Blueing of ferrous metal workpieces - which are first coated with water repellent oil and heated before being exposed to steam which forms ferrosoferric oxide coating

摘要

The workpieces are first coated with a water-repellent and volatile material, pref. an oil, and are then fed into the first chamber of a continuous furnace. In the first chamber, the workpieces are heated in a current of air to above the temp. of rust formation (i.e. above the dew point), and also to volatilise the oil. The workpieces next travel into a second furnace chamber contg. hot steam, so a coating of Fe3O4 forms on the surface of the workpieces. The amt. of air flowing through the first chamber is pref. adjusted so a non-explosive or non-combustible atmos. is formed in this chamber. Useful for the blueing of electrical steel laminations or other pieces which are machined or partly machined. The use of batch type furnaces involving long and expensive processes can be eliminated.