JPH0523843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling mill rolls, and in particular,
This invention relates to a method for cooling rolling rolls that enables mist cooling even for low-strength rolls such as those made of Ni-grain cast iron.

Generally, when cooling rolling rolls, a spray cooling method using cooling water with a cooling water pressure of 2 to 50 Kg/cm ² and a cooling water amount of 10 to 500 t/Hr per roll is adopted. However, this cooling method requires a large amount of cooling water, resulting in poor cooling water consumption (cooling water amount/rolled material weight).
There is a drawback in that the cooling water falls onto the rolled material, causing a drop in temperature.

Therefore, some companies are considering adopting a so-called mist cooling method that uses a small amount of water and air together in order to improve the cooling water consumption rate and prevent the temperature of the rolled material from dropping. lump mill,
It has the disadvantage that it is limited to shape steel mills, hot rolling roughening mills, etc., and cannot be used in hot rolling finishing mills, etc. That is, compared to the spray cooling method, the mist cooling method uses a smaller amount of cooling water and therefore generally has lower cooling performance. For this reason,
Blossoming mills and shaped steel rolls that use special cast steel rolls with a relatively high tensile strength of 30 to 70 Kg/ ^mm2 at the center of the roll, and the time in contact with the rolled material is relatively short and the roll surface temperature does not become very high. In mills, hot rolling roughening mills, etc., the thermal stress is small, so a sufficient cooling effect can be expected even with a mist cooling method. However, hot rolling finishing mills, especially
In hot-rolling finishing mills that use rolls made of Ni-grain cast iron, the tensile strength at the center of the roll is as low as 15 to 30 kg/ ^mm2 , and the time in contact with the rolled material is long and the roll surface temperature becomes high, resulting in thermal stress. becomes larger. Therefore, a mist cooling system with low cooling ability could not be used because the difference between the temperature at the center of the roll and the temperature at the roll surface would become too large and the roll would break.

The present invention was made in view of the current situation, and
Mist cooling is possible even in low-strength rolls such as hot-rolling post-mills that use rolls made of Ni-grain cast iron, thereby improving the cooling water consumption rate and preventing temperature drops due to cooling water in the rolled material. The object of the present invention is to provide a method for cooling a mill roll.

For this purpose, the inventor actually measured the surface temperature and center temperature of the roll during rolling, and came to the following conclusion.

That is, the roll surface temperature rises more rapidly in the early stage of rolling as the rolling pitch becomes shorter, and thereafter becomes saturated at a high temperature. On the other hand, the temperature at the center of the roll increases later than the temperature at the roll surface, and thereafter gradually approaches the saturation temperature of the surface. Thermal stress is generated in the roll due to the temperature difference between the roll surface and the center, and when the total stress obtained by adding this thermal stress and the residual stress of the roll exceeds the tensile strength of the roll center, breakage occurs. Therefore, by controlling spray cooling and mist cooling to suppress thermal stress, mist cooling becomes possible in all hot mills.

The present invention was made based on this knowledge, and calculates the thermal stress of the rolling roll by inputting the roll surface temperature from the surface temperature detection section and the roll center temperature from the center temperature detection section into the calculation section.
The present invention is characterized in that forced cooling by spraying and slow cooling by mist are selectively controlled based on the magnitude of this thermal stress and the strength of the center portion of the roll.

An example of implementing the method of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, with the right side showing the roll seen from the front via the central control unit, and the left side showing the same roll seen from the side. show.

In this FIG. 1, 1 and 2 are a pair of upper and lower rolling rolls that roll a rolled material 3, and both rolling rolls 1 and 2 are spray-cooled by a large amount of high-pressure cooling water from a spray nozzle 4, and are spray-cooled by a large amount of high-pressure cooling water from a mist nozzle 5. The system is designed to be cooled by a small amount of low-pressure cooling water and mist cooling using a mixed flow of air. These two nozzles 4, 5 are switched and controlled by a control signal from a control device 6, as shown in FIG.

Of the two rolls 1 and 2, for example, the upper roll 1 has a roll surface temperature T ₁ measured by a detection probe 7 such as an infrared thermometer, as shown in FIG.
is detected at all times or at a constant pitch, and a thermocouple is embedded in the center 8 of the roll 1 so that the roll center temperature _T2 is constantly detected via a slip ring or the like. It's summery.
These two temperature signals T ₁ and T ₂ are respectively input to the calculation device 9, where the thermal stress of both rolling rolls 1 and 2 (actually rolling roll 1) during rolling is calculated, and this thermal stress and rolling rolls 1 and 2
A calculation result based on the tensile strength at the center of the nozzle is output to the control device 6, and the control device 6 switches and controls both nozzles 4 and 5 based on this signal.

Next, a method for cooling the rolling rolls 1 and 2 will be explained.

First, the various conditions of the roll, namely the residual stress σC at the center of the roll, the tensile strength σB at the center of the roll, the Young's modulus E, the coefficient of linear expansion α, and the Poisson's ratio V, are input into the calculation device 9. These values are approximately constant values once the material, manufacturing method, shape, etc. of the roll are determined, so input the values obtained by actual measurements in advance.

When rolling is started in this state, the roll surface temperature T ₁ and the roll center temperature T ₂ during rolling are constantly input to the calculation device 9 from the detection probe 7 and the center portion 8 . The calculation device 9 calculates the thermal stress σZ based on both temperature signals T ₁ and T ₂ using equation (1) shown below.

σZ=Eα/1-V・(T ₁ −T ₂ )/2 ...(1) Based on this calculation result, the calculation device 9 calculates the sum of the thermal stress σZ and the residual stress σR at the center of the roll. It is calculated whether or not exceeds the value obtained by dividing the tensile strength σB at the center of the roll by a required safety factor Sf, and outputs the result to the control device 6.

Based on this signal, the control device 6 outputs a control signal to open the spray nozzle 4 and close the mist nozzle 5 when the relationship σZ + σR > σB/Sf (2) holds true, and also outputs a control signal to open the spray nozzle 4 and close the mist nozzle 5, and σB/Sf≧ When the relationship σZ+σR (3) holds true, a control signal for closing the spray nozzle 4 and opening the mist nozzle 5 is output.

However, in the early stage of rolling where the above formula (2) holds true, that is, when the thermal stress σZ becomes large,
Both rolling rolls 1 and 2 are forcibly cooled by spray cooling with cooling water from the spray nozzle 4, and the temperature difference between the inside and outside of the rolls 1 and 2 becomes smaller, the thermal stress σZ becomes smaller, and the above equation (3) is established. When the time comes, gentle cooling is performed by mist cooling from the mist nozzle 5. As a result, rolls 1 and 2 are
Even if the roll center is made of a material with low tensile strength σB such as Ni grain cast iron, mist cooling is possible without roll breakage. Therefore, it is possible to improve the cooling water consumption rate and prevent a drop in the temperature of the rolled material 3, and since the rolling pitch can be shortened from the beginning of rolling, it is also possible to improve productivity.

〔Example〕

A cooling experiment of a post-hot rolling finishing mill performed using the apparatus shown in FIG. 1 is shown below.

(1) Conditions of use a Roll material Ni grain cast iron (Tensile strength at roll center σB...25Kg/mm ² ) b Spray cooling Cooling water pressure...20Kg/cm ² Water amount per roll...300t/Hr c Mist Cooling Cooling water pressure…1Kg/cm Water volume per ² rolls…10t/Hr Cooling air pressure…1.5Kg/cm Compressed air volume per ² rolls…600Ncm ³ /Hr (2) Cooling method As described above, inside and outside the rolls Thermal stress σZ was calculated by constantly detecting the temperatures T ₁ and T ₂ of the roll, and the comparison with the tensile strength σB at the center of the roll automatically controlled switching between spray cooling and mist cooling.

(3) Results Figure 2 shows the state of switching control using both cooling methods. In the figure, solid line graph A shows the change in roll surface temperature _T1 due to spray cooling, solid line graph B shows the change in roll center temperature _T2 , The broken line graph C shows the changes in the roll surface temperature _T1 due to mist cooling, and at the time of the arrow MAX, the temperature difference between the inside and outside of the roll reaches its maximum, and the thermal stress σZ also reaches its maximum, and the thermal stress σZ gradually increases as the rolling time t passes. It shows a tendency to become smaller. In the combined spray and mist cooling method according to the present invention, as shown in Fig. 2, spray cooling Rs is performed at the beginning of rolling when the thermal stress σZ is large, and when the thermal stress σZ is weakened (approximately after rolling). 40 minutes), the spray cooling Rs was automatically switched to the mist cooling R ^M , and the mist cooling R ^M was performed thereafter. Further, rolling was possible without any roll breakage.

As a result, it was confirmed that compared to the conventional cooling method using only spray, the effect of preventing temperature drop in rolled material was improved by about 20%, and the cooling water consumption rate was improved by 50%. Furthermore, it has been confirmed that productivity can be improved because the rolling pitch can be shortened from the beginning of rolling.

In addition, in one aspect of the above implementation, the thermal stress σZ
All conditions including upper and lower rolling rolls 1,
2, so the temperature inside and outside of the upper roll 1 is measured only, but cooling control of both rolls 1 and 2 may be performed separately.
Further, the temperature signals from both rolling rolls 1 and 2 are respectively inputted to a single arithmetic unit 9 via, for example, a priority circuit, and when at least one of them satisfies the relationship of equation (2), both rolls 1 and 2 are 2 by spray cooling,
Both rolls 1 and 2 may be cooled with mist when both satisfy the relationship of the above equation (3).

As explained above, the present invention constantly calculates the thermal stress during rolling by detecting the roll surface temperature and roll center temperature, and spray cooling and mist cooling are performed based on the magnitude of this thermal stress and the roll center strength. Since the automatic switching control is performed, mist cooling is possible in all hot mills including the post-hot rolling finishing mill. As a result, compared to a cooling method using only spray, it is possible to reduce the consumption of cooling water and prevent the temperature of the rolled material from decreasing.
Compared to a cooling method using only mist, the rolling pitch can be shortened from the beginning of rolling, so productivity can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a graph showing a switching control method between spray cooling and mist cooling according to the present invention. 1, 2...Rolling roll, 3...Rolled material, 4...
Spray nozzle, 5... Mist nozzle, 6... Control device, 7... Detection probe, 8... Center, 9
...Arithmetic unit, T ₁ ...Roll surface temperature, T ₂ ...
Roll center temperature.

Claims (1)

[Claims] 1 The roll surface temperature from the surface temperature detection section and the roll center temperature from the center temperature detection section are input into the calculation section to calculate the thermal stress of the rolling roll, and based on the magnitude of this thermal stress and the roll center strength. ,
A method for cooling a rolling roll, characterized by switching control between forced cooling by spray and slow cooling by mist.