Workshop Technology
The purpose of a riser is to

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

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Workshop Technology
Extrusion

Is extensively used for making bolts and nuts
Is used for reducing the diameter of round bars and tubes by rotating dies which open and close rapidly on the work
Is used to improve fatigue resistance of the metal by setting up compressive stresses in its surface
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

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Workshop Technology
For arc welding

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

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