Introduction to Basic Manufacturing Processes and ... - always yours

344 Introduction to Basic Manufacturing Processes and Workshop Technology
3. Flux application
Soldering cannot be done without a flux. Even if a metal is clean, it rapidly acquires an
oxide film of submicroscopic thickness due to heat and this film insulates the metal from the
solder, preventing the surface to get wetted by solder. This film is broken and removed by
the flux. The flux is applied when parts are ready for joining.
4. Application of heat and solder
The parts must be held in a vice or with special work holding devices so that they do
not move while soldering. The parts being soldered must be heated to solder-melting and
solder-alloying temperature before applying the solder for soldering to take place the assembly
so that the heat is most effectively transmitted to the being soldered.
As soon as the heat is applied, the flux quickly breaks down the oxide film (the insulating
oxide layer barrier between the surface and solder). Now solder is applied which immediately
melts and metal to metal contact is established through the medium of molten solder. Finally,
the surplus solder is removed and the joint is allowed to cool. Blow torches dipping the parts
in molten solder or other methods are also used for soldering.
17.14.2 Solders
Solders are alloys of lead and tin. Solder may also contain certain other elements like
cadmium, and antimony in small quantities. The percentage composition of tin and lead
determines the physical and mechanical properties of the solder and the joint made. Most
solder is available in many forms-bar, stick, fill, wire, strip, and so on. It can be obtained in
circular or semi-circular rings or any other desired shape. Sometimes the flux is included with
the solder. For example, a cored solder wire is a tube of solder filled with flux.
17.14.3 Solder Fluxes
The flux does not constitute a part of the soldered joint. Zinc chloride, ammonium chloride,
and hydrochloric acid are the examples of fluxes commonly used in soldering. The function
of fluxes in soldering is to remove oxides and other surface compounds from the surfaces to
be soldered by displacing or dissolving them. Soldering fluxes may be classified into four
groups-
(1) Inorganic fluxes (most active)
(2) Organic fluxes (moderately active)
(3) Rosin fluxes (least active), and
(4) Special fluxes for specific applications
17.15 QUESTIONS
1. What is welding? How is it classified?
2. What are the advantages, disadvantages and applications of welding joints over other joints?
3. Explain the various types of joints commonly used in welding.
4. Explain the different kinds of welding positions with neat sketch.
5. Using neat sketch show the various standard location of elements of a welding symbol.
6. Classify the various welding processes in detail. Describe each in brief.