JPH0466226A - Method for predicting size of furrowing on tension leveler and method for deciding driving condition - Google Patents

Abstract

PURPOSE:To improve the surface quality of band plate by modeling the movement for correcting the band plate on the tension leveler and predicting the size of furrowing. CONSTITUTION:By modeling the movement of the band plate S being bent and bent back with the correcting rolls WR1, WR2, predicting the size of furrowing generated on the band plate S from the model equation applying the plate thickness of band plate S, the yield stress or proof stress, the yield elongation, the unit tension, the length of band plate between the correcting rolls, the radius of correcting roll and the intermesh, the driving condition for the tension leveler is decided so as to enter this predicting value in the prescribed range. Therefore, the quality of the surface of band plate can be kept highly.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tension leveler used for straightening metal strips such as hot-rolled steel strips. When correcting the shape of the board,
This invention relates to a technique for preventing uneven defects occurring on the surface of a strip.

<Prior Art> Tension levelers have conventionally been used to correct the shape of metal bands IN (hereinafter referred to as band plates) such as hot-rolled steel plates, and to descale them prior to pickling.

This tension leveler applies bending strain to the strip by winding it around a plurality of straightening rolls arranged sequentially in the direction of movement of the strip at the top and bottom of the strip. control the speed
At the same time, tension is applied to the strip to impart a required elongation strain, thereby correcting defects in the shape of the strip in the width direction and longitudinal direction.

However, when straightening a strip using such a tension leveler, uneven defects may remain on the surface of the strip after straightening.

Conventionally, this irregularity defect is called a chatter mark or a buckle, and literature analyzing the cause of its occurrence has been published.For example, "Plasticity and Processing Vol.

10 N [1107 (1969-12) p 885~
According to ``Experiments and Analysis of Tensigon Leveler 911'', the cause of chatter marks is due to differences in the temporary shape caused by vibrations during operation (tension vibration), and it is thought that they can be prevented by improving operating conditions. There is.

In addition, the causes of chatter marks are tension vibration and opening 58.
-151918, 59-76622, 59-1
No. 37121, No. 60-121020, No. 61-38
Techniques such as Japanese Patent No. 713 are disclosed.

Furthermore, “Plasticity and Processing Vo1.14 N[L154 (
197341) p904-911 and Vol, 20
NCL218 (1979-3) p 192-199
According to ``Experiments on Chatter Marks Caused by Tensilin Levelers'', undulations that become peaks of chatter marks have already occurred in the middle of roll winding, and roll winding is unstable due to reverse bending at the outlet. It is said that chatter marks occur or become accentuated due to this phenomenon.

<Problem to be solved by the invention> However, the pitch etc. of uneven defects that occur on the surface of the strip do not necessarily depend on the threading speed or the tension fluctuation cycle, and can be corrected by suppressing tension vibration and II mechanical vibration as much as possible. Even if this is done, uneven defects (hereinafter referred to as fold wrinkles) may remain on the surface of the strip.

These wrinkles become a big problem when the surface quality of the strip is strictly required in recent years, and cannot be solved by the techniques disclosed in the above-mentioned publications.

Therefore, especially when hot-rolled steel sheets are shipped as they are pickled, in order to satisfy strict quality requirements, the shape is corrected using a skin bath mill before or after pickling without using a tensilin leveler. This added extra steps to the normal processing steps, causing various problems such as an increase in production steps and delays in delivery.

In addition, it has been analyzed that chatter marks occur due to instability caused by reverse bending of the board, but in this case as well, the pitch and depth of fold wrinkles have not been quantitatively understood, and therefore tension leveling It has not yet reached the point where it is possible to set operating conditions.

The present invention solves the vJB problem of the conventional technology by analyzing a model of the generation process of tatami wrinkles and quantitatively understanding the size of the tatami wrinkles that occur, thereby making it possible to effectively use the tensidan leveler. The purpose is to provide technology that can be used.

Means for Solving the Problem> The present invention relates to a method for predicting the size of tatami wrinkles in a Tensidin leveler. It is assumed that the rod has a length equivalent to the length of the strip, and the area that does not yield in compression when bent back is considered to be an elastic floor, and when the rod is placed on the elastic floor in the longitudinal direction of the strip, The band is modeled assuming the phenomenon that causes bending, and is based on a model equation that uses the thickness of the band, yield stress or yield strength, yield elongation, unit tension, straightening roll length, straightening roll radius, and intermesh. By predicting the pitch and/or depth of the fold wrinkles that occur on the board, the method for determining the operating conditions of the tension leveler is to make sure that the predicted pitch and/or depth of the fold wrinkles is below a predetermined value. The problem of the prior art was solved by determining the values of the unit tension or plastic elongation of the intermesh of the straightening roll and the strip plate.

For Kusaku The present invention will be explained in detail with reference to FIGS. 1 to 5.

The present inventors modeled and investigated the behavior of a strip when it undergoes bending straightening in a Tensigin leveler.

Fig. 1 shows an example of the configuration of a Tensigin leveler, in which two support rolls SR, SRx and two straightening rolls WR, WR, are placed above and below a strip S in the traveling direction of the strip Fi, S (arrow F
), the band Fis is wound around both straightening rolls WR, WR, with a required intermesh IM to impart bending strain, and its advancing speed is further controlled by a priddle roll (not shown). At the same time, tension is applied to give a predetermined elongation strain.

This state is shown in more detail in FIG. 2. In FIG. 2, the strip S is bent by the straightening roll WR+ on the entry side and then bent back between it and the next straightening roll WR.

The conditions in this case are the bending curvature radius ρ of the strip S, the intermesh IM, the strip length l between the two straightening rolls WR, WR, and the vi positive roll radius R.

The surface of the strip S has knot-like unevenness, that is, wrinkles.

Here, as a mechanism for generating fold wrinkles, in the process where the strip is wrapped around the straightening roll, the surface of the strip on the non-contact side (outer surface) with the straightening roll undergoes plastic deformation due to bending and tension. It was assumed that this is nothing but plastic instability behavior that occurs due to compressive deformation caused by the surface in contact with the roll being subjected to compression deformation (reverse bending), that is, buckling deformation of the strip surface.

Then, a schematic analysis was performed as shown in FIG. First, the outer surface SF of the strip plate bent as shown in part A shown in FIG. 2 undergoes tensile yielding and undergoes plastic elongation as shown in FIG. 3(a). Next, when this part leaves the straightening roll, it is bent back and undergoes compressive yielding as shown in Figure 3 (axis), and when this yield stress reaches the buckling limit, Figure 3 (C)
As shown in FIG. 2, uneven folds are formed, and concave portions are generated as shown in section B in FIG. 2, and these form several knots of pitch L within the length l of the strip.

Therefore, we considered the range where this It1 phenomenon occurs as a bar with a length corresponding to the length l of the strip between the straightening rolls, and considered its thickness as the range where compression yields, and the other part as an elastic bed. .

Under these assumptions, a model analysis was performed on the assumption that the rods were placed in close contact with each other on an elastic floor with their lengths facing in the longitudinal direction of the strip.

FIG. 4(b) shows the distribution of plastic strain when the strip is bent, and it can be seen that plastic strain ε due to tensile yield exists on the outer surface of the strip. ε6 is plastic strain due to compressive yield on the inner surface, but it is very small.

FIG. 4(c) shows the distribution of plastic strain when the strip is bent back.

In the figure, the range η×L/2 is the range of compressive yield considered as the thickness of the bar, and the other part is the range considered as the elastic bed. And V is the plasticity modulus of the strip, where, σ: Unit tension σy: Yield stress ρ: Working curvature radius ε, Bi-elastic elongation = σ, /E E: Young's modulus The model assumed in this way is As shown in Figure 5, the compressive load P per unit width when the rod subjected to this compression buckles is:
2).

In this case, buckling is caused by the energy ΔU in the simple compression deformation mode and the energy ΔU in the bending deformation mode on the elastic floor.
This occurs when the sum of Uh and the deformation energy ΔU of the elastic floor become equal.

Δυ, −ΔUb+Uf −・−・−・−(
3) Therefore, assume the deformation of the rod using the following equations and find these energies.

Pg” Bending energy ΔU of the rod.

Here, this is the number of nodes in the length l of the rod, that is, nm1t
/L.

(i) Compression energy of the rod ΔU1 Length l of the rod undergoing deformation as shown in equation (3)
The amount of contraction Δl is ff13 where, ■: Amount of moment of inertia of cross section: Bending moment of the bar G1ft Deformation energy of the elastic floor ΔU.

If the spring constant of the elastic floor is β, then the compressive energy ΔU is as follows: ΔU1 = P ・Δ1 (3) From formula ~■, the load P at the time of buckling is calculated as , l ) ·--------- · - (8) Furthermore, the critical load Pcr that causes buckling is determined as the value when one of a1 to am is 0 (the others are set to 0).

・−・・−・・−・ (9) Here, find the value of n. When β takes the value when n moves from nn to nn+1, the following formula 〇I holds true.

π'El Therefore, once the value of β is determined, the value of n can be determined. In the case of a tension leveler, it is thought that it will buckle in a state where it has already yielded, so E→EP and β2EP (EP:
Considering that the critical Young's modulus at the time of buckling), the equation (OU) becomes as follows.

=n"(n"+1)"・-- can.

Next, the deflection of the rod, that is, the depth δ of the wrinkles, is determined from n given by the formula 00.

This can be obtained from the following equation 21 if the strain difference Δε between the front and back surfaces of the inelastic beam is given.

π! h In this case, Δε is given as η °− Δε= ρ, and therefore, the depth δ of the fold wrinkles is calculated from the formula 00 as described above. It becomes possible to quantitatively predict the pitch L and the depth δ from the equation.

Then, the operating conditions of the tension leveler are determined so that the predicted pitch L and depth δ of the fold wrinkles satisfy the surface quality required of the strip plate to be corrected by the tension leveler.

In other words, the intermesh IM of the straightening roll is adjusted so that the pitch and depth δ of the tatami wrinkles is less than a predetermined value, and the unit tension σi1 of the band plate or the plastic elongation rate ε is set instead of this unit tension σ. By setting the speed of the priddle rolls and straightening to obtain the desired surface quality, it is possible to obtain a strip with excellent surface quality.

<Example> Regarding the strip plate shown below, the pitch L and depth δ of the fold wrinkles generated were determined using the model equation shown in the following equation.

Target band Low carbon steel plate (hot rolled steel plate) Plate thickness t = 4.5 ■ Young's modulus E = 2. I x 10 kgf/
mj Yield stress σy = 30kgf/mj Tension leveler straightening roll radius = 40mm Straightening roll spacing F, P-90mm The results are shown in Figure 6. Figure 6(a) shows the tatami wrinkles obtained under the above conditions. This is the relationship between the depth δ and the intermesh IM, and similarly, FIG. 6(b) is the relationship between the pitch L of the fold wrinkles. Then, the target strip was corrected by changing the intermesh, and then the depth of the tatami wrinkles δ was actually measured.
In this case, the plastic elongation rate ε was corrected at two levels of 0.5% and 2.0%, and the O mark indicates ε. = 0.5%, the x mark is ε. -2.0%, it can be seen that both cases match well with the predicted values.

Furthermore, in view of the quality requirements of the target strip, the range of specifications was limited as follows.

(il) To have sufficient shape correction ability, the plastic elongation rate ε is set to 0.3% or more.

1ii1 To avoid impairing the quality of the material, the plastic elongation rate ε is limited to 1.1% or less.

Gi9 must have sufficient descaling ability; for this purpose, an intermesh IM of 1O- or higher is required.

In the case of this target strip, the depth δ of the wrinkles is 2.9n
Below, there was a condition that the pitch L had to be 2.3 pitches or less.

The operating conditions of the tensigine leveler under such constraints are shown in Fig. 7. Fig. 7(a) shows the relationship between the depth of fold wrinkles and the intermesh under the above conditions.
Similarly, c) is the relationship between the fold pitch and the intermesh, and in both cases, the shaded area is the range that satisfies the above conditions.

In this case, the intermesh is 1 for the fold wrinkle depth.
Up to 3.5 pitches are allowed, but 1 for tatami-jiwa pitches.
The limit is one cabinet. However, if emphasis is placed on descaling ability, it is better to make the intermesh a little larger, so 1
The plastic elongation rate ε was determined by strictly controlling the tension. 0.
It was set to be in the range of 5 to 1.0%.

As described above, when the operating conditions of the Tensilon leveler were determined and hot-rolled steel sheets were straightened, the shape straightening effect and descaling were good, and there were no problems with the quality of the steel sheet surface.

Therefore, a separate process using a skin pass mill is no longer necessary.

<Effects of the Invention> As described above, the present invention can quantitatively predict the pitch and depth of wrinkles that occur when straightening a strip using a tension leveler, and furthermore, it is possible to quantitatively predict the pitch and depth of fold wrinkles that occur when straightening a strip using a tension leveler. Since the operating conditions of the leveler can be determined so that the leveler falls within the range of It is also possible to eliminate the processing step using a mill, and the economic effects such as reduced production costs and shortened delivery times are truly significant.

[Brief explanation of the drawing]

Fig. 1 is an example of the configuration of a tensile leveler, Fig. 2 is an explanatory diagram of bending and unbending of a strip by a straightening roller, Fig. 3 is an explanatory diagram of a schematic analysis in the present invention, and Fig. 4 is an illustration of the occurrence of damage to the strip. FIG. 2 is an explanatory diagram of the plastic strain distribution, in which (a) is the time of bending, and b) is the time of unbending. FIG. 5 is a diagram showing the model of the present invention, and FIG. 6 is a diagram showing a comparison between the predicted value and the actual measured value of the size of fold wrinkles according to the present invention. (bJ is a diagram showing the relationship between the intermesh and the pitch of the fold wrinkles. Figure 7 is an example of a method for determining operating conditions for a tensile leveler. (b) is a diagram showing the relationship between the intermesh and the pitch of the tatami wrinkles. Intermesh IM (Ilm) (b') Intermesh IM (m ) (a) Intermesh IM (■) Figure (b) Intermesh IM (m)

Claims (2)

[Claims] (1) A method for predicting the size of fold wrinkles in a tension leveler, in which a strip is once bent by a straightening roll,
Then, the range that yields in compression when it is bent back is regarded as a bar with a length corresponding to the length of the strip between the straightening rolls, and the range that does not yield in compression when it is bent back is regarded as an elastic bed, and the bar is elastic. The model assumes the phenomenon of compressive buckling when the strip is placed on the floor in the longitudinal direction, and the strip thickness, yield stress or yield strength, yield elongation, unit tension,
The size of fold wrinkles in a tension leveler, which is characterized by predicting the pitch and/or depth of fold wrinkles occurring in a strip from a model equation using the length of the strip between straightening rolls, the radius of the straightening roll, and the intermesh. prediction method. (2) A method for determining operating conditions in a tension leveler, in which a strip is once bent by straightening rolls, and then bent back to yield compression by a rod with a length corresponding to the length of the strip between the straightening rolls. , and the range that does not yield in compression when bent back is regarded as an elastic floor, and the rod is modeled assuming a phenomenon in which compression buckling occurs when placed in the longitudinal direction of the strip on the elastic floor, and the thickness of the strip,
The pitch and/or depth of wrinkles that occur in the strip is predicted from a model formula using the yield stress or yield strength, yield elongation, unit tension, strip length between straightening rolls, straightening roll radius, and intermesh, and this prediction is performed. Operating conditions in a tension leveler characterized by determining the unit tension or plastic elongation of the intermesh of the straightening roll and the strip so that the pitch and/or depth of the folded wrinkles is less than a predetermined value. How to decide.