How Is A Tungsten Crucible Made?

Tungsten crucible is a crucial high-temperature-resistant container widely used in environments involving extreme heat and high vacuum. It finds broad applications in industrial fields such as single crystal growth, rare earth smelting, and vacuum melting. The main production process of tungsten crucibles involves five steps: preparation of high-purity tungsten powder, powder pressing and forming, high-temperature sintering, precision machining, and surface treatment.

1. Preparation of High-Purity Tungsten Powder

The tungsten powder used typically has a purity of ≥99.95%. The powder particles must be uniform and free of impurities to ensure the product’s density and performance under high temperatures.

2. Powder Pressing and Molding

The loose tungsten powder is compacted into a “Tungsten crucible blank” with a certain shape, size, and density, laying the foundation for the subsequent sintering process. Two common forming methods are used depending on the product size and shape:

▸ Compression Molding

This method is suitable for small, simple-shaped tungsten crucibles, such as cylindrical ones with small diameters. Tungsten powder is loaded into a metal mold, and uniaxial pressure (typically 50–200 MPa) is applied using a hydraulic press. This compacts the powder into a shape matching the mold cavity. Compression molding is efficient and equipment-friendly, but it can result in non-uniform density distribution, with higher density near the mold walls and lower density in the center, leading to potential stress concentrations.

▸ Cold Isostatic Pressing (CIP)

For large, thin-walled, or complex-shaped crucibles (e.g., diameter over 300 mm), cold isostatic pressing is typically used. Tungsten powder is filled into an elastic mold, sealed, and placed in a high-pressure chamber. A liquid medium applies pressure uniformly in all directions (100–300 MPa), resulting in a blank with even density, lower internal stress, and density up to 50–60%, ideal for high-performance crucibles.

3. High-Temperature Sintering

The Tungsten crucible blank is sintered in a vacuum or hydrogen atmosphere at 2000–2500°C, fusing the tungsten particles into a dense solid structure with excellent mechanical and thermal stability.

4. Precision Machining

Using diamond tools or abrasive grinding wheels, processes such as turning, grinding, and boring are applied to refine the inner/outer diameter, height, and wall thickness. Dimensional tolerance can reach ±0.01 mm, and custom structures like flanges or grooves can be added as needed.

5. Surface Treatment

Surface finishing includes polishing and cleaning. Mechanical or electrolytic polishing reduces surface roughness (Ra ≤ 0.8 μm), helping to minimize impurity adsorption and chemical reaction during high-temperature use, while also improving thermal shock resistance.