Wire Forming Process of Vanadium Wire
The production of vanadium wire involves multiple steps, integrating both hot and cold processing methods to optimize the plastic deformation and performance of metal vanadium. The detailed steps of the process are as follows:
1. Initial Blank Preparation
Molding: High-purity vanadium powder (purity ≥99.5%) is mixed with a binder and pressed into molds to form fragile, rod-like blanks. Controlling the pressure (typically 200-300 MPa) ensures uniform density throughout the billet.
Pre-Sintering: The billet undergoes pre-sintering at high temperatures (around 1200-1400°C) in a hydrogen or inert gas environment. This step causes the metal particles to begin consolidating, increasing the billet's density to 60%-70%, though the material remains brittle and hard at this stage.
2. Hot Processing
Complete Sintering and Heat Treatment: A second round of sintering at higher temperatures (1400-1600°C) facilitates further grain growth, achieving a dense structure with up to 85%-95% density. The grain size can be tailored through annealing or solution treatment to enhance the material's suitability for subsequent processing steps.
Hot Extrusion: The sintered vanadium rod is heated to 1200-1500°C and extruded through a mold, forming a thicker vanadium wire with a diameter of approximately 10-20 mm. This process refines the grains and eliminates internal defects.
Hot Forging: The high-temperature vanadium rod is continuously forged using a high-speed hammer (operating at a frequency of around 10,000 strokes per minute). This reduces the rod's diameter to 5-10 mm and creates a fibrous crystal structure that improves toughness.
3. Cold Processing
Multiple Drawing:
Rough Drawing: The hot-processed wire is cold-drawn using a carbide wire drawing die (initial aperture 5-10 mm). The reduction in diameter during each pass is controlled between 10%-20%, with lubricants applied to reduce surface friction.
Finishing Drawing: The vanadium wire is further drawn using a diamond wire drawing die (with apertures ranging from 0.1-1 mm) in several fine drawing stages until the target diameter (such as 0.05-2 mm) is achieved. At this stage, careful control of drawing speed and periodic intermediate annealing (after every 3-5 passes) is crucial to prevent vanadium wire breakage.
4. Surface Treatment and Finishing
Pickling/Polishing: A mixture of nitric acid or hydrofluoric acid is used to remove surface oxidation layers and scratches, enhancing the vanadium wire’s surface finish and corrosion resistance.
Coating Treatment (Optional): For specialized applications, the vanadium wire can be coated with zinc or rare earth alloys to enhance oxidation resistance and electrical conductivity.
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