After the degreasing and surface cleaning process, reed blades undergo annealing to remove magnetic remanence and improve magnetic permeability. A low magnetic remanence prevents sticking and higher permeability enhances sensitivity. Annealing also softens the hardened blades from pressing, to ensure the spring forces of the cantilever are better for ensuring low contact resistance.
Annealing is usually done, as per definition of the process, with fast heating and slow heating. This softens metals and makes them more malleable and ductile for formations. Less load on the press is also used and the life of the press tools are also more when working with softened parts.
Blades are loaded into a individual jigs which are then loaded into an annealing pot, and sealed tight. Special gases are used to flush the inside of the pot and the annealung cycle is started. The gas also ensure the surface finish of the reed blades are bright. Gas is used throughout the annealing process curve and lasts for many hours.
Prescribed heating and cooling curves with dry and wet gases result in soft annealed blades with a smooth grain structure. The blades gradually cool down also in the furnace over some hours, then inspect for grain structure and smoothness. Some samples of reed bladses are tested for hardness at this stage to make sure they are within limits. Some annealed blade samples are sputter coated, sealed in glass tubes to check remanence levels before the entire batch goes for sputtering.
