In this article we will discuss about the processes used for joining metals. Learn about:- 1. Welding 2. Brazing 3. Soldering 4. Gas Cutting Process and Equipment or (Oxyacetylene Gas Cutting Process).
1. Welding:
In olden days, in order to join two pieces of metals, riveting was done. But nowadays for joining two pieces of metals welding is done.
So, welding is a process of joining two pieces of metals by heating them.
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Nowadays welding is used in almost all the industries since it is the easiest and rapid method of joining the metals.
Nowadays methods have also been developed to weld dissimilar metals. One important feature of welding is that the strength of the welded joint is more than 100% when compared to the metals.
It is used in joining metals in following fields:
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(a) In fabrication of tanks, vessels, boilers.
(b) In automobile industry.
(c) In structural work, i.e., to fabricate trusses, frames.
(d) In pipe line fabrication.
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(e) In ship building, motor building i.e., in general, in all the types of joining metals, welding is used.
Requirements of Good Welded Joints:
The following requirements of good welding joints are:
(i) For good welded joints, the surfaces should be clean. The cleaning can be done by using wire brush.
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(ii) Proper edge preparation should be done as discussed below otherwise the joint may not have required strength. The edges must be prepared depending upon the thickness.
Various types of edge preparations for butt welds:
The square butt weld is used for the sheets having thickness between 1-5 mm.
Single V or Single U butt welds are used for the plates having thickness between 5-15 mm.
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Double V or Double U butt welds are used for welding plates above 15 mm thickness.
2. Brazing:
Brazing is a process of joining two pieces of similar or dissimilar metals. In this case as non-ferrous metal or alloy in the molten form is supplied in between the metals to be joined and allowed to solidify.
The melting point of filler material is about 425°C but which is lower than the melting point of parent metals. During brazing no forging action is present and also the parent metal parts do not melt.
The various brazing metals and alloys are Copper, Brass, Bronze, Silver alloys, Aluminium alloys etc.
Based on heating source the various brazing processes are:
(i) Torch brazing
(ii) Furnace brazing
(iii) Resistance brazing etc.
Advantages:
(i) Dissimilar metals can be joined
(ii) It is a quick process
(iii) It is used for joining pipe fittings, carbide tips on the tools etc.
Limitations of Brazing:
1. Brazing cannot be performed on hardened steel.
2. Aluminum brazing needs a special technique and is very expensive
3. Soldering:
Soldering is a process of joining two pieces of metals. In this case a molten fusible metal called solder is supplied and allowed to solidify.
The melting point of solder is below 420° C. Generally Lead and Tin alloys are used as solder materials.
Some of the solders are:
(i) Soft Solder. Lead 37% and tin 63%.
(ii) Medium Solder. Lead 50% and tin 50%.
(iii) Electricians Solder. Lead 58 % and tin 42 %.
(iv) Plumbers Solder. Lead 70% tin 30%.
As one might have seen with the radio repairers that, when the current is supplied to the solder gun, the front end of it becomes hot. This hot end when brought in contact with solder material, it melts. This molten material is used for joining wires in radios, tape-recorders etc. The molten metal, when cools, produces solder joints.
Types of Soldering Processes:
(i) Soft Soldering:
It is used in sheet metal work and it has less strength.
(ii) Hard Soldering:
It is employed when stronger joint is required.
Based on the method of heating source, the soldering processes may be, resistance soldering, torch soldering, furnace soldering etc.
Application:
It is mainly used in joining wires in radios, tape-recorders, printed circuit boards etc.
Advantages:
1. It produces liquid and gas-tight joints quickly.
2. The cost of the joint is quite low.
3. The temperature of soldering is low.
4. The equipment used for soldering is simple, cheap and easy to handle.
5. It is the most economical method.
Drawbacks:
The joints are not strong enough to withstand the constant jerks and pulls, which is the main drawback of the process.
4. Gas Cutting Process and Equipment or (Oxyacetylene Gas Cutting Process):
In gas welding, heat energy required to heat the surfaces is obtained by the combustion of oxygen and acetylene. These gases are mixed in proper proportions in the torch which is provided with regulators. When the gases are burnt a flame is produced.
The flame so produced is used to heat the steel to red hot colour. Then a jet of pure oxygen is blown on the red hot surface. The steel is burnt i.e., iron oxide (slag) is produced, which under pressure falls down and the steel is cut.
The equipment used in Gas welding and gas cutting:
1. Gas Torch or Welding Torch:
In this gas torch proper mixing of oxygen and acetylene takes place. The torch is provided with regulators to regulate the mixture of gases. When the combustion takes place flame will be produced at the tip.
2. Torch Tip:
It is that part of the torch through which gases pass just before their ignition and burning.
3. Pressure Regulator:
The function of a pressure regulator is to reduce the cylinder pressure to the required working pressure and also to produce steady flow of gas.
4. Hose and Hose Fittings:
Hose pipes are used to convey gases from the cylinder to the torch. They should be strong and durable.
5. Goggles:
Goggles fitted with coloured lenses are provided to protect the eyes of the operator from harmful heat.
6. Gloves:
These are used to protect the hands of the operator.
7. Spark Lighters:
These are used for lighting the torch.
8. Oxygen and Acetylene Cylinders:
These are commercially available in the market or acetylene gas.