Note: Descriptions are shown in the official language in which they were submitted.
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Pro~ramme-~ontrolla~le E~lectroma~neffc C~ontin~lQ~s C~Mould , :
The invention relates to a prograrnme-controllable eleetromagnetic continuous casting
mould for producing continuously cast ingots of various dimensions in whieh an
S eleetromagnetic inductor determines the cross-sectional dimensions of the molten metal
column, the mould contains a dummy base that can be lowered and a frame with a pair of
faeing stationary side walls and a pair of facing end walls the distance between which can
be variedr where the side walls and end walls together form the opening to the mould and `~
each of the walls comprises an inductor part with inductor coil and a screen. The invention
10 relates also to a proeess for performing the continuous casting proeess using the adjustable
eleetromagnetie mowld aeeording to the invention.
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Continuous casting moulds are employed for easting molten metal from a crueible or the ~ ~ ~
like into a mould thus-enabling workpieces with solid or hollow cross-section to be ; ~;
15 produced. Conventional casting deviees for easting metals into the form of ingots or billets ;
as starting material for further processing e.g. by extrusion or rolling comprise of a water- -
eooled mould i.e. a rnould that is open at the top, has parallel walls and an initially tight-
fitting dummy base that can be lowered; the mould walls are normally hollow and are
cooled with water. When the metal is poured into the mould, it solidifies rapidly on the
20 walls and base of the mould forming a bowl, the contents of which are still molten. During
continuous casting the base of the mould is lowered and, at the same time, sufficient
molten metal poured into the mould that the level of metal in the mould remains constant. . ~ :
As a result, the ingot grows ~n length downwards during whieh time it is sprayed on all
sides with a coolant, normally water, an is thus cooled in a controlled manner. -
.
The grain structure of the solidified metal depends, amongst other things, on the rate of
eooling, so that depending on the manner of eooling a different grain structure is formed in
the edge zone and in the core of the continuously cast ingot. For extruded and rolled
produets it is advantageous to have fine-grained alloys. In the ease of eonventional con-
30 tinuous casting e.g. when casting aluminium ingots with eonventional moulds, there is
usually a 2 to 5 mm deep es)arse grained zone at the edge of the ingot. -
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For eontinuous easting me~al rolling slabs and other sueh east lengths a speeial mould is
employed for eaeh width and thiekness of ingot, whieh is espeeially uneconomieal when ~
35 only few ingots of a partieular dimension are required. - `
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In order to eliminate this problem, at least in part, the German patent publication 1 059
626 proposes manufacturing ingots with elongated cross-section using a mould in the form
of a closed ring with parallel side walls and end walls in which at least one of the end walls
within the ring can be shifted. The adjustment to the mould opening necessary to produce
5 a specific ingot width must be undertaken prior to casting, whereby care must be taken to
ensure that the mould is closed tightly around its whole periphery.
Elec,romagnetic casting moulds (EMC moulds) represent a different kind of mould for
continuous casting. Instead of the above mentioned cooled mould, there is an induction
10 coil ~inductor) to which a constant high-frequency alternating voltage is applied that
induces a corresponding electrical current. This electrical current creates a magnetic field
with a magnetic field force whose vertical components Hy~ i.e. the components acting in
the direction of the mould ~is, induces an eddy current in the molten metal passing
through the space inside the mould during casting, said eddy current flowing in the
15 direction opposite to that of the current in the inductor. The interaction of Hy and the
induced eddy current produces a force which is directed into the centre of the melt and has
a magnitude which is proportional to the strength of the eddy current and the magnetic
Qeld strength Hy~ This force represents a so ca~ed electromagnetic force. The equilibrium
between this and the metallo-static pressure in the melt determines the shape and
20 dimension of the cast ingot.
The principle of the electromagnetic continuous casting mould is based, therefore, on the
fact that a strong current flowing through the inductor coil generates a strong magnetic
f1eld which in turn creates an eddy current in the melt with the result that the interaction
25 between the magnetic field and eddy currents holds the melt together. Using such
electromagnetic moulds the melt is fed at a predetermined rate onto a dummy base inside
the coil-shaped electric~ inductor. The dummy base is lowered at a speed in keeping with
the rate of casting. High frequency alternating current in the inductor generates an
electromagnetic field force that keeps the melt within the inductor in a shape that is
30 determined essentia~y by the inner contour of the inductor coil. By jetting with a coolant,
e.g. spra i g the ingot with water as it is lowered, the su face layer of the ingot solidi les
~- rapidly. he use of t is EMC mould results i thin edge zones with a fine-grained
~; structure. Furthermore, the tendency for the formation of ext emely smal voids, i.e
hollow spaces resulti g from non-uniform solidi Ication, and for segregation i.e. non-
; 35 uniform dist ibution of ~loying elements is reduced.
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The construction of a conventional continuous casting mould is therefore fundamentally ~ -
different from that of an electromagnetic continuous casting mould. In the case of the con-
ven~ional mould, the mould in serves to conduct away the heat of the melt by contact with
the melt. Also, it forms a container-wall for the melt, and must therefore form a tight seal
5 around the whole periphery. The electromagnetic mould, however, does not come into
contact with the melt. It serves to guide the melt in a specific manner and normally
contains devices for influencing the magnetic field in other ways. The electromagnetic ; `,
mould is therefore essentially different from the conventional mould so that there is no
possibility of transferring features of one type of mould design to the other. ;,
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A further development of the EMC mould is described in the US patent 3,605,865 in that, ;
by means of a downward tapering electromagnetic screen comprising a ring of non-magnetic metal that terminates at the bottom, at a level corresponding approximately to
the mid-height of the inductor, the axial magnetic field is adjusted to such an extent that at
15 all points in the column of metal the lateral metallostatic pressure is essentially equal to the ;
electromagnetic force; as a result of which differences in cross-section in the ingot being ~ ~ -
cast are avoided.
By employing a concentric metal ring of high electrical conductivity within the electro-
20 magnetic screen, and namely such that the said ling is positioned at the upper end of the
-screen and can be adjusted in height with respect to the screen, the electromagnetic field of
the inductor generates eddy currents in the melt the magnetic field of which counteracts
that of the inductor. Consequently, the resultant magnetic field at the surface of the melt
` ~zone is only small and so at this place pronounced turbulence in the melt that can lead to - ~ -
25 casting defects at the surface of the ingot is avoided. ~ ~ ;
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~; In conventional continuous casting, as with continuous casting with electromagnetic
moulds, the final ingots exhibit slightly concave side walls. This concavity of the ingot
sidèlwall faces;is~due to a shrinking process during the cooling of the melt and occurs
30 especially Oll the flat sides of long-format, rectangular rolling slabs. The curvature of the
ingot faces resulting from the shrinking process depends amongst other things on the
format, alloy and casting rate. Typical values for the shrinkage are S tO 10 mm on each
side of ingots with a format of 300 x 1000 mm, made of a Mg-containing aluminium alloy
and cast at a rate of 5 to 8 cm per minute. Such deviations in fla~ness of the surface are
35 undesirable in that they lead to an increased amount of scrap on scalping and cause
difflculties with respect to straightness during rolling.
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With conventional continuous casting moulds this concavity of the walls is taken into
account by making the inner faces of the mould curve outwards. The melt leaves the
mould with outward curved faces that then become flat as a result of shrinkage. The same
principle can also be applied to EMC moulds.
S
Another possibility for compensating for the shrinkage in the case of EMC moul~s is,
according to the Gerrnan patent publication DE-OS 28 48 808, to employ a metallic
conduc-tive coil having a ho~ow space to accomodate an inductor with coolant passing
through it, the vertical dimension of the inductor at the middle of the side being many time
10 that of the vertical dimension at its corners. The solution proposed in DE-OS 28 48 808
makes use of the consideration that the shape and dirnension of the melt on continuous
casting in the electromagnetic alternating field - apart from the shape of the inductor as
seen in plan view - depends essentia~y on the vertical component Hy of the magnetic field
force prevailing in the melt; according to DE-OS 28 48 808 this can be effected by locally
15 reducing ~he current densily in the conductor i.e. preferably in the middle of its side-wall
Ma~y because of the close dimensional tolerances required, manufacturing
electromagnetic condnuous casdng moulds is complicated and expensive. The numerous
20 different ingot formats make it necessary to keep a corresponding large number of moulds
in reserve, which is also uneconomic~.
Described in the European patent EP 0 109 357 is an electromagnetic condnuous casting
mould with adjustable cross-section that features special blocking elements for selectively
25 posit~oning and securing the end walls to the side wa~s. A special clamping facility on the
; ~ end walls connects the inductor coils and the related screening for the individual walls so
that closed loops are forrned inside the mould. The clamping fac~ity features a camshaft
which, when turned causes pistons to bring special contact elements into contact. These
clamping facilities have to be set for each of the contacts on both sides betweeniside wa~s
30 and end wa~s. The contact pressure for the contact elements depends solely on the
rolatlon of the cnmshaft.
European patent 0 156 764 descri~s an electromagnetic continuous casting mould by
means of which an end wall is displaceably secured to the side walls via releasable f ing
35 bolts, whi e the related inductor coi s and screens are connected to closed loops by mea s
of a clamping device with pistons in piston shafts. The piston shafts are connected to a
pressure chamber via branch lines or channels, the pressure chamber being filled with a
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compression medium which can be put under pressure by means of a master cylinder. This : ;
conshuction ensures uniform movement of the pistons in the piston shafts and uniforrn
contact pressure.
S All of the electromagnetic continuous casting moulds for casting rolling slabs and the like ;
forms of ingot made of metal, such as e.g. Iight-weight metal, are such that prior to casting :
the mould width has to be adjusted by hand for each ingot width, which is very time
consuming and normally leads to a long interruption of the production line. This has in
particular an unfavourable influence on production time and production costs when only
; ; 10 few ingots of a particular width are required.
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The object of the present invention is to provide an electromagnetic mould which avoids
the above mentioned disadvantages and enables the resultant cross-section to be varied
without manually positioning the end or side walls prior to casting.
1 5
That object is achieved by way of the invention in that the dummy base which can be
lowered has fixed dimensions, the mould frame is such that at least one end wall is
displaceably mounted on the adjacent side walls, the position of the displaceable end wa~s
can at ~1 ~mes be determined by a measuring facility, the positioning of each displaceable
20 end wa~ takes place by means of a drive controlled by a control unit, and the inductor
coils and screens of the individual walls are connected via ~exible electrical conductors to
closedloops.
In order to produce ingots with the flattest possible side wa~s, the facing, stationary side
25 walls that are usefully approxirnately perpendicular to the end walls and, together with
these end walls, form the mould opening, are segmented as described in EP 0 109 357 and
/or are provided with ~ inductor that e.g. as in DE OS 28 48 808 exhibits different vertical
dimensions at the edge and in the middle of the side wall.
30 According to the present invention the width of the ingot can be set by programme~
controlled :regulation of the mould opening or the distance between the end wa~s, whereby
this may take place by positioning either only one end wa~ or e.g. by displacement of both
end walls in opposing directions. No~ally, however, it is sufficient to displace only one
~ end wa~ in order to set the distance between a pair of facing end w~ls. The following
35 description therefore refers to the adjustment of one single end wall, although for certain
mould designs symmetnc~ and simultaneous displacement of both end walls with respect
to the centre of the mould can be advantageous. The present disclosure encompasses,
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however, adjustment of the mould opening by means of only one end wall as well as
sirnultaneous adjustment of both facing end walls.
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Using the EMC mould according to the invention the distance between the end walls may '
5 be varied usefully in a range from 10 to 1000 mm, in particular from 100 to 500 mm.
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The flexible electrical conductors serve to connect the inductor coils and screens of the : ' ~ '",'
individual walls so that a closed inductor loop and an electrically continuous ;' '
electromagnetic screen is formed. The flexible electrical conductors preferably exhibit high '~
10 electracal conductivity and are of such a length that they do not limit the movement of the . '' ';. . ' ,, ~
end walls. The conductors used by way of preference for this purpose are copper strips or . ' '- ' . .,Y
stranded copper wares. ~ . '
' In a further preferred version of the condnuous casting mould according to the invention ' '
15 the flexible electrical conductors are at least in part in the form of conductors transporting '~
coolant, e.g. conductors in the form of flexible hoses with the electrical conductor on the '~ "~.. ', ',.
sleeve and separated from' the coolant by an insulator. ' : ' ' .'' ' '
The drive~ for the displaceable end walls may for example take place by hydraulic, '
20 pneumatic or electromagnetic means. Usefully each end wall is positioned and secured by '
means of at least one axle shaft e.g. Iying parallel to the direction of movement of the end
wall; the said shaft may be~ in the form of a solid or hollow section or a piston-shaped
element.
25 ~ Each displaceable end wall is e.g. positioned by means of at least one axle shaft according
to~a prede~termmed~programme.~When employing only one shaft per side wall the shaft is '~
usefully~ situated at the middle of the end wall. When employing a plurality of axle shafts
per end w~all, it must be made certain that all such shafts provide synchronised movement ;'"; '~
of'the end wall.
The t~hrust required to position and secure the end wall is provided usefully by means of a ,'
motor dri~en shaft and such that the rotary movement of the shaft can be converted by ' ' '
means of gearing into an axial thrust m a direction parahel to the axle. If a plurality of
drive shafts are employed for displacing the end wall, or if a plurali~,r of moulds according ` ~
35 ta the invention are~ driven in parallel, the axle shafts involved are driven by a common ~' ' ~ ' `'
drive ~shaft in order to ensure synchronous movement. ' ' '. ' ~
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The types of gearing that come into question for this purpose are e.g. drawing, articulated,
screw or wheel type gearing. Preferred are gear wheels in the form of single or multi-step
gearing. These permit slip-free transmission of rotational movement of the drive shaft to
the axle shaft(s) with defined transmission ratio.
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Suitable cogged wheel gears are e.g. the cylindricàl spur gear, bevel-gear or worm gear
type. The cylindrical cogged wheels may be straight, sloping, arrow-shaped (herringbone
~ ~ wheels) or screw-shaped (worm wheels) and may be threaded inside or outside. Bevel-
; gear wheels exhibit a conical surface with straight, inclined or arc-shaped cogging.
: 10
The displacement of the end wall required to adjust the size of the mould may e.g. be
per~ormed by means of an axle shaft perrnanently attached to the end wall, the other end of
the shaft being in the form of a cog-rack which engages - if desired via transition gearing -
with a cogged wheel that is permanently connected to the drive shaft. ~
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The axle shaft(s) may be attached to the end wall e.g. by bolting, clamping, riveting or
welding. Preferred however, for ease of exchange of the mould elements subjected to
wear, are releasable connecting means.
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;20 An other possibility for converting the rotational movement of the drive shaft to an axial
displacement of the end wall lies e.g. in the transmission of the turning movement of the
drive shaft to the axle shaft(s) by means of cogged gearing where the drive shaft and axle
shaft each feature a cogged wheel that is permanently attached to the related shaft. The
turning movement of the axle shaft(s) can then be converted to an axial movement of the -
25 end wall e.g. by means of a spindle gear, i.e. a threaded bore in the end wall or in an -~
extension to the end wall, into which a spindle shaft with threading on the outside engages.
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The use of the described mould according to the invention for manufacture of
n ~ icontinuously cast~ingots of different dimensions with a dummy base of fixed dimensions
30 shows a great advantage in terms of costs over known EMC moulds with end walls that
are attached to the side walls, normally by means of bolts or the like, as no manual
adjustment of the mould is necessary prior to casting and therefore no interruption of
production takes place. This advantage is particularly effective for a plurality of EMC ~ ;
moulds working in parallel as all the moulds can be adjusted at the same time e.g. by
35 means of a common drive shaft. : -
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Furthermore, the EMC mould according to the invention makes it possible to select ingot
dimensions over a continuous range, whereas the EMC moulds to date normally permit
the end wall to be moved to only three to five positions. ~ -
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S The EMC mould according to the invention is suited to continuous casting ingots of metal,
usefully of light metal and in particular for the production of continuously cast ingots of
aluminium and its alloys. : .
The invention relates also to a process for continuous casting metal ingots using ~n
10 electromagnetic continuous casting mould according to the present invention. ;
The distance between the mould end walls is in accordance with the invention initially set ;;
such that the initial cross-section of the melt column defined by the mould walls or by the
field force created in the inductor corresponds essentially to the cross-section defined by
15 the dummy base that can be lowered, and the distance between the mould end walls is
programme-controlled in the course of continuous casling by a drive facility that is
regulated~by the control unit in conjunction with the lowering of the dumrny base, and
such that the cross-sectional dimensions of the resultant metal column are continuously or
stepwise adjusted to the dimensions of the desired ingot.
In the process according to the invention the melt is limited in shape by the ~,,.. ,!:,,,,,~,,",~,
electromagnetic f1eld force to the space enclosed by the inductor., so that-at no point in "`".i'"'?''~`"`'
time and in~particular at ths start of casting does the process according to the invention
require a light seal between the mould frame and the dummy base.
~; ~ The distance between the end walls is regulated by the control unit preferably on a dme~
~; deper.dent basis via a fixed, predeterrnmed prograrnme, a so called target curve.
Re~ lating the distance between the end walls takes place in a further preferred 'manner in
30 which the positioning of each moveable end wall,effected by the control unit,takes place ~` ` ` `
on the basis of the difference bet~veen the measured, time-dependent position of the end
wall in question and a given time-dependent value (target value) in a programme.
; At the start of the process according to the invention the cross-section of the molten
35 column may be selected to be larger or smaller than the cross-section of the ingot to be
produced. As the dummy base is lowered the si~e of the cross-section may be altered in
steps or continuously to arrive at a chilled ingot of the desired cross-section, whereby at ` ~:
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the start of the casting process a conical part or a plurality ot conical parts following
stepwise one after the other is formed. The cone or stepped conical parts may e.g. be in
the shape of a blunted pyramid or blunted cone.
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5 The shape of the conical ingot parts is essentially a result of the rate of change of distance
between the end walls combined with the rate of lowering the dummy base. The control of
the process is preferably such that the surface normals to the conical shaped parts of the
ingot lie at an acute angle of 25 in minimum i.e. the corresponding angle of the blunted
cone or blunted pyramid part of the ingot lies at an angle of 25 to 90.
~: 10 , ..
In order to minimise the amount of scrap during further processing of the ingot, the
maximum depth to which the dummy base is lowered until the necessary melt cross- ~ ;
section for the desired constant ingot dimensions is reached i.e. the height of the blunted
pyramid or blunted conical part of the ingot is usefully less than 50 cm and in particular
15 less than 30 cm.
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In contrast with the known methods for continuous casting in which the position of the ~:
end walls has to be decided and fixed, normally by means of bolts, the present process
according to the invention which allows continuous adjustrnent of the mould dimensions,
20 permits ingots of any dimension selected by the customer to be produced at favourable
cost. .
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The invention offers further advantages, ~atures and details with respect to the continuous
casting mould according to the invention. These are revealed in the following examples in
25 the figuresshown.
Figure 1 shows a plan view of controllable electromagnetic moulds according to the ;
presentinvention.
30 Figure 2 shows a perspective view of an end wall that is displaceably mounted on a side ;
wall and whose position can be adjusted by means of a spindle gear.
Figure 3 shows a section through the mould wall along the line III - III in figure 1.
35 Figure 1 shows a system of controllable electromagnetic moulds, whereby - in order to
provide a clearer view - by way of example two such moulds 60 are illustrated. Each
mould 60 features a mould frame 62, containing a pair of facing side walls 20 and a pair of ~ ~
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facing, moveable end walls 10, which together form the mould opening 12. The side walls
and end walls each comprise of an inductor pari with induction coil and a screen 28. The
Induction coil 70 of the side wall 20 is connected electrically by connection 18 to the
induction coil of the end wall which is not shown here. The electrical connection of the
5 screen 28 attached to the side wall 20 to the screening attached to the end wall takes place
via connection 19. The electrical connections 18 and 19 are made via flexible electrical
conductors of high electrical conductivity. Copper strips and braided copper wires are
employed for that purpose. The side walls 20 of each mould 60 are rigidly connected at a
predetermined distance by sections 25. The end walls 10 are mounted such ~hat they can
10 be rnoved on sliding rail contacts 15 which exhibit recesses into which the guide rails 16
mounted on the surface 21 of the side walls 20 fit, and can be displaced in a sliding manner
by the axle shafts 30. The axle shafts are connected via a gearing mechanism 32 to the
drive shaft 34 which is the common drive for a series of parallel continuous casting moulds
60. The drive shaft 34 is driven by an electric rnotor 40 the control of which takes place
lS via a control unit - not shown here according to a given programme and the required
positioning of the end wall given by the position measuring facility 50.
Figure 2 shows a perspective view of an end wall that is displaceably mounted on a side
wall and is adjustable by means of a spindle gear drive; the mould dummy base is not
20 shown here. Figure 2 shows therefore in an exemplified manner the principle of an end
wall drive. ~ sliding shoe 15 is secured to the side wall 10 by bolts or rivets. The sliding
shoe 15 features for example at least one recess into which a guide rail 16 on surface 21 of
the side wall 20 fits. so that the end wall 10 is displaceably mounted on the side wall 20.
Th~e position of the end wall 10 is thus fixed by axle shaft 30. In the exemplified
25 embodiment of the end wall drive according to the invention the sliding shoe 15 features a
further recess in the forrn of a threaded bore which is penetrated by a threaded rod or
spindle 36 so that a rotational movement produced by the drive shaft 34 is transmitted via
the cogged gearing 32 to the axle shaft which is at least partly in the in the form of a
, spindle~ 36 and, in conjunction with the threaded bore in the sliding shoe 15, is converted
30 into continuous displacement of the end wall 10.
:
According to figure 3 a side wall 20 of the mould 60 features a mould frame 62 onto
which insulated body 64 is secured by means of bolts 66. Against this, held in place by
bolts 68 lies an induction coil 70 which is cooled by a cooling channel 72. Mounted on the
35 mould frame 62 by further bolts 74 is an electromagnetic screen 28 which leaves a gap 76
open to the induction coil 70; a stream of coolant emerges &om a water chamber 80 via
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channel 82 onto the surface of a cast ingot 54 - shown only in broken lines in figure 1. The
end walls 10 also have a similar construction to that of the side walls 20.
Using an EMC mould according to the present invention it is possible by means of5 programme-controlled positioning of the end walls to alter the mould opening in a . ~
continuous, uninterrupted manner to the desired dimensions of the ingot to be cast, so that :
ingots of any desired dimensions can be manufactured at favourable cost.
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