FIELD OF THE TECHNOLOGY
[0001] The present invention relates generally to methods and apparatuses for producing
steel intermediate products. In particular, the present invention relates to methods
and apparatuses for in-line rolling of billets from continuously cast blooms.
BACKGROUND
[0002] Rolling mills are installed for producing finished steel products, for example, for
local markets in developing world countries and near markets for finished steel products,
such as mild steel bar for use in civil construction. In countries where there is
no significant production of semi-finished (cast) steel products, these rolling mills
will typically rely on importing steel billets from other countries that have a larger
steelmaking capacity, to finish for their local markets. This is prevalent in many
developing world countries because even local production of steel intermediate products
from recycled steel is not possible due to the scarcity of steel scrap generated locally,
and the difficulties with providing a reliable and cost-effective supply of electrical
power to operate an electric arc furnace. Therefore, imported billets are 're-rolled'
to produce the finished steel products. These 're-rolling mills' typically take a
starting billet size of up to 150mm by 150mm square (225 square centimetres) and are
typically much smaller and have fewer production capabilities in terms of variety
of input and output products, and production rate, compared to larger, dedicated rolling
mills.
[0003] In the 1960s, production of billets was achieve by rolling cast ingots, each weighing
10 tons or more and such ingots were rolled into billets in a separate billet rolling
mill. This antiquated method had no problem with rolling the ingots into the 150mm
needed for the re-rolling mills described above. However, such a billet production
method resulted in high end losses and has additional rolling costs, and so it was
not particularly effective or efficient.
[0004] Since the 1970s, the "Continuous Casting" process has completely replaced the old
ingots casting practice for producing intermediate steel products, and so now square
or round billets are typically directly casted from liquid steel using a "Continuous
Casting Machine", rather than being rolled from cast ingots.
[0005] With today's very large capacity steel mills, producing, say, over 2 million tons
of steel products annually, the continuously casted billets are of much larger cross
section than is capable of being rolled by a 're-rolling' mill. For example, continuous
casting machines producing "bloom" strands having a cross section of greater than
150mm by 150mm square, and up to 400mm by 400mm square (typically 240mm by 240mm square
or in the case of a tube continuous casting machine, 250mm round) are now commonplace
at the larger steel producing facilities. These blooms are larger than the typical
maximum size billet of 150mm by 150mm square that can be rolled by the re-rolling
mills described above.
[0006] It is in this context that the present invention is devised.
SUMMARY OF THE INVENTION
[0007] Viewed from one aspect, the present invention provides a method of continuously producing
steel intermediate products as claimed in claim 1.
[0008] In accordance with the present invention, excess steel bloom production by a large
capacity continuous steel casting machine can be directly converted to billets by
an in-line hot rolling process, without the need for additional heating or reheating
of the blooms before rolling. In this way, there is no need for a separate billet
rolling mill to produce re-rollable billets from the continuously cast blooms, and
as a result, this additional investment, double handling, extra manning, heating and
rolling losses that would result from rolling reheated bloom lengths and which would
make such billet production uneconomical, is avoided. In this way, large capacity
multi-strand continuous casting machines are enabled to efficiently directly produce
re-rollable billets by an in-line rolling process at the same time as producing larger
blooms. By enabling, preferably selectable, production of readily-exportable billets
directly from continuously cast bloom strands, large capacity steel intermediate production
facilities can export surplus production for use in re-rolling mills in countries
that rely on importing steel billets.
[0009] In embodiments, the cast bloom strands fed in-line to the rolling mills are still
hot from the continuous casting, and wherein no additional reheating of the blooms
is performed between the casting and hot rolling.
[0010] Preferably, the bloom strands have a cross sectional area above 230 square centimetres,
and preferably the rolled billets have a cross sectional area below 230 square centimetres.
Blooms typically are dimensioned above 150mm square (and up to 400mm square), the
rolled billets typically are dimensioned below 150mm square.
[0011] In embodiments the method further comprises: feeding the bloom strands through respective
straightening rollers; operating each rolling mill at a speed based on a reference
speed of the straightening rollers of the particular bloom strand fed to that rolling
mill. Using the speed of the individual straightening rollers for each continuously
cast strand as a reference speed for the rolling speed of the rolling mill for that
strand in this way enables the billets to be reliably hot rolled and the material
flow balance to be maintained on a strand-by-strand basis.
[0012] The use of cantilevered rolling mill stands allows the rolling of each bloom strand
to not interfere with the adjacent strand of the multi-strand bloom casting machine,
and it allows the length of the rolling mill across all stands to be kept low and
to be positioned as close as possible to the exit of the strands from the continuous
casting machine, enabling the blooms to be rolled while still hot from the casting
process, and before they have cooled. Conventional rolling mills, in which the rollers
are "simply supported" with bearing supports at both ends of the rolling axis, would
be too large to fit between the adjacent strands on exit from the continuous casting
machine, and so would only be usable to roll the cast blooms if the strands were spaced
further apart on exit from the continuous casting machine or moved further apart somehow
by rollers. This is simply not practical.
[0013] In embodiments the drive mechanism and motor for each cantilever rolling mill stand
is arranged outside the outermost strands produced by the continuous casting. In this
way the bulky drive mechanism and motor components will not occupy space immediately
above or below the bloom strands, such that the cast blooms are not interfered with.
[0014] In embodiments the drive mechanism and/or motor for the or each cantilever rolling
mill stand is connected to the respective cantilever rolling mill stand by respective
long shafts arranged so as to distance the drive mechanism and/or motor from the hot
blooms. This enables the drive equipment and motors to be operated away from the high
temperature environment immediately surrounding the cast blooms, improving their lifetime
and reliability, and allowing conventional motors and mechanisms to be used that are
not required to be designed to withstand extreme environments and temperatures.
[0015] In embodiments each of the rolls for a given cantilever rolling mill stand is driven
by an individual motor.
[0016] In embodiments the angle of the axes of the subsequent rolling mill stands is set
at 90 degrees to each other. Arranging the cantilevered rolling mill stands in this
way allows the rollers to access the bloom strands from away to the sides of the bloom,
reducing the extent to which the rollers and the rolling mill housing interfere with
the space immediately surrounding the cast blooms. Further, by alternating the axes
of the rollers in this way, the rolling mill housings and stands can be offset from
each other and/or positioned alternately above and below the cast blooms allowing
the rollers to be positioned close to each other axially along the strand, allowing
the rolling mill to occupy a short length along the strand such that the cast strand
can be rolled at a uniform temperature without significant cooling between the rolling
mill stands. In embodiments each rolling mill comprises at least two, or preferably
at least four, in-line cantilever rolling mill stands arranged to roll increasingly
small billet sizes. In embodiments, each rolling mill stand will work on two faces
of the bloom (for example, if the bloom is a 240mm by 240mm square cross section bloom)
and the next rolling mill stand will work on the opposite two faces, rolling the cast
blooms into smaller size billets.
[0017] In embodiments, it may not be desirable to further roll the bloom strands. Therefore
the cantilever stands may be moved out of the line of the bloom casting without interrupting
the casting process. The rolls of cantilever stands are separated from each another
to at least a distance wide enough for the rolling mill stands to clear the bloom
and be moved out of the bloom casting line.
[0018] In embodiments the housing for the bearing supports for each cantilever rolling mill
stand is configured as a replaceable cassette, for example, that interfaces with the
motor and drive mechanism. This will facilitate a quick changing of the rolls, for
example when the rolls become worn, reducing downtime.
[0019] In embodiments, the rolling mill and each rolling mill stand is selectably operable
or engageable with the cast blooms, allowing the bloom strands to be selectably hot
rolled into billets optionally of varying sizes. This allows the output of the continuous
casting machine to be selectably variable in size, allowing production to adapt readily
to demand, for example, fluctuations in demand in domestic and/or export markets for
cast blooms and (rolled) billets.
[0020] In embodiments protective cooling or insulating jackets are provided around the housing
for the bearing supports and/or the motor and/or drive mechanism for each cantilever
rolling mill stand.
[0021] In embodiments only one or both of the outermost strands of the plurality of continuously
cast bloom strands is hot rolled into a billet. By rolling only the outermost strand(s),
the degree to which the rolling mill interferes with the space around the cast bloom
strands, and the degree to which the steel mill needs to be re-engineered to accommodate
the rolling mill is minimized. In addition the requirements for the rolling mill stands
are less stringent as the space requirements for rolling only the outermost strand(s)
(due to the space availability to the sides of the strands) are less than those required
for the innermost strands. In addition, excess production of continuously cast blooms,
for example, for the domestic market, can, by operating on the outermost bloom strands,
easily be hot rolled in-line into billets in the continuous casting process for direct
export, for example, to developing world countries for re-rolling in a billet re-rolling
mill.
[0022] Viewed from another aspect, the present invention provides apparatus as claimed in
claim 13.
[0023] In embodiments the continuous casting apparatus comprises a tundish arranged to collect
liquid steel and provide said liquid steel to plural moulds arranged side by side
to continuously produce plural bloom strands.
[0024] In embodiments, the continuous casting apparatus is configured to operate in the
methods in accordance with the embodiments described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention, may best be understood by reference to the following description of
certain exemplary embodiments together with the accompanying drawing in which:
[0026] FIG. 1 illustrates an apparatus and method of operation thereof for in-line rolling
of billets from continuously cast blooms in accordance with an embodiment of aspects
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] The detailed description set forth below in connection with the appended drawings
is intended as a description of presently preferred embodiments of the invention,
and is not intended to represent the only forms in which the present invention may
be practised. It is to be understood that the same or equivalent functions may be
accomplished by different embodiments that are intended to be encompassed within the
spirit and scope of the invention. Furthermore, terms "comprises," "comprising," or
any other variation thereof, are intended to cover a non-exclusive inclusion, such
that apparatuses and method steps that comprises a list of elements or steps does
not include only those elements but may include other elements or steps not expressly
listed or inherent. An element or step proceeded by "comprises ...a" does not, without
more constraints, preclude the existence of additional identical elements or steps
that comprises the element or step.
[0028] Referring now to Figure 1, which shows an apparatus 100 for in-line rolling of billets
from continuously cast blooms in accordance with an embodiment of the present invention,
a continuous casting machine 110 comprises a ladle 112, tundish 114, multiple permanent
moulds 116 for forming strands 118 and straightening rollers 120 for straightening
the strands.
[0029] Molten steel is tapped into the ladle 112 from one or more furnaces (not shown).
The ladle 112 has at its bottom a pipe opening which is arranged above and drains
liquid steel into a holding bath or tundish 114. The tundish 114 acts as a buffer
reservoir and has shrouds or pipe openings into the permanent moulds 116. The liquid
steel drains from the tundish 114 into the permanent moulds 116 which are shaped and
liquid cooled to form a solidified exterior casing for the strands 118 that are formed
by the hardened steel dropping due to gravity from the open bottom of the permanent
moulds 116. In this case, five permanent moulds 116 are provided, but the number of
permanent moulds could be greater or fewer than this, but is preferably at least two,
and even more preferably greater than two or an even higher number in order to give
a high production capacity. Each of the continuously cast strands 118 is then passed
through sequences of pairs of individual straightening rollers that guide the strands
to extend in a horizontal direction and straighten the strands as they move along
between the rollers and cool and further solidify.
[0030] The continuous casting machine 110, and the permanent moulds 116 in particular are
configured such that the strands 118 are formed as blooms having a cross sectional
area above 230 square centimetres, in this case 240mm by 240mm square.
[0031] The continuous casting machine 110 has a high production capacity of, say 2 million
tonnes a year, with a production speed of at least 4 metres per minute, and can operate
continuously for a number of years of production between servicing. When this production
capacity of continuously cast blooms exceeds demand, for example in the domestic market,
which would lead to an increase in inventory of cast blooms, in accordance with the
present invention, the apparatus 100 operates to hot roll one or more of the bloom
strands 118 into billets 140 by operation of the in-line rolling mills 150, which
can for example be exported to developing world markets for direct use in re-rolling
mills. The rolled billets are formed to have a cross sectional area below 230 square
centimetres, in this case 150mm by 150mm square.
[0032] The apparatus 100 is arranged such that the cast bloom strands 118 fed in-line to
the rolling mills 140 in use are still hot from the continuous casting. No apparatus
is provided arranged to perform additional reheating of the blooms between the casting
and hot rolling.
[0033] The in-line rolling mills 150 comprise a plurality of cantilever rolling mill stands
152 in which the bearing supports for the rollers 154 of each stand support the rollers
at only one end. The drive mechanism and motor 156 for each cantilever rolling mill
stand 152 is arranged outside the outermost strands 118 produced by the continuous
casting. In embodiments different to that shown in Figure 1, the drive mechanism and/or
motor 156 for the cantilever rolling mill stands 152 can be connected to the respective
cantilever rolling mill stand 152 by respective long shafts arranged so as to distance
the drive mechanism and/or motor 156 from the hot blooms 118. To further reduce heating
effects, in other embodiments protective cooling or insulating jackets can be provided
around the housing 158 for the bearing supports and/or the motor and/or drive mechanism
156 for each cantilever rolling mill stand 152. Motors may be arranged to individually
drive each of the rollers 154 for a given cantilever rolling mill stand 152.
[0034] For clarity's sake, in Figure 1, the second cantilevered rolling mill stand 152 of
each rolling mill is drawn with the drive mechanism and motor 156 and the housing
158 below the strands 118 at floor level. However, in other embodiments, to avoid
mill scale build up on the machinery, the rolling mills 150 can be arranged such that
the drive mechanism and motor 156 and the housing 158 of the cantilevered rolling
mill stands 152 are never positioned underneath the strands 118 by, for example, positioning
certain components above floor level.
[0035] The housing 158 for the bearing supports for each cantilever rolling mill stand 152
is configured as a replaceable cassette, for facilitating a quick changing of the
rolls, e.g. when worn, reducing down time.
[0036] Each rolling mill 150 (for each strand) comprises two in-line cantilever rolling
mill stands 152. In other embodiments, more than two or preferably at least four,
cantilever rolling mill stands are provided, arranged to roll increasingly small billet
sizes. The angle of the axes of the rollers of the first cantilever rolling mill stand
for a given bloom is set at 45 degrees to the top surface of the bloom. The angle
of the axes of the subsequent rolling mill stands is set at 90 degrees to each other.
[0037] Each rolling mill 150 is configured to operate at a speed based on a reference speed
of the straightening rollers of the particular bloom strand 118 fed to that rolling
mill. This ensures a balance to the flow of material through the rolling mills 150.
[0038] As shown in Figure 1, both of the outermost strands of the plurality of continuously
cast bloom strands 118 is hot rolled into a billet. The in-line rolling mills 150
are in position and operate continuously such that rolled billets are always produced.
The rolling mills 150 can be selectively engaged such that billet production can be
responsive to variation in demand for cast bloomed and rolled billets for re-rolling.
Therefore the cantilever stands may be moved out of the line of the bloom casting
without interrupting the casting process. The rollers 154 of the cantilever stands
are separated from each another to at least a distance wide enough for the rolling
mill stands 150 to clear the bloom and be moved out of the bloom casting line.
[0039] The invention is applicable not just to square blooms, but also to round blooms for
which appropriate permanent moulds and straightening rollers need to be provided.
The roll pass section then needs to be adjusted accordingly to produce billets of
the desired square (or other) cross section.
[0040] In a further embodiment of the present invention, the strands are cast in a process
of sequence continuous casting. This process enables different temperatures of liquid
steel to be continuous-continuously casted, i.e. without interruption. This process
increases productivity by eliminating the need to prepare for starting a new individual
casting process each time. Through the use of adjustable cantilevered rolling mill
stands the present invention allows for the blooms width to be adjusted and liquid
steel of different temperatures to be cast continuously. Steel of different temperatures
may be utilised by replacing the tundish comprising the steel of a different temperature.
[0041] The description of the preferred embodiments of the present invention has been presented
for purposes of illustration and description, but is not intended to be exhaustive
or to limit the invention to the forms disclosed. It will be appreciated by those
skilled in the art that changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is understood, therefore, that
this invention is not limited to the particular embodiment disclosed, but covers modifications
within the scope of the present invention as defined by the appended claims.
1. A method of continuously producing steel intermediate products, comprising:
casting liquid steel into plural moulds to continuously produce plural bloom strands;
and
feeding one or more of the bloom strands in-line to respective rolling mills configured
to be selectively engageable to hot roll the input continuously cast bloom strands
to produce rolled billets,
wherein the rolling mills comprise two or more cantilever rolling mill stands in which
bearing supports for the rollers of each stand support the rollers at only one end,
and wherein the angle of the axes of the rollers of the first cantilever rolling mill
stand for a given bloom is set at 45 degrees to the top surface of the bloom and wherein
the angle of the axes of the subsequent rolling mill stands is set at 90 degrees to
each other.
2. A method as claimed in claim 1, wherein the cast bloom strands fed in-line to the
rolling mills are still hot from the continuous casting, and wherein no additional
reheating of the blooms is performed between the casting and hot rolling.
3. A method as claimed in claim 1 or 2, wherein the bloom strands have a cross sectional
area above 230 square centimetres, and wherein the rolled billets have a cross sectional
area below 230 square centimetres.
4. A method as claimed in claim 1, 2 or 3, further comprising:
feeding the bloom strands through respective straightening rollers;
operating each rolling mill at a speed based on a reference speed of the straightening
rollers of the particular bloom strand fed to that rolling mill.
5. A method as claimed in any preceding claim, wherein a drive mechanism and a motor
for each cantilever rolling mill stand is arranged outside the outermost strands produced
by the continuous casting.
6. A method as claimed in any preceding claim, wherein each of the rolls for a given
cantilever rolling mill stand is driven by an individual motor.
7. A method as claimed in any preceding claim, wherein each rolling mill comprises at
least two, or preferably at least four, in-line cantilever rolling mill stands arranged
to roll increasingly small billet sizes.
8. A method as claimed in any preceding claim, wherein a housing for the bearing supports
for each cantilever rolling mill stand is configured as a replaceable cassette.
9. A method as claimed in any preceding claim, wherein protective cooling or insulating
jackets are provided around a housing for the bearing supports and/or a motor and/or
a drive mechanism for each cantilever rolling mill stand.
10. A method as claimed in any preceding claim, wherein only one or both of the outermost
strands of the plurality of continuously cast bloom strands is hot rolled into a billet,
and wherein at least one innermost bloom strand is provided.
11. A method as claimed in any preceding claim, wherein the plural bloom strands are cast
in a process of sequence continuous casting.
12. A method as claims in any preceding claim, wherein the rollers of the cantilever rolling
mill stands are separated from each another to at least a distance wide enough for
the cantilever rolling mill stands to clear the bloom and be moved out of the bloom
casting line.
13. Apparatus for continuously producing steel intermediate products, comprising:
continuous casting apparatus arranged to, in use, continuously produce plural bloom
strands; and
one or more in-line rolling mills each arranged to be selectively engageable to receive
and hot roll, in use, one of the continuously cast bloom strands to produce rolled
billets,
wherein the rolling mills comprise two or more cantilever rolling mill stands in which
bearing supports for the rollers of each stand support the rollers at only one end,
and wherein the angle of the axes of the rollers of the first cantilever rolling mill
stand for a given bloom is set at 45 degrees to the top surface of the bloom and wherein
the angle of the axes of the subsequent rolling mill stands is set at 90 degrees to
each other.
14. Apparatus as claimed in claim 13, wherein continuous casting apparatus comprises a
tundish arranged to collect liquid steel and provide said liquid steel to plural moulds
arranged side by side to continuously produce plural bloom strands.