A method for manufacturing a graphite mandrel

Abstract

The application discloses a preparation method of a graphite core rod and belongs to the technical field of vacuum induction furnace accessory preparation. The method comprises the following steps: 1) intercepting a graphite electrode as a processing raw material of the graphite core rod; 2) precisely processing the graphite electrode; and 3) performing surface coating treatment on the machined graphite core rod semi-finished product, coating a SiC transition layer and a PyC protective layer in sequence, and ensuring that the coating and the core rod body are tightly combined, free of bubbles and peeling; after the coating is completed, the coating is naturally air-dried to obtain a graphite core rod finished product. The application aims to provide a preparation method of a graphite core rod, and high-purity, high-thermal-shock-resistance, high-precision and long-service-life graphite core rods are prepared by optimizing raw material selection, forming processes and quality control, the service life of the core rod is prolonged, and the laboratory use cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of vacuum induction furnace component preparation technology, and particularly relates to a method for preparing a graphite core rod. Background Technology

[0002] Vacuum induction furnaces are commonly used metal smelting equipment in laboratories, and their accompanying graphite core rods play a crucial role in supporting the crucible and controlling the thermal field. Primarily used for the sintering of crucibles in vacuum induction furnaces, the graphite core rod is placed inside a newly made crucible, and the power of the furnace is adjusted to allow the graphite core rod to heat up slowly. This ensures that the fused magnesia in the crucible is fully sintered and bonded together, forming a robust crucible wall. Therefore, the performance of the graphite core rod directly determines the service life of newly made crucibles in vacuum induction furnaces.

[0003] The graphite core rods currently used in the laboratory are made of ordinary graphite, which suffers from insufficient purity, structural defects, and dimensional deviations. During use, these core rods are prone to thermal shock cracking, oxidation ablation, and even breakage. Furthermore, graphite core rods have a short lifespan and high operating costs, making it difficult to meet the core requirements of vacuum induction furnaces for high purity, high thermal shock resistance, high precision, and long lifespan. Therefore, it is necessary to develop a targeted, process-controllable, and stable graphite core rod for vacuum induction furnaces. Summary of the Invention

[0004] To overcome the shortcomings of existing graphite core rods, such as insufficient purity, structural defects, dimensional deviations, and susceptibility to thermal shock cracking, oxidation ablation, and even breakage during use, as well as their short service life and high operating costs, the present invention aims to provide a method for preparing graphite core rods. By optimizing raw material selection, molding process, and quality control, this method enables the preparation of high-purity, highly thermally shock resistant, high-precision, and long-life graphite core rods, thereby extending their service life and reducing laboratory operating costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] The present invention discloses a method for preparing a graphite core rod, comprising:

[0007] 1) Cut a section of graphite electrode to be used as raw material for processing graphite core rods;

[0008] 2) Precision machining of the graphite electrode using CNC lathes and grinders, including: end face flattening, outer diameter fine grinding, and corner rounding; wherein, after outer diameter fine grinding, the surface roughness Ra≤0.8μm, and the tolerance of diameter and length is controlled within ±0.05-0.1mm; all edges and corners of the mandrel are machined into transition fillets of R0.5-2mm; a hole is opened at a certain distance from the top to facilitate hoisting of the mandrel;

[0009] 3) Surface coating treatment

[0010] The semi-finished graphite mandrel after machining is coated with a SiC transition layer and a PyC protective layer in sequence to ensure that the coating is tightly bonded to the mandrel body, without bubbles or peeling; after the coating is completed, it is naturally air-dried to obtain the finished graphite mandrel.

[0011] Furthermore, graphite electrodes replaced by steel mills are used to prepare core rods, thus making use of waste materials.

[0012] Furthermore, in step 2), after processing is completed, the surface of the core rod is cleaned with a graphite cleaner to remove processing debris and obtain a graphite core rod semi-finished product.

[0013] Furthermore, graphite electrodes with a diameter greater than 300 mm were selected and cut to a length of 600 mm as raw materials for subsequent processing.

[0014] Furthermore, the rough sample was machined using a CNC lathe and grinding machine. After precision grinding of the outer diameter, the surface roughness Ra=0.6μm, and the diameter and length tolerances were ±0.08mm. The edges of the upper and lower bottom surfaces were machined into R1mm transition fillets. A hole with a diameter of 16mm was drilled 90mm from the top to facilitate the hoisting of the mandrel. After machining, a cone-shaped graphite mandrel with an upper bottom diameter of 240mm, a lower bottom diameter of 220mm, and a height of 520mm was obtained.

[0015] Furthermore, a SiC transition layer with a thickness of 80 μm was coated on the surface of the processed graphite core rod using chemical vapor deposition.

[0016] Furthermore, a PyC protective layer was coated using chemical vapor infiltration, with a coating thickness of 40 μm.

[0017] Furthermore, the coating process is protected with high-purity argon throughout.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] The graphite core rods prepared using this invention have high dimensional accuracy, excellent thermal shock resistance, and long service life. Through precision machining of rounded corners and coating protection, the risks of stress concentration, oxidation ablation, and fracture during the installation and use of the graphite core rods are reduced, effectively lowering the cost of laboratory use. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 External dimensions of the graphite core rod of this invention. Detailed Implementation

[0022] The following is in conjunction with the appendix Figure 1The preparation method of graphite core rod for 100kg vacuum induction furnace is further described in detail.

[0023] A method for preparing a graphite core rod for a 100kg vacuum induction furnace, specifically including:

[0024] 1. Select graphite electrodes with a diameter greater than 300mm and cut them to a length of 600mm as raw materials for subsequent processing.

[0025] 2. The rough sample was machined using a CNC lathe and grinding machine. After precision grinding of the outer diameter, the surface roughness Ra=0.6μm, and the diameter and length tolerances were ±0.08mm. The edges of the upper and lower bottom surfaces were machined into R1mm transition fillets. A 16mm diameter hole was drilled 90mm from the top to facilitate the hoisting of the mandrel. After machining, a cone-shaped graphite mandrel with an upper diameter of 240mm, a lower diameter of 220mm, and a height of 520mm was obtained. After machining, the surface was cleaned with a special graphite cleaner to remove machining debris without damaging the graphite fiber structure.

[0026] 3. A SiC transition layer with a thickness of 80 μm is coated on the surface of the processed graphite core rod using chemical vapor deposition; then a PyC protective layer with a thickness of 40 μm is coated using chemical vapor infiltration; high-purity argon is used for protection throughout the coating process, and the coating is allowed to air dry naturally to obtain the finished graphite core rod.

[0027] Feedback from laboratory use indicates that the graphite core rods prepared according to this invention are used for sintering fused magnesia crucibles. The crucibles are heated evenly, and the fused magnesia is fully bonded together to form a strong crucible wall. One graphite core rod can be used more than 20 times, while the previous ordinary graphite core rods can only be used a maximum of 10 times. The service life is doubled, reducing the cost of laboratory use.

[0028] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a graphite core rod, characterized in that, include: 1) Cut a section of graphite electrode to be used as raw material for processing graphite core rods; 2) Precision machining of the graphite electrode using CNC lathes and grinders, including: end face flattening, outer diameter fine grinding, and corner rounding; wherein, after outer diameter fine grinding, the surface roughness Ra≤0.8μm, and the tolerance of diameter and length is controlled within ±0.05-0.1mm; all edges and corners of the mandrel are machined into transition fillets of R0.5-2mm; a hole is opened at a certain distance from the top to facilitate hoisting of the mandrel; 3) Surface coating treatment The semi-finished graphite mandrel after machining is coated with a SiC transition layer and a PyC protective layer in sequence to ensure that the coating is tightly bonded to the mandrel body, without bubbles or peeling; after the coating is completed, it is naturally air-dried to obtain the finished graphite mandrel.

2. The method for preparing the graphite core rod according to claim 1, characterized in that, Graphite electrodes replaced by steel mills were used to prepare core rods, thus making use of waste materials.

3. The method for preparing the graphite core rod according to claim 1, characterized in that, In step 2), after processing, the surface of the core rod is cleaned with a graphite cleaner to remove processing debris, thus obtaining a graphite core rod semi-finished product.

4. The method for preparing the graphite core rod according to claim 1, characterized in that, Select graphite electrodes with a diameter greater than 300 mm and cut them to a length of 600 mm as raw materials for subsequent processing.

5. The method for preparing the graphite core rod according to claim 4, characterized in that, The rough sample was machined using a CNC lathe and grinding machine. After precision grinding of the outer diameter, the surface roughness Ra=0.6μm, and the diameter and length tolerances were ±0.08mm. The edges of the upper and lower bottom surfaces were machined into R1mm transition fillets. A 16mm diameter hole was drilled 90mm from the top to facilitate the hoisting of the mandrel. After machining, a cone-shaped graphite mandrel with an upper bottom diameter of 240mm, a lower bottom diameter of 220mm, and a height of 520mm was obtained.

6. The method for preparing the graphite core rod according to claim 5, characterized in that, A SiC transition layer with a thickness of 80 μm was coated on the surface of the processed graphite core rod using chemical vapor deposition.

7. The method for preparing the graphite core rod according to claim 6, characterized in that, A PyC protective layer was coated using chemical vapor infiltration, with a coating thickness of 40 μm.

8. The method for preparing a graphite core rod according to claim 6, characterized in that, The coating process is protected by high-purity argon throughout.

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