US2206888A - Method of continuous metal casting - Google Patents

Description

y 1940. c. T. GREENIDGE 2,206,888

METHOD OF CONTINUOUS METAL CASTING Filed Nov. 8, 1958 INVENTOR Cjzqrlesil. Greenidye %,m. M

Patented July 9, 1940 METHOD OF CONTINUOUS METAL CASTING Charles T. Greenidge, Columbus, Ohio, assignor, by mesne assignments, to Edward R. Williams and Julia Lee Cox Williams, as joint tenants witlrright of survivorship Application November 8, 1938, Serial No. 239,490

6 Claims.

This application relates to the continuous casting of metal in a definite shape and form and is particularly applicable to what is known in the art'as continuous casting. In the art of continuous casting the supply of molten metal, either ferrous or non-ferrous, is continuously fed to one end of a mold cavity of suitable cross-section which is kept at a desirable temperature by a circulating fluid in contact with the outside of the mold wall and the cast metal withdrawn from the opposite end of the mold cavity without substantially interrupting the continuity of the ingot during the entire process. By means of continuous casting, ingots of a desired shape and of indefinite length and having superior properties may be cast in an economical and expeditious manner.

In the continuous casting of metal as described in United States Patent No. 2,079,644, issued'May 20 11, 1937, to Edward R. Williams, a suitable method of and apparatus for continuous casting is described in detail. -My invention is an improvement on the method therein described' In casting continuous ingots by the process 86 outlined in the Williams Patent No.'2,0'79,644, while generally satisfactory results have been obtained there is in some instances a tendency for the forming ingot to stick in the tube and for the ingot skin to rupture. This is probably 80 caused either because the frictional resistance between the wall of the forming ingot and the mold wall is greater than the strength of the ingot skin or because the heat removed through the mold wall is not suflicient to produce a skin of 8| sufiicient thickness and strength to overcome any frictional resistance which may be present. It is also possible that, due to the fact that the .ingot skin immediately starts to shrink away from the interior of the molding tube as soon as the metal 40 is partly or'wholly solidified, an air gap is formed between the ingot wall and the mold wall which insulates the ingot and reduces the heat transfer from the ingot to the mold wall. The .molten' metal inside the ingot skin would then deliver 4| heat to the ingot skin which, because of the air gap and absence of direct contact with the mold wall, would not be transferred to the mold at a suificiently rapid rate, and consequently the skin would be reheated and weakened to such an ex- 50 tent that it would rupture.

When rupture of the ingot skin occurs, the molten metal will escape through the opening and will immediately form a new skin when the metal comes in contact with the cold metal wall.

This new skin has the appearance of a scab ingot above the rupture and the operation must then be stopped. It is also possible. that, due 10 to the formation of these scabs or rough spots,

the diameter of the ingot is increased at this point and the increased diameter and roughened sur- 1 faces will so increase the friction between the formed" ingot and the mold tube walls that more force is required to draw down the ingot than the ingot wall will stand. This may also be a contributing factor to the rupture of the ingot wall.

I have discovered that sticking of the ingot in the molding tube and rupture of the ingot skin can be avoided by coating the inner wall of the molding tube with a material which has .a melting temperature much below the temperature of the formed ingot skin. For example, rolling mill lubricant may beapplied to the inside of themolding tube. While one would expect that this would be almost instantly burned out, this is not the case because of the high rate at which the walls of the molding tube are cooled and also because of the limited amount of available oxygen; so that a small amount of lubricant will last an amazingly long time. Also, by having an oxidizable material on the wall of the molding tube, the limited amount of oxygen that may enter between the tube wall and the solidifying metal is consumed so that oxidation of the metal itself is avoided. It is not necessary, however, that the material be a readily oxidizable one as a slow oxidizing material or a non-oxidizable material may also be advantageously employed as a coating material to form a film.

The reason why the coating or film acts to facilitate the withdrawal of the ingots has not as yet been definitely ascertained. It may function:

As a thermal contactor to continue the heat transfer from the ingot to the mold wall when most intimate contact between the two) as when the fllm was added.

As a lubricant onlyin which case it may function to reduce the frictional resistance between the skin of the ingot and the mold wall, and thus enable a thinner skin to be sufficient to resist the stresses incident to withdrawal.

As a plastic mold wall to produce a temporary wall of smaller diameter than the tube itself which, as the frictional resistance increases, can be squeezed out of the way and thus prevent sumcient frictional resistance to induce the rupture of the skin.

To prevent wetting of the walls of the molding tube or cooling cylinder by the formed ingot, thus reducing any tendency for, adhesion or increase of frictional resistance between the ingot and the mold wall.

In the accompanying drawing there is represented a vertical section through a casting apparatus of the type to which the present invention pertains. The view illustrated corresponds to Figure 1 of the Williams Patent No. 2,079,644.

In the drawing, is represents a thin wall molding tube of cylindrical form and fabricated from metal such as copper or brass having high thermal conductivity. The tube is open at both ends and is housed within a casing or jacket It in such a way as to provide a shallow cooling chamber i1 between the tube and the casing. A stool element IS in the form of an ingot blank is located within and has a sliding fit with the tube l5. At the beginning of the pouring operation the blank is located at such a position within the tube l5 as to provide a pouring cavity H3 at the top of the tube. is delivered from the furnace by any suitable means such as a tiltable ladle 20 and is received by a pouring box 2| secured to the apparatus adjacent to the top of the 'tube. The molten metal poured into cavity l9 is'supported on the upper end of the ingot blank or stool i8 and bonded thereto by disconnectable lugs 22. In order to maintain a substantially constant temperature differential between the inner and outer surfaces of the molding tube I 8 and to effectually remove the heat from the outer surface of the mold tube IS, a cooling medium such as water is introduced into the chamber I! through a pipe 23. The cooling water, after passing through the cooling chamber or jacket space I! is discharged from the bottom thereof through the discharge pipe 24.

The lower end of the blank I8 is engaged by suitable withdrawing mechanism having driven rollers 25 which contact the sides of the blank and also the sides of the ingot as it is being withdrawn. The rate of pouring and the rate of withdrawal of the unit are synchronized so that the level of the metal in the molding tube will remain substantially constant. Heat is withdrawn from the metal at such a rate as to allow a skin to form. which is sufliciently strong so that the ingot may be withdrawn without rupture of the skin wall.

I have found that other lubricants beside oil and grease may be advantageously employed, for example, tri cresyl phosphate alone or mixed either with an oil or grease of high viscosity of either mineral or vegetable origin. The lubricant preferably should have a fairly high boiling point and a fairly high viscosity. I have also found that by coating the interior of the mold Molten metal to be cast tube with a film of graphite, lead, solder or chromium, satisfactory results have been obtained in some instances.

While I have described a preferred embodiment of my invention, it will. be understood that the invention may be otherwise practiced within the scope of the following claims.

I claim:

1. In the method of continuous casting of metal in a thin molding tube of high thermal conductivity cooled by a flowing thin sheet of fluid in v contact with the outer walls of the tube, the step of maintaining on the inner wall of the tube a fllm of lubricating material having a melting point substantially lower than that of the metal being cast.'

2. In the method of continuous casting of metal in a thin wall molding tube of high thermal conductivity cooled by a thin flowing sheet of fluid forced along andin contact with the outer walls of the tube, the step of introducing on the inner wall of the tube and maintaining therealong for substantially the length of the tube a lubricant having a melting point substantially lower than that of the metal being poured.

3. In the method of continuous casting of metal in a thin-walled molding tube of high thermal conductivity cooled by a shallow sheet of fluid forced at high velocity along the outer walls of the tube, the step which consists of applying at intervals to the molding surface of the tube and maintaining therealong for substantially the length of the tube a lubricating material which is fluid at a temperature substantially lower than that of the metal being poured.

4. In the method of continuous casting of metal in a thin-walled molding tube of high thermal conductivity cooled by a shallow sheet of.fluid forced at high velocity along the outer walls of the tube, the step which consists of applying to the molding surfaces of the tube in the vicinity of the metal being cast a lubricating material containing tri cresyl phosphate and maintaining said lubricating material in contact with the molding surface of the tube for a substantial proportion of the length of the tube.

5. In the method of continuous casting of metal in a thin-walled molding tube of high thermal conductivity cooled by a shallow sheet of fluid forced at high velocity along the outer walls of the tube, the step which consists of applying to the molding surfaces of the tube in the vicinity of the metal being cast a lubricating material containing tri cresyl phosphate and a vegetable oil and maintaining said lubricating material in contact with the molding surface of the tube for a substantial proportion of the length of the tube.

6. The method of continuously casting metals of high heat content which comprises pouring the metal into a thin-walled molding tube of high thermal conductivity, scouring the exterior of the tube with a thin sheet of cooling fluid flowing at high velocity, withdrawing the metal from the opposite end of 'the tube after casting, introducing a lubricating fluid against the side walls of the tube and keeping the inner surface of the tube sufliciently cool to maintain the lubricant along the interior of the tube throughout the operation and precluding the evaporation of such fluid before the pouring operation is substantially completed.

CHARLES T. GREENIDGE.

DISCLAIMER 2,206,888.C'harles T. Green'idge, Columbus, Ohio. Mm'ncn on Con'rnwccs I METAL CASTING. Patent dated July 9, 1940. Disclaimer filed March 3, 1942, by the assignees, Edward R. Williams and Julia Lee 002: Williams.

Hereby enter this disclaimer to claim 1 of said patent. [Ofiicial Gazette March 24,'1942.]

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