With the continuing surge in the price of the key elements used in cemented carbide tool production, tungsten carbide and cobalt, and Japan’s almost total reliance on the import of these raw materials, it is no surprise that many Japanese companies are seeking to increase the amount of tungsten carbide they recycle.
Currently Japan is said to recycle 25% of carbide tools, the USA around 50% and 40% in Europe. Sumitomo Electric Hardmetal Corp is one of Japan’s leading carbide producers and the company has been recycling WC-Co tools for several decades using a high temperature process, the zinc process, and the Coldstream process.
The zinc and Coldstream processes allow the direct conversion of scrap carbide into usable powder. In the zinc process, in which the treatment is performed at below 1,000°C , no WC grain growth takes place and therefore recycled W powder has the same composition as the original scrap material. This requires strict sorting of the carbide scrap to prevent impurities.
In addition to zinc processing, a ‘wet chemical treatment’ process to recycle ammonium paratungstate (APT) from WC scrap, with unrestricted use in the production of new carbide tools, has also been developed at SEI. However, because it requires a greater number of steps using a large amount of chemicals and energy, plus the associated environmental impact, the process was not used extensively.
The company now reports in SEI World (April 2011) that it has been working with the Japan Oil, Gas and Metals National Corp (JOGMEC), and with support from Japan’s Ministry of Economy, Trade and Industry, since 2007 to improve the ‘wet chemical treatment’ recycling method to recover tungsten and cobalt from waste carbide tools.
SEI states that the large number of stages involving multiple chemical processes currently used have been reduced, helping to cut energy costs and provide a low cost recycled powder.
A new recycling plant is planned.