What sucks about flux

Chris Carlen · 2005-08-07T16:36:19+00:00

Hi:I have obtained a sample quantity of something closely resembling unobtainium.It is lead-free solder with a melting point of 217C, cored with activated rosin flux. CASTIN alloy from Aim, with composition Sn96.5Ag2.5Cu0.5Sb0.5Aim claims that the wetting action of SAC type alloys decreases with increasing Ag content, and that the 2.5% Ag gives a more optimum wetting than 3.0% Ag typical of SAC305 which is likely to be the industry standard lead-free.They implicate Motorola in having a lot to do with the choice of SAC305, though the fact that CASTIN is patented probably doesn't help.Also, the 0.5% antimony helps to keep grain size consistent over a range of cooling rates which is a large plus for an alloy to be used in hand soldering/rework. Slow cooling tends to cause large grain sizes, resulting in the very frosty appearance of lead-free solder joints.If you have experimented with any SAC305 hand soldering, you will discover that it is possible for the alloy to harden to a shiny joint, but the cooling must occur at a very rapid rate, and having a lot of flux helps as well.The CASTIN's antimony content seems to help make the frosty surface remain as finely grained as possible, and also if a cross section of the joint is examined under a microscope, the CASTIN is more homogeneous with respect to grain size, whereas non-Sb bearing SAC alloys are much more heterogeneous. Thus CASTIN could be expected to deliver more consistent joint strength in non-automated soldering methods.In my initial experiments with the RA-cored CASTIN, I am greatly impressed by how well it wets and flows, as well as its tendency to give a more mildly frosty surface appearance than what often results with SAC305.I think it is the RA flux though, not just the alloy composition that leads to the very good wetting action of RA-cored CASTIN. But perhaps the two factors together are as close to a optimum lead-free as is possible to achieve. It really is not much different from working with...

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Fred Abse 21 years ago

IIRC, back in the 1960s. Not a fully centrifugal clutch, but very light springs, assisted by bob weights. Idling, you could push it out with one finger. Revving, it got tighter. Problem was, the springs got weak, and it would actually stay disengaged idling.

The one I saw was a home market 2CV, in France, about 1970.

I remember those. Infinitely variable transmission using vee belts and expanding pulleys. Well, Holland is pretty flat :-)

"Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

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Jim Thompson 21 years ago

Ah! The joys of our youth! It's funny now, but I don't recall that it was amusing then ;-)

...Jim Thompson

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Paul Burke 21 years ago

Apparently they were only fitted on the few manufactured in Slough (UK), about 1953 onwards.

Paul Burke

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Paul Burke 21 years ago

I had a Citroen Ami 6 with that. The Ami was the same chassis and (600cc) engine as the 2CV, but with a heavier, estate-car type body. We called it the Clockwork Rat.

Once my sister-in-law was driving it, and she forgot about the unusual gearchange gate arrangement in the summer queue to turn right to Chatsworth House. She pushed it into gear straight forwards, jackrabbited the clutch, the car took off backwards- and with that clutch it was virtually unstallable. About three miles of queue behind us did likewise in a great hurry.

That was about 3 months before the carburetter caught fire.

Paul Burke

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Boris Mohar 21 years ago

Especially when you found out where it's been.

Boris Mohar

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Tim Williams 21 years ago

...Kiss my ars[enic]!

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Joerg 21 years ago

Hello John,

Oh yes. Didn't you hate that "ka-cloink" sound when the bowden wire to the clutch went?

The worst I had in my Citroen 2CV was when shifting one-two- thr....whoopsa, there was the engine revving up and the whole stick coming out of the dash. In the middle of rush hour traffic. Luckily fixing that car rarely took more than some scrap wire and a few minutes.

Shortly after that I picked up a hitchhiker and when he saw a bent welding rod coming out of the dash instead of the usual stick his face turned pale.

The synchromesh in a lot of those types of cars tended to vanish over time. I guess the cost reducers figured that you'd be able to shift without after a few years of practice. So they might those rings kind of smallish.

Regards, Joerg

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Fred Abse 21 years ago

With AMIs like that, who needs ennemis?

"Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

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