Tungsten carbide, renowned for its remarkable hardness and wear resistance, is a crucial material in various industrial applications, ranging from cutting tools to wear-resistant parts in machinery. Let's find out how tungsten carbide is produced.
What is the composition of tungsten carbide?
Tungsten carbide, with the chemical formula WC, is composed of equal parts tungsten and carbon atoms. It is a fine gray powder that can be pressed and formed into shapes through sintering.
- Density: With a density of about 15.6 g/cm3, tungsten carbide is significantly denser than carbides such as silicon carbide, which has a density of around 3.21 g/cm3.
- Hardness: Tungsten carbide has a hardness comparable to diamond and is much harder than other carbides like silicon carbide (SiC) or titanium carbide (TiC), making it an excellent material for cutting tools and abrasives.
- High melting point: 2780-2830 ℃
What are the raw materials for producing tungsten carbide?
- Tungsten ore: Of all the available pentominoes, the most widely known is black ore as the primary source of tungsten.
- Ammonium paratungstate (APT): A purified chemical compound derived from tungsten ore that serves as an intermediate production of tungsten metal and tungsten carbide.
- Tungsten oxide: Produced by calcinating APT at high temperatures, which is then reduced to tungsten metal powder in a hydrogen atmosphere.
- Carbon sources: Such as soot or graphite, are used to convert tungsten metal powder into tungsten carbide through a high-temperature carburization process.
How is tungsten carbide made?
- Batch Calculation: Since tungsten powder contains a small amount of oxygen, the calculation must consider not only the carbon needed for the carburization of tungsten but also the carbon required for the reaction between carbon and oxygen in the powder.
- Material Mixing: The quality of tungsten carbide powder depends on the uniformity of the mixture of tungsten powder and carbon black. If the mixture is uneven, the tungsten carbide powder may develop a core of unreacted material and stratification. In the production process of hard metals, tungsten powder is generally mixed with carbon black in a ball mill for 2-4 hours. The mixture is considered uniform when the naked eye observes no stratification.
- Material Carburization: The carburization of tungsten powder typically takes place in a graphite carbon tube furnace. The carburization process is selected based on the particle size of the tungsten powder and the desired particle size of the tungsten carbide. Generally, the carburization temperature for fine tungsten powder is 1300-1350°C, while for coarse tungsten powder, it is 1600°C. The carburization time ranges from 1-2 hours.
- Ball Milling: This is carried out in a ball mill. The duration of ball milling is determined by the specific process, usually around 2 hours. The material is then sieved under closed conditions: fine tungsten carbide particles through a 200-mesh sieve, medium particles through a 250-mesh sieve, and coarse particles through a 60-mesh sieve.
- Sintering: The blended powder is compacted into a desired shape, and then is heated around 1500 ℃, which causes the particles to fuse, forming a homogeneous and dense cemented carbide body.
The manufacturing process of tungsten carbide underscores the blend of science and craftsmanship required to produce this indispensable material. As industries continue to demand high-performance materials, the quest for innovation in tungsten carbide production persists, ensuring its relevance in various applications for years to come.
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