US3210812A

US3210812A - Continuous casting mold

Info

Publication number: US3210812A
Application number: US248793A
Authority: US
Inventors: Jr John D Berwick
Original assignee: Scovill Inc
Current assignee: Scovill Inc
Priority date: 1962-12-31
Filing date: 1962-12-31
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12

Description

Get. 12,1965 J. D. BERWICK, JR

CONTINUOUS CASTING MOLD Filed Dec. 51. 1962 INVENTOR.

United States Patent 3,210,812 CONTINUOUS CASTING MOLD John D. Berwick, Jr., North Haven, Conn., assignor to Scovill Manufacturing Company, Waterbury, Conn., a corporation of Connecticut Filed Dec. 31, 1962, Ser. No. 248,793 5 Claims. (Cl. 2257.2)

My invention is an improvement in molds for the continuous casting of metal in relatively smaller cross-sections than those produced in the usual continuous casting process.

One of the objects of the invention is to provide an improved mold capable of casting rods or the like at a satisfactory rate, from brass containing approximately 15% zinc. I am aware that the continuous casting of copper has been done by the use of a water-cooled graphite die mounted in a copper supporting jacket. Such a mold has not been feasible for the casting of zinc-containing alloys, one of the reasons being that zinc oxide forms along the mold surfaces. This, of course, increases friction and tearing of the metal around the outer surface of the rod.

For successful continuous casting, it is of the utmost importance to avoid friction to the greatest possible extent between the metal being cast and the surface of the die. The material employed for the die is usually a fine grained dense graphite having a high polish on the bore. During the formation of the casting, the molten metal enters from a suitable source of supply, such as a holding furnace, and as it passes the chilled area of the mold, it freezes into a shell which increases in thickness and rigidity until the shell shrinks away from contact with the mold due to contraction of the solidifying metal. It is important that the chilling take place as rapidly as possible in order that the distance along which the shell must travel in frictional contact shall be as short as possible.

Accordingly, another object of the invention is to provide an improved mold capable of an increased rate of heat transfer between the copper jacket and graphite die over former installations where the graphite die is in direct contact with the interior of the copper jacket. It is possible to machine the interfitting surfaces of the die and jacket, but there will, nevertheless, be minute quantities of air trapped at the interface even if they are put together under compression.

On the other hand, my invention makes possible solidto-solid contact between the die and water-cooled copper jacket which is free of gas or any other fluid, thus greatly enhancing the thermal contact and permitting more rapid heat withdrawal.

Another feature of my improved mold has to do with substantially increasing the area of the water-cooled jacket which is exposed to the coolant as compared to the area of maximum heat withdrawal from the metal being cast. This is accomplished by counterboring the graphite die over a portion of its length at the bottom end and extending the jacket below the actual forming portion of the die. Thus, by the use of metal of high heat conductivity, such as copper, the heat can be withdrawn very rapidly from a concentrated area where the metal is freezing.

The solid-to-solid contact is accomplished by a layer of metal which is cast in situ in an annular space between the die and copper jacket. Molten lead poured into such a space has been found to provide a much better thermal contact between the die and the jacket than is possible by the fitting of any machined surfaces.

In the accompanying drawing, I have shown for the purpose of illustration, one embodiment which the invention may assume in practice. In the drawing:

FIG. 1 is a diagrammatic view, mostly in vertical secice tion, of a portion of the casting apparatus incorporating my invention; and,

FIG. 2 is a cross-section on line 2-2 of FIG. 1.

Metal is supplied in a molten state at about C. superheat from a holding furnace, the bottom wall of which is indicated by the numeral 3. This furnace bottom may be of silicon carbide supported by a fire-brick wall 4, with a layer of refractory cement between them. The graphite die 5 has its upper end protruding preferably above the bottom wall 3 of the holding furnace. The die is of general cylindrical shape having a smooth polished bore 6 and having a tapered bottom end 7 fitted tightly into the supporting jacket 8 which is of relatively high heat conducting metal, such as copper.

At the lower end, there is a counterbore 9 of somewhat larger diameter than the bore 6 but yet sufficiently small, that it will serve to help guide the casting rod away from the die. All except the bottom portions of the die and jacket, are separated by an annular space into which there is poured molten lead 10, which extends preferably from about the top of the copper jacket to a point well below the bottom of the bore 6. The upper portion of the graphite die 5 is surrounded by refractory material 11 between the die 5 and the bottom wall of the furnace, and the lower portion is enclosed by the copper jacket 8. The copper jacket is surrounded throughout a major portion of its length by a water chamber 12 formed by a metal enclosure 13. Under casting conditions, water circulates continuously through this chamber around the copper jacket 8, and

suitable connections

14 and 15 may be provided for this purpose.

The diagrammatic view in FIG. 1 indicates a pair of withdrawal and

feed rolls

16 and 17 which may be contoured to engage the surface of the round r-od R. These rolls can be driven from any suitable source of power at the desired rate, which source of power can be connected or disconnected periodically by means of a magnetic clutch. A suitable timer can be arranged to control such a clutch so that the feed can be intermittent. In a typical example, the feed may be on for four seconds, and off for one second. Thus, if the indicated feed rate is 15" per minute, the net rate is 12" per minute.

In operation under casting conditions, the molten material from the holding furnace 3 flows downwardly through the bore 6 in the graphite die 5 to the chill section of the mold, which for practical purposes, is relatively short, extending from its upper limit about the level of the lead layer 10, to the counterbore 9. I have found that in casting a rod, this chill section of the mold can be held to about 1 /8". The metal will, of course, start to freeze around the inner surface of the bore 6 and it can be assumed that at the beginning of the four-second feed interval, it Will solidify along some such line as indicated at L At some point when the metal is cooled sufficiently-it can be assumed to be about the bottom-most portion of the line L -the rod material will shrink slightly away from the surface of the die, thereby reducing the rate of heat extraction. Thus, the zone of maximum heat transfer at the beginning of the cycle may be that indicated by the lines Z During the continuance of the cycle through the four-second period, this zone while being maintained at the same minimum extent, will actually move downwardly so that the line of solidification will be somewhat like the dotted line L The zone of maximum heat withdrawal at this time of the cycle is indicated by the lines Z When the rod feed is interrupted for one second, some of the molten metal above the line L will cool so that at the beginning of the next feed cycle of four seconds, the zone of maximum heat removal will be that indicated by Z1.

Patented Oct. 12, 1965 By extending the copper jacket a substantial distance below the chill zones, a much larger area of copper jacket can be exposed to the cooling water, thus making it possible to extract the heat very rapidly from the narrow cooling-area of the metal. This factor, along with the solid metal-to-metal contact between the graphite die 5 and the copper jacket 8 which is provided by the layer of lead 10, makes it possible to extract the heat much faster than with any other known continuous casting molds, which means that the band or zone of maximum heat withdrawal can be kept to a minimum. This makes it possible to cast at satisfactory rates without doing damage to the cast material, such as is caused by excessive friction between the metal and the die in the freezing zone.

While I have indicated only one die extending from the holding furnace 3, obviously any desired number can be employed to increase the rate of production from one holding furnace.

The counterbore 9 is of only slightly larger diameter than the bore 6. This leaves a narrow clearance space between the lower portion of the graphite die and the rod, which may be of the order of in width. Thus, if there is any tendency for any zinc oxide to form in that portion of the mold, it can be readily blown away by an air jet. This lower portion of the die, nevertheless, helps to guide the hot rod on its downward path away from the chill zones. The eflective chilling portion itself of the die is so short that the lowermost zone of maximum heat withdrawal is so close to the bottom of this chilling portion that there is little chance for any oxide to form. All of these factors make it possible for the first time that I am aware to cast zinc-containing alloys, particularly copper alloys having a zinc content of 15% or higher.

While the specific embodiment shown in the drawing produces a round rod, it will be apparent that the invention may be used in the production of various other shapes; for example, oval, square, irregular or tubular.

What I claim is:

1. In apparatus for continuous casting of metal, a stationary mold comprising a hollow die of graphite, into which molten metal flows at the upper end and from which solidified metal emerges at the bottom end, a supporting water-cooled jacket for said die consisting of metal having a high rate of heat conductivity, the lower end portion of said die fitting tightly in said jacket, the die and jacket above the tightly fitted lower portion being thermally joined by metal cast in situ therebetween, such cast metal having a substantially lower melting point than that of said jacket.

2. In apparatus for continuous casting of metal, a stationary mold comprising a tubular graphite die whose upper end is adapted to project into a source of molten metal, a supporting jacket of copper into which the bottom end of said graphite die is directly fitted, there being an annular space between the copper jacket and graphite die throughout a substantial portion of its length and a layer of molten lead cast in situ in said space to provide a solid-to-solid contact between the die and copper jacket, and means for supplying a liquid coolant to the outer surface of said copper jacket throughout the major portion of the length of said jacket which is in contact with said lead.

3. In apparatus for continuous casting of metal the combination defined in claim 2 wherein said graphite die has a counterbore at its bottom end and wherein said.

layer of lead overlaps said counterbore.

4. In apparatus for continuous casting of metal the combination defined in claim 2 wherein said graphite die has a counterbore at its bottom end and wherein said layer of lead overlaps said counterbore, and wherein the portion of said copper jacket exposed to theliquid coolant extends below said layer of lead.

5. In combination with the apparatus for continuous casting of metal as defined in claim 2; means for efiecting intermittent withdrawal of the rod from the mold.

References Cited by the Examiner UNITED STATES PATENTS 2,176,991 10/39 Crampton et al. 2257.2 2,245,224 6/41 Poland 2257.'2 2,999,800 9/61 Reeside 22-203 XR 3,059,295 10/62 Vosskuehler 22-572 MARCUS U. LYONS, Primary Examiner.

Claims

1. IN APPARATUS FOR CONTINUOUS CASTING OF METAL, A STATIONARY MOLD COMPRISING A HOLLOW DIE OF GRAPHITE, INTO WHICH MOLTEN METAL FLOWS AT THE UPPER END AND FROM WHICH SOLIDIFIED METAL EMERGES AT THE BOTTOM END, A SUPPORTING WATER-COOLED JACKET FOR SAID DIE CONSISTING OF METAL HAVING A HIGH RATE OF HEAT CONDUCTIVITY, THE LOWER END PORTION OF SAID DIE FITTING TIGHTLY IN SAID JACKET, THE DIE AND JACKET ABOVE THE TIGHTLY FITTED LOWER PORTION BE-