Whichever engineering production field you choose
almost all of them require joining of component at some stages or other.
And these necessary joints can be
particularly of two kinds.
- Temporary joint
- Permanent joint
When we talk about temporary joint it
encircles parts that are joined or fastened by nut, bolt, screw, clamps,
coupling etc.
Most probably you find such kind of
joints in household machineries or furniture etc.
And the other one is permanent joint
that includes fastening that can’t be removed once done.
It is required possibly in areas where
high safety is concerned like in boiler shells, turbines etc.
Permanent joint includes riveting,
soldering, brazing and the most important is welding which is very widely used
in industries, workshops, fabrication, building construction and also in
aircraft industries.
Now every metal joining process is
unique in its own way and all of them have their advantages, limitations and
area of application.
1) WELDING
However we all know and have heard much
about welding.
Welding is the most convenient form
of joining in any industry
When we have a product of very big size
to be manufactured then doing so by casting or machining is rather very
difficult.
Under such scenario its easy to
manufacture it in parts and then joining them by welding to produce it as a big
whole product component.
So welding is very important metal
joining process and it gives us a permanent kind of joint.
By welding method you can join two
pieces of metal either of same kind or different metals together.
The metal pieces can be joined by
heating the ends of the metals to be joined, and there can be application of
pressure or without pressure, by adding of filler metal or without filler metal
to join them. This whole process of joining is called as welding.
2) SOLDERING
When two or more pieces of sheet metal
needs to be joined by means of some fusible alloy or metal called as solder
which is applied in the molten state then this whole process is called as
soldering.
The solders are usually made out of
metals like lead and tin.
The soldering process used for metal
joining can be either
- Soft soldering
- Hard soldering
Soft soldering
Soft soldering is used where thin metal
sheets are to be joined. And the work piece joined shouldn’t undergo high temperature
or high pressure.
Under soft soldering the melting point
of the solder i.e. tin and lead is nearly around 150o C to 350o C.
In soldering process the soldering iron
is generally heated by use of electric power so that the heat of the iron can
melt the solder metal.
Hard soldering
The melting point of hard solder is
quite high as compared to that of soft solder.
Hard solder is usually done to obtain
good strength.
And here the solder contains tin and
silver instead of tin and lead. Thus the melting point rises to 600oC
to 900oC.
The solder is in form of paste which is
applied on the sheets by the help of brush and then a blow torch is used to
melt the solder parts.
3) BRAZING
Brazing also is a metal joining process
where you can join any two metals but the filler metal that you need to use is
non-ferrous filler metal or alloy.
The melting point of the filler metal
is above 450oC but lower compared to that of base metal.
The filler metal is introduced between
the metal surfaces by the help of capillary action.
Usually for brazing copper base alloy
and silver base alloys are used as filler metal. And along with this a suitable
flux named borax is also used.
The brazing filler metals are available
in the form of the tin wires, rod or plate which makes it easier to enter into
the joints of metals by capillary action.
However its important to know that when
we compare soldering and brazing then brazing provides us better mechanical
strength.
4) RIVETING
A rivet also tends to be a permanent
mechanical fastener that gives us permanent joint.
At the initial stages a rivet is in the
form of a smooth cylindrical shaft having a head on one end. And the end
opposite to head is called tail.
During its installation the rivet is
inserted into a punched or drilled hole of two metal and the free end i.e. the
tail is hammered hard so that the tail forms the shape of head .
Since both the sides now possess head
after riveting so the metal gets tightened together.
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