Friday, 7 October 2016

Powder Rolling

This process involves feeding of powders between rolls to produce a coherent and brittle green strip. This green strip is then sintered & re-rolled to obtain a dense, finished product.
Steps: 1) preparation of green strip, 2) sintering, 3) densification of sintered strip, 4) final cold rolling and annealing Parameters affecting powder rolling are roll gap, roll diameter, roll speed, powder
characteristics; Roll gap => large roll gap leads to decrease in green density; very small roll gap leads to edge cracking; roll diameter => increase in density and strength with increase in roll dia. for a given strip thickness; roll speed => Kept low, 0.3-0.5 m/s;
Powder => irregular powder with rough surfaces provide better strip density
In densification stage, either repeated cold rolling followed by annealing or hot rolling of strip can be followed Applications: nickel strips for coinage, nickel-iron strips for controlled expansion properties, Cu-Ni-Sn alloys for electronic applications, porous nickel strip for alkaline batteries and fuel cell applications.

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