NL1013339C2 - Detecting fold back, heat buckles or pinching in cooled, tempered strip metal, using a microphone as the strip passes around a tension roll - Google Patents

Abstract

Tears or creases in the metal band (1) are detected acoustically as the band travels around a roll (3). A method for detecting fold-back, heat buckles or pinching in a metal band, especially strip steel, comprises the acoustic detection of tears or creases as the band travels around a roll. Independent claims are also included for (a) a continuous tempering installation for strip metal, with a microphone (5) fitted to the first tension roll in the cooling zone, in order to carry out this detection method, and (b) a strip metal processing method using this installation.

Description

METHOD AND APPARATUS FOR DETECTING A FOLDED HEAT BUCKLE OR PINCH IN A METAL STRAP

The invention relates to a method for detecting a folded-over heat buckle or pinch in a metal strip, and to a device for carrying out this method.

Cold belt rolling changes the structure of the material of a steel belt. The material of the belt can then be provided with the desired strength and the desired elongation by annealing the belt, whereby recrystallization occurs. Annealing can be performed in various ways; one of them uses a continuous annealing device. The belt to be treated is supplied as a continuous belt to an annealing furnace by connecting roller belt to each other in a known manner. To enable the connection, an entrance loop tower has been placed in front of the annealing furnace. The annealing furnace consists of several sections, where the belt is passed through by guiding it over (pulling) rollers. After the annealing furnace, the belt passes through a cooling zone, consisting of a slow-cooling section and a fast-cooling section, where the belt is passed through in a number of passes. With an extensive continuous annealing device, an after-annealing furnace with an after-cooling zone follows. This is followed by an exit loop roller and scissors for winding the continuous belt 20 into separate rolls. It is possible to place a re-rolling device between the exit loop roller and the scissors, in which the continuous belt is subjected to a final re-rolling operation, with which the hardness of the material can be influenced. Tensioning rollers are placed between the different parts of the continuous annealing device in order to keep the belt under tension at all times.

It has been found that strong deformations of the belt, called heat buckles, can occur in the cooling zone, in particular in the slow-cooling section. As the continuous annealing device continues to run, folds in the heat buckles may develop in the longitudinal direction of the belt; several 30 folds can also develop side by side. When a heat buckle thus folded over itself is passed over a tension roller after cooling of the belt and undergoes a marked change of direction, the heat buckle can tear or crease. In a 101333q -2 number of cases, the belt will thereby be weakened to break, causing a prolonged production failure. In all cases, a cracked or creased heat buckle will result in rejection of the portion of the belt where the tear or crease is present. When a rewinding device is present, a folded over heat buckle can also damage the rewinding rollers.

In order to detect a folded-over heat buckle, it is known to inspect the tire visually with the aid of a camera, whereby the camera image is displayed on a monitor. When a folded-over heat buckle is detected, the belt's travel speed is reduced to prevent breakage of the belt.

A drawback of this is that the monitor with the camera image has to be viewed continuously, which is not quite possible in practice. This means that a folded-over heat buckle can be missed, which entails the risk of breakage of the belt, and the possibility that the re-rollers will be damaged if a re-roll device is fitted.

15 Another disadvantage of the visual inspection is that the folded-over heat buckles are not always clearly visible.

In addition, pinches can occur in other metal belts that do not pass through an oven, such as in an aluminum belt.

It is an object of the invention to provide an improved detection of folded heat buckles or pinches in a metal strip.

It is another object of the invention to provide a detection that will detect a folded-over heat buckle or pinch with great certainty.

It is yet another object of the invention to automatically detect folded heat buckles or pinches without the need for continuous visual inspection.

According to a first aspect of the invention, one or more of these objects are achieved by a method of detecting a folded heat buckle or pinch in a metal belt, in particular a steel belt, wherein tearing of the folded heat buckle or pinch when the metal strip is bent over a roll, it is detected acoustically.

Such a method makes use of the fact that a folded-over heat buckle or pinch that tears or creases produces a (shrill) sound 1013339-3. This sound can be perceived with the human ear, but can be lost in background noise or not perceived due to other activities of an operator. By recording the noise at the roll where the folded heat buckle or pinch cracks or creases, for example with the help of a microphone, and then processes it, it is possible to acoustically detect the cracks or creases of a folded heat buckle or pinch and a generate a warning signal to warn the operator. This can then decrease the pulling force on the belt, so that a possible belt breakage can be prevented. When a re-rolling device is present, the re-rolling rollers 10 can also be opened so that they are not damaged. Finally, it is possible to register in which part of the belt the folded heat buckle or pinch is present, so that that part of the belt can remain unused during later processing of the belt, or can be cut out of the belt. The method can be used in cold-belt rolling, but also, for example, in tinning lines.

Preferably, the acoustic detection of a folded-over heat buckle takes place during the treatment of the metal strip in a continuous annealing device, after cooling following annealing or after-annealing, since it has been found that no noise can be detected in the annealing furnace or after-annealing furnace falls. Due to the temperature in the oven (400 ° C or higher), the material is quite soft and the heat buckle does not tear, 20 or makes no noise, so that the detection of the folded heat buckle is only possible after cooling.

More preferably, detection takes place immediately after cooling. By detecting in this line in the line, as much time as possible is left to intervene and prevent breakage of the belt or damage to the re-rolling device.

According to a preferred method, the sound is measured at the location of the roll and a frequency spectrum of the sound is determined. The sound of the tearing or creasing of the heat buckle or the pinch is visible in the frequency spectrum as a number of peaks, which protrude to a greater or lesser extent above the background noise level.

Preferably, part of the background noise in the measured sound is filtered out of the frequency spectrum. The part of the frequency spectrum with the most noise can therefore be disregarded.

1013339 -4-

Preferably, the low-frequency portion of the sound is filtered out of the frequency spectrum, preferably the frequencies below 3 kHz. This makes it easier to detect the (chirping) sound.

According to a preferred method, detection in three or more frequency ranges of the frequency spectrum is performed. By comparing the noise level in these three or more areas, accidental disturbances in one frequency area can be disregarded.

Preferably, the detection is performed in the frequency ranges of 3-4 kHz, 5-7 kHz and 7-10 kHz. In these regions, the peaks in the frequency spectrum relative to the background noise caused by the tearing or creasing of a folded heat buckle or pinch are highest.

According to a preferred method, the sound level in a frequency range is always measured over a short period of time, preferably over 0.1 sec, after which the effective value thereof is determined. Because a folded 15 heat buckle or pinch tears or creases in a short period of time, usually in less than 1 second, the measurement period should be short. In order to display and compare the sound level, a mathematical operation is performed to determine the effective value. The determination of the effective value should preferably be carried out very frequently, for example in subsequent time periods of 0.1 sec.

Preferably, the noise level in the frequency range is also measured over a long period of time immediately prior to the short period of time, preferably over 10 seconds, after which the effective value of this noise level is determined and this effective value is subtracted from the effective value of the noise level. over the short period of time, to obtain a cleaned effective value over the short period of time. In this way, the effective value of the short period of time is always cleared of the effective value over the longer period of time that precedes it, and which consists wholly or largely of background noise. This makes the peaks in the frequency spectrum caused by the tearing or creasing of a folded-over heat buckle or pinch more clearly detectable.

1013339 -5-

Preferably, an alarm is given when the displayed effective value of the sound level over the short period of time exceeds a predetermined value. The operator is then automatically notified when a folded heat buckle or pinch cracks or creases.

According to a preferred method, the cleaned effective values are determined over the short period of time of three frequency ranges and an alarm signal is given when in at least two of the three frequency ranges the cleaned effective value exceeds an associated predetermined value. Thus, if a disturbance occurs in one frequency range, for example a peak in the frequency spectrum caused by a whistle of a bad bearing, then an alarm for the rupture or crease of a folded heat buckle or pinch is not wrongly given.

Preferably, the method is performed digitally. This makes it easy to make changes in the filterings, the duration and the like. According to a second aspect of the invention, there is provided a continuous annealing device for annealing a metal strip, in particular a steel strip, comprising an annealing furnace and a cooling zone, one or more tension rollers being arranged after the cooling zone. According to the invention, a microphone is connected to the first tensioner after the cooling zone, which is connected to associated sound processing equipment, for acoustically detecting the cracks or creases of a folded heat buckle in the metal belt when it bends around the first tensioner, using of the above method.

Preferably, the sound processing equipment is coupled to the measuring and control equipment of the device to automatically change the speed of the belt and / or the part of the belt in which the folded heat buckle detects a folded-over heat buckle in the tire. is available to register automatically. Without the need for operator intervention, possible adverse effects of the folded heat buckle in the metal belt are hereby prevented, and the part in the belt with the folded heat buckle can be easily traced later.

Preferably, the sound processing equipment is coupled to measuring and control equipment of the continuous annealing device, in order to automatically open the re-rollers of the re-rolling device when detecting a heat buckle folded over in the belt. This will automatically prevent damage to the rollers.

The invention will be elucidated on the basis of an exemplary embodiment, with reference to the drawing.

Fig. 1 schematically shows a portion of the continuous annealing device for a metal strip according to the invention.

Fig. 2 shows a frequency spectrum of the measured sound at the time of tearing a folded heat buckle.

FIG. 3 shows the effective values of the frequency spectrum of FIG. 2 in the frequency range of 3-4 kHz measured over time periods of 0.1 sec, for 60 sec.

Fig. 4 shows the effective values of FIG. 3, cleared of environmental noise.

Fig. 1 shows in a very schematic manner a part of a continuous annealing device for a steel strip 1, which is eventually wound into a roll 2. During the annealing process, the metal strip 1 passes through an annealing and afterglow section A, in which the strip has a temperature of about 700 ° C during the annealing and a temperature of about 400 ° C during the afterglow. The belt 1 is then cooled in a cooling section B, after which the belt is further guided by means of tensioning rollers 3 and 4 to a re-rolling device C, in which the belt is passed through re-rolling before being wound into the roll 2. The continuous annealing device can also without afterglow section and / or without re-rolling device.

When cooling after annealing or afterglow, especially in the slow cooling section, locally strong deformations, called heat buckles 25, can occur. When a heat buckle is bent over a roll, the buckle in the longitudinal direction of the belt will be partly folded on itself. When the folded heat buckle is bent over a roll after the cooling zone, the heat buckle usually tears or creases. A cracked heat buckle can lead to breakage of the metal belt, and a folded-over heat buckle can damage the rollers of the post-rolling device.

It has been determined experimentally that a folded-over heat buckle does not yet tear or wrinkle, or cause no noise when the tire is still hot.

1013339 -7-

The folded-over heat buckle only produces an audible noise when the belt has cooled down sufficiently and is bent over a roll, so that the folded-over heat buckle rips or creases audibly. According to the invention, a microphone 5 is therefore arranged at the tensioning roller 3 which follows directly on the cooling section 5 B. Optionally, the microphone could already be placed in the last part of the cooling section B near a deflecting roller.

The microphone 5 measures the sound at the location of the roller 3 and passes it on to sound processing equipment in the form of a computer 6. In the computer, the sound is converted into a frequency spectrum as shown in Fig. 2.

FIG. 2 shows the frequency spectrum at the time of tearing a bent heat buckle. The peaks can be seen at approximately 500 Hz, 2500 Hz, 3500 Hz, 5500 Hz and 8500 Hz. It can be clearly seen that these peaks are not much higher than the background noise, making the sound to be detected difficult to perceive. The noise level is shown relatively and is therefore not related to a value in 15 dB, for example.

Since the noise is high in relation to the sound, especially in the frequency range below 3 kHz, this part of the spectrum is filtered out. To analyze the remaining spectrum, three frequency ranges are taken from the remaining spectrum, namely the frequency ranges of 3-4 kHz, 5-7 kHz, 20 and 7-10 kHz. This is done using filter techniques and equipment that are known to a person skilled in the art.

The effective value of the signal in that area is calculated every 0.1 second per area. For the 3-4 kHz range, this is shown in Fig. 60 seconds. 3. For the areas with higher frequencies, the effective values are lower, since the amplitudes at those frequencies are lower, see Fig. 2.

Although in FIG. 3 two clear peaks can be seen at 26 seconds and 42 seconds, it is not clear whether the peak at 2 seconds also indicates a bent heat buckle. Also, the sound of a ripping or crinkling bent heat buckle can largely disappear into the background noise.

Therefore, for each effective value over 0.1 seconds, the effective value over the preceding 10 seconds is also determined. This value is a measure of the noise in that time region. Subtracting the effective value of the signal 1013339 -8- over 10 seconds from the effective value over 0.1 second, the noise is largely filtered out from the measured signal.

Fig. 4 shows the cleaned effective value in the frequency range 3-4 kHz. Fig. 4 now clearly shows that there are only two peak values at 26 and 42 seconds.

Such effective values can also be determined for the frequency ranges 5-7 kHz and 7-10 kHz. By setting a limit value per frequency range, it is possible to automatically signal whether there is a heat buckle. In the case of FIG. 4, the limit value could be set at the noise level 1.5.

In the event of a disturbance of the frequency spectrum, in most cases a disturbance will occur in one frequency, for example the whistling of an old bearing. To prevent false alarms, the cleaned effective value is therefore determined in three different areas, and an alarm is only raised that a bent heat buckle has been detected when the cleaned effective value exceeds the corresponding limit value in two of the three frequency ranges. If the limit value is exceeded in only one frequency range, it is assumed that this is a malfunction and not a bent heat buckle, and no alarm is raised.

20 In the event of an alarm, the operator can be warned by a light and / or sound signal. It is also possible that the computer is coupled to the measuring and control equipment of the continuous annealing device of the belt 1. Immediately after detecting a bent heat buckle, the speed can be reduced, so that the belt will not break, and the rollers are opened so that they are not damaged. It can also be registered in which part of the belt the bent heat buckle is present, so that this part can be left unused or cut out of the belt in a later treatment of the belt.

The method according to the invention is generally applicable for detecting folded pinches in a metal strip, for example a steel strip in a tin line. The method is also applicable for aluminum belts, for example. A heat buckle is the specific name for a pinch that arises in a belt that is passed through an oven.

1013339 -9-

The invention has been described above with reference to an exemplary embodiment. It will be understood that the invention is not limited to this example; the scope of protection is defined by the following claims.

1013339

Claims (16)

Method for detecting a folded-over heat buckle or pinch in a metal belt, in particular in a steel belt, characterized in that tearing or creasing of the folded-over heat buckle or pinch when bending the metal belt is detected acoustically over a roll. 2. A method according to claim 1, characterized in that the acoustic detection of a folded-over heat buckle takes place during the treatment of the metal strip in a continuous annealing device, after cooling following annealing or after-annealing. Method according to claim 2, characterized in that the detection takes place immediately after cooling. 15 Method according to any one of the preceding claims, characterized in that the noise is measured at the location of the roll and a frequency spectrum of the noise is determined. Method according to claim 4, characterized in that part of the background noise in the measured sound is filtered out of the frequency spectrum. 6. Method according to claim 4 or 5, characterized in that the low-frequency portion of the sound is filtered out of the frequency spectrum, preferably the frequencies lower than 3 kHz. Method according to claim 4, 5 or 6, characterized in that the detection is carried out in three or more frequency ranges of the frequency spectrum. 30 Method according to claim 7, characterized in that the detection is carried out in the frequency ranges of 3-4 kHz, 5-7 kHz and 7-10 kHz. 1013339 - 11 - Method according to any one of claims 4-8, characterized in that the sound level in a frequency range is always measured over a short period of time, preferably over 0.1 sec, after which the effective value thereof is determined. 5 Method according to claim 9, characterized in that the noise level in the frequency range is measured over a long period of time immediately prior to the short period of time, preferably over 10 seconds, after which the effective value of this noise level is determined and this effective value 10 is subtracted from the effective value of the noise level over the short period of time to obtain a cleaned effective value over the short period of time. 11. Method according to claim 10, characterized in that an alarm signal is given when the displayed effective value of the noise level over the short period of time exceeds a predetermined value. Method according to claim 11 in combination with claim 7 or 8, characterized in that an alarm signal is given when in at least two of the three frequency ranges the cleaned effective value exceeds an associated predetermined value. Method according to any one of the preceding claims, characterized in that the method is performed digitally. 25 Continuous annealing device for annealing a metal strip, in particular a steel strip, comprising an annealing furnace and a cooling zone, wherein one or more tension rollers are arranged after the cooling zone, characterized in that at the first tension roller after the cooling zone a microphone is placed which is connected to associated sound processing equipment to acoustically detect the tearing of a folded heat buckle in the metal 1013339-12 band when it bends around the first tensioner roller, using the method of any one of claims 1 - 13. 15. Device as claimed in claim 14, characterized in that the sound processing equipment is coupled to measuring and control equipment of the device, in order to automatically change the speed of the tape when detecting a folded-over heat buckle in the tire, and / or automatically register the part of the belt that contains the folded heat buckle. 10 16. Device according to claim 14 or 15, to which a post-rolling device with rollers has been added, characterized in that the sound processing equipment is coupled to measuring and regulating equipment of the continuous annealing device, in order to detect a folded heat buckle in the tire. to automatically open the after-rollers of the after-reel device. 1 1013339 Method for manufacturing a metal strip, in which the method according to any one of the preceding claims 1-13 is included.