SOLDERINGBRAZING

AND BRAZE WELDING

OBJECTIVES

Define the terms soldering, brazing, and braze welding

Advantages and disadvantages of liquid-solid phase bonding

Properly clean, assemble, and perform required practice joints

Functions of fluxes in making proper liquid-solid phase bonded joints

INTRODUCTIONSoldering and brazing are classified by the AWS as liquid-solid phase bonding processes

• Base material stays solid and filler material is liquid• Hot Gluing

Phase is the temperature at which bonding takes place

Soldering and brazing differ

• Soldering takes place below 840° Fahrenheit• FAA says its 800F?????????????????????

Capillary action is the force that pulls water up into a paper towel

Braze welding does not need capillary action

Steps in Sweat Soldering

1) Copper pipe is cleaned

2) Flux is applied

3) Heat is applied

4) Solder is added

5) Solder is drawn into fitting via heat (capillary Action)

6) Pipe is wiped cleaned

7) Brazing steps are the same except for Brazing filler metal s added instead of solder.

SOLDERING/BRAZING APPLICATIONS

Steps in Braze Welding

1) Base material is cleaned

2) Flux is applied

3) Heat is applied

4) Braze is added

5) Braze material is added into a joint. Capillary Action is not used.

6) Post Braze weld is cleaned

BRAZE WELDING

Figure 31-2 Capillary action pulls water into a thin tube.

ADVANTAGES OF SOLDERING AND BRAZING

Some advantages of soldering and brazing:

• Low temperature• Permanently or temporarily joined• Dissimilar materials can be joined• Speed of joining• Less chance of damaging parts• Slow rate of heating and cooling• Parts of varying thicknesses can be joined• Easy realignment

Disadvantage

• Service Temp!!!!!!!!!!!!!!!!!

MECHANICAL PROPERTIES

Tensile strength of a joint is its ability to withstand being pulled apart

Brazed joints have a tensile strength 4-5 times higher than the filler metal itself

As joint spacing decreases, surface tension increases the tensile strength

Shear strength is ability of a joint to withstand a force parallel to the joint

For a solder or braze joint, the shear strength depends upon the amount of overlapping area

The greater the area overlapped, the greater the strength

TENSILE AND SHEAR STRENGTH

DUCTILITYDuctility is the ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together to bend without failing.

Most soldering and brazing alloys are ductile metals

Fatigue resistance is the ability to be bent repeatedly without exceeding the elastic limit

Elastic LimitPlastic Limit

For most soldering or brazing joints, fatigue resistance is low

Fatigue failures may occur as a result of vibration and/or cycles of load.

FATIGUE RESISTANCE

FLUXESFluxes used in soldering and brazing have three major functions:

• Remove oxides that result from heating parts• Promote wetting• Aid in capillary action (if soldering or brazing)

Flux must be thin, when heated to its reacting temperature

Fluxes are available in many forms

Paste

Liquid

Powder

SOLDERING AND BRAZING METHODSGrouped according to method of applying heat:

• Torch (TB)• Furnace• Induction• Dip

TORCH SOLDERING AND TORCH BRAZINGAdvantages of using a torch:

• Versatility• Portability• Speed

Disadvantages of using a torch:

• Overheating• Skill• Fires

FURNACE SOLDERING AND BRAZINGAdvantages of using a furnace:

• Furnace brazing is a semi-automatic process• Temperature control • Controlled atmosphere (Common atmospheres used include: inert,

reducing or vacuum atmospheres all of which protect the part from oxidation)

• Uniform heating• Mass production

Disadvantages of using a furnace:

• Size• Heat damage

Figure 31-20 Furnace brazing permits the rapid joining of parts on a production basis.

INDUCTION SOLDERING AND BRAZINGInduction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, where eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal.

Advantage of the induction method is speed

Disadvantages of the induction method:

• Distortion• Lack of temperature control• Incomplete penetration

DIP SOLDERING AND BRAZINGThe parts to be joined are fixtured and the brazing compound applied to the mating surfaces, typically in slurry form. Then the assemblies are dipped into a bath of molten salt (typically NaCl, KCl and other compounds) which functions both as heat transfer medium and flux.

Advantages of dip processing:

• Mass production• Corrosion protection• Distortion minimized

Disadvantages of dip processing:

• Steam explosions • Corrosion• Size• Quantity

FILLER METALSShould be selected by considering as many of the criteria as possible

Welders decide most important criteria

Soldering and brazing metals are alloys

Figure 31-27 Solder being shaped as it cools to its paste range.

SOLDERING ALLOYSUsually identified by their major alloying elements

Base metal can be joined by more than one solder alloy

TIN-LEADMost popular solder

Least expensive

Most commonly used on electrical connections

Never used for water piping

BRAZING ALLOYSThe AWS 's classification system for brazing alloys uses the letter B

Next series of letters indicate the atomic symbol of metals used

Not all available brazing alloys have an AWS classification

Some special alloys are known by their trade names

COPPER-ZINCMost popular brazing alloys

Available as regular and low-fuming alloys

Tendency to burn out when overheated

If breathed in, it can cause zinc poisoning

If you think you have zinc poisoning, get medical treatment immediately

COPPER-ZINC AND COPPER-PHOSPHORUS A5.8Known as brazing rods

Referred to as phos-copper

Vast differences among the five classifications

Five classifications of copper-zinc filler rods:

• BRCuZn• BRCuZn-A• BRCuZn-B• BRCuZn-C• BRCuZn-D

If overheated will cause zinc fumes

JOINT DESIGNSpacing between parts being joined greatly affects tensile strength

Strongest joints are obtained when parts use lap or scarf joints

Some joints can be designed so that the flux and filler metal may be preplaced

Joint preparation is very important

Figure 31-28 The joining area should be three times the thickness of the thinnest joint member.

BUILDING UP SURFACES AND FILLING HOLESSurfaces on worn parts are built up again with braze metal

Ideal for parts that receive limited abrasive wear

Braze buildup has no hard spots

• Good for flat and round stock

Holes in light-gauge metal can be filled using braze metal

Figure 31-51 When building up a surface, alternate the direction of each layer.

SILVER BRAZINGMelting temperature for alloys is around 1400° Fahrenheit

Copper pipe glows a dull red

Best types of flame to use:

• Air acetylene• Air MAPP• Air propane• Any air fuel-gas mixture

SOLDERINGPractices use tin-lead or tin-antimony solders

Both have low melting temperature

Best type of flame:

• Air acetylene• Air MAPP• Air propane• Any fuel-gas mixture

SUMMARYBrazing and soldering have many advantages

• Very versatile• Ability to join many different materials with a limited variety of fluxes

and filler metals

Soldering can be permanent or temporary

Be creative in the way you apply these processes