Conference

The 2013 technical conference will feature more than 400 individual presentations covering advancements in all phases of ironmaking, steelmaking, rolling and finishing processes, and the various engineering, equipment and process technologies involved in today’s steel production. Register for full conference or just one day. Either way, you’ll increase both your knowledge and your network!

Program Development and topics
AIST Conference programs are developed by Technology Committee members representing iron and steel producers, their allied suppliers and related academia. Committees focus on ironmaking, steelmaking, finishing processes, and various engineering and equipment technologies. Sessions currently being developed focus on the following topics:

• Safety and Health
• Environmental Technology
• Cokemaking
• Ironmaking
• Electric Steelmaking
• Oxygen Steelmaking
• Specialty Alloy and Foundry
• Ladle and Secondary Refining
• Continuous Casting
• Hot Sheet Rolling
• Cold Sheet Rolling
• Galvanizing
• Tinplate and Electrogalvanizing
• Plate Rolling
• Rod and Bar Rolling
• Pipe and Tube
• Rolls
• Metallurgy — Steelmaking and Casting
• Metallurgy — Processing, Products and Applications
• Energy and Utilities
• Electrical Applications
• Computer Applications
• Project and Construction Management
• Maintenance and Reliability
• Lubrication and Hydraulics
• Refractory Systems
• Material Handling
• Cranes
• Packaging, Shipping and Transportation Methods
• Sensors

Exposition

About AISTech 2013
AISTech 2013 will feature international technologies from the world over, allowing steel producers to compete in today’s global market. If you are involved in the steel industry, you can’t afford to miss this event. Whether you present, attend or exhibit, take advantage of this opportunity to discover ways to make your job easier and improve your productivity.
Why Exhibit?
AISTech 2013 — The Iron & Steel Technology Conference and Exposition is your best opportunity to meet face-to-face with the individuals who specify, purchase, design and operate a variety of plants and facilities associated with the production and processing of iron and steel. Thousands of steel-related professionals — your customers and prospects — will be at this event, so you won’t want to miss this great opportunity!

Consider these facts:

Audience Quality: The most popular reasons for attending AISTech are “New Process or Product Technology” and “Latest Research and Development.”
International Scope: Each year, more than 40 countries participate in AISTech.
Meet and Greet: Trade shows are an excellent place to start new customer relationships and reinforce existing ones.
Purchasing Authority: One out of two AISTech attendees has buying influence for the industry’s products and services.
Cost-Effective: Individual sales calls are expensive. AISTech is the perfect opportunity to meet hundreds of new customers in one place, at one time.
Value Considered: 75% of AISTech’s exhibitors repeat, and 50% reserve their space for next year on-site.
As an exhibitor at AISTech, you’ll have unrivaled access to the world’s most qualified steel industry buyers — people who authorize billions of dollars in spending to expand and improve facilities to meet world demand for their products.

Audience
AISTech attendees meet with other steel industry professionals to exchange technical knowledge and learn about the latest products and services in the industry. From foreman to president and from engineer to operator, they come to the exposition to find out what’s new in technology, methods and equipment. We encourage exhibitors to showcase their latest technical equipment and services so that attendees can witness live, working demonstrations of their unique capabilities.

The Largest Wire & Cable Marketplace in the Americas

GEORGIA WORLD CONGRESS CENTER

A T L A N T A , G E O R G I A , U S A

A P R I L 2 3 – 2 5 , 2 0 1 3

Exhibit Hours:

TUESDAY, APRIL 23 • 10:00 a.m. – 5:00 p.m.

WEDNESDAY, APRIL 24 • 10:00 a.m. – 5:00 p.m.

THURSDAY, APRIL 25 • 10:00 a.m. – 3:00 p.m.

Download: Interwire 2013 Free Pass.

Please use this invitation and join us at the Georgia World Congress Center, April 23-25, 2013, where—as our guest—you will have complimentary admission to the Interwire exhibit floor. Interwire is the only place in the world this year to experience a wire and cable marketplace this vast, where more than 400 companies are represented. This is your opportunity for face-to-face dialog with the industry’s leading international wire and cable producers and suppliers. Displays cover more than 150 product categories for the ferrous, nonferrous, and electrical wire and cable segments.

Highlights include:

Operating Machinery | Production Solutions | Networking | International Pavilions

Figure 1 General View of the Optical Flatness Inspection Station

Figure 1 shows the table at the entry end with a sample ready to be drawn through the optical unit. The pads at the beginning and the end of the sample are used to mark the beginning and the end of the sample for the test results.

Figure 2 shows the unit with the sample having been driven through the gauge head. You can see in this photo the roller guides and timing belt drive. The speed of the drive is adjustable, but the normal traverse run takes but a few seconds.

Figure 2 the sample having been traversed showing the drive and guides

The gauge electronics and display as configured for the test table shows several graphs and displays after the sample has been drawn through the test gauge. Figure 3 shows the arrangement of the controls. The display at the left is the normal run screen for the VIP 08, but in this case, the display shows the relative I-units along each of 85 lines across the sample. The shorter lines are lower in the display and the longer ones to the top. The length of each line is calculated from the angle of the surface measurement which is updated at the rate of 50 times per second. Figure 4 shows the details of the right hand monitor screen. The display on the right screen has several smaller windows. The first in the lower right is the overall 3-D view of the sample created from the measurements. The one to the upper left is the height variation of the selected measurement line over the length of the sample. This allows the system to measure and display the height of the buckles even at the center of the sample which is almost impossible with feeler gauges and other test gauges.

Figure 3 General View of the System Electronics and Displays

Figure 4 Details of the Evaluation Screen

This system has 2 uses. The first is to be able to evaluate the ability of the VIP 08 to work on the actual materials that will be processed at your plant by sending test pieces to our office. The second is as a flatness inspection station at your site which will surely evaluate the flatness of your material in a tension free condition and with no chance that the measurement affects the results.

“Please visit us at Booth 716″

Explore a new frontier

Operational Excellence is within your reach at the NEW WAI Operations Summit & Wire Expo. And what better way to start implementing change than with an overview of the products and services available from the industry’s leading equipment manufacturers and materials suppliers? Use this invitation for complimentary admission to the exhibits, May 22-23, 2012.

Highlights

See wire and cable machines, accessories, and solutions for wire processing, extrusion, cleaning, wire drawing, process control, material handling, and much more. Product and services from more than 200 exhibitors cover the ferrous, nonferrous, electrical, fiber optic, and general segments of the industry. Don’t miss the on-floor production solutions demonstrations on Tuesday afternoon from 3:30 – 5:00 p.m. Plan ahead. View the full list of products and services and read detailed booth descriptions.

Exhibit hours

Tuesday, May 22: 10:00 a.m. – 5:00 p.m. | Wednesday, May 23: 10:00 a.m. – 3:00 p.m.

Summit Sponsors | Platinum level: ACIMAF and Sonoco; Gold level: Carris Reels Inc.; Continuus-Properzi S.p.A.; and SIKORA International Inc.; Silver level: Wire & Plastic Machinery Corp.; and Woodburn Diamond Die Inc.; Bronze level: Gold Metal Recyclers; and Red Kite Management (USA) LP. Onsite: Amacoil Inc.; Baum’s Castorine Co. Inc.; Carris Reels Inc.; Commission Brokers Inc.; Davis-Standard LLC; Lloyd & Bouvier Inc.; SIKORA International Inc.; and Woodburn Diamond Die Inc.

Product Info March 2011

The latest milestone in B+S history is the development and sale of a high performance, high-precision slitting line for wide materials complete with automatic packing line.

B+S, the mechanical engineering company specializing in the cutting of thin and delicate material already started expanding its product range from slitting lines and stretch-bend leveling lines to the processing of wide materials.

The line in development deals with the slitting of aluminum materials with a very delicate surface and an automatic packing line.

The raw material with a width of 1900 mm will be cut into 50 individual strips. The line speed reaching 600 m/min can handle material varying between 0,3 mm – 2,0 mm.

The line will be equipped with a vacuum brake roll so that strips with a highly delicate surface can be processed.

An electrostatic oiling unit is integrated into the brake frame so that the strips can be oiled both on top and underneath.

A flying cut-to-length shear is situated at the entry side of the line to cut scrap pieces at the beginning and the end of the coil.

Part of this line are an edge trimming shear as well as two changeable slitter stand so, that test cuts can be made outside the line.

To round off this line there is a complete automatic packing line with strapping table, weighing station, vacuum suction plate as well as two stacking places with roller ways to transport the coils stacked on pallets.

This line will start production at the Austrian company AMAG in January 2012.

Burghardt + Schmidt GmbH ● Raiffeisenstraße 24 ● 75196 Remchingen
Tel.: +49 (0) 72 32 / 36 61 – 0 ● ww.b-s-germany.de

Download PDF: B+S Product Info March 2011

Today, due to ever increasing requirements, a significant quality criterion to distinguish excellent from adequate suppliers is strip flatness. It is no longer sufficient that the strip flatness be measured and controlled in one of the cold rolling mills in the process chain. The strip flatness must also be kept in view in the following stages of strip processing, which is logical since any thermal strip treatment and any winding and unwinding may change the strip flatness again.

This is where VIP 08 optical shape meter has its application. The target process is not the cold mill but the pickling line, the winding line, the cut-to length line, the levelling line or the coating line. The VIP 08 may also be installed successfully at the hot rolling mill.

If the line, in which the measurement takes place, also has control elements for the flatness control (saddle adjustment, cooling, roll bending or others), VIP 08 may be combined with the proven Vollmer flatness control or also with other flatness control systems.

VIP 08 has also been applied for the flatness measurement of plate material.

Design:

The main components are the light source, the CCD camera and the evaluation unit.

The light source is installed on one side (on the drive side, for example), suspended above the material and the camera on the other side of the material. The system can be designed so that the space directly over the strip is entirely free.

See Figure 1.

Figure 1 – Arrangement of lamp and video camera on-line

The light source creates an approximately 80 mm wide light pattern on the strip material over the entire material width. This light pattern is viewed by the camera.

Particularly attractive is that a free space of only 200 mm is necessary in strip direction. VIP 08 can detect material widths of up to 3000 mm.

Supplementary features for hot mill applications are cooling units and more substantial protection designed into the frame.

Evaluation:

The matrix image, taken by the camera, is read into the industrial PC via a video interface. This system is for processes the video data mathematically to create 200 lines of shape measurements in I-units.

In the next step, these standardized flatness values are processed for visualization and storage. These steps are presently done on 2 processor systems that are connected via TCP/IP.

The standard signal transmission to the line, to a flatness control, to level 2 communication, etc. can be via a TCP/IP network, Profibus DP or discrete digital and analog input and output signals as needed by the application.

Figure 2 – System Overview Screen

Visualization:

The visualization on an industrial monitor (with keyboard and mouse or trackball) in the customer´s control panel typically shows the current flatness in I-Units (1 I-Unit = 10 μm/m). The flatness measurement over the length of the material is shown in the lower part of the main visualization screen in a so-called “carpet” graph.

Stored recordings of measured strips can be played as a video. Both the strip and the line data and the control commands of the control modes are shown. Extensive diagnostic functions are available. Network printer or office workstations are optionally available, can be connected as needed.

Figure 3 – Visualization Example

Measurement Method:

The video signal of the CCD camera shows the light reflection on the material surface.

Camera image 1 shows a relatively flat strip section. Image 2 shows a clear distortion of the light reflection. An image is evaluated every 20 ms and read out in lines.

While comparable optical systems detect height differences of the measurement object per the triangulation process, VIP 08 scans the inclination angles of the material surface elements cyclically.

This measurement method requires moving material. With unflat material, there are different material flow rates over the strip width, due to the relative strip length differences in the material. As long as the material is not cut (in a cut-to-length line, for example), they are shown as very small inclination angle differences in the material surface. These angle differences are used by VIP 08 for the flatness measurement. The measured angles of the strip sections, adjoining over the strip width and not overlapping, form the basis for the determination of the flatness.

A parallel height difference due to vibrations will cause no impairment of the measured parameters (angles). The method is based on the measurement of the angle between the intersection lines, the tangent toward the strip surface on the measurement point in relation to the reference elements. A sufficiently long strip section, including a minimum of 2.5 wave lengths, must be recorded for the determination of the forming indices, ensuring that the resulting measurements will achieve the required accuracy.

Up to 250 measurement points are available for the maximum strip width, resulting in a resolution of about 4 mm with a 1m wide strip (measurement zone width). This high resolution is of particular advantage for the view within the strip edges.

Figure 5 – 3D Display of Strip Sample

The measured inclination angles of the surface elements in relation to the area in strip direction are smaller under strip tension than in tensionless condition. Due to the high sensitivity, even smallest amount of unflatness can be measured and defined realistically by including strip and machine parameters (e.g. the actual total strip tension, E-module, strip thickness, …).

Due to the high sensitivity, VIP 08 can measure extremely small levels of unflatness. Strip, considered as an absolutely flat surface by the human eye, shows a regular longitudinal structure within a range of 0.1 – 0.2 I-units when looking closer at the following example using VIP 08. The resolution of the symmetrical axial flatness error is in line with the distribution of the cooling spray nozzles in the case below:

Figure 6 – Example of VIP 08 Flatness Measurement

Comparative Measurements:

Experienced users know various alternative technologies to measure the strip flatness within the process, such as shapemeter rolls (various principles), laser triangulation processes and light section technologies.

In order to verify the new VIP 08 process of the optical surface inclination angle evaluation, VIP 08 has been installed in various lines parallel to tested and approved shapemeter systems. Test installations in stretch-bend-level lines, pickling line and hot rolling mill have been run. Measurements in comparison to the BFI roll, the laser triangulation system and a segmented measurement roll that has been developed exclusively for application in stretch-bend-level lines have all proven to be consistent.

Example #1 – Comparison with Shape Roll

Figure 7 – Comparison with shape roll on-line (snapshot)

Y Axis = I-Units
Red Graph = VIP 08

X Axis = Strip Width
Blue Graph = Shape Roll

Results shown over the length of the coil:

Figure 8 – Comparison with shape roll over the entire strip length

The recordings show the on-line parallel measurement of a shape roll and the VIP 08 installed beside. Since the shape roll had 40 measurement zones, the VIP 08 measurement values have also been compressed to 40 measurement zones for better comparison.

Example #2 – Comparison with Laser Based Shape Measurement

Figure 9 – Comparison with laser measurement over the entire strip length

As in test case 1, figure 8, this graphic illustrates the flatness measurement over the entire strip. The colors represent the magnitude of the flatness error. The horizontal axis is across the width of the strip and the vertical axis corresponds to the coil length. The color ranges of the I-unit error are identical for both charts.

Since the laser measurement system was limited to 11 traces, the VIP 08 measurement values have also been compressed to 11 measurement traces.

Example #3 – Comparison with Vollmer Shape Roll

This final example is from a continuous SBL process line. In this case, the line is used to flatten strip that has already been rolled to final gauge. The process puts the material under high tension and with a roller leveler section, removes the stress differential that creates the unflatness. The gauge is mounted in the coiling section of the line in which the tension has been reduced. The measurement in this case has been compared to a Vollmer segmented roller with strain gauges to measure the relative tension from which the flatness error is calculated. In this case, it was possible to create both readings on the same graphical display. The upper view shows the current values of the shape (two measurement curves: blue = VIP08, yellow = segmented roller) and the lower view shows the flatness results over the length of the coil. With a strip width of almost 400 mm, the segmented roller is limited to 7 measurement zones. The VIP 08 measurement values have accordingly been compressed to 7 measurement traces.

Figure 10 – Comparison with Vollmer Shape Roll

Shape Control Systems:

An automatic control of the strip flatness is not possible in many lines because of missing control elements. The flatness measurement will then be used to draw conclusions for the optimum setting of upstream processes or to increase the productivity of a line or to avoid damage. It may also be used to provide a report of the flatness of the material for the purchasers of the material.

If the line in which the flatness is measured has control elements to affect the flatness, then automatic strip flatness controls will then be applied, optimizing the strip flatness with a feedback control loop.

By means of a regression analysis, the measured flatness is divided per the existing functions of the machine control elements. Among others, the following control elements have need used with the Vollmer Shape Control System.

# Tilt Control (Error of the 1. order)

# Bending Control (Error of the 2. order)

# Saddle Adjustment (Error of the n-th order)

# Cooling Control (Error of the n-th order)

# Axial Adjustment (Error of the n-th order)

Technical Data:

Applications:
Stretch-bend-level lines, hot and cold mills, pickling lines, trimming lines and many more, form measurement of plates, sheets resp.

Material:
Steel, copper, brass, bronze, aluminum, special alloys, coatings of 0 to 70 N/mm• specific strip tension

For „exotic“ surfaces (we take the liberty of calling surfaces exotic that have not been tested by VIP 08 or Vollmer yet) samples of up to 2000 mm length and 1500 mm width can be sent to Vollmer. This is the maximum dimension that can be measured on our inspection bench with VIP 08. The inspection bench is in our main plant in Hagen, Germany. Samples can be measured there upon receipt of an order to countercheck shapemeter systems using VIP 08 or to verify the suitability for the measurement of „exotic“ surfaces using the VIP 08.

Meas. range: 0.1 – 600 I-units

Resolution: 0.01 I-units

Noise level: 0.00005 I-units

Meas. frequency: 50 Hz

Data output: > 0,4 s

Meas. zone width: max. strip width about / 250

Width measurement: +/- 1.5 x meas. zone width

Strip speed: 0.15 – 25 m/s

Strip temperature: up to 1200° C

Required space

(free view on strip: about 200 mm

Overall width

of components: max. 300 mm

Examples of Application:

Figure 12 –Pickling Line

Figure 13 –Hot Rolling Mill

Summary and Conclusion:

VIP 08 is a new measurement technology that installs easily and offers a very competitive price. The service of the unit is simple so that we hope it will find a wide market.

VIP 08 offers competitive systems to existing versions when the line runs with strip tensions up to about 70 N/mm• (10 KPSI).

For us at Vollmer it is a great pleasure to get to know so many new contacts and customers since we introduced VIP 08 on the market in November 2009. After so many years in the business, this system will develop further fields of application for us in addition to our previously established markets in the metals producing field.

February 2010, Andreas Selent

The VIP 08 Optical Flatness Measurement System is a recent development for use in the metal producing industry. When the strip tensions are lower than 70 N/mm2 (10 KPSI), it affords the user the ability to measure continuous strip flatness without contact to the strip and to display the results in the industry standard “I-unit” format.

The system consists of a row of halogen lamps installed in a ‘mirrored light box’ as shown in figure 1. This row creates a ribbon of light on the surface of the strip that spreads across the strip width. Mounted on the other side of the strip is a video camera that is pointed at the strip and views the entire reflected beam.

Figure 1 – Arrangement of lamp and video camera on line.

The video camera image is read into a PC using an interface card. The general principle of the measurement is that when the strip is flat, the light beam image will be straight and consistent. But, if there are flatness imperfections, the beam edge will move side to side due to these imperfections.

The PC software analyzes the video image by reading the position from a reference point to the light edge at 200 locations along the beam. These 200 readings are scanned 50 times per second and each second a reading of the relative shape at the 200 points is calculated using a patented set of mathematical tools. These tools break down the video readings to give the amplitude and frequency of the shape errors which can then be converted to I units of shape variation. The data is then brought to a monitor for presentation to the operator (see figure 2). Further, the data may be interpolated using linear regression analysis to create the needed components for use with automatic shape control systems.

Figure 2 Typical monitor window of shape measurement

There are several methods to measure strip shape that have been developed over the years. In order to verify the accuracy of the VIP 08, several side by side tests were run on process lines (SBL), cold rolling mills and hot rolling mills. Data taken during these tests lead to the conclusion that the VIP 08 was capable of reaching the same level of accuracy and control as these other systems when the strip tension was below 70 N/mm2 (10 KPSI). Here is a short description of the results of these tests. In example 1, the top graph is a ‘snapshot’ view of the strip shape along the length of the coil. The color graphs below show the shape measurement over the full length of the coil in a ‘carpet’ view. The color code in both views in the same and represents the level of out of flatness in I units.

Example #1 – Comparison with Strain gauge based shape roll on Cold Rolling Mill

Y axis = I Units Red Graph = VIP 08 X axis = Strip Width Blue Graph = Shape Roll

Results shown over the length of the coil

Top view = VIP 08 Bottom View = Shape Roll

Example #2 – Comparison with Laser based shape measurement on steel hot rolling mill

VIP 08 Laser

As in case 1, this graphic illustrates the flatness measurement of the entire strip. The color represents the flatness error, the horizontal axis is across the width of the strip and the vertical axis is along the length of the coil. The color ranges of I unit error is the same for both charts.

Example #3 – Comparison with Vollmer Shape Roll on Stretch-Bend-Level (SBL) Process Line

This final example is from a continuous SBL Process line. In this case, the line is used to flatten strip that has already been rolled to final gauge. The process puts the material under high tension and with a roller leveler section, removes the stress differential that creates the unflatness. The gauge is mounted in the coiling section of the line in which the tension has been reduced. The measurement in this case has been compared to a Vollmer segmented roller with strain gauges to measure the relative tension from which the flatness error is calculated. In this case, it was possible to create both readings on the same graphical display. The display is shown below. The upper display shows the current values of the shape and the lower view shows the flatness results over the length of the coil.

The Blue Graph is the VIP08 and the Yellow Graph is the shape roll.

by Gert Mücke and Frank Gorgels

Flatness measurement in cold rolling mills and strip processing lines is most commonly car-ried out with measuring rolls designed to operate simultaneously as deflector rolls. The known BFI-shape measuring roll, with more than 800 worldwide installed and successful op-erating applications, is also based on this principle. According the latest design force sensors are mounted in axially parallel bores, which are executed as through-holes close to the shell surface of a solid roll body. This arrangement provides a robust design with a completely gap-free roll surface over the entire cylinder width. The new roll type opens up new variation possibilities of the roll surface design as well as new applications of this measuring system. The high load capacity of the piezoelectric force sensors and the non-contacting optical sig-nal transmission contribute to a fail-safe and nearly maintenance-free system.

STATE OF THE ART

Out-of-flatness may occur on strip and sheet metal both during the production of these prod-ucts in hot and cold rolling mills and during downstream treatment processes. This is caused by localized differences in the degree of plastic deformation across the strip width or thick-ness, which in turn lead to differences in the level of internal stresses in the strip material. Deviations from ideal strip flatness occur when the internal stresses in the strip exceed a certain critical value, called the critical buckling stress.

In cold rolling mills, strip is produced and coiled under tension, which partially can assume high values. Length deviations being present in the strip are stretched out by the applied ten-sion in such a way that the strip appears to be flat during rolling. However, latent flatness deviations are present in the strip and appear later when the strip is uncoiled. This can result in production stoppages, reduced output and poorer quality. In order to be able to influence flatness deviations during the rolling process itself, using the adjustment systems on rolling stands, flatness measuring systems are required. These measuring systems have to be ca-pable of being used in diverse types of rolling mills and strip treatment lines and must deliver precise results, irrespective of the steel grade and its dimensions. Since the strip is subjected to longitudinal tension in most strip treatment lines, the tensile stress distribution, which itself is dependent on the length distribution, is used to determine deviations in strip flatness. Vari-ous methods are used to determine the tensile stress distribution.

Some measuring methods apply external forces to the strip, causing it to be displaced, in order to determine the differences in strip tension. These forces can be generated by mag-netic fields or by oscillating negative-gauge pressure (vacuum principle), for example. The measurement of the local displacement is then used to determine the equivalent strip tension distribution across the strip width.

Displacement measuring systems are normally installed between the roll gap of the rolling mill and the deflector roll before the coiler (Fig. 1a). However, since the strip is unsupported and moves freely through this space, strip displacements may occur that are not attributable to longitudinal tensile stresses and will therefore cause spurious measurements.

In thin strips, the longitudinal tensile stress applied to the strip may therefore result in elastic necking and folding (Fig. 1b). These folds generate a bending resistance similar to that of corrugated plate/sheet, which will restrict the extent of strip displacement under the applied displacement forces and will cause errors in flatness measurement.

In thick strips, bending of the strip around the deflector roll will cause a length bow which in turn results in a cross bow due to cross contractions. If this cross bow has superimposed flatness deviations, such as long strip edges, the direction of the cross bow will change from upwards to downwards in an uncontrolled manner during displacement of the strip. The flat-ness measuring system then wrongly registers this change of direction as a flatness devia-tion (Fig. 1a)

Length bows and the resulting cross bows can be caused by other factors besides bending of the strip around the deflector roll. They may also occur due to asymmetries in the roll gap, which will aggravate the formation of the cross-bow due to the bending process.

There is another bow-effected influence on the result of flatness measurements obtained with displacement measuring systems. As the length bow becomes more pronounced, so does the distance of the strip from the measuring system, so that the strip may move out of the range of the measuring system (Fig. 2b). Experience has shown that, unless additional strip guidance rolls are installed, displacement measurement systems are suitable only for strip thicknesses in the range of 0.2mm and 2mm.

Displacement methods using the vacuum principle have an additional drawback. The positive atmospheric pressure prevailing at the strip edges results in an undefined pressure condition in this zone, so that no precise measurement is possible. Measurements in this zone are, however, especially important for flatness control.

The methods most commonly used to measure strip flatness deviations measure the radial force exerted by the longitudinally tensioned strip as it is deflected around the deflector roll. This radial force varies locally as a function of differences in tensile strength distribution across the strip width. By using suitable measuring rolls with measuring zones distributed across the width of the roll cylinder it is possible to determine the local radial force and to calculate the tensile stress and hence the length distribution across the strip width (Fig. 3a).

Because there is direct contact between the strip and the measuring roll, these measuring systems are free of the error sources inherent in the above-described displacement measuring systems.

The well-known BFI Flatness Measuring Roll, of which more than 800 are now in use around the world in a wide variety of cold-rolling mills and strip treatment facilities, also operates on this deflection roll principle. BFI’s strategy is to replace the deflector rolls which are in any case required before the coiler with measuring rolls designed to operate simultaneously as deflector rolls. This avoids the installation of separate measuring systems that would take up additional space (Fig. 3b).

The flatness measuring roll as the core of the BFI flatness measuring system has been sys-tematically improved over the past few years. The main focus of this development effort has been to improve the measuring roll construction and to broaden the range of possible appli-cations in strip production. The particular characteristics of the latest roll generation are de-tailed below.

BFI FLATNESS MEASURING ROLL (A-TYPE)

Mechanical Structure

The roll body is made of roll steel and consists of a solid roll body exhibiting an uninterrupted, smooth, gap-free and homogeneous roll surface over its entire cylinder width (Fig. 4).

Fig. 4: BFI flatness measuring roll (A-type)

Depending on customer preference, the surface of the roll body may be hardened or plated with a wear-resistant material such as hard chromium or tungsten carbide. Elastomer (spe-cial rubber) or polyurethane coatings can be applied to the roll body without extensive sur-face preparation. Similarly, the roll surface can be provided with different roughnesses or textures to produce defined roll-to-strip friction conditions where this is desirable for process reasons. Especially for use in higher strip temperature ranges as encountered in the produc-tion of silicon steel strip, for instance, the roll body can also be supplied in a high-temperature version for temperatures up to 300°C.

According to the measuring operation requirements, the roll body can be manufactured to different diameter and cylinder width specifications. The measuring rolls produced to date vary between 160 and 700 mm in diameter and between 550 and 2400 mm in width. The roll necks may be either integral with the roll body or attached to it as separate components via flanges. To accommodate the force sensors, axially parallel bores are provided in the end faces of the roll body (Fig. 5).

Fig. 5: Measuring roll body with axial bores

Arranged at a distance of 5 to 11 mm from the shell surface, these bores may be through-holes extending over the full cylinder width or be produced as blind holes. The diameter of the sensor mounting bores can be between 30 mm and 50 mm, depending on the force sen-sor type employed. Between 2 and 6 such axial bores can be provided, depending on the desired number of force sensors and the wrap angle of the strip around the roll body when in service. Special tapered sleeves have been developed to receive force sensors which are introduced into the bores from the roll end face and positioned at different depths. By means of the tapered sleeves the force sensors are fixed in place with a high level of prestress..

Depending on the bore depth, up to 24 force sensors can be fitted in a single bore in this manner. By offsetting the sensors over the width of the measuring roll cylinder, the sensors can be axially positioned so that there will be one sensor every 10 mm from one bore to the next. This is particularly beneficial for precise measurements in the strip edge area or where tensile stresses vary widely within narrow strip zones.

Fig. 6: Axial bore with mounted force sensor

Electronic structure

As with previous BFI Flatness Measuring Rolls, the new generation rolls use proven piezo-electric force sensor technology (Fig. 7). These force sensors are very small yet can handle high loads at extremely low levels of elastic deflection. The action of mechanical pressure loads on the piezo quartz sensor produces a charge which is converted into a force-proportional voltage by the so-called charge amplifier. The piezoelectric sensors are passive force sensors requiring no electrical power supply.

Fig. 7: Piezo force sensor (Kistler standard type 9051A)

Outstanding features of these piezo quartz force sensors include:

• extremely broad measuring range: 0.01 N to 120.000N

• broad temperature range: -196°C to 200°C or 300°C

• high linearity: < 0.3 %

• high load capacity: 144 kN

• high stiffness up to: 9 kN/micron

• very low hysteresis: < 0.5 %

Since the force sensors in different bores are distributed at different angular positions over the circumference of the measuring roll, the staggered sensors are not exposed to strip loads simultaneously. So they can be connected in parallel to provide input to a common charge amplifier (Fig. 8).

Fig. 8: Data logging, -transmission and -processing

In conjunction with this charge amplifier with “on-line” switchable gain, these force sensors can deliver readings of a constantly good resolution across different force ranges. On a 20high reversing cold rolling mill for stainless steel strip, for instance, the system can meas-ure forces over a 1:200 range without any change in resolution quality.

This high measured-value resolution is achieved by:

• Adapting the charge voltage converters to the rolling mill and production parameters

• Online switching of the charge voltage converters between 3 amplification ranges during rolling mill operation

• High resolution of over 1/4000 (72 dB) per amplification range

For reliable transmission of force measuring signals from the flatness measuring roll to the measurement processing unit, the signals are digitised and encoded by pulse code modulation. The transfer of signals from the rotating measuring roll to the stator unit is achieved in a non-contact manner by means of infrared light. The charge amplifiers, encoders and trans-mission modules are integrated into one compact unit in a housing flanged to the measuring roll (Fig 9).

Fig. 9: Charge amplifier and transmission unit

This housing also contains a 5000 ppr incremental encoder which allows precise correlation of the sensor positions with the force signals. It can also be used as a measuring transmitter for mass flow control, for example.

Following the transmission of the digitised signals from the rotating measuring roll via the stator to the electronic interface unit placed in the switchgear room, the signals are decoded and fed to the processing algorithms. The measuring signals, operating and equipment pa-rameters are linked via these processing algorithms in the DSP processor so that the flat-ness data obtained can be output as required for control and display purposes.

The data communication to display and control the flatness at the rolling mill is based on the TCP/IP protocol.

Special features

In existing measuring systems, the measuring zone distribution and the number of measuring points are fixed. With the new BFI measuring roll (type A), on the other hand, the special sensor installation technology means that the number of sensors and their positioning can be adjusted after delivery without any modification to the roll body. System adjustments of this kind can be made directly on-site in the user’s facilities. This is especially useful in cases when a change in production calls for a different zone distribution or when a sensor has to be replaced.

Since the measuring roll with its smooth, gap-free and entirely homogeneous surface is out-wardly completely identical to a normal deflection roll, its behaviour during the production process and its handling during maintenance operations, such as regrinding, is similar to that of any standard deflection roll normally used in its place.

Operating Experience Gathered To Date

More than 60 units of the new measuring roll type with axial bores and gap-free surfaces are now either in industrial operation or in production. The measuring rolls are distributed by the German BFI-licensees Achenbach Buschhütten GmbH, SMS DEMAG AG, Siemens AG., Sundwig GmbH, Friedrich Vollmer Feinmessgerätebau GmbH as well as Hess Engineering, USA und Kobe Steel, Ltd., Japan.

These rolls vary between 160 and 700 mm in diameter and between 450 and 2400 mm cylinder width. The surfaces of the rolls currently in service are:

• hardened to HRC 58 ^+3/_-2

• hardened and textured

• hard chromium plated to HV 950

• tungsten carbide plated

• rubberised

The main applications to date include skin pass mills, reversing mills, carbon steel tandem mills, cluster mills for high-grade steel strip, rolling stands for electrical sheets as well as aluminium and copper rolling mills. Over the whole production range of cold rolled products the operating measuring rolls have satisfied the highest demands on strip surface quality.

The operating experience accumulated so far confirms the expected functionality of the system and the high repeatability of the measuring signals. The sensor measuring accuracy is less than 1 I-Unit and the roll measuring accuracy is down to 2 I-Units.

Contact:

Frank Gorgels

Betriebsforschungsinstitut (BFI)

E-mail: Frank.Gorgels@bfi.de