US3457984A

US3457984A - Process and apparatus for the continuous casting of steel

Info

Publication number: US3457984A
Application number: US577695A
Authority: US
Inventors: Hiroshi Yoshida; Hideo Okabe; Kenji Sasaki; Hiroshi Nonaka; Kichizaemon Nakagawa; Kiyoyuki Igarashi
Original assignee: Kawasaki Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1965-10-01
Filing date: 1966-09-07
Publication date: 1969-07-29
Anticipated expiration: 1986-07-29
Also published as: NL6613656A; BE686852A; GB1155884A; FR1495365A; LU52085A1; AT283614B; CH442632A

Description

July 29, 1969 HIROSHI YOSHIDA ETAL 3,457,984

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Filed Sept. 7, 1966 '7 Sheets-Sheet l 25 24 3 r g "m July 29, 1969 HIROSHI YOSHIDA ETAL 3,

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Filed Sept. '7, 1966 7 Sheets-Sheet 2 July 29, 1969 HIRDSHI YOSHIDA ETAL 3,457,934

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Filed Sept. 7, 1966 7 Sheets-Sheet 3 July 29, 1969 HIROSHI YOSHIDA ETAL 3,

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Filed Sept- 7, 1966 '7 Sheets-Sheet 4 July 29, 1969 HIROSHI YOSHIDA ETAL 3,457,984

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Filed Sept. 7, 1966 7 Sheets-Sheet 5 y 29, 1969; HIROSH! YQSHIDAI ETAL 3,457,984

PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEEL Q Filed Sept. 7, 1966 7 Sheets-Sheet 6 Fig .20.

July 29, 1969' HIROSHI YOSHIDA ETAL 3,457,934

PROCESS AND APPARATUS FOR THE coNTINUoUs CASTING OF STEEL Filed Sept. 7, 1966 7 Sheets-Sheet 7 F lg .30,

g 6 3 -\.LQ D. I O: 5 6 E 3133 a. g Q Thckness of a 4 steel striphn ySOC Length of longest side of ca se' L) United States Patent Oflice 3,457,984 Patented July 29, 1969 3,457,984 PROCESS AND APPARATUS FOR THE CONTINUOUS CASTING OF STEET. Hiroshi Yoshida, Hideo Okabe, Kenji Sasakr, II IIOShI Nonaka, and Kichizaemon Nakagawa, Chiba-sh], and Kiyoyuki Igarashi, Narashino-shi, Japan, assignors to Kawasaki Steel Corporation, Kobe-sh], Hyogo-ken, Ja an a cor oration of Japan p Filed Sept. 7, 1966, Ser. No. 577,695 Claims priority, application Japan, Oct. 1, 1965, 40/ 60,061 Int. Cl. 322d 11/00 US. Cl. 164-86 Claims ABSTRACT OF THE DISCLOSURE In a method and apparatus for continuous casting comprising: the combination of conveying a plurality of steel strips of indefinite length over deflector rolls in a downward vertical direction, the deflector rolls cooperating with auxiliary forming rolls producing protruding flanges on the edges of said strips, conveying additional steel strips of indefinite length over additional deflector rolls in a downward vertical direction adjacent to the first-mentioned steel strips, said additional deflector rolls cooperating with additional auxiliary forming rolls to form flanges on the edges of the additional steel strips and to further shape the flanges of the first-mentioned steel strips and introduce the flanges of the adjacent steel strips in lapped relationship, and further including joining means to form seals of the lapped flanges to produce an open-ended polygonal tubular hollow body adapted to receive continuous casting of molten metal, the present invention further being provided with means for cooling the tubular body and a guide assembly, insertable in the open end thereof and acting as a splash guard and cooperating with the forming rolls to insure passage of the steel strips over the deflector rolls.

This invention relates to a process and apparatus for the continuous casting of steel, and more particularly to a process and apparatus for the continuous casting of an indefinite length of steel strand from molten steel.

Many processes have been developed to improve the art in the continuous casting of steel, and one of the most practical processes now commercially available is the so called reciprocating mold type process using a reciprocating motion of an open-ended mold from the bottom of which steel strand is withdrawn. However, the reciprocating mold process involves considerable expense in construction as well as maintenance due to the complicated mechanism of reciprocating motion. In addition, there is a danger that a solidifying skin formed on the castisg may be broken by the friction or impact of the mold as it reciprocates causing molten steel to flow from the damaged casting. Therefore, to prevent this possibilty of casting damage, the cross sectional area of the steel strand is reduced and the withdrawal speed of the strand is slowed thereby reducing productivity.

There has also been proposed a continuous casting process using an endless chain conveyor mold constituted by an inclined mold chamber through which a continuous strand of steel is withdrawn in a downwardly inclined direction, In this process the problem of sealing of the mold element joints has not been successfully overcome thereby causing difliculty in cooling the mold elements as well as limiting the strand withdrawal speed and pro dueing many surface defects on the strand.

Other processes which have been proposed but never widely used are the continuous casting of metal using metal strips or bands which move downwardly to form a continuous casing. The molten metal is poured into the casing formed by the strips or bands where it solidifies with the strips or bands. Further, a process has been proposed wherein a tubular casing is formed by a strip and molten metals such as copper and brass are poured in the casing. However, many difiiculties have occurred with the use of these processes in steel casting because of a low heat conductivity, a high melting point and a high specific gravity of steel. The primary problem is the complete enclosing of the molten metal. This is of extreme importasce since the outside strips or bands are liquid cooled and damage to the casting will occur if any of the cooling fluid should penetrate into the solidifying casting. Also, if the enclosing strips or hands are not sealed tight, leakage of the molten steel may be appeared. An additional problem is that the joints of the metal strips or bands must be of suflicient strength to prevent possible separation due to the static pressure of the poured molten steel. Yet another problem is that bulging of the steel strips or bands will occur unless they are of sufficient thickness. This will limit the casting speed and thereby reduce productivity.

Therefore, it is a primary object of the present invention to provide a process and apparatus for the continuous casting of steel which will overcome all of the above as well as other problems and deficiencies of previously used casting methods.

Another object of the present invention is to provide a process for making an indefinite length of steel strand from molten steel with a high productivity rate.

A further object of the present invention is to provide an apparatus for the production of steel strand having a good surface quality in an inexpensive and highly eflicient manner.

Another object of the present invention is to providet an apparatus for forming a continuous casing which will be clompletely sealed to prevent any leakage of the molten stee Still another object of the present invention is to provide a process and apparatus for making a metal clad object having a core made of a metal such as steel.

A further object of the present invention is to provide an apparatus which is of relatively simple construction and easy to manufacture, which is automatic and rapid in its operation, and which is Well adapted for the purposes described.

According to the present invention, the foregoing and other objects are attained by providing a continuous casting process and apparatus wherein molten steel is directly poured into a polygonal tubular hollow casing (hereinafter referred to as continuous case) of a desired section which is formed by a plurality of steel strips or bands. This continuous case operates to define the cross section of the steel strand to be continuously cast and to trans mit outwardly the sensible heat of the molten steel. In this regard, the continuous case functions like a mold but travels together with the steel strand, and, therefore, the case itself becomes an outer skin of the strand.

The specific nature of the invention as well as other objects, uses and advantages thereof will clearly appear from the following description and from the accompanying drawings, in which:

FIG. 1 is a side elevation view, partly in section, of the apparatus of the present invention;

FIG. 2 is a front elevational view, partly in section, of the apparatus of the present invention;

FIG. 3 is a perspective view of the continuous casting apparatus of the present invention;

FIG. 4 is a horizontal sectional view of the first forming stage;

FIG. 5 is an enlarged view of a portion of FIG. 4 clearly depicting the first forming operation;

FIG. 6 is a horizontal sectional view of the strips forming the continuous case at the first forming operations without showing the forming apparatus;

FIG. '7 is a horizontal sectional view of the second forming stage;

FIG. 8 is an enlarged view of a portion of FIG. 7 clearly depicting the second forming operation;

FIG. 9 is a horizontal sectional view of the strips forming the continuous case at the second forming operation without showing the forming apparatus;

FIG. 10 is a perspective view of a guide assembly used in the apparatus of the present invention;

FIG. 11 is a vertical sectional view taken along the line xx of FIG. 10;

FIG. 12 is a vertical sectional view taken along the line yy of FIG. 10;

FIG. 13 is a horizontal sectional view of the seam welding operation;

FIG. 14 is a horizontal sectional view of the strips forming the continuous case after the welding operation;

FIG. 15 is a sectional view similar to FIG. 11 showing a modified guide assembly;

FIG. 16 is a sectional view similar to FIG. 12 showing another view of the modified guide assembly;

FIG. 17 is a horizontal sectional view showing a modification of the forming rolls consist of single stage;

FIG. 18 is an enlarged view of a portion of FIG. 17 clearly depicting the forming operation using the forming rolls of FIG. 17;

FIG. 19 is a horizontal sectional view of the strips forming the continuous case at the forming operation using the forming rolls of FIG. 17;

FIGS. 20-22 are horizontal sectional views showing various forms of multiple lapping of the edges of the strips forming the continuous case;

FIG. 23 shows the successive forming steps of the multiple lapping of FIG. 20;

FIGS. 24-29 show various forms of mechanically joining the edges of the strips forming the continuous case; and;

FIG. 30 is a graphic chart showing the relationship between the production rate and the length of the longest side of the case in cross section and the thickness of the strip forming the continuous case.

Referring now to the drawings, as shown in FIGS. 1-3, the molten steel is continuously poured from a ladle 1 through a tundish 2 into a rectangular continuous case 5 formed by

steel strips

3, 3, 4 and 4. Although this preferred embodiment uses four strips to form a rectangular continuous case, it will be appreciated that more or fewer strips will be required depending on the cross section desired for the continuous case.

The continuous case 5 filled with molten steel therein is supported at the outside thereof by a plurality of roller supports 6 and 7 while being cooled by high pressure water discharged from a plurality of spray nozzles (not shown) provided on the

conduit pipes

8, 9 of the cooling means. The molten steel 10 in the continuous case 5 is cooled by the cooling means due to its surface contact with the inside surfaces of the continuous case 5. As shown in FIGS. 1

and 2, the molten steel 10 is solidified from the outer surfaces in contact with the continuous case 5 inwardly to the core thereof to form the steel strand 11.

The steel strand is withdrawn by a suitable mechanism (not shown) in synchronism with the downward movement of the continuous case 5. The mechanism to withdraw the steel strand may also be used for moving the continuous case 5 downward or two separate mechanisms can be provided. As the steel strand and the continuous case 5 are being withdrawn, either the case 5 can be pulled off the steel strand by suitable means or the steel strand and case 5 can be left joined.

A fundamental idea of the present invention will be obtained from the above description. In carrying out the present invention, it is understood that the following conditions and requirements will be met.

First, it is required that each joint of adjacent strips which form the continuous case be tightly sealed to prevent the molten steel from flowing out therefrom or the cooling water from penetrating thereinto. If the tightness of the joint seals is defective permitting cooling water to penetrate into the continuous case, the quality of the steel strand would not only be lessened but it would give use to the danger of an explosion. Further, as is obvious, the flowing out of the molten steel would produce a condition requiring stoppage of production.

Second, each joint of adjacent strips should be of suflicient strength so that the joints will not fail and separate due to the ferrostatic pressure of the poured molten steel.

Third it is necessary that the sheet thickness of the steel strips used for constructing the continuous case should be sufficiently thick to prevent the case from bulging outwardly. Any slight bulging would make it impossible to maintain the desired cross sectional shape of the steel strand and further, it would lead to the breakage of continuous case.

Tests have shown that the sheet thickness will be limited by the continuous casting speed (withdrawal speed) and other operating conditions such as section dimension. The relationship between the withdrawal speed and the sheet thickness is shown in the following empirical formulas:

where From the formula, it is seen that the larger the section of steel strand and the thinner the sheet thickness of the steel strip, the smaller the possible maximum speed of withdrawal. FIG. 30 is a graphic chart showing the allowable maximum value of the withdrawal speed (V) of steel strand at various lengths (L) of the longest side of continuous case in cross section for different steel strip thicknesses (m).

On pouring the molten steel, it has been found that there will arise turbulence of the molten steel due to the pouring stream thereof and a solidifying thin shell will be washed off. Sometimes, this washing 01f may attack the continuous case. In this event, the greater the strip thickness, the less the danger of breakage.

Therefore, it follows that the thicker the steel strip, the safer its operation. However, with the increase of sheet thickness, the consumption of steel strip will be increased with the result that it would be not only economically disadvantageous, but also the forming and joining of the continuous case would be difficult. It has been found that the thickness of the steel strip should be in the range of 0.2 to 3.2 mm. and preferably 0.6 to 1.6 mm.

The outside of the continuous case is sprayed with a cooling fluid such as water supplied by the cooling means. It will be apparent that the volume of cooling water employed .depends upon the thickness of the steel strip, the cross section, and the withdrawal speed of the steel strand. Tests have shown that approximately 0.2 ton of water per square meter of the surface area of the continuous case every minute is required for proper cooling. This volume of water is required because the temperature of the surface of the continuous case should not be higher than the temperature of 600 C. when the molten steel having the temperature of 1500-1600" C, is poured into the continuous case, and further, the undesirable expansion of the continuous case must be limited.

Discussing now more specifically the preferred embodiment of the invention illustrated in FIGS. 1-14, two

steel strips

3, 3 of relatively wide sheet and two

steel strips

4, 4 of relatively narrow sheet are utilized to form a continuous case 5 having a rectangular cross section. In this embodiment, the apparatus used in connection with the

strips

3, 3 or 4, 4 is symmetrical, and the Working process in connection with the strip joints is also symmetrical, and therefore, only one strip or one strip joint will be discussed to simplify the description.

The wide strip 3 is continuously supplied from a reel 13 where it passes through a pair of pinch rollers 14 and a plurality of side guides 15 into a space between a deflector roll 16 and an upper curved portion 18 of a guide assembly 17 whereby the strip 3 is deflected by the deflector roll 16 in a vertical downward direction.

As shown in FIGS. 10 to 12, the guide assembly 17 comprises two duplicate sections each having a pair of upper curved portions 18, a pair of wide vertical portions 24, a lower curved portion 31, a narrow vertical portion 39 and a protector wall 100. The guide assembly 17 is preferably formed in two sections to -simplify construction and to permit relative adjustment between the sections to aid in accommodating the steel strips 4. The guide assembly protects the forming means from any splashing of the molten steel as it is being poured into the continuous case 5. The guide assembly also prevents any splashing of the molten steel on to the inner surfaces of the continuous case 5 which would tend to roughen the inner surfaces of the continuous case 5.

In addition to deflecting the wide strip 3 vertically downward the deflector roll 16 also is part of the first forming stage 22 shown in more detail in FIGS. 4 and 5. The deflector roll 16 comprises a cylindrical middle portion 19' and two frusto-

conical portions

19, 19. Cooperating with the deflector roll 16 are a pair of forming rolls 21 with frusto-conical portions 20. The frusto-

conical portions

19, 19 on roll 16 complement frusto-conical portions 20 on rolls 21 to bend the steel strip 3 between them.

The two wide deflector rolls 16 and the four complementary forming rolls 21 along with upper curved portions 18 of the guide assembly 17 comprise the first forming stage 22.

As the steel strip 3 passes through the first forming stage 22, both edges of strip 3 are bent at an angle of about 45 to form

flanges

23, 23 as shown best in FIG. 6. To make this forming angle as large as possible would be advantageous for the subsequent forming steps, however, the initial forming bend is limited by the mechanical properties of the steel strip, the sheet thickness and the diameter of the forming rolls. It has been found where preforming with deflecting is carried out, a bending angle up to approximately 75 can be easily achieved with the flange width preferably in the 10 to 20 mm. range. In this forming step, the strip 3 passes through a gap between the wide deflector roll 16 and the wide vertical portion of the guide assembly 17 to attain an accurate forming of the strip 3.

From the first forming stage 22, the pre-forrned strip 3 with the

flanges

23, 23 at both edges is passed into the second forming stage 27 comprising narrow deflector rolls 25, and wide forming

rolls

26, 2 6.

Narrow steel strip 4 is continuously supplied from a reel 28 between pinch rolls 29 and side guides 30 into a space between narrow deflector roll 25 and the lower curved portion 31 of the guide assembly 17 where the strip 4 is deflected to a vertical downward direction into second forming stage 27 to meet preformed strip 3.

In the second forming stage 27, the narrow deflector rolls 25 comprise a cylindrical body the axial length of which is equal to the Width of narrow strip 4. The wide forming roll 26 comprises a cylindrical body 33 and a cylindrical body 34 of reduced diameter at each end of said cylindrical body 33.

The edge of narrow strip 4 together with the partly bent flange 23 of wide strip 3 is introduced in lapped relation into the gap between the roll surface end of the narrow deflector roll 25 and the annular end 37 of the wide forming roll 26. As a result, the flange is bent to an angle of approximately whereby the flange 23 and the end of strip 4 are lapped to form a protruded lapped portion or lapping 38. All during this operation, the

strips

3 and 4 are accurately aligned by the

vertical portio

4 and 39, respectively, of the guide assembly 17.

The four

strips

3, 3 and 4, 4 form a rectangular body with four protruded lappings 38, the cross sections of which is clearly shown in FIG. 9. To form sealed joints at lapping 38, the lapping 38 must be completely sealed together to prevent penetration of the cooling Water or outflow of the molten steel.

In FIGS. 1 to 3 and 13, there is shown the preferred embodiment of using seam welding to seal the lappings 38. The welding means 40 comprises a seam welder 41 at each corner.

Each seam welder 41 has a pair of

rotary electrodes

42 and 43 and an air cylinder 44 which urges one electrode 42 toward the other electrode 43. A pair of holding rolls 45 are provided immediately above the rotary electrodes to hold the lappings 38 tightly. The four lappings 38 are pressed and electrically welded in a vertical direction as they pass between

rotary electrodes

42 and 43. The

rotary electrodes

42 and 43 may or may not be driven. Thus, the completely sealed continuous case 5 of prescribed cross section as shown best in FIG. 14 is formed from four

steel strips

3, 3 and 4, 4.

It will be understood that the above description is of a preferred embodiment for manufacturing the continuous case 5. However, the invention is not limited to this embodiment and may be carried out by the use of certain modifications which are described below.

The cross section of the continuous case 5 may be of any suitable polygonal shape besides the preferred rectangular shape. The number of sides of the polygonal cross section to be formed will determine the number of steel strips required.

In order to obtain the perfectly sealed continuous case, it is necessary to use a steel strip free from any variations in sheet width and which will be correctly aligned on the deflecting and forming rolls. To this end, the edges of the strip should be trimmed in advance of forming preferably by providing a side trimmer (not shown) in the processing line as the strip leaves the reel. In addition, the use of side guides or other types of edge position controllers are essential for proper alignment of the strip.

In the above-described embodiment, the deflector roll 16 performed a deflecting function as well as a forming function. This dual function was used in order to make the distance between the molten steel level in the case and the tundish nozzle as short as possible. It will be apparent to one skilled in the art that the deflector roll may be separate from the forming roll. If made separate, the deflector roll need not be a rotatable roll but may be a fixed curved member. The roller supports 6, 7 may also be fixed curved surfaces and in many instances the support 7 may be omitted for the narrow width steel strip 4.

In the guide assembly 17 described in the preferred embodiment, each section included the wide vertical portion 24 and the narrow vertical portion 39 formed integral with each other. It will be appreciated that these

portions

24 and 39 can be separately formed since each portion deals with a difierent steel strip.

It has been found that the proximity of the guide assembly 17 to the molten steel can sometimes produce heating problems which can affect the guiding elements of the assembly. To prevent this overheating problem, there is shown in FIGS. 15, 16 a guide assembly 47 which is similar in all respects to guide assembly 17 having upper curved portions 18', wide vertical portions 24' and narrow vertical portions 39 with the addition of a water jacket 46 having piping 46 to circulate the cooling water.

There is shown in FIGS. 17, 18 a forming assembly 48 which will simultaneously perform the deflecting and forming operations to produce a continuous case having a modified form of lapping. In this modification, the edges of

strips

3 and 4 are bent at an angle of 45 to form

flanges

49 and 50 whereby the lapping 51 as best shown in FIG. 19 is produced. The forming assembly 48 consists of wide strip rolls 54 having frusto-conical portions 52 at its ends and narrow strip rolls 55 having frustoconical portions 53 at both ends. This forming assembly 48 can attain an operation of deflection and formation in a single step. In the single step flange forming, a bending angle in the range of to 75 is preferred.

In place of the above mentioned single lappings,

double lappings

59, 60 and 61 shown in FIGS. to 22 are easily formed. For example, in reference to the double lapping 59, a series of forming assemblies, illustrated in FIG. 23, af may be utilized.

Various designs of forming assemblies can be used depending on the properties and thickness of the steel strips, the cross section of the continuous case, and the type of lapping desired.

In the preferred embodiment discussed above, the seam welding by electric resistance is shown, although any welding process, such as fusion welding, pressure welding and brazing may be employed. However, the seam welding method is the most suitable method for the high speed continuous welding required. to firmly seal the lappings together, other various mechanical joining methods may be used in addition to the welding procedure already discussed. Several examples are shown in FIGS. 24 to 29. FIG. 24 shows the formation of a joint 63 by bending the double lapping 59 at an angle of 90. FIG. shows a mechanical joint formed by placing a groove in the double laping 59 with a set of grooving rolls 64 and 65.

Another joining method shown in FIG. 26 can be applied to both single and double lappings. In addition to the steel strip for use in the continuous case, a narrow steel strip 67 having notches 68 is formed into a V-shape by a series of

rollers

69, 70 and a guide member 71 whereby it surrounds a lapping joint 72. A series of

rollers

73 and 74 apply pressure to steel strip 67 to obtain a firm reinforced joint 75.

The mechanical joining methods shown in FIGS. 27 to 29 can also be applied to either single or double lapping. The process of FIG. 27 utilizes a cut out tongue piece 76 from the lapping 77 which is folded along the lapping 77. In FIG. 28, there is shown the use of rivets 78 to form a tightly sealed lapping 79 and in FIG. 29, fasteners 80 are used to join the lapping 81.

EXAMPLE The continuous case was made by the two stage forming means with seam welding as described in detail in the embodiment of FIGS. 1l4. A low carbon cold rolled steel strip having a thickness of 0.6 to 1.0 mm. was employed as the strip material for the continuous case. The main forming roll of the forming means was 150 mm. in diameter. The width of each lapping at the four corners of the continuous case was 15 mm. The lapping was con tinuously welded by a pair of rotary electrodes having a diameter of 200 mm. The continuous case was cooled by water applied at the rate of about 0.4 ton per square meter of surface area every minutes at a pressure of 4.5 kilograms per square centimeter. The molten steel was an ordinary carbon steel with a chemical analysis of: (MS-0.17% carbon, 0.220.36% silicon, 0.63-1.22% manganese, 0.0l0-0.0l8% phosphorus, 0.01 l0.024% sulfur, and the balance iron. The temperature of the molten steel was about 1500 C.

The following table shows the withdrawal speed of the steel strand and the casting productivity under the above conditions when the thickness of the steel strip and the continuous case cross section are varied.

TABLE Continuous Withdrawal I case section Thickness of speed, n1./ Productiv- Example size, mm. strip, mm. min. ity, t./hr.

250x900 1. 0 2. 2 223 250X900 0. 6 1. 4 144 250x1, 500 1.0 1.0 250X1, 500 0. 6 0. 7 118 It has been proved that a high casting productivity and an excellent advantage are obtained by the present invention. In addition, it has been found that the steel strand thus produced in accordance with the present invention has a surface quality at least as good as the product produced by conventional casting processes.

In the foregoing example, a continuous casting product from an ordinary carbon steel was described; however, it will be appreciated that all grades of steel used in continuous casting processes can readily be used in the present invention.

Thus, there has been provided an eflicient and economical continuous casting process and apparatus which are well adapted to attain the ends and objects set forth in the description, and which may be readily modified in several ways so as to best adapt the process or apparatus to the conditions of the particular casting operation.

It will be understood that variations of the process as outlined above and of the apparatus for carrying out the process may be made within the spirit and scope of the invention hereinbefore set forth and hereinafter claimed.

What is claimed is:

1. A process for the continuous casting of steel comprising:

supplying a plurality of steel strips to a position adjacent a supply vessel containing molten steel, moving said strips in a vertical downward direction to make an open-ended tubular hollow body, forming the edges of said strips into protruded lappings at each corner of said body,

joining said lappings of said body to make a sealed continuous case,

pouring said moten steel into said case,

cooling and supporting said case to solidify said molten steel and to prevent bulging of said case, and withdrawing said cast steel downwardly at a speed of a value of V given by the following formula:

2. Apparatus for the continuous casting of steel comprising:

a plurality of steel strips of indefinite length,

a deflecting roller associated with each steel strip for moving said steel strip in a vertical downward direction to make an open-ended polygonal tubular hollow body, at least some of said deflector rolls being provided with frusto-conical end portions,

an auxiliary forming roll of frusto-conical configuration cooperating with a frusto-conical end portion of said deflecting rolls to provide flanged edge portions on at least some of said steel strips,

means for introducing the flanged edges of some of said strips in lapped relationship with the edge portions of the remaining steel strips, said means being adapted for bending said flanged portions in complementary configuration with the edge portions of said remaining steel strips,

means for joining said lapped edge portions to make a sealed continuous case,

means for supplying molten steel into said case, a plurality of vertically spaced roller supports abutting and extending the width of a respective steel strip of said case,

a conduit pipe provided with a plurality of spray nozzles located below and adjacent each of said roller supports and extending axially the length thereof for discharging a coolant over the surface of said joined steel strips, and

means for withdrawing said cast steel downwardly.

3. The structure as recited in claim 2, wherein said auxiliary forming rolls comprise deflecting rolls for said remaining said steel strips, each of said forming rolls being provided with frusto-conical edge portions cooperating with the edge portions of adjacent deflector rolls to form lapped, adjacent flanged edge portions on adjacent steel strips.

4. The structure as recited in claim 2, wherein said joining means includes Welding apparatus provided with rotary electrodes engaging opposed surfaces of the lapped edge portions.

5. The structure as recited in claim 2, and further including:

a forming guide assembly including means cooperating with said deflecting rollers for insuring passage of the steel strips over the deflecting rollers and additional means insertable in the polygonal enclosure for providing a guard for the splashing of molten metal introduced into the polygonal enclosure.

References Cited UNITED STATES PATENTS J. SPENCER OVERHOLSER, Primary Examiner R. SPENCER ANNEAR, Assistant Examiner US. Cl. X.R.