Description Technical Field

[0001 ] The present invention relates to an assembly of winding or twisting

equipment for a cord comprising steel filaments and a detector.

[0002] The invention also relates to a method for detecting an event such as a steel filament fracture or a steel filament weld during twisting or winding of a cord comprising steel filaments.

Background Art

[0003] Non-destructive testing or inspection of steel wire ropes is known in the art.

[0004] Old British patent GB 306,232 already discloses electro-magnetic testing of steel wire ropes or other articles of magnetisable material. The steel wire rope under test forms part of a magnetic flux path. Variations in the mass of the steel wire rope cause magnetic flux variations which may be indicative of broken wires inside the steel wire rope.

[0005] The technique of magnetic flux detection for steel wire ropes has been continuously improved and perfected. For example, US-A-4, 096,437 and US-A-5,565,771 disclose the use of Hall effect sensors and improved circuitry and algorithms in electromagnetic wire rope testing.

[0006] All these techniques have in common that they are applied on relatively thick wire ropes, i.e. wire ropes with a diameter exceeding 5 to 10 mm so that a minimum amount of magnetisable material is present.

[0007] Another common feature of these techniques is that they are applied after manufacture of the wire rope. For example, some magnetic flux leakage detectors are installed in the elevator on the elevator rope in order to monitor for possible wire fractures during service in order to prevent complete failure of the rope. In other words, these detection techniques check the status of the wear of a wire rope during its service life in order to predict its life time.

[0008] Up to now attempts to apply the techniques of magnetic flux detection on cords adapted for the reinforcement of polymers or rubbers have failed for several reasons.

[0009] Cords for the reinforcement of polymers or rubbers typically comprise between two and one hundred thirty three or even more steel filaments, e.g. between two and twenty-seven steel filaments. The steel filament diameter typically ranges from 0.03 mm to 0.60 mm, e.g. between 0.10 mm and 0.40 mm. The purpose of the system is to detect fractures of single filaments inside the cord, which means that the system must be able to recognize "events" where the change in mass of is magnetisable material is small. As a result, threshold values which trigger the alarms must be kept small as well. The drawback, however, is that a lot of false alarms are triggered.

[0010] The problem of the false alarms becomes heavier if one wants to apply the magnetic flux detection during manufacturing of the cords.

[001 1 ] Indeed, the equipment used for manufacturing cords has a lot

magnetisable material in the neighbourhood of the detector and parts of this material are moving or rotating during the manufacture thereby influencing the amount of magnetic flux in the detector.

[0012] Another problem is that the cords are subject to vibrations during and just after manufacturing. These vibrations cause fluctuations in the magnetic flux or are picked by the sensor or detector, thus disturbing the signal.

[0013] The use of magnetic actuators in the winding equipment or twisting

equipment may also largely influence the magnetic flux in the detector and leads to an increased number of unwanted false alarms. Examples of such magnetic actuators are magnetic brakes or relays.

Disclosure of Invention

[0014] It is an object of the present invention to avoid or at least to mitigate the drawbacks of the prior art. [0015] It is a further object of the present invention to decrease and even to avoid the number of false alarms of magnetic flux leakage detection during the manufacturing or winding of cords.

[0016] According to a first aspect of the present invention, there is provided an assembly of a winding or twisting equipment and a detector.

The winding or twisting equipment is adapted for winding or twisting one or more cords which comprises or comprise magnetisable filaments.

The detector is installed on or is connected to the equipment.

The detector comprises:

a) a magnet allowing passage of the cord or cords,

b) a sensor for measuring variations in magnetic flux caused by the passing cord or cords,

c) a sampler for sampling variations in the magnetic flux,

d) a module for transforming these variations from the time domain in the frequency domain, e.g. by applying a fast Fourrier transform to these variations,

e) a decision module for deciding whether or not to stop working of the equipment depending upon the result of the values in the frequency domain, e.g. the values of the fast Fourrier transform.

[0017] The weight of the cords typically ranges from 0.5 g/m to 50 g/m, e.g. from 0.5 g/m to 35 g/m.

[0018] Within the context of the present invention, the term "magnet" refers to any device having a magnetic north pole and south pole. The magnet can be a permanent magnet or a electro-magnet.

[0019] Within the context of the present invention, the term "sensor" refers to an induction spool or to a semi-conductor sensor. An example of a semiconductor sensor is a Hall probe. [0020] With the transformation to the frequency domain, e.g. by means of the fast Fourier transform, the variations in the magnetic flux are no longer analyzed in the time domain but in the frequency domain. The frequency domain has proven to discriminate more between on the one hand the "events" that need to be detected such as filament fracture, knot or weld, and "events" that need not to be detected such as vibrations, influence of magnetic actuators, influence of neighbouring magnetisable machine parts, ... As a result, the triggering of false alarms has been drastically reduced.

[0021 ] In a preferable embodiment of the invention, the detection has been taught with "events" to be detected and "events" not to be detected. For example, during tuning or calibrating of the detection system, a steel cord with the presence of a weld at the level of a steel filament or a steel cord with one or more broken steel filaments is guided through the detector. The typical frequencies and amplitudes generated by these events are memorized in the system. Later on, during standard use of the system, the twisting apparatus and / or the winding apparatus are stopped each time a similar pattern of frequencies and amplitudes is seen by the system.

[0022] Preferably the detector also has an event detector module applying a

threshold to the variations. This event detector module has the advantage that only in case the variations exceed a certain threshold, the calculations of the frequency transformation algorithm are started. So in regime, i.e. without any threshold exceeded, no calculations need to be carried out.

[0023] Most preferably, this threshold is dynamic and is not a predetermined and fixed value. For example, this threshold is a number of times the normal ("normal": in the absence of events to be avoided) noise value.

[0024] According to a second aspect of the present invention, there is provided a method for detecting an event such as a magnetisable filament fracture or a magnetisable filament weld during twisting or winding of a cord comprising magnetisable filaments.

The method comprises the steps of:

a) passing the cord through a magnet after twisting the cord or before winding the cord,

b) measuring variations in magnetic flux caused by the passing cord, c) sampling variations in the magnetic flux,

d) transforming these variations from the time domain in the frequency domain, e.g. by applying a fast Fourrier transform to these variations, e) deciding whether or not to stop twisting or winding depending upon the values in the frequency domain.

[0025] As mentioned, steps d) and e) are only initiated once a certain threshold is being exceeded.

[0026] Preferably, in step e) the frequencies of the variations are compared with a set of reference frequencies and / or amplitudes which correspond to events to be avoided.

Brief Description of Figures in the Drawings

[0027] Figure 1 explains the principle working of magnetic flux detection for

failures on steel cord;

[0028] Figure 2a is a time domain curve of a filament fracture;

[0029] Figure 2b is a frequency curve of a filament fracture;

[0030] Figure 3a is a time domain curve of vibrations;

[0031 ] Figure 3b is a frequency curve of vibrations;

[0032] Figure 4a is a time domain curve of magnetic brake coupling;

[0033] Figure 4b is a frequency curve of magnetic brake coupling;

[0034] Figure 5a is a time domain curve of a filament knot;

[0035] Figure 5b is a frequency domain curve of a filament knot;

[0036] Figure 6a is a time domain curve of a cord weld;

[0037] Figure 6b is a frequency domain curve of a cord weld;

[0038] Figure 7a is a time domain curve of a kink;

[0039] Figure 7b is a frequency domain curve of a kink; [0040] Figure 8 is a schematic drawing of an assembly of, on the one hand a twisting equipment and a winding equipment, and, on the other hand, a detector.

Mode(s) for Carrying Out the Invention

[0041 ] The present invention is useful for detecting failures on cords which

comprise one or more magnetisable filaments. The terms magnetisable filaments refer to filaments made of a ferromagnetic material, i.e. a material with a relative magnetic permeability μ _Γ that is greater than one. Examples of ferromagnetic materials are iron, low-carbon steel, high- carbon steel, micro-alloyed high-carbon steel.

[0042] The relative magnetic permeability μ _Γ of pure iron varies between 150 and 5000 and that of 0.90 weight per cent carbon steel varies between 50 and 100.

[0043] A typical low-carbon steel composition has a carbon content ranging

between 0.04 wt % and 0.20 wt %. The complete composition may be as follows: a carbon content of 0.06 wt %, a silicon content of 0.166 wt %, a chromium content of 0.042 wt %, a copper content of 0.173 wt %, a manganese content of 0.382 wt %, a molybdenum content of 0.013 wt %, a nitrogen content of 0.006 wt %, a nickel content of 0.077 wt %, a phosphorus content of 0.007 wt %, a sulfur content of 0.013 wt %.

[0044] A typical high-carbon steel composition has a minimum carbon content of 0.65 wt %, a manganese content ranging from 0.40 wt % to 0.70 wt %, a silicon content ranging from 0.15 wt % to 0.30 wt %, a maximum sulfur content of 0.03 wt %, a maximum phosphorus content of 0.30 wt %. There are only traces of copper, nickel and / or chromium.

[0045] In a micro-alloyed high-carbon steel composition, following elements may be added to the composition:

chromium (%Cr): in amounts ranging from 0.10% to 1 .0%, e.g. from 0.10 to 0.50%; nickel (%Ni): in amounts ranging from 0.05% to 2.0%, e.g. from 0.10% to 0.60%;

cobalt (%Co): in amounts ranging from 0.05% to 3.0%; e.g. from 0.10% to 0.60%;

vanadium (%V): in amounts ranging from 0.05% to 1 .0%, e.g. from 0.05% to 0.30%;

molybdenum (%Mo): in amounts ranging from 0.05% to 0.60%, e.g. from 0.10% to 0.30%;

copper (%Cu): in amounts ranging from 0.10% to 0.40%, e.g. from 0.15% to 0.30%;

boron (%B): in amounts ranging from 0.001 % to 0.010%, e.g. from 0.002% to 0.006%;

niobium (%Nb): in amounts ranging from 0.001 % to 0.50%, e.g. from 0.02% to 0.05%;

titanium (%Ti): in amounts ranging from 0.001 % to 0.50%, e.g. from 0.001 % to 0.010%;

antimony (%Sb): in amounts ranging from 0.0005% to 0.08%, e.g. from 0.0005% to 0.05%;

calcium (%Ca): in amounts ranging from 0.001 % to 0.05%, e.g. from 0.0001 % to 0.01 %;

tungsten (%W): e.g. in an amount of about 0.20%;

zirconium (%Zr): e.g. in an amount ranging from 0.01 % to 0.10%;

aluminum (%AI): preferably in amounts lower than 0.035%, e.g. lower than

0.015%, e.g. lower than 0.005%;

nitrogen (%N): in amounts less than 0.005%;

rare earth metals (%REM): in amounts ranging from 0.010% to 0.050%. The cords must contain at least one filament of a ferromagnetic material. Hybrid cords which comprise both organic filaments or material and carbon steel filaments are not excluded. Hybrid cords which comprise both stainless steel filaments and carbon steel filaments are neither excluded. However, cords with only stainless steel filaments are usually not fit, since the majority of the stainless steels are not ferromagnetic. The majority of stainless steels have a relative magnetic permeability μ _Γ in the close to one. Despite this property, the assembly according to the invention is still adapted to detect the presence of welds in stainless steel filaments since the welding operation influences the magnetic permeability at the level of the welds.

[0047] Figure 1 is a schematic drawing aiming to explain the principle working of the magnetic flux detection of failures in a steel cord.

[0048] The detector has a cylindrical permanent magnet 102 with a north pole 104 and a south pole 106. Magnetic flux lines 108 travel inside the permanent magnet from the south pole 106 to the north pole 104. The magnetic flux path 108 is closed outside the magnet 102 by a steel cord 1 10 passing through the magnet 102 in direction 1 12. The steel cord 1 10 is saturated by the magnetic flux. A steel cord 1 10 without any defects or failures has the same mass or volume of magnetic material passing through the magnet 102. Ideally, i.e. making abstraction of vibrations and influence of neighboring magnetic materials, the magnetic flux Φ does not change and the inductions coils do not detect changes in flux Φ.

[0049] One of the "events" which must be detected is filament fracture. Suppose the steel cord 1 10 has a steel filament fracture resulting in a missing steel filament along a certain length or at a certain spot 1 14. This change of magnetic mass results in flux leakage and in a deviation of the flux pattern 1 16.

[0050] One of the other "events" which is often desirable to be detected is bird caging or kinks or basket formation. This is the phenomenon where filaments become loose. This loosening of the filaments is illustrated at 1 18 in Figure 1 . Bird caging causes either a change in mass of

magnetisable material or a change in symmetry. This causes a change in axial magnetic flux pattern 120. [0051 ] The axial magnetic flux detector 122 can detect the deviating axial magnetic flux pattern 120. The flux leakage detector 124 can detect the magnetic flux leakage.

[0052] Figure 2a shows the change 220 in magnetic flux (d tVdt) when a filament fracture occurs. Curve 222 is a sinus corresponding to a reference frequency determined by the speed of the twisting equipment or of the winding equipment.

[0053] Figure 3a shows the change 330 in magnetic flux (d tVdt) as a result of unavoidable vibrations of the steel cord.

[0054] Figure 4a shows the change 440 in magnetic flux (d tVdt) as a result of the influence of magnetic brakes in the neighborhood of the detector.

[0055] Figure 5a shows the change 502 magnetic flux (d tVdt) as a result of the the occurrence of a filament knot.

[0056] Figure 6a shows the change 602 in magnetic flux (d tVdt) as a result of the occurrence of a weld in one steel filament.

[0057] Figure 7a shows the change 702 in magnetic flux (d tVdt) as a result of the occurrence of a kink or bird caging.

[0058] These phenomena, filament fracture, kink, weld, knot, vibrations and

influence of magnetic brakes, can happen simultaneously or not. Putting predetermined threshold values will lead to a lot of false alarms.

Calibrating the detector or the algorithm for each type of steel cord construction has failed to offer a solution.

[0059] Figure 2b is the frequency domain curve of Figure 2a after fast Fourrier transformation.

Figure 3b is the frequency domain curve of Figure 3a after fast Fourrier transformation.

Figure 4b is the frequency domain curve of Figure 4a after fast Fourrier transformation.

Figure 5b is the frequency domain curve of Figure 5a after fast Fourrier transformation.

Figure 6b is the frequency domain curve of Figure 6a after fast Fourrier transformation.

Figure 7b is the frequency domain curve of Figure 7a after fast Fourrier transformation.

[0060] A filament fracture leads to frequency data 224. A filament knot leads to frequency data 504. A weld leads to frequency data 604. A kink or bird cage leads to frequency data 704. All these data 224, 504, 604 and 704 are below the reference frequency 226, 336, 446, 506, 606 and 706.

These data are clearly distinguishable from frequency data 334 of the vibrations and from the frequency data 444 of the influence of the magnetic brakes.

As a result, decision algorithms based upon the frequency domain will lead to a reduced number of false alarms.

[0061 ] Figure 8 illustrates an assembly 800 of, on the one hand a twisting

equipment 810 and/or a winding equipment 820, and, on the other hand, a detector 830. The detector 830 is installed on or is connected to the twisting equipment 810 or winding equipment 820.

[0062] As a matter of example only the twisting equipment 810 illustrated is a double-twister (also called buncher) and shows one way to make a 1x3 steel cord, i.e. a steel cord having three steel filaments.

[0063] Two steel filaments 81 1 are unwound from two spools 812 which are

positioned outside. The third steel filament 813 is unwound from an internal spool 814. The steel filaments 81 1 , 813 are led to a reversing pulley 815 at which level they receive already a first twist per rotation of flyer 816. The thus partially twisted steel filaments 81 1 , 813 are guided over the flyer 816 to a guiding pulley 817. At the level of the guiding pulley 817 the three partially twisted steel filaments 81 1 , 813 receive a second twist per rotation of flyer 816 to form the final steel cord 818.

[0064] The finalized steel cord 818 passes through the magnetic flux detector 830 and is further guided to be wound eventually on a spool 822. [0065] The invention is not linnited to a detector installed on a double-twisting equipment but is also applicable to tubular twisting machines or so-called cabling machines and to single-twisting machines.

[0066] The invention is neither limited to a detector installation between twisting equipment and winding equipment, but can be installed on a twisting equipment only or on a winding equipment only.

[0067] List of Reference Numbers

102 permanent magnet

104 north pole

106 south pole

108 magnetic flux line

1 10 steel cord

1 12 direction of movement of the steel cord

1 14 filament fracture

1 16 flux leakage lines

1 18 bird caging

120 axial magnetic flux lines

122 axial magnetic flux detector

124 leakage flux detector

220 time variation in magnetic flux when filament fracture

222 reference signal

224 frequency variation in magnetic flux when filament fracture

226 reference frequency

330 time variation in magnetic flux when vibrations

334 frequency variation in magnetic flux when vibrations

336 reference frequency

440 time variation in magnetic flux because of influence magnetic break 444 frequency variation in magnetic flux because of influence magnetic break

446 reference frequency

502 time variation in magnetic flux when filament knot

504 frequency variation in magnetic flux when filament knot reference frequency

time variation in magnetic flux when weld

frequency variation in magnetic flux when weld reference frequency

time variation in magnetic flux when kink

frequency variation in magnetic flux when kink reference frequency

assembly of winding/twisting equipment and detector twisting equipment

filaments coming from outside flyer

external spools

filament coming from inside flyer

internal spool

reversing pulley

flyer

guiding pulley

twisted cord

winding equipment

spool for winding

detector