WO2000021706A1

WO2000021706A1 - Method and device for producing a metal strip and reducing the risk of such a strip breaking

Info

Publication number: WO2000021706A1
Application number: PCT/EP1999/007777
Authority: WO
Inventors: Tamis Lambertus Maria Leek; Frits Van Der Meulen; Johannes De Lange
Original assignee: Corus Technology Bv
Priority date: 1998-10-09
Filing date: 1999-10-08
Publication date: 2000-04-20
Also published as: ZA200102770B; JP2002527248A; BR9914364A; AU765675B2; AU1038600A; EP1154874A1; NL1010281C2; KR20010088858A; CN1332662A

Abstract

Method for producing a metal strip, in which the risk of the strip breaking is reduced in a path in which the strip is conveyed under stress in the strip direction, in which method, in a prior feed path of the metal strip, any defects which are present in the edges of the strip are detected, and measures are then taken to reduce the consequences of these defects in terms of the risk of the strip breaking, in which method, at full strip velocity, a section of the edge which is of limited length and within which a defect has been detected is cut out by a driven shearing system which is moved towards and away from the strip transversely to the edge, the direction of which shearing system follows the path of the shearing cut, and the driven shearing parts, at the location of the shearing point, having a velocity component in the strip direction which corresponds to the strip velocity.

Description

METHOD AND DEVICE FOR PRODUCING A METAL STRIP AND REDUCING THE RISK OF SUCH A STRIP BREAKING

The invention relates to a method for producing a metal strip, in which the risk of the strip breaking is reduced in a path in which the strip is conveyed under stress in the strip direction, in which method, in a prior feed path of the metal strip, any defects which are present in the edges of the strip are detected, and measures are then taken to reduce the consequences of these defects in terms of the risk of the strip breaking. The invention also relates to a device for use in carrying out the novel method. A method of the type disclosed is used, for example, for treating a cold-rolled steel strip in a continuous annealing line, although the invention is not limited to this option.

Generally, during the production of thin steel strip, the steel is successively subjected to so-called hot-rolling and cold-rolling treatments, in order to achieve the final desired thickness of a few tenths of a millimetre. However, these operations cause metallurgical changes in the steel which make it less suitable for further processing.

A conventional method for improving the processing properties consists in guiding the strip through a continuous annealing furnace under a slight tensile stress.

In this connection, a known problem consists in the fact that, in the initial section of the steel-strip production, defects may have formed in the edges of the strips, which defects, when the strip is placed under stress in the furnace, may cause the strip to break. Continuous annealing furnaces are extremely complicated installations in which a very considerable length of time is required for the strip to be threaded through. If a strip breaks, this loss of time leads to enormous production losses. It is therefore essential to limit the breakage of strips to an absolute minimum.

A conventional method aimed at achieving this consists in detecting defects in the edge of the strip in the feed path of the metal strip prior to the annealing path. In many cases, an opto-electronic system is used for this purpose, with which a defect which is detected by a camera is translated into an electronic signal. It should be noted that defects may comprise hairline cracks leading from the edge of the strip, but also loose flaps at the edge or relatively coarse inclusions. Sudden changes in strip width may sometimes also be regarded as defects. A defect results in a local increase in stresses in the strip when the strip is placed under stress. This increase in stresses may initiate a crack which leads to the strip breaking. The simplest measure following the detection of a defect consists in the movement of the strip being stopped and in a piece being removed from the edge of the strip at the location of the defect. Although such a measure prevents the strip from breaking, it leads to production losses, and furthermore a section of strip has been subjected to a different heat treatment. This may also lead to differences in quality in the annealed strip. The object of the invention is therefore to carry out subsequent measures which are such that the consequences of defects in the edges of the strip are avoided without having to change the velocity of the strip in order to achieve this. The intention of such measures is to obtain an annealed strip which has been subjected to the same heat treatment over its entire length and thus also does not exhibit any differences in quality. The invention consists in the fact that, in the method described in the introduction, at full strip velocity, a section of the edge which is of limited length and within which a defect has been detected is cut out by a driven shearing system which is moved towards and away from the strip transversely to the edge, the direction of which shearing system follows the path of the shearing cut, and the driven shearing parts, at the location of the shearing point, having a velocity component in the strip direction which corresponds to the strip velocity. This novel method entirely eliminates the possible source of a strip breaking while the strip remains unaffected by differences in velocity or the action of additional force outside the area in which the shearing cut is made. The complete elimination of an edge defect ensures that it is no longer possible for cracks to form from the edge and to progress into the rest of the strip.

More particularly, the invention relates to a method in which the driven shearing system comprises a pair of cutting rollers which are located on either side of the strip, which pair of rollers, during shearing, is rotated about an axis which is transverse with respect to the strip and runs through the shearing point, with the shafts of the cutting rollers directed perpendicularly to the path of the shearing cut at the location of the shearing point. The use of cutting rollers in this way as part of a shearing system prevents a force from being exerted on the rest of the strip by the shearing system in a direction which is transverse to the shearing cut. Since the section which is cut out is of limited length, with the shearing cut leading from the edge, through the material, and ending back at the edge, the cutting rollers, during shearing, will in each case have to adopt a different position. To prevent the shearing system from exerting a tensile or decelerating influence on the strip, it should be ensured that the velocity component of the cutting rollers in the strip direction at the location of the shearing point always corresponds to the strip velocity. This means that the velocity of the cutting rollers has to be adapted at each point of the shearing cut. The orientation of the shearing system also has to be continuously adapted to each subsequent position of the shearing cut. This rotation of the shearing system is dependent on the shape of the shearing cut. The invention furthermore relates to a device for reducing the risk of strip breaking in an installation comprising a feed system for a metal strip and a treatment system, in which the strip is held under stress, which device, in the feed system, comprises a detector for detecting any defects which are present in the edges of the strip. According to the invention, this device comprises a system which is provided in order to remove a section from the edge within which a defect has been detected by shearing at full strip velocity, which system comprises the following components: a pair of cutting rollers which are positioned on either side of the path of the strip and form a shearing system; - a first controllable motor with a transmission system in order to drive the cutting rollers in opposite directions; a second controllable motor with an axis which is perpendicular to the plane of the strip and runs through the shearing point of the shearing system, which motor is drive-connected to the shearing system in order to change its shearing direction; a pivot arm which, at its free end, bears the second controllable motor and which is able to pivot in a plane which is parallel to the surface of the strip, transversely with respect to the strip direction; a third controllable motor for driving the pivot arm; - a control system which is able to actuate the three motors simultaneously, in combination, and as a function of a detected edge defect, in such a manner that a section of the edge, which section is of limited length and contains the defect, is cut out by the shearing system.

According to the invention, it is more particularly preferable that the control system of the novel device is furthermore able to actuate the second controllable motor in such a manner that the shafts of the cutting rollers remain aligned perpendicularly to the path of the shearing cut at the location of the shearing point, and that the first motor can be actuated in such a manner that the cutting rollers, at the location of the shearing point, have a velocity component in the strip direction which corresponds to the strip velocity.

It has already been noted above that the novel method is not limited to use on steel strips which, after they have been cold-rolled, are passed through an annealing furnace. It is also conceivable for the method to be applied to metal strips of different compositions and also to metal strips which are passed through other treatment installations, for example a coated strip. Nevertheless, it has been found that the invention provides particularly good results when applied to the treatment of cold- rolled steel strip in a continuous annealing line. The invention will now be explained with reference to a number of figures which diagrammatically illustrate the application of the invention to a continuous annealing line for steel strip. In the drawings:

Fig. 1 diagrammatically depicts an annealing line. Fig. 2 diagrammatically depicts how a section is cut out of the edge of a strip.

Fig. 3 shows a plan view of the position of the novel device with respect to a moving strip.

Fig. 4 shows a view in the direction of IV-IV in Fig. 3.

Fig. 5 shows a component of the novel device. In Fig. 1, reference numeral 1 denotes a cold-rolled steel strip which is unwound from a coiler 2 and, after treatment, is rolled up onto a recoiler 3. Reference numeral 4 diagrammatically denotes a continuous annealing furnace. Before entering the annealing furnace 4, strip 1 passes through an entry buffer 5, and after leaving the furnace it is passed through an exit buffer 6. Arrows diagrammatically indicate that the volume of strip in the entry buffer 5 and in the exit buffer can be varied. This makes it possible to absorb discontinuities in the passage of the strip without the movement of the strip inside the annealing furnace becoming irregular. Such irregularities in the movement of the strip may arise if a new strip is being placed onto coiler 2 and has to be welded to the old strip in a welding device 7. Similarly, a full coiler 3 can be cut free from strip 1 , after which the strip has to be guided onto a new coiler.

A detector 8 is positioned in front of entry buffer 5. The detector 8 which is depicted is located above one of the edges of the strip and is of a type which uses a camera located above the strip to view halogen illumination which comes from below the strip. The light which is received by the camera is detected and translated into a crack or some other form of defect. Downstream of the detector, in the strip direction, there is a device 9 for shearing a section, which is of limited length and within which a defect has been detected by detector 8, out of the edge at full strip velocity. The device 9 is controlled by the signal which emanates from detector 8. Details of this control arrangement are not described in more detail below. Since edge defects may be formed in both edges of the strip, a detector 8 and a device 9 will generally be arranged on either side of the strip, in the vicinity of the two edges, and function independently of one another.

Fig. 2 shows a plan view of a steel strip 1 which is moving in the direction indicated by the arrow. Reference numeral 10 shows a defect in the edge, which defect is depicted by an acutely tapering notch. When stress is applied to the strip inside the annealing furnace 4, there is a real risk of this notch causing a continuous crack, which may lead to the strip breaking. Line 11 denotes the passage of the shearing point of a shearing system with respect to the strip 1. This path will run part way through the strip 1 , thus forming a shearing cut 12. For illustration purposes, the figure shows how, in this way, at a strip velocity of 12 metres per second and a depth of an edge crack 10 of approximately 100 mm, a section with a length of 2500 mm is cut out. It will be clear that these figures serve merely to illustrate a specific edge crack, and that the dimensions of the strip may vary depending on the nature of the edge defect which is observed.

Figs. 3 and 4 show the positioning and movement of the shearing system with respect to strip 1 in more detail. A U-shaped frame 16 bears a pair of cutting rollers 17 which, together, form a shearing mechanism. By moving the frame 16 towards the edge of the strip 1, the cutting rollers 17 form the shearing cut 12 in the strip (cf. Fig. 2). The shape of the U-shaped frame 16 is such that the limbs of the U are able to engage sufficiently far around the edge to be able to cut out edge defects of the maximum expected dimensions. In Fig. 5, frame 16 is shown in more detail as part of a larger unit. It can be seen from this figure that a drive motor 18 for driving cutting rollers 17 is attached to the frame 16.

As can also be seen from Figs. 3 and 4, frame 16 is connected to a drive motor 15, the axis of which runs vertically through the shearing point of the cutting rollers 17. Motor 15 is used to align the frame 16 with respect to the shearing cut, in such a manner that the shafts of the cutting rollers 17 are always directed peφendicular to the shearing cut. This ensures that this shearing cut can be made as clean as possible and cannot itself give rise to the formation of edge defects. Motor 15 is located at the free end of a pivot arm 14, the pivot point of which is formed by the shaft of a motor 13.

Motors 13 and 15 are servomotors which are suitable for bringing about very accurate, small rotations. Motors of this nature are generally known from the moving robot field. Motor 18 also has to be accurately controllable, in order to be able to adapt the velocity of the pair of rollers to the inclination of the shearing cut with respect to the strip direction. This is because the velocity components of the cutting rollers in the strip direction, at the location of the shearing point, have to correspond to the strip velocity, in order to prevent longitudinal slipping of the cutting rollers along the belt.

A control system which actuates the motors 18, 13 and 15 simultaneously and in combination, specifically as a function of a detected edge defect, is not shown but is present in the device. This is because it is necessary, at the same time, for the pivot arm 14 to be pivoted sufficiently far for the section which is to be sheared off to cut out the edge defect completely, for the motor 15 to align the frame 16 with respect to the local inclination of the shearing cut while the shearing cut is being formed, and for the motor 18 to adapt the velocity of the cutting rollers to the strip velocity and the inclination of the shearing cut at that particular location.

It has been found that by providing the shearing cut 12 with the form of a sinus wave, the rotational speed of motor 15 can remain virtually constant during shearing. Fig. 5 shows the shearing system itself in more detail. This figure indicates how frame 16 can rotate with respect to the fixed casing of motor 15. Drive motor 18 drives a shaft 19 which drives a toothed belt 20. This toothed belt 20 in turn drives shafts 21 and 22 at the same speed but in opposite directions, which shafts 21 and 22 drive the cutting rollers 17 (not shown). The path of toothed belts 20 is not shown in detail but, since this is a simple drive system, said path will be obvious to the person skilled in the art.

In order to allow the cutting rollers to be of small diameter, and in order to be able to design the frame 16 with a high level of strength, it is important for the two U- limbs of the frame 16, through which the shafts 21 and 22 run, to be at a short distance apart. If strip 1 vibrates, or if an edge of a strip is slightly corrugated, this could entail the risk of the cutting rollers not cutting cleanly into the edge of the strip. To this end, the system is furthermore provided with clamping jaws 23 and 24 which ensure that the edge of the strip can be clamped in place at all times when the shearing system is being pivoted towards the edge of the strip.

Claims

1. Method for producing a metal strip, in which the risk of the strip breaking is reduced in a path in which the strip is conveyed under stress in the strip direction, in which method, in a prior feed path of the metal strip, any defects which are present in the edges of the strip are detected, and measures are then taken to reduce the consequences of these defects in terms of the risk of the strip breaking, characterized in that, at full strip velocity, a section of the edge, which is of limited length and within which a defect has been detected, is cut out by a driven shearing system which is moved towards and away from the strip transversely to the edge, the direction of which shearing system follows the path of the shearing cut, and the driven shearing parts, at the location of the shearing point, having a velocity component in the strip direction which corresponds to the strip velocity.

2. Method according to Claim 1, characterized in that the driven shearing system comprises a pair of cutting rollers which are located on either side of the strip, which pair of rollers, during shearing, is rotated about an axis which is transverse with respect to the strip and runs through the shearing point, with the shafts of the cutting rollers directed perpendicularly to the path of the shearing cut at the location of the shearing point.

3. Device for reducing the risk of strip breaking in an installation comprising a feed system for a metal strip (1) and a treatment system (4), in which the strip (1) is held under stress, which device, in the feed system, comprises a detector

(8) for detecting any defects which are present in the edges of the strip, characterized in that this device comprises a system (9) which is provided in order to remove a section from the edge within which a defect has been detected by shearing at full strip velocity, which system comprises the following components: a pair of cutting rollers which are positioned on either side of the path of the edge and form a shearing system; a first controllable motor with a transmission system in order to drive the cutting rollers in opposite directions; - a second controllable motor with an axis which is peφendicular to the plane of the strip and runs through the shearing point of the shearing system, which motor is drive-connected to the shearing system in order to change its shearing direction; a pivot arm which, at its free end, bears the second controllable motor and which is able to pivot in a plane which is parallel to the surface of the strip, transversely with respect to the strip direction; a third controllable motor for driving the pivot arm; a control system which is able to actuate the three motors simultaneously, in combination, and as a function of a detected edge defect, in such a manner that a section of the edge, which section is of limited length and contains the defect, is cut out by the shearing system.

4. Device according to Claim 3, characterized in that the control system is furthermore able to actuate the second controllable motor in such a manner that the shafts of the cutting rollers remain aligned peφendicularly to the path of the shearing cut at the location of the shearing point, and that the first motor can be actuated in such a manner that the cutting rollers, at the location of the shearing point, have a velocity component in the strip direction which corresponds to the strip velocity.

5. Device according to Claim 3 or 4, characterized in that the shearing system is furthermore provided with clamping jaws which ensure that the edge of the strip is clamped in place when the shearing system is pivoted towards the edge of the strip.