JPH11290917A - Hot finish rolling method of steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the rolling load in the hot finish rolling of a steel strip by sticking a lubricant containing water to the peripheral surfaces of work rolls which are held at specified surface temp. and adding reduction to the steel strip after forming a dry coating film of the lubricant before the steel strip reaches the biting position. SOLUTION: A material 1 to be rolled is reduced between work rolls 2, 2 and the hot finish rolling of the steel strip 1 is executed by jetting the lubricant to the peripheral surfaces of the work rolls from spray nozzles 3 while cooling the work rolls 2 by jetting cooling water from the spray nozzles 4. At this time, by using a matter consisting of water, water dispersing resin and dispersant and adjusting the volume of cooling water, or the like, the roll surface temp. is taken as >=100 deg.C. By this heat, the water is evaporated in a short time from a homogeneous liquid coating film 5 of the lubricant which is formed by jetting the lubricant on the peripheral surface of the roll, the dry coating film 6 is obtained. This dry coating film 6 is stuck to the surface of the roll 2 and, by well demonstrating sufficient lubricating action during reduction, the rolling load is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot finish rolling method for a steel strip. More specifically, the present invention relates to a hot finish rolling method capable of significantly reducing a rolling load as compared with a conventional method.

[0002]

2. Description of the Related Art When a hot-rolled steel strip is manufactured, supplying a lubricant to a work roll in hot finish rolling reduces a friction coefficient between the roll and the rolled material and reduces a rolling load. As a result, it is widely used because it is effective in reducing the basic unit of roll and the basic unit of electric power.

An oil-based liquid lubricant is the most commonly used lubricant for hot-rolled rolls at present. A typical example of the oil-based liquid lubricant is disclosed in Japanese Patent Application Laid-Open No. 2-127499.
There is a hot-rolling oil as disclosed in Japanese Patent Publication No. The hot-rolling oil is, for example, a synthetic ester base oil obtained by adding a solid lubricant to the base oil. Examples of the solid lubricant include mica, graphite (graphite) powder, potassium titanate, and phosphoric acid. Potassium or the like is used. And
Such hot rolling oil is generally supplied by spraying directly from a nozzle toward a roll surface immediately before the steel material is bitten by the roll.

[0004] In addition to the above oil-based liquid lubricant,
There are solid lubricants for hot rolls. As disclosed in Japanese Patent Application Laid-Open No. Sho 62-156199, this solid lubricant has grease or wax as a base material and a solid lubricant added to the base material. For example, graphite or the like is used. The solid lubricant is supplied by being directly applied to the surface of the roll by a screw-type extruder as shown in Japanese Patent Publication No. 55559/1985.

[0005] Further, there is a lubricant for hot rolling using graphite (graphite). The hot rolling lubricant using graphite is obtained by dispersing graphite powder in a viscous aqueous solution as disclosed in, for example, JP-A-1-167396. The lubricant for hot rolling is supplied by spraying onto the roll surface from a spray nozzle, and in this case, graphite is supplied between the roll and the material in a state of being dispersed in a viscous liquid. Therefore,
It is said that the viscous aqueous solution needs to have a certain high viscosity in order to ensure adhesion to the roll surface.

[0006]

If the steel sheet is hot-rolled using the various lubricants described above, a load reduction effect of about 15% to 20% can be obtained as compared with the rolling load at the time of non-lubricating rolling. Can be Nevertheless, there has been a continuing demand for increasing the rolling reduction to reduce the thickness of the steel strip and for high-speed rolling to improve productivity. Are required to be able to be manufactured at a low cost without major equipment modification. Therefore, a reduction in the rolling load that exceeds the conventional hot lubricating rolling method has been awaited.

Accordingly, the present invention proposes a hot strip finish rolling method for a steel strip which can further reduce the rolling load as compared with the conventional hot lubricating rolling method for a steel sheet.

[0008]

Means for Solving the Problems The present inventors have conceived of using a lubricating resin film as a lubricant in hot lubricating rolling of a steel sheet for the purpose of further improving lubrication performance. As a result of studying a method of firmly adhering this resin film to the roll surface, the present invention has been reached.

That is, according to the present invention, when a steel strip is subjected to hot finish rolling, a lubricant comprising water, a water-dispersible resin and a dispersant is adhered to the peripheral surface of a work roll having a surface temperature of 100 ° C. or higher. Forming a dry film of the lubricant on the peripheral surface of the work roll until the lubricant reaches the biting position by rotation of the work roll, and then applying a reduction to the steel strip. Hot finish rolling method.

[0010]

According to the present invention, a lubricant composed of water, a water-dispersible resin and a dispersant is applied to the surface of a work roll and dried to form a strong dry film of the lubricant. Therefore, a lubricating film more firmly adhered than a conventional liquid lubricant, grease or wax is obtained, and the film is rolled while being securely held between the work roll and the material to be rolled. Therefore, the lubricant can be used effectively. As a result, it is possible to achieve a rolling load reduction ratio of 40%, which cannot be achieved by the conventional technology.

Hereinafter, the present invention will be described more specifically with reference to the drawings. In general, in hot finish rolling of steel strip, the work roll surface temperature during rolling is complicated by heat transfer by contact with the material to be rolled, temperature rise by reduction, cooling by cooling water injection, heat release to the atmosphere, etc. Due to the influence, it is extremely difficult to actually measure the roll surface temperature at each part during one rotation of the roll. Therefore, generally, the roll surface temperature during rolling is estimated by heat conduction simulation. According to the document, when the temperature of the steel material to be rolled is about 1000 ° C., the surface temperature of the work roll rises to a maximum of about 450 ° C. at the contact portion with the material to be rolled. On the roll exit side, cooling water is applied to the roll surface from a spray nozzle, so that the roll surface temperature becomes 100 ° C. or less.

In the present invention, by adjusting the amount of cooling water or the like,
The surface temperature of the roll is set to 100 ° C. or higher, and a lubricant composed of water, a water-dispersible resin, and a dispersant is adhered to the peripheral surface of the roll. That is, as shown in FIG. 1, a lubricant is spray-coated from a nozzle 3 toward a roll peripheral surface corresponding to a position in front of a position where the material to be rolled 1 bites into a work roll 2, and a uniform liquid coating 5 is formed. It is formed continuously. At this time, since the surface temperature of the roll is 100 ° C. or more due to the adjustment of the amount of cooling water injected from the nozzle 4, the water in the liquid coating film 5 evaporates in a very short time, and The dried film 6 is formed at a stage before reaching the insertion position. The dry film 6 is firmly adhered to the surface of the roll 2 and plays a sufficient role of lubrication during rolling, so that the rolling load can be reduced.

On the other hand, when the conventional oil-based liquid lubricant shown in FIG. 2 is used, the material 1 to be rolled is directed toward the roll peripheral surface at a position immediately before the position where it is engaged with the work roll 2. The oil-based liquid lubricant is spray-applied from the nozzle 7 by means of a spray. However, since the oil-based liquid lubricant 8 has an adhesive strength enough to be wiped off with a waste cloth, the material to be rolled is pressed during rolling. The lubrication was not sufficiently held between the work rolls, and the same lubricating action as in the present invention was not obtained. Also, when using the aqueous viscous liquid of the conventional method or when using a solid lubricant, the lubricant adhered to the roll peripheral surface at a position immediately before the position where the material to be rolled is engaged with the work roll. The adhesive force was only strong enough to be wiped off with a waste cloth, and was not sufficiently held between the material to be rolled and the work roll during rolling, so that a lubricating effect equivalent to that of the present invention could not be obtained. .

As described above, the adhesion of the dry film according to the present invention is not only significantly higher than the adhesion of the liquid lubricant of the conventional method, but also of the solid lubricant of the conventional method. Is also excellent.

The water-dispersible resin constituting the lubricant used in the present invention includes a vinyl resin used as a raw material for paints and adhesives. Preferred resins applicable to the present invention include, for example, There are the following.

Vinyl acetate copolymer resin, vinyl acetate / acryl copolymer resin, vinyl acetate / veova copolymer resin, vinyl acetate / malate copolymer resin, vinyl acetate / ethylene copolymer resin, vinyl acetate / ethylene / vinyl chloride copolymer Resin, acrylic copolymer resin, styrene copolymer resin, acrylic / styrene copolymer resin, ethylene / acrylic copolymer resin, ethylene / acrylic ester-based multi-component copolymer, polyvinyl alcohol resin, methacrylic resin, methacrylic acid / styrene Copolymer resin and the like.

These resins can be used alone or in combination of two or more. The water-dispersible resin used in the present invention is not limited to the above example. Regardless of which resin is used, the important role of the resin is to form a strong dry film and to intervene between the roll and the material to perform a lubricating action. At the time when the material bites into the roll, the lubricant is in a completely dried film and firmly adheres to the roll surface. The mixing ratio of the water-dispersible resin in the lubricant used in the present invention depends on the type of the resin, the ease of application and the ease of drying, but generally ranges from 5% by weight to 20% by weight.
It is about wt%.

A dispersant is also incorporated in the lubricant. The dispersant is for dispersing the water-dispersible resin in water, and includes, for example, a surfactant. This dispersant may be added in a very small amount that exhibits a dispersing action.

The position at which the lubricant is sprayed is not particularly limited, and may be, for example, a position 30 to 150 ° away from the biting position at a roll center angle in a direction opposite to the rotation direction. If the temperature is less than 30 °, the surface temperature of the roll will be 100 ° C
Even with the above, it is difficult to sufficiently evaporate the water in the lubricant until it reaches the biting position. If it exceeds 150 °, the amount of the sprayed lubricant increases and the loss increases. In addition, it interferes with the backup roll and makes spraying difficult.

Next, the reason why the surface temperature of the roll is set to 100 ° C. or higher will be described. Roll speed in hot finish rolling of thin steel sheet is 0.5 m / s to 25 m / s in roll peripheral speed.
Range. The diameter of this work roll is about 0.8 m
Therefore, the time required for the roll to make a half turn is about 2.5 seconds to 0.05 seconds. In order for the applied lubricant to dry and form a strong film, it is necessary to increase the roll temperature.

FIG. 3 shows the effect of the work roll temperature on the time until the lubricant dries. As is evident from this figure, the roll surface temperature must be 100 ° C or higher in order to dry the lubricant in a short time from application to the work roll surface until it reaches the biting position for the material to be rolled. There is.

[0022]

EXAMPLE An ordinary steel plate (sheet thickness 4 mm, plate width 50 mm, length 150 mm) heated to 1000 ° C. using an experimental rolling mill (work roll diameter 140 mm, roll body length 140 mm, two-high rolling mill). mm) was rolled to a thickness of 2 mm in one pass with a reduction of 50% (roll peripheral speed)
0.33 m / s).

The rolling was performed under the following six types of lubrication conditions. Condition 1: No lubrication, Condition 2: Spray application of high-viscosity esterified product to the inlet roll surface, Condition 3: Spray a mineral oil with 30wt% of graphite powder and a small amount of dispersant added to the inlet roll surface Coating, condition 4: 30 wt% of graphite powder in water, a small amount of dispersing agent and carboxyvinyl polymer added and thickened are spray-coated on the inlet roll surface. Condition 5: Roll of solid wax containing 30 wt% of graphite powder. Condition 6: A lubricant containing 10 wt% of vinyl acetate copolymer resin and a small amount of dispersant added to water is spray-coated on the surface of a work roll with a roll surface temperature of 120 ° C, dried and bitten by the roll A strong dry film is formed up to the position. Of the above lubrication conditions 1 to 6, conditions 1 to 5 are comparative examples using non-lubricated or conventional representative lubricants, and condition 6 is a conforming example according to the present invention.

Table 1 summarizes the experimental results. To evaluate the lubrication performance, the rolling load in the case of non-lubricated rolling (condition 1)
Relative evaluation was performed based on the percentage of the rolling load when the ratio was set to 100. That is, the smaller the value of the rolling load ratio, the higher the lubrication effect.

[0025]

[Table 1]

From Table 1, the rolling load under each lubricating condition is as follows: if condition 1 is 100%, condition 2 is 90%, condition 3 is 90%, condition 4 is 85%, and condition 5 is 85%. Thus, the lubricating condition of the present invention, condition 6, is 60%, which indicates that the rolling load is significantly reduced, and that the lubricating performance is much better than the conventional method.

[0027]

Thus, according to the present invention, the surface temperature of a work roll during rolling is set to 100 ° C., and a lubricant composed of water, a water-dispersible resin and a dispersant is adhered to the work roll. By drying and rolling down the lubricant until it reaches the biting position of the roll, a dry film of the lubricant is firmly held between the rolled material and the roll during rolling, and a good lubrication effect is exhibited. The rolling load can be reduced by 60% (reduction rate 40
%), Which is a reduction in the rolling load that could not be achieved by the conventional technology.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a hot finish rolling method using a lubricant according to the present invention.

FIG. 2 is a diagram illustrating a conventional hot finish rolling method using a lubricant.

FIG. 3 is a graph showing the effect of the surface temperature of a work roll on the drying time of a lubricant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rolled material 2 Work roll 3 Lubricant spray nozzle 4 Roll cooling water spray nozzle 5 Lubricant liquid film 6 Dry lubricant film 7 Lubricant spray nozzle 8 Lubricant liquid film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C10M 107: 40 107: 02) C10N 30:08 40:24

Claims (1)

[Claims] In a hot finish rolling of a steel strip, a lubricant comprising water, a water-dispersible resin and a dispersant is attached to a peripheral surface of a work roll having a surface temperature of 100 ° C. or higher. Forming a dry film of this lubricant on the peripheral surface of the work roll until the agent reaches the biting position by rotation of the work roll, and then applying a reduction to the steel strip, which is characterized by hot finishing. Rolling method.