Welding in Pediatric dentistry

1. Welding and Soldering
Dr. Deepashree Paul

2. Joining Processes: Welding, Brazing, Soldering
1. Brazing and Soldering: Melting of filler only
• Brazing: higher temperature, ~brass filler, strong
• Soldering: lower temp, ~tin-lead filler, weak
2. Welding: Melting of base metals
3. Both: Join parts to form complex product
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3. • Definition of welding proposed by the AWS is
an
• "operation which aims to get localized
coalescence produced by heating to a
suitable temperature, with or without
applying pressure and filler metal,
producing parts with strong welded
union, nonporous and free of corrosion.”

4. Brazing
• Steel base metal + Brass filler rod is
common
• Lower temp than welding: retains heat
treatment (if present), minimizes grain
growth.
• Strong but slow (careful preparation,
cleanup)
• Furnace brazing is easily automated

5. TYPES OF WELDING
• Stick Welding
• Metal Inert Gas Welding
• Tungsten Inert Gas Welding
• Spot Welding

6. Shielded Metal Arc Welding (SMAW): “Stick welding”
• Older, simple technology
• The electrode is also the filler rod
• Only for steel
• Strong welds if done properly (but often not)
• Very high heat input: good for thick parts, bad for grain
growth and distortion

7. Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)
• ~Complex mechanism but simple to perform and easy to automate
• The electrode is also the filler rod, fed continuously from a spool. It
melts in the arc.
• For steel or aluminum
• Low skill level can achieve good weld
• Medium heat input: distortion and grain growth are significant

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Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)
A fair/typical quality MIG weld (still hot!)

9. Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)
• The electrode is tungsten (not consumed)
• The filler rod is separate and fed manually
• High skill level required to achieve good weld
• Difficult to automate
• Low heat input and small weld bead: distortion and grain growth are
minimized

10. Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)
• Typical good quality TIG welds

11. Resistance Spot Welding (RSW): “Spot Welding”
• No filler rod: electrical current is passed through metal under
pressure
• Low skill level required
• Easy to automate
• Low heat input and no weld bead: distortion and grain growth are
minimized

12. Distortion from Welding Processes
• Non-uniform shrinkage of weld bead
• Difficult to maintain alignments
• Solution: Rigid fixtures, pre-compensate for warping, loose
tolerances

13. Weld bead profile: Convex or Concave?
• Solidification of molten bead leads to shrinkage
• Shrinkage of a concave bead leads to tension on surface 
tends to crack
• Shrinkage of a convex bead leads to compression on surface 
does not crack
• Generally, slightly convex beads are preferred.

14. Welding Flaws

15. Welding Flaws:
Incomplete Penetration
(not enough heat input)

16. SOLDERING

17. DEFINITION
• Soldering involves joining two
components of metal with an
intermediate metal whose melting
temperature is lower than the parent
metal.
It’s defined as the joining of
metals by the fusion of filler
metal between them, at a
temperature below the
solidus temperature of the
metals being joined and
below 450°C.

18. Silver solders
•They are low fusing –fusion temp-600-750°C
•Used with stainless steel or other base metal
alloys
•Resistance to tarnish and corrosion is not as
good as gold solders
•But have strength comparable to gold solders
•Composition
•Silver -10-80 %
•Copper -15-30%
•Zinc -4-35%
•with small amounts of cadmium, tin and
phosphorus.
•The formation of silver-copper eutectic is
responsible for the low melting range of silver
solder.

19. • HEAT SOURCE
• The most common instrument used as heat source
is gas- air or gas- oxygen torch. The type of torch
depends on the type of fuel.
• The fuels used are :-
• Hydrogen -low heat content, so heating is slow.
• Natural gas - heat content is four times that of
hydrogen.
• Acetylene - high flame temperature, but variation in
temperature from one part of the flame to the other
part is more than 100°C. So positioning of the torch
is critical. It is chemically unstable gas, decompose
to carbon and hydrogen. carbon can get
incorporated in to nickel and palladium alloys.
• Propane - is the best choice. Have highest heat
content & good flame temperature.
• Butane - has similar flame temperature and heat
content. Both are readily available. Uniform in
quality, virtually water free and burn clean.

20. • FLAME The flame can be divided in to four zones
• Cold mixing zone (unburned gas)
• Partial combustion zone (neutral zone)
• Reducing zone
• Oxidizing zone (burned gas).
• The portion of the flame that is used to heat the
soldering assembly should be the neutral or slightly
reducing part, because this produces the most
efficient burning process and most heat.
• Improperly adjusted torch or improperly positioned
flame can lead to oxidation of the substrate or filler
metal and result in a poorly soldered joint.
• If unburned portion of flame is used carbon may be
introduced to the substrate or filler.
• To prevent oxide formation the flame should not be
removed once it has been applied to the joint area
until soldering process has been completed.

21. PARENT METAL
•The parent metal is the metal or alloy to be joined. This
is also known as a substrate metal or base metal.
Soldering operation is the same for any substrate metal,
but the ease of soldering is not same for any substrate
metal.
The composition of parent metal determines-
•Melting range
•Oxide that forms on the surface during heating
• Wettability of the substrate by the molten solder.
• Soldering should take place below the solidus
temperature of the parent metal.

22. • Composition of alloy determines
• the oxides that form on its surface during
heating. The flux used should be able to reduce
these oxides, inhibit further oxidation and
facilitate its removal.
• the wettability of the substrate by the molten
solder alloy. The solder chosen must wet the
metal at as low a contact angle as possible to
ensure wetting of the joint area.
• Manufacturer of the alloy should provide
guidance and instruction regarding the flux to be
used with that alloy.
• A low temp soldering is preferred rather than
the high temp soldering for Stainless steel wire
to prevent carbide precipitation and to prevent
an excessive softening of the wire. So silver
solders are generally preferred.

23. REQUIREMENTS OF A SOLDER
• Fuse safely below the sag or creep temperature
of the parent alloy.
• Resist tarnish and corrosion.
• Non pitting.
• Free flowing.
• Match the color of the parent metal.

24. JOINT DESIGN
• Spacing between parts being joined greatly
affects tensile strength
• Strongest joints are obtained when parts use lap
or scarf joints
• Some joints can be designed so that the flux
and filler metal may be preplaced
• Joint preparation is very important

25. Types of Joints

26. • CLASSIFICATION OF SOLDERS
• Soft solders
• Hard solders
• Precious metal solders
• Non precious metal solders
• SOFT SOLDERS They are lead- tin eutectic alloy
with a low melting point. Sometimes called as
plumbers solder. They have low fusion range of
about 260°C or less. Soft solders lack corrosion
resistance, so they are impractical for dental use.
• HARD SOLDERS Hard solders have higher meting
temperature & possess greater hardness and
strength. Heating is done with gas torch or special
devices. Two types of hard solders are used in
dentistry

27. COMPOSITION OF SOLDERS
• Gold
• Silver
• Copper
• Tin
• Zinc
• Gold solders are designated by fineness.

28. SOLDERING FLUX
• Flux means flow.
• Improve the flow of a metal
• Chemicals that limit the flow of metals
are called antifluxes

29. FUNCTIONS AND TYPES OF A FLUX
• PROTECTOR
It covers the metal surface and prevents oxide formation.
• REDUCER
It helps to reduce the oxides present on the metal
surface.
• SOLVENTS
It dissolves any oxide presence and removes it.
The resulting solution of oxides or other extraneous matter in
flux constitutes “slag”.

30. COMPOSITION OF A FLUX
• Borax glass
• Boric acid
• Silica
• Fluoride
According to their composition
Borax fluxes
Fluoride fluxes
According to the pH of the flux
•Acidic fluxes – SiO2
•Basic fluxes – CaO, lime CaCO3
LIMESTONE
•Neutral – Fluorspar
(Ca.F2),Borax (Na2B4O2)

31. • BORAX FLUXES
• Borax from Persian burah
• Also called sodium borate , or sodium tetraborate , or
disodium Tetraborate. They are based on boric or borate
compounds such as boric acid/boric anhydrate and
borax.
• It is usually a white powder consisting of soft colourless
crystals that dissolve easily in water.
• Borax has a wide variety of uses:-
• It is a component of many detergents, cosmetics, and
enamel glazes.
• It is also used to make buffer solutions in biochemistry
as a fire retardant as an insecticide as a flux in
metallurgy.
• They act as protective fluxes and reducing fluxes for low
stability. oxides such as copper oxide and are used for
noble metal alloys.

32. • They are available in
• Liquid form : Solution of borax/boric acid in
water. Indicated for soldering of orthodontic
appliances and bridges in which minimum
amount of flux is required.
• Paste form : Formed by mixing borax with
petroleum jelly. Required when fluxes are
needed in large quantity.
• Powder form : Contains a mixture of borax,
basic acid, silica flour and finely divided
charcoal. Charcoals reducing agent and silica
holds molten flux in surface of hot metal. This
is usually used for casting operation.

33. • FLUORIDE FLUXES
• Composition:-
• Potassium fluoride – 50-60%
• Borax glass - 6-8%
• Potassium carbonate – 8-10%
• As the choice of flux is dictated by the type of
alloys to be soldered, the fluoride flux is used
with alloys containing base metals even if a
gold/silver solder is used. Some fluoride
containing fluxes involve toxic fluorides when
heated, so inhalation of fumes should be
avoided.

34. SUPER FLUX
•A combination of high melting salts is used
as fluxes to combine the good characteristics
of each ingredient and create superior flux.
•A formula for efficient flux is
• Borax glass – 55 parts
•Boric acid – 35 parts
•Silica - 10 parts
•The ingredients may be fused together and
then crushed to fine powder.

35. • Too little flux tends to burn off and will be
ineffective.
• Excess flux remains trapped within filler metal
and cause a weakened joint.
• Flux combined with metal oxides forms a glass
during soldering process that is difficult to
remove completely. A two step method for
removing residual flux
• Blast joint immediately after removal from
investment with alumina abrasive particles
followed by boiling in water for about 5
minutes.

36. ANTIFLUX
• Used to restrict the flow of the metal.
• Most common anti-fluxes used is graphite.
• Better fluxes like Rouge in chloroform can
be used.
• It is applied on the surface of specific area
where the solder should not flow into. It is
applied before applying flux or solder.
• E.g.: Graphite in the form of lead pencil.
Disadvantage of graphite is that it can burn
off on prolonged heating at high
temperature.
• In such cases whiting (CaCO3 in alcohol and
water suspension) is used.

37. QUALITIES OF AN IDEAL SOLDER
• FILLER METAL/SOLDER
• Ease of flow at relatively low temperature.
• Sufficient fluidity to freely flow when melted.
• Ability to wet substrate metal.
• Strength compatible with that of the structure
being joined. Resistance to tarnish and
corrosion.
• Acceptable colour to give an inconspicuous
joint.
• Resistance to pitting during heating.

38. The joining area should be three times the thickness of the
thinnest joint member.

39. When building up a surface, alternate the direction of each layer

40. Best types of flame to use:
•Air acetylene
•Air MAPP
•Air propane
•Any air fuel-gas mixture

41. SOLDERING AND BRAZING
METHODS
Grouped according to method of applying heat:
• Torch
• Infrared
• Laser
• Furnace
• Induction
• Dip
• Oven

42. TORCH SOLDERING
• Soldering is done under direct flame.
• A gas air torch is used for this purpose.
• The torch flame has two parts – the
reducing part (is at a higher temperature)
and the soft brush part.

43. • The solder should be melted using the
soft brush flame.
• The flame should be constantly swiped
over the solder for a period of 4 -5
minutes.
• At no point of time the flame should be
held in a stationary position.

44. INFRARED SOLDERING
• Used for low fusing connectors.
• Good accuracy.
• Similar strength as conventional
soldering.
• Protective eyewear is necessary.

45. LASER SOLDERING
• Done to join Ti components of dental
crowns, bridges and partial denture
frame works.
• Pulsed high power Neodymium lasers are
used.
• Low thermal influence preferred in
dentistry.
• Superior joint strength.

46. FURNACE SOLDERING
• Advantages of using a furnace:
• Furnace brazing is a semi-automatic process
• Temperature control
• Controlled atmosphere (Common atmospheres
used include: inert, reducing or vacuum
atmospheres all of which protect the part from
oxidation)
• Uniform heating
• Mass production
• Disadvantages of using a furnace:
• Size
• Heat damage

47. Furnace brazing permits the rapid joining of parts on a
production basis

48. SOLDERING TECHNIQUE
• The design of the connector is
determined while fabricating the wax
pattern.
• All the solder connectors require about
0.25mm parallel spaced between the
parent components.
• The smaller units are inserted separately
in the mouth.

49. • A thick mix of quick setting plaster is molded
over the inserted units.
• Once the plaster sets, it is removed along with
the inserted units.
• Plaster index is inverted.
• Components of the prosthesis will be visible.

50. • A triangular piece of utility wax should
be placed to index restoration in order to
shape the soldering assembly.
• The units are invested and the
investment is allowed to bench set.
• Invested wax is eliminated using boiling
water or chloroform.

51. • Area of the restoration surrounding the
joint should be coated with anti-flux.
• After coating the flux and the anti-flux,
the assembly is preheated in a burnout
furnace.
• Connectors are soldered using a torch or
a furnace.

52. • The parts to be joined are fixtured and the brazing
compound applied to the mating surfaces, typically in
slurry form. Then the assemblies are dipped into a bath
of molten salt (typically NaCl, KCl and other compounds)
which functions both as heat transfer medium and flux.
• Advantages of dip processing:
• Mass production
• Corrosion protection
• Distortion minimized
• Disadvantages of dip processing:
• Steam explosions
• Corrosion
• Size
• Quantity

53. CERAMIC/ACRYLIC VENEERING
• The ceramic or acrylic veneers in metal resin
or metal ceramic restorations are usually
added after soldering.
• Ceramic veneering is done in 3 steps
1. METAL PREPARATION.
2. PORCELAIN APPLICATION.
3. PORCELAIN FIRING.

54. SOLDERING INVESTMENT
• These are silica –bonded investments
that are fused quartz.
• Fused quartz is used because it is the
lowest thermally expanding form of
silica.

55. SOLDERING FOR METAL CERAMIC
RESTORATION
• It is usually done prior to ceramic application
hence it is also known as pre ceramic
soldering.
• Post ceramic materials are also available.

56. • Pre ceramic soldering is done at a temperature
of 1075 to 1120 degree celsius whereas post
ceramic soldering should be done at a
temperature of 920 degree celsius because
ceramic may begin to sag at higher
temperatures.

57. SOLDERING INVESTMENT
• These are silica –bonded investments
that are fused quartz.
• Fused quartz is used because it is the
lowest thermally expanding form of
silica.

58. SOLDERING FOR METAL CERAMIC
RESTORATION
• It is usually done prior to ceramic application
hence it is also known as pre ceramic
soldering.
• Post ceramic materials are also available.

59. • Post ceramic soldering should be done
after ceramic firing.
• Ceramic portions should be finished only
after soldering.

60. ADVANTAGES OF PRE CERAMIC
SOLDERING
• The metal framework can be soldered
and tried in prior to ceramic build up.
• Minor casting errors can also be patched
up during ceramic build up.

61. DISADVANTAGES OF PRE CERAMIC
SOLDERING
• Difficult to build ceramic on already
soldered units.

62. ADVANTAGES OF POST CERAMIC
SOLDERING
• Porcelain can be properly build up due to
better access.

63. DISADVANTAGES OF POST CERAMIC
SOLDERING
• The metal and porcelain may sag at high
soldering temperatures.
• It is more technique sensitive.
• The solder should be re-glazed and re-
fired.

64. OVEN SOLDERING
• Performed under vacuum or air.Performed under vacuum or air.
• A piece of solder is placed in the jointA piece of solder is placed in the joint
space and it is heated to a standardspace and it is heated to a standard
temperature in the furnace.temperature in the furnace.
• Superior joint strength.Superior joint strength.

65. DISADVANTAGES
• The parent metal will sag or melt ifThe parent metal will sag or melt if
heated for a long time.heated for a long time.

66. SOLDERING FAILURES
• Failure to clean the parts to be joined
• Improper fluxing
• Poor flow of solder
• Over heating of the solder can lead to pitted joint of low
strength Besides porosities and brittleness from oxides,
gases, or foreign matter resulting from the soldering
procedures as factors for increasing the incidences of failure
of soldered joints.
• Creep, corrosion, stress corrosion cracking, corrosion-fatigue,
and corrosion-erosion.
• Gas embitterment can also be generated by gases formed
from electrochemical processes. Hydrogen embitterment
from corrosion is a very well-known phenomenon that occurs
with some material-solution combinations and at
temperatures comparable to physiologic conditions.

67. CONCLUSION
• The choice of solder material has extreme importance in
determining the properties of the soldered joints. Silver solders
are popular because of their lower fusion temperatures and
easy-handling characteristics. Soldering is still a useful and
needed procedure for the joining of metallic parts. The choice of
whether free-hand or investment, torch or oven, or pre or post
ceramic soldering techniques are used, as well as variations in
gap distance and high- or low-fusing soldering alloys, is in many
instances up to the discretion of the dental surgeon and
technician. The breakage of soldered components is one of the
pitfalls associated with this joining procedure. Even though
following guidelines should theoretically prevent them from
occurring, solder failures are not rare.

68. THANK YOU 