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

Dr.Reem Gamal

Welding

Types:-

pressure welding (cold welding)

spot welding

laser.

PRESSURE WELDING

Pure gold at mouth T

Dr.Reem Gamal

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