Note: Descriptions are shown in the official language in which they were submitted.
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"METHOD TO CONTROL THE AXIAL POSITION OF SLABS EMERGING FROM
CONTINUOUS CASTING AND RELATIVE DEVICE"
FIELD OF THE INVENTION
This invention concerns a method to control the axial
position of slabs emerging from continuous casting, and the
relative device, used in rolling plants with a rolling train
located in line with the continuous casting, to obviate the
problems of misalignment of the slab emerging from casting
with respect to the axis of the first rolling stands.
The invention is applied both in cases where the slab is
sheared to size into segments, and also in the case where
the slab is worked without interruption from the casting to
the train.
To be more exact, the invention is applied in conventional
plants for thin slabs, in plants for long slabs from about
m to about 60 m, and in plants of the semi-endless type
with long slabs of up to 300 m.
BACKGROUND OF THE INVENTION
20 One of the problems which businessmen operating in the
field of rolling plants complain of is that concerning the
control of the axial position of the slab with respect to
the axis of the first rolling stands located downstream of
the heating furnace.
For it is well-known that, since the slab emerging from
the continuous casting is subjected to the steps of
extraction, pre-rolling and straightening, it rarely keeps a
correct alignment with respect to the axis of feed; this
creates problems when it enters the rolling stands and
during the rolling steps.
Moreover, as it passes inside the tunnel, heating or
temperature-maintenance furnaces, the slab can be subject to
lateral displacements which take it off-axis.
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If the slab arrives misaligned with respect to the axis of
the first stand, rolling becomes difficult, particularly in
the case of rolling thin slabs.
In fact, to compensate for the misalignment after the slab
has entered the stand, and to make sure that it enters the
downstream stand correctly, it is necessary to level the
rolls of the first stand, which has negative effects on the
symmetry of the transverse section profile of the slab
itself.
Although this does not create serious problems when the
product is very thick, for example above 2 mm, for thin
products there are serious problems regarding the guiding of
the strip in the rolling mill, even though the strip is
guided for only a limited segment, since making up the
difference in thickness between one side and the other
causes different elongations on the two sides and therefore
causes the strip to bend on the horizontal plane.
Rolling becomes difficult if not impossible to manage,
moreover, for thicknesses of about 0.6=0.8 mm.
To try to solve these problems at least in part,
conventional solutions provide various means to obtain the
progressive axial centering of the slab with respect to the
rolling axis; these means generally act inside or downstream
of the tunnel furnace.
However, it sometimes happens that the slab entering the
furnace is already misaligned to such an extent that it can
also be subject to a progressive slipping towards the sides
and the walls of the furnace, possibly causing serious
damage to the furnace itself and obviously also to the slab
and the entire casting process.
The present Applicant has devised and embodied this
invention to overcome this shortcoming which causes serious
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operational, technological and quality problems in rolling
plane products, particularly thin plane products.
SUMMARY OF THE INVENTION
The invention is set forth and characterised in the
respective main claims, while the dependent claims describe
other characteristics of the main embodiment.
The purpose of the invention is to center and axially
align a slab emerging from the continuous casting machine so
that it arrives at the entrance to the first stands, whether
they be roughing stands, pre-finishing stands or finishing
stands, perfectly aligned with the axis of said stands.
Another purpose is to obtain this alignment already
upstream of the tunnel furnace in order to prevent risks of
the progressive lateral displacement of the slab which can
cause the advancing slab to rub or knock against the walls
of the furnace .
Another purpose is to obtain this alignment with a simple
solution, which can be installed on pre-existing plants too,
without substantial modifications to the configuration of
the plant, and which will guarantee an efficient result
substantially for every rolling condition and for every type
of product being worked.
The invention provides to detect a possible misalignment
of the axis of the slab with respect to the rolling axis at
least at one point, advantageously two or more, arranged
upstream of the furnace and/or inside the furnace itself.
The misalignment signal is sent to a command and control
unit which, according to the position of the leading end of
the slab inside the furnace and according to the entity of
said misalignment, commands a controlled and differentiated
activation of at least some of the pairs of extractor rolls
of the extraction and straightening assembly located
downstream of the casting machine.
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To be more exact, at least one pair of said extractor
rolls is commanded to achieve a differentiated pressing of
one side of the slab and the other, in order to
progressively cancel this misalignment.
The detection of the misalignment may be carried out
periodically, and in this case the intervention made by the
pairs of extractor rolls to correct the misalignment will
also be periodical.
In the preferential embodiment of the invention, the
detection of the misalignment is continuous, and the action
of the pairs of extractor rolls, in terms of differentiated
pressing, is continuously modulated according to the values
of misalignment which continually reach the command and
control unit.
The regulation of the misalignment performed by pressing
the slabs by the extractor rolls in a differentiated manner
may be associated with other methods to align the slab, for
example performed inside the furnace or downstream thereof,
in the event that the correction made upstream of the
furnace is not sufficient and such as to ensure a precise
alignment of the slab with the rolling axis.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other characteristics of the invention will
become clear from the description of some preferential
embodiments, given with reference to the attached drawings,
wherein:
Fig. 1 is a schematic side view of a rolling line directly
connected with the continuous casting to which the
invention is applied;
Fig. 2 is a schematic view from above of a segment of the
line shown in Fig. 1;
Fig. 3 shows a detail of the segment shown in Fig. 2;
Fig. 4 shows an application of the invention.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The rolling line 10 shown schematically in Fig. 1
comprises a rolling train 19 arranged in line with a
continuous casting 11 including a mold 13 and an extraction
and straightening assembly 12 comprising a plurality of
pairs of rolls 25.
Downstream of the assembly 12 there are shears for
shearing to size 14 and a heating and/or temperature-
maintenance furnace 15 which feeds the slabs 24 at
temperature to a rolling train 16, in this case with two
stands 17, which may be a roughing or pre-finishing train
according to the case.
Between the train 16 and the finishing train 19, in this
case, there is a system to equalize and restore the
temperature 18, while downstream of the finishing train 19
there is a winding assembly 21 to wind the strip produced.
In this case, between the heating furnace 15 and the train
16 there are conventional lateral guide systems 20, a
descaling assembly 22 and an edging assembly 23.
According to the invention, upstream of the furnace 15
there are means 26 to detect the axial position of the
advancing slab 24, and particularly to detect the entity of
the discrepancy 0 between the rolling axis 27 and the axis
28 of the slab 24.
This discrepancy, as can be seen in Fig. 2, can
progressively increase inside the furnace 15 and cause a
lateral sliding (shown by the arrow 29) which can take the
slab 24 to rub against or knock the walls of the furnace 15,
with obvious and serious damage to the furnace and to the
slab, and with the risk of interrupting the casting process.
Said means 26 in this case comprise two detector units,
respectively 31a and 31b, able to detect in two different
points the axial position of the slab 24 upstream of the
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furnace 15, which then send said signal to a processing unit
30.
In one embodiment of the invention, the detectors could
also be located inside the furnace 15 or immediately at the
outlet thereof.
The processing unit 30 is able to continuously acquire the
signal indicating the position of the slab 24 and to
calculate the exact position, in terms of distance and
discrepancy O of its axis 28 with respect to the rolling
axis 27, of the leading end of the slab 24 inside the
furnace 15.
According to this calculation, the processing unit 30 is
able to regulate the activation of at least some of the
pairs of rolls 25 of the extraction and straightening
assembly 12 in order to achieve a differentiated pressing in
the direction of the width, between one side and the other
of the slab 24, in order to at least partly eliminate this
misalignment.
To be more exact, as shown in Fig. 4, the processing unit
30 commands actuators 32 to be activated, able to incline a
relative roll 25 with respect to the nominal position of its
own axis 33, normally substantially horizontal, in order to
achieve a differentiated pressing on the sides of the slab
24.
This correction of the reciprocal position of the rolls 25
can also occur starting from a situation in which the rolls,
in their nominal position, are not parallel, for example,
due to thermal dilation or other factors beyond the control
of the system.
The control system detects in this case a situation of
misalignment, and corrects it by progressively pressing more
or less on one side of the rolls 25 of the extraction
assembly 12.
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The differentiated pressing action may concern one, some
or all the pairs of rolls 25 of the assembly 12 according to
the entity of the discrepancy D detected; the pressing
action may also be continuously modulated according to the
continuous detections of the means 26 and according to the
calculations and data processing made by the unit 30.
Since the differentiated pressing action is made on the
product emerging from the mold 13, the differences in
thickness created on the width of the slab 24 do not cause
problems and can be recovered during the first rolling steps
- roughing or pre-finishing - when the lateral sliding of
the material is not constrained by the rolling rolls.
In this way, the slab 24 entering the furnace 15 arrives
substantially aligned with the rolling axis 27, and the
risks of progressive slipping towards the walls of the
furnace are avoided.
In the event that the discrepancy ~ is too great, and
cannot be corrected by means of the differentiated pressing
action alone, this action can be combined with other
alignment systems which act inside or downstream of the
furnace.
Although the invention has been described with reference
to several preferential embodiments, it is obvious that
modifications and variants may be made thereto by a person
skilled in this field, but these shall remain within the
field of protection defined by the attached claims.
