US3667534A

US3667534A - Steel ingot making method

Info

Publication number: US3667534A
Application number: US123394A
Authority: US
Inventors: Tatsuro Kanokogi; Kunio Yasumoto
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1971-03-11
Filing date: 1971-03-11
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

A method for semi-continuously casting long-length, large steel ingot by pouring molten steel into a thin walled, water cooled, long-length mold made of iron, steel or cast iron which does not thermally deform, in contact with the molten steel during pouring and withdrawing the solidifying ingot down through the mold at suitable speed without directly water cooling the solidifying ingot until a predetermined length of ingot is obtained, and then holding the ingot in the mold for a while till the ingot solidify enough to draw out from the mold on to a truck which carry away the said ingot to further processing and apparatus thereof.

Description

United States Patent Kanokogi et al.

[54] STEEL INGOT MAKING METHOD [72] Inventors: Tatsuro Kanokogi, Osaka; Kunio Yasumoto, Hyogo, both of Japan 3,421,572 1/1969 Reihman ..l64/280X 51 June 6,1972

3,455,370 7/1969 Easton et a]. ..l64/260 X 3,528,483 9/1970 Mallener 1 64/282 X 3,528,487 9/1970 Wognum et al l64/83 X 3,565,158 2/1971 Ciochetto ..l64/83 X 3,581,806 6/1971 Neumann et a1 ..l64/83 X Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel AttorneyRalph E. Bucknam, Jessie D. Reingold and Robert R. Strack ABSTRACT A method for semi-continuously casting long-length, large steel ingot by pouring molten steel into a thin walled, water cooled, long-length mold made of iron, steel or cast iron which does not thermally defonn, in contact with the molten steel during pouring and withdrawing the solidifying ingot down through the mold at suitable speed without directly water cooling the solidifying ingot until a predetermined length of ingot is obtained, and then holding the ingot in the mold for a while till the ingot solidify enough to draw out from the mold on to a truck which carry away the said ingot to further processing and apparatus thereof.

5 Clains, 16 Drawing figures PAIENTEBJUH 6 m2 SHEET 3 BF 4 Fig.9B

Fig.9A

DISPLACEMENT TIME I UP AND DOWN OSCILLATION CURVE |OF THE MOLD CYCLE OF COMPRESSION AND RELAXATION OF [THE WALL OF THE MOLD Fig. l0

STEEL INGOT MAKING METHOD This application is a continuation of Ser. No. 703,385, filed Feb. 6, 1968, now abandoned.

This invention relates to a method and apparatus for semicontinuously casting good quality steel ingot with a comparatively large cross section and length.

Usually steel ingots have been manufactured by means of top pouring method in which molten steel is directly poured from ladle into a cast iron mold, or by the bottom pouring method in which molten steel in introduced from the bottom of the mold through a runner installed at the lower part of the mold. According to those conventional processes, steel ingots must be drawn out from the mold after the molten steel has solidified.

Some continuous casting methods have been also provided, in those processes molten steel are continuously cast into water cooled bottomless molds and partially solidified steel are continuously drawn out downward and then solidification of the steel is acceleated by spraying cooling water on the surface of the ingot by means of the secondary cooling system. This cooling prevents also deformation of the ingot and break out of liquid steel, thus also casting speed may be increased.

However, these conventional casting methods have some advantages and also some disadvantages. For example, in the top pouring method, installations are very simple and this method is widely utilized for manufacturing every size of steel ingots and various kinds of steels, but if too large are cast, a lot of molten steel will scatter due to the head from the ladle, and scattered drops damage the steel, increase non-metallic inclusion, especially at the initial pouring stage. Further, the above non-metallic inclusions are often entrapped in the steel ingot, or sticked to the inner surface of the mold, causing a rough surface of the steel ingot. These above mentioned disadvantages cause a lower the quality of the steel ingot, increase work load for surface conditioning, and at the same time decrease the yields of ingot.

In the bottom pouring method, considerable amounts of expenses and work loads are required for assembling and stripping the mold, and fragments from refractory material used in a runner or guiding pipe are often carried into ingot with molten steel, causing defects in the ingot. Moreover the yields of ingot is lowered due to cut off of steel solidified in the runner or pipe.

In the continuous casting method, a slab, bloom or billet can directly be obtained. However, there is a tendency to generate various defects inside or on the surface of cast product due to thermal and deformation stresses caused by direct water cooling or by pinch rolls under the mold. Therefore, it is almost impossible to apply this continuouscasting method to manufacturing ingots of special steels such as l3 Cr, 18 Cr, high Mn, high C-Cr steel, etc., or rimmed steel ingot.

In recent huge steel works, various kinds of steel must be manufactured, the size of ingot becomes bigger and bigger and production speed becomes greater, therefore the above mentioned various defects in conventional ingot casting methods become more conspicuous and it is very desirable to develop an new ingot casting technology with extensive versatility.

Object of this invention is to develop improved method and equipments for semi-continuously casting large and long size ingot with excellent quality of various kinds of rimmed, semikilled and killed steel, by using a thin walled, water cooled bottomless mold, without direct water cooling of the ingot.

Another object of this invention is to provide a method and apparatus for preventing bulging of ingot and reducing friction between the inner surface of mold and the steel ingot being cast by forced elastic deformation of the mold wall.

Another object of this invention is to provide a method and apparatus to handle and truck the produced ingot ready to put into a soaking furnace for further processing.

Above and other purposes of this invention are accomplished at first by using a thin walled long-length water cooled mold which does not thermally deformed on pouring the molten steel. A movable bottom plate in the mold receive the molten metal from a ladle at the upper part of the mold. The mold cools the molten steel in the mold through water cooled wall to the extent suitable for withdrawing in the mold, the bottom plate begins to descend at a desired speed holding the solidifying steel on it, while the pouring of molten steel continues. Thus the length of the steel ingot increases gradually in the water cooled mold without any direct water cooling on the solidifying ingot surface. When the solidified ingot becomes a predetermined length, pouring of molten steel is stopped and the solidifying ingot is held in the water cooled mold for some length of time by stopping the withdrawing apparatus to solidify enough suitable for withdrawing from the mold and loaded onto the ingot trucks and carried out to the following step.

The second feature of this'invention is to use a specially designed thin walled long length, bottomless mold made of iron, steel or cast iron. The mold has water inlet pipes and manifolds and outlet pipes and manifolds, and is constructed of inner mold wall and outer back up wall. The cooling water channels are machined longitudially from manifold to manifold on the outer side of the inner wall, and closed by .the backup wall. Both walls are welded together to make passages for cooling water. The upper part of the mold is rather rigidly constructed, and the lower part is elastically deformable. The thermal stress generated in the mold wall due to the contact with molten steel is restricted within the yield strength of the mold material by cooling with water, thereby any permanent deformation of the mold being prevented.

The third feature of this invention is to provide means to reduce friction between the solidifying ingot and the mold wall and to prevent bulging of the solidifying ingot caused by the ferrostatic pressure of the molten steel by installing a pushpull device on outside backup wall of the mold. The push-pull device periodically push inward and pull outward the wall of the mold, that is to say, alternatively compress and relax the wall of the mold against the solidifying ingot with relation to the up and down reciprocating motion of the mold.

The fourth feature of this invention is to provide means for reducing amount of foreign substances and non-metallic inclusion in the molten steel and preventing entrainment of said foreign substances and inclusions inside and on the surface of the steel ingot, and also controlling the direction of flow of the down-coming molten steel thereby to improve the quality of the ingot and further making easier addition of deoxidizing agent in the molten steel.

The thin mold wall according to the present invention is constructed of inner wall and outer backup wall, and is elastically deformable by the outer push-pull force. The inner wall made of iron, steel or cast iron can easily be machined to have many longitudinal channels or fins throughout the mold length, and can rigidly be welded or bolted together to the backup wall made of iron, steel or cast iron to make passages for cooling water. In order to extent the endurance of the mold, metal plating or plasma jetting of hard chromium or molybdenum may be applied on the inner surface of the mold which contacts with the molten steel. The mold may be provided with any suitable means of feeding lubricant on the inner surface of the mold. Corrosion and adhesion of dirt in the cooling water channels can also be prevented by metal plating with chromium, nickel, zinc, tin, etc. or chemical coat- This invention will be more fully understood referring attached drawings.

FIG. 1 is an embodiment of the present invention showing a longitudinal sectional and side elevational view of a steel ingot making apparatus;

FIG. 2 is a top plan view of the steel ingot making apparatus illustrated in FIG. 1;

FIGS. 3 and 4 are longitudinal sectional views of the steel ingot making apparatus, showing another embodiment of this invention. FIG. 3 indicates the status before pouring and FIG. 4 indicates the status after drawing out an ingot;

FIGS. 5, 6 and 7 indicate a mold according to this invention. FIG. 5 is a top plan view of the mold, FIG. 6 is a longitudinal sectional view taken substantially on the vertical plane of line VI-VI of FIG. 5, and FIG. 7 is a longitudinal sectional view taken substantially on the vertical plane VIIVII of FIG.

FIG. 8 is 'a longitudinal sectional view of a truck to carry out an ingot;

FIG. 9 A and B are side elevational views to explain push and pull operation at the side of the mold;

FIG. is to explain the relation between a cycle of up and down reciprocating motion of the mold and a cycle of pushing inward and pulling outward the walls of the mold;

FIG. 1 l is a cross sectional view to explain assembling structure of the inner walls of the mold and the backup wall;

FIGS. l2, l3 and 14 are cross sectional views showing an example of the assembled structure of the inner wall of the mold; and

FIG. is a longitudinal sectional view which shows other embodiment while pouring molten steel according to the present invention.

Referring to FIGS. 1 and 2, molten steel 1 is fed to the upper pouring part of mold 5 by lifting a stopper 4 of pouring ladle 3 which is transferred above the pouring deck 2. A support 7 of a withdrawing device for an steel ingot is longitudinally penetrated through steel ingot truck 8 from bottom and is installed in mold 5. Bottom plate 9 is connected to the top of support 7. At first molten steel 1 is poured on the above-mentioned bottom plate 9 in the mold 5.

When the meniscus reaches to the predetermined level in the mold, the pouring rate iscontrolled by operating stopper nozzle 4 to maintain the meniscus at the prescribed level, while support 7 is lowered together with bottom plate 9 by ingot drawing out mechanism 6 such as system of hydraulic cylinder and piston or etc. The steel ingot cooling and solidifying in the mold which is forcibly watercooled is drawn down at a synchronous speed corresponding to the pouring speed of the molten steel. During this step, mold 5 is subjected to continuous reciprocating motion by reciprocating motion device 12. The reciprocating motion of the mold can easily be generated by any well-known technique such as eccentric cam, crank and rod, or hydraulic cylinder. However, as shown in FIG. 10, it is desirable that the speed of downward motion of the mold is made the same with the drawing out speed of the ingot and ascending speed of the mold is made several .times that of the downward motion. It is most suitable that the distance of the reciprocating motion is from 5 mm to 50 mm, the cycle is from to 50 per minute and the push-pull distance of mold wall is between 0 and 10 mm.

When the pouring of molten steel into the mold is started, push-pull device 13 at the central part of the mold is operated, and as shown in FIG. 9, the forced reciprocating motion to push the inner wall inward and to pull the inner wall outward is given to wall of the mold. As shown in FIG. 10, the operation of this push-pull device 13 is synchronized with the up and down reciprocating motion of the mold, and when the motion of the mold is downward, the inner wall of the mold is pushed inward and presses the surface of the steel ingot which is solidifying. When the motion of the mold is upward, the

inner wall is forcibly pulled outward, thereby friction between the mold and the ingot is released.

As shown in FIGS. 6 and 7, this push-pull device is located near the central part of the mold and gives alternatively push and pull action to the inner surface of the mold, thus the walls of the mold is compressed and relaxed. A hydraulic cylinder of this device is installed on the outer backup wall of the mold, but a cam, crank or rod may be used. The cyclic action of push and pull against the mold by the push-pull device reduces the friction between the inner wall of the mold and ingot, and as the same time prevents bulging of the steel ingot due to the static pressure of molten steel, thereby the drawing down of the ingot become more easy. However, when the cross sectional area of the mold is comparatively small and the pouring speed is slow, the push-pull device may be omitted.

Thus ingot 14 is gradually drawn down within the mold 5, while being solidified and cooled. When the length of the ingot reaches the predetermined length, the pouring nozzle of the ladle 3 is closed to stop the pouring, and the ingot is hold in the mold until the ingot is solidified enough to be drawn out from the mold. Support 7 of ingot withdrawing device 6 is finally lowered to the position indicated in FIG. 8. That is, the sufficiently solidified and cooled ingot 14 is completely drawn out of mold 5, and set on the truck 8, the support 7 is automatically separated from bottom plate 9 and the ingot is loaded on the truck 8 with bottom plate 9 and the support 7 is further decend. Then, truck 8 runs on rails 17 by power to carry out the ingot to the prescribed place. Then another truck loaded with another bottom plate is set just under the mold and support 7 is raised together with new bottom plate upto predetermined level in the mold and then, the next pouring starts again. In the example explained in FIGS. 1 and 2, truck 8 is guided on rails 17 by a chain 16, and is carried away to the position 8 shown in dotted line. In order to plan more high efficiency and mass production, the truck should be selfpropelled or be linked and pulled by an electric locomotive for successive operation. The mold must be cooled during pouring step and for the whole period while an ingot exists in the mold, to prevent thermal deformation of the mold. The pushpull device of the mold is cyclically operated during the pouring but when the pouring is finished, the action of the pushpull device is stopped in compression or relaxation state, thus to prevent bulging of the ingot.

FIGS. 3 and 4 show another embodiment of this invention in which the height of the ingot making installation can be lower than that of the current installation and the expense required for construction of the installation can be reduced. That is, the ingot truck 8 is placed just under mold 5 and the cooled and solidified steel ingot is withdrawn by shifting mold 5 up. To this purpose, several hydraulic cylinders 15 for lifting the mold upward are installed at pouring deck 2, and, as shown in FIG. 4, the mold is lifted upward by pushing up pistons in the cylinders thereby to withdraw the solidified steel ingot, and then the ingot is loaded on truck 8 and carried away. The cycle of reciprocating motion of the mold is synchronized with the withdrawing speed and the push-pull motion at'the side of the mold. The cyclic action of push-pull motion elastically deforms the wall of the mold, as shown in FIGS. 9 and 10. As indicated by the dotted line in FIG. 98, when the mold is in the down motion at the same speed as the withdrawing speed of ingot, the inner wall of the mold is inwardly compressed. When the mold is in the up motion, the wall of the mold is outwardly pulled, that is, inflated as shown in FIG. 9A. The wall of the mold must be elastically deformable.

FIG. 10 illustrates the above mentioned operation. The ratio of t t t, represents time period of downward motion or compression and represents time of upward motion or relaxation, is selected between 1:1 and 10:1, according to the bulging characteristic of the steel ingot. The upper part or pouring part of the mold is rather strongly assembled and the under part of the mold is thin walled and lengthy and must be elastically deformable inward and outward by external force, as shown in FIG. 9. The mold is forcibly water-cooled. As shown in FIGS. 5, 6, 7 and 15, the mold used in this invention is equipped with inlet pipes 21, and cooling water is led to manifold 22 from this inlet pipes 21. Then, the cooling water is collected at manifold 25 through many longitudinal channels 24 (refer to FIGS. 11, 12, 13 and 14) installed at the inner wall of mold 23 and discharged from

outlet pipes

26 and 27. The mold illustrated in the Figures is equipped with the inlet-pipe and inlet manifold at the upper part and with the outlet pipes and outlet manifolds at the bottom part. But the cooling water may be led to flow from the bottom toward the top of the mold.

Main characteristics of the structure of this mold for ingot making are:

1 Cooling efiiciency of the mold can be improved by selecting a proper ratio of cross sectional length of the mold contacting with the molten steel (refer to FIG. 13) to total cross sectional length of the channels of cooling water.

2 By selecting a proper thickness of the inner wall of the mold, corresponding to the thermal conductivity of the mold material (iron, steel or cast iron), the temperature increment at the inner surface of the mold is made less thermal deformation of the mold being kept within allowable limit.

3. The mold can be elastically deformable because the thickness of the mold is very thin.

For example, in FIGS. 1 l, 12, 13 and 14, when an iron plate with 12 mm thickness is used as an inner wall of mold 23 (42 in FIG. 13) and the ingot is drawn out at speed of 300 mm/min., the maximum temperature of the inner surface of the mold contacting with molten steel can be kept within 300 C, by maintaining the flow speed of cooling water in longitudinal cooling water channel 24 to 4 m/sec., and the cross sectional dimension of the cooling water channel to be 8.8 mm depth and 4 mm width, and the pitch of the channel to be mm. According to the excellent cooling effect, any thermal deformation caused by the thermal expansion due to contact with the molten steel is restricted within the elastic limit or yield strength of the material of the mold, even when the mold is reinforced with backup wall 28 etc. Thus the wall of the mold according to the present invention does not show any permanent set or permanent thermal deformation due to repeated heating for long period. Then the mold of the present invention can be used for long periods of time without any thermal deformation.

FIG. 11 shows the structure of the inner wall of the mold and the back up wall. The inner wall of the mold 23 made of iron, steel or cast iron, is worked with machines to make many channels 32 and fins 31 alternately. By tightly fitting back up wall 28 made of iron, steel or cast iron with inner surface of the wall, many longitudinal channels for cooling water are formed. Both walls are welded together at 34 at necessary position through the preliminary drill hole of the back up wall, said hole in the back up wall 28 is plugged at 36 with plug 35. Or the inner wall of the mold and the back up wall are fixed together and longitudinal channels of cooling water 24 is constructed by preliminary drilling small holes 37 in the back up plate and by plug-welding or bolting small holes 37 with finv part 31 of the inner surface material. The bolting method is not explained in the Figure. The cross sectional configuration of the mold can be square, rectangular, poligonal or circular, etc. However, the rectangular shape with a circular are at the corner as shown in FIGS. 12 and 13 is commonly used. FIG. 12 explains an example of an assembled mold in which four'sides are welded together with the proper circular are R at each inner surface comer. FIG. 13 illustrates an example of the angular or circular tubular mold which is comparatively advantageous for the small cross sectional mold. An inner wall 42 of the mold is a welded angular or circular tube, and provided with many fins 43 and channels 44 mechanically worked on the outside surface of the inner wall. A back up wall 45 is fixed to the inner wall to make the tubular mold. Further, FIG. 14 illustrates an example of the partial cross section of the mold which is advantageous for making large cross sectional slab ingot mold. This mold is constructed together by welding with four walls at 47. The circular are at comer 27 is larger than right angle.

For prevention of abrassion and improvement of smoothness between the inner surface of the mold and the steel ingot, the inner surface of the mold may be metal plated or plasma jetted by hard chromium or molybdenum. Further, for prevention of dirt adhesion, rusting and corrosion, and improvement of heat extraction efficiency, every inner surface of i the longitudinal channels of cooling water is metal-plated by chromium, nickel, zinc or tin, etc., or chemically treated by such as molybdenic acid treatment and chromic acid treatment. For improvement of smoothness between the mold and the steel ingot, it is preferably to provide a lubricating oil system on the mold. Vegetable oil such as rapeseed oil, various mineral oil or oils with or without proper deoxidizing agent may be used asthe lubricating oil.

As described before, one object of this invention is to provide useful means for reducing the amount of foreign substances and non-metallic inclusion in the molten steel and for preventing entrainment of said undesirable substances. One of these means is shown in FIG. 15. According to this means, molten steel 1 is at first poured from ladle 3 into a ceramic crucible 72 situated at the center of the mold. The ceramic crucible has several holes 73 near bottom. As the poured molten steel in the crucible is maintained in it for some period, dirts and non-metallic inclusions float up to the surface of the molten steel in the crucible, then only clean molten steel slowly flows out through the holes. The direction of flows through the hole may be changed depending on the direction and configuration of holes 73,for example, horizontal, upward or any other desired direction.

According to this means any slag is not carried in the flow of the molten steel poured into mold, surface appearance and structure of the ingot are considerably improved, and the quality of the ingot are also greatly improved. In this crucible, further, any type deoxidizing agents such as rod, strip, block or powder can easily be added into the molten steel.

FIGS. 8 and 15 illustratethe operation for semi-continuous casting of ingot of this invention. It is desirable that bottom plate 9 can be smoothly and firmly fixed to and separated from the top of the support 7. For this purpose various well-known bar connecting technics such as connector or a conventional train coupler, etc. may beused. An actual practice of this is explained hereunder:

When the support 7 of ingot withdrawing device 6 ascends, it is connected to the bottom plate 9, and then further thrusts through central hole of ingot truck 8. The support is, then, inserted in mold 5. As molten steel is poured into the mold, bottom plate 9 is withdraw together with solidified ingot thereon. The connection and disconnection between the support and the bottom plate is accomplished as follows. As shown in FIG. 8, enlarged top 53 of the support 7 fits into the concave cavity 52 of the connector 51 combined to the bottom plate. The support is, then, held by a pair of hooks 56 which have roller 55 at one end and are pulled inward by spring 57. Roller guide plate 58 is placed slantwise, at the lower part of ingot truck 8. When a steel ingot 14 is withdrawn downward on the truck, rollers 55 push the roller guide plate 58, hook 56 is opened and, then, support 7 is automatically separated from connecter 51.

What is claimed is: I

l. A method for semi-continuously casting long-length, large steel ingots comprising providing a thin-walled, watercooled, long-length mold having elastically deformable side walls and made of iron, steel or cast iron which does not thermally deform when in contact with the molten steel during pouring, pouring molten steel into said mold, withdrawing the solidifying ingot down through the mold at suitable speed without direct cooling by water until a predetermined length of ingot is obtained, moving said mold downwardly on the downward stroke of a reciprocating device and simultaneously applying a compressing, lateral motion to the elastically deformable side walls of the mold to push said side walls inwardly to press the surface of the solidifying ingot and prevent bulging of the latter caused by the static pressure of the molten steel, moving said mold upwardly on the upward stroke of said reciprocating device and simultaneously applying a relaxing lateral motion on the elastically deformable side walls of the mole to release the friction between the mold and the ingot, said downwardly and upwardly reciprocating motion of said mold and said compressing and relaxing lateral motion of said mold side walls being efiected cyclically and in synchronism, whereby the drawing down of the ingot is facilitated by the cyclical and synchronized downwardly and upwardly reciprocal motion relative to said compressing and relaxing lateral motion, holding theingot in the mold for a period of time until the ingot solidifies enough, drawing out the mold, and carrying away the ingot to further processing.

2. A method according to claim 1 in which the thin walls of the mold are compressed and relaxed in relation to the reciprocating down and upward motion of the mold to prevent bulging of the solidifying ingot and to reduce the friction between the mold and the solidifying ingot.

3. A method according to claim 1 wherein said reciprocating motion and said lateral push-pull motion are generally linear, such that when said reciprocating motion is directed downwardly, said push-pull motion is directed laterally inwardly to press the surface of the solidifying steel ingot, and when said reciprocating motion is directed upwardly, said push-pull motion is directed laterally outwardly to pull the inner wall of the mold laterally outwardly.

4. A method according to claim 1 further comprising circulating cooling water through longitudinal channels in said mold, said channels having inner surfaces coated with a metal plating.

5. A method according to claim 1 further comprising circulating cooling water through longitudinal channels in said mold, said channels having inner layers subjected to a molybnate and chromate chemical treatment.

Claims

1. A method for semi-continuously casting long-length, large steel ingots comprising providing a thin walled, water-cooled, long-length mold having elastically deformable side walls and made of iron, steel or cast iron which does not thermally deform when in contact with the molten steel during pouring, pouring molten steel into said mold, withdrawing the solidifying ingot down through the mold at suitable speed without direct cooling by water until a predetermined length of ingot is obtained, moving said mold downwardly on the downward stroke of a reciprocating device and simultaneously applying a compressing, lateral motion to the elastically deformable side walls of the mold to push said side walls inwardly to press the surface of the solidifying ingot and prevent bulging of the latter caused by the static pressure of the molten steel, moving said mold upwardly on the upward stroke of said reciprocating device and simultaneously applying a relaxing lateral motion on the elastically deformable side walls of the mole to release the friction between the mold and the ingot, said downwardly and upwardly reciprocating motion of said mold and said compressing and relaxing lateral motion of said mold side walls being effected cyclically and in synchronism, whereby the drawing down of the ingot is facilitated by the cyclical and synchronized downwardly and upwardly reciprocal motion relative to said compressing and relaxing lateral motion, holding the ingot in the mold for a period of time until the ingot solidifies enough, drawing out the mold, and carrying away the ingot to further processing.