JPH0985318A - Prevention of nose bending of hot rolling stock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent nose bending due to the temperature difference between upper and lower surfaces of a stock to be rolled in hot rolling by controlling the number of revolution of upper and lower rolls in a hot mill based on the temperature difference so that nose bending of the rolling stock is offset using the relationship previously investigated between the temperature difference between upper and lower surfaces and the amount of nose bending. SOLUTION: A stock 1 to be rolled having finished descaling is subjected of advance into a roughing mill 2 in the hot rolling line, the temperatures between upper and lower surfaces of the end part of the rolling stock 1 before being bitten into the rough mill 2 are respectively measured with upper and lower thermometors 3 provided at the inlet side of the roughing mill 2, and temperature data of the upper and lower surfaces are inputted into a controller 4. The relationship between the temperature difference and the number of revolution of upper and lower rolls required for offsetting nose bending is stocked in the controller 4, the temperature difference between upper and lower surfaces is calculated based on temperature data inputted from thermometors 3, the rotational ratio of upper and lower rolls corresponding to the temperature difference is instructed to the driving device of the mill 2 by refering the temperature difference to the relationship, whereby the material 1 to be rolled is subjected to smoothly pass through.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing the nose bending of a hot rolled material which prevents the nose bending phenomenon in which the tip of the hot rolled material warps upward or downward.

[0002]

2. Description of the Related Art In hot rolling of a steel sheet, so-called nose bending occurs in which the tip of the rolled material is warped upward or downward. The cause of this phenomenon is that the water sprayed on the material to be rolled in the descaling performed before rolling remains on the upper surface of the material to be rolled and the cooling of the upper surface progresses from the lower surface side. It is said that the extension is large.
Therefore, nose bending in hot rolling generally tends to warp.

When the nose bend is noticeable during hot rolling, it causes threading troubles and equipment damage particularly on the finishing rolling mill and its entry side. Therefore, the following method has been conventionally proposed in order to prevent the nose from bending.

The bottom surface temperature of the tip of the rolled material is lowered by water cooling, and the tip has a downward tendency (Japanese Patent Publication No. 56-49164 and Japanese Patent Publication No. 58-566).
No. 41). Since it is considered that the main cause of the nose bend of the rolled material is the roughness difference between the upper and lower rolls, the roughness difference between the upper and lower rolls is eliminated by polishing the roll surface according to the amount of the nose bend (Japanese Patent Publication No. 57-38325). ). Although it is not hot rolling, the nose bending caused by the rolling correction in the thick plate rolling is prevented by increasing the speed of the lower roll corresponding to the rolling reduction amount (Japanese Patent Publication No. 3-5242).

[0005]

However, since the nose bending in hot rolling is caused by the temperature difference between the upper and lower surfaces over the entire length of the material to be rolled, the lower surface of the tip of the material to be rolled is forcibly cooled. However, the expected tendency cannot be obtained. On the contrary, in this method, there is a concern that a temperature difference occurs in the longitudinal direction of the material to be rolled, which may cause instability of the strip in the finish rolling mill.

The cause of nose bending in hot rolling is mainly due to the temperature difference between the upper and lower surfaces of the material to be rolled. Therefore, even if the roughness difference between the upper and lower rolls is eliminated, the nose bending is hardly prevented.

Similarly, in the method of accelerating the lower roll in accordance with the reduction correction amount in the plate rolling, the temperature difference between the upper and lower surfaces of the material to be rolled is not taken into consideration. It has no effect on bending of the nose during hot rolling.

An object of the present invention is to provide a method for preventing the nose bending of a hot rolled material which can surely prevent nose bending due to the temperature difference between the upper and lower surfaces of the material to be rolled in hot rolling.

[0009]

[Means for solving the problem] Nose bending in hot rolling is
This is mainly caused by the temperature difference between the upper and lower surfaces of the rolled material. on the other hand,
When the upper and lower roll rotation speeds of the hot-rolled material are given a difference, the surface on the high speed side is stretched more than the surface on the low speed side, so that nose bending can be intentionally generated.

According to the method of preventing nose bending of the present invention, the upper and lower surface temperatures of the material to be rolled are measured by the upper and lower thermometers installed on the inlet side of the hot rolled material, and the temperature difference is determined and investigated beforehand. Using the relationship between the temperature difference of the lower surface and the amount of nose bend, by controlling the upper and lower roll rotation speed of the hot rolling mill based on the temperature difference so that the nose bend of the rolled material is offset,
The above object is achieved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

In hot rolling, as shown in FIG. 1, the material 1 to be rolled, which has undergone descaling, enters a rough rolling mill 2 of a hot rolling line. In the method of the present invention, the upper and lower surface temperature of the tip of the rolled material 1 before being bitten into the rough rolling mill is measured by the upper and lower thermometers 3 and 3 provided on the inlet side of the rough rolling mill 2. The measured temperature data of the upper and lower surfaces is input to the control unit 4. The controller 4 controls the number of rotations of the upper and lower rolls 5, 5 of the rolling mill 2 as follows using the input temperature data.

Generally, the lower surface temperature of the material 1 to be rolled is higher than the upper surface temperature. Therefore, when this rolled material 1 is rolled by the rolling mill 2, the tip of the rolled material 1 warps upward. This amount of nose bending increases as the temperature difference ΔT between the upper and lower surfaces (lower surface temperature-upper surface temperature) increases. On the other hand, the upper and lower rolls 5, 5
The rotation speed of the rolled material is generally the same, but when the rotation speed of the upper roll is made higher than that of the lower roll, the tip of the rolled material tends to warp downward. Therefore, by setting the rotation speed of the upper roll larger than that of the lower roll in accordance with the temperature difference ΔT between the upper and lower surfaces, it is possible to cancel the nose bend caused by the temperature difference ΔT.

FIG. 2 shows the relationship between the temperature difference ΔT necessary to offset the nose bend and the upper and lower roll rotation speed ratio n. The upper and lower roll rotation speed ratio n is (upper roll rotation speed-lower roll rotation speed)
/ It is represented by the number of rotations of the lower roll. If the material to be rolled and the operating conditions such as the rolling reduction are the same, a certain relationship is established between the temperature difference ΔT and the upper and lower roll rotation speed ratio n.

The control unit 4 stocks the relationship between the temperature difference ΔT necessary to offset the nose bend for each operating condition and the upper and lower roll speed ratio n, and the temperature input from the thermometers 3 and 3 is stored. The temperature difference ΔT between the upper and lower surfaces is calculated from the data, and the temperature difference ΔT is collated with the above relationship to select the upper / lower roll rotational speed ratio n corresponding to the temperature difference ΔT. Then, the upper / lower roll rotation speed ratio n is instructed to the drive device of the rolling mill 2.

As a result, the material 1 to be rolled has a temperature difference ΔT between the upper and lower surfaces thereof, but does not bend when subjected to rolling by the rolling mill 2. As a result, the leading end of the rolled material smoothly passes from the rough rolling mill 2 to the finish rolling mill.

In rough rolling, a rolling mill usually has 2 to 5 stands, and a total of 5 to 8 passes are rolled. However, since the nose bending becomes large each time the stand is passed, each stand has its own stand. It is good to offset the nose bending that occurs.
When the upper and lower roll rotation speed ratios necessary to offset all nose bends at the 1st stand are collectively given, nose bend in the opposite direction occurs,
Since this remains up to the final stand, there is a possibility that the passage of the rough rolling mill may be hindered.

In producing a hot-rolled steel sheet having a material of austenitic stainless steel and a width of 1000 to 1400 mm, the temperature difference between the upper and lower surfaces of the material to be rolled is measured on the inlet side of the first rough rolling mill, and all the temperature differences are measured according to the temperature difference. The upper and lower roll speed ratios were changed in order to offset the self-generated nose bend in the rough rolling mill of No.
The temperature difference was 10 to 30 ° C., and the control range of the upper and lower roll rotation speed ratio was 0 to 12%.

There was no sheet passing trouble that occurred at a rate of 0.03% of the total rolling amount on the finishing rolling mill and its entry side.

[0020]

As described above, the nose curl prevention method of the present invention surely prevents nose curl caused by the temperature difference between the upper and lower surfaces, which has not been effective measure so far, and prevents the passing of the strip due to the nose curl. Avoiding it will have a great effect on improving operational efficiency and protecting equipment.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a device configuration suitable for implementing the present invention.

FIG. 2 is a table showing a relationship between a temperature difference between upper and lower surfaces and a ratio of rotation speeds of upper and lower rollers, which is necessary to prevent bending of the nose.

[Explanation of symbols]

 1 rolled material 2 rolling mill 3 thermometer 4 control unit

Claims (1)

[Claims] 1. The upper and lower surface temperatures of the material to be rolled are measured by upper and lower thermometers installed on the inlet side of the hot-rolled material, and the temperature difference is determined. Using the relationship with the amount, the nose bend of the hot rolled material is characterized by controlling the upper and lower roll speeds of the hot rolling mill based on the temperature difference so that the nose bend of the rolled material is offset. Prevention method.