RU2264873C2 - Strip cold rolling method - Google Patents

Abstract

FIELD: rolling products in wide-strip cold rolling mills.

SUBSTANCE: method is realized due to determining and controlling main power, force and technological parameters of rolling process. Method comprises steps of subjecting rolling rolls along lines of contact between backup and rolling rolls and rolled strip to local action of constant and(or) variable field with magnetic flux density in range 0 - 70 Tl; changing value of magnetic flux density along each contact line for achieving desired values of friction coefficients between backup and rolling rolls and also between rolling rolls and rolled strip due to decreasing or increasing magnetic flux density value depending upon predetermined reduction degree; lowering or increasing rolling effort in any stand of rolling mill for sustaining constant reduction degree Δh at the same mounting of rolling rolls. Decrease of friction coefficient f₀ is detected due to comparing linear velocity values of backup and rolling rolls. At lowering revolution number of idle rolls relative to drive rolls, magnetic flux density along line of their contact and rolling effort are increased. During period of lowering speed of strip at outlet of rolls, magnetic flux density and rolling effort are increased along contact line between rolling rolls and metal. Decreased friction coefficient between rolling roll and strip is detected due to comparing linear velocity values of strip and rolling rolls.

EFFECT: possibility for artificial control with use of magnetic fields of friction coefficients along contact lines of idle and drive rolls and metal without changing reduction modes in mill, elimination of roll slip, lowered wear of rolls.

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Description

The invention relates to rolling production and can be used on broadband cold rolling mills in order to avoid increased wear of the rolls due to mutual slipping.

A known method for the production of strips [1], in which in order to increase the durability of the operation of work and backup rolls during their transshipment, the location of the upper and lower work rolls is rotated. The disadvantage of this method is the use when rolling strips of work rolls with S-shaped profiling and the complication of the transshipment operation.

A known method of cold rolling of a strip [2], in which in order to avoid increased wear of the rolls due to mutual slippage between the work and backup rolls during the strip rolling process, the basic rolling parameters are additionally measured and calculated, including the tangent of the roll angle and the rest friction coefficient contact of the rolls, after which, for each mill stand, the condition tgβ≤0.9f _{0 is} checked and if it is not satisfied for at least one stand, the compression in this stand is increased.

The disadvantage of this method is that, in particular, it does not take into account the difference in the friction coefficients on the upper and lower work rolls on the contact surface, as a result of which the rolling process acquires an asymmetric character, which is expressed in the inequality of the compressions from the side of each roll. In addition, with an increase in compression, the rolling speed increases (provided that the given mill productivity is maintained), and therefore, the peripheral and linear speeds of the work and backup rolls increase. In this case, the friction coefficient f ₀ decreases, and the probability of slipping increases, since the condition for joint rotation of the backup and work rolls is limited: tgβ <f ₀ . At a speed of 5 m / s to 15 m / s, the friction coefficient f _y with a steady rolling process between the work roll and the metal takes an almost constant value [3]. With an increase in compression, the contact angle increases and the condition α _max ≤2f _y may be violated, and therefore, the phenomenon of slipping of the work roll relative to metal may occur [3]. In the last stand of the rolling mill, it is generally impossible to increase the reduction, since the mill is tuned to a certain final thickness. In addition, the change in the compression in any mill stand will necessitate the adjustment of the compressions in all other stands of the rolling mill that do not correspond to standard reductions.

In view of the foregoing, it can be concluded that it is impossible in practice to exclude slipping of idle rolls relative to drive rolls by increasing strip compression, without violating the steady rolling process.

The objective of the invention is to provide the ability to control the magnitude of the coefficient of friction f ₀ in the contact between the work rolls and backup rolls and the friction coefficient f _y between the work rolls and metal in a steady rolling process and, as a consequence, avoid slipping between them.

This problem is achieved by the fact that in the method of cold rolling strips, which includes the determination and regulation of the main energy and technological parameters of rolling, the rolling rolls along the contact lines between the support and work rolls and the rolled strip are subjected to a local in power constant and (or) alternating field with magnetic induction in the range from 0 to 70 T, the magnitude of the magnetic induction along each contact line is changed, achieving the required values of the friction coefficients between the supporting and working E rolls and between work rolls and the strip, increasing or decreasing values of the magnetic induction as a function of a predetermined amount of reduction, increase or reduce the rolling force in any of millstands to maintain a constant compression Δh = const at a constant setting of the work rolls, reducing the coefficient of friction f ₀ by comparing the fixed linear velocity supporting and working rolls and with decreasing speed drive idle rolls relative increase the magnetic flux density on a line of contact and rolling force With decreasing speed output strip from the rolls increasing the flux density and the rolling force along the line of contact between the work rolls and the metal, and a decrease f _y friction coefficient between the work roll and the strip is fixed by comparing the linear velocity strip and work rolls or perform these steps simultaneously.

It was experimentally established that the coefficient of friction when sliding metallic bodies relative to each other both in the area of machine friction and in the area of elastic-plastic contact when exposed to bodies by a magnetic field varies depending on the value of magnetic induction [4].

Thus, magnetic induction can be considered a factor by which, in the steady rolling process, it is possible to control the friction coefficient both in the contact between the rolls and in the contact between the strip and the metal, preventing the rolls from slipping relative to each other and the metal and without resorting to a change strip compression modes recommended for use on the mill.

In order to determine the possibility of artificially changing the friction coefficient f when metal bodies move relative to each other without changing the conditions and modes of motion, the author conducted an experimental study to determine the friction coefficient when moving a cold-rolled strip sample over the surface of a tool steel plate in a magnetic field with magnetic induction up to 2 T.

Figure 1 shows a graph of the coefficient f from the magnetic induction B.

From the graph it follows that at B≈0 the friction coefficient f = 0.075, that is, it is approximately equal to the known coefficient of friction during cold rolling. With a gradual increase in magnetic induction on the surface of the sample, the friction coefficient also increased.

Thus, the phenomenon of changes in the friction coefficient under the influence of a magnetic field can be used in practice in rolling, acting on the contact zones with local magnetic fields of a certain power depending on the specific steel grades and rolling modes.

By placing magnetic systems in the contact zones between the back-up and work rolls and the strip, it is possible to force the coefficient of friction to be smaller or larger.

From the well-known expression ▽ h = f ² R it can be seen that a change in the coefficient of friction f causes a change in the absolute compression ▽ h.

, получим P=n·σ·b·f·R (где n - коэффициент, σ - сопротивление деформации, b - ширина полосы, R - радиус рабочего валка).Substituting this expression into the well-known expression for the rolling force P = n · σ · b ·

, we obtain P = n · σ · b · f · R (where n is the coefficient, σ is the deformation resistance, b is the strip width, R is the radius of the work roll).

From the obtained expression it follows that in order to maintain the condition ▽ h = const, it is necessary to increase the rolling force with the help of pressure devices, controlling its value through the data on the linear speeds of the rolls and the rolled strip, excluding slipping.

Figure 2 shows the layout of the local magnetic devices of the rolling stand QUARTO, allowing to act on the contact zone between the rollers and the strip of magnetic fields f of various intensities.

An example implementation of the method.

Mill x / rolling 5 stand 1700.

The diameter of the work rolls is 500 mm.

Each stand is equipped with an automatic control system for the coefficients of friction in the contact zones using a magnetic field.

Control system - a system for monitoring linear speeds of rolls and strip.

Coefficient of friction in a magnetic field between a work roll and a backup roll

f _op = 0.15.

Coefficient of friction in a magnetic field between a work roll and a strip

f _rp = 0.09.

The initial state is the linear speed of the rolls are equal to v _o = v _p and

v _p = v _p , slip is absent.

Suppose that, for various reasons, both conditions are violated during the rolling process: the back-up roll skips relative to the work roll, and the work roll skips relative to the strip. In this case, the friction coefficients decrease.

In this case, the magnetic systems located between the rolls and the strip increase the magnetic induction values in the respective contact zones, and the friction coefficients are forcibly increased until the linear speeds of the rolls and the strip are equal. At the same time, the rolling force increases by a certain amount. And, on the contrary, with an unacceptable increase in the friction coefficients, magnetic systems reduce the magnitude of the magnetic induction in the corresponding zones and the friction coefficients are forcibly reduced. At the same time, the rolling force also decreases. In both cases, the amount of compression does not change.

The proposed method allows, when the magnetic systems are turned on, to carry out rolling on the mill without slipping at any given values of the friction coefficients in the function of magnetic induction: f = φ (c).

Forcibly decreasing or increasing the values of the friction coefficients in the contact zones during rolling, they achieve stable rolling in all stands of the rolling mill.

The proposed method x / rolling provides high quality strips and extends the technological capabilities of the rolling mill.

Sources of information

1. RF patent N 221044, Inventions of the world, issue 15, N16 / 2003.

2. RF patent N 2210442, Inventions of the world, issue 15, N16 / 2003.

3. A.P. Grudev. Theory of rolling, M. "INTERMET ENGINEERING".

4. L.G. Delyusto. Some problems of improving the technology of hot and cold rolling of wide strips during the modernization of rolling mills. Herald of Mechanical Engineering, N1, 2004.

Claims (1)

A method of cold rolling strips, including the determination and regulation of the main energy and technological parameters of rolling, characterized in that the rolling rolls along the contact lines between the support and work rolls and the rolled strip are subjected to a local power constant and / or alternating field with magnetic induction in the range from 0 to 70 T, change the magnitude of the magnetic induction along each contact line, achieving the required values of the friction coefficients between the backup and work rolls and between the work and rolls and strip, increasing or decreasing the values of magnetic induction depending on a given amount of compression, increase or decrease the rolling force in any of the mill stands to maintain a constant value of compression Δh = const with the work rolls being fixed, the decrease in the friction coefficient f _{0 is} fixed by comparison linear speeds of the back-up and work rolls and with a decrease in the speed of the idle rolls relative to the drive rolls increase the magnetic induction along the line of their contact and the rolling force, with a decrease Exit strip from the rolls increasing the flux density and the rolling force along the line of contact between the work rolls and the metal, and decreasing the friction coefficient f _Y between the work roll and the strip is fixed by comparing the linear velocity of the work rolls and the strip or perform these steps simultaneously.

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