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
1999-07-19
2001-01-23
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
C072S008600, C072S009200, C072S205000, C072S365200
Reexamination Certificate
active
06176112
ABSTRACT:
BACKGROUND INFORMATION
The present invention relates to a method and a device for dynamic adjustment of the roll gap in a roll stand of a mill train having multiple stands.
FIELD OF THE INVENTION
For strip rolling in a mill train as described, for example, U.S. Pat. No. 3,170,344 and an artivular by S. Duysters et al. entitled “Dynamic Modeling Of The Finishing Train of Hoogovens' Hot Strip Mill And Optimization of Thickness Control Parameter,” Journal A, vol. 31, no. 4, Dec. 1, 1990, pp 8-15, describe that for strip rolling in a mill train, in hot wide strip finishing strip mill and optimization of thickness control parameters” Journal A, vol. 31, no. 4, Dec. 1, 1990, pages 8 through 15, XP00017, in particular in hot wide strip finishing mills, there is on average a greater deviation in thickness at the head of first strips and conversion strips due to technological factors. On the basis of the thickness measurement downstream from the finishing train, the object of thickness control is to adjust the deviating strip thickness to the original setpoint or an advantageously redisposed setpoint as quickly as possible. There is a disturbance in mass flow, hereinafter referred to as a mass flow disturbance of the first type, due to the required control action at the screw-down position, e.g., of the last stand. This disturbance is even greater, the more quickly the thickness error is eliminated. However, there is a different upper limit for each strip for the allowed mass flow disturbance and thus for the thickness control rate, and this limit is determined by the correction potential available in loop control for the steepness of disturbance, which depends on the rise error response of the control system.
In principle, the screw-down system, whether hydraulic gap control (HGC) or motor-driven gap control (MGC), has a higher dynamic response than the main drives, so it is possible for the screw-down system to generate mass flow disturbances whose correction would exceed the dynamic response of the controlling element of the loop control, and thus they can no longer in principle be corrected by the loop control Therefore, . . . the desired rate of correction of thickness errors and the allowed mass flow disturbances with respect to the loop control.
In addition to the greater mass flow disturbances due to the thickness control, i.e., mass flow disturbances of the first type which are relevant only at the head of the strip, substantial mass flow disturbances can also occur under certain conditions due to divergence effects of the AGC algorithm (AGC=automatic gauge control; a function of load roll gap disturbance compensation based on roll separating force) which is based on positive feedback. These disturbances, hereinafter referred to as mass flow disturbances of the second type, may occur with a distribution over the entire strip due to divergence effects. The AGC algorithm is based in principle on a positive feedback response in the manner of a geometric series. The series normally converges so that the screw-down position merges into a new steady-state end value after a load roll gap disturbance. In the event of the unfavorable mechanical condition whereby the screw-down and roll separating force measurement in the stand are arranged together (e.g., top-top) instead of opposite one another (e.g., top-bottom), the series may diverge for the duration of frictional grip occurring in the stand window, so the AGC algorithm then diverges until frictional grip is broken, resulting in considerable mass flow disturbances of the second type.
To prevent great mass flow disturbances of the first type, the thickness control is usually adjusted relatively slowly to always be on the safe side. The allowed mass flow disturbance is different with each strip and each roll stand, depending on the roll pass schedule, i.e., it depends on numerous influencing factors, but its size is unknown, so a considerable portion of the control rate which is actually possible with most strips is not utilized in this compromise.
To limit the effects of mass flow disturbances of the second type which are possible with certain constellations, only an AGC undercompensation factor of considerably less than one has proven feasible there so far. The resulting loss of efficiency in correcting skid marks, i.e., cold spots in the strip, would have to be accepted with this compromise.
SUMMARY
An object of the present invention is to provide a method and a device which avoids the above-mentioned disadvantages of known methods and devices.
The object is achieved according to the present invention by providing a method and device which dynamically adjusts the roll gap in a roll stand of a mill train having multiple stands for rolling a strip, with a strip supply, i.e., a loop, between two roll stands being adjusted and limited by loop or strip supply control, the dynamic response of the adjustment of the roll gap being limited as a function of state variables of the loop or strip stock control. Such a method has proven especially suitable in avoiding the above-mentioned disadvantages. The method of achieving this object according to the present invention is also superior to a strict limitation as a function of state variables of the mill train as described in European Patent No. 680,021 A1, for example, or a limitation described in German Patent No. 195 11 267 C1. Dynamic response in setting the roll gap is advantageously limited by limiting the rate at which the roll gap is adjusted. It has proven advantageous when reducing the roll nip in this way to perform the rate limitation independently of the rate limitation when increasing the roll gap.
The roll gap of roll stands in a mill train having multiple stands is usually adjusted by strip thickness controllers which determine the roll gap setpoint as a function of the system deviation of the thickness controller, i.e., the difference between a predetermined required strip thickness and the actual strip thickness. The size of the system deviation before entering the strip thickness controller is advantageously limited as a function of state variables of the loop or strip stock control.
In another advantageous embodiment of the present invention, the roll gap is adjusted according to a roll gap setpoint by a hydraulic gap control (HGC), with the rate of change of the additional HGC setpoint being limited according to
FIG. 1
or an equivalent parameter. In an alternative advantageous embodiment of the present invention, the roll gap is adjusted by a motor-driven gap control (MGC), with the equivalent thickness system deviation being limited according to
FIG. 2
or an equivalent parameter. Limitation of the additional HGC setpoint in hydraulic gap control and limitation of the equivalent thickness system deviation with motor-driven gap control have both proven to be especially suitable for limiting the rate in the adjustment of the roll gap.
In another advantageous embodiment of the present invention, the dynamic response and the rate of adjustment of the roll gap are limited as a function of at least one of the following parameters:
strip stock upstream from the roll stand or an equivalent parameter;
strip stock downstream from the roll stand or an equivalent parameter;
system deviation of the loop or strip stock control, i.e., the difference between the setpoint and the actual value of the loop height or the strip stock, for the loop or the strip supply upstream from the roll stand;
system deviation of the loop or strip stock control for the loop height or the strip stock downstream from the roll stand
time derivative of the strip stock upstream from the roll stand;
time derivative of the; strip stock downstream from the
roll stand time derivative of the system deviation of the loop or strip stock control for the loop height or the strip stock upstream from the roll stand;
time derivative of the system deviation of the loop or the strip stock control for the loop height or the strip stock downstream from the roll stand;
roll separating force;
motor current of the
M{umlaut over (u)}ller Matthias
Sykosch Ralf
Kenyon & Kenyon
Siemens Aktiengesellschaft
Tolan Ed
LandOfFree
Method and device for dynamic adjustment of the roll gap in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for dynamic adjustment of the roll gap in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for dynamic adjustment of the roll gap in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2551714