Mechanical Structure of Induction Coils

Induction coils must be tightly coupled to the workpiece, but sufficient mechanical and electrical clearances must also be provided. Typically, a complete induction coil design with operating devices and matching components, such as capacitors and transformers, must be implemented. The design must also consider the effects of leakage flux heating, vibration, water, and oil; therefore, the induction coil should be manufactured after the electrical design is completed.

The conductor is generally copper with high thermal conductivity and is cooled by water. Most induction coils consist of pipes with segmented water supply. However, sometimes oil or a “viscous” quenching medium can be used to achieve the dual function of cooling the conductor and quenching the workpiece. In some short-cycle, one-time spray quenching operations, the conductor may not be zoned for cooling because spray quenching can achieve both of these effects. Silver plating is often used to improve the surface thermal conductivity, especially at contact surfaces. A typical induction coil is shown.

induction coils

Most moving induction coils are single-turn and carry powerful currents up to 20 kA. Because reducing the voltage eliminates the risk of voltage breakdown in the presence of quenching media, a single-turn inductor powered by a matched transformer is suitable. The conductor should be robust and durable to ensure long lifespan and dimensional stability. Another advantage of reducing the voltage is that it allows for tight coupling between the inductor coil and the workpiece, thereby improving heating efficiency and achieving a precise heat-hardening zone.

Due to the high frequency (3.10 or 450 kHz), the current is concentrated on the inner surface.

All welds must be silver brazed; high-temperature brass solders, such as copper-silver alloys, should not be used because the weld resistance is too high and the weld is brittle, often prone to cracking with thermal expansion.

Because of the strong electromagnetic force on the inductor coil, it must be mechanically reinforced and securely fixed.

The water sprayer can be installed inside the inductor coil or manufactured separately.

Clearly, ring-shaped and cylindrical induction coils are suitable, but they are not the only shapes. Sometimes other shapes are also appropriate, such as horseshoe shapes (straight or curved). A curved horseshoe-shaped induction coil can be used where it is impossible to surround a cylindrical surface.