RU2243048C1 - Method for preparing coil of hot rolled strip for cooling - Google Patents

Abstract

FIELD: rolled stock production, namely cooling of coils of hot rolled strips.

SUBSTANCE: method comprises steps of coiling strip at constant temperature with variable specific tension along thickness of coiling; at coiling mean portion (along length of strip) with constant specific tension (directly before starting strip bending to turn of coil) increasing value of bending resistance due to changing temperature of strip by feeding cooling agent onto it.

EFFECT: enhanced quality of strip products due to equalizing physical and mechanical properties along length of hot rolled strip, reduced time period for cooling coiled strip.

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Description

The invention relates to rolling production, in particular to the cooling of rolls of hot rolled strips.

There is a method of preparing for cooling a roll of hot rolled strip, which consists in winding the rolled strip at a constant temperature with a constant specific tension of ≈0.3 of the yield strength of the strip material at a winding temperature [Korolev A.A. Mechanical equipment of rolling shops of ferrous and non-ferrous metallurgy. M., "Metallurgy", 1976, 544 p. with ill.].

The main disadvantage of this method is that the constant density of turns during winding creates conditions for unequal cooling rates during cooling of the coil, which leads to unacceptable unevenness of the values of mechanical properties along the length of the strip.

A known method of preparing for cooling a coil of hot rolled strip, the essence of which is that when winding a coil with a constant temperature, the winding of the inner turns is carried out to a winding thickness of 0.05 ... 0.08 of the total thickness of the coil winding with a specific tension uniformly decreasing from 0.35 ... 0.28 to 0.27 ... 0.21 of the yield strength of the strip material, the middle part of the roll is wound with constant tension, and the outer windings of the roll are wound up to a winding thickness of 0.06 ... 0, 11 of the total winding thickness with uniformly increasing specific tension to a thickness of 0.28 ... 0.38 from the mentioned yield strength [A.S. No. 1827882, according to the application No. 4600722 of 11.11.88].

The disadvantage of this method is manifested in the following. When winding a strip with a constant temperature to create a variable density of contact between the turns of the roll, the value of the specific tension of the strip varies from 0.21 to 0.38 of the yield strength of the strip material at the temperature of the coil. However, in most cases, to reduce the density of turns in the middle part of the coil winding, reducing the specific tension to 0.21 from the yield strength of the strip material at a given temperature is not enough to eliminate the uneven distribution of mechanical properties along the length of the finished strip. An attempt to reduce the specific tension value below the specified value will lead to a loss of the correct form of the roll and to disruption of its winding process.

The technical problem solved by the invention is to improve the quality of products from the strip by aligning the physicomechanical properties along the length of the hot rolled strip and reducing its cooling time in a roll.

To solve the problem in the known method of preparing for cooling a coil of a hot-rolled strip, including winding the coil at a constant temperature with a varying specific tension along the thickness of the winding, during the winding of the middle part along the length of the strip with constant specific tension, according to the proposal, immediately increase the strip formation the value of resistance to bending, changing the temperature by applying a cooler to it.

When the direction of movement changes (from horizontal to inclined before the formation of the next round of roll on the reel drum), the strip experiences a state of elastoplastic bending.

The tension created by the torque of the reel drum overcomes the resistance to elastoplastic bending of the strip material at a given temperature and puts the next coil of a roll with a certain density on the previous coil. An attempt to reduce the contact density of the coils of the roll by reducing the specific tension of the strip leads to a decrease in the forces supporting a certain value of the friction forces between the coils and between the first coil and the reel drum. This will lead to instability of the winding of the coil of the correct shape and even to the disruption of the process of winding the strip into a roll due to loss of adhesion of the reel drum to it.

To achieve greater tightness of the turns of the middle part of the coil winding, without reducing the minimum allowable tension of the strip, before starting the formation of the coil of the roll from a horizontally located strip, a cooler, such as water, is fed onto its surface, thereby reducing the temperature of the strip compared to its constant value. Thus, at the moment of elastoplastic bending of the strip, the deformation resistance to this bending increases at a constant tension level of the strip itself. This additional deformation resistance makes it possible to increase the tightness of the contact of the turns at the same level of strip tension, which does not allow loss of stability of the winding process.

At the same time, a certain decrease in the temperature of the strip in the middle part of the coil winding reduces the amount of heat in the most slowly cooled part of the roll, which also helps to equalize the cooling rates along the coil turns, and therefore, align the physicomechanical properties along the length of the finished hot rolled strip and reduce the total time cooling roll.

The implementation of the method of preparing for cooling a coil of hot rolled strip according to this invention is as follows. A slab of steel 40 with a cross section of 240 × 1500 mm, weighing 31 tons, is heated in a methodical furnace to a temperature of 1250 ° C and rolled in a line of a continuous broadband mill 2000 to a final thickness of 4.0 mm. The temperature of the end of the rolling is 850 ° C. The rolled strip is cooled on a discharge roller table by laminar streams of water to the same winding temperature along the length of the strip 635 ° C. The yield strength of a strip of steel 40 at this temperature is σ _st = 19 kgf / mm ² . The rolled and chilled strip is assigned to the winder and is “linked” to the winder drum. After the strip is captured by the winder by braking the rotation of the pulling rollers, a specific winding tension is created q = 0.32 σ _st i.e. 6.08 kgf / mm ² (the total tension of the winding is 36.5 tf) and carry out the winding of the inner turns (3-7 turns), which is 0.05-0.08 of the total thickness of the winding. As the inner coils are winded, the specific tension is reduced to 0.21 σ _st , i.e. from 6.08 kgf / mm ² to 4.0 kgf / mm ² (the tension decreases from 36.5 tf to 24.0 tf) and the middle part of the roll is wound with this tension. At the same time, water is supplied from the collectors installed at the top and bottom to the bend zone of the strip to the reel drum to reduce the temperature of the metal at the bend by changing the pressure of the water in the collectors. The feed water reduces the temperature of the strip at the inflection point, which determines an increase in σ _st to 21 kgf / mm ² . Thus, the preserved value of the tension (24.0 tf) makes it possible to maintain normal parameters of the strip winding process into a roll, and the increased deformation resistance of the strip to bending (by 2.0 kgf / mm ² ) further increases the leakage of the coil turns in the middle part of its winding. When winding the last section of the strip (3-5 turns), the collectors of the additional water supply are turned off, and the specific tension value is adjusted to 0.38 of the value of σ _st (i.e. to 7.22 kgf / mm ² , with a total tension of 43.3 tf). The necessary magnitude of the winding tension is created by increasing the current values of the armature of the winding motor.

The finished roll is removed from the reel drum and cooled according to the regimes adopted for strips of this steel grade (temperature control; in air; accelerated cooling with water). Since the outer turns are wound with greater tension with less bending resistance on the strip side than the middle part of the roll, the middle turns of the roll have a winding density even lower than at minimum tension according to the known method of preparing the coil for cooling. This is manifested in a more uniform cooling rate of various turns of the roll and, as a consequence, in a more uniform distribution of physical and mechanical properties along the length of the finished strip. In addition, the lower density of the winding of the middle turns of the coil increases their cooling rate, which reduces the overall cooling time of the coil. The test results of winding rolls in various modes from the bands of the above-described range are shown in the table.

Claims (1)

A method of preparing for cooling a coil of a hot-rolled strip, including winding the coil at a constant temperature with varying specific tension along the thickness of the winding, characterized in that during the middle part winding along the length of the strip with constant specific tension immediately before the formation of the strip into the coil, the value of bending resistance is increased, changing the temperature of the strip by supplying a cooler to it.