1. Soldering, Brazing and Braze Welding
Ag Metals I
Welding Principles & Applications
Chapter 31

2. Objectives Define the terms soldering, brazing and braze welding
Explain the advantages and disadvantages of liquid-solid phase bonding
Describe the functions of fluxes in making proper liquid-solid phase bonded joints

3. Introduction
Soldering and brazing are classified by the AWS as liquid-solid phase bonding processes
This means…
The filler metals is melted
The base material or materials is not melted
The phase is the temperature at which bonding takes place between the filler and base
The bond between the base material and filler material is metallurgical because no alloying or melting of the base metal occurs
If done correctly, this bond results in a joint that has 5 X’s the tensile strength of that of the filler metal

4. Soldering & Brazing Soldering Brazing
Takes place at a temperature below 804˚ F
Brazing
Takes place at a temperature above 804˚ F
This is the only difference between the two

5. Brazing Brazing Braze Welding
Parts being joined must be fitted so the joint spacing is very small
This small spacing allows capillary action to draw the filler metal into the joint when the parts reach the proper phase temperature
Does not need capillary action to pull filler metal into the joint

6. Advantages of Soldering and Brazing
Low temperature
Permanent or Temporary Joining
Dissimilar materials can be joined
Speed
Less chance of damage
Slow rate of heating/cooling
Parts of varying thickness can be joined
Easy realignment

7. Tensile Strength The joints ability to withstand being pulled apart
Brazed joints can be made to have a tensile strength of 4-5 X’s higher than the filler metal itself
As joint spacing decrease, surface tension increases the tensile strength of the joint

8. Shear Strength A joints ability to withstand a parallel force
Depends upon the amount of overlapping area of the base parts
The great the area of overlap, the greater the strength

9. Ductility The joints ability to bend without failing
Most soldering and brazing alloys are ductile metals making the joints they are made with ductile as well

10. Fatigue Resistance
The joints ability to be bent repeatedly without exceeding its elastic limit and without failure
Fairly low for most soldered or brazed joints
Fatigue failures may also occur as a result of vibration

11. Corrosion Resistance The joints ability to resist chemical attack
Compatibility of base metals to filler metals will determine corrosion resistance

12. Functions of Flux
Remove any oxides that form as a result of heating the parts
Promote wetting
Aid in capillary action

13. Flux in General
When heated to its reacting temperature must be thin and flow through the gap provided at the joint
As it flows through the joint it absorbs and dissolves oxides, allowing the molten filler metal to be pulled in behind it.
Once the joint is complete the flux material should be completely removable

14. Types of Fluxes Solids Powders Paste Liquids Sheets Rings Washers
They are also available mixed with filler metal, inside the filler metal or on the outside of filler metal

15. Fluxing Action
Will remove light surface oxides, promote wetting, and aid in capillary action
But they do not eliminate the need for good joint cleaning
Flux will not remove oil, dirt, paint, glue, heavy oxides or other surface contaminants

16. Soldering & Brazing Fluxes
Soldering Fluxes are chemical compounds such as
Muriatic acid (hydrochloric acid)
Sal ammoniac (ammonium chloride)
Rosin
Brazing Fluxes are chemical compounds such as
Chemical compounds such as
Fluorides
Chlorides
Boric acids
Alkalies

17. What They Do
React to dissolve, absorb or mechanically break up thin surface oxides that are formed as the parts are being heated
Must be stable and remain active through the entire temperature range of the solder or braze filler metal
Chemicals react as either acids or bases
Some dip fluxes are salts

18. General Methods are grouped according to which heat is applied Torch
Furnace
Induction
Dip
Resistance

19. Torch Soldering and Brazing
Oxyfuel or air-fuel torches
Acetylene is the most often used but is not as preferable when compared to other fuel gases
This is due to uneven heating

20. Torch Soldering and Brazing
Advantages
Disadvantages
Versatility
Portability
Speed
Overheating
Skill
Fires

21. Furnace Soldering and Brazing
Parts are heated to their soldering or brazing temperature by passing them through a furnace

22. Furnace Soldering and Brazing
Advantages
Disadvantages
Temperature control
Controlled atmosphere
Uniform heating
Mass production
Size
Heat damage

23. Induction Soldering and Brazing
Uses high frequency electrical current to establish a corresponding current on the surface of the part
The current on the part causes rapid and very localized heating of the surface only
Little if any internal heating of the part except by conductivity of heat from the surface

24. Induction Soldering and Brazing
Advantages
Disadvantages
Speed
Very little time is required for the part to reach the desired temperature
Distortion
Lack of temperature control
Incomplete penetration

25. Dip Soldering and Brazing
Two types
Molten flux bath
Molten metal bath

26. Molten Flux Method
Soldering or brazing filler metal in a suitable form is preplaced in the joint and the assembly is immersed in a bath of molten flux
The bath supplies the heat to preheat the joint and fuse the solder or braze metal and it provides protection from oxidation

27. Molten Metal Method
Prefluxed parts are immersed in a bath of fused solder or braze metal which is protected by a cover of molten flux
Method is confined to wires and other small parts
Once removed from the bath, the ends of the wires or parts must not be allowed to move until the solder or braze metal has solidified

28. Dip Soldering and Brazing
Advantages
Disadvantages
Mass production
Corrosion protection
Distortion minimized
Steam explosions
Corrosion
Size
Quantity

29. Resistance Soldering and Brazing
Electric current is passed through the part
Resistance of the part to the current flow results in the heat needed to produce the bond
Flux is usually preplaced
Material must have sufficient electrical resistance to produce the desired heating
Machine used in this process resembles a spot welder

30. Resistance Soldering Brazing
Advantages
Disadvantages
Localized heating
Speed
Multiple spots
Distortion
Conductors
Joint Design

31. Special Methods Ultrasonic method Diffusion Infrared Light
Uses high-frequency sound waves are used to produce the bond or aid with heat in the bonding
Diffusion
Uses pressure and may use heat or ultrasound to form a bond
Infrared Light
Uses infrared light to heat the part for soldering or brazing

32. Heating Process to be used
Material being joined
Strength desired
Joint design
Availability and cost
Appearance
Service (corrosion)
Heating Process to be used
Costs
The type of filler metal used should be selected by considering as many of the above criteria as possible

33. General Soldering and brazing metals are alloys or two or more metals
Each alloy is available in a variety of percentage mixtures
Almost all have a paste range
A paste range is the temperature range in which a metal is partly solid and partly liquid as it is heated or cooled
It is important that joints not be moved during this stage, if they are they may crumble like dry clay and destroy the bond

34. Soldering Alloys Usually identified by their major alloying elements
The major types of solder alloys are
Tin-lead
Tin-antimony
Cadmium-silver
Cadmium-zinc

35. Tin-lead Most popular Least expensive 61.9% tin and 38.1% lead
Melts at 362˚F
No paste range
Most commonly used on electrical connections
Must never be used for water piping
Also not allowed by most codes for use on water or food handling equipment

36. Tin-antimony Higher tensile strength & lower creep
Most common is 95/5 or 95% tin, 5% antimony
Most commonly used in plumbing because it is lead free

37. Cadmium-silver Excellent wetting, flow and strength Expensive
High temp solders because they retain their strength at temperatures above other solders
Used to join aluminum to itself or other metals
Most often seen used in piping for air conditioning equipment

38. Brazing Alloys
Denoted by the letter B to indicate the alloy is used for brazing
Next series of letters in the classification indicates the atomic symbol of metals used to make the alloy

39. Copper-zinc Most popular brazing alloy
Available as regular and low-fuming
Zinc in the braze metal has a tendency to burn out if overheated
Overheating is indicated by a red glow on the molten pool which gives off white smoke
The white smoke is zinc oxide, if breathed in it can cause zinc poisoning. Use of low fuming alloy helps eliminate this problem
Examples of low fuming alloys are RCuZn-B and RCuZn-C

40. Copper-zinc & Copper-phosphorus A5.8
Copper-zinc filler rods are often grouped together and called brazing rod
5 classifications
Copper-zinc
Navel Brass
Manganese-Bronze
High silicon-Bronze
Nickel-Bronze

41. Copper-phosphorus Referred to as phos-copper
Good fluidity and wettability
Used in A/C and plumbing to join copper piping

42. Copper-phosphorus-silver
Referred to as sil-phos
Similar to copper-phosphorus except the silver gives the alloy better wetting and flow characteristics
Not necessary to use flux when joining copper pipe
Most common brazing alloy used in A/C compressor fittings

43. Silver-copper
Can be used to join almost any metal, except aluminum, magnesium, zinc and a few other low-melting metals
Often referred to as silver braze
Most versatile
Among most expensive alloys except gold

44. Nickel
Used for joining materials that need high strength and corrosion resistance at elevated temperatures
Applications include
Joining turbine blades in jet engines
Torch parts
Furnace parts
Nuclear reactor tubing
When used on copper based alloys, the nickel may diffuse into copper, stopping its capillary flow

45. Nickel and Nickel Alloys A5.14
Increase being used as a substitute for silver-based alloy
More difficult to use than silver due to lower wetting and flow characteristics
Higher strength than silver
7 classes
BNi-1: high strength, heat resistant, used in jet engine parts
BNi-2
BNi-3: high flow rate, excellent for close fitted joints
BNi-4: higher surface tension than other nickel filler rods, allows larger fillets and poor-fitted joins to be filled
BNi-5: high oxidation resistance and high strength at elevated temps, can be used for nuclear applications
BNi-6: extremely free flowing, good wetting characteristics, high corrosion resistance
BNi-7:high resistance to erosion and can be used for thin or honeycomb structures

46. Aluminum-silicon Used to join most aluminum sheet and cast alloys
AWS type 1 flux must be used
Must guard against overheating

47. Copper and copper alloys A5.7
BCu-1
Used to join ferrous, nickel and copper-nickel
BCu-2
Similar applications to 1
Contains organic compounds to tie up porosity

48. Silver & Gold
Used in small quantities when joining metals that are under corrosive conditions and high joining ductility is needed or low electrical resistance is important
Increasing price and decreasing availability

49. Joint Design
Spacing between the parts being joined affects tensile strength
Strongest joints are obtained when the parts are lapped
Butt joint strength can be increased by increasing the area being joined
Joint preparation is also very important
Surfaces must be clean and free of oil, dirt, paint, oxides
Soldering or brazing should begin as soon the parts are cleaned to avoid further contamination

50. Building Up Surfaces and Filling Holes
Braze metal can be used to build up worn parts
Ideal for parts that receive limited abrasive wear because buildup is easily machinable
Has no hard spots to make remachining difficult
Good for both round and flat stock
Low temperature used does not tend to harden the base metal
Holes in light gauge metal can be filled and ground flush leaving a strong patch with minimum distortion

51. Summary
Brazing and soldering are process that have many great advantages that are often overlooked.
They are an excellent process for portable applications and the versatility makes them great choices for many jobs.
Their ability to join may different materials with a limited variety of fluxes and filler metals reduces the need for a large inventory of materials.