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Recycling of hardmetal

Why recycle ?

Recycling of hardmetal scrap has been gaining in popularity in recent years and is today a very important factor in the world’s tungsten supply chain. The driving forces behind this development have been

  • economic ( savings in raw material costs can be achieved by recycling )
  • environmental ( recycling reduces the environmental impact )
  • strategic ( tungsten is a valuable and limited resource mined in only a few countries )

There are two main recycling processes:

  • chemical processes in which scrap goes through the same hydrometallurgical process as concentrates from tungsten mining
  • zinc process in which scrap is processed directly into tungsten carbide-cobalt alloy powder in a furnace process

Zinc process for direct recycling of hardmetal scrap

The zinc process employed by Tikomet involves the processing of hardmetal scrap together with zinc on graphite boats in a special furnace. During the process the molten zinc reacts with the cobalt binder phase of the hardmetal. There is a volume expansion associated with this reaction and as a result the hardmetal swells to a porous cake. After the reaction has gone to completion the zinc is distilled off and recovered so that it can be used again.

After the treatment of the scrap in the furnace the porous cake is milled into powder. Subsequently, fine milling and homogenization is carried out to obtain a high quality tungsten carbide-cobalt powder ( zinc reclaim powder ) which can be used as raw material in the production of ready-to-press powder for new hard metal tools.

The zinc process involves no chemical modification of the raw material. Therefore

  • the tungsten carbide grain size of the hardmetal does not change during the processing
  • the powder obtained contains also the cobalt binder metal ( in case of insert scrap also the cubic carbides TaC, TiC, NbC are retained )

The fact that there is no chemical modification means that clean and well sorted scrap is required as raw material in order to assure a reclaimed powder of high quality. In this respect the zinc process differs from the chemical processes where mixed scrap and scrap containing impurities can be used.

An insert in the various stages of the zinc process
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Applications of tungsten carbide-cobalt powders produced by the zinc process

In the production of new hardmetal tools the tungsten carbide-cobalt powder produced by the zinc process is typically mixed with virgin tungsten carbide and cobalt powders. The amount of recycled material which can be used in the production of ready-to-press powder varies in the 20…80 % range depending on the application.

The advantages of the zinc process can be summarized as follows:

  • attractive economics compared with chemical recycling
  • environmentally friendly technology ( zinc recovered and reused, no emissions as the process is a furnace process, lower energy consumption and lower carbon dioxide emissions compared with the processing of virgin raw materials such as concentrates from mining operations )

Traditionally zinc reclaim powders have been used in applications such as indexable inserts and hardmetal pins for tire studs. Today the use has expanded to new applications such as

  • hardmetal rods for drills and end mills
  • hot rolls
  • mining compacts
  • thermal spray powders
  • wear part
  • wood working tools

Tikomet has carried out extensive testing related to these applications. If you are interested in using zinc reclaim powder in one of these applications, our technical experts stand ready to work with you to provide the best possible product for your needs.

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