Repairings and maintenance of mould of di pipe manufacturing process
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-06
- Publication Date
- 2026-08-13
Abstract
Description
REPAIRINGS AND MAINTENANCE OF MOULD OF DI PIPE MANUFACTURING PROCESSFIELD OF INVENTION
[0001] The embodiments of present disclosure are in general related to the Hot Zonal improvement of ductile iron spun pipe manufacturing process and more particularly but not exclusively related to the repair and / or maintenance of Metal Mould of Continuous Casting Machine of Ductile Iron Spun Pipe Manufacturing process. The embodiments of present invention results in enhancement of quality, productivity and production capacity of Ductile Iron Spun Pipe manufacturing.BACKGROUND
[0002] Among the various pipe manufacturing techniques, Ductile Iron Spun pipe manufacturing is widely used for both ferrous and non-ferrous metals. These pipes are produced using centrifugal casting in either metal moulds or resin-lined moulds. However, the Ductile Iron Spun pipe manufacturing process presents numerous challenges, due to the application of complex engineering principles, thermodynamics, and refractory materials.
[0003] The quality and productivity of Ductile Iron Spun pipe manufacturing depends on the efficiency and effectiveness of several hot-zone components, including pouring spouts ofthe induction furnace, GF converter & hopper, transfer ladles of the blast furnace, induction furnace & GF converter, fall chutes, runners, and metal moulds.
[0004] The metal moulds play a critical role in determining the final shape and dimensions ofthe product, product quality, rejection rates, and extent of rejection. During the manufacturing process, metal moulds often experience hairline cracking and localized damage due to rotational and thermal fatigue. These issues intensify as the pipe size increases, typically ranging from DN 80 to DN 5500: DN80 to DN 250- In this size range, the metal mould's surface area-to-liquid metal volume ratio is high, resulting in relatively fast cooling; DN 300 to DN 650- Here, the surface area-to-volume ratio is moderate, leading to moderate to fast cooling of the metal mould; DN 700 to DN 1200- In this range, the surface area-to-volume ratio decreases further, creating a high thermal gradient and extending the solidliquid cooling range; DN 1200 to DN 2000 - With a reduced surface area-to-volume ratio, the metal solidification time increases significantly, which negatively impacts mould lifespan; DN 2000 to DN 5500- For these sizes, the mould’s surface area, weight, thickness, and liquid iron volume present severe challenges, often becoming problematic for manufacturers.
[0005] As pipe size increases, the decreasing surface area-to-liquid metal volume ratio shortens the metal mould’s potential lifespan. For larger moulds, high metal volume and temperature necessitate frequent stress relief and peening operations. These operations incur high costs, and despite significant expenditure, in moulds often develop hairline cracks and localized damage, requiring postmachining and rework. Additionally, it reduces hourly production rates and increases rejection rates.
[0006] Since Ductile Iron Spun Pipe plants operate continuously (24x7), there is minimal downtime for preventive repairing or maintenance. This demands frequent replacement of parts and equipment and the maintenance of extra inventory, resulting in substantial capital and operational costs.
[0007] KR19990018856A relates to a composition of a repairing material which improves the service life of a solid bond with the base material and an increase in corrosion resistance when repairing the damage and dropping of the ladle I tundish internal refractories in contact with the molten steel, sintered or molten alumina, Ultrafine powdered alumina, magnesia, zircon, silica, bauxite, and ruxite, mullite, from 80 to 97 parts by weight of one or two or more types of refractory raw materials, 2 to 15 parts by weight of a Na-Si binder, a curing regulator 0.5 It iscomposed of a repair material composed of ~5.0 parts by weight, and after the addition of water to the repairing material is a technique for repairing it by a patching method using iron or other tools to the damaged internal refractories.
[0008] CN103159485A discloses a refractory fettling material, which is prepared by the following raw materials in parts by weight: 60-80 parts of magnesia aggregate, 5 ~ 20 parts of magnesia powder; 5-10 parts of asphalt; 1-5 parts of hexametaphosphate sodium; 1-4 parts of caprolactam; 5-15 parts of potassium nitrate, 10-30 parts of iron oxide, and 10-30 parts of calcium phosphate.
[0009] CN101367667A relates to the refractory patching mixture of a foundry ladle is characterized in that: it is composition, and each component that it comprises and the weight percent that accounts for composition thereof are: Repair material matrix 55~90%, silicon carbide 1~35%, ultrafine silica powder are or / and alumina powder 3~15%, aluminous cement 0.5~15%, tripoly phosphate sodium STPP or Sodium hexametaphosphate 99 0.01 ~3%, sodium cellulosate or sodium alginate 0.001~2%; Described repair material matrix is one or more the composition in corundum, alumina, the flint clay.
[0010] KR20030041539A discloses refractories used for repairingthe damaged parts of hot iron runner of blast furnace urgently are provided to shorten the repairing time and extend the life of hot iron runner. The refractories comprise the components of: fused alumina with different particle sizes such as 3-5mm(3-6wt.%), l-3mm(16-22wt.%), 0.5-lmm(14-18wt.%), and up to 0.074mm (15-17wt.%); 7-12wt.% ofSiC; 3-4wt.% of graphite powder; 5-7wt.% of carbon black for the increase of adhesion, 6-8wt.% of cokes powder(0.5-lmm); 3-4wt.% of silicon for the increase of strength; 13-14wt.% of tar for good workability; and 3wt.% of organic fiber, calculated by extrapolation.
[0011] CN1837150A relates to a thermal-state dry-coating repairing mix for metallurgical furnace liner and its production method and using method, which mainly comprises the following constituents (by weight percent): magnesiumoxide MgO 0-95%, aluminum oxide A12O3 0-93%, calcium oxide CaO 0-65%, silicon oxide Si020-65%, carbon C 0-35%, other findings including binding agent, mineralization agent, agglutinant, metallic aluminum powder and metallic silicon powder 0-18%, the manufacturing process consists of base-material slacking and sifting, particle pre-processing, proportioning base material and findings, modification pre-processing, mixing, homogenization handling, drying and packaging.
[0012] Although the cited reference does disclose repairing mixtures containing refractory oxides, carbon derivatives, silicate derivatives, there is still a need for a composition that is specialized as a Chemically Bonded Refractory Patching Mix (specifically a CCh-Silicate system) used for the online or offline repair of damaged inner surfaces of the steel moulds (dies) used in Centrifugal Casting and such composition to allow for the rapid filling of gouges, cracks, or defects on the metal mould without requiring welding (which induces thermal stress). Therefore, it is critical to develop solutions to address these challenges effectively. This includes improving manufacturing processes for large pipes, enhancing the durability and lifespan of metal moulds, streamlining maintenance, reducing costs and downtime, and minimizing rejections.
[0013] The embodiment of the present invention offers significant solutions to these challenges associated with metal moulds in spun pipe manufacturing.OBJECTS OF THE PRESENT DISCLOSURE
[0014] Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as listed herein below.
[0015] It is an object of the present disclosure to provide the repairing and / or maintenance solutions in hot conditions as well as cold conditions for the moulds of Ductile Iron Spun pipe manufacturing process.
[0016] It is an object of the present disclosure to provide a refractory mixture for moulds of DI pipes that is helpful in enhancement of the life of the equipment of the hot Zone.
[0017] It is yet another object of the present disclosure to provide a refractory mixture for the moulds that is helpful in easier removal of slag.
[0018] It is yet another object of the present disclosure to provide a refractory mixture usedin repairing and / or maintenance of the moulds that is recyclable and re-used in repairing and or maintenance operations that further reduce costs.
[0019] It is yet another object to provide disclosure to provide a refractory mixture for repairing the moulds in either hot condition or cold condition by applying the mixture in the form of paste- brushing or spraying or gunning till damaged portion / or surface is completely leveledSUMMARY
[0020] Despite of perfect science of the manufacturing, the geometry to the product such as different size, thickness and Length, product quality, productivity and costing, governs by the Metal Mould.
[0021] The metallic mould is a plain low carbon alloys steel, which is of moderate Hardness, High Yield Strength and Ultimate Tensile Strength ratio & Moderate percentage Elongation, High percentage Reduction of Area and Moderate Combination of Hardness resulting in Fair Machinability, Peening (Stress Relieving), Grinding as well as Repairing.
[0022] The metal Moulds also have a good impact strength. Although the thermal and rotational fatigue varies to a great extent. This Depends on Forming Process of Mould, Cast Microstructure, Inclusion Ratings, Effective Heat treatment, Quality Assurance Planning (QAP) of Mould Preparation, Usages of Mould, Effective Peening (Stress Relieving), Quality Assurance Planning (QAP) of Repairing Moulds, Surface Treatment of Moulds and Corrosion of Moulds.
[0023] These moulds are low carbon Low alloys steel that comprises of Carbon (C)- 0.10% / 0.28%, Silicon (Si)- 0.15% / 0.35%, Manganese (Mn) - 0.20% / 0.75%, Sulphur (S) - 0.001% / 0.020%, Phosphorous (P) - 0.001% / 0.025%, Nickel (Ni) -0.05% / 0.50%, Molybdenum (Mo) - 0.25% / 0.45%, Chromium (Cr) 2.1% / 2.65%, Boron (B) and Vanadium (V) - 0.001% / 0.15%. Further, other Elements - Copper (Cu), Aluminum (Al), Titanium (Ti), Zinc (Zn), Cobalt (Co), Bismuth (Bi), Niobium (Nb), Tin (Sn), Calcium (Ca), Lead (Pb), etc. - Max. 0.80%).
[0024] Moulds are supplied in duly Heat Treated and Stress Relieved conditions, where Mechanical Properties are 1100 < UTS (MPa) > 700, 1000 < YS (MPa) > 650, 28 < Elongation (%) > 10 (on 4 times diameter of gauge length), 65 < REDUCTION OF AREA(RA) (%) > 10, 125 < Izod Impact (Joule) > 45, 301 < Hardness (BHN) > 217.
[0025] The embodiments of the present invention discloses the repairing and / or maintenance of Metal Mould through the application of specific compositional coating. The repairing and / or maintenance requirements of Metal Mould of DI pipes varies according to the size of DI pipe to be manufactured. The coating pertaining to size of pipe is function of compositional mixture, particle size, viscosity of mixture, condition of application, Mould class, RPM of Mould, number of coats, Grades of pipes, Mode of Mixing, Pumps / pumping. The embodiment of the present invention is thus disclosed according to size of DI pipes.
[0026] Further, the repair strategy shifts significantly depending on whether the system is operational or during a shutdown. Hot condition repairing cycle (hereinafter referred as "hot conditions”) are performed to minimize downtime, and in hot condition repairing cycle the refractory mixture is usually applied via spraying or patching. Cold condition repairing cycle (hereinafter referred as "cold conditions”) allow for more thorough surface preparation and thicker layering. Cold condition repairs often involves casting or manual trowelling. Layering isdone progressively, ensuring each layer is sufficiently bonded to the substrate or the previous layer to prevent delamination.
[0027] In an embodiment, the mixture is a composite ceramic paste designed to bond to steel and withstand molten iron temperatures (+1400°C). the Refractory Aggregates comprise of Alumina Castable I Fire Clay that Provides the bulk volume and thermal insulation; Zirconia (ZrOz) that is added for its high refractoriness and non-wetting properties and it prevents the molten iron from sticking to the patch (fusion) and resists the high thermal shock better than silica alone; Magnesia (MgO) enhances resistance to basic slags and increases refractoriness; and the Graphite Powder acts as a solid lubricant and release agent and it ensures that the cast pipe does not stick to the repaired patch when extracted.
[0028] In an embodiment, the preferable composition for the refractory mixture (repair slurry) include aluminous refractory base material like Alumina Castable (35%-65% w / w); Graphite Powder (35%-65% w / w); refractory oxides like Zirconia (15% - 50% w / w), Silica (15%- 50% w / w), Magnesia (25%- 50% w / w); Fire Clay (15%- 45% w / w); Sodium Silicate (Naz SiOs.xHzO) (3%- 8% w / v); Dry ice or CO2 gas. This composition allows for the rapid filling of gouges, cracks, or alligator skin defects on the metal mould without requiring welding (which induces thermal stress). The inclusion of Dry Ice (Solid CO2) or CO2 gas acts as the hardening agent to instantly cure the Sodium Silicate binder. The Sodium Silicate (Naz SiOs.xHzO) is the liquid binder (Water Glass) that hardens when exposed to CO2. In Hot condition Repairing cycles, mixing crushed dry ice directly into the paste or applying it over the patch cools the spot immediately (counteracting the hot mould heat) and further releasing concentrated CO2 gas to trigger an instant, deep cure of the patch.
[0029] The primary advancement this composition enables is in-Situ Repair (repairing the mould while it is still on the machine and hot). In conventionalrepairing method the damaged moulds had to be removed, cooled down, machined, or welded (which causes stress cracks), and then re-peened. This caused massive downtime. In the present embodiments, an operator mixes the Refractory Paste (Alumina / Zirconia / Graphite + Sodium Silicate). The paste is troweled into the gouge / crack on the hot mould. Further, the operator blasts it with CO2 gas or presses Dry Ice against it. The binder sets in seconds, creating a hard ceramic plug. Further, the mould can be used again immediately. The graphite / zirconia ensures the iron slides over the patch without ripping it out.
[0030] In an embodiment, the particle size distribution of the compositional coating mixture comprises fine, medium, and coarse particles. The specific percentage combination of these particle sizes is determined by the size of the DI pipe being repaired. Preferably, a combination of fine and medium-sized particles is used for repairing smaller DI pipes, while coarser grains are employed for larger DI pipes. The preferable particle size in range of- Alumina Castable range is 0.01 to 3.0 mm, for Graphite Powder range is 0.01 to 0.1 mm, for Zirconia range is 0.1 to 1.0 mm, for Silica range is 0.01 to 0.8 mm, for Magnesia range is 0.01 to 0.15 mm, and for Fire Clay range is 0.1 to 0.8 mm.BRIEF DESCRIPTION OF DRAWINGS
[0031] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure.Fig 1 lists different combinations of mixtures for repairing and / or maintenance solutions for moulds based on the DI pipe size.DETAILED DESCRIPTION
[0032] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is 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 spirit and scope of the present disclosure as defined by the disclosure.
[0033] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[0034] If the specification states that a component or feature "may”, "can”, "could” or "might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0035] As used in the description herein and throughout the description that follow, the meaning of "a,” "an,” and "the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in” includes "in” and "on” unless the context clearly dictates otherwise.
[0036] The use of "including” "comprising” or "having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms "a” and "an” herein do not denote a limitation of quantity but rather denote the presence of at least one of the referenced items. Further, the use of terms "first” "second” and "third” and the like, herein does not denote any order, quantity, or importance, but rather are used to distinguish one element from another.
[0037] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member canbe referred individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the description herein.
[0038] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skilled in the art. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[0039] The present disclosure relates to discloses the repairing and / or maintenance of Metal Mould through the application of specific compositional coating. The repairing and / or maintenance requirements of Metal Mould of DI pipes varies according to the size of DI pipe to be manufactured. The coating pertaining to size of pipe is function of compositional mixture, particle size, viscosity of mixture, condition of application, Mould class, RPM of Mould, number of coats, Grades of pipes, Mode of Mixing, Pumps / pumping. The embodiment of the present invention is thus disclosed according to size of DI pipes. Fig 1 lists different combinations of mixtures for repairing and / or maintenance solutions for moulds based on the DI pipe size.
[0040] In an embodiment, the preferable Revolution Per Minute (RPM) of mould for coating ranges between 25% to 70% of RPM used during manufacturing of DI Pipes. Further, the specific RPM range may be adjusted based on the size of the DI pipe being repaired.
[0041] In an embodiment, for repair and maintenance process, the preferred mould temperature ranges from room temperature (RT) to 580°C. The specific working temperature is selected based on the size of the DI pipe being repaired.
[0042] In an embodiment, spraying is the preferred method for applying the coating on pipes up to DN 800. For pipes up to DN 1500, sprinkling is preferred. For larger-sized pipes, a combination of brushing, gunning, and then either spraying or sprinkling is utilized for applying the coating.
[0043] In an embodiment, the repair process utilizes a specified coating based on the class of the mould. The class of moulds are either forged or cast or machined or forged and machined or casted and machined.
[0044] In an embodiment, the specified viscosity, measured or mentioned in seconds, refers to the time required for a standard viscosity cup to empty. This measurement is correlated with the Baume scale to ensure consistency in the coating material's application properties. Viscosity plays an important role in maintaining the quality coating.
[0045] The dimension of DI Pipe is crucial in selecting the coating and its relevant parameters to attribute the repair and maintenance quality.
[0046] METAL MOULD FOR DN 80-150: The DN 80-150 Metal Mould is a specialized, high-performance tooling component used in the centrifugal casting of Ductile Iron (DI) pipes. It serves as the primary shaping vessel, defining the outer diameter and surface finish of the finished pipe. Designed for the Small Diameter production range, these moulds are engineered to withstand extreme cyclical thermal shock and high rotational G-forces. These moulds are forged from high-grade alloy steels designed for Hot Work applications. The most commonstandard is 21CrMolO (or similar Chromium-Molybdenum grades) and typically having 220-260 HB (Brinell Hardness), High yield point (> 600 MPa) to resist deformation at elevated temperatures.
[0047] In one of the embodiment of present invention, the repairing and / or maintenance ofthe DN 80-150 Metal Mouldis preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions. The coating of refractory mixture is either water-based mixture. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w with preferable particle size of 0.01 to 3.0 mm; and Graphite Powder of 35% -65% w / w with preferable particle size of 0.01 to 0.1 mm. The particulate aluminous refractory base material includes Alumina Castable.
[0048] To achieve a high-quality surface finish during the repairing process of the DN 80-150 Metal Mould, an operator utilizes the refractory mixture (Alumina Castable and Graphite powder) maintained at a preferable viscosity in the range of 25-30 seconds, providing a fluid consistency ideal for rapid, uniform application. To ensure the correct solids-to-liquid concentration, the preferable QAP Baurne is kept less than or equal to 50, which prevents the mixture from becoming overly dense and clogging the delivery lines. This mixture is prepared through an automated Metering & Mixing system to ensure chemical homogeneity before being discharged via Metering and Pressure Pumping. The high-pressure delivery allows for a single coating, which is sufficient to fully seal the mould surface when Peening has been utilized to create a textured mechanical bond. This standardized repair protocol is suitable for all grades of pipe, including Ductile Iron, Iron, Steel, and Stainless Steel, ensuring the refurbished mould is ready for immediate return to high-temperature production.
[0049] METAL MOULD FOR DN 200-300: The DN 200-300 Metal Mould is a heavy-duty forged steel die used for casting Ductile Iron pipes primarily for city water mains and primary distribution networks. These moulds are designed tohandle significantly higher thermal loads than the 80-150 range, as the mass of molten metal increases exponentially with the diameter. Due to the thicker pipe wall, the mould stays hot for longer during each cycle. Common alloys used include 21CrMolO or 30CrMoV9. Typically has a surface hardness of about 230-270 HB.
[0050] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 200-300 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions. The coating of refractory mixture is either water-based mixture. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w, with preferable particle size of 0.01 to 3.0 mm; Graphite Powder of 35% -65% w / w, with preferable particle size of 0.01 to 0.1 mm; and fire clay of 15% - 45% w / w, with preferable particle size of 0.1 to 0.8mm. The particulate aluminous refractory base material includes Alumina Castable.
[0051] For DN 200-300 Metal Mould restoration, the repairing process utilizes a medium-bodied refractory slurry maintained at a preferable viscosity in the range of 35-60 seconds. This consistency ensures that the material is thick enough to fill minor surface irregularities while remaining fluid enough for precise application. To maintain the structural integrity of the suspension, the preferable QAP Baume is controlled to be less than or equal to 70, striking an ideal balance between solids concentration and flowability. The mixture is prepared using a synchronized Metering & Mixing mode to ensure exact ratios of the refractory oxides and binders, followed by delivery through Metering and Pressure Pumping. This pumping system provides the constant force required to apply preferably one coating, which effectively seals the mould's interior. The process is specifically designed to bond with surfaces where Peening has been performed, as the dimpled texture provides the mechanical anchorage needed to preventthe coating from peeling under high thermal stress. This refurbishment protocol is suitablefor various grades of pipe, including Ductile Iron, Iron, Steel, and Stainless Steel, ensuringthe metal mould is protected against the intense heat ofthe casting cycle.
[0052] METAL MOULD FOR DN 350-450: The DN 350-450 Metal Mould is a high-strength, forged alloy steel tube used to manufacture large-scale transmission pipes for trunk water lines and industrial cooling systems. Due to the significant volume of molten iron required for these diameters, these moulds feature specialized cooling geometries and advanced metallurgy to resist sagging or permanent warping during the casting cycle. Unlike smaller moulds, the DN 350-450 range often utilizes high-molybdenum and vanadium-enhanced steels like 30CrMoV9 or 21CrMoV10. Typically has a surface hardness of about 240-280 HB.
[0053] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 350-450 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions. The coating of refractory mixture is either water-based mixture. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w, with the preferable particle size of 0.01 to 3.0 mm; Graphite Powder of 35% -65% w / w with the preferable particle size of 0.01 to 0.1 mm; and refractory oxides like Zirconia of 15%-50% w / w with preferable particle size of 0.1 to 1mm, or Silica of 15%- 50% w / w with preferable particle size of 0.01 to 0.8mm. The particulate aluminous refractory base material includes Alumina Castable.
[0054] To achieve a durable and heat-resistant internal surface during the repairing process DN 350-450 Metal Mould, the operator utilizes a high-performance refractory slurry maintained at a preferable viscosity in the range of 45-70 seconds. This heavy-medium consistency is specifically designed to provide a thick, protective barrier that can withstand the extreme thermal loads of larger casting cycles. To ensure the chemical density and solid content areoptimized for maximum insulation, the preferable QAP Baume is maintained at less than or equal to 75, preventing the mixture from becoming too diluted to be effective. The preparation involves a dedicated Metering & Mixing mode to ensure the binders and refractory oxides are perfectly homogenized before being discharged through Metering and Pressure Pumping. This delivery method provides the hydraulic force required to atomize the viscous mixture into a uniform, single coating. This single-pass application is engineered to bond with mould surfaces where Peening has been performed, utilizing the induced surface roughness to mechanically lock the ceramic layer in place. This refurbishment standard is suitable for all grades of pipe, including Ductile Iron, Iron, Steel, and Stainless Steel, ensuring the metal mould remains dimensionally stable and protected against the intense heat of molten metal.
[0055] Metal Mould for DN 500-750: The DN 500-750 Metal Mould is a massive, forged alloy steel component designed for high-tonnage centrifugal casting. Due to the enormous volume of molten metal involved, these moulds are engineered with a specific focus on structural rigidity and high-capacity thermal dissipation. A single pipe in this range can weigh several tons, requiring the mould to maintain its dimensional accuracy while under extreme centrifugal load and thermal expansion. Typically to preventthe mould from sagging or becoming ovalshaped under its own 40-ton weight at high temperatures, premium alloys such as 30CrMoV9 or custom Cr-Mo-V modified steels are used, achieving surface hardness of 250-290 HB.
[0056] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 500-750 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions. The coating of refractory mixture is either water-based mixture. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w, with the preferable particle size of 0.01 to 3.0 mm; GraphitePowder of 35% -65% w / w, with the preferable particle size of 0.01 to 0.1 mm; and refractory oxides like Zirconia of 15%-50% w / w, with preferable particle size of 0.1 to 1mm, or Silica of 15%- 50% w / w, with preferable particle size of 0.01 to 0.8mm. The particulate aluminous refractory base material includes Alumina Castable.
[0057] For the advanced refurbishment of DN 500-750 metal moulds, the repairing process utilizes a high-density refractory mixture maintained at a preferable viscosity in the range of 60-80 seconds, ensuring a thick, resilient consistency. To guarantee the chemical concentration and density of the suspension, the preferable QAP Baume is kept less than or equal to 90. This mixture is prepared through a precise Mode of Mixing, Metering & Dosing, which allows for exact control over the binder-to-refractory ratio before being delivered by a Metering, Plunger, or Dosing pump. The system is engineered to apply one or two coatings onto mould surfaces where Peening has been performed to provide the necessary mechanical key for the ceramic bond. This robust repair method is suitable for various grades of pipe, including Ductile Iron, Iron, Steel, and Stainless Steel, providing a high-performance thermal barrier for even the most demanding casting environments.
[0058] METAL MOULD FOR DN 800-1200: The DN 800-1200 Metal Mould is an elite-class industrial die, often custom-engineered for specific high-capacity infrastructure projects. Operating these moulds requires sophisticated machinery capable of spinning up to 60 tons of weight (mould + iron) with extreme precision. The primary challenge at this diameter is thermal expansion control and ensuring the mould maintains a perfectly cylindrical shape under its own massive weight while heated to extreme temperatures. Typically to withstand the immense hoop stress (outward pressure) of the spinning metal and the weight of the mould itself, manufacturers use premium Chrome-Moly-Vanadium (CrMoV) alloys like21CrMoV10 or high-tensile variants, wherein the mould undergoes specialized heat treatment to ensure the hardness (260-300 HB)
[0059] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 800-1200 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions and cold conditions. The coating of refractory mixture is either water-based mixture for hot conditions or alcohol-based mixture in cold conditions. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w, with the preferable particle size of 0.01 to 3.0 mm; Graphite Powder of 35% -65% w / w, with the preferable particle size of 0.01 to 0.1 mm; and refractory oxides like Zirconia of 15%-50% w / w, with preferable particle size of 0.1 to 1mm, or Silica of 15%- 50% w / w with preferable particle size of 0.01 to 0.8mm, or Magnesia of 25%- 50% w / w, with preferable particle size of 0.01 to 0.15mm. The particulate aluminous refractory base material includes Alumina Castable.
[0060] For the most rigorous mould (DN 800-1200 Metal Mould) restoration requirements, the repairing process utilizes an ultra-high-density refractory slurry maintained at a preferable viscosity in the range of 70-120 seconds. This thick, paste-like consistency is engineered to fill deep structural voids and significant fire-cracking in the metal surface. To ensure the chemical concentration remains potent enough for maximum thermal insulation, the preferable QAP Baume is maintained at less than or equal to 100. This extremely high solids content provides a robust shield against the intense heat of larger casting cycles. The preparation of this heavy-duty mixture requires a specialized Mixing, Metering, and Dosing protocol to ensure the binders and heavy refractory powders are perfectly homogenized. Due to the high resistance ofthe 120-second viscosity fluid, it is delivered via a Metering, Plunger, or Dosing pump, which provides the mechanical muscle needed to move the material through the spraylance. The system is designed to apply one to three coatings, allowing for a layered build-up that effectively resurfaces the mould. This repair standard is essential for mould surfaces where Peening has been performed to provide the deep mechanical anchorage required to hold multiple ceramic layers. This heavyrefurbishment protocol is specifically suitable for grades of pipe such as Ductile Iron and Iron, where high-mass pours demand the most resilient thermal barriers available.
[0061] METAL MOULD FOR DN 1200-2500: The DN 1200-2500 Metal Mould is a colossal engineering marvel designed to cast pipes that can exceed 8 feet in diameter. The primary challenge at this scale is the management of massive inertial forces and thermal expansion. A mould of this size can weigh as much as a small locomotive, and when filled with molten iron, the total rotating mass requires specialized heavy-duty casting machines with high-torque drive systems and advanced vibration dampening. Typically to handle the centrifugal "hoop stress" and the weight of nearly 10-15 tons of molten iron per pipe, these moulds utilize premium CrMoV (Chromium-Molybdenum-Vanadium) steels with deephardening heat treatments acquiring surface hardness of 280-320 HB.
[0062] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 1200-2500 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions and cold conditions. The coating of refractory mixture is either water-based mixture for hot conditions or alcohol-based mixture in cold conditions. The composition of the refractory mixture comprises Graphite Powder of 35% -65% w / w, with preferable particle size of 0.01 to 0.1 mm; and refractory oxides like Zirconia of 15%-50% w / w, with preferable particle size of 0.1 to 1mm, and / or Silica of 15%-50% w / w, with preferable particle size of 0.01 to 0.8mm.
[0063] For critical surface restoration (DN 1200-2500) in high-mass casting environments, the repairing process utilizes an ultra-viscous refractory pastemaintained at a preferable viscosity in the range of 90-200 seconds. This heavybuild consistency is specifically designed to fill significant surface voids and deep structural irregularities that thinner mixtures cannot bridge. To ensure maximum thermal shielding and material density the preferable QAP Baume is controlled at less than or equal to 100, indicating a highly concentrated suspension of refractory solids. Given the extreme thickness of the 200 -second viscosity mixture, the preferable mode of mixing involves specialized Mixing, Metering, and Dosing to ensure the heavy powders are fully wetted and the binders are evenly distributed. Delivery is handled by Metering, Plunged, or Dosing pumps, which provide the high-torque hydraulic force required to move this dense material through the system without clogging. This protocol specifies a preferable number of two to four coatings, allowing for a layered build-up technique that creates a thick, resilient ceramic wall. Unlike other methods, this specific application requires no Peening, as the multi-coat thickness and chemical bonding agents are designed to adhere to the base metal without the need for mechanical dimpling. This robust refurbishment standard is suitable for grades of pipe including Ductile Iron, Iron, and Steel, providing an elite-level barrier for the most demanding large-diameter casting operations.
[0064] Metal Mould for DN 2500-5500: The DN 2500-5500 Metal Mould is a specialized ultra-heavy die used to cast the world’s largest ductile iron pipes. The engineering challenges at this scale are dominated by rotational inertia and gravitational deflection. Typically, to prevent the mould from deforming under its own astronomical weight, these moulds utilize specialized Ni-Cr-Mo-V (Nickel-Chrome-Moly-Vanadium) high-tensile steels, acquiring surface hardness of 300-350 HB.
[0065] In one of the embodiment of present invention, the repairing and / or maintenance of the DN 2500-5500 Metal Mould is preferably accomplished by layered coating of refractory mixture (repair slurry) in hot conditions and coldconditions. The coating of refractory mixture is either water-based mixture for hot conditions or alcohol-based mixture in cold conditions. The composition of the refractory mixture comprises a particulate aluminous refractory base material of 35% -65% w / w, with the preferable particle size of 0.01 to 3.0 mm; Graphite Powder of 35% -65% w / w, with the preferable particle size of 0.01 to 0.1 mm; and refractory oxides like Zirconia of 15%-50% w / w, with preferable particle size of 0.1 to 1mm, Silica of 15%- 50% w / w with preferable particle size of 0.01 to 0.8mm, Magnesia of 25%- 50% w / w, with preferable particle size of 0.01 to 0.15mm; fire clay of 15% - 45% w / w, with preferable particle size of 0.1 to 0.8mm; and / or Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v; Dry ice or CO2 gas The particulate aluminous refractory base material includes Alumina Castable.
[0066] For the most intensive structural restoration of large-scale casting dies (DN 2500-5500 Metal Mould), the repairing process utilizes an ultra-high-density refractory paste. This mixture is maintained at a preferable viscosity in the range of 120-200 seconds, creating a thick, gap-filling consistency designed to rebuild significant surface loss and deep fire-cracks. To ensure the chemical concentration provides maximum thermal shielding, the preferable QAP Baume is controlled at less than or equal to 100, ensuring a high solids-to-liquid ratio. Due to the extreme density of this heavy-build suspension, the preferable mode of mixing involves specialized Mixing, Metering, and Dosing to achieve a perfectly homogenized slurry. This viscous material is delivered via Metering, Plunger, or Dosing pumps, which generate the high hydraulic pressure required to atomize and move heavybodied fluids through the spray lance. The protocol calls for a preferable number of three to six coatings , allowing for a precision multi-layered application that builds a durable, thick ceramic wall. In this specific heavy-refurbishment cycle, no Peening is specified, as the significant thickness of the multi-coat application and specialized chemical binders are designed to provide structural integrity without the need for fresh mechanical dimpling. This elite standard is suitable for gradesof pipe including Ductile Iron and Iron, providing the ultimate thermal defense against the prolonged heat exposure characteristic of massive, large -diameter molten metal pours.
[0067] In an alternative embodiment, the disclosed method for repairing and maintaining moulds for DI pipes may also be applied to the manufacturing, repair, or maintenance of moulds for shorter length of ferrous and non-ferrous mother hollow pipes, stainless steel pipes, heat-resistant steel pipes, and duplex or super duplex stainless-steel pipes of various similar sizes.
[0068] The embodiments of the invention are prone to numerous modifications and variations, all of which are within the scope of the same inventive concept. Further, the material, composition, and devices used may of course be replaced / altered with other technically equivalent ones; the steps may furthermore be performed in a different sequence.
Claims
CLAIMS:I / We claim:
1. A refractory mixture for repairing and / or maintenance Metal Mould of distinct sizes of Ductile Iron Spun pipe, such refractory mixture comprising:particulate aluminous refractory base material of 35%-65%w / w; Graphite Powder of 35% -65% w / w; andfire clay 0% - 45% w / w.
2. The refractory mixture as claimed in claim 1 is water-based mixture.
3. The refractory mixture as claimed in claim 1 can be applied in hot condition repairing cycle.
4. The refractory mixture as claimed in claim 1 wherein the aluminous refractory base material is Alumina Castable.
5. The refractory mixture as claimed in claim 1 wherein particle size of aluminous refractory base material is 0.01 to 3.0 mm.
6. The refractory mixture as claimed in claim 1 wherein particle size of Graphite Powder is 0.01 to 0.1 mm.
7. The refractory mixture as claimed in claim 1 wherein particle size of fireclay is 0.01-0.80 mm.
8. The refractory mixture as claimed in claim 1 wherein the metal mould of distinct sizes including metal mould for DN 80-150; metal mould for DN 200-300.
9. The refractory mixture as claimed in claim 8, wherein for repairing and / or maintenance of metal mould for DN 80-150, the refractory mixture includes particulate Alumina Castable of 35%-65%w / w; Graphite Powder of 35%-65% w / w.
10. The refractory mixture as claimed in claim 8, wherein for repairing and / or maintenance of metal mould for DN 200-300, the refractory mixture includes particulate Alumina Castable of 35% -65% w / w; Graphite Powder of 35% -65% w / w; and fire clay of 15% - 45% w / w.
11. A refractory mixture for repairing and / or maintenance Metal Mould of distinct sizes of Ductile Iron Spun pipe, such refractory mixture comprising:particulate aluminous refractory base material of 15% -85% w / w; Graphite Powder of 35% -65% w / w; andrefractory oxides of 15%-50% w / w.
12. The refractory mixture as claimed in claim 1 wherein particle size of aluminous refractory base material is 0.01 to 3.0 mm.
13. The refractory mixture as claimed in claim 11 wherein the aluminous refractory base material is Alumina based Cement (ABC).
14. The refractory mixture as claimed in claim 1 wherein particle size of Graphite Powder is 0.01 to 0.1 mm.
15. The refractory mixture as claimed in claim 11 wherein the refractory oxide include Zirconia of 15%-50% w / w, with particle size of 0.1 to 1mm.
16. The refractory mixture as claimed in claim 11 wherein the refractory oxide include Silica of 15%-50% w / w, with particle size of 0.01 to 0.8mm.
17. The refractory mixture as claimed in claim 11 wherein the refractory oxide include Magnesia of 25%-50% w / w, with particle size of 0.01-0.15mm.
18. The refractory mixture as claimed in claim 11 is water-based mixture.
19. The refractory mixture as claimed in claim 11 is alcohol-based mixture.
20. The refractory mixture as claimed in claim 11 can be applied in hot condition repairing cycle and cold condition repairing cycle.
21. The refractory mixture as claimed in claim 11 wherein the metal mould of distinct sizes including metal mould for DN 350-450; metal mould for DN 500-750; metal mould for DN 800-1200.
22. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 350-450, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Zirconia of 15%-50% w / w.
23. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 350-450, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Silica of 15%- 50% w / w.
24. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 500-750, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Zirconia of 15%-50% w / w.
25. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 500-750, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Silica of 15%- 50% w / w.
26. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of DN 800-1200, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Zirconia of 15%-50% w / w.
27. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 800-1200, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Silica of 15%- 50% w / w.
28. The refractory mixture as claimed in claim 21 wherein for repairing and / or maintenance of metal mould for DN 800-1200, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; and Magnesia of 25%- 50% w / w.
29. A refractory mixture for repairing and / or maintenance Metal Mould of distinct sizes of Ductile Iron Spun pipe, such refractory mixture comprisingGraphite Powder of 35% -65% w / w; andrefractory oxides of 15%-50% w / w30. The refractory mixture as claimed in claim 29 wherein particle size of Graphite Powder is 0.01 to 0.1 mm.
31. The refractory mixture as claimed in claim 29 wherein the refractory oxide include Zirconia of 15%-50% w / w, with particle size of 0.1 to 1mm.
32. The refractory mixture as claimed in claim 29 wherein the refractory oxide include Silica of 15%-50% w / w, with particle size of 0.01 to 0.8mm.
33. The refractory mixture as claimed in claim 29 is water-based mixture.
34. The refractory mixture as claimed in claim 29 is alcohol-based mixture.
35. The refractory mixture as claimed in claim 29 can be applied in hot condition repairing cycle and cold condition repairing cycle.
36. The refractory mixture as claimed in claim 29 wherein the metal mould of distinct sizes including metal mould for DN1200-2500.
37. The refractory mixture as claimed in claim 36 wherein for repairing and / or maintenance of DN1200-2500, the refractory mixture includes Graphite Powder of 35% -65% w / w; and Zirconia of 15%-50% w / w.
38. The refractory mixture as claimed in claim 36 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Graphite Powder of 35% -65% w / w; and Silica of 15%- 50% w / w.
39. The refractory mixture as claimed in claim 36 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Graphite Powder of 35% -65% w / w; Zirconia of 15%- 50% w / w; and Silica of 15%- 50% w / w.
40. A refractory mixture for repairing and / or maintenance Metal Mould of distinct sizes of Ductile Iron Spun pipe, such refractory mixture comprisingParticulate aluminous refractory base material of 35% -65% w / w; Graphite Powder of 5% -65% w / w;refractory oxide of 15%-50% w / w;bonding agent of 3% - 45% w / w; andcuring reactant.
41. The refractory mixture as claimed in claim 40 wherein particle size of aluminous refractory base material is 0.01 to 3.0 mm.
42. The refractory mixture as claimed in claim 40 wherein the aluminous refractory base material is Alumina Castable.
43. The refractory mixture as claimed in claim 40 wherein particle size of Graphite Powder is 0.01 to 0.1 mm.
44. The refractory mixture as claimed in claim 40 wherein the refractory oxide include Zirconia of 15%-50% w / w, with particle size of 0.1 to 1mm.
45. The refractory mixture as claimed in claim 40 wherein the refractory oxide include Silica of 15%-50% w / w, with particle size of 0.01 to 0.8mm.
46. The refractory mixture as claimed in claim 40 wherein the refractory oxide include Magnesia of 25%-50% w / w, with particle size of 0.01-0.15mm.
47. The refractory mixture as claimed in claim 40 wherein the bonding agent include fire clay of 15% - 45% w / w, with particle size of 0.1-0.8mm.
48. The refractory mixture as claimed in claim 40 wherein the bonding agent include Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v.
49. The refractory mixture as claimed in claim 40 wherein the curing reactant is dry ice.
50. The refractory mixture as claimed in claim 40 wherein the curing reactant is carbon dioxide gas.
51. The refractory mixture as claimed in claim 40 is water-based mixture.
52. The refractory mixture as claimed in claim 40 is alcohol-based mixture.
53. The refractory mixture as claimed in claim 40 can be applied in hot condition repairing cycle and cold condition repairing cycle.
54. The refractory mixture as claimed in claim 37 wherein the metal mould of distinct sizes including metal mould for DN 2500-5500.
55. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; fire clay of 15% - 45% w / w; and Dry ice.
56. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; fire clay of 15% - 45% w / w; and carbon dioxide gas.
57. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v; and Dry ice.
58. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v; and carbon dioxide gas.
59. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; fire clay of 15% - 45% w / w; Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v; and Dry ice.
60. The refractory mixture as claimed in claim 49 wherein for repairing and / or maintenance of metal mould for DN1200-2500, the refractory mixture includes Alumina Castable of 35% -65% w / w ; Graphite Powder of 35% -65% w / w; Zirconia of 15%-50% w / w; Silica of 15%- 50% w / w; Magnesia of 25%- 50% w / w; fire clay of 15% - 45% w / w; Sodium Silicate (Naz SiOs.xHzO] of 3%- 8% w / v; and carbon dioxide gas.