The most important element in the repair of any equipment is soldering. Solder, fluxes, solder paste - all this must be taken into account when performing repair work. If everything is relatively clear with solder - usually tin-lead solders with different melting points are used for this (depending on the composition of the alloy), then what about the flux? What is it for?
The main purpose of the flux is to remove oxides from the surface, as well as to reduce surface tension in order to improve solder spreading. In addition, soldering flux serves to protect the joint from environmental influences.
What are fluxes
According to their effect on metal surfaces, fluxes are of the following types.
- Active (also called acid). They contain hydrochloric acid, fluorine and chloride metals. Active soldering flux intensively dissolves the oxide film that forms on the metal surface, thereby providing high mechanical strength of the future joint. It should be remembered that the active flux is not suitable for repairselectrical equipment, as its residues corrode the soldering point over time.
- Acid-free. These include rosin, as well as fluxes prepared on the basis of rosin with the addition of turpentine, alcohol or glycerin. Acid-free soldering flux not only cleans the metal surface from oxides, but also protects it from further oxidation. In addition, the use of rosin does not cause surface corrosion. Commonly used when soldering copper, bronze and brass products.
- Activated. They are prepared from rosin, to which phosphoric or hydrochloric aniline, salicylic acid and hydrochloric acid diethylamine are added in small quantities. Activated soldering flux can be used on a wide variety of metals and alloys (iron, copper, nickel, bronze, nichrome, silver, steel). It can also be used to solder oxidized copper alloy parts without stripping them first.
- Anti-corrosion. These fluxes are made from phosphoric acid with the addition of various solvents and organic compounds. In addition, some of these fluxes may contain organic acids. Anti-corrosion flux is used for soldering copper and its alloys, as well as silver, platinum and constantan.
- Protective. These include olive oil, wax, petroleum jelly, powdered sugar. Protective fluxes do not have a chemical effect on the metal, and also protect the cleaned surface from oxidation.
Also for soldering cast iron, carbon steels, and copper and its alloysborax (sodium tetraborate) is used, which is a white crystalline powder with a melting point of 741oC.
Also, borax (more precisely, its mixture with boric acid in a 1:1 ratio) is used for soldering stainless steel and hard heat-resistant alloys.
As a flux for brass products, a mixture consisting of equal parts of s alt and calcium chloride is used.
Aluminum soldering requires a flux with a low melting point. Typically aluminum brazing flux contains 30 to 50% potassium chloride.
Soldering flux is available in powder, liquid or paste form. In addition, there are special solder pastes in which the solder particles are already contained with the flux.
Things to know when soldering
When choosing a flux for soldering, not only the material of the parts to be soldered is taken into account, but also what kind of solder is used. The melting point of the flux must not exceed the melting point of the solder.
Regardless of the type of flux used, the place to be soldered after completion of work must be wiped with a cloth soaked in acetone or rectified alcohol. Then clean this place with a brush or brush moistened with any solvent to remove flux residues. This is especially true of the active flux, since the products of its decomposition not only pollute the place of soldering, but are also a source of corrosion.
