Brazing / Adhesive Bonding Flashcards
When do you use brazing / soldering?
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
What temperature are joining processes carried out at?
Room or slightly above.
Define brazing.
When a filler metal is melted and distributed throughout joint by capillary action.
Base metals don’t melt, only filler.
What temperatures are brazing fillers melted at?
above 450C, but below melting temp of metals being joined
Will the brazed joint be weaker or stronger than the filler metal? Why?
Stronger,
small clearances are used,
metallurgical bonds occur between the base and filler, geometric constraints of the base parts.
What are the disadvantages of brazing?
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
What joint types are most likely to be brazed?
Butt and lap joints, because they provide larger surface area for bonding.
What are some typical filler metals?
Aluminum, silicon, copper, zinc, gold, silver
What are some typical base metals?
Aluminum, nickel, copper, steel, cast iron
What are desirable properties of brazing fillers?
Low surface tension in liquid phase
High fluidity
Adequate strength
What are some of the heating methods in brazing?
Torch Furnace Induction Resistance Dip (molten salt or molten metal bath) Infrared
Define soldering
Brazing, but filler metal melts below 450C.
Lower energy required, easier heating, easy repair, but low strength, and bad at elevated temps
What are solders (soldering fillers) made of?
Alloys of tin and lead
How are soldered joints secured?
Mechanically
What is the function of flux in soldering and brazing?
To melt during the process, remove oxide films and tarnish, promote wetting, and then be displaced by the molten solder or braze.
How is soldering done?
Same as brazing, as well as hand soldering, wave soldering (multiple lead wires), and reflow soldering
What are the attachment mechanisms of adhesive bonding?
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)
What are the four types of adhesive joints? Which are strongest?
Shear and tension strongest
Cleavage and pulling weakest
How are synthetic adhesives usually cured?
Mixing catalyst with polymer prior to applying Heating Radiation Evaporating water Pressure
Why is surface preparation important in adhesive bonding, and how is it done?
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
