Silicon coated wire.

[Terence Lynock]

Around six months ago I wired up some models with silicon coated wire from a far eastern supplier, to keep things tidy I tacked the wire down with spots of Ca or hot glue.

I have decided to scrap out a couple of models that suffered in the house move and started to strip out all usable electronics and found that where the glue was stuck to the cable the silicon rubber had rotted, it just pealed away from the wire cores.

Be very careful of this stuff, it could cost you a model...

[Erfolg]

Terrance

 

In recent years I have only used GC or HK silicon cable, with to date no apparent issues.

 

I Suspect that the cable I purchased in the UK could well have had its origins in the Far East.

 

Could it be an issue with CA with this type of cable in general.

 

There is a well known phenomena called environmental stress cracking (ESC) where contact of a polymer with a chemical causes long term failure. I am also sure we all have stories where polymers have been adversely affected with otherwise innocuous substances.

 

Another reaction we all potentially recognise is that of CA with canopy type materials.

 

Perhaps I am suggesting this type of issue is an ever present problem, where we need to be vigilant, and exchange information as you have done.

[Martin Harris - Moderator]

I suspect that CA kicker degraded some servo cable - luckily, quickly enough for me to notice before the covering went on...

[Kozmyk]

I thought CA wouldn't adhere properly to silicone rubber unless a primer was used first.

[Tom Wright 2]

I use thin strips off industrial grade velcro.Iworks really well.

[James40]

I wouldn't use CA on cables no matter what country they originated from, hot glue or epoxy yes but CA can be nasty stuff.

[Barrie Dav 2]

Where do you get your industrial grade velcro Tom?

[Vecchio Austriaco]

Strange behaviour of the silicon - normally this material shouldn't be affected by chemicals. Also the stress cracking mentioned by Erfolg shouldn't be critical as the wires are not outside but inside the plane.... So the UV radiation is limited. In any case we learned that Erfolg has experience in the cable industry.... (which I know since some time)

One thing is that silicone rubber insulation is very weak from mechanical point of view - so if the glue sticks to the material it is very easy to tear it of the conductor.

[Tom Wright 2]

From a guy who works at a local stainless steel fabricating company barry.It comes on 50m rolls I will send you some if you let me have your contact details ,the adheasive backing is brilliant.

VECCHIO your comment re silicon is correct .

[Barrie Dav 2]

Tom. I've PM'd you

 

Barrie

Edited By Barrie Dav 2 on 31/01/2011 14:00:47

[Tom Wright 2]

Barry i am new to this tinternet thing PM;d?

[Tom Wright 2]

Must be personal message ? what do i do?

[Barrie Dav 2]

I'l send you a private message (PM). Go to your account. Entitled 'My Account' and look up 'My Messages' in the list. You should see in there any private message sent to you by a forum member.

[Barrie Dav 2]

Tom. I'm having a problem with sending messages. I'll write to you as soon as the problem is sorted.

[David Ashby - Moderator]

Barrie, you won't be able to message Tom as he hasn't enabled the function (no public profile).

[David Ashby - Moderator]

Tom, I've just enabled your profile so making it easier for folks to message you.

[Barrie Dav 2]

Thank you David. All is clear..........

 

Barrie

[Tom Wright 2]

Thanks david.

[Tom Wright 2]

Barry I have students who want to fly now I will get back around 4.30 pm ish.

[Tom Wright 2]

David I will do a profile asap thanks for your help may need more yet.

[Peter Beeney]

 

I first met this phenomenon a few back. The accompanying photo says it all. This was a mates rx pack for a large petrol-engined model, he handed it to during one flying session, it was nearly in that state, and said would I like to take a ganders? It seemed he’d noticed a glint of copper when peering into the fuz and this is what it was. The battery was about 3 months old and the silicone insulation was completely perished or perhaps just simply rot. It was falling off the wires as you touched it. We thought long and hard about what may have caused this, some petrol traces from his hands, or fumes perhaps, but as he was very careful when handling the petrol anyway, as he said, he didn’t like the stuff so kept his hands dry, so we ruled that out. Later I put some other silicone insulation, and some normal fuel tubing in some neat petrol and after 4 days it had gone very sticky but did not show any signs of falling apart.

When I saw it I quickly cut the wires at the battery, and later rewired it with a standard Futaba battery wire and plug. I never heard any more, so it must have been ok after that, he may well still be using it, I must ask him.

I wrote to the old Flight Power establishment about this and included some other photos, plus a small sample of this wire as well. I also suggested that any other batteries wired from the same rolls of original wire may have a problem. Needless to say, no reply. But then I’ve never read or heard of of anyone else ever having a problem either, which seems slightly odd.

It did cross my mind at the time, that had this gone unnoticed, then shorted in flight, with a fully charged pack this may well then have been put down to just one more lithium polymer battery fire. So how many other fires have been caused by something like this?

As an aside, and completely different, back in the eighties there was some telephone cable, multi-conductor for use in the exchanges. This is very low voltage, so the insulation is a thin PVC type material. The many wires are squeezed tight inside the outer sheath, and it was suddenly noticed that a clear liquid, like glycerine, was dripping out of the ends! Under pressure, the insulation was reverting back to it’s liquid state! I guess some questions were quickly being asked! Accompanied by a load of cross-talk, maybe?

Seems as though there is always something of interest going on.

PB

Edited By Peter Beeney on 31/01/2011 15:15:50

[Erfolg]

Vechchio

 

I was not thinking of UV degradation, where photons knock of an atom and then oxygen cross links typically with hydrogen. Wow you have really taken me back, to my days as a student

 

I was thinking really of the type of problem that occurred when the big yellow gas pipes were used, and some chemicals used in testing could cause stress cracking.

 

Putting my engineers hat on, working for BICC, I remember that very few pure polymers were used in industry. Typical additions were, plasticisers, colourants, extenders (make it go further), and as i vaguely remember it the list goes on and on. Also some polymers take on water into their structure, and did not become suitably flexible until they did.

 

My own opinion is that many plastics are not stable over the long term, as say stainless steel. They are often adversely affected by some chemicals, yet can be very good with other chemicals. Often you will feel tacky plastics, where the plasticizer has leached out, or maybe a white powdery film on surfaces exposed to the environment.

 

One aspect that many, including some engineers do not recognise, is that the working temperature of polymers can be very narrow, that is compared  with metallic materials. They become embrittled often around 0C yet much more than say 100C they can be melting, the specified performance data being fixed on say 20C, anything else, do not count on the data.

 

Do not think I am anti plastics, as I am not, i see them as materials with their own set of limitations.

Edited By Erfolg on 31/01/2011 15:38:17

[Vecchio Austriaco]

Silicon rubber doesn't contain softeners - therefore the problem of softener migration which could make things either sticky or brittle should not happen,.

What you normally find in silicone compounds are mineralic fillers - sometimes for their special properties (fire performance) or sometimes just to delute the compound to make it cheaper.

Whatever caused the problem - it shows that we have to be carefull - such a defect as shown in the pictures could easily lead to a fire due to short circuit.

[Tom Wright 2]

Hi David done it.

[Tom Wright 2]

Hi David I think the profile is on? when you have a min could you confirm,thanks .