JPH0218167B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in an automatic plate thickness control device for controlling plate thickness in a multi-stage continuous rolling mill having a plurality of rolling stands. Conventionally, there has been a device of this type as shown in FIG. In the figure, 1 is a work roll, 2
3 is a back-up roll, 3 is a roll opening automatic positioning device, 4 is a rolling mill main drive speed control system, 5 is a rolling force detector (hereinafter referred to as a load cell), and 6 is a gauge meter type automatic plate thickness controller for each stand. Automatic plate thickness control (AGC) is performed based on the principle shown in the principle block diagram of Fig. 2 without considering the rolling force mix between the stands installed in the stand. In Fig. 2, 21 is an automatic position setting device (APC) characteristic model, 22 is a rolling mill characteristic model, 23 is a mill (elastic) constant, 24 is a lock-on value memory, 25 is a gain (influence coefficient), and 26 is a tuning The variation in thickness at the exit side, the amount of screw movement, and the variation in rolling force at each stand are given by the following gauge meter formula. △h=△P/M+△S......(1) △h; Output plate thickness variation △P; Rolling force variation △S; Screw movement amount M; Mill constant Therefore, in the automatic plate thickness control device, (1) In order to make the thickness variation on the outlet side of the formula zero, if the roll opening setting reference is given to the automatic roll opening positioning device shown in Fig. 1 and 3 so that △S = -△P/M, the output of each stand can be adjusted to zero. It is possible to reduce the side plate thickness deviation to zero. Next, the operation will be explained. In Figure 1,
When the material to be rolled 5 arrives at the rolling stands of each stage and is bitten by the work rolls 1, a rolling load P is generated according to the rolling mill characteristics 22 in FIG. 2, and the rolling force detector 5
(Fig. 1). For this rolling load P, the tip plate thickness of the rolled material S is calculated using the Mill (elasticity) constant 23 and the tuning rate 26, and is stored as a lock-on value. As rolling progresses and load fluctuations occur, plate thickness deviation Δh ^c is calculated, and ΔS is manipulated until Δh ^c becomes zero. As a result, the screw movement ΔS is expressed by the following equation (2). ΔS=−α·ΔP/M (2) By substituting equation (2) into equation (1), equation (3) for the control deviation of the exit plate thickness due to AGC control can be obtained. △h=(1-α)・△P/M...(3) As can be seen from equation (3), if the tuning rate α is set to 1, the variation in the thickness of the outlet side should be reduced to zero.
If we look at the actual usage of conventional equipment, it is normal that it is used with α<1 due to factors such as rolling force fluctuations. To explain this rolling force fluctuation in more detail (considering the case of α=1), the rolling force decreases due to the local temperature drop of the rolled material (S) such as skid marks.
When Pa increases, the gauge meter type AGC detects that the plate thickness increases by ΔPa/M and moves the screw by ΔS to counteract this increase. As is well known, if the plastic modulus of the material to be rolled is Q, the rolling load changes by -[MQ/(M+Q)]ΔS due to the screw movement by ΔS. Therefore, in the end, the screw is −(M
+Q)/M・△Pd/M, and the rolling load increases by (M+Q)/M・△Pd. Thus, the plate thickness deviation on the exit side can be limited to zero, but the rolling load is (M+Q)/M・△Pd,
Compared to △Pd without AGC, (M+Q)/
M times, which causes variations in the crown and shape of the finished product, as will be explained in detail below. For this reason, on the contrary, it is necessary to use α < 1 within a range where crown fluctuations and shape fluctuations are allowable, and as a result, there is an inconvenience that the plate thickness deviation according to equation (3) must remain. This invention was made to eliminate the above-mentioned drawbacks of the conventional method. By keeping the rolling load variation rate at each stand at a constant value, it is possible to prevent deterioration of the product shape and reduce the load on a specific stand. It is an object of the present invention to provide an automatic plate thickness control device that prevents deterioration of product quality due to concentration and enables control such that the plate thickness at the exit side of the final stand becomes a target value (plate thickness fluctuation is zero). Now, in order to maintain the crown, flatness, etc. of the finished product, it is important to minimize the load fluctuations in the final stand and to keep the load fluctuations between the stands at a predetermined ratio. The exit plate crown C _ri in hot rolling is expressed by the following equation (4), C _ri = α _pi・Pi−α _CBi・R _CBi −α _CWi・R _CWi −
α _Bi・P _Bi ……(4) However, Pi: Rolling load, P _Bi : Bending force,
R _CBi : Backup roll crown, R _CWi : Work roll crown, α _pi , α _CBi , α _CWi , α _Bi : Coefficient determined by rolling conditions, i: Stand number. C _ri = h _Ci − h _ei However, h _Ci , h _ei : Thickness of the central part and end of the plate on the exit side of the i-stand Considering the crown variation within one plate, Equation (4) is
R _CBi and R _CWi are almost constant, and the bending force P _Bi
Since operations are not normally performed within the plate, it is necessary to minimize load fluctuations in the rolling load Pi. This is particularly important in the final stand where the final crown value of the product is determined. Furthermore, when considering the flatness of a product, the relative crown constant condition (formula (5)) for flatness fibers is well known. C _ri −1/h _i −1=C _ri /h _i ……(5) However, h _i : average plate thickness at exit side of i stand (=2h _Ci + h _ei /3) From formulas (4) and (5), In order to maintain the rolling strength, the rolling load variation ΔPi must satisfy the following equation (6) when the rolling stand specifications are the same. |△Pi−1/h _i −1−△Pi/h _i |<ε …(6) ε: Limit value to prevent flatness change. Considering the above conditions, the present invention shows a case where the following equation (7) is used as a control equation for load fluctuation. △Pi/miPi=constant...(7) In equation (7), Pi is the initial rolling load, and △Pi means the variation from the initial load. mi is a parameter (positive value) for each stand, and for stands that need to satisfy the condition of equation (6), mi = h _i /Pi, and for the final stand where you want to reduce load fluctuation, crown fluctuation In order to satisfy the tolerance value of load fluctuation determined by the tolerance value.
Select mi smaller than other stands. As shown in equations (17) to (19) below, the rolling load fluctuation of each stand is mostly due to the deformation resistance Ki of the rolled material.
Its value can be predicted by the rolling schedule, and the plate crown variation associated with it can also be predicted from equation (4).Conversely, the rolling It is possible to predict the limit value of load fluctuation and determine mi at the final stand accordingly. In addition to the above theoretical basis, the value of mi should also be determined based on the experience of actual operation, so the optimal value for operation should be determined and stratified according to the product dimensions, steel type, etc. and stored in a table. The material to be rolled shall be extracted according to the rolling schedule of the material to be rolled. Next, the principle of operation of the automatic plate thickness control device of the present invention will be explained. This invention is applicable to a rolling mill with any number of stands, but for the sake of simplicity, a three-stand continuous rolling mill will be described as an example. This invention controls the rolling load fluctuations described above by rationally selecting the tuning rate of AGC using a gauge meter. The rolling load fluctuations and plate thickness fluctuations using the gauge meter method will be explained in detail below. The rolling load Pi at each stand is the entrance plate thickness Hi,
It is given by the following equation (8) as a function of the outlet plate thickness h _i and the deformation resistance Ki. Pi＝1.15bi・Ki√( _−i )・Qp ……(8) However, Ri: Roll radius, Qp: Rolling force function, bi:
Plate Width Therefore, if we focus on the variation from the time of biting of the rolled material, △Pi=Q _Ki・△Ki−Qi・△h _i +Q _Hi・△Hi ……(9). However, Qki=∂Pi/∂Ki, Qi=∂Pi/∂h _i , Q _Hi =∂Pi/
∂Hi Also, from the gauge meter formula, △h _i = △Si + △Pi/Mi... (10) where Si: roll opening fluctuation, Mi: Mill constant From equation (2), which is the basis of gauge meter AGC control, △Si= −α _i・△Pi/Mi ……(11) However, αi: i stand gauge meter tuning rate From equations (9), (10), and (11), △Pi=1−ηi/1−αi・ηi {Q _Ki・△Ki＋Q _Hi・△Hi
} ...(12) h _i = (1-αi)・△Pi/Mi ...(13) However, ηi=Qi/Mi+Qi Influence coefficient Qi=∂Pi/∂h _i Plasticity coefficient (12), (13) Equations are the equations that give the load fluctuation and exit side plate thickness at the tuning rate αi, respectively. Now, since the load variation formula has been obtained above, the present invention will be explained in detail using this formula below. From equation (8), we obtain the following (14) for Q _Ki . Q _Ki = ∂Pi / ∂Ki = Pi / Ki ... (14) where Pi is the rolling load when the rolled material is bitten. Furthermore, due to the known property of deformation resistance, △Ki/Ki = △Ki-1/Ki-1... (15) Also, since the thickness of the exit side of the i stand is the thickness of the inlet side of the i+1 stand, △h _i = △Hi+1... (16) If we rearrange equation (12) for stands #1 to #3 using equations (14), (15), and (16), (for simplicity's sake, regardless of the discussion book, △H ₁ = 0) △P ₁ /P ₁ = 1-η ₁ /1-α ₁ η ₁・△K ₁ /K ₁ ... (17) △P ₂ /P ₂ = {1-η ₂ /1-α ₂ η ₂・1−η ₁ /1−α ₁
η ₁・1−α ₁ /M ₁・QH ₂・P ₁ /P ₂ +1−η ₂ /1−α ₂ η ₂ }・△K ₂ /K ₂ ...(18) △P ₃ /P ₃ = {1−η ₃ /1−α ₃ η ₃・1−η ₂ /1−α ₂
η ₂・1−η ₁ /1−α ₁ η ₁・1−α ₂ /M ₂・1−α ₁ /M ₁
QH ₃・QH ₂・P ₁ /P ₃ +1−η ₃ /1−α ₃ η ₃・1−η ₂ /1−α ₂ η ₂・1−
α ₂ /M・QH ₃・P ₂ /P ₃ +1−η ₃ /1−α ₃ η ₃ ｝△K ₃ /K
₃ ...(19) Also, if the control equation (7) for rolling load fluctuation is written for three stands, it becomes equation (20). △P ₁ /m ₁ P ₁ = △P ₂ /m ₂ P ₂ = △P ₃ /m 3 P _{3 ...} (20) (17) to (19) are three-dimensional simultaneous equations, and η ₁ ,
Since both Mi and Pi are constants that are determined at the time of initial setting or when the material is bitten, αi can be determined by providing three conditional expressions. Since the thickness variation on the exit side of the final stand (stand #3 in the above example) should be zero for the sake of product quality, if α ₃ = 1 is selected from equation (13), then by adding the condition of equation (20), α ₁ and α ₂ can be found. If formula (20) is applied to formulas (17), (18), and (19), each αi becomes the following (21) to (23). α ₁ = 1 + M ₁ /Q ₁ × (1-ε ₁₃ ) + (1-ε ₁₂ )・QH ₃ /
Q ₂・P ₂ /P ³ /1+QH ₃ /Q ₂・P ₂ /P ₃ +QH ₃・QH ₂ /Q ₂・Q ₁
・P ₁ /P ₃ ... (21) α ₂ = 1 + M ₂ /Q ₂ × (1 - ε ₂₃ ) + (ε ₂₁ - ε ₂₃ )・QH ₂
/Q ₁・P ₁ /P ₂ /1+QH ₃ /Q ₂・P ₂ /P ₃ +QH ₃・QH ₂ /Q ₂・Q
₁・P ₁ /P ₃ ... (22) α ₃ = 1 ... (23) However, ε _ij = mj / mi > 0 ... (24) In equations (21) and (22), the tuning rate αi The value may be more than 1, but it is a gauge meter method.
AGC becomes unstable when αi>1/ηi=1+Mi/Qi (25), and equation (21) clearly satisfies this. Regarding equation (22), finding the conditions to satisfy equation (25) is ε ₂₁ > (Q ₁ /QH ₂・P ₂ /P ₁ +1) (QH ₃ /Q ₂・P ₂ /P ₃ +ε
₂₃ ) ...(26) Equation (26) is obtained, and under normal rolling conditions, (26)
Since the formula is fully satisfied, it is impossible for the gauge meter AGC to become unstable at all. For example, if we take the latter three stands of hot rolling as an example, for a material with a product thickness of 2.7 mm and a strip width of about 1000 mm, P ₁ = 1200 TON Q ₁ = 550 TON/mm P ₂ = 1100 TON Q ₂ = 880 QH ₂ = 600 TON/mm mm P ₃ = 650TON Q ₃ = 1080 QH ₃ = 900TON/mm, and equation (26) becomes equation (27) ε ₂₁ <1.84ε ₂₃ +4.83 ...(27) ε ₂₁ = m ₁ /m ₂ = (△P ₂ /P ₂ ) / (△P ₁ /P ₁ ) and ε
Since the value of ₂₁ is usually selected close to 1, equation (27) is fully satisfied. If the tuning rate is determined using the above equations (21) to (23), the load movement fluctuation between stands will satisfy equation (26). Table 1 is a numerical example. (In this table, PU is an abbreviation for Per Unit.)

[Table] In Table 1, rows 1-1 to 1-5 are calculation conditions,
2-1 to 2-4 are examples of calculations of load fluctuations, outlet plate thickness fluctuations, etc. by the method of this invention. Rows 3-1 to 3-3 are
For the case without AGC (αi = 0), lines 4-1 to 4-
3 and rows 5-1 to 5-3 are conventional gauge meters
The cases of AGC are shown respectively. In this table, row 2-
Δh _iu in 4, 3-3, 4-3, and 5-3 indicates the outlet side plate thickness variation in each case normalized by the outlet side plate thickness variation in the case without AGC (αi=0). Comparing rows 2-4, 4-3, and 5-3 in Table 1, the thickness deviation at the exit side of the final stand using this method is zero, and αi = 1 (row 5-3) using the conventional method. It is clear that it has the same effect as the case. On the other hand, looking at the load fluctuations, comparing rows 2-3 and 5-2, the method of the present invention not only can significantly reduce the load fluctuations of the final stand compared to the conventional type (αi = 1), but also It has the important advantage of being able to maintain load fluctuations at a predetermined ratio. That is, (ΔP ₂ /P ₂ )/(ΔP ₁ /P ₁ )=0.973/1.216=0.8, (
ΔP ₂ /P ₂ ) / (ΔP ₁ /P ₁ ) = 0.584 / 1.216 = 0.48 Also, looking at lines 4-2 and 4-3, the conventional AGC
When the tuning rate αi is decreased (1 → 0.8)
Compared to the change in plate thickness on the exit side, the reduction in load change is not sufficient, and this is where conventional gauge meters are applied.
One of the limitations of AGC has been reached. As explained above, according to the present invention, it is possible to determine the tuning rate so that the variation in rolling load at each stand becomes a predetermined ratio between the stands, and the thickness deviation at the exit side of the final stand can be made zero, so that the average plate thickness can be reduced. This greatly contributes not only to the control of the crown but also to the improvement of the crown and flatness of the finished product shape quality. Next, an embodiment of the present invention will be described using FIG. 3. In Fig. 3, 1 is a work roll of a hot continuous rolling mill, 2 is a back-up roll, 3 is a roll opening automatic positioning device, 4 is a rolling mill main drive speed control system, and 5 is a rolling force detector (load cell). , 6 is a gauge meter type automatic plate thickness control device, 7 is a tuning rate calculating device according to the present invention, 8 is a setting calculator having a model for schedule calculation, etc., and S is a material to be rolled. This invention can be applied to a continuous rolling mill with any number of stands, but for simplicity, only three stands are shown in the figure. Now, when the material to be rolled reaches a predetermined position in front of the continuous stand, the schedule is calculated by the setting calculator 8 using a known method, and each equipment of the rolling mill is set to a predetermined state, and the tuning rate calculation device 7
Various parameters to calculate tuning rate αi
Give Qi, Q _Hi , Mi, mi, Pi _c . Here, Pi ^c is the predicted calculated value of the initial rolling load Pi. Furthermore, the value of mi is extracted according to the rolling schedule from the values stored in layers as described above. Immediately after the parameters are given, each stand tuning rate αi is determined using equations (21) to (23), and each stand gauge meter
is given to the AGC device 6. The reason why Pi ^c was used instead of the actual rolling load Pi to calculate αi was to calculate αi before the material was bitten, and even if Pi ^c was used, the error given to αi was small. When the material S is bitten into each stand work roll 1, each stand gauge meter AGC is carried out based on the principle shown in Fig. 2, and when the material S is bitten into the final stand, the actual rolling of all stands is started at that timing. Since the reaction force Pi is obtained, the tuning rate calculating device 7 recalculates αi using (21) to (23) and sets it in the gauge meter AGC6. Thereafter, each stand gauge meter AGC continues until the rolled material S passes through each stand. In the above embodiments, a continuous rolling mill was described, but a single-stand reversible rolling mill that performs multiple passes may be used, and the same effects as in the above embodiments can be obtained. As described above, according to the present invention, it is possible to maintain rolling load fluctuations at a predetermined ratio between stands in the longitudinal direction of the material over the entire length, and it is possible to maintain not only the average thickness of the finished product but also the thickness distribution in the width direction. Not only can it contribute to improving shape quality such as certain crowns and flatness, but it can also contribute to improving plate thickness accuracy because it can minimize load fluctuations on the final stand and select a tuning ratio of 1. be.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a multi-stand continuous rolling mill equipped with a conventional automatic plate thickness control device, Fig. 2 is a principle diagram of gauge meter type automatic plate thickness control, and Fig. 3 is an example of an embodiment of the present invention. FIG. In the figure, 6 is a gauge meter type automatic plate thickness control device, 7 is a tuning rate calculation device, and 8 is a setting calculator. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A final stage rolling stand having a gauge meter type automatic plate thickness control means and having a tuning rate of 1, and two stages each having the gauge meter type automatic plate thickness control means. The above-mentioned front-stage rolling stands, storage means for individually storing the tuning ratios for setting each material to be rolled and each rolling condition in each of the front-stage rolling stands; and a retrieval means for retrieving the tuning rate from the storage means according to the rolling conditions and setting it in each of the pre-rolling stands, and for sequentially rolling the material to be rolled according to the set tuning rate. In the plate thickness control device, the settings for each of the preceding rolling stands are determined using the material of the material to be rolled, the rolling conditions in all the preceding rolling stands, and the rolling conditions in the final rolling stand. An automatic plate thickness control device comprising a calculation means for calculating the tuning rate.