Grinding and Finishing

Fine grinding is performed in high-speed, water-cooled hammer mills in which feed rate, mill speed, and screen openings under the mill can be varied to obtain the powder characteristics desired; thus, grinding is another operation in which powder properties can be changed. The powder leaving the hammer mills is fed to screens, where the oversize is separated and returned for additional grinding. The -100 mesh powder is classified in an air classifier, and the fines are transferred to the blending operation. Oversize material is returned for regrinding or is used as melting stock.

The products of the grinding and classifying operations range in apparent density from approximately 1 to 4 g/cm3. They are stored in drums to which a drying agent such as silica gel or camphor is added to prevent further oxidation. To produce high volume finished powder that meets customer specifications, powder is selected from various batches in the proper proportions and mixed in a blender. The lot is sampled before being removed from the blender, and if required, adjustments of the particle size distribution are made before the powder is packed in shipping drums. Table 5 lists the physical characteristics of several representative blends.

Table 5 Properties of typical commercial grades of electrolytic copper powders

Chemical

properties

Physical properties

Copper,

Hydrogen

Acid

Apparent

Sieve analysis, % Tyler

%min

loss, % max

insoluble, % max

density,g/cm3

+60 +100

+150

+200

+325

-325

99.8

0.15

0.06

2.5-2.7

. . . 5 max

1-13

11-24

20-30

40-55

99.8

0.15

0.06

2.3-2.5

. . . 1 max

6 max

50-60

40-50

99.7

0.20

0.06

2.0-2.3

0.8

5-15

85-95

99.7

0.20

0.06

1.75-1.95

trace

5-15

85-95

99.7

0.20

0.06

1.25-1.45

trace

10 max

90 min

99.7

0.20

0.06

0.9-1.1

trace

10 max

90 min

0 0

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