FIELD OF INVENTION
[001] The present subject matter described herein is related to extruded refractory tubes without restricting scope of the invention to the same and its method of production. More particularly, to a composition of refractory ceramic tubes having good refractoriness, heat and thermal shock resistance for use as carrying molten metal in foundry and other related applications.
BACKGROUND AND PRIOR ART OF THE INVENTION
[002] Ceramic tubes with high refractoriness are used in carrying molten metal from ladle to mould and in particularly in pressure casting of applications. These are made from high temperature resistance refractory materials and fabricated into tubes by extrusion process.
[003] Prior Art US2847739A & US3201837A provide method and apparatus for pressure pouring of metal articles. Prior Art US5919392A provides a pouring tube assembly for a bottom-pouring casting apparatus or pouring tank arrangement. The pouring tube assembly includes a mechanical constraint for the pouring tube, holding casting and parting ring, which results in a secure union of the components. Prior Art GB1155427A and Prior Art US3529753A disclose refractory pouring tube of the type employed in pressure casting molten steel made by ramming and firing. Prior Art US4953762A provided a pouring tube consisting of an inner tubular portion formed of a refractory heat insulating material and an outer skin consisting essentially of a fibrous mat intimately laminated to the refractory heat insulating material inner tubular portion.
[004] Prior Art US3067050 and Prior Art US 3121640 provide Alumina refractory compositions using calcined alumina upto 90 % selected from bauxite, kynaite etc , this is suitable for refractory bricks or cast refractory products. Prior Art US5954989 gives refractory pouring tube containing upto 95 % Al2O3 and 5 % Carbon this is suitable only for continuous casting where tube is not exposed oxidation. Prior Art US5691052 provides refractory

tubes with impervious outer surface made by oxidation when it brought to
temperature above 1000C. The external layer contains 4 to 9 % Carbon
whereas inner layer made of refractory grains of <50 microns. Prior Art IN
203669 Pouring tube of refractory material consisting of a tubular part
equipped at its upper end with a plane plate, the side and lower faces of
said plate and the upper end of the tubular part being protected by a metal
case, said plate being reinforced, in its lower face, by mechanical means
increasing its stiffness, characterized in that said mechanical means
increasing the stiffness of the plate are comprised of two U-shaped pieces arranged on both side of the tube and fixedly attached to the part of the metal case protecting the lower face of the plate and to the upper end of the tubular part sand said U-shaped pieces are arranged with their lateral arms parallel to the direction of the guides on which said plate slides.
[005] There is no disclosure for manufacture of tubes at relatively low temperature say below 1300oC but having thermal resistance to use at above 1600oC hot molten metal and good thermal shock resistance. Moreover, known invention does not teach how to manufacture tubes with impervious coating in situ by firing at temperature where both refractory and glaze matures at same temperature.
[006] None of the above prior arts can fulfill the requirements of the invention for which it is designed. Hence, the present invention has been introduced.
OBJECTS OF THE INVENTION
[007] It is therefore the object of the invention to overcome the aforementioned and other drawbacks in prior art.
[008] The principal objective of the present invention is to provide for a refractory composition which can withstand molten metal upto 1620 0C and has good thermal shock resistance for applications in pressure casting applications.
[009] Another object of the present invention is to provide for a method of manufacture of such refractory tubes by extrusion process with impervious outer surface

[0010] Still another object of the present invention is to provide for a method of manufacture of such refractory tubes by extrusion process with impervious outer surface by firing at same temperature.
[0011] These and other objects and advantages of the present subject matter would be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0012] One or more drawbacks of the conventional technology based on existing apparatus and processes are overcome, and additional advantages are provided through a novel a composition of refractory ceramic tubes having good refractoriness, heat and thermal shock resistance for use as carrying molten metal in foundry and other related applications.
[0013] Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0014] In an embodiment of the present subject matter, the composition of extruded refractory tubes comprises first part consisting of inert refractory grains and powders, second part consisting of reactive materials and third part
containing clays.
[0015] In another embodiment of the present subject matter, the inert refractory
grains and powders include sintered mullite, fused mullite, sintered
alumina, fused alumina, fused silica, fused zircon or combination of these refractory grains and powders.
[0016] In another embodiment of the present subject matter, the source of alumina is calcined alumina.
[0017] In another embodiment of the present subject matter, the clay is a combination of china clay and ball clay.

[0018] In another embodiment of the present subject matter, the first part is selected from larger particle size varying upto 3 mm.
[0019] In another embodiment of the present subject matter, the second part is selected from particle size below 10 microns.
[0020] In another embodiment of the present subject matter, a method of
manufacturing extruded refractory tubes comprising the steps of mixing of first
part, second part and third part with water in a high intensity mixer,
extrusion of tubes in a high pressure screw extruder, applying vacuum, cutting tubes in length ranging between 2.3 m to 2.6m, drying of tubes, firing of dried tubes in kilns between 1200 to 1300oC and coating of fired tubes with a ceramic slurry containing glass forming raw materials.
[0021] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0022] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein are not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0024] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects,

and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0026] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0028] The refractory tubes used in pressure casting application requires to withstand high temperature of molten metal of 1620oC and should have good thermal shock resistance for repeated use. The outer surface should be impermeable for impeding passage of air and to avoid slag attack. These tube of length up to 2.5 metres and hanged with holder during use. Hence, they should not bend nor any shrinkage duding use. Extrusion is a preferred process compared to casting or ramming to get uniform compact and flawless tubes. However, extrusion of refractory material is very challenging. Addition of more clay to induce good plasticity retards refractoriness and increase

shrinkage. Hence, batch composition is optimized meeting these both competing requirements.
[0029] The present disclosure discloses a novel composition of refractory ceramic tubes having good refractoriness, heat and thermal shock resistance for use as carrying molten metal in foundry and other related applications.
[0030] In accordance with an embodiment of the present subject matter, the
composition of extruded refractory tubes comprises first part comprising of inert
refractory grains and powders, second part consisting of reactive materials
such as alumina preferably calcined alumina and and third part containing clays
i.e. a combination of china clay and ball clay. The inert refractory grains and
powders are prepared by high temperature treatment such as sintering or
fusion such as sintered mullite, fused mullite, sintered alumina, fused
alumina, fused silica, fused zircon or combination of these refractory grains and powders.
[0031] In another aspect of the present subject matter, the first part is selected from larger particle size up to 3 mm and the second part is selected from particle size below 10 microns.
[0032] The present subject matter further discloses a method of manufacturing extruded refractory tubes comprising the steps of mixing of first part, second part and third part with water in a high intensity mixer, extrusion of tubes in a high pressure screw extruder, applying vacuum, cutting tubes in length ranging between 2.3 metres to 2.6 metres, drying of tubes, firing of dried tubes in kilns between 1200 to 1300oC and coating of fired tubes with a ceramic slurry containing glass forming raw materials.
[0033] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein,
embody the principles of the present subject matter and are included within its
scope.
ADVANTAGES:

[0034] The refractory tubes thus produced have good thermal shock resistance;
[0035] The refractory tubes can withstand the flow of molten metal of more than 1600oC when used as pouring tubes in pressure casting applications.
WORKING OF THE INVENTION:
[0036] A method of manufacturing of refractory tubes by extrusion process where the production method involves the mixing of three parts of ceramic raw material in a high intensive or similar mixer with water to make paste.
[0037] Extrusion of tubes are carried out in high pressure screw extruder which is a continuous extrusion and applying vacuum. The required length of tubes in the range of 2.3 metres to 2.6 metres are cut and dried. The dried products are fired in the kilns at 1200-1300oC, more preferably 1220 to 1280 0C. For producing tubes with impervious outer surface, a ceramic slurry is prepared containing glass forming raw materials. These slurry is coated onto the tube either by dipping or spraying preferably under vacuum. The dried tubes are fired in the temperature range 1220 oC to 1280 0C. This coating process can be done on the unfired tubes or fired tubes to get the outer surface of the tubes are made impervious. The glaze and refractory are matured in the same temperature.
EXAMPLES:
EXAMPLE 1
[0038] Raw material used for first part is Sintered mullite and fused silica. Raw material used for second part is calcined alumina. Raw material used for second part is clay. Amount of sintred mullite is 30 % Amount of fused Silica is 12 % Amount of calcined alumina is 34 %. Amount of clay is 24 %These weighed powders are mixed in a high intensive or similar mixer with 11 % water to make paste. Extrusion of tubes are carried out in high pressure screw extruder which is a continuous extrusion. Vacuum is applied during extrusion. Diameter of tube is 160 mm with wall thickness of 30 mm. The tubes are cut in 2.5 m length and dried. Drying is done for 2 days in natural drying and then slowly in controlled heating over till 150oC The dried products are fired in the kilns at temperature between 1230oC.

[0039] Fired tubes are tested for bulk density, water absorption, thermal expansion and thermal shock resistance. Thermal shock resistance is tested by heating the tube samples to 1000 oC and quenching in water. Number of cycles that the ceramic tiles withstood without any crack is recorded. The refractory tubes thus produced has good thermal shock resistance and withstood molten metal flow though it when used in pressure casting applications.
[0040] Characteristics of tubes thus produced are as follows:-
[0041]Chemical Composition:
• Al2O3 : 55 to 60 %
• SiO2 : 35 to 40 %
• Fe2O3 : 1 to 2%
[0042] Physical Properties
• Bulk Density : 2.2 to 2.4 gm/cc
• Apparent Porosity :22 to 25 %
• Sp. Gravity : 2.8 to 3.0 gm/cc [0043] Mineralogical (XRD) Phases :
Major Phase: Mullite
Minor Phases: Cristobalite, Quartz and Alumina/Corundum
Coefficient of Thermal expansion: 4 to 5 X 10-6 /oC
Thermal shock resistance: No cracks after 10 cycles of 1000oC & water quench
EXAMPLE 2
[0044] Ceramic tubes are produced as per example 1. The fired tubes are cut into required length at both ends. Tubes are coated with glaze slurry by spraying. Glaze slurry is prepared by mixing silica and clay powder with fluxes such as dolomite, talc and feldspars. Glaze slurry is prepared by wet milling these powder in water and maintaining specify gravity of slurry in the range of 1.8. Coating is done by spraying on the tube outer surface

while both end of the tubes are closed and connected to vacuum pump. After drying, the coated tubes are fired in the kilns at 1230oC. Fired tubes has impervious glazed surface on the outer surface. The refractory tubes thus produced has good thermal shock resistance and withstood molten metal flow though it when used in pressure casting applications.
EXAMPLE 3:
[0045] Ceramic tubes are produced as per example 1. However before firing
these tubes are taken for coating. The dried tubes are cut into required length at
both ends. Tubes are coated with glaze slurry by spraying. Glaze slurry is
prepared as per Example 2 and coating is done as per Example 2. After drying,
the coated tubes are fired in the kilns at 1230oC. Fired tubes has impervious
glazed surface on the outer surface. Fired tubes are tested for bulk density,
water absorption, thermal expansion and thermal shock resistance. The
refractory tubes thus produced has good thermal shock resistance and
withstood molten metal flow though it when used in pressure casting
applications. Characteristics of tubes thus produced are as given in Example 1.
[0046] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or

more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0047] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0048] Although embodiments for the present subject matter have been
described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to

those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations, which fall within the scope of the present subject matter.

We Claim:
1. A composition of extruded refractory tubes , the composition comprises:
first part comprising of 40 to 50 % inert refractory grains and
powders ;
second part comprising of 30 to 38% reactive materials such as calcined alumina; and third part comprising 22 to 28% clays.
2. The composition of extruded refractory tubes as claimed in claim 1,
wherein inert refractory grains and powders including sintered mullite,
fused mullite, sintered alumina, fused alumina, fused silica, fused zircon ,
alternatively a combination of these refractory grains and powders.
3. The composition of extruded refractory tubes as claimed in claim
1, wherein the source of alumina is calcined alumina.
4. The composition of extruded refractory tubes as claimed in claim 1, wherein the clay is a combination of china clay and ball clay.
5. The composition of extruded refractory tubes as claimed in claim 1, wherein the first part is selected from particle size up to 3 mm.
6. The composition of extruded refractory tubes as claimed in claim 1, wherein the second part is selected from particle size below 10 microns.
7. A method of manufacturing extruded refractory tubes comprising the steps of:
mixing of first part, second part and third part with water in a mixer;
extrusion of tubes in a screw extruder;
applying vacuum;
cutting tubes in length ranging between 2.3 metres to 2.6 metres;
drying of tubes;
firing of dried tubes in kilns between 1200 to 1300oC; and
coating of fired tubes with a ceramic slurry containing glass forming raw materials.