BDS [Orthodontics] course

1. SOLDERING AND WELDING
PROF (Dr.) SAIBEL FARISHTA

2. SOLDERING
DEFN:
 Soldering is a method of uniting two
metals by means of a metallic fusible
alloy (solder) Which is more fusible
than metals and is used in the molten
stage

5. Requirements Of A Good
Solder
 Melting point should be below that of
metals to be soldered
 Strength and hardness should be as
near as the metal to be soldered
 Solder should melt and flow freely
 Should not tarnish or corrode

6. Theories Of Soldering:
 Mechanical union soldering
– Lower surface tension
– Capillary attraction
– Flow (from position of lower temp to higher
temp)
 Chemical union soldering: The solder
flows and alloys between the two metals
and a intermediate alloy is formed in the
middle which fuses completely with the two
pieces of metal

7. Varieties Of Solders
 Soft solder-contains Sn and Pb and they
have a Lower melting point. They are not
used in dentistry as they are not strong
and are liable to corrode.
 Hard solder-Used in dentistry as they are
stronger, more resistant to tarnish and
corrosion and have a higher melting point.

8. Types Of Hard Solders
• Gold solder: Used for gold and
platinum work (Platinised gold should
always be soldered by 18 K gold
solder)
• Contains Gold-65%,Cu-14%.Ag-15%,
Zn-3.5%

9. Types Of Hard Solders
• Silver solder-- stainless steel is
mainly soldered by silver solder there
are two grades (A & B). The best
silver solder that is used for stainless
steel is known as B grader or
Turbines silver solder and it contains:
Silver 43%, copper 37%, Zn 20%
and melts at 7750 C

10. Flux
 Flux: is a reducing agent which
absorbs the metallic oxides as they are
formed and thus prevents oxidation of
the metal during heating.

11. Gold Solder
 Fluxes used in gold solders are :
 Borax-glass 55%
 Boric acid 35%
 Fine silica 10%
 Petrolatum

12. Fluxes Used In Stainless
Steel Soldering
 Ordinary borax
 Blue borax
 Equal parts of Boric acid and
potassium fluoride They are mixed
together and dissolved and evaporated
to solid residue, the residue is crushed
and when required, paste is made with
water and used

13.  It is necessary to prevent the steel
surfaces being oxidized. If it occurs it
may be difficult for the solder to
adhere. Hence a reducing flame
should always be used for soldering
 and the operation should be done
quickly as possible to prevent
oxidation.

14. Requirements Of A Flux
 Flow easily
 It should melt easily
 It should be able to wet the solder &
metal surface to form an intimate contact
between the two
 It should not have effervescence or bubble
 It should also be able to remove the
undesirable oxides & the impurities
present on the surface.

15. Factors Required For
Successful Soldering
 Perfect cleanliness: metal surfaces
should be free of oxide,sand paper the
area, pickle it in acid or boil in solution
of sodium bicarbonate,put it in water
and then wash it with alcohol do not
touch the area to be soldered.
 Good contact between the metal
surfaces for strong joint

16.  Temperature should be within the range of
the solder.
 If over-heated the solder will ball up due to
loss of zn and sn
 In stainless steel soldering avoid over
heating of the steel as it may soften the
metal.
 Suitable amount of flux should be used.

17.  Specific solders should be used eg-
gold for gold soldering and platinum
and silver solder for stainless steel.
 Use very little solder for a strong joint.

18. Methods Of Soldering
 Free hand soldering
 By investing or assembling the parts on a
cast. Plane gas can be used for soldering,
provided it can be made into fine jet, air
jet can be added.
 Soldering can also be done by carbon
electrode, by using a ordinary welder.
 However flame is the best and easiest
method of soldering.

21. WELDING

22. Welding
 Welding is the process of uniting two
pieces of metal without the
intervention of any other metal or
alloy as in soldering

24. Electric Welding
Stainless steel requires electric welding or
application of heat in Some form with the aid
of pressure if necessary for union.
TYPES OF ELECTRIC WELDING
ARC WELDING SPOT
WELDING
LASER WELDING

25. Spot Or Resistance
Welding
Used in stainless steel. Heat is applied
indirectly through the resistance of the
metal. It is considered as the most
permanent and satisfactory way of
uniting stainless steel

27.  When a current passes through a
metal conductor due to resistance,
heat is generated and the quantity of
heat produced depends on two factors
 Amount of current
 Resistance to the current

28. Resistance to the current is offered by the
metals to be welded together. In spot
welding heat required is generated by the
resistance offered to the electric current by
the parts to be joined the temperature of
the heat generated should be near the
melting point of the metals, hence heavy
current is used.
Current Used = 250 - 750 amps

29. Principles Of Welding
 Maximum Current Should Be Used For A
Short Time to Prevent The Metal From
Getting Softened And Deformation.
 The Time Of Current Flow Should Be 1/25
To 1/50 Of A Second.( A Switch Is Provided
To Regulate The Flow)
 It Is Necessary To Press The Two Metal
Parts Firmly And To Maintain The Pressure
Till The Weld Has Cooled.

30. Types Of Spot Welding
 Manual switch type tapping method
using a switch to step on.
 Dial or pulsation type
 Capacitor welder

31. Capacitor Welder
 Electronic device where the timing is
reduced to a shorter fraction, energy is
stored in the capacitor in a predetermined
amount.
 The moment the contact is made a current
flows and a small explosion takes place on
the point of contact of the metal.
 Excessive heat is not generated, this is
known as electronic discharge welding

32.  The sparking during welding is due to
only a small part of the metal getting
hot while the rest is cold.

33. WELD DECAY
 With increase of time or increase in
the amount of welding excessive heat
is produced resulting in weld decay, it
occurs in 18/8 austenitic steel, it is
essentially a process of formation of
corrosion due to excessive heat.

34. THANK YOU