Workshop Technology
The purpose of a riser is to

Act as a reservoir for the molten metal
Deliver the molten metal from pouring basin to gate
Deliver molten metal into the mould cavity
Feed the molten metal to the casting in order to compensate for the shrinkage

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Workshop Technology
For arc welding

Direct current is used
Alternating current with high frequency is used
Alternating current with low frequency is used
Any one of these

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Workshop Technology
Rotary swaging

Consists of pressing the metal inside a chamber to force it out by high pressure through an orifice which is shaped to provide the desired form of the finished part
Is used for reducing the diameters of round bars and a tube by rotating dies which open and close rapidly on the work
Is extensively used for making bolts and rivets
Is used to improve fatigue resistance of the metal by setting up compressive stresses in its surface

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