soldering, brazing and welding

what is welding?

the process of joining two pieces of similar metals without adding another metal. the metals are heated to a sufficiently high temperature, causing them to melt and flow together, forming a solid joint upon cooling.

what is soldering?

the process of joining two or more metal components, or building up a localized area, by heating them to a temperature below their solidus point and filling the gap with a molten filler metal. the filler has a melting temperature below 450 °C, allowing the metals to bond without melting the base materials.

what are the ideal requirements for a solder?

1. it should melt at low temperatures

2. when melted, it should be wet and flow freely over the parent metal

3. its color should match that of the metal being joined (same color as parent metal)

4. should be resistant to corrosion and tarnish

5. it should be resistant to pitting during heating and application

what are the two major groups of solders?

1. soft solders

2. hard solders

what are soft solders?

they have a low melting range of about 260C. they lack good corrosion resistance, thus, they are not recommended for dental use

what are hard solders?

they have a higher melting temperature and they have greater strength and hardness compared to soft solders. they are more commonly used in dentistry. they are also used for jewelry trade, such as gold and silver solders

what are the different types of applications of soldering in dentistry?

1. for the soldering of various types of wires in orthodontics

2. in pedodontics it is used to construct various types of space maintainers

3. in fixed prosthodontics it is used for:

   • the joining of various components of fixed partial prostheses

   • for the repair of holes in crowns and bridges

   • to develop contact points in crowns

   • for cutting and rejoining an ill fitting prostheses

4. in removable partial prosthodontics it is used for soldering of clasps

what is the fusion temperature of dental solders?

it should be at least 500C lower than that of the parent metal

what should the flow of a dental solder be like?

a good flow and wetting of the parent metal by the solder is essential to produce a good bond

what factors affect flow?

• the melting range affects it. solders with a shorter melting range have a better flow

• composition of a parent metal can affect it, such as gold and silver based alloys having a better flow compared to nickel based alloys

the presence of an oxide layer on a parent metal affects what?

it reduces the flow

solders have good what?

they have good tarnish and corrosion resistance

how does hardness increase in solders?

it increases as the fineness of solders decreases

how should the strength be in dental solders?

it should be almost equal to that of the soldered parent alloys

for a solder to be wet and flow properly, what must the parent metal be free of?

it must be free of oxides

what are fluxes and their functions?

it is the latin word for flow. its function is to remove any oxide coating on the parent metal as well as protecting the metal surface from oxidation during soldering

how can fluxes be divided?

based on activity into 3 types:

• protective type, which covers the metal surface and prevents access to oxygen so oxide cannot form

• reducing type, which reduces any oxide present on the surface to free metals and oxygen

• solvent type, which dissolves any oxide present and carries it away

what are the steps of the soldering process?

1. selection of solder

2. cleaning and polishing of components

3. assembly of the bridge in soldering investment

4. application of flux

5. preheating the bridge assembly

6. placement of solder

7. application of hot gas flame to joint and solder

8. cooling of assembly followed by reducing in water

what are the requirements for a successful soldering?

• cleanliness. the metal should be free of oxides

• there should be a small gap between the parts

• selection of solder-proper color, proper fusion temperature, and good flow

• correct flux type and the proper amount

• flame neutral or reducing in nature to prevent oxidation

• controlled temperature and time

when is the term welding used?

if two pieces of similar metal are joined together without the addition of another metal

when is welding in dentistry used?

1. in orthodontics to join flat structures like bands and brackets

2. in pedodontics to wield bands and other appliances to one another

3. in prosthodontics to join wrought wire clasps and repair of broken metal dentures

what is cast-joining?

it refers to the connection of two parts, often base metal alloys, using a third metal that is cast into the space between them. in this method, the union of the two parts does not depend on fusion or chemical bonding but rather on mechanical retention, which is achieved by proper flow of the new metal during casting

what is the free hand soldering technique?

the parts are assembled and held in contact manually while the heat and solder are applied

what is the investment soldering technique?

the parts to be joined are mounted in a soldering type of investment. the hardened investment holds it in position while the heat and solder are applied

how is welding done?

by passing an electric current through the pieces to be joined. these pieces are also pressed together

what are two ways welding can be done?

either in an electric spot welding machine, with the wire or the band to be welded placed between the two copper electrodes of the welder or through laser and plasma welding, with the laser welding primarily used to join titanium components that are used in dentistry for bridges and partial denture frameworks