1. Material Selection
The core is usually made of silicon steel laminations or amorphous steel.
These materials are chosen for:
High magnetic permeability
Low core losses (hysteresis and eddy current losses)
Good electrical resistivity (to reduce eddy currents)
27Q105
Silicon steel coil model 27Q105 usually refers to the cold-rolled oriented silicon steel coil produced by Wuhan Iron and Steel. Its specific meaning is as follows:
27: Indicates that the nominal thickness of the silicon steel sheet is 0.27mm.
Q: Represents oriented silicon steel, "Q" is the first letter of the Chinese pinyin of the word in "oriented".
105: Indicates the iron loss value of the silicon steel under certain test conditions, which means that under the P17/50 test conditions (i.e., the frequency is 50Hz and the magnetic induction intensity is 1.7T), the iron loss value is not greater than 1.05W/kg. The smaller the number, the better the performance of the silicon steel, the lower the iron loss, and the more energy-saving it is.
2. Lamination Preparation
Cold-rolled grain-oriented (CRGO) steel sheets are commonly used.
Steel sheets are typically 0.23 mm – 0.35 mm thick.
The sheets are coated with an insulating layer to reduce eddy current loss.
Raw material preparation and cutting
Cutting to Size
The laminations are cut into precise shapes depending on core design:
Stacking or Assembling
Laminations are stacked together to form the core.
In core-type transformers, laminations form a rectangular or square shape.
In shell-type transformers, the windings are surrounded by the core.
Step-lap stacking helps in reducing magnetizing current and noise.
4. Clamping and Annealing (for large cores)
Core stacks are clamped together tightly to avoid vibrations.
Annealing may be done to relieve stress and improve magnetic properties.
5.. Core Assembly with Windings
In small transformers, the core is inserted into pre-wound coils.
In large transformers, windings are built around the limbs of the core.
6. Final Finishing
Apply varnish or insulation coating.
Core grounding is ensured (to avoid circulating currents).
Sometimes, the assembled core is vacuum-dried or baked to remove moisture.