Induction heating coil design
1. Higher flux density near the heating area means a higher current is generated in the part.
The coil should be coupled as close to the part as possible, and the largest possible number of magnetic flux lines therefore intersect the workpiece at the heating point. This allows for maximum energy transfer.
2. The greatest number of flux lines in a solenoid coil are toward the center of the coil.
The flux lines are concentrated inside the coil, providing the maximum heating rate at that location.
3. The geometric center of the coil is a weak flux path.
Flux is most concentrated closer to the coil turns themselves, and decreases with distance from the turns.
If a part were placed off center in a coil, the area closer to the coil turns would intersect a greater number of flux lines and thus be heated at a higher rate. The area of the part away from the copper coil experiences less coupling and would be heated at a lower rate.
This effect is more pronounced in high-frequency induction heating.
4. The magnetic center of the inductor is not necessarily the geometric center.
At the point where the leads and coil join, the magnetic field is weaker.
This effect is most pronounced in single-turn coils. As the number of coil turns increases and the flux from each turn is added to that from the previous turns, this condition becomes less important.
Due to the impracticality of always centering the part in the work coil, the part should be offset slightly toward this area in static heating applications. If possible, the part should be rotated to provide uniform exposure.
5. Coil must be designed to prevent cancellation of the magnetic field.
If opposite sides of the inductor are too close, the coil does not have sufficient inductance required for efficient heating. Putting a loop in the coil at the center will offset this effect. The coil will then heat a conducting material inserted in the opening.
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