Building a finishing gauge for round steel. Hot rolled 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 the total number of rolling passes will 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 extracts for each pair of calibers, taking into account their redistribution, so that the initial pairs of calibers would have big values hoods, and the latter are smaller.
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 following sizes: - diameter or height of the caliber, equal to the hot dimension of the diameter of the final profile 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 workpiece is square, then for a convenient grip of the workpiece, we build the first equiaxed caliber along the course of rolling 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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Calibration of profiles and rolls intended for rolling round and square steel
TO hot rolled round steel according to GOST 2590-71, profiles are classified that have a cross-sectional shape of a circle with a diameter of 5 to 250 mm.
In the general case, the calibration scheme for round steel can be divided into two parts: the first is a calibration for rough and middle groups of stands and satisfies a number of profiles, being in this sense common for several final profiles of various sections (square, strip, hexagonal, etc.) , and the second is intended as a specific system for the last three or four stands and is characteristic only of this round steel profile. In draft and middle groups of stands, caliber systems can be used: rectangle - box square, hexagon - square, oval - square, oval - vertical oval.
For the last three to four profiling stands, the gauge system is also not constant. A certain pattern is observed only in the last two stands: the finishing stand has a round pass, the pre-finishing stand is oval, the pass of the third stand from the end of rolling can be of various shapes, on which the sizing system depends.
General schemes of calibers of the last four passes when rolling round steel. It follows from these schemes that oval calibers of two shapes are used as pre-finishing calibers: one-radius and with rounded rectangles - the so-called "flat" calibers. The first scheme is used when rolling round steel of most profile sizes, the second - mainly for round steel of large diameters and reinforcing steel.
According to the first general scheme of rolling, seven types of calibers used in the preshape stand can be noted. According to the second general scheme, only two types of calibers have found the greatest use: box square 1 and square 3, cut into the barrel of the roll when located diagonally.
The systems and form of calibers used for rough and middle groups of stands can be very diverse and depend on a number of factors, the main of which are the type of mill and the design of its main and auxiliary equipment.
Currently, there are a number of techniques for constructing a finishing gauge for round steel: outlining the gauge with two radii from different centers; chamfering at the roll connectors in order to prevent the stripe of small thickness undercuts of the roll with caliber collars; the formation of a release by the outline of the caliber along the connector, etc. Practice shows that a finishing gauge, outlined by one radius and having only one size - the inner diameter, does not meet the requirements for obtaining a geometrically correct high-quality profile, especially a large diameter profile. As a rule, in such a caliber, even with the slightest change in technological conditions (lowering the rolling temperature, the development of pre-finishing caliber rolls, increasing the height of the oval, etc.), the streams are overflowing with metal. Obtaining a profile in accordance with the shape of the finishing pass requires constant control of the dimensions of the pre-finishing oval bar. In cases of gauge overflow, it is not always possible to maintain the profile diameter, even within the plus tolerance.
In order to eliminate the noted shortcomings, it is recommended to design a finishing gauge with camber (release) for a round steel profile, i.e., to provide for a slightly larger horizontal diameter compared to the vertical one. This is also necessary due to the fact that the roll of oval section entering the finishing pass has a lower temperature in places at the ends of the major axis and the thermal shrinkage of the finished profile during cooling in the direction of the horizontal diameter is somewhat greater than in the direction of the vertical diameter. Intensive wear of the finishing caliber of round steel along the vertical due to greater reduction also contributes to the excess of the size by 1-1.5% of the horizontal diameter over the vertical one.
Round steel at domestic plants tend to be rolled to minus tolerances.
Determining the size of the horizontal diameter using the finishing gauge connector is recommended using analytically derived equations (N.V. Litovchenko), taking into account the dimensions of the profile diameters.
1,06
1,05
1,04
1,03
1,02
1,01
0 1.0 1.2 1.3 1.4 1.5 1.6 1.7 1.8 h / b
Figure 1.5 - Graph of the stability of the strip during rolling on a smooth barrel depending on h / b and ε
1) describe the manufacturing technology of blooms; sequence of operations; characteristic parameters.
2) draw sketches: blooms, models of ingots, side faces, distortions of sections, etc.
Control questions
1 What is the main task of the technological process of rolling production?
2 What is a technological scheme for the production of rolled products?
3 What is a semi-product of rolling production?
4 What do you know technological schemes production of semi-finished products and finished products?
5 What technological schemes for the production of rolled products can be organized using the processes of continuously cast billets?
6 What is roll gauge, roll gauge and smooth barrel?
7 What is the maximum reduction and its effect on rolling?
8 What is the roll angle and its effect on rolling?
9 Under what conditions is the strip turning carried out?
10 How are the broadening and stretching of the rolled strip found?
11 What is strip stability and what indicator is it characterized by?
Laboratory work No. 2. Studying the methods of sizing rolls for rolling simple section profiles
2.1 Purpose of work
Familiarize yourself with the systems of gauges for obtaining a round and square profile, mastering the methods for calculating the main calibration parameters.
2.2 Basic theoretical information
Calibration is the order of rolling a successive series of transitional sections of rolled profiles. Calibration calculations are carried out according to two schemes: in the course of rolling (from the billet to the final profile) and against the rolling stroke (from the final profile to the billet). For both schemes, in order to calculate and distribute the deformation coefficients over gaps, it is necessary to know the dimensions of the original workpiece.
The rolling of section profiles begins in drawing calibers, i.e., calibers connected in pairs, designed for metal drawing. Different schemes of crimping and drawing calibers are used, for example, box, rhombus-square, rhombus-rhombus, oval-square, etc. (Figure 2.1).
Of all crimp (pull) calibers, the most common is the box caliber scheme. Often there is a scheme of a smooth barrel - a box caliber.
 |
a) - box; b) - rhombus - square; c) - rhombus - rhombus; d) - oval - square
Figure 2.1 - Schemes of drawing calibers
When rolling medium - and low-grade steel, the rhombus-square gauge scheme is widely used. The scheme of geometrically similar rhombus-rhombus gauges, in which after each pass the roll is turned over by 90 °, is used quite rarely. Rolling according to this scheme is less stable than in the rhombus–square scheme. It is mainly used for rolling high-quality steels, when small reductions are made under the conditions of plastic deformation with a drawing up to 1.3.
The oval-square drawing scheme is one of the most common and used on medium-, small-section and wire mills. Its advantage over other schemes is the systematic updating of the roll angles, which helps to obtain the same temperature over its cross section. The roll behaves stably when rolling in oval and square calibers. The system is characterized by large extracts, but their distribution in each pair of calibers is always uneven. In the oval caliber, the hood is larger than in the square one. Large hoods make it possible to reduce the number of passes, i.e. increase the economic efficiency of the process.
Consider the calibration of rolls for some simple and shaped profiles of mass production, for example, round profiles with a diameter of 5 to 250 mm and more are obtained by rolling.
Rolling round profiles is carried out according to various schemes depending on the diameter of the profile, the type of mill, the rolled metal. Common to all rolling schemes is the presence of a pre-finishing oval pass. Before the task of the strip in the finishing gauge, it is turned over by 90 °.
Usually the shape of the pre-finishing gauge is a regular oval with a ratio of the lengths of the axes 1.4 ÷ 1.8. The shape of the finishing pass depends on the diameter of the rolled circle. When rolling a circle with a diameter of up to 30 mm, the generatrix of the finishing pass is a regular circle; when rolling a circle of a larger diameter, the horizontal size of the pass is taken 1-2% more than the vertical one, since their temperature shrinkage is not the same. The drawing ratio in the finishing pass is assumed to be 1.075÷1.20. Round profiles are rolled only in postings in one pass in the last - finishing caliber.
The so-called universal scheme for rolling a round strip along the square-step-rib-oval-circle system is widespread (Figure 2.2). When rolling according to this scheme, it is possible to control the dimensions of the strip emerging from the rib pass over a wide range. In the same rolls it is possible to roll round profiles of several sizes, changing only the finishing pass. In addition, the use of a universal rolling scheme provides good descaling from the strip.
1 - square; 2- step; 3 - rib; 4 - oval; 5 - circle
Figure 2.2 - Scheme of rolling profiles of circular cross section
When rolling a round profile, relatively small size Often a square-oval-circle caliber scheme is used. The side of the pre-finishing square, which significantly affects the production of a good round profile, is taken for profiles of small sizes equal to the diameter d , and for profiles of medium and large sizes 1.1 d.
When calculating the roll sizing of continuous mills, it is especially important to determine the rolling diameters. This allows the rolling process to be carried out without the formation of a loop or excessive strip tension between the stands.
In rectangular calibers, the rolling diameter is taken equal to the diameter of the rolls along the bottom of the caliber. In rhombic and square - variable: the maximum at the gauge connector and the minimum at the top of the gauge. The circumferential speeds of various points of these calibers are not the same. The strip exits the groove with a certain average speed, which corresponds to the rolling diameter, which is approximately determined by the average reduced height of the groove
font-size:14.0pt">In this case, the rolling diameter
font-size:14.0pt">Where D - the distance between the axes of the rolls during rolling.
The simplest calibration calculation is for mills with individual roll drives. In this case, the overall elongation ratio is determined
,
(10
)
where Fo ~ cross-sectional area of the original workpiece;
fn is the cross-sectional area of the rolled profile.
Then, taking into account the ratio 
distribute the hood over the stands. Having determined the rolling diameter of the finishing stand rolls and assuming the required rotational speed of the rolls of this stand, the calibration constant is calculated:
font-size:14.0pt">where F 1 ... Fn - cross-sectional area of the strip in stands
1, ..., n; v 1 ,...vn are the rolling speeds in these stands.
The rolling diameter of the rolls when rolling in a box caliber
EN-US" style="font-size:14.0pt">2)
Where k- caliber height.
When rolling in square calibers
font-size:14.0pt"> (13 )
Where h - side of a square.
After that, the dimensions of the intermediate squares, and then the intermediate rectangles, are determined from the hoods. Knowing the calibration constant WITH, determine the frequency of rotation of the rolls in each stand
n= C / FD1 (14 )
Square profiles are rolled with sides from 5 to 250 mm. The profile may have sharp or rounded corners. Usually a square profile with a side of up to 100 mm is obtained with non-rounded corners, and with a side of more than 100 mm - with rounded corners (the radius of curvature does not exceed 0.15 of the side of the square). The most common rolling system is square-rhombus-square (Figure 2.3). According to this scheme, rolling in each subsequent caliber is carried out with 90° canting. After tilting the roll, which has left the rhombic caliber, its large diagonal will be vertical, so the strip will tend to tip over.
Figure 2.3 - Scheme of rolling a strip of square section.
When constructing a finishing square gauge, its dimensions are determined taking into account the minus tolerance and shrinkage during cooling. If we designate the side of the finishing profile in the cold state as a1, and the minus tolerance is ∆a and take the coefficient of thermal expansion equal to 1.012 ÷ 1.015, then the side of the finishing square caliber
font-size:14.0pt">where a are the hot sides of the square profile.
When rolling large square profiles, the temperature of the workpiece corners is always lower than the temperature of the edges, so the corners of the square are not straight. To eliminate this, the angles at the top of the square gauge are made larger than 90° (usually 90°30"). At this angle, the height (vertical diagonal) of the finishing gauge h \u003d 1.41a, and the width (horizontal diagonal) b = 1.42a. The margin for broadening for squares with a side of up to 20 mm is assumed to be 1.5 ÷ 2 mm, and for squares with a side of more than 20 mm 2 ÷ 4 mm. Hood in fine square gauge is taken equal to 1.1÷1.15.
In the production of a square profile with sharp corners, the shape of the pre-finishing rhombic pass is essential, especially when rolling squares with a side of up to 30 mm. The usual form of diamonds does not provide squares with corners of the correct form along the parting line of the rolls. To eliminate this drawback, pre-finishing rhombic calibers are used, the top of which has a right angle. The calculation of the square profile calibration starts with the finishing gauge, and then the dimensions of the intermediate drawing gauges are determined.
2.3 Methods for calculating the calibration parameters of simple profiles
2.3.1 Rolling a round profile with a diameter d = 16 mm
In calculations, be guided by the data in Figure 2.4 (Section 2.4).
1 Determine the area of the finishing profile
qcr1 = πd2 / 4, mm2 (16)
2 Select the elongation ratio in the finishing pass µcr and the total elongation ratio in the round and oval calibers µcr s within µcr = 1.08 ÷ 1.11, µcr ov = 1.27 ÷ 1.30.
3 Determine the area of the pre-finishing oval
qw2 = qcr1 µcr, mm2 (17)
4 Approximately take the broadening of the oval strip in the round gauge ∆b1 ~ (1.0 ÷ 1.2).
5 Pre-finishing oval dimensions h2 = d - ∆b1, mm
b2 = 3q2/(2h2 +s2);
where the depth of cut in the rolls (Figure 2.4) is hvr2 = 6.2 mm. Therefore, the gap between the rolls should be equal to s2 = h2 - 2 6.2, mm.
6 Determine the area of the pre-finishing square (3rd gauge)
q3 = qcr µcr ov, mm2 hence the side of the square c3 = √1.03 q3 , mm,
and the height of the caliber h3 = 1.41 s3 - 0.82 r, mm (r = 2.5 mm), then according to Figure 2.4 we determine the depth of the cut of the 3rd caliber into the rolls hvr3 = 9.35 mm, therefore, the gap is 3 - eat caliber s3 = h3 – 2 hvr3, mm.
∆b2 = 0.4 √ (с3 – hov avg)Rks (с3 – hоv avg) / s3 , mm/ (18)
where how cf = q2 / b2 ; Rks \u003d 0.5 (D - hov cf); D – mill diameter (100÷150 mm).
Check the filling of the prefinishing oval pass. In case of overflow, a smaller draw ratio should be adopted and the size of the pre-finishing square should be reduced.
8 Check the total draft between the workpiece with side C0 and square c3 and distribute it between the oval and square gauges:
µ = µ4 ov µ3 kv = С02 / s32 (19)
We distribute this total hood between the oval and square calibers in such a way that the hood in the oval caliber is greater than in the square one:
µ4 = 1 + 1.5 (µ3 - 1); µ3 = (0.5 + √0.25 + 6µ) / 3 (20)
9 Determine the area of the oval
q4 = q3 µ3 , mm2 (21)
The height of the oval h4 is determined in such a way that when rolling it in a square gauge there is room for broadening then:
H4 = 1.41 s3 - s3 - ∆b3, mm (22)
The value of the broadening ∆b3 can be determined from the graphs given in the textbook, "Calibration of rolling rolls", 1971.
The diameter of the laboratory mill is small, so the broadening should be reduced using extrapolation.
B 4 \u003d 3 q 4 / (2 h 4 - s 4 ), mm (23)
where s 4 \u003d h 4 - 2 h vr 4, mm; h BP 4 = 7.05 mm.
10 We determine the broadening in the 4th oval caliber (as in pp7)
font-weight:normal"> ∆b4 = 0.4 √ (С0 – h4 sr)Rks (С0 – h4 sr) / С0 , mm (24)
We check the filling of the 4th oval caliber. The results are summarized in Table 2.1, where it turns out that the 4th oval caliber is necessary for the 1st pass of a square billet with side C0, i.e. above, we started the calculation from the last 4th pass (final or required profile section) carried out in the 1st caliber of the rolls.
2.3.2 Rolling a square profile with side c = 14 mm
In calculations, we also focus on the data of Figure 2.4 (Section 2.4).
1 Determine the area of the finishing (final) profile
Q1 \u003d s12, mm2 (25)
2 Select the elongation ratio in the finishing square pass and the total elongation ratio in the square and pre-finishing rhombic passes, i.e. µkv = 1.08 ÷ 1.11; µkv µr = 1.25 ÷ 1.27.
3 Determine the area of the prefinishing rhombus
Q2 = q1 µkv, mm2 (26)
4 Approximately take the broadening of the rhombic strip in a square gauge equal to ∆b1 = 1.0 ÷ 1.5
5 Determine the dimensions of the prefinishing rhombus
H2 = 1.41s – ∆b1 , mm b2 = 2 q2 / h2 , mm. (27)
The depth of cut in the rolls for this caliber according to Figure 2.1 hvr2 = 7.8 mm, therefore, the clearance s2 = h2 - 2 hvr2, mm.
6 Determine the area of the pre-finishing square
h3 = qkv µkv r, mm2 whence the side of the square c3 = √1.03 q3
2.4 Necessary equipment, tools and materials
The work is carried out on a laboratory mill with roll calibration as, for example, shown in Figure 2.4. As blanks, both for round and square rolled profiles, blanks with square section. 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 | |||||||||||||
| Article Index |
|---|
| Rolled steel production: classification of rolling machines, technological processes of rolling |
| Pipe mills and special purpose mills |
| Classification of rolling mills according to the number and arrangement of rolls |
| Blooms and slabs production |
| The main features of the technological process of rolling on blooming |
| Production of blanks on billet mills |
| Long products production |
| Calibration of rolls for rolling square profiles |
| Calibration of rolls for rolling of round profiles |
| Peculiarities of roll calibration for angle steel rolling |
| Production of rolled products at medium-section mills |
| Production, rails, beams, channels |
| Raw material for rolling rails, beams and channels |
| Arrangement and location of equipment for rail and beam mills |
| Technological process of rail rolling |
| Rail quality control |
| Rolling of I-beams |
| Characteristics of the equipment and its location on the universal beam mill |
| Wire rod production |
| Continuous wire mill 250 MMK |
| Machine for continuous casting and rolling of steel rod |
| Strip and tape production |
| Rolling of hot-rolled strips and sheets |
| Raw material and its heating |
| plate rolling process technology |
| Production of two-layer sheets |
| Cold rolling of sheets |
| Production of special types of rolled products |
| Production of periodic profiles |
| Finned tube production |
| All Pages |
Calibration of rolls for rolling of round profiles
GOST 2590-71 provides for the production of round steel with a diameter of 5 to 250 mm.
The rolling of this profile, depending on the steel grade and dimensions, is carried out in different ways (Fig. 2.7 ).
Figure 2.7. WaysI -X round steel rolling:
I - oval, rhombus or hexagon;II . IV. V- smooth barrel or boxcaliber;III - decagonal or box calibers; VI- square or hexagonal gauges; VP - circle, etc.; VIII- lancet caliber, smooth barrel or box caliber; IX, X- oval, etc.
Ways 1 And 2 differ in 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 obtaining a number of adjacent sizes of round steel (Fig. 2). Method 3 is that the prefinishing 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 sidewalls in this caliber contributes to better descaling. Because this way allows wide adjustment of the dimensions of the strip coming out of the rib gauge, it is also called universal gauge. Methods 5 and 6 differ from the rest in higher hoods and greater stability of the ovals in the wiring. However, such calibers require precise adjustment of the mill, since with a small excess of metal, they overflow and form burrs. Methods 7-10 are based on the use of an oval-circle sizing system
A comparison of possible methods for producing round steel shows that methods 1-3 make it possible in most cases to roll the entire range of round steel. Rolling of quality steel should be carried out according to methods 7-10. Method 9, as it were, is intermediate between the oval-circle and oval-oval systems, it is most convenient in terms of regulating and adjusting the camp, as well as preventing sunsets.
In all considered methods of rolling round steel, the shape of the finishing and pre-finishing passes remains almost unchanged, which contributes to the establishment of general patterns of metal behavior in these passes for all cases of rolling.
Drawing2.8 Example of sizing round steel according to method 2
The construction of a finishing gauge for round steel is carried out as follows.
Determine the estimated diameter of the caliber (for a hot profile when rolling to minus) dG = (1,011-1,015)dX is the tolerance part +0.01 dX where 0.01 dX- increase in diameter for the above reasons: dX = (d 1 + d 2 )/2 – diameter of a round profile in a cold state. Then
dG = (1,011-1,015) (d 1 + d 2 )/2
Where d 1 And d 2 – maximum and minimum allowable diameter values.
Pre-finishing gauges for a circle are designed taking into account the accuracy required for the finished profile. The more the shape of the oval approaches the shape of a circle, the more accurately the finished round profile is obtained. Theoretically, the most suitable profile shape to obtain the correct circle is an ellipse. However, such a profile is rather difficult to hold at the entrance to the finishing round gauge, so it is used relatively rarely.
The flat ovals hold the wires well and, in addition, provide large swages. With small reductions of the oval, the possibility of size fluctuations 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.
For round profiles of medium and large sizes, the ovals, outlined by one radius, turn out to be too elongated along the major axis and, as a result, do not provide a reliable grip of the strip by the rolls. The use of sharp ovals, in addition to not providing an accurate circle, adversely affects the stability of the round gauge, especially in the output stand of the mill. The need for frequent replacement of rolls sharply reduces the productivity of the mill, and the rapid development of calibers leads to the appearance of second grades, and sometimes marriage.
The study of the causes and mechanism of the development of calibers showed that the sharp edges of the oval, which cool faster than the rest of the strip, have a significant resistance to deformation. These edges, entering the caliber of the finishing stand rolls, act on the bottom of the caliber as an abrasive. Rigid edges at the tops of the oval form hollows at the bottom of the gauge, which lead to the formation of protrusions on the strip along its entire length. Therefore, for round profiles with a diameter of 50-80 mm and more, a more accurate profile execution is achieved by using two or three radius ovals. They have approximately the same thickness as an oval outlined by one radius, but due to the use of additional small radii of curvature, the width of the oval decreases.
Such ovals are flat enough to hold them in wires and provide a secure grip, and a more rounded contour of the oval, approaching the shape of an ellipse in its shape, creates favorable conditions for uniform deformation in width. .bands in round gauge.
The essence of the invention: the finishing gauge is symmetrical with respect to the horizontal plane of the parting, and each part of the gauge is formed by three arcs of a circle of the same radius, while the central arc is limited by an angle of 26 - 32 °, and the centers of the side arcs are shifted beyond the axis of symmetry of the streams by 0.007 - 0.08 of the radius arcs. 1 ill.
The invention relates to the processing of metals by pressure and is intended for use primarily in ferrous metallurgy, as well as in mechanical engineering. The aim of the invention is to simplify the setting of the caliber and increase the yield. The drawing schematically shows a finishing gauge for rolling round steel. The proposed finishing gauge for rolling round steel contains two streams 1 and 2, symmetrical about the horizontal axis X and vertical axis Y. Each of these streams has three sections 3,4 and 5, formed by arcs AB, BC, CD, A "B" , B"C" and C"D" of the same radius R. The central arcs BC and B"C" are limited by an angle of 26-32 o and are outlined by a radius R from the point of intersection of the X and Y axes of the caliber. Lateral arcs AB, A"B" and CD, C"D" are also outlined with a radius R, but from centers shifted beyond the vertical axis of symmetry Y of the caliber in the direction opposite to these arcs. The arcs AB and CD are outlined from the centers O 2 and O 1, and the arcs A "B" and C "D from the centers O 3 and O 4. The displacement of the centers behind the vertical axis of symmetry Y is equal to half the tolerance field for the finished profile. The gauge is equipped releases (built with a "collapse") 6. They are built according to well-known methods, drawing from points A, D and A "D", tangent to the arcs A 1 AB, CDD 1 and A 1 A "B", C "D" D 1. The upper and lower strands are installed with a gap 7 of size S. During the operation of the rolling mill, before rolling in a new finishing pass, the gap S is set such that the height of the pass corresponds to the minimum allowable value of the size of the circle diameter. After that, rolling is carried out. as the caliber grooves wear out, it is adjusted. In this case, the criterion is the "ovality" of the profile. Rolling is carried out in the caliber until it wears out in width, corresponding to the maximum allowable size of the diameter of the circle along the width of the caliber (X axis). After that, they proceed to rolling in a new As a result of increased wear of the strands in sections 4 and 5, the limit value of the diameter of the finished profile in the corresponding sections is obtained almost simultaneously with the corresponding dimensions along the X axis. If the dimensions of the central arcs 1 go beyond the limits specified in the claims, the positive effect of its use decreases, this can be seen from the table, which shows the results of rolling a circle of 1600 mm. As the experimental rolling data showed, as a result of using the proposed finishing pass for rolling round steel, metal removal from the finishing pass increased by 38%; the yield of second grades decreased by 60%. The claimed finish pass for rolling round steel is of undoubted interest to National economy, as it will reduce metal consumption: significantly increase labor productivity by at least 12% by reducing the time for transshipment.
Claim
FINISHING GAUGE FOR ROLLING ROUND STEEL, formed by two streams symmetrical with respect to the horizontal plane of the parting, limited by arcs of circles, characterized in that, in order to simplify the setting of the caliber and increase the yield of good, each of the streams is formed by three arcs of the same radius, while the centers of the side arcs are displaced for the vertical axis of symmetry of the streams by 0.007 0.08 of this radius, and the central arc is limited by an angle of 26 32 o .
DRAWINGS
,MM4A - Early termination of a USSR patent or patent Russian Federation on the invention due to non-payment in fixed time maintenance fees
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