US3511304A - Float control valve for continuous casting - Google Patents

Description

May 12, 1970 MW G /m United States Patent O 3,511,304 FLOAT CONTROL VALVE FOR CONTINUOUS CASTING Richard Baier, New Brunswick, and Paul `lohn Kranz, Westfield, NJ., assignors to American Smelting and Refining Company, New York, N.Y., a corporation of New Jersey Filed Sept. 13, 1967, Ser. No. 667,566 Int. Cl. B22d 11/10 U.S. Cl. 164-82 4 Claims ABSTRACT OF THE DISCLOSURE This application is concerned with a float control valve for continuously casting metals. The valve has a tube which extends from the bottom of a container for molten metal into the top of a mold in which the metal is to be cast. The lower end of the tube serves as a valve seat. Within the tube is a shaft which extends into the molten metal container and which has at its bottom a cup which surrounds the bottom of the tube. The lower portion of the shaft adjacent the tube is tapered. The tapered portion of the shaft and the bottom of the cup together with the lower end of the tube provide a throttle opening for throttling the delivery of molten metal into the mold.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to the continuous casting of metals, and more particularly to automatically feeding metals to a mold for continuously casting metal, and especially a copper metal.

Cross-references to related application This invention represents an improvement over the invention disclosed in application Ser. No. 461,296, tiled June 4, 1965 in the name of Richard Baier, now U.S. Pat. 3,349,838, issued Oct. 31, 1967.

According to the prior invention disclosed in said application Ser. No. 461,296, the valve comprises a tube depending from a holding container and extending into the top of the mold below its free surface. Within this tube is a shaft having at its bottom a cup which surrounds the tube. The movable parts of the valve constitute a stopper member and comprise a material which has less specific gravity than the metal being cast. The stopper member has an interlocking member for interlocking the stopper with the container so that the container and stopper may be removed from the mold as a unit.

Substantially the entire stopper is immersed in the molten metal-shaft, abutment, and most of the cup-and thus substantially all parts are available to impart buoyancy to the stopper. The effect of this buoyancy is to close the feed tube when the metal level in the mold gets too high, and to open the tube when the metal level in the mold gets too low.

The prior invention has, in general, performed satisfactorily, particularly with slower casting speeds and large sizes of molds, but is subject to certain difliculties, particularly with higher casting speeds and smaller diameter molds. One of the main difficulties of the prior invention is that it is subject to hunting By hunting we mean a rapid rise and fall of liquid level in the mold which in some cases may extend for as much as one inch above and one inch below, normal desired casting level of liquid in the mold. In other words, the amplitude of liquid hunting has been one to two inches or more, and in some cases has caused the molten metal to overflow the mold. This variation in liquid level is much greater than the variation in the movement of cup or stopper.

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It is an object of the present invention to overcome hunting and to provide an arrangement which is simple in construction and more reliable in operation.

Other objects and features of the ivention will be more apparent from the following description when considered with the accompanying drawings.

SUMMARY OF THE INVENTION Broadly, in one aspect, the invention comprehends a system for controlling metal ow for continuous casting comprising a mold having an open top and an open bottom, a container above the mold for holding the molten metal to be cast, a feed tube in communication with said container and extending down into the mold, the lower end of said tube constituting a seat member, a valve stopper comprising a valve member, and a shaft disposed within said tube and connected to said valve member. The stopper has a portion immersed below the level of molten metal in said mold and a Vernier portion above said level. The stopper also has interlocking means for interlocking the stopper 4with respect to said container. The valve member and the seat member have telescoping relationship to each other and dene a throttle opening having throttling surfaces, at least one of which is tapered, whereby a relatively large longitudinal movement of said valve member relative to said seat member causes a relatively small change in throttle opening. Preferably the valve member comprises a cup with a bottom wall and side wall; the side wall surrounds the tube, the cup having openings for distributing metal in a predetermined manner, and the valve member having a relatively gradual taper adjacent the bottom wall and a relatively steep taper adjacent the gradual taper.

In accordance with the process aspects of the invention, the buoyancy of the stopper is used during the casting procedure to contract the size of the throttle opening whereby a relatively large stopper movement causes a relatively small change in the throttle opening. In a narrower aspect, in operating the valve during the casting procedure, the stopper is moved upwardly through a substantial range to cause a relatively large change in the throttle opening and the stopper is further moved upwardly through a relatively great range to impart a smaller change in throttle opening and thereafter completely closing the throttle opening.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, the single gure is a fragmentary central vertical cross section through a holding container and mold with the invention applied thereto. The top of the container and bottom of the mold are broken away for simplicity of disclosure.

In the following description and in the claims, various details will be identified by specific names, for convenience, but they are intended to be as generic in their application as the art will permit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, the apparatus as shown cornprises mold 10, container 11 (which may be a portable ladle), and automatic valve 12. The mold 10 comprises a metal jacket 20 having a graphite liner 21, and may be of the type disclosed and claimed in U.S. Pat. No. 3,098,- 269, dated July 23, 1963, sometimes referred to as a stable mold.

The present invention is described with special reference to casting phosphorized deoxidized copper, but the invention is applicable to casting other types of copper and other metals. In this description, it is rst assumed that the casting operation has been started and the process is functioning at full running speed.

The mold and valve 12 may be circular in horizontal cross section, while the ladle 11 may be of any shape in horizontal cross section. The position of the valve parts shown in the drawing is a normal running position with the valve partially open.

The ladle 11 is filled to a suitable level with molten phosphorized copper. Molten copper flows from ladle 11 to the mold. It freezes in the mold, and the solid billet 13 is withdrawn from the bottom of the mold in any way desired.

At full running speed, the metal is fed and the billet withdrawn at such rate as to cause the metal to freeze in the form of a crater 15, forming a crater shell 14. The crater shell 14 is lled with molten metal having its own free surface 16 in the mold. The proper level of molten metal in the mold is maintained by the automatic valve 12, to be described.

The valve 12 comprises a relatively stationary seat member 17, and a relatively movable stopper 18. The seat member 17 comprises the lower edge of a feed tube 19 depending from the bottom of the container 11 and extending below the surface of the molten metal in the mold 10. Seat member 17 has a feathered outer edge. The tube 19 has an upper end 32 with a plurality of slots 33 permitting molten metal to flow into the tube even when the shaft head 31 engages end 32. Cement 29 holds tube 19 tight in the bottom of container 11.

The stopper 18 comprises a cup 22 and a shaft 23 with head 31. Cup 22 has a bottom 24 with a plurality of feed holes 25, a side wall 26, and an open top 28.

Adjacent the cup bottom 24 is a plug or needle 41 having a conical surface 39 of relatively gradual slope above which is a second conical surface 38 of somewhat steeper slope. These surfaces telescope within the seat 17 to form a variable throttle opening `40. When the cup 22 is in uppermost position, the smaller taper 39 is suiciently small to provide a slight clearance between it and the adjacent inner wall of seat 17 so that the valve can be completely closed by engaging the cup bottom 24 against the bottom of seat 17 without engaging the smaller taper 39 with the inner edge of seat 17.

In the position shown, the cup 22 is partially immersed in the molten metal in the mold, and its side wall 26 extends to a point below the top of the mold 10. The shaft 23 passes loosely through the tube 19 and is connected to the bottom 24 of the cup 22. The top of the shaft 23 has a round enlarged upper head 31 engageable with the top 32 of the tube 19 which projects above the bottom of the ladle 11.

The movable valve stopper 18 (cup and shaft) may be made of clay graphite or other material which has less specific gravity than the molten copper 'being continuously cast. Buoyancy is obtained by partial immersion of the cup 22 in molten metal in the mold, by immersion of the abutment 31 in molten metal in the ladle 11, and by immersion of shaft 23 in molten metal in tube 19. The tube 19 may also be made of clay graphite.

For casting phosphorized copper, it is preferred to use a protective layer of discrete particles of carbonaceous material, such as flake graphite, lamp black, pulverized anthracite, etc., floating on the surface of molten metal in the mold. Part of this cover 34 may be outside cup 22, and part 35 may be inside the cup.

In operation, so long as the metal level 16 in the mold 10 remains at normal height as shown in the drawing, molten metal will continue to ow down between the feed tube 19 and shaft 23 through the throttle opening 40 into bottom of cup 22 and through the outlet holes 25 into the crater 15.

The function of the valve depends upon Archimedes principle which states that a body immersed in a uid is bouyed up by a force equal to the mass of the fluid displaced. For proper operation, the valve member must rise and fall with the free surface 16 of liquid in the mold. When the free surface rises, the valve member must rise, and when the free surface falls, the valve member must fall.

To make the stopper 18 responsive to change in free surface level, it is necessary to have a part of the stopper projecting above the free surface 16 in the mold at all times. This part, in the form shown, is the upper margin of the valve wall 26. The immersion to a variable extent of this margin is an important factor, and for this reason, will sometimes be referred to as the Vernier portion of the stopper.

As an example of one manner in which the Vernier portion operates, let it be assumed that the level of metal in the mold is sufficiently high to completely close the throttle opening 40 (between seat 17 and cup bottom 24). This means that the Vernier portion must be immersed sufficiently to import to the stopper an upwardly acting buoyant force equal to the head H of molten metal extending from the top metal surface 36 in the ladle to the valve seat 17. This stops all metal flow into the mold.

As the congealed casting is withdrawn from the bottom of the mold, the molten level in the mold drops, which decreases the amount of immersion of the Vernier margin of the cup 22. This reduces the upward force of buoyancy, permitting the head of molten metal to force the stopper downwardly, opening the valve and permitting molten metal to flow through throttle 40 and thecup holes into the mold.

The stopper 18 will of course continue to descend as long as the metal level in the mold descends; this is accompanied by an increase in metal ow through the valve because of the wider opening 40. As the stopper descends, and as the increased metal ilow into the mold causes the mold level to rise, the Vernier margin of the cup becomes immersed to a greater extent, which in turn increases the upward force of buoyancy on the stopper, which in turn tends to close the throttle opening.

This regulating action will, of course, continue during the entire pouring operation-the stopper descending with descent of free surface 16, thereby increasing rate of metal flo-w into the mold, and the stopper rising with rise of free surface, thereby reducing metal flow through the valve into the mold.

It will be noted that the velocity head of the owing metal raises the -metal level in cup 22 above the free level 16 in the mold. This downward flow of metal produces a downward force on the stopper 18 which is resisted by the force of buoyancy.

The instant valve has many advantages. The stopper is self-heating in that all .movable parts (except the Vernier margin) are immersed in the metal being continuously cast, and, overall, are of less specic gravity than the metal. The mass density is virtually and no counterweights are necessary to supplement the buoyancy of the movable stopper immersed in the liquid metal. The force of buoyancy is sufficient to overcome the Weight of the stopper 18 and the downward force caused by the downward ow of molten metal from the ladle into the mold. Also, the fiow of metal through the annular space between the feed tube 19 and shaft 23 is subject to the Bernoulli effect, which keeps the shaft 23 and needle 41 centered so that, While the valve is performing its regular function, it is completely self-floating and self-centering in that no moving part of the stopper engages the feed tube or any stationary part of the ladle.

A further advantage is the dual submersion of both cup 22 and head 31. In case it is desired to change the shape or size of the cup, a corresponding change can be made to the shaft head to maintain total displacement of the stopper the same, or to change it if desired.

The holes in the distributing cup 22 can have any pattern, and be directed at any angle, depending upon operating conditions such as size of the mold, the metal being cast, and the speed of casting, etc.

The central pilot shaft 23 and upper head 31 hold all parts of the mold together as a unit, enabling the ladle and valve to be removed from the mold, and replaced into the mold, as a unit. When the ladle 11 is raised, it carries all of its valve parts with it. The selfcentering action of the pilot shaft holds the cup 22 centered with respect to the tube 19, and with respect to the mold, and prevents tilting or cocking of the cup with respect to the valve seat 17.

Ihe valve may be used to cast the metals, all as disclosed in prior application Ser. No. 461,296 above mentioned which is made a part hereof by reference.

While the theory of successful operation of the present invention is not completely understood at the present time, the following explanation is given to assist in teach ing the invention, with the understanding that this explanation is not given in any limiting sense.

The working head, that is, the distance from the liquid level in the ladle 11 to the liquid level in the mold 10 is determined by the buoyancy of the entire immersed stopper system, exclusive of the upper edge 26 of the cup, sometimes referred to as the Vernier portion. The permissible variation in liquid level in the ladle is determined by the buoyancy in the cup wall above the liquid level in the mold `when the valve is completely closed, which part of the wall has been referred to as the Vernier portion.

The invention has numerous advantages. It is thought that an important factor in preventing hunting is the use of a needle valve, preferably on the buoyant self-centering central shaft, and the fact that a relatively large vertical movement of the stopper is necessary to produce a relatively small change in throttle opening.

The valve also has the advantage of capability of complete closure. Such capability is especially advantageous in preventing the mold from overflowing.

In regular operation full closure rarely occurs because the smaller taper 39 provides a sufficiently small throttle opening that matches slower casting speed and larger taper 38 provides a sufficiently large throttle opening that matches higher casting speed. Casting speed can be easily changed by changing the speed of withdrawal of the solid casting, the valve making the necessary adjustment without causing hunting.

The present invention is especially insensitive to the height of liquid level 36 in the ladle 11. Tests indicate that the ladle liquid level may vary as much as seven inches with a corresponding variation of only about three-quarters of an inch in normal working mold level 16. This variation in liquid level in the mold is entirely permissible and should not be confused with hunting which is a harmonic departure from the normal mold level.

Since with molds of the size disclosed below, normal operating levels run from between one inch and two inches below the top of the mold, this small variation in operating level caused by the large variation in liquid level in the ladle is not serious.

Tests further indicate that the above insensitivity of liquid level in the mold with change in liquid level of the ladle occurs throughout a wide range of casting speeds, for example from about 20 inches to 45 inches per minute in speed of cast product withdrawn from the bottom of the mold.

Tests also indicate that the liquid level 36 in the ladle may vary from a lower level, in which the top head 31 is uncovered, to an upper level where the hydraulic head (distance from ladle level to liquid level 16 in mold) is suciently great to overcome the buoyancy of the stopper 18.

To further assist in understanding the invention, we give certain sizes and dimensions. These are mainly examples and should not be taken in any limited sense.

The inside cross section of the mold may have a variety of shapes and sizes; for example, it may be circular with a diameter in the order of 3 to 5 inches or greater. By way of further example, inside mold cross section may also be square with a diagonal of say 5 inches. Such square cross sections may be used for Wirebars.

The length of the mold may be from 6 to l2 inches and the normal liquid level may be from l to 2 inches below the top of the mold. The casting speed may be in the order of 20 inches per minute of the cast product or higher. The continuous casting procedure may be conducted with or without reciprocation of mold 10. Mold reciprocation, when employed, may normally have an amplitude from 1 to 4 mm. and from 10i to 700 complete strokes per minute.

As one example of actual dimensions of the throttle, the inside diameter of tube 19 at seat 17 may be 1.25 inches. The diameter of shaft 23 at the top of steep taper 38 may be 0.875 in. The diameter of the plug 41 at the intersection of the two tapers 38 and 39 may be 1.187 in. The diameter of the plug 41 at the bottom of the smaller taper 39 may be 1.225 in. Using these gures the area of throttle opening 40 may be as follows:

With the cup bottom 24 nearly engaging the seat 17, the area of throttle opening may be 0.06 sq. in. When the point defining the intersection of tapers 38 and 39 is opposite the inner edge of seat 17, the throttle opening may lbe 0.12 sq. in. When the cup 22 is at its lower-most position with the top of steep taper 38 opposite the inner edge of seat 17, the area of throttle opening may be 0.63 sq. in. This is equal to the cross section of the annular space between central shaft 23 and tube 19.

The axial length of the smaller taper 39 may be 1/z inch and the axial length of the larger taper may be 1/2 inch, thus providing a stroke for the valve of 1 inch between full-open and full-closed position. It will thus be seen that the throttle opening increased only about 0.06 sq. in. with 1/2 inch movement of needle valve from full-closed to half-open position, and increases about 0.50 sq. in. from half-open to full-open position.

Prior to starting up a casting operation, the ladle with attached valve is removed from the mold, placed to one side, and heated by a blowtorch. After preheating the ladle and valve, the assembly is returned to the mold to place the valve in operating position in the mold.

It will be understood, of course, that for starting, the mold will have the conventional starting plug inserted in its lower open end for starting purposes.

The molten copper is then fed to the ladle which ows through the valve (since the valve will be in wide open position) into the empty mold. When the level of metal in the mold reaches proper height, the valve will start functioning to limit further rise of metal level in the mold; at the proper time, the starting plug will be lowered and the continuous casting operation started. Preferably, the starting plug is lowered when the smaller taper 39 is disposed opposite the throttle edge 17. In other words, for starting a casting operation and for slow casting speeds the smaller taper 39 controls throttle opening, while for higher speeds the steep taper 38 controls throttle opening.

While certain features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that, in accordance with the doctrine of equivalents, various omissions, substitutions and changes may :be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a system for controlling metal flow for continuous casting, a mold having an open top and an open bottom, a container above the mold for holding the molten metal to be cast, a feed tube in communication with said container and extending down into the mold, the lower end of said tube constituting a seat member, a movable valve stopper comprising a valve member, a shaft disposed Within said tube and connected to said valve member, said stopper having a portion immersed below the level of molten metal in said mold and a Vernier portion above said level, said valve stopper adapted to rise and fall with a free surface of the molten metal in the mold,

said stopper also having interlocking means for interlocking said stopper with respect to said container, said valve member and seat member having telescoping relation and defining a throttle opening, said throttle opening having throttling surfaces and said valve member having a relatively gradual taper for a substantial distance adjacent a lower portion of the valve member and a relatively steep taper for a substantial distance above and adjacent said gradual taper, whereby a relatively large longitudinal movement of the relatively gradual tapered portion of said valve member relative to said seat member causes a relatively small change in throttle opening.

2. In the apparatus of claim 1 said valve member comprising a cup with a bottom wall and side wall, said side Wall surrounding said tube, said cup having openings for distributing metal in a predetermined manner, said valve member having a relatively gradual taper adjacent said bottom wall and a relatively steep taper above and adjacent said gradual taper.

3. In a method for controlling the metal ow to a mold for continuous casting and for maintaining a substantially fixed level of metal in the mold, said mold having an open top and open bottom, a container above the mold, a feed tube connecting said container and extending down into the mold, a floating valve stopper comprising a shaft within said tube and having a buoyancy member immersed in both the metal in the container and the metal in the mold, said shaft and tube having telescoping, throttling surfaces defining a throttle opening, and said valve stopper having a relatively gradual taper for a substantial distance adjacent a lower portion of the valve member and a relatively steep taper for a substantial distance above and adjacent said gradual taper, said method comprising flowing metal from the container through the space between said shaft and tube and through the throttle opening, using the buoyancy of the stopper to control the size of said throttle opening, the valve stopper rising and falling with a free surface of liquid metal in the mold whereby a relatively large longitudinal movement of the relatively gradual tapered portion of said valve stopper causes a relatively small change in throttle openin g.

4. In the method of claim 3 moving said stopper upwardly through a substantial range by using the buoyancy of the stopper to cause a relatively large change in throttle opening, further moving said stopper to a relatively great range by using the buoyancy of the stopper to impart a smaller change in throttle opening and thereafter completely closing said throttle opening using the buoyancy of the stopper.

References Cited UNITED STATES PATENTS 2,243,425 5/ 1941 Junghans 164-82 2,277,375 3/1942 Tama 164-281 X 2,876,509 3/1959 Gardner 164-136 X 3,050,792 8/1962 Lipman et al. 164-136 X 3,349,828 10/1967 Baier 164-281 FOREIGN PATENTS 844,956 7/1952 Germany.

J. SPENCER OVERHOISER, Primary Examiner R. S. ANNEAR, Assistant Examiner U.S. Cl. X.R. 164-281

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