PTFE Ring: Pressed Cold, Sintered Out of the Mould (Brubaker & Hanford 1946)

PTFE will not flow like other plastics, so it cannot be injection moulded. Du Pont's answer was to press the powder cold into shape, take it out of the mould, and only then heat it above 327 °C. The soft, weak pressing keeps its shape in the furnace and comes out tough. This is their Example IV: a ring 8 in across. Source: M. M. Brubaker and W. E. Hanford (du Pont), US 2,400,099 (1946), Example IV. The press, die and furnace are ours. Picture drawn by Youblob.