Induction melting

Component Consumable vacuum-arc melt Plasma Plasma cold-hearth melt melt Electron-beam cold-hearth melt Induction melt... 

Nylon hot melt Induction heating of preapplied patch Any Clean surfaces critical high energy cost cool-down time parts breakage... 

Experimental results are in general conformity with the Avrami equation, but the interpretation of various observations is still complicated in many instances. One intriguing observation is that the induction period for nucleation is inversely proportional to the length of time the liquid is held in the liquid state after previous melting. This dependence on prior history may be qualitatively understood... 

Induced anisotropy Induction Induction furnaces Induction heating Induction melting... 

Properties. Silver difluoride melts at 690°C, bods at 700°C, and has a specific gravity of 4.57. It decomposes in contact with water. Silver difluoride may react violently with organic compounds, quite often after an initial induction period. Provisions must be made to dissipate the heat of the reaction. Small-scale experiments must be mn prior to attempting large-scale reactions. 

Fig. 1. Main types of electric furnaces (a) resistance furnace, indirect heat (resistor furnace) (b) resistance furnace, direct heat (c) arc furnace (d) induction furnace. A, charge to be heated or melted B, refractory furnace lining C, electric power supply D, resistors E, electrodes F, electric arc G,...

A. G. E., Robiette, Electnc Melting Practice, John Wiley Sons, Inc., New York, 1972, 412 pp., arc, induction resistor, and special melting furnaces are discussed. 

J. R. RoteUa and G. A. Walzer, Estimating Cupola and Induction Melting Using a Computer Model, AES Transactions, American Eoundryman s Society, Chicago, fll.,pp. 331-335. 

Frequency Selection. When estabhshing the specifications for a coreless induction furnace, the material to be melted, the quantity of metal to be poured for each batch, and the quantity to be produced per hour must be considered simultaneously. Graphs have been developed that combine these factors with practical experience to indicate possible solutions for a specific requirement. 

Hearth. The induction melting coil is almost always round and in the form of a right cylinder. It is highly desirable that the refractory lining within the coil be uniform in thickness, so most hearths are cylindrical whether they hold a few kg or 59 t. There are a few instances of a smaller coil being attached to the bottom of a larger hearth, so the hearth could be modified to suit a particular requirement (10). Oval cods have been budt and operated satisfactordy, but they are rare. 

The term channel induction furnace is appHed to those in which the energy for the process is produced in a channel of molten metal that forms the secondary circuit of an iron core transformer. The primary circuit consists of a copper cod which also encircles the core. This arrangement is quite similar to that used in a utdity transformer. Metal is heated within the loop by the passage of electric current and circulates to the hearth above to overcome the thermal losses of the furnace and provide power to melt additional metal as it is added. Figure 9 illustrates the simplest configuration of a single-channel induction melting furnace. Multiple inductors are also used for appHcations where additional power is required or increased rehabdity is necessary for continuous operation (11). 

HBI has been successfully melted in cupolas (hot or cold blast), induction furnaces (coreless or channel), and electric arc furnaces. It can be a valuable charge material for ductile and malleable irons as well as steel. It is of particular value in making ductile iron castings because of its very low residual element content. 

Induction Furnace. The high frequency coreless induction furnace is used in the production of complex, high quaUty alloys such as tool steels. It is used also for remelting scrap from fine steels produced in arc furnaces, for melting chrome—nickel alloys and high manganese scrap, and more recentiy for vacuum steelmaking processes. 

Vacuum and Atmosphere Melting. A coreless high frequency induction furnace is enclosed in a container or tank which can be either evacuated or filled with a gaseous atmosphere of any desired composition or pressure. Provision is made for additions to the melt, and tilting the furnace to pour its contents into an ingot mold also enclosed in the tank or container without disturbing the vacuum or atmosphere in the tank (Fig. 2). 

Fig. 2. Schematic arrangement of a furnace in a vacuum chamber equipped with charging and mold locks for vacuum induction melting (1) (a) front cross...

The zinc is normally melted in a gas, oU, or coal-fired reverberatory furnace with a capacity up to 100 tons or in a low frequency induction furnace with a capacity of a few tons. The more highly aUoyed compositions are more effectively melted and mixed in low frequency induction furnaces. The furnace must be refractory-lined to eliminate iron pickup by the molten metal. The metal temperature is maintained below 500°C to minimize loss by oxidation. A ladle is used to transfer the metal for casting into molds the pouring temperature is usuaUy ca 440°C. Zinc scrap is not generaUy suitable for remelting because it may contain undesirable impurities. 

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