Production Sintering Practices Vacuum Sintering

The use of cold-walled vacuum furnaces generally is preferred for sintering of titanium powders. The furnace should be equipped with a diffusion pump that has a sufficient capacity to accommodate outgassing during heat up and maintenance of high vacuum (133 MPa, or 1 x 10-3 mm Hg) at peak temperatures. Heating elements of molybdenum or graphite cloth with a temperature limit of at least 1245 °C (2275 °F) can be used.

The use of cold traps is necessary to condense vaporized sodium chloride and other impurities that may impair diffusion pump performance. Because significant outgassing occurs during heating, a control system that cuts power to the furnace when a preset pressure level (400 MPa, or 3 x 10-3 mm Hg) is reached should be used. Heating may be restored when higher vacuum is achieved again.

This type of system automatically compensates for variations in furnace load, lubricants, or compact density, for example. The use of an inert gas recirculating system for cooling is optional, except for alloys requiring rapid cooling through the fi-Qt temperature range. While a cooling system can improve furnace through put, the added difficulties and costs of additional valving (sources of leaks) and maintenance of a water-cooled heat exchanger should be considered carefully before making the installation.

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