U.S. patent application number 13/928558 was filed with the patent office on 2014-01-09 for side dam with insert.
This patent application is currently assigned to NUCOR CORPORATION. The applicant listed for this patent is NUCOR CORPORATION. Invention is credited to Alan J. DENO, Rama Ballav MAHAPATRA, Jay Jon ONDROVIC, Mark SCHLICHTING.
Application Number | 20140008032 13/928558 |
Document ID | / |
Family ID | 49877618 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140008032 |
Kind Code |
A1 |
ONDROVIC; Jay Jon ; et
al. |
January 9, 2014 |
SIDE DAM WITH INSERT
Abstract
A composite side dam for a continuous twin roll caster includes
a substrate made of a refractory material capable of withstanding
casting temperature and having edge portions adapted to engage
casting rolls and having a nip portion adjacent a nip between
casting rolls and upper portions extending across the side dam to
form a lateral restraint for a casting pool, an insert of at least
10 mm in thickness positioned in a pocket in the substrate and
extending to engage the molten metal and extending from the upper
portions of the substrate and positioned in the pocket to within 30
mm from the nip portion by insertion adjacent the upper portions of
the substrate, and the insert adapted to fit into the pocket of the
substrate to form a side dam formed of a refractory material having
consumption rate less than 10 mm per hour. The material forming the
insert may be between 40 and 60% SiAlON material and the remainder
hBN material, or mullite material as described by FIG. 11, or
between about 60 and 63 mole percent Al.sub.2O.sub.3 and the
remainder SiO.sub.2, or fused silica, such as between 40 and 60%
fused SiO.sub.2 and the remainder hBN material.
Inventors: |
ONDROVIC; Jay Jon;
(Brownsburg, IN) ; DENO; Alan J.; (Jamestown,
IN) ; SCHLICHTING; Mark; (Crawfordsville, IN)
; MAHAPATRA; Rama Ballav; (Brighton-Le-Sands,
AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NUCOR CORPORATION |
Charlotte |
NC |
US |
|
|
Assignee: |
NUCOR CORPORATION
Charlotte
NC
|
Family ID: |
49877618 |
Appl. No.: |
13/928558 |
Filed: |
June 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61666918 |
Jul 1, 2012 |
|
|
|
Current U.S.
Class: |
164/418 |
Current CPC
Class: |
B22D 11/0622 20130101;
B22D 11/066 20130101 |
Class at
Publication: |
164/418 |
International
Class: |
B22D 11/06 20060101
B22D011/06 |
Claims
1. A composite side dam for a continuous twin roll caster
comprising: (a) a substrate shaped to form a side dam and made of a
refractory material capable of withstanding casting temperature in
a twin roll caster and having edge portions adapted to engage end
portions of casting rolls and having a nip portion adapted to be
adjacent a nip between casting rolls and upper portions extending
across the side dam to form a lateral restraint for a casting pool
of molten metal during operation in a twin roll caster, (b) an
insert of at least 10 mm in thickness positioned in a pocket in the
substrate and extending to engage the molten metal in operation of
a twin roll caster and extending from the upper portions of the
substrate such that the insert can be positioned in the pocket to
within 30 mm from the nip portion of the substrate by insertion
adjacent the upper portions of the substrate to engage end portions
of the casting rolls during operation of the twin roll caster, and
(c) the insert adapted to fit into the pocket of the substrate to
form a side dam formed of a refractory material having consumption
rate less than 10 mm per hour.
2. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the material forming the insert is
comprised of SiAlON material.
3. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the material forming the insert is between
40 and 60% SiAlON material and the remainder hBN material.
4. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the material forming the insert is
comprised of mullite material as described by FIG. 11.
5. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the material forming the insert is between
about 60 and 63 mole percent Al.sub.2O.sub.3 and the remainder
SiO.sub.2.
6. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the material forming the insert is
comprised of fused silica material.
7. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the material forming the insert is between
40 and 60% fused SiO.sub.2 and the remainder hBN material.
8. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the consumption rate of the refractory
material forming the insert is at least as great as the wear rate
of said material.
9. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the insert is between 10 mm and 40 mm in
thickness.
10. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the insert is between 10 mm and 40 mm in
thickness.
11. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the insert is between 10 mm and 40 mm in
thickness.
12. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the insert is between 10 mm and 40 mm in
thickness.
13. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the insert is a firm fit positioned in the
pocket.
14. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the insert is a firm fit positioned in the
pocket.
15. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the insert is a firm fit positioned in the
pocket.
16. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the insert is a firm fit positioned in the
pocket.
17. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
18. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
19. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
20. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
21. The composite side dam for a continuous twin roll caster as
claimed in claim 13 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
22. The composite side dam for a continuous twin roll caster as
claimed in claim 14 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
23. The composite side dam for a continuous twin roll caster as
claimed in claim 15 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
24. The composite side dam for a continuous twin roll caster as
claimed in claim 16 where the insert has edge portions of a reverse
angle of at least 3.degree. to engage edge portions of the pocket
in the substrate.
25. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the insert is positioned in the pocket
with a ceramic cement.
26. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the insert is positioned in the pocket
with a ceramic cement.
27. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the insert is positioned in the pocket
with a ceramic cement.
28. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the insert is positioned in the pocket
with a ceramic cement.
29. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the thickness of the insert is greater
than depth of the pocket.
30. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the thickness of the insert is greater
than depth of the pocket.
31. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the thickness of the insert is greater
than depth of the pocket.
32. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the thickness of the insert is greater
than depth of the pocket.
33. The composite side dam for a continuous twin roll caster as
claimed in claim 1 where the insert extends toward the nip portion
to allow at least a 2.5 mm radius in the insert adjacent nip
portions of the side dam.
34. The composite side dam for a continuous twin roll caster as
claimed in claim 2 where the insert extends toward the nip portion
to allow at least a 2.5 mm radius in the insert adjacent nip
portions of the side dam.
35. The composite side dam for a continuous twin roll caster as
claimed in claim 4 where the insert extends toward the nip portion
to allow at least a 2.5 mm radius in the insert adjacent nip
portions of the side dam.
36. The composite side dam for a continuous twin roll caster as
claimed in claim 6 where the insert extends toward the nip portion
to allow at least a 2.5 mm radius in the insert adjacent nip
portions of the side dam.
37. Apparatus for continuously casting metal strip comprising: (a)
a pair of counter-rotatable casting rolls laterally positioned to
form a nip there between through which thin strip can be cast, (b)
a pair of confining side dams adjacent the ends of the casting
rolls capable of confining a casting pool of molten metal supported
on the casting rolls and formed on the casting surfaces above the
nip, (c) each side dam is a composite comprising a substrate made
of a refractory material capable of withstanding casting
temperature and extending from the upper portions of the substrate
to a nip portion adapted to be adjacent a nip between casting rolls
and such that the insert can be positioned in the pocket by
insertion adjacent the upper portions of the substrate to engage
end portions of the casting rolls to within 30 mm from the nip
portion of the substrate during operation of the twin roll caster,
and an insert of at least 10 mm in thickness positioned in a pocket
in the substrate and extending to engage the molten metal and the
end portions of the casting rolls in operation of the twin roll
caster, and the insert adapted to fitted into the pocket of the
substrate to form the side dam formed of a material having a
consumption rate less than 10 mm per hour, and (d) a metal delivery
system disposed above the nip and capable of discharging molten
metal to form the casting pool supported on the casting rolls.
38. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert of the substrate
is comprised of SiAlON material.
39. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert of the substrate
is between 40 and 60% SiAlON material and the remainder hBN
material.
40. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert is mullite
material as defined by FIG. 11.
41. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert between about 60
and 63 mole percent Al.sub.2O.sub.3 and the remainder
SiO.sub.2.
42. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert of the substrate
is comprised of fused silica material.
43. The apparatus for continuously casting metal strip as claimed
in claim 37 where the material forming the insert of the substrate
is between 40 and 60% fused SiO.sub.2 and remainder hBN
material.
44. The apparatus for continuously casting metal strip as claimed
in claim 37 where the consumption rate of the refractory material
forming the insert is at least as great as the wear rate of said
material.
45. The apparatus for continuously casting metal strip as claimed
in claim 37 where the insert of the substrate is between 10 mm and
40 mm in thickness.
46. The apparatus for continuously casting metal strip as claimed
in claim 38 where the insert of the substrate is between 10 mm and
40 mm in thickness.
47. The apparatus for continuously casting metal strip as claimed
in claim 40 where the insert of the substrate is between 10 mm and
40 mm in thickness.
48. The apparatus for continuously casting metal strip as claimed
in claim 42 where the insert of the substrate is between 10 mm and
40 mm in thickness.
49. The apparatus for continuously casting metal strip as claimed
in claim 37 where the insert is a firm fit positioned in the pocket
of the substrate.
50. The apparatus for continuously casting metal strip as claimed
in claim 38 where the insert is a firm fit positioned in the pocket
of the substrate.
51. The apparatus for continuously casting metal strip as claimed
in claim 40 where the insert is a firm fit positioned in the pocket
of the substrate.
52. The apparatus for continuously casting metal strip as claimed
in claim 42 where the insert is a firm fit positioned in the pocket
of the substrate.
53. The apparatus for continuously casting metal strip as claimed
in claim 37 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
54. The apparatus for continuously casting metal strip as claimed
in claim 38 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
55. The apparatus for continuously casting metal strip as claimed
in claim 40 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
56. The apparatus for continuously casting metal strip as claimed
in claim 49 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
57. The apparatus for continuously casting metal strip as claimed
in claim 50 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
58. The apparatus for continuously casting metal strip as claimed
in claim 51 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
59. The apparatus for continuously casting metal strip as claimed
in claim 55 where the insert has edge portions of a reverse angle
of at least 3.degree. to engage edge portions of the pocket in the
substrate.
60. The apparatus for continuously casting metal strip composite
side dam as claimed in claim 37 where the insert of the substrate
is positioned in the pocket with a ceramic cement.
61. The apparatus for continuously casting metal strip as claimed
in claim 38 where the insert of the substrate is positioned in the
pocket with a ceramic cement.
62. The apparatus for continuously casting metal strip as claimed
in claim 40 where the insert of the substrate is positioned in the
pocket with a ceramic cement.
63. The apparatus for continuously casting metal strip as claimed
in claim 42 where the insert of the substrate is positioned in the
pocket with a ceramic cement.
64. The apparatus for continuously casting metal strip as claimed
in claim 37 where the thickness of the insert of the substrate is
greater than depth of the pocket.
65. The apparatus for continuously casting metal strip as claimed
in claim 38 where the thickness of the insert of the substrate is
greater than depth of the pocket.
66. The apparatus for continuously casting metal strip as claimed
in claim 40 where the thickness of the insert of the substrate is
greater than depth of the pocket.
67. The apparatus for continuously casting metal strip as claimed
in claim 42 where the thickness of the insert of the substrate is
greater than depth of the pocket.
68. The apparatus for continuously casting metal as claimed in
claim 37 where the insert of the substrate extends toward the nip
portion to allow at least a 2.5 mm radius in the insert adjacent
nip portions of the side dam.
69. The apparatus for continuously casting metal as claimed in
claim 38 where the insert of the substrate extends toward the nip
portion to allow at least a 2.5 mm radius in the insert adjacent
nip portions of the side dam.
70. The apparatus for continuously casting metal as claimed in
claim 40 where the insert of the substrate extends toward the nip
portion to allow at least a 2.5 mm radius in the insert adjacent
nip portions of the side dam.
71. The apparatus for continuously casting metal as claimed in
claim 42 where the insert of the substrate extends toward the nip
portion to allow at least a 2.5 mm radius in the insert adjacent
nip portions of the side dam.
Description
BACKGROUND AND SUMMARY
[0001] This invention relates to the casting of metal strip by
continuous casting in a twin roll caster.
[0002] In a twin roll caster, molten metal is introduced between a
pair of counter-rotated casting rolls that are cooled so that metal
shells solidify on the moving roll surfaces and are brought
together at a nip between them. The term "nip" is used herein to
refer to the general region at which the rolls are closest
together. The molten metal may be delivered from a ladle into a
smaller vessel or series of smaller vessels from which it flows
through a metal delivery nozzle located above the nip, forming a
casting pool of molten metal supported on the casting surfaces of
the rolls immediately above the nip and extending along the length
of the nip. As the molten metal formed into shells are joined and
pass through the nip between the casting rolls, a thin metal strip
is cast downwardly from the nip.
[0003] The casting pool is usually confined between side dams held
in sliding engagement with end surfaces of the casting rolls so as
to constrain the two ends of the casting pool against outflow. Side
dams at the ends of the casting rolls prevent leakage of molten
metal from the casting pool and maintain the casting pool at a
desired depth. As the casting rolls are rotated, the side dams
experience frictional wear, causing arc-shaped grooves to form in
the side dams along the circumferential surfaces of the casting
rolls. In order to compensate for this wear, the side dams are
movable to gradually shift inward under compression forces while
having the side dams biased against the ends portions of the
casting rolls in order to maintain a seal with the casting
rolls.
[0004] When casting steel strip in a twin roll caster, the thin
cast strip leaves the nip at very high temperatures, of the order
of 1400.degree. C. If exposed to normal atmosphere, it will rapidly
form scale by oxidation at such high temperatures. A sealed
enclosure that contains an atmosphere that inhibits oxidation of
the strip is therefore provided beneath the casting rolls to
receive the thin cast strip, and through which the strip passes
away from the strip caster. The oxidation inhibiting atmosphere may
be created by injecting a non-oxidizing gas, for example, an inert
gas such as argon or nitrogen, or combustion exhaust reducing
gases. Alternatively, the enclosure may be substantially sealed
against ingress of an ambient oxygen-containing atmosphere during
operation of the strip caster, and the oxygen content of the
atmosphere within the enclosure is reduced during an initial phase
of casting, by allowing oxidation of the strip to extract oxygen
from the sealed enclosure as disclosed in U.S. Pat. Nos. 5,762,126
and 5,960,855.
[0005] The length of a casting campaign of a twin roll caster has
been generally determined in the past by the useful life of the
core nozzle, tundish and side dams. Multi-ladle sequences can be
continued by use of a turret allowing sequential ladles of molten
metal to be transferred to the operating position. The focus in
extending casting campaigns, therefore, has been extending the
useful life of the core nozzle, tundish and side dams, and in turn
reducing the cost per ton of casting thin strip. Wear and
replacement of the side dams has usually limited the casting
campaign, where the casting campaign was typically stopped and the
worn side dams replaced. The core nozzles and tundish with
remaining useful life were typically replaced at the same time so
the length of the next campaign is not limited, with attendant
waste of useful life of refractories and increased cost of casting
steel. In the past, one focus has been on improving refractory
materials. Graphitized alumina, boron nitride and boron
nitride-zirconia composites are examples of suitable refractory
materials for the side dams, tundish and core nozzle components.
SiAlON (i.e, silicon alumina oxy-nitride) refractory material has
also been proposed for use in making side dams.
[0006] Also, the side dams wear independently of the core nozzles
and tundish, and independently of each other. The side dams must
initially be urged against the ends of the casting rolls under
biasing forces, and "worn-in" to be adequately seated against
outflow of molten steel from the casting pool. The biasing forces
applied to the side dams may be reduced after an initial wear-in
period, but there continued to be significant wear of the side dams
throughout the casting operation. The useful life of the side dams
has remained a limiting factor in the length of casting campaigns
and the cost of casting thin strip. The core nozzle and tundish
components in the metal delivery system could have a longer life
than the side dams, and could normally continue operating through
several additional ladles of molten steel supplied extending the
casting campaign and dramatically reducing the cost of casting thin
strip.
[0007] Disclosed is a composite side dam for a continuous twin roll
caster substantially increasing the use life of the side dams and
reducing the cost of casting thin strip. The composite side dam
comprises a substrate shaped to form a side dam and made of a
refractory material capable of withstanding casting temperature in
a twin roll caster. The substrate has edge portions adapted to
engage end portions of casting rolls, and has a nip portion adapted
to be adjacent a nip between casting rolls and has upper portions
extending cross the side dam to form a lateral restraint for a
casting pool of molten metal during operation in a twin roll
caster. An insert of at least 10 mm in thickness is positioned in a
pocket provided in the substrate to engage the molten metal in
operation of a twin roll caster and extend from the upper portions
of the substrate to within 30 mm from the nip portion of the
substrate, by insertion adjacent the upper portions of the
substrate to engage end portions of the casting rolls during
operation of the twin roll caster. The insert is adapted to fit
into the pocket of the substrate to form a side dam formed of a
refractory material having consumption rate less than 10 mm per
hour.
[0008] The material forming the insert may be comprised of SiAlON
material and may be between 20 and 60% SiAlON material and the
remainder may be hBN (i.e, hexagonal boron nitride) material. The
material forming the insert alternatively may be comprised of
mullite material defined by FIG. 11 (between about 60 and 63 mole
percent Al.sub.2O.sub.3 and the remainder SiO.sub.2). The material
forming the insert also alternatively may be comprised of fused
silica material between 20 and 60% fused SiO.sub.2 and the
remainder hBN. The consumption rate due to contact with molten
metal of the refractory material forming the insert may be at least
as great as the wear rate due to abrasive contact with the casting
rolls of the material forming the substrate.
[0009] The insert may be between 10 mm and 40 mm in thickness, and
may have a thickness greater than a depth of the pocket in the
substrate. The insert may have edge portions of a reverse angle of
at least 3.degree. to engage edge portions of the pocket in the
substrate. Further, the insert may have a firm fit in the pocket of
the substrate. Alternatively or in addition, the insert may be
positioned in the pocket of the substrate with a ceramic cement.
Additionally, the insert may extend toward the nip portion to allow
at least a 2.5 mm radius in the insert adjacent nip portions of the
side dam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A-1G illustrate various aspects of an exemplary
continuous twin roll caster system.
[0011] FIG. 2 illustrates an exemplary embodiment of a side dam
holder, used in the system of FIGS. 1A-1G.
[0012] FIG. 3A is a front view of a side dam used in the system of
FIGS. 1A-1G.
[0013] FIG. 3B is a top view of the side dam shown in FIG. 3A.
[0014] FIG. 3C is an isometric view showing the back side of the
side dam shown in FIG. 3A.
[0015] FIG. 4 is an exploded assembly view of the side dam of FIGS.
3A-3C.
[0016] FIG. 5 is a back view of two actual side dams previously
used similar to the side dam of FIGS. 3A-3C.
[0017] FIG. 6 is a front view of the two side dams shown FIG. 5
after use in a twin roll caster system.
[0018] FIG. 7 is an enlarged view of a portion of one of the side
dams shown in FIG. 6.
[0019] FIG. 8 is a table reporting measured number of snake eggs
with each coil of thin cast strip through a number of heats in a
casting campaign adjacent the operator side and drive side side
dams with previous side dams and the presently described side
dams.
[0020] FIG. 9 is a graph showing snake eggs recorded during the
casting campaign reported in FIG. 8, along with coil sequence
during the campaign.
[0021] FIG. 10 shows two actually used side dams: on the left a
side dam of a previous design and on the right a side dam of the
present invention taken during the same casting sequence.
[0022] FIG. 11 is a graph defining mullite material for the present
invention.
[0023] FIG. 12 shows two graphs comparing the number of snake eggs
in a casting campaign using previous side dams and composite side
dams of the present invention.
[0024] FIG. 13 shows two graphs comparing the number of snake eggs
in a casting campaign using previous side dams and composite side
dams of the present invention.
[0025] FIG. 14 shows two graphs comparing the number of snake eggs
in a casting campaign using previous side dams and composite side
dams of the present invention.
DETAILED DESCRIPTION
[0026] FIGS. 1A-1G illustrate various aspects of an exemplary
continuous twin roll caster system. The illustrative twin roll
caster comprises a twin roll caster denoted generally as 11
producing a cast steel strip 12 which passes within a sealed
enclosure 10 to a guide table, which guides the strip to a pinch
roll stand 14 through which it exits the sealed enclosure 10. The
seal of the enclosure 10 may not be complete, but appropriate to
allow control of the atmosphere within the enclosure and limit
access of oxygen to the cast strip within the enclosure as
hereinafter described. After exiting the sealed enclosure 10, the
strip may pass through other sealed enclosures and may be subjected
to in-line hot rolling and cooling treatment.
[0027] Twin roll caster 11 comprises a pair of laterally positioned
casting rolls 22 forming a nip 15 there between, to which molten
metal from a ladle 23 is delivered through a metal delivery system
24. Metal delivery system 24 comprises a tundish 25, a removable
tundish 26 and one or more core nozzles 27 which are located
between the casting rolls above the nip 15. The molten metal
delivered to the casting rolls forms casting pool 16 supported on
the casting surfaces of the casting rolls 22 above the nip 15. The
casting pool of molten steel is confined at the portions ends of
the casting rolls 22 by a pair of side dams 35, which engage the
end portions of the rolls by operation of a pair of hydraulic
cylinder units 36 acting through thrust rods 50 connected to side
dam holders 37.
[0028] The casting rolls 22 are internally water cooled by coolant
supply and driven in counter rotational direction by drives, so
that metal shells solidify on the moving casting roll surfaces as
the casting surfaces move through the casting pool 16. These metal
shells are brought together at the nip 15 to produce the thin cast
strip 12, which is delivered downwardly from the nip 15 between the
rolls.
[0029] Tundish 25 is fitted with a lid 28. Molten steel is
introduced into the tundish 25 from ladle 23 via a shroud 29. The
tundish 25 is fitted with a slide gate valve 34 to selectively open
and close the outlet 31 and effectively control the flow of metal
from the tundish to the removable tundish 26. The molten metal
flows from tundish 25 through an outlet 31 through a shroud 29 to
removable tundish 26 (also called the distributor vessel or
transition piece), and then to core nozzles 27. At the start of a
casting operation a short length of imperfect strip is produced as
the casting conditions stabilize. After continuous casting is
established, the casting rolls are moved apart slightly and then
brought together again to cause the leading end of the strip to
break away so as to form a clean head end of the following cast
strip to start the casting campaign. The imperfect head end of the
strip drops into a scrap box receptacle 40 located beneath caster
11 and forming part of the enclosure 10 as described below. At this
time, swinging apron 38, which normally hangs downwardly from a
pivot 39 to one side in enclosure 10, is swung across the strip
outlet from the nip 15 to guide the head end of the cast strip onto
guide table 13, which feeds the strip to the pinch roll stand 14.
Apron 38 is then retracted back to its hanging position to allow
the strip to hang in a loop beneath the caster, as shown in FIGS.
1B and 1D, before the strip passes to the guide table where it
engages a succession of guide rollers.
[0030] The twin roll caster illustratively may be of the kind which
is illustrated in some detail in U.S. Pat. Nos. 5,184,668 and
5,277,243, and reference may be made to those patents for
appropriate constructional details.
[0031] Referring to FIGS. 1E and 1G, the support assembly for the
side dams 35 is shown. The first enclosure wall section 41
surrounds the casting rolls 22 and is formed with side plates 64
provided with cut-out shaped to snugly receive and support the side
dam plate holders 37, which in turn support the side dams 35 that
are pressed against the ends portions of casting rolls 22 by the
cylinder units 36. The interfaces between the side dam holders 37
and the enclosure side wall sections 41 are sealed by sliding seals
66 to maintain sealing of the enclosure 10. Seals 66 may be formed
of ceramic fiber rope or other suitable sealing material. The
cylinder units 36 extend outwardly through the enclosure wall
section 41, and at these locations the enclosure is sealed by
sealing plates 67 fitted to the cylinder units so as to engage with
the enclosure wall section 41 when the cylinder units are actuated
to press the pool closure plates against the ends of the casting
rolls. Cylinder units 36 also move refractory slides 68 which are
moved by the actuation of the cylinder units to close slots 69 in
the top of the enclosure, through which the side dams 35 are
initially inserted into the enclosure 10 and into the holders 37
for application to the casting rolls. The top of the sealed
enclosure 10 is closed by the tundish 26, the side dam holders 37
and the slides 68 when the cylinder units are actuated to urge the
side dams 35 against the casting rolls 22.
[0032] When it is determined that the side dams 35 need to be
change, typically due to wear, a preheating sequence is commenced.
The core nozzle 27 and the removable tundish 26 are also typically
replaced at the same time. This preheating of the second tundish
26' and second core nozzle 27' is started while casting is
continuing at least 2 hours before transfer to the replacement
sequence, and the preheating of the second side dams 35' is started
at least 0.5 hours before transfer to the replacement sequence.
This preheating is done in preheating heaters 50, 54 and 57,
typically preheating chambers, in locations convenient to the
caster 11, but removed from the operating position of the
refractory components during casting.
[0033] During this preheating of the replacement refractory
component, casting typically continues without interruption. When
the refractory component to be replaced (namely, the tundish 26,
the core nozzle 27 and the side dams 35), the slide gate 34 is
closed and the tundish 26, the core nozzle 27 and the casting pool
16 are drained of molten metal. Typically, the tundish 26' and side
dams 35' are preheated and replaced as individual refractory
components, and the core nozzle is preheated and replaced as a
singular or two piece refractory component, but in particular
embodiments may be preheated and replaced in pieces or parts as
those portions of the refractory component are worn or otherwise
need to be replaced.
[0034] When the preheating is completed and the change in side dams
is to take place, the slide gate 34 is closed and the tundish 26,
core nozzle 27 and casting pool 16 are drained and casting is
interrupted. A pair of transfer robots 55 remove the first side
dams 35 from the operating position, and then a pair of transfer
robots 56 transfer the second side dams 35' from the preheating
chamber 57 to the operating position. Note that transfer robots 55
and 56 may be the same as shown in FIG. 1A if there is a place for
the transfer robots to rapidly set aside the removed first side
dams 35. However, to save time in removing the side dams 35 and
positioning the second side dams 35' in the operating position, two
pairs of transfer robots 55 and 56 may be employed. Following
positioning of the second side dams 35' in the operating position,
the side gate 34 is opened to fill the tundish 26 and core nozzle
27 and form casting pool 16, and continue casting.
[0035] Each transfer robot 55 and 56 is a robot device known to
those skilled in the art with gripping arms 70 to grip the core
nozzle 27 or 27' typically in two parts, or side dams 35 or 35'.
The transfer robots can be raised and lowered and also moved
horizontally along overhead tracks to move the core nozzle or the
side dams from a preheating chamber at a separate location from the
operating position to the caster for downward insertion of the
plates through the slots 69 into the holders 37. Gripping arms 70
are also operable to remove at least portions of worn core nozzle
27 or side dams 35. The step of removing the worn side dams 35 is
done by operating cylinder unit 36 to withdraw the thrust rod 50
sufficiently to open the slot 69 and to bring side dam 35 into
position directly beneath that slot, after which the gripping arm
70 of the transfer robot 55 can be lowered through the slot to grip
the side dam 35 and then raised to withdraw the worn side dam. The
side dams 35 may be removed when they become worn to specified
limits as will be explained further below, and may be removed one
at a time as worn to a specified limit. During a casting run and at
a time interval before the side dams 35 have worn down to an
unserviceable level, the wear rate of the side dams 35 may be
monitored by sensors, and the preheating of replacement side dams
35' is commenced in preheat furnaces at preheating chamber 57
separate from the caster 11.
[0036] To change the side dams 35, when the molten steel is drained
from the metal delivery system and casting pool, cylinder units 36
are operated to retract the side dam holders 37 and to bring the
side dams 35 directly beneath the slots 69 which are opened by the
retraction movement of the slides 68. Transfer robots may then be
lowered such that their gripping arms 70 can grip the side dams 35
and raised and remove those worn side dams, which can then be
dumped for scrap or refurbishment. The transfer robots are then
moved to the preheat chambers where they pick up the replacement
side dams 35' and move them into position above the slots 69 and
the retracted side dam holders 37. Side dams 35' are then lowered
by the transfer robots into the plate holders, the transfer robots
are raised and the cylinder units 36 operated to urge the preheated
replacement side dams 35' against the end of the casting rolls 22
and to move the slides 68 to close the enclosure slots 69. The
operator then actuates slide gate 34 to initiate resumption of
casting by pouring molten steel into tundish 26 and core nozzle 27,
to initiate a normal casting operation in a minimum of time.
[0037] It may be desirable to replace a side dam or dams 35 when
worn to specified limits, such as when the dam(s) become or will
become unserviceable. For example, the wear of the side dams may be
monitored by means of load/displacement transducers mounted on
cylinders 36. The cylinders will generally be operated so as to
impose a relatively high force on the side dams 35 during an
initial bedding-in period in which there will be a higher wear rate
after which the force may be reduced to a normal operating force.
The output of the displacement transducers on cylinders 36 can then
be analyzed by a control system, usually including a computerized
circuit, to establish a progressive wear rate and to estimate a
time at which the wear will reach a level at which the side plates
become unserviceable. The control system is responsive to the
sensors to determine the time at which preheating of replacement
side dams must be initiated prior to interrupting the cast for
replacement of the side dams.
[0038] FIG. 2 illustrates an exemplary embodiment of a side dam
holder 37 for use in the continuous casting system. The side dam
holder 37 is used in the system of FIGS. 1A-1G, in accordance with
various aspects. The side dam holder 37 includes three attachment
portions 210, 220, and 230. In the embodiment shown in FIG. 2, the
attachment portions 210, 220, and 230 are notches or troughs
(typically stainless steel) that are capable of receiving and
supporting a side dam without exposed portions of the side dam
holder 37 extending substantially beyond an outer surface of the
side dam adjacent the side dam holder.
[0039] A composite side dam 35 for the continuous twin roll caster
11 embodying the present invention is shown in FIGS. 3A, 3B, and
3C. The composite side dam comprises a substrate 72 shaped to form
a side dam and made of a refractory material such as boron nitride
zirconium capable of withstanding casting temperatures in a twin
roll caster. The substrate 72 has edge portions 74 adapted to
engage end portions of casting rolls 22, and has a nip portion 76
adapted to be adjacent the nip 15 between casting rolls 22. The
substrate also has a pocket 82 into which an insert 80 is fitted as
described below, and has upper portions 78 extending cross the
pocket 82 of side dam 35 to form a lateral restraint for a casting
pool 16 of molten metal during operation in the twin roll caster
11.
[0040] FIG. 4 is an exploded assembly view of the side dam of FIGS.
3A-3C illustrating the assembly of the insert 80 into the pocket 82
of the substrate 72.
[0041] FIGS. 5, 6 and 7 show side dams as shown in FIGS. 3A-3C
showing how the side dams wear with use in a campaign to make thin
strip in a twin roll caster. Specifically, FIG. 5 shows a back view
of a pair of actual side dams similar to the side dam illustrated
in FIGS. 3A-3C previously used in a casting campaign to make thin
steel strip. FIG. 6 is a front view of the pair of side dams shown
in FIG. 5 after use in a campaign in a twin roll caster to make
thin steel strip. And FIG. 7 is an enlarged view of a portion of
one of the side dams shown in FIG. 6 showing a close up of the wear
adjacent nip 15 of the side dam after use in a casting
campaign.
[0042] As shown in FIGS. 3A through 7, the insert 80 is of at least
10 mm in thickness and may be positioned in a pocket 82 in the
substrate 72. The insert 80 is adapted to engage molten metal in
the casting pool in operation of the twin roll caster 11. The
insert 80 extends from the upper portions engaging upper portions
78 of substrate 72 such that the insert 80 can be positioned in the
pocket 82 to within 30 mm from the nip portion 76 (as shown in FIG.
7) by insertion adjacent the upper portions 78 of the substrate 72
as shown in FIG. 4, and adapted to engagement of the casting rolls
22 during operation of the twin roll caster 11. The insert 80 may
extend to between 15 to 25 mm from the nip portion 76 of the
substrate 72, and in any event, may extend toward the nip portion
76 to allow at least a 2.5 mm radius R in the insert 80 adjacent
nip portions of the side dam 35.
[0043] The insert 80 is formed of a refractory material that may
have a consumption rate less than 10 mm per hour, and in any event,
at least as great as the consumption rate to the substrate 72. The
material forming the insert 80 comprises a SiAlON material. The
material forming the insert 80 may be between 20 and 60% SiAlON
material and the remainder hBN material. In another embodiment the
material forming the insert 80 alternatively may be comprised of
mullite material defined by FIG. 11 (between about 60 and 63 mole
percent Al.sub.2O.sub.3 and the remainder SiO.sub.2). In a further
embodiment, the material forming the insert 80 may be between 20
and 60% fused SiO.sub.2 and the remainder hBN material. The
consumption rate of the refractory material forming the insert 80
should be at least as great as the wear rate of the material of the
refractory forming the substrate 72.
[0044] As shown in FIG. 4, the insert 80 may have a thickness
between 10 mm and 40 mm. The insert 80 also may have a thickness
greater than a depth of the pocket 82 in the substrate 72. The
insert 80 may have edge portions 84 of a reverse angle J of at
least 3.degree. to engage edge portions 86 of the pocket 82 in the
substrate 72. The reverse angle J may be between 3.degree. and
5.degree.. The insert 80 may form a firm fit when positioned in the
pocket 82 so that the insert 80 is held in position to form with
the substrate 72 the composite side dam 35 without ceramic cement
or other adherent binder. Alternatively, the insert 80 may also
have a ceramic pin or screw 88 as shown in FIG. 5 extending through
the substrate 72 into the insert 80 to hold the insert 80 in firm
engagement with substrate 72. Also, in addition or in the
alternative, the insert 80 may be held in position in the pocket 82
with a ceramic cement.
[0045] Generally, in campaigns in casting thin strip, solidified
skulls may form from time to time adjacent the side dam and also
the delivery nozzle when the distance between the side dam and
nozzle is not maintained. These skulls may also be formed on the
side dams surfaces protruding into the casting pool beyond the
casting rolls surfaces. When these skulls drop through the roll
nip, they may cause the two solidifying shells at the casting roll
nip to separate and "swallow" additional liquid steel between the
shells causing the strip surface to reheat and, in extreme cases,
may cause the strip to break disrupting the continuous production
of coiled strip. These dropped skulls formed in the cast strip are
known as "snake eggs." In any event, snake eggs can cause defects
to occur in the cast strip. The snake eggs are detected as lateral
force spikes on the side dams at the roll nip, as well as visible
bright bands across the width of the cast strip. Snake eggs usually
apply resistive forces against the side dam, in addition to the
forces on the side dam generated by the ferrostatic head in the
cast pool, and can cause the side dam to lift from the casting roll
edge resulting in the leakage of steel between the side dam and the
casting roll. Snake eggs passing through the nip between the
casting rolls may cause lateral movement of the casting rolls along
with upward movement in the side dams. To resist the increased
forces generated by the snake eggs, the side dams are typically
biased toward the casting rolls with appropriate higher lateral
forces.
[0046] An advantage of the present invention can be seen by FIGS. 8
and 9. FIG. 8 shows the snake egg count adjacent the side dams and
the protruding surfaces of the side dams on both the operator side
and the drive side of the caster for each coil during the casting
campaign. As shown in FIGS. 8 and 9, measurements were taken and
reported on both the drive side and the operator side of snake eggs
of more than 2 kN in force, more than 3 kN in force, and more than
5 kN in force. As indicated by the brackets, during the first part
of the campaign the side dams were of the previous design of solid
refractory, and during the latter part of the campaign composite
side dams of the present invention were employed. As shown by FIG.
8, snake egg numbers as high as 50, 60 and 111 of force greater
than 2 kN were reported for coils where side dams of the previous
solid design were used. Whereas, snake egg numbers never greater
than 9 or 11 were reported where composite side dams of the present
invention were used. Note that with both of the side dams of the
previous design and side dams of the present invention the larger
numbers of snake eggs occurred toward the end of the use of the
side dam. FIG. 9 graphically shows the increase in both amplitude
and number of the snake eggs between using the side dams of the
previous solid design and composite side dams of the present
invention.
[0047] FIG. 10 shows the difference in textures of the side dam, on
the left of the previous solid design and of the side dam on the
right of the presently disclosed composite design. These two side
dams were employed and used in the same casting campaign so a
direct comparison could be made. As seen by comparison, the texture
of the wear on the composite side dam is more even with the present
composite side dams than the wear on the previous side dam of a
solid design.
[0048] Referring to FIGS. 12, 13, and 14, a comparison of the snake
eggs count adjacent to the side dam at the start up of the sequence
and at the tail out of the sequence when using side dams of a
previous design and composite side dams of the current invention is
shown. In FIG. 12 is shown the average snake egg count and spread
of snake eggs where the force exerted by the snake eggs in roll
separation is greater than 2 kN for the previous standard of solid
side dams (as described above) and the composite sides of the
present invention. In FIG. 13 is shown the average snake egg count
and the spread of snake eggs where the force exerted by the snake
eggs is between 3 and 5 kN for the previous standard of solid side
dams (as described above) and the composite sides of the present
invention. And in FIG. 14 is shown the average snake egg count and
spread of snake eggs where the force exerted by snake eggs is
greater than 5 kN for the previous standard of solid side dams (as
described above) and the composite sides of the present invention.
In each case, the number of snake eggs and the force spread exerted
by the snake eggs was greatly reduced with use of the composite
side dams of the present invention.
[0049] Specifically, in FIG. 12 an average of 70 snake eggs and a
spread of 65 to 75 snake eggs of greater than 2 kN force were
reported for campaigns where side dams of the previous solid design
(or standard) were used. Whereas, the average number of snake eggs
was 8 and a spread of 5 to 15 snake eggs of greater than 2 kN force
were reported where composite side dams of the present invention
were used.
[0050] In FIG. 13 an average of 21.27 snake eggs and a spread of 17
to 25 snake eggs of between 3 and 6 kN force were reported for
campaigns where side dams of the previous solid design (or
standard) were used. Whereas, the average number of snake eggs was
2.75 and a spread of 1 to 5 snake eggs of between 3 and 6 kN force
where composite side dams of the present invention were used.
[0051] In FIG. 14 an average of 3.66 snake eggs and a spread of 3
to 4.3 snake eggs of greater than 5 kN force were reported for
campaigns where side dams of the previous solid design (or
standard) were used. Whereas, the average number of snake eggs of
0.51 and a spread of 0.2 to 0.8 snake eggs of greater than 5 kN
force were reported where composite side dams of the present
invention were used.
[0052] The increase in yield was also dramatic between the use of
the previous solid standard side dams and the composite side dams
of the present invention. The comparative results are set forth in
Tables 1 and 2 below. Table 2 shows an increased in yield when
composite side dams were used compared to side dams of the previous
solid design (Table 1) in both prime from liquid metal and prime
from coiled. Out of the eight comparative sequences presented, five
of the comparative runs encountered problems at the end of the
casting, such as: choking, snakes eggs, and coiler issues. No major
problems were present in the sequences performed using composite
side dams of the present invention.
TABLE-US-00001 TABLE 1 Prime Prime Secondary/ from from Seq Liquid
Coiled Prime (tons) Scrap coiled liquid 6923 581 539 509.9 29.5 95%
88% 6924 347 322 292.2 29.6 91% 84% 6925 585 551 498.5 52.1 91% 85%
6926 536 236 215.4 20.8 91% 40% 6927 347 322 309.0 12.9 96% 89%
6928 574 437 413.7 23.1 95% 72% 6929 347 319 292.4 26.9 92% 84%
6943 452 427 389.6 37.5 91% 86% 3767 3153 2920.7 232.4 93% 78%
TABLE-US-00002 TABLE 2 Prime Prime Secondary/ from from Seq Liquid
Coiled Prime (tons) Scrap coiled liquid 6937 553 518 496.3 21.7 96%
90% 6938 335 314 306.8 7.4 98% 92% 6939 327 307 296.1 10.8 96% 90%
6940 548 518 495.6 22.0 96% 90% 6941 563 533 524.3 8.2 98% 93% 6942
555 528 512.7 15.0 97% 92% 6944 348 319 304.3 14.9 95% 87% 6945 459
338 295.9 41.7 88% 64% 3689 3374 3232.0 141.7 96% 88%
[0053] As seen from the data above, a significant improvement in
yield was reported for castings performed with composite side dams.
The casting sequences performed using side dams of the previous
solid design produced an average yield of 78%. As presented in
Table 2, the casting sequences performed using composite side dams
of the present invention produced a 10% yield increase for an
average yield of 88%.
[0054] While it has been described with reference to certain
embodiments, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted
without departing from scope. In addition, many modifications may
be made to adapt a particular situation or material to the
teachings without departing from its scope. Therefore, it is
intended that it not be limited to the particular embodiments
disclosed, but that it will include all embodiments falling within
the scope of the appended claims.
* * * * *