Note: Descriptions are shown in the official language in which they were submitted.
1~'79()99
The present invention relates to a method for produc-
ing a steel strip by hot rolling in a continuous way.
For producing a hot strip coil from a stell slab, the
steel slab is subjected to surface defect detection, and removed
of the surface defects by hot scarfing, etc. The steel slab thus
surface-conditioned ls heated in a reheating furnace, then subject-
ed to rough rolling, intermediate rolling in some cases, finishing
rolling, cooling on a run-out table, and is coiled on a coiler.
The rolling is intermittently slab by slab. In this case, the
forward end of the hot strip coming out of the last stand of the
finishing rolling train is normally maintained in a running speed
of 1600 to 1800 f.p.m. from while it runs on the run-out table. -
When the forward end of the hot strip runs on the run-out table at
- a higher speed, it leaps vigorously, often causing flying. When
the forward end of the hot strip is coiled on the coiler, the run-
ning speed of the hot strip is increased up to the speed designated
by the mill operation or determined by a specific hot strip produc-
tion line.
In this way, in case of an intermittent rolling proce-
dure in which the rolling is done slab by slab, it is necessary tomaintain the running speed of the hot strip while the forward end
of the hot strip comes out and reaches the coiler, and the produc-
tivity of the hot strip mill is low because and idle time of ope-
ration exists between the completion of rolling of a preceding slab
and the starting of rolling a subsequent slab.
Further, the temperature of the hot strip lowers consi-
derably before the forward end of the hot strip reaches the coiler,
because the running speed of the hot strip is maintained at a remar-
kably low speed while it comes out of the finishing rolling mill
3Q train and reaches the coiler as mentioned above.
In case of rolling a hot strip, however, it is requir-
ed that the temperature of the hot strip at the exit side of the
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1~79099
finishing rolling mill train is within a certain zone in order tomaintain a required quality of the hot strip, and for this requi-
rement, the temperature at which the steel slab is extracted from
a slab heating furnace must be maintained higher so as to compen-
sate the temperature lowering mentioned before. This is the rea-
son why the heat unit can not be lowered in the hot strip rolling.
m irdly it is required that the hot strip from its for-
ward end to the finishing end is subjected to a uniform heat his-
tory in order to control the quality, but as mentioned before, the
running s'peed of the hot strip must be maintained at a remarkably
low speed while the forward end comes out of the finishing rolling
mill train and reaches the coiler, so that it is almost impossible
to avoid the irregularity of the heat history in the length direc-
tion of the hot strip.
Fourthly, the forward end and the finishing end of the
hot strip must be cut off, because they are in the tongue-like or
fish tail-like shape, thus lowering the production yield.
In order to perform the hot rolling continuously, it
has been proposed to bond successively the steel materials to be
rolled. According to this method, the end portion of a preceding
steel material being rolled is overlapped with the forward end
portion of a subsequent steel material being rolled, and the roll-
ing is done on the overlapped portions to bond the preceding and
subsequent steel materials, and thus bonded materials are supplied
to the finishing hot rolling step to perform the hot rolling con-
tinuously. In this method, however, it is necessary that both sldes
of the overlapped portions are temporarily welded, that the thicX-
ness of scales on both inside opposing surfaces of the overlapped -
portions is maintained 40 ~u or less, that the length in the rolling
direction of the overlapped portions is at least 1/2 of the width
of the steelmaterial being rolled~, and thatthe overlappedportions are
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1C~79099
rolled with a reduction percentage 30 % or higher at the initial
stage of the finishing rolling step.
Therefore, the method according to the above Japanese
Laid-Open Patent Specification has disadvantages that a welding
machine is required for performing the temporary welding of the
both sides of the overlapped portions while the material running,
that the production yield is low because of the necessity to over-
lap the materials over a length of at least 1/2 of the width of
the material, and that a rolling equipment of large capacity is
required because at least 30 % reduction is done on the overlapped
portions at the initial rolling of the subsequent material in the
finishing rolling mill train.
The object of the present invention is to provide a
production method of hot strip by continuous hot rolling which eli-
minates completely the above problems and disadvantageous confront-
ed with by the conventional methods and can be carried out advan-
tageously on a commercial scale.
The above object of the present invention is achieved
by the following features that in a method in which a steel slab
heated to its rolling temperature is subjected to a rough hot rol-
ling, an intermediate hot rolling lf necessary and a finishing hot
rolling to obtain a hot strip, a forward end portion of a steel
band rolled by the hot rough rolling and, if necessary, subsequen-
tly by the intermediate hot rolling is overlapped with a finishing
end portion of a preceding steel band similarly rolled before or
during the hot finishing rolling step, with insertion between the
overlapped portions of the both hot bands of an oxide scale-fusing
agent which reacts with the oxide scale present on the opposing
surfaces of the overlappe~ portions by the heat of the overlapped
portions and forms a low melting point substance having high
flowability, at least one metallic nail-like member is driven into
the overlapped portions to temporarlly fixed the overlappeJ portions
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1079~99
if necessary and the overlapped portions are bonded by rolling re-
duction and subjected to the hot finishing rolling to obtain a
steel hot strip continuously.
For the continuous production of the hot strip by the
hot rough rolling step, the intermediate rolling step, if necessary,
and the hot finishing rolling step, the steel slabs may be bonded
one after another before the hot rough rolling or the steel bands
after the rough rolling are bonded between the rough rolling step
and the finishing rolling step, or in same cases between the inter-
mediate rolling step and the finishing rolling step or the roughrolling step.
However, when the steel slabs are bonded before the
hot rough rolling step, the rough rolling step and the finishing
rolling step must be associated, but such association through the
whole mill stands is difficult to achieve by the present rolling
technics, and as the steel slabs have a relatively large thickness
the jointed (overlapped) portion after the finishing rolling step
occupies a considerable length in the final hot strip which must be
cut off, thus resulting in considerable lowering of the production
yield.
Whereas, when the steel bands after the rough rolling
step are bonded as above, the disadvantages by the slab bonding
can be eliminated.
Therefore, the present invention is limited to the
bonding of the steel bands after the rough rolling step and thus
according to the present invention, the forward end portion of a
steel band obtained by the hot rough rolling, or in some cases fur-
ther by the intermediate rolling is overlapped and bonded with the
finishing end portion of a preceding steel band before or during
the finishing rolling step.
The bonding, however, must be performed with the fol-
lowlng considerations that the bonded portions are not adverse to
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the rolling condition and the bonding is done in a very short period
of time, and the bond strength must stand for at least the rolling
under tension in the finishing rolling step.
For the above considerations, the finishing end por-
tion of the preceding steel hot band is overlapped with the forward
end portion of the subsequent steel hot band and the overlapped
portions are bonded together by pressure in the present invention.
As mentioned just above, the strength of the portions bonded by
pressure must be enough to stand for the rolling under tension of
the steel hot band in the finishing rolling step. The pressure bond-
ing can be achieved by contact bond of the opposing surfaces of the
base metals of the overlapped portions of the hot bands. However,
the oxide scale present on the surface of the steel band hinders
the bonding by pressure of the base metals, and thus the oxide sca-
le must be removed before the bonding.The oxide scale may be remo-
v~ed by a mechanical grinding such as brushing or by a gas grinding
such as ~ hot scarfing using the oxygen gas, but it is extremely dif-
ficult to remove the oxide scale from the running steel band i~ a
short time by the above means, and if removed, a new oxide scale is
formed soon on the steel band surface and this newly formed oxide
scale hinders the bonding.
According to the present invention, for removal of the
oxide scale present on the surfaces of the finishing end portion of
a preceding steel band and on the surface of the forward end portion
of a subse~uent steel band, a scale-fusing agent which reacts to the
oxide scale at the temperature of the steel bands to be bonded and
forms a low melting point substance having high flowability is in-
serted betweeen the overlapped end portions to be bonded by the rol-
ling and is squeezed out. Together with the low melting point sub-
stace being squezed out, the oxide scale is substantially removedfrom the band surfaces of the overlapped end portions so that sa-
tisfactory bonding of the opposing metal surfaces can be obtained.
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1079099
The temperature of the steel bands at the time of their bonding by
pressure is advantageously not less than 1000C and as the steel
band is supplied to the hot finishing rolling mill train normally
at a temperature between about 1000 and 1050C, a desirable pressu-
re bonding temperature can be maintained without any specific consi-
deration so far as the rolling is done under the ordinary hot rol-
ling conditions.
As the scale-fusing agent used in the present invention,
one or~more i5 selected from the group consisting of oxides, complex
oxides, chlorides, sulfates, nitrates, carbonates and phosphates in
the powder form of Li, Na, K, Mg, Ca, Ba, B, Al, Si, Pb, P and Fe
which reacts with the oxide scale with the heat (not lower than
1000C) contained in the hot steel bands to w'nich the agent is appli-
ed and forms a low melting point substance having high flowability.
For the application of the scale fusing agent to the
surfaces of the hot steel bands to be bonded together, in case of
the oxides or complex oxides, for example boron oxides or complex
oxides, they may be applied directly in the form of B203.for exam-
ple, or they may be applied in the form of boric acid ( H2B03) which
is dehydrated immediately into the boron oxide because the hot band
is at high temperatures not lower than 1000C so that the same re-
sult can be obtained as the boron oxide (B2O3) is applied. Therefo-
re, in the present invention the oxides or complex oxides include
substances which decompose at a temperature not lower that 1000C
to produce an oxide.
As described above, the scale-fusing agent is applied
to the opposing surfaces of the overlapped portions of the hot steel
bands and the overlapped portions are bonded by the rolling and the
- oxide scale which has been converted into the low melting point
substance is squeezed out so that a satisfactory bondage between
the opposing metal surfaces is obtained. However, in order to as-
sure the bondage, it is desirable to avoid the slipping of the op-
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1079099
posing surfaces in the overlapped portions before the completion of
the bondage, and it is also desirable to avoid the increase in the
width and warping of the overlapped portions during the rolling.
In this way, a satisfactory bondage can be obtained.
The slipping between the opposing surfaces of the over-
lapped portions, and the width increase and warping of the over-
lapped portions during the rolling can be avoided by temporarily
fixing the overlapped portions mechanically, and as the mechanical
temporary fixing means according to the present invention, at least
one nail-like member made of carbon steel or low ally steel, for
example, is driven through the overlapped portions to temporarily
fixed them. This can be done easily in a very short period of time
during the running of the steel bands. As t~e means for drivin~
the nail-like member through the overlapped portions, in may be do-
ne by one or more known nail driving gun of explosion, high pressu-
re gas or compressed air type.
The nail-like member is required to have a strength
higher than that required for driving through the overlapped por-
tions at the high temperature, but when the strength of nail-like
member is excessively high, it damages the roll surace during the
subsequent rolling and thus an excessively high strength of the nail-
like member should be avoided. Preferably, nail-like members should
be selected which have such a character that the strength lowers as
they receive heat from the steel band and becomes almost equal to
the strength of the steel band during the subsequent rolling.
The number of the nail-lide members to be driven per
unit surface area of the overlapped portions should be limited to
the minimum required for maintaining the stability of the rolling
of the overlapped portions. An excessive number of the nail-lide
members driven through the overlapped portions will lower the strength
of the overlapped portions, often resulting in rupture thereof dur-
ing the subsequent Folling
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1079099
The present invention will be more clearly understood
from the following description of preferred embodiments with refe-
rence to the attached drawings.
Fig. 1 shows on example of the apparatuses used for
carrying out the method according to the present invention.
Fig. 2 shows the overlapped portions of the steel bands
temporarily fixed by the nail-like members.
Fig. 3(a)(b)(c) show respectively the modes of during
the nail-like members into the overlapped portions.
In Fig. 1, 1 represents the last stand of a hot rough
rolling mill train. A hot band 2 prepared by rolling a soaked
steel slab in the hot rough rolling mill train comes out of the
last stand l of the said mill train and advances on the roller of
the delay table in the direction of the arrow (a) to direct to the
first stand 9 of a hot finishing rolling mill train. The delay
table arranged between the last stand 1 and the first sta~d 9 is
.: -
composed of a fixed delay table 10 having rollers 12, a tilting
delay table 10' having rollers 12' and a fixed delay table 10"
having rollers 12". m e tilting delay table 10' is so structured
as to shift from its horizontal position to its tilted position
as the piston rod 13 of the hydraulic unit 11 provided at the
forward end rises.
In Fig. 1, a part of the preceding hot band 3 which has
been rough hot rolled is already introduced in the finishing
hot rolling mill train, while the tail end of the hot band 3
is on the roller 12 of the delay table 10 at the inlet side
of the hot rolling mill train, and the lead end of the subsequent
rough hot rolled hot band 2 is overlapped on the tail end of
the hot band 3 .
The tail end of the preceding hot band 3 is detected
by the hot metal detector 4 (infrared measuring meter) when it
has passed the hot metal detector 4 . The detection signal is
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sent to the spraying device 5 which stores and sprays the oxide
scale fusing agent, and this spraying device 5 starts to operate
immediately when it receives the signal from the hot metal detec-
tor 4 that the tail end of the hot band 3 has passed the hot
metal detector 4 and sprays the oxide scale fusing agent on the
tail end of the hot band 3 for a predetermined period of time.
When the hot metal detector 4 detects the tail end
of the hot band 3 , the detection signal is simultaneously sent
to the operation circuit of a solenoid valve 11' , which actuates
a hydraulic unit 11 for tilting the delay table 10' .
When the operation circuit rçceives the signal from the
hot metal detector, the hydraulic unit 11 operates to tilt
the delay table 10' . The detection signal emitted when the
hot metal detector 4 detects the tail end of the hot band 3
is sent to a rotation control deyice (not shown) for controlling
the rotation speed of the rollers 12' and 12 of the delay
table.
When the rotation control device receives the signal
from the hot metal detector 4 , the rotation speed of the rollers
12' and 12 is increased to increase the running speed of the
subsequent hot band 2 .
In this way, the lead end of the hot band 2 overlaps
over the tail end of the hot band 3 on which the oxide scale
fusing agent has been sprayed.
Meanwhile, before the hot metal detector 4 detects
the tail end of the hot band 3 , the rotation speed of the roll-
ers 12 , 12' and 12" of the delay table 10 , 10' and 10"
is controlled so as to cause the preceding hot band 3 and the
.,
subsequent hot band 2 run at a constant distance and at the
same speed.
As the hydraulic lifting rod 13 rises, the delay table
10' shifts from its horizontal position to its tilted position as
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1079099
shown, and on the other hand, as the running speed of the hot band
2 is increased over that of the hot band 3 so that the forward end
portion of the hot band 2 begins to overlap over the finishing end
portion of the preceding hot band 3.
At a forward position in the advancing direction of the
hot bands, there is positioned another X-ray measuring meter 6
above the hot band 3. When the forward edge of the hot band 2 is
detected by the X-ray measuring meter 6 while it is r-unning and
overlapping over the finishing end portion of the hot band 3, the
lifting rod 13 of the hydraulic unit 11 is caused to get down to
restore the delay table 10' to its original hoxizontal state, and
at the same time the rotation control device of the rollers 12, 12'
of the delay table 10, 10' is actuated to synchronize the running
speed of the hot band 3 with that of the hot band 2. In this way
the overlapping of the end portions of both bands is completed.
The overlapped portions run on the rollers 12" of the
delay table 10" and are introduced into the first stand 9 of the
, hot finishing rolling mill train, where the overlapped portions
are bonded by the rolling reduction. During the rolling reduction,
the oxide scale on the opposing surfaces of the overlapped portions :
, is squeezed out because it has been already,converted into the low
melting point and fluid substance by reaction with the oxide scale-
fusing agent, so that the base metal of the opposing surfaces is
substantially exposed thereby and a metal-to-metal bonding is ob- '
; tained'.' The bonding may be performed by a pressing means such as
a rotary press (not shown) before the overlapped portions enter -
the first stand 9.
The hot bands thus bonded are~cont'inuously finish-rolled
in'the.hot finishing rolling mill train.
During the bonding of the overlapped portions by the
rolling or the pressing, it someti~es occurs that the overlapped
portions deviate from each other, increase in width, or warp.
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Therefore, it is desirable that the overlapped portions are
temporarily fixed as described below and then rolled or pressed
to bond them.
As shown in Fig. 1, the hammering device 7 and the
X-ray measuring meter 8 are arranged closer to the finishing
rolling mill train than the X-ray measuring meter 6 . The
X-ray measuring meter 8 detects the overlapped portion, namely,
the lead end of the hot band 2 on which the tail end of the hot
band 3 overlaps.
When the X-ray measuring meter 8 detects the lead head
of the hot band 2 the detection signal is sent to the hammering
device 7 , so that the hammering device 7 is actuated to drive
the nail-like members successively into the overlapped portions
of the tail end of the hot band 3 and the lead end of the hot
band 2 . In this way, the overlapped portions of the tail end
of the hot band 3 and the léad end of the hot band 2 are
temporarily fixed. Then the temporarily fixed overlapped portions
are introduced into the first stand 9 of the hot finish rolling
mill train where the overlapped portions are bonded by the roll-
ing reduction and then the hot bands thus bonded are continu-
, , ously ! subjected;to the finishing rolling by the first and
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107909g
subsequent stands of the hot finishing rolling mill train.
The driving of the nail-like members 14 into the over-
lapped portions may be done in such a manner as they penetrate just
across the hot bands 2 and 3 as shown in Fig. 2 or in such a manner
as they penetrate the hot bands 2 and 3 with both end projecting out
the both surfaces, or penetrate partially across the overlapped por-
tions as shown in Fig. 3(a) to (c).
In the above embodiment, the preceding and subsequent
hot bands are bonded between the last stand of the hot rough rolling
mill train and the first stand of the hot finishing rolling mill
train to continuously produce the hot strip. However, without
deviating from the scope and spirit of the present invention, the
last stand 1 of the hot rough rolling mill train may be replaced
by the first stand of the hot finishing rolling mill train, and
the first stand 9 of the hot finishing rolling mill train may be
replaced by the second stand of the hot finishing rolling mill train
so as to bond the hot bands between these stands durin~ the finish-
ing rolling.
Further, the bonding of the preceding and subsequent
hot bands may be done in certain cases after an intermediate rol- -
ling step following the hot rough rolling step.
; m us, the preceding and subsequent hot bands which
have been passed through the intermediate rolling step are bonded
between the hot finishing rolling step or during the continuous
hot finishing rolling.
~he present invention will be more clearly understood
from the following axamples.
A low-carbon steel slab of 250 mm in thickness and 10 m
in length is continuously hot rolled to obtain a steel hot strip.
m e above low-carbon steel slabs were soaked to 1200C,
reduced by the hot rough rolling mill train 1 to obtain steel
hot bands of 30 mm in thickness, and these hot bands are successi-
vely bonded one by one and continuously hot rolled under the con-
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1079~99
ditions shown in the table below.
No. 1 and No. 2 in the table are comparative examples
in which no oxide scale-fusing agent was applied and the overlapped
portions were temporarily fixed by the nail-like members. In Nos.
3 to 12, which are examples of the present invention, the bonding
of the hot bands was done before the hot finishing rolling. In Nos.
13 and 14, which are also examples of the present invention, the
bonding of the hot bands was performed during the hot finishing rol-
ling.
As clearly shown in the table, although the temporary
fixing by the nail-like members alone permits the subsequent conti-
nuous hot rolling, a relatively large number of nail-like members
are required for affording an enough bonding strength of overlapped
portions which satisfactorily stands for the subsequent hot fini-
shing rolling. The number of the nail-like members driven into
the overlapped portions should be appropriate. If the number is
too small, the nail-like members will be broken by the tension dur-
ing the finishing rolling step so that the desired effects o the
temporary fixing can not be obtained. On the other hand, if the num-
ber is too large, the overlapped portions into which the nail-like
members are driven would rupture during the finishing rolling due
to too many penetrations by the nail-lide members.
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:~79099
.. . .
Oxide* Over- Number Temp.at
Steel Scale Amount lapp- of Press- Re- which
NO. Width ~using ;ng Nail- Bond- duc- Bonding
Material Agent Length like ing tion is
Member Device Rate done
Driven~
.
MM g/m2 mm %~C
Low
Carbon 1200 - - 200 10 R.P.** 40 1050
Steel
Slab
2 " 1200 - - 200 20 Fl*** 301045
3 " 1200 No.l 30 200 4 R.P. 401050
104 " 1200 No.1 30 200 - R.P. 401060
" 1200 No.1 30 200 4 Fl 301060
6 " 1200 No.2 100 100 4 R.P. 20 1040
7 " 1200 No.2 100 300 - R.P. 20 1050
8 " 1200 No.2 200 100 4 R.P. 20 1050
9 " 1200 No. 3 200 100 4 R.P. 20 1065
" 1200 No.4 200 100 4 R.P. 20 1055
11 " 1200 No.5 200 100 4 R.P. 20 1050
12 " 1200 No.6 200 100 4 R.P. 20 1050
~13 " 1200 No.2 100 100 4 R.P. 40 1010
; 20 14 " 1200 No.2 100 300 - R.P. 40 1010
* Composition of oxide scale fusing agent : -
No-l B2O3(50%) - Na2B4O7t50%)
No.2 : B2o3(45.6%) - SiO~(17.5%) 2
- A12O3(4.5%) - CaO(5.0%) - MgO(2.4%)
No.3 : P2O5(60.9%) ~ B2O3(5-3%) K20 (16- %)
-Na2O (9.8%) - Lio ~4.8%) - A12O3(3.2%)
No.4 : NaCl
No.5 : NaNO3 ` `
No.6 : Na2SO4
*!* R.P. = Rotary Press
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1~79099
*** Fl = First stand of hot finishing rolling mill train
According to the present invention in which the oxide
scale-fusing agent is applied to the opposing surfaces of the over-
lapped portions so that a strong bondage is achieved by pressure
between the exposed metal of the opposing surfaces, thus affording
a continuous and stable hot rolling operation even under the seve-
re conditions in the subsequent hot finishing rolling step. Further,
when the overlapped portions are temporarily fixed by the nail~ e
members, it is possible to avoid the deviation of the opposing sur-
faces of the overlapped portions, and the width increase and warplingof the overlapped portions so that an accurate and firm bondage can
be obtained. It is also possible to reduce the length of the over-
lapped portions and thus a good production yield can be assured.
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