JPS594924A - Edge drop correcting method - Google Patents

Abstract

PURPOSE:To eliminate necessity of edge trimming by performing stretch bending on rolled strip and giving specified plastic elongation and thereby practically eliminating edge drop of the metallic strip. CONSTITUTION:When a metallic plate is rolled, the thickness is reduced suddenly in the edge of the plate. The metallic strip in which edge drop is caused by rolling is stretched and bent by, for instance, a tension leveller to give plastic elongation corresponding to the amount of edge drop. Thus, edge drop of the metallic strip is eliminated, edge trimming becomes unnecessary and the yield is improved.

Description

[Detailed description of the invention] The present invention relates to a method for straightening edge drops of metal strips.

In rolling a metal plate, edge drops are unavoidable because the degree of flattening of the rolls is small at the edges of the plate (hereinafter referred to as "edges"). That is, apart from the overall cross-sectional shape (medium convex, flat, middle gate, etc.), the thickness decreases rapidly from around the edge 10 to 50 of the board width to the edge. This plate thickness reduction amount (edge drop amount) is quite large (0 in large steel hot strips).
．． For this reason, in thin steel sheets such as real strip and cold strip, the vicinity of the edges is often trimmed, which is a major cause of a decrease in yield.

It can be said that no special measures have been taken to reduce edge drop in the current production line, and that it has been left unaddressed.

Several studies have been carried out on methods to reduce the rolling process by devising rolling methods, but as summarized in Table 1, the effects are small or difficult to implement.

Table 1: Known Edge Drop Reduction Methods The purpose of the present invention is to provide a novel and simple edge drop correction method, which flattens the area around the edge of a metal band and eliminates the need for conventional edge trimming. It is something.

According to the present invention, there is provided a method for straightening edge drops of a metal strip, characterized in that a predetermined plastic elongation corresponding to the amount of edge drop caused by rolling the metal strip is imparted to the metal strip by bending and tensioning.

The required plastic elongation for the edge drop amount δ is such that the amount of plate thickness reduction in the non-edge drop portion is 0.7 δ to 5 δ, as will be explained later.

The bending and tensioning process of the present invention can be performed, for example, with a tension leveler. Tension levelers are used for the purpose of correcting defects in the shape of inspection steel strips. That is,
During rolling, the elongation rate in the longitudinal direction varies slightly depending on the position in the width direction, which causes elongation in the middle, ear waves, etc. However, when a slight plastic elongation is applied with a Tensilon leveler, the portions that had little elongation during rolling will elongate. , the total elongation rate becomes approximately uniform in the width direction, and the strip becomes approximately flat. The elongation rate required to correct this shape defect is approximately 0.3~
When the elongation rate is 0.5% or less, there is almost no need for a higher elongation rate. For this reason, the current tension leveler has a maximum elongation rate of 1
Most of the products have specifications of about 1.5% and are used with a small elongation rate that is the minimum necessary, so the reduction in plate thickness and width shrinkage due to tension levelers is very small and is ignored in actual manufacturing. On the other hand, the elongation rate in the present invention is greater than that in the conventional tension leveling, and it is necessary to take into account the reduction in plate thickness and width.

The principles and embodiments of the invention will now be described with reference to the accompanying drawings.

The present invention is based on the finding from experiments conducted by the present inventors that ``bending and tensioning of a metal strip causes a phenomenon opposite to edge drop during rolling.''

First, this experiment will be explained. A cold-rolled steel plate with a thickness of 1.0 m and a width of 200 m was subjected to bending and tensile processing using a tension leveler with five φ50 work rolls while varying the reduction amount and tension, and the elongation rate and plate thickness were measured. In order to obtain a large elongation rate, the material was passed through a tension leveler multiple times, which is equivalent to passing through a tension leveler with a large number of rolls once. Since the cold-rolled steel sheet used was a slit product, there was no edge drop before the experiment, and the thickness was almost uniform in the width direction. This experiment revealed the following phenomenon.

(1) As the elongation increases, the plate thickness decreases, but the decrease in plate thickness is small only near the edges, so a phenomenon exactly opposite to edge drop (hereinafter referred to as edge-up phenomenon) occurs. The plate thickness uniformly decreases at least 20 degrees inside the edge.

(2) As the elongation increases, the difference in plate thickness between the edge and the area other than the edge increases monotonically. That is, even if the plate thickness near the edge is different from the inner part, the edge-up phenomenon progresses in the same way as in the case of the initial uniform plate thickness.

(3) Even if the reduction amount and tension of the tension leveler are changed, if the total elongation is kept the same by adjusting the number of passes through the tension leveler (i.e. the number of rolls), the edge amplifier phenomenon will occur to the same degree and the plate thickness distribution will be approximately the same. Become. (Some differences occur.) (4) The elongation in the longitudinal direction is uniform in the width direction. Therefore, no shape defects occur.

(5) Since the elongation in the longitudinal direction is uniform and the reduction in plate thickness is non-uniform, the strain in the width direction (width shrinkage) is non-uniform in the width direction due to the constant volume condition in plastic deformation of metal materials. The area near the edge is shrinking more than the inner area.

An example of measuring the plate thickness distribution in this experiment is shown in Figure 1.
The horizontal axis in FIG. 1 indicates the distance from the center of the plate width of the base material, and the vertical axis indicates the plate thickness value. Curves a-d show:

Curve a: Thickness curve of base material (cold rolled coil) B: Bending tension, thickness curve 01 after passing 10 rolls Bending tension, thickness curve 68 Bending tension after passing 30 rolls, after passing 60 rolls From the plate thickness in Figure 1, the phenomena (1) and (2) above are clearly observed. The strain in the width direction was calculated from the measured values of elongation and plate thickness under the condition of constant volume, and a graph is shown in Fig. 2 along with the plate thickness reduction rate.

Figure 2 was calculated from the experimental results after passing through 60 rolls shown in Figure 1. The curve e shows the strain in the plate thickness direction (plate thickness reduction), and the curve f shows the strain in the plate width direction (plate width shrinkage).

From Fig. 2, it is clear that the phenomenon (5) mentioned above in bending and tension processing is clearly observed, and that near the edges the width shrinkage occurs to the same degree as the plate thickness reduction, and that
It can be seen that the width shrinkage is small and close to plane distortion on the inside of 0 wa or more.

The above phenomenon is observed in materials with different thickness, width, yield stress, elastic modulus, etc., as well as in non-ferrous materials such as aluminum and copper, making it clear that this phenomenon is universal. became.

It has also become clear that this phenomenon occurs in exactly the same way even in strips with edge drops.

The above experimental results show that edge drop can be almost canceled by applying an appropriate amount of plastic elongation through bending and tension.

The amount of plastic elongation required to cancel edge drop is determined by the plate thickness,
Varies depending on conditions such as material. When the esociation phenomenon occurs significantly, the required plastic elongation becomes smaller. From experiments conducted with various materials and under various conditions, the amount of thickness reduction in the non-edge drop part required to cancel the edge drop is usually 1. It became clear that the value was in the range of 5δ to 5δ. Therefore, a plastic elongation that reduces the plate thickness by 1.5 δ to 5 δ is given by bending and tension, and the magnitude of this elongation is usually about 2% to 10%.

It can be seen from FIG. 3 that the edge drop caused by rolling has been almost eliminated by the bending and pulling at the tension leveler. In this example, the edge drop range and the edge up range match, and the shape of the edge drop and the shape of the edge amplifier are also vertically symmetrical and the same, so the area near the edge becomes almost completely flat.

If the edge drop range and the edge amplifier range do not match, it is not possible to completely eliminate edge drops, but since the two ranges are not significantly different, this method reduces edge drops to a level that is sufficiently effective for practical use. It is possible to do so.

Example II: 6 on the fixed side and 5 on the movable side near the entrance of the soaking zone of the continuous annealing furnace
A leveler consisting of a book roll that can adjust the amount of reduction was installed, and the plastic elongation corresponding to the amount of edge drop measured on the entry side was given by adjusting the amount of reduction and tension of the leveler.
Edge drop was improved from 5% to 0-2%.

[Brief explanation of the drawing]

FIG. 1 is a graph of experimental results showing the edge-up phenomenon that is the basis of the present invention. FIG. 2 is a graph showing the results of FIG. 1(d) converted into strain in the width direction, where e represents strain in the thickness direction and f represents strain in the width direction. FIG. 3 is a graph showing the results of an example of the present invention. Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Masahiko Arai 1st 1o09rObθ 4θ 2002θ 406θ 8θ
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Claims (1)

[Claims] 1. A method for straightening edge drops in a metal strip, characterized in that a predetermined plastic elongation corresponding to the amount of edge drop caused by rolling the metal strip is applied to the metal strip by bending and tensioning.