US3795270A

US3795270A - Method of and means for sealing a stopping and withdrawing head in a continuous casting mold for steel

Info

Publication number: US3795270A
Application number: US00225148A
Authority: US
Inventors: F Fiala; J Zeller
Original assignee: Concast AG
Current assignee: SMS Concast AG
Priority date: 1971-02-11
Filing date: 1972-02-10
Publication date: 1974-03-05
Anticipated expiration: 1991-03-05
Also published as: ZA72873B; GB1368653A; DE2206021A1; CA955722A; JPS5118226B1; IT951024B; CH527010A

Abstract

A method of and means for sealing a stopping and withdrawing head in a continuous casting mold for steel, wherein prior to the commencement of pouring the clearance gap between the stopping and withdrawing head and the wall of the mold is sealed with a heat insulating seal that can be introduced into this gap. The steel in contact with the seal in the clearance gap during solidification is stopped from dangerously penetrating the seal by penetration-retarding elements distributed within the cross section of the seal.

Description

United States Patent 1 Fiala et al.

[ 1 Mar. 5, 1974 1 1 METHOD OF AND MEANS FOR SEALING A STOPPING AND WITHDRAWING HEAD IN A CONTINUOUS CASTING MOLD FOR STEEL [75] Inventors: Ferdinand Fiala, Thalwil; Josef Zeller, Weesen, both of Switzerland [73] Assignee: ConcastvAG, Zurich, Switzerland [22] Filed: Feb. 10, 1972 211 App]. No.; 225,148

[30] Foreign Application Priority Data Feb. 11, 1971 Switzerland 2017/71 [52] US. Cl. .l 164/274, 164/82 [51] Int. Cl B22d 11/08' [58] Field of Search 164/82, 274, 282

[56] References Cited UNITED STATES PATENTS 2,852,821 9/1958 Pond 164/278 3,274,653 9/1966 Foldcssy et al. 164/274 3,525,381 8/1970 Lecse et al 3,623,534 ll/l97l Brennan 164/82 FOREIGN PATENTS OR APPLICATIONS 704,512 4/1941 Germany 164/274 Primary Examiner-Rl Spencer Annear Attorney, Agent, or Firm-Werner W. Kleeman 57] ABSTRACT A method of and means for sealing -a stopping and withdrawing head in a continuous casting mold for steel, wherein prior to the commencement of pouring the clearance gap between the stopping and withdrawing head and the wall of the mold is sealed with a heat insulating seal that can be introduced into this gap. The steel in contact with the seal in the clearance gap during solidification is stopped from dangerously penetrating the seal by penetration-retarding elements distributed within the cross section of the seal.

9 Claims, 2 Drawing Figures 1 METHOD OF AND MEANS FOR SEALING A STOPPING AND WlTI-IDRAWING HEAD IN A CONTINUOUS CASTING MOLD FOR STEEL BACKGROUND OF THE INVENTION drawing head and the wall of the mold is sealed with a heat insulating seal that can be introduced into this gap.

pending upon the cross-section of the casting. When A the stopping and withdrawing head is in position this clearance gap must be sealed to prevent liquid steel from flowing out through this gap when pouring begins.

A known method of preventing the steel from escaping is to cover the clearance gap. For this purpose the gap and the side of the stopping and withdrawing head facing the steel are covered with metal chips, metal powder or metal granules. These metal chips, powder or granules advantageously should be of the same composition or a similar composition as the cast metal. When the steel is poured into the mold larger-sized sharp-edged agglomerates are formed by fusion and sintering, and when the casting is withdrawn they scratch and score the mold walls. In view of its unreliability this method of sealing has not found favor in practice.

Another state-of-the-art method of sealing the clearance gap is to insert and ram asbestos into the gap or to introduce refractory materials, preventing direct contact between the asbestos or the refractory material and the molten steel by covering them with chill scrap. However, effective protection of the seal by chill scrap is a process that is very time-consuming and therefore adversely affects the productivity of such a plant. Moreover, in this method of forming-a seal, fusion and sintering of the chill scrap between the hot casting and the stopping and withdrawing head gives rise to the formation of a layer permeated with sharp angular particles which also scratch and score the walls of the mold when the casting is withdrawn. Another drawback of this method of scaling is that in the course of withdrawing the casting from the mold into the following guiding apron the chill scrap which is. partly still loose falls out and increases the wear experienced by the rollers or cooling plates of the apron. Another difficulty arises in the application of this method of sealing if in addition to horizontal joints it is also necessary to seal and cover slanting, vertical or hook-shaped undercut sections with chill scrap. The chill scrap must be secured by special means to prevent it from slipping or from being washed away.

' and means for sealing a stopping and withdrawing head I Yet another technique which is known is to seal these clearance gaps exclusively by inserting and ramming in asbestos. However, for the continuous casting of high melting metals, such as iron and steel, asbestos has not been found to be suitable because at the high melting temperatures of these metals the sealing effect of the asbestos is destroyed by fissuration and slagging and the liquid metal can then escape.

SUMMARY OF THE INVENTION Hence, from what has been explained above, it should be apparent that the technology of continuously casting metals is still in need of an effective method of in a continuous casting mold for steel which is not associated with the aforementioned drawbacks and limitations of the prior art constructions and techniques. Therefore, a primary objective of the present invention is to provide just such new and improved method of and means for sealing a stopping and withdrawing head in a continuous casting mold for steel which is not associated with these previously considered drawbacks and limitations of the state-of-the-art and effectively and reliably fulfills the need still prevailing in the art.

Another and more specific object of the present invention relates to a new and improved method'of and means for sealing a stopping and withdrawing head in a continuous casting mold in a manner promoting reduction in the time required for making the seal and lessening the idle or downtimes of the casting machine.

Yet a further but equally significant object of this invention is to avoid the wear of the mold and the fouling of the casting equipment by loose scrap which occurs when practicing the above-discussed prior art sealing techniques, and further to facilitate the production of seals on stopping and withdrawing heads having hookshaped profiles or the like.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method aspects of this development contemplates preventing un desirable penetration of the steel which is in Contact with the seal in the gap during solidification by distributing throughout the cross-section of the seal penetration-retarding elements.

When utilizing the method aspects of this development, it is possible to seal a stopping and withdrawing head by means of an asbestos cord provided with penetration-retarding elements, for instance ina slab casting plant, within a matter of about 2 minutes. The need to cover the seal with chill scrap, according to prior art techniques heretofore discussed and proposed in this technology, can be entirely dispensed with and the drawbacks associated therewith completely eliminated. Thus,'wear of the mold is reduced and fouling of the subsequently arranged apron by loose chill scrap is impossible. Another notable advantage of the proposed method resides in the ability of being able to pre-form the seal outside of the mold. Stopping and withdrawing heads having, for instance, hook-shaped profiles or other difficult configured profile configurations, can be thus rapidly and efficiently sealed.

As already discussed above, not only is this invention concerned with the method of sealing a stopping and withdrawing head in a continuous casting mold for steel, but also with the means for the performance of such method. The physical hardware used in the practice of such method comprises a seal formed of a sealing material and metal penetration-retarding elements, these metal penetration-retarding elements having at least 50 times the thermal conductivity of the sealing material and about six times its thermal capacity per unit of volume.

Now, in accordance with a preferred manifestation of the invention, it is possible to halt in a particularly rapid manner penetration of the cast metal, typically the steel into the seal if the seal consists of asbestos cord containing metallic retarding elements. 5 to 50 percent by volume of the seal should consist of retarding elements.

Now in order to improve the load bearing capability of the seal so as to sustain the ferrostatic pressure of the steel and to improve the formability of the seal, it is contemplated according to a further aspect of this invention to construct the retarding elements of steel wires.

In accordance with still a further feature of this invention, the depth of penetration of the steel into the seal can be even further reduced if the heat insulating sealing material completely surrounds the individual retarding elements which are distributed throughout the cross-section of the seal.

Moreover, according to a further facet of the invention, it is possible to considerably reduce the time required for sealing, particularly in the case of large slab sections and stopping and withdrawing heads having a hook-shaped coupling section, by suitably pre-forming the seal prior to its insertion into the mold in accordance with the shape and periphery of the stopping and withdrawing head.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. I is a vertical sectional view through a partially illustrated mold of a continuous casting plant illustrating the stopping and withdrawing head in its moldinserted position; and

FIG. 2 is a perspective view showing a pre-formed seal for a stopping and withdrawing head having a hook-shaped profile or section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, a stopping and with-' drawing head I, also referred to in the art as a dummy bar head, and which has been only partially shown in the drawing, will be seen to close the open bottom end ofa continuous casting mold 2. The stopping'and withdrawing head I is separated from the wall 3 of the continuous casting mold 2 by a clearance gap or space 4. In order to form a gap 6 that can be conveniently sealed the upper edge of the stopping and withdrawing .head 1 is provided with a bevel or chamfer 5. Now a seal 8 is introduced into this gap 6 between the mold wall 3 and the chamfer 5 of the stopping and withdrawing head 1, introduction of such seal being undertaken for instance by ramming same into the gap 6. In the embodiment under consideration, the seal 8 is formed of asbestos which incorporates an external heat insulating-asbestos layer 11 and metal penetration-retarding elements 10, here in the form of soft steel wires distributed throughout the cross-section of the seal 8 as will be more fully explained hereinafter. Further, while the foregoing materials for the seal 8 constitute a particularly useful constructional form of seal, other materials can be efficaciously employed in the practice of the invention as will be also more fully discussed hereinafter.

With the benefit of the preceding disclosure and discussion, in particular of the seal 8, the inventive method for sealing the stopping and withdrawing head 1 in the continuous casting mold 2 will now be considered:

When the steel is poured into the continuous casting mold 2, it begins to solidify, on the one hand, at the neighborhood of the gap at the mold wall 3, and, on the other hand, at the region of the stopping and withdrawing head I. The steel which makes contact with the seal 8 first heats-up the external heat insulating asbestos layer 11 of such sealv 8. The penetration-retarding ele' ments 10, in the case under consideration the soft steel wires, which are present beneath the external asbestos layer 11, dissipate some of the heat penetrating such layer 11 and retard by a number of seconds damage to this layer by fusion, slagging or disintegration. Yet, it is impossible to prevent such damage, so-that ultimately the molten steel will come into contact with the outermost layer or group of metal penetration-retarding elements 10 facing the inflowing steel. This contact between the steel and the penetration-retarding elements 10 accelerates the take-up of heat by these retarding elements, thereby reduces the temperature of the penetrating steel towards its solidification point. At the same time, the surface tension of the molten steel rises and hinders further penetration into the seal 8. Heating of the outermost layer or group of penetrationretarding elements 10 usually results in such being melted. Depending upon the width of the clearance gap, the cooling effect of the environment, the steel temperature, the nature of the sealing material, the nature of the penetration-retarding elements, and so forth, the described chain of events may repeat itself throughout one or a number of further layers. However, the steel entering the outermost layers of the seal 8 is cooled and solidifies before it is possible for there to occur harmful penetration, i.e. metal breakout through the seal. At the same time, the steel in the region of the gap above the seal 8 also cools at the mold wall 3 and at the stopping and withdrawing head I. A solidified strandlayer or crust forms a kind of bridge above the seal and continued heating of the seal or even its destruction cannot then result in further deleterious effects. The purpose and functionality of the proposed seal is then fulfilled if its sealing ability is preserved long enough for the bridging crust above it to be sufficiently strong and itself to form a seal from the molten core.

Now when employing the combination of asbestos the sealing material and iron as the penetrationretarding element, the latter would have about 250 times the thermal conductivity of the asbestos and about seven times its thermal capacity per unit of volume.

However, other sealing materials could also be used, such as glass fibers, slag fibers, refractory felts, refractory plates and the like. Moreover, the penetrationretarding elements could be present in the sealing material in pulverulent or granular form. Also ceramic retarding elements, such as quartz sand, could be incorporated in the seal in place of the metallic elements. Ceramic retarding elements will not fuse, but they can still operate to hinder the penetration of the liquid steel long enough to enable the above-considered bridging to occur in the neighborhood of the sealing gap.

Now with the seal illustrated by way of example in FIG. 1, the steel wires are completely enclosed at all sides by the asbestos so as to provide an efficacious retarding effect. The gauge of the wire amounts to for instance 0.8 mm. and the center distance between the wires is about 2 mm. The proportion of the seal 8 constituted by the penetration-retarding elements is about 10 percent by volume. In fact, it has been found to be advantageous if the proportion of the seal 8 constituted by the penetration-retarding elements is in a range of about. 5 to 50 percent by volume of the seal. Further, the penetration-retarding elements advantageously I should possess at least 50 times the thermal conductivity of the sealing material and about six times its thermal capacity per unit of volume.

Turning attention now to FIG. 2, there is illustrated a seal which has been pre-formed according to the shape and periphery of a stopping and withdrawing head 21. In this embodiment, suchstopping and withdrawing head 21, as indicated in phantom lines, possesses a hook-shaped profile. The preforming of the seal 20 outside of the mold can be undertaken at a pattern corresponding to the shape or configuration of the stopping and withdrawing head 21. The introduction of such seal 20 is also feasible without the expenditure of a great deal of time in those instances where the stopping and withdrawing heads possibly possess undercut zones.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

l. The combination with a continuous casting mold for metals, especially steel, of a means for sealing a stopping and withdrawing head during the start of the continuous casting operation, said sealing means comprising a preformed seal constituting the sole sealing means for sealing the stopping and withdrawing head, said seal containing a sealing material and penetrationretarding elements embedded in said sealing material, said penetration-retarding elements possessing at least 50 times the thermal conductivity of the sealing material and about 6 times its thermal capacity per unit of volume, at least during the start of casting the materials of the seal preventing penetration of steel into the seal to an extent which would be destructive of the seal and its sealing action, said sealing means being removed from the mold together with the stopping and withdrawing head after the start of the continuous casting operation and not participating in the actual continuous casting operation for producing cast products. 2. A method of sealing a stopping and withdrawing head in a continuous casting mold for metal, especially steel, solely by means of a seal, comprising the steps of employing a composite pre-formed heat insulating seal formed of successive alternate regions of a heatinsulating material and a heat-withdrawal material hav ing a greater thermal conductivity than that of the heatinsulating material, sealing the clearance gap between the stopping and withdrawing head and the wall of the mold only by means of the composite pre-formed heat insulating seal having said alternate regions ofsuch materials by introducing the heat insulating seal into the gap prior to commencement of the casting operation, casting metal into the mold, and between the start of the casting operation and the formation of a self sealing metal crust between the mold wall and the stopping and withdrawing head preventing by means of the materials of the seal penetration of metal into the seal to an extent which would be destructive of the seal and its sealing action, and after the formation of the metal crust removing the stopping and withdrawing head together with the composite pre-formed heat insulating seal from the mold so that said pre-formed heat insulating seal does not participate in the actual continuous casting operation for producing cast products.

3. A method of sealing a stopping and withdrawing head in a continuous casting moldas defined in claim 2, including the step of selecting the materials of the seal and their dimensions such that damaging penetration of the metal into the seal is prevented from the start of casting and at least up to the formation of the self-sealing metal crust between the mold wall and the stopping and withdrawing head.

4. A method of sealing a stopping and withdrawing head in a continuous casting mold as defined in claim 2, further including the step of pre-forming said seal as a function of the shape and periphery of the stopping and withdrawing head prior to insertion into the mold.

5. The combination as defined in claim 1, wherein said sealing material comprises asbestos cord and said penetration-retarding elements are formed of metal.

6. The combination as defined in claim 1, wherein 5 to 50 percent by volume of the seal is composed of said penetration-retarding elements.

7. The combination as defined in claim 1, wherein said penetration-retarding elements are composed of soft steel wires.

8. The combination as defined in claim 1, wherein said penetration-retarding elements are distributed throughout the cross-section of the seal, said sealing material embodying a heat insulating-sealing material which surrounds the individual penetration-retarding elements at all sides.

9. The combination as defined in claim 1, wherein said seal is pre-formed in accordance with the shape and periphery of the stopping and withdrawing head prior to insertion into the mold.

Claims

1. The combination with a continuous casting mold for metals, especially steel, of a means for sealing a stopping and withdrawing head during the start of the continuous casting operation, said sealing means comprising a preformed seal constituting the sole sealing means for sealing the stopping and withdrawing head, said seal containing a sealing material and penetration-retarding elements embedded in said sealing material, said penetration-retarding elements possessing at least 50 times the thermal conductivity of the sealing material and about 6 times its thermal capacity per unit of volume, at least during the start of casting the materials of the seal preventing penetration of steel into the seal to an extent which would be destructive of the seal and its sealing action, said sealing means being removed from the mold together with the stopping and withdrawing head after the start of the continuous casting operation and not participating in the actual continuous casting operation for producing cast products.

2. A method of sealing a stopping and withdrawing head in a continuous casting mold for metal, especially steel, solely by means of a seal, comprising the steps of employing a composite pre-formed heat insulating seal formed of successive alternate regions of a heat-insulating material and a heat-withdrawal material having a greater thermal conductivity than that of the heat-insulating material, sealing the clearance gap between the stopping and withdrawing head and the wall of the mold only by means of the composite pre-formed heat insulating seal having said alternate regions of such materials by introducing the heat insulating seal into the gap prior to commencement of the casting operation, casting metal into the mold, and between the start of the casting operation and the formation of a self-sealing metal crust between the mold wall and the stopping and withdrawing head preventing by means of the materials of the seal penetration of metal into the seal to an extent which would be destructive of the seal and its sealing action, and after the formation of the metal crust removing the stopping and withdrawing head together with the composite pre-formed heat insulating seal from the mold so that said pre-formed heat insulating seal does not participate in the actual continuous casting operation for producing cast products.

3. A method of sealing a stopping and withdrawing head in a continuous casting mold as defined in claim 2, including the step of selecting the materials of the seal and their dimensions such that damaging penetration of the metal into the seal is prevented from the start of casting and at least up to the formation of the self-sealing metal crust between the mold wall and the stopping and withdrawing head.