Molybdenum crucibles are usually set according to their usage scenarios, manufacturing processes and technical requirements. In different applications, the geometric accuracy requirements of molybdenum crucibles may be different, especially in high temperature and high-pressure environments, where accuracy control is critical. The following are some common molybdenum crucible geometric accuracy standards that are applicable to different molybdenum crucible manufacturing processes.
- Common geometric accuracy requirements
- Dimensions
the molybdenum crucible are the basic requirements for its geometric accuracy, usually including parameters such as diameter, outer height, and outer wall thickness.
Outer diameter accuracy: The outer diameter of the molybdenum crucible needs to be precisely controlled, usually requiring an error of no more than ±0.1–0.5 mm. For more demanding applications (such as single crystal growth, semiconductor manufacturing, etc.), the accuracy may need to reach ±0.05 mm.
External height accuracy: The external height (height or depth) is usually required to have an error within **±0.1 mm. The external height deviation of high-precision molybdenum crucibles is usually controlled within ±0.05 mm**.
Outer wall thickness: Wall thickness uniformity is an important criterion for evaluating the quality of molybdenum crucibles. The wall thickness error is usually required to be controlled between **±0.05–0.2 mm**.
- Inner diameter
The inner diameter usually directly affects the volume and performance of the crucible. Its accuracy requirements are generally as follows:
Inner diameter accuracy: The inner diameter error is usually required to be controlled within ±0.1-0.2 mm. For more sophisticated applications (such as high-purity smelting, single crystal cultivation, etc.), the inner diameter error may be required to be within ±0.05 mm.
- Wall thickness uniformity
the molybdenum crucible must be uniform, especially for crucibles with high requirements for high-temperature melting. Uneven wall thickness may lead to unbalanced thermal stress and affect its service life. The wall thickness error is usually required to be controlled between **±0.05–0.1 mm.
- Surface accuracy
- Surface roughness
molybdenum crucible is crucial to its thermal stability, chemical stability and volume requirements. Its surface roughness standards are usually:
External surface: Roughness Ra is usually required to be between 0.2–1.0 μm (depending on the specific application).
Inner surface: In order to prevent metal oxidation and increase service life, the roughness of the inner surface is generally required to be controlled between 0.2-0.5 μm.
For some high-precision crucibles that require very smooth surfaces (such as for high-temperature synthesis, electronic material manufacturing, etc.), the roughness may need to reach Ra ≤ 0.2 μm.
- Shape accuracy
- Roundness
The roundness of molybdenum crucible is an important indicator to measure its shape symmetry and processing accuracy, usually requiring:
Roundness error: The outer roundness error is usually required to be controlled within **±0.1 mm**.
- Concentricity
Concentricity refers to the consistency of the axis between the inner and outer walls of the crucible. A higher precision crucible needs to ensure that the inner and outer walls maintain good concentricity, usually requiring:
Concentricity error: The concentricity error of the inner and outer walls is usually required to be within **±0.1 mm**.
- Welding joint accuracy
If the molybdenum crucible is manufactured by welding, the accuracy of the weld joint is also critical. Common weld joint accuracy requirements are as follows:
Joint height difference: The height difference of the welding joint is usually required to be controlled within **±0.1 mm** to ensure the uniformity of the welding joint.
Joint strength: The strength of the welded joint must meet certain standards and usually needs to remain stable under high temperature and high-pressure conditions to avoid cracks.
- Factors affecting the geometric accuracy standard of molybdenum crucible
- Manufacturing process
Different manufacturing processes such as forging, welding, and casting will directly affect the geometric accuracy of the molybdenum crucible. Forging and welding usually require higher precision, while the dimensional error of the cast crucible is larger.
Cold working or heat treatment may play a crucial role in precision control, especially in the post-processing stage of molybdenum crucibles.
- Detection Methods
The control of geometric accuracy usually relies on precision measuring tools (such as vernier calipers, three-dimensional coordinate measuring machines ( CMMs ), laser scanners, etc.) for detection. Different detection methods have different accuracy, which is determined according to production batches and quality requirements.
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