US3661196A - Method and apparatus for continuously casting hollow rounds - Google Patents

Abstract

A method and apparatus for continuously casting a hollow round for manufacturing seamless tubing. Apparatus includes an openended tubular water-cooled mold and a tubular water-cooled lance suspended within the mold, leaving an annular cavity therebetween. Molten metal is poured into the cavity. Outside and inside skins solidify on the metal, at first leaving a liquid core between the two skins. There is a problem that the inside skin tends not to remain concentric with the outside skin. Invention provides magnetic means acting on plugs within the inside skin to hold the two skins in a concentric relation.

Description

United States Patent [151 3,661,196 Kummant 1 May 9, 1972 54] METHOD AND APPARATUS FOR 2,600,254 6/1952 Lysobey...................,........lS/DIG. 33 CONTINUOUSLY CASTING HOLLOW 3,428,371 2/1969 Lyman.. ..308/l0 ROUNDS 3,487,876 l/l970 Bucci ..l64/282 X [72] inventor: Karl E. Kumrnant, Amherst, Ohio [73] Assignee: United States Steel Corporation [22] Filed: Oct. 2, 1970 [2|] Appl. No.: 77,470

[52] [1.5. CI ..l64/85,164/l48, l64/28l,

164/282, l8/DlG. 33

[5 l] Int. Cl ..B22d 11/02 [58] Field of Search 1 64/85, 146-148, 164/281, 282; l8/DIG. 33

[56] References Cited UNITED STATES PATENTS 2,324,645 7/1943 Prehler ..l8/DlG. 33

- SCILL A 71/18 Ul'tIMN/SI Primary Examiner-Robert D. Baldwin Altorneywalter P. Wood [57] ABSTRACT A method and apparatus for continuously casting a hollow round for manufacturing seamless tubing. Apparatus includes an open-ended tubular water-cooled mold and a tubular water-cooled lance suspended within the mold, leaving an annular cavity therebetween. Molten metal is poured into the cavity. Outside and inside skins solidify on the metal, at first leaving a liquid core between the two skins. There is a problem that the inside skin tends not to remain concentric with the outside skin, Invention provides magnetic means acting on plugs within the inside skin to hold the two skins in a concentric relation.

9 Chins, 7 Drawing Figures CO Qv PATENTEnm 9 m2 ll/ENTOR KARL E. KUHMANT h is Attorney PATENTEDMAY 9:972 3661.196 sum 3 0F 3 LL? FYI; s

INVENTOR POWER sol/RC5 KARL E. KUMMANT re ay fl is A Home METHOD AND APPARATUS FOR CONTINUOUSLY CASTING HOLLOW ROUNDS This invention relates to an improved method and apparatus for continuously casting hollow rounds of metal for manufacture of seamless tubing.

One type of apparatus for continuously casting metal products of solid cross section includes a water-cooled mold open at both ends, trains of vertically spaced guide rolls below the mold, a set of power-driven pinch rolls below the guide rolls, and a curved casting guide below the pinch rolls. Before a casting operation begins, a starter bar is inserted upwardly through the pinch rolls and guide rolls to the mold. A stream of molten metal is poured through the mold into contact with the top of the starter bar, which descends through the guide rolls and pinch rolls ahead of the casting. A skin of metal solidifies on the outside of the casting within the mold, but the core at first remains liquid. As the casting passes the guide rolls, water sprays are applied to its surface, whereby the core progressively solidifies. Initially the leading end of the casting attaches itself to the top of the starter bar, but the starter bar is disconnected as the casting passes through the pinch rolls. At first the pinch rolls restrain descent of the starter bar, but after the casting is part way through the guide rolls, the pinch rolls propel the starter bar and casting. After the starter bar is disconnected, bending rolls within the casting guide bend the casting 90 so that it travels horizontally from there on for further processing. Reference can be made to Foldessy, U.S. Pat. No. 3,338,297 for a more complete showing of such apparatus.

Efforts to apply analogous procedures to the continuous casting of hollow rounds have not been successful. If a lance or mandrel is positioned within the mold to provide an annular cavity in which the hollow round is formed, there is a problem in cooling and solidifying the inside surface of the casting. When an inside skin solidifies, an annular liquid core remains between the inside and outside skins, which core does not solidify throughout until the casting descends a substantial distance below the mold. This leads to another problem that it is difficult to maintain the inside skin in a concentric relation with the outside skin before the intervening core fully solidi fies. Unless the two skins remain concentric, the hollow round does not have walls of uniform thickness, and is not acceptable for manufacture of seamless tubing.

An object of my invention is to provide an improved method and apparatus for continuously casting hollow rounds and overcoming problems encountered heretofore.

A further object is to provide a method and apparatus of the foregoing type in which 1 subject both the inside and outside surfaces of a hollow-round casting to water sprays, and in which I employ an improved technique for maintaining the inside skin in a concentric relation with the outside skin.

A more specific object is to provide an improved method and apparatus for continuously casting hollow rounds in which I employ magnetic means for detecting any eccentricity of the inner skin, and additional magnetic means for correcting such eccentricity.

In the drawings:

FIGS. 1 and 10 together are a vertical sectional view of an apparatus for continuously casting hollow rounds in accordance with my invention;

FIG. 2 is a side elevational view of the mechanism embodied in the apparatus for handling the starter bar;

FIG. 3 is a vertical sectional view of a portion of my novel lance extension and magnetic positioning mechanism for maintaining the inside skin of the casting in concentric relation with the outside skin;

FIG. 4 is an exploded side elevational view, partly in section, of the upper portion of the starter bar and its detachable stool;

FIG. 5 is a horizontal section on line V-V of FIG. 3; and

HG. 6 is a schematic wiring diagram.

FIGS. 1 and la together show an open-ended tubular mold l and a tubular lance 12 extending through the mold. leaving an annular cavity l3 therebetween. The mold is fixed to vertically spaced pairs of beams 14. The lance is suspended from a ball joint 15 carried by a pair of beams 16 spaced above the first-named beams. Oscillating mechanisms 17 and 18 are connected to beams 14 and 16 respectively for oscillating the beams, mold and lance up and down in unison, as is commonly done with molds used for continuously casting products of solid cross section. Since suitable oscillating mechanisms are well known, I have indicated them only diagrammatically. A hollow round casting C is shown emerging from the bottom of the mold. After leaving the mold, the casting passes through conventional guide rolls [9 and water sprays 20. Farther down the casting passes through conventional pinch rolls and bending rolls, not shown.

A refractory lined tundish 21 and one or more refractory lined troughs 22 are supported above the top of mold 10 in the space between the mold and beams 16. The tundish is of U- shape in plan and has a central passage 23 to accommodate lance 12, which passage has a sufficiently large inside dimension not to interfere with oscillation of the lance. The bottom wall of the tundish has pouring nozzles 24 corresponding in number to troughs 22 and positioned above the respective troughs. The tundish contains a supply of molten metal M, which may be introduced from any suitable ladle or the like, not shown. Flow of metal through the nozzles is controlled by gates 25 slidably supported on the bottom of the tundish. The troughs slope downwardly toward the mold to discharge metal continuously into the annular cavity 13 between the mold and lance.

Before I start a casting operation, I insert a tubular starter bar 26 and detachable annular stool 27 into the bottom of the annular cavity 13. FIGS. 2 and 4 show a preferred construction of starter bar and mechanism for handling it. The upper end of the starter bar is of reduced diameter and fits within a groove 28 in the bottom face of the stool. The stool has a plurality of radial bolts 29 which span its groove 28. The upper edge of the starter bar has a series of upwardly open L-shaped slots 35 which receive bolts 29 in their horizontal segments to connect the stool to the starter bar. The upper face of the stool carries a plurality of upstanding bolts 36. As molten metal fills the annular mold cavity 13, the starter bar and stool are withdrawn continuously from the mold. The bolts 36 become embedded in the partially solidified casting and thus attach the stool to the casting. At the proper point in the descent of the casting, l rotate the starter bar through a small arc to disconnect it from the stool. Such rotation aligns the vertical segments of slots 35 with bolts 29. The starter bar then descends more rapidly than the casting and pulls free from its stool 27. The latter continues on with the casting through the bending rolls, etc.

As FIG. 2 shows, the mechanism for handling the starter bar 26 includes a stand 37 located below the guide rolls 19. The upper end of the stand carries a set of pinch rolls 38, motors 39 for driving these pinch rolls and fluid-pressure cylinders 40 for advancing or retracting the pinch rolls into or out of engagement with the starter bar. I mount a table 41 within the lower portion of the stand and connect this table with upstanding fluid-pressure cylinders 42 fixed to the outside of the stand for raising and lowering it. The table carries a rotatable head 43 and a pair of fluid-pressure cylinders 44 connected to the head through suitable linkages or gearing for rotating the head through a small arc in either direction. The head carries a pair of pivoted gripper arms 45. A fluid-pressure cylinder 46 interconnects the two arms. The various cylinders have the usual connections and controls (not shown) for admitting and discharging fluid.

To raise the starter bar 26 preliminary to beginning a casting operation, I operate cylinders 40 to engage the pinch rolls 38 with the starter bar, and I operate motor 39 to drive these pinch rolls. At this time the gripper arms 45 are disengaged from the bar, and I operate cylinders 42 to raise the table 41 and head 43 to their uppermost position. When the casting operation begins, I retract the pinch rolls 38. Just before the lower end of the casting reaches the position at which the starter bar is to be disconnected, I operate cylinder 46 to move the gripper arms 45 into engagement with the starter bar. Thereafter I operate cylinders 44 to rotate the starter bar through the arc necessary to align the vertical segments of slots 35 with bolts 29, as already described. I release the pressure in cylinders 42, whereupon the starter bar drops free.

As FIG. 1 shows, mold includes an internal replaceable sleeve 49, preferably of copper, spaced from its outer wall. Annular horizontal partitions 50 divide the space between the sleeve and the outer wall of the mold into a plurality of comartments 51. Preferably l mount vertically extending annular baffles 52 within these compartments. The lower and upper portions of the compartments have water inlets 53 and 54 respectively. The lance 12 includes an outer replaceable sleeve 55, also preferably of copper, and spaced concentric outermost, intermediate and innermost tubes 56, 57 and 58 within the sleeve. The tubes define water circulating passages between the sleeve and the innermost tube 58. l connect a water inlet 59 and outlet 60 with the upper portions of the outermost tube 56 and intermediate tube 57 respectively. I connect another water inlet 61 with the upper end of the innermost tube 58.

As FIG. 3 shows, I suspend a tubular lance extension 64 from a ball joint 65 at the bottom of lance 12. The lance extension is formed of two sections connected end-to-end with a ball joint 66. The lance extension communicates with the innermost tube 58 of the lance. Water introduced to the innermost tube flows downwardly through this tube and through lance extension and discharges through nozzles 67 in the latter.

With the construction thus far described, molten metal poured into the annular cavity 13 is chilledon its outside by water which circulates around the sleeve 49. This metal is chilled on its inside by water which circulates within sleeve 55, and by water discharging through nozzles 67. Additional water may be sprayed on the outside of the casting beneath the mold through conventional nozzles 20, as already described. This arrangement solidifies outside and inside skins E and l of progressively increasing thickness on the casting, leaving a liquid core L between the two skins. At some distance below the mold the casting solidifies throughout. My invention, as hereinafter described, overcomes a problem that the two skins tend not to remain perfectly concentric as the casting travels between the bottom of the mold and the level at which the casting solidifies throughout.

In accordance with my invention, l mount an annular watercooled plug 68 on the upper section of the lance extension 64 and two similar plugs 69 and 70 on the lower section of the lance extension (FIG. la). The uppermost plug 68 lies just below the ball joint 65 and only a short distance below the mold 10. The lowermost plug 70 lies just above the level at which the product solidifies throughout. The plugs are of magnetic material, preferably mild steel. The inside skin of the casting rides against the plugs, whereby the plugs serve to position this skin.

l mount a first opposed pair of positioning magnets 71 and 71a and a second such pair 72 and 72a opposite the uppermost plug 68 adjacent the outside skin arranged as FIG. 5 shows. Immediately above the two pairs of positioning magnets, l mount similarly arranged pairs of detecting magnets, one pair of which is shown at 73, 73a in FIGS. 1 and 6. l mount similar positioning and detecting magnets opposite each of the other plugs 69 and 70, but I have not repeated the description. Since the casting is hot and above its Curie point, it has negligible magnetic effect even though it may be of ferrous material. lf the inside skin tends to become eccentric at any level, one or more pairs of detecting magnets detect the fact that the corresponding plug 68, 69 or 70 is off-center with respect to the magnets, whereupon the corresponding pair of positioning magnets act to pull the plug back to its centered position and restore concentricity.

l have shown the positioning magnets arranged with their poles in the same horizontal plane, which is the arrangement I use for castings of relatively large diameter (for example 10 inches or more). For smaller diameters, flux leakage and spacer limitations make this arrangement less practical. Hence 1 may place each magnet with its poles in the same vertical plane, one above the other.

FIG. 6 shows schematically the electric circuit in which I connect one pair of positioning magnets 71 and 71a and the corresponding pair of detecting magnets 73 and 73a. The circuits for the other magnets are similar. Magnets 71 and 71a have windings 76 and 76a. Magnets 73 and 73a have windings 77 and 77a. l energize the circuit from a suitable AC power source connected to lines 78.

I connect the primary winding of a transformer 79 across lines 78. 1 connect one end of the secondary winding of the transformer with one end of each winding 77 and 770 on the detecting magnets 73 and 73a through respective capacitors 80 and 80a. 1 connect the other end of the secondary winding with the other end of the windings 77 and 770 through resistors 81 and 81a respectively. I ground this end of the secondary winding, as indicated at 82. I connect a larger resistor 83 and a solid state rectifier 84 in series with each other and in parallel with resistor 81, and a similar resistor 83a and rectifier 84a in parallel with resistor 81a.

As long as plug 68 is centered, the two windings 77 and 770 are in a state of near-resonance with their series capacitors 80 and 80a. The winding and capacitor pass current through resistors 81 and 81a and produce an AC voltage drop therethrough. The addition of resistors 83 and 83a in series with rectifiers 84 and 84a permit pick-up of a DC voltage drop at measuring output terminals 85 and 850. Under a balanced condition terminals 85 and 85a are at equal small positive potential with respect to ground. If, for example, plug 68 is displaced to the left, the air gap between the plug and the detecting magnet diminishes, the inductance of this side of the circuit increases, and the circuit ceases to be in resonance. A smaller current flows through resistor Bl than through resistor 810, thus lowering the positive potential at terminal 85 and raising the potential at terminal 854:.

I connect the power input terminals of DC power amplifiers 88 and 88a across lines 78. l connect the power output terminals of these amplifiers to the respective windings '76 and 76a of the positioning magnets 71 and 710. I connect the control terminals of the amplifiers to terminals 85 and 85a and to grounds as indicated at 89 and 89a. When the potential at terminal 85 drops as described, the current through winding 76 drops and magnet 71a exerts a stronger force on the plug than magnet 7]. In this manner the plug returns to a concentric position and the resonance of the circuit is restored. Similar action takes place at any of the other magnets to maintain the plugs concentric at all times.

From the foregoing description, it is seen that my invention affords a simple reliable method and apparatus for continuously casting hollow rounds and maintaining a uniform wall thickness. The magnetic means assures that the plugs remain centered in the casting and thus prevent any non-uniformity.

lclaim:

l. A method of continuously casting a hollow-round comprising pouring molten metal continuously into an annular mold cavity, cooling the outside and inside surfaces of the metal within the mold and thereby forming outside and inside skins on the hollow-round within the mold leaving a liquid core between said skins, continuously withdrawing the partially solidified hollow-round from the bottom of the mold over water-cooled plugs of magnetic material, continuing the cooling of both surfaces of the hollow-round until the hollowround solidifies throughout at a level spaced below the mold, detecting any eccentricity of the inside skin between said mold and said level, and correcting magnetically with said plugs such eccentricity.

2. A method as defined in claim 1 in which said plugs are acted on magnetically to detect eccentricity of said inside skin.

3. A method as defined in claim 1 in which a tubular starter bar is inserted in said mold from beneath preliminary to commencing a casting operation, and is disconnected from the partially solidified hollow-round by rotating it through a small arc.

4. Apparatus for continuously casting a hollow-round comprising a tubular watercooled mold, a water-cooled lance suspended within said mold leaving an annular cavity therebetween, means for pouring molten metal into said cavity, whereby a partially solidified hollow-round having solidified outside and inside skins and a liquid core emerges from the bottom of said mold, which hollow-round solidifies throughout at a lower level, an extension on said lance below said mold, at least one water-cooled plug of magnetic material on said extension between the bottom of said mold and the level at which the hollow-round solidifies throughout, said plug being of a shape to ride against said inside skin, and magnetic means outside the hollow-round for maintaining said plug and said inside skin in a concentric relation with said outside skin.

5v Apparatus as defined in claim 4 in which said magnetic means includes opposed pairs of detecting magnets and positioning magnets opposite said plug, said detecting magnets responding to any shift in the position of said plug to change the attractive force exerted by said positioning magnets to restore said plug to a position concentric with said outside skin.

6. Apparatus as defined in claim 4 in which said extension is formed in sections, and including ball joints connecting said extension with said lance and said sections end-to-end, there being at least one plug on each section and corresponding magnetic means opposite each plug.

7. Apparatus as defined in claim 6 in which said extensions are tubular for conducting cooling water to said plugs, and including nozzles carried by said extensions for applying cooling water to the inside of the hollow-round below the mold.

8. Apparatus as defined in claim 4 including a tubular starter bar, a stool carried by said bar, means for inserting said starter bar into the bottom of said cavity, and means for rotating said starter bar through a small arc to disconnect it from said stool.

9. Apparatus as defined in claim 8 in which said starter bar has a plurality of L-shaped slots in its upper edge and said stool has bolts received in said slots for connecting the stool and starter bar.

t i i i

Claims (9)

1. A method of continuously casting a hollow-round comprising pouring molten metal continuously into an annular mold cavity, cooling the outside and inside surfaces of the metal within the mold and thereby forming outside and inside skins on the hollowround within the mold leaving a liquid core between said skins, continuously withdrawing the partially solidified hollow-round from the bottom of the mold over water-cooled plugs of magnetic material, continuing the cooling of both surfaces of the hollowround until the hollow-round solidifies throughout at a level spaced below the mold, detecting any eccentricity of the inside skin between said mold and said level, and correcting magnetically with said plugs such eccentricity.

2. A method as defined in claim 1 in which said plugs are acted on magnetically to detect eccentricity of said inside skin.

3. A method as defined in claim 1 in which a tubular starter bar is inserted in said mold from beneath preliminary to commencing a casting operation, and is disconnected from the partially solidified hollow-round by rotating it through a small arc.

4. Apparatus for continuously casting a hollow-round comprising a tubular water-cooled mold, a water-cooled lance suspended within said mold leaving an annular cavity therebetween, means for pouring molten metal into said cavity, whereby a partially solidified hollow-round having solidified outside and inside skins and a liquid core emerges from the bottom of said mold, which hollow-round solidifies throughout at a lower level, an extension on said lance below said mold, at least one water-cooled plug of magnetic material on said extension between the bottom of said mold and the level at which the hollow-round solidifies throughout, said plug being of a shape to ride against said inside skin, and magnetic means outside the hollow-round for maintaining said plug and said inside skin in a concentric relation with said outside skin.

5. Apparatus as defined in claim 4 in which said magnetic means includes opposed pairs of detecting magnets and positioning magnets opposite said plug, said detecting magnets responding to any shift in the position of said plug to change the attractive force exerted by said positioning magnets to restore said plug to a position concentric with said outside skin.

6. Apparatus as defined in claim 4 in which said extension is formed in sections, and including ball joints connecting said extension with said lance and said sections end-to-end, there being at least one plug on each section and corresponding magnetic means opposite each plug.

7. Apparatus as defined in claim 6 in which sAid extensions are tubular for conducting cooling water to said plugs, and including nozzles carried by said extensions for applying cooling water to the inside of the hollow-round below the mold.

8. Apparatus as defined in claim 4 including a tubular starter bar, a stool carried by said bar, means for inserting said starter bar into the bottom of said cavity, and means for rotating said starter bar through a small arc to disconnect it from said stool.

9. Apparatus as defined in claim 8 in which said starter bar has a plurality of L-shaped slots in its upper edge and said stool has bolts received in said slots for connecting the stool and starter bar.

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