using the formula:
Using formulas (3.7) and (3.8), we determine the numerical values of the draws for all rolling passes along the draw passes:
For j= 7(14;13)
We enter all values of hoods for exhaust and finishing calibers in Table 3.1.
Determination of cross-sectional areas of rolled products in drawing gauges.
Let us determine the cross-sectional area of the rolled product after each rolling pass using the formula:
where is the cross-sectional area of the roll;
The area of the next section of the roll along the rolling path;
Drawing in the next caliber in the rolling process.
According to the condition, after the last, i.e., 26th, pass, the cross-sectional area of the roll should be equal to 28.35 . Thus, for.
The cross-sectional area of the workpiece before the first pass is equal to the cross-sectional area of the original workpiece. This value must be obtained from the product. However, due to the accumulation of rounding errors during calculations, in order to accurately obtain the value, it is necessary to adjust the extraction value in the first pass:
The obtained values of the rolled cross-sectional areas for all rolling passes are entered into Table 3.1.
Table 3.1 Calibration table
|
Type of caliber |
Sectional area of the roll F, |
||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
oval |
|||||
|
Rib oval |
|||||
|
Pre-finishing oval |
|||||
|
Finishing round |
4. Determination of caliber sizes
The diagram for constructing a finishing round K-th gauge is shown in Fig. 4.1. The diagram shows the following dimensions: - diameter or height of the gauge, equal to the hot size of the diameter of the final round-rolled profile; - roll gap; - caliber release angle; - caliber width.
Fig. 4.1 Diagram of a round gauge
The size of the gap between the rolls is determined by the formula:
The width of the caliber and the width of the strip will be equal to the diameter of the caliber.
Values and select the following:
The diagram for constructing a pre-finishing oval (K-1) gauge for rolling an oval strip intended for subsequent rolling in a finishing round gauge of a round profile with a diameter of no more than 80 mm is shown in Fig. 4.2. We will calculate all the required dimensions:
Fig. 4.2 Diagram of an oval caliber
The height of the caliber is equal to the height of the strip, which is determined by the formula:
where is the cold diameter of the finished round profile being rolled;
Coefficient that takes into account the widening of the oval stripe in a finishing round gauge.
The dullness of the stripe is determined by the formula:
Rice. 4.3 Dependence of the coefficient on the width of the rib oval stripe, the preceding rib oval caliber
The bandwidth is determined by the formula:
where is the cross-sectional area of the oval strip after passing the pre-finishing oval gauge. The radius of the outline of the pre-finishing oval gauge is determined by the formula:
We assign the value of the gap between the rolls:
The width of the caliber is determined by the formula:
Determine the fill factor of the caliber:
The value must be within the limits.
We enter the main dimensions of finishing and pre-finishing gauges in Table 4.1.
Construction of exhaust gauges.
For the oval-rib oval drawing gauge system, we first build all the oval rib gauges according to the diagram in Fig. 4.4 and the calculation given below. When rolling a square profile, the last one in the rolling process is an equiaxial square gauge, which at the same time is a pre-finishing square gauge. In our case, the initial profile of the rolled workpiece is square, then for convenient gripping of the workpiece, we build the first equiaxial gauge during rolling according to the diagram in Fig. 4.4. Then we build all the oval gauges according to the diagram in Fig. 4.2. and the calculation below.
Rice. 4.4. Scheme of rib oval caliber
For all ribbed oval gauges, i.e. for all calibers, the caliber dimensions are determined in the following sequence.
Example calculation for caliber 26.
Width of rib oval stripe
where is the cross-sectional area of the oval rib strip.
Height of rib oval stripe
The caliber width is
where is the fill factor of the caliber, equal to 0,92…0,99 , we will accept in advance.
Caliber outline radius
The dullness of the band is equal to:
The height of the roll gap is determined from the range where is the diameter of the rolls of the corresponding rolling stand.
In this case, the condition must be met
We carry out the calculation similarly for all other x calibers. We enter all the main dimensions of rib oval gauges in Table 4.1.
For all non-equiaxial gauges (Fig. 4.2.), the dimensions are determined against the rolling stroke.
For each non-equiaxial oval gauge, the dimensions are determined in the following sequence.
First, we determine the broadening in the equiaxed oval ribbed gauge next to the given gauge in the course of rolling using the formula:
where is the broadening determined from the graph in Fig. 4.6. depending on the width of the oval rib strip in question;
The diameter of the stand rolls for a given equiaxed pass.
Fig.4.6. Dependence of the magnitude of the widening of an oval strip in a ribbed oval gauge on the width of the ribbed oval strip during rolling in rolls.
The height of the oval stripe is:
The height of the caliber is equal to the height of the strip, i.e.
The dullness of the oval stripe is equal to:
where is the coefficient determined from the graph in Fig. 4.3.
Preliminary value of the width of the oval strip:
where is the cross-sectional area of the strip after passing the caliber in question.
The value of the average absolute compression of the metal in the oval gauge under consideration is equal to (for):
where is the width of the rhombic oval strip in the previous caliber under consideration.
The rolling radius of the roll is equal to:
where is the diameter of the rolls of the stand under consideration.
The average height of the strip at the exit into the considered caliber is equal to:
The broadening of the metal in an oval caliber is determined by the formula:
The width of the oval stripe is:
The radius of the caliber outline is determined by the formula:
We will assign a preliminary value of the roll gap from the range if the condition is met.
Caliber fill factor:
After this, we check the condition for normal filling of the caliber with metal.
Let us carry out the calculation for the 3rd non-equiaxial oval gauge using the above formulas.
We carry out the calculation similarly for all other calibers. We enter the main dimensions of all intermediate oval calibers in the table. 4.1.
Table 4.1. The penetration depth of the gauge is determined by the formula:
Table 4.1 Calibration table,
|
Rolling pass no. |
Strip height |
The width of the line |
Caliber height |
Caliber width |
Shaft clearance |
Cutting depth |
|
5. Calculation of rolling speed
We determine and enter into Table 5.1 all the values of the rolling diameters of the rolls. In this case, for oval gauges we will define them in terms of the radii determined by formula (4.31). For all other gauges, the rolling diameters of the rolls are determined by the formula:
where is the diameter of the roll barrel of the corresponding caliber;
The cross-sectional area of the strip at the exit from the corresponding gauge;
Bandwidth at the outlet of the caliber.
Let's carry out the calculation for caliber 2.
Then we determine the number of revolutions per minute of the rolls in the last stand during rolling according to the formula:
where is the rolling speed at the exit from the last stand, which is determined
working conditions of the mill, 8 0 m/s;
Rolling diameter n-oh cage, mm.
where is the cross-sectional area of the strip after passing n-th cage, i.e. final rolled products, .
To ensure some strip tension between the stands, the calibration constant for each rolling pass must be slightly reduced as we move from the first pass to subsequent ones. Therefore, the calibration constant for the penultimate pass is:
By analogy, against the rolling stroke, we determine the calibration constant for all rolling passes, i.e.
The rotation speed of the rolls for each pass is determined by the formula:
We enter all values in table 5.1.
The strip speed after each rolling pass is determined by the formula:
where in and in.
We enter all values in table 5.1.
We carry out the calculations similarly for all other calibers, and enter all the calculation results in Table 5.1.
Table 5.1. Calibration table
|
Rolling pass |
Rolling diameter of rolls, |
Calibration constant |
Roll rotation speed, |
Lane speed, |
|
6. Calculation of temperatour rolling mode
The task of calculating the temperature regime of rolling is to determine the temperature of the initial heating of the workpiece before rolling and to determine the temperature of the roll after each rolling pass.
Small section wire rolling mill 320 has the temperature of the billet at the furnace outlet before the first rolling stand 107 0 . When rolling in a 20-stand group and a wire block, the temperature of the rolled product at the exit from this block is 1010…1070 . The heating temperature of the workpiece for rolling a square profile made of steel 45, taking into account the table. 6.1. and technological capabilities of the mill furnace 320 we take equal 12 50 , and at the exit from the 20th stand the temperature of the rolled product is taken equal to 107 0 .
The rolling temperature for rolling passes is assumed to be equal to the average, i.e.
7. Determination of friction coefficient
The coefficient of friction during hot rolling of metals can be determined by the formula for each rolling pass:
where is a coefficient depending on the material of the rolling rolls; for cast iron rolls, for steel rolls;
A coefficient that depends on the carbon content in the rolled metal and is determined from table. 7.1. (m/u 2130 p. 60).
A coefficient that depends on the rolling speed or the linear speed of rotation of the rolls and is determined from the table. 7.2. (m/u 2130 p. 60).
Similarly, using formula (7.1), we calculate the friction coefficient for each rolling pass; we enter all the necessary data and calculation results in Table 7.1
Table 7.1
|
Rolling pass no. |
|||||
8. Calculation of rolling force
Determination of the area of metal contact with the roller.
Contact area of the rolled metal with the roller i caliber is determined by the formula:
where and are the width and height of the strip at the outlet of the caliber;
and - width and height of the strip at the outlet of the caliber;
The influence coefficient of the caliber shape, determined from the table. 8.1. (m/u 2130 p. 60). - radius of the roll along the bottom of the caliber.
The radius of the roll along the bottom of the groove is determined by the formula:
where is the diameter of the roll barrel; and - height and roll gap of the caliber. Let's calculate the first pass:
We calculate all values in the same way and enter them into the table. 8.1.
Determination of the stress state coefficient of the deformation zone.
The stress coefficient of the deformation zone during strip rolling for each rolling pass is determined by the formula:
where is a coefficient that takes into account the effect of the width of the deformation zone on the stress state;
Coefficient taking into account the influence of the height of the source;
Coefficient taking into account the effect of rolling in a caliber.
The coefficient is determined by the following dependence
The coefficient is determined by the dependence
where is the caliber shape coefficient for non-shaped calibers (square, rhombus, oval, circle, hexagon, etc.);
Gauge shape factor for shaped gauges.
Let's calculate the first pass:
Determination of resistance to plastic deformation.
The resistance to plastic deformation of the rolled metal for each rolling pass is determined in the following sequence.
Let's determine the degree of deformation
Then we determine the strain rate
where is the rolling speed in mm/s, we take from the table. 5.1.
determined by the formula:
Let's calculate the first pass:
We enter all values in the table. 8.1.
Determination of average pressure and rolling force.
The average rolling pressure for each rolling pass is:
Rolling force for each pass
Let's calculate the first pass:
We enter all values in table 8.1
Table 8.1. Calibration table
|
Rolling pass number |
Metal temperature |
Friction coefficient, f |
Contact area |
Stress factor states, |
|
Continued Table 8.1.
|
Rolling pass number |
Resistance to plastic deformation |
Average rolling pressure, |
Rolling force, P, kN |
Rolling moment |
Power pro- rollers N, kW |
|
9. Raseven torque and rolling power
The rolling moment is determined by the formula:
Similarly, we determine the moment of inertia for each rolling pass, and enter all the calculation results into the table.
Determination of rolling power
The rolling power is determined by the formula:
Calculation example for the first rolling pass:
Similarly, we determine the power for each pass, and enter all the calculation results in Table 8.1.
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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, ingot models, side faces, section distortions, etc.
Control questions
1 What is the main task of the rolling production process?
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 patterns of crimping and drawing gauges are used, for example, box, rhombus-square, rhombus-rhombus, 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 a round profile, there is comparatively no large 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. The draw in a finished square caliber is taken to be 1.1÷1.15.
When producing a square profile 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 in the range 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 dimensions and tolerances of the gauge 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, the dimensions of finishing gauges for hot rolling of steel profiles should be 1.010-1.015 times larger than the dimensions of the finished profiles.
The dimensions of the calibers increase during rolling due to their depletion. When dimensions equal to the nominal plus tolerance are reached, the caliber becomes unsuitable for further work and is replaced with a new one. Therefore, the greater the tolerance on profile dimensions, the longer the service life of the gauges, and, consequently, the productivity of the mills. Meanwhile, the increased tolerance leads to excessive consumption of metal for each meter of length of the manufactured product. It is necessary to strive to obtain profiles with dimensions that deviate from the nominal ones in a smaller direction.
In practice, calibers are not built with positive calibers, but according to average tolerances or even with some minus. Improving the equipment of rolling mills, improving production technology and introducing automatic equipment for setting rolls will contribute to the production of rolled products with increased accuracy.
GOST 2590-71 provides for the production of round steel with a diameter of 5 to 250 mm.
Rolling of this profile is carried out differently depending on the steel grade and dimensions (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 obtain a number of adjacent sizes of round steel (Fig. 117). Method 3 is that the pre-finishing oval can be replaced with 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 side walls in this caliber allows for better scale removal. Since this method allows you to widely adjust the size of the strip coming out of the rib gauge, it is also called universal sizing. Methods 5 and 6 differ from the others 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 calibration system.
Comparison possible ways obtaining round steel shows that methods 1-3 allow in most cases to roll the entire range of round steel. Rolling of high-quality steel should be carried out using methods 7-10. Method 9 is, as it were, intermediate between the oval-circle and oval-oval systems, and is the most convenient in terms of regulating and adjusting the mill, as well as preventing sunsets.
In all the considered methods of rolling round steel, the shape of the finishing and pre-finishing passes remains almost unchanged, which helps to establish 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 calculated diameter of the gauge (for a hot profile when rolling at minus) d g = (1.011÷1.015)d x - part of the tolerance +0.01 d x, where 0.01d x, - increase diameter for the reasons stated above; d x = (d 1 +d 2 /2) - diameter of the round profile in the cold state. In practice, when calculating, the second and third terms of the right side of the equality can be considered approximately the same, then
d g = (1.011÷1.015)(d 1 +d 2)/2,
where d 1, d 2 are the maximum and minimum permissible diameter values according to GOST 2590-71 (Table 11).
Depending on the size of the rolled circle, the following tangent angles α are selected:
We accept the gap value t (according to rolling data), mm:
Based on the data obtained, the caliber is drawn.
Example. Construct a finishing roll for rolling round steel with a diameter of 25 mm.
- Let's determine the calculated diameter of the gauge (for a hot profile) using the equation above.
We find from the table: d 1 = 25.4 mm, d 2 = 14.5 mm; whence d g = 1.013 (25.4 + 24.5)/2 = 25.4 mm. - We choose α=26°35′.
- We accept the gap between the rollers as t=3 mm.
- Using the data obtained, we draw the caliber.
Pre-finishing gauges for the wheel are designed taking into account the accuracy required for the finished profile. The closer the oval shape approaches the shape of a circle, the more accurate the finished round profile is. Theoretically most suitable form profile to obtain the correct circle is an ellipse. However, such a profile is quite difficult to maintain when entering a finishing round gauge, so it is used relatively rarely.
Flat ovals are well held by wires and, in addition, provide large compressions. But the thinner the oval, the lower the accuracy of the resulting round profile. This is explained by the degree of broadening that occurs during compression. The broadening is proportional to the compression: where there is small compression, there is small broadening. Thus, with small oval compressions, the possibility of size variations in a round gauge is very insignificant. 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, ovals outlined by one radius turn out to be too elongated along the major axis and, as a result, do not provide reliable grip of the strip by the rolls. The use of sharp ovals, in addition to the fact that it does not ensure an accurate circle, has a detrimental effect on the durability 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 production of calibers leads to the appearance of second grades and sometimes defects.
A study of the reasons and mechanism for producing 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 groove of the finishing stand rolls, act on the bottom of the groove as an abrasive. The hard 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 above, 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 is reduced.
Such ovals are flat enough to hold them in the wires and provide a reliable grip, and the more rounded contour of the oval, approaching the shape of an ellipse, creates favorable conditions for uniform deformation across the width of the strip in a round gauge.
