A melted plug is a threaded metal cylinder usually made of bronze, brass or gunmetal, with a tapered hole drilled completely through its length. The hole is sealed with a low melting metal metal that flows out when a predetermined high temperature is reached. The initial use of fusible plugs is as a safety precaution against low water levels in steam engine boilers, but then applications extend their use to other closed vessels, such as air conditioning systems and tanks for transporting petroleum gases that are corrosive or liquid.
Video Fusible plug
Destination
A fusible plug operates as a safety valve when dangerous temperature, rather than harmful pressure, is achieved in a closed vessel. In the steam engine, the fusible plug is screwed into the crown sheet (top plate) of the fire box, usually extending about an inch (25mm) into the above water chamber. The goal is to act as the last security device in place when the water level falls very low: when the top of the plug is out of the overheated water, the melting point of the low nucleus melts and causes noisy. the release of steam into a fire box serves to alert operators of the danger before the top of the fire box itself runs completely dry, which can lead to major failures on the boiler. The temperature of the exhaust gases in the steam engine fire box can be up to 1000 ° F (550 ° C), where the copper temperature, from which historically most of the firebox is made, softens to a state no longer able to maintain boiler pressure and a great explosion will occur if water is not put into the boiler quickly and fire is removed or extinguished. The hole through the plug is too small to have a major effect in reducing the vapor pressure and a small amount of water, if any, that passes through it is not expected to have a major impact in extinguishing the fire.
Maps Fusible plug
History
It was discovered in 1803 by Richard Trevithick, a proponent of a high-pressure steam engine (as opposed to atmosphere), as a result of an explosion in one of his new boilers. His critics are eager to denounce the whole concept of high-pressure steam, but Trevithick proves that the accident happened because his firefighters have neglected to keep the kettle full of water. He published his discovery widely, without patents, against these criticisms.
Experiments
Experiments conducted by Franklin Institute, Boston, in the 1830s initially doubted the practice of adding water as soon as the release of steam through the device was recorded. The steam boiler is equipped with a small observation window of glass and heated beyond the normal operating temperature with the water level below the top of the fire box. When water is added, it is found that the pressure rises abruptly and the observation glass is destroyed. The report concludes that high metal temperatures have evaporated the added water too quickly and that the explosion is an inevitable result. It was not until 1852 that this assumption was challenged: Thomas Redmond, one of the agency's own inspectors, specifically dismissed this theory in its investigation into a boiler explosion on Redstone on the Ohio River on April 3 of that year. The 1907 inquiry in Wales came to the same conclusion: Rhymney Train's steam locomotive was accidentally sent out with its safety valve fitted wrongly. The pressure on the boiler increases until the injector fails; the crown sheets became revealed, weakened by the heat of the fire and with a loud burst. The investigation, led by Colonel Druitt of the Railway Inspectorate, dismissed the theory that engineers had succeeded injecting injectors and that sudden flooding of cold water had caused an explosive steam generator. He cites the experimental results by the Manchester Steamers Association, the national boiler certification and insurance agency, which proves that the current copper weight (considered to be specific heat) is insufficient to generate enough steam to increase boiler pressure altogether. Indeed, the addition of cold water has caused the pressure to fall. From then on it was accepted that the correct action in the operation of the fusible plugs was to add water.
Cored fusible plugs
The original design is a simple solid plug filled with low-melting-point alloy slugs. When this melts, it melts first as a narrow channel through the plug. Steam and water soon begin to pass through this. The nucleus fusible plugs were developed in the 1860s to provide wide opening as soon as the alloy softened. This version has a brass or solid bronze center, soldered into place by a low melting point alloy layer. When hot, the plug does not release any steam or water until the alloy melts sufficiently to remove the center plug. The plug now fails dramatically, opening all bore immediately. The full-bore jet is likely to be noticed.
Unplug the unknown
The shortage of this tool was discovered on March 7, 1948, when the crown sheets of Firebox Princess Alexandra, Coronation Pacific of London, Midland and Scottish Railway, failed when transporting passenger trains from Glasgow to London.. The investigation determined that the two water meters were damaged and on the way earlier on that day one or both of the melting plugs were melted, but this had escaped from the machine crew because a strong draft carried steam escaping from them.
Maintenance
Composition of the alloy
Investigations show the importance of alloys on plug aging. Alloys are initially favored because they offer lower eutectic melting points than pure metal. It was found that although alloys were poorly aged and could encourage the development of the oxide matrix on the surface of the plug water, this matrix has a very dangerous melting point that makes the plug unusable. In 1888 the US Steamship Inspection Service made the requirement that spark plugs be made of pure tin and replaced annually. It avoids lead and also zinc contamination. Zinc contamination is considered a very serious problem so the plug case is also changed from brass (copper-zinc alloy) to zinc-free copper-zinc bronze, to avoid the risk of zinc migrating from the housing into the blend of the plug.
Plug aging
In 1920 an investigation by the US Bureau of Standards, in conjunction with the Ship Inspection Service, found that in the use of encrustation and oxidation above the melting core can increase the melting point of the device and prevent it from working when needed: a melting point of more than 2000 Â ° F (1100 Â ° C) in the examples used have been found. The typical current practices in the locomotive require new plugs for inspection after "15 to 30 working days (depending on water conditions and locomotive use) or at least once every six months," depending on the pressure and temperature of the boiler operation.
Other apps
The fused plug principle is also applied to the transport of liquid petroleum gases, where the fusible plugs (or small patches exposed from the membrane layers of the container) are designed to melt or become porous if too high a temperature is reached: a controlled release, at a typical temperature of 250 Â ° F (120 Â ° C), preferably than the release of explosive ("BLEVE") at higher temperatures. Corrosive gas containers, such as those used for liquid chlorine, are equipped with one or more fusible plugs with operating temperatures of about 158 ​​to 165 ° F (70-74 ° C).
Fusible stoppers are common in aircraft wheels, usually on larger or high-performing planes. The enormous heat load imposed by abnormal landing and braking conditions (and RTO especially) can cause high pressure on the tire to rise to the point where the tire may explode, so a fusible plug is used as a relief mechanism. The released gas may be directed to cool the braking surfaces.
Unsuitable plugs are sometimes mounted on the air compressor receiver as a precaution against ignition of possible lubricating steam. If the action of the compressor heats air above a safe temperature, the core will melt and release pressure.
Car air conditioning systems are generally equipped with fusible plugs, operating at 100-110 ° C, but from concerns about the environmental effects of any cooling gases released this function has been taken over by an electrical switch.
A fire-resistant type (Patent issued 1867) uses a fusible plug to extinguish its contents with water if the external temperature is too high.
See also
- Boiler explosion
References
Source of the article : Wikipedia
0 Comments