US3317994A

US3317994A - Method of conditioning metal for hot forming

Info

Publication number: US3317994A
Application number: US390666A
Authority: US
Inventors: Daniel B Cofer; George C Ward; Dale D Proctor
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1964-08-19
Filing date: 1964-08-19
Publication date: 1967-05-09
Anticipated expiration: 1984-05-09

Description

May 9, 1967 D. B. COFER ETAL 3,317,994

METHOD OF CONDITIONING METAL FOR HOT FORMING Filed Aug. 19, 1964 2 Sheets-Sheet l INVENTORS DANIEL B. COFER GEORGE C4 WARD BY DALE D. PROCTOR METHOD OF CONDITIONING METAL FOR HOT FORMING y 1967 D. B. COFER ETAL 2 sheetssheet 2 Filed Aug.

INVENTORS DANIE L B. COFER GEORGE CI WAR D BY DALE D. PROCTOR Mil 7 I? I United States l atent Cfilice 3,317,994 Patented May 9, 1967 3,317,994 METHOD OF CONDITIONING METAL F OR HOT FORMING Daniel B. Cofer, George C. Ward, and Dale D. Proctor, all of Carrollton, Ga, assignors to Southwire Company, Carrollton, (221., a corporation of Georgia Filed Aug. 19, 1964, Ser. No. 390,666 11 Claims. (Cl. 29-528) ABSTRACT OF THE DISCLOSURE What is disclosed herein is a method of hot-forming a non-homogenized metal which involves the compression of the metal to the extent necessary to substantially destroy the dendritic structure of the metal as an initial step in or prior to generally conventional hot-forming. The method is disclosed in terms of compressing a copper bar to reduce its cross-sectional area by at least 36% and in terms of using a roll-stand positioned between a continuous casting machine and a' rolling mill to provide the necessary compression. The method results in a resistance to cracking and splitting during hot-forming such as that achieved in the prior art by homogenizing the metal prior to hot-forming.

This invention relates generally to the rolling of metal and more particularly to a method of conditioning metal for hot-forming such as by hot rolling.

In the hot rolling of metal, cracking and splitting of the metal is frequently encountered as the result of a characteristic commonly known as hot shortness. Moreover, cast metal usually has internal stresses due to nonuniform cooling rates during casting or due to straightening the metal after casting. These stresses also cause cracking and splitting of the metal during rolling or forming.

The cracking and splitting of metal as the result of hot shortness or internal stresses can be avoided by homogenizing the metal prior to hot rolling. This is because homogenizing a metal disperses alloying and other elements and compounds from grain boundaries between dendrites within the metal into the dendrites. The result is an increase in tensile strength to a degree suflicient to resist cracking and splitting because of hot shortness or internal stresses.

The homogenizing of a metal requires that the metal be held at a temperature above the recrystallization temperature of the metal for an extended period of time. Where the metal to be hot rolled is initially at room temperature, the elevated temperature and the period of time at this elevated temperature required for homogenizing the metal are obtained simply by reheating the metal to hot rolling temperature since this provides time and temperature conditions sufficient for homogenization. Where the metal to be hot rolled has not been allowed to cool to room temperature from its casting temperature, the elevated temperature and the period of time at this elevated temperature required for homogenization of the metal can be obtained only by holding the metal at approximately casting temperature for an extended period of time. This is commonly known as soaking. Thus, whether a metal to be hot rolled is at room temperature or at casting temperature, homogenization of the metal prior to rolling is time consuming and frequently requires extensive equipment and space.

Moreover, neither of the above techniques for homogenizing a metal is suited tothe continuous casting and hot rolling of metal since it is impractical to cool and reheat continuously cast metal before it is fed to a rolling mill or to hold continuously cast metal at an elevated temperature for the length of time required to accomplish homogenization as the metal is continuously fed from a casting machine to a rolling mill. Thus, the homogenization of a metal prior to hot rolling is a generally unsatisfactory method of preventing splitting and cracking of the metal during hot rolling and is a particularly unsatisfactory method of accomplishing this objective where it is desired to continuously roll continuously cast metal.

The invention disclosed herein substantially eliminates these and other problems associated with the rolling of metal in that it conditions a metal so that the metal may be rolled without any significant tendency to crack or split even though the metal has not been homogenized and even though the metal would crack and split in the absence of conditioning in accordance with the invention.

'The metal to be rolled is conditioned for hot rolling by reducing the cross-sectional area of the metal without splitting and cracking to that extent necessary to destroy the columnar dendritic structure therein.

The conditioning is accomplished at substantially hot rolling temperature prior to hot rolling or as the initial step in hot rolling. After the metal has been conditioned in accordance with the invention, the metal may be hot rolled into substantially any shape without cracking and splitting of the metal occurring. This is because the destruction of the columnar dendritic structure provides a metal having a greatly increased tensile strength. The tensile strength attained is sufiicient to prevent cracking and splitting because of hot shortness or internal stresses and the metal is as suitable for hot rolling without cracking and splitting as metal which has been homogenized. The invention is practicularly well adapted to the continuous casting of metal since the required reduction of the cross-sectional area of the metal as cast without cracking or splitting is easily accomplished at a rapid rate and this rate permits the metal to be conditioned for rolling as the metal is continuously fed from a continuous casting machine to a rolling mill or similar apparatus.

These and other features and advantages of the invention will be more clearly understood from the following detailed description and the accompanying drawings in which the like characters of reference designate corresponding parts in all figures and in which:

FIG. 1 is a top plan view of the apparatus suitable to practice the present invention and positioned to condition metal being fed from a continuous casting machine into a conventional rolling mill;

FIG. 2 is an enlarged elevational view of the compression rolls of the apparatus shown in FIG. 1;

FIG. 3 is a diagrammatic drawing of the compression rolls shown in FIG. 2 illustrating with velocity triangles the velocity relationships in the rolling grooves of the rolls;

FIG. 4 is a cross-sectional representation of a cast metal bar prior to conditioning for rolling in accordance with the present invention;

FIG. 5 is an enlarged view of a portion of the representation of a cast metal bar shown in FIG. 4.

FIG. 6 is a cross-sectional representation of the cast bar shown in FIG. 4 after conditioning for rolling in accordance with the present invention.

The following detailed description discloses a specific embodiment of the invention but the invention is not limited to the details disclosed since it may be embodied in other equivalent forms.

Referring to FIG. 1 and FIG. 2, the apparatus chosen for the purpose of illustration of the present invention is seen to comprise generally a base 10, a left upright 11, a right upright 12, an upper roll 14 mounted on a shaft 15, and a lower roll 16 mounted on a shaft 18. The

rolls

14 and 16 are rotatably positioned parallel to each other between the left upright 11 and the right upright 12 by shafts 15 and 18, and the shaft 18 extends through the left upright 11 to a clutch 13 which serves to join the shaft 18 in known manner to the drive shaft 19 of a motor 20 mounted on a platform 17 adjacent the left upright 11.

The motor 213 drives the roll 16 through the shaft 18 and the shaft 15 is joined within the right upright 12 to the shaft 18 so that as the shaft 18 rotates in a particular rotational direction, the shaft 15 rotates in the opposite rotational direction and at the same rotational speed as the shaft 18. Thus, the motor 2d serves to rotate the rl1s14 and 16 in opposite directions at substantially identical rotational speeds.

4 The spacing between the

rolls

14 and 16 is adjustable by rotation of a wheel 23 at the upper end of a shaft 27 extending from within the right upright 12. It will now be understood that those features of the apparatus described above are generally conventional with two-roll rolling stands as known to those skilled in the art and that it is for this reason that known details of construction have not been described. It will also be understood that When a cast metal bar 21 is received from a casting means such as a casting machine 49 of known type having a wheel 41 and a belt 42 and inserted between the

rolls

14 and 16 from the left as viewed in FIG. 1, the

rolls

14 and 16 reduce the cross-sectional area of the metal bar 21 and force the metal bar 21 to the right to be received by a hot-forming means such as a conventional rolling mill 22 or similar compressing means positioned as shown in FIG. 1. w

Positioned above the base in the path of the metal bar 2121s it moves through the

rolls

14 and 16 are a pair of

guide rolls

38 and 39 rotatably carried by supports 45 attached to the base 10. The guide roll 38 is shaped to receive and support the metal bar 21 as it approaches the

rolls

14 and 16 and the guide roll 39 is shaped to receive the metal bar 21 as it exits the

rolls

14 and 16 to be fed to a rolling mill 22 or similar apparatus.

As is best seen in FIG. 2, each of the

rolls

14 and 16 has a groove 30 having the shape of a semi-ellipse. Together the grooves 30 define an elliptical rolling channel 29 in which the metal bar 21 is compressed as it passes between the rolls 14- and 16. This rolling channel 29 serves to prevent excessive spreading of a metal bar 21 having the cross-sectional shape shown in FIG. 4 as it is compressed by the

rolls

14 and 16 to produce the crosssectional shape of the metal bar 21 shown in FIG. 6.

Moreover, as is best shown in FIG. 3, the rolling channel 29 provides linear speed relationships in the metal bar 21 as the metal bar 21 passes between the

rolls

14 and 16 which physically prevent cracking and splitting of the metal bar 21 as the result of abrupt changes in velocity Within the metal bar 21 as it is being rolled by the

rolls

14 and 16. This is because the elliptical shape of the rolling channel 29 causes the

rolls

14 and 16 to have different linear tangential velocities as they engage different portions of the metal bar 21. As indicated by the

arrows

32 and 34 in FIG. 3, that portion of each groove 31 nearest the axis of rotation of

rolls

14 and 16 has the smallest tangential velocity and those portions of each groove 30 at its outer edges have the greatest tangential velocity.

It will be understood that those portions of each groove 36 between that portion indicated by an arrow 32 as hav ing the smallest tangential velocity and those portions indicated by an arrow 34 as having the greatest tangential velocity will progressively increase in tangential velocity from the smallest tangential velocity to the largest tangential velocity. It will also be understood that this velocity relationship within the rolling channel 29 tends to force the outer edges of a metal bar 21 inwardly toward the center of the rolling channel 29 when the metal bar 21 is fed between the

rolls

14 and 16. From the foregoing, it will be seen that the apparatus provides a means for reducing the cross-sectional area of a metal bar 21 while at the same time physically preventing cracking or splitting of the metal bar 21 even though the metal in the metal bar 21 has not been homogenized.

The cross-section of the metal bar 21 after passing between the

rolls

14 and 16 is substantially that shown in FIG. 6. The metal bar 21 having this cross-sectional shape is particularly well adapted for rolling in a rolling mill 22 or similar apparatus into rod or other forms. However, the purpose of the

rolls

14 and 16 is to substantially reduce the cross-sectional area of the metal bar 21 without cracking or splitting occurring, and it will be understood that rolling channels 29 having other configurations which physically prevent the splitting or cracking of the metal bar 21 as its cross-sectional area is reduced Will condition the metal bar 21 for subsequent hot rolling into substantially any cross-sectional shape without cracking or splitting. This is because the size of the rolling channel 29 is selected so that the reduction in the cross-sectional area of the metal bar 21 as it passes between the

rolls

14 and 16 is sufficientiy great to destroy the dendritic structure of the metal bar 21, and because it is this particular amount of reduction in the crosssectional area of the metal bar 21 without splitting or cracking of the metal bar 21 which conditions the metal bar 21 for conventional rolling operations. Thus, any apparatus arrangement suited to reducing the cross-sectional area of a metal bar 21 to a degree suflicient to destroy the dendritic structure within the metal bar 21 while physically preventing the cracking or splitting of the metal bar 21 is suitable for conditioning the metal bar 21 for hot rolling.

From the foregoing description of an embodiment of the invention, it will be seen that the invention conditions a metal bar 21 by compressing or squeezing the metal bar 21 so as to reduce the cross-sectional area of the metal bar 21 while at the same time physically preventing cracking or splitting of the cast bar 21 as it is compressed. The compressing or squeezing is accomplished prior to hot rolling with the metal bar 21 in substantially its as cast condition a hot-forming temperature or as the initial step in hot rolling the metal bar 21. As shown in FIG. 6, the cross-sectional shape of the metal bar 21 after passing through that embodiment of the apparatus described herein resembzes an ellipse, and it has been found that such a cross-sectional shape provides a metal bar 21 'which permits the metal bar 21 to be easily rolled by a rolling mill 22, or similar apparatus, into the shape of a rod or any other desired shape. However, it will be understood that the cross-sectional shape of the metal bar 21 before and after passing between the

rolls

14 and 16 may be any of a wide variety of shapes. This is because of the rolling channel 29 shape may be any shape which reduces the cross-sectional area of the metal bar 21 While physically restricting and controlling the side spread of the metal bar 21 so as to prevent splitting and cracking of the metal bar 21.

Regardless of the rolling channel 29 shape selected to physically prevent cracking and splitting of the metal bar 21, the invention reduces the cross-sectional area of the metal bar 2.1 to that extent necessary to destroy the dendritic structure of the metal bar 21. The amount by which the cross-sectional area of the metal bar 21 must be reduced to destroy the dendri-tic structure of the metal in the metal bar 21 depends upon the particular metal from which the metal bar 21 is cast and the cross-sectional area of the metal bar 21 before passing between the

rolls

14 and 16. Accordingly, it will be understood that the spacing between the

rolls

14 and 16 is varied in accordance with the metal in the metal bar 21 and the cross-sectional area of the metal bar 21 before conditioning in accordance with the invention.

For a continuously cast metal bar 21 of cop-per which has internal stresses, which exhibits the characteristic of hot shortness to an undesirable degree, or which has both internal stresses and the characteristic of hot shortness to an undesirable degree, it has been found that a reduction in the cross-sectional area of the metal bar 21 by at least approximately 36 percent with a single compression will result in the destruction of the dendritic structure of the copper. The reduction is accomplished at substantially the hot rolling temperature of copper and a metal bar 21 of copper may be subsequently hot rolled with a plurality of sequential compressions into substantially any desired form without undesirable cracking or splitting.

The amount of reduction of the cross-sectional area of the metal bar 21 where the metal bar 21 is of a metal other than copper will be readily apparent to those skilled in the art or may be readily obtained empirically using known metallurgical techniques. The temperature at which the reduction is accomplished will be substantially the hot rolling temperature of the metal and will also be readily apparent to those skilled in the art.

Regardless of the metal from which the metal bar 21 is cast, once the dendritic structure of the metal bar 21 is destroyed, the metal bar 21 is conditioned for hot rolling in a rolling mill 22 or other apparatus using conventional hot rolling techniques. The conditioning of the metal bar 21 by the invention is represented by a comparison of FIG. 4 and FIG. 5 with FIG. 6. In FIG. 5, the cast bar 21 is represented as having columnar dendrites 2-4 and with segregated alloying and other elements and compounds trapped at the grain boundaries 25 of the dendrites 24.

FIG. 6 represents the metal bar 2-1 represented in FIG. 4 and FIG. 5 after the metal bar 21 has been conditioned in accordance with the invention. .It will be seen from FIG. 6 that in the metal bar 21', the dendritic structure has been completely destroyed. This eliminates the grain boundaries at which the alloying and other elements and compounds indicated by the letter S in FIG. 5 were segregated and substantially increases the tensile strength of the metal in substantially the same manner as homogenizing the metal. As a result, the tensile strength of the metal in the metal bar 21 is sufficiently great to resist cracking and splitting because of hot shortness, internal stresses, or both when the metal bar 21 is subsequently hot rolled.

From the foregoing description of the invention disclosed herein, it will now be understood that when a metal bar 21 having internal stresses or substantial amounts of elements and compounds causing hot shortness is conditioned for hot rolling by the destruction of.

the dendritic structure prior to rolling, the metal bar 21 maybe hot rolled in any suitable conventional apparatus such as the rolling mill 22 without cracking or splitting of the metal bar even though the metal is not homogenized prior to rolling in the rolling mill 22. Thus, the invention is ideally suited to the rolling of continuously cast metals since apparatus may be used in combination with the rolling mill 22 as shown in FIG. 1 to condition and feed the metal bar 21 continuously into the rolling mill 22 from a casting machine 40'. When the invention disclosed herein is used with a rolling mill 22 it provides a convenient and elfective rolling operation in which the metal bar 21 is efiiciently conditioned and rolled.

It will of course be understood that the present invention is in no way limited to the particular device here presented by way of illustration, but many changes and modifications may be made, and the full use of equivalents resorted to Without departing from the spirit or scope of the invention as defined in the appended claims.

What is claimed as invention is:

1. In a method of hot-forming non-homogenized continuously cast copper, the steps of passing said copper in substantially its as cast condition and at a hot-forming temperature from a casting means to a hot-forming means, conditioning said copper for subsequent hot-forming by substantially completely destroying the dendritic struc ture of said copper as said copper passes between said casting means and said hot-forming means by a single compression of said copper to reduce its cross-sectional area by at least 36%, and hot-forming said copper in said hot-forming means with a plurality of sequential compressions.

2. In a method of hot-forming a non-homogenized continuously cast copper bar, the steps of feeding said bar at a hot-forming temperature to a compressing means, initially compressing said bar by a single compression of said bar to the extent necessary to reduce its cross-section by at least 36% and to substantially destroy its dendritic structure, and subsequently compressing said bar by a plurality of sequential compressions in each of which the cross-section of said bar is changed to the extent necessary to provide a hot-formed product having a predetermined cross-section.

3. The method of claim 1 including restricting said copper during said conditioning said copper so as to prevent cracking of said copper.

4. The method of claim 1 in which said conditioning said copper includes passing said copper between rolls,

in a roll-stand.

5. The method of claim 1 in which said hot-forming means is a rolling mill having a plurality of roll-stands and in which said hot-forming includes passing said copper through said roll-stands in sequence.

6. The method of claim 4 in which said rolls define an elliptical rolling channel shaped to restrict the lateral spread of said copper.

7. The method of claim 1 in which said casting means is a casting Wheel of a casting machine and in which said hot-forming means is a rolling mill having a plurality of roll-stands.

8. The method of claim 2 including restricting said bar during said initially compressing said bar so as to prevent cracking of said bar.

9. The method of claim 2 in which said single compression is by passing said bar between rolls in a rollstand.

10. The method of claim 9 in which said subsequently compressing said bar is by passing said bar between rolls in a plurality of roll-stands.

11. The method of claim 9 in which said rolls define an elliptical rolling channel shaped to restrict the lateral spread of said bar.

References Cited by the Examiner UNITED STATES PATENTS 2,264,288 12/1941 Betterton -76 X 2,710,433 6/1955 Properzi 22-200.1 X 3,146,525 9/1964 Bongiovanni 29-528 3,234,052 2/ 1966 Wikle 148-2 X 3,259,975 7/1966 Chapman 29-528 3,274,681 9/1966 Lohman 29-528 OTHER REFERENCES Part 2: Continuous Casting-Progress Report on the Properzi Process by J. B. Russell, Modern Metals, April 1964, pp. 56 and 58.

JOHN F. CAMPBELL, Primary Examiner. R. F. DROPKIN, Assistant Examiner.

Claims

2. IN A METHOD OF HOT-FORMING A NON-HOMOGENIZED CONTINUOUSLY CAST COPPER BAR, THE STEPS OF FEEDING SAID BAR AT A HOT-FORMING TEMPERATURE TO ACOMPRESSING MEANS INITIALLY COMPRESSING SAID BAR BY A SINGLE COMPRESSION OF SAID BAR TO THE ENTENT NECESSARY TO REDUCE ITS CROSS-SECTION BY AT LEAST 36% AND TO SUBSTANTIALLY DESTROY ITS DENDRITIC STRUCTURE, AND SUBSEQUENTLY COMPRESSING SAID BAR BY A PLURALITY OF SEQUENTIAL COMPRESSION IN EACH OF WHICH THE CROSS-SECTION OF SAID BAR IS CHANGED TO THE EXTENT NECESSARY TO PROVIDE A HOT-FORMED PRODUCT HAVING A PREDETERMINED CROSS-SECTION.