Bobbin
A spool is a rectangular or cylindrical section of pipe with or without side flanges on which a spool of wire , thread or tape can be wound. The term is mostly used in connection with inductive components such as transformers , coils , chokes and antennas , since the conductor usually either has to be wound up in the form of a wire to fit a magnetic core, or the geometry of an air coil is determined by a coil body. Flanged bobbins often have openings for leading out the wire ends. Likewise, there are usually pins in the bobbins so that the ends of the winding can be connected.
material
Bobbins are often made of plastic . A common method for this is injection molding technology , which offers a very economical manufacturing option. In the past, bobbins were assembled from punched individual parts. The basis was a kit mostly made of impregnated hard paper. This technique is still used today with larger bobbins.
Typically polyamide (PA), more rarely also polybutylene terephthalate (PBT) or polyethylene terephthalate (PET), but almost always glass fiber reinforced polymers are used as material for coil bobbins . Thermosets such as phenolic resins are also used somewhat less frequently . For bobbins in the area of SMD technology, polyphenylene sulfide or liquid crystal polymer are more likely to be used. In addition to mechanical and thermal properties, plastics are often subject to the widespread requirement in electrical engineering for poor flammability ( UL listing ) and high tracking resistance (CTI).
Designs
In the field of plastic injection molding manufacturers, some companies have specialized in coil bodies and the needs for manufacturers of winding goods. Corresponding bobbins are offered in catalogs for the usual core designs such as ferrite cores , laminated cores and cut tape cores . Coils for EI, EE, M / E, UI, EP, ETD, EFD, PQ, EC, PC, RM core designs are widespread. For the coil formers together with the core, there are also suitable housings, which are suitable, for example, for stable attachment, protection against contact or for potting with cast resin .
Connection technology
Since a winding for a coil has at least one beginning and one end, and these ends require an electrical connection to the circuit, it is advisable to integrate connecting pins in the coil body flange to which the wire ends can be wound or connected. The pins are usually made of a bronze and often have a surface protection made of tin . The electrical connection between wire and pin is often made with a soldering process. Since dip soldering is often used here at high temperatures with simultaneous burning off of the enamel insulation of the copper wire, the plastic of the coil body must have a high short-term temperature resistance. These connecting pins are either inserted directly into the injection molding tool and thus overmolded or subsequently inserted into holes provided in the coil former. A common method in Asia is the use of a “lead frame” (stamped part), which is inserted into the injection molding tool and holds the pins together with external connecting webs. The outer area of the lead frame is then punched out on the finished, injection-molded coil body.
various
For the mass production of winding goods , fully automatic winding machines are available on the market, which are supplied with bobbins as bulk goods and which release finished inductive components with assembled core and contacted wire ends every second.
In rare cases, ceramic is also used as the coil body material. In this case, the high-frequency properties or the temperature resistance are often decisive.
In English usage, the terms “bobbin” or “coil former” are used for bobbins.