REFRACTORY POURING DEVICE

Abstract

The invention relates to a refractory pouring device. Such a device is used for teeming of molten metal, in particular in a so-called continuous casting process.

Description

The invention relates to a refractory pouring device. Such a device is used for teeming of molten metal, in particular in a so-called continuous casting process.

Refractory pouring devices of the generic type are known i.a. from EP 1133373 B1 and EP 0346378 B1. All of these devices feature a generally tube-like design with a central longitudinal pouring channel.

After assembling of the device, i.e. in its mounted state, the following applies: An inlet opening of the pouring channel is arranged at an upper end section of the device, at least one outlet opening is arranged at its lower end section. Molten metal enters the pouring channel/the device via said inlet opening and leaves the pouring channel/the device via one or more outlet openings.

Said flow of melt is controlled by a so-called stopper rod, acting onto the inlet opening of the device or a so called slide-valve mechanism. All this is prior art, well known to the skilled person and will not be further described here.

EP 1590114B1 discloses a pouring device for use in a so-called tube changing machine.

A basic problem in prior art pouring devices is severe wear/abrasion along the sliding top surface of the device, thus limiting the service time of the corresponding pouring tube/nozzle and increasing the danger of air ingress because of reduced tightness between the upper surface of the pouring device and associated construction elements.

According to EP 0346378B 1 a wear resistant hard refractory material is formed at least around a peripheral edge of the inlet opening.

EP 1133373B1 discloses a pouring device comprising a ceramic tube element, supported in a metallic can, in which a ceramic support element is encapsulated.

Both embodiments are characterized by a multi layer sliding surface around the inlet opening.

In other words: Both embodiments are characterized by at least one joint along the upper sliding surface of the pouring device, said joint defining the contact zone between different ceramic materials. Different ceramic materials provide different physical properties (like different thermal expansion) causing further problems to keep the respective surface areas of pouring device and adjacent construction elements in intimate contact under heat load.

It is therefore an object of the invention to disclose a possibility to overcome these drawbacks in prior art devices.

The invention is based on the following considerations:

• • The partial replacement of the ceramic material around the inlet opening of the pouring device by a refractory material of improved wear resistance and temperature stability may increase the possible overall life-time of the pouring device but may reduce the service-time of the pouring device in view of leakages in the system, caused by different thermal expansions in adjacent areas of the ceramic surfaces.
  • In prior art devices the basic tube element is made of an alumina-graphite material. Alumina graphite surface are prone to gouging and finning as a result of a relative softness of the material. Therefore the upper sliding surface of an embodiment in accordance with EP 1133373B1 becomes subject to damage during movement, for example during insertion/ejection from a tube changer machine. Again the danger of air ingress during casting may increase.
  • The invention therefore focusses on the requirement of gas tightness. Highest tightness and insofar prevention of dangerous air ingress into the system can be achieved best in case of a large 2-dimensional contact area between the surfaces moved relative to each other. This requirement may be achieved best by 2 flat/planar sliding surfaces, wherein each sliding surface features constant physical properties during use. Constant physical properties may be reached best by surfaces of constant chemical composition which then necessarily feature constant physical properties, including the avoidance of any gaps, joints etc. in the respective surface areas.
  • The arrangement of a one piece refractory layer to provide a continuous sliding surface could overcome the problems mentioned but only as part of a corresponding compound system.
  • The idea is to provide the pouring device with a refractory, monolithic, continuous layer which surrounds the inlet opening of the pouring channel, thereby providing a continuous sliding surface, which additionally covers the upper free end of a main tube element, which further extends downwardly in a cup like fashion thereby overlapping the outer peripheral surface of the adjacent end segment of said tube element and which at the same time provides a collar for the attachment of the pouring device at corresponding fixation means, such as a tube changer machine.

In its most general embodiment the invention relates to a refractory pouring device featuring a central longitudinal pouring channel with an inlet opening at its first end section and at least one outlet opening at its second end section, comprising:

• • a ceramic tube element extending at a distance to the inlet opening of the pouring channel up to the at least one outlet opening of the pouring channel,
  • a ceramic envelope, covering the ceramic tube element at least at its end segment adjacent to the inlet opening of the pouring channel, in fact
  • all over its outer peripheral surface,
  • all over its annular end face, and
  • all over a transition region in between, wherein
  • the ceramic envelope is a one piece envelope, made of a monolithic ceramic material and providing an outwardly protruding collar at the first end section of the pouring device.

Insofar the pouring device comprises substantially two constructional elements, the basic tube element and the envelope at its upper end segment. The envelope not only provides an outer coverage of the upper end segment of the tube element which at the same time defines a collar by which the pouring device may be mounted in a corresponding tube changing machine but it encapsulates this upper end segment such that the upper annular (ring shaped) end face of the tube element is as well completely protected.

Only this part of the envelope now provides the top layer of the pouring device and thus the sliding surface at risk.

The inlet opening is now exclusively defined (surrounded) by said material of said envelope, no joints, seals etc. influencing the wear behavior of the most endangered refractory part of the device.

Depending on its thickness (in the longitudinal direction of the device) the upper layer of the envelope further defines the upper end of the pouring channel, the lower part of which being defines by the basic tube element. Both should be in full alignment with each other to reduce the danger of wear and clogging.

This amended pouring device differs from known embodiments especially by the following characteristics:

• • the ceramic envelope is a one-piece element covering the more or less flat upper surface as well as the cylindrical outer surface of the tube element
  • the ceramic envelope provides the upper sliding surface
  • the upper sliding surface is made completely of a monolithic ceramic material
  • the material for said envelope may be selected individually
  • the envelope may be cast in one operation cycle
  • an outer metal can may serve as a template during casting
  • the upper sliding surface hat no gaps, joints etc
  • the upper sliding surface may by planar (in a technical sense, meaning that tolerances in height/thickness/unevenness being <1 mm, especially <0.5 mm, <0.3 mm or <1 mm.
  • the ceramic envelope is imposed onto the ceramic tube element

The general construction of the pouring device may be amended by one or more of the following features:

The ceramic envelope may be shaped as an inverted cup with a hole in its bottom, said hole defining the inlet opening of the pouring channel.

The hole may extend in alignment with the pouring channel. In other words: The pouring channel has at least 2 sections: an upper section defined by the through opening of the envelope and a lower section defined by the pouring channel of the tube element. In a best mode these two sections are in alignment so as to provide one continuous pouring channel, the inner surface of which features only one ring shaped discontinuity, namely the borderline between the envelope and the tube element.

The ceramic tube element can be made of any suitable refractory material and manufactured by casting, pouring, ramming or pressing, especially isostatic pressing. An isostatically pressed/manufactured element provides the highest abrasion resistance and life/service time.

The tube element can be made of an alumina/graphite grade, despite its relative (mechanical) softness as all its outer surfaces prone to gouging and/or finning are now encapsulated by said envelope.

The ceramic envelope is typically a cast element although it may be as well a preshaped/pre-manufactured workpiece. Casting is performed by using a suitable/corresponding template, either a lost template or a template remaining part of the pouring device. Casting has advantages in terms of simplicity of manufacture and reinforcement of the “head area”, i.e. the upper part of the pouring device, which particularly is subject to thermo mechanical stresses during teeming. In this respect use of a so-called self-flowing or free-flowing monolithic refractory material to provide the envelope section of the pouring device has several advantages, i.e. high density without physical agitation means. A suitable free-flowing mass is disclosed in EP 525394B1.

The invention includes an embodiment, as illustrated in the attached drawing, wherein that part of the ceramic envelope covering the outer peripheral surface of the ceramic tube element is surrounded, at least partially, by a metallic can. For sake of clarity: The upper ceramic surface, the sliding surface, always remains uncovered as well as the inlet opening.

The ceramic material of the envelope may be reinforced by discrete mechanical elements, especially by mechanical elements of a different material, such as refractory or metal fibres, needles etc.

Another reinforcement option is to design such elements as anchors which are fixed at least at one of the ceramic tube element and the metallic can. Both variants are illustrated in the attached drawing.

As mentioned above one important advantage of the pouring device is that said part of the ceramic envelope covering the annular end face of the ceramic tube element may provide a stepless/seamless gliding surface, arranged at a distance to the annular end face of the ceramic tube element. The avoidance of any gaps, joints etc. increases the stability, life/service time of the device while at the same time decreases the possibility of unwanted air ingress characteristically.

This is best achieved by an embodiment wherein the gliding surface is arranged at a distance to the annular end face of the ceramic tube element and perpendicular to the central longitudinal pouring channel or the central longitudinal axis of the pouring channel/the device respectively.

As disclosed above the pouring device may be installed in the bottom of a metallurgical vessel in a fixed position (fixed i.a. by a mortar) or in a change system like a mechanical so-called tube changer as generally disclosed in EP 1590114B1.

Insofar the upper end section of the pouring device (that part of the envelope, surrounding the upper end segment of the tube element) may be constructed as a collar with either a cylindrical, frustoconical or cubic design. Insofar the corresponding sliding surface may have either an outer circular or a rectangular shape, always with said inlet opening within its periphery and in most cases in its center.

In this context the invention provides two further alternatives with respect to the design of the bottom face of the respective collar:

This bottom face(s) may either extend perpendicular to the central longitudinal axis of the pouring channel or in an inclined fashion.

When the pouring device is intended to be used in a tube changer device the cubic collar area typically provides four bottom faces, serving as corresponding bearing surfaces for corresponding fixation means such as compression springs. Further options insofar are disclosed in the accompanying description of an embodiment.

Typically the pouring channel has a circular cross section at least along the first end section of the pouring device.

Embodiments of the invention will now be described with reference to the accompanying drawing, in which

FIG. 1 is a schematic cross-sectional view of the upper end section of a pouring device for use in a tube changer system

FIG. 2 is a schematic cross-sectional view of the upper end section of the pouring device according to FIG. 1 perpendicular to the presentation of FIG. 1

FIGS. 3a,b are cross-sectional views of a complete pouring device and c is a schematic 3-dimensional view of the upper part of this pouring device, partly cut-off

The pouring device, illustrated in an orientation according to its mounted state, features a generally tube like design with a central longitudinal pouring channel 30, defining an inlet opening 32 at a first, upper end section U and two outlet openings 34,36 at a second, lower end section L.

The pouring device comprises a substantially cylindrical tube-element 10, made of an alumina-graphite grade (60 m-% Al₂O₃, 30 m-% C, 10 m-% SiO₂) and isostatically pressed, with an increased wall thickness at its upper free end segment 10u, defining an upper annular surface 10s, being arranged in a more or less horizontal orientation. The tube element 10 provides a first part 301 (the main part) of the central longitudinal pouring channel 30.

Pouring channel 30 has a circular cross section between its inlet opening 32 and its outlet openings 34, 36 arranged at a distance to bottom 10b of tube element 10. As illustrated in the Figures pouring channel 30 is deflected at its lower end in two opposite directions and both lines merge into said outlet openings 34, 36 arranged in the ceramic wall of tube element 10.

A ceramic envelope 20 covers said tube element 10

• • all over the outer peripheral surface 10p of its upper free end segment 10u
  • all over the annular surface 10s at the upper end of end segment 10u
  • all over a transition region 20t in between
    thus giving the envelope 20 a cup shape (pot shape) with its bottom 20b on top (inversed cup-shape). Bottom 20b includes a central through hole 30u, defining a second, upper part of pouring channel 30 and its inlet opening 32.

The total length of the envelope 20 (in the direction of the central longitudinal axis A-A of the pouring channel 30) is D, extending from its free upper surface 20g downwardly towards outlet openings 34, 36 but ending at a distance to said openings 34,36.

The ceramic envelope 20 is a one piece envelope, made of a monolithic refractory concrete high in alumina, namely: 70 m-% Al₂O₃, 20 m-% SiO₂, 1 m-% Fe₂O₃, 4 m-% MgO, 5 m-% other components, all in grain size<1 mm, which becomes free-flowing after addition of about 9 m-% water per 100 m-% refractory material.

As may been seen in the Figures envelope 20 has different sizes at different areas. The largest wall thickness is around end segment 10u of tube element 10, while the cylindrical section extending downwardly has the smallest wall thickness. That part of envelope 20 extending on top of surface 10s of tube element 10 and providing an upper layer (bottom 20b) as well as the upper sliding surface 20g has a thickness in between.

To improve the adhesion between envelope 20 and tube element 10, the peripheral outer surface 10p provides female elements such as gaps, depressions etc. into which the material of the envelope may extend during casting.

In this embodiment upper surface 20g is flat (planar) to the greatest possible extent and seamless, as this surface provides a monolithic, continuous gliding surface when installed in a corresponding tube changer arrangement or mounted to a slide gate mechanism. These mounting and fixation means are not illustrated in detail (as known by the skilled person) but only symbolized by line 40 in FIG. 2.

The outer peripheral area of envelope 20 is covered by a metallic can 50, following the varying shape of tube element 10 and envelope 20. This can ends at a distance to sliding surface 20g (non-visible in FIG. 3c). In other words: sliding surface 20g protrudes can 50 slightly, in the embodiment by 2.5 mm.

Anchors (only one of which being illustrated by numeral 60 are protruding from can 50 to reinforce the cast ceramic material of envelope 20.

While tube element 10 is of substantially cylindrical shape envelope 20 (and correspondingly can 50) presents different geometric shapes over its length D:

• • the upper part, hereinafter referred to as collar C, has a substantially cubic shape
  • the lower part, hereinafter referred to as pipe section P, has a substantially cylindrical shape
  • along the intermediate part, hereinafter referred to as transition region T, the design changes from said cubic to said cylindrical shape, as best seen in FIG. 3.

Said collar C or its outer metallic can 50 respectively, thus provide four bottom sides CB1, CB2, CB3, CB4 along said transition region T, serving as a bearing surfaces when said pouring device is installed in a corresponding tube changer mechanism in the bottom area of a corresponding metallurgical vessel.

As illustrated in the Figures opposing bottom sides CB1, CB2 extend more or less perpendicular to the central longitudinal axis A of pouring channel 30 while bottom sides CB3, CB4 provide an angle a of about 45 degrees with respect to said axis A.

Said bottom sides CB3, CB4 may be flat (planar) or curved with respect to central longitudinal axis A. A design with curved bearing surfaces corresponds to that of EP 2269751B1.

In the lower part, specificly above outlet opening 34,36, tube element 10 is not covered any more by said envelope 20 and/or can but features an external glaze.

The walls of pouring channel 30 including inlet and outlet opening are glazed as well.

Claims

1. Refractory pouring device featuring a central longitudinal pouring channel (30) with an inlet opening (32) at its first end section (U) and at least one outlet opening (34,36) at its second end section (L), comprising:

a) a ceramic tube element (10) extending from an area at a distance to the inlet opening (32) of the pouring channel (30) to the at least one outlet opening (34,36) of the pouring channel (30),

b) a ceramic envelope (20), covering the ceramic tube element (10) at least at its end segment (10u) adjacent to the inlet opening (32) of the pouring channel (30), in fact b1) all over its outer peripheral surface (10p), b2) all over its annular end face (10s), and b3) all over a transition region (20t) in between, wherein

c) the ceramic envelope (20) is a one piece envelope, made of a monolithic ceramic material and providing an outwardly protruding collar (C) at the first end section (U) of the pouring device.

2. Refractory pouring device according to claim 1, wherein the ceramic envelope (20) is shaped as an inverted cup with a hole in its bottom, said hole defining the inlet opening (32) and upper part (30u) of the pouring channel (30).

3. Refractory pouring device according to claim 2, wherein the upper part (30u) of the pouring channel (30) extends in alignment with a lower part (301) of the pouring channel (30) defined by said ceramic tube element (10).

4. Refractory pouring device according to claim 1, wherein the ceramic tube element (10) is an isostatically pressed element.

5. Refractory pouring device according to claim 1, wherein the ceramic envelope (20) is a cast element.

6. Refractory pouring device according to claim 1, wherein that part of the ceramic envelope (20) covering the outer peripheral surface (10p) of the ceramic tube element (10) is surrounded, at least partially, by a metallic can (50).

7. Refractory pouring device according to claim 1, wherein the ceramic envelope (20) is a reinforced by mechanical elements of a different material.

8. Refractory pouring device according to claim 1 or 6, wherein the ceramic envelope (20) is a reinforced by anchors (60) which are fixed at least at one of the ceramic tube element (10) or the metallic can (50).

9. Refractory pouring device according to claim 1, wherein that part (20b) of the ceramic envelope (20) covering the annular end face (10s) of the ceramic tube element (10) provides a stepless gliding surface (20g), arranged at a distance to the annular end face (10s) of the ceramic tube element (10).

10. Refractory pouring device according to claim 1, wherein that part (20b) of the ceramic envelope (20) covering the annular end face (10s) of the ceramic tube element (10) provides a stepless gliding surface (20g), arranged at a distance to the annular end face (10s) of the ceramic tube element (10) and perpendicular to the central longitudinal pouring channel (30).

11. Refractory pouring device according to claim 1, wherein the pouring channel (30) has a circular cross section at least along the first end section (U) of the pouring device.

12. Refractory pouring device according to claim 1, wherein the ceramic tube element (10) has a larger wall thickness at its end segment (10u) surrounded by said ceramic envelope (20) than at its end segment adjacent to the outlet opening (34,36).

13. Refractory pouring device according to claim 1, wherein the ceramic envelope (20) has a cubic or cylindrical outer shape in its part (C,T) surrounding the end segment (10u) of the tube element (10).

14. Refractory pouring device according to claim 1, wherein said collar (C) provides at least one bottom face (CB1, CB2, CB3, CB4) extending perpendicular to the central longitudinal pouring channel (30).

15. Refractory pouring device according to claim 1, wherein said collar (C) provides at least one bottom face (CB1, CB2, CB3, CB4) extending at an angle a between 15 and 70 degrees relative to a central longitudinal axis (A) of the pouring channel (30).