US3613767A

US3613767A - Continuous casting and rolling of 6201 aluminum alloy

Info

Publication number: US3613767A
Application number: US824220A
Authority: US
Inventors: Daniel B Cofer; Joseph A Bass
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1969-05-13
Filing date: 1969-05-13
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: JPS4926162B1; GB1282334A; CA926278A; DE2021664A1; CH517535A; FR2047660A5

Abstract

A method of continuously manufacturing a heat treatable aluminum base alloy rod, such as 6201 aluminum alloy rod containing from 0.50 to 0.9 percent silicon, from 0.6 to 0.9 percent magnesium and the balance essentially aluminum, comprising heating the metal to a molten state, continuously pouring and cooling the metal to form a cast bar at a temperature above the temperature at which the alloy metals begin to precipitate, continuously lengthening and reducing the cross-sectional area of the bar in a rolling mill to form rod and reducing the temperature of the rod to a temperature level below the crystallization temperature of the alloy metals within a time period which is short enough to keep the alloy metals from precipitating.

Description

United States Patent [72] inventors Daniel B. Coier 3,011,928 12/1961 Kopec et a1 266/3 X Carrollton; 3,266,945 8/ 1966 l-lelling et al... 148/ 1 1.5 A Joseph A. Bus, Bremen, both of Ga. 3,333,624 8/ 1967 Cofer et a1. 164/87 [21] Appl. No. 824,220 3,349,471 10/1967 Bell et a1 164/87 X [22] F l y 3, 1969 OTHER REFERENCES [45] Patented Oct. 19, 1971 Modem Metal A 19 Assignee southwire p y 5, pr. 64, T8200. M7. pp. 54, 56 & 58.

Carrollton, Ga. Primary ExaminerR. Spencer Annear Attorney-Jones & Thomas [54] CONTINUOUS CASTING AND ROLLING OF 6201 ALUMINUM ALLOY 2 Claims, 1 Drawing Fig ABSTRACT: method of continuously manufacturing a heat treatable aluminum base alloy rod, such as 6201 aluminum [52] US. Cl 164/76, u rod containing from Q50 to Q9 percent Silicon, f 06 164/87, 164/89 to 0.9 percent magnesium and the balance essentially alu- [51] Int. Cl B2211 1 H12 minum, comprising heating the meta] to a molten state com [50] Field of Search 164/76, 87, finuously pouring and cooling the metal to form a cast bar at a 89, 270, 278, 283; 266/3; 148/2, 11-5 A temperature above the temperature at which the alloy metals begin to precipitate, continuously lengthening and reducing [56] Reerences cued the cross-sectional area of the bar in a rolling mill to form rod UNITED STATES PATENTS and reducing the temperature of the rod to a temperature 1,931,912 10/1933 Whitzel 148/1 1.5 A level below the crystallization temperature of the alloy metals 2,710,433 6/ 1955 Properzi. 164/283 X within a time period which is short enough to keep the alloy 2,994,328 8/1961 Lewis 266/3 X metals from precipitating.

. COOLING 25 TOWER 9 SUMP ROLLING MILL [8 29 13 I 6 2a COILER PATENTEDUBT 19 l97l 3,613,767

CASTING Daniel B. Cofer BYJOSQph A Bass yd'wm 4* m ATTORNEYS INVENTORS.

CONTINUOUS CASTING AND ROLLING OF 6201 ALUMINUM ALLOY BACKGROUND OF THE INVENTION 6201 aluminum alloy is a high-strength aluminum-magnesium-silicon alloy which in wire form and in the heat-treated condition has a tensile strength of over 46,000 p.s.i., elongation greater than 3 percent, and an electrical conductivity greater than 52.5 percent IACS. In the past, 6201 aluminum alloy redraw rod and similar aluminum alloy redraw rods have been manufactured for commercial use by a plurality of separate steps which include DC casting an aluminum ingot, reheating the ingot to about 700 to 850 F., hot rolling the cast ingot to redraw rod, and solutionizing the rod at a temperature of approximately l,000 F. and water quenching the rod. The rod is cold drawn to form wire, and the wire is artificially aged at temperatures between 250 and 450 F. This procedure is capable of producing wire having tensile strength and electrical conductivity characteristics which are similar to or in excess of those for 6201 aluminum.

While the foregoing procedure produces an acceptable product, this batch process, or noncontinuous casting process, is capable of producing only a limited amount of rod; that is, a given sized billet will product only a corresponding mass of rod, and the lengths of separately produced rod must be welded together to form longer lengths of rod. When the billet is reheated and rolled to form rod, it is customary to crop the leading end of the rod since it is of inferior quality. Thus, a

substantial amount of waste is experienced in the former procedure. An elongated rod which comprises several lengths of batch produced rods welded together will include poor grain structure at the places where it is welded together, which effects tensile strength and conductivity. Furthermore, it is virtually impossible to create identical conditions in the reheating and rolling of different billets, and the lengths of rod welded together will usually have difierent grain characteristics.

In order to reheat the rod in the prior art system, the rod must be carefully handled in order to achieve uniform heating and in order to produce a uniform product. For instance, the oven into which the rod is placed for solutionizing must create relatively even heat distribution in order that the rod be uniformly heated. Furthermore, the rod usually must be arranged so that there is enough circulation of the air or gases in the oven between the coils to assure proper heat distribution. It is customary to place individual coils of rod on portable racks which space the coils from each other for this purpose; however, the racks occupy space in the oven and reduce the volume of rod that can be heated. While the purpose of reheating the rod is to solutionize the rod, it is desirable to keep the rod from reaching a temperature substantially higher than its solutionizing temperature since the overlapping portions of the rod in the coils of rod tend to become tacked or welded to each other. This tacking together of the portions of the rod creates surface blemishes on the rod when pulled apart, and frequently the coils remain tacked together so that several coils of rod tend to pay out together. Thus, even heat distribution within the solutionizing oven is a practical necessity so that the rod can be rapidly and uniformly solutionized to hold the hazard of rod tacking to a minimum.

The prior art process provides a substantial amount of time in which the aluminum can oxidize, as when the cast ingot cools or is being reheated, when the rod from the rolling mill cools or is being reheated for solutionizing, and when the solutionized rod from the reheating oven cools. The result is that the rod becomes substantially oxidized, which makes it relatively hard for redrawing purposes, and which causes the rod to have a relatively dull finish. Of course, when the rod is more highly oxidized and harder, it is more difficult to draw and the draw dies deteriorate rapidly. Thus, the separate steps required in the prior art process of forming 6201 aluminum alloy rod are expensive in that separate handling of the rod is required between and during each step, the product must be handled in a careful manner, and extra equipment must be available and maintained to handle the product.

SUMMARY OF THE INVENTION Briefly described, the present invention comprises a method of continuously manufacturing aluminum base alloy rod, such as 6201 aluminum rod, without the necessity of reheating the ingot or the rod during the process. The bar emerging from the casting machine is passed through a rolling mill, a quench tube, and then coiled in a continuous process. The heat of the cast bar emerging from the casting machine is not dissipated and the bar temperature is maintained in the solutionizing temperature range of the metal as the rod is passed to the rolling mill. The rod is hot worked in the rolling mill and quenched immediately as it emerges from the rolling mill so that the time lapse from the point where the bar enters the rolling mill to where the rod is quenched to a temperature level below the crystallization temperature of the alloy metals is less than the time required for the alloy metals to precipitate to the grain boundaries of the metal. After the rod is quenched it is at a temperature below the temperature where immediate and substantial precipitation occurs, which provides for sufficient time in which the rod can be drawn into wire or otherwise treated. When the rod is subsequently cold-drawn into wire it has an unusually high tensile strength and relatively high electrical conductivity, and an unusually bright appearance.

Thus, it is an object of this invention to provide an improved method for producing aluminum alloy products.

Another object of this invention is to provide a method of continuously manufacturing aluminum alloy rod without the necessity of reheating an ingot or the rod to produce a product having high tensile strength and high conductivity charac teristics.

Another object of this invention is to provide an improved 6201 aluminum product and a method for forming such a product.

Another object of this invention is to provide an economical and expedient method of manufacturing 6201 aluminum rod.

Another object of this invention is to provide an improved 620l aluminum product with a more uniform heat treat along its entire length. Other objects, features and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevational view of a casting machine, rolling mill, quenching tube, and coiler, utilized in the procedure herein set forth.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawing, in which like numerals indicate like parts throughout the several views, FIG. ll shows casting machine 10, rolling mill l1, quench tube assembly 12, and coiler 13. In summary, the process of the invention comprises pouring molten metal from a furnace (not shown) into casting wheel 10a of casting machine 10. The molten metal is cooled and solidified in casting wheel 10a and extracted as a solid bar 15 and guided toward and through rolling mill 11. The product is lengthened and reduced in its cross-sectional area within rolling mill 11, and emerges as wrought rod 16. Rod 16 is passed through quench tube assembly 12 which includes first stage quench tube 18, pinch rollers 19, second stage quench tube 30, pinch rollers 21, and rod conduit 22. The rod emerges from rod conduit 22 and is formed into coils by coiler 13. Pump 24 receives the quenching liquid from sump 25 and pressurizes first stage quench tube 18. The quenching liquid is passed through quench tube 18 in a direction of flow which is along the path of travel of rod 16 and is passed through a conduit system to cooling tower 26, where it is cooled and recirculated back to sump 25. Pump 28 receives quenching liquid from sump 29 and pressurizes second stage quench tube 20. The quenching liquid of the second stage quench tube is passed through quench tube 20 in a counterflow relationship with respect to the movement of rod 16, and is passed through a conduit system to cooling tower 30 where it is cooled and recirculated back to sump 29. Thus, the quenching liquids are maintained at controlled temperatures during the quenching process.

In more detail, the molten metal processed through the apparatus is a heat treatable aluminum alloy. 1f the product to be formed is to be 6201 aluminum, the ranges of silicon and magnesium contents are from 0.50 to 0.90 percent, and from 0.60 to 0.90 percent, respectively. The range of silicon and magnesium alloys can vary in this metal beyond the range for 6201 alloy to 0.2 to 1.3 percent and to 0.3 to 1.4 percent, respectively, if desired. The metal in its molten state is poured through a fiber glass screen into a holding pot maintained at a temperature above 1,200 F., usually at about l,270 F. From the holding pot, the metal is poured into casting wheel a where it is cooled and solidified into a cast bar 15. The cast bar is stripped from casting wheel 10a and passed to rolling mill 1! at a temperature high enough so that the metal is solutionized, usually between 960 to 1,000 F. As the cast bar passes through rolling mill 11, the bar is hot formed and coated with a soluble oil concentration maintained at about 40percent and at a temperature below 200 F., usually at about 160 F. Rolling mill 1 1 includes a plurality of roll stands which compress the cast bar alternately from top to bottom and side to side, which functions to lengthen the cast bar and reduce the cross-sectional area of the cast bar, so that the cast bar is progressively formed into redraw rod. The volume of soluble oil concentration in rolling mill 11 is maintained at a level of about two thirds the volume in a typical continuous casting system for EC. rod. The temperature and volume of the coolant applied to the rod in the rolling mill are adjustable so that when the rod 16 emerges from rolling mill 11, the temperature of the rod is at a level so that the rod is still within its hot fonning temperature range, which is usually above 650 F., so that the alloy metals have not precipitated from the aluminum. The low volume of coolant applied to the rod in the rolling mill requires a higher concentration of lubricant, approximately 40 percent solution as compared to approximately 10 percent for an EC. rod system, and the flow is adjusted so that approximately equal flow of coolant is maintained at each roll stand.

Immediately upon leaving the rolling mill, rod 16 passes into quench tube 18 where it is rapidly cooled or quenched by water. Since the portion of rod 16 emerging from rolling mill 11 is at a high temperature and is highly ductile at this point and unable to withstand significant compression, pinch rolls 19 are placed between first stage quench tube 18 and second stage quench tube 20 in order to reduce the effects of compression in rod 16 as it emerges from rolling mill 11. As the rod emerges from quench tube 18, it will have solidified to an extent such that it is able to withstand the compression and friction of pinch rolls 19; however, the quenching process of the rod is not complete at this point. Thus, the rod passes from pinch rolls 19 into second stage quench tube 20 where a soluble oil solution is used as the quenching liquid and the quenching procedure is completed. The distance between first stage quench tube 18 and second stage quench tube 20 is small and the rate of travel of the rod is high enough so that no significant delay in the quenching of the rod is encountered. As the rod emerges from second stage quench tube 20, it is passed between pinch rolls 21 and through rod conduit 22, toward coiler l3. Pinch rollers 21 function to eliminate any compression forces in rod 16 as it passes through second stage quench tube 20, and also to urge the rod through arcuate rod conduit 22 to coiler 13.

The quenching liquid flows through second stage quench tube 20 in a counterflow relationship in respect to rod 16, which enables the system to maintain a positive control over the temperature of the rod as it emerges from second stage quench tube 20. The quenching liquid flowing through the quench tube 18 can pass either in convergent or counterflow relationship with respect to rod 16 since a massive volume of quenching liquid is forced into contact with rod 16, and accurate control over the temperature dissipation from the rod cannot be maintained atthis point.

The cast bar enters the first roll stand of the rolling mill in the solutionizing temperature of the metal which is a temperature above the temperature at which the alloy metals begin to precipitate to the grain boundaries of the metal, and the rod emerges from the second stage quench tube at a temperature below which any immediate substantial precipitation of the alloy metals occur. This temperature range is from about 850 to about 400 F.

The present invention will be more readily understandable from a consideration of the following examples:

EXAMPLE 1 An alloy with a metal analysis in the holding furnace of approximately 0.69 percent magnesium, 0.51 percent silicon, 0.37 percent iron, and the balance essentially aluminum was maintained at a temperature approximately between l,280 F. to l,300 F. The metal was poured through a fiber glass screen into a holding pot. The metal in the holding pot was maintained in a temperature range of from about l,270 to 1,280 F. The metal was cast at a speed of approximately 8,500 pounds per hour on initial start-up, with gradual increases in speed of approximately 5 minutes each, to a speed of about 10,000 pounds per hour.

As the cast bar was stripped from the casting wheel, it was maintained in a temperature range of from about 940 to 960 F. As the cast bar entered the rolling mill, it was at a temperature estimated at 940 F. and entered at a casting speed of 40-46 feet per minute.

The soluble oil concentration of the rolling mill was about 40 percent and maintained at a temperature of approximately 160 F. The gallon per minute of flow of soluble oil was estimated at gallons per minute and all the roll stands had approximately equal coolant flow. The temperature of the rod leaving the rolling mill was in the range from 675 F. to 725 F. The volume and temperature of the soluble oil solution in the rolling mill was adjusted to control the temperature of the rod at this point. The rod traveled a distance of less than 8 inches from the last roll stand of the rolling mill to the first stage quench tube. The time lapse from a section of the rod entering the first roll stand to emerging from the second stage quench tube was approximately 9 seconds. The first stage quench tube was approximately 5 feet in length and maintained full of flowing cold water in the same direction of movement as the direction of movement of the rod. The pinch rolls were hydraulically driven at a speed sufficient to exert tension on the rod extending back toward the rolling mill, which eliminated any twisting of the rod in the last three roll stands of the mill and aided in pushing the rod through the delivery tube. Soluble oil of about 4 percent concentration in water was circulated through the second stage quench tube in countertlow relationship to the rod at a rate of approximately 150 gallons per minute. As the rod emerged from the second stage quench tube, its temperature was approximately 250 F.

The rod produced by this method was three-eights inch in diameter, had a tensile strength of approximately 25,000 p.s.i. 15 percent elongation, and was of a good commercial quality. No problems were encountered in drawing the rod to 0.067 diameter wire. The rod was drawn after being allowed to age naturally for 2 days. When artificially aged for 3 hours at approximately 300 F., the wire had a tensile strength of approximately 48,000 p.s.i., 8 percent elongation, and conductivity of about 52.5 lACS. The rod showed no more degree of oxidation than does EC material, and the wire drawn from this rod was as bright as EC material, which is very bright when compared to 6201 wire manufactured by the previously known processes.

EXAMPLE n The process of example I is substantially repeated except that the speed of the casting machine is decreased and the cooling system of the casting machine is adjusted so that the cast bar enters the rolling mill at a temperature of 850 F. and requires a time lapse of 30 seconds to emerge from the second stage quench tube in the form of rod. The volume of the coolant applied in the quench tubes and rolling mill is adjusted so that the rod emerges at a temperature of 400 F. The wire drawn from the rod has a tensile strength of over 46,000 p.s.i., elongation greater than 3 percent, and electrical conductivity greater than 52.5 percent lACS. The rod is also very bright.

EXAMPLE Ill The process of example I is substantially repeated except that the metal analysis in the holding furnace is approximately 0.8l percent magnesium, 0.78 percent silicon, 0.30 percent iron, and the balance essentially aluminum. The speed of the casting machine is decreased and the cooling system adjusted so that the cast bar enters the rolling mill at a temperature of 855 F. and requires a time lapse of 19 seconds to emerge from the second stage quench tube in the form of rod. The volume of coolant applied in the quench tubes is adjusted so that the rod emerges at a temperature of 390 F. The wire drawn from the rod has a tensile strength of over 46,000 psi. elongation greater than 3 percent, and electrical conductivity greater than 52.5 percent lACS. The rod is also very bright.

EXAMPLE IV The process of example III is substantially repeated except that the bar enters the rolling mill at 900 F. and leaves the second stage quench tube at 250 F. in a time lapse of 12 seconds. The wire drawn from the rod has a tensile strength of over 46,000 p.s.i., elongation greater than 3 percent, and electrical conductivity greater than 52.5 percent IACS. The rod is also very bright.

It has been found that the temperatures and other conditions in the process can be varied within recognizable limits without detriment to the characteristics of the product. For instance, the temperature of the molten metal in the pouring pot and the metal bar extracted from the casting wheel appear to have no efiect on the quality of the 6201 alloy rod as long as the temperature is not lowered below the solutionizing temperature. The critical temperatures of the process appear to be the temperatures of solutionizing and crystallization, which in the case of aluminum alloy metals is a range of temperatures since the different alloy metals apparently crystallize and solutionize at different temperature levels. The rod must pass from the metal solutionizing temperature through the alloy crystallization temperature range in a short time so that the quenching function is able to freeze the metals in a substantially homogenized condition. This temperature range is estimated to be above 600 F., in most instances and considered to usually be above about 750 F., and the time lapse should normally be less than 30 seconds; however, these figures vary in accordance with the percentage of alloy metals in the solution. The temperature of the soluble oil solution in the rolling mill should be maintained sufficiently low to carry out its cooling function, but can vary to a temperature as high as 200 F., or even higher if enough volume of solution is forced into contact with the rod to sufficiently cool the rod. The distance between the rod entrance to the rolling mill and the rod entrance to the first stage quenching tube and the resulting time lapse taken for a segment of the rod to travel between these points can be increased as long as the alloy metals do not have time enough in which to precipitate. Moreover, the rolling mill can be run hot to allow the rod to enter the quench tubes with the alloy metals in solution.

The length of the rod formed by this process is virtually unlimited since the process is continuous" The grain structure of the rod is substantially uniform throughout its entire length since the temperature conditions throughout the system are malntamed re atively constant. For instance, the pouring temperature and the temperature of the product extracted from the casting wheel will be substantially constant, the adjustments made to the flow and temperature of the soluble coolant in the rolling mill will be small after the system has been started and stabilized. Of course, the rod produced by the continuous system will have no welded joints. Since there is virtually no time delay between casting and rolling, between rolling and quenching, there will be virtually no opportunity for the product to oxidize. Thus, the product can be easily drawn into wire, and the drawing dies will not deteriorate rapidly as they would when the product has been allowed to oxidize and become hard. The appearance of the product is improved over that from a batch process in that it is much brighter and is comparable to E.C. rod. Since the rod is relatively cool before it is coiled, there is virtually no opportunity for the rod in overlapping coils to stick or tack to itself, and the rod can pay out without hazard to the operator or the equipment. Also, the rod surface will not become damaged by tacking. The equipment used in casting and rolling the product is virtually the same as utilized in the casting and rolling of EC rod, so that very little special equipment is required. For instance, no equipment is required to move the billets or the coiled rod from the casting apparatus to the rolling mill, and from the rolling mill to solutionizing ovens, and solutionizing ovens are not required. The rod can be coiled in dense coils since it does not have to be reheated and quenched as required in the old process. The densely would coils can be formed in much larger and heavier packages since the packages do not have to be handled and placed in the small reheating ovens.

While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

We claim:

1. A method of continuously casting and rolling 6201 aluminum alloy rod containing from about 0.5 to about 0.9 weight percent silicon, about 0.6 to 0.9 weight percent magnesium and the remainder essentially aluminum comprising the steps of:

a. pouring a 6201 aluminum alloy into the casting groove of a continuous casting wheel at at temperature above about 1,200 F.;

. removing a cast 6201 aluminum alloy bar from the casting groove of the casting wheel and passing the bar to a hot-rolling mill so that the bar enters the mill at a temperature of 850 F. to 1,000 F., said bar having been maintained at a temperature of at least 850 F., between the wheel and the mill;

c. hot-rolling the 6201 aluminum alloy bar while coating a soluble oil on the bar as it is rolled, said soluble oil being at a temperature of less than 200 F.; and

d. quenching the hot-rolled rod immediately after it exits the hot-rolling mill to a temperature of less than 400 F., the time interval between entrance into the hot-rolling mill and completion of quench to a temperature of less than 400 F., being between 9 and 30 seconds.

2. A method of continuously casting and rolling 6201 aluminum alloy rod as defined in claim 1 wherein the step of quenching the hot-rolled rod comprises:

a. quenching the hot-rolled rod with water in a first quench operation;

b. urging the rod along its path from the first quench operation to a second quench operation; and

c. quenching the rod with a soluble oil and water solution in the second quench operation.

Claims

2. A method of continuously casting and rolling 6201 aluminum alloy rod as defined in claim 1 wherein the step of quenching the hot-rolled rod comprises: a. quenching the hot-rolled rod with water in a first quench operation; b. urging the rod along its path from the first quench operation to a second quench operation; and c. quenching the rod with a soluble oil and water solution in the second quench operation.