Metal Joining And Dental Lasers
Question 1. Write a short note on soldering and welding.
Or
Describe briefly soldering and welding.
Or
Describe briefly welding and soldering.
Or
Write a short note on soldering brazing and welding.
Or
Write in brief on soldering and welding.
Answer:
Soldering: Soldering is a process in which two or more metals are joined together by melting and flowing a filler metal (solder) into the joint.
Types of Soldering
There are three types of soldering, i.e.
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- Soft soldering
- Hard soldering
- Brazing
- Soft Soldering
- In soft soldering, there is the joining of two metals by use of a filler metal having a very low melting temperature usually below 350°C.
- Soft soldering uses a lead—tin alloy as a filer material.
- As it melts at a very low temperature, it does not generate excessive heat and so it is used in the electronic industry where more heat can lead to the damage of components.
- Soft soldering is very commonly used by plumbers because of the soft and moldable nature of the filer.
- Here filer is melted by an electronic gun or iron.
- Soft soldering is unsuitable for application in dentistry as the joint is weak and has a very low load-bearing capacity.
- These joints lack corrosion resistance.
- Lead used is hazardous to health and is contraindicated for use inside the oral cavity.
- Hard Soldering:
- In hard soldering, the joining of two metals is done by the use of a filer metal that has a melting temperature of less than 450°C.
- Hard soldering needs a heat source that can generate a medium temperature such as a gas torch.
- Hard soldering generates a strong joint, so this type of soldering is commonly used in dentistry as well as in other fields such as jewelry, food cans, and the refrigeration industry.
- Brazing:
- Brazing is a procedure in which there is joining of two metals together by fusion of filler metal between them having a melting temperature of more than 450°C.
- It provides the strongest joints but also requires the highest temperatures to melt the filler metal.
- It needs a very high-temperature source from specialized equipment, i.e. carbon arc torch and goggles to protect the eye from high heat and bright light.
- It is mainly used in the repair of cast iron objects, in making wrought iron furniture, and in the automobile industry.
Steps in Soldering:
- Clean and assemble the surfaces which are to be joined.
- A proper gap should be maintained between the surfaces which are to be soldered.
- A suitable flux as well as solder is applied to the joint.
- Heat should be applied by a gas torch to the parts which are to be joined.
- Reducing zone of flame is used and solder should be heated till it becomes cherry red.
- Cleaning and polishing of the joint should be done.
Clinical Applications of Soldering:
- For soldering various wires in orthodontics.
- In pedodontics for constructing various space maintainers.
- In fixed prosthodontics:
- For joining various components of fixed partial
prosthesis - For repair of perforations in crown and bridges
- To develop a contact point in the crown
- For cutting and re-joining an ill fitting distorted bridge.
- For joining various components of fixed partial
- In removable partial prosthodontics for soldering of clasps.
Welding:
Welding is the process by which two pieces of similar metals are joinedtogether without the addition of another metal.
Types of Welding:
- Cold welding: In this type of welding, there is no use of heat. This is carried out by hammering or pressure, for example, Gold foil filing
- Hot welding: In this type of welding, the heat of enough intensity should be used for melting the metals which are joined. This heat source can be from an oxyacetylene flame or high amperage electric current.
Methods of Welding:
Spot Welding: The apparatus which is used for spot welding is known as an ortho- deontic spot welder.
- Clean the parts which are to be joined.
- It should be checked that the surfaces of electrodes are smooth, flat, and perpendicular to the long axis. Both ends should be in proper contact with each other.
- Welder settings should be adjusted as per the manufacturer.
- The proper electrode should be selected. For thin material broad electrode is used and for thick material narrow electrode is used.
- As this is done, this causes an even distribution of weld nuggets.
- Weld mates should be inserted between the electrodes and should be closed together, press the switch to allow a large current to pass through the pieces.
- A combination of heat and pressure will join metal pieces together. This welding is known as spot welding.
Pressure Welding: If two metal parts are placed together and sufficient large force is applied perpendicular to the surface, pressure welding occurs, for example, Pure gold and gold foil.
Laser Welding: In laser welding, the beam is focused at the joint to melt the opposing surfaces. The two liquid surfaces contact and form a weld on solidification.
Applications of Welding:
- In orthodontics to join flat structures like bands and brackets.
- In pedodontics, to weld bands and other appliances.
- In prosthodontics, to join wrought wire clasps and repair of broken metal partial dentures.
Question 2. Write a short note on flux and anti-reflux.
Or
Write a note on flux and anti-reflux.
Or
Write short answers on flux and anti-reflux.
Answer:
Flux:
It is the compound that is applied to the metal surfaces which is to be joined to prevent the formation of oxides which reduce the strength of soldered area.
The function of Flux:
Flux plays three roles, i.e.
- Flux removes impurities, i.e. dirt, oil, and oxide from the joint. These impurities weaken the joint
- It acts as a reducing agent. As the metal gets heated to melt solder, increase temperature leads the metal to reoxidize, so the reducing agent prevents this reoxidation.
- It acts as a wetting agent and decreases the surface tension of solder which increases its flow and wettability.
Classifiation of Flux:
- According to their main purpose:
- Surface protection type: This flux covers the metal surface and prevents access to oxygen so that no oxides can form.
- Reducing agent type: It reduces any oxide present and exposes clean metal.
- Solvent type: It dissolves, oxide and drives them away.
- According to their pH:
- Acidic flux: Silicon dioxide
- Basic flux: Calcium oxide and calcium carbonate
- Neutral flux: Fluorspar and borax
- According to their source:
- Organic: Used in soft soldering purposes which need lower temperature
- Inorganic: These are acid based. Used in brazing procedures which require high temperatures.
- According to their composition:
- Borax flux:
- Used for noble metal alloys
- Act as protective fluxes and reduce fluxes
- Fluoride flux: Used with base metal alloys.
- Borax flux:
Composition of Flux:
Application of Flux:
- Flux should be painted on the substrate metal at the junction of pieces to be joined.
- Pre-fixed solders are available in tube form with the flux being contained in the tube. So there is no need to apply flux separately
Antiflxes of Flux: The flow of solder can be prevented by the use of an antireflux material. It is applied to the surface before the flux or solder is applied. Soldiers will not flow into an area where antireflux has been applied.
Examples:
- Graphite (soft lead pencil)
- Rouge (iron oxide)
- Whiting (calcium carbonate)
- In an alcohol and water suspension.
Question 3. Write a short note on dental soldiers.
Answer:
The word soldering is used if two pieces of metal are joined by means of a third (filer) metal.
Ideal Requirements of Dental Solder:
- It should melt at a low temperature.
- When melted, it should be wet and flow freely over the parent metal.
- Its color should match that of the metal being joined.
- It should be resistant to tarnish and corrosion.
- It should resist pitting during heating and application.
Application of Solders:
- For soldering various types of wires in orthodontics.
- In pedodontics, construct various types of space maintainers.
- In fixed prosthodontics for:
- Joining the various components of fixed partial prostheses.
- To develop a contact point in the crown.
- For repair of perforation in crown and bridge.
- In removable partial prosthodontics for soldering of clasps.
Types of Solders:
They may be divided into two major groups:
- Soft solders
- Hard solders.
- Soft Solders: Soft solders have a low melting range of about 260°C. They lack corrosion resistance and so are not suitable for dental use.
- Hard Solders: These have a higher melting temperature and greater strength and hardness.
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- They are melted with the help of gas blow torches or occasionally in an electric furnace. Hard solders are more commonly used in dentistry.
- Two types of hard solders used in dentistry are gold solders and silver solders.
Composition Of Gold Silver Solder:
Properties Of Gold Silver Solder:
Uses Of Gold Silver Solder:
Question 4. Write a short note on welding.
Answer:
Welding is the process by which two pieces of similar metals are joined together without addition of another metal.
Types of Welding:
- Cold welding: In this type of welding, there is no use of heat. This is carried out by hammering or pressure, for example, Gold foil filing
- Hot welding: In this type of welding, heat of enough intensity should be used for melting the metals which are joined. This heat source can be from an oxyacetylene flme or high amperage electric current.
Methods of Welding:
Spot Welding: The apparatus which is used for spot welding is known as ortho- deontic spot welder.
- Clean the parts which are to be joined.
- It should be checked that the surfaces of electrodes are smooth, flt, and perpendicular to the long axis.
- Both ends should be in proper contact with each other.
- Welder settings should be adjusted as per the manufacturer.
- The proper electrode should be selected.
- For thin material broad electrode is used and for thick material narrow electrode is used.
- As this is done, this causes an even distribution of weld nuggets.
- Weld mates should be inserted between the electrodes and should be closed together, press the switch to allow a large current to pass through the pieces.
- A combination of heat and pressure will join metal pieces together.
- This welding is known as spot welding.
Pressure Welding: If two metal parts are placed together and a sufficient large force is applied perpendicular to the surface, pressure welding occurs, for example, Pure gold and gold foil.
Laser Welding: In laser welding, the beam is focused at the joint to melt the opposing surfaces. The two liquid surfaces contact and form a weld on solidification.
Applications of Welding:
- In orthodontics to join flat structures like bands and brackets.
- In pedodontics, to weld bands and other appliances.
- In prosthodontics, to join wrought wire clasps and repair of broken metal partial dentures.
Advantages of Welding:
- It is very easy to use and is not technique sensitive.
- Here solder of flux is not required.
- The ideal technique for joining the flat surfaces
- There are less chances of joint failure.
- Welding produces strong joints
- As heat generated is less, work can be done by hand without the use of specialized instruments.
Failures in Welding
- If weld mates are not clean various impurities such as grease, saliva, and cement lead to the failure of the joint.
- Due to the improper selection of electrode size.
- If the electrode consists of debris or cement particles on it, then the joint can fail.
- If electrodes do not touch each other properly, sparking can occur and there is localized overwelding which can weaken the joint.
- Too high or low pressure at the time of joining can compromise joint strength.
- As heat generated by current is not optimum welding failure can occur.
Question 5. What are soldering and welding?
Answer:
- Soldering: Soldering is a process in which two or more metals are joined together by melting and flowing a filler metal (solder) into the joint.
- Welding: Welding is the process by which two pieces of similar metals are joined together without the addition of another metal.
Question 6. Write a short note on Laser welding.
Answer:
- Laser welding is a recent advancement in the welding procedures.
- In laser welding, the laser used is a pulsed neodymium laser with a very high power density.
- The laser unit consists of a small box that contains the laser tip, an argon gas source, and a stereo microscope with lens crosshairs for the correct alignment of the laser beam with the components.
- The maximum depth the laser can penetrate is 2.5 mm.
- The heat generated is small, so the parts can be hand-held during welding and it can be done close to the ceramic or even resin facings without damaging it.
Indications Of Laser Welding:
- Laser welding is used mainly to join titanium components.
- This is because the commercially pure titanium (cpi) used in dentistry for fixed and removable partial denture frameworks is highly reactive in the air.
- Ordinary soldering procedures result in a weak joint because of the formation of a thick layer of titanium oxide (especially when heated above 850°C).
- Laser welding or plasma welding can be done at lower temperatures.
Mechanism Of Laser Welding:
- When the light beam reaches the surface of the metal, the metal absorbs its energy, converting it into heat that penetrates into the interior of the metal by conduction.
- Owing to a high concentration of heat, the metal is taken to its melting point, and a series of events culminates in the formation of a keyhole or spots that will be filled with the melted metal.
Advantages Of Laser welding:
- Lower heat generation.
- It can be executed directly in the working model.
- Allows welding in regions near the resins and porcelain portions without fear of damage to these materials.
- No oxide formation because of the inert argon atmosphere.
- Joints made of the same pure titanium as the components, thus reducing the risk of galvanic corrosion.
- It produces a keyhole that concentrates the energy absorbed in a small region resulting in high penetration and formation of a narrow heat affected zone (HAZ) that results in less distortion compared to conventional welding methods.
- Less time expended.
- Allows welding with the structures in close contact or with minimal space for bragging using filer metal
Disadvantages Of Laser welding:
- Residual stress introduced into welding joints is a consequence of the heating and cooling cycles of the welding process. This affects the mechanical behavior of laser—welded structures.
- Argon gas can cause porosities which can lead to the failure of welded structures.
- Insufficient penetration of the laser beam can cause a big defect or internal failure if the equipment is not adjusted properly.
- High cost of the equipment.
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