Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
2000-01-10
2001-03-27
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
active
06205829
ABSTRACT:
The invention relates essentially to a method of regulating a multi-frame hot rolling mill, and in particular a multi-frame mill that does not have force sensors. The method is intended more particularly to eliminate interfering tension/compression stresses to which a product is subjected while being rolled, which product may be of the bar, sheet, or metal section member type.
BACKGROUND OF THE INVENTION
As is known, rolling operations lead inevitably to variations appearing to some extent in the magnitudes that are associated with deformation of the metal being rolled. This is a consequence in particular of the fact that the rolling forces and torques, the temperature of the rolled product, and the coefficients of friction do not remain accurately constant during rolling. Inaccuracies due to the way the rolling process is controlled cannot be eliminated completely, and for example there are small variations in instantaneous speeds. There are also disturbances which are due to oscillations caused by imperfections in the drive system of the mill or indeed to wear of the tools used. Variations in the rolling magnitudes and dimensional variations of the product as fed to the mill also contribute to degrading the dimensional attributes of the finished product. As a consequence of all these disturbances, the reference tensions specified by a rolling plan for the various frames of a mill are not complied with. This gives rise to tension or compression stresses being present in those portions of the product that are situated in the intervals between frames.
Tension or compression appear in a product that is engaged in a plurality of successive frames in a continuous run particularly when the product is being inserted into the frames and when the preadjusted speed of each frame is not perfect. If the downstream frame is tending to pull the upstream frame then the product present between the frames will be working in traction; if the upstream frame is tending to push the downstream frame by means of the product, then it is subjected to compression. The difference between the speed Vs
n−1
of a product leaving an upstream frame and its speed Ve
n
entering the following frame downstream gives rise to stress &Dgr;&tgr; which is expressed by Hooke's law, and is as defined below:
Δ
τ
=
E
∫
(
Ve
n
-
Vs
n
-
1
)
ⅆ
t
L
where &Dgr;&tgr; is the variation in tensile or compressive stress to which the metal is subjected between the two frames, where L is the distance between the frames, and where E is Young's modulus.
When the outlet speed Vs
n−1
of the upstream frame referenced n−1 is not in balance with the inlet speed Ve
n
of the following frame referenced n, then the stress in the metal in the interval between the frames modifies and the operating point of each of the two frames shifts towards an equilibrium point where the outlet speed from the upstream frame is equal to the inlet speed of the following frame. As is known, this modification gives rise to modifications in the thickness of the rolled metal and to variations in the slip in the two frames concerned. A phenomenon arises whereby the rolling process is self-stabilizing, but this phenomenon is to the detriment of dimensional tolerances for the product and for the desired profile.
Tensile and compressive forces also appear in a product engaged in a plurality of successive frames during rolling whenever the product is not totally uniform over its entire length and presents variations in section and/or hardness that are associated, for example, with variations in temperature. Thus, variation in the hardness of a product entering a frame n−1 gives rise to variation in its section on leaving said frame and to variation in downstream slip, thus leading to a modification in the rate at which metal is output from the frame.
To remedy those drawbacks, there exist control systems applied to multi-frame mills that include means for monitoring traction in the various intervals between frames by individually regulating the ratio of rolling torque over rolling force on a frame-by-frame basis. Such regulation requires sensors to be present, and in particular rolling force sensors which are expensive, difficult to install and maintain, and which constitute a potential source of breakdowns. In addition, that solution which requires the presence of sensors is not always applicable, particularly in rolling mills for producing bars or girders in which such sensors are rarely installed.
OBJECTS AND SUMMARY OF THE INVENTION
The invention thus provides a method of estimating and regulating tension and compression in a multi-frame rolling mill working on hot metal products.
According to a characteristic of the invention, starting from an initial situation while a product is being passed into the various frames of the run, torque is measured at each frame through which the product passes at the moment when said product reaches the following frame downstream therefrom, the measured value is stored as a reference value, and the frame for which the measurement is made is switched from speed regulation to torque regulation. The last frame into which the product enters acts as a speed controlling frame for all other frames situated upstream therefrom, thereby enabling it to retain torque equal to its reference torque by varying its speed.
Continuous updating of the estimated traction torque and of the rolling torque for zero traction is performed at each frame, and the estimated inter-frame traction values make it possible to regulate these values to levels which are predefined in the rolling plan. This makes it possible to set out to perform rolling with minimal inter-frame traction levels, as recommended by numerous mill operators.
According to a characteristic of the invention, from the moment when reference torque measurements have been stored as rolling reference values, a distribution key for traction stresses between frames of the run is used such that:
Δ
C
T
,
i
=
Δ
C
i
-
λ
i
∑
λ
i
S
o
R
i
r
i
where:
&Dgr;C
T,i
corresponds, depending on its sign, to the variation in the traction or compression stress for the frame of rank i amongst the n frames of the run;
R
i
and r
i
are the working radius and the reduction ratio for the frame of rank i;
S
0
corresponds to the sum of the measured resistive torque variations (&Dgr;C
i
) as seen by the mechanism (&Dgr;C
i
.r
i
) and divided by the lever arm (&Dgr;C
i
.r
i
/R
i
), where &Dgr;C
i
is the variation in the resistive torque C
i
relative to the reference torque stored for the frame of rank i;
with &lgr;
i
equal to zero, either if the product S
0
.&Dgr;C
i
is negative, or if the product S
0
.&Dgr;C
i
is positive when dealing with the first frame and the measured variation of resistive torque &Dgr;C
i
offset as a function of speed through the second frame exceeds a parameterizable threshold, or else if the product S
0
.&Dgr;C
i
is positive while the measured variation of resistive torque &Dgr;C
i−1
is greater than a second parameterizable threshold and said measured variation of resistive torque &Dgr;C
i−1
offset as a function of the speed through the frame i, where i>1, is less than a third parameterizable threshold; or
&lgr;
i
is equal to &Dgr;C
i
if the product S
0
.&Dgr;C
i
is positive when dealing with the first frame and the measured variation of resistive torque &Dgr;C
i
offset as a function of speed through the second frame is less than a fourth parameterizable threshold, or indeed when dealing with some other frame and the measured variation of resistive torque &Dgr;C
i−1
is less than a fifth parameterizable threshold, or said torque variation &Dgr;C
i−1
offset as a function of the speed through frame i, where i>1, is greater than a sixth parameterizable threshold.
The invention also provides a system for controlling a multi-frame rolling mill that operates on hot metal products, in which the frames
Alstom
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tolan Ed
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