Keywords: Sintered molybdenum rod; Processing defects; Control measures; Preventive measures
1. Introduction
Sintered molybdenum rods have the advantages of high melting point, high strength, good electrical and thermal conductivity, and corrosion resistance. They are widely used in fields such as aviation, electronics, industry, medicine, and chemistry. In the processing of sintered molybdenum rods, defects such as cracks, layering, surface contamination, and shape size deviations may occur, which not only affect the appearance and performance of the products but also may lead to product scrap, increasing production costs. Therefore, it is of great significance to study the defect control and preventive measures in the processing of sintered molybdenum rods.
2. Common Defects in the Processing of Sintered Molybdenum Rods
2.1 Cracks
Cracks are one of the common defects in sintered molybdenum rods. They can be divided into irregular cracks and transition surface cracks. Irregular cracks are mainly caused by factors such as foreign matter in the powder, uneven loading during pressing, and uneven exhaust during pressing. For example, when foreign matter is mixed into the molybdenum powder, it can cause stress concentration during pressing and sintering, leading to crack formation. Transition surface cracks are often caused by uneven loading of Shaped billet（special-shaped billets） during pressing, resulting in uneven density distribution and cracks at the transition parts.
2.2 Layering
Layering defects in sintered molybdenum rods are mainly caused by uneven loading during pressing of profiled（special-shaped parts） or poor matching of the dimensions of each part during loading. When the loading density of different parts of the billet is inconsistent, it can easily lead to layering during subsequent processing.
2.3 Surface Contamination
Surface contamination of sintered molybdenum rods may be caused by factors such as unclean operation, contact with oil stains, or contamination from other powders during the pressing process. For example, if the pressing equipment is not cleaned in place, residual oil stains or other impurities may adhere to the surface of the molybdenum rod during pressing, affecting its surface quality.
2.4 Shape and Size Deviations
Shape and size deviations of sintered molybdenum rods can be caused by factors such as incorrect process calculation, inaccurate pressing process, or poor surface finish of the pressing mold. For example, if the process parameters during pressing are not well controlled, the density distribution of the billet may be uneven, resulting in shape and size deviations during subsequent processing.
3. Control Measures for Defects
3.1 Crack Control
- Before pressing, the molybdenum powder should be strictly screened to remove foreign matter. At the same time, the powder should be subjected to far-infrared drying treatment to prevent powder caking.
- During pressing, ensure uniform loading of the powder. For Shaped billet, the loading density of each part should be carefully checked to ensure consistency.
- Control the pressing speed and exhaust evenly to avoid stress concentration caused by rapid pressing or uneven exhaust.
3.2 Layering Control
- For profiled pressing, the loading method should be optimized to ensure uniform loading density of each part. For example, auxiliary tools can be used to adjust the loading position and amount of the powder.
- Before pressing, the dimensions of each part of the billet should be carefully matched to avoid layering caused by dimensional mismatch.
3.3 Surface Contamination Control
- Strictly implement standardized operations during the pressing process. Operators should wear clean work clothes and gloves to avoid contact with oil stains and other impurities.
- Regularly clean the pressing equipment and tools to ensure their cleanliness. Before each use, the equipment and tools should be wiped with a clean cloth to remove residual impurities.
- Avoid mixing the molybdenum powder with other powders during storage and transportation to prevent cross-contamination.
3.4 Shape and Size Deviation Control
- Strictly perform process calculations to ensure the accuracy of process parameters. Before production, a sample test should be carried out to verify the rationality of the process parameters.
- Control the pressing process accurately. For example, the pressing pressure, pressing speed, and holding time should be strictly controlled according to the process requirements.
- Improve the surface finish of the pressing mold. Regularly check and maintain the mold to ensure its dimensional accuracy and surface quality.
4. Preventive Measures
4.1 Material Selection and Preparation
- Choose high-quality molybdenum powder as the raw material. The purity of the molybdenum powder should be greater than 99.95%, and the particle size distribution should be uniform.
- Before using the molybdenum powder, it should be subjected to strict quality inspection, including chemical composition analysis, particle size distribution detection, and purity testing.
4.2 Equipment Maintenance and Management
- Establish a regular equipment maintenance system. The pressing equipment, sintering furnace, and other related equipment should be regularly inspected, maintained, and repaired to ensure their normal operation.
- For key equipment such as the pressing mold, a detailed maintenance record should be established to track its usage and maintenance status.
4.3 Process Optimization
- Continuously optimize the pressing and sintering processes. Through experiments and production practice, find the best process parameters to improve the quality and performance of sintered molybdenum rods.
- Introduce advanced processing technologies and equipment. For example, hot isostatic pressing (HIP) process can be used as necessary to improve the density and crystal grain fineness of the products.
4.4 Quality Inspection and Control
- Establish a complete quality inspection system. From raw material inspection to finished product inspection, each link should be strictly controlled to ensure that the products meet the quality requirements.
- Strengthen the training of quality inspection personnel to improve their professional skills and quality awareness. At the same time, regularly conduct quality audits and assessments to find and solve quality problems in a timely manner.
In the processing of sintered molybdenum rods, defects are inevitable, but through effective control measures and preventive measures, the occurrence of defects can be reduced and the quality of products can be improved. In the actual production process, enterprises should combine their own actual situation（actual situation）, continuously optimize the processing technology and management level, and strive to produce high-quality sintered molybdenum rods to meet the needs of the market. At the same time, with the continuous development of science and technology, new materials, new processes, and new equipment will continue to emerge, providing more possibilities for the improvement of sintered molybdenum rod processing technology.