Soldering and welding Flashcards
Soldering vs welding process
Soldering is joining of metals by fusion of filler metal between them (glue!)
Welding is union of metal with or without filler metal (more like to fill in gap)
Temperature of soldering vs welding
Soldering takes place at temperature below solidus temperature of metals being joined. Both metals are solid. Only filler metal is molten, and filler metal has melting point less than 450ºC
Welding takes place at high temperature
How does strength of joint in soldered/welded metals compare to parent metals
Stronger, increased mechanical properties
Why is soldering rather than welding used for constructing dental appliances and joining ortho components
High temperature required for welding may result in distortion of casting
What is the effect on soldering of oxide that forms on surface of parent metal during heating
Oxide layer blocks interactions between solder and parent metal
Why is wettability of substrate by molten solder important
Allow molten solder to spread, otherwise weak
Requirements of soldering (4)
Surface must be clean and free of grease and residues
Surface of colour matte not glossy
Superficial roughness of surface to be soldered
Compatible with fluxes
What does flux do
Prevents re oxidation. Reduce oxides formed on surface
What are the 3 types of fluxes
- Surface protection
- Reducing agents
- Solvents
What are surface protection fluxes
Cover metal surface to prevent oxygen access. Oxides not formed
What are reducing agent fluxes
Reduce oxides and expose clean meta
What are solvent fluxes
Dissolve oxides and drive them away
What happens if too much flux is painted on
Flux remains trapped within the filler metal and weakens the joint
What happens if too little flux is painted on
Flux will burn off and there is more oxide than flux. Flux ineffective
Why must solder/filler metal have mechanical properties comparable to structures joined
Otherwise will become the weakest link and make whole structure weak
