US3147521A

US3147521A - Continuous casting and forming process

Info

Publication number: US3147521A
Application number: US131056A
Authority: US
Inventors: Boehm Arnold Henry
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-08-10
Filing date: 1961-08-10
Publication date: 1964-09-08
Anticipated expiration: 1981-09-08

Description

Se t. 8, 1964 A. H; B'OEHM CONTINUOUS CASTING AND FORMING PROCESS 4 Sheets-Sheet 2 Filed Aug. 10. 1961 W m A w Mn 3 Sept. 8, 1964 v A. H. BOE'HM 3,147,521

CONTINUOUS CASTING AND FORMING PROCESS Filed Aug. 10 1961 4 Sheets-Sheet 3 F527. 15 I.

INVENTOR. ARNOLD HENRY BQEHM xrroamsvs P 3, 1954 A. H. BOEHM 3,147,521

commuous CASTING AND FORMING PROCESS Filed Aug. 10. 1961 4 Sheets-Sheet '4 INVENTOR ARNOLD HENRY BOEHH AT TORNE Y5 United States Patent 3,147,521 CQNTINUUUS CASTING AND FGRMENG IRQQESS Arnoid Henry lioehm, 5629 Rand Ave., Cote Saint Luc- Montreai, Quebec, Canada Filed Aug. 10, 1961, er. No. 131,956 Claims. ill. 22-2di9.l)

This invention relates to continuous casting and, more particularly, relates to an improved method and apparatus for the continuous casting of billets.

Continuous casting of metal strands has the basic theoretical advantage that the strand can be formed to the dimensions required by, for example, a rolling mill for fabrication of intermediate or final products of the cast material. Further, fabrication of cast sections having a cross-sectional shape approximating the shape of the finished production would be advantageous. For example, in the fabrication of structural beams, it is desirable that the beam blank be formed approximately to the dimensions of the desired finished product to eliminate intermediate steps in the formation thereof. In such applications, continuous casting of sections to the approximate size required by the mill would have significant commercial advantages.

Unfortunately, however, the continuous casting of sections of small transverse area, for example, of 2" x 2" billets, encounters economic problems which vitiate some of its contemplated advantages. For example, in the casting of molten metal, the melt or heat is formed in quantities dictated by the economies of the steel production facilities. Thus, the continuous casting process must be compatible with such facilities.

To cast the billets directly by molds of the continuous casting type in such small sizes would require a large plurality of strands. The large number of strands is required to maintain the productive rate (in tons per hour) of material cast at a level which would be compatible with the production of the molten material. For example, a hundred ton heat must be poured within an hour. If the metal is held in the ladle for more than one hour, the material will cool down below the temperature necessary for successful casting.

Simple compounding of a number of molds for small section strands, while feasible up to about eight molds, is not economical, since each strand requires a separate mold, separate mold withdrawal rollers and associated equipment along with the necessary labor force to operate such equipment. The fact that the small molds are subject to washout and flow difficulties makes a com- .pounded arrangement very difficult to handle in production.

In US. Patent 2,975,493 there is disclosed a mold to cast a plurality of billets coupled together by channels, which channels allow horizontal flow of the metal into each billet shaped section of the mold from a central nozzle or nozzles. However, in order to provide the requisite casting capacity, this type of mold is limited to relatively large-size billets. If applied to small molds, such as molds 2" x 2." billets, the mold will be subject to the flow difficulties, such as washout, due to stream deflection by nozzle clogging or erosion, in the same manner as individual billet molds. Compounding such molds to achieve desired casting rates will, of course, generate practical problems similar to those of compounding of individual billet molds.

Filling of the mold by a plurality of nozzles positioned above each of the billet shapes will lend complexity to the nozzle arrangement vitiating the desired simplicity of the formation of the strand.

It is, therefore, one object of this invention to provide an improved method for the casting and forming of a plurality of billets at high casting rates.

It is a further object of this invention to provide an improved method and means for the continuous casting of a plurality of billets at a continuous high productive rate.

It is a further object of this invention to provide an improved casting and forming process for the casting of a slab of dimensions compatible with simple casting at high casting rates and forming the cast strand into sections of small cross-sectional dimensions by deforming the solidified skin while the strand interior is still molten.

In accordance with these objects, there is provided, in a preferred embodiment of this invention, a continuous casting mold to cast a relatively thin slab of metal. The mold is water-cooled and may be reciprocated in conventional manner. The slab dimensions are sufficiently large to provide the desired high casting rate, thus to enable employment of the process for casting of heats of conventional tonnage in a time sufficiently short to preclude the cooling of the material in the ladle.

As the slab leaves the exit of the mold shaft, the walls of the cast strand are relatively thin, being sufficiently thick only to contain the hydrostatic pressure of the molten metal in the interior thereof. At the exit end of the mold, I provide a plurality of forming rollers to deform the skin, thereby to shape the slab into a plurality of billets joined at the corners thereof. To prevent tearing of the skin, the folding or crimping of the skin must take place in gradual fashion, and for this reason, I provide a series of rollers which are positioned to fold the skin gradually into the desired shape. Further, the plurality of rollers must be carefully positioned since the skin must be folded without change of the peripheral or axial length thereof. Thus, as the casting proceeds, the rollers will fold the skin in increasing increments, and at the same time the distance between adjacent rollers must be correspondingly adjusted to suit the changing dimensions of the slab.

In some applications it will be found that the skin is diflicult to bend due to the thickness thereof. The difficulties of folding the skin must be recognized since the skin is supported only by the hydrostatic pressure of the molten metal in the core of the strand. In such application, I have found it preferably to provide the mold with corrugations in the shaft thereof which corrugations provide bearing points for subsequent folding of the skin by the forming rollers.

Thus, in either embodiment there is provided a mold dimensioned to continuously cast a slab at casting rates compatible with use of production heats. The slab emerges from the mold with a thin skin containing a core of molten metal. The skin is then formed by forming rollers until the section is formed into a plurality of billets which are attached together by intervening skin.

By this method and means of formation, successful casting of a section comprising a plurality of 2" x 2" billets may be accomplished at rates approximating tons per hour which is entirely satisfactory for utilization of conventional heats from steel furnaces. The individual billets may then be separated by slitting rollers or other means into a plurality of billets. Alternatively, adjacent billets may be allowed to remain joined as, for example, for use as structural beam blanks.

In some embodiments, the hydrostatic pressure of the molten core may cause bulging of the skin between forming rollers. In such applications, it is desirable to provide idler rollers between adjacent forming rollers.

In some applications it may be desirable to form the strand in continuous fashion. In such applications a die or secondary mold may be employed below the strand casting mold. The secondary mold provides skin formation in the same manner as the forming rollers but provides skin support over a longer portion of the slab surface. The secondary mold is preferably a split mold which is reciprocated along the casting axis. When the mold is moving with the casting, the mold is closed to form the casting skin along the entire length of the mold. The slower cooling in the secondary or forming mold, as contrasted with roller and water spray operation, will have some advantages in those applications where it is desired to have very thin webs between the, formed billets and where skin rupture may be prevalent.

Further objects and advantages of this invention will be pointed out hereinafter in connection with the following detailed description of a preferred embodiment of this invention taken in combination with the accompanying drawings, of which:

FIG. 1 is a plan view of a continuous casting plant in diagrammatic form in accordance with the present invention;

FIG. 2 is a plan side view of a portion of the casting plant shown in FIG. 1 to enlarged scale;

FIG. 3 is a plan elevation View of the casting plant shown in FIG. 2;

FIGS. 4-8 are cross sectional views taken along

lines

44, 55, 66, 77, and 88 respectively of PEG. 3;

FIG. 9 is a cross section view taken along lines 99 of FIG. 1;

FIG. 10 is a cross sectional view of a mold constructed in accordance with another embodiment of this invention;

FIG. 11 is a cross section view, in diagrammatic form, of a casting plant in accordance with another embodiment of this invention;

FIG. 12 is a sectioned elevation view of the plant shown in FIG. 11;

FIGS. 13, 14 and are cross sectioned views of the casting formed by the plant of FIGS. 11 and 12 taken respectively along lines 13-13, 14-14 and 15- 15 of FIG. 12;

FIG. 16 is an elevation view to an enlarged scale, of the forming mold used in the casting plant shown in FIGS. 11 and 12;

FIG. 17 is a side view of the forming mold shown in FIG. 16;

FIG. 18 is a plan View of another embodiment of the drive for the mold shown in FIGS. 16 and 17; and

FIG. 19 is a plan view of the drive shown in FIG. 18 during a portion of the operation cycle thereof.

Referring to 'FIGS. 1-9 there is shown a continuous casting plant according to the instant invention which comprises a mold 1 to receive the molten metal poured by ladle 2 through an intermediate tundish 3 to maintain the desired hydrostatic head on the metal poured therefrom.

The mold may be mounted on the mold table 4 for reciprocation thereof in conventional fashion.

The mold is water cooled through inlet and outlet ducts 5 and 6 respectively to chill the molten material poured therein, forming a solidified skin. The strand '7 consisting of the solidified skin 12 encasing the molten core 13 is continuously removed from the bottom of the mold. The strand is then passed through a plurality of rollers 16-29 positioned astraddle the strand. The rollers are rotatably mounted rollers (which may be water cooled) to deform the relatively thin skin of the casting in a plurality of corrugations 21 as illustrated. Water sprays from jets 22 may be utilized to cool the strand and to maintain the skin thickness. Idler rollers 21 may be provided to support the strand corrugations between forming rollers.

The rollers perform the operation of folding the thin skin of the cast strand into corrugated form. Since the skin is relatively fragile, the corrugation must be commensurately shallow in the first rolling operation, performed by the roller 1e urged into engagement with the 4g. faces of the slab. To support and form the edges of the slab, edge rolls 2 are provided. The forming step is shown in FIG. 5. Each roll in the roller is of V-shaped form to fold the skin. The hydrostatic pressure of the molten core will urge the skin against the roller face for the forming operation.

Subsequently, rollers 17 and 1&5 are provided to deepen the corrugations in the cast strand, as illustrated in FIGS. 6 and 7. As illustrated in FIG. 7, after forming by roller 18, the opposite skins of the casting touch to completely enclose the molten metal 13 Within the core of the individual billets 26, permitting each billet to solidify individually and concentrating any impurities in the center of the billet where any impurities are less harmful.

The rollers fold the skin of the cast strand into corrugations. Because of the fragile nature of the skin, it is necessary that the folding operation be conducted in such manner as to prevent change in the peripheral or axial dimension of the strand skin. For example, formation which would tend to stretch the skin of the cast strand would rupture the skin and cause a breakout of the molten material enclosed by the skin. Thus, as the strand progresses the gap between rollers is not only closed but the shape of individual rollers must be altered in accordance with the change in width of the formed strand. It will be seen that the peripheral dimension of the skin remains constant and, as the skin is corrugated, the thickness of the strand is gradually decreased with commensurate change in width. In the embodiment illustrated, the width decreases but in some embodiments, the width may increase, dependent upon the relative dimensions of the initial slab.

Finally, there is provided

rollers

19 and 20 to form the strand into a plurality of billets 26 attached together by a thin Web section 30. For example, the billets may be 2" x 2" square and thus suitable for direct rerolling. The strands may then be cut apart by roller separators 32 which may also serve the function of pinch rolls or may be independent of the pinch rolls. Separation may be assisted by localized heating of the web by torches 34 or may be accomplished entirely by cutting torches 34. Adjacent billets may be left attached to form blanks for such operations as formation of structural beams. Additionally, the strand may be cut into axial lengths by traveling torches in the conventional fashion. While billet formation has been particularly illustrated, it will be noted that the forming operation could be applied to other cast sections of small cross sectional dimensions.

In some applications it may be found that folding of the skin of the casting is difficult merely by application of the rollers to the slab form as it emerges from the mold. Since the skin is not supported by solid structure but merely encloses molten material, creasing thereof may be difficult. In such applications, the mold shown in FIG. 10 may advantageously be employed.

In FIG. 10 there is shown a mold 36 having a mold shaft 38 of generally slab form. However, the mold is provided with a plurality of spaced-apart protrusions 40 to pre-corrugate the skin 12 of the slab cast thereby. The pre-corrugations of the slab wall provide means for locating the forming rollers. Also, since the skin is precorrugated, the forming by the rollers is made easier. The existence of the indentations eliminates the necessity of overcoming the beam resistance of a straight skin on the strand. The folding operation is then performed by progressively inserted rollers as explained in connection with the embodiment shown in FIGS. 1-9.

Thus, it can be seen that the mold may take an initial shape conducive to high productive rates, that is, of a relatively thin slab. The large surface area of the thin slab is conducive to the formation of a skin of sufficient thickness to contain the molten core even at high productive rates. For example, the strand for a 12 billet (2%" square) section may be cast at a rate of four thousand pounds per minute corresponding to a speed of casing of 190 inches per minute with a mold having approximate dimensions of 5-' x 43". Thus, the heat from the melts of conventional sizes may be utilized by this method without duplication of the equipments to produce a plurality of small strands of billet form with the attendant complications and expense thereof. a

The mold dimensions may be varied in accordance with the desired billet size. Since there are no constrictions within the mold to inhibit transverse metal flow, the mold may be filled by conventional nozzles and provision for a plurality of nozzles spaced along the mold is unnecessary over and above the usual'precautions well known to this type of casting art.

In many applications, it is desirable to prevent the skin thickness from becoming too great during the forming process, so that the material between adjacent billets may be maintained desirably thin. Maintenance of a thin web between billets will ease the problem of cutting apart the billets and removing protruding portions of the web after separation. Further, the forming of the skin utilizes the hydrostatic pressure of the molten core. The thinner the skin can be maintained, the more precise will be the formation of the periphery.

In such applications, the embodiment shown in FIGS. 11-l7 may advantageously be employed.

In FIGS. 11-17 there is shown a mold 1 which is a brass mold water cooled by ducts 42 and mounted on a mold table 4 which is reciprocated in conventional fashion. The mold is dimensioned to cast a thin slab 7 of metal as explained in connection with the embodiment shown in FIGS. 1-9. The dimensions of the slab allow the casting of material at rates compatible with production of the molten metal.

Below the mold 1 is mounted a secondary or forming mold 44. The secondary mold is mounted upon a mold table 80 which is reciprocated by cam 45 at a cyclic rate related to the rate of casting by deriving the cam rotation drive power from the motors driving the pinch rollers. Such linkage is conventional to the art and is not illustrated. The mold table is prevented from tilting by coaction of the rod guides 47 with the cylindrical bearing pockets 49. The pockets house the springs 51 for return of the table after deflection by the cam lobe. The reciprocation cycle, illustrated by dotted line 46, may be of the order of 3 to 4 inches.

The mold shaft has a rectangular entrance aperture 48 and side walls 50 which are provided with outwardly extending tapered triangular sections 52 to form the slab progressively as illustrated by the sections shown in FIGS. 13-15.

The secondary or forming mold may be water cooled by ducts 54 and may be formed of relatively inexpensive material, such as a cast iron. The mold may be lubricated by rapeseed oil, mineral oil or other conventional lubricants.

For progressive forming of the cast slab, it is advantageous to construct the mold as a split mold and to synchronize the opening and closing of the mold with the reciprocation cycle.

For this purpose, the mold halves, 56, 56 are respectively supported by shafts 60, 62 journaled in

bearings

64, 66. The

bearings

64, 66 are carried in a journal block 68 mounted upon a yoke 70 afiixed to the mold table 80. The entrance aperture of each mold half is radiused at 72 to provide clearance for opening the mold by pivoting the mold halves about the mounting shafts.

To open and close the mold, there is provided a pull rod 74 for each mold half. The pull rod 74 is coupled to the mold through an eye 76 which engages a clevis pin 78 extending into the mating eyes of lugs 82. A drive rod 84 engages the pull rod by coaction of the pin 86 thereon with the eyes of the cap nut 88 threadably secured to the pull rod. This coupling allows the pull rod to deflect as the mold halves pivot. The threaded engagement provides means for adjustment of the efiective length of the pull rod. The drive rod 84 is'reciprocably mounted within a bushing 90 mounted in a structural member 92 aflixed to the mold table. A flanged housing 94 encloses a nut 96 to define the position thereof. The nut 96 engages the threads 98 on the drive rod 84 so as to reciprocably drive the drive rod 96 as the nut is oscillated synchronously with reciprocation of table 86.

To oscillate the nut at a cyclic rate related to reciprocation of the mold table 84 there is provided a drive lug 100 and a biasing lug 102. A spring 164 is coupled between the aperture 166 in the biasing lug 162 and structural member 107 mounted on the mold table to bias the nut into the rotative position in which the mold is open. As the mold table 86 is driven downwardly in its reciprocating cycle, the lug 101 strikes thedog 108 pivotally mounted by pin 110 on the machine frame. The stop 112 defines the operative position of the lug and spring 114. biases the dog into such position. As the drive table moves down, the nut'96 is rotated thereby to drive

rods

74 and 34 to close the mold halves. As the mold halves close, the slab contained therein is formed into the desired section. At the bottom of the stroke, the lug 161) Will clear the dog 108 and the biasing spring 104 will return the nut 96 to its original position, opening the mold.

On the upward stroke of the mold table, the dog will merely be deflected out of the way against the bias of spring 114 until the lug 100 clears the dog, readying the device for another reciprocating cycle.

In this manner the spring mold continually forms the slab into the desired cross sectional shape which, in the embodiment illustrated, consists of a plurality of billets of small cross sectional dimensions coupled together. Since the cooling of the walls of the slab is slower in a mold in comparison with the water sprays illustrated in FIGS. 1-9, the thickness of the skin will remain desirably small during formation assisting in section casting. However, the mold supportably forms the skin of the entire slab. If a slight rupture of the thin skin occurs, it will be held and the skin break healed by the chilled mold plates.

It is often also advantageous to pre-corrugate the slab in the casting mold as explained in connection with the pre-corrugations of the slab as illustrated in FIG. 9. The forming mold may be so constructed as to completely slit the adjacent billets in the forming mold by the inclusion of slitting knives in the secondary mold.

In lieu of the mechanical drive illustrated in FIGS. 11-17, hydraulic drives for opening and closing of the mold may be used, as shown in FIGS. 18 and 19.

In FIGS. 18 and 19 there is shown the pull rod 74 coupled to the piston of hydraulic cylinder 120. The cylinder is preferably a double acting cylinder supplied with hydraulic fluid through lines 122 and 124 which are energized selectively by valve 126. Valve operation is controlled by a cam follower assembly having a cam follower roller 132 which is rotatably mounted on shaft 134 at the end of arm 136, which arm is connected to the cam follower assembly by shaft 138. The arm is biased into the horizontal position by the coaction of spring which arm 142 formed integrally with arm 136. The cam 144 is mounted on the frame of the casting machine and is provided with a protruding cam surface 146.

Thus, in operation, as the table 80 of the forming mold is driven downwardly, the cam roller 132 will follow the cam surface to move valve 126 thereby to supply hydraulic fiuid to cylinder 120 to energize rod 74, thereby closing the mold for the interval when the roller 132 is on the cam surface 146. On the return of the mold table in the upward stroke, it is, of course, undesirable to close the mold. During the upward stroke the roller 132 will be deflected against the bias of spring 140 to prevent mold closure on the upward stroke as illustrated in FIG. 18. Thus, only on the downward stroke is the mold closed, remaining open during the remainder of the reciprocation of the mold cycle on table 80.

This invention may be variously modified and embodied within the scope of the subjoined claims.

What is claimed is:

1. The method of casting a plurality of small billets at casting rates sufficiently high to enable pouring of heats of conventional tonnage which consists of the steps of continuous casting a narrow slab by forming a thin peripheral skin of metal cooled to solidify the skin and to encase the molten core, progressively crimping the skin Without changing the peripheral length thereof to form a plurality of integrally formed billets of small cross sectional area joined by said crimped skin in side by side position, and cooling the billets to solidify the molten core therein.

2. The method in accordance with claim 1 which includes the step of severing the skin between billets after solidification of the core thereof to form individual billets.

3. The method in accordance with claim 1 in which the skin is formed by forming rollers engaging the peripheral skin.

, thereof to serve as a guide for the positioning of said forming rollers.

References Cited in the file of this patent UNITED STATES PATENTS 1,074,089 Moore Sept. 23, 1913 2,108,753 Low Feb. 15, 1938 2,565,959 Francis et a1 Aug. 28, 1951 2,578,213 Welblund- Dec. 11, 1951 2,603,114 Colinet July 14, 1952 2,714,752 Wilson Aug. 9, 1955 2,711,577 Leach June 28, 1955 2,975,493 Morton et al. Mar. 21, 1961 FOREIGN PATENTS Great Britain Jan. 23, 1957

Claims

1. THE METHOD OF CASTING A PLURALITY OF SMALL BILLETS AT CASTING RATES SUFFICIENTLY HIGH TO ENABLE POURING OF HEATS OF CONVENTIONAL TONNAGE WHICH CONSISTS OF THE STEPS OF CONTINUOUS CASTING A NARROW SLAB BY FORMING A THIN PERIPHERAL SKIN OF METAL COOLED TO SOLIDIFY THE SKIN AND TO ENCASE THE MOLTEN CORE, PROGRESSIVELY CRIMPING THE SKIN WITHOUT CHANGING THE PERIPHERAL LENGTH THEREOF TO FORM A PLURALITY OF INTEGRALLY FORMED BILLETS OF SMALL CROSS SEC-