KR100742884B1 - Method for deciding change point of back up roll in rolling mill through accumulative fatigue control - Google Patents

Abstract

The present invention relates to a method for determining the time of replacement of a reinforcement roll in a rolling mill composed of a work roll and a reinforcement roll supporting the work roll. Its purpose is to calculate the cumulative fatigue based on the rolling load fluctuating in real time and the number of revolutions in the load, and to calculate the fatigue stresses of the rolls by considering the local stress concentration due to the wear of the rolls. It is to provide a way to replace the reinforcement roll before this occurs.

The present invention for achieving the above object,

In the method of determining the point of time of replacement of the reinforcement roll of the rolling mill comprising a work roll in direct contact with the rolled material and a reinforcement roll supporting the work roll,

Obtaining the contact stress of the reinforcement roll by Equation 1,

[Equation 1]

Where σ _c is the contact stress, P is the rolling load, l is the widthwise contact length of the reinforcement roll and the work roll.

        b is the contact field generated by the roll deflection,

Obtaining the actual contact stress by substituting the contact stress (σ _c ) obtained above into Equation 3,

[Equation 3]

Where σ _act is the actual contact stress, Rc is the stress concentration rate, k is a constant, and Wd is the wear depth

Substituting the actual contact stress obtained in Equation 4 to obtain the rotational speed N _i of the reinforcement roll until failure occurs, and then measuring the actual rotational speed ni of the reinforcement roll,

 [Equation 4]

Where a1 and a2 are constants and s _critical are critical stress values

Obtaining fatigue degree (Fi) by substituting Ni and ni obtained in Equation 5,

 [Equation 5]

Calculating the fatigue fatigue by calculating the fatigue degree of the reinforcement roll at a predetermined period and substituting it into Equation 6,

 [Equation 6]

If the cumulative fatigue degree (F) obtained above is greater than the _critical fatigue (F _critical ) to determine the replacement time of the rolling mill reinforcement roll through the cumulative fatigue control, including the step of determining the replacement time of the reinforcement roll as the technical gist do.

Rolling mill, work roll, reinforcement roll, roll replacement time, cumulative fatigue

Description

Method for deciding change point of back up roll in rolling mill through accumulative fatigue control}

1 is a graph showing the change in rolling load according to rolling time

2 is a graph showing the cumulative fatigue diagram according to the contact stress and the roll rotational speed

3 is a schematic diagram of stress concentration of work roll and reinforcement roll

4 is a graph showing a control system of the present invention.

Figure 5 is a flow chart showing the replacement judgment sequence of the reinforcement roll of the present invention

6 is a graph showing the stress concentration rate according to the wear of the roll

7 is a conceptual diagram simplifying the fatigue characteristics in one dimension

The present invention relates to a method for determining the time of replacement of a reinforcement roll in a rolling mill composed of a work roll and a reinforcement roll supporting the work roll. More specifically, the fatigue failure is calculated by calculating the cumulative fatigue based on the rolling load fluctuating in real time and the number of revolutions at the load, and calculating the fatigue experienced by the roll while considering the local stress concentration caused by the wear of the roll. It relates to a method that can replace the reinforcement roll before the phenomenon occurs.

In general, in the case of the work roll in direct contact with the rolling material, the quality of the product becomes a problem when the surface of the roll is rough, and the shape of the plate becomes poor when the roll wear amount is more than a predetermined standard. Under these two conditions, the roll replacement cycle is empirically determined. Contact stress with the material, contact vibration stress with the reinforcing roll, and fatigue accumulation of the surface resulting from the cyclic thermal stress load received from the high temperature material are not a problem. The cumulative fatigue degree (F) is known to be 0.1 or less under the conventional roll replacement cycle, and spalling, which is a local failure phenomenon due to fatigue accumulation, is also known to occur within this cumulative fatigue degree.

However, since the reinforcement roll does not have a very direct effect on the surface quality or the shape quality of the above-mentioned products, the use of a long period compared to the work roll increases the possibility of spalling due to fatigue accumulation and the process is stopped when the spalling occurs. Because of the large losses that must be disposed of, the replacement cycle is usually determined uniformly regardless of the empirically changing conditions within the most stable range.

In general, even though similar rolls are used in the hot rolling process and they have similar working conditions, the replacement cycle of the reinforcement rolls is in the range of 1 to 4 weeks. to be. It is difficult to establish an accurate and reasonable replacement criterion because empirically deciding a roll replacement cycle takes a lot of time and effort, and also because rolling conditions and roll conditions are constantly changing. The fatigue accumulation can be evaluated by an open and simple method based on the average rolling load per material, the rotation length calculated from the material length and the roll diameter, but this method has the following problems. As shown in Fig. 1, the rolling load is continuously changed even during rolling of the material, and if the range of stress load as shown in Fig. 2 is in the range of σ _a and σ _b and the average stress is σ _ave , the actual cumulative fatigue and average Accumulated fatigue calculated by stress is not accurate.

In addition, in the calculation of the contact vibration stress, it is calculated on the premise that the contact surface of the work roll and the reinforcement roll is flat, so that an error of several tens of percent may occur. The reason for this is that during actual rolling as shown in FIG. 3, a portion where stress is locally concentrated due to abrasion of the work roll and the reinforcement roll occurs, and spalling due to fatigue failure also occurs at the portion. For this reason, it is difficult to set a proper replacement standard by theoretical calculation and to set a standard based on experience.

The present invention for solving the problems of the prior art as described above calculates the cumulative fatigue based on the rolling load fluctuating in real time under the specified roll conditions and the number of rotations in the load, while considering the local stress concentration due to the wear of the roll By calculating the fatigue of the rolls close to the actual ones, it is advised to replace the rolls before fatigue breakdown occurs, so that the replacement cycle of the reinforcement rolls can be set as long as possible to meet the given conditions. Its purpose is to save time and manpower, and to prevent losses caused by spalling accidents.

In the present invention for achieving the above object, in the method of determining the time of replacement of the reinforcement roll of the rolling mill composed of a work roll in direct contact with the rolled material and a reinforcement roll supporting the work roll,

Obtaining the contact stress of the reinforcement roll by Equation 1,

[Equation 1]

Where σ _c is the contact stress, P is the rolling load, l is the widthwise contact length of the reinforcement roll and the work roll.

        b is the contact field generated by the roll deflection,

Obtaining the actual contact stress by substituting the contact stress (σ _c ) obtained above into Equation 3,

[Equation 3]

Where σ _act is the actual contact stress, Rc is the stress concentration rate, k is a constant, and Wd is the wear depth

Substituting the actual contact stress obtained in the above equation (4) to obtain the rotational speed (N _i ) of the reinforcement roll until failure occurs, and then measuring the actual rotational speed (ni) of the reinforcement roll,

 [Equation 4]

Where a1 and a2 are constants and s _critical are critical stress values

Obtaining fatigue degree (Fi) by substituting Ni and ni obtained in Equation 5,

 [Equation 5]

Calculating the fatigue fatigue by calculating the fatigue degree of the reinforcement roll at a predetermined period and substituting it into Equation 6,

 [Equation 6]

If the cumulative fatigue degree (F) obtained above is greater than the _critical fatigue (F _critical ) is configured to include the step of determining the replacement time of the reinforcement roll.

Hereinafter, the present invention will be described in detail.

The contact stress is calculated using the rolling load and contact area detected by the load cell detector, and the contact area is calculated from the geometrical relationship between the work roll and the reinforcement roll and the Young's Modulus of the roll. The rotation speed of a roll is calculated from the pulse generator PLG attached to the motor side which drives a roll. The wear of the roll uses the prediction result of the shape control computer for controlling the plate phenomenon or the measurement result of the on-line profile measuring device of the ultrasonic or vehicle loading method.

After the roll starts and rolling starts, the fatigue damage is continuously calculated in real time to calculate the cumulative fatigue, and the worker is warned if the fatigue exceeds a predetermined range. 4 is an example of the reinforcement roll fatigue identification system of the present invention,

A rolling load detector 41 for detecting a pushing load,

Pulse generator 42 for measuring the rotational speed of the reinforcement roll,

Control unit for calculating the cumulative fatigue from the input information related to the roll and the rolling load detector and the data of the pulse generator,

Shape control computer with wear prediction system for indicating roll wear

Online profile meter to measure actual wear profile

It consists of a monitor to visually show the accumulated fatigue head calculation results to the operator.

A prochart for calculating cumulative fatigue in this system is shown in FIG. 5.

In order to calculate the cumulative fatigue, first, input necessary data such as Young's modulus of work roll and reinforcement roll and fatigue characteristic of reinforcement roll (S-N Diagram). When the actual rolling starts, the contact load is calculated by inputting the rolling load detected by the rolling load detector in Equation 1.

Where σ _c is the contact stress, P is the rolling load, l is the widthwise contact length of the reinforcement roll and the work roll.

b is the contact field generated by the roll deflection

In Equation 1, b is obtained by Equation 2 from the rolling load, the length of the roll, the radius of the roll, and the Young's modulus of the roll.

Where E is the Young's Modulus of the roll and R is the radius of the roll

The Young's modulus of the roll uses the data input to the control unit. Young's modulus of the roll is reumyeo depending on the material of the roll, in the case of chromium, the cast iron is about 22000kg / mm ^2, the case of nickel grain case of 19000kg / mm ^2, the reinforcement roll forging 21000kg / mm ^2.

The contact stress σ _c obtained by Equation 1 is calculated on the assumption that both the reinforcement roll and the work roll are in equilibrium, and this value may vary depending on the wear condition of the roll. Therefore, the actual stress is obtained by reflecting the stress concentration degree according to the wear of the roll. 6 shows the stress concentration rate according to the wear of the work roll and the reinforcement roll. In extreme wear, the actual contact stress can be greater than 30% of the calculated contact stress. At this time, the wear depth of the work roll is the actual depth including thermal expansion and mechanical wear at high temperature, the wear of the reinforcement roll is the wear depth caused entirely by mechanical wear.

Since wear is important information for shape control of products, wear depth is usually calculated by predictive calculation in shape control computer. Actual wear depth can be obtained by using ultrasonic distance sensor or contact load comparison profile meter. Can also be measured. The actual contact stress is obtained by substituting the contact stress obtained above with the wear depth Wd in Equation 3.

Where σ _act is the actual contact stress, Rc is the stress concentration rate, k is a constant, and Wd is the wear depth

In Equation 3, the constant k is about 3.5 to 5 as an experimental value.

When the actual contact stress is obtained from Equation 3, the stress cycle number Nf from the contact stress to the fracture is calculated. The stress cycle number Nf can be calculated | required using SN curve provided from a roll supplier. For ease of calculation, as shown in FIG. 7, the linear function is applied above the specific stress value of infinity, and fatigue calculation is not performed below the specified value. For example, in the case of a forged reinforcing roll, σ = 1030-127.5log (N) may indicate the relationship between the stress of the straight section and the cycle. The actual calculations include the relationship between the stress and the rotational speed of the straight line, σ _act = a-blogN (a and b are arbitrary constants), and the form of rotational speed Nf = exp (c + dσ _act ) (c and d are arbitrary constants) Ni may be represented as follows according to the stress condition.

Where a1 and a2 are constants and s _critical are critical stress values

Therefore, Ni can be calculated | required by Formula (4). The actual rotation speed ni of the reinforcement roll measured by the Ni and the pulse generator is substituted into Equation 5 to obtain the fatigue degree Fi during the corresponding time.                     

Next, the fatigue degree is continuously calculated according to the calculation cycle, and the cumulative fatigue degree obtained by linearly adding the calculated fatigue degree is calculated. The cumulative fatigue under varying vibration stress can be expressed by Equation 6 according to the linear cumulative damage of Miner.

The cumulative fatigue degree F is calculated by Equation 6, and when the cumulative fatigue degree is greater than the _critical fatigue degree (F _critical ), it is determined that the reinforcement roll is replaced. It is desirable to empirically determine the _{critical criticality} (F _critical ) in the range of 0.65 to 0.75. The reason is that if the critical fatigue (F _critical ) is less than 0.65, it is possible to make an error of changing the roll early. If the critical fatigue is more than 0.75, the roll replacement time may be missed.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Accumulated fatigue damage by calculating the actual local contact stress according to the rolling load and the wear state of the roll in accordance with Equations 1, 2, and 3 and calculating the fatigue degree by Equations 4, 5 and 6 under the given stress conditions. The reinforcement roll was replaced when the degree was calculated and the critical fatigue was greater than 0.7. In this case, k is set to 4.3 / mm. The result of replacing the reinforcing roll according to the present invention is shown in Table 1 below along with the conventional replacement cycle.

stand Reinforcement Roll Replacement Cycle Conventional example Inventive Example R2 3 8 R3 3 18 R4 3 14 F1 3 3 F2 3 3 F3 2 2 F4 2 2 F5 One 2 F6 One 2 F7 One 3 Average 2.2 5.7

As shown in Table 1, it can be seen that according to the present invention, the replacement cycle can be extended by an average of 2 times or more as compared with the related art.

division Frequency of spalling (number of spalls / roll operations) Conventional example 3.1 Inventive Example 1.2

As shown in Table 2, it is possible to minimize spalling, which is a fracture phenomenon due to fatigue accumulation, thereby reducing the effect of reducing spalling accidents.

As described above, according to the present invention can extend the replacement cycle of the reinforcement roll to reduce the consumption of the roll to reduce the manpower and time required for the roll replacement operation and further to prevent the loss caused by spalling accident There is.

Claims (2)

In the method of determining the point of time of replacement of the reinforcement roll in the rolling mill consisting of a work roll in direct contact with the material to be rolled and a reinforcement roll supporting the work roll, Obtaining the contact stress of the reinforcement roll by Equation 1, [Equation 1]

Where σ _c is the contact stress, P is the rolling load, l is the widthwise contact length of the reinforcement roll and the work roll.         b is the contact field generated by the roll deflection, Obtaining the actual contact stress by substituting the contact stress (σ _c ) obtained above into Equation 3, [Equation 3]

Where σ _act is the actual contact stress, Rc is the stress concentration rate, k is a constant, and Wd is the wear depth Substituting the actual contact stress obtained in Equation 4 to obtain the rotational speed N _i of the reinforcement roll until failure occurs, and then measuring the actual rotational speed ni of the reinforcement roll,  [Equation 4]

Where a1 and a2 are constants and s _critical are critical stress values Obtaining fatigue degree (Fi) by substituting Ni and ni obtained in Equation 5,  [Equation 5]

Calculating a cumulative fatigue degree by substituting the equation (6) by calculating the fatigue degree of the reinforcement roll at a predetermined period;  [Equation 6]

When the cumulative fatigue degree (F) obtained above is greater than the _critical fatigue (F _critical ) determining the replacement time of the rolling mill reinforcement roll through the cumulative fatigue control, characterized in that it comprises the step of determining the replacement time of the reinforcement roll. The method of claim 1, wherein the critical fatigue degree (F _critical ) is determined in a range of 0.65 to 0.75.

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