Mitsubishi Heavy Industries Technical Review Vol. 51 No. 3 (September 2014)
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Development of Strip Shape Meter withHigh Accuracy Under Severe Conditions of Hot Strip MillSHINYA KANEMORI*1

RYOHEI KINOSE*2

SHUJI MANIWA*3

TAKAO OWADA*4HIDEAKI FURUMOTO*5SHIGEKI SUEDA*1

Mitsubishi-Hitachi Metals Machinery, Inc. has developed and has been manufacturing andmarketing contact type inline strip shape meters for hot rolling in order to enable continuous
accurate measuring of strip shape during rolling and improve strip threading stability on hot strip
mills. The inline strip shape meter is designed to accurately measure the shape of a strip, evenunder a harsh, hot, humid and dusty environment. This shape meter consists of seven segmented
rolls aligned in the strip width direction. Low hysteresis is attained by applying torque meters at
each segment. In addition, an internal water cooling system is employed and it was confirmed thatsufficient durability, even in harsh environments, was established. The strip shape meter has been
operating satisfactorily for more than eight years on an actual hot strip mill. This paper describesthe development details of the strip shape meter.

|1. Introduction
Hot rolling has tended to produce harder and thinner products, as represented by high tensile
strength steel, and therefore inline strip shape measurement has been required for the improvementof strip shape control accuracy and the attainment of stable rolling. Optical measurement devices1
are already in practical use. At a major part of strip length where tension acts on the strip, however,the strip shape is hidden and cannot be measured. Therefore we have developed a strip shape meterthat uses a torque meter to accurately measure the width directional distribution of the tension in
the rolling direction, which corresponds to the strip shape (Looper Shape Meter, hereinafterreferred to as LSM)2-4. This device employs a method that separates the tension control roll (looperroll) between the rolling stands in the width direction and measures the tension distribution acting
on each separated roll. This method has low hysteresis and can perform accurate detection.
Through laboratory tests and trials on the actual hot strip mill, it was verified that this device had
sufficient durability even under the harsh conditions of hot rolling.

|2. Device structure and features of LSM
2.1

Device structure and features

Figure 1 shows an external view of the LSM installed between stands of the finishing mill.
The device is installed replacing the existing looper on the upstream side of the final stand of thefinishing mill. The device consists of seven segments aligned in the width direction and uses thetorque meters explained below to accurately measure the width directional distribution of thetension in the rolling direction. As a result, the device can measure the shape of the strip beingrolled. In addition, the looper roll between the rolling stands can easily be replaced with the device,and LSM has almost the same tension control performance primarily demanded on the inter-standlooper system.
*1

Hiroshima Research & Development Center, Technology & Innovation Headquarters*2

General Manager, Plant Engineering & Planning Expedition Department, Mitsubishi-Hitachi Metals Machinery, Inc.

*3

Manager, Electrical & Automation Engineering Group, Electrical & Automation Systems Department,
Mitsubishi-Hitachi Metals Machinery, Inc.

*4

Manager, Design Group 1, Rolling Mill Design Department, Mitsubishi-Hitachi Metals Machinery, Inc.

*5General Manager, Research & Developing Office, Technical Developing Department, Mitsubishi-Hitachi Metals Machinery, Inc.

Mitsubishi Heavy Industries Technical Review Vol. 51 No. 3 (September 2014)28

Figure 2 shows the structure of the segment roll. Torque meters are installed on both sides ofthe center block. Force from the roller is directly received by them through the arm. The roller issupported by the spherical roller bearing, and torque corresponding to the distribution of thetension in the segment roll can be measured by the torque meters on both sides. The torque meters
are covered by a shield and air-purged to prevent the intrusion of water and dust. For the protectionof the torque meters against radiative heat from a hot rolled strip, an internal water coolingstructure is employed for the center block and the apron above the segment.

Figure 1 External view of LSM for hotrollingThis figure shows an external view of the LSM
installed between stands of the finishing mill and hotrolled strip.

2.2
(1)

Figure 2

Structure of segment roll

Force from the roller is directly received by the two
torque meters on both sides through the arm.

Shape calculating method and measurement system
Shape calculating method
The strip width directional component of the tension in the rolling direction wasapproximated by the following Chebyshev polynomials5:
T(x)=C0+C1Φ1(x)+C2Φ2(x)+C4Φ4(x)[1]where x is the non-dimensionalized strip width directional position.
The torque meter measurement value {Mi} is represented using the tension distribution
coefficient {Cj}={C0, C1, C2, C4}.
{Mi}={Aij}{Cj}[2]where i (i=1-14) corresponds to the number of each torque meter, j (j=0, 1, 2, 4) is the order oftension distribution, and {Aij} is the coefficient relating the torque to the tension distributionthat is represented as the distance between the roller and the torque meter, strip width or otherfactors. The primary component is the side wave shape and the secondary component is thecenter buckling or edge wave shape. This tension distribution is calculated by the following
formula using the least squares method:{Cj}=({Aij}t･{Aij})-1{Aij}t･{Mi}
(2)

[3]

Measurement system
Figure 3 shows the structure of the measurement system. Measurement data are sentfrom fourteen torque meters aligned in the width direction to the shape calculation device. At
the same time, the looper angle, strip speed, strip thickness, strip width and other data are sentfrom the level 1 and level 2 controllers to the shape arithmetic unit. The calculated strip shapeis transmitted to the control pulpit and then displayed on the HMI (Human Machine Interface)screen.

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Figure 3 Configuration of measurement system

This figure shows the measurement system configuration where torque measured by the shape
meter and thermocouple data are sent to the shape arithmetic unit, and the calculated strip
shape is transmitted to the pulpit through Ethernet and then displayed on the HMI screen.

|3. Laboratory test results(1)

Heating test
In order to protect the torque meter against radiant heat from the hot rolled strip with atemperature of 900°C or higher, an internal cooling structure is employed for the center blockand the apron above the segment roll. For verification of the cooling effect, one segment torquemeter assembly was heated by a heater, and then the temperature of the torque meters and theapron were measured using thermocouples.
Figure 4 shows the temperature measurement results. Although the heater temperaturerose to 900°C approximately 20 minutes after the start of heating, the torque meter temperature
was saturated at approximately 60 minutes. At 180 minutes, the torque meter temperature wasapproximately 29°C, which was far below the maximum allowable temperature of 60°C.

Figure 4

Heating test resultsThis figure shows the results from the measurement of torque meter temperature
after one segment torque meter assembly was heated to a temperature of 900°Cor higher.

(2)

Verification of torque measurement accuracy
For accurate measurement, it is important to reduce the hysteresis caused by sliding parts.
Because the LSM measures tension distribution directly with the torque meter and therefore has
few sliding parts, hysteresis causing measurement disturbance is low. For verification of this,
hysteresis was measured in a laboratory test. Small weights were hung on four different pointson the segment roll to perform loading and unloading (0.6, 1.2, 1.8, and 3.6 Nm), and measured
values indicated by the torque meters on both sides were recorded. The test was implemented
under conditions as close to the actual machine as possible by heating for one hour or longer
using a heater.

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Figure 5 shows the measurement results. The horizontal axis represents the output oftorque meter A, and the vertical axis represents output of torque meter B. In Figure 5, the solid
circle represents the test point for loading and the open circle represents the test point forunloading. The dotted line represents the value calculated based on the weight and the distanceto the torque meter. The relationship between torque A and torque B corresponds well to thecalculated value and hysteresis as low as 1 Nm or less was verified.

Figure 5 Verification results of torque measurement accuracy

This figure shows the relationship between torque output values measured by thetorque meters on both sides in the segment roll on which small weights wereloaded and unloaded.

|4. Results of application to actual line
4.1

Durability verification result

The LSM was installed, replacing the existing looper, between stands on the upstream side of
the final stand of an actual finishing mill to perform a verification test. Figure 6 shows applicationof the LSM to the actual line.
The final strip thickness was 2.04 mm and the width was 1287 mm. The torque meter
temperature during approximately 10 minutes of continuous rolling could be maintained atapproximately 25°C. After rolling, there were no signs of intrusion of water or dust and the LSM
was in a healthy condition. The LSM has been operated for more than eight years and soundness
has been able to be maintained under the harsh conditions of actual equipment.

Figure 6

Application of LSM to actual line

This figure shows rolling using the LSM.

4.2

Shape measurement results

Figure 7 shows an example of the shape measurement results. The final strip thickness was
2.44 mm and the width was 1513 mm. Torque was high at both ends and the center, and low at thequarter point as in graph (a). The strip shape calculated with the torque measurement value showeda smaller elongation on the workside, a center buckling and a quarter buckling as in graph (b), andit could be decomposed into the primary, secondary and quaternary components as in graph (c), (d)and (e), respectively.

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Figure 7 Strip shape measurement results

This figure shows the calculation results of strip shape (total, primary, secondary and quaternary components)
based on the torque measurement value in actual rolling.

|5. Conclusion
We have developed an inline strip shape meter for hot rolling and obtained the following
results.
(1) The small hysteresis realized by the torque meter construction was verified in a laboratory
test.
(2) The strip shape measured on an actual line could be decomposed into the primary, thesecondary and the quaternary components.
(3) Sufficient durability of the LSM was verified under the harsh conditions of hot rolling.
(4) The LSM has been operating for more than eight years on an actual line and has beenutilized as a useful monitoring tool for the operator.
The shape meter is expected to prevent tail pincher accidents and defective shapes by using
the measurement results for leveling and bender force adjustment, and therefore can contribute tostable strip threading-out and the improvement of productivity.

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