WO2016113196A1

WO2016113196A1 - Casting nozzle with external resilient gasket

Info

Publication number: WO2016113196A1
Application number: PCT/EP2016/050278
Authority: WO
Inventors: Giovanni COTZA; Doriano MAURO
Original assignee: Vesuvius Crucible Company; Vesuvius Group, S.A.
Priority date: 2015-01-12
Filing date: 2016-01-08
Publication date: 2016-07-21

Abstract

The present invention concerns an ingot casting shroud (1) comprising structural walls made of a refractory material defining an inner bore (5) extending along and centered about a longitudinal axis, X1, from a bore inlet (5u) located at an inlet end of the ingot casting shroud to a bore outlet (5d) located at an outlet end of the ingot casting shroud, said ingot casting shroud further comprising: (a) An inlet portion (2) including the inlet end and the bore inlet (5u), (b) A tubular portion (3) adjacent the inlet portion and extending along the longitudinal axis, X1, and through which the inner bore extends, and (c) An outlet portion (4) including the outlet end and bore outlet (5d), said outlet portion being adjacent to the tubular portion (3) and separated from the inlet portion (2) by said tubular portion, and comprising an outlet structural wall made of a refractory material defined by an outer outlet peripheral surface (4out) separated from the bore by a thickness of the outlet structural wall, Characterized in that, a portion of the outer outlet peripheral surface (4out) extending over a perimeter of the outlet portion is provided with a resilient layer (6) having a resiliency of at least 70%, wherein the resiliency is defined as the ratio, H1 / HO, of the thickness, H1, of a product after the compression and relaxation of a compressive force which reduces the original thickness to 50% of its original thickness, HO, to its original thickness, HO, measured at room temperature on a sample (6t) of dimensions L1 x L2 x HO collected from the resilient layer (6).

Description

Casting nozzle with external resilient gasket

FIELD OF THE INVENTION

[0001 ] The present invention concerns an ingot casting shroud ensuring an air tight fluid communication between a ladle and an ingot mould. In particular, it concerns a new ingot casting shroud comprising an outlet portion provided with a resilient layer ensuring a snug fit between the outlet portion of the ingot casting shroud and an inlet portion of the mould. The resilient layer acts as a sealing gasket.

BACKGROUND OF THE INVENTION

[0002] In ingot metal casting processes a metallurgic vessel such as a ladle or tundish is brought into fluid communication with individual moulds defining the geometry of individual ingots or billets. The individual moulds are filled and the metallurgic vessel is moved to fill other such moulds. Note that whilst the processes are herein described with reference to "a mould" it is clear that such expression as used herein includes also the case where more than one mould is filled during one casting sequence, since a series of moulds can be in fluid communication with a single mould inlet, or the metallurgic vessel may have more than one opening through which metal flows out into a corresponding number of moulds. [0003] Molten steel has a strong affinity for oxygen resulting in the formation of defects such as non-metallic inclusions which are detrimental to the quality of the metal. Oxygen is present in air and for this reason it is important to shield the molten metal from any contact with air during casting, in particular in the flow thereof between the metallurgic vessel and the mould. Various solutions have been proposed to this effect. In particular, a casting shroud in the form of a tube is often used between a ladle and a tundish or a mould, or between a tundish and a mould. Submerged shrouds are also extensively used, such that the outlet of the shroud is immersed in the molten metal filling the mould.

[0004] Documents EP0198123 and JP H01 157750 relate to continuous casting installations and describe a type of connection between two refractory elements including flexible seals. [0005] Ingot metal casting differs from continuous metal casting in the fact that one metallurgic vessel moves from mould to mould to fill them sequentially, whilst in continuous metal casting, a tundish steadily remains in fluid communication position with a single continuous mould. For this reason, casting shrouds and, in particular, submerged casting shrouds are better suited for continuous casting operations than for ingot casting as the shroud hinders the moving of the metallurgic vessel from a mould to the other. It follows that, when tubes are used in ingot casting they must therefore be short and cannot be submerged as they should not penetrate too deep into the mould inlet. This reduces their shielding efficacy against contact with air. [0006] To further shield the metal stream from contact with air, in particular non-submerged tubes particularly used in ingot casting processes, a blanket of inert gases such as Ar, He, N2, and even CO2 is flushed over the stream of molten metal, (cf. e.g., US4178980 or US4657587). To yield a sufficient gas blanket, the consumption of inert gases can be quite high. It is also known from EP0073573 and US 3991813 to use flexible parts for shielding molten metal from oxidation. However, the arrangements described in these two last documents are rather complex and expensive.

[0007] There therefore remains a need for an ingot casting shroud that can be used in ingot casting processes allowing the easy moving of the shroud from one mould to another and yet affording an efficient shield against contact of the molten metal stream with air. The present invention proposes a solution to this problem with a novel and original concept of ingot casting shrouds. These and other advantages of the present invention are described with more details in the following.

SUMMARY OF THE INVENTION [0008] The present invention is defined in the attached independent claims. Preferred embodiments are defined in the dependent claims. In particular, the present invention concerns an ingot casting shroud comprising structural walls made of a refractory material defining an inner bore extending along and centered about a longitudinal axis, X1 , from a bore inlet located at an inlet end of the ingot casting shroud to a bore outlet located at an outlet end of the ingot casting shroud, said ingot casting shroud further comprising:

(a) An inlet portion including the inlet end and the bore inlet,

(b) A tubular portion adjacent the inlet portion and extending along the longitudinal axis, X1 , and through which the inner bore extends, and

(c) An outlet portion including the outlet end and bore outlet, said outlet portion being

adjacent to the tubular portion and separated from the inlet portion by said tubular portion, and comprising an outlet structural wall made of a refractory material defined by an outer outlet peripheral surface separated from the bore by a thickness of the outlet structural wall, wherein a portion of the outer outlet peripheral surface extending over a perimeter of the outlet portion is provided with a resilient layer having a resiliency of at least 70%, wherein the resiliency is defined as the ratio, H 1 / HO, of the thickness, H1 , of a product after the compression and relaxation of a compressive force which reduces the original thickness to 50% of its original thickness, HO, to its original thickness, HO, measured at room temperature on a sample of dimensions L1 x L2 x HO collected from the resilient layer. A method of measurement of the resiliency is described in continuous. [0009] I a preferred embodiment, said resilient layer comprises an outer resilient peripheral surface which is tapered towards the outlet end. This geometry allows the centering of the nozzle with a mould inlet of complementary funnel-shaped geometry as the nozzle is pressed into position. To provide higher mechanical stability, allowing higher pressures to be applied to position the nozzle into contact with said mould inlet, it is preferred that the outer outlet peripheral surface of the outlet portion defined by the structural walls made of a refractory material on which is provided the resilient layer, is tapered too and substantially parallel to the outer peripheral surface, when the resilient layer is in a non-compressed state.

[0010] The smallest thickness, HO, of the resilient layer in a non-compressed state, defined as the shortest distance between the outer outlet peripheral surface and the outer resilient peripheral surface is preferably comprised between 10 and 50 mm, more preferably between 20 and 35 mm, The resilient layer preferably has a resiliency of at least 75%, more preferably at least 80%, most preferably at least 85%. In a preferred embodiment, the resilient layer (6) has a height, L2, measured normal to a circumferential direction of, and parallel to the outer resilient peripheral surface (6out) of the resilient layer comprised between 40 and 100 mm, preferably between 50 and 80 mm.

[0011 ] The ingot casting shroud preferably comprises a gas channel arranged to flush a gas over at least a portion of the outer outlet peripheral surface to create an inert gas blanket at the interface between ingot casting shroud and mould inlet. The resilient layer should then be porous and permeable to a gas. The gas channel would then be arranged to flush said gas through said porous resilient layer. For example, the gas channel may comprise a gas outlet which opens at a ring shaped groove extending along part or the whole of a perimeter of the outer outlet peripheral surface, the ring shaped groove should be in fluid communication with the resilient layer. A porous resilient layer can be a foam material, such as a ceramic foam or a metal foam. It preferably consists, however, of a non-woven ceramic fiber mat. The ceramic fibers may for example comprise 70 to 80 wt.% SiC and 15 to 30 wt.% MgO, The ceramic fiber mat typically has a density in a non-compressed state comprised between 90 and 150 kg / m³, preferably between 1 10 and 135 kg / m³.

[0012] In a preferred embodiment, an intermediate layer is sandwiched between the resilient layer and the outer outlet peripheral surface. The intermediate layer should have a higher compressive modulus than the resilient layer. When gas is provided, the intermediate layer preferably presents an open porosity

[0013] . Any portion of the resilient layer which, in use, is exposed to the atmosphere is preferably provided with a gas-impervious layer sealing such portion of the resilient layer. This allows the reduction of gas used for blanketing the system.

[0014] In a preferred design of an ingot casting shroud according to the present invention, the largest diameter, D6,4m, of the outlet portion is substantially larger than the diameter, D6,3, of the tubular portion where it is connected to said outlet portion, wherein a diameter, D6, is defined as the length of a straight segment intersecting the longitudinal axis, X1 , and joining two points of the outer surface of the ingot casting shroud and included in a plane, π1 , normal to the longitudinal axis, X1 , and forming an angle, θ , with a reference diameter, DO, also included in plane, π1.

[0015] The present invention also concerns a metal ingot casting installation comprising: (a) a ladle filled with molten metal and provided with an ingot casting shroud as defined above, and

(b) a mould defined by a cavity and comprising an inlet portion of geometry complementary with the geometry of the outlet portion of the ingot casting shroud such that when the outlet portion of the ingot casting shroud is inserted into the inlet portion of the mould, it fits snugly with the resilient layer being compressed

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates embodiments of ingot casting shrouds according to the present iinvention.

Figure 2 illustrates a perspective view of an ingot casting shroud showing the collection of a sample for testing the resilience of the resilient layer. Figure 3 schematically illustrates a time-deformation curve measured during a resilient test.

Figure 4: illustrates how an ingot casting shroud according to the present invention engages into an inlet of an ingot casting mould.

[0016] DETAILED DESCRIPTION OF THE INVENTION

[0017] An ingot casting shroud (1 ) according to the present invention comprises structural walls made of a refractory material defining an inner bore (5) extending along and centered about a longitudinal axis, X1 , from a bore inlet (5u) located at an inlet end of the ingot casting shroud to a bore outlet (5d) located at an outlet end of the ingot casting shroud. As illustrated in Figure 1 , it comprises:

(a) An inlet portion (2) including the inlet end, and the bore inlet (5u); the inlet end is suitable for being coupled to an outer surface of the bottom floor of a metallurgic vessel (21 ) such as a ladle or a tundish,

(b) A tubular portion (3) adjacent the inlet portion and extending along the longitudinal axis, X1 , and through which the inner bore extends, and

(c) An outlet portion (4) including the outlet end and bore outlet (5d), said outlet portion being adjacent to the tubular portion (3) and separated from the inlet portion (2) by said tubular portion; the outlet portion comprises an outlet structural wall made of a refractory material defined by an outer outlet peripheral surface (4out) separated from the bore by a thickness of the outlet structural wall, [0018] A portion of the outer outlet peripheral surface (4out) extending over a perimeter of the outlet portion of the ingot casting shroud is provided with a resilient layer (6) having a resiliency of at least 70%. As illustrated in Figures 2&3, the resiliency is defined as the ratio, H1 / HO, of the thickness, H1 , of a product after the compression and relaxation of a compressive force which reduces the original thickness to 50% of its original thickness, HO, to its original thickness, HO, measured at room temperature on a sample (6t) of dimensions L1 x L2 x HO collected from the resilient layer (6). The characterization of the resiliency of the resilient layer (6) is carried out as follows.

[0019] A sample (6t) of dimensions L1 x L2 x HO is collected from the resilient layer (6) as illustrated in Figure 2. Since the resiliency properties of the resilient layer (6) are not necessarily isotropic, it is important to select the compression direction, which is parallel to HO, as the direction closest to the direction of compression of the resilient layer (6) when the outlet portion of the ingot casting shroud is inserted into the inlet of a casting mould as illustrated in Figure 4(b). The value of the resiliency is not particularly sensitive to the initial thickness, HO, of the sample (6t). In case of doubt as to the direction of compression in use of the resilient layer, HO will be the thickness of the smallest dimension available of the resilient layer (6). HO is generally comprised between 10 and 50 mm, preferably between 15 and 45 mm, more preferably between 20 and 35 mm, most preferably between 25 and 30 mm. L1 is preferably equal and normal to L2. L1 and L2 are preferably equal to 50 mm. If the resilient layer does not afford the collection of a sample (6t) of a length of 50 mm in one of the directions L1 or L2, the length of one of the dimensions, say L1 , is equal to 50 mm, and the other, say L2, is as large as possible, but in any case larger than or equal to HO. Resiliency testing on various materials has shown no significant variation attributable to variations within +40% of the dimensions of L1 or L2. The sample (6t) is conditioned during 24 h at room temperature (between 18 and 23°C) and relative humidity (between 40 and 80%) before testing. In practice, the smallest thickness, HO, of the resilient layer in a non-compressed state, is preferably defined as the shortest distance between the outer outlet peripheral surface (4out) and the outer resilient peripheral surface (6out). To summarize, it is preferred that the sample have a dimension of HO x 50 x 50 mm, wherein HO is comprised between 15 and 50 mm, preferably between 20 and 35 mm. [0020] The initial thickness, HO, of the sample (6t) is measured by methods known in the art. The L1 x L2 surface of a thus conditioned sample is placed between parallel flat plates of a compression testing machine. A compression load is applied onto the L1 x L2 surface of the sample (6t) in the direction, HO, at a rate of 2 mm / min, until the thickness has been reduced by 50%, i.e., H = HO / 2 as shown in Figure 3. The sample is maintained compressed at 50% of its initial thickness during 5 min, after which the load is released and the sample is left to spring back to a thickness, H1 , measured 5 min after the load was released. The ratio, H1 / HO expressed in % defines the value of the resiliency of the resilient layer (6). It is not necessary to record the whole curve as represented in Figure 3, as it suffices to measure the values of the thicknesses, HO, before testing and, H1 , after testing to yield the value of the resiliency of the sample. [0021 ] In a preferred embodiment represented in Figures 1 , 2, and 4, the resilient layer (6) comprises an outer resilient peripheral surface (6out) which is tapered towards the outlet end. This geometry has the advantage, as shown in Figure 4, that when the outlet portion of the shroud is engaged into an inlet funnel of the mould of complementary geometry, the bore of the shroud is automatically centered with respect to the mould inlet, as the resilient layer is compressed substantially normal to the outer surface (6out) of the resilient layer, forming a protective gasket preventing air from contacting the molten metal stream. Because the resilient layer has a resiliency of at least 70%, the shroud can be moved from one mould to another and still act as a protective gasket. In order to ensure a mechanical stability of the resilient layer (6) when compressed against the inlet funnel of the mould, it is advantageous that the outer outlet peripheral surface (4out) of the outlet portion defined by the structural walls, is also tapered and substantially parallel to the outer resilient peripheral surface (6out), when the resilient layer is in a non-compressed state.

[0022] A higher resiliency is advantageous for casting operations requiring many changes of moulds. In this case, it is preferred that the resilient layer (6) have a resiliency of at least 75%, preferably at least 80%, more preferably at least 85%. To profit in full of the resilient and protective effects of the resilient layer (6) it preferably has a height, L2, comprised between 40 and 100 mm, preferably between 50 and 80 mm, wherein L2 is measured normal to a circumferential direction of, and parallel to the outer resilient peripheral surface (6out) of the resilient layer. The smallest thickness of the resilient layer in a non-compressed state, defined as the shortest distance between the outer outlet peripheral surface (4out) and the outer resilient peripheral surface (6out) is preferably equal to HO, the initial thickness of the sample (6t) to be tested for characterization of the resiliency of the resilient layer as discussed supra. This way, the collection of the sample is very easy and does not require cutting the sample along a plane parallel to L1 X L2. The thickness of the resilient layer is preferably comprised between 10 and 80 mm, more preferably between 20 and 50 mm, most preferably between 25 and 35 mm.

[0023] The resilient layer (6) may consist of a non-woven ceramic fiber mat or of a foam material, preferably a ceramic foam or a metal foam. It is preferably a non-woven ceramic fiber mat. Although never in contact with the high temperature stream of molten metal, the ceramic fibers must nonetheless resist the relatively high temperatures encountered in use. For example, the fibers

[0024]

[0025] may be silica based, comprising 70 to 80 wt.% S1O2 and 15 to 30 wt.% MgO. The fiber mat may have a density in a non-compressed state comprised between 90 and 150 kg / m³, preferably between 1 10 and 135 kg / m³. For example, a ceramic fiber mats suitable for use as resilient layer (6) are Isofrax® blankets supplied by Unifrax, such as Isofrax® 1260C, available in thicknesses, HO = 13, 25, 38, and 50 mm.

[0026] As illustrated in Figure 1 (b), an intermediate layer (8) having a higher compressive modulus than the resilient layer (6) can be sandwiched between the resilient layer (6) and the outer outlet peripheral surface (4out). In case the resilient layer (6) has open porosity, such as with a non-woven fiber mat, said intermediate layer (6) should preferably have an open porosity too. Furthermore, a substantially gas-impervious layer (9) can advantageously be applied to seal a portion of the resilient layer (6) which would otherwise be in contact with the atmosphere absent such gas impervious layer (9). Referring to Figure 1 (b), wherein the outer peripheral surfaces of both outlet (4out) and resilient layer (6out) have a funnel-shaped trunco-conical geometry, a substantially gas-impervious layer (9) is preferably provided over the top surface of the resilient layer (6) defining the broad base of the trunco-conical shape. Indeed, referring to Figure 4(b), it can be seen that when the outlet portion (4) of the ingot casting shroud is engaged into a complementary funnel shaped inlet (1 1 u) of a mould (1 1 ) compressing the resilient layer, the top surface of the resilient layer remains exposed to the atmosphere. In case the resilient layer (6) has an open porosity and is thus permeable to gases, a substantial volume of such gases used to blanket the outlet portion of the shroud could escape in the atmosphere thus increasing the cost of production.

[0027] Whilst in continuous casting processes, submerged shrouds can be used, wherein the stream of flowing molten metal never contacts air, since the outlet of such submerged shrouds is below the level of metal in the mould, submerged shrouds cannot be used in ingot casting processes because the submerged shroud, penetrating deep into the mould inlet would hinder the moving of the metallurgic vessel (21 ) from one ingot mould to the next. When prior art ingot casting shrouds would compromise with an intermediate penetration of the shroud in the mould inlet (1 1 u) compensated by flushing a heavy blanket of inert gas, the present invention proposes to "seal" the coupling between ingot casting shroud and ingot mould inlet (1 1 ). The term "seal" is to be understood in a broad sense, since the gasket formed by the resilient layer (6) may be permeable to gases, even after compression upon engagement into the mould inlet. For this reason, the ingot casting shroud of the present invention may further comprise a gas channel (7) arranged to flush a gas over at least a portion of the outer outlet peripheral surface (4out). If the resilient layer (6) is permeable to gases, then the gas channel (7) is preferably arranged to flush said gas through said porous resilient layer. As illustrated in Figure 1 , the gas channel (7) comprises a gas outlet (7d) which preferably opens at a ring shaped groove (7g) extending along part or the whole of a perimeter of the outer outlet peripheral surface (4out), said ring shaped groove (7g) being in fluid communication with the resilient layer (6). The ring shaped groove (7g) distributes the inert gas over the whole outer outlet peripheral surface (4out) which can percolate through the gas permeable resilient layer. With this embodiment, the volume of inert gas required for protecting the molten metal stream from contact with air is reduced and, at the same time the protecting effect is enhanced with respect to prior art ingot casting installations.

[0028] The temperature in use of the outer outlet peripheral surface (4out) depends on the thickness of the outlet structural wall separating it from the bore through which the hot molten metal flows. The thicker said outlet structural wall is, the lower the temperature of the outlet peripheral surface (4out). The range of materials which can be selected for the resilient layer (6) is larger with low service temperatures. As shown in Figures 1 &2, it is therefore advantageous if the largest diameter, D6,4m, of the outlet portion is substantially larger than the diameter, D6,3, of the tubular portion where it is connected to said outlet portion (4). The diameter, D6, is defined as the length of a straight segment intersecting the longitudinal axis, X1 , and joining two points of the outer surface of the ingot casting shroud and included in a plane, π1 , normal to the longitudinal axis, X1 , and forming an angle, θ , with a reference diameter, DO, also included in plane, π1. The inverted T-shape of the shroud thus allows to separate the resilient layer further away from the bore (5) with lower service temperatures.

[0029] An ingot casting installation according to the present invention comprises, as illustrated in Figure 4,

(a) a ladle filled with molten metal and provided with an ingot casting shroud (1 ) as discussed above, and

(b) a mould (1 1 ) defined by a cavity and comprising an inlet portion (1 1 u) of geometry complementary with the geometry of the outlet portion (4) of the ingot casting shroud.

[0030] As shown in Figure 4(b), upon engaging the outlet portion of the ingot casting shroud into the inlet portion of the mould, the resilient layer (6) is compressed in the direction of the thickness, HO, and fits snugly in the mould inlet channel (1 1 u). If the resilient layer is impervious to gases, it forms a sealing gasket protecting the molten metal stream from contact with air. If the resilient layer (6) has an open porosity, as for example in case it is formed of a non-woven fiber mat, then an inert gas can be blown through the resilient layer by means of the gas channel (7) preferably opening at a gas channel (7g) in fluid communication with the porous resilient layer. This way a blanket of inert gas is formed between the stream of molten metal and air in a more efficient way and using substantially lower amounts of inert gas.

References

1 Ingot casting nozzle

2 inlet portion

3 tubular portion

4 outlet portion

4out outer outlet peripheral surface

5 inner bore

5d outlet of inner bore

5u inlet of inner bore

6 resilient layer

6out outer resilient peripheral surface of resilient layer

6t resilient layer sample for resiliency test

7 gas channel

7d gas outlet

7g ring shaped groove

8 intermediate layer between resilient layer (6) and outer outlet peripheral surface (4out) 9 non porous layer sealing part of the resilient layer (6)

1 1 ingot mould

1 1 u ingot mould inlet

21 metallurgic vessel (e.g., tundish or ladle)

D6,i diameter of element i, i = 3, 4, 6 measured at angle, Θ, of axis, X1

D6,im maximum diameter, D6,i, of element i, i = 4, 6,

X1 longitudinal axis

Claims

1. Ingot casting shroud (1 ) comprising structural walls made of a refractory material defining an inner bore (5) extending along and centered about a longitudinal axis, X1 , from a bore inlet (5u) located at an inlet end of the ingot casting shroud to a bore outlet (5d) located at an outlet end of the ingot casting shroud, said ingot casting shroud further comprising:

(a) An inlet portion (2) including the inlet end and the bore inlet (5u),

(c) An outlet portion (4) including the outlet end and bore outlet (5d), said outlet portion being adjacent to the tubular portion (3) and separated from the inlet portion (2) by said tubular portion, and comprising an outlet structural wall made of a refractory material defined by an outer outlet peripheral surface (4out) separated from the bore by a thickness of the outlet structural wall,

Characterized in that, a portion of the outer outlet peripheral surface (4out) extending over a perimeter of the outlet portion is provided with a resilient layer (6) having a resiliency of at least 70%, wherein the resiliency is defined as the ratio, H1 / HO, of the thickness, H1 , of a product after the compression and relaxation of a compressive force which reduces the original thickness to 50% of its original thickness, HO, to its original thickness, HO, measured at room temperature on a sample (6t) of dimensions L1 x L2 x HO collected from the resilient layer (6).

2. Ingot casting shroud according to claim 1 , wherein said resilient layer (6) comprises an outer resilient peripheral surface (6out) which is tapered towards the outlet end and wherein, the outer outlet peripheral surface (4out) of the outlet portion is preferably tapered too and substantially parallel to the outer resilient peripheral surface (6out), when the resilient layer is in a non- compressed state.

3. Ingot casting shroud according to the preceding claim, wherein the smallest thickness, HO, of the resilient layer in a non-compressed state, defined as the shortest distance between the outer outlet peripheral surface (4out) and the outer resilient peripheral surface (6out) is comprised between 10 and 50 mm, preferably between 20 and 35 mm.

4. Ingot casting shroud according to any one of the preceding claims, wherein the resilient layer (6) has a resiliency of at least 75%, preferably at least 80%, more preferably at least 85%.

5. Ingot casting shroud according to any one of the preceding claims, wherein the resilient layer (6) consists of a non-woven ceramic fiber mat or of a foam material, preferably a ceramic foam or a metal foam.

6. Ingot casting shroud according to the preceding claim, wherein the ceramic fibers comprise 70 to 80 wt.% Si0₂ and 15 to 30 wt.% MgO,

7. Ingot casting shroud according to the preceding claim, wherein the ceramic fiber mat has a density in a non-compressed state comprised between 90 and 150 kg / m³, preferably between 1 10 and 135 kg / m³.

8. Ingot casting shroud according to any one of the preceding claims, wherein an intermediate layer (8) is sandwiched between the resilient layer (6) and the outer outlet peripheral surface (4out), said intermediate layer having a higher compressive modulus than the resilient layer (6).

9. Ingot casting shroud according to any one of the preceding claims, further comprising a gas- impervious layer (9) sealing a portion of the resilient layer (6).

10. Ingot casting shroud according to any one of the preceding claims, wherein the largest diameter, D6,4m, of the outlet portion is substantially larger than the diameter, D6,3, of the tubular portion where it is connected to said outlet portion (4), wherein a diameter, D6, is defined as the length of a straight segment intersecting the longitudinal axis, X1 , and joining two points of the outer surface of the ingot casting shroud and included in a plane, n1 , normal to the longitudinal axis, X1 , and forming an angle, θ , with a reference diameter, DO, also included in plane, n1.

1 1. Ingot casting shroud according to any one of the preceding claims, wherein the resilient layer (6) has a height, L2, measured normal to a circumferential direction of, and parallel to the outer resilient peripheral surface (6out) of the resilient layer is comprised between 40 and 100 mm, preferably between 50 and 80 mm.

12. Ingot casting shroud according to any one of the preceding claims, further comprising a gas channel (7) arranged to flush a gas over at least a portion of the outer outlet peripheral surface (4out).

13. Ingot casting shroud according to the preceding claim, wherein the resilient layer is porous and permeable to a gas and wherein the gas channel (7) is arranged to flush said gas through said porous resilient layer.

14. Ingot casting shroud according to the preceding claim, wherein the gas channel (7) comprises a gas outlet (7d) which opens at a ring shaped groove (7g) extending along part or the whole of a perimeter of the outer outlet peripheral surface (4out), said ring shaped groove (7g) being in fluid communication with the resilient layer (6).

15. Metal ingot casting installation comprising (a) a ladle filled with molten metal and provided with an ingot casting shroud (1 ) according to any of the preceding claims, and (b) a mould (1 1 ) defined by a cavity and comprising an inlet portion (1 1 u) of geometry complementary with the geometry of the outlet portion (4) of the ingot casting shroud such that when the outlet portion of the ingot casting shroud is inserted into the inlet portion of the mould, it fits snugly with the resilient layer (6) being compressed.