JPS6139127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides an average wall thickness control method in which the average wall thickness of the raw pipe at the exit side of the plug mill is kept constant by manipulating the roll reduction position for each raw pipe in plug mill rolling in the manufacturing process of seamless steel pipes. This invention relates to a thickness control method.

The basic structure of the seamless steel pipe rolling process in the Mannesmann Plug Mill pipe manufacturing method generally consists of the steps of perforating a billet with a piercing mill and stretching it with a drawing machine (not necessarily necessary for small diameter sizes) to obtain a blank pipe; A step of rolling and elongating the raw tube in two passes with a plug mill, a step of polishing the inner surface of the obtained long tube with a reeling mill, a reheating furnace step of reheating as necessary, and The final process consists of reduction rolling using a sizing mill to make the outer diameter of the raw tubes uniform. Therefore, the outer diameter and wall thickness of the product are ultimately determined on the exit side of the sizing mill. It is important to keep the wall thickness of a product constant for reasons such as improving quality and improving material or product yield. However, although sizing mills can make the outer diameter of the product constant, it has not been possible to make the wall thickness of the product constant, and recently it has only been possible to control it within a certain range, so plug mills are used exclusively. It has been devised to control the

Conventional plug mills have the following methods to maintain a constant average wall thickness, each of which has its own problems.

The first method is to directly measure the wall thickness of the raw pipe with a hot online wall thickness gauge at the exit side of the plug mill, and control the roll rolling position using feedback or feedback. This method remains at the research and development stage because hot online wall thickness gauges have not yet been put into practical use. The reason for this is that although the radiographic method is most likely to be used as a wall thickness gauge, it is necessary to ensure a time constant to respond to high-speed rolling, source capacity and shielding equipment, design of safety measures, installation location, and vibration of the raw tube. This is because there are many problems such as a decrease in measurement accuracy due to

The second idea is to measure the length of the raw pipe for each pass instead of using a wall thickness gauge, and use the cross-sectional area characteristic value (for example, the weight value of the unit length of the raw pipe) instead of the average wall thickness value. For control, there is a method that combines the rolling load value and mill spring value, which incorporates the plate thickness control method in strip rolling. Currently, this method is the mainstream, but the problem is that the rolling force value cannot be known without rolling, so it cannot be directly incorporated into the formula for calculating the roll reduction position, and it is also difficult to use for feedback control. In recent high-speed rolling, a rolling time of 3 to 5 seconds is of little value. In order to cover this, methods are being considered to predict the rolling load value using factors such as actual rolled values, temperature measurement values of the raw pipe, rolling conditions such as steel type and rolling speed, etc., and various prediction formulas are being considered. Although these methods have been proposed, the current situation is that none of them are accurate considering the complex formulas that include many factors. The reason for this can be pointed out as follows.

Originally, this method was intended to directly apply plate (strip) thickness control to steel pipe rolling, and it was difficult to connect items with different dimensions so easily, and since rolling theory involved three-dimensional and complex processing,
Currently, it is hardly in use, and the most important factor, the temperature during rolling, is difficult to measure over the entire length of the raw tube, and it is difficult to select an appropriate representative value. The mill spring value of a plug mill stand is different from that of a plate, and is difficult to define and measure. Even if the mill spring value can be determined, it is actually not a constant value and varies depending on the caliber diameter, and if multiple caliber rolls are used, it also varies depending on the position of the caliber used, and it also varies depending on the roll diameter. In this situation, there are too many examples of such values.

In single-caliber plug mills that have recently begun to be installed, the stand has a high rigidity value, so changes in the rolling load value have little effect on wall thickness, and methods that do not use the rolling load value have been attracting attention.

This invention has been devised in view of the above circumstances, and is mainly aimed at plug mills with stands with high rigidity values, and it is possible to easily measure each pass without using the rolling force value. Calculate the roll reduction position using the average wall thickness value of the raw pipe on the exit side as the target value,
This is a plug mill average wall thickness control method whose main purpose is to give commands to the plug mill.

In other words, the method of the present invention is a control method in which the average wall thickness of the raw pipe on the outlet side of the plug mill in the Mannesmann plug mill pipe manufacturing method is kept constant, and the first pass is based on the actual value of the roll reduction position in the elongate mill, which is the previous process. and the actual value of the cross-sectional area characteristic value of the raw pipe on the exit side of the mill, the actual rolling value of the raw pipe rolled in the previous plug mill, and the target value of the cross-sectional area characteristic value of the raw pipe on the exit side of the first pass. The second pass is based on the actual value of the cross-sectional area characteristic value of the raw pipe on the exit side of the first pass, the actual rolling value of the raw pipe rolled in the previous plug mill, and the cross-sectional area characteristic value of the raw pipe on the exit side of the second pass. It is characterized by calculating and setting the roll rolling position of each pass using the target value so that the average wall thickness value of the raw pipe on the exit side of each pass of the raw pipe to be rolled this time in the plug mill is constant. This is a method for controlling the average wall thickness of pipes in plug mills.

FIG. 1 shows a flowchart according to an embodiment of the present invention. The cross-sectional area characteristic value used instead of the average wall thickness value of the raw pipe is the weight per unit length (hereinafter abbreviated as unit weight) calculated from the weight value of the raw pipe and each actual measurement value of the length value of the raw pipe at each mill. ). After the raw materials or raw tubes come out of the heating furnace 1, they are weighed one by one using a weighing machine, and the weighed weight W is input into the calculator 2 and stored in correspondence with the number of the raw material or raw tube. When the perforated raw pipe is rolled in the elongate mill 3 which is a pre-process of the plug mill pipe 4, the actual value S ₀ of the roll rolling position of the elongate mill 3 at that time and the raw pipe on the exit side after rolling are The actual length value _L1 is input to the computer 2 and stored. Therefore, the Elongate Mill 3, which is the pre-process of the plug mill,
The unit weight on the exit side is expressed as (W/L ₀ ).

When the raw tube reaches the front of the plug mill (for example, at the timing when it is inserted into the plug mill pass line), the already stored information and the target value of the unit weight of the raw tube at the exit side of the first pass of the plug mill (W/L ₁ ) and the actual value of the unit weight of the raw pipe that has already been rolled by the plug used by the raw pipe, calculate the roll rolling position of the first pass where the target value is the unit weight of the raw pipe on the exit side of the first pass. Calculate and set the value (S ₁ ).

S ₁ ⁽ⁱ⁾ =a ₁ (W/L ₁ ) ⁽ⁱ⁾ +b ₁ (W/L ₀ ) ⁽ⁱ⁾ +d ₁ S ₀ ^(
i) +c ₁ + ₁ ^(i-1) ...(1) where c ₁ is a constant term for one pass, i is the rolling number with the same plug used, and ε ^(i-1) is the rolling number with the same plug used already. This is a correction term related to the original pipe, and is defined, for example, as follows.

Many other forms are possible, such as ₁ ^(i-1) = ε ₁ ^(i-1) , ₁ ^(i-1) = α・₁ ^(i-1) , etc.

Each coefficient a ₁ , b ₁ , c ₁ , and d ₁ in equation (1) is determined based on the value obtained by subjecting the actual values of each factor in equation (1) to multiple regression analysis. Further, when each of the above coefficients is modified for each rolling using adaptive control, it is not necessary to determine them very strictly, so there is no need to be very careful. Considering that equation (1) includes a constant term and that we want to incorporate an integral element, it is actually preferable to use the following equation (3), which incorporates the actual values from the previous rolling. .

S ₁ ⁽ⁱ⁾ −S ₁ ^(i-1) = a ₁ {(W/L ₁ ) ⁽ⁱ⁾ −(W/L ₁ ) ^(
i-1) } +b ₁ {(W/L ₀ ) ⁽ⁱ⁾ −(W/L ₀ ) ^(i-1) } +d ₁ {S ₀ ⁽ⁱ⁾ −S ₀ ^(i-1) }+ ₁ ^{( i-1)} ...(3) Here, S ₁ ^(i-1) is the actual value of the roll rolling position of the front blank pipe, i is the rolling serial number for the same plug used, and it is the same as that of the recent automatic plug changing device. Plug mills with attached plugs usually use two sets of plugs, and the rolling characteristics differ depending on the set of plugs, so if you look at the time series distribution, it will look like Figure 2.If you look at the simple rolling order, there will be large fluctuations, but the rolling characteristics will differ depending on the set of plugs. This is because each set is stable.

Equation (3) handles wear of the rolls and plugs and changes in the friction coefficient over time in a feedback manner, and can respond to changes in rolling conditions by modifying the coefficient through adaptive control, making it possible to obtain high accuracy and high operating rates. I can do it. After 1-pass rolling, the actual value of the roll reduction position (S ₁ ) and the actual length value of the raw pipe on the 1-pass exit side (L ₁ ) are input into the computer and ₁ ^(i-1) is updated.

For the second pass, the actual value of the unit weight on the output side of the first pass (W/L ₁ ) ⁽ⁱ⁾ and the target value of the unit weight on the output side of the second pass (W
/L ₂ ) and the actual value of the unit weight of the raw pipe that has already been rolled with the plug used by the raw pipe, calculate and set the calculated value (S ₂ ) of the roll rolling position for the second pass. .

S ₂ ⁽ⁱ⁾ =a ₂ (W/L ₂ ) ⁽ⁱ⁾ +b ₂ (W/L ₁ ) ⁽ⁱ⁾ +c ₂
+ ₂ ^(i-1) …(4) S ₂ ⁽ⁱ⁾ −S ₂ ^(i-1) =a ₂ {(W/L ₂ ) ⁽ⁱ⁾ −(W/L ₂
) ^(i-1) } +b ₂ {(W/L ₁ ) ⁽ⁱ⁾ −(W/L ₁ ) ^(i-1) } + ₂ ^(i-1) …(5) Here, i, ₂ ^{(i -1)} is a correction factor calculated using the same method as the first pass.For the same reason as the first pass, it is actually (5)
Preferably used in formula form. After two-pass rolling, the actual value of the roll reduction position (S ₂ ) and the actual length value (L ₂ ) of the raw pipe on the exit side of the two-pass are input into a computer and stored.

While repeating this kind of control, when the timing of plug replacement and the set value of the plug diameter to be used at that time are sent from the console to the computer, the above-mentioned correction terms ₁ ^(i-1) and ₂ ^(i-1) are added. At the same time as resetting, the diameter difference between the previously used plug and the next used plug is calculated, and if it is not zero, the calculated value of the roll reduction position is corrected according to the diameter difference.

In addition, the difference in the target value of the unit weight of the raw pipe on the exit side for each pass {(W/L ₁ ) ⁽ⁱ⁾ −(W/L ₁ ) ^(i-1) } and {(W
/L ₂ ) ⁽ⁱ⁾ −(W/L ₂ ) ^{(i-1 )} } is normally zero, but when securing the length is the priority in combination with control in a sizing mill and rolling of fixed length material, may be a non-zero value.

Note that the number of rolling passes in a plug mill is usually two, but even in the case of three passes, the roll rolling position for the third pass can be calculated and set by the same method as in the case of two passes.

FIG. 3 and FIG. 4 are charts showing the results of verifying the validity of the above-mentioned equations (1) and (4) using actual rolling data. The horizontal axis in Figure 3 is the actual measured value of weight per unit length on the outlet side of one pass of the plug mill.
The vertical axis is the value obtained by substituting the actual data into the terms other than the first term on the right side of equation (1) and back calculating W/L ₁ in the first term on the right side. The plot in the figure shows the calculated unit weight corresponding to the measured unit weight of a pipe with an outer diameter of 257 mm, and the deviation from the center line at an angle of 45° shows the deviation between the measured unit weight and the calculated unit weight. What this figure means is that the first term on the right side of equation (1) W/
The actual unit weight obtained by rolling with the roll reduction position S ₁ calculated by giving the target unit weight on the 1-pass exit side to L ₁ is within the range of deviation from the target unit weight as shown in Figure 3. This means that it falls within the range of . In other words, when the control method of the present invention is not applied, the actual measured unit weight on the output side of one pass is approximately 4 kg/
m (46.5 to 50.5 Kg), whereas when the control method of the present invention is applied, the fluctuation range of the actual measured unit weight is within the range of approximately 2 Kg/m or less (within the deviation indicated by the broken line in the figure). This means that the validity of equation (1) is proved by this.

Figure 4 is expressed in the same way as Figure 3, the horizontal axis is the actual measured value of weight per unit length on the plug mill 2-pass exit side, and the vertical axis is the weight excluding the first term on the right side of equation (4). This is the value obtained by substituting the actual data into the term and back calculating W/L ₂ of the first term on the right side. The plot in the figure shows the calculated unit weight corresponding to the measured unit weight of the same pipe as in Figure 3, and the deviation from the center line at an angle of 45° is the deviation between the measured unit weight and the calculated unit weight. show. What this diagram means is (4)
The measured unit weight obtained by rolling with the roll reduction position S ₂ calculated by giving the target unit weight on the 2-pass exit side to W/L ₂ in the first term on the right side of the equation is as shown in Figure 4 with respect to the target unit weight. This means that the deviation is within the range shown in . In other words, when the control method of the present invention is not applied, the measured unit weight on the 2-pass outlet side fluctuates in the range of approximately 2 kg/m (44.5 to 46.5 Kg/m), whereas when the control method of the present invention is applied. In this case, the variation range of the actual measured unit weight is approximately 1Kg/m
This means that the deviation is within the following (within the deviation indicated by the dashed-dotted line in the figure), and the validity of equation (4) is thus proven.

As described above, according to the present invention, the average wall thickness is This allows highly accurate control to keep the value constant.

[Brief explanation of the drawing]

Fig. 1 is a flowchart of control according to the present invention, Fig. 2 is a diagram for explaining the rolling characteristics of each plug, and Figs. 3 and 4 show the target unit weight and This is an example of actual data showing the validity of the relational expression for the roll reduction position. 1...Heating furnace, 2...Calculator, 3...Elongate mill, 4...Plug mill.

Claims (1)

[Claims] 1 In the Mannesmann plug mill pipe manufacturing method, in which the average wall thickness of the raw pipe on the exit side of the plug mill is kept constant, the first pass is based on the actual value of the roll reduction position in the elongate mill, which is the previous process, and the actual value of the roll reduction position on the exit side of the mill. The actual value of the cross-sectional area characteristic value of the raw pipe, the actual rolling value of the raw pipe rolled in the plug mill last time using the same plug, and the target value of the cross-sectional area characteristic value of the raw pipe on the output side of the first pass. The second pass uses the characteristic value of the cross-sectional area of the raw pipe on the exit side of the first pass, the actual rolling value of the raw pipe rolled in the plug mill last time using the same plug, and the cross-sectional area of the raw pipe on the exit side of the second pass. Using the target value of the characteristic value, calculate and set the roll rolling position of each pass so that the average wall thickness value of the raw pipe on the exit side of each pass of the raw pipe to be rolled this time in the plug mill is constant. A method for controlling the average wall thickness of a pipe in a plug mill, which is characterized by: