JP3288220B2 - Cold tandem rolling method and cold tandem rolling mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling method and apparatus for a cold tandem rolling mill having four or more cold rolling mills, which can realize high productivity and reduce manufacturing costs.

[0002]

2. Description of the Related Art In a cold tandem rolling mill, when a work roll speed is increased or a rolling reduction is increased, heat scratch occurs. The heat scratch is a seizure flaw caused by a metal contact between a work roll and a rolled material, which is generated as a result of an increase in the interface temperature between the roll in the roll bite and the rolled material and breakage of an oil film in the roll bite.

[0003] When heat scratches occur, the surface defects of the products are generated, so that not only the product yield is reduced, but also the productivity is remarkably reduced due to the necessity of changing the work rolls of the rolling stand having the heat scratches. . Therefore, regarding the prevention of heat scratch, for example, a method using a rolling lubricating oil having excellent seizure resistance as disclosed in JP-A-5-98283, and a method disclosed in JP-A-56-111505 are disclosed. As described above, there are a method of controlling the coolant amount to lower the temperature of the plate or the work roll, and a method of reducing the work roll speed as disclosed in Japanese Patent Application Laid-Open No. 6-63624.
Each of the methods relates to a method for preventing an increase in the interface temperature between the roll in the roll bite and the rolled material or preventing the oil film from breaking even if the interface temperature in the roll bite increases. However, the use of rolling lubricating oil with excellent seizure resistance may increase the cost, and controlling the temperature of the plate and roll by controlling the amount of coolant is effective but has some problems in its responsiveness. A decrease in speed has a problem that productivity decreases.

[0004] As a method of preventing heat scratch without causing a decrease in productivity and an increase in manufacturing cost, Japanese Patent Application Laid-Open No. 60-49802 discloses that a rolling schedule and a tension are changed. The control amount was limited for hardware reasons.

[0005]

In the conventional cold tandem rolling method, the above-mentioned effects are limited. The reason for this is that, for example, in the method of preventing heat scratch without causing a decrease in productivity and an increase in manufacturing cost, there is a problem that when the rolling schedule is changed, the thickness accuracy may be temporarily deteriorated. . In the case of the method of changing the tension, the rolling pressure is reduced by increasing the tension, and the heat generated by friction is reduced, so that the effect of preventing heat scratch can be obtained. When considering the above, the plate is easily broken. Further, in the existing cold tandem rolling mill, heat scratch is likely to occur in the subsequent stand, and the tension can be increased only between the stands due to equipment problems. Therefore, the entrance side tension tends to be larger than the exit side tension in the latter stage stand. For this reason, slips and chattering between the rolled material and the work rolls are liable to occur in the subsequent stand, and a new problem occurs.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional method as described above, and the gist of the present invention is to provide a cold tandem rolling machine having a cold rolling machine having four or more stands. A cold tandem rolling method in which rolling is performed by applying a rolling tension of 30% or more of the deformation resistance of a rolled material at least in a final rolling stand when cold rolling is performed in a rolling mill, and a cold rolling mill having four or more stands In a cold tandem rolling mill having a coiler or a coiler and bridle rolls on the output side of a cold tandem rolling mill and a cold tandem rolling mill,

[0007]

[Outside 3]

The sum of the output of the main motor of one output coiler of the cold tandem rolling mill or the output of the main motor of one output coiler and the output of the main motor of the output bridle roll is W _c , If the output of the main motor of the final rolling stand of the tandem rolling mill was W _M,

[0009]

[Outside 4]

[0010]

DETAILED DESCRIPTION OF THE INVENTION The higher the rolling speed, the more
The amount of rolling lubricant introduced into the roll bite increases and the coefficient of friction decreases. Therefore, the advance rate defined by the ratio between the exit side plate speed and the work roll speed decreases. Further, the advance rate decreases as the entrance tension is greater than the exit tension. Therefore, the higher the speed and the higher the entry side tension, the smaller the advance rate tends to be. By the way, depending on the type of steel and the rolling schedule, slip and chattering occur when the advance rate falls below a certain value (limit value). When the slip occurs, the relative sliding speed between the rolled material in the roll bite and the work roll rapidly increases, so that frictional heat increases sharply and heat scratch occurs. Also,
When chattering occurs, not only the portion becomes out of the specification of the plate thickness but also chatter marks are generated, so that the surface quality is impaired. Therefore, in order to prevent slip and chatter, it is necessary to make the value of the advance rate larger than the above-mentioned limit value. For this purpose, the value of the output tension must be increased in consideration of the balance with the value of the input tension.

FIG. 1 shows the occurrence rates of chattering and slip obtained from an experiment in which the tension is changed over a wide range (the occurrence rate of chattering and slip when the tension application ratio κ = 0.05 is 1) and the negative tension. It is a figure showing the relationship of an addition ratio.
Here, κ is a tension load ratio, which is an index indicating the level of tension at the entrance side and the exit side of the rolling stand, and is expressed by tension / deformation resistance of the rolled material. That is, assuming that the tension load ratio between the entrance side and the exit side of the rolling stand is κ _b and κ _f , the entrance side tension σ _b and the exit side tension σ _f in the rolling stand are the rolling stand obtained from the tensile test of the rolled material. 0.2% yield strength σ _yi and σ of rolled material on entry and exit
_yo multiplied by the tension load ratio, ie, σ _b = κ _b σ
_yi, the σ _f = κ _f σ _yo. In the following description, when the tension load ratio or κ is described, the tension load ratio or κ includes both the tension load ratios κ _b and κ _f on the entrance side and the exit side of the rolling stand.

As is apparent from FIG. 1, in order to realize stable rolling without chattering or slippage, the tension negative load ratio κ needs to be 0.3 or more. FIG. 2 shows the effect of the tension load ratio κ on the rolling load ratio [the rolling load during tensionless rolling (κ = 0) is set to 1] obtained from an experiment when the tension load ratio was changed. . Also, FIG. 3 shows the work roll wear amount after rotating about 100,000 times under the same rolling conditions as shown in FIG. 4 shows the effect of the tension load ratio κ on the weight (weight reduced from the weight) [wear at the time of tensionless rolling (κ = 0) is assumed to be wear resistance 1].

2 and 3, the larger the tension load ratio κ, the smaller the pressure and the contact arc length in the roll bite, and the greater the effect of the tension load ratio on the rolling load ratio and wear resistance. Was revealed. Fig. 4 shows the tension on the surface defect occurrence ratio (product surface defect occurrence ratio caused by heat scratching, chattering, or foreign matter entering between a plate and a roll or between a work roll and an intermediate roll) determined from experiments. The effect of the load ratio κ [the surface defect occurrence rate during tensionless rolling (κ = 0) is set to 1] is shown. From FIG. 4, it has been clarified that the surface defect occurrence rate decreases as the tension load ratio κ increases, and no surface defects occur at a boundary of the tension load ratio κ = about 0.3.

From the above, the tension load ratio κ is 0.3 or more, preferably 0.4 or more, that is, the tension is 30% or more of the deformation resistance of the rolled material on the entrance and exit sides of the rolling stand.
It is preferable to apply an ingress and egress tension of 40% or more. As a result, rolling can be performed without generating heat scratches, chattering, slippage, and the like, and the rolling load can be reduced, and rolling can be performed while maintaining abrasion resistance that can maintain the roughness of the work roll surface for a long period of time. If the tension load ratio κ exceeds 0.7, effects such as reduction of rolling load and improvement of wear resistance are saturated,
If there is a minute crack at the end of the rolled material in the width direction, the plate may be broken, so the upper limit of the tension load ratio is preferably set to 0.7.

The tension load ratio may be set for each stand as described above, but may be set only for a rolling stand where heat scratch, slip and chattering are likely to occur. In particular, in the final rolling stand where the rolling speed is the fastest, since heat scratch, slip and chattering are likely to occur, at least in the final rolling stand,
It is desirable to set the tension load ratio κ to 0.3 or more, preferably 0.4 or more.

Next, a cold tandem rolling mill for realizing the above-described rolling method will be described. In the existing tandem rolling mill, the rolling speed at the normal operation level (1000 to 20) is used.
00 m · min ⁻¹ ), the output of the main motor of one coiler on the exit side of the final stand is small, so that the tension level on the exit side of the final stand cannot be increased. In the present circumstances,
The output of one output coiler or the sum of one output coiler and the main motor of the output bridle roll has a product thickness of 0.
In the case of a thick cold tandem rolling mill in which products of 6 mm or more account for 50% or more of the total production, the output of the main motor of the rolling mill at the final stand is 47% or less, and the product sheet thickness is 0.
In cold tandem rolling mills, in which thin products of less than 6 mm account for more than 50% of the total production, the output is less than 32% of the output of the main motor of the rolling mill in the final stand. Therefore, when rolling low carbon steel, the tension level at the exit side of the final stand is usually 5 to 5.
It is about 10kgf · mm ^-2 . In the case of low carbon steel, deformation resistance is 60-70kgf near the final stand due to work hardening.
・ Because it is about mm- ² , the above tension level is 7
It is a low value of about 17%. As described above, since the final stand exit side tension is a low value, the final stand entrance side tension has to remain at a low value from the viewpoint of preventing the above-described slip and chattering. In addition, since the final stand entry side tension is equal to the output side tension of the rolling stand immediately upstream of the last stand, the entry side tension also has a low level, and the upstream side tension also has a low value. For the above reasons, the rolling tension in the conventional cold tandem rolling mill is at most 20% of the deformation resistance.
It is only about degree.

The maximum output side tension of the final rolling stand is inversely proportional to the thickness, the sheet width, and the sheet speed of the final stand, and is proportional to the output of the main motor of the coiler system or the total output of the main motor of the coiler system and the bridle roll. . Here, the output of the main motor refers to the maximum output of the main motor. Therefore, the higher the rolling speed, the smaller the maximum tension that can be obtained. That is, the higher the rolling speed, the larger the tension load ratio becomes.

Therefore, as means for increasing the tension load ratio during high-speed rolling, it is necessary to increase the output of the main motor of the coiler system, that is, to replace the main motor with a larger maximum output or to add bridle rolls. There is. Therefore, in order to make the tension load ratio κ 0.3 or more, preferably 0.4 or more in the final rolling stand, the output of the main motor of the final stand and the output of the main motor of the coiler system or the coiler system and the bridle roll It is necessary to optimize the total output of the main motors. For that purpose, first, it is necessary to seek the work performed by the rolling mill and the work performed by the coiler system, that is, the work performed by the coiler alone or the bridle roll.

First, in order to find the work performed by the rolling mill,
Calculate rolling load, rolling torque, advance rate, etc. The rolling load P can be determined by using, for example, the Hill load equation shown in equation (1).

[0020]

(Equation 1)

Where b is the plate width, K _m is the deformation resistance, σ _b
And σ _f are the entrance and exit tensions, R ′ is the work roll radius after flattening, H and h are the entry and exit plate thicknesses of the rolling mill, r is the rolling reduction, and μ is the friction coefficient. The deformation resistance K _m is expressed by equation (2) using the values of the constants a, ε ₀ , and n obtained from the results of a tensile test performed in advance. H _S is the thickness of the material (the thickness of the first stand entrance side), and ε is the strain.

[0022]

(Equation 2)

Next, the rolling torque T (for two upper and lower rolls) is expressed by equation (3) using, for example, Hill's equation, and the advance rate f _S is expressed by equation (4) using, for example, the equation of Brand & Ford. expressed. Further, the flattened roll radius R ′ in the equations (1), (3) and (4) is obtained by coupling with the equation (1) using the Hitchcock equation shown in the equation (5). be able to.
In Equation (5), E is the Young's modulus of the roll, ν is the Poisson's ratio of the roll, and π is the pi.

[0024]

(Equation 3)

The work W _M of the rolling mill forms a unit time is expressed by Equation (6) using the rolling torque T and advanced rate f _S combined upper and lower rolls two pins described above. Note that R is the roll radius, and V _O is the exit side plate speed of the rolling stand. _{W M = TV O / {R} (1 + f S)} (6) work W _M in this way rolling mill forms a unit time can be easily obtained. Moreover, as is clear from equation (3), the work W _M forming the unit of the rolling mill time consists of a work which is generated in all the tension before and after work and rolling mill occurring in the roll bite. By equalizing the total tension on the rolling stand and the total tension on the discharge side, the work generated by the total tension before and after the rolling mill is eliminated.Therefore, considering the entire tandem rolling mill, the total tension on the entrance and the exit on the rolling mill is equal. , That is, Hσ _b = hσ _f
Is more preferable.

The work W _C formed by the coiler system, that is, the coiler alone or the coiler and the bridle roll is represented by the following equation (7). W _C = V _O κσ _y hb (7) From equation (7), it is clear that the larger the tension load ratio κ, the more work the coiler system does.

Using the above equation, the ratio of the work W _c formed by the coiler system to the work W _M formed by the rolling mill per unit time is compared. Table 1 shows typical calculation results. In Table 1, a thin system in which the product thickness is rolled to less than 0.6 mm, and a product thickness of 0.
Rolling conditions for a thick final stand for rolling to 6 mm or more were assumed. However, the constant of the equation (2) representing the deformation resistance is a value previously obtained by a tensile test, a = 67 kgf · mm ⁻² ,
ε _o = 0.03, n = 0.2, and the friction coefficient used was a typical friction coefficient μ = 0.05 obtained under normal rolling conditions in the final stand of cold rolling.

The roll radius in Table 1 is a typical roll radius used in the final stand of a normal cold tandem rolling mill, and the rolling reduction, the work roll speed, and the material thickness are those of a normal cold tandem. Values in the range of typical rolling conditions in rolling are used.

[0029]

[Table 1]

Under these conditions, assuming a case where the thickness of the exit side of the final stand is less than 0.6 mm and a case where the thickness is 0.6 mm or more, the coiler system is used in a unit time when the tension load ratio is changed. The work performed by the mill and the work performed by the rolling mill were calculated and compared. From rolling conditions shown in Table 1, as the same delivery side h and compared the reduction ratio r of the same tension negative pressure ratio κ is large, the higher the roll radius R is large rolling mill work W _M increases forming a unit time coiler system , The ratio of the work W _c performed per unit time to the work W _{M performed by} the rolling mill per unit time decreases, and when the tension load ratio is increased, the ratio of the work performed by the coiler system increases. system is the ratio of the work W _M a work W _c and mill forms a unit time that forms a unit time is can be seen that large.

By the way, the work load of the last stand is defined by the output of the motor of the last stand, and the work load of the coiler system is determined in consideration of the work load of the last stand. In the present invention, since it is necessary to determine the ratio in consideration of the tension application ratio κ, the work of the coiler system is determined by considering the rolling conditions such as the roll speed, the roll diameter, and the rolling reduction of the work of the final stand. It is necessary to decide in consideration of the workload of the last stand evaluated. As can be seen from Equations (1) to (6), the work amount of the final stand rolling mill increases as the rolling reduction and the roll diameter increase, so that the condition where the work amount is large,
Conditions where the rolling torque is large and therefore the rolling reduction and the roll radius are large, that is, the roll radii of No. 4 and No. 8 in Table 1 are 25.
It is desirable to examine the capacity of the coiler system based on the work amount under the conditions of 0 mm and the rolling reduction of 30% or more.

From the above, when examining an advantageous rolling facility in implementing the method of the present invention, that is, in order to sufficiently exert its capacity, the maximum work that can be performed by the final stand must be reduced. We need to specify the minimum work that a coiler must do. Since the maximum work that can be performed by the final stand is determined by the output (maximum output) of the main motor of the final stand, the minimum work to be performed by the coiler system is also the output (minimum output) of the main motor of the coiler system. Is determined by Accordingly, as shown in the rolling conditions described above, the minimum output of the main motor required coiler system if Motomare the ratio of the work W _M a work W _c and rolling mill coiler system forms a unit time is formed in the unit time, It can be easily obtained from the maximum output of the main motor of the rolling mill.

Now, in order to perform stable cold tandem rolling as described above, the tension application ratio κ needs to be 0.3 or more. For this purpose, as can be seen from Table 1, the work of the coiler system is 50% of the work of the rolling mill in the final stand in the cold tandem rolling mill for producing a product having a product thickness of 0.6 mm.
%, And a cold tandem rolling mill for producing a thin product having a product thickness of 0.2 mm requires at least 35% of the work of the rolling mill in the final stand. That is, the output of the main motor of the coiler system is 50% or more of the main motor of the rolling mill in the final stand in a cold tandem rolling mill for producing a product having a product thickness of 0.6 mm. 2mm
In a cold tandem rolling mill for producing thin products of the type described above, 35% or more of the output of the main motor of the rolling mill in the final stand is required.

Instead of generating a large tension only by the output side coiler, a bridle roll for tension load may be installed between the final stand and the output side coiler in consideration of the change of the coiler. In this case, the exit coiler 1
It suffices that the total output of the base and the outgoing bridle roll satisfies the above condition.

[0035]

[Outside 5]

When the output of the main motor of one output coiler or the output of one main motor of the output coiler and the output bridle roll is W _c , and the output of the main motor of the rolling mill at the final stand is W _M. ,

[0037]

[Outside 6]

At this time, as described above, the total rolling tension (the value obtained by multiplying the rolling tension by the sheet thickness and the sheet width) is set to the same value on the inlet side and the outlet side of the rolling mill, so that the rolling mill has an excess. Since no load (including mechanical loss) is applied and the unit power consumption is improved, it is preferable to equalize the total rolling tension at the entrance and exit of the rolling mill.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cold tandem rolling mill used in the practice of the present invention is described below.
An outline is shown in FIG. In FIG. 5, a cold tandem rolling mill
Is composed of a four-stand four-high rolling mill. Rolled material
(1) is rolled at each rolling stand, bridle roll
It is wound by a coiler (3) through (2). Pressure
The rolling conditions are shown below. In addition, 2 with bridle roll
0kgf · mm^-2In the case, between the rolling mill exit side and bridle roll
Tension is 30kgf ・ mm ^-2And the bridle roll exit side ~
The tension between the coilers is 10kgf ・ mm^-2Is the meaning of the bra
0kgf / mm with idle roll^-2If the rolling mill exit side ~
Tension between ridle rolls is 30kgf ・ mm^-2And bra
The tension between the middle roll exit side and the coiler is 30kgf^-2
Is the meaning of

The work roll diameter (D): φ480mm work roll velocity _{(V R): 1000m · min} -1 entry side tension _{(σ b): 21.4kgf · mm} -2 (κ b ≒ 0.32) exit side tension (Σ _f ): 30 kgf · mm ^-2 (κ _f ≒ 0.40) Inlet thickness (H): 0.84 mm Outlet thickness (h): 0.60 mm Plate width (b): 988 mm Material thickness (H _S ): 3.2mm Material: Low carbon steel σ _y = 67 (ε + 0.03) ^0.2 kgf · mm ^-2 Rolling lubrication: Tallow based 2% emulsion (60 ° C) Bridle roll tension: 0kgf · mm ^-2 , 20kgf · mm- ² originally, this tandem mill has a rolling speed of 1800 m
There are ^-1 ability, but insufficient motor output exit side coiler side in the case of applying the present invention to its rolling speed. Therefore, the rolling speed was reduced, and the work of the exit side coiler system was set to 0.5 or more of the work of the final stand at that time.

As a conventional rolling method, under the same conditions as shown in Table 2, the entry side tension is 12 kgf · mm ⁻² (κ _b = 0.1
8) Rolling was performed with an output side tension of 5 kgf · mm ^-2 (κ _f = 0.07) and a bridle roll tension of 0 kgf · mm ^-2 , and compared with the present invention. FIG. 6 shows the wear resistance of the work roll in terms of the surface roughness of the work roll. In the conventional rolling, when the rolling tonnage is about 200 tons, the surface of the work roll becomes too smooth and slip occurs, so that the work roll has to be rearranged. However, even when the surface roughness of the work roll was 400 tons in rolling tonnage by using the present invention, no slip was generated as compared with the conventional surface roughness at which slip occurred. Therefore, by using the present invention, the wear resistance of the work roll was improved about twice or more.
Further, by using the present invention, the surface defects (occurrence rate of about 2% of the total production amount) which have conventionally occurred are not generated at all. This effect could be obtained independent of bridle roll tension. However, when the bridle roll tension is 0 kgf · mm ^-2 , some of the wound coils may have flaws due to tight tightening.
Preferably, the tension level of the coiler is not significantly increased by applying bridle roll tension.

It is apparent that by modifying the motor output on the coil side to half or more of the output on the output coiler side of the final stand, there is no need to reduce the speed and the productivity is increased. As described above, by applying the present invention, it is possible to realize high productivity and reduce manufacturing costs.

[0043]

According to the present invention, when cold rolling is performed by a tandem rolling mill, at least the rolling tension at the final stand is 30% or more of the deformation resistance of the rolled material, that is, the tension load ratio is 0.1%.
With three or more, occurrence of slip and chattering can be reduced. Thereby, a great effect can be obtained in preventing the occurrence of surface defects of the steel sheet and in improving the wear resistance of the roll.

Further, since the output of the final rolling stand and the output of the coiler system can be appropriately set in consideration of the tension load ratio in the final stand, a rolling mill necessary to reduce the occurrence of slip and chatter can be provided. Can be properly obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of a tension load ratio on a slip chattering rate.

FIG. 2 is a view showing the influence of a tension load ratio on a rolling load ratio.

FIG. 3 is a view showing the influence of a tension load ratio on wear resistance.

FIG. 4 is a diagram showing the influence of the tension load ratio on the incidence of surface defects.

FIG. 5 is a schematic diagram of a cold tandem rolling mill used in the present invention.

FIG. 6 is a diagram showing the effect of the present invention, and is a diagram showing the relationship between the roll surface roughness and the rolling tonnage.

[Explanation of symbols]

 1: Rolled material 2: Bridle roll 3: Coiler

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-210307 (JP, A) JP-A-61-71120 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 1/00-1/46 B21B 37/00-37/78

Claims (2)

(57) [Claims] When cold rolling is performed in a cold tandem rolling mill having four or more cold rolling mills, at least 30% of the deformation resistance of the rolled material in the final rolling stand.
A cold tandem rolling method characterized in that rolling is performed by applying the above rolling tension. 2. A cold tandem rolling mill having a cold tandem rolling mill having four or more cold rolling mills and a coiler or a coiler and a bridle roll on an output side of the cold tandem rolling mill. Manufactured by rolling mill [Outside 1] Alternatively, when the sum of the output of the main motor of one output coiler and the output of the output bridle roll with the main motor is W _c , and the output of the main motor of the final rolling stand of the cold tandem rolling mill is W _M , 2]