joining of metals

Question 1

What is soldering?

Answer 1

joining of two metals or alloys using a third alloy (solder alloy)

Question 2

What is solder alloy?

Answer 2

alloy used for joining of two metals or alloys

Question 3

What are the requiements of solder alloys?

Answer 3

• must have lower melting temperature than the two metals to be soldered
• must have sufficient flow when melted
• must have sufficient strength when hardened
• must have sufficient resistance to tarnish and corrosion
• must have acceptable color similar to the two metals

Question 4

What are the types of dental solders?

Answer 4

• gold
• silver

Question 5

What are the properties of gold solder?

Answer 5

• used for soldering of gold alloys
• composed of Au, Cu, Ag, Zn and phosphorous that reduces the melting temp
• described by fineness
• the number does not describe the actual fineness of solder but rather the fineness of the gold alloy parts on which the solder was to be used, however the fineness of the solder should be less than that of the parts being joined, since the solder of reduced fineness has a lower melting range

Question 6

What are the properties of silver solder?

Answer 6

Used for soldering of base metal alloys.
Composed of Ag ,Cu, Zn and phosphorous.
The formation of silver-copper eutectic alloys is responsible for the low melting temperature of silver solder

Question 7

What are fluxes?

Answer 7

materials applied to the parts to be soldered in the form of powder, liquids, or paste

Question 8

What are fluxes used for?

Answer 8

• protect the parts to be soldered and the solder alloy from oxidation
• dissolve oxides if present
• increase flow of the solder alloy
• decrease the melting temperature of the solder alloy

Question 9

What are the types of fluxes?

Answer 9

• borax
• fluoride

Question 10

What is borax flux?

Answer 10

• used with gold solders
• it is composed of silica, borax and boric acid

Question 11

What is fluoride flux?

Answer 11

• used with silver solder
• composed of k-fluoride and boric acid
• strong therefore able to remove passivity at the soldered joint

Question 12

What are antifluxes?

Answer 12

materials used for limitation of the molten solder alloy to the solder joint only, so applied to the undesirable areas. e.g. graphite

Question 13

What are the soldering techniques?

Answer 13

• free hand
• investment soldering

Question 14

What is free hand soldering?

Answer 14

• two parts are approximated using hands, and then the flame is placed on the bench so that both hands are free to hold the parts in position
• the solder alloy is melted on one part, then the two parts are held together
• this method is not accurate and therefore, not used in dentistry

Question 15

What is investment soldering?

Answer 15

• the parts are placed on the master cast
• apply sticky wax to fix the parts
• the assembled parts are placed in an investment material
• remove sticky wax using hot water
• apply flux and antiflux
• melt the solder alloy using the reducing zone of air-gas blow torch
• after cooling and quenching, finishing and polishing is done

Question 16

What are the causes of soldering failure?

Answer 16

• the surface is not clean
• improper fluxing
• improper antifluxing
• poor flow of the solder alloy if not sufficiently heated
• wide gap distance (more than 0.005 inch)
• overheating of the solder alloy produce pitted joint of low strength
• using oxidizing zone

Question 17

What is welding?

Answer 17

joining of two metals or alloys without using a solder alloy

Question 18

What are the types of welding?

Answer 18

• pressure welding
• spot welding
• laser welding

Question 19

What is an example of pressure welding?

Answer 19

if two pieces or pure gold are condensed together, they join

Question 20

What is spot welding?

Answer 20

• metals or alloys to be spot welded must have low electrical conductivity (as stainless steel), because this resistance to electrical conductivity will liberate heat during passage of the electric current (using a spot welder machine), which cause partial melting at the point of electrode application and this causes fusion between the two pieces
• this technique is not used for joining gold alloys because they are good conductors to electricity, and hence the current will not find resistance when it passes through the gold pieces to be welded

Question 21

What are the advantages of laser welding?

Answer 21

• rapid, clean method and also can be performed close to ceramic or acrylic veneers without causing damage to it as a small amount of heat is generated
• laser welding is used for joining of titanium components where the soldering procedures are technically sensitive