The Welin breech block was a revolutionary stepped, interrupted thread design for locking artillery breeches, invented by Axel Welin

Axel Welin

Axel Welin , was a Swedish inventor and industrialist.Ernst Axel Martin Welin studied at the Royal Institute of Technology in Stockholm from 1879 to 1884. Between 1886 and 1888, Welin worked as a weapons designer for Thorsten Nordenfelt in London. In 1889 he started his own engineering firm, the...

 in 1889 or 1890. Shortly after, Vickers

Vickers

Vickers was a famous name in British engineering that existed through many companies from 1828 until 1999.-Early history:Vickers was formed in Sheffield as a steel foundry by the miller Edward Vickers and his father-in-law George Naylor in 1828. Naylor was a partner in the foundry Naylor &...

 acquired the British patents.

Design

The screw design incorporated multiple "steps" of threads of progressively increasing radius, each step occupying the same circular sector

Circular sector

A circular sector or circle sector, is the portion of a disk enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. In the diagram, θ is the central angle in radians, r the radius of the circle, and L is the arc length of the...

, such as the four steps seen in the accompanying photograph of a 16-inch gun breech and block.

Each step engaged with its matching thread cut in the gun breech when inserted and rotated. A gap in the thread steps was still necessary for the insertion of the largest step before rotation, so the area of the breech secured by threads in the block was number of steps / (1 + number of steps) x length of the screw.

This was a major improvement on previous non-stepped designs such as the de Bange system

Charles Ragon de Bange

Charles Ragon de Bange , often simply called de Bange, was a Polytechnician and a French artillery colonel of the 19th century. He invented the first effective obturator system for breech-loading artillery. Its basic principle of functioning is still widely in use to this day...

, which had only a single thread step and hence only half of the block's circumference had a thread which engaged with the breech, necessitating a fairly long screw to achieve a secure lock. The much greater threaded area of the Welin block allowed it to be shorter, allowing faster opening as it could be swung down or to the side after being withdrawn a much shorter distance than previous designs. It was also simpler and more secure.

The Welin breech was a single motion screw, allowing it to be operated much faster than previous interrupted-thread breeches, and it became very common on British and American large calibre naval artillery and also field artillery above about 4.5 inches (110 mm).

Though the US Navy was offered the design a year or two after its invention, they declined and the American Bethlehem Steel

Bethlehem Steel

The Bethlehem Steel Corporation , based in Bethlehem, Pennsylvania, was once the second-largest steel producer in the United States, after Pittsburgh, Pennsylvania-based U.S. Steel. After a decline in the U.S...

spent the next five years in trying to circumvent Welin's patent, before having to buy it through Vickers.

External links

• Royal New Zealand Artillery Association, Breech Mechanisms