Measuring and testing – Sheet – woven fabric or fiber
Reexamination Certificate
2002-04-09
2004-04-20
Noori, Max (Department: 2855)
Measuring and testing
Sheet, woven fabric or fiber
Reexamination Certificate
active
06722194
ABSTRACT:
The invention concerns a process and a device for detecting latent flatness defects of a metal band product running along a longitudinal direction.
When rolling metal bands, and notably thin rolled sheet, flatness defects may be observed once the band is in resting position, but that may be in latent condition in the band, as said band is maintained under tensile load. Such defects are due generally to small variations over the width of the band, to the elongation carried out by the rolling process and may be corrected while acting on the rolling conditions and, in particular, on the distribution, in the transversal direction, of the clamping pressure applied between the working rolls.
To that effect, modern rolling mills are fitted, usually, with means enabling to correct the gap profile to the let the product through
Often, the stand of the rolling mill is fitted with actuators bearing upon the chocks of the working rolls in order to bring said rolls closer or apart, with a cambering effect of the rolls.
In another arrangement, fractional spraying means enable to act thermally on the profile of the rolls.
It is thus possible to act on the profile of at least one back-up roll which comprises a ductile envelope mounted to rotate around a fixed shaft and bearing upon said shaft by a plurality of actuators whereof the position and the pressure are adjustable, whereas said actuators are distributed over the width of the band.
Usually, these means of adjustment are controlled thanks to information given by a measuring device placed downstream of the rolling mill and sensitive to the variations, over the width of the band, of the tensile load applied to said band, which correspond themselves to the variations in elongation of the longitudinal fibres of the band.
Such a measuring device consists, generally, of a deflector roll comprising a cylindrical body mounted to rotate around an axis perpendicular to the longitudinal running direction of the band. Said band is applied under tensile load to an angular sector of the external surface of the roll that is fitted with a series of sensors enabling to measure the variations in the local application pressure of the band. These detectors are spaced from one another and distributed over the whole length of the roll, whereas the band is divided into a series of longitudinal zones each corresponding to a detection zone whereof the width is set, whereon the measurement conducted by the sensor is integrated in order to assess the latent defect to be corrected in the corresponding longitudinal zone.
To avoid interferences between the measurements conducted on two adjacent measuring zones, the sensors are advantageously offset angularly from one zone to the next.
Generally speaking, a measuring roll comprises therefore a plurality of detection zones distributed over its whole length and each fitted with a sensor for transmitting a signal related to the application pressure of the corresponding section of the band, when this detection zone passes through the angular sector where the band is in contact with the roll.
As the band is under tensile load, the roll must sustain the deflection and comprises therefore, usually, a central tubular body of sufficient thickness to provide the necessary strength and fitted, on its external surface, with a plurality of recesses wherein the measuring sensors are located, whereas each recess is enclosed, outwardly, by a protection wall to avoid direct contact between the sensor and the running band.
In certain arrangements known, the pressure applied by the band in the detection zone is measured directly by means of a strength sensor, for example of the piezo-electric or quartz type, which is interposed between the bottom of the recess and the protection wall whereon the band is applied.
To obtain information directly representative of the pressure applied, the protection wall may consist of the external surface of a cap-shaped piece that encloses the recess outwardly but a slight clearance ought to be left between this cap and the lateral surface of the recess, a clearance that may be filled with dirty particles (DE-A-19747655).
In certain arrangements known, the protection cap consists of a wall imbedded in a countersink provided on the periphery of the recess. However, as the sensor is clamped between the bottom of the recess and the protection wall which rest on the bottom of the countersink, the pressure measurement is disturbed by deflection resistance of this wall.
To remedy these shortcomings, it has been suggested in the document U.S. Pat. No. 3,324,695, to cover the roll with a continuous envelope applied onto the external surface of the resistant body of the roll as a hoop, whereas each recess of a sensor is covered by a portion of this envelope forming a thin protection wall.
In such a case, as described, for example, in document U.S. Pat. No. 4,356,714, the pressure applied by the band is not measured directly, but the deformation of the thin wall resulting from this pressure, by means of a position sensor having two elements mounted to slide radially one inside the other and resting, in opposite directions respectively, on the bottom of the recess and on the internal surface of the thin wall, in the centre of said wall.
This thin wall stretched above the sensor and sensitive to the pressure applied by the product, behaves like a plate imbedded on its edges and the conventional formulae in the mechanics of materials enable therefore to assess the pressure applied onto the ductile wall from the deflection measured at the centre of the plate.
Advantageously, the position sensors may be of the <<LVDT >> type, having a primary winding and two secondary windings mounted opposite one another, between which variable magnetic coupling is created by a mobile core linked with the displacement of the stem of the sensor.
The roll is associated with an automatic measuring system which enables, at each rotation, to send a measuring pulse to the primary winding of each sensor and to read the induced signal at the terminals of the secondary windings. An angular position encoder enables to conduct the measurement under load when each sensor passes through an application zone of the band. Another measurement is conducted in empty condition when the sensor is situated inside the angular application sector. The difference between the measurement under load and the measurement in empty condition provides the deflection at the centre of the plate, from which the pressure applied can be determined and, consequently, the tensile load in the corresponding longitudinal zone of the band.
The measurement in empty condition can be conducted in any angular position of the roll which does not correspond to the measurement under load for one of the sensors. Said sensors are therefore distributed judiciously on the surface of the roll in order to enable easy management of the measurements in empty condition and under load, during a rotation of the roll (U.S. Pat. No. 4,356,714).
Until now, such flatness measurement rolls had only been used in cold rolling facilities for which the temperature of the band remains moderate.
Indeed, if a pressure sensor clamped between the bottom of the recess and the closing cap of said recess is used, the expansions of the different parts, in case of rising temperature, may cause excessive friction and, consequently, faulty measurements.
This shortcoming does not exist in the systems where position sensors covered with a closing plate are used. However, this plate consists of a thin wall which takes on the temperature of the band immediately and is therefore subject to thermal deformation. Moreover, as the rotational speed is high, the centrifugal force may also induce a slight deformation.
The comparison of the value under load of the signal with a value in empty condition measured at each rotation, enables to reset the sensor and to measure the actual deflection of the plate, but to do so, the body of the roll should remain at substantially constant temperature and this is only valid
Faure Jean-Paul
Malard Thierry
Arent Fox Kintner & Plotkin & Kahn, PLLC
Noori Max
Vai Clecim le Polyedre
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