Lubricant Removal

Pressing lubricants used for cemented carbides range from low levels (0.5 to 2.5 wt%) of simple paraffins for pressed parts up to high levels of various synthetic polymers for extruded, injection molded, and slurry cast parts. The heating rate used for lubricant removal in a hydrogen atmosphere depends on the type and amount of lubricant used and the size of the pressed part. Heating rates as high as 15 to 20 °C/min (25 to 35 °F/min) to 500 °C (930 °F) can be used for pressed cutting inserts containing 1 to 2% paraffin. Much slower rates (0.5 to 4 °C/min, or 0.9 to 7 °F/min) are required for larger parts or for parts with higher lubricant contents.

Commonly used lubricants, such as paraffin, evaporate readily in vacuum at 100 to 250 °C (210 to 480 °F). Consequently, heating rate should be controlled in this temperature range to prevent excessive pressure within the compact due to evolving lubricant vapors. A condenser is used in the vacuum line to remove the portion of the lubricant vapor that condenses at —10 to 90 °C (50 to 195 °F). The interior walls of the furnace are sometimes used to condense paraffin vapor to liquid, which is subsequently drained to the bottom of the furnace to enter the main condenser. Other furnaces employ carrier gases such as H2, argon, or N2 to completely remove paraffin vapors to external condensers. Carbowax is another common lubricant used in lieu of paraffin and is removed under atmospheric H2.

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