As the Name implies, Joints classified under this group are those that will not easily be separated. They are made to be permanent and any effort to separate the parts will result in the deformation of the surfaces or parts that were joined. Therefore, these joints are adopted where removal of parts are not envisaged in the near future.
Permanent Joints include: Self secured joints, riveting, soldering, brazing, welding etc.
Self Secured Joints
These are joints achieved through suitable folding and compressing of the edges together without application of heat.
Self secured joints are only applicable to sheet metal (metals with thin section) specifically, sheet metals of not more than 1.5mm or less, as metals with thicker section would pose difficulties during folding compressing exercise thereby resulting in indecent and untidy joints.
Types
Paned down joints
Knock up joints
Grooved joints
Riveting
This process of joining two or more metals together does not involve the application of heat as when welding or soldering but simply the use of prepared metal rod with head called rivet into an already drilled holes of corresponding clearance followed by the application of hammer blows or pressure.
Generally, rivets are manufactured from any of the following metals such as mild steel, aluminum, copper, and brass. This is because those metals can be easily worked.
Rivets is being done with the aid of hammer blows, this method is the workshop method of riveting. In this method, when holes have been drilled on the parts to be joined, rivet is fixed into the nip or the rivet gun and inserted into the drilled holes and upon pulling the lever of the rivet gun, it will mechanically expand the shank of the rivet and pull-pin is cut off and flushes with the head.
Types
Snap or round head
Countersunk head
Pan head
Flat head
Mushroom head.
Soldering
Soldering is the joining of metal components by means of a fusible metal or alloy called solder with a melting point below 400° C. This means that the solder must be of lower melting point than the metals to be soldered, if the process is to be carried out quickly and economically.
A solder is an alloy of Lead and Tin.
Types
Soft Soldering
Hard Soldering
Brazing
This process requires the use of special solder called spelter or brass rod, this is the alloy of copper and zinc. The composition is in the following approximate proportion of copper 65% , zinc 35% with a melting temperature of about 600°C bit below the melting point of the parent metal.
The brazing process requires a source of heat which includes either Oxy-acetylene or Oxy-propane, that is a gas unit with a welding torch, brass rod, spark lighter, wire brush, welding goggles etc.
Welding
Welding is a process of permanent joining of two materials through localized coalescence resulting from a suitable combination of temperature, pressure and metallurgical conditions.
Types
Gas welding
Arc welding
Resistance welding
Solid state welding
Thermo chemical welding
Radiant energy welding.