US2871530A - Continuous casting mold, its manufacture and use - Google Patents

Description

Feb. 3, 1959 H. c. P. WIELAND 2,871,530

CONTINUOUS CASTING MOLD, ITS MANUFACTURE AND USE .Filed Sept. 12, 1955 2 Sheets-Sheet 1 fl, IIAVIIIIIII Q .3 N

n l 7* Il@ h N-l N m INVENTOR.

HA/s CR W/ELA/vo j ,2M-f M ATTORNEY Feb. 3, 1959 H. c. P. wlELAND 2,871,530

CONTINUOUS CASTING MOLD, ITS MANUFACTURE AND USE vll/111111111);l

60 INVENTOR HANS C P W/ELAND ATTORNEY United States Patent yCONTINUOUS CASTING MOLD, ITS MANUFACTURE AND USE Hans C. P. Wieland, Ulm, Germany, assigner to Wieland- Werke A. G., Ulm, Germany, a corporation of Germany Application September 12, 1955, Serial No. 533,590

This invention relates to a continuous casting mold, its manufacture and use in the continuous casting of metal.

` More particularly it relates to a billet mold, its manufacture and use for the continuous casting of copper, especially oxygen-bearing copper such as tough pitch copper, and particularly large size billets of such metal.

In continuous casting procedures, molten metal is introduced into one end and the casting is withdrawn from the other end of an open-ended chill mold. During the formation of the casting the molten metal freezes into a shell which increases in thickness and rigidity until the shell shrinks away from contact with the mold due to the contraction of the solidified metal in the shell. In the mold, greatest heat transfer takes place in that portion of the mold wall which is in contact with the molten metal and said shell thereof to the point where the latter shrinks away from direct contactwith the mold.

In attempting to use molds having a graphite liner disposed in a Huid-cooled jacket, it has been found difficult, if not impossible, especially in molds for casting shapes having a large cross-sectional dimension, to main-tain contact between the jacket and the liner during `the casting operation, particularly in the area corresponding to the area of greatest heat transfer between the liner and the metal being cast in the mold. Itis believed that such lack of contact is due to differences in distortion, caused at least in part by difference in expansion, of the liner as compared with the jacket at the temperatures existing in the mold under the casting conditions.

The principal advantage of the invention resides in the fact that it provides a method and means for enhancing contact between the liner and the jacket, particularly in the said area of greatest heat transfer. It has been found that practice of the invention results in improved surface characteristics in the casting and at the same time permits the use of higher casting rates than would otherwise be possible. These and other advantages and objects will be more apparent from the following detailed description of the invention.

Broadly, the invention contemplates the continuous casting of molten metal in an open-ended mold, having a fluidcooled jacket with a graphite liner disposed therein which denes a mold cavity, while causing the jacket to press against the liner to maintain the latter preloaded in compression by said jacket during the casting operation, at least in the area of greatest heat transfer between the liner and the jacket thereby enhancing contact between these two elements during the casting operation.

. The` invention also contemplates an open-ended mold comprising a mold cavity-defining graphite liner having a conveXedly curved outer surface and a fluid-cooled metal jacket having a correspondingly concavely curved inner surface, said liner being disposed in said jacket with said convex liner surface presented to Said concave jacket surface and with the jacket preloading the liner in compression at least to the extent required to maintain the liner under compression at the temperatures encountered 'forced int-o the jacket.

Fatented Feb. 3, 1959 in the mold under the casting conditions, in the area in which greatest heat transfer takes place between the liner and the jacket.

The liner may be fabricated of any grade or quality of graphite including materials containing graphite such as graphite coated carbons which are not wetted by the molten metal being cast. Although the jacket may be made of any metal or alloy, it preferably is fabricated of steel, copper or copper based metal with copper being the most preferred material for making the jacket. Preferably also, the liner is a thin unitary graphite tube and the jacket comprises a tubular copper sleeve the outer surfare of which is adapted to be cooled by direct contact with water. In the most preferred mold the entire surface of the liner facing the sleeve is maintained under compression by the sleeve.

For convenience, these iits between jacket and liner will sometimes be referred to as a compression fit. This may take the form of a force t or a shrink t," as discussed below.

In making the mold a graphite core is positioned in a jacket which is adapted to be preloaded in tension, with the jacket `compressing the core to preload the latter in compression at least to the extent set forth above. For best results in making the mold, an oversize graphite core is prepared having outer dimensions which are larger than the inner dimensions of the jacket in which the core is to lit. As an example of a force lit the core is then forced into place in the jacket thereby placing the jacket under tension and the core under compression. Thereafter material from the interior of the core is removed to obtain a graphite liner of the size and shape for the desired casting. A core of suicient oversize is selected so as to establish therein the requisite compression as it is Preferably the core and jacket are at ordinary room temperature during said forcing step. However, if desired, a shrink fit may be employed; that is the jacket may be heated or the core may be cooled or both of these latter expedients may be employed as an alternative procedure or in conjunction with the forcing step. Although the core which is employed in the mold fabricating process is preferably a unitary hollow tubular shape having oversized inner and outer dimensions, it

ymay also be a solid or segmented shape.

The invention is further illustrated in the examples' and in the accompanying drawings which form a part of this specification. It should be understood however that the examples and drawings are given for purposes of illustration and the invention in its broader aspects is not limited thereto.

In the drawings:

Fig. 1 is a diagrammatic elevation with parts in section, illustrating a continuous casting process according to the invention;

Fig. 2 is a view along line 2-2 of Fig. 1 taken in the direction of the arrows;

Fig. 3 is an enlarged vertical section of a mold for practicing the invention;

Fig. 4 is a view along the line 4?4 of Fig. 3 taken in the direction of the arrows;

Fig. 5 is a diagrammatic4 view in vertical section illustrating the first step in the preferred method of mounting an oversize graphite core in a mold jacket;

Fig. 6 is similar. to Fig. 5 showing the core partly in position in the jacket;

Fig. 7 is similar to Fig. 6 but shows the core completely in position in the jacket;

Fig. 8 illustrates a method of adjusting interior dimen sions of -the core to a desired liner thickness.

Referring now to the drawings and more particularly to Figs. 1 and 2, the system will first bel briefly described.

In these figures, parts are shown largely diagrammatically for simplicity. The system comprises, in general, a vertical mold 10 which may be a reciprocable mold fed with molten metal 'from a furnace (not shown) through con-v duit 11 whichmay be a metallic-tube lined with graphite 12. The casting issues from the bottom of the mold and passes into andthrough tank 13. provided below the tank 13 with power-driven rolls and a saw (not shown), for lowering the casting at a icontrolled rate and cutting the withdrawn .casting into desired lengths.

i The mold 1li comprises, in general, a water-cooled jacket 2li having a graphite liner 2.1. Themold maybe supported by a reciprocable frame indicated in general by numeral 22. The reciprocating mechanism may c' prise a set of four bell cranked levers '313 pivoted to a tionary support by pivots24. Tie .rods Z connect the pairs of bell cranks 23. vleinks 26 connect the bell cranks to the frame 22. A motor 27 drives a crank 23 connected by 4connecting rods 29 to the bell cranks 23.

` The motor 27 may be of variable speedor some other device may be provided, to control the number of vertical strokes per minute of time imparted 4to the mold. By adjusting the length of the lever arms or the eccen'tricity of the crank 2S, the length of the stroke may be varied.

Water tank 13 may be suitably independently supported in a position below but adjacent the bottom of the mold. A rubber water seal 33 is provided which works against the casting. The casting is cooled sutilciently Vby the 'time it leaves the bottom of the tank so that no overheating of the rubber seal is encountered.

Cooling Water may be supplied to the water jacket through supply pipe 34; the water entering the jacket through tangential inlet 35'. The water passes through the mold in a cir-cular path and issues from the `bottom thereof through restricted annular orice 36 which, because of its relatively small cross-section in relation to the volume of water delivered to the mold through pipe' 34, causes the water passage 37 in the jacket to be lilled with Water. The annular orihce 36 directs the water issuing from the water jacket against the outside surface of the casting issuing from the bottom of the mold. The water then drops into water tank 13 from which it is withdrawn through pipe 38 at a rate to maintain a desired level of water in tank 13. The advantage of this arrangement is that there is substantially no 'contact of air with the casting until the latter emerges from tank 13 'at which point the casting is sutliciently cooled to prevent, or at least drastically reduce oxidation of the surface of the casting.

Referring now to Figs. 3 and 4, the mold will now be described -in detail. The mold corresponds to mold 10, jacket 2h' to jacket 2t), liner 21' to liner 2l, and inlet 3S to inlet 35. Jacket 20f is formed of an inner cylindrical member 41 telescoped within outer cylindrical member 4Z. Plates 43 and 44 suitably attached, as by Welding, to the top and bottom respectively of member 42, serve as end-closing ktlanges to form a water jacket between members 41 and 42. The upper end portion of member 4l may be provided with a shoulder 45 having a flange portion 46, which form a seal and a support with plate 43. The lower outer edge of member 41 may be beveled and spaced from the beveled inner edge of plate i4 by vmeans offset screws 47. The position of member 41 may be adjusted to adjust the size of the annular orifice 36; this latter'being adjusted to a cross-sectional area which is less than that of the inlet 3S thereby maintaining the cooling jacket full of cooling huid.

`The liner 2i is inserted under pressure into member 41, in a manner to 'be described more fully hereinafter. The bottom of the inserted liner may abut shoulder 4S with which member 41 may be provided adjacent its lower inner edge. .Retainer ring 49 vmay be mounted on the top ofthe mold by screws 50 whichrnay be threaded into The system imay 'be plate 43. Ring 49 may project over the top edge of liner 21', as shown, to assist in maintaining the liner as well as member 41 in position in the mold. It will be noted that there is substantially no interference with the longitudinal and transverse expansion and contraction, including thermal expansion and contraction, of duid-cooled member 41 by member 42 and plates 43 and 44 and set screws 47.

The preferred mode of mounting the `liner in member 41 under the requisite pressure .is .illustrated ,in Figs. 5 through 8. In these .figures also, the various parts lare shown diagrammatically for simplicity. Referring to Fig. 5, the member 41 is placedon the bed 55 ofa press, and oversize graphite core 56 is placed on top of said member with the axis of the core aligned with that of member 4l. Either or both of the outer lower edge of core 56 or the upper inner edge of member 41 maybe appropriately beveled to assist in starting .the movement of the core into the member 41. The head 57 ofthe press is then brought to bear against the top of the core. Thereafter suflicient force is applied to the press to force the core into the member 41 until the core is inthe position shown .in Fig. 7; the core being compressed and its dimensions reduced as it enters the member 41, as illustrated in Fig. 6.

The size of dimension A ,of .core 56 (see Fig."5).is such that the graphite is maintained preloaded in :compression by the member 41 at the temperatures towhich the graphite and said member are exposed in the .mold under the casting conditions. 'Preferablythe entire length L of the core possesses `the .oversized .dimension Af If desired, however, ythe core may be .oversized only in that part Bof its length which represents that .portion of the resulting liner in which greatest heat .transfer takes place the :mold from .the metal being cast to the liner and trom the latter to the :member 41. i i

In accordance with the invention, the inner` dimension C of the core (see Fig. 5) is suchas to provide a .core thickness T which is greater than 'that of the desired liner thickness .after `the .core is disposed in ymember 41. The thickness T is selected to 4insure sufficient-:core strength to permit insertion `of the core into said member Without breakage. After insertion,the core is machined away to the desired dimension D to provide :thefliner thickness E shown in Fig. 8. As shown in this latter ligure, this may be accomplished by placing thecor'e mounted in the member .41 in the chuck 60.0f a suitable lathe after which the core is lturned down with cutting tool 61 .to liner thickness E which 'for best yresults in casting is about '2-3 mm. thick.

The 'core 56 may be a solid or 4hollow shape which. may be either unitary or segmental in structure; and thelner produced therefrom may be a unitary or segmented structure. It is most convenient, however, to prepare a one piece liner vfrom a corresponding hollow core. Although best results are obtained with billet-tmolds-having circular liners surrounded by circular jackets, molds having other shapeswmay be used in accordance with the invention, particularly molds having liners -with 4a convexedly curved outer surface in contact with -a correspondingly concave'd inner jacket wall. Also, `instead-of the mounting procedure described in connection with-Figs. 5 through 7, the member41 may be appropriately `segmented, the segmented Vportions vof the member maybe placed around core 56 and drawn tight yagainst lthe-core to obtain the requisite compression although such alternative procedure is not preferred.

In starting the casting process, a rod having dimensions to t the mold cavity defined by liner 21 may be inserted .into'mold 10 through the bottom lof tank 131m Fig. l. Thereafter the feeding lof cooling water intothe jacket through conduit 34 and molten metal through conduit 11 vis begun; the rod `being withdrawn vas the metal freezes. The head of .the rod may be provided 2,871,5sof

with projecting means, such as a bolt, around which the initial casting freezes thereby locking it to the rod, so as to permit the rod to withdraw the casting from the mold.

In operating the process after it has been started, molten metal is introduced into the mold at a rate consistent with the rate of Withdrawal of the casting to maintain a desired metal level in the mold. As heat is extracted from the molten metal, the latter freezes into shell X which, as the casting is withdrawn from the mold, increases Vin thickness and rigidity until it shrinks away from contact with liner 21 at a point Z,7 due to lthe contraction of the frozen metal in the shell. Accordingly the area of greatest heat transfer in the mold is confined to the liner area W between the top of the metal level in the mold and the point Z as in this area the liner and the metal being cast, are in direct contact withpeach other.

Below point 2, heat is transferred from the casting to the liner at a reduced rate due to the loss of contact. To insure against the danger of spillage of molten metal due to rupture of shell X, the bottom of the mold is located well away from point Z; the locationof which point and the size of area W being governed by the rate at which heat is withdrawn from the casting in relation to the casting rate, In general a mold having a length greater than about 5 inches insures against this danger.

In any particular mold the distance to Which the pool of unfrozen metal Y extends into the casting is controlled by the casting rate i. e. the slower the rate of withdrawal of the casting the shallower the pool and vice versa. Any casting rate may be used including a rate which establishes a shallow pool of metal whose bottom is close to the top of the mold as well as one with which the pool extends well beyond the lower edge of the mold. In general, however, and particularly in casting tough pitch copper, it is preferred to adjust the casting rate so that the bottom of the pool of unfrozen metal is adjacent the bottom of the mold.

The heat which is extracted by the moldlfrom the metal being cast ows into the cooling water in jacket 20 passing through liner 21 and jacket wall 41 bo-th of which possess high thermal conductivity and permit a high rate of heat flow when in contact with each other. However, if contact between these two members is reducedor destroyed ow of heat is seriously impaired inasmuch as even an extremely thin gap or gas layer possesses a remarkable insulating capacity. Any such impairment of heat flow between the liner and the jacket drastically affects the temperature gradient across and between these members, and causes a large increase in the temperature of the liner surface facing the metal being cast.

In the absence of the present invention, it is believed that contact between the liner and wall 41, especially in the area of greatest heat transfer in the mold, is not maintained but instead is reduced or' destroyed during the casting of metal in the mold. It is believed that such reduction or loss of contact is caused by a difference in expansion between these two members which, due to the difference in their coefficients of expansion, is sufficient to cause the member 41 to expand away from the liner even though the liner temperature is higher than that of member 41. As a consequence, ow of heat in the mold is impaired and the temperature of the liner becomes excessive thereby resulting in the production of inferior surface characteristics in the casting and at the same time a reduction in the casting rates that can be employed in any particular mold.

On the other hand, with the present invention, contact between the liner and the jacket is maintained during the casting procedure due to the fact that the expansion of the liner is as great as that of member 41. The difference in thermal expansion in these two members is made up by expansion of the liner as the compression thereon is reduced by the thermal expansion of member 41 so that the total expansion of the former is as great as that of the latter.

surface characteristics that are obtained when the inven tion is practiced.

The invention may be employed to cast any metal or alloy. It is most useful for casting metals such as steel, silver, nickel, aluminum, `magnesium, and particularly copper, It is especially useful for casting oxygen-bearing copper such as tough pitch copper in any desired size and for casting large size billets (i. e. those greater than about three inches in diameter) of oxygen free or phosphorous deoxidized copper. Heretofore it has not been possible to cast tough pitch copper successfully in the large quantities and with the quality required by industry.

In practicing the invention, the mold preferably is reciprocated at a suitable rate with a suitable stroke and molten metal is introduced into the mold at a rate to maintain the level thereof below the top of the mold. However, if desired, a stationary mold `may beused. Likewise the mold may be kept lled with a columnof metal, for example by attaching the to-p of the mold to the bottom of a suitable furnace such as a holding fur# v as it is being withdrawn; this being the preferred procedure with relatively small shapes.' vWith relatively large shapes, however, it is preferred to stop the casting when a desired length has been produced. This length is then removed from the-mold and the casting of another length is begun.

The invention is further illustrated in the accompanying examples:

' Example I A cylindrical graphite liner was inserted into a cylindrical copper jacket as illustrated in Figs. 5 through 8. The outside diameter of the graphite core (dimension A Fig. 5) was 7.0168 inches7 its inside diameter,(dimension C) was, 6 inches. The inside diameter of the copper jacket member 41 was 7.0000 inches; its outside diameter was 7.354 inches. Contrary to expectations, it was found that the graphite core was readily forced into member 41 without breaking. After being forced into the jacket in the position shown in Fig. 7 the inside surface of the core was turned down as shown in Fig. 8 to obtain a liner having an inside diameter of 6.760 inches.

This assembly was then heated from room temperature (82 F.) to 390 F. At the later temperature the liner was still tightly disposed in member 41.

Example Il A liner and jacket assembly were prepared as set forth in Example 1. This assembly was incorporated into a mold illustrated in Figs. 3 and 4 -Which are drawn approximately to scale. The length of the mold was 250 mm. The thus prepared mold was used in the continuous casting system shown in Fig. 1 for the continuous casting of tough pitch copper. v

Moltentough pitch copper was introduced into the mold from the forehearth of a heating furnace through a conduit (numeral 11, Fig. l) having an outlet diameter of 5.5 mm. The mold was reciprocated at a frequency vof about 60 cyles per minute with a stroke of about 4 It is believed thatthis accountsk for the twiny benets of increased casting rates together with improved lower edge of the mold and the liner 21 remained tight in member 41 during the entire casting procedure.

i A tough pitch copper billet was continuous cast at the rate of two tons per hour, the casting being cut'into suitable lengths as it emerged from tank 13. The surface of the casting Was smooth and free of annular folds and overlappings. The"-smoothness of the surface ywas such that substantially no water leaked-through the rubber seal 33 in the bottom yof water tank 13. There was no discernible reduction in the thickness of the liner even after a considerable period of use of the mold; this fact indicating that the liner was not attacked by the oxygen contained in the tough pitch copper.

Example III The procedure of Example II was repeated except that in this instance phosphorous deoxidized copper was cast. The surface of the casting that kwas produced was also smooth Aand free of annular folds and-overlappings. Substantially no water leaked through seal 33 and in addition there was no discernible decrease in the thickness of the Y liner after long periods of use.

While certain -novel features of the inventionfhave been disclosed herein, and arepointed out in the annexed claims, it will be understood ,that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit ofthe invention.

This application is a continuation-in-part of my application Serial #235,987, led July 10, 1951, entitled: Continuous Casting of Metals, now Patent No. 2,772,- 459, granted Dec. 4, 1956. t

I claim: p

1. In a system for continuously casting metal, a mold comprising a metal supporting jacket adapted to be cooled 3 conditions, comparatively cool as compared to said area of greatest lheat transfer, the contacting walls of said jacket rand liner being vcircumierentially continuous, the outer diameter of the liner before assembly being considerably larger ythan the Acorresponding inner diameter of the jacketto provide, after assembly, a severe compression t; the severity of said iit being such that, under castingfconditions, that portion of said graphite liner at said area of greatest lheat transfer has reserve elastic expansive force and the immediately contacting portion of the jacket has reserve elastic contractive force, thereby providing a fluid-free, solid-to-solid contact at the interface between jacket and liner, said compression t being more severe than that necessary to maintain, under casting conditions,

a uid-free, solid-to-solid contact at the interface between' jacket and liner merely near the cooler ends of the liner.

2. In a systemk for continuously casting metal according yto claim 1, said jacket comprising a sleeve of copper base metal, said liner being substantially as thin as is compatible with requisite mechanical strength to adjust itself to distortion caused by difference in temperature to which different parts of liner are subjected, said compression t being such as to maintain, under casting conditions, a fluid-free, solid-to-solid contact at substantially the entire area between jacket and liner.

References Cited in the le of this patent UNITED STATES PATENTS 2,131,070 Poland Sept. 27, 1938 2,135,183 Junghans Nov. 1, 1938 2,136,394 Poland et al Nov. 15, 1938 2,169,893 Crampton etal Aug. 15, 1939 2,176,991 Crampton et al Oct. 24, 1939 2,225,373 Goss Dec. 17, 1940 I 2,245,224 Poland June l0, v1941 2,264,288 lBetterton et al. Dec. 2, 1941' 2,284,703 Welblund et al June 2, 1942 2,747,244 Goss May 29, 1956 2,772,459 Wieland Dec. 4, 1956 .FOREIGN PATENTS 504,519 Great Britain Apr. 26, 19,39

884,911 France May 10, 1943 705,856 Great Britain Mar. 17, 1954

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