Workshop Technology
The welding set up is said to have straight polarity, when

Work is connected to the negative terminal and the electrode holder is earthed
Work is connected to the positive terminal and the electrode holder to the negative terminal
Work is connected to the negative terminal and the electrode holder to the positive terminal
Work is connected to the positive terminal and the electrode holder is earthed

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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
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 to improve fatigue resistance of the metal by setting up compressive stresses in its surface

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Workshop Technology
A jolt machine is used to

Ram the sand harder at the pattern face with decreasing hardness towards the back of the mould
Produce uniform packing of sand in the mould
Produce uniform sand hardness throughout the mould
Ram the sand harder at the back of the mould and softer on the pattern face

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