470. Tail stock centres which do not revolve with the workpiece are known as
A.Non-revolving centres
B.Dead centres
C.Live centre
D.Independent centres

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471. Parkerizing process is
A.A zinc diffusion process
B.An oxidising process used for aluminium and magnesium articles
C.A process used for making thin phosphate coatings on steel to act as a base or primer for enamels and paints
D.The process of coating of zinc by hot dipping

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472. In electro-discharge machining, the tool is made of
A.Tungsten carbide
B.Properly heat treated alloy steel
C.Diamond
D.Brass or copper

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473. Which is false statement about electrodischarge machining
A.It can machine very hard materials
B.Very good surface finish is obtained
C.Section to be machined should be thick
D.Metal removal rate is very slow

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474. In electro-chemical milling operation, the gap between tool and work is kept of the order of
A.No gap, both are in contact with each other
B.0.25 mm
C.0.75 mm
D.1.25 mm

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475. In spark erosion machining process, the gap between tool and workpiece is filled with
A.A photo etchant
B.Brine solution
C.Acid solution
D.A liquid dielectric

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476. In the electro-discharge machining process, the workpiece and the electrode are submerged in
A.A dielectric fluid
B.An abrasive slurry
C.An electrolytic solution
D.Vacuum

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