*Brazing & Braze Welding With Oxyacetylene

DefinitionA group of process that use heat to melt a metallic bonding agent, but not the base metal. The adhesion quality of the bonding agent binds the parts together when cooled.*

*Three Common ProcessesSolderingBrazing Braze welding

*Non-fusion welding Advantages & DisadvantagesWhat are the advantages of non fusion welding.What are some of the disadvantages of fusion welding.

*Four Requirements of Non fusion WeldingClean metalAppropriate filler rodCorrect fluxHeat

*Non-fusion Requirements1. Clean MetalNon-fusion processes bond metal by adhesion.--not a polished surface.CleanPolishedWhat is the best method to use?Requires a clean surfaceWhat is adhesion?Can you think of one critical condition that is required for adhesion to be successful?

*Non-fusion Requirements2. Appropriate Filler MaterialDifferent filler materials are available for non fusion welding.Brazing: Brazing rod are available as bare rods or flux coated.Soldering: Solder can be solid or flux core.Flux core can be acid or rosin.Can be tin, silver or zinc alloy.

Is filler material available in other forms?Yes

*Non-fusion Requirements3. FluxThree purposes of flux.Chemically clean the metalShield from oxidation and atmospheric contaminationPromote wettingFlux must be compatible with the metal and filler material.What are the three common forms that are used for fluxes?

*Non-fusion Requirements4. HeatSufficient heat (BTUs) must be available to raise the base metal temperature above the melting point of the filler rod.The decision on heat source to use is based on the mass of metal that must be heated, the welding process and the availability of equipment.

*Non fusion Heat Sources

OxyacetyleneAir acetyleneAir propane (LPG)OxypropaneMAPPElectric soldering ironElectric soldering gun

*Controlling HeatMetals are excellent conductors of heatHeat applied to joint moves away from the joint.The greater the mass of metal that must be heated--the greater the heat requirement.Excessive heat will cause the flux to burn.Contaminates the joint.Joint must be re cleanedManipulation of the heat source may necessary to heat both pieces evenly.

Soldering*

DefinitionA nonfusion process that uses a metal alloy that melts below 840 oF.

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*SolderingSolder is divided into two categories;SoftHardRelies upon capillary action.Describe soft soldering?How is hard soldering different from soft soldering?What is capillary action?What are the requirements for capillary action?

*Soldering ProcessThe joint area is cleaned and fluxed.A heat source is used to raise the temperature of the base metal above the melting of the filler metal (

*TinningTinning is the process of applying a thin layer of filler rod to the surface of the metal.When would the tinning process be used?

*BrazingA process that uses a metal alloy that melts above 840 oF, but less than the melting point of the base metal. Brazing relies on capillary action to draw the filler metal into the joint or to keep it in the joint.

*Brazing ProcessThe joint area is mechanically cleaned and fluxedFlux can be applied before the joint is assembled, or during the brazing process.The joint is assembled.May require clamping.A heat source is used to raise the temperature of the base metal above the melting of the filler metal (>840 oF).Must insure the joint is not overheated.If this occurs the flux will burn and contaminate the joint.When the joint becomes contaminated it must be recleaned and refluxed before the welding can continue.The filler metal is added to the joint.The filler metal flows into the joint and adheres to the surfaces.The heat source is removed and the filler metal solidifies, bonding the surfaces together.

*Brazing JointsThe tensile strength of brazing filler material is less than steel.The strength of the weld is increased if the joints are modified to increase the surface area.Tensile strength of brazing rod is ~40,000 psi.Tensile strength of steel electrode is 36,000 to 50,000 psi.

*Braze weldingA process that uses a metal alloy that melts above 840 oF, but less than the melding point of the base metal. Braze welding is the same process as brazing except it does not use capillary action and a visible bead is formed.Process: The joint area is cleaned and fluxed.A heat source is used to raise the temperature of the base metal to the melting temperature of the filler metal.If excessive heat is added to the joint, the flux will burn.When this occurs the process must start over.The filler metal is added to the joint.The filler metal adheres to both surfaces forming a bead.The puddle must be heated until the key hole collapses.The heat source is removed and the filler metal solidifies, bonding the surfaces together.

*Braze WeldingKey HoleWhen the brazing rod is melted in the puddle, it will bridge across at first--form a key holeSufficient heat must be added to cause the key hole to collapse.Failure to collapse the key hole will result in a joint that has incomplete penetration.

*Braze WeldingJointsThe five (5) standard joints can be used for braze welding.Name them.The five (5) standard welding positions can be used for braze welding.Name them.

*Questions?

***Lower temperatureEasy assemblyWeld dissimilar metalsAllows disassembly/realignmentJoin metals of different thicknessesJoint different types of metal_______Lower tensile strengthNot efficient method for thick metal Not efficient method for large parts**Adhesion is the tendency of dissimilar particles and/or surfaces to cling to one another.

Grinding*barstrippastepowderliquid*Pastepowderliquid****is the ability of a liquid to flow against gravity where liquid spontaneously rises in a narrow space such as a thin tube or is drawn in between to closely spaced surfaces

Requires very small gap between metal surfaces, clean surfaces and flux.

Soft solderingLead or lead replacement solderLower tensile strengthCopper pipe and sheet metalStained glassHard solderingStrongerSilver based solders**Soldering seams. Makes it easier to get the filler material to fill the joint and bond the metals together.

******ButtLapTCorneredge_____

flathorizontalvertical upvertical downoverhead*