Machinery's Handbook, 31st Edition
1572
Brazing Table 2. Guide to Selection of Brazing Filler Metals and Fluxes
AWS Brazing Flux Type No.
Effective Temperature
Flux Method of Use b
Filler Metals Recommended a
Flux Supplied As Powder Powder Paste or Powder Paste or Powder Paste, Powder, or Liquid Paste, Powder, or Liquid
Base Metals Being Brazed
Range, ° F ( ° C)
Flux Ingredients
All brazeable aluminum alloys All brazeable magnesium alloys Alloys such as aluminum-bronze; aluminum- brass containing additions of aluminum of 0.5 percent or more Titanium and zirconium in base alloys
700–1190 (371–643) 900–1200 (482–649)
Chlorides, Fluorides Chloides, Fluorides
1, 2 3, 4 3, 4
BA1Si
1 2
BMg
Chlorides, Fluorides, Borates, Wetting agent
1050–1800 (566–982)
1, 2, 3
BCuZn, BCuP
4 c
700–1600 (371–871)
Chlorides, Fluorides, Wetting agent
BAg
6
1, 2, 3
Boric acid, Borates, Fluorides, Fluorates,
All brazing filler metals except BA1Si and BMg All brazing filler metals except BA1Si, BMg, and BAg 1 through BAg 7
700–2000 (371–1093)
3
1, 2, 3
Wetting agent Must contain fluorine compound Borax, Boric acid Borates, Wetting agent
Any other brazeable alloys not listed above
1000–2200 (538–1204)
5
1, 2, 3
No fluorine in any form
a Abbreviations used in this column are as follows: B, brazing filler metal; Al, aluminum; Si, silicon; Mg, magnesium; Cu, copper; Zn, zinc; P, phosphorus; and Ag, silver. b Explanation of numbering system used is as follows: 1—dry powder is sprinkled in joint region; 2—heated metal filler rod is dipped into powder or paste; 3—flux is mixed with alcohol, water, monochlorobenzene, etc., to form a paste or slurry; 4—flux is used molten in a bath. c Types 1 and 3 fluxes, alone or in combination, may be used with some of these base metals also. metals may be considered as grouped into the seven standard classifications shown in Table 1a and Table 1b. These are aluminum-silicon; copper-phosphorus; silver; nickel; copper and copper-zinc; magnesium; and precious metals. To avoid confusion, Table 1a and Table 1b give the filler metal’s solidus and liquidus temperatures, rather than the melting and flow points. The solidus is the highest temperature at which the metal is completely solid or, in other words, the temperature above which the melting starts. The liquidus is the lowest temperature at which the metal is completely liquid, that is, the temperature below which the solidification starts. Fluxes for Brazing.— In order to obtain a sound joint the surfaces within and adjacent to the joint must be free from dirt, oil, and oxides or other foreign matter at the time of brazing. Cleaning may be achieved by chemical or mechanical means. Some of the mechanical means employed are filing, grinding, scratch brushing and machining. The chemical means include the use of trisodium phosphate, carbon tetrachloride, and trichloroethylene for removing oils and greases. Fluxes are used mainly to prevent the formation of oxides and to remove any oxides on the base and filler metals. They also promote free flow of the filler metal during the course of the brazing operation. They are made available in the following forms: powders; pastes or solutions; gases or vapors; and as coatings on the brazing rods. In the powder form a flux can be sprinkled along the joint, provided that the joint has been preheated sufficiently to permit the sprinkled flux to adhere and not be blown away by the torch flame during brazing. A thin paste or solution is easily applied and when spread on evenly, with no bare spots, gives a very satisfactory flux coating. Gases or vapors are used in controlled atmosphere furnace brazing where large amounts of assemblies are mass-brazed. Coatings on the brazing rods protect the filler metal from becoming oxidized and eliminate the need for dipping rods into the flux, but it is recommended that flux be applied to the base metal since it may
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