Our Technical Advices
Crimping for connection of heating or conductive yarns within a multi-layer fabric or composite part or mold
Connections with our heating or conductive yarns can cause hot spot risks. This risk is even more important when high powers are involved, for heating molds or composite parts for instance.
Within flexible structures, vibration and industrial washing withstanding are key for these connection.
Conventional crimping of ultrafine conductive wires
We recommend to use small crimping to assure good connection between your different sensors or électrodes within flexible or stretchable structures that have to be washed.
Please choose the right diameter, related to the wires, as crimp bush !
Our wires being often ultrafine and flexible, it is important to choose the closest crimping diameter to enter the wire , or both wires eventually.
Crimp bush illustrated here Under are rather made for data transfe. In case of use for heating applications, make sure that the material is withstanding high temperature and , even more important, that it has enough length and thickness to cope with the current , so that the connection remains a cold spot ( to be checked with thermographic camera if case of doubt).
To assure the insulation, it is recommended to place a shrink bush , but it is also important to limit the bending constraints just at the rigid crimp output!
How to crimp or connect electro heating wires whan you cannot weld? In any case, avoid screw-connectors !
Most of the resistive based alloy yarns we manufacture are note weldable. Therefore we recommend to use crimping connections.
What about usual screw connections ?
Our flexible conductive yarns are made from a high number of ultra-thin filaments to improve their fatigue life. As you can see on the drawing below, a single screw connection will only connect a few number of the fibers through the screw or the internal surface of the connecting device. As we work with resistive fibers, all the current will go through this limited number of fibers before the load can spread through the whole cross section of the wire. This will cause over heating of these fibers and a very dangerous hot spot in the vicinity of the connection point.
What kind of connections do we recommend ?
To get an ideal connection, all the fibers of the cross section should be in direct contact with the conductive material of the power input connector. In reality, we consider a connection as acceptable when all the fibers on the external layer of a yarn are in direct contact with the power input cable or the crimping connector on a sufficient length.
What can be used as a crimping connector ?
The connection shall be a "cold spot". To do so, the connector materials must be very conductive (copper or aluminium for instance). The shape of this connector shall be a small tube just fitting the diameter of the heating wire, plus the diameter of the conductive yarn (see picture below). Many solution exist on the market, most of time with an outside thermo-shrinkable insulating material.
How to manage fatigue issues at the crimp and thin flexible wire interface ?
The interface between the rigid connector and the flexible heating yarn is where the strain applied to the heating wires is the highest. As a result, it is where the fatigue issues usually occur. If a wide angle of movement exist, we recommend to move the connector to an area where these movements are more limited or to add a movement limitation device or a thermo shrink sleeve.