Rolling and calibration of rolls to obtain products of round and square section. Hot rolled round steel. Calibration of profiles and rolls intended for rolling round and square steel Building a finishing gauge for round steel
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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
To 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"
Made by a student of group D-41
Rudova E.V.
Checked by Ph.D. assistant professor
Bobarikin Yu.L.
Gomel 2012
1. Introduction
2. The choice of finishing calibers and the calculation of the cross-sectional areas of the roll
3. Choice drawing calibers and calculation of roll sections
4. Determining the dimensions of calibers
5. Calculation of the rolling speed
6. Calculation temperature regime rolling
7. Determination of the coefficient of friction
8. Calculation of rolling force
9. Calculation of rolling moment and power
caliber section profile rolling rolls
1 . Introduction
The basis of section rolling production technologies is the plastic deformation of metal in various types calibers of rolling mill rolls.
Section profiles are rolled from a billet in several passes in the calibers of rolling rolls, which give the rolled metal the required shapes. For the production by rolling of a metal assortment of a simple and shaped profile (round, square, hexagonal, strip, angular, channel, tee, etc.), it is necessary to calculate the calibration of rolling rolls.
Calibration of rolls called the definition of forms of dimensions and the number of calibers measured on rolls to obtain a finished profile.
Roll gauge- this is the 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 a billet of the required profile of the required shape and dimensions within the accepted tolerances, as well as good quality rolled products, maximum rolling productivity, minimum wear and energy consumption spent on the operation of the rolling mill.
Profile rolling is initially carried out in drawing calibers designed only to reduce the cross-sectional area of the rolled billet. With a decrease in the cross-sectional area of the workpiece, the latter is stretched in length without approaching the cross-sectional shape of the strip to the required one, therefore these calibers are called exhaust. After passing through the drawing passes, the workpiece is rolled in the finishing passes. Finishing calibers are divided into pre-finishing and finishing calibers. In pre-finishing gauges (there may be several or one), with a further decrease in area, the configuration of the section approaches the given shape of the finished profile, and its individual elements are formed. In the finishing pass (it is always the same), the required shapes and size of the profile are finally formed, it is placed on the last rolling pass.
2. The choice of finishing calibers and the calculation of cross-sectional areaseny peal
Choice of quantitytva and forms of finishing calibers
The number and shape of the finishing gauges, i.e. finishing and pre-finishing gauges, depends on the shape of the finished or final profile and on the accepted finishing gauge calibration system.
For a round profile, the finishing gauges are the pre-finishing oval gauge and the finishing round gauge. After the pre-finishing oval pass, the roll of the oval profile passes through 90° tilting and enters the finishing round pass, where the round profile is finally formed (Figure 2.1). In this case, the shape of the pre-finishing oval caliber depends on the dimensions of the finishing profile. The figure shows a pre-finishing oval gauge for medium and small finishing profile sizes.
Rice. 2.1 Scheme of finishing calibers of a round profile
The turning of the roll can be carried out with the help of special turning wires between rolling stands for continuous mills or turning devices, between rolling passes for foundry mills. In addition, on continuous mills, the condition of turning by 90° can be carried out by alternating roll stands with horizontal and vertical arrangement of the axes of the rolls.
For rolling a round profile in the group of finishing calibers, a finishing round and pre-finishing oval calibers are used.
Determination of the dimensions of the final profile in the hot stateIresearch institutes
To increase the service life of the calibers, the calculation is made to obtain a profile with minus tolerances of its dimensions. In order to take into account the reduction in the dimensions of the profile rolled in the hot state during cooling, it is necessary to multiply the size of the profile in the cold state by the coefficient 1,01-1,015 .
Taking a minus tolerance for a round end profile, we find the size of the circle in the cold state:
Hot Finishing Wheel Size:
Determination of elongation coefficients in finishing calibers.
For a finishing round caliber, the elongation coefficient where k is the number of finishing calibers, as well as for a pre-finishing oval caliber, we determine from the graph in Fig. 2.2.
Fig. 2.2 The dependence of the elongation coefficients in the finishing circle, as well as in the pre-finishing oval, on the corresponding circle diameter .
Note: if a round profile with a diameter of less than 12 mm inclusive is rolled, then the elongation coefficients in the finishing and pre-finishing passes are determined according to practical recommendations for a specific profile. Taking into account the structural features of the rolling mill 150 BMZ, we take the average drawing equal to 1.25.
Determination of cross-sectional areas of profiles in finishing potsbrah.
The areas of profiles in finishing calibers are determined by the dependencies:
where is the cross-sectional area of rolled products in the finishing caliber, determined by
according to the hot dimensions of the final profile; - cross-sectional area of the roll in the last pre-finishing pass; - cross-sectional area of the roll in the penultimate pre-finishing pass. Let us determine the cross-sectional area of the strip in a finishing round pass:
The cross-sectional area of the strip in the pre-finishing oval caliber is:
The cross-sectional area in the last draft pass and, accordingly, in the last pass of rolling of the drawing group of passes, is determined by the formula:
3. Choice of drawing calibers andcalculation of the cross-sectional areas of the roll
Selecting a drawing system
As a rule, drawing calibers are formed according to certain systems, which are determined by the alternating shape of the calibers of the same type.
Each draw gauge system is characterized by its pair of draw gauges, which determines the name of the draw gauge system.
Pair of drawing calibers- these are two successive calibers in which the workpiece from an equiaxed state in the first caliber approaches a non-equiaxed one, and in the second one again into an equiaxed one, but with a decrease in the cross-sectional area.
The following systems of drawing calibers are used: rectangular caliber system, rectangle-smooth barrel system, oval-square system, rhombus-square system, rhombus-rhombus system, square-square, universal system, combined system, oval-circle system, oval-ribbed oval system.
On small- and medium-section modern continuous rolling mills, systems are more often used: rhombus-square, oval-square, oval-circle and oval-ribbed oval.
These sizing systems ensure good quality of rolled products and a stable position of the roll in the calibers.
When rolling in drawing calibers, the roll is always tilted or rotated around its longitudinal axis at a certain angle (usually 45° or 90 °) at the transition of the roll between the stands from the first caliber of a pair of calibers to another caliber.
Turning can be replaced by alternating horizontal and vertical rolling stands, which provides a turning effect without turning the workpiece.
Turning the roll or alternating horizontal and vertical rolling stands or rolls is necessary to transfer the uneven state of the workpiece after the passage of the first caliber of a pair of drawing calibers into an equiaxed state in the second caliber of the pair.
One of the most promising sizing systems is the oval - ribbed oval system, which provides a stable rolling mode and good quality of rolled products.
In this system, in oval calibers, the workpiece goes into an unequal oval state with a large difference in the dimensions of the oval axes, and in ribbed oval calibers, into an equiaxed oval state with a small difference in the dimensions of the axes after deformation of the previous unequal oval along the major axis. Thus, the workpiece sequentially passes through the types of calibers: oval - ribbed oval - oval - ribbed oval, etc. until the required reduction in the section of the workpiece is obtained.
Determination of the average extract inarah drawing calibers and numbersrolling passes.
To determine the number of rolling passes n First, we determine the estimated number of pairs of drawing calibers:
where is the cross-sectional area of the workpiece in the hot state;
Sectional area of the workpiece in the last drawing pass.
Having determined the exact number of pairs of drawing calibers, then it is necessary to set the corrected value of the average drawing for a pair of drawing calibers
The number of rolling passes in drawing passes is:
The number of rolling passes for the entire rolling technology is:
Where To- the number of finishing calibers.
Here it is necessary to check whether total number rolling passes exceed the number of rolling stands of the mill according to the inequality:
Where With- the number of rolling stands of the mill.
The cross-sectional area of the workpiece in the hot state, taking into account the wide tolerance for the cross-sectional size, is determined by the nominal cross-sectional size:
For the oval system - rib oval. Accept.
The calculated number of pairs of drawing calibers is:
We accept the exact number of pairs of drawing calibers.
The corrected value of the average drawing for a pair of drawing calibers is equal to:
The number of rolling passes in drawing passes according to (3.3) is:
The number of rolling passes is:
Let us check condition (3.4): .
The results of the distribution of rolling passes and types of calibers by mill stands are entered in Table 3.1.
Definition of hoods for pairs of hoods.
The extract of each pair of calibers is determined by the dependence:
where is the change in the value
When making changes in the values of extracts for each pair of calibers, it is necessary to take into account the equality 0 of the algebraic sum of all changes, i.e. 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 would have smaller ones.
We will make changes for each pair of calibers according to expression (3.5), remembering that the algebraic sum of these changes should be equal to 0:
Determination of hoods by rolling passes in the hood systemandcalibers
Let's define hoods for edge ovals with the known formula:
Extracts for ovals are determined by the formula:
Using formulas (3.7) and (3.8), we determine the numerical values of drawings for all passes of rolling along drawing passes:
For j= 7(14;13)
All hood values for drawing and finishing calibers are entered in Table 3.1.
Determination of the cross-sectional areas of the roll in drawing calibers.
Let us determine the cross-sectional areas of the roll after each rolling pass according to the formula:
where is the cross-sectional area of the roll;
The area of the rolled section following in the course of rolling;
Extraction in the next caliber in the course of rolling.
By 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 in the calculations, in order to accurately obtain the value, it is necessary to correct the extrusion value in the first pass:
The obtained values of the cross-sectional areas of the roll for all rolling passes are entered in Table 3.1.
Table 3.1 Calibration table
|
Type of caliber |
Cross-sectional area 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 |
|||||
|
Prefinishing oval |
|||||
|
Finish round |
4. Determining the dimensions of calibers
The scheme for constructing a finishing round K-th caliber is shown in Fig. 4.1. The diagram shows the following dimensions: - diameter or height of the caliber, equal to the hot size of the diameter of the final profile of round bars; - inter-roll gap; - caliber release angle; - caliber width.
Fig. 4.1 Scheme of a round caliber
The value of the inter-roll gap is determined by the formula:
The width of the gauge and the width of the strip will be equal to the diameter of the gauge.
Values and select the following:
The scheme for constructing a pre-finishing oval (K-1) - th caliber of rolling an oval strip intended for subsequent rolling in a finishing round caliber of a round profile with a diameter of not more than 80 mm is shown in fig. 4.2. Let's make calculations of all necessary sizes:
Fig. 4.2 Scheme of the 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 rolled finishing round profile;
Coefficient that takes into account the broadening of the oval strip in the finishing round caliber.
The blunting of the strip is determined by the formula:
Rice. 4.3 Dependence of the coefficient on the width of the ribbed oval strip preceding the ribbed oval gauge
The bandwidth is determined by the formula:
where is the cross-sectional area of the oval strip after the passage of the pre-finishing oval caliber. The outline radius of the pre-finishing oval gauge is determined by the formula:
We assign the value of the inter-roll gap:
The gauge width is determined by the formula:
We determine the fill factor of the caliber:
The value must be within the limits.
The main dimensions of the finishing and pre-finishing calibers are entered in Table 4.1.
Construction of drawing calibers.
For the system of drawing calibers oval - ribbed oval, first we build all ribbed oval calibers according to the scheme of Fig. 4.4 and the calculation below. When rolling a square profile, the last one in the course of rolling is an equiaxed square caliber, and at the same time it is a pre-finishing square caliber. In our case, the initial profile of the rolled billet is square, so for convenient gripping of the billet, we build the first equiaxed pass along the rolling course according to the scheme of Fig. 4.4. Then we build all oval calibers according to the scheme of Fig. 4.2. and the calculation below.
Rice. 4.4. Diagram of a ribbed oval gauge
For all ribbed oval gauges, i.e. for all - x calibers, the dimensions of the caliber are determined in the following sequence.
Calculation example for caliber 26.
Width of rib oval strip
where is the cross-sectional area of the rib oval strip.
Rib oval strip height
The gauge width is
where is the filling factor of the caliber, equal to 0,92…0,99 , pre-accept.
Gauge outline radius
The bluntness of the strip is:
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
Similarly, we carry out the calculation for all other - x calibers. We enter all the main dimensions of ribbed oval calibers in table 4.1.
For all non-equiaxed calibers (Fig. 4.2.), Dimensions are determined against the rolling stroke.
For each -th non-equiaxed oval caliber, the dimensions are determined in the following sequence.
First, we determine the broadening in the equiaxed ribbed oval groove following the given caliber in the course of rolling according to the formula:
where is the broadening determined from the graph in Fig. 4.6. depending on the width of the considered rib oval strip;
The diameter of the stand rolls for a given equiaxed pass.
Fig.4.6. Dependence of the value of the broadening of the oval strip in the ribbed oval caliber on the width of the ribbed oval strip during rolling in rolls.
The height of the oval strip is:
The height of the caliber is equal to the height of the strip, i.e. .
The bluntness of the oval strip is equal to:
where is the coefficient determined from the graph in Fig. 4.3.
Preliminary value for the width of the oval strip:
where is the cross-sectional area of the strip after the passage of the considered caliber.
The value of the average absolute reduction of the metal in the considered oval caliber is (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 considered stand.
The average height of the strip at the exit to 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 strip is:
The radius of the outline of the caliber is determined by the formula:
The preliminary value of the inter-roll gap will be assigned from the range, subject to the condition.
Gauge fill factor:
After that, we check the condition of normal filling of the caliber with metal.
Let's make a calculation for the 3rd non-equiaxed oval caliber according to the above formulas.
Similarly, we carry out the calculation for all the rest - calibers. The main dimensions of all intermediate oval calibers are entered in Table. 4.1.
Table 4.1. the depth of cut of the caliber is determined by the formula:
Table 4.1 Calibration table,
|
No. of rolling pass |
Strip height |
The width of the line |
Caliber Height |
Gauge width |
Roll gap |
Insertion depth |
|
5. Calculation of the rolling speed
We determine and enter in table 5.1 all the values of the rolling diameters of the rolls. In this case, for oval gauges, we define through the radii determined by the formula (4.31). For all other calibers, the rolling diameters of the rolls are determined by the formula:
where is the diameter of the barrel of rolls of the corresponding caliber;
The cross-sectional area of the strip at the outlet of the corresponding caliber;
The width of the strip at the exit from the caliber.
We will carry out the calculation for 2 calibers.
Then we determine the number of revolutions per minute of the rolls in the last stand in the course of rolling according to the formula:
where is the rolling speed at the exit from the last stand, which is determined by
mill working conditions, 8 0 m/s;
Rolling roll diameter n-oh cage, mm.
where is the sectional area of the strip after the passage n th stand, i.e. final rental, .
To ensure some strip tension between the stands, the calibration constant for each rolling pass must be slightly reduced as you move from the first pass to the next. 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 speed of rotation of the rolls for each pass is determined by the formula:
All values are entered in table 5.1.
The strip speed after each rolling pass is determined by the formula:
where in and in.
All values are entered in table 5.1.
Similarly, we carry out the calculation for all other calibers, and enter all the results of the calculations in Table 5.1.
Table 5.1. Calibration table
|
Rolling pass |
rolling diameter of rolls, |
Calibration constant, |
Roll speed, |
lane speed, |
|
6. Tempera calculationtour mode rolling
The task of calculating the temperature regime of rolling is to determine the temperature of the initial heating of the billet before rolling and to determine the temperature of the roll after each rolling pass.
Fine wire rolling mill 320 has the temperature of the billet at the outlet of the furnace in front of 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 outlet of this block is 1010…1070 . The heating temperature of the billet for rolling a square profile of steel 45, taking into account the table. 6.1. and technological capabilities of the mill furnace 320 take equal 12 50 , and at the exit from the 20th stand, the temperature of the rolled products is taken equal to 107 0 .
The temperature of the roll for the rolling passes is taken equal to the average, i.e.
7. Determination of the coefficient of friction
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 rolls; for cast-iron rolls, for steel-;
Coefficient depending on the carbon content in the rolled metal and determined from Table. 7.1. (m / s 2130 p. 60).
The coefficient depending on the rolling speed or on the linear speed of rotation of the rolls and determined from Table. 7.2. (m / s 2130 p. 60).
Similarly, using formula (7.1), we calculate the friction coefficient for each rolling pass, enter all the necessary data and calculation results in Table 7.1
Table 7.1
|
No. of rolling pass |
|||||
8. Calculation of rolling force
Determination of the contact area of the metal with the roll.
The contact area of the rolled metal with the roll i-th caliber is determined by the formula:
where and are the width and height of the strip at the exit to the caliber;
and - width and height of the strip at the exit from the caliber;
The coefficient of influence of the shape of the caliber, determined by tab. 8.1. (m / s 2130 p. 60). - the radius of the roll along the bottom of the caliber.
The radius of the roll along the bottom of the caliber is determined by the formula:
where is the diameter of the roll barrel; and - height and inter-roll clearance of the caliber. Let's calculate the first pass:
All values are calculated in the same way and entered in the table. 8.1.
Determination of the stress state coefficient of the deformation zone.
The stress state 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 on the stress state of the width of the deformation zone;
Coefficient taking into account the influence of the focus height;
Coefficient taking into account the effect of rolling in the pass.
The coefficient is determined by the following relationship
The coefficient is determined by the dependence
where - caliber shape factor 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 plastic deformation resistance of the rolled metal for each rolling pass is determined in the following sequence.
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.
define by the formula:
Let's calculate the first pass:
All values are entered 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:
All values and are entered 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 |
Plastic deformation resistance |
Average rolling pressure, |
Rolling force, P, kN |
rolling moment |
Power pro- rollers N, kW |
|
9. Raseven torque and rolling power
The moment of rolling is determined by the formula:
Similarly, we determine the moment of inertia for each rolling pass, we enter all the results of the calculation in 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, we enter all the results of the calculation 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 the stability of the strip during rolling on a smooth barrel depending on h / b and ε
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Laboratory work No. 2. Studying the methods of sizing rolls for rolling simple section profiles
2.1 Purpose of work
Familiarize yourself with the systems of gauges for obtaining a round and square profile, mastering the methods for calculating the main calibration parameters.
2.2 Basic theoretical information
Calibration is the order of rolling a successive series of transitional sections of rolled profiles. Calibration calculations are carried out according to two schemes: in the course of rolling (from the billet to the final profile) and against the rolling stroke (from the final profile to the billet). For both schemes, in order to calculate and distribute the deformation coefficients over gaps, it is necessary to know the dimensions of the original workpiece.
The rolling of section profiles begins in drawing calibers, i.e., calibers connected in pairs, designed for metal drawing. Different schemes of crimping and drawing calibers are used, for example, box, rhombus-square, rhombus-rhombus, oval-square, etc. (Figure 2.1).
Of all crimp (pull) calibers, the most common is the box caliber scheme. Often there is a scheme of a smooth barrel - a box caliber.
 |
a) - box; b) - rhombus - square; c) - rhombus - rhombus; d) - oval - square
Figure 2.1 - Schemes of drawing calibers
When rolling medium - and low-grade steel, the rhombus-square gauge scheme is widely used. The scheme of geometrically similar rhombus-rhombus gauges, in which after each pass the roll is turned over by 90 °, is used quite rarely. Rolling according to this scheme is less stable than in the rhombus–square scheme. It is mainly used for rolling high-quality steels, when small reductions are made under the conditions of plastic deformation with a drawing up to 1.3.
The oval-square drawing scheme is one of the most common and used on medium-, small-section and wire mills. Its advantage over other schemes is the systematic updating of the roll angles, which helps to obtain the same temperature over its cross section. The roll behaves stably when rolling in oval and square calibers. The system is characterized by large extracts, but their distribution in each pair of calibers is always uneven. In the oval caliber, the hood is larger than in the square one. Large hoods make it possible to reduce the number of passes, i.e. increase the economic efficiency of the process.
Consider the calibration of rolls for some simple and shaped profiles of mass production, for example, round profiles with a diameter of 5 to 250 mm and more are obtained by rolling.
Rolling of round profiles is carried out according to various schemes depending on the diameter of the profile, type of mill, rolled metal. Common to all rolling schemes is the presence of a pre-finishing oval pass. Before the task of the strip in the finishing gauge, it is turned over by 90 °.
Usually the shape of the pre-finishing gauge is a regular oval with a ratio of the lengths of the axes 1.4 ÷ 1.8. The shape of the finishing pass depends on the diameter of the rolled circle. When rolling a circle with a diameter of up to 30 mm, the generatrix of the finishing pass is a regular circle; when rolling a circle of a larger diameter, the horizontal size of the pass is taken 1-2% more than the vertical one, since their temperature shrinkage is not the same. The drawing ratio in the finishing pass is assumed to be 1.075÷1.20. Round profiles are rolled only in postings in one pass in the last - finishing caliber.
The so-called universal scheme for rolling a round strip along the square-step-rib-oval-circle system is widespread (Figure 2.2). When rolling according to this scheme, it is possible to control the dimensions of the strip emerging from the rib pass over a wide range. In the same rolls it is possible to roll round profiles of several sizes, changing only the finishing pass. In addition, the use of a universal rolling scheme provides good descaling from the strip.
1 - square; 2- step; 3 - rib; 4 - oval; 5 - circle
Figure 2.2 - Scheme of rolling profiles of circular cross section
When rolling a round profile of relatively small dimensions, a square-oval-circle caliber scheme is often used. The side of the pre-finishing square, which significantly affects the production of a good round profile, is taken for profiles of small sizes equal to the diameter d , and for profiles of medium and large sizes 1.1 d.
When calculating the roll sizing of continuous mills, it is especially important to determine the rolling diameters. This allows the rolling process to be carried out without the formation of a loop or excessive strip tension between the stands.
In rectangular calibers, the rolling diameter is taken equal to the diameter of the rolls along the bottom of the caliber. In rhombic and square - variable: the maximum at the gauge connector and the minimum at the top of the gauge. The circumferential speeds of various points of these calibers are not the same. The strip exits the groove with a certain average speed, which corresponds to the rolling diameter, which is approximately determined by the average reduced height of the groove
font-size:14.0pt">In this case, the rolling diameter
font-size:14.0pt">Where D - the distance between the axes of the rolls during rolling.
The simplest calibration calculation is for mills with individual roll drives. In this case, the overall elongation ratio is determined
,
(10
)
where Fo ~ cross-sectional area of the original workpiece;
fn is the cross-sectional area of the rolled profile.
Then, taking into account the relation 
distribute the hood over the stands. Having determined the rolling diameter of the finishing stand rolls and assuming the required rotational speed of the rolls of this stand, the calibration constant is calculated:
font-size:14.0pt">where F 1 ... Fn - cross-sectional area of the strip in stands
1, ..., n; v 1 ,...vn are the rolling speeds in these stands.
The rolling diameter of the rolls when rolling in a box caliber
EN-US" style="font-size:14.0pt">2)
Where k- caliber height.
When rolling in square calibers
font-size:14.0pt"> (13 )
Where h - side of a square.
After that, the dimensions of the intermediate squares, and then the intermediate rectangles, are determined from the hoods. Knowing the calibration constant WITH, determine the frequency of rotation of the rolls in each stand
n= C / FD1 (14 )
Square profiles are rolled with sides from 5 to 250 mm. The profile may have sharp or rounded corners. Usually a square profile with a side of up to 100 mm is obtained with non-rounded corners, and with a side of more than 100 mm - with rounded corners (the radius of curvature does not exceed 0.15 of the side of the square). The most common rolling system is square-rhombus-square (Figure 2.3). According to this scheme, rolling in each subsequent caliber is carried out with 90° canting. After tilting the roll, which has left the rhombic caliber, its large diagonal will be vertical, so the strip will tend to tip over.
Figure 2.3 - Scheme of rolling a strip of square section.
When constructing a finishing square gauge, its dimensions are determined taking into account the minus tolerance and shrinkage during cooling. If we designate the side of the finishing profile in the cold state as a1, and the minus tolerance is ∆a and take the coefficient of thermal expansion equal to 1.012 ÷ 1.015, then the side of the finishing square caliber
font-size:14.0pt">where a are the hot sides of the square profile.
When rolling large square profiles, the temperature of the workpiece corners is always lower than the temperature of the edges, so the corners of the square are not straight. To eliminate this, the angles at the top of the square gauge are made larger than 90° (usually 90°30"). At this angle, the height (vertical diagonal) of the finishing gauge h \u003d 1.41a, and the width (horizontal diagonal) b = 1.42a. The margin for broadening for squares with a side of up to 20 mm is assumed to be 1.5 ÷ 2 mm, and for squares with a side of more than 20 mm 2 ÷ 4 mm. The extract in the finishing square caliber is taken equal to 1.1÷1.15.
In the production of a square profile with sharp corners, the shape of the pre-finishing rhombic pass is essential, especially when rolling squares with a side of up to 30 mm. The usual shape of rhombuses does not provide squares with corners correct form along the parting line of the rolls. To eliminate this drawback, pre-finishing rhombic calibers are used, the top of which has a right angle. The calculation of the square profile calibration starts with the finishing gauge, and then the dimensions of the intermediate drawing gauges are determined.
2.3 Methods for calculating the calibration parameters of simple profiles
2.3.1 Rolling a round profile with a diameter d = 16 mm
In calculations, be guided by the data in Figure 2.4 (Section 2.4).
1 Determine the area of the finishing profile
qcr1 = πd2 / 4, mm2 (16)
2 Select the elongation ratio in the finishing pass µcr and the total elongation ratio in the round and oval calibers µcr s within µcr = 1.08 ÷ 1.11, µcr ov = 1.27 ÷ 1.30.
3 Determine the area of the pre-finishing oval
qw2 = qcr1 µcr, mm2 (17)
4 Approximately take the broadening of the oval strip in the round gauge ∆b1 ~ (1.0 ÷ 1.2).
5 Pre-finishing oval dimensions h2 = d - ∆b1, mm
b2 = 3q2/(2h2 +s2);
where the depth of cut in the rolls (Figure 2.4) is hvr2 = 6.2 mm. Therefore, the gap between the rolls should be equal to s2 = h2 - 2 6.2, mm.
6 Determine the area of the pre-finishing square (3rd gauge)
q3 = qcr µcr ov, mm2 hence the side of the square c3 = √1.03 q3 , mm,
and the height of the caliber h3 = 1.41 s3 - 0.82 r, mm (r = 2.5 mm), then according to Figure 2.4 we determine the depth of the cut of the 3rd caliber into the rolls hvr3 = 9.35 mm, therefore, the gap is 3 - eat caliber s3 = h3 – 2 hvr3, mm.
∆b2 = 0.4 √ (с3 – hov avg)Rks (с3 – hоv avg) / s3 , mm/ (18)
where how cf = q2 / b2 ; Rks \u003d 0.5 (D - hov cf); D – mill diameter (100÷150 mm).
Check the filling of the prefinishing oval pass. In case of overflow, a smaller draw ratio should be adopted and the size of the pre-finishing square should be reduced.
8 Check the total draft between the workpiece with side C0 and square c3 and distribute it between the oval and square gauges:
µ = µ4 ov µ3 kv = С02 / s32 (19)
We distribute this total hood between the oval and square calibers in such a way that the hood in the oval caliber is greater than in the square one:
µ4 = 1 + 1.5 (µ3 - 1); µ3 = (0.5 + √0.25 + 6µ) / 3 (20)
9 Determine the area of the oval
q4 = q3 µ3 , mm2 (21)
The height of the oval h4 is determined in such a way that when rolling it in a square gauge there is room for broadening then:
H4 = 1.41 s3 - s3 - ∆b3, mm (22)
The value of the broadening ∆b3 can be determined from the graphs given in the textbook, "Calibration of rolling rolls", 1971.
The diameter of the laboratory mill is small, so the broadening should be reduced using extrapolation.
B 4 \u003d 3 q 4 / (2 h 4 - s 4 ), mm (23)
where s 4 \u003d h 4 - 2 h vr 4, mm; h BP 4 = 7.05 mm.
10 We determine the broadening in the 4th oval caliber (as in pp7)
font-weight:normal"> ∆b4 = 0.4 √ (С0 – h4 sr)Rks (С0 – h4 sr) / С0 , mm (24)
We check the filling of the 4th oval caliber. The results are summarized in Table 2.1, where it turns out that the 4th oval caliber is necessary for the 1st pass of a square billet with side C0, i.e. above, we started the calculation from the last 4th pass (final or required profile section) carried out in the 1st caliber of the rolls.
2.3.2 Rolling a square profile with side c = 14 mm
In calculations, we also focus on the data of Figure 2.4 (Section 2.4).
1 Determine the area of the finishing (final) profile
Q1 \u003d s12, mm2 (25)
2 Select the elongation ratio in the finishing square pass and the total elongation ratio in the square and pre-finishing rhombic passes, i.e. µkv = 1.08 ÷ 1.11; µkv µr = 1.25 ÷ 1.27.
3 Determine the area of the prefinishing rhombus
Q2 = q1 µkv, mm2 (26)
4 Approximately take the broadening of the rhombic strip in a square gauge equal to ∆b1 = 1.0 ÷ 1.5
5 Determine the dimensions of the prefinishing rhombus
H2 = 1.41s – ∆b1 , mm b2 = 2 q2 / h2 , mm. (27)
The depth of cut in the rolls for this caliber according to Figure 2.1 hvr2 = 7.8 mm, therefore, the clearance s2 = h2 - 2 hvr2, mm.
6 Determine the area of the pre-finishing square
h3 = qkv µkv r, mm2 whence the side of the square c3 = √1.03 q3
2.4 Necessary equipment, tools and materials
The work is carried out on a laboratory mill with roll calibration as, for example, shown in Figure 2.4. As blanks, both for round and square rolled profiles, blanks with a square section are used. In principle, this laboratory work is of a calculated nature and ends with filling in tables 2.1 and 2.2.
Figure 2.4 - Calibration of rolls for a round and square profile
Table 2.1 - Calibration of the round profile ø 16 mm
pass number | caliber number |
Caliber form | Caliber dimensions, mm | Strip dimensions, mm |
||||||||||
hvr | b | s | h | b | with (d) |
|||||||||
square billet |
||||||||||||||
Oval | 7,05 | |||||||||||||
Goal of the work: familiarization with the principles of sizing rolls for rolling square and round profiles.
Theoretical information
I. General issues of roll sizing.
Long products are obtained as a result of several: consecutive passes, the number of which depends on the ratio of the sizes and shapes of the initial and final section, while in each pass the section changes With a gradual approach to the finished profile.
Rolling of section metal is carried out in calibrated rolls: i.e. in rolls with special cutouts corresponding to the required configuration of rolled stock in a lath pass. Annular cut in one roll / fig. 4".L/ is called stream I, and the gap between two streams located one above the other working together, taking into account the gap between them, is called gauge 2.
Rolling in calibers, as a rule, is an example of a pronounced non-uniform deformation of the metal and V most cases by constrained broadening.
When calibrating rolling rolls, the amount of reduction by passes has to be taken simultaneously with the determination of the successive shapes and sizes of the calibers /Fig. 42.2/, providing high-quality rolled products and accurate profile dimensions.
Gauges used in rolling are divided into the following main groups depending on their purpose.
Crimp or draw gauges - designed to reduce the cross-sectional area of the billet mm mm. Drawing calibers are square with a diagonal arrangement, rhombic, oval. A certain combination of these calibers forms caliber systems, for example, rhombus-square, oval-circle, etc. /Fig.42.3/.
Rough go preparatory calibers", in which, along with a further reduction in the section of the rolled product, the profile is processed with a gradual approximation of its dimensions and shapes to the final section.
Finishing or finishing gauges , to complete the profile. The dimensions of these calibers are 1,2...1,5% more finished profile; the allowance is given for the shrinkage of the metal when it is cooled.
2. Caliber elements
Gap between rolls. The height of the caliber is the sum of the depth of the virez in the upper h t and lower h2, rolls and magnitudes S between rolls
During rolling, the pressure of the metal tends to push the rolls apart, while the gap 5 increases, which is called the recoil, or spring, of the rolls. Since the gauge drawing is displayed 
compresses its shape and dimensions at the time of the strip passage, then the gap between the rolls when installed in the stand is reduced less than the gap indicated in the drawing by the amount of return of the rolls. At the same time, it is necessary to take into account the fact that during operation the distance between the rolls change in steel grade, wear of rolls, etc. / have to be changed in order to adjust the mill. This setting can be carried out if there is a gap between the rolls, which is accepted for shrinking mills I...I.5%, for other mills 0.5..1 %
on the roll diameter.
Issue caliber. The side walls of the box caliber / fig. 42.3 "have some slope To roll axes. This inclination of the walls of the caliber is called release. During rolling, the release of the pass provides a convenient and correct insertion of the strip into the pass and the free exit of the strip from the pass. If the walls of the caliber are perpendicular to the axis of the rolls, a strong pinching of the strip would be observed, and there would be a danger of binding the rolls, since broadening almost always accompanies the rolling process. Typically, the release of the caliber is squeezed in percent /~ 100 %/ or in degrees µ and is accepted for box gauges 10..20%
Top and bottom pressure It is very important during rolling to ensure a straight exit of the strip from the rolls. For this purpose, wires are used, since during rolling there are reasons that caused the strip to bend towards the upper and lower rolls, this requires the installation of wires on the lower and upper rolls. But this setting
can be avoided if the strip is given a certain direction in advance, which is achieved by using rolls with different diameters. The difference between the diameters of the forks is conventionally called "pressure", Will the diameter of the upper roll is larger, they speak of "upper pressure" / fig. 42.4/,
if the diameter of the lower roll is assumed to be large, then in this case there is "neither 
lower pressure". The pressure value is expressed as a difference in diameters in millimeters. For long sections, they tend to have an upper pressure of more than I %
from the average diameter of the rolls.
Calibration of profiles and rolls intended for rolling round and square steel
TO hot rolled round steel according to GOST 2590-71, profiles are classified that have a cross-sectional shape of a circle with a diameter of 5 to 250 mm.
In the general case, the calibration scheme for round steel can be divided into two parts: the first is a calibration for rough and middle groups of stands and satisfies a number of profiles, being in this sense common for several final profiles of various sections (square, strip, hexagonal, etc.) , and the second is intended as a specific system for the last three or four stands and is characteristic only of this round steel profile. In draft and middle groups of stands, caliber systems can be used: rectangle - box square, hexagon - square, oval - square, oval - vertical oval.
For the last three to four profiling stands, the gauge system is also not constant. A certain pattern is observed only in the last two stands: the finishing stand has a round pass, the pre-finishing stand is oval, the pass of the third stand from the end of rolling can be of various shapes, on which the sizing system depends.
General schemes of calibers of the last four passes when rolling round steel. It follows from these schemes that oval calibers of two shapes are used as pre-finishing calibers: one-radius and with rounded rectangles - the so-called "flat" calibers. The first scheme is used when rolling round steel of most profile sizes, the second - mainly for round steel of large diameters and reinforcing steel.
According to the first general scheme of rolling, seven types of calibers used in the preshape stand can be noted. According to the second general scheme, only two types of calibers have found the greatest use: box square 1 and square 3, cut into the barrel of the roll when located diagonally.
The systems and form of calibers used for rough and middle groups of stands can be very diverse and depend on a number of factors, the main of which are the type of mill and the design of its main and auxiliary equipment.
Currently, there are a number of techniques for constructing a finishing gauge for round steel: outlining the gauge with two radii from different centers; chamfering at the roll connectors in order to prevent the stripe of small thickness undercuts of the roll with caliber collars; the formation of a release by the outline of the caliber along the connector, etc. Practice shows that a finishing gauge, outlined by one radius and having only one size - the inner diameter, does not meet the requirements for obtaining a geometrically correct high-quality profile, especially a large diameter profile. As a rule, in such a caliber, even with the slightest change in technological conditions (lowering the rolling temperature, the development of pre-finishing caliber rolls, increasing the height of the oval, etc.), the streams are overflowing with metal. Obtaining a profile in accordance with the shape of the finishing pass requires constant control of the dimensions of the pre-finishing oval bar. In cases of gauge overflow, it is not always possible to maintain the profile diameter, even within the plus tolerance.
In order to eliminate the noted shortcomings, it is recommended to design a finishing gauge with camber (release) for a round steel profile, i.e., to provide for a slightly larger horizontal diameter compared to the vertical one. This is also necessary due to the fact that the roll of oval section entering the finishing pass has a lower temperature in places at the ends of the major axis and the thermal shrinkage of the finished profile during cooling in the direction of the horizontal diameter is somewhat greater than in the direction of the vertical diameter. Intensive wear of the finishing caliber of round steel along the vertical due to greater reduction also contributes to the excess of the size by 1-1.5% of the horizontal diameter over the vertical one.
Round steel at domestic plants tend to be rolled to minus tolerances.
Determining the size of the horizontal diameter using the finishing gauge connector is recommended using analytically derived equations (N.V. Litovchenko), taking into account the dimensions of the profile diameters.
Flat types of rolled products (sheets, strips) are usually rolled in smooth cylindrical rolls. The specified rolled thickness is achieved by reducing the roll gap. Section profiles are rolled in calibrated rolls, i.e. rolls having annular grooves corresponding to the roll configuration in sequence from the workpiece to the finished profile.
An annular cut in one roll is called a stream, and the gap between two streams in a pair of rolls located one above the other, taking into account the gap between them, is called a caliber (Fig. 8.1).
Usually, a square or square blank is used as the starting material. rectangular section. The task of calibration includes determining the shape, size and number of intermediate (transitional) sections of the roll from the workpiece to the finished profile, as well as the order of the calibers in the rolls. Roll sizing is a system of sequentially arranged calibers that ensure the production of rolled products of a given shape and size.
The border of the streams on both sides is called the connector or gauge gap. It is 0.5…1.0% of the roll diameter. The gap is provided to compensate for elastic deformations of the elements of the working stand that occur under the influence of the rolling force (the so-called recoil, stand spring). In this case, the center distance increases from fractions of a millimeter on sheet mills to 5 ... 10 mm - on crimping mills. Therefore, when setting up the gap between the rolls is reduced by the amount of return.
The slope of the side faces of the caliber to the vertical is called the release of the caliber. The presence of a slope contributes to the centering of the roll in the caliber, facilitates its straight exit from the rolls, creates room for the broadening of the metal, and provides the possibility of restoring the caliber during regrinding (Fig. 8.2). The release value 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 calibers, the release is 10 ... 25%, for draft shaped - 5 ... 10%, for finishing - 1.0 ... 1.5%.
IN- gauge width at the connector, b- the width of the caliber in the depth of the stream, h to- caliber height, h p- the height of the stream, S- caliber clearance.
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 the average diameter includes the gap between the rolls.
The middle line of the rolls is a horizontal line that bisects the distance between the axes of the two rolls, i.e. this is the line of contact of imaginary circles of two rolls of equal diameter.
Gauge neutral line - for symmetrical gauges, this is the horizontal axis of symmetry; for asymmetric gauges, the neutral line is found analytically, for example, by finding the center of gravity. The horizontal line passing through it divides the area of the caliber in half (Fig. 8.3). The gauge neutral line 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 caliber area (Fig. 8.4).
The ideal option seems to be when the neutral line of the caliber is located on the middle line, i.e. they match. Then the sum of the moments of forces acting on the strip from the side of the upper and lower rolls is the same. With this arrangement, the strip should exit the rolls strictly horizontally along the rolling axis. In a real 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 go up or down. To avoid such a situation, the strip is forcibly bent 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 an upper pressure, if - a lower one.
In this case, the neutral line of the caliber is displaced with the middle line by an amount X(see fig.8.1) and 
, A 
. Subtracting the second equality from the first, we get . Where . Knowing and it is easy to determine the initial and .
For example, mm and mm. Then 
mm and mm.
Typically, section mills use an upper pressure of about 1% of . On bloomings, a lower pressure of 10 ... 15 mm is usually used.
In the rolls, the calibers are separated from each other by piles. In order to avoid stress concentration in the rolls and rolls, the edges of the calibers and collars are conjugated with radii. Deep in the stream 
, and at the connector 
.
8.2 Caliber classification
Calibers are classified according to several criteria: by purpose, by shape, by location in the rolls.
According to the purpose, there are crimping (drawing), draft (preparatory), pre-finishing and finishing (finishing) calibers.
Crimping calibers are used to draw the roll by reducing its cross-sectional area, usually without changing the shape. These include box (rectangular and square), lancet, rhombic, oval and square (Fig. 8.5).
Draft gauges are designed to draw the roll with the simultaneous formation of a cross section closer to the shape of the finished profile.
Prefinishing calibers immediately precede the finishing ones and decisively determine the receipt of a finished profile of a given shape and size.
Finishing gauges give the final shape and dimensions to the profile in accordance with the requirements of GOST, taking into account thermal shrinkage.
According to the shape, the calibers are divided into simple and complex (shaped). Simple calibers include rectangular, square, oval, etc., shaped - angular, beam, rail, etc.
According to the location in the windrows Distinguish between closed and open calibers. Calibers are considered open, in which the connectors are within the caliber, and the caliber itself is formed by streams cut into both rolls (see Fig. 8.5).
Closed ones include calibers, in which the connectors are outside the caliber, and the caliber itself is formed by an incision 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 calibers are used in various combinations. Such combinations are called caliber systems.
8.3 Drawing gauge systems
The system of box (rectangular) calibers is mainly used when rolling rectangular and square billets with a cross-sectional side of more than 150 mm on blooming, swaging and continuous mills, in roughing stands of section mills (Fig. 8.7). The advantages of the system are:
- 
the possibility of using the same caliber for rolling workpieces of various initial and final sections. By changing the position of the upper roll, the dimensions of the caliber change (Fig. 8.8);
Relatively shallow incision depth of the stream;
Good conditions for scale removal from the side faces;
Uniform deformation across the workpiece width.
The disadvantages of this system of calibers include the impossibility of obtaining blanks of the correct geometric shape due to the presence of slopes of the lateral faces of the calibers, 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 billets and roughing stands of section mills as a transition from the box gauge system to produce billets with a square side of less than 150 mm. The advantage of the system is the possibility of obtaining 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 section side of less than 75 mm. It is used in roughing and pre-finishing stands of section mills. Provides drafts up to 1.8 per pass, small cut of oval caliber into rolls, systematic updating of roll angles, which contributes to a more uniform temperature distribution, stability of rolls in calibers.
In addition to the above, the systems rhombus-rhombus, oval-circle, oval-oval, etc. are used.
8.4 Calibration schemes for simple profiles (square and round)
Rough pass rolls for rolling square profiles can be made in any system, but the last three passes are preferably in a rhombus-square system. The angle at the top of the rhombus is taken up to 120 0 . Sometimes, for better fulfillment of 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 of up to 25 mm, the finishing gauge is built in the form of a geometrically regular square, and with a side of more than 25 mm, the horizontal diagonal is taken 1 ... 2% more than the vertical one due to the temperature difference.
Rough gauges for rolling round profiles are also performed in any system, and the last three gauges - 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 shaped with one radius, a flat oval is used for greater stability of the roll in a round caliber.
Figure 8.9 shows the calibration schemes of the rolls of the mill 500, which show the above systems of drawing passes in the roughing stands, the calibration of square, round and other profiles.
8.5 Calibration considerations for flange profiles
,
Where a d- the 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, in which the tolerance obviously exceeds the value of thermal shrinkage, the calculation of the calibration is carried out on a cold profile.
3. In order to achieve maximum productivity, rough passes are calculated taking into account the maximum grip angles, followed by refinement in terms of roll strength, 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 roll wear, t .e. at low elongation ratios. Usually in fine gauges m\u003d 1.05 ... 1.15, in pre-finishing m = 1,15…1,25.
The total number of passes during rolling on reversing mills, in trio stands, on linear type mills must be odd so that the last pass is in the forward direction.