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Customized
NHD
High-purity graphite crucibles with a central bore are industrial high-temperature smelting vessels made from high-density, high-purity graphite. They are formed through CNC machining in a single piece and feature a through-hole in the bottom for flow control. Unlike standard graphite crucibles without such a bore, the center hole enables the fulfillment of special operational requirements such as molten metal flow control, venting for pressure relief, and continuous casting and discharge. It serves as a core consumable in continuous smelting, precious metal purification, and molten metal diversion processes. The base material is high-purity, dense graphite, which inherently possesses high-temperature resistance, chemical stability, self-lubrication, and high thermal conductivity. After forming, the crucible features a precision-machined, integrated central bore with smooth, burr-free walls that prevent metal slag from adhering, eliminating issues such as bore blockage or liquid leakage.
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Jiangxi Ningheda New Material, a wholly-owned subsidiary of Jiangxi Ningxin New Materials Co., Ltd., was established in 2017. Equipped with a complete set of proprietary CNC machining equipment, the company can customize the center hole diameter, depth, crucible outer diameter, wall thickness, and overall height according to customer operating conditions. It supports both small-batch trial orders and large-volume long-term supply, complemented by comprehensive factory testing, packaging and logistics, and after-sales technical services.
The crucible body is made from high-purity isostatic graphite. After undergoing multidirectional isostatic pressing, high-temperature sintering, and graphitization, it is precision-machined on CNC machining centers. The isostatic pressing process eliminates internal defects and density inconsistencies commonly found in extrusion and compression molding, enabling the crucible to achieve industry-leading performance in mechanical strength, thermal conductivity uniformity, and thermal stability.
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Structural Components | Design Features | Feature Benefits |
Cylindrical crucible | Straight or slightly tapered design, with a smooth inner wall | Maximizes internal volume, minimizes metal residue, and makes cleaning easier |
Tapered neck | 45°–60° taper transition | Guide the molten metal flow toward the center to reduce oxidation and spatter |
Center-Aligned Nozzle | Inner diameter tolerance: ±0.1 mm; available in single-hole or multi-hole configurations | Precise alignment with the casting machine’s nozzle, ensuring stable and controllable flow |
Flat Bottom/Rounded Bottom | Customized for Each Furnace Type | Fits snugly against the induction coil or heating chamber, ensuring high heat transfer efficiency |
Socket Reinforcement Ring | Optional reinforced flange | Enhance the mechanical strength of the pot mouth to prevent chipping during gripping |
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Material Performance Specifications
Performance Metrics | Value | Unit |
Bulk Density | ≥ 1.78 | g/cm³ |
Maximum grain size | 15-25 | μm |
Ash Content | ≤ 600 | ppm |
Resistivity | 10 ~ 13 | μΩ·m |
Flexural Strength | ≥ 35 | MPa |
Compressive Strength | ≥ 70 | MPa |
Shore Hardness | 50 ~ 60 | HSD |
Maximum Operating Temperature | 1700 | ℃ |
Thermal Shock Resistance | Excellent | — |
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Range of Customizable Specifications
Parameters | Scope of Customization |
Outer Diameter of the Crucible | Φ30mm ~ Φ300mm |
Total Height of the Crucible Body | 50mm ~ 400mm |
Center Aperture | Φ3 mm to Φ30 mm (can be customized based on flow requirements) |
Wall Thickness | 5mm ~ 30mm |
Material Grade | NX603/NX604/NX605/NX614/NX615 |
Why Is the Center-Hole Design Critical?
In vacuum pressure casting and centrifugal casting processes, the method of pouring molten metal directly determines the yield of castings. Traditional open-top crucibles require manual or robotic pouring, which can easily lead to the following issues:
Metal Oxidation: Extensive contact with air leads to the formation of oxide scale
Temperature Loss: Long pouring paths result in significant temperature drop of the molten metal
Splatter contamination: Impact on the mold or runner causes cold shuts and porosity
Operational hazards: Risk of high-temperature molten metal spillage
Ningheda’s center-hole crucible enables “point-to-point” pouring through a precision nozzle at the top. The molten metal is injected directly into the mold gate via the center hole, with the entire process conducted under vacuum or a protective atmosphere. This significantly reduces oxidation and temperature drop, increasing the yield by 15% to 25%.
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Comparison Items | Isostatic Graphite (This Product) | Standard Molded Graphite |
Forming Methods | Multidirectional Isostatic Pressing (Isotropic) | Unidirectional Molding (Anisotropic) |
Bulk Density | ≥1.78 g/cm³ | 1.60~1.75 g/cm³ |
Mechanical Strength | High, uniform in all directions | Higher vertically, lower horizontally |
Thermal Shock Resistance | Excellent; does not crack when subjected to rapid cooling or heating | Generally, it is prone to cracking horizontally. |
Service Life | Long (suitable for precision casting) | Short (suitable for rough smelting) |
Machining Accuracy | Up to ±0.1 mm | ±0.2mm |
Applicable Scenarios | Jewelry Casting, Non-Ferrous Metal Casting, Laboratory | Rough copper smelting, large-scale smelting |
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Precision Casting of Non-Ferrous Metals
In small-batch precision casting of copper alloys (brass, bronze), aluminum alloys, and zinc alloys, center-hole crucibles, when used in conjunction with automated casting systems, enable metered pouring, reduce oxidation and slag inclusion, and improve metal yield.
Laboratories and Research Institutions
Used in metallurgical laboratories for alloy formulation research and development and sample preparation. The precision center hole ensures consistency in the melt volume for each sample, and when used in conjunction with analytical instruments, guarantees the reproducibility of experimental data.
Precision Casting for Jewelry
Used for vacuum-pressure casting of precious metal alloys such as gold, karat gold, platinum, and palladium. The center-hole design is perfectly matched to vacuum casting machines, ensuring precise mold filling of molten metal under inert gas protection. This results in high surface finish on castings and significantly reduces post-casting polishing time.
To maximize the service life of graphite casting crucibles with a center hole, please follow these operating procedures:
1. Pre-use Baking: Place the crucible in a dry environment and slowly heat it to 200°C at a heating rate of ≤100°C/h. Hold at this temperature for 2 hours to remove adsorbed moisture. Never place the crucible directly into a high-temperature furnace; sudden heating may cause the crucible to crack.
2. Loading Guidelines: Do not exceed 80% of the crucible’s internal volume when loading. Leave gaps between metal ingots to prevent them from pressing against the crucible walls during thermal expansion. Never force cold metal ingots directly into a preheated crucible.
3. Temperature Control: Avoid direct exposure of the crucible walls and nozzle area to strongly oxidizing flames. Use in a vacuum or inert atmosphere (nitrogen/argon) to significantly extend service life.
4. Material Removal: After melting and casting are complete, allow the crucible to cool naturally to below 300°C before removal. For continuous operation, a dual-crucible rotation system is recommended. Use a soft graphite rod to clean out residues; do not scrape the inner surface with metal tools.
5. Storage Conditions: Store in a well-ventilated, dry environment with a relative humidity of ≤60%. For long-term storage, apply a thin layer of graphite powder to the surface to prevent moisture absorption.
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Q1: Can the diameter and angle of the center hole be customized?
A: Absolutely. Center hole diameters range from Φ3 mm to Φ30 mm, and we can machine tapered, straight, or stepped holes. We can also design double-center holes, eccentric holes, or multi-hole structures based on your metal flow requirements.
Q2: Aside from graphite crucibles with center holes, what other graphite products can be customized?
A: We support customization of the full range of graphite products, covering four major manufacturing processes: graphite crucibles with center holes, graphite ingot molds, graphite heating elements, graphite sealing rings, graphite sleeves, graphite rods, EDM graphite electrodes, sintered graphite arks, high-purity graphite blocks, and various custom-shaped graphite molds with or without holes. We can produce these according to customer drawings.
Q3: How can we establish a long-term, stable supply partnership with your company?
A: 1. Direct supply from the source factory ensures strict quality control and competitive factory-direct pricing, guaranteeing mutual benefit for both parties;
2. 24-hour rapid response to inquiries, with a dedicated account manager providing one-on-one support throughout the entire order process;
3. We provide free technical support for application compatibility, optimize crucible selection, and help reduce customers’ consumable costs. Friendly Reminder: When requesting a quote, please include precise dimensional drawings, required graphite purity parameters, and center-hole process requirements so we can provide an accurate quote and the optimal manufacturing solution.
Q4: What are the key precautions for the daily use of graphite crucibles with center holes?
A: Four core operating guidelines to protect the center hole structure and extend service life: ① Before using a new crucible, slowly bake it to 500°C to dry it out, and store it in a dry environment; ② Allow space for thermal expansion when loading material; do not fill the crucible to capacity or compress the material; ③ Handle the crucible gently during pouring and transfer to avoid strong impacts on the center hole walls; ④ Do not direct a strong oxidizing flame at the side walls or the center hole opening to minimize oxidation loss.
Q5: How can I prevent the center hole from clogging during casting?
A: First, ensure thorough preheating and that the molten metal temperature meets process requirements; second, prevent debris from falling into the nozzle during charging; we can also optimize the nozzle’s cone angle and inner wall finish to improve flow. If clogging occurs, our engineers can assist in analyzing the cause.
Q6: What should I do if the dimensions of the received product do not match specifications?
A: We conduct 100% dimensional inspection before shipment. If dimensional deviations are caused by our fault, we promise to provide a free replacement or refund and cover the shipping costs.
Q7: Can you provide samples? Who pays for shipping?
A: Yes. We typically provide samples of standard sizes free of charge (but you are responsible for international express shipping costs). For special, oversized samples, we only charge the basic material cost.
+86-795-4605783 
sales@nhdcarbon.com 
No. 966 of Tiangong South Avenue, High-tech Industrial Park, Fengxin County, Yichun City, Jiangxi Province, China.