Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-12-03
2001-05-01
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
48, C164S154600, C164S455000, C072S012200
Reexamination Certificate
active
06225609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control method for obtaining a desired coiling temperature by way of cooling a rolled strip in the hot rolling process of metals and its system.
2. Related Background Art
Quality control in hot sheet metal rolling process is largely divided into two following controls: (1) Product size control such as strip thickness control for controlling rolled strip thickness in its lateral center, strip width control, strip crown control for controlling lateral width distribution, and flatness control for controlling strip lateral elongation, and (2) temperature control of rolled strip. The temperature control of rolled strip includes two following controls: (1) Temperature control for controlling the temperature of rolled strip at the delivery side of finishing rolling mill and (2) coiling temperature control for controlling the temperature of the rolled strip in front of the coiler.
Generally, in a hot rolling mill, a heating furnace, a roughing mill, a finishing mill, a run out table (ROT) on which a cooler is installed and a coiler are serially arranged. Typical temperatures of strips are: 1200 to 1250 degree C. at the delivery side of the heating furnace, 1100 to 1150 degree C. at the delivery side of the roughing mill, 1050 to 1100 degree C. at the entry side of the finishing mill, 850 to 900 degree C. at the delivery side of the finishing mill, and 500 to 800 degree C. at the coiler. In almost all cases, the strength, toughness and other properties of rolled strips depend on positive cooling to which the strips are subjected while the strips come out from the finishing roll and reach the coiler. Therefore, coiling temperature control is extremely critical for final material quality.
FIG. 10
is a schematic block diagram showing a typical coiling temperature controlling system according to the prior art, inclusive of applications: In the drawing, after a stripping sheet
1
is finishing rolled into the strip
1
at the finishing mill
4
, the strip
1
is transported on the ROT and finally coiled by the coiler
6
while guided by the pinch roll
5
. The finisher delivery pyrometer (FDT)
2
is provided at the delivery side of the finishing mill
4
, and the coiling pyrometer (CT)
3
is provided at the entry side of the pinch roll
5
. On the ROT
10
is installed a cooling device consisting of n pieces of cooling units (also collectively referred to as cooling bank)
7
a
,
7
b
,
7
c
, . . . . The cooling units respectively inject cooling water to cool the strip
1
. In this connection, in the drawing ROT
10
is drawn like a straight line, but actually a number of rolls are arranged for rotation, to transport the strip
1
.
The valves installed in the cooling banks
7
a
,
7
b
,
7
c
, . . . for controlling cooling water flow rate may be closing valves or flow control valves. But, the two or three cooling banks nearest to the coiling pyrometer
3
may be flow rate controllable valves or a number of small flow rate closing valves to have finer feedback control, which is to be described in more detail later.
The coiling temperature controller
24
is installed to control the opening and closing of each valve at the cooling banks
7
a
,
7
b
,
7
c
, . . . to control cooling water flow rate. To the coiling temperature controller
24
are fetched the temperature indications of the finishing delivery pyrometer (FDT)
2
and the coiling pyrometer (CT)
3
, output pulses of the pulse generator
9
a
connected the driving motor of the finishing roll
4
and the pulse generator
9
b
connected the coiler
6
, as well as calculational information for setting the finishing roll
4
which is made by the finishing roll setting calculation means
8
.
The coiling temperature (CT) control system
24
is divided into the following two subsystems from the viewpoint of its purpose: (1) The first subsystem which determines which cooling banks
7
a
,
7
b
,
7
c
, . . . is or are used for cooling so that the CT should coincide with the target coiling temperature T
CT
AIM
, mainly based on the temperature measurement T
FD
ACT
of the strip
1
(detected by FDT
2
) locating right thereunder, and (2) the second subsystem which corrects a deviation of actual coiling temperature T
CT
ACT
from the target coiling temperature T
CT
AIM
.
The first subsystem consists of the material temperature prediction means
13
, the material tracking means
14
, the cooling water flow rate setting means
22
and the temperature model learning means
23
, while the second subsystem consists of the target temperature correction means
16
, the feedback control means
17
and the cooling water flow rate changing means
21
.
Now, description will be made for the CT control system
24
according to the prior art as follows:
According to the prior art, a total length of rolled strip
1
is divided into a number of conceptual segments as a material cooling unit. The performance of the cooling banks
7
a
,
7
b
,
7
c
, . . . are decided, so that, at the point of time when a certain segment of the rolled strip passes a specific rolling stand (e.g., the (m−j)th stand) of the finishing rolling mill
4
, the segment temperature should become the target coiling temperature T
CT
AIM
, which is calculated based on the temperature measurement T
FD
ACT
of the strip
1
locating right under FDT
2
and the setting calculational information of the rolling mill setting calculation means
8
. Therefore, by counting the output pulses of the pulse generators
9
a
and
9
b
, the material tracking means
14
detects the location of the strip
1
on ROT
10
at any state at the time of (1) “before the head end of the strip
1
reaches the coiler
6
”, (2) “while coiling the strip
1
”, and (3) “after the tail end of the strip
1
passes through the finishing mill
4
”.
In this connection, tracking of the strip
1
is not limited to the method which counts the output pulses of the pulse generators
9
a
and
9
b
, but, for example, another method such as provision of material sensor midway of ROT
10
can be used.
The temperature model learning means
23
provides necessary information for prediction of material temperature to the material temperature prediction means
13
, based on the temperature measurement T
FD
ACT
of the strip detected by FDT
2
and the actual coiling temperature T
CT
ACT
to be detected by CT
3
.
At a timing when the k-th strip segment from the head end of the strip
1
just reached the (m−j)th stand of the finishing mill
4
, the material temperature prediction means
13
predicts the probable material temperature which takes place when the k-th segment is to be applied with cooling water at the cooling bank
7
a
. The cooling water flow rate setting means
22
judges whether the material temperature predicted at the (m−j)th stand can achieve the target coiling temperature T
CT
AIM
. When “YES”, only the cooling bank
7
a
is used. When “NO” or higher than target, the downstream cooling bank
7
b
is used together. Then, again, the material temperature is estimated by the material temperature prediction means
13
. The above-described operation is repeated until the target coiling temperature T
CT
AIM
is obtained.
In this connection, why these calculations must be done at the timing when the segment just reached the (m−j)th stand of the finishing mill
4
is as follows: In general, an opening or closing of the valves or a flow rate change to be made in the cooling bank controller would have dead time or response delay, or the calculational operation to be done therein would take much time, thereby necessitating the compensation for these delays. Therefore, when these loss times can be minimized, a referenced stand such as the (m−j)th stand can be brought to more downstream stand, expecting more accurate coiling temperature.
Thus, when the cooling water flow rate to be applied to a reference segment is determined, and when the referenced segment reached the i-th stand while the material tracking means
14
Goudo Hideho
Imanari Hiroyuki
Yamahashi Kozo
Foley & Lardner
Kabushiki Kaisha Toshiba
Paschall Mark
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