JP4284396B2 - High area reduction rolling method - Google Patents

Description

The present invention relates to a method for rolling a long product such as a steel wire rod, steel bar, or bar steel manufactured by hot rolling.

The target steel material is manufactured by a method in which a steel slab is used as a material and hot rolling with a perforated roll is repeated and finished to a predetermined size. Taking a wire as an example as a major problem in manufacturing, the area reduction rate is normally limited to 10 to 30% per pass, so the number of passes is 25 to 35 times. A large number of rolling mills are required, and the equipment costs including spare parts are high, which is a heavy burden on operating costs such as energy loss, roll wear, and maintenance of incidental equipment. Currently, the problem is not so strongly conscious due to the effect of high-speed mass production method, but if high reduction in area ratio is possible, it will not only solve the above-mentioned problems such as reduction of equipment cost but also disadvantageous in cost for small investment and small-scale production. There is a possibility that it will not become, and management is highly expected.

The first reason that the area reduction rate is limited as described above is that the cross-sectional aspect ratio (= width / thickness) becomes excessive when a large reduction is performed to obtain a high area reduction. In the next pass that is squeezed in the width direction, taole, buckling, twisting, etc. are likely to occur, and the desired shape is not easily obtained. Therefore, the reduction must be subdivided. Eventually the number of passes does not decrease.

The second reason is that even though the rolling reduction is performed, as the rolling reduction ratio increases, the widening increases at an accelerated rate, and the increase in the area reduction ratio with respect to the rolling down decreases rapidly.

The third reason is that once the aspect ratio becomes excessive, the excess circumference becomes inevitable due to the excessive perimeter, so that uneven skin accumulation is unavoidable in subsequent rolling, and wrinkle damage is likely to occur. This is because local accumulation of the decarburized layer is amplified.

As described above, mere large pressure not only does not provide a sufficient area reduction ratio, but also causes an excessive aspect ratio to induce a reduction in surface quality.

In the following, the preceding examples of the high area reduction rolling method will be examined.
Reference 1 describes the PCRM method (Planetary Cross Rolling Mill). According to this method, the cylindrical material can be stretched by about 6 times (reduction rate of about 84%) by drawing and rolling by rotating and revolving a conical inclined three-way roll. However, due to the speed restriction due to the structure of the rolling mill, it can be applied effectively to rough rolling (approximately 0.1 m / s), but after intermediate rolling (1-100 m / s), where the running speed is accelerated. Has the problem of being difficult to apply.

According to the method disclosed in Japanese Patent Application Laid-Open No. 2000-197907, the area reduction rate is improved to 55% by applying a forward / backward tension of about 85% of the yield stress of the material to the material in reversible cold rolling of a thin plate. Can do. In the conventional method, it is at most about 40% due to the problem of shape control. For plate-like materials that do not cause widening, the reduction ratio = area reduction ratio, and it can be understood that the addition of tension facilitates the reduction of surface area, but for rod and wire materials where widening by reduction is inevitable. Does not mention anything, and the effectiveness of the method is unclear.

Document 2 proposes a theory and specific measures for reducing the loss due to widening and improving the rolling efficiency. According to this, when a material under tension of Y / √3 (Y: yield stress of material) is rolled down, no widening occurs and the rolling reduction ratio is reduced. As a result, it can be easily understood that the increase in the aspect ratio is suppressed. From this theory, it is derived that when the tension exceeds the above value, the strain in the rolling direction further increases, and when the ultimate yield stress value is reached, it becomes twice the rolling strain. There is no experiment or mention about the specific deformation behavior in the range of Y / √3 or more.

According to this specific measure, three or more rolling mills are necessary to generate tension, and the first and last stages have one-side tension. In the case of one-side tension, the effect is estimated to be almost halved. Therefore, overall, the widening is suppressed to some extent and the rolling efficiency is improved, and it is possible to increase the partial rolling reduction rate and increase the area reduction rate, but not so much as to greatly reduce the number of rolling mills.

Edited by Japan Iron and Steel Institute, Steel Handbook 4th Edition, Volume 3-2, Volume 3, 10 ・ 4 ・ 1-4 Special rolling mill JP2000-197907 Saito, Utsunomiya et al .: Plasticity and processing 40-465 (1999-10), p.966-p.970: “Development of stretch-controlled rolling mill and application to flat wire rolling”

It is a significant problem for those skilled in the art to greatly reduce the number of rolling passes and to simplify the entire rolling equipment by processing rods and linear materials with a high reduction in area. In that case, 1) Rolling efficiency drops and the surface reduction rate reaches a peak at a mere high pressure, and the aspect ratio becomes excessive, so that subsequent forming, that is, dimensional and shape defects, wrinkle scratches, and local decarburization defects occur. 2) The above-described inclined rolling method is effective for rough rolling, but cannot be used in a region where the rolling speed is high after intermediate rolling. 3) The result of suppressing widening by applying tension. In particular, there is a problem that the effect is limited in the method of improving the area reduction rate.

In view of the above problems, the present invention provides a rolling method capable of obtaining a high surface area reduction even when the rolling speed is high, and suppressing the increase in the aspect ratio and causing no difficulty in subsequent rolling. The first purpose.

Other objects of the present invention are 1) that it can be carried out with relatively simple and inexpensive equipment in accordance with the purpose of the problem, and 2) reducing decarburization defects due to local accumulation of the decarburized layer of the skin unavoidable for hole rolling, 3) To reduce the frequency of surface flaws due to imperfect pass lines. 4) To improve rolling energy efficiency.

In solving the above-mentioned problems, the inventor noticed that no widening occurred under certain conditions in the process of investigating the influence of backward tension in hot rolling of steel wire, and stretching has already occurred by the roll bite. I discovered that. This is beyond the range of conventional tension rolling, and is defined as over-tension rolling, and the following inventions have been made by quantitatively examining the expression conditions.

The first invention is a method of hot rolling a bar, wire, or strip steel material while applying tension in the rolling direction, and rolls the steel material supplied to the rolling mill at a constant speed by the pulling force of the rolling mill itself. A back tension equal to the yield force of the steel material at the bite inlet is generated to induce stretching of the steel material at the inlet, and as a result, the increase in cross-sectional aspect ratio is suppressed and the reduction in area ratio is eliminated by eliminating the widening due to rolling. Is a rolling method with a low aspect ratio and a high area reduction rate characterized by increasing the thickness.

The second aspect of the invention is the low aspect ratio / high area reduction rolling method according to the first aspect of the invention, wherein the roll diameter ratio γ is set according to the formula (1).
μ ² γ> 2k / (1−h) + 2k + k (1-h) / 2 −−−−− (1)
However,
h: Total reduction ratio (= Thickness G after rolling of material / Thickness Ho before rolling)
k; shape factor (circle, oval; k = (π / 4) ² , rectangle; k = 1)
μ: Coefficient of friction between roll and steel γ: Roll diameter ratio (= roll diameter 2R / thickness Ho before rolling)

In the third aspect of the invention, the aspect ratio α is reduced to the equation (4) by adjusting the speed ratio of the material before and after rolling within the range according to the equation (2) or (3) according to the cross-sectional shape of the material. Is adjusted within the range according to the formula (5) or the formula (6), respectively, the low aspect ratio / high area reduction rolling method according to the second invention.
Rectangular: 1.0 / h <Vi / Vo ≦ 1.0 / (he × h) ----- (2)
Circle, oval; 1.0 / f <Vi / Vo ≦ 1.0 / (he ² × f) ----- (3)
Common to each cross section; 1 / h> α ≧ he / h ----- (4)
Rectangle: he × h ≦ r <h ----- (5)
Circle, oval; he ² × f ≤ r <f ------ (6)
However,
he = [− B−√ (B ² −4AC)] / 2A −−−−− (7)
A = 9, B = -6h-2F / k, C = h (h + 2F / k)
he; Drawing reduction ratio (= thickness He just before biting / thickness Ho before rolling)
F: Friction index (= μ ² γ)
Vo: Speed of the supplied steel before rolling
Vi; Speed after rolling
f: Area reduction ratio in net rolling (= cross-sectional area after rolling / cross-sectional area immediately before biting)
α: Specific aspect ratio (= section aspect ratio after rolling / aspect ratio before rolling)
r; Area reduction ratio (= cross-sectional area after rolling / cross-sectional area before rolling = 1-area reduction ratio)

4th invention arrange | positions two rolling apparatuses by the rolling method as described in 1st invention, 2nd invention, or 3rd invention in series, and reduces steel material 2 path | pass in the same direction or a right angle direction, and is the material of a circular cross section. If the diameter ratio is reduced to 0.1 to 0.5, the thickness ratio should be reduced to 0.1 to 0.5 and the width ratio to 0.2 to 1.0 in the case of a rectangular cross-section material. Is a rolling method with a low aspect ratio and a high reduction in area.

The fifth invention is a tension rolling device in which a material is supplied at a constant speed and rolled at a specific speed, and the material supply device having a restraining force that can withstand the rear tension of the rolling mill, and the roll diameter ratio follows the formula (1). A rolling mill composed of a perforated roll or a flat roll, a speedometer for detecting the speed of the material before and after rolling, a length measuring device for detecting the dimension of the rolled material, and a material receiving signals from the detectors A control device that sets and adjusts the rolling ratio before and after rolling according to formula (2) or (3) according to the material cross-sectional shape and the prescribed rolling reduction, and controls the dimension after rolling to a prescribed value. It is a low aspect ratio / high area reduction rolling device characterized by comprising:

In a sixth aspect of the present invention, the material supply device comprises either a pinch roller having a built-in multi-stage bending roller that applies repeated bending to the material in the cold or hot state, or a cold rolling mill that pre-rolls the material. A low aspect ratio / high area reduction rolling apparatus according to a fifth aspect of the present invention.

The first effect of the above invention is that the tension acting on the material by the pulling force by the roll is made equal to the yield force of the material for the rod, wire, and strip steel material supplied at a constant speed. Stretching is induced in the material by the roll bite. As a result, even if the rolling reduction ratio is set larger than usual, the widening due to rolling disappears or turns into a narrowing width, the excessive increase in the aspect ratio is suppressed, and subsequent rolling problems are eliminated, and the surface area is reduced more than the rolling reduction ratio. The rate can be easily obtained. Further, as a first condition for quantification, a roll diameter ratio that generates a reduction force of a size necessary for stretching is defined by the equation (1), and as a second condition, the reduction force is converted into a drawing force required for stretching. Since the ratio of the pre-rolling speed / post-rolling speed is defined by the formula (2) or (3), not only a low aspect ratio and a high area reduction ratio can be obtained, but they can be adjusted extensively. It becomes possible. The processing corresponding to the conventional six passes can be performed in one pass, and the number of rolling mills required in the rolling mill can be greatly reduced.

The second effect is that the structure of the rolling device is composed of a material constant speed supply device, a general double rolling mill having a relatively large roll diameter, and a control device thereof, and requires no special mechanism or design. Combined with the effect of 1, the whole rolling equipment is made cheap and simple.

Third, when the cross section is reduced, the ratio of simple stretching is large and the aspect ratio is kept small, so that abnormal accumulation and local accumulation of the side surface skin due to the reduction seen in conventional rolling in the next pass are less likely to occur. That is, the problem of decarburization defects and wrinkle scratches is solved. A significant reduction in the number of passes is also effective in reducing various surface flaws caused by passes.

Fourthly, the processing energy efficiency is improved by the fact that no widening occurs, the power loss due to the roll contact, the cooling of the steel material, and the like are small.

Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a schematic side view of a low aspect ratio / high area reduction rolling apparatus showing an embodiment of the present invention inserted in the middle of a step of finishing a steel slab into a wire rod by hot tandem rolling. The apparatus mainly comprises a front and rear two-stage rolling mill and a control system for stabilizing the rolling state. FIG. 2 shows the dimension symbols for the situation in which a circular cross-section material is being rolled down by a rolling mill.

In FIG. 1, a flat roll 4 having a roll diameter based on the formula (1) is used for the former rolling mill 3 of the present invention. First, the roll gap G is set corresponding to the predetermined reduction ratio h, and then the material speed ratio Vi / Vo is set based on the equation (3).

The hot material 1 is fed from the existing rolling mill 0 at a constant speed Vo while being tracked by the speedometer 10 ", and is heated and softened while passing through the induction heating device 2. The tip is a flat roll 4 of the preceding rolling mill 3. The difference between the two speeds is so large that a tension in the rolling direction is generated immediately on the material 1. The tension is set to a sufficiently large roll diameter ratio γ, so that the rolling force is reduced. Therefore, the pull-in force P (= friction coefficient x rolling force) tends to exceed the tensile yield force of the material, so that the material 1 is supported by the softening due to the temperature rise, and the roll bite 5 (hatched line in FIG. 2) The roll bite shrinks in approximately the same ratio in both the rolling direction and the width direction until the first part), and as a result of the stretching, the roll bite shrinks sequentially, the pulling force decreases, the stretching amount decreases, and it stabilizes at a certain equilibrium point. Therefore, after that, the reduced circular section The material is reduced by the flat roll 4. That is, over-tensile rolling is stabilized.

Total reduction is distributed to pre-stretching and net rolling. The former area reduction ratio r is the square of the drawing reduction ratio he, and the latter area is reduced in width by the rear tension, so that rolling efficiency is improved, and when combined, the area reduction ratio is remarkably improved.
On the other hand, as for the cross-sectional shape, the total width becomes equal to or less than that before rolling when the reduced width due to stretching and the small widening corresponding to the net rolling are added together, the increase in aspect ratio due to rolling is remarkably suppressed. From the above, even if the total reduction ratio is set to 50% or more, the aspect ratio is within about 1.5 or less (3 or more in the conventional method), and the subsequent rolling becomes extremely easy and high reduction ratio rolling over the total reduction ratio is achieved. Is made.

The material 6 in which the cross-sectional shape is a flat oval with a low aspect ratio is a constant speed Vi by the brake roll 15 having sufficient drawing resistance against the rear tension of the rear rolling mill 7 and the rolling direction is lower than the previous stage. It is supplied to a subsequent rolling mill 7 arranged by turning 90 degrees, and is guided to a predetermined hole type of a hole roll 8 having several types of circular holes. As in the case of the former rolling mill, the roll diameter is set according to the formula (1), the post-rolling speed is set according to the formula (3), and the roll is rolled in the oval major axis direction under the generation of the rear tension necessary for stretching. To return to the circular cross section.

Since it is over tension rolling, the width is equal to or less than that before rolling. Therefore, rolling with a hole width smaller than the material width is possible. This is not noticed at all by the conventional hole rolling.

Here, if the total rolling reduction of the latter rolling mill is set to be the same as that of the former stage, the change in the aspect ratio of the latter stage is almost the same as that of the former stage. This means that when the rear stage is squeezed in the direction perpendicular to the front stage, the aspect ratio before the front stage, that is, a circular cross section is necessarily returned. From the above, the circular cross-section material can be greatly reduced to a circular cross-section (diameter about 1/3 to 1/9) in two passes.

It should be noted that the constant speed supply of material may be disrupted by backward tension. Since the rolling temperature of the existing rolling mill 0 is relatively low as compared with the former stage rolling, if it is not driven, the drawing force becomes relatively large, while the rear tension becomes relatively small because of the high area reduction ratio, and the former is superior. Constant speed supply is possible.

In order to maintain the material supply speed at a predetermined value, the material speedometer 10 ″, the length measuring devices 9 and 9 ′ for tracking the width, height, and speed of the material on the downstream side of each roll, and the Doppler speedometer 10, 10 ′, respectively. Is installed, and signals from the two length measuring devices and the speedometers are sent to the controller 11, and the number of revolutions of the rolling mills 3 and 7 is controlled by the signal from the controller 11.

When the supplied material cross-sectional dimension is relatively large, the stress acting on the material is tracked by the load cells 14 and 14 'installed between the roll chock 12 and 12' of the rolling mill and the stands 13 and 13 '. And used for dimensional control and speed control.

FIG. 3 shows the application of the present invention to secondary rolling of a wire. A coiled wire 21 is used as the material. The pinch roller 22 cold-draws and feeds the material, but the built-in multi-stage bending roller 23 has two functions of descaling for smooth energization and drawing resistance for the rolling mill. The wire 21 traveling at a constant speed is directly heated by the energization heating device 24 and subjected to hot rolling. The high tension rolling mill 25 and the control system 27 perform high reduction rolling from a circle to an oval.

Use a cold rolling mill that can easily obtain sufficient drawing resistance instead of a pinch roller, and if the material is cold lightly pressed in advance to make the cross-sectional shape oval, it returns to a circle with one stand of overtension rolling. Can be made.

The embodiment of the present invention has been qualitatively described above. Hereinafter, the theoretical basis of the present invention and the quantitative relationship between various factors will be clarified.
If the material supply speed, rolling speed, and other factors are in an appropriate state for a material having a square cross section, the material is stretched and (tension generated in the material) + (retraction force by the roll) = (maximum drawing) (Equation 9) is established from the equilibrium equation (8) (force μ × P) and the geometrical relationship.
Y × He × He + ΔH × P = μ × P = μ × Y × L × He (8)
L = √ (ΔH × R) ----- (9)
ΔH = He-G ---- (10)
Y: Yield stress, He: Material thickness after stretching, P: Rolling force,
L: Roll / material contact length, ΔH: Net reduction amount,
The explanation of the symbols is also shown in [0017], [0018] terms and in FIG.

If the cross section is a circle or oval, the tension on the left side of equation (8) may be multiplied by (π / 4) ² .
A rectangle is identical to a square. Rearranging the above equation gives a quadratic equation representing the force balance.
A′He ² + B′He + C ′ = 0 −−−− (11)
Here, γ = 2R / Ho, μ ² γ = F, a shape factor k (in the case of a square cross section; k = 1, in the case of a circular cross section; k = (π / 4) ² ) is introduced, and both sides are Ho ² Divide by to make it dimensionless and find the solution.
Ahe ² + Bhe + C = 0 −−−− (12)
A = 9, B = -6h-2F / k, C = h (h + 2F / k)
he = [− B−√ (B ² −4AC)] / 2A −−−−− (7)
That is, the drawing reduction ratio he is calculated from the total reduction ratio h and the friction index F.

The occurrence of stretching means that the following equation is established, and when substituting into the equation (7), the equation (1) is derived.
he <1.0
F = μ ² γ> 2k / (1-h) + 2k + k (1-h) / 2 −−−−− (1)
That is, the first necessary condition for over-tensile rolling is expressed by equation (1).
FIG. 4 illustrates the formula (1), and an appropriate range of the roll diameter ratio γ is indicated by hatching. The value of γ is usually about 3 to 20 from rough rolling to finish rolling, but the vicinity of the upper limit is so because of the dimensions of finish rolling, and there is no special reason. From the figure, it is understood that the roll diameter ratio must greatly exceed the conventional level in over-tensile rolling. The above is the specific basis for the roll diameter ratio γ described in the second invention.

The specification of the speed ratio, which is the second condition for over-tensile rolling, will be described.
In the state where normal rolling is maintained, the following formula is established from the physical distribution constant.
Vi x Si = Vo x So ---- (13)
Vi: Material delivery speed, Si: Material delivery cross section, So: Material entry cross section

The cross-sectional area ratio Si / So is expressed by the following formula in the case of a rectangular cross section.
Si / So = He ² × Hr / He / Ho ² = he ² × hr
On the other hand, from the definition
he × hr = He / Ho × G / He = G / Ho = h
Therefore, Si / So = he × h ---- (14)

In the case of a circle or oval, Si / So is the product of the area reduction ratio he ² due to stretching and the area reduction ratio f of the net rolled part, and f is the ratio of the portion of the contraction circle excluding the split circle due to flat rolling. It is.
f is calculated from the integral formula of the split circle with the net reduction ratio hr as a variable.
Si / So = he ² × f ---- (15)
f≈ (2h / he × √ (1- (h / he) ² ) + sin ⁻¹ (h / he)) / π −− (16)

From the above, the speed ratio Vi / Vo is as follows. If the speed ratio exceeds this, the pulling force is lost and the balance is lost, resulting in slip rolling.
Rectangular: Vi / Vo = 1 / (he × h) ---- (17)
Circle, oval; Vi / Vo = 1 / (he ² × f) ----- (18)

The above explanation is a case where maximum stretching is obtained. On the contrary, when the speed ratio is decreased by a small amount, the increase in the pulling force is relatively superior to the yield force, and the stretching is maintained, and the specific aspect ratio α is slightly increased and the surface reduction ratio r is slightly increased. This action continues until the draw reduction ratio he is 1.0. Therefore, it is understood that the phenomenon of over-tension rolling in which stretching occurs up to the roll bite can occur within a certain range with respect to the speed ratio, and the amount of deformation changes depending on the speed ratio. The lower limit speed at which over-tensile rolling occurs is as follows if he = 1.0 on the right side of equations (17) and (18).
Rectangular; Vi / Vo> 1 / h ---- (19)
Circle, oval; Vi / Vo> 1 / f ---- (20)

Summarizing the above, the speed ratio range in which over-tensile rolling appears is as follows.
Rectangular: 1 / h <Vi / Vo ≦ 1 / (he × h) ----- (2)
Circle, oval; 1 / f <Vi / Vo ≦ 1 / (he ² × f) ----- (3)
This is the second condition for over-tensile rolling and is the specific basis for the speed ratio Vi / Vo in the third invention. FIG. 5 illustrates the formulas (2) and (3), and shows the range of the speed ratio at which over-tensile rolling occurs for a predetermined rolling reduction. From the figure, it can be seen that the range of the speed ratio increases as the rolling reduction increases.

The specific aspect ratio α at the upper and lower limits will be described.
If we ignore the widening approximately, regardless of the cross-sectional shape,
α ≒ He / G = he / h
Corresponding to the speed ratio in the equations (2) and (3), α changes within the range shown in the following equation.
1 / h> α ≧ he / h ----- (4)

Obtain the area reduction ratio r at the upper and lower speed ratio limits. Si / So in the equations (14) and (15) actually represents the reduction ratio r. Therefore, the following equation can be easily obtained.
Rectangle; h> r ≧ he × h −−−−− (5)
Circle, oval; f> r ≧ he ² × f −−−−− (6)

6 illustrates equation (4), and FIG. 7 illustrates equations (5) and (6).
The figure also shows α and r for tensionless rolling. However, the roll diameter ratio was set to 20 and 15, which are realistic. Calculation of the values of α and r was obtained by Yanagimoto's equation in Reference (3). In this case, the reason why the area reduction ratio is excessively small and the aspect ratio is excessive with respect to the rolling reduction is that the roll diameter ratio is relatively excessively large and the widening is excessively large. The region between over-tensile rolling and non-tensile rolling in the figure corresponds to known tension rolling.
From the figure, it can be seen that over-tensile rolling has a significantly lower aspect ratio and higher area reduction than non-tensioned rolling, and that α and r vary greatly corresponding to the range of speed ratio. That is, even at a constant rolling reduction, it is possible to control α and r to desired values by adjusting the speed ratio.

Reference (3); Yanagimoto: Plasticity and processing 5-40 (1964-5), p.315-p.322: "Study on empirical formula for obtaining width expansion value of wire and plate"

From the above, when the total reduction ratio h is given, the drawing reduction ratio he, the rolling reduction ratio hr, the area reduction ratio r, the specific aspect ratio α, and the speed ratio Vi / Vo are calculated. FIG. 8 shows a calculation example of he, hr, and area reduction ratio r ′ when μ = 0.4 and γ = 35 for a circular cross section, and μ = 0.4 and γ = 50 for a square cross section. From the figure, once entering the range of over tension, the drawing reduction ratio he decreases almost linearly with respect to the total reduction ratio h, i.e., the drawing portion increases steadily, resulting in a low aspect ratio and high area reduction. Understood. Furthermore, if he = 1.0, the lower limit speed ratio, the lower limit area reduction ratio, the lower limit ratio aspect ratio, etc. are calculated in order.

Even when two over-tensile rolling mills are continued, if the specific conditions are met, there is no peculiar phenomenon and similar phenomena and effects are accumulated. In the fourth aspect of the invention, the basis for specifying the thickness ratio and width ratio by two-stage rolling is the range where the implementation is easy and the effect is sufficient.

The reason why the control system is an indispensable factor in the fifth invention is that the speed ratio has a decisive influence on the aspect ratio and the area reduction rate in the range in which over-tensile rolling is maintained as described above.

Although there is a problem in control accuracy, as a first experiment, a wire diameter of 5.5 mm was supplied at a linear speed of 4 cm / s while being cold-rolled by a pinch roller with a flat roll at a light reduction rate of 20%. It was heated to 1000 ° C. by induction, and hot rolled with a flat roll having a roll diameter of 200 mm at a peripheral speed of 12 cm / s in the same direction at a reduction rate of 50%. The cross-sectional shape changed from 5.5 mm circle to 4.4 × 5.75 oval to 2.2 × (3.6 to 3.7) oval. The specific aspect ratio was about 1.3 and the area reduction ratio was about 0.7, confirming over-tensile rolling. From the above, it can be said that the theory of the present invention basically has no major mistakes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of a low aspect ratio / high area reduction rolling device for hot rolled wire rod according to an embodiment of the present invention. Dimensional symbols in the rolling situation are shown. The example which applied this invention to the secondary rolling of a wire is shown. The roll diameter ratio which is the 1st required condition of over tension rolling is shown. The speed ratio which is the 2nd necessary condition of over tension rolling is shown. The range of reduction ratio and specific aspect ratio in which over-tensile rolling is maintained is shown. The range of the rolling reduction and area reduction rate in which over-tensile rolling is maintained is shown. The relationship between reduction and deformation in the upper limit condition of over-tensile rolling is shown.

Explanation of symbols

0: Existing rolling mill 1: Material 2: Induction heating device 3: Front rolling mill 4: Flat roll 5: Roll bit 6: Material after rolling 7: Rear rolling mill 8: Perforated roll 9, 9 ': Length measuring instrument 10 , 10'10 ": Speedometer 11: Controller 12, 12 ': Roll chock 13, 13': Stand 14, 14 ': Load cell 15: Brake roll 21: Wire coil 22: Pinch roller 23: Bending roller 24: Electric heating Apparatus 25: Over tension rolling mill 26: Controller 27, 27 ': Speedometer 28: Length measuring device

Claims (6)

In a method of hot rolling a rod, wire, or strip steel material while applying tension in the rolling direction, the steel material at the roll bite inlet is drawn by the pulling force of the rolling mill itself with respect to the steel material supplied to the rolling mill at a constant speed. A backward tension equal to the yield force of the steel is generated to induce stretching in the steel material at the entrance, and the increase in the cross-sectional aspect ratio (= width / thickness) is suppressed and the reduction in area is reduced by eliminating the widening caused by rolling. A method of rolling with a low aspect ratio and a high area reduction rate characterized by increasing the thickness.
The roll aspect ratio γ is set according to the equation (1), and the low aspect ratio / high area reduction rolling method according to claim 1.
μ ² γ> 2k / (1−h) + 2k + k (1-h) / 2 −−−−− (1)
However,
h: Total reduction ratio (= Thickness G after rolling of material / Thickness Ho before rolling)
k; shape factor (circle, oval; k = (π / 4) ² , rectangle; k = 1)
μ: Coefficient of friction between roll and steel γ: Roll diameter ratio (= roll diameter 2R / thickness Ho before rolling) By adjusting the speed ratio of the material before and after rolling within the range according to the formula (2) or (3) according to the cross-sectional shape of the material, the specific aspect ratio α is set to the formula (4), and the reduction ratio r is set to the formula (5). Or it adjusts in the range according to (6) Formula, respectively, The low aspect-ratio and the high area reduction rolling method of Claim 2 characterized by the above-mentioned.
Rectangular: 1.0 / h <Vi / Vo ≦ 1.0 / (he × h) ----- (2)
Circle, oval; 1.0 / f <Vi / Vo ≦ 1.0 / (he ² × f) ----- (3)
Common to each cross section; 1 / h> α ≧ he / h ----- (4)
Rectangle; he × h ≦ r <h −−−−− (5)
Circle, oval; he ² × f ≤ r <f ------ (6)
However,
he = [− B−√ (B ² −4AC)] / 2A −−−−− (7)
A = 9, B = -6h-2F / k, C = h (h + 2F / k)
he; Drawing reduction ratio (= thickness He just before biting / thickness Ho before rolling)
F: Friction index (= μ ² γ)
Vo: Speed of the supplied steel before rolling
Vi; Speed after rolling
f: Area reduction ratio in net rolling (= cross-sectional area after rolling / cross-sectional area immediately before biting)
α: Specific aspect ratio (= section aspect ratio after rolling / aspect ratio before rolling)
r; Area reduction ratio (= cross-sectional area after rolling / cross-sectional area before rolling = 1-area reduction ratio) Two rolling devices according to the rolling method according to claim 1 or claim 2 or claim 3 are arranged in series to reduce the steel material in two passes in the same direction or at a right angle. It is reduced to 0.1 to 0.5, and in the case of a material having a rectangular cross section, the thickness ratio is reduced to 0.1 to 0.5, and the width ratio is reduced to 0.2 to 1.0. Aspect ratio / high area reduction rolling method. A tension rolling device in which a material is supplied at a constant speed and rolled at a specific speed, and a material supply device having a restraining force that can withstand a rolling mill rear tension, and a hole-type roll or a flat roll whose roll diameter ratio conforms to the formula (1). A rolling mill comprising a roll, a speedometer for detecting the speed of the material before and after rolling, a length measuring device for detecting the dimension of the rolled material, and a speed ratio of the material before and after rolling in response to a signal from each detector Corresponding to the cross-sectional shape of the material and a predetermined rolling reduction, and a control device that controls and sets the dimension after rolling to a predetermined value by setting and adjusting the roll rotation speed according to the formula (2) or (3). Features a low aspect ratio and high area reduction rolling device. The material supply device comprises either a pinch roller having a built-in multi-stage bending roller for repeatedly bending the material cold or hot, or a cold rolling mill for pre-rolling the material. 5. A low aspect ratio / high area reduction rolling apparatus according to 5.

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