US2136394A - Casting metal - Google Patents

Description

Nov. 15, 1938. F. F. POLAND El AL CASTING METAL Filed June.29, 1935 2 Sheets-Sheet l INVENTORS BY lflllfld l ATTORN Y 2 Sheets-Sheet 2 BYZ'arl E [indmrr ATTORN Nov. 15, 1938. F. F. POLAND ET Al;

CASTING METAL Filed June 29, 1935 Patented Nov. 15,

CASTING METAL Frank F. Poland, New Brunswick, and Karl A. Undner, Railway, N. J.

Application June 29,

8 Claims.

This invention relates to improvements in the continuous casting of copper and copper-base alloys.

It has long since been proposed to produce castings of indefinite length by introducing the liquid metal into a mold or die, cooling the metal by extraction of heat through the die walls and continuously wihtdrawing the solidified metal. However, in spite of the vast amount of effort expended along this line, in times past, the pro posal never met with success. In fact, the results were so disappointing that other methods and means, such as withdrawing the heat down the previously congealed casting, were proposed in efforts to successfully cast the metal in a continuous manner.

By reason of certain improvements provided by the present invention it is now possible to successfully cast copper or copper-base alloys in a continuous manner by an operation in which the metal is caused to solidify by extraction of the heat through the die wall.

As a result of long and varied experimentation and investigation, it has been discovered that the principal reason for the repeatedly unsuccessful attempts to continuously cast copper or its alloys by processes embodying the concept of extracting heat through the die walls, was the failure to fully appreciate and properly evaluate the essential characteristics of the die or mold itself. Based upon this discovery, it has now been found that in order to successfully cast copper in the manner contemplated that the material comprising the die must possess certain characteristics.

Among these characteristics, our investigations have shown that the die or mold material must be one which is not only refractory and which will take an extremely smooth finish but it must also possess a fair degree of heat conductivity and remain stable with respect to thermal change and shock. Further it must be non-wettable with respect to the metal, 1. e., it must act in a manner similar to that exhibited by mercury and unlike that exhibited by water in a glass tube, and it must be of a particle size not exceeding 40 microns and of a porosity of not more than 20% with pore spaces of 40 microns maximum. It will be understood that the figures relating to par icle size, porosity and pore space are maximum and that lower figures are preferable if the material meets the other characteristics.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended 1935, Serial No. 29,064

hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which- Fig. l is an elevation in section of one form of apparatus for practising the invention,

Fig. 2 is an elevation in section of the die shown. in Fig. 1,

Fig. 3 is an elevation in section of a composite die, and

Fig. 4 is an elevation in section of a somewhat different die.

Referring now to the drawings, there is shown a furnace i0 mounted on platform l2 supported by beams l4. Mounted upon refractory blocks [6 is receptacle I 8 for holding the molten metal 20. The furnace I0 is heated by any suitable means (not shown) such as oil or gas burners or electric heating means.

Extending downwardly from the bottom of the receptacle I8 and fitted therein is the mold or die 22 having a channel or passageway 24 and surrounded by cooling jacket 26 appropriately connected with cooling fiuid inlet 28, overflow tube 30 and outlet 32. A plate 34 defines chamber 36 directly beneath the mold 22 and gas inlet 38 leads to the chamber 36. Rolls III are provided for withdrawing the metal from the mold as it solidifies.

As previously stated, the die or mold must be of material possessing certain definite characteristics and standards. Among the materials embraced by the invention are boron carbide (B40) and graphite of extreme density, it being borne v in mind that the latter is not to be confused with ordinary graphites or even graphites which are ordinarily referred to as dense and which are inoperative in the present process. In other words, only such graphite as will meet the spe-' cific requirements heretofore referred to are contemplated.

Utilizing a material which falls within the specifications already set forth, however, the construction of the die or mold may be greatly varied and several variations in construction are shown in the accompanying drawings. In Figs. 1 and 2 there is shown a relatively simple mold construction comprising a die 22 having collar 42 countersunk in the bottom of the receptacle l8. The channel 24 of the die tapers slightlyto facilitate the ready withdrawal of congealed metal. Surrounding the mold is jacket 26 adapted for the circulation of water or other cooling fluid from the inlet 28 to outlet 32 via overflow II.

Inasmuch as the most important consideration from the standpoint of the die is the surface which contacts the metal in the congelation zone, it is only necessary to utilize material having the characteristics heretofore enumerated for the lining of the mold. This allows the remainder of the mold to be made of other material thus permitting substantial savings in cost. Composite dies may thus be provided as illustrated in Figs. 3 and 4.

Referring to Fig. 3, there is shown a mold in which only the liner 44 is of material contemplated by the invention, the main body 46 of the mold being, for example, ordinary dense graphite. The liner 4 is secured in the body portion 48 by threads 50. Between the bottom of the receptacle 48 and the top of the cooling jacket-I6 is a mica sleeve 52 surrounded by a heating coil 54 enclosed in insulation 58, thus permitting a substantial superheat to be imparted to the metal just prior to its chilling which has been found of value in improving the quality of the cast metal. The composite die shown in Fig. 4 is similar to that shown in Fig. 3, the heating coil and insulation being omitted.

In operation the bottom of the die or mold is closed with a suitable plug prior to the introduction of the metal into the receptacle l8 in a manner similar to that shown in Trotz U. S. Patent No. 705,721. The closing device may appropriately comprise a rod of the same diameter as the desired casting and it preferably extends through the rolls 40 thus facilitating the withdrawal of the rod at the start of the casting operation.

The copper or copper alloy to be cast is then introduced into the receptacle i8 and maintained in the proper liquid condition therein. A suitable cooling fluid. such as water, is circulated through the jacket surounding the die to congeal the metal in the mold. The metal first entering the mold will weld to the closing plug and at the appropriate time a longitudinal movement is imparted to the starting rod thus withdrawing the casting from the mold. As the casting is withdrawn, additional metal is congealed above thus providing a casting of continuous length. Nonoxidizing gas, such as illuminating gas, is preferably introduced into the chamber 38 through the inlet 38 to prevent oxidation of the mold assembly which in some instances would otherwise be considerable at the temperatures employed.

The following specific examples of actual operations will serve to illustrate how the invention may be practised.

Example 1 Inthis instance a die of very dense graphite comprising graphite formed by chemical precipitation and cemented under high pressure with colloidal carbon as the bond, was used. The casting assembly was of the type illustrated in Fig. 3 with a nickel-chromium coil encircling the die between the receptacle and the water jacket. The main body portion of the die consisted of ordinary dense graphite. The total length of the die was seven and one-half inches with the die proper, of material possessing the essential characteristics heretofore enumerated, extending for a distance of approximately five and two tenths inches downwardly from the upper portion of the die. The top of the water jacket was three and seventy-five hundredths inches from the top of the die, which latter had a diameter of one and one-half inches.

At the start of the run the copper had a temperature of 2140 F. and was withdrawn at the rate of one and l four tenths inches per minute. Thereafter the temperature of the copper was increased to approximately 2175" l". and the rate of withdrawal increased to approximately three inches, which conditions were maintained until the end of the run. The metal produced was found to be thoroughly sound, of excellent surface and composed of angular crystals disposed at an angle of approximately 45.

Example 2 Using a construction such as shown in Fig. 4 with a one inch diameter die tapering at the rate of 0.25 inch per foot, molten copper at 2125 F. was withdrawn at the rate of approximately two inches per minute, which rate was gradually increased to four and three tenths inches per minute and continued until the end of the run. The temperature of the continuously cast rod, which was of excellent surface and sound throughout, was approximately 1800" F. as it emerged from the die. An examination of the casting showed that with speeds of withdrawal below three inches per minute the crystals were angular but with withdrawal speeds above that figurethe crystal structure was radial.

Example 3 Employing a mold of the type shown in Fig. 4 in which four inches of the die insert was surrounded by the cooling jacket, phosphorus copper comprising approximately three and one-half pounds 01' phosphorus per ton of metal was cast at a temperature of 2210 F. with a withdrawal rate of three inches per minute, the temperature of the emerging rod being approximately 1565 F. The rate of withdrawal was increased to a speed of six inches per minute employing a metal temperature of 2060 F. with the emerging cast ing exhibiting a temperature of 1670 F. The casting thus continuously produced was sound throughout and exhibited an entirely radial crystal structure. a

It will thus be appreciated that by employing a die having the characteristics heretofore described, copper or copper-base alloys may be successfully cast continuously in operations embodying the principle of heat extraction through the walls of the mold or die. It may also be added that in addition to forming the die (at least that part contacting the metal) from material which will meet the standards specified, it is also preferred to provide a slight taper for shapes less than about two inches in diameter to assist in the withdrawal of the castings. In casting larger shapes, for example, billets of three inches or more in diameter, the taper may well be dispensed with as the contraction of the copper upon solidification is suiilcient to provide adequate clearance.

It is not at present exactly known why the material from which the die is formed must have the characteristics which have been found so essential but it is possible that the productionof radial or angular crystals such as are formed when the heat is withdrawn through the die wall, set up conditions which do not exist in the case of longitudinal crystallization. Whatever the explanation, however, it is clearly demonstrated by the invention that the use of a polished die made from material of the class described, such as boron carbide or exceedingly dense graphite permits the continuous casting of copper by processes in which the heat is extracted through the die wall by a surrounding cooling medium.

While certain novel features of the invention have been disclosed and are pointed 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 of the invention.

What is claimed is:

1. A process for continuously casting metal which comprises supplying the metal to a mold formed of refractory, heat-conducting material which is non-wettabie with respect to the metal and which exhibits a maximum porosity and pore space of 20% and 40 microns respectively, circulating a cooling fluid around the metal in said mold thereby withdrawing heat from the metal through the die walls and causing the metal to solidify and withdrawing the cast metal from said mold. g

2. A process for casting metal which comprises continuously supplying molten metal to a mold having congealed metal in the bottom-thereof, the inner surface of said mold consisting of a refractory, heat-conducting .material of particle size not exceeding 40 microns and exhibiting not more than 20% porosity, congealing additional metal to that present in the bottom of themold by circulating a cooling medium around the mold and withdrawing the resulting casting as additional metal is congealed within the mold.

3. In the art of continuously casting copper, that improvement which comprises passing the copper through a die of refractory, heat-conducting material, non-wettable with respect to copper, the particles and pore spaces 'of which do not exceed 40 microns and circulating a cooling medium around said die thereby solidifying the metal by extraction ofheat through the die walls.

4. Metal casting apparatus comprising a receptacle for molten metal, a refractory, heatconducting die communicating with said receptacle and in which the metal is solidified, said die consisting of material non-wettable with respect to the metal being cast and having particles and pore spaces not exceeding 40 microns and a maximum porosity of 20% and cooling means surrounding said die for the extraction of heat through the walls of the latter.

5. Apparatus for continuously casting copper comprising a reservoir for molten copper, a mold of boron carbide communicating with said reservoir and adapted to receive molten copper therefrom, means for circulating a cooling fluid about said mold to effect solidification of copper therein and means for withdrawing the cast copperfrom said mold as additional quantities of same,

are congealed.

6. Apparatus for continuously casting copper andalloys thereof comprising, a reservoir, a composite mold adapted to receive metal from said reservoir and retain same until solidified, the

interior surfaces of said mold consisting of a sleeve of refractory material non-wettable with respect to copper and of maximum particle. size and pore spaces of 40 microns with a porosity not exceeding 20%, a cooling means associated with said mold for withdrawing heat through the walls thereof and means for regulating: the rate of withdrawal of the casting from said mold.

'7. Apparatus for continuously casting copper comprising the combination with a receptacle defining a reservoir for molten copper, of a refractory, heat conducting die communicating withv the receptacle for receiving molten copper from the receptacle and defining a congelation chamber for the molten copper, the said die having at least its surface which is in contact with the molten copper consisting of dense graphite having particles and pore spaces not exceeding 40 ceeding 20%. a

FRANK Fr POLAND. KARL A. LINDNER.

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