Several methods of stress relief annealing are available:
Batch Annealing (760 to 840 degrees centigrade, typically 800 degrees centigrade +/-20 degrees)
The material is packed carefully into an inner cover before annealing for two hours at the specified temperature in a dry atmosphere. Excessive temperature gradients during the heating and cooling cycles must be avoided to prevent lamination distortion. It should be noted that the size of the lamination would influence the duration of the annealing cycle.
Mesh Belt Annealing (800 degrees centigrade +/-10 degrees)
Stacks of laminations are annealed in a mesh belt furnace when it is required that they are held at the specified temperature for about one hour. Annealed laminations are subject to distortion, but this may be controlled by the adjustment of stack height and cooling rate in the inert atmosphere.
Roller Hearth Annealing (800 degrees centigrade +/- 10degrees)
Roller hearth annealing (30 to 60 seconds at the specified temperature in an air atmosphere) of single laminations should result in the laminations being stress free and non-oxidised (the rapid anneal prevents oxidation).
Annealing of wound toroidal cores
Wound toroidal cores may be annealed in batch furnaces or in mesh belt furnaces under the conditions described above. It is important that the cores are not excessively stressed during winding and that they are not subjected to rapid rates of cooling.
Domain Refined Material
Stress relief annealing of laser domain refined material reverses the reduction of the core losses produced by the laser treatment.