June 21, 2009

Manufacturing of AAC/ACSR Conductors

The first step in the manufacture of AAC/ACSR conductors is the manufacture of aluminum conductor wire of required diameter which is obtained by wire drawing of E.C. grade aluminum rods. One end of the aluminum rods of 9.8 mm O.D is tapered and pointed on a pointing machine before the actual drawing operation begins. Wire drawing is a process of converting higher cross sectional wires of rods into lower cross section by way of cold drawing the material through smaller diameter dies. These machines contain from 3 to 4 dies from the larger finished wire sizes to 9 dies for fine wire sizes. The reduction in area per die usually varies from 20 to 25 per cent. The wire is drawn through each die by a power driven drum to the next die and coiled in the following power driven drum and so on. The size of the wire is progressively reduced till the wire emerging from the last die is of the required cross section. The peripheral speeds of drums are increases with each reduction and appropriate dies selected to match the peripheral speeds.

For drawing wires to sizes finer than 1.5 mm diameter, cone type machines with diamond dies are employed. As many as 25 dies may be accommodates in one machine, but machines with 12-17 dies are more common. Finishing speeds range from 5,000 to 8,000 ft.per minute fro medium fine size and upto 4,000 ft. per minute for fine size. Aluminum wire are cold drawn with adequate supply of aqueous lubricant is maintained on the wire during their passage through dies. Lubricants in paste, powder, or solid from held in boxes in front of the dies, are used for bull-blocks. A mixture of tallow, mineral oil, or compounded oils and greases are used for drawing aluminum wires. Multiple die machines are wet lubricated and die blocks, emulsion of beef tallow, compounded mineral oils, and proprietory drawing paste emulsions are used for aluminum wires. Oils give better and brighter finishes than emulsion.

Frequently the die is roughened. Several machine are available for die maintenance. A rough driller and semi automatic polishers are required. The rough driller is so-called because a coarse abrasive (silicon carbide 220 grit) is used as an abrasive for drilling the approach angles accurately and economically. The semi automatic polisher are used to polish the approach angles, using diamond dust or finer carbide as an abrasive. It is advisable to bend slightly the back relief at the 90 angle.

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