Self-supported coils are coils made of wire that is coated with a thermoplastic layer - the bonding varnish. The term selfbonding enamel wire already indicates it: This wire is bonded during the winding process to give the coil the necessary stability without any other aids, especially in the case of air coils. The use of selfbonding wire can offer advantages over a bobbin coil in some cases, since coil formers as well as adhesive tapes or lacquering steps are not required.
There are many types of coils and even experienced engineers sometimes lose track of which types of coils exist and which coils are suitable for which applications. In a new series, HuiLong provides an overview with the most important info on coil production.
Hot air baking during winding has the advantage that a downstream bonding process is not necessary. Hot air bonding is cost-effective and is mainly used for wire diameters below 0.200 mm.
After the coils are wound, the unit is heated in an oven, which melts the baking varnish and bonds the adjacent turns of wire together.
Resistance bonding is similar to oven bonding except that heat is generated by current flow through the formed coils. The time, voltage and amperage depend on the application.
Some bondcoat enamels can be activated by the application of certain solvents during or after coil winding. The solvent can be applied to the wire via a wick during the winding process, or the finished coils can be immersed in a solvent bath after winding. In either case, the unit should be heated again to remove the remaining solvent and complete the bonding of the coils.
Self-bonding coils are practical when space is limited in an application and there is no way to fit a bobbin. On the other hand, there are also cases where winding a bondable magnet wire on a bobbin is useful. Self-bonding coils also serve to bring the winding as close as possible to the metal in the circuit, which gives them greater magnetic capabilities.
Self-bonding coils are used, among other things, for applications in medical technology or in the military, where as much copper as possible must be used in the smallest possible space, in order to increase the performance of a linear motor, for example. Furthermore, baked varnish coils are found in sensors, in drive coils of motors, in RFID applications, in magnetic locks as well as in audio and frequency isolation circuits. Self-supported coils are also widely used for high frequency tuning, interference suppression and high saturation inverter chokes.
Self-bonding wires can be differentiated by the chemical basis of their coating, but mainly by their thermal and technical properties as well as by the preferred bonding process. Wire manufacturer such as HuiLong can provide individual advice here.
The decision whether or not to use a self-bonding coil depends on the project; for many coils, this decision is likely to be influenced by the space required to finish the component and the quantities required. The choice for a self-bonding coil usually results in lower costs and shorter process times for smaller quantities:
On the other hand, the additional assembly effort due to the flying wire ends must be taken into account for higher series sizes. As a rule of thumb, this applies to quantities of around 10,000 or more self-bonding air coils.
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