US3087213A - Method for continuous casting - Google Patents

Description

pril 30, 19 s. R. MILLIKEN ET AL 3,087,213

METHOD FOR commuous CASTING Filed Nov. 25. 195'? I W W W Ni [5; r x I 1 NH! so enter/P.

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ATTORNEY United States Patent 3,087,213 METHOD FOR CONTINUOUS CASTlNG Spencer R. Millikan, Lower Bnrrell Township, Westmoreland County, and Earl J. Schafer, Whitehall, Pa., as-

signors to Aluminum Company of America, Pittsburgh,

Pa., a corporation of Pennsylvania Filed Nov. 25, 1957, Ser. No. 698,567 4 Claims. (Cl. 22-492) This invention relates to a method for the continuous and semi-continuous casting of ingots of aluminum base alloys containing 0.1 to 15 percent magnesium. In particular, it relates to a method wherein the mold is provided with a lubricant containing an organic BF carrier compound which will yield boron trifluoride vapors at elevated temperatures so as to provide about the metal ingot a protective atmosphere which reduces or eliminates undesirable surface eifects such as heavy oxidation, tearing, cold shuts, or the like.

The term continuous," as herein used, refers to the progressive and uninterrupted formation of a cast body or ingot in a mold or die which is open at both top and bottom. The pouring operation may continue indefinitely if the cast body is cut into sections of suitable length below the mold or the pouring operation may be started and stopped in making each ingot. In the latter case the process is often referred to as being semi-continuous.

For convenience, an aluminum base alloy containing 0.1 to 15 percent magnesium, alone or in combination with other elements, will be hereinafter referred to as an aluminum-magnesium alloy.

It is well-recognized that considerable difficulty is experienced in the continuous casting of aluminum-magnesium alloy ingots. The surface of the ingot is often heavily oxidized and marred by tearing, exudation, and other defects, all of which may result in an unacceptable ingot. It has been found that these surface defects are often attributable to the heavy oxidation of magnesium at the external surface of the ingot and that the particles of these oxides of other oily-compounds act as focal points for further oxidation on and within the surface.

It is an object of this invention to provide a method for continuous and semi-continuous casting of aluminummagnesium alloy ingots, wherein heavy oxide formation on the surface is greatly reduced, if not substantially eliminated.

It is also an object to provide a method for continuous and semi-continuous casting of aluminum-magnesium alloy ingots, wherein cold shuts and tearing of the ingots are substantially eliminated.

It is a further object to provide a method for the continuous and semi-continuous casting of aluminumrnagnesium alloy ingots wherein an oxidation-inhibiting film is 'formed on the surface of the ingot.

It has been discovered that the above objects, and others which will become evident herein, may be obtained by a method for continuous and semi-continuous casting of aluminum-magnesium alloy ingots, wherein the mold is lubricated with a grease or oil composition containing an organic BF -carrier compound which will yield boron trilluoride at the elevated temperatures of the casting process. It has further been found that the boron trifiuoride content of the mold lubricant should be between 0.1 and 1.0 percent by Weight of the entire composition.

It has previously been determined that inorganic compounds such as ammonium, potassium and sodium i'luoroborates in mold lubricants are not effective oxidation inhibitors in the casting of alumium-magnesium alloy 3,087,213 Patented Apr. 30, 1963 "ice ingots. Furthermore, the use of such substances has generally been found to increase cold shuts and tearing.

The term aluminum-magnesium alloy," as herein employed, refers to an aluminum base alloy containing 0.1 to 15 percent magnesium, with or without the presence of other elements, such as from 0.1 to 12 percent copper, or 0.25 to 14 percent silicon or 0.1 to 20 percent zinc, or 0.1 to 3 percent manganese, or combinations of two or more of these elements. Any of the foregoing alloys may also contain one or more of the following elements, often referred to as hardeners, in the following percentages:

0.05 to 0.5 percent chromium 0.01 to 0.5 percent titanium 0.25 to 2.5 percent nickel 0.01 to 0.5 percent boron 0.002 to 2 percent beryllium 0.1 to 0.5 percent molybdenum 0.1 to 0.5 percent zirconium 0.1 to 0.5 percent tantalum 0.1 to 0.5 percent columbium 0.1 to 0.5 percent cobalt However, the total amount of the latter elements should not exceed about 3 percent.

The term organic BF -carrier compound, as used herein, refers to organic compounds or complexes which will yield boron trifiuoride in a reactive state at temperatures above 45 C. but below about 500 C. These carrier compounds are selected from the group consisting of R-HBF, and X-BF where R represents a nitrogencontaining organic compound having a basic character such as an amine or amide, and where X represents an organic substance or carrier which will sorb or hold BF when treated therewith.

Generally, the R-HBF, compounds may be described as being the products of reaction between the nitrogencontaining organic compound and hydrofluoroboric acid, HBF Those organic substances which contain sorbed or held B1 comprise a wide range of complexes, and in a few instances perhaps compounds, which may be prepared in various ways but which, for the most part, may be conveniently prepared by exposing the base material X to direct contact with gaseous B1 Whether these substances be compounds or complexes or a solution of B1 in the base material or merely the undefined result or reaction product of the treatment with BF of a material which has an unsatisfied valence which will act as an acceptor of B1 they are, for the purposes of this invention, alike if they will yield BE; in a reactive state at the temperatures developed in the casting mold.

The formula R-HBF may be described as the reaction product of hydrofluoroboric acid, HBF.,, and an aliphatic carbocyclic or heterocyclic, mono or polyamine or hydroxy amine or amide, or an alkaloid, or carbocyclic diazo compounds, or any other basic nitrogen-containing organic compound. Amines such as the following can be used; butyl amine, di-n-butyl amine, amyl amine, ethylhexyl'amine, dodecyclamine, didodecyclamine, tetraethylamine, dioctadecyclamine, tetramethylamine, trihexylamine, ethylene diamine, diethylene triarnine, triethylene tetramine, di(2-ethylhexylarnine), N-phenyl-N,N,N-trimethylamine, tri-n-amyl amine, aniline, N-octadecyl- N,N,N-trimethylarnine, 3-phenyl propylamine, Z-pentyl- 4,5-dimethyl-4-hexanooxyethyl 2 oxazoline, 2-pentyl-4, N-dodecylbenzyl N,N,N trimethylamine, 4-bis(hexano oxymethyD-Z-oxazoline, 2-nonyl-4-ethyl-4-caproxymethyl-2ethyl oxazoline, monoethanolamine, diethanolarnine, triethanolamine, aminoethanolamine, diethylarninoethanol, 3-di-n-amylaminopropylamine, monoisopropanolamine, phenyl ethanolamine, phenyl dicthanolamine, o-dimethylaminoethyl-p-octyl, phenol, 4-amino-3-pentadecyl phenol, nitron, phenyl morpholine, and l-hydroxyethylheptadecenyl lyoxalidine. Examples of amides which can be used are acetamide, propionamidc, butyramide, benzamide, cinnamide, nicotinamide, diacetamide, triacetamide, n-hexadecylamide and n-octadecylamide. Among the alkaloids which may be used are neurine, morphine, brucine, cocaine, and other substances employable are the diazo compounds formed from substances such as aniline, p tluoroaniline, nitroaniline, o-tluidine, xylidine and naphthylamine.

The carrier or substance represented by X in the formula X-BF may be selected from a wide range of organic substances, among them being: ethylamine, diethylamine, phenyl-dimethylamine, acetonitrile, acetamide, aniline, pyridine, butyric acid, benzoic acid, trimethylamine oxide, diethyleneglycololeate, butyl stearate, acetamide, n-hexylether, morpholine, dioxane, urea, oleic acid, linoleic acid, lard oil, cetyl alcohol, diethylenetriamine, oxazoline and tallow.

The formulae X-BF and R-HBF it should be understood, do not necessarily imply an equimolecular ratio between X and BF or R and HBF but rather that the organic material may be associated with BF or H313, in any proportion.

When either X-BF or R-HBF, is used, the carrier compound should be added to the lubricant so as to provide between 0.1 and 1.0 percent by Weight of boron trifluoride in the total composition. Amounts of less than about 0.1 percent do not provide the benefits of this invention and amounts in excess of 1.0 percent are found to result in excessive vapor formation, tending to produce surface defects. Generally, it is preferred to use a lubricant composition containing between 0.3 and 0.5 percent by weight of boron trifluoride.

Generally, the lubricant is usually applied to the mold prior to the commencement of casting by manually brushing or swabbing it onto the mold surface. However, in some instances, especially in high-speed production lines, an automatic or semiautomatic feed system may be employed by which the lubricant is initially applied and may be supplied intermittently or continuously during the casting drop.

Referring to the attached drawing, diagrammatically illustrated is one form of apparatus by which a liquid or semi-liquid lubricant may be continuously or intermittently fed to the mold surfaces. Seated upon the rectangular mold shell 2 is a lubricant feed device 4 having tubes or channels 6 and outlets 8. Lubricant is supplied under pressure to the channels 6 through feed lines 10 and is discharged through the outlets 8 whence it spreads across the lip 12 and onto the walls of the mold 2. Due to its liquid or semi-liquid state, it flows downwardly along the wall to the interface between the mold and the ingot 14, and below.

Lubricant is desirably supplied at a low rate so that sudden chilling of the liquid metal meniscus is prevented. It is also desirable that the lubricant feed be prevented from impinging directly upon the surface of the molten metal, such as by use of a lip or other means which will direct the flow onto the sides of the mold.

The mold lubricant to which the carrier substance is added may be of a mineral, animal or vegetable base, or a combination thereof. Generally, however, lubricants must prevent wetting of the mold by the liquid metal and provide a lubricating film on the mold at all times. If oils are employed, it is preferred that a continuous system of lubrication be employed, especially in the casting of longer ingots, since the lighter hydrocarbon oils have a tendency to distill or carbonize. Greases or semisolid hydrocarbon materials are conveniently employed because of their higher heat resistance and ability to provide a more durable lubricating film.

Generally, the conditions of casting determine the amount of lubricant, and also the degree of viscosity if continuous lubrication is employed; however, excessive amounts are undesirable because of flammability and carbonization. Volatile liquid vehicles may be employed in the lubricant composition as an aid in application or transportation; however, the lubricating base itself should be relatively heat-stable, i.e., have a fairly high boiling point and fairly high viscosity.

Combination of greases and oils have been satisfactorily employed, as have been compositions containing various additives such as silicones, graphite, extreme pressure agents, etc. Generally, however, the lubricant base should comprise at least 50 percent of the total composition.

Another aid often employed in the casting process is vibration of the mold during the casting drop, which has been found of assistance in reducing tearing and cold shuts. If so desired, this vibration method may be used in combination with the method of the instant invention.

Illustrating the efiicacy of the present invention are the following examples wherein aluminum-magnesium alloys were cast by a semi-continuous process. Generally, in each case, the aluminum mold shells were brushed with a lubricant composition consisting of 1.0 percent by weight of di-n-butylammonium tetrafiuoroborate in a standard mold grease (50 percent of lard-50 percent of calcium-lead base grease containing about 15 percent graphite). The metal pouring temperature was between 1275 F. and 1300 F. and lowering rates of 2 /2 to 4 inches were employed. Water sprays were used to chill both ingot and mold.

Example 1. An alloy nominally composed of aluminum, 5.0 percent magnesium, 0.1 percent manganese, 0.1 percent chromium and 0.15 percent titanium was cast into extrusion ingots 8 inches and 14 inches in diameter, the mold lengths being 8% inches and 18 inches, respectively, and the molten metal heads being about '7 inches and 16 inches. Attempts to cast this alloy by previous commercial practice, i.e., using a standard commercial lubricant containing no BF additive, resulted in acceptance of only 15 to 20 percent of the ingots due to severe tearing and cold shuts in addition to heavy oxidation. When the lubricant containing BF was employed, visual inspection of the ingots indicated that surface oxidation and exudation had been greatly reduced and that cold shuts and tearing had been substantially eliminated, permitting acceptance of more than percent of the ingots.

Example 2.An alloy nominally composed of aluminum, 3.5 percent magnesium and 0.25 percent chromium was cast into ingot 8 inches and 9 inches in diameter, the mold length being 8% inches and the molten metal head about 7 inches. Standard practice had been unsatisfactory, allowing only 17 to 25 percent acceptance. The ingots cast by the present method exhibited only light oxidation and considerably reduced exudation; further, cold shuts and tearing were substantially eliminated, thus permitting acceptance of more than 80 percent of the ingots.

Example 3.An alloy nominally composed of aluminum, 5.25 percent magnesium, 0.8 percent manganese, 0.1 percent copper and 0.1 percent chromium was cast into ingots 8 inches and 9 inches in diameter, the mold length being 8% inches and the metal head about 7 inches. Visual examination revealed little oxidation and exudation and only rare instances of cold shuts and tearing.

Example 4.An alloy nominally composed of aluminum, 1.0 percent magnesium and 0.3 percent manganese was cast into ingots 9 inches and 11 inches in diameter, the mold lengths being 8% inches and 10 inches, respectively, and the molten metal heads about 7 inches and 8 inches. Upon visual examination, exudation and oxidaton were found to be insignificant and cold shuts and tearing were noted to be substantially eliminated.

Having thus described the invention, we claim:

1. In the continuous and semi-continuous casting of aluminum base alloy ingots containing 0.1 to 15 percent magnesium, the method wherein the mold is lubricated with a composition containing an organic BF -carrier compound selected from the group consisting of R-HBF and X-BF where R represents a basic nitrogen-containing organic compound and X represents an organic substance which will sorb or hold BF when treated therewith, said carrier compound decomposing at least in part to yieid boron trilluoride in an active state as it is heated to a temperature between 45 and 500 C. during the casting process.

2. In the continuous and semi-continuous casting of aluminum base alloy ingots containing 0.1 to 15 percent magnesium, the method wherein the mold is lubricated with a composition containing an organic BF -carrier compound selected from the group consisting of R-HBF, and X-BF where R represents a basic nitrogen-containing organic compound and X represents an organic substance which will sorb or hold BF; when treated therewith, and the BB, content being between 0.1 and 1.0 percent by weight of the total lubricant composition, said carrier compound decomposing at least in part to yield boron trifiuoride in an active state as it is heated to a temperature between 45 and 500 C. during the casting process.

3. The method of claim 2 wherein the BF; content is between 0.3 and 0.5 percent by weight of the total lubricant composition.

4. In the continuous and semi-continuous casting of ingots of aluminum base alloys containing from 0.1 to 15 percent magnesium wherein the mold and emerging ingot are chilled by the direct application thereto of a liquid coolant, the method of substantially eliminating the occurrence of cold shuts, tears and heavy oxide formation on the ingot surfaces comprising lubricating the mold with a composition containing an organic BP -carrier compound selected from the group consisting of R-HBF and X- BP where R represents an organic basic nitrogencontaining compound and X represents an organic substance which will sorb or hold BF when treated therewith and the BF}, content being between 0.1 and 1.0 percent by weight of the total lubricant composition, said carrier compound decomposing at least in part to yield boron trifluoride in an active state as it is heated to a temperature between and 500 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,092,033 Stroup Sept. 7, 1937 2,135,183 Junghaus Nov. 1, 1938 2,137,715 Erdrnann et al Nov. 22, 1938 2,380,202 Stroup July 10, 1945 2,611,743 Kipp Sept. 23, 1952 2,747,244 Goss May 29, 1956 FOREIGN PATENTS 645,202 Great Britain Oct. 25, 1950

Claims (1)

1. IN THE CONTINUOUS AND SEMI-CONTINUOUS CASTING OF ALUMINUM BASE ALLOY INGOTS CONTAINING 0.1 TO 15 PERCENT MAGNESIUM, THE METHOD WHEREIN THE MOLD IS LUBRICATED WITH A COMPOSITION CONTAINING AN ORGANIC BF3-CARRIER COMPOUND SELECTED FROM THE GROUP CONSISTING OF R HBF4

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