How to roll a square out of a circle yourself. Calibration of rolls for rolling round profiles
Rolling on the designed casting and rolling module with a planetary cross-rolling mill is carried out in 13 stands, which, as shown in Fig. 7, are conventionally identified in the following groups: crimping (in the form of a planetary stand), roughing (6 stands), intermediate (4 stands) and 2 finishing groups (2 stands each).
In a planetary cross-roller crimping stand, rolling is carried out from a round cast billet into a round rolled billet with a high degree of deformation.
Subsequently, rolling of high-precision round high-strength alloy steel with a diameter of 18 mm is carried out as follows.
In the roughing group of stands, rolling from a round billet into an oval profile is carried out using one of the systems drawing gauges ok - oval - rib oval system, which is most suitable for production round profiles high precision made of high strength alloy steels.
The necessary transition to a rhombic and square shape of the roll with subsequent longitudinal division is carried out in special gauges of the preparatory group of stands according to recommendations and methods.
And finally, in the finishing groups of rolling stands, each thread of divided rolled stock is produced according to the square-oval-circle system, which is widely used for converting a square section into a round one (for rolling small sections round steel.
The calibration of round steel with a diameter of 18 mm is calculated against the rolling stroke.
Calculation of calibers of the finishing group of mill stands. For rolling round steel, several calibration schemes are used, which are used depending on the profile size, steel quality, type of mill and its range, as well as other rolling conditions. However, in all cases the pre-finishing gauge is either a conventional single-radius oval or a flat oval. But pre-finishing single-radius oval gauges with an axial ratio = 1.5 are more widely used, and for good stability in round gauge the oval profile should have a significant bluntness. The preparatory gauge is a separating gauge producing two diagonal rolls.
With all rolling methods, the finishing round gauge is made with a “camber” - release to prevent overflow of the gauge and to obtain the correct round profile. The construction of such a round gauge is shown in Fig. 14.
Fig. 14.
When designing a finishing round gauge, it is necessary to take into account the thermal expansion of the metal and tolerances for deviations in the dimensions of the finished profile.
The construction of a round gauge is carried out as follows. On the diameter circle, rays drawn from the center of the caliber at an angle to the horizontal axis determine the points at which the sides of the caliber begin to release and determine the width of the caliber.
To calculate the diameter of the profile in the hot state in the finishing stand of the mill (stand 13), the expression is used
=(1.0121.015)(+) (1)
where is the diameter of the profile in a cold state;
Minus tolerance
We will perform the calculation when rolling 30KhGSA alloy steel into a high-precision round profile. And, then, according to GOST 2590-88, the tolerances will be: +0.1mm and -0.3mm, and the profile diameter in the hot state will be
1.013 (18-) = 18.1 mm.
The width of the finishing gauge (according to Fig. 14) will be
Where is the release angle, which in practice for round steel diameters of 10-30 mm is taken to be 26.5
And then = = 20.22 mm.
The gap between the collars of caliber - S is chosen within the range (0.080.15) and then,
S = 0.111.81 = 2.0 mm.
The intersection points of the clearance lines S with the release line determine the width of the stream incision, which is defined as
Substituting the values we get
20.22 - = 18.22mm. (3)
The rounding of the shoulders is carried out with a radius
= (0.08 - 0.10) and then
0.008518.1 = 1.5mm.
The profile will be round if width =. In this case, the degree of filling of the caliber will be
A correctly made round profile in the finishing gauge of the 13th stand will have a cross-sectional area
The finishing group of stands has both groups of stands with a nominal roll diameter of 250 mm, with the finishing (13th) - horizontal rolls, and the pre-finishing (12th) - vertical rolls.
So, the finishing (13th) stand has a round gauge, the pre-finishing (12th) stand has a single-radius oval gauge, and the preparatory gauge (11th) stand is a dividing double diagonal square.
The nominal diameter of the rolls of the 11th stand, already included in preparatory group stands are 330mm.
The rollers of the finishing and pre-finishing group of stands are made of bleached cast iron. The rolling speed of high-precision round sections made of high-strength alloy steels in the finishing stand of the mill is assumed to be about 8 . Rolling temperature 950°C.
To determine the drawing coefficient in a finishing caliber, you can use the formula, which has the form
1.12+0.0004 (6)
Where - corresponds to the diameter of the finishing gauge in the hot state, i.e. =
1.12=0.0004 1.81 = 1.127
The broadening in the finishing circle is determined by the formula, which has the form
?= (7)
Where D is the nominal diameter of the rolls, mm.
1.81=2.3mm.
A simple single-radius oval gauge can be used as a pre-finishing gauge, the construction of which is shown in Fig. 15
Fig. 15.
To construct the gauge, the dimensions of the height of the oval gauge and the width are determined in accordance with the compression mode adopted when calculating the calibration. Practical calibrations use ovals with aspect ratios
Pre-finishing oval area
257.3 1.127=290. (8)
The thickness of the pre-finishing oval = is determined as
18.1-2.3=15.8mm. (9)
Width of finishing oval
26.2mm. (10)
Compression in finishing gauge
26.2-18.1=8.1mm. (eleven)
Engagement angle in finishing gauge
Arccos(1-)=arccos(1-)=15°19" (12)
The permissible grip angle can be determined using a method taking into account the values of the coefficients for the oval-circle rolling scheme according to the formula
where v is the rolling speed, ;
Coefficient taking into account the condition of the roll surface (for cast iron rolls =10);
M - coefficient taking into account the grade of rolled steel (for alloy steel M=1.4);
t is the temperature of the rolled strip, ?;
The degree of filling of the previous caliber during rolling;
K b; ; ;; ; ; - the values of the coefficients determined for various rolling schemes (drawing calibers) are determined from the table; for the oval-circle system (=1.25; =27.74; =2.3; =0.44; =2.15; =19.8; =3.98).
Let us assume the degree of filling of the pre-finishing oval gauge = 0.9
And, then the maximum permissible value of the grip angle in the finishing gauge will be
Because the<, условия захвата в чистовом калибре обеспечивается.
The ratio of the axes of the oval profile specified in the finishing gauge is
If the degree of filling of the pre-finishing oval gauge = 0.9, we find the width of the pre-finishing oval gauge
29.1mm. (15)
The caliber shape factor is defined as
The radius of the outline of an oval-caliber stream
17.4mm. (16)
Let us determine the permissible ratio of the axes of an oval strip according to the condition of its stability in a round gauge using the method according to the formula
Where: ; ; ; ; ; - values of the coefficients determined for the oval-circle rolling scheme, determined from the table (
Since the profile stability conditions are met.
The gap S along the oval caliber collars is accepted according to the limits (0.15-0.2)
S=0.16 =0.16 15.8=2.5mm. (18)
Radius of rounded corners in oval gauge = (0.1-0.4).
The blunting of an oval caliber in practice is most often
0.2 15.8=3.2mm (20)
The cross-sectional area of one of the preparatory squares in the double dividing gauge of the 11th stand can be determined as for a conventional diagonal square gauge.
And then its area will be equal
The elongation coefficient of the preparatory square in the oval gauge of the 12th stand can be determined according to the recommendations of the method. Thus, according to this method, it is recommended that the overall elongation coefficient when rolling a square in an oval and round gauge is determined from a graph depending on the diameter of the resulting round steel. For a given diameter of round steel equal to 18 mm, the overall elongation coefficient will be = 1.41. And since
The area of the given square will be determined by formula (21) and will be
290 1.25=362 .
The construction of a standard diagonal square gauge is shown in Fig. 16
Rice. 16.
The apex angle should be 90° and =. The filling degree of the square gauge is recommended to be 0.9. It can be approximated
And then the side of the square caliber - c will be
19.2mm. (25)
The radius of curvature of the top of a square gauge is defined as
=(0.1h0.2) = 0.105 19.2 = 2mm (26)
The rounding of the riot is performed with a radius, which is defined as
= (0.10h0.15) = (0.10h0.15) = 0.11 19.2 = 3mm. (27)
The height of the profile emerging from the square caliber will be slightly less than the height of the caliber due to the rounding of the vertices with a radius, and then
0.83= 19.2-0.83 2=25.5mm (28)
As already noted, the gauge in the 11th stand is a double diagonal square gauge in which the separation is rolled. Construction and general form this caliber is shown in Fig. 17. In the same figure, the outline of the roll from the 10th stand entering this caliber is superimposed.
Fig. 17.
Longitudinal separation of a multi-strand roll with a controlled tear is carried out by creating tensile stresses in the jumper area under the action of axial forces from the side surfaces of the ridges of double-strand gauges embedded in the metal, as can be shown in Fig. 18.
Fig. 18.
At the moment of gripping, due to the crushing of the surface of the roll by the inner side faces of the caliber streams, a normal force N and a frictional force T arise. The resultant of these forces can be decomposed into transverse Q and vertical P components. Under the influence of the force P, the metal is compressed by the rollers, the force Q promotes the stretching of the jumper in the transverse direction and causes the appearance of a tensile resistance force of the jumper S and a resistance force to the plastic bending of the outer workpiece towards the connector of caliber G.
By measuring the thickness of the bridge of the specified roll - and the gap between the ridges of the rolls - t of the separating gauge (see Fig. 17), it is possible to change the radius of curvature of the front ends of the divided profiles at the exit from the rolls and the conditions for separating the roll. The absence of a break in the neck at the point of separation of the profile neck makes it possible to obtain a high-quality surface of the finished profile with a minimum number of subsequent passes with compression of the separation points. In this regard, the method of longitudinal separation of rolled products by controlled tearing is recommended for use in finishing stands of rolling mills.
Studies of the longitudinal separation of double-thread rolled material by controlled tearing have shown that the thickness of the web of the rolled material inserted into the separating cage should be equal to 0.5 x 0.55 of the side of the square.
The study of the gap between the roll ridges affects the change in the curvature of the front ends of the divided square profiles when exiting the rolls. So, the straightness of the output was obtained with a gap = 16 mm equal to the thickness of the jumper, then we select
From the practice of calculating calibrations when rolling and separating square profiles, the compression ratio of the sides of a square profile is taken in the range of 1.10-1.15. And then, from the expression (by choosing) we determine the side of the square in 10 gauge
19.2 1.125=21.6 mm. (29)
The area of the dividing double gauge of the 11th stand is actually equal to twice the area of the calculated diagonal square.
And then (30)
The distance between the axes of the streams in the caliber of the 11th stand - , is determined as
The length of the jumper between the streams in this caliber is determined as
As stated above, the thickness of the jumper in the 10th stand can be determined as
To check for the capture of the rolled material entering the gauge of the 12th stand, it is necessary to calculate the absolute compression in this gauge and compare it with the permissible data.
When a square profile enters an oval gauge, the absolute compressions along the middle and edges of the profile will be different and are determined geometrically by the superposition of the square profile section on the oval gauge and will be in the middle of the gauge
Compression at the extreme points of a square in an oval caliber based on geometric transformations will be approximately?.
As you can see, these absolute reductions are less than the absolute reductions in the 13th gauge and, therefore, with the same nominal diameter of the rolls and the same material, checking for acceptable gripping conditions is not required.
Taking into account the above, the construction and general view of the preparatory gauge in the 10th stand (before rolling-separation) can be presented in Fig. 19.
Fig. 19.
Some caliber dimensions can be determined as follows: we take the length of the jumper based on existing calibrations during rolling-separation;
radius of curvature of the top of the square gauge in this stand
The value can be determined according to Fig. 17 using the formula
The height of the roll coming out of the caliber of the 10th stand
The distance between the axes of the streams in the caliber of the 10th stand - , is determined as
The size of the gap along the gauge collars in the 10th stand is taken as mm.
The area of the roll emerging from the gauge of the 10th stand can be determined according to Fig. 17 as
Substituting the values of the indicated parameters we get
The area of the undivided roll in the caliber of the 11th stand is equal to twice the area of the diagonal square roll, i.e.
And then, the drawing coefficient in the gauge of the 11th stand is determined as
Theoretical width of the roll coming out of the 11th stand
Theoretical width of the roll emerging from the 10th stand (with a radius of curvature at the collar = 5)
To check the capture of the rolled material entering the gauge of the 11th stand, it is necessary to calculate the absolute compression at characteristic points of the gauge and compare it with the permissible data.
Thus, the magnitude of absolute compression in the area of the jumper of a two-thread roll will be
and in the area where stream axes break, it will be
alloy steel rolled casting module
So, as you can see, here the region of the roll jumper needs to be checked for the capture condition.
The grip angle in the area of the jumper when rolling in the 11th stand gauge can be determined as
where: D is the nominal diameter of the rolls in the 11th stand (D = 33 mm).
The permissible grip angle in this caliber can be determined using the method of M.S. Mutyeva and P.L. Klimenko, this requires a rolling speed in this stand, which will
5.67 m/s, (45)
and then the maximum permissible grip angle is determined by the formula (t = 980?)
Because the conditions for capture in the 11th separating caliber are met.
The gauge in the 9th stand of the intermediate group of stands is located in vertical rolls and can largely resemble a diagonal square gauge, but has its own characteristics. It is designed for rolling rhombic bars and in the area of the connector has a more cramped shape than a regular diagonal gauge. Rolling in this caliber involves deformation processing of future lateral horizontal parts of double-strand rolled products, which will be subjected to rolling-separation. Taking into account the above, the construction and general appearance of this preparatory gauge in a 9-stand can be presented in Fig. 20.
Fig.20.
To determine a number of caliber parameters, we use some empirical dependencies obtained in similar calibrations during rolling-separation.
So, the side of the square, as for the 10th gauge, can be determined as
The value representing the middle part of the caliber is recommended to be taken as 40% of the diagonal part of the caliber.
Based on practical data, we take the slope of the beads in the middle part of the caliber within 25%, this allows us to obtain the maximum width of the roll.
The width of the diagonal square part of the gauge will be
Based on practical data from rolling-separation calibrations, we assume that the radii of curvature at the tops of the gauges and at the shoulders are the same and equal to 5 mm, i.e. mm.
The gauge thickness of the 9th stand will be
Thickness of the roll coming out of the 9th stand gauge
Also, based on practical data, we accept the size of the gap along the caliber collars as 5 mm, i.e. mm.
The area of the roll emerging from the 9th stand can be determined as
and then, substituting the values of the indicated parameters, we get
The drawing coefficient in a 10-stand gauge is determined as
To check the grip of the rolled material entering the caliber of the 10th stand, it is necessary to calculate the absolute compression in this stand.
Since the shapes of the gauges of the 9th and 10th stands are very different in configuration, we will replace their area with the reduced one (rectangular shape), where the width of the strip will be equal to the width of the roll, and the thickness of the reduced strip can be determined
The given absolute compression value will be
The given value of the grip angle in the caliber of the 10th stand will be
As you can see, the given capture angle is significantly less than the previously calculated maximum values for similar conditions and, therefore, the capture condition must be met.
The most appropriate form of 8-stand gauge is a rhombic gauge located in horizontal rolls. The construction and general appearance of this caliber is shown in Fig. 21.
Fig.21.
The dimensions of the rhombic gauge are determined in the process of calculating the calibration, taking into account the specified value of the elongation coefficient in the caliber, the correct filling of the caliber, and also taking into account the obtaining of section dimensions that satisfy the rolling conditions in the next caliber.
In practice, rhombic calibers are used, characterized by size.
To prevent the formation of “straps” in the gaps of the gauge, it is recommended to take the filling degree of the gauges
We determine the maximum permissible grip angle in this caliber using the formula of M.S. Mutyev and P.L. Klimenko, if v = 3.9 m/s; t=990? and steel rolls according to the formula, at v=2-4m/s
and then the value of the maximum absolute compression will be
When rolling a rhombic billet in a square gauge (conventionally, we can consider rolling a rhombic billet in a 9-gauge). The side of a reduced square can be defined as
The possible width of the roll coming out of the rhombic caliber of the 8th stand will be
We accept the drawing coefficient in the 9th gauge; we can calculate the rolling area in the 8th gauge as
And then, the thickness of the roll coming out of the rhombic gauge of the 8th stand will be
The widening of the rhombic strip in a square gauge, if the side of the square (diagonal) gauge is >30mm, is determined by the following formula.
and then, substituting the values, we get
Taking into account the widening, the width of the roll in the 9th gauge should be
and as you can see, such a roll from a rhombic gauge into a square one can be rolled without overfilling the gauge, because and as you can see.
The remaining dimensions of the rhombic caliber are determined from the following empirical recommendations
The ratio of the diagonals in the caliber is calculated
We take the gap at the caliber connector to be equal to 5 mm, i.e. .
Theoretical height of a rhombic gauge - can be determined by the formula
The bluntness of the rhombic stripe at the caliber connector is defined as
Theoretical width of a rhombic gauge - defined as
The vertex angle - in can be defined as
From (74)
in = 2 arctg1.98 = 126.4°
Side of a rhombus - defined as
In the roughing group of stands, consisting of 6 working duo stands with alternating horizontal and vertical rolls, the rolling of a round billet with a diameter of 80 mm, arriving from a crimping cross-roller planetary stand, is rolled along an oval-rib oval drawing pass system. This system has become widespread in the rolling of high-precision round steel from alloy and high-strength steels on continuous mills.
In the 7th stand of the roughing group, the gauge is a ribbed oval located in the vertical rolls. The construction and general appearance of this caliber are presented in Fig. 22.
Fig.22.
Based on practical data, the drawing coefficient in the rhombic caliber of the 8th rolling stand in the form of a rib oval can be recommended within the range of 1.2-1.4. And then, the area of the roll coming out of the gauge in the form of a rib oval in the 7th stand will be
The total elongation factor in the roughing group of stands will be
where is the area of the round bar coming out of the planetary crimping cage, .
Previously, based on practical foreign data, it was shown that taking into account the deformation of continuously cast billets with a diameter of 200 mm in a planetary stand, the optimal kinematic dependence of the roll coming out of this stand should have a circular cross-section with a diameter of 80 mm.
The average draft ratio in this caliber system will be
Usually, as practice shows, in a ribbed oval caliber the draft is within the limits, and in oval calibers the draft is usually higher. And then, taking the hood in oval rib calibers, it is recommended to calculate the hood in oval calibers using the formula
In the 2nd stand, the circle must be rolled in an oval caliber, which leads to a decrease in the drawing coefficient and then
At ratio, the roll becomes unstable when rolling in a ribbed oval gauge. Usually ovals with a ratio are used. In ribbed oval calibers, the ratio between the height and width of the caliber is
Let us determine the permissible grip angle in the rhombic gauge of the 8-stand, if v = 3.4 m/s; t = 995? and cast iron rolls, according to the formula in the range v = 2-4m/s.
And then, the value of the maximum absolute compression at, will be
The thickness of the roll coming out of the 7th stand will be determined as
The width of the roll coming out of the 7th stand will be determined as
The radius of the oval is determined by the formula
The rounding of the collar is performed with a radius
We accept the size of the gap
The amount of blunting of the oval at is determined to be equal to the size of the gap, i.e. mm.
The general layout of the drawing passes of the roughing group of the mill stands is shown in Fig. 23.
Fig.23.
So, as you can see, in the 6th stand the gauge is oval and is located in horizontal rolls.
The area of an oval of this caliber is determined as
The oval gauge is single-radius and schematically no different from the previously considered oval gauge in the chit group of stands (see Fig. 15).
Oval gauge height
where is the widening of the oval stripe in the rib oval caliber, it is recommended to determine by the formula
where D is the diameter of the rolls, equal to 420 mm
Width of roll coming out of oval gauge
As is known, the area of an oval caliber is
Formula (93) can be represented as quadratic equation, the solution of which allows us to determine
after opening the brackets we get
And then, the absolute compression in the rib oval gauge of the 7th stand will be mm.
Let us determine the permissible grip angle in the rib oval of the 7th stand, if v = 2.8 m/s; t = 1000? and steel rolls and then, according to the formula in the range of 2-4 m/s, the permissible grip angle will be
And then, the value of the maximum permissible compression at.
As you can see, the capture conditions are met, and there will be broadening.
The final dimensions of the oval in the 6th stand gauge will be
The remaining dimensions of the oval gauge will be: the radius of the streams is defined as
The gap S along the caliber collars will be
Corner radius
As can be seen from Fig. 23, in the 5th stand the gauge is a rib oval and is located in vertical rolls.
Calibration of rolls in pairs of gauges of the 4th and 5th stands, 2nd and 3rd stands is carried out similarly to the given calculations for the calibration of gauges of 6th and 7th stands and, according to the general layout of the gauges (see Fig. 23), in the 2nd stand the gauge is made in the form single-radius oval and located in horizontal rolls. This caliber involves rolling a round profile with a diameter of 80 mm, coming from a 3-roll planetary crimping stand with an oblique arrangement of rolls.
The drawing coefficient in the oval gauge of the 2nd stand will be
Where is the cross-sectional area of the round bar (80 mm in diameter) coming from the planetary crimping stand.
Absolute compression along the vertices in an oval gauge of a 2-stand will be
The average absolute reduction when rolling a circle in an oval gauge of the 2nd stand will be
When rolling a round billet in an oval gauge, the expansion can be determined using the approximate formula
The possible width of the roll in the oval caliber of the 2nd stand will be
which, as you can see, is somewhat smaller and, therefore, there will be no overflow of the caliber.
Calibration of a crimping cross-roller planetary stand consists of installing inclined conical rolls, which, when rotating around their axis and planetary motion, should form a gap with the required inscribed circle (in the case under consideration, 80 mm in diameter) at the exit of the product from the rolls, and similarly with the required inscribed circle (diameter 200mm) at the entry of the workpiece into the rolls. The task of calibrating rolls includes determining the length of the deformation zone, which is determined by the conical part of the roll, the angle of inclination of the rolls, and the diameter of the rolls.
The general diagram of the deformation zone, indicating the calibration parameters of inclined conical rolls necessary for rolling the workpiece in question, is presented in Fig. 24.
Determining the parameters indicated in the diagram is the task of calibrating the rolls of the crimping cross-shaft planetary stand.
Fig.24.
The dimensions presented in Fig. 22 characterize the following parameters:
Distance from the rolling axis at the crossing point;
The same, but total along the roll axis;
and are the radii of the workpiece and rolled product, respectively;
Angle of inclination of the generatrix of the deformation zone cone;
The angle of inclination of the forming surface of the roll;
Ш - angle of crossing of the roll with the rolling axis;
Accordingly, the radii of the roll at the pinch, the calibrating section and the maximum (at the entry of the workpiece);
A - tangential displacement of the roll (not shown in the figure).
Based on practical data obtained from the design conditions and operating experience of similar mills, it is recommended to select some elements and parameters for roll calibration within the following limits:
(i.e. the diameter of the roll at the pinch);
(i.e. maximum roll diameter);
W = 45-60° (i.e. we take the crossing angle w = 55°);
the angle between the line of centers of the workpiece shaft and the projection line of the roll is = 45°.
Draw coefficient in the 1st stand
The remaining two working rolls of the crimping stand have the same dimensions as those presented above for the roll being calculated.
In the calibration calculations, the parameters of rolling speed and temperature across the stands were used.
Thus, the exit velocities from the stands were calculated using the formula
And then, taking the speed of the finished roll (in the form of a circle with a diameter of 18 mm) from the last stand of the mill 8 m/s, we obtain:
The entry speed of the workpiece into the 1st (planetary) stand will be approximately 7.9 m/min.
The overall change in metal temperature during rolling can be determined by the formula
Where and is a decrease in the temperature of the metal due to heat transfer by radiation and convection to the environment;
Decrease in metal temperature due to heat transfer by thermal conductivity upon contact with rollers, wires, rollers of roller tables;
An increase in metal temperature due to the conversion of mechanical deformation energy into heat.
And then, based on the use of the method, the change in the rolling temperature during rolling in the caliber and moving to the next caliber will be
Where is the temperature of the roll before entering the considered caliber, ?;
P - perimeter of the cross section of the roll after passage, mm;
F is the cross-sectional area of the roll after passing, ;
f - cooling time of the roll, s;
Increase in metal temperature in the caliber, ? and is determined by the formula
p - metal resistance to plastic deformation, MPA;
m is the elongation coefficient.
So, for example, the change in metal temperature during the movement of the workpiece from the heating furnace to the 1st stand of the mill according to formula (200) will be (if the heating temperature of the workpiece, f =, P = n 200 = 628 mm, F = 31416)
The increase in metal temperature in the 1st (planetary) stand due to intense deformation can be determined by formula (201) taking p = 100 MPa and and then
The final temperature of the metal after rolling in each stand, taking into account the change in rolling temperatures calculated using formulas (107) and (108) and the practical corrections made, will be: and
The main dimensions of the roll and calibration parameters when rolling a circle with a diameter of 18 mm from a workpiece with a diameter of 200 mm along the mill stands are given in Table 3.
Table 3. Basic calibrations for passes when rolling a 18mm circle from a 200mm workpiece.
|
Aisle no. |
Type of caliber |
Roll arrangement |
Roll size |
Compression, mm |
Widening |
Caliber area, F, mm |
Coef. Hoods, m |
Rolling temperature, t,? |
Rolling speed v, m/s |
Note |
|
|
Thickness, h |
|||||||||||
|
Initial conditions: |
Heating temperature |
||||||||||
|
3-roll |
Oblique |
Kosovalk. Planets. Cage. |
|||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
Vertical |
||||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
Vertical |
||||||||||
|
Single radius oval |
Horizontal |
||||||||||
|
Rib oval |
vertical |
||||||||||
|
Horizontal |
|||||||||||
|
Diagon. square type |
Vertical |
||||||||||
|
Double diagonal. square type |
Horizontal |
||||||||||
|
Double diagonal square |
Horizontal |
Separation of rolled material in caliber |
|||||||||
|
Single radius oval |
Vertical |
45° tilting |
|||||||||
|
Horizontal |
Calculation diagrams of roll calibers for all mill stands when rolling a circle of 18 mm from a continuously cast billet 200 mm are shown in Fig. 25.
The dimensions and tolerances of the gauge are somewhat different from the dimensions and tolerances of the rolled profile, which is explained by the different coefficients of thermal expansion of metals and alloys when heated. For example, dimensions finishing gauges for hot rolling, steel profiles should be 1.010-1.015 times larger than the dimensions of the finished profiles.
The dimensions of the calibers increase during rolling due to their depletion. When dimensions equal to the nominal plus tolerance are reached, the caliber becomes unsuitable for further work and is replaced with a new one. Therefore, the greater the tolerance on profile dimensions, the longer the service life of the gauges, and, consequently, the productivity of the mills. Meanwhile, the increased tolerance leads to excessive consumption of metal for each meter of length of the manufactured product. It is necessary to strive to obtain profiles with dimensions that deviate from the nominal ones in a smaller direction.
In practice, calibers are not built with positive calibers, but according to average tolerances or even with some minus. Improving the equipment of rolling mills, improving production technology and introducing automatic equipment for setting rolls will contribute to the production of rolled products with increased accuracy.
GOST 2590-71 provides for the production of round steel with a diameter of 5 to 250 mm.
Rolling of this profile is carried out differently depending on the steel grade and dimensions (Fig. 116).
Methods 1 and 2 differ in the options for obtaining a pre-finishing square (the square is precisely fixed diagonally and it is possible to adjust the height). Method 2 is universal, as it allows you to obtain a number of adjacent sizes of round steel (Fig. 117). Method 3 is that the pre-finishing oval can be replaced with a decagon. This method is used for rolling large circles. Method 4 is similar to method 2 and differs from it only in the shape of the rib gauge. The absence of side walls in this caliber allows for better scale removal. Because this method allows you to widely adjust the size of the strip coming out of the rib gauge, it is also called universal gauge. Methods 5 and 6 differ from the others in higher hoods and greater stability of the ovals in the wiring. However, such calibers require precise adjustment of the mill, since even with a small excess of metal, they overflow and form burrs. Methods 7-10 are based on the use of an oval-circle calibration system.
A comparison of possible methods for producing round steel shows that methods 1-3 allow, in most cases, to roll the entire range of round steel. Rolling of high-quality steel should be carried out using methods 7-10. Method 9 is, as it were, intermediate between the oval-circle and oval-oval systems, and is the most convenient in terms of regulating and adjusting the mill, as well as preventing sunsets.
In all the considered methods of rolling round steel, the shape of the finishing and pre-finishing passes remains almost unchanged, which helps to establish general patterns of metal behavior in these passes for all cases of rolling.
The construction of a finishing gauge for round steel is carried out as follows.
Determine the calculated diameter of the gauge (for a hot profile when rolling at minus) d g = (1.011÷1.015)d x - part of the tolerance +0.01 d x, where 0.01d x, - increase diameter for the reasons stated above; d x = (d 1 +d 2 /2) - diameter of the round profile in the cold state. In practice, when calculating, the second and third terms of the right side of the equality can be considered approximately the same, then
d g = (1.011÷1.015)(d 1 +d 2)/2,
where d 1, d 2 are the maximum and minimum permissible diameter values according to GOST 2590-71 (Table 11).
Depending on the size of the rolled circle, the following tangent angles α are selected:
We accept the gap value t (according to rolling data), mm:
Based on the data obtained, the caliber is drawn.
Example. Construct a finishing roll for rolling round steel with a diameter of 25 mm.
- Let's determine the calculated diameter of the gauge (for a hot profile) using the equation above.
We find from the table: d 1 = 25.4 mm, d 2 = 14.5 mm; whence d g = 1.013 (25.4 + 24.5)/2 = 25.4 mm. - We choose α=26°35′.
- We accept the gap between the rollers as t=3 mm.
- Using the data obtained, we draw the caliber.
Pre-finishing gauges for the wheel are designed taking into account the accuracy required for the finished profile. The closer the oval shape approaches the shape of a circle, the more accurate the finished round profile is. Theoretically, the most suitable profile shape for obtaining a perfect circle is an ellipse. However, such a profile is quite difficult to maintain when entering a finishing round gauge, so it is used relatively rarely.
Flat ovals are well held by wires and, in addition, provide large compressions. But the thinner the oval, the lower the accuracy of the resulting round profile. This is explained by the degree of broadening that occurs during compression. The broadening is proportional to the compression: where there is small compression, there is small broadening. Thus, with small oval compressions, the possibility of size variations in a round gauge is very insignificant. However, the opposite phenomenon is true only for the case when a large oval and a large hood are used. The oval for small sizes of round steel is close in shape to the shape of a circle, which makes it possible to use an oval of single curvature. The profile of this oval is outlined with only one radius.
For round profiles of medium and large sizes, ovals outlined by one radius turn out to be too elongated along the major axis and, as a result, do not provide reliable grip of the strip by the rolls. The use of sharp ovals, in addition to the fact that it does not ensure an accurate circle, has a detrimental effect on the durability of the round gauge, especially in the output stand of the mill. The need for frequent replacement of rolls sharply reduces the productivity of the mill, and the rapid production of calibers leads to the appearance of second grades and sometimes defects.
A study of the reasons and mechanism for producing calibers produced by N.V. Litovchenko showed that the sharp edges of the oval, which cool faster than the rest of the strip, have significant resistance to deformation. These edges, entering the groove of the finishing stand rolls, act on the bottom of the groove as an abrasive. The hard edges at the tops of the oval form hollows at the bottom of the gauge, which lead to the formation of protrusions on the strip along its entire length. Therefore, for round profiles with a diameter of 50-80 mm and above, more accurate profile execution is achieved by using two- and three-radius ovals. They have approximately the same thickness as an oval outlined by one radius, but due to the use of additional small radii of curvature, the width of the oval is reduced.
Such ovals are flat enough to hold them in the wires and provide a reliable grip, and the more rounded contour of the oval, approaching the shape of an ellipse, creates favorable conditions for uniform deformation across the width of the strip in a round gauge.
Oval-circle system
Figure 1.8. Diagram of metal rolling in a gauge system
"oval-circle".
The system is a special case of the “oval-rib-oval” system and, if necessary, allows you to create “universality” of calibration, ensuring the production of round profiles of standard diameters from intermediate working stands (during the rolling of metal in the mill), which reduces downtime of the mill for transshipment . However, the “universality” of roll calibration systems somewhat complicates the implementation of the metal compression mode on the mill, which to some extent can be attributed to the disadvantages of the system. The low stability of a single-radius oval in a round gauge prevents the rolling of metal while maintaining high values of the partial “draw” of the metal, and the value of the average “draw” of the metal in the “oval-circle” system is (). It is not rational to use the gauge system as an exhaust system, although it is indispensable as a finishing system, which is successfully implemented at the 350 OEMK mill.
Some elements of calibers of simple form are common to all types of calibers.
The gap between the rolls (roll collars), . Under the influence of forces from the rolled metal, the distance between the rolls increases due to the selection of gaps in the stand parts and the elastic deformation of the stand. At the same time, the height of the caliber will increase. Therefore, the drawing of the gauge should show its shape and dimensions at the time of rolling the strip, that is, together with the gap (Figure 5.1).
The gap allows you to change the height of the gauge during rolling, thereby changing the profile of the rolled metal. With a large gap, the contact zone between the metal and the rolls is small, the contour of the pass is not closed, and therefore the performance of the dimensions and shape of the rolled product deteriorates. For this reason, the gaps in finishing calibers should be minimal.
The gap size is taken as a fraction of the nominal diameter of the rolls (Table 1.2.) or the height of the pass (strip height).
Table 1.2. Minimum gaps between roll collars
| Group of stands of small-section (medium-section) and wire line of mill 350 | No. of cages | , mm |
| Rough group |  |
|
| I intermediate | ||
| II intermediate | ||
| Finishing | ||
| Finishing block |  |
Figure 1.9. Scheme of construction and typical elements of a caliber: a – a geometric figure forming a caliber and the contours of the surfaces of a pair of smooth rolls (here the contours are two solid thin lines); b – roll streams with curves; c – position and dimensions of the rolled strip; d – final caliber diagram.
Caliber width represents a horizontal characteristic dimension relative to the roll axis (hereinafter horizontal and vertical will be implied relative to the roll axis) geometric figure forming a caliber (Figure 1.9.).
Caliber height- characteristic vertical size of the geometric figure forming the caliber (Figure 1.9.).
Gauge insertion width- this is the width of the geometric figure forming the caliber at the level of intersection with the line of the roll collar (Figure 1.9.).
Gauge plunge depth- this is the distance from the roll collar to the bottom point of the gauge (Figure 1.9.).
Radiuses of curvature along the bottom of the caliber and along the shoulders usually expressed in fractions of the caliber height. Curves make a smooth transition in places where there is a sharp change in the caliber contour or at the collar-caliber boundary (Figure 1.9.). Roundings are necessary to reduce stress concentrations in the roll elements.
Collar width between grooves (end flange) – the horizontal size of the uncut part of the roll barrel between adjacent grooves (between the last gauge and the edge of the working surface of the roll).
The width of the collar between the calibers:
End flange width:
, (1.4)
where is the length of the roll barrel (Appendix 1)
Number of streams on the roll barrel;
In expression (1.4) two quantities vary: . The resulting value must satisfy condition (1.5). Thus, in addition to finding the dimensions of the piles, the number of streams on the barrel is selected.
Caliber release. To ensure free exit of the strip from the rolls without pinching, the width of the stream should increase from the bottom to the center of the groove. Therefore, the side walls of the caliber are made inclined relative to the contour of the geometric figure forming the caliber. The tangent of the angle of inclination is called the caliber release. Sometimes caliber output is expressed as a percentage.
Strip height - vertical characteristic size of the strip emerging from the rolls.
The width of the line - horizontal characteristic size of the strip emerging from the rolls.
Dulling the stripe at the gauge connector (Figure 1.9) shows the vertical size of the part of the rolled strip free from contact with the rolls.
The width and bluntness of the strip are additional geometrically clear parameters that describe an important characteristic of rolling in calibers - degree of filling of the caliber with metal. The degree of filling is determined by the formula.
The range of round and square profiles is very wide due to the wide variety of their uses. Square cross-section products (made of steel) are rolled with a square side from 6 to 200 mm or more, round cross-section - from 5 to 300 mm in diameter. Dimensions (diameters) from 5 to 9 mm correspond to rolling wire, on wire mills (wire rod); the interval of their sizes is 0.5 mm. Product sizes from 8 to 380 mm are rolled on small-section mills at intervals of 1 and 2 mm; from 38 to 100 mm - on medium-section mills with an interval of 2-5 mm and from 80 to 200 mm - on large-section mills with an interval of 5 mm. Larger product sizes are rolled on a rail and beam mill.
The most convenient for rental of round profiles are oval calibers (Next "caliber" - "K.";), alternating with square ones according to the system square-oval-square (Fig. 3.11, a) or according to the system square - rhombus - square (Fig. 3.11, b); in both cases square gauges in rolls located on the edge. Such distribution and alternation of metals contributes to better compression and processing of all layers of metal.
When rolling products with a round cross-section with a diameter of 5 to 20 mm, the K system, alternating, square - oval (Fig. 3.11, a). Round rolling with a diameter of more than 20 mm is carried out in calibers, alternating according to the system square-diamond (Fig. 3.11, b). In both systems, the last three Ks are common:
- pre-finishing square;
- pre-finishing oval;
- finishing circle.
Since rolling is carried out in a hot state, to obtain products of the required diameter (measured in a cold state) The dimensions of the finishing gauge should be adjusted to take into account shrinkage.
Due to the greater cooling effect of the rolls in the vertical direction, the thermal shrinkage of the vertical diameter is less than that of the horizontal one. Adjustment of the dimensions of the finishing caliper is ensured if the vertical diameter of the caliber is assumed to be dv = 1.01 dx, and the horizontal diameter dg = 1.02 dx.
The gap between the rolls, depending on the diameter of the roller, is taken in the range from 1 to 5 mm; The radius of rounding of the corners of the rolls near the gap r is 0.1d x (Fig. 3.11, f).
Rolling of square-section products is carried out in calibers, an alternating system rhombus-square (Fig. 3.11, c). This system is often used for rolling square profiles larger than 12 mm. Calibration begins with determining the size of the finished slab, taking into account unequal temperature shrinkage in the vertical and horizontal directions. For this purpose, the angle at the top of the finishing gauge is taken equal to 90°30" or 181/360 rad (Fig. 3.11, d).
Then the vertical diagonal of the finished K. d in = 1.41 C mountains, and the horizontal diagonal d g = 1.42 C mountains, where C mountains is the side of the square in the heated state, equal to 1.013 C n. The profile that comes out of such a K., when solidified, will have an exact square shape. The corners of a finished square K. are not rounded. The gap between the rollers is taken to be from 1.5 to 3.0 mm.
Flat products (sheets, strips) are usually rolled in smooth cylindrical rolls. The specified rolled thickness is achieved by reducing the gap between the rolls. Rolling of long sections is carried out in calibrated rolls, i.e. rolls having annular grooves corresponding to the rolling configuration sequentially from the workpiece to the finished profile.
The annular cutout in one roll is called a groove, and the gap between two grooves in a pair of rolls located one above the other, taking into account the gap between them, is called a caliber (Fig. 8.1).
Typically, a square or rectangular blank is used as the starting material. The calibration task includes determining the shape, size and number of intermediate (transition) sections of the rolled product from the workpiece to the finished profile, as well as the order of arrangement of the gauges in the rolls. Roll calibration is a system of sequentially located calibers that ensure the production of rolled products of a given shape and size.
The boundary of the streams on both sides is called a socket or gauge gap. It is 0.5...1.0% of the roll diameter. The gap is provided to compensate for elastic deformations of the working cage elements that occur under the influence of rolling force (the so-called recoil, cage spring). At the same time, the interaxial distance increases from fractions of a millimeter on sheet mills to 5...10 mm on crimping mills. Therefore, when adjusting, the gap between the rolls is reduced by the amount of recoil.
The slope of the side faces of the caliber towards the vertical is called caliber release. The presence of a slope facilitates the centering of the rolled product in the pass, facilitates its straight exit from the rolls, creates space for the widening of the metal, and provides the possibility of restoring the pass during regrinding (Fig. 8.2). The amount of release is determined by the ratio of the horizontal projection of the side face of the caliber to the height of the stream and is expressed as a percentage. For box gauges the output is 10...25%, for rough shaped gauges - 5...10%, for finishing gauges - 1.0...1.5%.
IN- width of the gauge at the connector, b- width of the caliber in the depths of the stream, h to- caliber height, h r- height of the stream, S- gauge gap.
The distance between the axes of two adjacent rolls is called the average or initial diameter of the rolls - Dc, i.e. these are the imaginary diameters of the rolls, the circles of which are in contact along the generatrix. The concept of average diameter includes the gap between the rolls.
The center line of the rolls is a horizontal line dividing in half the distance between the axes of the two rolls, i.e. this is the line of contact of the imaginary circles of two rolls of equal diameter.
Neutral line of the caliber - for symmetrical calibers this is the horizontal axis of symmetry; for asymmetrical calibers, the neutral line is found analytically, for example, by finding the center of gravity. A horizontal line passing through it divides the area of the caliber in half (Fig. 8.3). The neutral line of the gauge determines the position of the rolling line (axis).
The rolling (working) diameter of the rolls is the diameter of the rolls along the working surface of the caliber: 
. In calibers with a curved or broken surface, the rolling diameter is determined as the difference and, where is the average height, equal to the ratio, is the area of the caliber (Fig. 8.4).
The ideal option seems to be when the neutral line of the caliber is located on the center line, i.e. they match. Then the sum of the moments of forces acting on the strip from the upper and lower rolls is the same. With this arrangement, the strip should exit the rolls strictly horizontally along the rolling axis. In the actual rolling process, the conditions on the contact surfaces of the metal with the upper and lower rolls are different and the front end of the strip can unexpectedly move up or down. To avoid such a situation, the strip is forced to bend more often down onto the wiring. The easiest way to do this is due to the difference in the rolling diameters of the rolls, which is called pressure and is expressed in millimeters - DD, mm. If , there is upper pressure, if - lower pressure.
In this case, the neutral line of the gauge shifts with the center line by the amount X(see Fig. 8.1) and 
, A 
. Subtracting the second equality from the first, we get . Where . Knowing and you can easily determine the initial and .
For example, mm and mm. Then 
mm and mm.
Typically, on section mills, an upper pressure of approximately 1% is used. On bloomings, a lower pressure of 10...15 mm is usually used.
In the rolls, the calibers are separated from each other by collars. To avoid stress concentration in the rolls and rolls, the edges of the gauges and collars are conjugated with radii. Deep in the stream 
, and at the connector 
.
8.2 Classification of calibers
Calibers are classified according to several criteria: by purpose, by shape, by location in the rolls.
According to their purpose, they are distinguished between crimping (extracting), roughing (preparatory), pre-finishing and finishing (finishing) gauges.
Crimping gauges are used to draw out rolled material by reducing its cross-sectional area, usually without changing its shape. These include box (rectangular and square), lancet, rhombic, oval and square (Fig. 8.5).
Roughing gauges are designed to draw out the rolled material while simultaneously forming a cross-section closer to the shape of the finished profile.
Pre-finishing gauges immediately precede finishing gauges and decisively determine the production of a finished profile of a given shape and size.
Finishing gauges give the final shape and dimensions to the profile in accordance with GOST requirements, taking into account thermal shrinkage.
Based on their shape, calibers are divided into simple and complex (shaped). Simple gauges include rectangular, square, oval, etc., shaped gauges include corner, beam, rail, etc.
By location in the windrows There are closed and open calibers. Open calibers include those in which the connectors are located within the caliber, and the caliber itself is formed by streams cut into both rolls (see Fig. 8.5).
Closed calibers include those in which the connectors are located outside the caliber, and the caliber itself is formed by an indentation in one roll and a protrusion in the other (Fig. 8.6).
Depending on the dimensions of the profile section, the diameter of the rolls, the type of mill, etc., drawing gauges are used in various combinations. Such combinations are called caliber systems.
8.3 Pull gauge systems
The system of box (rectangular) gauges is used mainly when rolling rectangular and square billets with a cross-sectional side of more than 150 mm on blooming, crimping and continuous mills, in roughing stands section mills(Fig. 8.7). The advantages of the system are:
- 
the possibility of using the same gauge for rolling workpieces of different initial and final sections. By changing the position of the upper roll, the dimensions of the caliber change (Fig. 8.8);
Relatively small depth of the stream incision;
Good conditions for the removal of scale from the side faces;
Uniform deformation across the width of the workpiece.
The disadvantages of this gauge system include the impossibility of obtaining workpieces of the correct geometric shape due to the presence of slopes on the side faces of the gauges, relatively low drawing ratios (up to 1.3), and one-sided deformation of the roll.
The rhombus-square system (see Fig. 8.7-c) is used in billet and roughing stands of section mills as a transition from the box gauge system to produce workpieces with a square side of less than 150 mm. The advantage of the system is the ability to obtain squares of the correct geometric shape, significant one-time hoods (up to 1.6). The disadvantage of the system is the deep cuts into the rolls, the coincidence of the ribs of the rhombus and the square, which contributes to their rapid cooling.
The square-oval system (see Fig. 8.7-d) is preferable for obtaining a workpiece with a cross-sectional side of less than 75 mm. Used in roughing and finishing stands of section mills. Provides draws up to 1.8 per pass, small penetration of the oval caliber into the rolls, systematic updating of the rolling angles, which contributes to a more uniform temperature distribution, and stability of the rolls in the calibers.
In addition to the ones mentioned above, rhombus-rhombus, oval-circle, oval-oval, etc. systems are used.
8.4 Calibration schemes for simple profiles (square and round)
Rough roll gauges for rolling square profiles can be made in any system, but the last three gauges are preferably in the rhombus-square system. The angle at the vertex of the rhombus is taken to be up to 120 0. Sometimes, to better fulfill the corners of the square, the angle at the very top of the rhombus is reduced to a straight line.
When rolling squares with a side up to 25 mm, the finishing gauge is built in the form of a geometrically regular square, and with a side over 25 mm, the horizontal diagonal is taken to be 1...2% larger than the vertical one due to the temperature difference.
Roughing passes for rolling round profiles are also performed in any system, and the last three passes are made in the square-oval-circle system. The side of the pre-finishing square for small circles is taken equal to the diameter of the finishing circle, and for medium sizes - 1.1 times the diameter of the circle.
Finishing gauges for circles with a diameter of less than 25 m are made in the form of a geometrically regular circle, and for circles with a diameter of more than 25 mm, the horizontal axis is used 1...2% more than the vertical one. Sometimes, instead of an oval formed by one radius, a flat oval is used for greater stability of the roll in a round gauge.
Figure 8.9 shows the roll calibration diagrams of the 500 mill, which show the systems of drawing gauges in roughing stands discussed above, calibration of square, round and other profiles.
8.5 Features of calibration of flange profiles
,
Where a d- size of the finishing profile at the temperature of the end of rolling,
a x- standard profile size;
Yes- minus size tolerance a x;
To- coefficient of thermal expansion (shrinkage) equal to 1.012...1.015.
For large profiles, for which the tolerance obviously exceeds the thermal shrinkage value, the calibration calculation is carried out on a cold profile.
3. In order to achieve maximum productivity, roughing passes are calculated taking into account the maximum grip angles with subsequent clarification on the strength of the rolls, engine power, etc. In finishing and pre-finishing passes, the reduction mode is determined based on the need to achieve the highest possible profile accuracy and low wear of the rolls, i.e. .e. at low elongation ratios. Usually in fine calibers m= 1.05…1.15, in pre-finishing m = 1,15…1,25.
The total number of passes when rolling on reversing mills, in trio stands, and on linear type mills must be odd so that the last pass is in the forward direction.
Loading...
