ThinLayerAnalysis.co.uk
Investigation of electrical crimp connector
Crimp
connectors are widely used, especially for automotive applications.
The connector is generally very reliable and is easy to fit,
without the use of solder. The high reliability may
be surprising when the environment is considered, often wet, maybe with
salt - ideal for the development of a corrosion cell. However,
this simple connector possesses a secret. Crimping relies on
squeezing the copper conductors so that they undergo plastic flow.
When correctly applied, the copper flows to fill any voids thus
preventing ingress of water and subsequent corrosion. It is
important that the conductors receive high pressure from all sides in
order to reduce the chance of subsequent creep releasing the wire.
Also, when a spade and receptacle are connected the very
high contact pressure ensures a true metal to metal contact, with the
sliding action breaking down the surface oxides. Thus a low
electrical resistance is achieved. Connectors are often
maufactured using copper alloys, such as brass (or even copper itself
which may be tinned) so that the potential for galvanic corrosion is
reduced or even eliminated.
A wide range of crimping tools are available, from professional devices
costing in excess of £100 to cheap plier type ones at less than a
pound. There is little question that the expensive tools are very
efficient, however, can a cheaper tool really provide sufficient force
to cause the wire to flow?
A brass crimp spade connector was fitted to a multi-strand
insulated copper conductor. Note that this tool is very simple
and makes little provision to avoid lateral spread of the
connector in the crimped region.
After setting in resin, the connector was sectioned near to the
midpoint of the crimped region and the cross section polished.
The result is part good and part not so good. On the left-hand
side one can see that there has been significant modification of the
circular cross section of the wires, with a very dense structure being
developed. Some flow of the brass of the connector is also
evident, especially around the very left-most wire. However, as
we look further to the right, the structure becomes more open.
Although most of the wires show some change of shape there are
plenty of spaces that would collect moisture by capillary action.
Also, the voids provide room for the copper to creep into over
time, reducing the internal compressive stress and thus permitting the
wires to loosen - again risking corrosion.
It will come as no surprise to find that the open end of the crimping
tool was towards the right, with the pivot to the left. The
scissor action necessarily means that a higher force, and a closer gap,
will be achived at the pivot end than the open part of the tool.
The result could be significantly improved by applying the tool twice
and using the end nearest to the pivot to squeeze both left and right
sides individually. However, for a quick and easy
connection where full current carrying capacity is not required, the
cheap crimping tool does a surprisingly good job.