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Brazing & Soldering © 2009 Harris Products Group Braze Safety • Keep your head out of the fumes • Use enough ventilation and exhaust at the flame or work piece to keep fumes and gases from your breathing zone and general area • Wear correct eye, ear, and body protection © 2009 Harris Products Group Brazing & Soldering • Filler metal melts at temperature below the melting point of the base metal • Filler metal flows through joint via principle of capillary attraction • Requires two closely fitted surfaces • Brazing takes place above 840°F/450C • Soldering occurs below 840°F/450C © 2009 Harris Products Group How does it work? © 2009 Harris Products Group Cohesion and Surface Tension • Cohesion, is the attraction of like molecules. Molecules on the liquid’s surface have stronger attraction. This is called surface tension. © 2009 Harris Products Group Adhesion Forces between unlike molecules is called adhesion. In a brazed joint there are strong adhesive forces between molten filler metal and the base metal walls. We call this wetting. © 2009 Harris Products Group Capillary Action Capillary action is a combination of surface tension and adhesion. It pulls the molten alloy through the joint, and allows you to braze in all positions. Filler Metal Capillary Area (closely fitted surfaces) Base Metals © 2009 Harris Products Group Tight clearance 0.0015 in./0.038 mm Wide clearance up to 0.010 in/0.254 mm Capillary action works best when close clearance can be maintained. Avoid a press fit – no clearance will limit braze alloy flow. © 2009 Harris Products Group Thermal Coefficient of Expansion Metals expand as temperature increases – watch for change in clearance. Maintain 0.002” – 0.005” at brazing temperature. © 2009 Harris Products Group Thermal Coefficient of Expansion Different types of metals expand and contract at different rates. Maintain 0.002” – 0.005” at brazing temperature. © 2009 Harris Products Group Parent Material Braze Alloy Parent Material Recommended braze clearance is: 0.002 in/0.050 mm to 0.005 in/0.127 mm © 2009 Harris Products Group Magnified Braze Joint © 2009 Harris Products Group CLEAN PARTS © 2009 Harris Products Group Clean Parts • Remove oil, grease, drawing compounds • Remove oxide w/Scotch Brite, wire brush, grinder, etc. • If grit blasting avoid embedding silicon, alumina, sand, etc. in base metal - hinders wetting • Chemical cleaning, acid, alkaline, chemical degreasing © 2009 Harris Products Group FLUX © 2009 Harris Products Group Brazing Flux • Dissolves surface oxides and protects against oxide formation during heating • Formulated to be active at braze alloy melting range • Is not designed to be the base metal “cleaner” • Is visually clear at about 1100º F – a good base metal temperature indicator © 2009 Harris Products Group White flux- for most brazing applications Black flux- for extended heating or high temperature localized heat © 2009 Harris Products Group 2000F 1225 F (663C)– Safety Silv 1500F 45 solidus 1190 F (643C) Dynaflow, Stay Silv 15 solidus 1000F Flux clear and quiet Flux begins to melt Flux bubbles 500F Water boils out FLUX BEHAVIOR DURING HEATING CYCLE © 2009 Harris Products Group Braze Flux Removal • Remove flux residue • Hot water & wire brush • Let filler metal solidify before quenching • Overheated parts may require different flux removal method: Grinding Chemical (dilute acid dip) cleaning © 2009 Harris Products Group Heating © 2009 Harris Products Group Only heat fitting = Poor heat transfer © 2009 Harris Products Group Heat tube first © 2009 Harris Products Group Heat fitting second – even heat © 2009 Harris Products Group Apply alloy when both parts reach brazing temperature © 2009 Harris Products Group Direct heat to fitting to draw alloy into fitting © 2009 Harris Products Group Heat tube © 2009 Harris Products Group © 2009 Harris Products Group © 2009 Harris Products Group Heat fitting © 2009 Harris Products Group Apply filler metal only when base metal is at brazing temperature Use flame to draw alloy into the joint © 2009 Harris Products Group Melting Point vs. Melting Range • Pure elements have a melting point. – Cu @ 1981F, (1083 C) – Sn @ 449F, (232 C) • Alloys have a melting range. • Solidus - Melting starts. Above this - part solid / part liquid. • Liquidus - Melting complete. Above this completely liquid. • Brazing usually starts at the liquidus temperature. – May be below liquidus. © 2009 Harris Products Group Copper – Phosphorus Filler Metals © 2009 Harris Products Group Copper – Phosphorus Filler Metals • Copper/phosphorus & copper/phosphorus/silver compositions • Harris 0 • Stay-Silv® 2, 5, 6, 15, Dynaflow® • Use to braze copper to copper • Also copper to brass with Stay-Silv® white flux • Do Not use on steel – joints may be brittle • AWS BCuP classification © 2009 Harris Products Group Examples: Solidus, Liquidus, Melting Range Copper Phosphorus Melting Ranges 1800 1600 1400 1200 1000 800 600 400 200 0 Blockade Harris 0 Harris 0HP Stay Silv 5 Stay Silv 5 LP Stay Silv15 Dynaflow Solidus 1178 1310 1310 1190 1190 1190 1190 Liquidus 1247 1475 1445 1500 1535 1480 1465 69 165 135 310 345 290 275 Melting Range © 2009 Harris Products Group Silver Braze Filler Metals © 2009 Harris Products Group Silver Braze Filler Metals • Safety-Silv® 30, 35, 38T, 40T, 45, 56 • Always requires use of Stay-Silv brazing flux • Primarily used on steel, stainless, nickel, copper alloys, and dissimilar applications • Tin added to lower temperature, nickel added for improved corrosion resistance and strength on carbides • AWS BAg Classification © 2009 Harris Products Group Examples: Solidus, Liquidus, Melting Range 1600 1205 1200 1350 1305 1220 1145 1150 800 400 85 60 200 0 Safety Silv 56 Solidus © 2009 Harris Products Group Safety Silv 50N Liquidus Safety Silv 35 Melting Range Soldering • Soldering is similar to brazing but at lower temperatures, below 840F / 450C • Solders are primarily tin based alloys with various additions of lead, silver, antimony, zinc, etc. • Heat sources include soldering irons, air/fuel torches, propane, and propylene © 2009 Harris Products Group Solders • Tin based solders have less strength than copper based brazing alloys, so solder joints require longer over lap. Usually 5X the minimum base metal thickness is specified to develop adequate strength. © 2009 Harris Products Group Soldering Flux • Like brazing flux, solder flux is designed to protect the base metal from oxidation • Flux is available in liquid and paste form • Solder flux is formulated to be active during solder melting ranges • Solder flux residue must be removed after soldering to prevent corrosion. Non-active rosin fluxes are available for electrical or electronic applications where post-solder cleaning is not practical © 2009 Harris Products Group General Strength Guidelines • Tensile Strength of a Brazed Joint – Joint strength depends on several factors: • Clearance between parts • Base metal composition • Service temperature • Joint quality (voids vs. good penetration) • Joint design • The bulk tensile strength of silver braze alloys is 40,000 - 70,000 psi. When brazing copper-based alloys, failure will often occur in the base metal. When brazing steel or other ferrous metals, joint strength over 70,000 psi can be achieved under the right conditions. • Keep in mind that braze joints are primarily lap type joints and strength is a combination of tensile and shear. Joint strength is directly influenced by the above mentioned factors. The only way to accurately determine tensile or other strength values is to test the brazed assembly. General Strength Guidelines To achieve adequate joint strength, pieces to be brazed should overlap 3 times the minimum base metal thickness. To achieve adequate joint strength, pieces to be soldered should overlap 5 times the minimum base metal thickness. © 2009 Harris Products Group Solder Joint Strength Can be stronger than brazing in some applications. Stay-Silv 15 © 2009 Harris Products Group Stay-Brite Solder The Most Common Braze Problem © 2009 Harris Products Group Inadequate Braze Penetration Void in capillary © 2009 Harris Products Group The Possible Result © 2009 Harris Products Group Product Information & Literature - A Guide To Brazing & Soldering Brochure - Harris Alloy Selection Wheel Chart - Harris HVAC/R & Plumbing Catalog - Website: www.HarrisProductsGroup.com - “Live Chat” on www.HarrisProductsGroup.com main page - Instant messaging product and/or application support - Monday thru Friday 8:00 AM – 5:00 PM EST - Access this feature at the top of the tool bar at our website © 2009 Harris Products Group © 2009 Harris Products Group
