Method and device for producing pipes, wires, moldings and similar elongated materials by drawing device

Abstract

1. A method for producing pipes, wires, mouldings and similar elongated materials using a drawing device, the method comprising: detecting and evaluating vibrational radiation in the material strand and / or in the drawing device during the drawing process for the purpose of detecting defects such as grooves or chatter marks caused by drawing; continuously subjecting said vibrational radiation to a spectral analysis so as to detect the occurrence or absence of radiation that increases and decays over time and / or pulsed radiation; and modifying the drawing speed in response thereto.

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for the production of pipes, wires, profiles and similar elongated materials according to the preamble of claims 1 to 6. [Background technology]

[0002] One of the manufacturing methods for the production of pipes, wires, moldings and similar elongated materials is drawing. In this form of tensile compression deformation, a strand of material, usually made of metal, is stretched through a drawing die. In doing so, the strand of material takes on the shape of the opening of the drawing die on the outside and usually becomes longer and thinner. If the strand of material is a hollow body, such as a pipe, a mandrel will interact with the drawing die and a gap, in particular an annular gap, can be formed.

[0003] Depending on the material, tool, wear, lubricant and process parameters, so-called chatter can occur during drawing, resulting in resonant vibrations which can lead to damage in the form of chatter marks in the material strand or even breakage of the material strand.

[0004] In order to detect and avoid chatter during the drawing process of pipes, it is known, for example as described in US Pat. No. 5,399,633, to use structure-based sound sensors to detect vibrations of the drawing system (machine having pipe, mandrel and drawing die) and to monitor by a fuzzy logic system whether the amplitude of the vibrations exceeds a limit value, with the aim of reducing the drawing speed to avoid chatter.

[0005] The difficulty here is that large amplitudes due to causes other than chatter can lead to a false reduction in the drawing speed. Moreover, chatter can only be reliably detected after it has already occurred. As a result, optimal material throughput is not achieved with the known methods.

[0006] Another difficulty with pipe drawing is that other defects, particularly grooves caused by the drawing, may not be detectable by known methods.

[0007] The same problem occurs in the drawing process of wires, molded products, etc. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. EP0780171A1 Summary of the Invention

[0009] The object of the present invention is to provide a method and a device for the production of pipes, wires, mouldings and similar elongated materials, which ensures a high material throughput while reliably eliminating defects such as chatter and grooves caused by drawing.

[0010] This problem is solved by the elements of claims 1 to 6.

[0011] Based on the above, a method for drawing pipes, wires, mouldings and similar strands of material using a drawing device is created, in which vibration radiation is detected and evaluated in the strand of material and / or in the drawing device during the drawing process in order to detect defects such as grooves or chatter marks caused by drawing, the vibration radiation is continuously subjected to a spectral analysis in order to detect the occurrence or absence of frequency-selective radiation and / or especially frequency-selective pulsed radiation that increases and decays over time, and the drawing speed is modified in response thereto.

[0012] Spectral analysis makes it possible to detect signal patterns that foretell the onset of chatter hundreds of milliseconds before it occurs. As known from the state of the art, chatter can be reliably prevented on the basis of an evaluation of the vibration amplitude. This also applies to broadband pulsed radiation, which is typical for grooves caused by drawing. These can also be detected by the spectral analysis of the present invention before the energy becomes too concentrated and leaves a mark on the material strand.

[0013] If such radiation is detected by the spectrum analysis, the drawing speed is preferably slowed down, and if not, the speed is increased, and adaptive control of the drawing speed based on this ensures that the highest possible drawing speed is always run.

[0014] The evaluation may be based on multi-dimensional pattern recognition developed by the applicant, for example as known from European Patent Application Publication No. EP2359106A2, which is incorporated herein by reference in its entirety.

[0015] It is particularly advantageous to divide the vibration radiation into low-frequency and high-frequency frequency regions and perform the detection in the low-frequency region. For this purpose, it is possible to base the spectrum or vibration intensity amplitude threshold, for example as a percentage of the maximum value in a time course. The low-frequency amplitude threshold can be, for example, 1%, 2%, 3%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, and the time course considered is 0.1 seconds, 0.2 seconds, 0.3 seconds, 0.4 seconds, 0.5 seconds, 1 second, 2 seconds, 3 seconds, 5 seconds, 7 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, 50 seconds, 1 minute, 2 minutes, 3 minutes, 5 minutes, 10 minutes, or a variable that is associated with the change in vibration intensity, such that the threshold increases with an increase in the change in vibration radiation and decreases with a decrease in the change in vibration radiation.

[0016] The invention also provides a drawing device for drawing pipes, wires, mouldings and similar strands of material in accordance with the method according to the invention, comprising a sensor for detecting vibrations occurring in the strand of material and / or in the drawing device during the drawing process and an evaluation device connected to the sensor for evaluating the detected vibrations in order to detect defects such as grooves or chatter marks caused by drawing, the evaluation device being arranged to subject the vibration radiation to a continuous spectral analysis so that the occurrence or absence of a radiation that increases and decays over time and / or a pulsed radiation is detected and to perform an open-loop or closed-loop control of the drawing speed depending on the detection.

[0017] Further features and embodiments of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0018] [Figure 1A] FIG. 1A is a longitudinal cross-sectional view of a pipe drawing apparatus. [Figure 1B] FIG. 1B is a partial perspective view of a pipe drawing apparatus. [Figure 1C] FIG. 1C is a longitudinal cross-sectional view of a pipe drawing machine with a fixed mandrel. [Figure 1D] FIG. 1D is a longitudinal cross-sectional view of a pipe drawing apparatus with a moving rod. [Figure 1E] FIG. 1E is a longitudinal cross-sectional view of a pipe drawing apparatus with a floating mandrel. [Figure 2A] FIG. 2A shows the vibration spectrum for nearly the entire pipe drawing process. [Figure 2B] FIG. 2B shows a portion of FIG. 2A. [Figure 2C] FIG. 2C shows the vibration spectrum during normal operation in the absence of chatter. [Figure 2D] FIG. 2D shows the state just before chatter begins to occur in the portion of FIG. 2A. [Figure 2E]FIG. 2E shows the individual vibration patterns of FIG. 2D. [Figure 2F] FIG. 2F shows the vibration of FIG. 2E. [Diagram 3] FIG. 3 shows the spectrum for adaptive control of the drawing speed. [Figure 4] FIG. 4 shows the cumulative chatter pulse. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A drawing device 1 for drawing pipes or the like, depicted diagrammatically in FIG. 1A, comprises a drawing die 2 and a sensor 5 for detecting vibration radiation. Through the drawing die 2, a pipe 3 is drawn in the direction of the arrow 4, and its outer diameter and pipe thickness are reduced. The sensor 5 is arranged here, for example, on the drawing die 2 and is connected to an evaluation device 6, for example a computer. The drawing die 2 shown by way of example has an opening 7, is here configured rotationally symmetrical about a central axis 8 and is tapered from an input diameter to an effective diameter. When passing through the drawing die 2, the pipe 3 is stretched and compressed during drawing to the desired target diameter. When determining the effective diameter, it must be borne in mind that the pipe 3 may become larger at the outlet of the tapered section depending on the degree of springback of the material, and may therefore become larger than the effective diameter of the drawing die 2. It is desirable for the diameter of the drawing die 2 to expand somewhat again at the outlet.

[0020] The drawing device 1 can comprise several drawing dies 2 (see FIG. 1B). Here, by way of example, three drawing dies 2a, 2b, 2c are shown, through which the pipe can be drawn simultaneously. At least one drawing die 2a is assigned a sensor 5a, shown here with the end of a cable. It is advisable to assign each drawing die 2a, 2b, 2c a sensor 5a, 5b, 5c, respectively. Preferably, the sensor 5 is coupled to the drawing die 2 itself or to an element firmly connected thereto.

[0021] The pipe 3 may be supported from the inside by an internal tool, which may be any suitable addition or replacement to the drawing die 2, to which the sensor 5 may be connected. For example, a mandrel 9 may be provided, which is attached to a mandrel rod 10 (see FIG. 1C). During the drawing process, the pipe 2 is drawn through an annular gap formed between the drawing die 2 and the mandrel 9, and has an outer diameter that corresponds to the dimensions of the drawing die 2 and an inner diameter that corresponds to the dimensions of the mandrel 9 plus some springback. In this case, the sensor 5 may be connected to the mandrel rod 10. The same applies when a moving rod 11 is used (see FIG. 1D). The moving rod 11 is inserted into the pipe instead of the mandrel 7 and is gripped by the pulling tool via a cylindrical head attachment 12 extending from the tip 13 of the pipe 2. The sensor 5 may be connected to the moving rod 11.

[0022] On the other hand, if a floating internal tool is provided, such as for example the floating mandrel 9 of Fig. 1E, this is not suitable for coupling the sensor 5. In this case, the sensor 5 is coupled to the drawing die 2 or an element firmly joined thereto.

[0023] Although in FIG. 1 a wire drawing apparatus is depicted for illustrative purposes, in the present invention the drawing apparatus 1 is suitable for drawing pipes, wires, moldings or other strands of material and can be equipped for this purpose with further components such as internal tools or pulling devices.

[0024] The sensor 2 is preferably a structure-borne sound sensor, for example a piezoelectric sensor, although other types of sensors can be used as well, provided they are capable of detecting vibrations in the frequency range of interest.

[0025] The sensor 2 is connected to the drawing die 2, the pipe 3 or the internal tooling or to a part that is vibrationally connected to the drawing die 2, the pipe 3 and / or the internal tooling, so that vibrations of the pipe 3 and / or the drawing die 2 and / or the internal tooling can be detected. In the simplest case the sensor is screwed on.

[0026] During the drawing process, vibrations occur in the pipe 3 and in the drawing device 1, in particular in the drawing die 2 of the external tool or in the internal tool, which are recorded by the sensor 5. For this purpose, the sensor 5 is designed to detect frequencies between a lower limit and an upper limit. The lower limit is 0 and the upper limit is ∞, ideally allowing the entire spectrum of interest to be recorded. In practice, an upper limit of at least 50 MHz, preferably at least 100 MHz, is useful. Frequencies below 90 kHz or 40 kHz are preferably attenuated or cut off, since they practically do not contain any useful information. A corresponding lower limit is useful, which may be set to 50 kHz, 100 kHz, 500 kHz or even 1 MHz.

[0027] The actual frequency range of the sensor 5 should be selected based on the material being stretched and the stretching speed, with a frequency range of about 180 kHz to 400 kHz proving to be particularly useful.

[0028] The vibrations detected by the sensor 5 during the processing of the workpiece pipe 3 are subjected according to the invention to a spectral analysis, for example in the form of a time-frequency analysis. For this purpose, the detected vibration spectrum can be temporarily stored in the evaluation device 6. Preferably, the evaluation device 6 is a computer equipped with a corresponding interface and suitable storage media.

[0029] In the evaluation device 6, the time-frequency analysis can be carried out during or after the detection in such a way that the vibration spectrum is graphically displayed and / or numerically analyzed.

[0030] The assessment may be displayed in three dimensions, having coordinates of time, frequency and amplitude (or maximum amplitude, intensity or the like), as illustrated in FIG.

[0031] Figure 2A shows the vibration spectrum for almost the entire pipe drawing process. It can be seen that a broadband, high intensity chatter signal occurs over almost the entire recorded frequency range, starting at about 7 seconds and persisting for a limited time.

[0032] This chatter is warned hundreds of milliseconds in advance by broadband waxing and waning emissions (see Figure 2B). Subsequent vibration lines show an increase in intensity. These can be recognized by pattern recognition and are significantly different from the vibration lines during normal operation without chatter (see Figure 2C).

[0033] Figure 2D is a part of Figure 2A, showing periodic vibrations just before chatter occurs. The individual vibration patterns are shown in Figure 2E. The vibrations are shown in Figure 2F.

[0034] By slowing down the extension speed in response to detecting such an increase or decrease in radiation, the vibration lines disappear and chatter can be avoided (see Figure 3).

[0035] If no broadband emission increase or decrease is detected for a longer period of time, the draw speed can be increased in accordance with the present invention, within the bounds of other further operating parameters, until such vibration lines become evident.

[0036] A possible control loop can be configured based on the accumulated chatter pulses (see FIG. 4).

[0037] The upper curve 14 in Fig. 4 starts at (0,0) and reaches an operating value 29 at reference numeral 15, which represents the accumulated chatter pulses, here in the exemplary frequency range 200 kHz to 400 kHz. Each time a chatter pulse is detected, this value is increased by 1.

[0038] A gradient analysis of the signal emission in the frequency domain is performed in the time direction. If the periodic emission, which is a precursor of chatter, disappears for a certain period of time after the first occurrence, the accumulated value is reset. The accumulated value is reset to 0 or a reset value (e.g. -5).

[0039] If a certain threshold is exceeded, a signal may be sent to the device, which may, for example, adjust its speed (particularly slow it down). If the vibrations predicting chatter disappear, the accumulated value may be decremented or reset in the manner described above, and the device may speed up.

[0040] The lower curve 16 of FIG. 4 shows an exemplary three-step speed control, but other embodiments can have four, five or more steps, or even (quasi-)continuous control. Here, the value -3 represents normal speed, the value -2 is the value to which the control is set at reference number 17, and represents a 25% speed reduction. The value -1 is the value to which the control is set at reference number 18, and represents a -50% speed reduction. At reference number 19, no chatter has been detected for a predefined period, so the speed can be returned to normal. The thresholds associated with the exemplary 25% and 50% reductions at the reference numbers 17 and 18 (and subsequent control points) are shown by the horizontal lines 20 and 21. The reduction can be in two or more steps and / or (quasi-)continuous.

[0041] According to the above-mentioned configuration, the present invention realizes adaptive control that maintains a drawing speed close to the maximum even if there are changes in the operating parameters (tool wear, deterioration of the lubricating oil, temperature change, etc.).

Claims

1. A method for manufacturing pipes, wires, molded products and similar long materials using a stretching device, The purpose is to detect defects such as grooves and chatter marks that occur during stretching, by detecting and evaluating vibration radiation in the material strand and / or stretching equipment during the stretching process. A method characterized by continuously subjecting the vibrational radiation to spectral analysis so as to detect the occurrence or absence of radiation and / or pulsed radiation that increases and decreases over time, and changing the stretching rate in response thereto.

2. The method according to claim 1, characterized in that the stretching speed is reduced when the occurrence of the aforementioned vibration radiation is detected.

3. The method according to claim 1 or 2, characterized in that the stretching speed is increased when the absence of the vibration radiation is detected.

4. The method according to claim 1, characterized in that the stretching speed is adaptively controlled.

5. The method according to claim 1, characterized in that the vibration radiation is divided into low-frequency and high-frequency regions, and detection is performed in the low-frequency region.

6. A stretching apparatus for stretching pipes, wires, molded products, and similar material strands, A sensor for detecting vibrations generated in the material strand and / or the stretching apparatus during the stretching process, The system includes an evaluation device connected to the aforementioned sensor, for the purpose of detecting defects such as grooves and vibration marks caused by stretching, and for evaluating the detected vibrations, The evaluation device is configured to continuously subject vibrational radiation to spectral analysis so as to detect the occurrence or absence of radiation and / or pulsed radiation that increases and decreases over time, and to perform open-loop or closed-loop control of the stretching speed in response to the detection.

7. The stretching device according to claim 6, characterized in that the sensor is connected to an external tool.

8. The stretching device according to claim 6, characterized in that the sensor is connected to an internal tool.

Images