joining of metals joining.pdf · soldering and brazing description of joining two pieces of metals...
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Joining
Of
Metals Dr.Reem Gamal
Joining of Metals
Soldering and brazing description of joining
two pieces of metals using third metal.
if T below425C Soldering
if T above 425C brazing
Welding :- is a word describe joining two
metals by applying heat or pressure or both
with no other metal involved.
Dr.Reem Gamal
Soldering
Soldering Procedures involve :-
Parent metals (metals to be joined)
solder alloy
Flux and antiflux
Heat source
Dr.Reem Gamal
Parent metals (metals to be
joined)
Soldering temperature
Type of suitable flux.
Dr.Reem Gamal
solder alloy The ideal requirements of the solder alloy include:
flow at T less than that of the parent alloys at least 56 oC)
Ability to wet the parent alloy
High mechanical properties
Suitable biocompatibility
Resistance to tarnish and corrosion
Acceptable color and other physical properties
Dr.Reem Gamal
Types of Solder alloys 1-Soft solder
2-Hard solder
Soft solder (plumber’s soldering) :
lead-tin eutectic alloy.
Advantage is its low melting T 260C
Disadvantage is low tarnish and corrosion resistance.
So it is not used in dentistry.
Dr.Reem Gamal
Hard solder:
high melting temperature
greater hardness & strength properties
high tarnish and corrosion resistance.
Tow type gold solder
silver solder
Dr.Reem Gamal
GOLD SOLDERS: gold solders in dentistry are composed of
gold (45-81%)
silver (8-30%)
copper (7-20%)and
tin, zinc and phosphorous melting temperature & flow qualities
Nickel may present instead of copper for white gold soldering.
Gold solders may be described in the karat form or finance.
The solder alloys usually 2 carat less than the parent alloys to be lower in melting range
.
Melting temperature range from 700-900 oC; so it is not suitable for soldering St-St &
base metal alloys why? .
Dr.Reem Gamal
SILVER SOLDERS:
silver solders in dentistry are composed of silver (10-80%)
copper (15-50%)
zinc (4-35%)
tin, cadmium and phosphorus to control melting temperature.
Have lower melting temperature range (600-650C) due to
formation of silver copper eutectic alloy
Used in stainless steel alloys and other base metal alloys
Dr.Reem Gamal
Flux and antiflux Flux = Flow.
Requirement of Flux - Melting T lower than the heated alloys - Not burn nor volatilize or decomposed Role of flux: - Dissolve any oxides formed on the surface of alloys
- Protect the surface from oxidation during heating at elevated temperature - Assist the free flow of the solder alloy
Dr.Reem Gamal
Types of flux:
Boric acid flux; borax, boric acid and silica
used with gold alloys
Fluoride flux; used with base metal alloys due to the oxide on the base metal alloys surface more stable Oxides
Antiflux:
Used to prevent the spreading of solder alloy into undesirable areas.
painting graphite or iron oxide which act as antiflux around
the solder joint area befor application of flux or solder alloy
Dr.Reem Gamal
Heat source:
Types of heat sources;
Gas – air
Gas-oxygen torch (oxyacetylene)
Infra red
LASER
Dr.Reem Gamal
Soldering technique
FREE HAND SOLDERING Assembling performed by free hand Advantage of this technique is its ease and time saving.
Disadvantage is its lower accuracy.
used in assembling orthodontic appliances
INVESTMENT SOLDERING
used in assembling bridges and similar restoration advantage is accuracy.
Dr.Reem Gamal
Practical points for soldering to
avoid failure using suitable type of flux
Correct solder type should be selected
The gap distance between the joined parts 0.13 mm.
For gas and gas-oxygen heating the blue zone why?.
Flame should not be withdrawn until the operation is completed because it give protection from oxidation especially at soldering T
Dr.Reem Gamal
Soldered T should remain below the melting T of
the parts to be joined over heat lead to:
porosity
Warpage
weld decay & recrystallization in the
case of base metal
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Welding
Types:-
pressure welding (cold welding)
spot welding
laser.
PRESSURE WELDING
Pure gold at mouth T
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SPOT WELDING
Eg;- St-St
N.B ;- metals that joined by spot welding
should have lower electrical conductivity
Dr.Reem Gamal
Laser welding
Advantages
Can be performed close to ceramic or polymer veneers the beam is confined
Can use with titanium where soldering
procedures are technically sensitive
Dr.Reem Gamal
THANK YOU
Dr.Reem Gamal