Melting point, fusible alloys

Historically, fusible alloys are low-melting-point metallic alloys with a temperature of fusion below the boiling point of pure water (100°C). By extension, other alloys with a melting point below 200°C are also included in this group. 

Alloys are mixtures of metals combined to obtain specific characteristics and enhanced properties for a particular application. The term fusible metals or fusible alloys denotes a group of alloys that have melting points below that of tin (232°C, 449°F). Most of these substances are mixtures of metals that by themselves have relatively low melting points, such as tin, bismuth (m.p. 275°C), indium (157°C),... 

TABLE 15.1 Melting Points of Fusible Alloys of Variable Composition... 

Note that all combinations of metals yield an alloy with a melting point significantly lower than that of any of the individual metals. Even more extensive listings of fusible alloy compositions and melting points are available. As a point of reference, paper will spontaneously begin to bum when heated to 451°F, just above the melting point of tin. 

The above techniques are not satisfactory for solid sample containing light fractions that will be lost if exposed to ambient conditions of pressure and temperature. Samples like these can best be handled by cooling the sample and encapsulating them in small sealed metal—fusible alloy—containers (capsules) or glass capillaries. The metal must have a low melting point. 

High temperatures may be obtained also with the aid of baths of fusible metal alloys, e.g. Woods metal - 4 parts of Bi, 2 parts of Pb, 1 part of Sn and 1 part of Cu - melts at 71 °C Rose s metal - 2 of Bi, 1 of Pb and 1 of Sn - has a melting point of 94 °C a eutectic mixture of lead and tin, composed of 37 parts of Pb and 63 parts of Sn, melts at 183 °C. Metal baths should not be used at temperatures much in excess of 350 °C owing to the rapid oxidation of the alloy. They have the advantage that they do not smoke or catch fire they are, however, solid at ordinary temperature and are usually too expensive for general use. It must be remembered that flasks or thermometers immersed in the molten metal must be removed before the metal is allowed to solidify. 

Steel is an alloy containing chromium, manganese, molybdenum, nickel, vanadium and boron. Copper-nickel alloy, bronze and aluminium alloys are used in making coins. Fusible alloys having low melting points are used as solder and fuses in electrical circuits. 

What is unusual about Onion s Fusible Alloy compared to other metals Onion s Fusible Alloy contains bismuth, lead, and tin. Compare the melting points of these metals to the melting point of Onion s Fusible Alloy. 

An alloy known as Wood s Fusible Alloy, which melts at a much lower temperature even, is composed of tin, two parts lead, two parts bismuth, seven parts cadimiun, one to two parts. This melts at about 68 centigrade, boiling point loo . 

Rose s metal A fusible alloy containing 50% bismuth, 25-28% lead, and tin. Its low melting point (about 100°C) leads to its use in fire-protection devices. 

Heat is the most obvious choice of a characteristic by which a fire can be automatically recognized. In the section on fire suppression systems, the fusible links in the sprinkler heads represented one type of heat detector. Alloys have been developed that will have reproducible melting points. When the temperature at the detector site exceeds the melting point of the alloy, contacts are allowed to move so that the device can either make or break a circuit, just as with a manual alarm system. There are plastics which can perform in the same manner. Fixed temperature systems are very stable and not prone to false alarms, but are relatively slow to respond. There are several other versions of these fixed temperature detectors, including bimetalhc strips, where the differential rate of expansion of two different metals causes the strip to flex or bend to either make or break the contact. Others depend upon the thermal erqransion of hquids. 

Wood s motal Alow-melting (71°C) alloy of bismuth (50%), lead (25%), tin (12.5%), and cadmium (12.5%). It is used for fusible links in automatic sprinkler systems. The melting point can be changed by varying the... 

The final wound structure is removed from the winding machine, and the mandrel/ workpiece is placed in an oven for curing. Various mandrels are used and can be made of hard chrome plated and polished ground steel, which may be of a segmented collapsible construction, but must have no concave curvature. If the part has complex geometry, then fusible low melting point alloys, a soluble plaster that can be removed with hot water after curing, or an inflatable bag can be used. In some instances, such as compressed natural gas (CNG) tanks, the mandrel is left in position as a liner. 

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