JPH0230303A - Method for hot rolling steel bar and wire stock - Google Patents

Abstract

PURPOSE:To prevent biting defects and to surely hold a sufficient percentage reduction by specifying a friction coefficient of the roll surface in a non-driven vertical rolling mill. CONSTITUTION:A continuous rolling mill 10 is composed of driven horizontal mills 1, 3, 5, 7 and non-driven vertical mills 2, 4, 6. A rolled stock 20 heated to a required temp. by a heating furnace is hot rolled by the mill 10. In that case, by bringing a friction coefficient of the roll surface of the mills 2, 4, 6 to be >=0.45, biting defects of the stock 20 are prevented, and by bringing a biting angle of the stock 20 to be larger, a sufficient percentage reduction is kept even in the mills 2, 4, 6. As the result, the total equipment scale is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for hot rolling steel bars and wire rods.

(Prior art) In conventional rolling of steel bars and wire rods, several driven horizontal rolling mills are arranged in tandem to roll several strands, or each driven horizontal rolling mill and vertical rolling mill are alternately driven. The mainstream is one that performs l-strand rolling.

In rolling by a rolling mill group consisting of only horizontal rolling mills, it is necessary to rotate the rolled material by 90° around the longitudinal direction between the rolling mills, and the work efficiency when changing rolls and guides is taken into account. The interval between each rolling mill is approximately 3-5-
The site area occupied by the rolling mill group as a whole increases. In addition, since the rolled material is twisted by 90 degrees, defects such as sagging and folding are likely to occur in terms of quality.

On the other hand, in the one-strand rolling method using a rolling mill group in which horizontal rolling mills and vertical rolling mills, both of which are driven, are arranged alternately, a steel bar or wire rod of better quality can be obtained than rolling with only a horizontal rolling mill group. The equipment cost of the rolling mill is extremely high, about 3 to 4 times that of a horizontal rolling mill (therefore, the equipment cost of the rolling mill group as a whole is also considerably higher than that of the horizontal rolling mill group alone. Considering that the area occupied by the drive device mounting column itself is larger than that of the drive device of the horizontal rolling mill, and considering the ease of work such as changing rolls and guides of the vertical rolling mill, the rolling mill spacing of this method is smaller than that of the horizontal rolling mill drive device. It needs to be longer than the machine-only method.

In view of the problems of the conventional rolling mill mentioned above, the applicant has
We have proposed the technology disclosed in Japanese Patent Publication No. 1121/1983 as a hot rolling method and apparatus for steel bars and wire rods that enables a compact rolling facility with relatively low equipment costs and a small footprint.

That is, in the hot rolling method for steel bars and wire rods that involves a horizontal rolling mill, a vertical rolling mill, and a horizontal rolling mill, after rolling the material to be rolled by an electric motor-driven horizontal rolling mill, a Steel bars and wire rods characterized in that the rolled material is rolled by a vertical rolling mill comprising driven vertical rollers, and then the rolled material is rolled again by a horizontal rolling mill driven by an electric motor and further disposed behind the vertical rollers. This is a hot rolling method.

Furthermore, in Japanese Patent Application Laid-Open No. 61-279301, the present applicant specifies the relationship between the distance between the driven horizontal rolling mill and the non-driven vertical rolling mill, the thickness of the rolled material between the stands, and the outer diameter of the work roll of each stand. It was revealed that rolling could be carried out without problems such as buckling or slipping of the rolled material, while maintaining the reduction in area in a non-driven vertical rolling mill to 83% or more of the reduction in area in a driven horizontal rolling mill.

(Intelligence B to be Solved by the Invention) However, with the technology of this patent application, there was a possibility that the material of the non-driven vertical rolling mill would be jammed incorrectly.

Additionally, there is Japanese Patent Application Laid-Open No. 61-165021, which discloses that this technology increases the surface friction coefficient of the rolls of a driven horizontal rolling mill, while decreasing the friction coefficient between the rolls of a non-driven vertical rolling mill and the rolled material. Although it is disclosed that the cross-sectional reduction ratio in non-driven vertical rolling can be increased by this technique, there is a problem with this technique from the viewpoint of material biting into the non-driven vertical rolls.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rolling method that solves the problems of the prior art as described above and can ensure a sufficient area reduction rate in a non-driven vertical rolling mill.

(Means for Solving the Problems) The present inventors conducted a number of hot rolling experiments using a model rolling mill regarding the hot rolling method for steel bars and wire rods proposed in Japanese Patent Publication No. 63-1121. Through this, the following issues were clarified.

First, when the leading edge of the rolled material is rolled by a driven horizontal rolling mill and pushed into a non-driven vertical rolling mill located at the rear, the rolled material may not be bitten depending on the surface condition of the vertical rolls of the non-driven vertical rolling mill. It has been found that there are cases where rolling becomes impossible. In other words, even if the reduction amount of the material in the non-driven vertical rolling mill is the same, if the surface of the vertical roll is rough (
If the friction coefficient μ is large), the rolled material will bite smoothly, but if the vertical roll surface is smooth (if the friction coefficient μ is small), the rolled material will not bite at all, or it will bite immediately after it bites. A phenomenon was observed in which the leading edge of the material stopped within the bite of the vertical roll. In such cases, the material is often deformed and buckled between the driven horizontal rolling mill and the non-driven vertical rolling mill, or a bulging phenomenon occurs, making it impossible to continue rolling. Ta.

Therefore, depending on the surface condition of the non-driven vertical rolls, the area reduction rate in the non-driven vertical rolling mill may have to be less than 83% of the area reduction rate in the driven horizontal rolling mill in order to prevent material biting failure. There was a problem.

The present inventors made the vertical rolling mill non-driven, and in order to obtain the same area reduction rate as in the case of a driven type, the inventors developed a method for rolling the non-driven vertical rolling mill by increasing the roll surface friction coefficient of the non-driven vertical rolling mill. The present invention was completed based on the knowledge that the critical biting angle of the machine into the roll becomes larger, making it less likely that defective biting will occur.

The gist of the present invention is to reduce the coefficient of friction of the roll surface of the non-driven vertical rolling mill to 0.45 in a rolling mill row consisting of one non-driven vertical rolling mill and driven horizontal rolling mills arranged before and after the non-driven vertical rolling mill.
This is a method for hot rolling steel bars and wire rods characterized by the above.

Here, as a means of increasing the friction coefficient of the roll surface of the above-mentioned non-driven vertical rolling mill, the roll surface is subjected to mechanical processing such as knurling processing or shit blasting processing, or chemical treatment such as pickling, to increase the friction coefficient of the roll surface. Examples include a method of increasing the coefficient of friction on the roll surface by applying weld overlay to the roll surface to form irregularities.

Thus, according to the present invention, by increasing the surface friction coefficient of the non-driven vertical roll, defective biting of the material is prevented, and by increasing the biting angle of the material, area reduction caused by the non-driving vertical rolling mill is prevented. The area reduction rate also increases, and it is possible to obtain an area reduction rate that is equal to or greater than the area reduction rate obtained by a driven horizontal rolling mill.

By the way, in the past, the friction coefficient was generally not considered much, but according to the present invention, the friction coefficient μ is adopted as a management index for rolling rolls, and it is always adjusted to μ≧0.45, so that the rolling Stable rolling is always possible without any trouble.

Therefore, from another aspect, the present invention provides continuous heating of steel bars and wire rods, including one or more rolling mill rows in which driven horizontal rolling mills are arranged before and after a non-driven vertical rolling mill. This hot rolling method for steel bars and wire rods is characterized in that hot rolling is continued while maintaining the friction coefficient of the roll surface of a non-driven vertical rolling mill at 0.45 or more.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a conceptual explanatory diagram of an experimental model rolling mill for carrying out the present invention.

Hl and IIs are driven horizontal rolling mills, ν2 is a non-driven vertical rolling mill, 11 is a horizontal roll, and 12 is a vertical roll.

FIG. 2 is a schematic plan view of a continuous rolling mill according to the present invention arranged in a steel bar factory.The continuous rolling mill 10 used in the present invention is a driven horizontal rolling mill 1.3.5.7 and a non-driven vertical rolling mill 2. .4.6, the reference numeral 20 indicates a rolled material, and 30 indicates an intermediate row tandem rolling mill.

The rolled material 20 heated to the required temperature in the heating furnace is passed through a driven horizontal rolling mill 1, 3.5.7 and a non-driven vertical rolling mill 2.4.
Hot rolling is performed by a rolling mill group consisting of 6 rolling mills. In that case, the friction coefficient of the non-driven vertical rolls is adjusted to 0.45 or more, so even in the non-driven vertical rolling mill 2.4.6, a sufficient area reduction rate can be ensured, the material quality is improved, and the The inherent characteristics of a rolling mill incorporating a driven vertical rolling mill are utilized. The effect can be seen if at least one non-driven vertical rolling roll is used to adjust the friction coefficient to 0.45 or more. Preferably all the friction coefficients are adjusted.

Note that the intermediate row tandem rolling mill functions to reduce the area and stretch the material rolled by the rough rolling mill to a shape that is closer to the product.

The present inventors used a model rolling mill in which two driven horizontal rolling mills and one non-driven vertical rolling mill were arranged close to each other as shown in Fig. 1 to conduct hot rolling under various conditions. As a result of conducting rolling experiments, the following findings were obtained.

The experimental conditions were: rolled material dimensions 96wm x 96m-square, horizontal row/l/(Hl) diameter 250mmφ, vertical o-/
l/ (Vt) diameter 250mm p, horizontal roll (H9)
and the pressure between the roll axes of the vertical roll (Vo)! (Ll) is 3
The horizontal roll (Hl) exit side thickness was 80Ill+.

(1) Three types of friction coefficient μ on the surface of the non-driven vertical roll are set: bride roll (friction coefficient 0.4), sit processing roll (friction coefficient 0.5), and knurling processing roll (friction coefficient 0.65). The rolling reduction limit (biting limit) of the non-driven vertical roll using each roll.
As a result of the investigation, it was found that as the friction coefficient μ increases, as shown in FIG. 3, the occurrence of poor biting becomes less likely, and the rolling limit of the non-driven roll increases.

(2) Based on the experimental results of It can also be seen from the figure that as the friction coefficient μ increases, the critical engagement angle increases, making it difficult for defective engagement to occur. The curve shown by the dashed line in Fig. 4 is the relationship expressed by θ = jan''μ, and as shown in Fig. 5, it is the friction that can be theoretically obtained when pushing the material into the non-driven vertical roll. The relationship between the coefficient and the embedding angle θ is the following: When the roll friction coefficient μ is, the condition for biting of the rolled material is μPcosθ>Psin
Since θ, μ> tan θ or θ< tan″
It becomes 1μ. Here, P is the surface pressure.

In addition, JP-A-61-165201 discloses that by reducing the friction coefficient of the roll surface of a non-driven vertical rolling mill, it is possible to increase the area reduction rate in the non-driven vertical rolling mill. Yes. In other words, the smaller the roll surface friction coefficient of the non-driven vertical rolling mill, the lower the pushing force required for indentation rolling of the material, and the greater the reduction amount in the non-driven vertical rolls.

Therefore, as a result of conducting a hot steel rolling experiment using the model rolling mill, the present inventors found that the friction coefficient μ of the surface of a non-driven vertical roll and the difference between a driven horizontal rolling mill and a non-driven vertical rolling mill are shown in FIG. In addition to the experimental values, the 0ro diagram shows the relationship between the compressive force (pushing force) between machines and the non-driven vertical roll rolling load.
Values calculated using the calculation formula derived from Van's general theory are also shown in dashed lines. From the same figure, it can be seen that the compressive force between the driven horizontal rolling mill and the non-driven vertical rolling mill, that is, the pushing force against the non-driven vertical rolls, is slightly reduced by reducing the friction coefficient. It is reasonable to judge that the effect of increasing the cross-sectional reduction rate in the roll is small (it is reasonable to judge that it is small, but rather, as shown in the relationships in Figures 3 and 4 above obtained by the present inventors, it is necessary to reduce the coefficient of friction μ) It is judged that this will create extremely disadvantageous conditions from the viewpoint of biting property.

On the other hand, another method to improve the biting property is to increase the diameter of the non-driven vertical rolls and reduce the biting angle θ, but as the diameter of the vertical rolls increases, It is necessary to increase the distance between the roll axes of the machine, which causes buckling of the material, and also makes it impossible to downsize the entire rolling mill (which is disadvantageous as it increases equipment costs).

According to the present invention, by using a rolling mill row in which driving horizontal rolling mills are arranged before and after a single non-driven vertical rolling mill, the entire rolling mill can be downsized, and the rolling mill can be reduced in size. By making the roll surface of the machine have a coefficient of friction of 0.45 or more, it is possible to improve the material biting property, and further increase the area reduction rate to improve rolling efficiency.

Next, the reason for limiting the friction coefficient of the roll surface of the non-driven vertical rolling mill (V) to 0.45 or more will be described.

The reason for the limitation is based on the research and experimental results of the present inventors.

The results of a hot steel rolling experiment conducted in the model rolling mill shown in Figure 1 are plotted on the vertical axis, the material area reduction rate rw in the non-driven vertical rolling mill rolls and the material area reduction rate r in the driven horizontal rolling mill rolls.
The ratio rv/7* to H is taken, and the friction coefficient μ between the material and the vertical roll of a non-driven vertical rolling mill is taken on the horizontal axis, and the results are summarized in a graph and shown in FIG.

The curve shown by the solid line in the figure is the limit line of the biting of the rolled material into the vertical rolls of the non-driven vertical rolling mill, determined from experimental values.

As can be seen from Figure 7, the friction coefficient μ between the roll and the rolled material during hot rolling is generally 0.35 or more when the roll is not processed or processed to increase the surface friction coefficient after machining, such as a bride roll. The ratio γw/T,I of the rolling area reduction rate of the non-driven vertical rolling roll and the rolling material reduction rate of the driven horizontal rolling roll is less than 0.45 and within a range that does not cause a biting defect in such a case. At most, it will be less than 0.83.

On the other hand, if the roll surface of a non-driven vertical rolling mill is processed to increase the friction coefficient of the roll surface, such as shot blasting or knurling, and the friction coefficient of the roll surface is set to 0.45 or more, it is within the range that does not cause defective biting. This makes it possible to set the area reduction rate γV of the rolled material on the non-driven vertical rolling mill rolls to 83% or more of the area reduction rate TII of the rolled material on the driven horizontal rolling mill rolls.

Furthermore, it was confirmed that the larger the friction coefficient μ becomes, the larger the limit value of γV/γ9 becomes. Therefore, based on the above results, in the present invention, the friction coefficient of the roll surface of the non-driven vertical rolling mill is limited to 0.45 or more. Preferably, the coefficient of friction is greater than or equal to 0.5, and the surface friction coefficient of any non-driven vertical mill rolls is adjusted accordingly.

Next, examples will be shown.

Embodiment A drive horizontal rolling mill with four stands (l, 3) as shown in FIG.
．． 5.7) and non-driven vertical rolling mill 3 stands (2, 4, 6
) Continuous rolling mill 1 consisting of 7 stands arranged alternately.
The present invention was applied to No. 0, and an intermediate row tandem mill 30 with all stands driven was disposed on the downstream side to carry out steel bar rolling. The outline of the continuous rolling mill 1o was as follows.

Number of stands = 7 stands 1st, 3rd, 5th, 7th stands: drive horizontal rolling machine 2nd
．． 4th and 6th stands: Non-driven vertical rolling mill work roll axis open circuit 1llL! : 0. h Continuous rolling mill length:
5.4m Horizontal and vertical work roll outer diameter Di: 550m5+beleft (material): 18 (ls+s Finishing) The pass schedule is shown in Table 1.

As can be seen from Table 1, the method of the present invention involves knurling-machining the roll surfaces of both the driven horizontal rolling mill roll and the non-driven vertical rolling mill roll to reduce the coefficient of friction to 0.
．． As a result of rolling with a larger size of 65, there was no rolling trouble, and the area reduction rate in the non-drive vertical rolling mill was 90 to 98% of the area reduction rate in the driven horizontal rolling mill, resulting in an excellent and efficient rolling schedule. I was able to get it.

As a comparative example, a steel bar was rolled according to the pass schedule shown in Table 1 in a case where the present invention was not applicable, that is, in the same continuous rolling mill 10, only the roll surface of each non-driven vertical rolling mill was given a bright (as-cut) finish. . At this time, the roll surface friction coefficient of each non-driven vertical rolling mill was 0.40.
Met. The result is slippage of the material in the upstream horizontal rolling mill when the tip of the rolled material gets caught in the non-driven vertical rolling mill, and buckling of the material between the driven horizontal rolling mill and the non-driven vertical rolling mill. Continuous rolling was impossible.

Therefore, the roll opening degree of each stand of the non-driven vertical rolling mill was adjusted to enable continuous rolling without causing the above-mentioned rolling troubles, resulting in the pass schedule shown in Table 2.

As can be seen from Table 2, the area reduction rate in the non-driven vertical rolling mill is much lower than 83% of the area reduction rate in the driven horizontal rolling mill, and the rolling efficiency is much lower than 90% when the present invention is implemented. It was a very bad schedule.

The present invention is not only applicable to new rolls before the start of rolling as in the above embodiments, but also has great effects when applied to used rolls that have been subjected to a considerable amount of continuous rolling.

In other words, when hot steel is continuously rolled for a long time, the roll surface wears out, and the knurling process when new is gradually worn out and loses its effectiveness. It is advisable to take measures to increase the friction coefficient, such as welding and providing unevenness. In other words, the friction coefficient is used as a control index for the rolling rolls, and rolling operations are carried out while maintaining it at 0.45 or higher.

Table 1 Table 2 (Effects of the Invention) According to the present invention, since the vertical rolling mill is a non-drive type, the entire equipment can be downsized and costs can be reduced, and the rolling reduction is substantially the same as in the case of a drive type. A pattern can be realized, and rolling troubles due to non-driven rolls will not occur.

[Brief explanation of the drawing]

Fig. 1 is a conceptual explanatory diagram of a model rolling mill for implementing the present invention; Fig. 2 is a plan explanatory diagram of a rolling line when a continuous rolling mill to which the method of the present invention is applied is arranged in a steel bar factory; Figures 3 and 4 are graphs summarizing the results of model rolling experiments conducted using a combination of a driven horizontal rolling mill and a non-driven vertical rolling mill; Figure 5 is a graph showing the bite limit of the non-driven vertical rolling mill. Explanatory diagram; FIG. 6 is a graph showing the results and theoretical curves of a combined model rolling experiment of a driven horizontal rolling mill and a non-driven vertical rolling mill; and FIG. 7 is a graph showing the material area reduction rate in the non-driven vertical rolling mill. It is a graph showing the relationship between the ratio of the area reduction rate of the material in the drive horizontal rolling mill and the friction coefficient μ. 1, 3.5.7: Drive horizontal rolling mill 2, 4.6:
Drive vertical rolling mill lO2 Continuous rolling mill 20: Rolling material 30: Intermediate row tandem mill 11 j Horizontal roll 12: Vertical rolls H+, Hs: Drive horizontal rolling mill v8: Non-drive vertical rolling mill Ll: Drive horizontal rolling mill roll shaft Distance between center and non-driven vertical rolling mill roll axis

Claims (1)

[Claims] In a method for continuous hot rolling of steel bars and wire rods, which includes one or more sets of rolling mill rows with drive horizontal rolling mills arranged before and after a non-drive vertical rolling mill, the rolls of the non-drive vertical rolling mill are A method for hot rolling steel bars and wire rods, characterized by making the surface friction coefficient 0.45 or more.