The terms "soldering copper" and "soldering iron" have the same
meaning. For simplicity, the term "soldering iron" will be used
throughout this text.
b. Hard soldering (silver soldering). The hard soldering method is used when
the materials to be joined are subjected to temperatures above the melting
temperature of soft solder or when a stronger joint is required than can be made by
using soft solder. Hard soldering is often called "silver soldering" or "silver
brazing". Hard soldering (silver soldering, or silver brazing) has been covered in
section V of this lesson. The remainder of this section will be devoted to the
fundamentals and general application in the soft soldering field only.
TYPES AND FORMS OF SOLDER.
a. Types of solder.
(1) The most common material used as a soft solder bond is an alloy
composed of 50 percent tin and 50 percent lead. This is known as "half and half"
or 50/50 solder, the tin content being represented by the first figure. Solders
having various other proportions of tin to lead, such as 60/40, 40/60, and 30/70,
may be obtained for use on certain jobs.
(2) It is essential that the solder "set" or alloy with the metal surface on
which it is applied. Tin is the principal "wetting" or alloying element of soft
solders; lead is added to decrease the cost of the mixture and because it has a low
melting point (like tin). Solders with a high lead content cool slower than
solders containing mostly tin; therefore, they leave a smoother joint.
(3) The 50/50 solder, which reaches the plastic stage at approximately
300F and turns liquid at 415F, is suitable for soldering automobile radiators,
iron, and sheet steel. An alloy of 60 percent tin and 40 percent lead is generally
used where the temperature of the work requirement is critical. This alloy has a
very narrow plastic range; it becomes plastic at approximately 360F and liquid at
approximately 370F. Solders containing 30 percent tin and 70 percent lead are
specially used for filling dents and welding joints on automobile bodies; they have
a wide plastic range and are most suitable to this type of work. This solder
becomes plastic at approximately 360F and remains mostly in that state until
approximately 495F, when it turns to a near liquid form.
b. Forms of solder. Soft solders are manufactured commercially in solid 1
pound bars and wire forms (fig 20). Solder is also obtainable in special forms
such as pellets, rings, washers, and other unusual forms for special applications.
Wire solder is wound on a spool and may be solid or contain a core of compressed
powdered rosin (rosin core solder) or acid (acid core solder). Cross sectional
views of a solid and several acid and rosin core solders are shown in figure 21.
To prevent the liquid acid from leaking from the acid core solder, the solder is
crimped at short intervals. Wire solder is designated by number, and the core size
determines the ratio of solder to flux, regardless of strand size, type of flux, or