Grade of soft solder required to achieve a nice rounded fillet

Hi - Can anyone suggest the required grade of soft solder necessary to achieve a nice rounded fillet when for example soldering copper to brass. I am currently using a standard off-the-reel electrical grade of solder which in practice tends to be too fluid in use and does not produce the required fillet.

Heat level and flux used will also play a part in how the solder runs/fillets. 50/50 lead/tin solder gives good workability/ fillet size control, but may be hard to find nowadays with its' lead content. Auto body lead alloy has similar workability.

Modern no-lead plumbing solder is very difficult to use when fillets / appearance are a concern, and any flux bought for use with it is rubbish (in my experience)

The plumbers type of solder has a wider melting range than the eutectic 60-40 tinmans fine. That enabled them to wipe the joints in lead pipes with a moleskin to get a smooth rounded surface.

For cable jointing the solder could be as much as 80% Lead. This solder goes through a 'pasty' stage between solid and liquid, allowing it to be wiped with a 'moleskin' lubricated with tallow. To see a cable jointer at work on 11kV cables was a treat compared with the usual 415V humdrum.

I do have some Kester Organic Core Solder available, the end face of the reel being marked up as SN05PB93.5AGO1.5 #50 HF1189CF. Other than that, no obvious sign of of type of grade. It would appear to be a lead free solder but I have not been able to find out the melting point. Can anyone advise please.

If it is marked Pb93.5 it is certainly not lead free, in fact it is getting towards pure lead. It should be good for wiped joints.

The marking 'SN05PB93.5AGO1.5' means:

Sn (Tin) 5%
Pb (Lead) 93.5%
Ag (Silver) 1.5%

Organic Core means it's an electrical solder, I suspect HF1189CF identifies the particular flux, probably Rosin.

Electrical solder is a lot more expensive than other types because electrical joints mustn't corrode over time and the flux mustn't conduct electricity. As strong fluxes can't be used for electrical work the metal must be very clean, unlike plumbing where cheap aggressive corrosive flux is OK and easier to use.

I don't know what happens when an electrical flux and chemical flux are mixed; I guess the Chemical flux dominates and it behaves like ordinary plumbing solder.

I couldn't find an exact match but 5% Tin and 95% Lead is used for tinning and joining metals. It's fully liquid at 594°F, ie high-melting point compared with 60:40 solder at 374°F.

Adding silver increases the alloys strength, so this is a electrical solder intended to hold joints in testing conditions. Jobs like soldering wires to an electric motor's commutator perhaps. Possibly it's designed to be melted with a torch or a machine.

So it needs to be hot but not that hot - it's still about 400°F cooler than Brazing.

Machinery's Handbook (20th Ed), doesn't give any clues about the filleting properties of Soft Solders, other than 40 Tin : 60 Lead is a wiping solder, and 20:80 was used for Car Body filling. (Is it still available?)

Dave

Plumbers solder used to be 70/30. You can increase the lead content of some electrical solder by simply adding some more lead to a pool of molten solder, then hammer the lump back into wire or cut off slivers depending on you application.

A look down CuP's list of solders will give an indication of their fillet forming properties, the ones you want are towards the bottom of the page

I think lead was eliminated from car production many years ago, the last car we used lead on was the Rolls Royce and that was an old design from the 70s but still in production in the 90s. I expect classic repair workshops still use lead but the H&S precautions were onerous in the factory, air fed suits and shower facilities and negative pressure discing booths were installed, a far cry from the open air discing and hot lead application on general production lines. It makes you wonder how dangerous it was as I can’t think of any one who suffered from any associated illness, perhaps they just used to die and no one knew why.

Mike

Hi All - Many thanks for all the advice offered - Very helpful