Paste Brazing & Soldering Alloys - Fusion Incorporated - #10

C lea n i n g

Brazed or SoldereickJoints

• Corrosive Generally composed of strong organic or inorganic acids which promote high-speed cleaning of metals with strong surface oxides. Corrosive residue should be removed to prevent damage to the joint.

Liquidus The lowest temperature at which a particular metal or metal alloy will remain in a completely molten state. Generally considered the melting point of a particular filler metal.

Oxidation (Also, Surface Oxides) A

chemical reaction promoted by oxygen and moisture in the air, wherein clean metal surfaces are covered with a metal oxide film which prevents proper wetting with soldering or brazing filler metal. Since oxidation accelerates during heating, the metal must not only be cleaned initially, but protected from oxidation during the joining process.

Slump The relative tendency of a paste alloy to sag or flow away from a slop­ing or vertical joint. Largely a function of paste rheology this may occur while the assembly is cold, or during heating - before the paste alloy has reached melting temperature.

Soldering A joining process whereby a non-ferrous filler metal is heated to melting temperature (below 840°F and below that of the base metal) and distributed between two or more close-fitting parts by capillary attraction. Upon cooling, the filler metal adheres tightly to the base metal of either part, achieving coalescence.

Solidus The highest temperature at which a particular metal or metal alloy will remain completely solid.

Wettability (Also, Wetting Action) The

ability of a specific flux and/or filler metal to flow onto a clean metal surface, unrestricted by oxidation or^ other impurities at the point of contact.

G lossary

As Applied to Fusion Paste

Brazing & Soldering

Cleanliness of a brazed or soldered joint - both before and after assembly -is most important. Fusion offers Fuze-Clean metal preparation chemicals for \precleaning and postcleaning of base metals. These products are supplied ip-a" dry powder form and prepared by mix­ing with water at a specific ratio and temperature^ince these materials do not ccmtain strong^acids, they are gen­erally safer than most conventional cleaning agents. Although conditions vary depending on the type of base and filler metals used, joint design, and performance requirements of the finished part, the following general guidelines may be helpful.

Although a proper flux will remove and exclude light oxidation during heating, foreign matter such as grease, oil, paint, cutting fluids, etc. should be cleaned away before the part reaches the assembly point. If not removed, such materials may inhibit proper capil-lary~attraction during heating and/or prevent the fluxlHeTfTfoTTT^ctrng-— directly on the metals being joined. Pre-cleaning methods may be divided into the following two categories:

Chemical Cleaning with solvents, acid or pickling baths compatible with the contaminants and the metals used. Such procedures should always be followed by thorough rinsing. Fusion offers the following pre-cleaner:

• Fuze-Clean AB An alkaline cleaner that removes heavy deposits of oil, grease, and soils from aluminum and brass surfaces.

Mechanical Removal of exceptionally heavy^deposits via brushing, grinding or ^-Wasting withlan abrasive agent. In the case of blasting, care must be taken that the abrasive itself is not left to contaminate the joint area. It is suggested that soldering or brazing be performed as soon as possible after any pre-cleaning operation.

A significant benefit of the Fusion Paste Process is that the type and amount of flux is carefully controlled, yielding mini­mal flux residues. Nonetheless, flux \residues of a corrosive nature must be removed to prevent damage to the joint over aRs^xtended period. Suggested cleaners ra^most popular Fusion fluxes are noted in the^elector charts on pages 7 and 11. Since these, too, may vary depending on the^ba^e metal, heating techniques, etc., tlwfollowing additional guidelines are offered:

Rosin Type Flux Residues Generally, these are non-corrosive and may be left on the part without damage to the joint area. If residue removal is desired, it may be removed using alcohols or chlorinated hydrocarbon solvents, or combinations of both famiJiesr—~

Intermediate and Corrosive Solder Fluxes (Halides) These fluxes leave a fused residue which absorbs airborne moisture, causing a slow chemical reaction at the joint. Removal is gener­ally accomplished by thorough washing in warm detergent water, or in hot water containing dilute hydrochloric acid, followed by hot water rinse.

Aluminum Brazing Fluxes (Water Wash­able) Generally about 90% of such residues may be removed by immersing the hot part in water. For more thor­ough cleaning, immerse parts in a 15% nitric acid/85% water solution, under agitation for 30 seconds at room temperature, followed by two hot water (60-70°C) rinses at 20 seconds each, then a final cold water rinse.

Low-Temperature Brazing Fluxes These residues may be removed with hot water - along or with detergents, alka­line cleaners, or acid cleaners. The most effective method is largely dependent on the base metals involved.

High-Temperature Brazing Fluxes (Borates) These hard, glass-like deposits are insoluble in many cleaners. They may be cracked off, however, by quenching the hot assembly in water immediately after brazing. A solution of dilute hydrochloric acid mayajso-be^" helpful. Fusion offers an all-purpose brazing postcleaner:

• Fuze-Clean FS Dissolves flux residues and heat scale on both ferrous and non-ferrous metals after brazing. It eliminates the use of strong acids and \ abrasive processes, besides removing \ rust, mill and heat scale directly on \the production line. Use in an ultra­sonic tank is recommended.

Atmosphere A controlled brazing or soldering environment achieved by xcluding oxygen and replacing it with oVie or a mixture of other gases. In roduction, this technique will minimize or eliminate the need for flux, as the atmosphere itself, combined with heat, acts to redLfce^existing surface oxides. Most often associated with furnace brazing.

Base Metal (Also, Parent Metal) The

alloy or pure metal which is to be joined via soldering or brazing.

Binder A blending agent which, when added to paste brazing or soldering alloys, keeps\the atomized filler metal and flux in stable suspension, prevents interaction of the two, and maintains extended shelf life.

Brazing A joining process whereby a non-ferrous filler metal is heated to melting temperature (above 840°F) and distributed between two or more close-fitting parts by capillary attraction, its liquidus temperature, the r~^l+ filler metal interacts with a thin layer of the base metaV-cooTing to form an exceptionally strong joint due to grain ----structure interaction!

Capillary Attraction A natural force of adhesion governed by the relative attraction of liquid molecules for each other and for those or two adjoining solids. As applied to soldering or braz­ing, the process by which liquid flux and filler metal are transported along the length of a close-fitting joint.

Dew Point A reference method of determining the amount of water vapor (and resultant oxygen) in a controlled-atmosphere brazing operation. The Dew Point is that temperature at which

water vapor of a given concentration will begin to condense, or become liquid.

Eutectic A specific alloy composition (two or more metals) that melts at a single temperature and not over a range: i.e., Solidus and Liquidus temperatures are the same.

Filler Metal An alloy or pure metal which, when heated, liquifies to flow into the space between two close-fitting parts, creating a brazed or soldered joint.

Fillet A clearly-defined bead of solder or brazing alloy which forms on and abound the completed joint.

Fitup The joint clearance between two base metals to be soldered ofbrazed. Although requirements vary by technique andiype^f joint, optimum range for paste brazing and soldering is generajjy<^02 to .004^nch.

Flux A material which, When heated, serves to remove and exclude surface oxides from the base metal. Blazing fluxes are generally of a highly corrosive nature. Solder fluxes may be classified into one of the following groups: ^

• Non-corrosive A rosin or mildly actrVe organic acid used in wetting clean surfaces and producing a residue which is neither electrically conduc­tive nor corrosive to the finished joint. Although such fluxes are active at elevated temperatures, they are inert at ambient temperature.

• Intermediate Generally, a mild organic acid which activates upon heating to achieve considerable stronger fluxing action than non-corrosive types. Relatively inert residue should be removed to ervstire^

_JojnUeliability.

Activated Rosin Fluxes Some rosin activators will cause corrosion under unusually hot or humid conditions. Most may be removed using alcohols or chlorinated hydrocarbon solvents, or combinations of both families.

Oily or Greasy Flux Residues Generally may be removed with an alkaline cleaner such as Fuze-Clean S.