Some manufacturers, however, anneal without pots but they aim to have the castings protected from the flame and air.
No. 110. Photomicrograph of No. 109 after Several Hours of Annealing
Handling devices have been designed which facilitate loading and unloading the furnaces. With these the many sets of pots or saggers which the furnace holds can be very quickly charged or removed.
After shaking the castings out of the cooled pots, the dark coating is removed from them by “tumbling” with iron shot, pieces of leather or other polishing material in tumbling mills after which they are ready for any machining which may be necessary.
Photomicrographs Nos. 109, 110, 113 and 35 which show the samples at 75 diameters magnification show the course of the annealing process. No. 109 was taken from an unannealed casting. No. 110 was of the same iron after approximately thirty hours in the furnace. No. 113 shows that after about forty-five hours nearly all of the iron-carbon chemical compound has been broken down into black patches of free carbon, surrounded by the white areas of pure iron. After about sixty hours all of the iron and carbon have been divorced and the annealing operation is complete, as is shown by photomicrograph No. 35.
No. 113. Photomicrograph of No. 109 When Nearly Annealed
No. 35. Completely Annealed Malleable Cast Iron