The introduction of lead – free alloys has heavily influenced not only the manual welding procedures, but also the duration of the tips that has significantly reduced. The higher percentage of tin contained in the LF alloys and a higher re-melting point make them extremely aggressive in their double action of corrosion (chemical action) and abrasion (mechanical action) and cause an evident shortening of the average life of the tips. The most common drawbacks are the perforation of the outer coating and consequently of the copper core and the lack of wettability of the work area of the tip.
In lead-free alloys, the tin content exceeds by more than 30% that contained in lead-based alloys, this has led to considerable increases in wear on the tips of welders. The effect of the very strong erosion action exerted by the tin on the surface of the tips affects the iron coating, an action strongly influenced by the higher working temperatures often used. The current metallurgical technology used in the construction of the tips, allows only to increase the thickness of the galvanic treatments to protect the heart of the copper tip and avoid a premature end; however, it should be considered that there is a limit beyond which an excess of galvanic iron deposit would impair thermal conduction.
For the most commonly used LF alloys it can be said that their remelting point is greater than about 30 / ° C compared to Sn / Pb alloys, but contrary to the current idea in manual welding operations it is not necessary to set the temperatures of the welders at levels higher than those already used previously.
The ideal working temperature should be maintained around 380 ° C, adapting it from time to time to the different thermal masses in play, but always bearing in mind that it is good that the temperature used is as low as possible.
Among the main variables of a manual welding process is the correct choice of the tip. Compatibly with the size of the welding joints to work on, the tip should be as large as possible. There is an analogy that illustrates the concept well: as in a larger tap is the mouth and the greater the flow of water that comes out, so for a larger welder is the tip and the greater the flow of heat that is in able to convey on the joint. The transmission of heat will be all the more effective as it will be appropriate cleaning and maintenance that ensures good wettability at the tip.
The tips of the welder at first sight are presented as simple objects, with a single body, in reality they are composed of various parts. The heart is made of copper, has the task of bridging between the temperature source of the welder and the welding joint; it is required a high thermal conductivity and for this reason it is this chosen copper that in addition to being a good current conductor is also a good conductor of heat. The copper is galvanically coated with an iron protection, this shirt has the task of providing a high resistance to wear and allow parallel to have an excellent wettability. The thermal conductivity of the iron is lower than that of copper (about five times)
so its thickness is designed to mediate the two required characteristics: give a good degree of protection without reducing the thermal conductivity of the tip. A galvanic chrome coating follows, which has the task of delimiting the wettable area, that is the work area of the tip that consequently requires to be clean and always tin-plated, to preserve the wettability of the tip and the efficiency in transferring the heat. The wettability of the tip is guaranteed by the formation of an intermetallic phase of a few microns between the facing iron and the tin of the soldering alloy. Because of the difficulty inherent in the process that leads to the coating, the geometry of the tip influences the thickness of the coating because the finer the tip and the more problematic the galvanic deposit of iron on the copper becomes.