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An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery guns. It is believed to have been invented in 1845. [1]
The system has also been used to close other applications, including the joint between helmet (bonnet) and breastplate (corselet) of standard diving suit helmets, and the locks of diving chambers.
An interrupted screw has a section of thread along its axis removed. The screw is mated with a partially threaded hole in the receptacle: threadless channels in the breechblock screw line up with the threaded parts of the screw, and vice versa. The screw can thus be smoothly inserted all the way into the receptacle, after which as little as one-eighth of a turn can engage the two sets of threads securely, sealing the joint.
The amount of rotation required to achieve full closure depends on the number of unthreaded sectors. The minimum balanced arrangement has two sectors of 90°, and requires 1/4 turn to lock. three sectors of 60° requires 1/6 turn to lock, and the typical arrangement on a diving helmet, four sectors of 45°, requires 1/8 turn to lock. [2]
In the artillery application, the screw is set into the breechblock and mated with a partially threaded hole at the rear of the weapon's chamber.
American engraver Benjamin Chambers, Sr. [3] received a patent [4] in 1849 for a wrought iron built-up gun "dissected screw breech" with "sectional screws" "cut therein for the purpose of speedily opening the breech for swabbing, depositing the load, and readily closing it again when the gun is to be discharged". His gun was built and tested with metallic cartridges, center-primed with a percussion cap, because the US Navy was initially interested, and chief of the Bureau of Ordnance Charles Morris recommended more developments, but the system was too expensive for the time and cheaper Dahlgren guns were adopted instead. [5]
Breech sealing was improved with the de Bange obturator in 1872, and all interrupted screw breeches with this system were generally known as the De Bange type.
The major weakness of the original designs was that only half of the circumference of the breechblock could be threaded, hence a fairly long breechblock was still required to achieve a secure lock. Axel Welin solved this problem with his stepped interrupted screw design: the Welin breech block of 1890. This design has threads of the block and breech cut in steps of successively larger radius. For example, this allows a breechblock with four steps to allow four-fifths of the block circumference to be threaded, allowing for a much shorter breechblock while still requiring only one-fifth of a turn to open or close. This is the basic design still in use with bagged charge artillery.
Interrupted screws are occasionally seen in loose gunpowder rifles, as this mechanism was historically one of the few practical ways to achieve a gas-proof seal with a breech-loading firearm that does not employ metallic cartridges. An earlier method was the use of a wedge to block the rear of the gun. [1]
The system has also been used to close other applications, including the joint between helmet (bonnet) and breastplate (corselet) of standard diving suit helmets, and the locks of diving chambers.[ citation needed ]
In firearm designs, the term single-shot refers to guns that can hold only a single round of ammunition inside and thus must be reloaded manually after every shot. Compared to multi-shot repeating firearms ("repeaters"), single-shot designs have no moving parts other than the trigger, hammer/firing pin or frizzen, and therefore do not need a sizable receiver behind the barrel to accommodate a moving action, making them far less complex and more robust than revolvers or magazine/belt-fed firearms, but also with much slower rates of fire.
In firearms terminology, an action is the functional mechanism of a breech-loading firearm that handles the ammunition cartridges, or the method by which that mechanism works. Actions are technically not present on muzzleloaders, as all those are single-shot firearms with a closed off breech with the powder and projectile manually loaded from the muzzle. Instead, the muzzleloader ignition mechanism is referred to as the lock.
Standard diving dress, also known as hard-hat or copper hat equipment, deep sea diving suit or heavy gear, is a type of diving suit that was formerly used for all relatively deep underwater work that required more than breath-hold duration, which included marine salvage, civil engineering, pearl shell diving and other commercial diving work, and similar naval diving applications. Standard diving dress has largely been superseded by lighter and more comfortable equipment.
A diving helmet is a rigid head enclosure with a breathing gas supply used in underwater diving. They are worn mainly by professional divers engaged in surface-supplied diving, though some models can be used with scuba equipment. The upper part of the helmet, known colloquially as the hat or bonnet, may be sealed directly to the diver using a neck dam, connected to a diving suit by a lower part, known as a breastplate, or corselet, depending on regional language preferences. or simply rest on the diver's shoulders, with an open bottom, for shallow water use.
A breechloader is a firearm, in which the user loads the ammunition from the breech end of the barrel, as opposed to a muzzleloader, in which the user loads the ammunition from the (muzzle) end of the barrel.
A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed spring acts directly on the firing pin to provide the impact force rather than it being struck by a hammer.
A rifled breech loader (RBL) is an artillery piece which, unlike the smoothbore cannon and rifled muzzle loader which preceded it, has rifling in the barrel and is loaded from the breech at the rear of the gun.
A breechblock is the part of the firearm action that closes the breech of a breech loading weapon before or at the moment of firing. It seals the breech and contains the pressure generated by the ignited propellant. Retracting the breechblock allows the chamber to be loaded with a cartridge.
Obturation is the necessary barrel blockage or fit in a firearm or airgun created by a deformed soft projectile. A bullet or pellet made of soft material and often with a concave base will flare under the heat and pressure of firing, filling the bore and engaging the barrel's rifling. The mechanism by which an undersized soft-metal projectile enlarges to fill the barrel is, for hollow-base bullets, expansion from gas pressure within the base cavity and, for solid-base bullets, "upsetting"—the combined shortening and thickening that occurs when a malleable metal object is struck forcibly at one end.
A rolling-block action is a form of firearm action where the sealing of the breech is done with a specially shaped breechblock able to rotate on a pin. The breechblock is shaped like a section of a circle. The breechblock is locked into place by the hammer, thus preventing the cartridge from moving backwards at the moment of firing. By cocking the hammer, the breechblock can be rotated freely to reload the weapon.
The Welin breech block was a revolutionary stepped, interrupted thread design for locking artillery breeches, invented by Axel Welin in 1889 or 1890. Shortly after, Vickers acquired the British patents. Welin breech blocks provide obturation for artillery pieces which use separate loading bagged charges and projectiles. In this system the projectile is loaded first and then followed by cloth bags of propellant.
This article explains terms used for the British Armed Forces' ordnance (weapons) and ammunition. The terms may have slightly different meanings in the military of other countries.
Locked breech is the design of a breech-reloading firearm's action. This is important in understanding how a self-reloading firearm works. In the simplest terms, the locked breech is one way to slow down the opening of the breech of a self-reloading firearm when fired. The source of power for the movement is recoil.
A falling-block action is a single-shot firearm action in which a solid metal breechblock slides vertically in grooves cut into the breech of the weapon and is actuated by a lever.
The Armstrong RBL 7-inch gun, also known as the 110-pounder, was a heavy caliber Armstrong gun, an early type of rifled breechloader.
An Armstrong gun was a uniquely designed type of rifled breech-loading field and heavy gun designed by Sir William Armstrong and manufactured in England beginning in 1855 by the Elswick Ordnance Company and the Royal Arsenal at Woolwich. Such guns involved a built-up gun construction system of a wrought-iron tube surrounded by a number of wrought-iron strengthening coils shrunk over the inner tube to keep it under compression.
Charles Ragon de Bange was a French artillery officer and Polytechnician. He invented the first effective obturator system for breech-loading artillery, which remains in use. He also designed a system of field guns of various calibers which served the French Army well into World War I: the Système de Bange.
The Reffye 85 mm cannon was a French artillery piece of the 19th century, developed by the French artillery General Jean-Baptiste Verchère de Reffye, superintendent of the works at Meudon. The weapon was adopted by the French Army from 1870. It was an 85 mm (3.35-inch) rifled breech-loading cannon, equipped with a breech screw, initially made of bronze.
The Reffye 75mm cannon was a French artillery piece of the 19th century, developed by the French artillery General Jean-Baptiste Verchère de Reffye, superintendent of the works at Meudon. The weapon was adopted by the French Army from 1873. It was a 75 mm rifled breech-loading cannon, equipped with a breech screw, initially made of bronze.
An Asbury Mechanism opens and closes the breech of heavy artillery for reloading with a projectile and bags of propellant. It was widely used for naval artillery of the world wars and similar coastal artillery and railway guns. The device was invented at the Washington Navy Yard in 1916 by draftsman Dorsey Frost Asbury. It is sometimes called a Smith-Asbury mechanism by the United States Navy in recognition of Asbury's supervisor, Lieutenant Commander George Leonard Smith, USN.