Chemical Wear of Tungsten Carbide Cutting Tools By Western Redcedar

The mechanisms responsible for excessive dulling of carbide-tipped wood tools in cutting unseasoned western red cedar (Thuja plicata Donn) were studied using X-ray spectrometry and scanning electron microscopy. Experimental results show that two major, groups of cedar extractives are the primary cause of the rapid dulling process. These extractives, tropolones and polyphenol lignans, were found to attack readily the matrix of elemental cobalt and, to a much lesser extent, tungsten carbide grains by forming metal chelates. The formation of these compounds was accelerated as the temperature was raised from 200 to 600C. It is shown that the continuous formation of cobalt chelates and their removal from reaction sites exposes the tungsten carbide grains. In the cutting process, these grains are then readily removed by mechanical action. The breakdown of the matrix and, therefore, excessive dulling might be prevented by two alternative methods: replacement of cobalt with a matrix of superior corrosion resistance; or by coating carbide inserts with corrosion and abrasion-resistant hard-metal materials.

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