Note: Descriptions are shown in the official language in which they were submitted.
1 ~ 5B~2 3
"~ON'I'L~ OLLING 'l'~:Ih (:~OrT'.l'Il~`llJ()lJS C~A~ MG OF M~æ'l'AI.,S"
'L`he present inven-liion relates to a rnethod and
app~rat-us f;or controllin~ the continuous castirig of a
metal. ~he descrip-tion which follows is based on the
I specific case of the continuous casting of steel, but
this is simply given as an example, as the inventicn
¦ relates to the continuous casting o~ metals in general.
It is well known that the process of continuous
castin~ of steel is highly complex, in particular in the
case of the continuous casting of strands of large cross-
¦ 10 sections, and that a large number of factors are taken
¦ into account when determining the optimum conditions for
continuous casting operations.
Amongst the aspec-ts of continuous casting which
should in particular be taken into account in a control
¦ 15 process are the level and the temperature of the liquid
¦ metal in the basket, the position of the nozzle in the
~ould, the level of the liquid metal in the mould, the
selection, the type, and the quantity of the covering
1 powder, bonding of the strand, the casting speed,
¦ 20 oscillationiof the mould, the conicity of the mould
faces, the heat exchange wlth respect to the mould and
I the first spraying zones at the exit of the mould, and
lastly the regulation of the rollers at the base of the
continuous casting mould.
~he following is an account of tthe effect of the
above factors on working co~ditl ns for continuous casting
1, ,
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1 1$~3
f ~tc~l
I-t is well known t-hat, in theS contimlo-us crl-Jting~
of steel, in p~lrticular when cas-ting strands ha-rlny;
large cross-sections, the upper surfacc of the strand
is covered with a covering material of suitable
composition during casting. This material plays a
multiple role, in par-ticular -to ensure, with respec~
to the air, adequate thermal insulation of the upper
surface of the strand and protection against oxidation,
! 10 to capture imp~rities in the steel, and to act as a
3 lubricant be-tween the s-trand and the mould~ to best
ensure heat transfer from the strand to the mould,
whilst accommodating oscillations of the mould.
i When this covering material is applied to the
15 surface of the strand during continuous casting, it mav
have physical aggregation states which vary i~nensely,
such as powder, paste, fibres, or flexible or rigid
geometrical shapes, acoording to the extent to which it
~ ; is processed.
Z 20 In the particular case of powder, this is in general
composed of CaO, S02, A1303, with a flux such as, for
example, CaF2, K20, Na20, and in most cases a, with
proportions depending on the features of the strand to
be cast and the casting conditions. ~he permanen-t
contact of this material with the continuously renewed
metal is most often obtained by a suitable configuration
of the end of the casting nozzls, by which some at least
2 3
of the Metal which is passLng 1;hrough it is co~tinuou~sly
directad towards thi-; material. 'l~lis covering powder
can be prepared in variou3 ways. Some powders are
syn-thetic mixtures of various pre-powdered constituer.ts,
whereas others are prepared by a premelting operation of
a mixture of suitable constituents, followed by powdering.
Moreover, the powders obtained in this way can be formed
~, into various shapes.
~ Recent experiments have shown ~hat not only the
J 10 chemical and mineralogical composition, and -thé treatments
for preparing these powders (mixing, melting, powdering,
addition of binder) have a very great effect on the
continuously cast product, but also the shaping of these
covering powders, e.g. if they have the form of sticks,
15 cubes, or other geometrical shapes, has a certain effect
on the properties of the product obtained by continuous
~ casting.
¦ Control of the casting process is normally carried
out by observing the behaviour and appearance of the
¦ 20~ surface of the strand during cooling from the point at
¦ which the strand emerges from -the spraying zone of the
continu~ous casting machine. However, this method has the
~ drawback that certain faults, due perhaps to the selection
i~ of an inedequate covering powder or to deterioration of
j 25 the covering powder, are only discovered at a late stage,
! and that the measures designed to prevent them are
subject to a delay before being effective. ~his means
4 2 3
-that lt is very dif-ficul-t ~o avoid quite consideI,able
sections of: t~.Le cas t str~lcl occasiona'lly ~eing re jected
or a-t least downgraded.
~, ~aking into account the above considerations, it
is possible to see the advantage of having a means of
'' controlling the adequa-te selection of ~he covering
powder in terms of the casting condi-tions and the
~ composition of the steel, and furthermore of ensuring
¦ ~ that this con-trol is continuous in order to detect all
faults as quickly as possible during casting and to
enable a remedy to be quickly applied.
' It is known that certain problems may arise when
i the steel passing through the casting nozzle and contacted
, with the covering powder has a ternperature which is too
I - 15 low or too high. In the first case, the metal may block
or at least restrict the flow from the casting nozzles
and in addition may not have enough calorific energy to
melt the covering powder with which it is contacted; if
it is insufficiently melted, the powder can ~either
absorb the impurities which separate from the steel nor
carry out its function of lubrica~t.
~,he level of the liquid metal in the basket, must
, also be regula-ted; if it becomes too low, the impurities
in the covering powder in the baske-t are drawn into the
mould and contaminate the continuously cast strand. The
position of the casting nozzle, in particular centering
and depth of lmmersion has, as is known, a considerable
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eEfect on -the path which -the llquid metal follows in
the mould and thexefore on the efficienc~ of -the effect
of -the covering powder. Verlficat:ion of the position of
this nozzle is at present usuall~ carried out by
inspecting the strand during cooling from the point at
I which the strand emerges froM the spraying zone of the
,1 casting machine, and is carried out for a number of
castings in order that empirical rules may be established.
However, -this method has the drawback that faults due to
10 incorrect positioning of the nozzle are only detected at
a late stage and that measures designed to correct the
nozzle are subject to some delay before taking effect.
~his does not prevént sometimes quite considerable
sections of the strand being rejected or at least down-
15 graded and in addition it does not enable rupture of the
surface of the strand, as a result of incorrect positioning
J of the nozzle~ to be anticipated. ~his demonstrates the
advantage o~ having continuous control of the position
of the nozzle, in particular a-t the moment of casting,
20 and a control which ensures that it is maintained or
I moved into the optimum position as required.
j ~ It is important to maintain the level of the upper
surface of the liquid metal in the mould as constant as
~i possible, in particular to avoid certain surface defects
25 in the strand. ~hese arise for example when the flow of
¦ covering material, as well as the lubricant film, are
I subject ~o alternate stresses due to the reciprocating
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1 iL5~A23
movem~rl~ oL the m~t~l SUl'f'aC~'~ If~ t i.s stretched too
far al.ong the mould wall by a dccrease or an increase
in the level o~ the metal, the fll7n tears. Va:riation
in the metal level may also cause rupture of -the strand
as a resul-t of slag borders being included.
~ he determination of the steel level in the mould
in addi-tion enables the flow for the cast;ng nozzle to
be controlled~
Normally the position of the upper surface of the
metal in the mould is monitored op-tically or by means of
level detectors, such as radioactive pick-ups; these
various conventional methods all ha.ve their own advantages
; and disadvantages.
i It is known that continuous casting conditions are
1 15 largely dependent on the quantity of covering powder used
I ~ during casting. ~he absence of lubricant, as a result of
the depletion of the covering powder, may give rise to
` fissures in the strand surface, resulting from a
frictional èffort which is too large being exerted by the
mechanical handling means, in particular for withdrawing
the strand. Moreover, excessive lubricant may disturb
the casting conditions, cause casting malfunctions,
and ~ r harm the quality of the strand.
It can be seen from the preceding r escription
that it would be advantageous to be able to continuously
dose the quantity of covering powder applied during
continuous casting and to do this in terms of the casting
,
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t conditions and the composition of the steel, in order
to restrlct, as stated above, the size of the rejected
sections.
Another very important aspect of continuous casting
~i 5 of the strand is the risk of the steel bonding to the
! \ mould. ~his phenomenon may result in the deterioration
of the strand surface and sometiraes even rupture of the
~; ~ . . . .
skin. It can therefore be seen that it is extremely
useful to have a rapid information means continuously
analysing this phenomenon.
~he casting speed, that is the speed at which the
~1 continuous cast strand is withdrawn from the mould, also
has a considerable effect on the quality of the product
j obtained. An incorrect selection of speed may cause
¦ 15 fissures and other defects superficially and i~ternally,
` and may even give rise to rupture.
It can easily be seen that the factors relating to
oscillation of the mould such as the frequency, the
` amplitude, or the shape, effect the surface quality of
the continuously cast product.
Quite an important cause of the appearance of
defects or even rupture in the continuous cast strand
is incorrect tapering of the faces of the continuous
~ casting mould. An insufficiently conical arrangement
1 25 Of the faces of the mould results in the formation of a
skin which is unable to resist the mechanical stresses
appli~d to the strand, and can thus give rise to rupture;
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furthermo:re, an arr~gernent which :is too conical give,
rise to strand-mould friction which is too lar~e,
resulting irl a skin having many surface defes-t~. It
goes withou-t saying that the conditions for -regula-ting
5~ the conicity of the faces of the ingot rnould vary
according to -the casting conditions and the composition
of the steel. It is importan-t, for this reason, to
ensure for each casting operation and each type of steel
suitable regulation of this conicity, which will avold
10 all these defects.
¦ It is known that an important problem in the
¦ continuous casting of metals lies in evaluating the heat
I excha~ge between the strand and the mould during
solidification. It is in fact very important to trace
~¦ 15 continuously the variations of heat exchange between the
¦ strand and the mould, in order to be able to take rapidaction if a defect is detected. ~rom this estimation of
the-heat flux between the strand and the mould, the
I solidification of the strand may easily be traced, and
t 20 thus the risks of defects appearing may be ~nticipated,
particularly surface defects such as rupture during
casting. Knowledge of the heat flux between the strand
and the mould also enables one to determine the mechanical
stresses of thermal origin to which the mould is subject
25 and in particular to anticipate any abnormal increase of
the temperature of the mould which ~ould prove detrimental
i to the mould.
.
~ eat e~charl~e betwoen the rnould anrl th,e strand i,5
curIently monitored by mea,;uring -the ternperclture ~rsriation
between the input ~nd t-he ou-tput of th,e cooling water for
the mould~ or by means of thermocouples incorporatsd in
the mould. However, -these two methods have drawbacks,
in particular requiring complex calculations for determining
continuously, the value of the hea-t flux, from ternperature
measurements taking into account the heat transfer
parameters which are linked to the particular specific
conditions for each casting operation and lor each
continuously cast metal, and in addition the quite
considerable response time between the time at which
the variation of the hea-t flux occurs and the time at
which it is detected by means of temperature measurements.
With respect to the second method in particular, this has
in addition the serlous drawback of weakening the mould
as a result of the introduction of thermocouples, which
decreases its mechanical strength.
~ hese conditions show that it would be advantageous
to have a-process, for continuously controlling the heat
flux between the strand and the continuous casting mould,
which does not have the above drawbacks~
Regulation of the rollers at the base of the mould
effects the quality of the cast product by the bias of
forces which these rollers-exert on the cast edge,
particularly in terms of clamping, determined by their
distance apart. For this reason it i~ very advantageous
to ha~Te a means of determining adequate regulation of
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the posi~ion and in par-ticular th~ (listarce apfJ.r t oi
the rollers at the base of -the mould (in p~-cticlllar
as regulation varies accord;ng to the type of cas-ting
operation and the composi-tion of the steel), in order
to prevent surface defects due to the effect of the base
rollers.
~ he present invention is based on the unexpected
disco-very -that -there is a cause to effect relationship
between, on the one hand, the frictional forces which
exist be-tween the strand and the mould during a
I continuous casting operation and, on the other hand,
i certain factors such as:
~ - the level of the liguid metal in the casting basket,
;~ - the temperature of the liguid metal in the casting
`, 15 basket,
;~ - the position of the casting nozzle in the mould,
- the level of the liguid metal in the mould,
- the type of covering material,
- the amount of covering materlal,
- the bonding of the strand,
- the;casting speed,
- factors concerning oscillations of the mould, such
as gulding suspension, and freguency.
- the conicity of the facas of the mould,
,25 - the heat exchange in the mould and at the first
Ispraying zones at the exit of the mould.
- regulation of the base rollers of -the mould.
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j (~his li.st; i.s not made in any par-ticul~r order and the
terms used have the mean.i.ngs given -to them by the
con.-text of the preceding descriptlon.) ~hese factors
. may be taken in isolation or combined in any number in
several groups, as the various factors may occur
~ simultaneously.
'! ~ Accordingly, the present invention provides a control
3 method in which a measured signal S is continuously
~ compared, this signal representing the frictional forces
;~ 10 which arise between the strand and the mould during a
3 eontinuous casting operation and obtained by selécting,
according to at least two frequency bands, thé constituents
of the signal represen.ting the above friction forces,
w~th a predetermined analog-type reference signal; as a
15 result of this comparison operation, the abnormal
behaviour of one or several of the continuous casting
. factors is detected, such as:
- the level and the temperature of the liquid metal in
. the casting basket,
20 - the position of the casting nozzle in the mould,
- the.type and amount of covering material,
~: - bonding of the s-trand,
¦ . - the casting speed,
- factors concerning oscillations of the mould, such
. 25 as guiding, suspension, and frequency,
- - the conicity of the mould faces,
- factors relating to regulation of the heat flux in
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the mou:Ld and at the f'ir,-t s~)r1ying zon~cJ ;k lt~ ex1t~
such as pressl1Ie an(l rate oL' flow of' t~e coolirlg
fluid,
- regulation of the rollers at the base of` the mou]d,
~ 5 and one or several of the actors are modified,
simultaneously or in sequence, in particular those
factors mentioned above, so that the measured signal is
as close as possible to the predetermined re erence
, signal which is considered ideal for satisfactory casting.
; 10 As a result of the method according to the invention,
behavioural differences of one or several of the a~ove
factors may be measured from tne predetermined behavoiur
; of the same factors resulting from previous castings of
a similar type which were considered satisfactory.
In -the conventional control system for continuous
casting, the determination of the abnormal character of
the behaviour of one or several of the above factors is
I carried out by direct determination using a technique
known ~ se. ~his direct determination may advantageously
be used additionally in the presen-t method.
In the case of the invention, the de-termina-tion of the
abnormal character of the behaviour of one or several of
the above factors may comprise t,he observation of a
predetermined reference signal Si, with i - 0, .....
; 25 n, if n parameters are considered, the signal varying
accordlng to the parame-ter in question.
It goes without saying that a re erence signal may
be used which has been predetermined during one or
23
i
~ severa.:l. pri.o.c castirlg ope.Latiorls having sirnilar
¦ characteristi.cs.
I ~he signal :representing the frictional forces is
jl preferably measured by the shift of movements of the
mould, for example its accelerations, which does not
exclude a measu~ement of the friction forces by means of
another physical ma~ni;ude which would be dependent on
it.
In order to avoid any ambigui-ty with respect to the
meaning of the terms "measured signal" and "reference
signal" 7 precise details are given as follows. ~he
terms "measured signal" and "reference signal" designate
both continuous and discontinuous recordin~s of the
friction forces, and even numerical values whlch represent
the friction forces which act on a determined length of
`1 the strand.
In order to make the object of the invention more
comprehensible, various applications of the method
I adapted to the case of certain continuous casting factors
~¦ 20 are given below wlth explanations; the different methods
~¦ of use~are given in an order which may be considered
j preferable if they are all to be achieved, but this order
j is not formally laid down.
he variation of the level of -the llquid metal ln
the casting basket is monitored by observing the
development of a signal S; if the measured signal S is.
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h:ighe-c ~harl or equa~ o a p-~edfterrrli.r~e(l v.rllue L~o~ it can
be seen thal the level. of the met;al i..5 not belo~r a fi~ed
-thresho:Ld; i:E -this is the case, r,leans suitable ~or
increasing this above the predeterrnined threshold are
actuated; the upper surface of the liquid metal may then
be cleaned and fresh covering powder ma-y finally be
added to the liqu~.d metal. After an interval which is
a function of -the temporal constant of response to the
beginning o:E casting and if the measured signal S has
' 10 again dropped below the predetermined value S0, the
continuous casting operation is continued; otherwise
another casting factor is tested~
~ According to another embodiment of the method according
! to the inven-tion~ which may be combined with any other
embodiment, if the measured signal ~ is higher than or
c~e~/~e~/
equal to a ~Y~ value S1 and if the temperature
of the liquid metal in the casting basket - to be ~
~,ç c er7~Q ~ ~ec~
-~eF~e~ - is not between ~ - A and ~C + B or equal to
these values (~C being an ideal predetermined temperature
value, and A and B being constants which are functions
~ . of the characteristics of -the continuous casting plant
-. and the t~pe of steel cast), observation is made to
establish whether the tempera-t~re of the liquid metal is
higher than ~ + B. If this is the case, the upper
; 25 surface of the liqui.d metal may for example be cleaned
.
' .and then covering materi.al of higher viscosity added. -
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I, After an inte:rvaL which is a flmctiorl of ~he ter~poral
i constc~nt of response o:` the corltinuous cas-tin~.plant and
I if the meas~red si.gnal S has agai.n become lower than or
equal to S1, -the con-tinuous castirlg operation is continued;
if not, ano-ther cas-ting factor i,s tested. If on the
other hand the temperature ~ is no-t higher than ~ -~ B
¦ and is therefore lower than ~ - A, subsequen-t measures
are undertaken such as cleaning of the upper surface of
the liquid metal and the addition of covering material
of a lower viScosit~J. AIter an interval which is a
~ - function of the -temporal constan-t of response of the
;~, continuous casting plant and if -the measured signal S
has again become lower than S1 the continuous casting
operation is con-tinued, if not, another casting factor
is tested.
. Examp].e
In the case of casting Al-Si medium killed steel
(format 1,90Q x 200 mm and casting speed 0.8m/min) the
¦ ~ following relationship was es.tablished between the
¦ 20 variation (~) with respec-t to the casting -temperature
. required (1,535~) and the variation of the measured
signal ~ S%)
i ~ TC _ _ a s%
_ 5 15
- 10 30
~ - 15 45
¦ According to a first variant of the method according
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to the invention a syi5 tem l:o:r detexmi.nin~-; trle tempera~ ~ e
of -the con-tinuously cast meta:l. is connecl~ed by a feedback
loop to a hea-ti.ng or cooling sy.Citem which regulates
the temperature of the liqu.id me-tal in, for examp].e, a
casting ladle or in an intermediate con-talner such as a
hea-ting basket.
- - According to ano-ther ernbodiment~ if the measured
signal S is higher than or eq-ual to a prede-termined value
S2 and if the values of the charac-teristic factors of
the centering and depth of immersion of the nozzle are
' not correct, these factors are adequately adjusted.
! After an interval which is a function of the temporal
3 constant of response of the con-tinuous casting plant
,' provided the meas~red signal S has again become lower
i 15 than the value S2, the continuous casting operation is.
i continued; if no-t9 another casting factor is tested.
Aecording to another embodiment, if the measured
signal S is higher than or equal to a predetermined
alue S3 and if the level of the liquid metal in the
continuous casting mould is not between a prede-termined
minimum-maximum interval, the level is ad.ju.sted
accordingly. After an interval which i.s a function of
the temporal constant of response of the con-tinuous
casting plant provided the measured signal S has again
become lower than the value S3, the casting operation is
continued; if not, another casting factor is tested.
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f:irst Variar.Lt of the abvve rnethod consi~ts in
~ that the information obtained with respect to the level
l of l~quid metal in the mould is sent by means of a feed-
3 back loop to a system for controlling the rnetal flow.T 5 A second variant of the above method consis-ts in
j that the information obtained with respect to the level
¦ of liquid metal in the mould is sen-t by means of a feed-
back loop to a system for controlling the speed of with-
I drawal of the continuously cast strand.
¦ 10 According to another embodiment, if the measuredsignal S is higher th&n or ~qual to a prédetermined
- value S4 and if the selection of the covering material
. is not correct, the surface of the liquid metal in the
mould is then cleaned &nd suitable covering material is
added. After an interval which is a function of the
temporal constant of response of the continuous casting
plan~, if the signal measured S has again become lower
than the value ~4, the continuous casting operation is
continued; if not, another casting factor is tested.
¦ 20 According to another embodiment, if ~he measured
signa~ S is higher th&n or equal to a predetermined
i value S5 and if the amount of covering material on the
T upper surface of the liquid metal in the mould is not
within a predetermined interval, observation is made.to
esta~lish whether there lS excess or insufficient covering
material and the quantity of covering material is adjusted
accordingly. Af-ter &~ interval which is a fu~lction of the
17.
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temporaL constant of re-;porl~3e of' the cont:lnuous casiting
plant, if the measured signa] $ has again, becoJ~e lower
than the predetermined value S5, -the continuous castin~
operation is continued; if no-t;, another cas-ting fac-tor
is tested.
A first variant of the above method consists in
that a curve C i8 used as a predetermined reference signal,
this curve having relative extrema in a system of axes
' having an abscissa the amount of covering material
3, 10 introduced per unit of time into the mould and as ordinate
the reference signal value S5, -this curve defining an
interval of values on the axis of the abscissae so that
~ it includes the extremum wh~ch correspon~s to ,the smallest
j value of the amount of covering material introduced per
l 15 unit of time, this value corresponding to a signal value
;I representing the satisfactory friction conditions. ~his
smallest value is defined arbitrarily in each case in
terms of the particular condi-tions of the casting in
- question, for example the size of' the strarld, the t~pe
of strand, and the features of the plan-t, using for
example the data provided by the constructor or previous
knowledge, whether empirical or no-t, which is known to be
valid for the plant in question.
Another variant of the above method consists in
that the comparison operation is followed by the emission
of a signal indicating whether the amount of covering
18.
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materia:L actually introduced per u~llt of t:ime and
correspo:ndi.ng to the value of the signal actually
¦ measured is inside or outside -the limi-ts of thé interval defined by -the abscissa axisO
l 5 Another variant consists in that the regulation sf
¦ the amo~nt of covering material added to the rnould is
carried out colitinuously by means of a feedback loop.
According to another embodiment, if.the measured
I signal S is higher than or equal to a predetermined
value S6, the surface of the liquid metal in the mould
! iS subsequently cleaned and then.supplied with a different
;~ covering material selscted so that it has one or several
¦ physicochemical properties different from the first, so
l that ths measured signal is brought as close as possible
¦ 15 to the predetermined reference signal, as stated above,
which is considered suited for successful casting; if
this is not the case, another casting factor is tested.
¦ According to a variant of the above method, the
physicochemical properties chosen should enable analysis
~ 20 of the manner and/or the degree of prefusion and/or the
.1~ shaping of the covering material.
Another variant of the above method consists in
~ ~ that the changes in properties of the covering material
j can be advantageously carried out con-tinuously and
adequately by a return loop.
According to ano-ther embodiment, if the measured
I signal S is higher than or equal. to a predetermined value
¦ S7 and if the appearance of the phenomenon of bonding
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of the steel is observcd, -the suL~ace Gf -tho liquid
metal in the moulcl i.i3 subsequentl~ cleaned and i~pplied
with covering material of a type differing frorrl that in
use at the moment that bonding appear6d. Af:ter an
interval which iiJ a ~unction of the tempora] constant
of response of the continuous ca3ting plant, if the
signal measured has again become lower than -the predeter-
mined value S7, the continuous castlng ope~ation is
continued. In the opposite case, that is i~ the measured
signal S is still higher than or equal to the predetermined
value S7 and ;f the phenomenon of bonding of the steel
continues, the surface of the liquid metal in the mould
is again cleaned, and covering ma-terial having a lower
viscosity than the preceding material is added. If the
bonding phenomenon continues, this operation is repeated
until all the possible choices of covering material have
been tried. After an interval which is a function of the
temporal constant of response of the continuous casting
~ plant, if the measured signal S has again become lower
than the predetermined value S7, the continuous casting
operation is continued; if not, another casting factor ii3
tested.
According to another embodiment, if the measured
signal S is higher than or equal to a predetermined
value S8 a~d if the casting s~eed V is not equal to
predetermined value Vc, Vc being the casting speed value
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considered ideal i'or the cJa,stirlgS in ~uestion, the cas-ting
; speed is adjus~e-l to the value V~. ~f'ter a-n intcrval
I which is a function of the ternporal constarlt of response
! of the continuous casting plant and if the measured
! 5 signal S has again become lower than the predetermined
value ~8~ the continuous castlng opera-tion is continued.
~ In the opposite case, that is if the measu~ed signal ~
-I is still higher than or equal to the predetermined value
S8, the casting speed V is reduced by an arnount V1, which
is a function of the technical features of the continuous
casting plant and the particular conditions for the type
of steel being cast, so that the risk of defects or even
~ rupture in the cast strand is limited; if not, another
¦ casting factor is tested.
In the accompan~ing drawings:
~igure 1 is a graph of the measured signal S (%)
against the casting speed V (m/min);
Figure 2 is a similar graph~ showing the situation
during normal casting and during abnormal casting
¦ 20 (rupture);
¦ Figure 3 is a logic diagram for -the control of a
continuous casting plant; and
Figure 4 is a block diagram of apparatus for use in
1 controlling a continuous casting plant.
¦ 25 A diagram giving the measured signal S in terms of
the casting speed ma~ be set up taking into account the
fi~ed values of the other casting factors and a speed
. ',
~1 .
.
I' .. ,
-
2 3
for the castjrLgr s-peed Vr, is choqerl cor-res-p(Jndin~!; to the~
rninimwn signa:L S which is compatib]c w-ith t'ne -technical
requirements for -the cast:ina, i~l ques-tion.
~ 'igure 1, given as a norl-limi-ting e~a~r~ple 7 shows how
-this particula-r application of the process accordingr to
the present invention may be utilized. ~his graph has ~-n
ordina-te 9 in conven-tional uni-ts (%), -the intensit~ of
the signal S representing the fric-tional forces between
the strand and the mould, and as a~Scissa,in metres/
minute, the casting speed; the resultant curve for a
powder of a given composition and a strand of given
characteristics is generally V-shaped; the area to be
chosen for the casting speed lS that which surrounds -the
Q, lowest point of the curve, which corresponds to the lowest
frictional forces and in addition the best lubrication.
, ~he method according to the invention is therefore in
keeping with the use of the above graph, which? in an
absolutely unforseen manner, gave a minimum.
According to another embodiment, if the measured sïgnal
S is higher than or equal to a predetermined value S~
~` and if the values of the oscillation factors of the mould
; are incorrect, the values of the osclllation factors of
the mould are adjusted. After an interval which is a
function of the temporal constant of response of the
continuous casting plant, if the measured signal S has
again become lower than the predetermined value S9, the
continuous casting operation is continued. In the opposite
case, that is if the signal S is still hlgher than or
~, . . .
$~23
.
equal ko the predetellmirled valus f,~, ano-ther castlng
I factor is -tested.
i According -to another ernbodiment, if the measu~ed
signal S i5 higher than or equal -to a predetermlned
~ 5 value S10 and if the adjustment of -the conicity of thej mould faces is incorrect, the conicity is suitably
adjusted. After an in-terval ~hich is a function of
the temporal constant o~ response of the continuous
casting plant, if the measu-red signal ~ has again become
lower than the predetermined value S10, the continuous
j casting operation is continued; if notj another casting
¦ factor is tested.
As a non-limiting exa~ple of the possibilities of use
of this application of the method according to the
invention, curves which are characteristic of casting
are given in ~igure 2, in which the levels of the
measured signals are the ordinate and the casting speeds
-are the abscissa. With respect to so-called "normal"
j casting operations, that is where an optimum conicity
. ..
is used, "malfunctioning" casting operations have a
q considerably increased signal level.
According to another embodiment, if the measured
; signal S is higher than or equal to a predetermined
! value S11 and if the factors relating to set-tings of the
¦ 25 heat flux in the mould and in the first spraying zones
when the strand emerges, that is flow, pressure, and
input temperature and heating of the cooling fluid, are
, 23.
not set to p:rede-termi.ned values, the vllue~ of t;he above
factors are adequately adjusted in order to give ag~.reerQent
with the predetermined values. After an interval which
is a function of the ternporal constarlt of response of the
continuous casting plant~ if the measured signal S has
. again become lower than the prede-termined value S11, t-he
continuous cas-ting operation is continued; if not,
another casting factor is tested.
According to a varian-t of tnis method, the pre~
determined values of the factors relating to heat flux i.n
. the mould and in the first spraying zones are obtained
; from the study of heat fl.ux recordings in the mould and
the first spra~ing zones in terms of the measured signal
~ ~ S and for continuous casting having similar characteris-
;¦ 15 tics.
.~ Another variant of the method consists in that the
operation for determining the heat flux between the strand
: and the mould is followed by the use of a control loop by means of which one or several cas-ting factors ma~J be adequately adjusted so that the heat flux follow~s a
determined ternporal development.
According to another embodiment,.which, similarly to
those described above, may be applied singly or in
combination with the others, if the measursd signal S is
higher than or equal to a predetermined value S12 and if
. the values of the factors relating to setting of the
roLlers at the base of the mould, and in particular -their
2L~.
4 2 3
.
I, distance apart, are not e~lurll to pre(le-terrnined value~,
t -these factors are adequa-te]y adjusted in orde-r to rnake
3~ them correspond. Af-ter an interval which is a func-tion
of the temporal constant of response of the continuous
cas-ting plant, if the rneasured signal S has again
become lower than the predeterrnined value S12, the
continuous casting operation is continued; if not, another
casting factor is tested~
According to a variant of the method~ the pre-
determined values of the factors relating to setting of
¦ - the rollers at the base of the mould, and in particular
~3 their distance apar-t, are obtained by means of recordings
¦ of the S signal values for these factors during similar
! casting operations.
~he opera-tions for recording, processing, and
comparing the meas~lred signal with the reference signal,
and the resultant regulating operations may be carried
out totally or partially by automatic systems.
As a non-limiting example, Figure 3 ~hows the logic
! 20 diagram fo~ the control of a particular continuous
! casting plant; the operations are given as follows.
I ~he different signs and coefficients used in this diagram
¦ and in the following lis-t of operations have the
following meaning: `
~ Measured signal (betwee: 0 and 100%)
Si ~'hreshold signal (surface defects, rupture, etc.);
Particular case of -the example: Si = S0 for all i-
25.
~'empor~l consta~lt oL re,pon,;e of t;he con-tir--uolls c;3skinp;
p~rln-t = 30 ,s.
= B = ~oa.
C~ Con-tinuous casting
5 Va Required casting speed
V Casting speed (actua])
~a ~9~ casting temperature (~)
~asting -temperatu~e (actual)
YES ' .
10 - NO
' CO~RO~ PROCESS OPERA~IO~TS
1. S ,~ S
-' 2 Casting speed = Va?
3. Correct casting speed.
~ 15 4. S ~ SO after 30 s ?
`~1 5. Continue continuous casting.
' 6. Reduce speed by 20%: V = V~ - 0.20 Va.
i 7- is there bonding ?
j - 8. Make V = O (temporary pause in casting).
20 9. Glean, then use powder (same type) of a differeni;
batch (pallet).
! 10. Res-tar-t and move cas-ting gradually to Va.
S ~ SO after 30 s ?
12. Continue continuous casting
25 13- ~emperature of contimlous casting from ~c ~ 10C
to ~C + 10a~ that is ~a - 10C ~ ~ ~a -~ 10 ?
14-. aasting emperature higher than ~C + 10a~ tha-t
is ~ ~a + 10 ?
26
1 ~ 1 2 ~
i
i
1 15~ C~lean then apply rnore viscous powtler~
i 16. Cle~L-then apply more fluid powder,
I 17- S~ S0 after 30 s ?
! 18. S~S0 after 30 s ?
19. Continue continuous ca,sting.
I 20. "
¦ 21. Steel level in basket too low
22. Correct steel level.
23. ~lean then re-apply powder of sarne type, using
new powder.
¦ 24. S ~ S0 after 30 s ?
~ 25. Continue continuous casting.
¦ 26. Is powder suited to ca~sting conditions being used
(predetermined type of powder)?
15 27- Clean, then apply correct powder,
28. S ~S0 after 30 s ?
29. Continue continuous casting.
30. Position, i.e. centering and/or depth of immersion
of the nozzle is correct ?
¦ 20 31. Correct position of no~zle "
¦ 32~ S ~S0 after 30 s ?
¦ 33- Gontinue continuous casting.
34. Lubricant feed required and/or sufficient ?
I 35- Add lubricant and, in particular case, powder.
¦ 25 36~ S~ S0 after 30 s ?
37- Continue continuous casting.
38~ Is the oscillation frequenc~ of the mould
correct ? 27
'1 2 3
39. Cor;rcc-t osc~Lla~,:i,oo f'requt,rlc~
40. S ~ SO (ir~ed~al;e ef.'fect~ with,out -ti~e de],a,y~
: 41. Continue conti,nuous casting~
42. Are -the rates of water flow ~Id./or pressure in
the Mould and the fixst spra~Jing zones (base
rollers) correc-t ?
43. Correct these flows and pressures.
. S ~SO af-ter 30 s ?
45. Continue contlnuous cas-ting.
46. Is th.e steel level in the mould correct ?
. Correct steel level by acting -~pon stopper/no~zle
' with baske-t slide valve and/or upon casting speed
(withdrawal stand).
48. S ~ SO(immediate eff,'ec-t, without time delay)?
' 15 49. Continue continuous casting.
.~ 50. Cleanj'then apply powder ~same type) of a
different batch (pallet).
' . 51. S ~ S0 after 30 s ?
. 52. Continue continuous casting.
20 53- Clean, then apply more fluid powder (different
type).
54. ~ ~ S0 af.'ter 30 s ?
55. Continue continuous casting.
~' 56. Stop sequence (casting).
25 57- Exarnination of mould and related factors (state
and adjustment)
. - correct oscilla-tion?
- correct conicity ?
23.
4 2 ~
- corLect su,,perlsion (sprirlgs) 7
- correct guiding (plates) ?
base rollers (alignment, cooling) ?
- wear of mould walls ?
- mould spats suitably placed ?
58. ~asting speed.
~¦ 59. Strand bonding.
60. Steel temperature.
I 61. Basket level.
f 10 62. Powder check.- 6~. Nozzle positionO
64. Amount of covering powder.
65. Oscillatlon frequency.
66. Cooling fluid flow.
15 67. Level in mould.
~he selected factors and the sequence of operations
as well as the values of vc7 A, B, Si and the temporal
constant of response o~ the continuous casting plant are
particular to the plant in question and are therefore only
7 20 given as an indication and not a rule.
Control apparatus which may be applied to a plant
for contimlously casting metals cornprises:
(a) a sensor for the movements of the continuous castirg
mould during the casting operation~
25 (b) electrical energy feed means for the sensor,
(c) two electronic chains connected in parallel to the
sensor output, the first enabling a signal solely
linked to the movements due to the oscilla-tion
29.
provided b~J Ih.e mo-u:ld to ~he produced, and the
second enabli.ng a signa:l. d.ependent on the aoove
movements as well as -lhe friction between the
s-trand and -the mould and -the withdrawa.l speed to
be produced,
. (d) a device enabling both. signals to be divided by
each o-ther, which enables a new signal to be
obtained, which has been found to represent the
phenomenon in question, that is the ingot-ingot
mould friction, in combination with -the extraction
j speed.
According to a constructional embodiment of -this
apparatus, the first chain compr:ises a band-pass filter
, of 0~1 to 3 times -the oscillation .frequency of the mould,
j 15 whereas the second chain comprises a band-pass filter of
3 to 1,000 times the oscillation frequency of the mould,
preferably from 4 to 10 times this frequency.
~he diagram shown in ~igure 4, given as a non-
limiti~-g example, enables the design of such apparatus to
be envisaged, being a block diagram of such apparatus.
In this..block diagram, C represents t-he sensor for the
mould movements, which is fed by an electrical supply 1.
~wo electronic chains connected in parallel to the output
of the sensor C are composed as follows:
~ the first: an adjustable amplifier 6, a band-pass
filter 7 of 0.2 to 3 Hz, a signal shunter 8 (which
may be short-circuited), a demodulator 9 which may
3o.
4 2 3
t
I ac-t on one o~ bo-th o~ the al-ternatiorl.q of.' the
! inP~t ~ignal,
- the second: an adjustable amplifier 2, a band-
1 pass filter 3 of ~-to 10 ~z, a signal shun-ter 4
j 5 (which may be sho:r.t-circui.ted), a demodulator 5
j which may act upon one or both of the alternations
of the input signal,
~ a module 10 providing the quoti.ent of the output
~, signal from the demodulator 9 divided by the out-
put signal from the demodulator 5, the value of the
s~gnal
quotient ~ S thus obtained being introduced
into a display device or a recorder 11.
~he above diagram is completed by:
~ - a corrector circuit 12j cancelling the signal between
¦ . 15 casting operations,
¦ - a sub-assembl-y 13 enabling high and low alarms to
¦ be set off.
- , I
~ ~''"' ' . ' .
: . ~
31.
.' '.
