Grades of Carbide
Cemented carbide is a product of powder metallurgy. Carbides of tungsten or titanium, and other trace elements are sintered at extremely high temperature into a 'binder' material (usually cobalt). An analogy can be drawn here with the surface of a road. If too much bitumen and not enough stone chippings were used, the surface would wear away in no time at all. Conversely, too many chippings and not enough bitumen would give a very wear-resistant surface, but it would not have the toughness necessary for the job and would crack up very easily. Similarly, with cemented carbide, more carbides and less cobalt binder gives a very wear-resistant but not very tough grade (suitable for finish machining), whereas more cobalt and less carbides gives a tough grade more suited to rough machining, but having less wear-resistance.
The performance and capabilities of the tool are not only affected by the proportions of carbide and binder. The grain size of the carbide itself is also influential on its characteristics. An insert with very small grains of carbide can hold a sharp cutting edge, whereas larger grains mean that blunter or 'reinforced' cutting edges often need to be employed. These are particularly useful where heavy cuts are used on long-chipping materials which tend to produce heavy crater wear on the top face of the insert.
All these differing combinations of mixes and grain sizes lead to ultra-efficient carbide grades, but they are generally aimed very specifically at particular materials, speeds, feeds, depths of cut and cutting conditions. Model engineers, however, tend to require a general purpose tungsten carbide grade that will work well on carbon steels, stainless steels and cast irons, as well as non-ferrous materials such as brass, bronze, aluminium, plastics and even wood. Our literature therefore concentrates on our unique grade of carbide, NJ17.
NJ17 is a fine-grained tungsten carbide with good edge sharpness. It combines good abrasive wear resistance with the toughness to withstand heavier cuts at moderate speeds. It can also tolerate a certain amount of abuse! NJ17 has a micro-thin, ultra-smooth top coating of Aluminium Oxide, giving excellent tool-life, coupled with good surface finishes and less tendency towards built up edge on the softer workpiece materials.