US3375863A - Apparatus for continuous casting metal tubes - Google Patents

Description

A ril 2, 1968 o. B. ATKIN ETAL 3,375,863

APPARATUS FUR CONTINUOUS CASTING METAL TUBES 3 Sheets-Sheet 1 Filed March 16, 1966 cuvm 4 lNVENTOR-S OLIVER B. ATKIN HOWARD q; A L/ y i ATTORNEYS Aprll 2, 1968 ATK|N ETAL 3,375,863 APPARATUS FOR CONTINUOUS CASTING METAL TUBES Filed March 16, 1966 1 l l/ l l/ a mmm q m a M m T w W m mm him 9 vi '6 m 1 m6 o. B. ATKIN ETAL 3,375,863 APPARATUS FOR CONTINUOUS CASTING METAL TUBES April 2, 1968 3 Sheets-Sheet Filed March 16, 1966 FIG. 8

FIG. 11

v INVENTORS OLIV HOWARD CUVIN ER B. ATKIN I MAFIA 41M United States Patent 3,375,863 APPARATUS FOR CONTINUOUS CASTING METAL TUBES Oliver B. Atkin, Hamden, and Howard Cuvin, Watertown,

Conn., assignors to Anaconda American Brass Company, a corporation of Connecticut Continuation-impart of application Ser. No. 430,287, Feb. 4, 1965. This application Mar. 16, 1966, Ser. No. 536,593

Claims. (Cl. 164281) ABSTRACT OF THE DISCLOSURE Apparatus and method for continuously casting metal tubes wherein molten metal is gravity fed from a crucible into a reservoir located in a cooling zone of a mold and mandrel assembly and the molten metal is then fed into a tubular space defined between the mandrel and mold, solidified and continuously withdrawn in the form of a thin walled tube. The reservoir is provided within the mandrel With channels extending outward therefrom or outside mold walls and extending inwardly through the mold. Channels which extend axially through the mandrel head are also provided in the combination to supplement the feed of molten metal to the tubular member in the cooling zone and to provide outlets for release of gases.

This is a continuation-in-part of our earlier filed copending application, Ser. No. 430,287, filed Feb. 4, 1965 and now abandoned.

This invention relates to the continuous casting of metal tubes, and more particularly, it relates to an improved mandrel and mold assembly in apparatus for the continuous casting of metal tubes, and to an improved method of continuously casting metal tubes.

The operation of continuously casting metal shapes is initiated by pouring molten metal into a crucible of an assembly for maintaining the metal in its molten state. The crucible has an outlet, usually in the bottom, and has a mold in which the molten metal is shaped and solidified connected to the crucible outlet. The mold is usually open at both of its ends, and as the molten metal solidifies into the metal shape defined by the mold, it contracts away from the walls of the mold, and therefore, can be linearly withdrawn from the mold on a continuous basis. In

order to cast the molten metal into tube shape, an elongated mandrel must be mounted to extend axially into the mold opening but spaced from the inner walls of the mold to define a tubular space between the mandrel and mold. When the molten metal is fed into this tubular space, it is advanced along the mold and mandrel, and the mandrel is of suflicient length that cooling and solidification of the metal occurs before the metal is advanced beyond thetip of the mandrel to form the solid tubular shape. It is essential to the formation of tubes according to the continuous casting technique that control be maintained over the amount of material fed into the tubular space to make certain that there is no interruption of the continuous casting and insure that the metal is molten when fed into the tubular space so that there will be no premature cooling of the metal before formation.

We have developed an improved mandrel assembly cooperatively positioned with a mold in continuous casting apparatus which permits the continuous casting of better quality tubes. Broadly stated, the invention is in continuous casting apparatus for the continuous casting of metal tubes having a crucible containing molten metal mounted in an assembly for maintaining a reservoir of molten metal therein. An outlet is provided in the outlet of the crucible through which molten metal is fed for casting and a mold in which the molten metal is shaped and solidified is connected with the outlet. Means are also included for withdrawing the solidified metal from the mold. The improvement is in combination with this type apparatus and particularly resides in a mandrel and mold assembly. The mandrel assembly is characterized by a mandrel head mounted at and substantially closing the inlet end of the mold with one end substantially within the crucible and the opposite end within the mold. An integral elongated mandrel of reduced circumference from the mandrel head extends from the opposite end of the mandrel head and is spaced from the inner walls of the mold to define an elongated tubular space therebetween. Secondary reservoir means extend below the mandrel head for maintaining molten metal adjacent the tubular space immediately below the mandrel head and channel means lead from the secondary reservoir to the tubular space for controlling the flow of metal from the secondary reservoir into the tubular space immediately below the mandrel head whereby the molten metal can be maintained molten Within the secondary reservoir and fed into the tubular space in its molten state.

This secondary reservoir can be provided by an axial bore extending through the mandrel head and into the mandrel, which bore is open at the top end of the mandrel head and has a closed bottom located within the elongated mandrel beyond the head. A plurality of circumferentially spaced channels of smaller size opening than the bore lead from substantially the bottom of the bore to the tubular space immediately below the mandrel head.

The secondary reservoir can also be provided by an exterior reservoir positioned along the outer wall of the mold, which exterior reservoir opens into the crucible and terminates with a closed bottom below the mandrel head. A plurality of circumferentially spaced inwardly extending channels are provided in the mold and have smaller size openings than the reservoir with the channels leading from substantially the bottom of the reservoir to the tubular space immediately below the mandrel head.

It is also contemplated to provide a collecting chamber immediately beneath the mandrel head by a reduction in diameter ofv the mandrel head to provide an enlarged tubular space maintaining a quantity of molten metal at the uppermost inlet end of the elongated tubular space so that a quantity of molten metal is always available for feeding between the mandrel and mold. In addi tion to maintaining the desired quantity of molten metal, when longitudinal openings are provided through the head, this' combined structure serves also as a means for gas release. This combination of a collecting chamber and gas release is particularly useful in the casting of thin walled tubes.

The mandrel assembly has particular application in combination with continuous casting apparatus in which the crucible outlet is provided at the bottom of the crucible and the mold is co-axially aligned with the crucible outlet so that the metal is continuously gravity fed into the mold. And, more specifically, by connecting the mandrel head to the inlet end of the mold to form a substantially unitary assembly, the advantages of an easily replace'able assembly are also realized.

It has been found that when molten metal is fed directly into a tubular space defined by a mandrel and mold during the casting of thin-walled tubes in the order of .04 to .25 inch wall thicknesses, the metal often has a tendency to freeze or solidify before it has fully coalesced into tube shape. This is particularly true of high copper and high nickel alloys which have higher melting points than some alloys, and tend to chill more rapidly. With a mandrel and mold having the construction described, it is possible to feed the molten metal into the cooled zone of the apparatus without solidifying it so that the metal can be fed into the tubular space while still molten, and thereby permit the liquid metal to coalesce into tube shape before solidification is effected. Thus the common feature of the invention is to provide means for maintaining a reservoir of molten metal in the normally cool zone of the apparatus in proximity with the inlet end of the tubular sizing space between the mandrel and mold so that there will be good liquid flow of metal into the annular space before solidification thereby insuring uniformity of size in the cast tube.

Thus, the method of the invention is in combination with a method of continuously casting metal tubes wherein molten metal is directly fed from a crucible into a cooled zone and shaped into tubular form in the cooled zone in a tubular space defined between a mandrel and mold, solidified, and continuously withdrawn from the annular space. The improvement relates to feeding the molten metal into the cooled zone to provide a reservoir of molten metal adjacent the tubular space, maintaining the molten metal in the reservoir and then feeding the molten metal from the reservoir into the tubular space. By this method, a substantial reservoir of molten metal is first fed into the cooled zone, and from that reservoir the relatively thin streams of metal required to form the thin-walled tubing can be fed into the tubular space without danger of freezing before they coalesce into tube shape.

Preferred embodiments of the invention are described hereinbelow with reference to the drawing wherein:

FIG. 1 is an elevation, partly broken away and partly in section of continuous casting apparatus of the invention;

FIG. 2 is an enlarged fragmentary section of a first embodiment of a mandrel and mold assembly in the continuous casting apparatus;

FIG. 3 is a fragmentary plan view of the mandrel assembly taken along lines 3-3 of FIG. 2;

FIG. 4 is an enlarged fragmentary section of a second embodiment of a mandrel and mold assembly in the continuous casting apparatus;

FIG. 5 is a plan view of the second embodiment of mandrel and mold assembly shown in FIG. 4;

FIG. 6 is an enlarged fragmentary section of a third embodiment of a mandrel and mold assembly in the continuous casting apparatus;

FIG. 7 is a plan view of the third embodiment of the mandrel and mold assembly shown in FIG. 6;

FIG. 8 is an enlarged fragmentary section of a fourth embodiment of a mandrel and mold assembly in the continuous casting apparatus;

FIG. 9 is a plan view of the fourth embodiment of the mandrel and mold assembly shown in FIG. 8;

FIG. 10 is an enlarged fragmentary section of a fifth embodiment of a mandrel and mold assembly in the continuous casting apparatus; and

FIG. 11 is a plan View of the fifth embodiment of the mandrel and mold assembly shown in FIG. 10.

The vertical continuous casting apparatus shown in the drawing consists of a crucible 10 which is shown substantially filled with molten metal 11. The crucible is mounted within a holding furnace assembly 12 which is constructed of an outer metal sheet 13 and is lined with a heat insulating material 14. A plurality of burners 15 extend through the side walls of the holding furnace 12 at spaced intervals to supply the necessary heat to the crucible to keep the metal molten.

At the bottom of the crucible 10 is a crucible outlet 16 which leads into an elongated cylindrical annular furnace opening 17. The cylindrical opening extends through the insulating material 14 and the outer sheet 13 at the bottom of the holding furnace assembly 12.

A cooling zone 18 extends from below the crucible outlet to the outlet from the apparatus and is defined in part by a copper cooling block 19 which is supported on a plate 20, and the plate in turn is supported on a pair of threaded bolts 21 which depend from a plate at the bottom of the holding furnace assembly 12. The cooling block has a plurality of water passages 22 formed therein so that a coolant such as cold water can be circulated through the block to maintain it cooled during operation. A cylindrical cooling block opening 23 extends axially and completely through the cooling block in co-axial alignment with the crucible outlet 16 and the annular furnace opening 17.

Positioned with its marginal inlet end 24 within the crucible outlet 16 and extending through the cylindrical furnace opening 17 and through the cylindrical cooling block opening 23 and in co-axial alignment with the cru cible outlet is a graphite mold 25. The mold is held in place in the crucible outlet 16 and the annular furnace opening by a deposit of refractory cement 26. As shown, the inlet end 24 of the mold extends slightly above the bottom of the crucible for the reason that this extension will insure that the metal flowing into the mold will not be partially cooled by the crucible bottom; this is particularly important at the start. An intermediate portion 27 of the graphite mold is within the cooling zone and its marginal outlet end 28 extends outwardly from the bot tom of the cooling block. The cooling block 19 surrounds a major length of the intermediate portion 27 of the graphite mold and is in heat exchange relationship therewith. At the marginal outlet end 28 of the mold is an outwardly flared portion 29 which seats in an annular recess 30 provided in the cooling block to retain the mold in the block against longitudinal displacement in the direction of travel of the metal shape passing therethrough.

At the inlet end of the mold 25, an inner marginal portion 31 thereof is of a larger diameter than the general remaining inside diameter of the mold, and an annular shoulder 32 is defined by this increase in diameter. Positioned within the mild in such a manner as to form a unitary structural assembly therewith is mandrel assembly 33, The mandrel assembly consists of an enlarged cylindrical head 34 which has a diameter substantially equal to the diameter of the inner marginal portion 31 and of a length such that its upper end 35 is substantially coextensive with the inlet end of the mold and its lower end 36 seats flush in the annular shoulder 32 and is within the mold. The cylindrical head is adhesively sealed to the inner marginal portion of the mold. Extending axially within the intermediate portion of the mold is an elongated tapered mandrel 37 which is generally frustro comically-shaped and is of a smaller diameter than both the cylindrical head 34 and the general inside diameter of the mold so that an elongated tubular space 38, preferably annular in section, is defined between the mandrel and the inner wall of the mold in which the molten metal is solidified and shaped into a tube. The tip 39 of the mandrel extends well into the cooling zone to a point surrounded by the cooling block to the extent necessary to insure that solidificatcion of the tube has occurred before the tip of the mandrel is reached by the continuously advancing metal.

As shown in FIGS. 2 and 3 a cylindrical axial bore 40 extends through the mandrel head 34 from the upper end 35 beyond the lower end 36 and into the mandrel 37; the bore has an open top end 41 at the upper end 35 and a closed bottom 42 located within the mandrel below the head so as to define a reservoir or well for an intermediate supply of molten metal. A plurality of circumferentially spaced radially extending channels 43 of a smaller size opening than the bore 40 extend radially outward and through the mandrel Wall from the bottom of the bore to the tubular space 38 below the mandrel head whereby molten metal can be maintained within the bore and thereby fed into the tubular space in its molten state.

Finally, spaced from the outlet end of the graphite mold are a set of rollers 44 which are powered in a con ventional manner to withdraw the metal shape from the mold.

In one example the mandrel and mold were designed to form a 1%" OLD. tube having a A" wall thickness. The mandrel 36 had its greatest diameter of 1 immediately adjacent the mandrel head and the ID. of the mold was 2". The axial bore had a diameter ofabout 1" and extended about /2" into the mandrel below the mandrel head. Six A" diameter channels were drilled through the mandrel into the bottom of the bore.

In operation, molten metal is periodically poured into crucible 10 to maintain a reservoir of molten metal for continuous operation of the molten metal. The molten metal is gravity fed to flow from the crucible outlet where it is restricted in its flow by the mandrel head 34- positioned therein. A controlled amount of metal flows through into theaxial bore 40 where a reservoir of molten metal is maintained molten within the cooling zone 18. The metal is then fed through the channels 43 and empties into the cooling zone 18 which extends from about the lower end .316 of the mandrel head through the cooling block 19 to the outlet end 28 of the mold. Thus, almost as soon as the metal is fed into the tubular space cooling is initiated, and it is important that the amount of metal flowing into the tubular space 38 be limited so that the metal will not solidify before the metal has coalesced into tube form within the tubular space. Once the metal issues from the channels 43, it flows together within the tubular space 38 and coalesces into tubular shape, the temperature of the metal is brought to its solidification temperature, e.g. the copper alloys would be brought to a temperature of 1000 to 1350 C. Circulation of water through the cooling block 19 at a temperature of about 2 to 25 C. has

been found sutficient to maintain the block at the low temperature necessary for solidification. Because the cooling is effected by the heat exchange relationship between the cooling block 19 and the mold 25, the metal in contact with the inner wall of the mold solidifies first, and as it solidifies it begins to contract away from the inner wall of the mold leaving a separation between the inner wall of the mold and the semi-solidified metal tube. Owing to this contraction, the mandrel is also preferably tapered or generally conical, as described, so that upon solidification the tube will be separated from both the inner wall of the mold and the mandrel and can thereby be withdrawn by means of the rollers on a continuous basis.

The simple construction of the substantially unitary mold and mandrel assembly gives clear advantages in continuous casting of tubes in apparatus of the gravity feed type wherein the metal flows from the bottom of a crucible. The mandrel and mold assembly can easily be replaced after extended use of the apparatus, and the mandrel and mold of the new assembly are prealigned so that upon mounting in the apparatus the apparatus is ready to operate. While the apparatus shown is designed for casting cylindrical tubes, it is intended that it is in keeping with the invention to form any tubular shape. All these advantages are achieved with the additional embodiments described below.

Referring now to FIGS. 4 and a second embodiment of a mold and mandrel assembly is shown. The basic construction of both the mold and mandrel shown in the embodiments to be described below remains essentially unchanged from that described in detail with respect to the first embodiment and therefore detailed description will be generally confined to the difierences in these embodiments. A generally cylindrical mold 46 has a mandrel assembly 47 mounted together, with the two forming a substantially unitary structure. The mandrel assembly consists of an enlarged cylindrical head 48 positioned at the inlet end of the mold and an elongated tapered mandrel 49 which is gene-rally frustro-conically shaped and is of smaller diameter than the mandrel head which extends axially into the mold and is spaced from the mold to define an elongated tubular space between the mold and mandrel. Similar to the first embodiment, an interior reservoir 50 is formed into the mandrel head and extends below the mandrel head into a portion of the mandrel 49 and it is provided with radially outwardly extending circumferentially spaced channels 51 of a smaller size opening than the bore which defines the reservoir.

In this embodiment the deposit of refractory cement 26 which holds the mold secured to the crucible 10 does not surround the marginal inlet end portion 52 of the mold and its absence thereby provides an annular exterior reservoir or well 53, the side walls of which are defined by a portion of the crucible and a portion of the outer wall surface of the mold and terminates with an annular bottom portion 54 which is substantially co-extensive with the bottom portion of the interior reservoir 50 provided in the mandrel. A plurality of radially inwardly extending circumferentially spaced channels 55 lead from the exterior reservoir to the annular space immediately below the mandrel head. The top of the exterior reservoir 53 is open to the crucible and a deposit of molten metal is maintained in the exterior reservoir and flows through the inwardly extending channels to the tubular space.

In FIGS. 6 and 7 a third embodiment is shown. Here a mandrel 56 and a mold 57 have generally the same configuration and are attached in the same manner as that described above. In this embodiment however, there is no reservoir provided in the mandrel; only an exterior reservoir 58 is provided by the concentric spacing of the mold relative to the crucible as described in the second embodiment above. The reservoir 58 has an annular configuration with a bottom portion 59 terminating below the mandrel head 60 of the mandrel. A plurality of radially inwardly extending circumferentially spaced channels 61 are provided and lead from the bottom portion of the annular exterior reservoir into the tubular space defined between the mandrel and the mold.

In FIGS. 8 and 9 the configuration and mold assembly shown is identical to the described with respect to the second embodiment above with one exception. Here an interior reservoir 62 is provided by a bore extending axially into the mandrel and an exterior reservoir 63 is provided by an annular space between the crucible and the mold on the exterior of the marginal inlet end of the mold. The dilference lies in the manner in which the channels extend from the reservoirs. As best shown. in FIG. 9, channels 64 which extend inwardly and are circumferentially spaced about the bottom of the interior reservoir extend at a tangent to the cylindrical bore defining the interior reservoir. Similarly, channels 65 which are circumferentially spaced and lead through the mold wall from the exterior reservoir are also arranged at a tangent to the inside diameter of the mold and thus, essentially at a. tangent to the tubular space which is preferable has an annular opening. With each other and with this tangential orientation of the channels the flow of metal into the tubular space is in a tangential direction and this insures that the space will be filled with metal so that when very thin-walled tubes are being continuously cast there will be no void in the formation of the tube wall.

A fifth embodiment is shown in FIGS. 10 and 11. In this embodiment a mandrel 66 of a partially difierent configuration from that described previously is shown, but it is set into a mold 67 in the same way described above. This embodiment is particularly designed for casting very thin-walled tubes with a wall thickness in the order of about 0.04 inch. Because of the thickness of the wall, the tubular space 68 between the mandrel and mold is of course very small. To provide a constant surplus of metal at the inlet of the tubular space, a collecting chamber 69 is defined immediately beneath an enlarged mandrel head 66 and the inlet end of the tubular space 68 and between the mandrel 66 and the mold 67. This collecting chamber is formed by the mandrel 66 inwardly beveled in a direction toward the mandrel head so as to provide an angled mandrel surface 70 of about 5 to 20 relative to the axis of the apparatus; thus the collection chamber gradually decreases in size toward the inlet end of the tubular space 68 to provide a steady gravity flow into the tubular space.

Because of the enlarged collection chamber beneath the mandrel head, it is possible to provide axially extending circumferential-1y spaced inlet channels 71 extending through the mandrel head and opening into the collection chamber. An annular exterior reservoir is provided about the inlet end of the mold and is open at its upper end to the crucible and closed at its bottom and radially inwardly extending channels 73 extend from the bottom of the reservoirs to the inlet end of the collection chamber 69. In has been found that the combination of the collection chamber with the axially extending channels 71 provides means for releasing gas caused during cooling upwardly through the channels.

It may be necessary to use these individual exterior reservoirs if it is found that excessive cooling is occurring in the exterior reservoir before complete metal flow can take place into the annular space.

Advantages can also be realized by beveling the man drel adjacent the mandrel head to provide a collection chamber in the other embodiments where small wall thickness tubes are to be formed.

We claim:

1. In continuous casting apparatus of the gravity feed type for the continuous casting of metal tubes having a crucible containing molten metal mounted on an assembly for maintaining a reservoir of molten metal therein, an outlet in said crucible through which molten metal is gravity fed for casting, a mold in which said molten. metal is shaped and solidified connected with said outlet, and means for withdrawing the solidified tube from the mold, the improvement in combination therewith of an integral mandrel and mold assembly formed of a non-metal, like graphite, comprising a mandrel head seated within the inlet end of the mold to form a substantially unitary assembly with the mold, with one end of the mandrel head substantially within the crucible and the opposite end within the mold, a cooling zone defined beneath the cmcible and extending from said opposite end of the mandrel head to the outlet end of the mold wherein the molten metal will solidify, an integral elongated mandrel of reduced circumference from said mandrel head extending from said opposite end of the mandrel head and spaced from the inner walls of the mold to define an elongated tubular space therebetween, a secondary reservoir open to the crucible and having its bottom. extending below said mandrel head into the cooling zone for maintaining molten metal adjacent the tubular space immediately below the mandrel head in the cooling zone, and channel means leading from the bottom of said secondary reservoir to said tubular space for controlling flow of molten metal from said reservoir into said tubular space immediately below said mandrel head, whereby a source of molten metal can be maintained molten in the cooling zone within said secondary reservoir and fed into the tubular space in its molten state to continuously cast thin walled tubes.

2. In continuous casting apparatus as in claim 1 wherein said secondary reservoir means is comprised of an axial bore extending through said mandrel head and into said mandrel, said bore having an open top end at the end of the mandrel head facing the crucible and a closed bottom looated within the elongated mandrel below said head, and a plurality of circumferentially spaced radially extending channels in said mandrel of a smaller size opening than said bore and leading from substantially the bottom of said bore to said tubular space immediately below said mandrel head.

3. In continuous casting apparatus as in claim 1 wherein said secondary reservoir means is comprised of at least one exterior reservoir positioned along the outer wall of the mold, said exterior reservoir opening into the crucible and terminating with a closed bottom below the mandrel head, and a plurality of circumferentially spaced extending channels in said mold and of smaller size opening than said reservoir leading from substantially the bottom of said reservoir to said tubular space immediately below said mandrel head.

4. In continuous casting apparatus as in claim 2 wherein at least one exterior reservoir is positioned along the outer wall of the mold, said exterior reservoir opening into the crucible and terminating with a closed bottom below the mandrel head, and a plurality of circumferentially spaced inwardly extending channels in said mold of smaller size opening than said reservoir leading from substantially the bottom of said reservoir to said tubular space immediately below said mandrel head.

5. In continuous casting apparatus as in claim 1 wherein a plurality of circumferentially spaced axially extending channels are provided in said mandrel head and lead from said crucible side of the mandrel head to the said elongated tubular space beneath the mandrel head.

6. In continuous casting apparatus according to claim 1 wherein said channel means extend radially inwardly from said secondary reservoir means.

7. In continuous casting apparatus according to claim 1 wherein said channel means extend tangentially inwardly from said secondary reservoir means.

8. In continuous casting apparatus according to claim 1 wherein a collecting chamber of increased size from said elongated tubular space is provided immediately beneath the mandrel head by a reduction in diameter of the mandrel adjacent said channel means.

9. In continuous casting apparatus according to claim 8 wherein means are provided for releasing gas from the collecting chamber.

10. In continuous casting apparatus according to claim 5 wherein a collecting chamber of increased size from said elongated tubular space is provided immediately beneath the mandrel head by a reduction in diameter of the mandrel adjacent said channel means.

References Cited UNITED STATES PATENTS 2,466,612 4/ 1949 Phillips et al 164-281 FOREIGN PATENTS 899,415 8/ 1944 France. 751,356 3/1951 Germany. 113,892 4/1945 Sweden. 231,523 6/ 1944 Switzerland.

J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

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