JPH0564217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a system for predicting and warning the occurrence of heat buckles that occur in a steel strip annealed in a continuous annealing furnace.

Prior Art and Problems Heat buckles that occur in the steel strip in a continuous annealing furnace where the steel strip is annealed while being transported are caused by the fact that the size of the strip is wide and thin, and the operating conditions are such that the material is too wide and thin. It is known from experience that this is likely to occur when the plate temperature increases. Conventionally, furnace operators used intuition and experience to predict the occurrence of heat buckles based on operational and process data such as the size of the strip, strip temperature, and tension, and selected operating conditions to prevent such occurrence. I was getting used to it. However, since the quantitative relationship between operating conditions and the occurrence of heat buckles is not clear, it is difficult to make accurate predictions, and as a result, it has not been possible to reliably prevent the occurrence of heat buckles, leading to operational problems such as plate breakage and line stoppages.

There is also a method that focuses on tension and predicts the occurrence of heat buckles when the measured tension is greater than a predetermined value than the critical tension determined based on the steel strip temperature and the strip temperature difference in the strip width direction. The accuracy of prediction is low because it does not take into account factors such as temperature and temperature changes.

Purpose of the Invention In view of the above points, the present invention aims to prevent the occurrence of heat buckles and prevent operational troubles by providing a device that accurately predicts the occurrence of heat buckles and issues a warning to furnace operators. It is.

Structure of the Invention The present invention provides a system for predicting and warning the occurrence of heat buckles that occur in a steel strip that is annealed while being guided by crowned rolls in a continuous annealing furnace. and means for calculating the maximum width direction compressive stress of the steel strip using the width direction temperature distribution of the roll, means for calculating the buckling limit stress of the steel strip wound around the roll as a cylindrical shell, and the maximum width The present invention is characterized by comprising means for comparing the directional compressive stress and the buckling limit stress and generating an alarm when the former becomes larger than the latter, which will be explained in detail below with reference to examples. .

Embodiments of the Invention In a continuous annealing furnace, a steel strip is guided by in-furnace rolls and conveyed through the furnace while meandering up and down, and is heated and annealed during this conveyance. The roll is equipped with a crown so that the steel strip does not come off the roll (doesn't walk) and ensures stable threading.
Also, tension is applied to the steel strip. These are the causes of heat buckles. In other words, when tension is applied in the length direction of the steel strip, the steel strip contracts in the width direction (compressive stress is generated in the width direction), and if the roll has a crown, the compressive stress distribution becomes uneven in the width direction, causing the steel strip to shrink in the width direction. maximum in the center. Heating takes place in the furnace, and the temperature of each part of the rolls and steel strip changes according to the respective thermal time constants when operating conditions such as threading speed and furnace temperature change, and these also affect the stress distribution. give.

Figures 1 and 2 are diagrams explaining these.
0 is a steel strip, and 12 is an in-furnace roll having a crown as shown. If the roll has a crown, the steel strip guided by the roll will also curve along the crown. When tension is applied to the steel strip 10, compressive stress is generated in the width direction, but if the roll has a crown, the compressive stress distribution is not uniform, and as shown by curve 14, it is large at the center (σmax) and small at the periphery (σmin). becomes. In addition, as shown by curve 20 in Figure 2, the threading speed is
When lowering by t1, the temperature at the center of the steel plate T ₁ and the temperature at the center of the roll T ₃ will change as shown by curve 22, the temperature at the edge of the steel plate T ₂ will change as shown by curve 24, and the temperature at the roll end T ₄ will change as shown by curve 24. As shown at 26, the temperature rises according to the respective thermal time constants. When the roll temperature changes, the roll diameter changes as follows due to thermal expansion, causing a change in the crown.

D ₁ ′=D ₁ (1+αT ₄ ) D ₂ ′=D ₂ (1+αT ₃ ) ……(1) Here, D ₁ and D ₁ ′ are the outer diameter of the roll end before and after the temperature change, D ₂ , D ₂ ′ is the outer diameter of the roll center before and after the temperature change, and α is the coefficient of linear expansion. As shown in Fig. 2, during temperature change, T ₄ < T ₃ and T ₃ < T ₂ , so changes in compressive stress distribution due to roll diameter expansion and steel strip temperature distribution both occur in the direction of addition. As a result, the compressive stress distribution in the width direction of the steel strip becomes significantly non-uniform, as shown by curve 16 in FIG.

It is known from experience that heat buckles occur at the portion where the steel strip is wrapped around a roll. In the present invention, heat buckling is considered to be a problem of buckling of a cylindrical shell. As is well known, the buckling limit is expressed by the following formula.

σk={E/√3( ^1-2 )}・t/r...(2) However, according to the experimental results, buckling occurs at a value lower than the value of equation (2), so if Poisson's ratio ν is 0.3, In this case, the following equation is used in the present invention.

σk=(0.2-0.3)·E·t/r (3) where E is Young's modulus, t is plate thickness, and r is roll radius. As is well known, the Poisson's ratio ν is ν=σu′/σu (4) where σu is the stress in the longitudinal direction and σu′ is the stress in the width direction. It can be estimated that heat buckles occur when σu′/σk...(5). Assuming that the stress distribution follows the crown shape, σu' is calculated as follows.

When the temperature of the steel strip is uniform: If L is the distance between the centers of the upper and lower rolls that guide the steel strip that is conveyed in a meandering manner in the vertical direction in the furnace, and B is the width of the steel strip, the following formula holds true. . Here, the width B is B= as shown in Figure 3.
₁ + 2 ₂ , D ₁ and D ₂ are the ends of the roll 12,
The outer diameters of the central part, σu ₁ and σu ₂ are the stresses in the central and end parts of the steel strip (longitudinal stress caused by tension), σu is the longitudinal stress in equation (4) above, and σu ₁ and σu ₂ are the stress of the steel strip. This is the stress when uniformly distributed in the band.

₁・σu ₁ + ₂ (σu ₁ +σu ₂ ) =σu ( ₁ + 2 ₂ ) …(6) σu ₂ =σu ₁ −π/2(D ₂ −D ₁ )E /(L+π/2・D ₂ ) ...(7) By rearranging (6) and (7), the following formula is obtained.

σu ₁ =σu+π/2(D ₂ −D ₁ )・₂ /B・E/(L+π/2・D ₂ )……(8) When there is a temperature difference in the width direction of the steel strip: Edge of the steel strip If the temperature is higher than the center by ΔT, σu ₁ and σu ₂ can be expressed by the following formula using the same concept as above.

σu ₁ =σu+π/2(D ₂ −D ₁ )+α・ΔT(L+π
/2D ₂ )/L+π/2・D ₂・₂ /B・E……(9) σu ₂ =σu−π/2(D ₂ −D ₁ )+α・ΔT(L+π/2D ₂
)/L+π/2D ₂・₁ + ₂ /B・E……(10) σu ₁ and σu 2 in equations (9) and ( ₁₀ ) are curve 16 in Figure 1.
As shown in these formulas, the temperature difference ΔT (=T ₂ − _{T 1} ) corresponds to σmax and σmin.
If there is, concentration of stress distribution in the center will be promoted. The product of σu ₁ multiplied by ν is the maximum width direction compressive force (σu′ mentioned above), and σu′=σu ₁・ν>σk (11) is the conditional expression for the generation of heat buckles.

From these results, heat buckles are more likely to occur when the steel strip tension is large and tension fluctuations occur due to acceleration and deceleration (because σu increases), when the steel strip temperature is high (E in equation (3) above decreases), and when the steel strip temperature is high (E in equation (3) above decreases). This is likely to occur when transient operational changes such as a rise in steel strip temperature (ΔT increases) occur, and when the plate width B is large and the plate thickness t is small ( ₂ in the above equation (8) is large, (3 ) is small)
Although it can be said that it is easy to occur, this matches the situation in which heat buckles occur in reality.

The present invention monitors the above equation (11) and issues an alarm when the equation holds true. An embodiment thereof is shown in FIG. 4. In this figure, 32 is a tension meter that measures the tension of the steel strip, 34 is a plate thermometer that measures the temperature in the width direction of the steel strip,
36 is a thermometer that measures the temperature in the width direction of the roll;
8 is a host computer, 44, 46, 48, 52 are arithmetic units, 54 is a comparator, and 56 is an alarm.

Temperature signal S1 obtained by the width direction plate thermometer 34
Using the material information I1 from the host computer 38, the calculator 44 calculates the Young's modulus E of the steel strip. Further, using the temperature signal S2 from the roll width direction thermometer 36, the calculator 46 calculates the roll crown as described in (1) above.
Calculate D ₁ ′ and D ₂ ′ in the equation. Also, the steel strip tension S4 from the tension meter 32 and the temperature signal _S1 from the plate thermometer 34
Using the material information I ₁ from the computer 38, the Young's modulus E, and the roll totals D ₁ ′ and D ₂ ′, the calculator 48 calculates the above (9).
σu ₁ is determined by the formula, and from this the stress in the steel plate width direction σu′=
Calculate σu ₁・ν. In addition, the arithmetic unit 52 uses the size information I2 (t, r in equation (3) above) from the host computer 38.
And the buckling limit stress σk is calculated using the Young's modulus E from the calculator 44. A comparator 54 compares these σk and σu', and causes an alarm 56 to issue an alarm if σu'>σk.

The temperature signal S2 may be actually measured by attaching a detection end such as a thermocouple to the roll, or an estimated value analytically calculated from the temperature distribution of the steel strip, the thermal inertia of the roll, etc. may be used. Also, tension gauge 32, plate thermometer 3
4. There may be a plurality of roll thermometers 36, etc., and the computing units 44, 46, 48, and 52 may be configured by hardware, but they may be realized by software using stored program computing units. Good too.

When the furnace operator hears the alarm from the alarm 56, he changes the operating conditions to prevent the occurrence of heat buckles and avoid operational troubles such as plate breakage and line stoppage.

Effects of the Invention As explained above, according to the present invention, the occurrence of heat buckles can be automatically predicted and an alarm can be issued, which greatly contributes to the stable and reliable operation of a continuous annealing furnace. Furthermore, in the present invention, a warning is issued to predict the occurrence of heat buckles when the maximum compressive stress in the width direction of the steel strip exceeds the buckling limit stress, so the crown of the roll and its temperature changes are taken into account, and a highly accurate predictive warning is provided. I can do it.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the stress generated in the steel strip, Fig. 2 is a curve diagram showing temperature changes in the steel strip and roll due to changes in the threading speed, and Fig. 3 is an explanatory diagram of stress calculation.
FIG. 4 is a block diagram showing an embodiment of the present invention. In the drawings, 10 is a steel strip, 12 is a roll, 48 is maximum width direction compressive stress calculation means, 52 is buckling limit stress calculation means, and 54 and 56 are comparison alarm means.

Claims (1)

[Scope of Claims] 1. A heat buckle occurrence prediction/warning device that occurs in a steel strip to be annealed while being guided by a crowned roll in a continuous annealing furnace, comprising: a tension applied to the steel strip; and means for calculating the maximum width direction compressive stress of the steel strip using the width direction temperature distribution of the roll, means for calculating the buckling limit stress of the steel strip wound around the roll as a cylindrical shell, and the maximum width 1. A heat buckle occurrence prediction/warning device comprising means for comparing directional compressive stress and buckling limit stress and generating an alarm when the former becomes greater than the latter.