Workshop Technology
The purpose of a riser is to

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
Deliver molten metal into the mould cavity

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Workshop Technology
For arc welding

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

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