Are crimp connections really cold welded?

[Fred Winterburn]

This was discussed in the condenser outside the distributor thread, but I thought it would make sense to start it over here. I must say that I have taken many crimps apart and have never seen any evidence of cold welding. Just tight mechanical connections. I'm not saying it doesn't happen, I'm just saying it likely doesn't happen very often. I've attached an old article (there are many others out there) that purports that the low to nil voltage drop of crimp connections over time is due to there being sites that are cold welded within the joint. However I've seen wires twisted together and covered with tape that several years later did not show any voltage drop even with considerable amperage through the circuit.  Yet, I have seen many corroded and high resistance crimps from the wire to connector interface  especially in automotive wiring. I like soldered joints for this reason, but crimps sometimes are the only practical alternative in which case I seal them with dielectric grease to keep salt and moisture out. What are other's experiences here?  Real personal experiences, not references to oft repeated lore or other publications if possible. Fred  

whitleycrimptheory_p142-74.pdf

[Lebro]

I will read that when I have more time (a lot more !)

Bob.

[stillp]

As I wrote in the other thread, when I had the Tech College facilities I sectioned a number of crimped terminations and had our metallurgy department polish and etch the surface then examine them under a microscope. The ones that were correctly crimped had achieved cold welds. The terminals were uninsulated, and crimp tool I used was the type that makes a dimple in one side of the terminal while supporting the round cross-section of the opposite side of the terminal.

Most of the problems with crimps are caused by using a tool that isn't matched to the terminals being used, or by the tool not being squeezed enough, hence the ratchet crimp tools that are insisted upon by (good) electricians.

After I left the college job I worked for an automotive component manufacturer for a few years, and found that the QA Manager had done some similar research with the same results, but on a much greater number of samples. In vibration testing soldered joints failed at a rate about 10 times that for crimped joints IIRC.

Strangely though, my wife worked for a company that made wiring looms for BL, and they tinned the ends of the wires before crimping!

NASA do not allow crimped joints on solid conductors. I believe this is because a single solid conductor is liable to break adjacent to the cold weld due to deformation of the crystal structure.

Pete

[RobH]

Perhaps the answer is the point made in that paper about crimps being a 'system'.  Industry users will source the whole system from one supplier, probably with certified compliance to some standard and will use them on wire of the correct specification - but does the same hold for the average DIY user? 

What are the chances of crimp connectors bought on e-bay that look about the right size, and a crimp tool from Screwfix or wherever, being compatible enough to be a system which provides the optimum joint as described ?  Unlikely perhaps?  There certainly seems to be a variation in crimp connectors in terms of dimensions and metal thickness depending on where they come from. 

 I have never been impressed by the strain-relief arrangements on the insulated crimp connectors where there is no plastic 'boot' used.  It is quite common to see a gap between the end of the insulation and the connector on DIY crimps.  For that reason I avoid using that type and  fit a heat-shrink sleeve to support the wire for at least 1/2 inch back from the joint as well as the plastic boot over the whole thing. 

 

[stuart]

1 hour ago, RobH said:

 

What are the chances of crimp connectors bought on e-bay that look about the right size, and a crimp tool from Screwfix or wherever, being compatible enough to be a system which provides the optimum joint as described ?  Unlikely perhaps?  There certainly seems to be a variation in crimp connectors in terms of dimensions and metal thickness depending on where they come from. 

 

 

Precisely why I hate to see the dreaded blue crimp connectors used anywhere on cars that come in as you can guarantee they werent made using a compatible system.

Stuart.

[roy53]

so what should we use    

[RogerH]

Hi Roy,

some thing like these - + the plastic boots.

https://www.vehiclewiringproducts.co.uk/c-60-terminals/c-72-non-insulated-terminals/c-74-blade-terminals

Roger

[stillp]

+ the same supplier's ratchet crimping tool.

Pete

[MikeF]

From what I recall... the criteria for crimping is gas tight, ie contact is so intimate oxygen , water vapour can not get in. Whether crimping or soldering is better is moot in my opinion as in real life it depends on technique. For sure soldering before crimping is not recommended as solder creeps under stress and this will eventually lead to failure of the crimp. Of course the duty cycle on our cars is not that onerous so the time to fail may be so long it is irrelevant which method was used.

 

Mike