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Induction Heating Coils

Overview

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The Importance Of The Induction Coil

Coil design is one of the most important aspects of an induction system. A well-designed coil provides easy part handling, maintains the proper heating pattern and maximizes the efficiency of the induction heating power supply.

Induction coils are normally made of copper tubing - an extremely good

conductor of heat and electricity - with internal diameters ranging from under

0.10" to over 5'. Coils are cold to the touch because they are cooled by

circulating water, and are most often custom-made to fit the shape and size of

the part to be heated. So coils can have single or multiple turns; have a helical, round or square shape; or be designed as internal (part inside coil) or external (part adjacent to coil).

Types of Induction coils

We will work with you to design and fabricate a coil that deliver maximum

heating efficiency for your part and process requirements. Visit our coil gallery to

get an idea of the wide range of coil designs we have worked with. Induction coils

are produced in a wide range of shapes and sizes – they can have single or multiple turns, have a helical, round, or square shape, and be designed as

internal (part inside the coil) or external (part outside the coil). We will work with you to design and fabricate a coil that deliver maximum heating efficiency for

your part and process requirements.

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  • Single-Position Helical – simple solenoid or helical wound coil, the number of turns depending on the part dimensions and heating requirements.

  • Multi-Position Helical - when high production requirements must be met, special coils can be designed to heat one part while the another part being loaded or unloaded.

  • Split Helical - when the part heating zone cannot be reached with a standard helical coil design, parts can often be successfully heated with a single or multi-turn split helical coil design.

  • Pancake Coil - rows of copper tubing shaped into a round flat shape roughly resembling a pancake, used to heat a surface that is basically flat.

  • Square Coil - one of the easier coil designs to fabricate, often the best choice for heating the outside of a square metal shaft or bar.

  • Hairpin - a relatively small loop-shape coil bent to conform to a shape of a specific part

  • Single Turn or Solid Coil - a round inductor with just one turn, the thickness depending on the part

  • Clamshell - when a single or double turn coil won will not work because of the part shape, a coil can be constructed from two identical halves that open and close, enabling heating of the full part OD.

  • Channel Coil - when your induction heating system is designed to supply a steady flow of parts on a conveyor belt, channel coils which allow for constant workflow and heat without completely surrounding the parts can be utilized. We can also design a curved channel coil if your process specifies a rotary turntable to move the parts in and out of the induction heating coil.

  • Fork coil - fork coils have two "tines" that effectively heat two opposite sides of a part

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Coil Coupling 

For maximum efficiency and heat transfer, the induction coil or inductor should be designed so that the part can be placed very close to it. The term “coupling” refers to the relative distance between the coil and the part being heated. So a short distance between the coil and part is often referred to as “tight coupling” while “loose coupling” means there is more of a gap.

Operating Frequency

The operating frequency of your induction heating process will depend largely on the specific process – brazing, shrink fitting, bonding, etc – and the size and shape of the part. Generally speaking, tighter coupling is preferable for lower operating frequencies. Coupling becomes less of an issue with higher frequency induction heating processes.

Cooling Considerations

Almost all induction heating coils are coiled with water flowing through the copper. For maximum heating efficiency it is critical to have maximum water flow. Overheating can cause the copper to crack, especially in processes with a relatively short heating cycle. A more gradual coil deformation due to overheating can occur with longer heating cycles.

To remedy overheating, the water flow rate can be increased and/or the water temperature can be lowered. Alternatively, additional cooling circuits can be introduced elsewhere in the system. We'll work with you to make sure your coil design incorporates sufficient cooling capacity for your process and part requirements.