Basic Rebuilding Part IV: Why Bother to Silver Solder? COLUMN BY RICHARD R. VENSEL It is a good idea to know the difference between solder with silver in it and silver solder. Solder can have a composition of jj 60/40 or 40/60, which | yy is the tin/lead composition. It melts at about 360 degrees F. Silver solder has 15 percent silver and the balance is cop- per with some phosphorus. It will melt at about 1,300 degrees F. Checking a soldered connection by pulling on the leads means nothing. Remember that some of these connec- tions live in an environment that reaches 350 degrees F on a daily basis, so what looks like a good connection and pull tests OK can become a fusible link very fast. We have all seen or had returned units with one or more unsol- dered brush leads just hanging there. Should I silver solder field studs to the field coils? This is usually not necessary due to the large area that is covered by the sol- der. Keep in mind that a good solder connection has all contact surfaces com- pletely covered by the solder and on the adjoining surfaces you should have a fillet with no voids. I always have a problem with ground brushes. I don’t have a spot welder, can silver soldering help here? Most of the time a ground brush can be replaced by simply cutting the brush lead about 1/2” up from where it is con- nected to the end plate and then silver soldering on a new brush to the short piece of the old brush lead just cut off. A good rule of thumb is to have an overlap between the old brush lead and the new brush lead so your silver solder joint is equal to the surface area of you brush lead. Stop making fusible links and start making good silver solder connections. This practice of silver soldering all field coil brushes will create a consistent quality process and you will be paid back many times for your investment outlay or upgrade. Richard Vensel is owner of Vensel Enterprises, Crystal Lake, Ill. ray) ae