Production Process
The production process of powder-metallurgical products basically includes the four steps of powder preparation, forming,sintering and finishing.
1.Titanium carbide production
The APT (ammonium para-tungstate) is calcined into tungsten oxide under high te-mperature. Subsequently the oxide is reduced to tungsten metal in a hydrogen atmosphere. The metal powder is then mixed with carbon and carburised under inert atmosphere at high temperatures. The production parameters are decisive for the WC grain size in the sintered carbide.
2.Powder preparation
The tungsten carbide is intensely mixed with the binder metal cobalt, nickel or iron, various grain growth inhibitors and materials,which promote compaction, by wet grinding so that a homogeneous suspension is created. Afterwards, the suspension is dried in a spray tower to produce a granulate with good flow characteristics. This granulate represents the basis for all forming processes.
3.Metal forming
The objective of the forming process is to obtain a near net shape sample. Pressing is normally carried out at room temperature with pressures reaching up to several tons per square centimetre.There are several ways of pressing blanks:During isostatic cold pressing the powder is filled into an elastic flexible hose and pressed into acompacted form through high liquid pressure. The powder blocks which are produced in this way can then be processed mechanically. All common machining methods like milling,cutting, drilling or turning maybe applied.In uniaxial pressing the pressing tool consists of a die and an upper and a lower punch. The carbide powder is filled into the die and then compacted to create the so called green carbide,which is ejected from the pressing die.Extrusion pressing is mainly used to produce rectangular bar or cylindrical rod, with or without axial hole(s). A plasticiser is added to the powder. The resulting paste is pressed through an extrusion nozzle. Before sintering, the plasticiser must be evaporated in special drying furnaces. Metal Injection Moulding (MIM) is a process used to produce more complex forms which cannot be produced by direct pressing. The paste preparation is similar to the extrusion process.
4.Sintering process
The sintering process converts the blank into a homogeneous and dense carbide with a high level of hardness. The material is sintered at temperatures between 1,300 and 1,500 °C (liquid phase sintering) and sometimes also at high pressure (up to 100 bar). The volume is reduced by up to 50 % during this process.
5.Finishing
In order to achieve the final requirements of surface finish, tolerances,etc. carbide parts can be subjected to a series of finishing processes such as grinding, spark erosion and coating.
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