The usual rack and pinion discharge doors deliver ore to 10 suspended Challenge feeders each actuated by the central stamp tappet of the 5 head mill it feeds. The friction block of the feeder is of the double groove type. The battery was erected in 1901. Each mortar rested on a block of kauri 20 feet x 5 feet x 2foot 6 inch set in a block of concrete running right across the site. The mortar weighs 3½ tons. It rests upon a double sheet of tarred felt and is anchored to the block by eight 1½ inch cotter bolts, 3 feet 11 inches long, the cotter and washer (4½ inches x 4½ x ½ inch) being accommodated in a recess 6 inches x 5½ inch x 4 inch in the side of the block. Steel lining-plates are used inside the mortars, the two end ones being ½ inch thick, those on either side of the feed opening are 1/8th inch, and those on the feed opening and the lower half of the back of the mortar are 5/8th inch. The latter lasts from three to six months.

The stamps when new weigh 1250lb. per head.

 

Ft

in

 

in

 

lb.

Head

1

2

x

9

diam

363

Shoe

0

9

x

9

diam

200

Stem

16

0

x

diam

500

Tappet

1

1

x

9

overall

187

Total

         

1250

 

To compensate for wear and keep the weight per head fairly even the last ten stamps have heads 2 foot in height and are fitted with partly-worn shoes from other stamps.

Fraser and Chalmer’s cast-steel heads and shoes are used and the dies are of local (Price Bros, Thames) cast-iron. They are 9 inches x 6 inches high and have an octagonal base. Formerly steel dies were used and the wear was consequently very uneven. The order of drop for the adjacent sets of 5 head is 1, 3, 5, 2, 4, and 10, 8, 6, 9, 7. The log-book rate is 106 drops per minute, but it is usually from 108 to 110; the height of drop is set to 7 inches which is reduced to 6 inches by the material in the die. When this increases by wear to 7 inches the tappets are raised to adjust it to 6 inches again. The height of discharge is ½ inch when the die is new. The cam-shaft for each set of 5 -head is separate and has its own driving pulley and friction clutch on the main shaft, the clutch being operated either from the cam-shaft floor or the stamp floor near the foot of the plates. Blanton cams are used, of the single-wedged type, and iron guides as well as plain wooden ones - the iron ones being preferred. Woven steel-wire screens are employed, 40 head being on 15 mesh and 10 head on 25 mesh (December, 1910). The stamp duty is 3.4 tons per head per 24 hours. The stamp duty during 1909 when 30 mesh screens were used (tube mills not being available) was 3.18 long tons (=3.56 short tons) per head per 24 hours, 44,800 tons being treated in the 12 months. The height of discharge was variable, being raised for rich ore to crush it more finely than general ore.