A shot tower is a

tower A tower is a tall structure, taller than it is wide, often by a significant factor. Towers are distinguished from masts by their lack of guy-wires and are therefore, along with tall buildings, self-supporting structures. Towers are specifi ...

designed for the production of small-diameter shot balls by

free fall In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on ...

of molten

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

, which is then caught in a water basin. The shot is primarily used for projectiles in shotguns, and for

ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...

radiation shielding Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposur ...

, and other applications for which small lead balls are useful.

Shot making

Process

In a shot tower,

is heated until molten, then dropped through a

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet materia ...

high in the tower. The liquid lead forms tiny

spherical A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ce ...

balls by surface tension, and solidifies as it falls. The partially cooled balls are caught at the floor of the tower in a

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

-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. The maximum size is limited by the height of the tower, because larger shot sizes must fall farther to solidify. A shot tower with a 40-meter drop can produce up to #6 shot (nominally 2.4mm in diameter) while an 80-meter drop can produce #2 shot (nominally 3.8mm in diameter). Polishing with a small amount of

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...

is necessary for lubrication and to prevent

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

History

The process was invented by William Watts of

Bristol Bristol () is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city in ...

, England, and patented in 1782. The same year, Watts extended his house in Redcliffe to build the first shot tower.. Use of shot towers replaced earlier techniques of casting shot in moulds, 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 was made by tumbling pieces of cut lead sheet in a barrel until round. The "wind tower" method, which used a blast of cold air to dramatically shorten the drop necessary and was patented in 1848 by the T.O LeRoy Company of New York City, meant that tall shot towers became unnecessary, but many were still constructed into the late 1880s, and two surviving examples date from 1916 and 1969. Since the 1960s the

Bliemeister method Shot is a collective term for small spheres or pellets, often made of lead. These were the original projectiles for shotguns and are still fired primarily from shotguns and less commonly from riot guns and grenade launchers, although shot shells ...

has been used to make smaller shot sizes, and larger sizes are made by the cold

swaging Swaging () is a forging process in which the dimensions of an item are altered using dies into which the item is forced. Swaging is usually a cold working process, but also may be hot worked. The term swage may apply to the process (verb) or ...

process of feeding calibrated lengths of wire into hemispherical dies and stamping them into spheres.

Examples

Gallery

File:Sparks Shot Tower 129-131 Carpenter St Philadelphia PA (DSC 3819).jpg File:CSIRO ScienceImage 11376 Shot tower.jpg File:Clifton hill shot tower melbourne australia.jpg File:Shot.tower.bristol.arp.jpg File:Melb-Central-shot-tower.jpg File:DubuqueShotTowerMay04.jpg File:Colonial Ammunition Company Shot Tower.jpg File:Shottower wytheco.jpg File:Szopienice Korczaka wieża ciśnień 1.jpg

References

External links

{{Commons category, Shot towers
"Gravity Molds Shot In A Modern Tower", October 1944, Popular Science
detailed and large article on subject of Shot Towers Metalworking Ammunition