Lathe Tools - 3: Carbide
|WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.|
|Carbides are made by blending micron-sized tungsten carbide and cobalt powders, then pressing the mixture in a mold and at a temperature high enough to cause the cobalt to flow. During this process the cobalt fills the spaces between the tungsten grains and thoroughly coats each grain. When the cobalt solidifies, it cements the grains together, forming a dense composite. This process is called "sintering" and the resulting tool is called "cemented" carbide.|
Cemented carbides get their hardness from the tungsten grains and their toughness from the tight bonds produced by the cementing action of the cobalt metal*. By varying the amount of cobalt the hardness, wear resistance and toughness (shock resistance) of the carbide can be changed.
The beginning of tungsten carbide production may be traced to the early 1920's, when the German electrical bulb company, Osram, looked for alternatives to the expensive diamond drawing dies used in the production of tungsten wire.
These attempts led to the invention of cemented carbide, which was soon produced and marketed by several companies for various applications where its high wear resistance was particularly important. The first tungsten carbide cobalt grades were soon successfully applied in the cutting and milling of cast iron. In the early 1930's, the pioneering cemented carbide companies launched the first steel-milling grades which, in addition to tungsten carbide and cobalt, also contained carbides of titanium and tantalum.