What fluxes are used for soldering

Fluxes — substances that ensure the removal of oxides from soldered metals formed during heating, as well as protection of metals cleaned before soldering from oxidation. The fluxes also contribute to a better spreading of the solder during soldering.

Fluxes are selected depending on the metals to be soldered or alloys and solder used, as well as the type of assembly and assembly work. The melting point of the flux must be lower than the melting point of the solder.

According to the effect on the metal, fluxes are divided into active (acidic), acid-free, activated, anticorrosive and protective.

Active streams contain hydrochloric acid, chloride and fluoride metals, etc. These currents intensively dissolve oxide films on the metal surface, which guarantees high mechanical strength of the connection. Flux residue after soldering causes intense corrosion of the joint and base metal.

When installing electrical equipment, active fluxes are not allowed, because over time their residues corrode the soldering place.

Acid-free fluxes include rosin and fluxes prepared on its basis with the addition of alcohol, turpentine, glycerin. Rosin in soldering plays a double role: it cleans the surface from oxides and protects it from oxidation. At a temperature of 150 ° C, rosin dissolves oxides of lead, tin and copper, purifying their surfaces when soldering. This is a very valuable property of rosin, its use in the soldering process does not corrode the surface. Rosin is used for soldering copper, brass and bronze.

Activated flows prepared on the basis of rosin with the addition of small amounts of hydrochloric acid or phosphate aniline, salicylic acid acid or hydrochloric acid diethylamine. These fluxes are used when soldering most metals and alloys (iron, steel, stainless steel, copper, bronze, zinc, nichrome, nickel, silver), including oxidized parts made of copper alloys without prior stripping. Activated flows are LTI flows, the composition of which includes ethyl alcohol (66 - 73%), rosin (20 - 25%), aniline salt (3 - 7%), triethanolamine (1 - 2%). Flux LTI gives good results when using POS-5 and POS-10 tin solders, provided increased junction strength. For soldering copper and copper alloys, constantan, silver, platinum and its alloys use anti-corrosion fluxes. They contain in its composition phosphoric acid with the addition of various organic compounds and solvents. Some anticorrosive fluxes contain organic acids. The remnants of these streams do not cause corrosion.

Anti-corrosion flux VTS consists of 63% technical petrolatum, 6.3% triethanolamine, 6.3% salicylic acid and ethyl alcohol. The remaining flux is removed by wiping the part with alcohol or acetone.

Protective fluxes protect previously cleaned metal surfaces from oxidation and have no chemical effect on the metal. This group includes inactive materials: wax, petroleum jelly, olive oil, powdered sugar, etc

For brazing carbon steels, cast iron, copper, copper alloys, they mostly use borax (sodium tetraborate), which is a white crystalline powder. It melts at a temperature of 741 ° C.

For soldering brass parts with silver solders with flux serves a mixture of 50% sodium chloride (table salt) and 50% calcium chloride. Melting point 605 ° C.

For aluminum soldering, fluxing temperatures below the melting temperature of the solder used are used. These streams usually contain 30-50% potassium chloride.

For soldering stainless steels, hard and heat-resistant copper alloys, copper-zinc and copper-nickel solders, a mixture of 50 ° / v borax and 50% boric acid, with the addition of zinc chloride.

To remove flux residues after soldering, use warm water and a hair brush.