CN117144092A - RH dip pipe and preparation method thereof - Google Patents

Abstract

The invention provides an RH dip pipe and a preparation method thereof, comprising a steel liner, wherein a casting layer formed by casting refractory material casting materials is arranged outside the steel liner, refractory bricks are arranged inside the steel liner, an insulating plate is fixed on the outer wall of a part, which is used for being inserted into molten steel, of the lower part of the steel liner, and the insulating plate is positioned in the casting layer; the steel liner is characterized in that a foam aluminum layer is fixed on the inner wall of the steel liner, a gap is reserved between the foam aluminum layer and the refractory bricks, a low heat conduction pouring material is poured into the gap to form a low heat conduction pouring layer, the upper end and the lower end of the foam aluminum layer are sealed in the low heat conduction pouring layer, and a hollow structure is arranged in the low heat conduction pouring material. The invention adopts the heat insulation plate, the low heat conduction castable and the foamed aluminum to reduce the temperature of the steel liner, reduce the thermal stress between the steel liner and the refractory material, and adopts the foamed aluminum easy to deform to further reduce the thermal stress between the steel liner and the refractory material in the using process, thereby prolonging the service life of the dip pipe.

Description

RH dip pipe and preparation method thereof

Technical Field

The invention relates to the technical field of RH dip pipes, in particular to an RH dip pipe and a preparation method thereof.

Background

RH, vacuum circulation degassing method for molten steel, is an external refining method for molten steel designed and developed together by German Ruhrstahl and Hereaeus. RH refining can be used for carrying out dehydrogenation, denitrification, deoxidation, decarburization and desulfurization on molten steel, homogenizing molten steel components and improving the cleanliness of the molten steel. The advantages are that: convenient operation, good refining effect, short treatment time and large production capacity. Thus, RH refining is an indispensable process for clean steel smelting. The RH dip pipe frequently bears rapid cooling and rapid heating in the production process, and because the expansion coefficients of the steel structure and the refractory material are different, refractory bricks in the steel structure are loosened and fall off, cracks are generated on the external casting material, the nitrogen content of molten steel is difficult to control due to air leakage, the steel structure at the gap is deformed, and the service life is greatly reduced. It follows that the RH dip pipe significantly affects the metallurgical function of RH.

CN202122474532.7 discloses a dipping pipe with an air cooling device, by adding an air cooling chamber on the outer surface of the inner container, the temperature of the inner container is reduced, continuous smelting is improved, and the service life is prolonged. CN201920757283.2 discloses a cooling device for an insert tube of an RH refining furnace, a cylindrical structure cooling chamber is welded above the outer wall of the insert tube, a cold water inlet tube and a hot water outlet tube are arranged at the outer wall of the cooling chamber, reddening and deformation of a metal steel structure of the insert tube are relieved, and the service life of the insert tube of the RH vacuum furnace is prolonged. Disadvantages: the structure is more complex, and the temperature drop in the process is increased.

CN201610554088.0 discloses a low-stress dip tube of an RH vacuum furnace, which comprises a refractory brick lining, a filling layer and a steel cylinder from inside to outside. The steel cylinder wall is not perforated, the bottom surface of the steel cylinder is welded with an annular metal round pipe or an annular metal round rod, buffer layers are paved on the outer wall below the top of the steel cylinder and the outer wall of the annular metal round pipe or the annular metal round rod, V-shaped metal anchoring pieces and double V-shaped metal anchoring pieces are uniformly welded on the outer wall of the steel cylinder and the outer wall of the annular metal round pipe or the outer wall of the annular metal round rod along the axial interval layering circumferential direction of the steel cylinder, and the V-shaped metal anchoring pieces and the double V-shaped metal anchoring pieces penetrate through the buffer layers. The damage and deterioration problems caused by the remarkable difference of the material properties of all parts in the composite structure of the dipping pipe are relieved, the structural stress and the thermal stress of the dipping pipe are reduced, and the service life of the dipping pipe is prolonged. Disadvantages: the temperature of the steel cylinder cannot be reduced, and the thermal stress is still alternately carried out.

The literature 'influences of steel liner slotting modes on thermal expansion of RH dip pipes, refractory materials, 2015, 49 (1): 56-58' in order to solve the problems of cracking, falling and the like of refractory materials for RH furnace dip pipes, a finite element model of the refractory brick-steel liner-castable composite structure dip pipe is established by utilizing ANSYS software, analysis and calculation are carried out on the steel liner slotting dip pipes, and simulation tests and practical application tests are carried out. The results show that slotting on the steel bladder is one of the effective ways to reduce the thermal expansion of the steel bladder. Disadvantages: the strength of the steel liner is reduced.

In summary, no related report has been made on a structure or a method for reducing thermal stress between the steel bladder and the refractory material and improving the impregnated tube in the use process without affecting the strength of the steel bladder.

Disclosure of Invention

According to the technical problems, an RH dip pipe and a preparation method thereof are provided.

The invention adopts the following technical means:

the RH dip pipe comprises a steel liner, wherein a casting layer formed by casting refractory castable is arranged outside the steel liner, refractory bricks are arranged inside the steel liner, and the RH dip pipe is characterized in that an insulating plate is fixed on the outer wall of a part, inserted into molten steel, of the lower part of the steel liner, and the insulating plate is positioned in the casting layer; the steel liner is characterized in that a foam aluminum layer is fixed on the inner wall of the steel liner, a gap is reserved between the foam aluminum layer and the refractory bricks, a low heat conduction pouring material is poured in the gap to form a low heat conduction pouring layer, a hollow structure is arranged in the low heat conduction pouring material, and the upper end and the lower end of the foam aluminum layer are sealed in the low heat conduction pouring layer.

Preferably, a plurality of anchors fixed with the outer wall of the steel bladder are arranged in the casting layer.

Preferably, the refractory castable is an alumina castable comprising: 10-15 parts of alumina with the granularity of 3-5 mm, 15-25 parts of alumina with the granularity of 1-3 mm, 20-30 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica powder, 3-6 parts of active alumina fine powder, 1-2 parts of high alumina cement, 1-1.5 parts of stainless steel fiber, 0.5-1 part of water reducer, 0.4 part of explosion-proof fiber, 4-7 parts of aluminum particle with the granularity of 0.5-2 mm and 6-7 parts of water.

Preferably, the low thermal conductivity castable includes: 10-15 parts of alumina with the granularity of 3-5 mm, 15-20 parts of alumina hollow spheres with the external diameter of 2-5 mm, 15-20 parts of alumina with the granularity of 1-3 mm, 20-25 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica micropowder, 3-6 parts of activated alumina fine powder, 1-2 parts of high alumina cement, 0.5-1 part of water reducer, 0.4 part of anti-explosion fiber and 6-7 parts of water.

Preferably, the gap is 30-50 mm.

Preferably, the thickness of the heat insulation plate is 10-30 mm, and the heat insulation plate is high-aluminum heat insulation plate, and the heat conductivity coefficient of the heat insulation plate is 0.035-0.09W/(m.K).

Preferably, the thickness of the foamed aluminum layer is 4.0-6.0 mm.

Preferably, the refractory bricks are chrome-free bricks.

The invention also discloses a preparation method of the RH dip pipe, which is characterized by comprising the following steps:

fixing the foamed aluminum layer on the inner wall of the steel liner;

determining the distance of the steel liner for inserting into the molten steel, and fixing the heat insulation plate on the outer wall of the part of the lower part of the steel liner for inserting into the molten steel;

the fireproof bricks are built in the steel liner, and the gaps are reserved between the foamed aluminum layers and the chromium-free bricks;

integrally placing the mixture into a mold, and injecting the refractory castable outside the mixture;

pouring the low-heat-conductivity castable in the gap, and sealing the upper end and the lower end of the foamed aluminum layer in the low-heat-conductivity castable;

vibration molding, maintenance, demoulding and baking to form the RH dip pipe.

Compared with the prior art, the invention has the following advantages:

in the traditional process, the aluminum oxide casting layer is directly arranged on the outer wall of the steel liner, the chromium-free brick is directly arranged on the inner wall of the steel liner, the dip pipe is subjected to rapid cooling or rapid heating change of temperature in the use process, and the thermal expansion coefficient of the steel liner is different from that of the aluminum oxide casting layer and the chromium-free brick, so that cracks are generated in the refractory material, air leakage is easy to occur, and the nitrogen content of molten steel is difficult to control. The steel structure at the gap is deformed, and the service life is greatly reduced. According to the invention, the heat insulation plate is arranged on the outer wall of the steel liner, the foam aluminum layer and the low heat conduction castable are arranged on the inner wall of the steel liner, so that the heat of the steel liner is reduced from the outside and the inside, the temperature change of the steel liner is small, the thermal stress between the steel liner and the refractory material is reduced, the foam aluminum is easy to deform, the thermal stress between the steel liner and the refractory material in the using process is further reduced, and the service life of the dip pipe is prolonged.

For the reasons, the invention can be widely popularized in the fields of RH dip pipes and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of an RH-immersed tube according to an embodiment of the present invention.

In the figure: 1. a steel liner; 2. molten steel; 3. a heat insulating plate; 4. chromium-free brick; 5. a low thermal conductivity casting layer; 6. an alumina casting layer; 7. an anchor; 8. a foamed aluminum layer.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be clear that the dimensions of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.

In the description of the present invention, it should be understood that the azimuth or positional relationships indicated by the azimuth terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal", and "top, bottom", etc., are generally based on the azimuth or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and these azimuth terms do not indicate and imply that the apparatus or elements referred to must have a specific azimuth or be constructed and operated in a specific azimuth, and thus should not be construed as limiting the scope of protection of the present invention: the orientation word "inner and outer" refers to inner and outer relative to the contour of the respective component itself.

Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present invention.

As shown in fig. 1, the RH dip tube comprises a steel liner 1, wherein an insulating plate 3 with the thickness of 10-30 mm is fixed on the outer wall of the part, which is used for being inserted into molten steel 2, of the lower part of the steel liner 1, and the insulating plate 3 is a high-aluminum insulating plate with the heat conductivity coefficient: 0.035-0.09W/(m.K); the inner wall of the steel liner 1 is fixedly provided with a foamed aluminum layer 8 with the thickness of 4.0-6.0 mm, the steel liner 1 is internally built with chrome bricks 4 or not, and a gap of 30-50 mm is reserved between the foamed aluminum layer 8 and the chrome bricks 4. And pouring low-heat-conductivity castable in the gap to form a low-heat-conductivity castable layer 5, and sealing the upper end and the lower end of the foamed aluminum layer 8 in the low-heat-conductivity castable layer 5. The low heat conduction castable 5 is provided with a hollow structure; and an alumina casting material is cast outside the steel liner 1 to form an alumina casting layer 6.

The alumina casting layer 6 is internally provided with a plurality of anchors 7 fixed with the outer wall of the steel liner 2. During installation, the anchor 7 is welded on the outer wall of the steel liner 2, then the heat insulation plate 3 is installed, a limiting device (such as a limiting pin and other structures) is arranged on the anchor 7 to prevent the heat insulation plate 3 from moving, and then casting is performed.

The alumina castable includes: 10-15 parts of alumina with the granularity of 3-5 mm, 15-25 parts of alumina with the granularity of 1-3 mm, 20-30 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica powder, 3-6 parts of active alumina fine powder, 1-2 parts of high alumina cement, 1-1.5 parts of stainless steel fiber, 0.5-1 part of water reducer, 0.4 part of explosion-proof fiber, 4-7 parts of aluminum particle with the granularity of 0.5-2 mm and 6-7 parts of water.

The low heat conduction castable comprises: 10-15 parts of alumina with the granularity of 3-5 mm, 15-20 parts of alumina hollow spheres with the external diameter of 2-5 mm, 15-20 parts of alumina with the granularity of 1-3 mm, 20-25 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica micropowder, 3-6 parts of activated alumina fine powder, 1-2 parts of high alumina cement, 0.5-1 part of water reducer, 0.4 part of anti-explosion fiber and 6-7 parts of water.

The invention also discloses a preparation method of the RH dip pipe, which comprises the following steps:

the foam aluminum layer 8 is fixed on the inner wall of the steel liner 1;

determining the distance of the depth of the steel liner 1 for inserting the molten steel 2, and fixing the heat insulation plate 3 on the outer wall of the part of the lower part of the steel liner 1 for inserting the molten steel 2;

the chrome-free brick 4 is built in the steel liner 1, and the gap is reserved between the foamed aluminum layer 8 and the chrome-free brick 4;

integrally placing the mixture into a mold, and injecting alumina castable outside the mixture;

pouring the low-heat-conductivity castable in the gap, and sealing the upper end and the lower end of the foamed aluminum layer 8 in the low-heat-conductivity castable;

vibration molding, maintenance, demoulding and baking to form the RH dip pipe.

Example 1

A foamed aluminum layer 8 with the thickness of 4.0mm is fixed on the inner wall of the steel liner 1; and determining the depth distance of the steel liner 1 for being inserted into the molten steel 2, fixing a 10mm thick heat insulation plate 3 on the outer wall of the part of the lower part of the steel liner 1 for being inserted into the molten steel 2, and building a chromium-free brick 4 in the steel liner 1, wherein a gap between the foamed aluminum layer 8 and the chromium-free brick 4 is 30mm. The aluminum oxide castable is integrally put into a die, and the aluminum oxide castable comprises the following components: 10 parts of alumina with the granularity of 5-3 mm, 25 parts of alumina with the granularity of 3-1 mm, 20 parts of alumina with the granularity of 1-0 mm, 35 parts of alumina with the granularity of less than 0.074mm, 2 parts of silica micropowder, 5 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 1 part of stainless steel fiber, 0.5 part of water reducer, 0.4 part of explosion-proof fiber, 4 parts of externally added aluminum particles with the granularity of 0.5-2 mm and 6-7 parts of water. And pouring low heat conduction castable into the gap between the foamed aluminum layer 8 and the chromium-free brick 4, and sealing the upper end and the lower end of the foamed aluminum layer 8 in the low heat conduction castable. The low heat conduction castable comprises the following components: 10 parts of alumina with the granularity of 5-3 mm, 15 parts of alumina hollow spheres with the external diameter of 2-5 mm, 15 parts of alumina with the granularity of 3-1 mm, 20 parts of alumina with the granularity of 1-0 mm, 30 parts of alumina with the granularity of less than 0.074mm, 3 parts of silica powder, 5 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 0.5 part of water reducer, 0.4 part of explosion-proof fiber and 6-7 parts of water. Vibration molding, demoulding after curing for 24 hours, and baking to obtain the low-heat-conductivity dip pipe, wherein the service life of the dip pipe is prolonged by 16 furnaces compared with the prior dip pipe.

Example 2

A foamed aluminum layer 8 with the thickness of 5.0mm is fixed on the inner wall of the steel liner 1; and determining the depth distance of the steel liner 1 for being inserted into the molten steel 2, fixing a heat insulation plate 3 with the thickness of 20mm on the outer wall of the part of the lower part of the steel liner 1 for being inserted into the molten steel 2, and building a chromium-free brick 4 in the steel liner 1, wherein a gap between the foamed aluminum layer 8 and the chromium-free brick 4 is 40mm. The aluminum oxide castable is integrally put into a die, and is injected into the die, and comprises the following components: 10 parts of alumina with the granularity of 5-3 mm, 20 parts of alumina with the granularity of 3-1 mm, 25 parts of alumina with the granularity of 1-0 mm, 35 parts of alumina with the granularity of less than 0.074mm, 2 parts of silica micropowder, 5 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 1.5 parts of stainless steel fiber, 0.5 part of water reducer, 0.4 part of explosion-proof fiber, 5 parts of externally added aluminum particles with the granularity of 0.5-2 mm and 6-7 parts of water. The low heat conduction castable is injected into the gap between the foamed aluminum layer 8 and the chrome-free brick 4, and consists of: 13 parts of alumina with the granularity of 5-3 mm, 17 parts of alumina hollow spheres with the external diameter of 2-5 mm, 10 parts of alumina with the granularity of 3-1 mm, 20 parts of alumina with the granularity of 1-0 mm, 30 parts of alumina with the granularity of less than 0.074mm, 4 parts of silica powder, 4 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 0.5 part of water reducer, 0.4 part of explosion-proof fiber and 6-7 parts of water. Vibration molding, demoulding after curing for 24 hours, and baking to obtain the low-heat-conductivity dip pipe, wherein the service life of the dip pipe is prolonged by 19 furnaces compared with that of the existing dip pipe.

Example 3

A foamed aluminum layer 8 with the thickness of 6.0mm is fixed on the inner wall of the steel liner 1; and determining the depth distance of the steel liner 1 for being inserted into the molten steel 2, fixing a 30mm thick heat insulation plate 3 on the outer wall of the part of the lower part of the steel liner 1 for being inserted into the molten steel 2, and building a chromium-free brick 4 in the steel liner 1, wherein a gap between the foamed aluminum layer 8 and the chromium-free brick 4 is 50mm. The aluminum oxide castable is integrally put into a die, and is injected into the die, and comprises the following components: 10 parts of alumina with the granularity of 5-3 mm, 25 parts of alumina with the granularity of 3-1 mm, 25 parts of alumina with the granularity of 1-0 mm, 30 parts of alumina with the granularity of less than 0.074mm, 4 parts of silica micropowder, 3 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 1.5 parts of stainless steel fiber, 0.5 part of water reducer, 0.4 part of explosion-proof fiber, 7 parts of externally added aluminum particles with the granularity of 0.5-2 mm and 6-7 parts of water. And pouring low-heat-conductivity castable into the gap between the foamed aluminum layer 8 and the chromium-free brick 4, and sealing the upper end and the lower end of the foamed aluminum layer 8 in the low-heat-conductivity castable. The low heat conduction castable comprises the following components: 10 parts of alumina with the granularity of 5-3 mm, 20 parts of alumina hollow spheres with the external diameter of 2-5 mm, 10 parts of alumina with the granularity of 3-1 mm, 20 parts of alumina with the granularity of 1-0 mm, 30 parts of alumina with the granularity of less than 0.074mm, 2 parts of silica micropowder, 6 parts of activated alumina fine powder, 1.5 parts of high alumina cement, 0.5 part of water reducer, 0.4 part of explosion-proof fiber and 6-7 parts of water. Vibration molding, demoulding after curing for 24 hours, and baking to obtain the low-heat-conductivity dip pipe, wherein the service life of the dip pipe is prolonged by 22 furnaces compared with the existing dip pipe.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (9)

1. The RH dip pipe comprises a steel liner, wherein a casting layer formed by casting refractory castable is arranged outside the steel liner, refractory bricks are arranged inside the steel liner, and the RH dip pipe is characterized in that an insulating plate is fixed on the outer wall of a part, inserted into molten steel, of the lower part of the steel liner, and the insulating plate is positioned in the casting layer; the steel liner is characterized in that a foam aluminum layer is fixed on the inner wall of the steel liner, a gap is reserved between the foam aluminum layer and the refractory bricks, a low heat conduction pouring material is poured in the gap to form a low heat conduction pouring layer, a hollow structure is arranged in the low heat conduction pouring material, and the upper end and the lower end of the foam aluminum layer are sealed in the low heat conduction pouring layer.

2. An RH dip tube according to claim 1, wherein said casting layer has a plurality of anchors secured to the outer wall of said bladder.

3. An RH dip tube according to claim 1, wherein the refractory castable is an alumina castable comprising: 10-15 parts of alumina with the granularity of 3-5 mm, 15-25 parts of alumina with the granularity of 1-3 mm, 20-30 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica powder, 3-6 parts of active alumina fine powder, 1-2 parts of high alumina cement, 1-1.5 parts of stainless steel fiber, 0.5-1 part of water reducer, 0.4 part of explosion-proof fiber, 4-7 parts of aluminum particle with the granularity of 0.5-2 mm and 6-7 parts of water.

4. An RH dip tube according to claim 1, wherein said low thermal conductivity castable material comprises: 10-15 parts of alumina with the granularity of 3-5 mm, 15-20 parts of alumina hollow spheres with the external diameter of 2-5 mm, 15-20 parts of alumina with the granularity of 1-3 mm, 20-25 parts of alumina with the granularity of 0-1 mm, 25-35 parts of alumina with the granularity of less than 0.074mm, 2-4 parts of silica micropowder, 3-6 parts of activated alumina fine powder, 1-2 parts of high alumina cement, 0.5-1 part of water reducer, 0.4 part of anti-explosion fiber and 6-7 parts of water.

5. An RH dip tube according to claim 1, wherein said gap is 30-50 mm.

6. An RH-impregnated tube according to claim 1 wherein said insulation panel is of thickness 10-30 mm and is of high aluminium and has a thermal conductivity of 0.035-0.09W/(m.k).

7. An RH dip tube according to claim 1, wherein the thickness of the foamed aluminium layer is 4.0-6.0 mm.

8. An RH dip tube according to claim 1, wherein the refractory brick is a chrome-free brick.

9. A method of preparing an RH-impregnated tube according to any one of claims 1 to 8, comprising:

fixing the foamed aluminum layer on the inner wall of the steel liner;

determining the distance of the steel liner for inserting into the molten steel, and fixing the heat insulation plate on the outer wall of the part of the lower part of the steel liner for inserting into the molten steel;

the fireproof bricks are built in the steel liner, and the gaps are reserved between the foamed aluminum layers and the chromium-free bricks;

integrally placing the mixture into a mold, and injecting the refractory castable outside the mixture;

pouring the low-heat-conductivity castable in the gap, and sealing the upper end and the lower end of the foamed aluminum layer in the low-heat-conductivity castable;

vibration molding, maintenance, demoulding and baking to form the RH dip pipe.