Safety fuse manufacture

These are not to be confused with Bickford fuse or safety fuse manufactured by the same company, which consists of a central thread surrounded by a core of black powder enclosed within a tube of woven threads, surrounded by various layers of textile, waterproof material, sheathing, etc. This is miner s fuse, and is everywhere known as Bickford fuse after the Englishman who invented the machine by which such fuse was first woven. The most common variety bums with a velocity of about 1 foot per minute. When the fire reaches its end, a spurt of flame about an inch long shoots out for igniting black powder or for firing a blasting cap. 

With a properly constructed safety fuse the core is almost impermeable to gases, but should faults occur, either during manufacture or due to mishandling afterwards, cracks may develop which enable the hot gases to... 

If the outer covers of safety fuse are pierced, e.g. by falling rock, water can penetrate and stop the combustion of the fuse. Much work has been done in efforts to obtain a waterproof fuse which will obviate this difficulty. This work, although not successful in its original purpose, has led to the development of igniter cord which has proved of considerable value in secondary blasting (see p. 148). Two types of igniter cord are manufactured, fast cord with a burning speed of 3 s m1 and slow cord with a speed of 30 s m-1. 

Most blackpowders contain 75% of potassium nitrate, 15% of charcoal and 10% of sulphur. For safety fuse, however, blackpowders are made with reduced amounts of potassium nitrate. Also manufactured are sulphurless powders, containing approximately 70% of potassium nitrate with 30% of charcoal. These sulphurless powders are used for ignition purposes where sulphur could cause corrosion of metallic components. 

Detonating Cord core of pentaerythritol tetra-nitrate (PETN) contained within a waterproof covering of textile or plastic available in several grades, each on spools of 500 or 1,000 feet. Manufactured by the Ensign-Bickford Company, Coast Fuse, Inc and Austin Powder Company SAFETY FUSE... 

The length of the fuse will depend on the safety period required. The structure of the fuse comprises (proceeding from the fuse interior outwards) a black powder core with one or two marking threads, the color of which indicates the identity of the manufacturer, two or three layers of yarn wound around it (jute, cotton, or some other yarn), a bitumen impregnation, and a plastic coating. 

One of the benefits of the prismatic cell is that it has the higher capacity typical of laminate cell, but it also may integrate some of the safety features of the small cells such as vents and, occasionally, thermal fuses. The prismatic cell may also use a mechanical connection to the cell which reduces the need to weld the bus bars to make the cell to cell connections in a pack. The issues of this cell format include the risk of cascading failure (much more energy is released in a large cell failure). In addition, as these cell formats are still produced in relatively low volumes, ramping up the manufacturing to volumes and quality that match those of the 18650 format will take time. 

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