PTFE Disc: Sintered in a Molten Nitrate Bath, Cooled Slowly (Brubaker & Hanford 1946)

A PTFE disc pressed cold, then sintered by dipping it in molten salt at 380 °C for half an hour. Instead of being quenched, it cools slowly between magnesite blocks. The patent says slowly cooled pieces are a little softer and less stiff, which is often better for machining. Source: M. M. Brubaker and W. E. Hanford (du Pont), US 2,400,099 (1946), Example II. The patent gives no nitrate-to-nitrite ratio. The mould, press, pot and burner are ours. Picture drawn by Youblob.