U.S. patent application number 16/340008 was filed with the patent office on 2019-11-28 for control method for roller quenching process of heavy-piece weight and large-section ultra-heavy plate.
The applicant listed for this patent is Northeastern University. Invention is credited to Xiangtao DENG, Tianliang FU, Bing HAN, Jun HAN, Jiadong LI, Yong LI, Xiuhua TIAN, Zhaodong WANG.
Application Number | 20190360066 16/340008 |
Document ID | / |
Family ID | 61277747 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190360066 |
Kind Code |
A1 |
FU; Tianliang ; et
al. |
November 28, 2019 |
CONTROL METHOD FOR ROLLER QUENCHING PROCESS OF HEAVY-PIECE WEIGHT
AND LARGE-SECTION ULTRA-HEAVY PLATE
Abstract
A control method for a roller quenching process of a heavy-piece
weight and large-section ultra-heavy plate has a specific heat
model, heat transfer coefficient model, temperature field model and
correction model. Plate parameters inputted include thickness,
length and carbon content, technological procedure, roller speed
and acceleration. Measured parameters include tapping temperature,
temperature after air cooling and temperature after self-tempering.
The temperature field model is used. Specific heat model and the
heat transfer coefficient model are invoked for calculating an air
cooling stage, water cooling stage and self-tempering stage in
sequence. Temperature fields are corrected through the correction
model. Simulated results include a group of cooling curves and
cooling speed curves at different thicknesses. Practical
temperature drop curves and cooling speed curves are obtained in
combination with actual production and part of actual debugging
process is replaced by model calculation.
Inventors: |
FU; Tianliang; (Shenyang,
Liaoning, CN) ; WANG; Zhaodong; (Shenyang, Liaoning,
CN) ; TIAN; Xiuhua; (Shenyang, Liaoning, CN) ;
DENG; Xiangtao; (Shenyang, Liaoning, CN) ; LI;
Yong; (Shenyang, Liaoning, CN) ; LI; Jiadong;
(Shenyang, Liaoning, CN) ; HAN; Bing; (Shenyang,
Liaoning, CN) ; HAN; Jun; (Shenyang, Liaoning,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Northeastern University |
Shenyang, Liaoning |
|
CN |
|
|
Family ID: |
61277747 |
Appl. No.: |
16/340008 |
Filed: |
November 2, 2018 |
PCT Filed: |
November 2, 2018 |
PCT NO: |
PCT/CN2018/113711 |
371 Date: |
April 5, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 1/60 20130101; C21D
9/46 20130101; C21D 1/62 20130101; C21D 9/0081 20130101; C21D 11/00
20130101; C21D 11/005 20130101; C21D 1/18 20130101 |
International
Class: |
C21D 11/00 20060101
C21D011/00; C21D 9/46 20060101 C21D009/46; C21D 1/62 20060101
C21D001/62; C21D 1/18 20060101 C21D001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 2017 |
CN |
201711282218.0 |
Claims
1. A control method for a roller quenching process of a heavy-piece
weight and large-section ultra-heavy plate, comprising the
following steps: step 1. reading plate information and process
parameters, comprising plate thickness, length, carbon content,
roller speed and acceleration; step 2. setting an initial heat
transfer coefficient, using a temperature drop calculation model,
invoking a specific heat model and a heat transfer coefficient
model, correcting a heat transfer coefficient of an air cooling
stage using a correction model of the heat transfer coefficient
according to a measured temperature drop of the air cooling stage
and then obtaining a temperature field of the air cooling stage;
step 3. determining a heat transfer coefficient of a water cooling
stage, comprising determining a water cooling heat transfer
coefficient of a high pressure stage and determining a water
cooling heat transfer coefficient of a low pressure stage, wherein
the water cooling heat transfer coefficient of the high pressure
stage is determined by empirical data from experiments; the water
cooling heat transfer coefficient of the low pressure stage is
determined by correcting the heat transfer coefficient of a water
cooling stage of the low pressure stage using the correction model
of the heat transfer coefficient at self-tempering temperature of
the surface during air cooling after quenching; a specific method
comprises: using a temperature field after tapping and air cooling
as an initial temperature field of the water cooling stage; giving
an initial heat transfer coefficient of the low pressure stage;
calculating the temperature field; using a temperature field after
water cooling as an initial temperature field of a self-tempering
stage for calculating a temperature value of a self-tempered
surface node; comparing the temperature value with a measured
value; invoking the correction model of the heat transfer
coefficient for correcting the water cooling heat transfer
coefficient; keeping the air cooling heat transfer coefficient
unchanged; reusing the temperature drop calculation model; and
invoking the specific heat model and the heat transfer coefficient
model for calculating the temperature field of the water cooling
stage and the temperature field of the self-tempering stage until a
difference value is within a permissible error; step 4. obtaining
temperature drop curves and cooling speed curves of different
positions in line with the actual situation in the plate quenching
process; the correction model of the heat transfer coefficient in
above step 2 and step 3 is as follows: an interval range [0, A] of
the initial heat transfer coefficient is given; an upper limit
value A is taken as the initial heat transfer coefficient for
calculating the temperature field; if a computed value is higher
than a target value, a range [A, 1.5A] of the heat transfer
coefficient is taken; the upper limit value of a previous interval
is taken as a lower limit value of a new interval in each interval
change, and 1.5 times of the lower limit value of the new interval
is taken as an upper limit value of the new interval until the
value of the heat transfer coefficient is the upper limit of the
interval and the computed value is lower than the target value;
this indicates that the actual convective heat transfer coefficient
is within this interval at this moment; in the interval, a golden
section method is used to continuously reduce the interval until
the difference value between the measured value and the target
value is within the permissible error; and at this moment, the heat
transfer coefficient value is an actual value.
2. The control method for the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate according to
claim 1, wherein cooling time in the temperature drop calculation
model is controlled as follows: the model of the plate conducts
calculation according to the roller position of the plate in three
parts: an air cooling stage before entering a quenching machine, a
quenching stage when entering the quenching machine and a
self-tempering stage after entering the quenching machine; the time
of the air cooling stage is determined as follows: a head and a
tail are respectively calculated; the head of the plate moves at
uniform speed before entering the quenching machine, and thus
calculation is conducted through a distance from the head to the
quenching machine and initial speed; after the head of the plate
enters the quenching machine, a roller begins to apply a certain
acceleration; thus, the tail of the plate begins to accelerate in
the air cooling stage; at this moment, the distance from the
quenching machine is the length of the plate; the air cooling time
for the tail is calculated through the initial seed, the distance
and the acceleration; the time of the quenching stage is determined
as follows: the time of the quenching stage is divided into a time
to go through the high pressure stage and a time to go through the
low pressure stage; firstly, the length of the high pressure stage
is determined; the quenching time of the head of the plate is
directly calculated according to the set initial speed and
acceleration of the roller; because the plate is accelerated
immediately when the head of the plate enters the quenching
machine, the speed at which the tail enters the quenching machine
is determined through the time and the acceleration of the air
cooling acceleration part; the time to go through the high pressure
stage is calculated according to the speed and the acceleration;
the time required for the plate to go through the low pressure
stage is determined according to swing time; and the time of the
self-tempering stage is determined as follows: a specific method
comprises: timing with a chronograph when the plate leaves the
quenching machine; measuring the self-tempering temperature in the
same position of the plate at different moments; stopping timing
after self-tempering; taking a maximum self-tempering temperature
as a target temperature in analog calculation; and taking a
corresponding time as the time of the self-tempering stage.
3. The control method for the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate according to
claim 1, wherein an initial temperature field model of each stage
in steps 2 and 3 is established as follows: the temperature when
the plate leaves a furnace is taken as an initial temperature field
of the air cooling stage; a simulated temperature field after air
cooling calculated by the temperature field model is compared with
the temperature measured at a temperature measurement point before
entering the quenching machine and corrected; finally, a practical
temperature field after air cooling is obtained and is taken as an
initial temperature field of the water cooling stage; the water
cooling stage requires no correction computation; and a model
calculation result is directly transmitted to the self-tempering
stage as the initial temperature field of the self-tempering
stage.
4. The control method for the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate according to
claim 1, wherein the output result in step 4 comprises heat
transfer coefficient values of the air cooling stage, the water
cooling high pressure stage and the water cooling low pressure
stage, temperature change curves and cooling speed change curves of
surfaces, quarters and centers of the head and the tail of the
plate.
5. The control method for the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate according to
claim 3, wherein the output result in step 4 comprises heat
transfer coefficient values of the air cooling stage, the water
cooling high pressure stage and the water cooling low pressure
stage, temperature change curves and cooling speed change curves of
surfaces, quarters and centers of the head and the tail of the
plate.
6. The control method for the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate according to
claim 1, wherein in the steps 2 and 3: 1) calculation of the
specific heat model: the specific heat coefficient is mainly
relevant to the carbon content and the temperature of the plate; a
set definite value is taken as the definition scope of the carbon
content; when the carbon content is not the above value, left and
right boundary values corresponding to the carbon content are
determined at first; the weight of the carbon content is determined
by interpolation; and then the interval of the temperature is
compared, thereby determining a specific heat value of the plate;
2) calculation of the heat transfer coefficient model: firstly,
specific heat values and heat transfer coefficient values of plates
with different carbon contents at different temperatures are
obtained through experiments; and then specific heat values and
heat transfer coefficient values corresponding to other carbon
contents and other temperatures are determined by interpolation; 3)
the temperature drop calculation model is as follows: a
one-dimensional unsteady heat transfer differential equation in a
cartesian coordinate system is established: .differential. T
.differential. t = a .differential. 2 T .differential. x 2 + Q . (
0 < x < d , t > 0 ) wherein a = .lamda. .rho. c
##EQU00006## x is the length of a divided cell; d is the thickness
of the plate; t is the time; T is the temperature; a is a
temperature conductivity; {dot over (Q)} is an internal heat
source; .lamda. is a heat transfer coefficient of a quenching
plate; .rho. is the density of the quenching plate; C is the
specific heat of the quenching plate; during calculation, latent
heat of phase change in the cooling process of the plate is counted
into the mean specific heat; therefore, the internal heat source
can be neglected; an initial condition is: T(x,0)=T0 (0<x<d,
t>0) boundary conditions are: { - .lamda. .differential. T ( x ,
t ) .differential. x | x = 0 = h x ( T ( 0 , t ) - T f ) ( x = 0 ,
t > 0 ) - .lamda. .differential. T ( x , t ) .differential. x |
x = d = h x ( T ( d , t ) - T f ) ( x = d , t > 0 ) ##EQU00007##
in order to improve the convergence and stability of Fourier number
and make the model have a smaller error, Crank-Nicolson difference
method is used; 1 2 ( .differential. 2 T .differential. x 2 ) i t +
1 2 ( .differential. 2 T .differential. x 2 ) i t + 1 = 1 a (
.differential. T .differential. .tau. ) i t ##EQU00008## t is the
time; i is a node, 0.ltoreq.i.ltoreq.I; the temperature field is
established as follows: an internal node is:
-F.sub.oxT.sub.i+1.sup.t+1(2+2F.sub.ox)T.sub.i.sup.t+1-F.sub.oxT.sub.i-1.-
sup.t+1=F.sub.oxT.sub.i+1.sup.t+(2-2F.sub.ox)T.sub.i.sup.t+F.sub.oxT.sub.i-
-1.sup.t a boundary node is: - F ox T i - 1 t + 1 + ( 1 + F ox + F
ox B ix ) T i t + 1 = F ox T i - 1 t + ( 1 - F ox - F ox B ix ) T i
t + 2 F ox B ix T f wherein F ox = a .DELTA. t .DELTA. x 2 B ix = h
x .DELTA. x .lamda. ##EQU00009## h.sub.x is a convective heat
transfer coefficient; T.sub.f is a water temperature; T.sub.i.sup.t
is a temperature value corresponding to the ith node of the plate
at time of t; F.sub.ox is the Fourier number; B.sub.ix is a Biot
number; stability conditions are: { 1 - F ox .gtoreq. 0 1 - F ox -
F ox B ix .gtoreq. 0 ##EQU00010## when the initial temperature
field and the heat transfer coefficient are known, the temperature
distribution at any node and at any moment is calculated by
difference.
Description
TECHNICAL FIELD
[0001] The present invention belongs to the technical field of
metallurgy, and relates to a control method for a roller quenching
process of a plate.
BACKGROUND
[0002] The temperature field distribution after quenching of an
ultra-heavy plate affects the physical performance and the
machining performance of the plate to a large extent. In
traditional immersion quenching, the plate is immersed into a
quenching pool or quenching tank, which is limited by the volume of
a container and causes low cooling speed and uneven distribution.
In roller quenching, the plate enters a quenching machine through a
rotating roller, and a high-pressure jet is sprayed on the surface
of the plate. Compared with the traditional quenching, the roller
quenching substantially increases cooling speed and the plate can
be cooled to room temperature in short time. However, due to large
thickness and slow heat transfer of the plate, there is a large
temperature difference between the center and the surface and
performance distribution is uneven after quenching. Calculation of
the quenching process can better improve this problem. By setting
different parameters, the temperature curve and the cooling speed
curve of the plate are calculated, and the temperature distribution
and cooling speed changes of the plate in different positions in
the cooling process are intuitively observed. Calculated results
can better serve the production and reduce the production cost.
[0003] Patent CN105445319A discloses a method and a device for
measuring a water cooling heat transfer coefficient of a plate
surface. Image information of a non-water-cooled surface of the
plate is collected by an infrared thermal imager to obtain an
actual cooling curve of the non-water-cooled surface. The whole
process from the water-cooled surface to the non-water-cooled
surface is simulated by finite element, and the water-cooled heat
transfer coefficient is continuously adjusted to obtain a simulated
cooling curve of the non-water-cooled surface. Patent CN102507636A
discloses a method for measuring an interface heat transfer
coefficient of steel in a rapid cooling process. A thermocouple is
connected to a temperature collection module through spot welding
to obtain temperature change data of the surface. Heat treatment
software is used to obtain the interface heat transfer coefficient
in the cooling process and to simulate temperature change in the
cooling process of workpieces. The simulated result is compared
with a measured result until a change tendency is fitted well. The
prior art does not involve any control method related to a roller
quenching process of a heavy-piece weight and large-section
ultra-heavy plate, and any specific method to correct the heat
transfer coefficient in the roller quenching process of the
heavy-piece weight and large-section ultra-heavy plate by using a
correction model.
SUMMARY
[0004] The purpose of the present invention is to provide a control
method for a roller quenching process of a heavy-piece weight and
large-section ultra-heavy plate. The method is suitable for model
control of the ultra-heavy plate in a quenching process, is used
for visually representing the temperature change and cooling speed
change of a head and a tail of the plate on the surface, the
quarter thickness and the center of the plate through curves in
combination with actual production based on a mathematical model,
and can be used for guiding adjustment of a technological
procedure, saving production cost and obtaining a product with good
plate shape.
[0005] The specific technical solution of the present invention is:
a control method for a roller quenching process of a heavy-piece
weight and large-section ultra-heavy plate comprises the following
steps:
[0006] step 1. reading plate information and process parameters,
comprising plate thickness, length, carbon content, roller speed
and acceleration;
[0007] step 2. setting an initial heat transfer coefficient, using
a temperature drop calculation model, invoking a specific heat
model and a heat transfer coefficient model, correcting a heat
transfer coefficient of an air cooling stage using a correction
model of the heat transfer coefficient according to a measured
temperature drop of the air cooling stage and then obtaining a
temperature field of the air cooling stage;
[0008] step 3. determining a heat transfer coefficient of a water
cooling stage, comprising determining a water cooling heat transfer
coefficient of a high pressure section and determining a water
cooling heat transfer coefficient of a low pressure section,
wherein the water cooling heat transfer coefficient of the high
pressure stage is determined; the quenching machine in the high
pressure stage has the main action of rapidly cooling the surface
temperature of the plate to a lower temperature; because the action
time of the high pressure stage is much lower than that of the low
pressure stage and cannot be directly obtained in actual
production, empirical data is obtained from experiments;
[0009] the water cooling heat transfer coefficient of the low
pressure stage is determined; when the plate leaves the quenching
machine, only surface temperature is directly obtained; the plate
surface has violent temperature change at the beginning of
quenching only in the quenching process; after that, the
temperature tends to be stable and is close to the temperature of a
convection medium until the plate leaves the quenching machine;
thus, the convective heat transfer coefficient cannot be directly
calculated. The temperature inside the plate cannot be directly
obtained. Thus, the water cooling heat transfer coefficient cannot
be directly calculated through the water cooling stage. When the
plate leaves the quenching machine, the inside temperature is still
higher than the surface temperature and the inside temperature is
transmitted to the plate surface by means of thermal conduction.
Thus, the heat transfer coefficient of a water cooling stage of the
low pressure stage is corrected using the correction model of the
heat transfer coefficient at self-tempering temperature of the
surface during air cooling after quenching. a specific method
comprises: using a temperature field after tapping and air cooling
as an initial temperature field of the water cooling stage; giving
an initial heat transfer coefficient of the low pressure section;
calculating the temperature field; using a temperature field after
water cooling as an initial temperature field of a self-tempering
stage for calculating a temperature value of a self-tempered
surface node; comparing the temperature value with a measured
value; invoking the correction model of the heat transfer
coefficient for correcting the water cooling heat transfer
coefficient; keeping the air cooling heat transfer coefficient
unchanged; reusing the temperature drop calculation model; and
invoking the specific heat model and the heat transfer coefficient
model for calculating the temperature field of the water cooling
stage and the temperature field of the self-tempering stage until a
difference value is within a permissible error; and
[0010] step 4. obtaining temperature drop curves and cooling speed
curves of different positions in line with the actual situation in
the plate quenching process.
[0011] Because the convective heat transfer coefficient in the
quenching process cannot be directly measured, the calculated
temperature and the measured temperature need to be compared and
the heat transfer coefficient is corrected using the correction
model so as to correct the temperature field. The correction model
of the heat transfer coefficient in above step 2 and step 3 is as
follows:
[0012] an interval range [0, A] of the initial heat transfer
coefficient is given; an upper limit value A is taken as the
initial heat transfer coefficient for calculating the temperature
field; if a computed value is higher than a target value, a range
[A, 1.5A] of the heat transfer coefficient is taken; the upper
limit value of a previous interval is taken as a lower limit value
of a new interval in each interval change, and 1.5 times of the
lower limit value of the new interval is taken as an upper limit
value of the new interval until the value of the heat transfer
coefficient is the upper limit of the interval and the computed
value is lower than the target value; this indicates that the
actual convective heat transfer coefficient is within this interval
at this moment; in the interval, a golden section method is used to
continuously reduce the interval until the difference value between
the measured value and the target value is within the permissible
error; and at this moment, the heat transfer coefficient value is
an actual value.
[0013] Further, in above steps 2 and 3:
[0014] 1) calculation of the specific heat model: the specific heat
coefficient is mainly relevant to the carbon content and the
temperature of the plate; a set definite value is taken as the
definition scope of the carbon content; when the carbon content is
not the above value, left and right boundary values corresponding
to the carbon content are determined at first; the weight of the
carbon content is determined by interpolation; and then the
interval of the temperature is compared, thereby determining a
specific heat value of the plate;
[0015] 2) calculation of the heat transfer coefficient model:
firstly, specific heat values and heat transfer coefficient values
of plates with different carbon contents at different temperatures
are obtained through experiments; and then specific heat values and
heat transfer coefficient values corresponding to other carbon
contents and other temperatures are determined by
interpolation;
[0016] 3) the temperature drop calculation model is as follows:
[0017] a one-dimensional unsteady heat transfer differential
equation in a cartesian coordinate system is established:
.differential. T .differential. t = a .differential. 2 T
.differential. x 2 + Q . ( 0 < x < d , t > 0 ) wherein a =
.lamda. .rho. c ##EQU00001##
[0018] x is the length of a divided cell; d is the thickness of the
plate; t is the time; T is the temperature; a is a temperature
conductivity; {dot over (Q)} is an internal heat source; .lamda. is
a heat transfer coefficient of a quenching plate; .rho. is the
density of the quenching plate; c is the specific heat of the
quenching plate;
[0019] during calculation, latent heat of phase change in the
cooling process of the plate is counted into the mean specific
heat; therefore, the internal heat source can be neglected;
[0020] an initial condition is:
T(x,0)=T0 (0<x<d, t>0)
[0021] boundary conditions are:
{ - .lamda. .differential. T ( x , t ) .differential. x | x = 0 = h
x ( T ( 0 , t ) - T f ) ( x = 0 , t > 0 ) - .lamda.
.differential. T ( x , t ) .differential. x | x = d = h x ( T ( d ,
t ) - T f ) ( x = d , t > 0 ) ##EQU00002##
[0022] in order to improve the convergence and stability of Fourier
number and make the model have a smaller error, Crank-Nicolson
difference method is used;
1 2 ( .differential. 2 T .differential. x 2 ) i t + 1 2 (
.differential. 2 T .differential. x 2 ) i t + 1 = 1 a (
.differential. T .differential. .tau. ) i t ##EQU00003##
[0023] t is the time; i is a node, 0.ltoreq.i.ltoreq.I; the
temperature field is established as follows:
[0024] an internal node is:
-F.sub.oxT.sub.i+1.sup.t+1(2+2F.sub.ox)T.sub.i.sup.t+1-F.sub.oxT.sub.i-1-
.sup.t+1=F.sub.oxT.sub.i+1.sup.t+(2-2F.sub.ox)T.sub.i.sup.t+F.sub.oxT.sub.-
i-1.sup.t
[0025] a boundary node is:
- F ox T i - 1 t + 1 + ( 1 + F ox + F ox B ix ) T i t + 1 = F ox T
i - 1 t + ( 1 - F ox - F ox B ix ) T i t + 2 F ox B ix T f wherein
F ox = a .DELTA. t .DELTA. x 2 B ix = h x .DELTA. x .lamda.
##EQU00004##
[0026] h.sub.x is a convective heat transfer coefficient; T.sub.f
is a water temperature; T.sub.i.sup.t is a temperature value
corresponding to the ith node of the plate at time oft; F.sub.ox is
the Fourier number; B.sub.ix is a Biot number;
[0027] stability conditions are:
{ 1 - F ox .gtoreq. 0 1 - F ox - F ox B ix .gtoreq. 0
##EQU00005##
[0028] when the initial temperature field and the heat transfer
coefficient are known, the temperature distribution at any node and
at any moment is calculated by difference.
[0029] Further, cooling time in the above temperature drop
calculation model is controlled as follows: the model of the plate
conducts calculation according to the roller position of the plate
in three parts: an air cooling stage before entering a quenching
machine, a quenching stage when entering the quenching machine and
a self-tempering stage after entering the quenching machine;
[0030] the time of the air cooling stage is determined as follows:
the plate has certain length; different positions take different
times to enter the quenching machine. Thus, a head and a tail are
respectively calculated; the head of the plate moves at uniform
speed before entering the quenching machine, and thus calculation
is conducted through a distance from the head to the quenching
machine and initial speed; after the head of the plate enters the
quenching machine, a roller begins to apply a certain acceleration;
thus, the tail of the plate begins to accelerate in the air cooling
stage; at this moment, the distance from the quenching machine is
the length of the plate; the air cooling time for the tail is
calculated through the initial seed, the distance and the
acceleration;
[0031] the time of the quenching stage is determined as follows:
the time of the quenching stage is divided into a time to go
through the high pressure stage and a time to go through the low
pressure stage; firstly, the length of the high pressure stage is
determined; the quenching time of the head of the plate is directly
calculated according to the set initial speed and acceleration of
the roller; because the plate is accelerated immediately when the
head of the plate enters the quenching machine, the speed at which
the tail enters the quenching machine is determined through the
time and the acceleration of the air cooling acceleration part; the
time to go through the high pressure stage is calculated according
to the speed and the acceleration; the time required for the plate
to go through the low pressure stage is determined according to
swing time; and
[0032] the time of the self-tempering stage is determined as
follows: a specific method comprises: timing with a chronograph
when the plate leaves the quenching machine; measuring the
self-tempering temperature in the same position of the plate at
different moments; stopping timing after self-tempering; taking a
maximum self-tempering temperature as a target temperature in
analog calculation; and taking a corresponding time as the time of
the self-tempering stage.
[0033] Further, an initial temperature field model of each stage in
steps 2 and 3 is established as follows: the temperature when the
plate leaves a furnace is taken as an initial temperature field of
the air cooling stage; a simulated temperature field after air
cooling calculated by the temperature field model is compared with
the temperature measured at a temperature measurement point before
entering the quenching machine and corrected; finally, a practical
temperature field after air cooling is obtained and is taken as an
initial temperature field of the water cooling stage; the water
cooling stage requires no correction computation; and a model
calculation result is directly transmitted to the self-tempering
stage as the initial temperature field of the self-tempering
stage.
[0034] Further, the output result in step 4 comprises heat transfer
coefficient values of the air cooling stage, the water cooling high
pressure stage and the water cooling low pressure stage,
temperature change curves and cooling speed change curves of
surfaces, quarters and centers of the head and the tail of the
plate.
[0035] The present invention has the following advantages:
[0036] 1) Initial parameters conform to the actual production
procedure.
[0037] Considering site production conditions, required measured
data can be directly obtained in production.
[0038] 2) The calculated results of each stage are corrected
according to the measured values, and the calculated results are
closer to the actual cooling curve of the plate.
[0039] 3) The output result comprises the cooling curves and the
cooling speed curves at different thicknesses, which can more
visually show the temperature difference of the center and the
surface, the cooling speed difference of the center and the
surface, the temperature difference between the head and the tail
and the cooling speed difference between the head and the tail, and
can be used to guide and adjust the production process.
[0040] 4) Part of site debugging is replaced by calculation to
reduce energy consumption and production cost.
DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a flow chart of a calculation process.
[0042] FIG. 2 shows temperature change curves obtained by
calculation.
[0043] FIG. 3 shows cooling speed change curves obtained by
calculation.
[0044] FIG. 4 shows cooling speed change curves after the high
pressure stage is filtered.
DETAILED DESCRIPTION
[0045] 1) Input of parameters. Including plate parameters:
thickness, length and carbon content; technological procedure:
roller speed, acceleration, length of the high pressure stage of
the quenching machine, tapping temperature and initial value of a
heat transfer coefficient; measured parameters: tapping
temperature, temperature before entering the quenching machine,
self-tempering time and temperature after self-tempering.
[0046] 2) Determination of the air cooling stage, the quenching
stage and the self-tempering stage. The plate has certain length;
different positions take different times to enter the quenching
machine. Thus, a head and a tail are respectively calculated; and
the head of the plate moves at uniform speed before entering the
quenching machine, accelerates after entering the high pressure
stage of the quenching machine and then swings in the low pressure
stage. The tail of the plate moves as follows: the air cooling
stage firstly moves at uniform speed before entering the quenching
machine, and accelerates after the head of the plate enters the
quenching machine; the high pressure stage accelerates, and then
the low pressure stage swings. The time of the air cooling stage
and the time of the high pressure stage are calculated through the
distance, the initial speed and the acceleration. The time of the
low pressure stage is determined through the set swing time. The
time of the self-tempering stage is determined by means of
timing.
[0047] 3) Calculation of the temperature field of the air cooling
stage. The initial temperature field is established by tapping
temperature. The specific heat and the heat transfer coefficients
of different nodes are respectively calculated in each time step.
Then, a temperature field model is invoked to calculate the air
cooling temperature field. The calculated result is compared with
the measured value. The correction model is invoked to correct the
air cooling heat transfer coefficient to obtain the temperature
field after air cooling.
[0048] 4) Determination of the time of the water cooling stage.
Times required for the head, the middle and the tail of the plate
to go through the high pressure stage of the quenching machine are
respectively calculated. The time required for the plate to go
through the low pressure stage is determined according to the swing
time.
[0049] 5) Calculation of the water cooling temperature field. The
temperature field after water cooling is calculated by invoking the
specific heat model, the heat transfer coefficient model and the
temperature field model and using the calculated temperature field
after air cooling as the initial temperature field.
[0050] 6) Calculation of the temperature field after
self-tempering. The specific heat model, the heat transfer
coefficient model and the temperature field model are invoked to
calculate the self-tempering temperature field by using the
temperature field after water cooling as the initial temperature
field and using the corrected air cooling heat transfer coefficient
value as the heat transfer coefficient value. The calculated result
is compared with the measured value. If the calculated result is
not within a permissible error, the correction model is invoked to
correct the air cooling heat transfer coefficient for recalculation
of steps 5 and 6.
[0051] 7) Output of the calculated result. The temperature drop
curves and the cooling speed curves of the head surface and the
tail surface, the quarter thickness and the center of the plate in
the air cooling stage and the quenching stage are drawn.
Embodiment
[0052] The thickness of the plate is 132 mm; the length is 7250 mm;
the carbon content is 0.15%; the roller speed is 0.2 m/s; the
acceleration is 0.00015 m/s.sup.2; the length of the high pressure
stage of the quenching machine is 3.2 m; the initial values of the
heat transfer coefficient are: 100 W/(m.sup.2K) for the air cooling
stage, 20000 W/(m.sup.2K) for the high pressure stage and 8000
W/(m.sup.2K) for the low pressure stage; water temperature is
22.1.degree. C.; tapping temperature is 910.degree. C.; the
temperature before entering the quenching machine is 830.degree.
C.; air cooling time is 45 s; the swing time of the low pressure
stage is 1560 s; the self-tempering time is 142 s; and the
temperature after self-tempering is 28.degree. C. The length of a
cell is 1 mm and the time step is 0.5 s. The calculation flow is
shown in FIG. 1.
[0053] Calculated results: the heat transfer coefficient value of
the air cooling stage is 124.64 W/(m.sup.2K) and the water cooling
heat transfer coefficient value of the low pressure stage is 2250
W/(m.sup.2K). The temperature drop curves are shown in FIG. 2. It
is known from the figure that the surface temperature of the plate
is rapidly reduced when the plate enters the air cooling stage and
then enters the water cooling high pressure stage. After entering
the low pressure stage, because the inside temperature is
transmitted outwards, the temperature rises a little. Compared with
the surface, the temperature of the quarter thickness and the
center is reduced slowly. The cooling speed curves are shown in
FIG. 3. After the cooling speed curves are compared with the
temperature drop curves, it is found that in the high pressure
stage, the cooling speed of the surface is rapidly increased; after
entering the low pressure stage, the cooling speed curve has a
negative value, which indicates that the temperature rises;
short-time cooling speed of the surface is much higher than that of
other moments, which is not convenient for observing the cooling
speed of other moments; thus, the cooling speed is shown in FIG. 4
after part of the cooling speed is filtered; it is found that the
cooling speed of the quarter thickness and the center is gradually
increased when the temperature difference between the center and
the surface is larger; and after this, with the decrease of the
temperature, the cooling speed is gradually decreased.
* * * * *