Brazing / Adhesive Bonding

Question 1

When do you use brazing / soldering?

Answer 1

When metals have poor weldability
When you are joining dissimilar metals
When the heat of welding might damage components
When the geometry isn’t suited for welding
When high strength is not required
When you need something to be quick and consistent, for high production rates

Question 2

What temperature are joining processes carried out at?

Answer 2

Room or slightly above.

Question 3

Define brazing.

Answer 3

When a filler metal is melted and distributed throughout joint by capillary action.
Base metals don’t melt, only filler.

Question 4

What temperatures are brazing fillers melted at?

Answer 4

above 450C, but below melting temp of metals being joined

Question 5

Will the brazed joint be weaker or stronger than the filler metal? Why?

Answer 5

Stronger,
small clearances are used,
metallurgical bonds occur between the base and filler, geometric constraints of the base parts.

Question 6

What are the disadvantages of brazing?

Answer 6

Joint strength is less than a welded joint, and less than the strength of the base metals
High temps may weaken a brazed joint
Colors may not match

Question 7

What joint types are most likely to be brazed?

Answer 7

Butt and lap joints, because they provide larger surface area for bonding.

Question 8

What are some typical filler metals?

Answer 8

Aluminum, silicon, copper, zinc, gold, silver

Question 9

What are some typical base metals?

Answer 9

Aluminum, nickel, copper, steel, cast iron

Question 10

What are desirable properties of brazing fillers?

Answer 10

Low surface tension in liquid phase
High fluidity
Adequate strength

Question 11

What are some of the heating methods in brazing?

Answer 11

Torch
Furnace
Induction
Resistance
Dip (molten salt or molten metal bath)
Infrared

Question 12

Define soldering

Answer 12

Brazing, but filler metal melts below 450C.

Lower energy required, easier heating, easy repair, but low strength, and bad at elevated temps

Question 13

What are solders (soldering fillers) made of?

Answer 13

Alloys of tin and lead

Question 14

How are soldered joints secured?

Answer 14

Mechanically

Question 15

What is the function of flux in soldering and brazing?

Answer 15

To melt during the process, remove oxide films and tarnish, promote wetting, and then be displaced by the molten solder or braze.

Question 16

How is soldering done?

Answer 16

Same as brazing, as well as hand soldering, wave soldering (multiple lead wires), and reflow soldering

Question 17

What are the attachment mechanisms of adhesive bonding?

Answer 17

Chemical bonding (primary bond is between adhesive and adherend)
Physical interactions (secondary bonds between surface atoms)
Mechanical interlocking (adhesive gets entangled in surface asperities of adherend)

Question 18

What are the four types of adhesive joints? Which are strongest?

Answer 18

Shear and tension strongest

Cleavage and pulling weakest

Question 19

How are synthetic adhesives usually cured?

Answer 19

Mixing catalyst with polymer prior to applying
Heating
Radiation 
Evaporating water
Pressure

Question 20

Why is surface preparation important in adhesive bonding, and how is it done?

Answer 20

Bonding requires clean surfaces to fully adhere
For metals, solvent wiping and sandblasting is used
For nonmetals, surfaces are mechanically abraded or chemically etched to increase roughness