Method and apparatus for controlling the strip temperature of the rapid cooling section of a continuous annealing line
Provided are a method and apparatus for uniformly controlling the strip temperature of the rapid cooling section of a continuous annealing line. A plurality of sets of cooling nozzle blocks for controlling the strip temperature is installed at the front and back sides of the strip, and is divided into lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks. Strip center temperature meters and widthwise direction temperature meters are installed at the intake and discharge sides of the rapid cooling section. Temperatures obtained using the strip center temperature meters and the width direction temperature meters are used to respectively control the spraying of mist for the lengthwise flow control nozzle blocks and the widthwise flow control nozzle blocks in order to uniformly control the strip temperature and minimize changes in the flatness of the strip. The widthwise temperature meters at the intake and discharge ends of the rapid cooling section of the continuous annealing line are used to detect the temperature. Feedback/feedforward control technique can be used to uniformly control the widthwise temperature of the strip through flow rate control over mist sprayed in the widthwise direction of the rapid cooling section.
1. A method of uniformly controlling a strip temperature in a rapid cooling section of a continuous annealing line, the method comprising steps of:
determining valve open ratios of lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks, the nozzle blocks spraying mist to front and rear sides of a strip, based on strip temperature measurement values and strip information;
determining opening compensation values of the lengthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted by deducing an actual discharge-side temperature of the strip at every period from a target discharge-side temperature of the strip with respect to the determined valve open ratios; and
determining opening values of a plurality of servo valves of the widthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted in a plurality of areas in a widthwise direction of the strip with respect to the determined valve open ratios,
whereby the strip temperature is uniformly controlled through flow rate control over the mist sprayed to the strip, and changes in flatness of the strip are minimized,
wherein the step of determining the valve open ratios of the lengthwise flow control nozzle blocks and the widthwise flow control nozzle blocks comprises steps of:
calculating a compensation cooling capacity from a present intake-side temperature, a discharge-side temperature and a target temperature of the strip using information on a thickness, a width and a steel type of the strip inputted from a next coil information input module;
calculating a flow rate value of the mist;
dividing the flow rate value of the mist with a number of blocks which is predetermined by a spray nozzle block determination module and calculating a valve flow rate coefficient C v using the divided flow rate value as an input value of a valve open ratios calculation module; and
finally determining valve open ratios of the blocks using the valve flow rate coefficient C v .
2. The method according to claim 1 , wherein, at the step of calculating the compensation cooling capacity, the compensation cooling capacity is calculated using an equation presented by Formula 3=Formula 1−Formula 2:
{dot over (Q)} s _ act =ρ s C ps ( T o _ act −T i _ act ) {dot over (V)} s Formula 1,
where {dot over (Q)} s _ act is the present cooling capacity (W/m 3 ·K) of the strip, ρ s is the density (Kg/m 3 ) of the strip, C ps is the specific heat (J/Kg·K) of the strip, T o _ act is the actual absolute temperature (K) of an RCS discharge-side plate, and {dot over (V)} s is the volume ratio (m 3 /sec) of the strip,
{dot over (Q)} s _ target =ρ s C ps ( T o _ target −T i _ act ) {dot over (V)} s Formula 2,
where {dot over (Q)} s _ target is the target cooling capacity (W/m 3 ·K) of the strip, ρ s is the density (Kg/m 3 ) of the strip, C ps is the specific heat (J/Kg·K) of the strip, T o _ target is the target absolute temperature (K) of a discharge-side plate, T i _ act is the actual absolute temperature (K) of an RCS intake-side plate, and {dot over (V)} S is the volume ratio (m 3 /sec) of the strip, and
Δ {dot over (Q)} s =ρ s C ps ( T o _ target −T o _ act ) {dot over (V)} s Formula 3,
where Δ{dot over (Q)} s is the compensation cooling capacity (W/m 3 ·K) of the strip.
3. The method according to claim 1 , wherein the step of calculating the flow rate value of the mist comprises:
calculating the flow rate value of the mist using Formula 5 obtained from Formula 4 below:
Δ
Q
.
s
=
(
C
pm
Δ
T
m
+
h
fg
)
ρ
m
V
.
m
,
and
Formula
4
V
.
m
=
Δ
Q
.
s
(
C
pm
Δ
T
m
+
h
fg
)
ρ
m
,
Formula
5
where C pm is the specific heat (J/Kg·K) of mist, ΔT m is the temperature variation (K) of mist, h fg is the phase transformation capacity (J/Kg) of mist, and {dot over (V)} m is the flow rate (volume ratio) (m 3 /sec) of mist.
4. The method according to claim 1 , wherein
the step of calculating the valve flow rate coefficient C v comprises calculating the flow rate coefficient C v using Formula 6 below:
{dot over (V)} m =C v √{square root over (Δ P )} Formula 6,
where C v is the valve flow rate coefficient (m 3 /hr), and ΔP is a valve pressure (Kg/cm 2 ), and
the step of finally determining the valve open ratios of the blocks comprises finally determining the valve open ratios of the blocks using Formula 7 below:
α= f ( C v ) Formula 7,
where α is the valve open ratio (%).
5. A method of uniformly controlling a strip temperature in a rapid cooling section of a continuous annealing line, the method comprising steps of:
determining valve open ratios of lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks, the nozzle blocks spraying mist to front and rear sides of a strip, based on strip temperature measurement values and strip information;
determining opening compensation values of the lengthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted by deducing an actual discharge-side temperature of the strip at every period from a target discharge-side temperature of the strip with respect to the determined valve open ratios; and
determining opening values of a plurality of servo valves of the widthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted in a plurality of areas in a widthwise direction of the strip with respect to the determined valve open ratios,
whereby the strip temperature is uniformly controlled through flow rate control over the mist sprayed to the strip, and changes in flatness of the strip are minimized,
wherein the step of determining the opening compensation values of the lengthwise flow control nozzle blocks is carried out using a lengthwise temperature controller comprising a proportional integration controller, and comprises:
calculating the flow rates of the mist using Formula 5 below:
V
.
m
=
Δ
Q
.
s
(
C
pm
Δ
T
m
+
h
fg
)
ρ
m
,
Formula
5
where C pm is the specific heat (J/Kg·K) of mist, ΔT m is the temperature variation (K) of mist, h fg is the phase transformation capacity (J/Kg) of mist, and {dot over (V)} m is the flow rate (volume ratio) (m 3 /sec) of mist;
calculating the valve flow rate coefficient C v using Formula 6 below:
{dot over (V)} m =C p √{square root over (Δ P )} Formula 6,
where C v is the valve flow rate coefficient (m 3 /hr), and ΔP is a valve pressure (Kg/cm 2 ); and
calculating the valve open ratios using Formula 7 below:
α= f ( C v ) Formula 7,
where α is the valve open ratio (%).
6. A method of uniformly controlling a strip temperature in a rapid cooling section of a continuous annealing line, the method comprising steps of:
determining valve open ratios of lengthwise flow control nozzle blocks and widthwise flow control nozzle blocks, the nozzle blocks spraying mist to front and rear sides of a strip, based on strip temperature measurement values and strip information;
determining opening compensation values of the lengthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted by deducing an actual discharge-side temperature of the strip at every period from a target discharge-side temperature of the strip with respect to the determined valve open ratios; and
determining opening values of a plurality of servo valves of the widthwise flow control nozzle blocks such that the flow rates of the spray mist are adjusted in a plurality of areas in a widthwise direction of the strip with respect to the determined valve open ratios,
whereby the strip temperature is uniformly controlled through flow rate control over the mist sprayed to the strip, and changes in flatness of the strip are minimized,
wherein the step of determining the opening values of the plurality of servo valves of the widthwise flow control nozzle blocks is carried out by dividing the strip into the plurality of areas, disposing the plurality of servo valves on the widthwise flow control nozzle blocks, the plurality of servo valves being divided in the widthwise direction of the strip so as to be respectively positioned in the plurality of areas, the flow rates of the plurality of servo valves being controlled by a widthwise temperature controller which deduces an actual widthwise temperature distribution value of the strip from a target widthwise temperature distribution of the strip and uses a resultant value as an input value thereof, the step of determining the opening values of the plurality of servo valves of the widthwise flow control nozzle blocks comprising:
calculating the flow rates of the mist with respect to the plurality of servo valves using Formula 5 below:
V
.
m
=
Δ
Q
.
s
(
C
pm
Δ
T
m
+
h
fg
)
ρ
m
,
Formula
5
where C pm is the specific heat (J/Kg·K) of mist, ΔT m is the temperature variation (K) of mist, h fg is the phase transformation capacity (J/Kg) of mist, and {dot over (V)} m is the flow rate (volume ratio) (m 3 /sec) of mist;
calculating the valve flow rate coefficient C v using Formula 6 below:
{dot over (V)} m =C v √{square root over (Δ P )} Formula 6,
where C v is the valve flow rate coefficient (m 3 /hr), and ΔP is a valve pressure (Kg/cm 2 ); and calculating the valve open ratios of the plurality of servo valves using Formula 7 below:
α= f ( C v ) Formula 7,
where α is the valve open ratio (%).