One of the only reliable ways in the past to make a good connection between a terminal and a wire was to solder them together. As an alternative to soldering, wire wrapping technology was developed to give electricians a safe and efficient means to connect wires to terminals while still providing a high level of reliability. Both soldering and crimping are two of the most common methods currently to secure wires in electrical applications and electronic items, but wire wrapping is still used for specific applications. The method of wire wrapping is to coil the exposed wire around the sharp corners of a terminal under mechanical tension. This makes wire wrapping helpful in situations when heat cannot be used, or connections and disconnections are repeated.
The use of wire wrapping puts a large amount of tension and compression forces on the terminal's edge to crush both oxide layers of the wire and terminal together. For the bond to occur, about 100,000 PSI is needed at the terminal’s edge. The result is an oxide-free metal-to-metal bond. Depending on manufacturer specifications, a wire wrap with more turns or function may be needed. To save time, pre-stripped wires can help by offering more reliability and determining the amount of turns that are needed, since a minimum number is required for wire function.
For wire wrapping to occur, a special rotating tool known a bit is required. A wire wrapping bit has large hole centralized in the face for marking the spot of rotation on the terminal. The contour of the bit is shaped in such a manner that it allows the proper amount of tension to occur while it guides the wire into a helix that is tightly spaced and consistent. When working with the bit, it is held by a collet, which is guarded by a metal tube called a sleeve. The sleeve helps the worker stay safe while keeping the wire in place during the wrapping process.
Wire wrapped connections can be done in two methods: regular, or a modified version. With the regular method, only exposed or un-insulated wire is used when wrapped around the terminal. The modified wrap uses exposed wire with 1.5 turns of insulated wire coiled around the terminal, requiring a modified version of a wire wrapping bit.
Using the modified wrap can greatly improve on mechanical stability in wires with low strength and thickness, by adding resistance to vibration. The gauge or diameter of the wire plays a big role in the chosen method used in wrapping. When the gauge of the wire is 24 AWG or larger, the regular method of wrapping is generally used. The modified wrap is generally used for a 26 AWG or smaller gauged wire and is used for most 28 to 30 AWG wire wraps exclusively.
When using wire wrapping technology, there are four common mistakes to look out for.
- Using the wrong bit or sleeve can cause loose non-uniform raps, or pig tailing.
- Insufficient turns can occur when the stripped end of a wire is not pushed all the way into the bit.
- Using too much pressure or pressing too hard can lead to overwrapping of the wire.
- By removing the tool before the wrap is completed a spiral and open wrap can result.
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