A Shot Tower is a tower designed for the production of shot
balls by freefall of molten Lead, which is then caught in a Water
basin.
The shot is used for projectiles in firearms. In a shot Tower, Lead
is heated until molten, then dropped through a Copper Sieve high up
in theTower. The liquid lead solidifies as it falls and bySurface
tension forms tiny spherical balls. The partially cooled balls are
caught at the floor of the tower in a water-filled basin. The now
fully cooled balls are checked for roundness and sorted by size;
those that are "out of round" are remelted.
A slightly inclined table is used for checking roundness. To make
larger shot sizes, a copper sieve with larger holes is used.
However, the maximum size is limited by the height of the tower,
because larger shot sizes must fall farther to cool. A polishing
with a slight amount of Graphite is necessary for Lubrication and
to prevent Oxidation.
The process was invented by William Watts of Bristol, UK, and
patented in the late 18th century. Watts extended his house in
Redcliffe, Bristol to build the first shot tower in 1782. Shot
towers replaced the earlier techniques of casting shot in molds,
which was expensive, or of dripping molten lead into water barrels,
which produced insufficiently spherical balls.
Large shot which could not be made by the shot tower were made by
tumbling pieces of cut lead sheet in a barrel until round. Shot
towers were replaced by the "wind tower" method by the end of
the19th century, which used a blast of cold air to dramatically
shorten the drop necessary.
Today the Bliemeister method is used to make smaller shot sizes,
and larger sizes are made by the cold Swaging process of feeding
calibrated lengths of wire into hemispherical dies and stamping
them into Spheres.
The tallest shot tower ever built still stands in the Melbourne,
Australia suburb of Clifton Hill. This brick structure was built in
1882 and is 80 metres or 263 feet high to the top of the small
chimney.
The Mt Eden Shot Tower marks the site of the former Colonial
Ammunition Company (CAC) and has a category 1 rating by the NZ
Historic Places Trust.
CAC was formed in 1885, by Major John Whitney and W H Hazard. This
was at the time of the “Russian Scare” when Tsar
Alexander brought some of his naval fleet into the North Pacific to
Vladivostok and it was feared that he was about to expand his
empire. Fortifications were built with all haste and the need for
ammunition independent of the supplies from Britain became urgent.
CAC was the first munitions factory in Australasia and later
established a factory in Melbourne.
CAC prospered and apart from the needs of the military, they
provided bullets for hunters and shot gun cartridges for duck
shooters.
The shot tower was built in 1914 to produce the small spherical
lead pellets for the shot gun enthusiasts. The pellets fired from
the gun formed a pattern when aimed at a bird. They were earlier
produced in Nelson, by a Mr Lylie, using a casting process that was
laborious and slow in production.
The first operator of the new Auckland shot tower was the same Mr
Lylie assisted by his two daughters. Lead blocks were raised to the
top of the tower by a lift, melted in a furnace and poured into a
pan with many small holes in the bottom so that small drops fell
down the 30 metre height of the tower as perfect spheres which
solidified in the air and splashed into soapy water at the base.
They were polished and sized with rejects being returned to the
molten metal. Production up to 1,000 tons per year was possible.Our
shot tower is somewhat unique in being a light steel structure and
built by an Auckland blacksmith W Wilson & Co. Other shot
towers, all built in the 19th Century are, two in the UK, four in
the USA, three in Australia and are in the form of brick
chimneys.
CAC was an essential industry through both the world wars and each
time expanded it’s manufacturing significantly. At the end of
WW ll it was producing up to 25lb shells.
ICI (Imperial Chemical Industries) of the UK who had been major
manufacturers of explosives with the NOBEL trade mark and following
Nobel’s patents for Gelignite, supplied explosives to the NZ
mining, quarrying and tunnelling activities and bought control of
CAC in about 1960. The General Manager of ICI explosives in New
Zealand was Dick Hazard, no doubt related to the CAC founder W H
Hazard.
A little known unique activity of CAC was the commercial harvesting
and canning of Toheroa, the large shellfish found on the West Coast
beaches North of Auckland. This was carried on for many years till
about 1975 when the fishery was closed.
Cache is magnetic in view of tower.
Accessible from the path.
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