12.05.2022 Views

Online Inspection System Inclusion Detection System IDS

Early Detection of Internal Inclusions and Shell Defects Using Magnetic Flux Leakage: IMS Messsysteme Presents Market-Ready Inclusion Detection System IDS for Cold-Rolled Strip Steel The demands placed on steel as a material are growing continuously due to the ongoing development of the material and its processing methods. This also applies to the purity of the steel. As a result, exact control of the production processes is essential for the production of high-quality end products in order to provide the finishing industry with flawless starting materials with homogeneous material structures. To be able to ensure this, it is important to determine various parameters over the entire length of the strip. A selective material inspection at the ends of the strip is not sufficient to reliably prevent material defects in the end products and possible damage to tools in the downstream forming processes. The innovative Inclusion Detection System IDS of IMS detects those defects continuously in a non-contact and non-destructive detection technique.

Early Detection of Internal Inclusions and Shell Defects Using Magnetic Flux Leakage: IMS Messsysteme Presents Market-Ready Inclusion Detection System IDS for Cold-Rolled Strip Steel

The demands placed on steel as a material are growing continuously due to the ongoing development of the material and its processing methods. This also applies to the purity of the steel.

As a result, exact control of the production processes is essential for the production of high-quality end products in order to provide the finishing industry with flawless starting materials with homogeneous material structures. To be able to ensure this, it is important to determine various parameters over the entire length of the strip.

A selective material inspection at the ends of the strip is not sufficient to reliably prevent material defects in the end products and possible damage to tools in the downstream forming processes.

The innovative Inclusion Detection System IDS of IMS detects those defects continuously in a non-contact and non-destructive detection technique.

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Whitepaper

Online Inspection System

Inclusion Detection System (IDS)


CONTENTS

05

Measurement Results

01

Introduction

02

03

Development of

IDS Measuring System

3.1 Sensor Technology

05 - 08

5.1 Laboratory Measurements

16 - 17

5.2 Operational Measurements

18 - 22

5.3 Calibration Coil

23

02

Task

03 - 04

3.2 Structure of the Sensor Block

3.3 Structure of the

Overall System

09 - 11

12- 13

06

Summary

24 - 25

04

Technical

Production Design

14 - 15

2

3


01

Introduction

02

Task

The exact control of production processes

in the manufacture of strip steel and flat

products is crucial for the production of

high-quality products with homogeneous

properties over their complete length.

For verification, it is necessary to determine

various material parameters over the

complete length and not just selectively at

the ends. Non-contact and non-destructive

testing methods are necessary.

The demands placed on steel as a material

are growing continuously due to the

ongoing development of the material and

processing methods. This also applies to

the degree of purity. In the cold strip sector,

even the smallest purity deficiencies or

inclusions have negative effects.

The inclusions remain in the material

despite the subsequent rolling processes

and take on elongated shapes through

deformation. If the inclusion does not reach

the surface of the material, detection by

optical systems is not possible. The relative

magnetic permeability of such inclusions

is significantly lower than that of the

surrounding material. This means detection

During steel production and the subsequent

casting process, inclusions get into

the melt during the metallurgical process.

Some of these non-metallic particles

remain in the products. The quantity,

particle size and spatial distribution of the

inclusions define the purity of the steel.

Non-metallic inclusions in flat steel

products can cause damage to the product

being manufactured and to the tools used

in further processing operations, such as

forming. This report describes the development

and operational results of a detection

system for online inspection of cold-rolled

strip for internal inclusions.

Figure 1: Schematic illustration of the magnetic field profile in the case of an internal inclusion

2

INTRODUCTION

TASK

3


y magnetic flux leakage is possible. The tested material is

magnetised, whereby a homogeneous magnetic field also

results on its surface if its structure is homogeneous.

If there are local areas in the material with significantly

lower permeability, caused by, for example, non-metallic

inclusions, cracks and indentations on the surface, the

magnetic resistance increases at this point. A part of the

magnetic flux is thus forced to the surface of the material.

The difference between the relative permeability of the

material and the surrounding air results in pronounced

magnetic refraction. The extent of the stray field emerging

from the material surface is therefore significantly greater

than the causal defect, which enables its detection.

03

Development of an IDS

Measuring System

3.1 Sensor Technology

The flux leakage detection system developed

for the detection of internal inclusions

offers the functionality of a complete flux

leakage test during ongoing production

operation. Electromagnets are used to

magnetise the material. Their power can

be adapted to the properties, structure and

geometry of the material being inspected

and can be switched off for maintenance

and cleaning purposes. The stray fields are

detected by means of GMR sensors.

The sensors used are GMR differential

sensors (gradiometers). They consist of 4

individual GMR sensors that are connected

in the form of a Wheatstone measuring

bridge. Two of these sensors each are

linked spatially as shown in Figure 2. A

differential signal is formed in dependence

on the difference in magnetic field strength

between the two sensitive areas.

The sensitive areas of the sensors used

have a centre-to-centre distance of 1 mm.

V0

Exit 2

Exit 1

0

Figure 2: GMR differential sensor

4

TASK

DEVELOPMENT OF AN IDS MEASURING SYSTEM | SENSOR TECHNOLOGY

5


The use of gradiometers enables a significantly

higher amplification compared

to absolute sensors (magnetometers) as

external fields have no influence on the

sensor signal. This means that particularly

small local magnetic field inhomogeneities

can be detected.

In the IDS measuring system, the material

is magnetised transversely to rolling direction.

This direction of magnetisation was chosen

on the basis of laboratory measurements

with artificial defects. These defects were

defined as through holes of different

diameters as well as grooves with a length

of 1 mm, a width of 100 µm and variable

depth. The internal inclusions occurring in

cold-rolled strip normally take on elongated

shapes due to the strong deformation.

Grooves, therefore, correspond most

closely to the defects that actually occur.

For holes, which correspond to compact

defects, approximately equivalent results

were obtained with all magnetisation

directions. For grooves, significantly better

signal-to-noise ratios were obtained with

magnetisation transverse to the rolling

direction. This can easily be explained by

the larger defect cross-section in this direction.

Figure 3 and 4 show the signal-to-noise

ratios for a through hole with a diameter of

100 µm and a groove with a depth of 25

µm, a width of 100 µm and a length of

1 mm.

- Magnetization

- Magnetization

Figure 4: SNR of a 100 µm through hole at different magnetisation directions and measuring distances

Magnetisation at a 45° angle to rolling magnetic field homogeneity, the yoke width

direction is not a compromise, as this was chosen so that a 48 mm wide area is

worsens the signal-to-noise ratio for measured in each case.

compact defects compared to parallel Consequently, multiple magnets are necessary

in order to cover the different material

magnetisation, without improving the

signal-to-noise ratio for elongated defects. widths. Since no measurement is possible

in the area of the pole shoes of the

With magnetisation transverse to the rolling magnets, the sensor modules are arranged

direction, the maximum yoke width of the in two rows for continuous coverage.

magnet is limited. Due to a suitable

Figure 3: SNR of a groove 25 µm deep, 100 µm wide and 1 mm long at different magnetisation directions and measuring distances

6

DEVELOPMENT OF AN IDS MEASURING SYSTEM | SENSOR TECHNOLOGY

DEVELOPMENT OF AN IDS MEASURING SYSTEM | SENSOR TECHNOLOGY

7


Figure 5 shows the dependence of the

signal-to-noise ratio on the distance

between the sensor and strip surface.

Starting from a minimum air gap of 200

µm, the ratio decreases almost linearly

by about 1 dB / 100 µm additional air gap as

the distance increases. In practice, an air gap

of 700 µm is sufficient for this application and

resolution.

20 μm groove

40 μm groove

70 μm hole

150 μm hole

03

3.2 Structure of the Sensor Block

One magnet and the sensor line inside each magnet were combined to form a compact

sensor module. This guarantees easy maintenance, repair and scalability of the measuring

system.

Figure 6 shows an opened module with its key components. A module contains the

sensors, the amplification and filtering of the sensor signals, AD converters as well as

the control of the electromagnet and stabilised voltage supplies. The sensor modules are

installed quickly and reproducibly on the measuring system using quick-release clamps

in conjunction with fitting screws. Mechanical adjustment is not necessary thanks to the

precise manufacture and assembly of the individual module components. The GMR sensors

are encapsulated into a sensor block within a protective and stabilising aluminium frame.

This hinders adhesion of dirt and provides protection against mechanical damage.

The sensor modules comply with protection class IP 64, which enables direct use in

harsh environments.

Figure 5: Signal-to-noise ratio of grooves and holes in dependence on the measuring distance

Figure 6: Sensor module

8

DEVELOPMENT OF AN IDS MEASURING SYSTEM | SENSOR TECHNOLOGY

DEVELOPMENT OF AN IDS MEASURING SYSTEM | STRUCTURE OF THE SENSOR BLOCK

9


Figure 7: Sensor block open

Figure 8: Sensor block encapsulated

Figure 10: Signal amplitude of a 1 mm x 100 µm x 30 µm groove depending on

its position.

For compact small defects, for example holes, the stray field is optimal for detection

with this sensor arrangement.

Figure 9: Replacement of sensor block

Compared to smaller sensors with higher spatial resolution, the sensors used are more

sensitive. This means that particularly weak signals of small defects can be detected

better. The defects detected by a sensor are determined via the signal amplitude.

The modular design ensures easy replacement

of the sensor block without

adjustment work.

A sensor module has an outer width of 95

mm, which allows two sensor module rows

to cover the material without gaps. Each

sensor module contains 48 GMR differential

sensors in the centre of the magnet.

The distance between the sensors

transversely to rolling direction is 1 mm.

This is advantageous as the size of the

stray fields of the smallest defects is also

above 1 mm. Figure 10 shows the signal

amplitude of a 1 mm long, 100 µm wide

and 30 µ deep groove.

Figure 11: Signal amplitude of different defects depending on their volume

10 DEVELOPMENT OF AN IDS MEASURING SYSTEM | STRUCTURE OF THE SEN-

DEVELOPMENT OF AN IDS MEASURING SYSTEM | STRUCTURE OF THE SENSOR BLOCK

11


03

3.3 Structure of the Overall System

The overall system is structured hierarchically. The individual levels work on a task basis

and are interconnected via fast network technology. The sensor signals are converted

from analogue to digital with a sampling rate of up to 187.5 kHz at a resolution of 15 bits.

Length-dependent scanning takes place with a constant longitudinal resolution (rolling

direction) of 0.1 mm.

The digitised sensor signals from up to eight sensor modules are fed to a common

Gig-E hub and converted to the Gig-E camera standard.

The Gig-E hubs are connected to a camera computer. This camera computer has

the following tasks:

Figure 12: Hardware structure

1. Signal pre-processing

2. Detection of defects

3. Feature computation

4. Classification

5. Control and adjustment of the sensor modules

The database server is superimposed on this camera computer. The database server

stores the defect images and contains the production and training database.

Visualisation of the defects as well as the connection to the customer database is

effected via the database server.

Figure 13 shows the signal processing with the detection, classification and

post-processor functions.

Figure 13: Signal processing

12

DEVELOPMENT OF AN IDS MEASURING SYSTEM | STRUCTURE OF THE OVERALL SYSTEM

DEVELOPMENT OF AN IDS MEASURING SYSTEM | STRUCTURE OF THE OVERALL SYSTEM

13


04

Technical Production Design

After extensive laboratory tests and use of a pilot system, a measuring system with 28

sensor modules (maximum material width 1344 mm) was installed and commissioned

in a tinning line in the first half of 2020.

Product data:

Strip thickness

0.1 – 0.6 mm (max. 1 mm)

Strip width

600 – 1,250 mm (measuring width 1,344 mm)

Strip speed

Max. 1000 m/min. at full resolution

Measuring distance > 0.5 mm

Measuring accuracy:

Detectable defect size Hole: 70 µm diameter; groove: 10 µm deep, 100 µm wide,

(substitute defect) 1000 µm long in strip 250 µm thick

The minimum defect size must be determined depending

on the application.

Distance influence 1 dB / 100 µm

Reproducibility >98%

Figure 14 IDS measuring system in operation

The measurement takes place on a deflection

roller with two rows of sensor modules.

The sensor modules can be adjusted to

different material thicknesses with the help

of servo motors.

To ensure mechanical stability, the sensor

module rows and their carriers are kept at

a constant temperature by means of water.

The water cooling also serves to dissipate

the waste heat of the sensor modules.

The measuring system also has a pneumatic

drive to move the sensor rows on

and off the strip surface completely. The

drive is activated automatically for quick

retraction of the measuring system from

the strip surface if there is a risk of collision

with the material being measured.

The distance of the sensor modules to the

strip surface is monitored permanently by

three capacitive distance sensors per sensor

module row. As an additional safety device,

the measuring system has an optical

wrinkle detector. This is a laser light barrier

which is installed in the strip run 10-20 m

in front of the measuring point. In the case

of wrinkles, the sensor rows are swivelled

away.

The measuring system can be moved to

park position outside the system. In this

position, the sensors are adjusted automatically

and maintenance work can be

carried out while the line is running. During

the adjustment, all sensors are standardised

to a defined magnetic sensitivity and

defective sensors are detected.

14 TECHNICAL PRODUCTION DESIGN

TECHNICAL PRODUCTION DESIGN

15


05

Surface defects on the opposite side of the material to the measuring system can also be

detected. Figure 17 shows the raw signal of grooves measuring 1 mm x 100 µm x 25 µm

in 200 µm thick steel strip. The first groove is on the side of the material facing the measuring

system, the second on the opposite side.

Measurement Results

5.1 Laboratory Measurements

The following figures show the raw signals of artificial defects: a hole with a diameter of

100 µm (Figure 15) and a surface groove measuring 1 mm x 100 µm x 30 µm in 200 µm

thick steel strip at a measuring distance of 500 µm and a speed of 500 m/min.

Figure 18: Groove signal profile, top and bottom strip side

Signal curve of a 100 µm

through hole

Signal curve of a 30 µm deep,

100 µm wide and 1 mm long groove

As can be seen in Figure 19, the speed has only little influence on the signal-to-noise

ratio of defect signals.

Signal to noise ratio at variable material speed,

100 μm through hole

Signal curve of a 10 µm deep,

100 µm wide and 1 mm long groove

Speed

Figure 19: Signal profile at different speeds

Figures 15 – 17:

Signal profiles of a 100 μm hole and 10 μm and 30 μm deep,

100 μm wide and 1 mm long grooves

16 MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

17


05

5.2 Operational Measurements

The internal inclusions measured are evaluated as follows:

1. Based on defect size (amplitude/volume)

2. Based on classification

e.g. shells, cracks, overlaps, M-defects, scratches, indentations

Figure 21: Large defects such as scratches and wrinkles

Some inclusions detected were located precisely by means of magnetic

particle inspection and examined subsequently by making 3 sections each

transverse to the rolling direction.

Figure 20: Compact defects, various representations

Figure 22: IDS image of defect 1 Figure 23: Magnetic particle image of defect 1

18

MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

19


Figure 29: 1st section, defect 2 Figure 30: 2nd section, defect 2 Figure 31: 3rd section, defect 2

Figure 24: 1st section, defect 1 Figure 25: 2nd section, defect 1 Figure 26: 3rd section, defect 1

Figure 27: IDS image of defect 2 Figure 28: Magnetic particle image of defect 2

Figure 32: IDS image of defect 3

Figure 33: Magnetic particle image of defect 3

20

MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

21


05

5.3 Calibration Coil

The complete measuring system, including the classification

performance, is checked cyclically by means of a

calibration coil. The calibration coil should contain as

many defects as possible. Cold strip from the production

of transitional slabs is suitable for this. A reproducibility

of >98% was achieved during the cyclical check.

Figure 34: 1st Section, defect 3

Figure 35: 2nd section, defect 3 Figure 36: 3rd section, defect 3

22 MEASUREMENT RESULTS | LABORATORY MEASUREMENTS

MEASUREMENT RESULTS | CALIBRATION COIL

23


06

Summary

Using high-quality measuring electronics and

advanced image processing, a high-resolution

measuring system for internal defects

and external material damage has been

developed.

The IDS measuring system is used for complete

evaluation of purity. The maximum strip

thickness at full sensitivity is 1 mm and is

scalable to any strip width. The measuring

system can be adapted to customer specifications.

The image processing with feature computation

and classification used distinguishes the

defects based on their size and type. The

classification is adapted to the respective

material and the customer specification.

The IDS measuring system avoids the delivery

of defective material and ensures perfect

product quality for the end customer. In addition,

the measurement results are used to optimise

the pre-material stages. By improving

quality and output, resources are conserved

and costs reduced.

24 SUMMARY

SUMMARY 25


IMS Messsysteme GmbH

Dieselstraße 55

42579 Heiligenhaus

Phone: +49 (0) 2056 / 975 – 0

Fax: +49 (0) 2056 / 975 – 140

Mail: info@ims-gmbh.de

www.ims-gmbh.de | www.ims-experts.com | www.imsocial.info

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!