Furnace pacing for multistrand mill

Details Furnace pacing for multistrand mill Furnace pacing for multistrand mill

2002-08-16

2004-03-16

Picard, Leo (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C072S365200, C072S010700

Reexamination Certificate

active

06708077

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to rolling systems, and more particularly to pacing the extraction of billets from a furnace.
During a rolling process to roll a ductile material, such as steel, billets of the material are extracted from a furnace and typically provided to a roughing mill, such as a breakdown mill. The roughing mill generally performs an initial rolling process on the billets, reducing the cross-sectional area of the billets while simultaneously lengthening the billets. These rolled billets, or “bars,” then can be provided to one or more multistrand stands in sequence, whereupon an additional rolling process is performed on the bars. The bars often are provided to a multistrand stand by alternating billets between two or more strands of the mill, allowing multiple bars to be rolled simultaneously, and thereby improving the throughput of billets.
However, due to variances in the properties of the billets, such as length, weight and/or temperature, and due to variances in the rolling system, such as slight changes in the speed of the rollers of the roughing mill and the mill, the amount of time spent rolling a billet or bar at a mill, i.e., the “rolling time,” varies considerably. Unless precaution is taken in the pacing of billets from the furnace, this variance in rolling time can result in collisions between billets during the rolling operation. In the event that a collision occurs, the mill typically is shut down for a considerable period and cranes often must be used to remove the collided billets. Due to the cost of repairing the damage and the loss of productivity during the downtime, a number of mechanisms to avoid collisions between billets have been developed.
One known mechanism for minimizing the potential for collisions between billets includes extracting billets at a set sequence that introduces time gaps between the billets/rods when they are provided to the roughing mill and/or the multistrand stand. These gaps serve to compensate for variances between the properties of the extracted billets and in the rolling system itself. However, in order to effectively compensate for billets and in the rolling system itself. However, in order to effectively compensate for foreseeable variances, the gaps generally are relatively large. As a result, the productivity of a rolling system that utilizes such a mechanism is degraded since the large gaps between billets reduce the throughput of billets through the system.
Accordingly, other mechanisms have been developed to regulate the gaps between billets by regulating the timing of the extraction (i.e., the pacing) of billets from the furnace. By regulating the timing, the size of the gaps between billets can be reduced somewhat while still compensating for the variance between the rolling times of extracted billets. These known regulated pacing mechanisms typically compare a predicted rolling time of a previously extracted billet with its actual rolling time, and based on an error between the two rolling times, adjust the timing of the extraction of a subsequent billet from the furnace. However, the predicted rolling times of billets typically are fixed, being based on only fixed properties of the billets, such as a fixed or average weight and/or length, and do not take into account the variances between the properties of individual billets. The use of fixed predicted rolling times often results in gaps larger than desired or necessary, thereby decreasing productivity, or gaps smaller than desired or necessary, thereby increasing the potential for collisions between billets.
In view of the limitations of known furnace pacing implementations, an improved system and method for regulating the extraction of billets from a furnace in a rolling system would be advantageous. Specifically, a method and apparatus for calling billets from a furnace at an optimum time to achieve a minimum gap between the tail end of one billet and the head end of the next in, for instance, a breakdown mill and in each strand of a multistand stand, is needed to maximize production.
SUMMARY OF THE INVENTION
The disclosed technique mitigates or solves the above-identified limitation in known implementations, as well as other unspecified deficiencies in the known implementations.
A method and system for pacing a furnace supplying a single strand breakdown mill feeding a multistand, multistrand stand is provided. The billets are extracted from the furnace and rolled to a round bar at the breakdown mill. The rolled bar can receive a head cut and a tail cut at the breakdown mill. The rolled bar is then transported to either the first strand or the second strand of, for instance, a multistand mill. Each strand receives a bar alternatively. In one embodiment, the pacing of the extraction of billets from the furnace is regulated such that there is a regulated gap between the billets at the each of the strands of the mill. The regulated gap can be selected to provide a balance between productivity and potential for collision, and preferably is between about 5 seconds and 20 seconds in length.
In accordance with one embodiment of the present invention, a method for pacing an extraction of billets from a furnace intended for a stand having at least one strand is provided. The method comprises the steps of extracting a first billet from the furnace at a first time, the first billet being intended for a first strand of the stand and predicting a rolling time of the first billet through the first strand based at least in part on at least one measured property of the first billet. The method further comprises the step of determining a first correction value based on an equation:
Cor
n
=Cor
n−1
+(Measured_Time
Strand1
−Rolling_Time
Strand1
−Cor
n−1
)*
k
where Cor
n
represents the first correction value, Cor
n−1
represents a previous correction value used to adjust a timing of an extraction of a previously extracted billet from the furnace intended for the first strand, Measured_Time
Strand1
represents a measured rolling time of the previously extracted billet at the first strand, Rolling_Time
Strand1
represents a predicted rolling time of the previously extracted billet at the first strand, and k represents a real-number adjustment factor. The method additionally comprises the steps of determining a first furnace time based at least in part on the predicted rolling time of the first billet, a desired gap between billets at the first strand, and the correction value, and extracting a second billet from the furnace at a second time subsequent to the first time, the second billet being intended for the first strand, and wherein a difference between the first time and the second time is substantially equivalent to the first furnace time.
In accordance with another embodiment of the present invention, a method for regulating gaps between billets provided from a furnace to alternating strands of a multistrand stand is provided. The method comprises the steps of extracting a first billet from the furnace at a first time, the first billet being intended for a first strand of the mill, extracting a second billet from the furnace at a second time subsequent to the first time, the second billet being intended for a second strand of the mill, extracting a third billet from the furnace at a third time subsequent to the second time, the third billet being intended for the first strand, and extracting a fourth billet from the furnace at a fourth time subsequent to the third time, the fourth billet being intended for the second strand of the mill. In this embodiment, the difference between the first time and the third time is based at least in part on a predicted rolling time of the first billet at the first strand, a desired gap between billets at the first strand, and a first correction value, and the predicted rolling time of the first billet is based at least in part on at least one measured property of the first billet.
Furthermore, the first correction value is based at least in part on

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