Note: Descriptions are shown in the official language in which they were submitted.
127~i4Z 7
Method and apparatus for continuous casting
The present invention relates to a continuous
casting method with a horizontal or inclined mold, with
subsequent treatment of the casting withdrawn from the
mold, as well as an apparatus for carrying out the method.
The object of the invention is to improve the re-
liability of the casting process, the quality of the casting
and its surface finish, as well as to enable smoother
casting progress and higher casting rates than is the case
with the horizontal casting methods in the prior art.
According to conventional horizontal contlnuous
casting methods, the mold is rigidly fastened to, and sealed
against, the holding vessel from which the melt is fed to
the mold, and which may be a casting box or a furnace, here-
inafter designated "casting box". Between this and the mold
there is a connection means such as a casting pipe or a
casting nozzle, which is also sealingly joined to the mold.
The latter is thus not able to move ~reely from the casting
box, casting pipe or casting nozzle, resulting in the pre-
vention of many functions regarded as absolutely necessary
for a reliable casting sequence in continuous casting plants
with vertical molds.
~ mong these functions may be mentioned the so-called
mold oscillation, i.e. the vertical, reciprocal motion of
the mold. This motion only has a short stroke of 5-20 mm in
the withdrawal direction of the casting, with a rapid return
to its upper position, this movement often being called "the
stripping stroke". The mold is usually given a somewhat
quicker movement than the casting for the movement in the
withdrawal direction, this movement oten being known as
"negative strip", since the relative move~ent thus occurring
counteracts the tendency of the melt to adhere to the walls
of the mold. Since there is friction between the rapidly
solidifying casting skin and the mold walls, any transverse
cracks caused by tensional stresses, are compressed during
the stripping stroke, these cracks then healing together.
lZ~76~27
The thermally most loaded mold part is revealed at the
stripping stroke, indeed for only a short time, but
sufficiently long to allow effective lubrication and a
certain thermal recovery of this m~ld part. In a vertical
mold, the slag par-ticles accompanying the melt are able to
rise to the surface of the melt, where they can be skimmed
off, or be compounded with so-called "casting powder", if
such is used.
In contact with the surface of the melt, the slag
and powder fuse and run down towards the meniscus between
melt and mold wall. From here the fusion is pulled by the
solidifying skin down through the mold to form a anti-
friction layer between the skin and the mold wall. The slag
particles that do not manage to float up to the surface
distribute themselves rather uniformly over the cross sec-
tion of the vertical casting.
The latter is not the case with horizontal casting according
to methods used up to now. The slag particles float up in
the casting and collect at its upper part. The rigid and
sealing joint between mold and casting box or its casting
pipe or casting nozzle allows neither the mold oscillation
mentioned above nor lubrication of the mold walls, and
accompanying advantages. There is a great risk that the
brittle casting skin solidifying in the stationary, hori-
zontal mold will be pulled off, since solidifying melt has
a tendency to adhere to the cas~ing pipe or nozzle or to the
mold wall, due to the absence of lubrication agent or anti
friction coating.
Stepwise withdrawal of the casting has been
practised to counteract the above-mentioned deficiencies
and disandvantages in horizontal casting. During the
stationary period here the skin solidifying in the mold
shall be given sufficient time to grow in thickness and
strength without being subjected to tensional stresses, so
that it will be better able to withstand them during the
casting withdrawal step. To ensure that the skin always
lZ764~7
ruptures at the same place~ and at the mold inlet end, a
so-called breaker block is inserted at the junction between
casting pipe and mold. The block usually has a smaller
through passage than that of the mold, partly to reduce
heat transfer at this place and partly thus to fix the
position of the weakest section of the solidifying metal,
i.e. the place of rupture. In spite of this block being
made from very resistant material it is subject to heavy
wear, and the consequent need of frequent replacement.
Since a lubricant or slide coating can not be used,
a liner of a material providing less tendency to stickyness
than conventional mold lining is sometimes used to reduce
the adherence of the melt to the mold wall. Graphite is the
material most used as lining, but it is worn rather ~ ckly
15 particularly on the underside of the mold, against which
the casting skin is urged by its own weight, and is thus
most subject to both mechanical and thermal stresses. This
one-sided engagement in the mold naturally results in un-
even heat dissipation along the periphery of the casting,
apart from uneven mold wear, especially as the casting
shrinks, causing an air gap between the upper side of the
casting and the mold.
he disadvantages mentioned above with horizontal
casting methods used up to now are avoided in the present
invention, and the advantages herinbefore described in
respect of casting with a vertical mold are regained. The
method and apparatus in accordance with the present in-
vention have the characterising features disclosed in the
accompanying claims.
In accordance with the present invention, the mold
is given a continuous or stepwise rotational movement, or
is reciprocally turned about its center line. By this means
there is obtained a more uniform and improved (intensified)
cooling action along the periphery of the casting, since
the casting is urged by its own weight against the under-
side of the mold, this side being thus most stressed ther-
mally and mechanically, but continually changing due to
~2~64~,7
the movement mentioned. In the casting of circular castings
there will furthermore be a peripheral relative ~ovement
between the skin and the mold surface, which will contri-
bute to reducing tensional stresses and thus reduce the
risk of withdrawal cracks on wit:hdrawing the casting, since
stationary friction is no longer present due to the
rotational movement of the mold. This rotational movement
may possibly be coupled to the mold oscillation such that
the mold is only turned in conjunction with the stripping
stroke. This will give the stripping stroke a helical path.
In addition, this mold motion affords the possi-
bility of a simplified cooling system for the mold. Thesystem otherwise used, a tubular mold with a surrounding
cooling jacket having the task of uniformly distributing
the flow and action of the cooling medium along the peri-
phery of the casting, may now be exchanged for the simpler
method of spraying the coolant on the mold, since its
rotation answers for evening out the cooling action.
The mold motion may either be provided by a
separate driving means or, when the casting on withdrawal
from the mold is also rotated (as will be described below),
with the aid of the friction present between casting and
mold wall. A relative movement between these surfaces or
a stepwise or jerky rotation can then take place by braking
the mold movement.
An oscillation, i.e. a reciprocatory movement, of
the horizontal or inclined mold, additionally gives
advantages put foreward above for the oscillation of a
vertical mold. There is thus achieved more effective lubri-
cation and thermal recovery in conjunction with the
stripping stroke, as well as the compression and healing
of any possible transverse cracks caused through using
nPgative strip. The requirement for the effective lubri-
cation and thermal recovery is~ however, that the mostaffected part, i.e. where the molten metal comes into
contact with the mold wall before a skin has been formed,
~276427
i.e. in conjunction with the striping stroke, is main-
tained free from melt, i.e. the melt continuously fed to
the mold is kept out of con-tact with this part of the
mold wall.
From the publication DE 2 548 940 it is known to
prevent, with the aid of the electromagnetic repelling
action generated in a control conductor arranged along a
joint and supplied with alternating current~ the pene-
tration by melt into the joint between two tubes, one of
which may be movable, and could easily be a mold, while
the other is a ceramic casting device through which melt is
fed to the mold.
The suxfaces on either side of the gap will
naturally be cleared of melt, as will be seen from FIG 5
in the publication. However, when the mold oscill~tes,
there is a risk that the joint or gap between the two parts
will be too large in the mold movement in the casting
direction, thus permitting melt to leak out. In order to
prevent such a situation when the mold oscillates, it is
safer to allow the forward end of the casting pipe to come
into the mold by a length at least corresponding to the
stroke of the oscillatory motion. The electric conductor
providing the repelling force must consequently be placed
outside the mold.
In the selection of current strength and frequency
it will of course be necessary to take into account the
wall thickness of the mold and its ability to let the
electro-magnetic flax through~ i.e. the electromagnetic
permeability of the mold material. For the most usual
metallic mold materials and thicknesses the frequency will
usually be 60 Hz or less. If the need arises, which may be
the case for larger casting dimensions, the electromagnetic
permeability can be facilitated by the use of other, pre-
ferably non-metallic material, e.g. graphite, in the
relevant mold part. This material can be formed into an
insert in the mold, the wall of which is thinned off
towards the inlet end.
~276~2 1~
In the rotation of a circular casting, the risk
of longitudinal cracks is less, irrespective of the mold
motion, if the meniscus, i.e. the line of contact between
melt and mold wall, has a varying distance to the mold
end or casting pipe mouth along the periphery of the
casting. This relationship occurs automatically for a
conductor loop arranged concentrically round the mold,
since the static pressure of the metal in the mold is
greater upwards than downwards, and this is the pressure
acting against the uniformly distributed repelling force.
However, this force acting on the melt, and thus the path
of the contact line (meniscus) round the periphery may be
varied with the aid of electromagnetic field p~operties
known per se. The repelling force may thus be weakened or
strengthened along desired areas by screens, asymmetric
coils or welding another material i~to the conductor for
a given distance such as to vary the current density.
The reason for the above-mentioned lessening of the
risk of longitudinal surface cracks is that for the
~unsymmetrical" line of contact the growth of the skin does
not only take place in the longitudinal direction but also
around the periphexy. For the contact line of a casting,
where the line is inclined to an imaginary plane at right
angles to the center line of the mold, the skin growth
takes place in the approximate form of a helix. The shrink-
age of the casting skin periphery due to the solidification
of the melt against the mold wall is thus continuously
compensated by a continuous supply of melt solidifying
against the mold wall, the melt thus making up the shrink-
age both peripherally and longitudinally, which does notcustomarily take place. The outer skin layer thus adjusts
itself better to the periphery of the mold and is in en-
gagement with the cooling mold wall for a longer distance
than is otherwise the case. From this it follows that the
gap between skin and wall will be less, and occur at a
greater distance from the meniscus than otherwise is the
case, simultaneously as the part of the casting given the
worst cooling, due to the gap formation as the casting
1276~27
rotates, once again comes into contact with the cooling
mold wall. In continuous casting according to conventional
methods, the gap formation in the mold is a great dis-
advantage in that the almost absent cooling action of the
mold caused by the gap formation results in inhibited
growth of the skin and even reheating and weakening of it,
with the frequent occurrence of cracks (bursting of the
skin) and eruption of melt outside the mold as a result,
especially with simultaneously increasing static pressure
Of the melt. Optimalisation of the mold length is attempted
so as to avoid this, such that the casting can be cooled
directly by spraying coolant over i~ as soon as possible.
The above-mentioned risk and the need of rapid, direct
cooling outside the mold does not occur when the casting
is rotated, for easily understood reasons. The mold may
therefore be made long and the risk of crack formation and
eruption of melt outside the mold are completely obviated.
The casting rate may therefore ~e increased such that
availability of space longitudinally for cooling the
casting right through will be the deciding factor for the
casting rate, and not as previously the risk of eruption of
melt outside the mold.
Due to repellance by the electromagnetic force of
melt from the mold wall, a more uniform and effective
distribution of anti-friction agent via one or more ducts
in the casting pipe is possible, particularly since this
repellance results in an inclined casting skin edge. The
mouth of the casting pipe may project into the space bet-
ween pipe and melt. This projecting pipe part can contain
supply and distribution ducts for the agent. When casting
steel the agent may comprise a vegetable or mineral oil,
a so-called casting powder or a metal with a considerably
lower melting point than that of the cast metal, e.g. lead,
vismuth, aluminium or other easily melted metal alloys.
Metals heavier than the cast metal should be supplied
through ducts in the lower part of the casting pipe, or
along the part facing the downwardly moving part of the
rotating mold, while metals lighter than the cast metal
lZ~76~;~7
should be supplied to the upper part of the mold or to
the upwardly moving part of it. This is to avoid a portion
of the heavier metal sinking in the melt, or the reverse,
which is that a portio~ of the lighter metal rises in the
melt. The flank of the projecting casting pipe facing
towards the rotational direction of the casting must be
give a configuration, i.e. inclination in relation to an
imaginary plane at right angles to the center line of the
mold, such that the risk of the rotating skin being thrust
in between the projecting casting pipe and the mold wall
does not exist.
Particularly with horizontal casting, there is the
risk of cavity formation at the center of the casting, as
a result of to low a pressure in the still liquid core
at the center of the casting, and which is not capable of
breaking through the already solidified metal. An incxease
in pressure may be achieved by inclining the casting a few
more degrees in the direction of casting, or by arranging
an electromagnetic force acting on the casting skin or wall
in the direction of casting. The magnetic field should be
placed where the temperature of the casting is still over
the curie point, and the conductor current strength and
frequency adjusted to the solidified skin or wall thickness
of the casting as well as the rotational speed thereof.
Casting tubular, or otherwise hollow castings can
be accomplished in accordance with the invention by a still
liquid core being prevented from filling out its surrou~r.g
skin with the aid of an electromagnetic force acting on
the casting in the opposite direction to that of casting.
The rotation of the casting guarantees a uniform skin or
wall thickness as well as the central location of the hole.
It is often an advantage to divide the electromagnetic
field into two or more sections. The electric windings
generating these sections are suitably mutually separated
with respect to curxent strength and frequency, as well as
being movable individually or all together along the
casting.
~ ~'769~27
When thin-walled castings, e.g. tubes, are to be cast, it is
simpler to incline the mold and casting upwards in the casting
direction. The level of the melt or its length inside t~e
casting skin is then allowed to determine the tube thickness,
which will be uniform, due to the rotation and uniform cooling
of the casting. Should a casting box which is in communication
with the mold and tippable about the centerline thereof be
used, the melt level or its length inside the skin may be
decided by the tipping angle of the bdx and thus the melt level
in it. Otherwise the flow of melt to the mold must be
controlled by other methodsr e.g. by a stopper and coupling
bash inserted in the box, a gate in the casting pipe between
box and mold or by electromagnetic control of the melt flow
through the pipe. Where there are two or multi-line machines
with a common casting box, one of the latter solutions will be
applicable, since a box tippable about the centerline of the
mold cannot be used. Advance of the tube thus formed is
suitably arranged using inclined rolls, which may optionally
have a machining function also, similar to the one in
conventional tube production methods.
According to an aspect of the invention there is
provided a method of continuous casting with a horizontal or
inclined mold and in line hot working of the solidified
casting, wherein the molten metal is supplied into the mold
opening from a molten metal container via an inlet tube having
its forward end projecting and opening out into the mold
opening, characterized by repelling the molten metal way from
the walls of the mold with an electromagnetic force acting
immediately downstream of the inlet tube opening and in a
substantially radial direction to the molten metal flowing into
the mold.
According to a further aspect of the invention there is
provided an apparatus for carrying out a continuous casting
process including: a casting box with a casting pipe fastened
to it and having an outlet for transferring melt from the box
to a mold; a horizontal or inclined, cooled mold having a
10831/LCM:jj
~ . . .
L27
longitudinal axis; means for discharging and conveying the
casting formed i~ the mold: means for defining a secondary
cooling stretch between the discharglng and conveying means
and the mold; means for rotatlng the mold about the
longitudinal axis; means for oscillating the mold along the
longitudinal axis; and inductive means placed outside the mold
in the vicinity of the input end of the mold for creating a
magnetic force acting in a radial direction on the melt as it
leaves the outlet of the casting pipe to urge the melt away
from the inner surface of the mold in the vicinity of the input
end.
The invention will now be described with reference to
the accompanying drawings on which
FIG 1 illustrates an apparatus in accordance with the
invention in a side view and partially longitudinal section.
FIG lA is a cross section along the line A - A in FIG
1,
FIG lB is a cross section along the line B - B in FIG
1,
FIG 2 illustrates an apparatus in accordance with the
invention in a side view and partially longitudinal section.
FIG 3 is a longitudinal section of a detail in an
inventive apparatus,
FIG 4 illustrates an apparatus in accordance with the
invention in a side view,
FIG 5 is a plan of the apparatus according to FIG 4, and
FIGS 6 - 8 illustrate means for further processing in
the apparatus according to FIGS 4 and 5.
A simple embodiment is illustrated in FIG 1 of a mold
1, freely movable in relation to a casting pipe 2 and cooled
by sprayed-on liquid 4. The mold comprises a simple tube,
suitably of a material having good conductivity, e.g. copper,
and is supported by rollers 5,6. These are provided with
flanges 7, which mate with the groove 8 milled into the tube.
The mold tube 1 is thus positionally fixed longitudinally,
while being able to expand freely in this direction. The tube
10831/LCM:jj
7~4~7
11
1 is provided with a chainwheel 9 at its discharge end for
rotation or turning (i.e. rotation through less than 360).
The chainwheel is driven by a motor via a sprocket 11 and chain
10. The motor is suitably reversible and with variable speed.
The drive means 12 for the sprocket 11 can be configurated in
several conventional ways.
~ conductor means 14 usually in the form of a coil is
placed around the inlet end of the mold 1. The mold consists
of a non-magnetic metal e.g. copper. The conductor 14 is
energized with an alternating electric current with appropriate
strength and frequency for being able to induce sufficient
electromagnetic flux energy for permeating the mold wall and
generating required eddy currents intensity in the molten metal
13 in front of the inlet tube 2 that opens out in the mold
opening. According to physical lows a repelliny force is,
thus, established acting on the molten metal and directed
perpendicular to the electromagnetic field and, thus, also the
mold wall. Consequently, the molten metal is pushed away from
the chilling mold wall in the action area of the
electromagnetic field, i.e. just in front of the inlet tube
tip. Consequently the molten metal is prevented from
solidifying against the mold wall along this area whereby a
bridge of solidified metal between the inlet tube 2 and the
strand shell 20 solidifying at a longer distance from the inlet
tube 2 cannot form. As a consequence the mold can be rotated
around its centerline or longitudinally oscillated or both at
the same time as well. When the mold 1 is oscillated the inlet
tube tip shall open out into the mold opening (i.e. the tube
boring 2' opens out inside the mold) at a distance from the
mold edge that is at least so long as the length of the mold
stroke length. The gap between the inlet tube tip and the mold
wall should preferably not be bigger than the molten metal at
a power interruption is prevented from leaking out but big
enough to allow the mentioned mold motions. This allowance may
be bigger than what is usual because the mold wall is always
chilled by sprayed-in cooling fluids into the gap between
10831/LCM:jj
~3L2~69
a
inductor coil 14 and the mold walls 1 so that the molten metal
will solidify at once upon contact with the mold wall. It is
conceivable to use direct current for arhieving the same
repelling eff~ct when the molten metal flows across the
electromagnetic field, but as this is not always the case, e.g.
at temporary stops of the strand withdrawal, an alternating
current brings about a better reliability.
The effective repelling power depends not only on the
current strength and frequency but also on the electromagnetic
permeability of the mold material. Therefore, copper is an
appropriate mold material inasmuch as it has got heat
conductivity. In order to facilitate the permeation of the
electromagnetic field the mold has been made so thin walled as
possible within the conductor area.
When the conductor coil is concentrically placed around
the mold as in FIG 1, the strand shell start to solidify with
an upwards increased distance from the inlet tube tip (2)
because the metallostatic pressure is decreasing upwards. The
tail end of the solidifying strand shell ~0 is indicated with
20' in FIG 1. This configuration is favorable with respect to
strand shell growth in particular as mentioned before. As the
distance between the conductor and the molten metal plays a
role for the magnetic field strength end, accordingly, the
repelling force as well, the inclination of the tail end of
the strand shell can be altered by changing the distance of the
conductor to the mold wall over its circumference, but the same
can be achieved by inserting shields on desirable places. An
anti-friction agent that reduces the tendency of metal to stick
by the mold wall as well as the friction between the solidified
strand shell and the mold wall is supplied through the pipe 16.
By the rotation of the mold, the agent will be well distributed
over the mold circumference.
10831/LCM:jj
,,
~Z~ 27
llb
The conductor arrangement 14 acting as an inductor for
the electromagnetic field consists usually of isolated turns
of a water cooled tube. For facilitating the electromagnetic
flux around the coil turns and for preventing stray current,
the conductor tubes are surrounded by a U-formed laminated iron
yoke open at the mold side.
The rollers 5,6 for mold tube rotation/turning and the
sprocket 11 with its drive are arranged in a frame to a base
plate 17. When oscillation, i.e. longitudinal reciprocatory
movement is desired for the rotating/turning mold tube, the
base plate can be carried by wheels, wheel segment or, as
illustrated in the FIG, by needle bearing pads 18. These
provide low friction for the reciprocatory movements of the
mold and its driving means.
This movement can take place using an eccentric, cam or
a cylinder-piston means 19, which may either be hydraulic or
pneumatic. As mentioned earlier, what is important here is
that in the mold movement in the casting direction the skin 20
formed on the casting in the mold is subjected to a pressure
in its longitudinal direction, thus to press together any
transverse ruptures occurring during the stripping stroke.
10831/LCM:jj
~1.27641fl~7
1 2
A stepping motor can be used for a stepping movement of
the mold, or a system built up together with the mold
oscillation, the mold then being rotated one step at the
stripping stroke. A certain amount of peripheral negative
strip may be used here, i.e. the mold is turned back a
small amount, e.g. by spring action in the means providing
the turning movement.
When very narrow or differently dimensioned
castings are to be produced, it is suitable to use roller
rings instead of allowing the mold to be supported directly
by the rollers, different mold sizes can then be inserted
in the roller ring.
When a single mold is fed from a casting box, which
may optionally be heated, it is advantageous to make the
box tippable, with the center line of the mold as turning
axis. In addition the box should be displaceable in the
transverse and longitudinal directions of the mold. An
arrangement for raising and lowering it is also desirable,
taking into account position adjustment of the casting
pipe of the box in relation to the mold opening.
The casting pipe may include an inner wear-resis-
tant refractory material such as zirconium oxide, alumina
with over 90% A1 0 , magnesite etc. If the inner tube is
wound with a electric resistance wire, an effective barrier
against heat transfer is obtained.
A peripheral negative strip may be used to
advantage when the mold is rotated stepwise. Possible
transverse cracks can then be pressed together and be
healed up. With chain or belt transmission this can be
readily arranged so that the non-driven transmission part
is pressed in, e.g. by a jockey wheel, a certain amount of
counter movement then taking place.
FIG 2 is a schematic side view of a casting,
partially in vertical section, in a multi-line casting
plant for manufacturing hollow castings, e.g. tubes with
desired wall thickness, hollow shaft or hollow blanks for
machining etc. The casting box 2~ is common to all the
~27~;~27
13
molds 21 and castings 20 sloping upwards in the casting
direction, where the castings may have different dlmensions.
The lateral spacing of the molds and castings is assumed
to be unalterable, and therefore the spacing of the casting
pipes 22 mounted on the box and projecting into the molds
must also be constant, i.e. unaffected by any expansion of
the plate casing 24 round the box due to heat. For this
reason the casing has been provided with a cooling jacket
between each pipe.
The casting box is placed on a slide 27, dis-
placeable in the longitudinal direction of the castings by
cylinder-piston means 26, the slide being a part of a
carriage 28, displaceable transverse this direction. This
arrangement allows rapid exchange of an emptied casting
box.
The melt 23 in the box 24 communicates via the
pipes 22 with each mold 21, which is thus filled to a level
corresponding to the melt level in the box 23. The length
of the melt core within the solidified casting skin, and
thereby the length along which the skin grows in thickness,
is thus dependent on the melt level in the box 23. Rapid
exchange of the box 24 requires the same inclination of
all casting pipes, molds and castings in FIG 2, but the
height of them in relation to a selected melt level in the
box can be varied from casting to casting, if so desired,
and the dimension of the molds and castings may also be
varied one from the other. When these parameters have been
decided, the desired wall thickness of each casting may
now be determined by selecting the appropriate withdrawal
and casting rates, these being set by the respective speeds
of the driving rolls 29. Continuous withdrawal of the
casting with its skin 20' from the mold has been enabled in
accordance with the present invention by an electromagnetic
field with a repelling action on the melt in the mold
having been arranged, and which prevents bridging over
between melt solidified on the casting pipe and the skin
solidified in the mold.
14
The electxomagnetic field is generated by the conductor
30 being passed through by a high-strength current and
placed level with the pipe about the mold 21. This
location is necessary so that the flow of melt through
the casting pipe 22 will not be disturbed, or quite simply
prevented, as would be the case if only penetration of
melt into the gap between mold and pipe were prevented
according to SE 417 484. This method can be used in
certain cases in combination with the present invention,
however, which will be explained more closely below.
The drive rolls are inclined in relation to the
center line of the casting to give the hollow casting 20,
and thereby the solidified casting skin 20 in the mold 21
a rotational movement. If the rotational speed of the skin
is made sufficiently large in relation to the rate of
withdrawal of the casting, the thickness of the skin
formed, i.e. the wall thickness of the casting, will be
the same all the way around the periphery. If optional
r~setting of this arrangement is desired, the drive means
of the casting may be placed on swive lable base plates,
with the aid of which the inclination of the rolls and
thus the rotational speed of the casting in relation to
its rate of withdrawal may be changed. In this case it is
of course simplest to have all the rolls either horizontal
or vertical, and not transverse, as illustrated in FIG 2.
The rotation or turning of the mold is performed by
a drive means, and according to FIG 2, this includes a
motor 31 with an operable clutch 32, a chain transmission
33 and a chainwheel rigidly mounted on the mold tube. In
certain cases, rotation of the mold 21 occurring due to its
friction against the rotating casting 20 being withdrawn
is sufficient. Here the mold drive means may be cut out by
disengaging the clutch 32. A braking means may be arranged
for periodically breaking or stopping this movement, such
means working on a clutch half, for example, and being
enabled or disabled by an electromagnet.
The casting may be cut into desired lengths by
conventional methods. However, a rotating casting affords
~7~
several possibilities of shaping heat working, some examples
of which are given later on in this description.
The withdrawal means for the casting 20 may be
optionally implemented so that a certain amount of heat
working, e.g. to given dimensions or shaping of the casting,
can be performed, but a forging machine arranged after the
drive rolls may also be a rational solution in the process
of continuously producing bar stock. The tools required for
such operations are naturally made from material suitable
for heat working, and are cooled with a suitable medium
where necessary.
Of course, the working operations mentioned above
may also be applied in horizontal continuous casting
apparatus for solid bars, possibly after the casting has
15 been given suitable dimensions by rolls, as illustrated in
figs 6 and 7.
The horiz~ntal casting, cast according to FIG 1,
can be rotated or turned, similar to the hollow one
upwardly inclined in its transport direction according to
20 FIG 2. Particularly in the horizontal casting of steel and
other metals difficult to melt, where the still unsolidi-
fied melt in the interior of the casting will be elongate
and sharply pointed, there will often be cavities and
porousness in the central zone of the casting. The ex-
planation of this is that more or less periodical bridgingsof chrystallised melt to in front of the core tip, before
the center of the casting as solidified completely. Another
reason is certainly the decreasing visosity of the more
and more tapering melt core in the interior of the casting
as a consequence of successive lowering of temperature and
separation on to chrystallisation cores. The static pressure
in the melt at the tip is too weak for melt to be urged
forward to fill the cavities resulting from solidification
shrinkages. Some success has been obtained in improving
the interior structure of the casting by using electro-
magnetic agitation of the melt in the core tip. However,
16
the tendency to have faults in the center may be reduced
by a certain amount of downward inclination of the cast-
ing reducing the static pressure in the core tips
together with the rotation of the casting.
An example is illustrated in FIG 3 of a plant
where mold unit and casting are inclined in the direction
of casting. It is also shown here how the mold tube 21
can be rotated or turned in a cooling jacket 40 of
approximately the same kind as used in vertical casting.
The electromagnetic inductor 41 is built into the jacket
40, which is made from a magnetic material, or is at
least pro~ided with welded-in strips of such material,
to prevent leakinq eddy currents from heating the jacket.
The annular yoke 42, consisting of laminated plates,
serves to facilitate and amplify the electromagnetic flux
round the conductor. When a large dimension is cast, a
means according to SE 417 484 may be used together with
the means 41, 42 of the present invention. The laminated
ring 44 between the electric conductor 43 and the casting
pipe 45, 46 prevents the electromagnetic, substantially
radially directed forces from closing in and disturbing
the flow of the melt 23 through the casting pipe 45, 46.
In order to prevent the melt from sticking to
the mold wall, should there be unintentional skew between
casting pipe and mold, the outer forward surface of the
pipe 45 has been made somewhat convex (at the arrow A),
the conductor 43 disposed around the pipe may now be
supplied with a current at a higher frequency than the
current supplied to the one around the mold, since there
is no electrically conductive material between melt and
conductor. The electromagnetic repelling force is indeed
lower for higher current frequency, but the heat
generated in the melt will be greater, which assists in
preventing adherence of solidified melt on the pipe and
bridging of solidified melt between it and the skin
solidified in the mold in the area where the action of
the elec-tromagnetic inductor arranged outside the mold
ceases.
This arrangement can be advantageous when the
casting is cut by a stationary cutter and when the
inductor 41 is supplied with direct current. As a
result of casting movement needing to be stopped and
movement of the melt substantially ceasing during the
cutting operation, the action of the repelling force
from the d.c. inductor 41 ceases. Melt bridging between
casting pipe 45 and skin 20' can consequently occurat 45',
since the action of the a.c. conductor 43 is maintained.
Melt is thus prevented from penetrating into the gap
between mold wall and ~ipe at 45',simultaneously as the
skin has managed to grow in thickness and strength
during its period of no movement, and can thus withstand
the extra tensional stress to which it is subjected
when advance of the casting (withdrawal of the mold)
takes place once again. Static friction is greater than
sliding friction, as is well known.
FIG 4 - 8 illustrate as examples a survey of
some different applications of an apparatus in accordance
with the invention, FIG 4 illustrating the casting
machine itself as seen from one side, and FIG 5 from
above. The casting 21, produced and rotating in this
machine is cut to desired casting lengths in the usual
way, using a blowtorch 51 in FIGS 4 and 5, or is
alternatively taken directly into a roll stand or forging
machine.
In FIG 6 a planetary rolling mill has been
utilised, and is characterised by a plurality of taper-
ing rolls 67 being driven planetarily round the casting
21, which is thus given the desired dimension. If so
desired, the rotating casting can be given a surface
treatment, such as a hot grinding descaling process or
working by one or more scraper tools arranged along the
casting. A heating or heat equalisation stretch may also
be desirable.
18
When the casting rotates, the planetary roll-
ing mill illustrated in FIG 5 may optionally be ex-
changed for, or supplemented by, stationray rotating
rolls 68 (FIG 7)~ thus making driving of the rollers
considerably more simplified compared with the mill
drive. Although the schematic figures merely show one
pair of mutually opposingly directed rolls nipping
the casting round its periphery, three or more rolls
are used to avoid breaking up or cavity formation in
the center of the casting. Of course, if so desired,
the rolling equipment may be exchanged for holaing
equipment.
The advantage with direct rolling of the
rotating casting is inter alia that different casting
dimensions can be achieved for one and the same cast-
ing dimension, even during the course of one casting
procedure, by setting the roll nip to the desired amount.
The rolled-down casting 21, still rotating and
without being cut, can then, possibly after passage
through a further heating or heat equalisation stretch
(unillustrated), be taken to a conventional mill, e.g.
for the production of reinforcing bars or wire. Rotation
of the casting must be stopped for this purpose. Accord-
ing to FIG 8, this takes place by the rotating roll
leader 69 taking the casting in circular form 70 into
the rotating drum 71, from which the casting is taken
out tangentially to the rolling mill 72 for further
rolling or shaping. Possibly necessary, unillustrated
equipment for temperature adjustment can be arranged in
the drum.
According to FIGS 4 and 5, casting is performed
from a ladle 54 provided with a sliding gate 52 and
casting pipe 53. In gate, and therewith the flow of melt
to the casting vox 24, may suitably be automatically
regulatable in respect of the filling level in the box.
The latter is tippable about the center line of the
'7
1 9
mold 20 and casting with the aid of a piston-cylinder
means 55, suitably auto~atically regulated in respect
of the melt level in the box 2~. To enable rapid ex
change of the box when it has become worn for one that
has been freshly prepared, these are each placed on a
carriage 56 which is movable transverse the casting
direction. To enable this movement, the casting box 24,
which has its castin~ pipe 22 projecting into the mold
opening, must be moved in the longitudinal direction of
the mold. The box is therefore placed on a slide 57,
which can be rapidly moved from its position during
casting with the aid of the piston-cylinder means 58.
The previously described electromagnetic inductor around
the foreward end of the tube mold 20 is denoted by the
numeral 59. Since the mold rotates, uniform cooling can
be achieved by direct spraying of water 60. The rotation
or turning of the mold is performed by the drive means
: 61, and longitudinal oscillation by the cylinder 62.
Secondary cooling is denoted by 63 and the support rolls
for the rotating casting 21 by 64. Along the casting
; there is a travelling means 65 for electromagnetically
acting on the melt at the center of the casting. The
inclined rolls 66 for roational advance of the casting
21 have been shown as lying in different planes, but
if it is desired to have rotation adjustable in relation
to the advancing rate, they should preferably be placed
such that they only engage against the casting from two
directions, in order to obtain a simpler drive, which
has already been mentioned in connection with FIG 2.
For the sake of clarity, drive equipment for the rolls
has not been shown in the FIG. This can be performed in
different conventional ways. The advancing rate can, of
course, be made automatically regulatable in respect of
the position of the liquid core tip, which may be sensed
by such as supersonic methods. Sinc~ the repelling force
exercised by the electromagnetic inductor 59 must always
~7~
be somewhat greater than the static pressure prevailing
in the lower part of the mold, it is suitable to
introduce here, as well, the automatic regulation of
current strength and/or frequency of the current
supplied to the inductor in relation to the indicated
melt level in the casting box.
The entire operational sequence in a plant like
the one described above can be automated using
conventional regulation and automating equipment,
resulting in the need for a minimum of staff. There is
a great advantage in that such a plant can be erected
at ground level, resulting in large savings in building
costs. Conveying, intermediate storage and heating
costs, which otherwise constitute a large part of the
cost of the finished product are also reduced.
