Project Description
  • 0
  • 23 August 2017



Most metals and alloys react with the gaseous atmosphere surrounding them. A layer of difficult to melt non-metallic compounds and in particular oxides form on their surface, The intensity of this process increases with temperature. This layer, present both on the surface of bonded elements as well as the melted filler metal, to a large extent hinders the spreading of the filler metal which results in the inability to create a durable bond between the brazed elements. Fluxes should be used in order to ensure the required purity of the bonded surfaces and the filler metal.


The primary requirements for the correct flux operation include:

  • the flux should not enter into chemical reactions with the filler metal (except for reaction brazing),
  • the flux should sufficiently clean oxides from the surfaces of the brazed object and filler metal and protect them against atmospheric influence during brazing.
  • the flux melting temperature should be below that of the filler metal and its evaporation temperature – higher,
  • fluxes in liquid form and gas form should improve the wetability of the surface of the shape, or improve the spreading of the filler metal,
  • fluxes should maintain their properties and chemical composition during the temperature increase under brazing,
  • the flux should not cause a strong corrosion and should not emit toxic gasses whilst brazing,
  • the flux should easily flow to the surface of the liquid filler metal and allow for the formation of a regular and smooth piece of filler metal surface during filler metal settling.
  • after brazing flux slag covering the bond should be as easy as possible to remove [2],
  • mutual attraction between the liquid flux and brazed metal should be less than that between the brazed metal and liquid filler metal, which is a pre-condition for the flux easily flowing to the surface


Due to their use, fluxes fall into two primary groups:

  • Flux for soldering
  • Flux for brazing

Flux for soldering
Flux for soldering classification by their main ingredients acc. to PN-EN 29454-1:2000

Flux typeCoverActivatorForm
Resin11 Colophony1 Without activator

2 Halide activator *

3 Non-Halide activator
Liquid A
Solid B
Paste C
2 Non-colophony (resin)
Organic11 Water soluble
2 Not water soluble

Non-organic 3

1 Salts
1 With ammonium chloride

2 Without ammonium chloride

2 Acids
1 Phosphoric acid

2 Other acids
3 AlkalisAmines and/or ammonium
* Other activators may be used.

Flux for brazing

Flux for brazing in accordance with PN-EN 1045:2001

ClassTypeMelting temp. rangeCharacteristics ingredientsUse designation

FH10550-880°Cboron compounds, simple fluoridesGeneral use flux
FH11550-800°Cboron compounds, simple and complex fluorides, chloridesbrazing copper alloys and aluminium
FH12550-850°Cboron compounds, free boron, simple and compound fluoridesbrazing stainless steel and other steels and hard metals
FH20700-1000°Cboron compounds, fluoridesGeneral use flux
FH21750-1100°Cboron compoundsGeneral use flux
FH30550-880°Cboron compounds, phosphates, silicatesbrazing using copper and nickel filler metals
FH40>1000°Cchlorides, fluoridesbrazing when the presence of boron is unwanted
FL2)FL10>550°Chygroscopic fluorides, mainly lithium compoundsbrazing aluminium and its alloys
FL20>550°Cnon-hygroscopic fluorides
1)Flux for brazing heavy metals

2)Flux for brazing light metals
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