Experimental and numerical characterisation of ferromagnetic ropes and non-destructive testing devices Aldo Canova (1), Fabio Degasperi (2), Francesco

Experimental and numerical Experimental and numerical characterisation of characterisation of

ferromagnetic ropes and ferromagnetic ropes and non-destructive non-destructive testing devicestesting devices

Aldo Canova (1), Fabio Degasperi (2), Francesco Ficili (4), Michele Forzan (3), Bruno Vusini (1)

(1) Dipartimento di Ingegneria Elettrica - Politecnico di Torino (Italy)(2) Laboratorio Tecnologico Impianti a Fune (Latif) – Ravina di Trento,

Trento (Italy)(3) Dipartimento di Ingegneria Elettrica - Università di Padova (Italy)

(4) AMC Instruments – Spin off del Politecnico di Torino (Italy)

OIPEEC Confference 2009 and 3rd International Stuttgart Ropedays18th - 20th March 2009 - Stuttgart, Germany

ContentsContents

• Magneto-Inductive (M-I) inspection: LF and

LMA signals

• Magnetic rope characterisation

• Design of Magneto-Inductive devices

• Experimental results


M-I inspection: the working principleM-I inspection: the working principle• A strong magnet is placed as close as possible to the rope,

thus obtaining the rope saturation.

• Rope defects cause a flux change (value and shape) that is revealed by means of a flux sensor

N S

N S

Reduction in the main flux

Local modification of the flux path


Type of sensors in use:

• coils (are sensitive to the flux changes)

• hall-effect (are sensitive to the flux density)

M-I inspection: the working principle

There are two (main) kinds of M-I instruments, depending on the way the flux is measured:

• LF (Localized Fault): the leakage flux is measured

• LMA (Loss of Metallic cross-section Area): the main flux is measured


LF InstrumentsLF Instruments

This is the most used technique to identify damages in a metallic rope

DamageMagnetic Flux distorsion

Very sensitive to the external broken wires Reduced sensitivity to the internal defects No quantitative information about damages

Working principle:• Rope defects cause a flaw of the magnetic flux• The flaw has two component: axial and radial


LMA instruments

Working principle:• Rope defects cause a

variation of the rope area• The main magnetic flux is

proportional to the rope area• The rope area is obtained by

measuring the main magnetic flux

Independent form position of broken wires (external or internal) Quantitative information Suitable to detect gradual changes of the rope section due to corrosion Reduced sensitivity for broken wires very closed (narrow gap) Strong influence of external leakage fluxes (end effects)


LF and LMA traces

Rope Profile

LMA

LF

Device length higher than width of loss metallic area

Narrow gaps


•The M-I test is significantly influenced by the magnetic behaviour of the metallic rope

•The magnetic behaviour of a metallic rope depends from its magnetic characteristic (B-H plane) and its hysteresis loops

Magnetic rope characterisation

Soft magnetic material

Hard (or semi hard) magnetic material


•The measurement of the B-H characteristic of a magnetic material has been obtained as interpolation of the vertexes of several symmetric hysteresis cycles. The measurement has been done establishing a magnetic field H, with a controlled magnitude and direction, in the region where the magnetic material is placed.


•The wire rod has been bended and welded at the edges, the total length of the ring was 60 cm. •The toroidal inductor has been built by winding 2050 turns around a rubber tube.

•The magnetizing inductor is made by 4 separate coils, 1000 turns, 16 cm length each with a diameter of 6 cm (ratio between the length and the diameter is around 10). •The field magnitude in the centre of the system is about equal to 6250 turns/meter, when the inductor is empty.



0

0.2

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0.6

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1

1.2

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1.6

1.8

2

0.0E+0 5.0E+3 1.0E+4 1.5E+4 2.0E+4 2.5E+4 3.0E+4 3.5E+4

H0 [A/m]

B [T

]

0

50

100

150

200

250

300

350

0 5000 10000 15000 20000 25000 30000 35000 40000

H0 [A/m]

m R

B-H characteristicRelative permeability of the sample wire rod

Rope NameRedaelli158 mm2

Redaelli473 mm2

Ercole[Reverse Lay]

497 mm2

Ercole[Reverse Lay]

1374 mm2

Chiusa1861 mm2

Rope Typestranded, core yarn,

Seale type

stranded, core yarn,, Warrington-Seale

type

metallic core, reverse lay, external stranded

metallic core, reverse lay, external stranded

rifle, double external layer with Z-formed

wires

Diameter [mm] 20 34 31 52 53

Construction 6(9+9+1)+PPC6(12+6/6+1)

+PPC12(6+1)+24

+18+ 12+6+112(6+1)+30

+24+18+12+6+1

1+6+12+18+24+30+32

+37

Number of wires 114 186 145 175 160

Lay Z/Z Z/Z - Z/S Z

Metallic cross section [mm2]

158 473 497 1374.3 1861



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2.2

0.0E+0 5.0E+3 1.0E+4 1.5E+4 2.0E+4 2.5E+4 3.0E+4 3.5E+4

MAGNETIC FIELD H0 [A/m]

Indu

ctio

n [e

quiv

alen

t] B

' [T

]

Radaelli 158 Radaelli 473 Reverse Lay 497 Reverse Lay 1374 Closed Rope 1861

Iron

•The magnetic behaviour of the metallic rope is far from a “soft material”


Magnetic rope characterisation•For the LF signal a low permeability is required

0

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400

0.0E+00 5.0E+03 1.0E+04 1.5E+04 2.0E+04 2.5E+04 3.0E+04 3.5E+04 4.0E+04 4.5E+04 5.0E+04

Magnetic Field H0 [A/m]

Re

lati

ve

pe

rme

ab

ility

mrel redaelli S = 1861 mm2

mrel Fune Redaelli S = 473 mm2

mrel Fune Ercole S = 1374.3 mm2

mrel Fune Ercole S = 497 mm2

mrel Fune Redaelli S = 158 mm2


Design of Magneto-Inductive devices•The performance evaluation of magnetic inductive detectors can be performed by studies of magnetic fields with numerical methods:

•Three dimensional domains•Non linear magnetic materials


Experimental results

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B [

T]

Axial Position [mm]

Simulation Experimental

Magnetic flux density trend inside the detector versus axial position without rope for the Device1

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-0.15

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-0.05

0.00

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B [

T]

Axial Position [mm]

Simulation Experimental

Magnetic flux density trend inside the detector versus axial position without rope for the Device 2

•The main performance indicator is the magnetic saturation of the rope which depends from the magnetic flux density at “no magnetic load” conditions (device without rope)•Without rope is possible to provide a comparison between experimental and simulated magnetic field


Experimental results•The magnetic behaviour under working conditions (with rope) can be simulated but is difficult to make experimental measurements.•To provide the measurements, a proper rope prototype consisting on two pieces facing each other has been realized, the faced surfaces have been suitable worked to make them smooth as possible. •The two lengths of rope are placed inside the detector and separated by a small air gap. The air gap allows the insertion of a probe for static magnetic field measurement.•The axial component of such magnetic flux density inside the air gap is closed to those reached inside the rope under test.

-100 -80 -60 -40 -20 0 20 40 60 80 100-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

B [

T]

Axial Position [mm]

Simulation without gap Simulation with gap of 1.5 (mm) Experimental with gap of 1.5 (mm)


Conclusions•The goodness of the M-I technique is linked to the magnetic behaviour of the rope under test•In the design of a M-I device is important to take into account the magnetic characteristic of the rope which is usually an unknown information•In the present paper the experimental characterization of a set of ropes with different size is presented and it puts in evidence that the rope material is far from “soft magnetic material” and requires high magnetic field for reaching the desired saturation level•The numerical field analysis of a M-I device is possible and a good agreement can be obtained between experimental and simulation results•The virtual prototyping allows a fast and reliable optimized design of M-I devices

Documents

Experimental and numerical characterisation of ferromagnetic ropes and non-destructive testing devices Aldo Canova (1), Fabio Degasperi (2), Francesco