Applying solder.

additional water is required to maintain full effectiveness. More water or flux

should be applied to the areas of the metal to be soldered while reheating or

changing the soldering iron. Unless the flux is refreshed the solder will not bond

to the metal.

(c) When using the acid-type or paste flux it is necessary to wash the

surface with water to remove all traces of flux residue. When cored solders are

used, separate fluxing is unnecessary since the flux and solder are applied in one

operation.

d. Applying solder.

(1) Solder should be applied directly to the joint before the flux has a

chance to evaporate. The tip of the soldering iron should be kept in contact with

the metals being soldered until the solder flows freely over the joint. Heating of

the metal should not be continued past this point or the solder will flow away from

the joint along the sides of the metal pieces. Insufficient heating of the metals

will prevent the solder from flowing freely, creating a weak cold joint.

(2) Bar and solid wire solders may be applied either to the tip of the iron

and flowed onto the work or applied directly to the heated surfaces. The latter

method is more advantageous because it is easy to tell whether or not the surfaces

have been sufficiently heated. The metals to be joined must be heated enough to

melt the solder. When using acid core or rosin core solders, the solder should not

be applied directly to the hot tip of the iron and dripped on the work but should

be applied directly on the surface (fig 25A). Melting acid or rosin core solders

on the hot tip will cause evaporation of the flux, possibly resulting in an

imperfect joint. After using acid core solders, the end of the solder wire should

be crimped before storing to prevent loss of acid.

Figure 25A.

Correct and incorrect methods of using cored solder.

(3) When soldering large joints, the movement of the soldering iron is

important. When the iron is moved too slowly, the molten solder tends to spread

away from the joint being soldered. If the iron is moved too rapidly, the solder

will not have a chance to melt completely, the cracks in the joint will not be

filled, and a weak joint will result. When soldering heavy materials, the iron

should be moved slowly. On light materials, whose melting point approaches that of

the solder, the iron should be held at one spot no longer than necessary to melt

the solder thoroughly. When using a very hot soldering iron, the angle of the iron

should be shifted as the work progresses so that more and more of the flat tinned

surface of the tip comes in contact with the surfaces being soldered. This

procedure will keep the applied heat more constant. With an electric soldering

iron, no shifting is necessary, for its heat remains stable.

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