1. Brazing & Soldering
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2. 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
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3. 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/450C
Soldering occurs below 840°F/450C
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4. How does it work?
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5. 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.
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6. 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.
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7. 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
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8. Wide clearance -
up to in/0.254 mm
Tight clearance -
in./0.038 mm
This experiment replicates a brazed joint. Two glass pieces were
clamped together. A tight clearance was held on one side while the
other side was spaced to provide a 0.010” clearance.
The colored water acts like molten braze filler between two metal
parts. Note how capillary action is more effective on the side with
the tighter clearance. This illustrates the importance of controlling
braze tolerance. We also find that tighter clearance and good
capillary action increase joint strength. Generally, 0.002” – 0.005”
(on a side), provides the best capillary action.
Note also the area at the clamp site. Here clamp pressure holds
the glass together so there is no clearance. A “press” or
interference fit has eliminated the capillary and the water flows
around this spot. Insufficient clearance in a brazed joint can cause
incomplete penetration or voids.
Clearance should be measured at brazing temperature. This is very
important in dissimilar metal joints. Clearance may be adequate at room
temperature, but different thermal coefficient of expansion rates may
reduce clearance during heating.
Capillary action works best when close clearance can be maintained. Avoid a press fit – no clearance will limit braze alloy flow.
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9. Thermal Coefficient of Expansion
Metals expand as temperature increases – watch for change in clearance. Maintain 0.002” – 0.005” at brazing temperature.
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10. Thermal Coefficient of Expansion
Different types of metals expand and contract at different rates. Maintain 0.002” – 0.005” at brazing temperature.
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11. Recommended braze clearance is: 0.002 in/0.050 mm to 0.005 in/0.127 mm
Parent Material
Braze Alloy
Parent Material
Recommended braze clearance is:
0.002 in/0.050 mm to in/0.127 mm
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12. Magnified Braze Joint
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13. CLEAN PARTS
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14. 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
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15. FLUX
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16. 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
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17. White flux- for most brazing applications
Fluxes play several roles in brazing. They dissolve metal surface oxide and shield the surface from oxidation formed during the heating process.
Black flux- for extended
heating or high temperature
localized heat
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18. FLUX BEHAVIOR DURING HEATING CYCLE
1225 F (663C)– Safety Silv
45 solidus
1500F
1190 F (643C) - Dynaflow, Stay Silv 15 solidus
Flux clear and quiet
1000F
Flux begins to melt
Flux bubbles
500F
Water boils out
FLUX BEHAVIOR DURING HEATING CYCLE
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19. 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
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20. Heating
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21. Only heat fitting = Poor heat transfer
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22. Heat tube first
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23. Heat fitting second – even heat
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24. Apply alloy when both parts reach brazing temperature
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25. Direct heat to fitting to draw alloy into fitting
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26. Heat tube
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29. Heat fitting
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30. Apply filler metal only when base metal is at brazing temperature
Use flame to draw alloy into the joint
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31. Melting Point vs. Melting Range
Pure elements have a melting point.
1981F, (1083 C)
449F, (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.
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32. Copper – Phosphorus Filler Metals
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33. 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
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34. Examples: Solidus, Liquidus, Melting Range
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35. Silver Braze Filler Metals
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36. 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
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37. Examples: Solidus, Liquidus, Melting Range
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38. Soldering
Soldering is similar to brazing but at lower temperatures, below 840F / 450C
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
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39. 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.
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40. 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
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41. 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 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.

42. 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.
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43. Solder Joint Strength
Can be stronger than brazing in some applications.
Stay-Silv 15
Stay-Brite Solder
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44. The Most Common Braze Problem
Many joint failures are caused by insufficient braze
filler metal in the joint capillary.
A build up of braze material outside the joint will
provide short term strength. It may pass a leak test,
for example, but continued stress or vibration may
cause later failure.
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45. Inadequate Braze Penetration
Void in capillary
This picture shows a braze that looks good from
the exterior but has insufficient penetration to
provide good long term strength.
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46. The Possible Result
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47. Product Information & Literature
- A Guide To Brazing & Soldering Brochure
- Harris Alloy Selection Wheel Chart
- Harris HVAC/R & Plumbing Catalog
- Website:
“Live Chat” on main page
Instant messaging product and/or application support - Monday thru Friday 8:00 AM – 5:00 PM EST
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