JPS6157896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing slips between strips in a coil that occur due to loosening of the coil when unwinding the coil in a pressure adjustment process of an annealed coil, etc. The purpose of this method is to prevent slips between the strips within the coil, thereby eliminating any slip damage on the strip surface and improving product yield.

Strip coils come in various sizes, but one example of a large one is an outer diameter of 2540 mm, an inner diameter of 711 mm, and a width of 711 mm.
There is one with a total weight of 1400mm and 50 tons. After annealing such coils in a box annealing furnace, light reduction rolling is performed in a temper rolling mill or the like in order to adjust the mechanical properties and correct the shape of the strip. This is called the pressure adjustment process. There is.

By the way, when the annealed coil before being subjected to the pressure regulating process is viewed from the side, it has a loose inner diameter part A and a tight outer diameter part B, as shown in FIG.
This cannot be avoided during the coil annealing and cooling process. That is, as shown in FIG. 2, the coils 1 are stacked in multiple stages with their axes vertical, placed on a substrate 3 via spacers 2, etc., and covered with an inner cover 4, and then assembled into a movable box furnace body. 5 and annealing the coil. In the box furnace, the coil is heated from three sides: both end faces, the outer circumferential face, and the inner circumferential face. After annealing, the coil is also cooled by radiation from both end faces, the outer circumferential face, and the inner circumferential face, so that during annealing and cooling after annealing. As shown in Figure 3, the behavior of the temperature inside the coil is related to the radial thickness of the coil.During heating, the radius of the coldest point is located near 1/3 of the thickness from the inner diameter, as shown by curve A.
Also, during cooling, the radius of the hottest point is in the vicinity of 1/3, as shown by curve B. In this annealing process, in addition to the initial surface pressure due to the winding tension before annealing, thermal stress due to heating and cooling of the coil is applied between the strips in the coil, and during cooling, the coldest (hot) point At the outer diameter part of the coil, the shrinkage strain of the strip is larger towards the outer periphery of the coil, resulting in a tighter condition. On the other hand, at the inner diameter part of the coldest (hot) point, the shrinkage strain of the strip is larger towards the inner periphery of the coil, and the strip becomes tighter towards the inner periphery. Since the contact pressure between the strips is released, if the adhesion between the strips in the coil is weak, a gap will be created between the strips in the coil, resulting in a loose state.

In the pressure regulating process, the annealed coil installed on the payoff reel is unwound to be passed through the temper rolling mill. At this time, one turn of the coil in the loose inner diameter part A of the coil is ``A'' and the next outer turn is ``Roll''. Then, as shown in an exaggerated manner in FIG. 4, a minute gap δ is created between A and B. When the coil is unwound, in order for the entire coil to make one revolution, the length of the inner one turn A and the outer one turn B are different, so when point E on B reaches point C, Point D above reaches point F which precedes point C, and the coil is rotated counterclockwise while applying clockwise torque as shown by the arrow → to the payoff reel to apply back tension to the unwinding strip. Even during unwinding rotation, the inner circumferential side of the coil gradually takes the lead. The leading edge of the inner peripheral side of the loose inner diameter portion is the loosening direction when viewed from the winding direction of the coil, and the starting point of the winding loosening is the point where the gap δ near the radius of the coldest (hot) point is the largest. Therefore, the loosening phenomenon during unwinding of an annealed coil occurs approximately 30 to 60 seconds during the acceleration period from the start of unwinding of the coil,
This is especially noticeable in coils with a large unit weight.

In addition, since the annealed coil has a loose inner diameter part A as mentioned above, the coil mounted on the payoff reel is allowed to move telescopically in the axial direction, and when the coil is unwound, it When viewed from above, the coil itself deforms as shown in FIG. 5, and the strip inside the coil flows sideways. In addition, when the coil is unwinded, the coil may become tightened for some reason.

In all cases, the loosening, crossflow, and tightening phenomena during unwinding of an annealed coil as described above result in the occurrence of relative deviations, that is, slips, between the strips in the loose inner diameter portion A of the coil. These are collectively referred to as loose winding, etc. The slip between the strips due to loose winding or the like creates scratches on the surface of the strip as shown in FIG. 6, which significantly impairs the quality of the cold-rolled steel sheet.

In the coil annealing process, extremely slow heating and
Although slow cooling may be used, such a method would significantly reduce the annealing ability and cannot be adopted from the viewpoint of productivity.

Figure 7 shows the external force F required to prevent the coil from loosening under the current operating conditions. That is, the size of the coil is expressed as the moment of inertia I _z , (I
_z = mk ² m: mass, k: radius of rotation), the larger the moment of inertia _I of the coil, the larger the external force F required to prevent winding from loosening, etc. According to experimental results, F (ton) ≧ 1.7×10 ^-3 _Iz (Kgms ² )
-2.6 was found to be able to prevent slips between strips within the coil. According to this result, I _z
With a small coil of about 1000Kgms ² , under normal operation, winding loosening is extremely rare even if no special force is applied to prevent winding loosening.

As can be understood from the above explanation, phenomena such as loosening of coil winding when unwinding the coil, etc.
The inner diameter of the coil is looser than the radius of the coldest (warmest) point in the coil, and when the coil is unwound, strips are formed between the strips at the loose inner diameter of the coil. By heating the inner diameter portion of the coil to raise its temperature immediately before applying the coil, the surface pressure between the strips based on the thermal stress in that portion may be increased, and the loose state of the inner diameter portion of the coil may be eliminated. By doing this, it is possible to prevent slips between the strips in the coil due to loosening of the coil winding or the like.

The present invention has been made based on the above knowledge, and after acknowledging the strain behavior that causes the above-mentioned loose inner diameter portion in the coil annealing process, the present invention By heating the inner diameter portion of the coil from the center hole side by applying a heating means to the coil, the surface pressure between the strips based on the thermal stress in this portion is increased, thereby preventing the loosening of the coil when unwinding the coil. This feature prevents slips between the strips within the coil caused by this.

Considering the coil to be equivalent to a thick-walled cylinder, and when the coil temperature distribution is T, the radial stress σ _r in the coil of arbitrary radius r is given by the following equation.

σ _r =Eα/1-γ{1/b ² -a ² (1-a ² /r
² ) ∫ ^b _a Trdr-1/r ² ∫ ^b _a Trdr} ... a: Coil inner diameter b: Coil outer diameter α: Coefficient of thermal expansion E: Young's modulus r: Poisson's ratio r: Arbitrary radius inside the coil Current strip If the plate width is B and the coefficient of friction between the strips is μ, then the force resisting slip at the radius r of the coil is 2 μσ _r πrB, so the external force F acting on the coil and trying to generate slip is: As long as F<2μσ _r πrB ……, no slip occurs. If a temperature distribution that satisfies this conditional expression is generated within the radius of the coldest (warmth) point within the coil, slips between the strips within the coil can be prevented.

Embodiments of the present invention will be described in detail below with reference to the drawings.

As a means for raising the temperature of the inner diameter portion of a coil having a loose inner diameter portion, it is effective to heat the coil from the inner circumference using fire, hot air, electric heater, induction heating, or the like. FIG. 8, FIG. 9, and FIG. 10 show an embodiment in which induction heating of a coil is used. As shown in FIG. 8, the coil 1 that has completed the annealing and cooling process is placed on a conveyor saddle 11 and is on standby while the preceding coil is being unwound for temper rolling. During this waiting period, the coil 1 is heated from its inner periphery by the induction heating machine 12 shown in FIG. That is, the induction heating machine 12 is mounted on a base 17 of a movable traveling truck 18 by a hydraulic cylinder 19, and includes an excitation coil 14 for induction heating that can be inserted into the center hole of the coil 1. The excitation coil 14 is wound around an insulated cylindrical frame 13 and is connected to a power source 15 via a power supply device 16 . If the heating coil 14 is inserted into the center hole of the coil 1 waiting on the conveyor saddle 11 and induction heating is performed, the temperature of the loose inner diameter portion of the coil 1 will rise.
Thermal stress generates surface pressure between the strips. In addition, Fig. 10 shows an induction heating coil with an additional iron core, and the movable iron core 20 and fixed iron core 21 equipped with the heating coil form a closed circuit when the heating coil is inserted, which is much better than the induction heating coil alone. Heating can be performed efficiently.

As is clear from the above detailed description, according to the present invention, when an annealed coil is unwound from the entry payoff reel of a temper rolling mill, the inner diameter portion of the coil is heated immediately before rolling. By increasing the temperature, the surface pressure between the strips based on the thermal stress in the area is increased, so it is possible to completely prevent slips between the strips in the coil due to loosening of the coil during unwinding. Since there will be no occurrence of scratches etc. on the product strip,
This greatly contributes to improving quality and product yield.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the state between strips in the coil in an annealed coil, Figure 2 is an explanatory diagram of the box furnace annealing process of the coil, and Figure 3 is a diagram showing the behavior of internal stress (strain) in the coil during the annealing process. 4 is an explanatory diagram of the winding loosening phenomenon during unwinding of an annealed coil, FIG. 5 is an explanatory diagram of the cross flow phenomenon during unwinding of the coil, and FIG. 6 is a diagram showing the state of scratches on the surface of the strip. , FIG. 7 is a diagram showing the relationship between the force to prevent winding loosening and the moment of inertia of the coil, and FIGS. 8, 9, and 10 are explanatory diagrams of an example using an induction heating machine when carrying out the present invention. . 1... Coil, 2... Spacer, 3... Board, 4... Inner cover, 5... Box furnace body, 6... Payoff reel, 11... Conveyor saddle, 12... Induction heating machine, 13... Insulating cylindrical frame, 14... Excitation coil, 15... Power supply,
16...Power supply device, 17...Base, 18...Traveling trolley, 19...Hydraulic cylinder, 20...Moving iron core, 21...Fixed iron core.

Claims (1)

[Claims] 1. When an annealed coil having a loose inner diameter section is unwound from the entry payoff reel of a temper rolling mill, etc., the inner diameter section of the coil is heated to raise its temperature immediately before rolling, thereby stripping the coil based on the thermal stress in that section. A method for preventing slips during unwinding of an annealed coil, which is characterized by increasing interfacial pressure to prevent slips between strips in a coil due to loosening of the coil during unwinding.