Soft soldering

Soldering is used not only to make a mechanical hond between surfaces but also to provide a leak-proof seal when Uqulds have to he contained. It can also be used to provide a permanent electrical connection. To provide a secure joint, it is essential that the joint surfaces are perfectly clean and free from rust, grease or any other substance likely to prevent good metal-to-metal union. The most likely cause of a bad joint, assuming the surface is clean, is the thin oxide film which is present on all metals. Oxide films can be removed using emery clotb or a flux. 

Fluxes used in soft soldering are either active or passive. 

An active flux chemically removes the oxide film, has an acid base, and is highly corrosive. These fluxes are usually hydrochloric acid in which zinc has been dissolved to form zinc chloride, known as killed spirits . Any joint prepared using an active flux must be thoroughly washed in warm water when soldering is completed, to remove any flux residue. For this reason an active flux is not suitable for electrical applications. 

A passive flux is used after the oxide film has been removed using emery cloth, to prevent the oxide film reforming. Passive fluxes are usually resin-based. Cored solder, containing a resin-based flux, is usually sufficient for electrical work. 

The type of heat source used for soldering depends largely on the size of the parts to be joined. The greatest problem is usually heat loss to the surrounding area by conduction through the metal. The temperature in the joint area must be high enough to melt the solder and allow it to flow and combine with the surfaces to be joined. 

A passive flux is used after the oxide film has been removed using emery cloth, to prevent the 

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The metal is employed to form numerous alloys with other metals. Brass, nickel silver, typewriter metal, commercial bronze, spring bronze, German silver, soft solder, and aluminum solder are some of the more important alloys. 

Alloys of tin are very important. Soft solder, type metal, fusible metal, pewter, bronze, bell metal. Babbitt metal. White metal, die casting alloy, and phosphor bronze are some of the... 

Lead—silver alloys are used extensively as soft solders these contain 1—6 wt % silver. Lead—silver solders have a narrower free2ing range and higher melting point (304°C) than conventional solders. Solders containing 2.5 wt % silver or less are used either as binary alloys or combined with 0.5—2 wt % tin. Lead—silver solders have excellent corrosion resistance. The composition of lead—silver solders is Hsted in ASTM B32-93 (solder alloys) (7). 

One of the interesting things about the lead-tin diagram (Fig. 4.1) is that all alloys containing between 2.5% and 81% of added lead start to melt at 183°C even though some - as we have just seen - don t become completely molten until they are quite a bit hotter. This is obviously a problem when we want to use soft solders in hot surroundings, because they will rapidly lose their strength as they get near to 183°C. 

Figure A 1.1 shows a phase diagram for the lead-tin system (the range of alloys obtained by mixing lead and tin, which includes soft solders). The horizontal axis is composition Xpg (at%) below and Wpg (wt%) above. The vertical axis is temperature...

Metal considered platinum, rhodium, silver aluminium bronzes, tin bronzes, gunmetals brasses, nickel silvers Nickel Lead, On and soft solders and cast iron... 

Joints in copper components may be a source of trouble. Copper/zinc brazing alloys may dezincify and consequently give rise to leaks . In some waters, soft solders are preferentially attacked unless in a proper capillary joint. Copper/phosphorus, copper/silver/phosphorus, and silver brazing alloys are normally satisfactory jointing materials. Excessive corrosion of copper is sometimes produced by condensates containing dissolved oxygen and carbon dioxide. Rather severe corrosion sometimes occurs on the fire side of fire-back boilers and on electric heater element sheaths under scales deposited from hard waters . 

Soldering Conventional soft solders can be used, but it is first essential to nickel- or copper-plate the molybdenum. 

SOFT SOLDERED JOINT BETWEEN 22 SW.G, SILVER WIRE AND RUBBER-COVERED COPPER CABLE... 

Thwaites, C. J., Soft-Soldering Handbook, Int. Tin Research Inst., London, Publication No. 533 (1977)... 

Hydrochloric acid is not to be used where austenitic SS, galvanizing, tinning, soft solder, or enamels are present. When properly inhibited, HC1 can be used to clean admiralty brass, bronze, cupro-nickel, and monel. 

The fired-on silver films on glass can be soft-soldered. They should be tinned with a solder containing some silver ordinary soft solder can bring about complete dissolution of the silver film. Matthey Ceramic Solder No. i is a suitable solder for the films. A resin-type flux should be used. Tinning can be carried out by dipping into the molten solder. 

All soft solders are alloys composed mainly of lead and tin mixed in proportions that vary from as little as 30% lead (and 70% tin), to as much as 98% lead (and only 2% tin). The brazing metals are mostly alloys of copper or silver their composition, as well as that of other alloys used since antiquity for soldering, are listed in Table 48 (Zhadkevich 2004). 

Fig. 3.14. Relative linear thermal expansion coefficient of (1) Invar, (2) Pyrex, (3) W, (4) Ni, (5) Cuo.7Ni03, (6) stainless steel, (7) Cu, (8) brass, (9) Al, (10) Torlon, (11) soft solder, (12) Vespel SP-22, (13) Hg, (14) In, (15) Araldite, (16) Stycast 1266, (17) PMMA, (18) Nylon, (19) Teflon [60]. Some additional data are Ag between (8) and (9) Stycast 2850 GT slightly larger than (9). The integral contraction between 300 and 4K is 103AL/L = 11.5, 4.2, 6.3 and 5.7 for Stycast 1266, Stycast 2850 GT, Vespel SP-22 and solders...

The mechanical and electrical contact between two metals may be made by soldering them together. Unfortunately most soft solder become superconducting at low temperature (see Table 4.3). 

Figure 4.12. The position in the Periodic Table of a few classes of commercially important metals. L Light metals, R Refractory metals, F Ferro alloy metals, P Precious metals, C Coinage metals and S Soft solder metals.

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