JP4604918B2 - Cold rolled steel sheet manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a cold rolled steel plate, in particular, when annealing the steel sheet after cold rolling, the metal plates to each other by crimping overlapping, when subjected to further subsequent step, its crimped portions The present invention relates to a method for suppressing the occurrence of defects that may occur on the surface of a metal plate.

  Since the metal sheet after cold rolling, for example, a cold-rolled steel sheet, is work-hardened by rolling, in many cases, it is annealed prior to being subjected to a subsequent process. For example, in the case of a low carbon steel sheet with a mass% of C: 0.1% or less, annealing can be performed in a relatively short time, so that a metal plate is continuously passed through a sealed annealing furnace other than the inlet and outlet. Annealing is performed in a type of continuous annealing line, but in the case of high carbon steel sheets with C: 0.3% or more, annealing for several tens of hours is required, so it is sealed in a box-type annealing furnace. In many cases, a type of annealing called batch annealing is performed, in which a metal plate is heated in an atmosphere.

Usually, when performing cold annealing on a cold rolled steel sheet, for example, as shown in FIG. 4, cold rolling-cleaning (removing oil such as rolling oil remaining on the surface of the cold rolled steel sheet) -batch annealing-temper rolling and fine rolling It goes through each manufacturing process.
Since oil such as rolling oil remains on the surface of the metal plate that has been cold-rolled, it remains, for example, by electrolytic degreasing with an orthosilicate sodium solution or alkaline degreasing in a cleaning line. Oil is removed.

  FIG. 5 schematically shows an example of the cleaning line. In FIG. 5, S indicates a metal plate. A payoff reel 10 unwinds the metal plate S wound up in a coil shape and supplies it to the cleaning line. Reference numeral 20 denotes a shear, which is convenient for welding by shearing the tail end of the preceding metal plate S and the leading end of the following metal plate S before welding the metal plate S by the next welder 30. Mold into shape. A welder 30 welds the leading end of the preceding metal plate S and the leading end of the following metal plate S. Reference numeral 40 denotes a wash tank, which removes oil remaining on the surface of the metal plate by electrolytic degreasing with an orthosilicate sodium solution or alkaline degreasing. Reference numeral 50 denotes a rinsing tank for washing away the chemicals remaining on the metal plate surface. Reference numeral 60 denotes a dryer, which dries and removes the liquid remaining on the metal plate S. A tension reel 70 winds up the metal plate S. Reference numeral 100 denotes the entire cleaning line.

  Some cold-rolled metal plates, such as cold-rolled steel plates, are literally plate-shaped, while others are wound in strips as long as several hundred meters in a coil shape. In general, batch annealing is performed in a state of being wound in a coil shape, but in the case of a small scale such as a trial production, it may be performed in a state where plate-shaped objects are stacked. The plate-like metal plates have a considerable weight when they are stacked, and a pressing pressure acts between the overlapping metal plates. Due to the tension at the time of winding, the metal plate wound in a coil shape is pressed between the metal plates constituting the overlapping windings even after being wound.

  In batch annealing, overlapping metal plates or metal plates wound in a coil shape are exposed to a high temperature for a long time. For this reason, for example, in the case of a metal plate wound in a coil shape, if the winding tension when winding in the coil shape on the exit side of the line such as the cleaning line which is the previous process is too high, It is known that the plate surfaces may be baked and pressure-bonded during annealing. When seizure occurs, when a metal plate wound in a coil is rewound into a product metal plate, the surface of the metal plate is not only defective, but if the degree of seizure is severe, metal When the plates are completely stuck together, and when they are rewound in the temper rolling line or the finishing line, which is a later process, they may be broken, broken, or unwound in severe cases. Even there.

Conversely, if the winding tension when winding on the line exit side such as a cleaning line is too low, when rewinding during annealing or in a finishing line such as temper rolling, which is a later process, Winding is loosened, and defects such as scuffs tend to occur on the surface of the metal plate.
In order to suppress the occurrence of the above seizure and scuffing, the winding tension in the line such as the cleaning line, which is the previous process, and the winding tension pattern from the inner winding toward the outer winding are optimized. In practice, however, it has been difficult to completely prevent defects such as seizure and rubbing from occurring on the surface of the metal plate only by the winding tension.

Even when a number of plate-shaped metal plates are stacked and annealed, they are pressure-bonded by their own weight, and when they are separated one by one, the pressure-bonded parts may be peeled off and defects may occur on the surface of the metal plate. Therefore, there was a similar problem.
Therefore, for example, an anti-seizure agent in which a liquid anti-seize agent or solid, such as an Al ₂ O ₃ or TiO ₂ solution (aqueous solution) or emulsion, is dispersed and suspended in a liquid is applied to a metal plate. A method as described in Non-Patent Document 1 is known.

In other words, the anti-bonding agent such as Al ₂ O ₃ and TiO ₂ is applied to the surface of the metal plate before winding the metal plate on the line exit side such as the cleaning line which is the previous process. Alternatively, by applying with a dedicated coating line, even if the winding tension is increased, defects such as seizure and scuffing are prevented from occurring on the surface of the metal plate as much as possible.
In addition, for example, when repeating cold rolling-annealing a plurality of times for grain oriented silicon steel sheets, Al ₂ O ₃ alone or an annealing separator containing this as a main component before final finish annealing (previous seizure inhibitor) It is known from Japanese Patent Application Laid-Open No. H11-228707 and the like.

That is, in the case of the grain-oriented silicon steel plate that is the subject of Patent Document 1, when an annealing separator such as MgO that has been often used in the past is applied, the MgO and the silicon compound in the surface layer of the grain-oriented silicon steel plate during annealing It reacts to form a forsterite film, which is said to improve annealing separability, but since this film is glassy, it promotes wear of molds and the like during processing in a later process. In this patent document 1, Al ₂ O ₃ is proposed instead as a substance that does not react with the silicon compound on the surface layer of the grain-oriented silicon steel sheet and that can also suppress the pressure bonding during annealing. Yes. Furthermore, as a coating method, a method of electrostatically coating the powder itself or its suspension is proposed.

On the other hand, prior to unwinding the directional silicon steel sheet after annealing and further processing to form an insulating film, it is possible to wash and remove the annealing separator with an acid or alkali according to Patent Document 2 and the like. Are known.
Iron and steel S1372 (1985) Japanese Unexamined Patent Publication No. 5-156362 JP 2005-187941

  However, in the method as described in Non-Patent Document 1, when the anti-seizure agent of liquid as described above or a solid anti-seize agent dispersed and suspended in a liquid is applied to a metal plate, In addition, since the liquid falls, there is a problem that the anti-seizing agent accumulates in a batch annealing furnace as well as a cleaning line and a dedicated coating line. In addition, when a metal plate wound in a coil shape is transported in a factory with a crane or the like, there is also a problem that the liquid falls and various adverse effects occur.

In addition, there is a problem that the liquid evaporates in the batch annealing furnace, thereby damaging the inner wall of the batch annealing furnace or forming a pattern as a stain on the metal plate.
Furthermore, the method as in Patent Document 1 is a proposal limited to the annealing of grain-oriented silicon steel sheets, and Al is stable in reaction with silicon compounds for the purpose of maintaining an effective amount of acid-soluble Al in steel. It only suggests ₂ O ₃ and is not a general method. In addition, the removal of the annealing separator after the annealing is not mentioned at all, and it is difficult to say that it is assumed to be put into practical use on an industrial scale. In addition, since no mention is made of the removal of the annealing separator, it can be said that there is a lack of consideration for peripheral equipment and the environment.

  In the method as disclosed in Patent Document 2, since an acid or alkali liquid is used to remove the annealing separator, corrosion measures for peripheral equipment such as circulation pipes and recovery tanks, and metal hydroxide to those peripheral equipment are used. It is necessary to take measures against the adhesion of objects. Furthermore, in order to prevent the metal hydroxide from adhering to the metal plate to be treated, another facility for cleaning the metal plate is required. There was a problem. In addition, in the unlikely event that acid or alkali leaks outside the factory, there has been a problem of adversely affecting the environment. Equipment measures for this were also necessary.

The present invention has been made to solve the above-described problems of the prior art.
That is, the present invention, prior to batch annealing the cold rolled steel plate, a powder having a high temperature melting point or glass transition point than the annealing temperature on the surface of the cold rolled steel plate was coated electrostatically, after the batch annealing The powder is washed with a neutral liquid, the liquid after the washing is recovered, the neutral liquid is newly replenished to a pH of 6.5 to 8.5, and then reused. a method for producing a cold rolled steel plate.
Further, the present invention is characterized in that the powder is mica.

According to the manufacturing method of a cold-rolled steel sheet of the present invention, or peeled off as the metal plate is crimped burned during batch annealing, by or become flaws rubbed by loosening, defects on the surface of the product metal plate the occurrence by electrostatically coating a powder having a high temperature melting point or glass transition point than the annealing temperature, while effectively suppressed, and their powder by applying an electrostatic, liquid The neutralized liquid such as water is used to remove the powder after annealing with simple equipment and methods, while preventing it from falling and accumulating, and further damaging the inner wall of the batch annealing furnace. It can be carried out.

  FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 indicates an electrostatic coating apparatus, and 3 indicates a nozzle. In the present embodiment, between the wash (alkali degreasing) tank 40 and the tension reel 70 of the cleaning line 100 shown in FIG. 5 or between the rinse tank 50 and the tension reel 70, for example, FIG. An electrostatic coating apparatus 1 as schematically shown is installed. Hereinafter, this case will be described as an example.

  In FIG. 1, 3 is a nozzle, and from its tip, a powder having a melting point or glass transition point higher than the annealing temperature of the metal plate S or a suspension of the powder in a liquid is charged. The powder is electrostatically applied to the metal plate S by spraying. Since the liquid used for the suspension evaporates, the powder remaining without evaporating adheres to the metal plate S reliably. Further, since the liquid used for the suspension evaporates, there is no problem that the liquid drops and accumulates around the cleaning line, in the factory, or in the batch annealing furnace.

For the purpose of preventing the powder from scattering, the electrostatic coating apparatus 1 preferably covers the entire case with a housing as shown by the broken line in FIG. Then, although a part of the illustration is omitted, in the present embodiment, 10 × 3 columns in the width direction are arranged.
The nozzles 3 may be arranged at the same position when the nozzles installed at different positions in the conveying direction of the metal plate S are viewed in the width direction of the metal plate S, but arranged in a staggered manner. Then, since powder adheres uniformly by the metal plate S, it is preferable. However, it is not limited to the two arrangements listed here.

The powder is recovered and reused by a circulation system including a pipe, a pump, and a recovery tank (not shown).
The number of nozzles 3 is not necessarily the width depending on the spray pattern of whether the nozzles 3 are arranged in the same position in the width direction of the metal plate S or staggered, and the distance between the nozzles 3 and the surface of the metal plate S. The number is not limited to 30 in a total of 10 directions × 3 rows, and may be appropriately determined according to the degree of uniformity required when the powder is attached to the metal plate S.

The casing indicated by a broken line of the electrostatic coating apparatus 1 may be made of a metal such as iron or aluminum, or may be a resin such as acrylic.
In the example of FIG. 1, the powder is injected from the upper side of the metal plate S through the nozzle 3, but it may be from only the lower side or from both sides.
The electrostatic coating apparatus 1 may be anything as long as it utilizes the principle that powder adheres to the metal plate S due to static electricity.

The injection condition is to increase the adhesion efficiency as much as possible, which is the ratio of the adhesion amount to the surface of the metal plate S with respect to the injection amount, but it is necessary to inject at least 3 to 5 times the desired adhesion amount. .
The powder to be applied is preferably insoluble or insoluble, having a melting point or glass transition point higher than the annealing temperature of the metal plate S such as calcium oxide, mica (mica), aluminum oxide, and potassium titanate.

Depending on the material and specific gravity of the powder to be applied, it is possible to prevent defects on the surface of the product metal plate by peeling the sticking due to seizure or loosening and rubbing the wound. It is preferable to secure an adhesion amount of approximately 0.5 g / m ² or more. In particular, mica (mica) is insoluble, so neutral liquids for washing powder, such as water, which will be described later, are recovered after washing, separated when reused and circulated, Since it is easy to collect and reuse, it is preferable for practical use on an industrial scale, and both powder and cleaning liquid are reused and only circulated in the circulation system etc. As such, it is preferable in consideration of the environment because they are not discharged outside the factory, including cases where other toxic substances used in the factory are mistakenly mixed. In addition, even if it flows out of the factory, the water containing it is neutral, and there is an advantage that it does not adversely affect the environment.

  As for the size of the powder, if it is too large, even if it can prevent crimping due to seizure, there is a possibility that the pressing rod will enter the metal plate when the winding tension is large, and if it is too small, Since the scattered powder leaks from the housing and dissipates throughout the cleaning line and other lines, cleaning and entering the gaps of other equipment can require a significant human load for maintenance. Because of concern, the maximum diameter is preferably in the range of 10 μm to 100 μm. However, even if it is out of this range, the effect of preventing crimping due to seizure is not reduced.

Since the direct contact between the overlapping metal plates is hindered by the powder application as described above, even if the take-up tension is increased to, for example, 200 MPa, it is not seized and pressed during annealing. . By increasing the winding tension, it is possible to suppress or prevent the occurrence of scuffing due to loosening after annealing.
The winding tension that can prevent the occurrence of winding looseness depends on the material and thickness of the metal plate, but at least 60 MPa is required. In the present invention, the coefficient of friction between the surfaces of the overlapping metal plates is reduced due to the application of the powder. In this respect, although there is a slight effect that winding looseness is likely to occur during annealing, Since it has the effect of suppressing the generation of scratches on the surface of the metal plate, even if the winding tension is lowered to, for example, 20 MPa, no scratches are generated due to loose winding after annealing.

  The following description is also an embodiment of the present invention. However, if the metal plate after the batch annealing is wound in a coil shape, for example, the next step after that For example, it may be used for one of the finishing lines shown in FIG. 2, the skin pass line, but the above powder is also used when rewinding from the payoff reel on such line entry side. By applying, the contact between the metal plates is hindered, so there is no case where the metal plates are burned out and cannot be rewound.

Also, since the melting point or glass transition point of the powder is higher than the annealing temperature, the powder still remains after the annealing is finished, so that the overlapping metal plates are displaced due to loose winding However, since the powder functions as a lubricant, no scuffing occurs.
FIG. 2 schematically shows an example of a skin pass line, which is one of the adjustment lines, and 200 indicates the entire skin pass line. 10 is a payoff reel, 70 is a tension reel, and 80 is a temper rolling mill (skin pass mill). Although illustration is omitted, there is a deflector roll or the like.

In the present embodiment, for example, by spraying water from the nozzle 3 between the payoff reel 10 and the temper rolling mill 80, the powder having a melting point or glass transition point higher than the annealing temperature according to the present invention. The body can be washed and removed.
In FIG. 2, the case where water is sprayed from the lower side of the metal plate S for cleaning is illustrated as an example, but it may be sprayed from the upper side or from both the upper and lower sides. Although not shown, it is also preferable to improve the cleaning action by using a brush roll equipped with a brush such as nylon together and rotating and rubbing the brush roll while spraying water. .

In FIG. 2, the nozzle 3 for cleaning the powder is disposed on the entrance side in the conveying direction with respect to the temper rolling mill 80, but may be disposed on the exit side or both sides of the entrance and exit. .
As in the case of the nozzle for applying the powder, the arrangement of the nozzle for cleaning the powder is preferably adjusted in the conveying direction and the width direction of the metal plate S.
It should be noted that the pressure of the cleaning liquid can be sufficiently removed even at a pressure of tap water, but the discharge pressure on the pump outlet side is preferably 0.5 MPa or more.

And since the said powder is hardly soluble and hardly reacts with water, as shown in FIG. 3, after collecting with water, it is separated, collected by a filter or by precipitation at the bottom of the collection tank, Can be reused.
In FIG. 3, 3 is a nozzle for washing powder, 5 is a recovery device such as a funnel, and 7 is a recovery tank.

As described above, the present invention is not limited to the embodiment described above.
For example, as long as the powder has a melting point or glass transition point higher than the annealing temperature of the metal plate S, it is not limited to calcium oxide, mica (mica), aluminum oxide, potassium titanate, etc. Even if it is not soluble or insoluble, there is no problem even if it is a substance that can be recovered by drying or can be eluted if it can be discharged into the environment.

The liquid for washing the powder is not necessarily limited to water as long as it is neutral, and it may be oil, oil-containing liquid, hydrocarbon, alcohol, or other liquid. Also good. Here, although it is a neutral range, in the case of the present invention, the pH is preferably 6.5 to 8.5, more preferably 7 to 8.
In this sense, the cleaning liquid does not need to be neutral at a pH = 7 in the strict sense, and dissolves slightly in water like Al ₂ O ₃ (alumina) to make the solution weakly alkaline. What is changed may also be used as the powder referred to in the present invention.

Furthermore, the range of the above values is not absolute. If something abnormal occurs, such as when a pump fails, the concentration of Al ₂ O ₃ (alumina) becomes excessive and the pH rises to 10. Such a case is allowed, and such a case is not completely excluded.
Lastly, the above description describes the embodiment in which powder is applied and removed in the cleaning line and skin pass line. However, installation space cannot be secured in these lines, or application and removal are performed. In order to eliminate even the subtle effects of time and to ensure the uniformity of application and removal, a dedicated powder application line and powder removal line may be used.

(Example of the present invention)
A cold-rolled steel sheet cold-rolled to a thickness of 0.8 mm with a carbon content of 0.78% and wound into a coil is installed on the outlet side of the dryer 60 of the cleaning line 100 as shown in FIG. 1 is applied to the surface of the cold-rolled steel plate corresponding to the metal plate S from the upper side and the lower side by the electrostatic coating apparatus 1 (including a powder recovery mechanism by the casing) as shown in FIG. Was electrostatically applied.

The conveyance speed of the cold rolled steel sheet corresponding to the metal plate S is 100 mpm, the distance from the cold rolled steel sheet at the tip of the nozzle 3 installed on the upper side and the lower side is 100 mm, and the unit area depends on the injection condition of 250 g / m / min An average adhesion amount per unit of 1 g / m ² or more was secured.
(Comparative example)
Except not carrying out electrostatic coating of powder, it passed on the same conditions as the above-mentioned example of the present invention, and made it a comparative example.
(Other conditions)
The cold-rolled steel sheets wound with the winding tension of the tension reel 70 of the cleaning line 100 set to 20 MPa, 80 MPa, and 140 MPa, respectively, were batch-annealed. Batch annealing was performed in a nitrogen atmosphere, and heating conditions were 710 ° C. for 20 hours. After annealing, it was rewound from the payoff reel 10 on the entrance side of the skin pass line 200 as shown in FIG.
(result)
The cold rolled steel sheet that was not electrostatically applied in the comparative example was a case in which the winding tension on the tension reel 70 of the cleaning line 100 was set to 20 MPa. It became. In the case of 80 MPa, seizure between the cold-rolled steel sheets occurred in part of the entire length and rewinding was possible, but seizure flaws occurred on the surface of the cold-rolled steel sheet. In the case of 140 MPa, the cold-rolled steel sheets were completely stuck together and could not be rewound.

In the case of the cold rolled steel sheet to which electrostatic coating was applied according to the example of the present invention, at 80 MPa and 140 MPa, neither scuffing due to deviation due to loose winding nor seizure flaws occurred. In the case of 20 MPa, there was a shift due to loosening during rewinding, but it did not become a wrinkle.
Next, the coil of the cold rolled steel sheet of the present invention is wound from the payoff reel 10 of the skin pass line 200 as shown in FIG. 2, which is one of the finishing lines corresponding to the next step. When rewinding, the surface of the cold-rolled steel sheet is washed with a water spray sprayed from the nozzle 3 installed on the lower side, and the sheet is fed at a conveying speed of 150 mpm, and adjusted to 1% elongation with a temper rolling mill 80. When quality rolling was performed, there was no problem in surface quality. The water used for washing was investigated after rolling one cold-rolled steel sheet wound up in a coil shape. As a result, the pH was 7.8. Therefore, in order to make it safe even if water is circulated, fresh water was replenished so that the pH of the water was kept at 7.5 or lower.

(Example of the present invention)
The conditions were the same as in Example 1, except that mica (mica) powder was electrostatically applied to the upper surface of the cold-rolled steel sheet. An average adhesion amount of 0.5 g / m ² or more per unit area was secured under the injection condition of 100 g / m / min.
Since mica (mica) has a lower specific gravity than the aluminum oxide of Example 1, the weight of powder required to prevent contact with the cold-rolled steel sheet is small, and adhesion is also good.

The winding tension on the tension reel 70 of the cleaning line 100 was wound as 80 MPa and 140 MPa as in Example 1, and then the cold-rolled steel sheet was batch annealed.
As a result, in the example of the present invention, neither a scuffing flaw caused by deviation due to loose winding nor a seizure flaw occurred under any condition.
Furthermore, when the cold-rolled steel sheet wound up in a coil shape in the above-described example of the present invention is rewound from the payoff reel 10 of the skin pass line 200 as shown in FIG. 2, it is injected from the nozzle 3 installed on the lower side. While cleaning the surface of the cold-rolled steel sheet with water spray, it passed at a conveying speed of 200 mpm and temper rolled with an temper rolling mill 80 at an elongation of 1%. There was no problem above. The recovered water could be circulated and reused as it was because there was no change at pH = 7.

The figure which shows an example of embodiment of this invention The figure which shows an example of embodiment of this invention The figure which shows an example of embodiment of this invention The figure which shows an example of the manufacturing process of a cold-rolled steel plate The figure which shows an example of a cleaning line typically

Explanation of symbols

S Metal plate 1 Electrostatic coating device 3 Nozzle 10 Payoff reel 20 Shear 30 Welder 40 Wash tank 50 Rinse tank 60 Dryer 70 Tension reel 80 Temper rolling mill 100 Cleaning line 200 Skin pass line

Claims (2)

Middle-cold rolled steel plate prior to batch annealing, the powder having a high temperature melting point or glass transition point than the annealing temperature on the surface of the cold rolled steel plate was coated electrostatically, after the batch annealing, the powder washed with gender of the liquid, recovering the liquid after the cleaning, after a 6.5 to 8.5 the pH is newly replenished liquid in the neutral, characterized in that it re-use, the cold rolled steel plate Production method. According to claim 1, method for producing a cold rolled steel plate, wherein the powder is mica.

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