Method of operating a reheating furnace in a hot rolling line and a reheating furnace employed therefor

A heating method of operating a furnace in a hot rolling line and a heating furnace therefor in which the reheating furnace is positioned between a continuous casting apparatus and a rolling apparatus rolling workpieces at a higher speed than they are cast by the casting process, the furnace serving as a heating and buffer zone. The reheating furnace includes at least three moving beams each having an independent driving mechanism, and coupling mechanisms which couple the neighboring moving beams for independent or synchronous movement, while the moving beams are so arranged that, by operating the driving mechanism, they are altered in their speeds to the discharging speed of the workpieces from the continuous casting process, or one or two of the moving beams are brought into idling state or driven at the rolling speed.

BACKGROUND OF THE INVENTION 
The present invention relates to a hot rolling process, and more 
particularly to a method of operating a reheating furnace in a hot rolling 
line. 
Commonly, in modern steel making plants, achievement of energy and labor 
savings and high efficiency has constantly been sought by making various 
processes involved continuous. The production line ranging from a 
continuous casting process to the rolling process has been included in 
such efforts, and making such process continuous has been attempted by 
arranging a reheating furnace between the continuous casting machine and 
the rolling mill. In the conventional arrangements as described above, 
since the speed for the continuous casting differs to a large extent from 
that of the rolling, with the latter being normally several times higher 
than the former, the reheating furnace employed is required to serve as a 
buffer or absorbing zone for absorbing the difference in through put 
capacity between the two processes as far as possible. More specifically, 
in order to meet the requirement as described above, it becomes necessary 
to employ a reheating furnace capable of simultaneously discharging 
workpieces for rolling at a higher speed and continuously being charged 
with workpieces from the casting process at a lower speed without altering 
the transportation rate of such workpieces. Additionally, such a reheating 
furnace should be so arranged as to achieve high operating efficiency of 
the rolling apparatus and labor saving through reduction, as far as 
possible, of the frequency of on-off operations for the rolling mill 
operated at high speed by storing therein a predetermined amount of 
workpieces to be rolled which have been cast continuously at low speed and 
also by collectively forwarding such workpieces in one group from the 
furnace to the rolling mill. For the purpose as described above, the 
reheating furnace must be provided, without increasing the length thereof, 
with heating and heat holding capability for retaining the heat of heated 
workpieces to be rolled until the workpiece last charged into the furnace 
has been heated up to the predetermined rolling temperature. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide an 
improved heating method for workpieces or materials to be rolled in a hot 
rolling line in which the idling time of a reheating furnace is 
advantageously shortened for efficient heating and holding of workpieces 
to be rolled, with simultaneous reduction of furnace length for 
substantial elimination of the disadvantages inherent in the conventional 
heating methods. 
Another important object of the present invention is to provide an improved 
reheating furnace for effecting the heating method as described above in 
an effecient manner at low installation cost. 
A further object of the present invention is to provide a reheating furnace 
of the above described type which is simple in construction and stable in 
operation and can readily be incorporated into the hot rolling line. 
In accomplishing these and other objects, according to one preferred 
embodiment of the present invention, a reheating furnace is arranged 
between the continuous casting apparatus casting billets or slabs at a low 
speed and a rolling apparatus rolling slabs at a higher speed than the 
slab is being cast, the reheating furnace serving as a heating and buffer 
zone. The reheating furnace includes at least three moving beams each 
having an independent driving mechanism, and coupling mechanisms which 
couple the neighboring moving beams for independent or synchronous 
movement, while the moving beams are so arranged that, by operating the 
driving mechanism, they are altered in their speeds to the discharging 
speed of the workpieces from the continuous casting process, or one or two 
of the moving beams are brought into idling state or moved at the rolling 
speed. By the above arrangement, not only is the idling time of the 
furnace advantageously reduced, but the length of the furnace is 
shortened, with substantial elimination of disadvantages inherent in the 
conventional reheating furnaces of such type.

Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout the 
several views of the accompanying drawings. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIG. 1 an arrangement of a 
hot rolling line ranging from the continuous casting apparatus C to the 
rolling apparatus R between which a reheating furnace H directly related 
to the present invention and described later in more detail with reference 
to FIGS. 2 to 5 is arranged as a heating and buffer zone. In the 
continuous casting apparatus C, molten metal m contained in a ladle 
C.sub.1 is fed into a tundish C.sub.2 to be subsequently molded in a mold 
assembly C.sub.3 into a continuous cast material, for example, in the form 
of a bar b, which is led between a number of pairs of guide rolls r.sub.a 
along a curved path through a straightener C.sub.4 and the like 
sequentially arranged, and is subsequently cut into workpieces i.e., 
billets or slabs and the like by cutting means C.sub.5 in a known manner. 
The billets s thus formed are further transported by transportation rolls 
r.sub.b to a charge table (not shown) arranged adjacent to the charge side 
Ha of the reheating furnace H and are charged into the furnace H by pusher 
means P. The billets s processed in the furnace H in a manner described 
later are then discharged from the furnace H onto a discharge table (not 
shown) arranged on the discharge side Hb of the furnace H by the action of 
the extractor means E, and are further fed into the rolling apparatus R by 
transportation rolls r.sub.c so as to be rolled, for example, into the 
form of steel plates f. 
Referring also to FIG. 2, the reheating furnace H according to the present 
invention, for example, of the walking beam type, includes a housing or 
furnace body Hf of refractory material supported above the ground by 
suitable support members (not shown), and longitudinally extending from 
the charge end Ha to the discharge end Hb of the furnace H for the 
workpieces W (i.e., the billets s), moving or walking beam means B movably 
accommodated in the furnace body Hf and longitudinally divided, for 
example, into three sections or moving beams B.sub.1, B.sub.2 and B.sub.3, 
and a plurality of burner means F, for example, axial-flow burners, 
provided in the furnace body Hf at predetermined intervals for heating the 
workpieces W. The moving beams B.sub.1, B.sub.2 and B.sub.3 are associated 
with each other through eccentric wheels 1 rotatably disposed below the 
beams B.sub.1 to B.sub.3 and coupled to a driving source (not shown) such 
as a motor or the like for vertical movement of the respective beams 
B.sub.1 to B.sub.3, hydraulic cylinder 2.sub.1, 2.sub.2 and 2.sub.3 also 
disposed below the beams B.sub.1 to B.sub.3 for horizontal driving of the 
beams, and coupling mechanisms 3.sub.1 and 3.sub.2 such as a magnetic 
clutches or the like provided between the neighboring beams B.sub.1 and 
B.sub.2, and B.sub.2 and B.sub.3 for independently driving each of the 
beams B.sub.1 to B.sub.3 or for synchronized driving of the beams B.sub.1 
to B.sub.3. For proper driving of the moving beams B.sub.1 to B.sub.3, the 
eccentric wheels 1 and hydraulic cylinders 2.sub.1, 2.sub.2 and 2.sub.3 
are coupled to a speed control circuit Xa of a control means X including a 
conventional logical operation circuit in a known manner, while the 
coupling mechanisms 3.sub.1 and 3.sub.2 are connected to a coupling 
control circuit Xb of the control means X. 
Referring also to FIG. 3, operations of the reheating furnace H of FIG. 2 
will be described hereinbelow. 
On the assumption that the workpieces, for example, billets W to be rolled 
produced by the continuous casting process C are continuously charged into 
the reheating furnace H at an intermediate transportation speed of 0.3 
m/min, starting from the state (a) of FIG. 3, the moving beams B.sub.1, 
B.sub.2 and B.sub.3 are subjected to associated driving by the coupling 
mechanisms 3.sub.1 and 3.sub.2 for simultaneous movements at a speed of 
0.3 m/min, and the workpieces W to be rolled are sequentially transported 
to the discharge end Hb, while being heated by the burners F shown in FIG. 
2 (FIG. 3(b). 
When all of the workpieces W have been charged into the furnace H, with a 
leading one of the workpieces W in the group of the workpieces reaching 
the discharge end Hb (FIG. 3(c), the moving beam B.sub.1 is cut off or 
separated from the moving beam B.sub.2 through actuation of the coupling 
mechanism 3.sub.1 by the control circuit Xb, while the beams B.sub.2 and 
B.sub.3 are associated with each other by the coupling mechanism 3.sub.2 
so as to move merely up and down at a low idling speed for effecting an 
idling process, i.e., heat-reserving process. Subsequently, after the 
elapse of a predetermined time, the workpieces W are discharged by the 
synchronized driving of the moving beams B.sub.2 and B.sub.3 at a high 
discharge speed of 0.58 m/min to be transported toward the rolling 
apparatus R. It is to be noted here that the discharging or transportation 
speeds for the beams B.sub.2 and B.sub.3 are to be altered by variation of 
the cycle time. 
Meanwhile, workpieces or billets W' newly produced by the continuous 
casting apparatus C are sequentially charged onto the beam B.sub.1 for 
being transported at the intermediate transportation speed of 0.3 m/min 
(FIG. 3(d)). More specifically, in the state of FIG. 3(d), the moving beam 
B.sub.1 transports the workpieces W' at the intermediate transportation 
speed of 0.3 m/min, while the moving beams B.sub.2 and B.sub.3 subjected 
to the associated movements through the coupling mechanism 3.sub.2 feed 
the workpieces W at a high transportation speed of 0.58 m/min. 
Subsequently, when the workpieces W on the moving beam B.sub.2 are 
transferred onto the beam B.sub.3, the beams B.sub.1 and B.sub.2 are 
subjected to the associated movement through the coupling mechanism 
3.sub.1 for sequentially transporting the workpieces W' at the 
intermediate transportation speed of 0.3 m/min, while the beam B.sub.3 
separated from the beam B.sub.2 by the functioning of the coupling 
mechanism 3.sub.2 continuously discharges the workpieces W at the high 
discharging speed of 0.58 m/min (FIG. 3(e)). In other words, in the state 
of FIG. 3(e), the beams B.sub.1 and B.sub.2 are subjected to the 
associated movement by the coupling mechanism 3.sub.1 and transport the 
group of the workpieces W' at the intermediate transportation speed of 0.3 
m/min, while the beam B.sub.3 discharges the workpieces W at the high 
discharging speed of 0.58 m/min. 
Upon completion of the discharging of the group of the workpieces W, the 
beam B.sub.3 is again associated in its movement with the beam B.sub.2 
being subjected to the associated movement with the beam B.sub.1 by the 
functioning of the coupling mechanism 3.sub.2, and is altered in its 
transportation speed to 0.3 m/min in synchronization with the beams 
B.sub.1 and B.sub.2 for sequentially feeding the group of the workpieces 
W' toward the discharge side Hb. Subsequently, the furnace H is brought 
back to the state of FIG. 3(c), and the workpieces W produced by the 
continuous casting apparatus C at a predetermined time interval are 
charged into the reheating furnace H irrespective of the rolling starting 
time. 
Referring now to FIGS. 4 and 5, there is shown in FIG. 4 a modification of 
the reheating furnace H of FIGS. 2 and 3. In the modified reheating 
furnace HA of FIG. 4, the furnace body HAf has a partition wall Hw built, 
for example, of refractory bricks at approximately the central portion 
thereof and longitudinally extending from the charge end Ha to the 
discharge end Hb of the furnace HA for dividing the interior of the 
furnace HA into two rows of independent heating sections H.sub.1 and 
H.sub.2 provided with separate inlets H1a and H2a and outlets H1b and H2b 
for the workpieces W respectively, while the heating sections H.sub.1 and 
H.sub.2 longitudinally divided at least into three portions include the 
moving beams B.sub.1, B.sub.2 and B.sub.3, and B.sub.1 ', B.sub.2 ' 
respectively in a manner similar to that of the furnace H of FIG. 2. 
Referring to FIG. 5, operations of the reheating furnace HA of FIG. 4 will 
be described hereinbelow. 
When the workpieces to be rolled, for example billets W cast by the 
continuous casting process C, are charged in the heated state into the 
first heating zone H.sub.1 at a charging speed (discharging speed) of 0.3 
m/min, the beams B.sub.1, B.sub.2 and B.sub.3 are driven at a 
transportation speed of 0.3 m/min for successively transporting the 
workpieces W which are being heated by the burners F shown in FIG. 2, and 
upon arrival of the workpieces W at an intermediate portion of the beam 
B.sub.2 (the amount of the workpieces W is equivalent to half the amount 
thereof cast by one continuous casting operation), subsequent workpieces W 
are changed over to be charged into the second heating section H.sub.2 and 
successively transported while being heated by the burners F shown in FIG. 
2 (FIG. 5(a)). Subsequently, when the leading end of the group of the 
workpieces Wa in the first heating section H.sub.1 has reached the 
discharge side H1b, the moving beams B.sub.2 and B.sub.3 are subjected to 
associated movement to start the idling process for keeping the group of 
the workpieces Wa heated (FIG. 5(b)). Thereafter, the group of the 
workpieces Wb in the second heating section H.sub.2 is also kept heated, 
while the workpieces W from a second continuous casting process are 
charged into the first heating section H.sub.1, and after transportation 
by the beam B.sub.1 for the predetermined period of time, the beams 
B.sub.2 and B.sub.3 in the first heating section H.sub.1 start the 
discharging process for discharging the workpieces Wa at the speed of 0.58 
m/min (FIG. 5(c)). Subsequently, when the workpieces W on the second beam 
B.sub.2 are transferred onto the beam B.sub.3, the moving beams B.sub.1 
and B.sub.2 are subjected to the associated movement at the transportation 
speed of 0.3 m/min for transporting the subsequent group of the workpieces 
Wa' also onto the beam B.sub.2 (FIG. 5(d)). Upon completion of the 
discharging of the workpieces W on the beam B.sub.3, beam B.sub.3 is also 
subjected to the associated movement with the beams B.sub.1 and B.sub.2 
for transporting movement at the speed of 0.3 m/min, and when the 
subsequent group of the workpieces Wa' (equivalent in amount to half the 
amount produced by the second continuous casting process) is charged, 
change-over is effected for charging into the second heating section 
H.sub.2, and thus, in a manner similar to that in the first heating 
section H.sub.1, the group of the workpieces Wb in the second heating 
section H.sub.2 is discharged at the speed of 0.58 m/min (FIG. 5(e)), 
while the beams B.sub.2 ' and B.sub.3 ' are sequentially changed over to 
the transporting speed of 0.3 m/min for transporting the subsequent 
workpieces Wb' toward the discharge side H2b. 
Thereafter, the furnace HA is brought into the state as shown in FIG. 5(b), 
and the workpieces continuously cast at the continuous casting process C 
remain heated in the first or second heating section H.sub.1 or H.sub.2 
for being continuously rolled by the rolling apparatus R at a 
predetermined time interval. 
It should be noted here that, although the present invention is mainly 
described with reference to the top and bottom firing type walking beam 
furnace in the foregoing embodiment, the invention is not limited in its 
application only to such a walking beam furnace, but may readily be 
applicable to a top firing type walking hearth furnace having a brick 
hearth. 
It should also be noted that the present invention is not limited in its 
application to a continuous hot rolling line ranging from the continuous 
casting apparatus to the rolling apparatus, but can effectively be 
employed as a buffer furnace for a continuous processing line from a 
blooming mill to a rolling apparatus, for example, a slabing mill, in the 
hot direct rolling process (HDR) which has recently been proposed. 
As is clear from the foregoing description, according to the present 
invention, the moving beam means of the reheating furnace is 
longitudinally divided into at least three portions or three moving beams, 
which can be driven by separate driving means respectively so that the 
high speed discharging and low speed continuous charging of the workpieces 
may be effected simultanteously through proper change-over of the driving 
mechanisms without altering the transportation rate of the workpieces to 
be rolled for effective utilization of the moving beams, and thus, it has 
been made possible to achieve energy saving, with reduced furnace length. 
Although the present invention has been fully described by way of example 
with reference to the attached drawings, it is to be noted that various 
changes and modifications will be apparent to those skilled in the art. 
Therefore, unless otherwise such changes and modifications depart from the 
scope of the present invention, they should be construed as being included 
therein.