Guide segment support system for continuous casting

An improved guide segment assembly for a continuous casting machine includes a support frame and a guide segment that includes a bottom segment portion having a number of support rolls for engaging a bottom surface of a continuously cast strand, and a top segment having a number of guide rolls thereon for engaging a top surface of the strand. A force applicator is provided for urging the top and bottom segment portions toward one another against mechanical stops in order to provide support for the strand that is sufficient to counter ferrostatic pressure within the strand. A resilient mechanism is positioned between the support frame and the guide segment for permitting limited movement between the support frame and the guide segment during abnormal casting conditions. As a result of the resilient mechanism, both the support rolls and the guide rolls will be amply protected against overload conditions during abnormal conditions such as cold withdrawals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the continuous casting industry. More 
specifically, this invention relates to an improved guide segment support 
system and method for supporting and guiding a cast strand after it 
emerges from a mold. 
2. Description of the Related Technology 
Metals such as steel are continuously cast into strands by pouring hot, 
molten metal into the upper end of a mold and continuously withdrawing a 
metal strand from the mold's bottom. As the molten metal passes through 
the mold, the surfaces of the metal that are adjacent to the mold walls 
are cooled, solidified and hardened to form a casing or shell of 
solidified metal around the molten metal in the strand. After leaving the 
bottom of the mold, the metal continues to cool and the casing or shell of 
solidified metal around the molten core thickens until the whole strand 
section is solidified. 
The shell of solidified metal around the molten core, as the continuous 
cast strand leaves the mold, is relatively thin and fragile, and requires 
support. Such support, in continuous casting of metals, is customarily 
provided by rolls which engage and support the opposite sides of the 
continuously cast strand. The supporting rolls immediately below the mold, 
where the shell of solidified metal is relatively thin, are usually of 
relatively small diameter and are longitudinally spaced closely together. 
To assist cooling of the slab and to prevent the rolls and bearings from 
overheating, these supporting rolls may be liquid cooled. Further away 
from the mold bottom, where the metal has cooled and the shell of solid 
metal has thickened, rolls of larger diameter, spaced at greater 
longitudinal distance, are usually employed. To control the casting speed, 
certain of the supporting and guiding rolls may be driven. Typically, of 
course, the supporting rolls are arranged about an arcuate path or apron 
that defines the path of the strand as it emerges vertically downwardly 
from the mold, then gradually bends about a 90 degree arc until it emerges 
as a fully solidified, horizontally oriented casting. Space is generally 
provided between the rolls for permitting introduction of spray water to 
cool the cast strand. 
Conventionally, the opposed supporting and guiding rolls are divided into 
segments. On the outside radius of the arcuate path that is defined by the 
guide rollers, a supporting frame (commonly referred to as a "banana 
beam") is provided to which these segments are attached. In order to 
permit repair and maintenance work to be effected on the segments, the 
segments are designed to be exchangeable. The segments of the apron can be 
exchanged with the help of a segment changing carriage which runs on rails 
extending parallel to the apron, or, in some machines, can be lifted out 
by a building-mounted crane system. The segments can be transferred to 
this carriage and carried thereon to a point where they can be removed 
from the plant and repaired or readjusted as may be required. 
Each segment includes a "bottom" portion containing a bottom set of rolls 
that engages the side of the strand that is closest to the supporting 
frame or banana beam, which is the side that defines the outer radius of 
the arc through which the strand is guided to move. The bottom portion of 
the segment is always, in the experience of the inventor, securely mounted 
to the supporting frame so that no relative movement is permitted between 
the bottom portion and the supporting frame. Each segment will also 
include a "top" portion that holds a top set of rolls for supporting the 
inner radius side of the strand. To provide the necessary support to the 
strand, and to counter ferrostatic pressure that develops in the strand 
during its vertical descent, the top portion and the bottom portion are 
urged together by a controlled force, which is typically exerted by a 
hydraulic mechanism that is mounted on the segment. The top and bottom 
portion alternatively are connected by a spring structure jacking 
mechanism that permits limited movement therebetween during operation. 
During normal casting operation, the top and bottom portions of the strand 
are urged together at a relatively constant force against mechanical stops 
so that the distance between the opposing top and bottom rolls is 
maintained constant. Unfortunately, the magnitude of this force can be so 
great that damage to the rolls, roll bearings, roll supports and segments 
can and often do occur, particularly during abnormal casting conditions. 
For example, if the casting machine is caused to stop for any length of 
time, it might be necessary to withdraw the solidified strand from the 
apron of support rollers by performing what is referred to in the industry 
as a "cold strand withdrawal." In this procedure, the fully solidified 
strand is caused to be bent into its desired final horizontal shape as it 
travels through the arc-shaped array of guide and support rolls by the 
pressure that is exerted on the strand by the rolls. In current systems, 
this often initiates failure of one or more guide rolls (usually, in the 
inventor's experience, by yielding or fracturing the bearing races), 
although it might take several weeks to find out which rolls are going to 
fail. Bearing failure, in the inventor's experience, most often occurs in 
the bottom portion of the segment, which is rigidly mounted to the banana 
beam. Of course, when failure does occur, it adversely affects the quality 
of the cast product, which is a major economic concern for the steel 
maker. Other conditions that can cause failure of the rolls include bulges 
or irregularities in the strand being cast. If the irregularity is on the 
top side of the strand, forces may be partially absorbed by the spring 
structure or by the opening of the hydraulic clamping cylinders by action 
of associated pressure relief valves. If the irregularity is on the 
bottom, though, the spring structure does not provide much protection 
against a force overload condition being applied against the lower rolls. 
A need exists for an improved strand support segment system that is 
designed so as to minimize the potential for early failure as a result of 
abnormal conditions such as cold strand withdrawal or the presence of 
irregularities in the strand being cast. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide an improved guide 
segment support system for a continuous casting system that is designed so 
as to minimize the potential for early failure as a result of abnormal 
conditions such as cold strand withdrawal or the presence of 
irregularities in the strand being cast. 
In order to achieve the above and other objects of the invention, an 
improved guide segment assembly for a continuous casting machine includes 
a support frame; a guide segment that includes a bottom segment portion 
having a number of support rolls thereon for engaging a bottom surface of 
a strand that has been cast in a continuous casting machine; a top segment 
portion having a number of guide rolls thereon for engaging a top surface 
of such a strand; force application structure for urging the top and 
bottom segment portions toward one another in order to provide support for 
the strand that is sufficient to counter ferrostatic pressure within the 
strand; and resilient structure, positioned between the support frame and 
the guide segment, for permitting limited movement between the support 
frame and the guide segment during an abnormal casting condition, whereby 
both the support rolls and the guide rolls will be amply protected against 
overload conditions during abnormal casting conditions. 
According to a second aspect of the invention, a method of guiding a strand 
of continuously cast material in a guide segment of the type that includes 
a bottom segment portion having a number of support rolls thereon for 
engaging a bottom surface of a strand, and a top segment portion having a 
number of guide rolls thereon for engaging a top surface of such a strand, 
the guide segment being mounted to a support member, includes steps of (a) 
urging the top and bottom segment portions together to support the strand 
between the support rolls and the guide rolls in an amount of force that 
is sufficient to counteract ferrostatic pressure that exists within the 
strand; and (b) in response to an abnormal casting condition that exerts 
force on the top or bottom segment portions that exceeds a predetermined 
maximum, resiliently adjusting the spacing between the guide segment and 
the support member, wherein force against either the support rolls or the 
guide rolls is relieved before it reaches failure-causing levels, whereby 
the guide segment is protected against damage in the event of abnormal 
casting conditions. 
These and various other advantages and features of novelty which 
characterize the invention are pointed out with particularity in the 
claims annexed hereto and forming a part hereof. However, for a better 
understanding of the invention, its advantages, and the objects obtained 
by its use, reference should be made to the drawings which form a further 
part hereof, and to the accompanying descriptive matter, in which there is 
illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Referring now to the drawings, wherein like reference numerals designate 
corresponding structure throughout the views, and referring in particular 
to FIG. 1, an improved guide segment apron assembly 10 for a continuous 
casting machine includes a support frame 12, which in the preferred 
embodiment (and as is generally known) follows a generally arcuate path 
along an outer radius of the path along which the strand of continuously 
cast material is guided by the guide segment apron assembly 10. Support 
frame 12 is also commonly referred to as a "banana beam." As may be seen 
in FIG. 1, the guide segment apron assembly 10 consists of a number of 
guide segments 14, each of which includes a bottom segment portion 16 
having a number of support rolls 18 thereon for engaging a bottom surface 
of a strand that has been cast in a continuous casting machine. Each guide 
segment 14 further includes a top segment portion 20 that has a number of 
guide rolls 22 thereon for engaging a top surface of the strand. As is 
generally known in this area of technology, a force application system 24 
is provided for urging the top and bottom segment portions 20, 16 toward 
another against mechanical stops 25 in order to provide support for the 
strand that is sufficient to counter ferrostatic pressure within the 
strand. In the illustrated embodiment, force application system 24 is 
embodied as a hydraulic cylinder 26. Alternatively, as is known in the 
art, other force application mechanisms can be used, such as a number of 
jack screws in conjunction with a spring mechanism. 
As may be seen in FIG. 1, the bottom segment portion 16 is supported with 
respect to the support frame 12 by a number of support feet 30, which are 
shown in cross section in greater detail in FIG. 2. Looking now to FIG. 2, 
it will be seen that each foot 30 incorporates a resilient mechanism 32, 
positioned between the support frame 12 and the guide segment 14, for 
permitting limited movement between the support frame 12 and the guide 
segment 14 during an abnormal casting condition. Examples of abnormal 
casting conditions that might cause such limited movement include a cold 
strand withdrawal procedure or the presence of irregularities in one or 
both of the sides of the casting. 
More specifically, as may be seen in FIG. 2, resilient mechanism 32 is 
connected between the support frame 12 and the bottom segment portion 16 
of the guide segment 14, and is designed to permit limited movement 
between the support frame 12 and the bottom segment portion 16. In the 
embodiment that is illustrated in FIG. 2, the resilient mechanism 32 is 
embodied as one or more preloaded disc springs 34 that is interposed 
between the support frame 12 and the bottom segment portion 16 of the 
guide segment 14. Also shown in FIG. 2 is a preloaded hold-down mechanism 
40 for resiliently holding the bottom segment portion 16 of the guide 
segment 14 to the support frame 12. Hold-down mechanism 40 includes a disc 
spring assembly 42 that is arranged to provide a downward force to a yoke 
36 that is connected to the bottom segment portion 16, through the support 
foot 30 and resilient mechanism 32, as may be seen in FIG. 2. A hydraulic 
nut 38 is provided to pretension the disc spring assembly 42. 
Alternatively, pretensioning could be effected by an external hydraulic 
jack or equivalent mechanism. 
Preferably, the resilient mechanism 32 is configured to permit an amount of 
deflection between the support frame 12 and the bottom segment portion 16 
during operation that is within the range of about 1/16th of an inch to 
about 1 inch. More preferably, the resilient mechanism 32 is configured to 
permit an amount of deflection between the support frame 12 and the bottom 
segment portion 16 that is within the range of about 1/8th of an inch to 
about 1/2 of an inch. In the embodiment of FIG. 2, the amount of permitted 
deflection corresponds to the amount of linear collapse that is provided 
by the preloaded disc springs 34. 
FIG. 3 depicts a resilient mechanism for providing limited movement between 
the support frame 12 and the bottom segment portion 16 that is constructed 
according to a second preferred embodiment of the invention. In this 
embodiment, a support foot 44 is mounted to the bottom segment portion 16, 
and a housing 46 is mounted to the support frame 12. A pin member 58 is 
positioned for movement within the housing 46. A stationary plate 52 is 
positioned statically within the housing 46 and is held in place with a 
pair of support bars 64. A bottom retainer plate 54, which is provided to 
retain the pin member 58 within the housing 46, is affixed to the housing 
46 by a plurality of retainer bolts 56. 
A tensioning disc spring 62 is provided within the housing 46 so as to be 
interposed between a head plate portion of pin member 58 and stationary 
plate 52. A cushioning disc spring 60 is interposed within the housing 46 
between the stationary plate 52 and a plunger 50 that is axially movable 
within the housing 46 and is sealed with respect thereto by a seal 66. As 
is shown in FIG. 3, pin member 58 extends through axial holes that are 
defined in plate 52, springs 60, 62, plunger 50 and support foot 44, and 
has a radial slot defined in a distal end that is positioned beyond 
support foot 44. A retaining bar 48 is positioned in the radial slot for 
keeping the pin member 58 retained in the support foot 44. A replaceable 
contact ring 68 is positioned within the support foot 44 for absorbing 
contact with the retaining bar 48. A hydraulic jack 70 may be positioned 
as shown in FIG. 3 for removing the retaining bar 48 during disassembly, 
such as for maintenance. 
During operation, downward forces that are applied to the bottom segment 
portion 16 will be absorbed by the cushioning disc spring 60. The 
tensioning disc spring 62 acts to keep pin member 58 pretensioned during 
operation, thereby preventing separation of the bottom segment portion 16 
from the support frame apron 12. 
In operation a strand of continuously cast material will be passed between 
the support rolls 18 on the bottom segment portion 16 and the guide rolls 
22 on the top segment portion 20. As this occurs, the force application 
system 24 forces the top and bottom segment portions 16, 20 toward one 
another, thus providing support pressure against the strand that counters 
the ferrostatic pressure within the strand. 
In the event of an abnormal casting condition, such as the presence of a 
bulge or irregularity on the surface of the strand, or in the event of a 
cold withdrawal procedure, greater forces are applied to the support rolls 
18 and the guide rolls 22. When such forces exceed a predetermined 
maximum, the resilient mechanism will be caused to deflect, thus relieving 
the pressure and reducing the likelihood of failure of one or more of the 
support rolls 18 or guide rolls 22. 
It is to be understood, however, that even though numerous characteristics 
and advantages of the present invention have been set forth in the 
foregoing description, together with details of the structure and f 
unction of the invention, the disclosure is illustrative only, and changes 
may be made in detail, especially in matters of shape, size and 
arrangement of parts within the principles of the invention to the full 
extent indicated by the broad general meaning of the terms in which the 
appended claims are expressed.