Soldering and welding .... this topic include what exactly is soldering and welding and its application in routine dental practice....

1. Presented by,
Dr Sumit Rajewar
BDS, MDS
(Pedodontics And Preventive Dentistry)

2. CONTENT:
 Definitions
 Ideal requirements of dental solder
 Soldering
1. Parent metal
2. Flux
A) Classification of flux
B) Ideal properties of flux
C) Application of flux
3. Anti-flux
4. Solder
A) Classification of solder
 Heat source

3.  General principles for soldering
 Methods of soldering
1. Investment soldering
2. Free-hand soldering
 Technique consideration for soldering
 Soldering defects
 Welding
 Types of welding
1. Spot welding
2. Pressure welding
3. Laser welding
4. Laser micro welding
 References

5. SOLDERING: Is 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.
BRAZING: Is 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 above 450°C.
.

6. WELDING: Two pieces of similar metal are
joined together without the addition of another
metal; that is, the metal pieces are heated to high
enough temperature so they join together by
melting and flowing

8.  It should melt at low temperature
 When melted, it should wet and flow freely over
the parent metal
 Its colour should match that of metal being
joined
 It should be resistance to tarnish and corrosion
 It should be resistance to pitting during heating

10. Soldering is often used in construction of dental
appliances.
Components of solder joint:
1. Parent metal
2. Flux
3. Anti-flux
4. Solder/filler metal

11.  The parent metal is the metal or alloy to be
joined.
 It is also known as substrate metal or base
metal.
 Soldering operation is the same for any

12.  The composition of parent metal determines:
1. Melting range
2. Oxide that forms on the surface during heating
3. Wettability of the substrate by the molten
solder.

13.  In Latin flux means “to flow”
 Purpose of flux is to remove any oxide coating
on the metal surfaces.
 They protect the alloy surface from oxidation
during soldering and dissolve metallic oxides as
they are formed.

14. A) CLASSIFICATION OF FLUX:
1. According to their primary purpose / activity
a. Surface protection type
b. Reducing agent type
c. Solvent type

15. 2. According to the pH of the flux:
a. Acidic fluxes – SiO2
b. Basic fluxes – CaO, lime CaCO3 LIMESTONE
c. Neutral – Fluoride flux (Ca.F2),Borax
(Na2B4O2)

16. 3. Based on boric or borate compound:
a. TYPE I – protective fluxes by forming a low
temperature glass
b. TYPE II – reducing fluxes for low stability
oxides such as copper oxides
c. TYPE III – fluoride flux

17. BORAX FLUXES
 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.
 They act as protective fluxes and reducing
fluxes for low stability oxides such as copper

18. •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 and finely divided charcoal. Charcoal is reducing
agent and silica holds molten flux in surface of hot
metal. This is usually used for casting operation.

19. FLUORIDE FLUXES
Composition:-
Potassium fluoride – 50-60%
Boric acid – 25-35%
Borax glass - 6-8%
Potassium carbonate – 8-10%

20.  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.

21. 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 super flux is
Borax glass – 55 parts
Boric acid – 35 parts
Silica - 10 parts

22. B) Ideal Properties of Flux
 Its melting point must be lower than that of solder.
 It should lie quietly on the work while being fused
and should not increase in volume.
 After fusing, it should spread evenly and remain on
the parent metal without volatization.
 It must dissolve metallic oxides or other surface
impurities likely to occur on the surface metal.
 It should be easily removable after soldering.

23. C) APPLICATION OF FLUX
 Painted on the substrate metal at the junction of
pieces to be joined.
 It may be Fused onto the surface of the parent
metal strip.

24.  Anti-Flux Materials used to restrict the flow of
solder are known as anti flux.
 It is applied on the surface of specific area
where the solder should flow. It is applied
before applying flux or solder.
 E.g.: Graphite in the form of lead pencil.

25.  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.

26.  Desirable properties of dental solders:
 The fusion temperature must be at least 50-
100°C i.e. lower than the melting temperature of
the alloys to be joined.
 It must have good affinity for the metals upon
which it is used.

27.  It must flow freely, quickly and smoothly over
the surfaces of the parts to be joined. Adhesion
of the solder to the metal is essential.
 Its strength and hardness should be
comparable with that of parent metal.
 It should not cause pitting of soldered joint.
 It must be resistant to tarnish and corrosion.

28. A) CLASSIFICATION OF SOLDERS
1. Soft solders & Hard solders
• SOFT SOLDERS:
 They have low melting range of about 260°C
 Soft solders lack corrosion resistance, so they
are not suitable for dental use.
 Eg. lead- tin eutectic alloy (plumbers solder).

29. • HARD SOLDERS
 Hard solders have higher meting temperature &
have greater strength and hardness.
 They are melted with gas blow torch or with
electric furnace.
 Two types of hard solders are used in dentistry:
gold solder & silver solder.

30. Gold Solder:
 Gold solders Has good
tarnish and corrosion
resistance
 Extensively used for crown
and bridge applications.
 Composition:
Gold – 45-81 wt %
Silver - 8-30 wt %
Copper -7-20 wt %
Tin –2–4 wt %
Zinc –2–4 wt %
They are high fusing with a fusion temperature range
of 750- 900° C

31. Silver Solder
 Silver solders Used in
orthodontic appliances
They have low 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%

33.  It is most important part of brazing and
soldering.
 The most commonly used heat source is gas-
air or gas- oxygen torch. And other is electric
furnace.
 various gases used are…
1) Hydrogen: lowest heat content(1000*C)
slow heating
So not indicated for soldering of large
bridges

34. 2) Natural gas: Temperature of 2680*C
4 times that of hydrogen
Available in non uniform in composition

35. 3) Acetylene: Highest flame temperature
(3140*C)
Higher heat content than hydrogen and natural
gas
Chemically unstable and decomposes readily into
carbon and hydrogen.

36. 4) Propane: Highest heat content (2385*C)
Having good flame temperature (2850*C)
Best choice

38. • Thoroughly clean the parts to be joined by
immersing in dilute hydrochloric acid and then
polish with pumice.
• The parts to be joined must be placed in closest
possible contact with each other.
• Excessive amount of solder must not be used.
The strength of the soldered joint is greatest
when the minimum of solder is used.

39. • The temperature of flame must be carefully
controlled and flame held at proper distance.
Over heating must be avoided.
• Solder must be heated to its melting point as
quickly as possible, when the solder has melted
and filled the space between parts, remove the
flame and work is quenched in water.
• Oxidation must be avoided by using suitable
reducing flux and reducing zone of torch flame.

41. 1) FREE-HAND SOLDERING
 Free hand soldering is used for soldering
orthodontic appliances.
 In this technique the parts to be soldered are
held in proper position by maintenance of gap
between parts manually.

42. Principle of free hand soldering:
 The parts to be soldered are cleaned and polished
 Parts should be in close approximation
 The liquid solder flows into the joint due to capillary
action.
 So optimum gap should be in 0.13 to 0.3 mm range
for proper flow and strength of joint
 Parts should be stable during application of heat

43.  Flux is applied to the joint area to allow a free
flow of solder and to prevent oxidation.
 The bridge assembly is preheated by the
application of reducing zone of flame.
 Oxidation of filler and parent material may
occur if proper zone of flame is not used.

44.  Flame provides protection from oxidation
especially at brazing temp.
 The solder is placed on the joint parts so
solder melts and flow into the gap
 As soon as soldering is completed, the
assembly is quenched in water.

45. 2) INVESTMENT SOLDERING
 Parts to be joined are mounted on a soldering type
of investment and are held in position by the
hardened investment during application of heat
and solder
 Parts to be soldered are assembled on a cast and
the parts are joined by sticky wax with the
investment
 And wax is eliminated with the help of boiling water
 Suitable solder is placed in the gap and subjected
to flame until completion of soldering

47. • Flame
• Gap
• Temperature
• Time

48. FLAME
The flame can be divided in to four zones
• Cold mixing zone (unburned gas)
• Partial combustion zone (oxidizing)
• Reducing zone

49. 2) Gap:
 The liquid solder is draw into the joint through
capillary action.
 Thus optimum gap should be there for proper
flow and strength of joint
 Gap width should be ranging from 0.13 to
0.3mm

50.  What happens if gap is too narrow?
 Low strength
 Porosity caused due to incomplete flow
 What happens if gap is to great?
 The joint strength will be the strength of solder

51. Temperature:
 Should be minimum required to
complete the brazing operation
 Prior to the placement of the solder,
parent metal is heated till it is hot
enough to melt the filler metal as soon as it
touches.
 A low temp will not allow the filler to wet the
parent metal

52. Time:
 The flame should be kept in place until the filler
metal has flowed completely into the connection
 Shorter time increases chances of incomplete
filling of joint
 Longer time increases possibility of diffusion
 Both conditions results in weaker joint

53. HYDROSOLDER
• This machine converts Water into oxy-hydrogen
fuel for an extremely hot and precise reducing
flame operating at 4850F.
• This machine is perfect for soldering and
brazing in the orthodontic laboratory
environment.

55. 1) Porosity or pitting:
 It may occur during finishing and polishing
due to volatilization of lower melting
components as s result of higher temp. and
longer time
causes-
 Incorrect fluxing
 Incorrect flaming
 Incorrect cleaning
 Incorrect spacing of parts

56. 2. Distortion of parts being soldered.
causes-
 Overheating
 Thermal expansion of the metal parts

58.  Wire to wire.
 Tube can be soldered to the bridge of the
Adam’s clasp.
 Attachment of springs to arch wire,
 Soldering lingual arch or palatal arch.
 Soldering of various type of space management
appliances.

60.  Two pieces of similar metal are joined together
without the addition of another metal.
 The metal pieces are heated to high enough
temperature so that they join together by
melting and flowing.

61. 1. Cold welding is done by hammering or
pressure. An example of cold welding is the
gold foil filling.
2. Hot welding uses heat of sufficient intensity to
melt the metals being joined.
The heat source is usually an oxyacetylene
flame or high amperage electricity.

62. • Basically two methods are followed:
1) Fusion welding: where the parts are melted
and joined, but pressure is not applied.
E.g: Gas welding, Laser welding
2) Pressure welding: where parts are heated and
pressed , but not melted.
E.g.: Spot welding

63. • SPOT WELDING
• PRESSURE WELDING
• LASER WELDING
• LASER micro WELDING

64. 1) Spot welding:
 The two clean metal surfaces to be welded are
placed together under pressure.
 Two ends of wire or band to be welded are
placed between two copper electrodes of
welder and pressed together
 When switch is pressed large current passes
through the wires or band on the copper
electrode.
 Combined heat and pressure fuses the metal
pieces at that point.

65. 2) Pressure welding:
 This is also called cold welding and does not
require heat application
 Gold foil is welded by pressure or cold welding
 Two layers of gold foil are joined by application
of pressure at room temperature.

66. 3) LASER welding:
 LASER (‘Light Application by Simulated
Emission of Radiation’)
 It is clearly documented that laser welding is
stronger than solder joints of comparable size.

67. LASER micro welding:
 The laser micro welder is high power industrial
laser capable of delivering 20J/pulse for
maximum of 6 mili seconds at a wire length of
1.06 microns.
 Micro welding can be done in intra-oral
orthodontic appliances such as normal arch
wire, ortho-surgical splint simulation, space
maintainers, retention devices etc

68. Spot welding may be used as method of fusing
• Stainless steel strip for making bands.
• Securing attachments to the bands
• Attaching springs to a rigid bow wire, or to
bands.
• It is used more in the construction of fixed

69. References
• Kenneth J. Anusavice(2004). PHILLIP’S Science Of Dental
Materials, ed 11, Chapter 33 Gold Alloy Solders, Soldering
Procedure, Page 563,564.
• William J. O’Brien(2002). Dental materials and their selection, ed
3, chapter 18, soldering, welding and electroplating. Page 249.
• SH Sorature (2002). Essentials of dental materials, ed 1, chapter
25, Soldering and welding, page 315.
• B.W.DARVELL (2001). Materials Science For Dentistry, Chapter
22 soldering and welding, 9th edition, page 486.